Journal Logo

Review Article

Overview of Randomized Controlled Trials in Primary Total Hip Arthroplasty (34,020 Patients): What Have We Learnt?

Matar, Hosam E. MSc, FRCS (Tr&Orth); Platt, Simon R. MB ChB, FRCS (Tr&Orth); Board, Tim N. MD, FRCS (Tr&Orth); Porter, Martyn L. FRCS

Author Information
JAAOS: Global Research and Reviews: August 2020 - Volume 4 - Issue 8 - p e20.00120
doi: 10.5435/JAAOSGlobal-D-20-00120

Abstract

Total hip arthroplasty (THA) is one of the most successful and cost-effective interventions in orthopaedic surgery.1 Since the inception of the modern low friction hip arthroplasty by Charnley2 at our institute, little has changed in the fundamentals of this operation. However, significant advances have been achieved in metallurgy and manufacturing processes, particularly with the highly cross-linked polyethylene (PE) ensuring excellent long-term outcomes of THA.3 Nonetheless, debate continues over the optimal surgical approach, implant fixation, head sizes, or bearing surfaces. National joint registry data play an important role in monitoring implants, measuring performance and survivorship nationwide such as the Scandinavian registries and the United Kingdom national joint registry, which also collects patient-reported outcome measures' data.4 However, in clinical research, high-quality randomized controlled trials (RCTs) provide strong evidence for the efficacy of healthcare interventions and inform evidence-based medicine.5,6 In particular, RCTs with results demonstrating clinically or statistically significant differences between two interventions indicate a positive effect of one intervention over another.7,8 A large number of RCTs have been conducted in THA over the years with only few reporting significant findings reflecting the lack of marginal effects of evaluated surgical interventions.9

In this systematic review of the literature, we therefore aim to evaluate published RCTs in primary THAs summarizing the available high-quality evidence.

Methods

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (PRISMA),10 we carried out the electronic searches in January 2018 and updated searches in January 2020. We searched the Cochrane Central Register of Controlled Trials (2020, Issue 1), Ovid MEDLINE (including Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid MEDLINE, and Versions) (1946-20 January 2020), and Embase (1980-20 January 2020). We limited our searches to the English language literature. In MEDLINE, we combined the subject-specific search strategy with the sensitivity maximizing version of the Cochrane Highly Sensitive Search Strategy for identifying randomized trials.11 The following search strategy was used [(rct OR randomised OR randomized OR “clinical trial” OR blinded OR “controlled trial”).ti,ab*ARTHROPLASTY, REPLACEMENT, HIP/(“total hip replacement*” OR “THA”").ti/Document type Clinical Trial OR Controlled Clinical Trial OR Randomized Controlled Trial].

We examined the titles and abstracts of articles identified in the search as potentially relevant trials. We obtained the full texts of trials that fulfilled our inclusion criteria (i.e., RCTs for THA) and those that were unclear from perusal of the abstracts. We excluded nonrandomized trials, trials on neck of femur fractures/revision surgery, systematic reviews, and meta-analyses. Trials that met our inclusion criteria were assessed by two authors (H.E.M. and S.R.P.) using a binary outcome measure of whether they reported statistically significant findings. These were then classified according to the intervention groups (surgical approach, fixation method, and design) in a narrative review summarizing the evidence. The results were expressed descriptively in numbers and percentages. SPSS 16.0 software (SPSS) was used for descriptive statistical analysis.

Results

The electronic searches produced 5141 records, and additional 6 records were identified from reference lists of some included studies. After removing duplicates and screening abstracts, 952 studies were assessed for eligibility, and 312 RCTs met the inclusion criteria and were included (Figure 1). The total number of patients in those 312 RCTs was 34,020. A steady increase has been observed in the number of RCTs published per year with the first conducted in the early 1990s to an average of 20 RCTs per year in the 2010s (Figure 2). Sixty-one RCTs (19.5%) reported significant differences between the intervention and the control groups. The trials were classified according to intervention groups (Table 1).

Figure 1
Figure 1:
Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram showing electronic searches results and included studies. RCT = randomized controlled trial
Figure 2
Figure 2:
Chart showing the number of RCTs per year of publication. RCT = randomized controlled trial
Table 1 - The Number of RCTs Classified per Group of Intervention and Percentage of RCTs With Significant Findings
Category No. of RCTs No. of RCTs With Significant Findings
Surgical approach 72 5 (6.9%)
Fixation 7 1 (14.3%)
Cement 16 5 (31.3%)
Femoral stem 46 3 (6.5%)
Head sizes 5 1 (20%)
Cup design 18 2 (11.2%)
Polyethylene 25 10 (40%)
Bearing surfaces 30 4 (13.3%)
Metal-on-metal THA 30 20 (66.6%)
Resurfacing 20 1 (5%)
Navigation 15 3 (20%)
Robotics 3 0
Surgical technique 12 5 (41.6%)
Closure, drains, and postoperative care 13 1 (7.7)
Total 312 61 (19.5%)
RCT = randomized controlled trial, THA = total hip arthroplasty

Surgical Approach

Seventy-two RCTs with 6728 patients evaluated different surgical approaches or related aspects with only five RCTs (6.9%) reporting significant differences between the intervention groups (Table 2). Hamilton et al12 evaluated the use of implant positioning software with fluoroscopy in anterior THA in 200 patients and reported closer results to target but with longer operative and fluoroscopy time. Takada et al15 compared direct anterior with anterolateral approaches in bilateral THA in 30 patients at a 1-year follow-up focusing on nerve injury and muscle atrophy measured on CT and MRI. They reported no differences in clinical outcomes despite significant differences in muscle atrophy and increased nerve injury with the anterior approach. Acetabular implant positioning was compared radiographically in 60 patients using supine versus lateral patient positioning through a modified Watson-Jones approach with more accurate cup positioning in the supine position.13 Moon et al14 compared two techniques of posterior soft tissue repair in 167 hips (150 patients) at a 28-month follow-up and reported better outcomes and less dislocations with trans-osseous repair compared with gluteus medius/short rotators tendon-to-tendon repair. Finally, Kruse et al16 compared radiographic outcomes of posterior and lateral approaches in 80 patients and reported that the femoral offset and abductor moment arm were significantly increased when using posterior compared with lateral approach.

Table 2 - Surgical Approaches' Randomized Controlled Trials With Significant Findings
Study Intervention Outcome Measures Results
Hamilton et al12 Surgical positioning software with fluoroscopy versus fluoroscopy-alone technique in anterior THA (n = 200) Cup placement time, total fluoroscopy time, and cup position Cups placed using software were significantly closer to the target abduction angle (P < 0.001) with fewer outliers.
Cup placement took longer in the software group (P < 0.001), and 2 seconds more total fluoroscopy time (P < 0.001).
Takada et al 13 Supine versus lateral position using the modified Watson-Jones approach (n = 60) Cup positioning on radiograph and CT (target abduction 40°) The supine group was significantly more accurate than lateral group (2.4° versus 4.5°; 95% CI 0.7–3.5; P < 0.01).
No significant difference in terms of radiographic cup anteversion.
Moon et al 14 Transosseous versus gluteus medius tendon (tendon-to-tendon) posterior repair at ∼28.8 months FU (n = 167 hips/150 patients) Failure of repair using radiopaque markers radiographically, dislocation rate Transosseous group failure was (18.4%) compared with tendon-to-tendon group (65%; P < 0.001).
Dislocation rate was significantly higher in the tendon-to-tendon group (7 versus 1.1%; P = 0.041).
Takada et al 15 Direct anterior (DA) versus anterolateral THA at 1-year FU (n = 30 bilateral) Lateral femoral cutaneous nerve (LFCN) injury, and tensor fascia lata (TFL) atrophy on CT and MRI Temporary LFCN injury in DA group only (23.3%).
The ratio of the 3-month postoperative to preoperative cross-sectional area of TFL on CT significantly lower on DA side (P < 0.01).
At 1-year MRI, the mean grade of fatty atrophy of TFL by Goutallier classification was significantly higher in DA (P = 0.03).
No significant difference in clinical outcomes between both sides at postoperative 1 year.
Kruse et al 16 Posterior versus lateral approach (n = 80) Radiographic cup position, femoral offset, abductor moment arm, and leg length discrepancy between the two approaches Mean anteversion was 5° larger in the posterior approach (95% CI, −8.1 to −1.4; P = 0.006).
Mean inclination was 5° less steep (95% CI, 2.7–7.2; P < 0.001) compared with the lateral approach.
The posterior approach had a larger mean femoral offset of 4.3 mm (95% CI, −7.4 to −1.3, P = 0.006), mean total offset of 6.3 mm (95% CI, −9.6 to −3; P < 0.001), and mean abductor moment arm of 4.8 mm (95% CI, −7.6 to −1.9; P = 0.001) compared with the lateral approach.
Femoral offset and abductor moment arm were significantly increased when using the posterior approach.
CI = confidence interval, THA = total hip arthroplasty

Twenty-two RCTs looked specifically at minimally invasive surgery techniques and compared the outcomes with standard techniques including anterior, anterolateral, and posterior approaches; none have reported significant differences in their measured outcomes. The remaining 45 RCTs were as follows (Appendix 1): mini-incisions and two-incision approaches in 13 RCTs, anterior versus posterior approaches in 9 RCTs, anterior versus lateral approaches in 7 RCTs, lateral versus posterior approaches 4 RCTs, variant posterior approaches such as repair of soft tissues or not in 4 RCTs, piriformis sparing approach in 2 RCTs, use diathermy and electrocautery in 2 RCTs, and one RCT for each supercapsular percutaneously assisted approach, trans-trochanteric approach, outpatient anterior approach and patient positioning; none of these 45 RCTs reported any significant differences.

Fixation (Cemented Versus Cementless) of Total Hip Arthroplasty

Seven RCTs compared cemented and cementless THA of different brands with a total of 1271 patients. Only one trial, Corten et al,17,18 reported significantly better survivorship for cementless THA in their 20-year follow-up report of their 93 patients from an original RCT sample size of 250 patients (P = 0.020). The cementless tapered stem had an extremely good survival rate of 99%. Radiographs showed evidence of mild stress-shielding around 95% of the cemented stems and 88% of the cementless stems; stress-shielding of grade 3 or greater was seen around the remaining 12% of the cementless stems. The remaining six RCTs reported no significant differences between cemented and cementless THA although their follow-up was only up to 5 years.

Cement Trials

Sixteen RCTs with a total of 979 patients evaluated cement comparing different viscosities or different types of cement restrictors with five RCTs (31.3%) reporting significant findings (Table 3). Koessler et al19 evaluated a modified cementing technique to reduce the intramedullary pressure in 120 patients and measured the embolic events using continuous perioperative transesophageal echocardiography reporting significant embolic events with conventional cementing techniques although no patient developed frank fat embolism syndrome. Visser et al20 compared three types of cement restrictors in 93 patients measuring their postoperative radiographs efficiently and reported significant failures with the Biosem restrictor (SEM). Degradable cement restrictors were reported to have significantly worse outcomes in three RCTs. Freund et al21 reported more failures with a resorbable restrictor with a longer cement plug although no difference was observed in stem loosening at a 2-year follow-up. Schauss et al22 also reported a shorter cement plug with nondegradable plugs in 130 patients compared with degradable restrictors. Finally, Wembridge et al23 compared PE with biodegradable cement restrictors in 32 patients and reported worse migration and longer cement plug with the biodegradable restrictors.

Table 3 - Cement Randomized Controlled Trials With Significant Findings
Study Intervention Outcome Measures Results
Koessler et al19 Conventional cemented versus modified cemented THA (vacuum drainage placed in the proximal femur to reduce the increase of intramedullary pressure during insertion of the prosthesis) (n = 120) Embolic events detected by continuous transesophageal echocardiography (TEE) hemodynamic monitoring and blood gas analysis were done during the perioperative period. Significantly more embolic events with the conventionally cemented group (93.3% versus 13.3% P < 0.05).
No clinical signs of fat embolism syndrome in any study patient.
Visser et al20 Biosem, Cemlock, or Thackray cement plugs in Stanmore hip prosthesis THA (n = 93) Occlusion and stability on postop radiographs Significantly more failures with Biosem:
The percentages of deficient plugs were Biosem 78% (25/32), Cemlock 32% (9/28), and Thackray 18% (6/33).
Comparison of the smaller sizes of the prosthesis versus the larger sizes showed a significant effect on the stability of the plugs.
Freund et al21 Resorbable (Shuttle stop) versus nonresorbable polyethylene cement restrictor at 2-year FU (n = 70) Migration of the restrictor, cement leakage, and possible early aseptic loosening More failures with displacement or leakage of the resorbable restrictor (3 versus 16; P < 0.01).
No differences in stem loosening or grade of radiolucent lines at 2 years.
Schauss et al22 Degradable versus nondegradable cement restrictor (n = 130) Distal migration during stem insertion, radiographs Better stability with nondegradable plugs
Cement plug length 27 versus 15 mm (P = 0.003).
Wembridge et al23 UHMWPE versus biodegradable cement restrictor (n = 32) Postoperative radiographs restrictor migration Worse results with biodegradable restrictor:
Mean migration was 3.0 versus 0.5 cm (biodegradable versus UHMWPE, P < 0.002).
UHMWPE = ultra-high-molecular-weight polyethylene

The remaining 11 RCTs reported no significant differences, including one RCT comparing Hardinge cement restrictor with an autogenous bone plug restrictor, one RCT compared the thickness of the cement mantle (thin versus thick), three RCTs comparing fluoride-containing acrylic cement with conventional cement, Palacos, or Palacos G cement. Additional six RCTs made the following comparisons between different types of cement with no significant differences reported; low/medium Simplex P cement versus high-viscosity Simplex AF cement (Stryker-Howmedica), Cemex Rx (Cemex System, Tecres, S.p.A.) versus Palaces R cement (Schering Plough, Labo NV), Palamed G (Biomet Merck) versus Palacos R cement (Schering Plough, Labo NV), SmartSet HV (DePuy CMW) versus Palacos R cement (Schering Plough), Palacos R (Schering Plough) versus Palacos R + G (Schering-Plough), and Palacos versus Palamed cement (Biomet Merck).

Femoral Stems Trials

Forty-six RCTs with 5242 patients evaluated aspects specifically related to femoral stems. Only three RCTs reported significant differences. Berger et al24 reported a significantly lower rate of cement mantle deficiencies when using stem centralizer in 60 patients (P < 0.001). In their trial of 39 patients at a 2-year follow-up, Tanzer et al25 assessed femoral bone remodeling using dual-energy radiograph absorptiometry after a titanium proximally porous-coated femoral implant with or without hydroxyapatite (HA)-tricalcium phosphate coating. The HA-tricalcium phosphate-coated stems had significantly less femoral bone loss. Luites et al26 compared 22 titanium and 20 HA-coated ProxiLock stems at a 2-year follow-up and reported significantly higher early failures with the ProxiLock stems requiring revision surgery.

The remaining 43 trials reported no significant differences (Appendix 1). These included eight RCTs comparing different cemented stems, nine RCTs comparing uncemented stems, three RCTs comparing collared versus collarless stems, six RCTs evaluated HA-coated stems, four RCTs evaluated porous-coated stems, nine RCTs evaluated short stems, and three RCTs looked at different preparation techniques of femoral stems.

Head Sizes

Five RCTs compared different head sizes in 889 patients. Only one large multicentre RCT, Howie et al,27 reported significant findings. They compared the dislocation rate between 28 and 36 mm metal heads on highly cross-linked polyethylene (HXLPE) at a 1-year follow-up in 533 patients with primary THA: 4.4% (12/275) versus 0.8% (2/258) (95% confidence interval, 0.9% to 6.8%) (P = 0.024). The remaining four RCTs reported no significant differences including 28 versus 32 mm ceramic-on-ceramic (CoC) THA; 32 versus 36 mm ceramic-on-PE THA, 28 versus 36 mm metal-on-cross-linked PE, and small head 28 mm metal-on-metal versus metal-on-PE.

Cup Design

Eighteen RCTs with 1778 patients evaluated aspects of acetabular component designs with two RCTs reported significant findings (11.2%). Faris et al28 evaluated the use of all-PE cemented cups (407 THA) with or without integrated cement spacers attached at the back of the cup to ensure a uniform cement mantle. They reported a significantly higher rate of failure with integrated spacers compared with no spacers at a 6.5-year follow-up. Stilling et al29 compared titanium uncemented cups with first-generation HA-coated cups at a 15-year follow-up with a significantly higher revision rate for HA-coated cups.

The remaining 16 RCTs were a heterogeneous group that made the following comparisons with no significant differences between the interventions in either clinical or radiographic outcomes, including solid versus cluster hole cups; scientific versus Omnifit cups; tantalum versus titanium cups; porous tantalum monoblock cup versus porous-coated titanium monoblock cup; trabecular metal cups versus titanium fiber-mesh cups; porous titanium versus conventional titanium cups; solid-backed versus cluster-hole cups all without screws; HA-coated versus porous-coated cups; cementless cup with or without screws; uncemented 61% high porosity versus 45% low porosity cups; BICON-PLUS versus BICON-PLUS NT cup; finger-packing versus cement pressurization cemented cups; cemented Charnley versus uncemented Duraloc 1200 cups; cemented PE versus uncemented porous-coated cups; cemented cups versus porous-coated cups, and all-poly press-fit RM cup with or without screw fixation.

Polyethylene Trials

Twenty-five RCTs with 2216 patients compared different types of PE particularly the effect of cross-linking on wear rates with a long-term follow-up (multiple publications). Ten RCTs (13 studies; Table 4) reported significant differences. Cross-linked polyethylene showed better wear characteristics compared with conventional PE at 5- and 10- and 15-year follow-ups.3032 Similarly, HXLPE consistently shown to have significantly better wear characteristics across different trials up to a 12-year follow-up3340 (Table 4). Vitamin E-infused HXLPE was also shown to have significantly better wear rates across two RCTs with a 3-year follow-up compared with ultra-high-molecular-weight polyethylene (UHMWPE).41,42 The remaining 12 studies reported no significant differences and made the following comparisons: cross-linked polyethylene versus PE in three trials; HXLPE versus PE in four trials; Vitamin E-infused HXLPE versus HXLPE in four trials; and one trial compared Sulene-poly (Sulene; Zimmer GmBH) versus Durasul-poly liner (Durasul; Zimmer that was sterilized by ethylene oxide) with no significant differences (Appendix 1).

Table 4 - Polyethylene Randomized Controlled Trials With Significant Findings
Study Intervention Outcome Measures Results
Geerdink et al30 XLPE versus conventional PE at 5-year FU (n = 127/133 hips) Polyethylene wear rates Better results with cross-linked at a mean wear rate of 0.083 (SD 0.056) versus 0.123 (SD 0.082) mm/yr.
Engh et al31 XLPE versus conventional PE at 10-year FU (n = 185) Revision for wear-related complications. Better survivorship at 10 years for XLPE 100% versus 94.7% (P = 0.003).
For unrevised hips, the mean linear wear rate was 0.22 versus 0.04 mm/yr for XLPE (P < 0.001).
Hopper et al32 XLPE versus conventional PE THA at 15 years (n = 85 hips) (230 hips/220 patients at the beginning of the trial) THA wear, osteolysis, revision rate, radiographic follow-up Cumulative incidence of revision at 15 years using reoperation for wear-related complications as an end point was lower in the XLPE group (0% versus 12%; P < 0.001).
Among unrevised THAs with a minimum 14-year radiographic follow-up: The mean steady-state linear wear rate for XLPE (0.03 ± 0.05 versus 0.17 ± 0.09 mm/yr P < 0.001).
Martell et al33 HXLPE versus conventional polyethylene (PE) at 2- to 3-year FU (n = 46) Polyethylene wear rates A significant reduction in 2- and 3-dimensional linear wear rates (42% and 50%) was found with the HXLPE group (P = 0.001 and P = 0.005).
Glyn-Jones et al34 HXLPE versus conventional PE at 3-year FU (n = 54) RSA analysis, creep and wear behavior Less wear with HXLPE with mean total penetration 0.35 mm (SD 0.14) for HXLPE versus 0.45 mm (SD 0.19) (P = 0.0184).
Significant difference (P = 0.012) in the mean wear rate for HXLPE was 0.03 (SD 0.06) versus 0.07 (SD 0.05) mm/yr.
Thomas et al35 HXLPE versus conventional PE at 7-year FU (n = 54) Wear rate, RSA Mean total femoral head penetration was significantly lower in HXLPE 0.33 versus 0.55 mm (P = 0.005).
The mean steady-state wear rate of HXLPE was 0.005 versus 0.037 mm/yr (P = 0.007).
Glyn-Jones et al36 HXLPE versus conventional PE at 10-year FU (n = 39/54) RSA wear, OHS Significantly less wear rate with the HXLPE group 0.003 (SD 0.023) versus 0.030 (SD 0.0.27) mm/yr.
Volumetric penetration from 1 to 10 years for the UHMWPE group was 98 versus 14 mm (P = 0.01).
Broomfield et al37 HXLPE versus conventional PE at 12-year FU (n = 25/54) Periacetabular osteolysis, CT Significantly lower incidence of periacetabular osteolysis in the HXLPE group (P = 0.042)
Calvert et al38 HXLPE versus conventional PE at 4-year FU (n = 119) Linear 3D and volumetric wear Linear, 3-dimensional, and volumetric wear rates were significantly less in HXLPE (P < 0.05).
Mutimer et al39 HXLPE versus conventional PE at 5-year FU (n = 122) Radiographs, wear rate The 2D wear rate for HXLPE was significantly less than standard poly 0.05 versus 0.26 mm/yr (P < 0.001).
Langlois et al40 HXLPE versus moderately XLPE in cemented component at 8-year FU (n = 68) Clinical outcomes, wear rates Better wear rates with HXLPE: The rate of penetration from one year onward was 0.0002 versus 0.1382 mm/year (P < 0.001).
Scemama et al41 HXLPE/Vitamin E-infused versus UHMWPE hybrid THA at 3-year FU (n = 74) Femoral head penetration radiographically Better wear rates with the Vitamin E group
Median creep 0.111 versus 0.170 mm (P = 0.046).
Median steady-state penetration rate 0.008 versus 0.133 mm/year (P = 0.043).
Rochcongar et al42 HXLPE/Vitamin E-infused versus UHMWPE cups at 3-year FU (n = 62) RSA wear rate The cumulative penetration after 3 years was 0.200 mm for the HXLPE/Vitamin E cup versus 0.317 mm for the UHMWPE cup (P < 0.0001).
PE = polyethylene; THA = total hip arthroplasty, HXLPE = highly cross-linked polyethylene, XLPE = cross-linked polyethylene, UHMWPE = ultra-high-molecular-weight polyethylene, RSA = radiostereometric analysis, OHS = Oxford Hip Score

Bearing Surfaces

Thirty RCTs with 5425 patients compared different bearing surfaces in THA with only four RCTs (13.3%) reporting significant findings (Table 5). Kim43 compared the PE wear rate between zirconia head and cobalt chromium heads in sequential bilateral THAs in 52 patients at a 7.1-year follow-up and reported lower wear rates with zirconia heads. von Schewelov et al44 compared four different articulations of 22.225 mm heads made from zirconium oxide ceramic or stainless steel, articulating against either standard UHMWPE or Hylamer; a modified-UMWPE, in 114 patients at a 5-year follow-up. They reported worse outcomes with zirconium oxide heads/Hylamer and advised against their use. Hylamer was later withdrawn from the market due to the high failure rate. Vendittoli et al,45 in a long-term RCT, compared conventional metal-on-PE articulations with alumina on alumina ceramic bearings with significantly better outcomes in favor of ceramic bearings. Finally, Atrey et al,46 in their 10-year follow-up trial of different bearing surfaces including ceramic-on-ceramic (CoC), reported a less wear rate with metal-on-cross-linked polyethylene compared with metal-on-UHMWPE.

Table 5 - Bearing Surfaces' Randomized Controlled Trials With Significant Findings
Study Intervention Outcome Measures Results
Kim 43 Zirconia head versus cobalt-chromium head in bilateral THA at 7.1-year FU (n = 52) Polyethylene wear, radiographic evaluations Significantly lower wear with zirconia heads:
The mean polyethylene wear rate was 0.08 mm/yr with zirconia heads versus 0.17 mm/yr with cobalt-chromium heads (P = 0.004).
Volumetric wear 350.8 versus 744.7 mm3 (P = 0.004).
von Schewelov et al44 4 articulations: Stainless steel/Enduron, stainless steel/Hylamer cup, zirconium oxide ceramic/Enduron, or zirconium oxide ceramic/Hylamer at 5-year FU (n = 114) Wear and migration RSA analysis Mean annual wear 0.11 mm for a stainless steel/Enduron articulation, 0.34 mm for stainless steel/Hylamer cup, 0.17 mm for zirconium oxide ceramic/Enduron, and 0.40 mm for zirconium oxide ceramic/Hylamer. The difference between the groups was significant (P < 0.008) except for stainless steel/Hylamer versus zirconium oxide ceramic/Hylamer (P = 0.26).
Zirconium oxide ceramic femoral head should not be used with a polymethylmethacrylate acetabular component.
Vendittoli et al45 Metal-on-poly versus alumina on alumina bearings at 9- to 15-year FU (n = 107 hips) Reoperation, revision rate, radiological outcomes (UCLA, WOMAC) Better outcomes with ceramic bearings:
Revision rate for aseptic loosening or wear 11.6% versus 1.4% (P = 0.017).
Significant difference in the UCLA score in favor of ceramic bearings (5.6 versus 4.8, P = 0.015).
No significant difference in for WOMAC score.
Atrey et al46 UHMWPE/metal head, XLPE/metal head, or ceramic-on-ceramic at 10-year FU (n = 97 hips) Radiological analysis of wear, HHS, WOMAC, SF-12 Significantly reduced rate of linear wear with XLPE (0.07 mm/yr) compared with UHMWPE (0.37 mm/yr) (P = 0.001).
Volumetric wear was also significantly reduced in the XLPE group (29.29 mm3/yr) compared with the UHMWPE group (100.75 mm3/yr) (P = 0.0001). THHS was significantly less in the UHMWPE group (P = 0.0188) than in the other two groups.
No difference in WOMAC or SF-12 between the groups.
THA = total hip arthroplasty, XLPE = cross-linked polyethylene, UHMWPE = ultra-high-molecular-weight polyethylene, HHS = Harris Hip Score

The remaining 26 RCTs reported no significant differences including 10 RCTs comparing CoC with ceramic-on-polyethylene bearings, 11 RCTs comparing CoC with metal-on-polyethylene bearings, four RCTs comparing metal-on-polyethylene with ceramic-on-polyethylene bearings and one trial compared different polyethylene liners with metal heads.

Metal-on-Metal Total Hip Arthroplasty

Thirty RCTs compared metal-on-metal (MoM) THA with other bearing surfaces in 2912 patients. This was a unique group of trials where nearly all RCTs that looked at metal ions in their reported outcomes found statistically significant higher levels of ions with MoM but similar clinical outcomes and patient-reported outcome measures. Trials that did not report on metal ion levels (10 RCTs) found no significant differences in their reported outcomes comparing MoM with other bearings (Appendix 1).

Hip Resurfacing Versus Total Hip Arthroplasty

Twenty RCTs looked at hip resurfacing in 1762 patients. Only one RCT (5%) reported statistically significant differences. Penny et al47 compared Articular Surface Replacement (ASR) hip resurfacing prosthesis with THA at a 2-year follow-up in 38 patients and found higher consistently higher metal ions levels with ASR (P ≤ 0.001). The remaining 19 trials reported no statistically significant differences although the majority were short-term follow-ups (2 to 5 years). These included 15 RCTs comparing outcomes of hip resurfacing versus THA; two RCTs compared hip resurfacing with MoM THA; one RCT compared cemented versus cementless femoral stem; and one RCT compared posterior versus anterolateral approach in hip resurfacing (Appendix 1).

Navigation and Robotics

Navigation was evaluated in 15 RCTs with a total of 1158 patients. Three RCTs (20%) reported significant differences with improved cup positioning (Table 6). The remaining 12 RCTs reported no significant differences including navigated versus free hand techniques for THA in 10 RCTs, one RCT compared fluoroscopy versus imageless navigation minimally invasive techniques, and one RCT compared navigated versus standard hip resurfacing (Appendix 1).

Table 6 - Navigation Randomized Controlled Trials With Significant Findings
Study Intervention Outcome Measures Results
Kalteis et al70 Free-hand versus computer assistance image-free navigation cup positioning (n = 45) CT scans for cup position More accurate positioning with navigation and deviations from the desired cup position (45° inclination, 15° anteversion) were significantly lower in the computer-assisted study group (P < 0.001).
Verdier et al71 NAVEOS navigation versus freehand cup placement THA at 3-month FU (n = 78) CT cup position measurements (safe zone: 15° ± 10° radiological anteversion and 40° ± 10° radiological inclination) Better cup positioning with navigation: Cups in the safe zone were 67% versus 38% (P = 0.012).
Navigation was discontinued prematurely in 6 patients (intention-to-treat analysis used). Complications: 1 dislocation and 1 infection, both in the freehand group.
Yamada et al72 CT-based 2D-3D navigation versus paired-point matched navigation group (PPM) (n = 80) Accuracy of cup orientation (absolute difference between the intraoperative record and the postoperative measurement) Better accuracy with CT-based 2D-3D matched navigation: Accuracy of cup inclination 2.5° ± 2.2° versus 4.6° ± 3.3° (P = 0.0016).
Accuracy of cup anteversion 2.3° ± 1.7° versus 4.4° ± 3.3° (P = 0.0009)
THA = total hip arthroplasty.

Furthermore, three RCTs evaluated the use of robotics in THA in 275 patients. In their early robotic RCT, in 2003, Honl et al48 randomized 154 patients to conventional or robotic-assisted THA and compared 2-year outcomes using Harris, Merle d'Aubigné, and the Mayo scores with no significant differences reported. However, the duration of robotic procedures was longer with 18% of attempted robotic implantations converted to manual implantations as a result of system failure. Dislocation was more frequent with robotics 11/61 versus 3/80 (P < 0.001) as well as revision surgery 8/61 (P < 0.001). Lim et al49 evaluated the effects of robotic milling versus manual rasping on the accuracy of short femoral stem positioning and on the clinical outcomes in 54 patients at a 2-year follow-up and reported no significant differences. Finally, Bargar et al50 reported a mean 14-year follow-up outcomes of 67 patients from 2 U.S. Food and Drug Administration trials who underwent conventional versus active robotic system THA. No statistically significant difference was observed in probability of a revision for wear or loosening. The robotic group had statistically significant higher Health Status Questionnaire pain and Harris pain scores but lower Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores.

Surgical Technique and Miscellaneous Trials

Twelve heterogeneous RCTs looking at surgical technical aspects of THA are presented in this group with 1098 patients. Five RCTs (41.6%) reported significant findings in favor of using a measuring device to minimize leg length discrepancy,51 high-efficiency particulate air to reduce colony-forming units within 5 cm of the surgical wound,52 better acetabular component positioning measured on postoperative CT scan with the use of patient-specific instrumentations,53 the use of transverse acetabular ligament for cup anteversion and inclination,54 and the use of digital inclinometer-assisted cup insertion technique55 (Table 7).

Table 7 - Surgical Techniques Randomized Controlled Trials With Significant Findings
Study Intervention Outcome Measures Results
Bose et al51 THA with or without measuring device for leg length discrepancy (n = 117) Leg length discrepancy radiographs Statistically significant decrease in limb-length inequality with the use of measuring device average LLD 8.8 versus 3.4 mm (P < 0.01).
Stocks et al52 Directed air flow high-efficiency particulate air (HEPA), system present but switched off or control filter during THA (n = 36) Airborne particulate, colony-forming units within 5 cm of surgical wound All particulate and bacterial counts at the surgical site were significantly lower in the directed air flow group (P < 0.001).
Small et al53 Patient specific versus standard surgical instruments THA (n = 36) Acetabular shell position on CT scan Better implant positioning with intervention group; differences found between planned and actual anteversion were −0.2° ± 6.9° for PSI versus −6.9° ± 8.9° (P = 0.018).
Meermans et al54 Freehand versus transverse acetabular ligament reference for acetabular anteversion (n = 80) Radiographic measurement of anteversion and inclination. Better component positioning using TAL as a reference: Anteversion: 21° (2° to 35°) versus 17° (2° to 25°) (P = 0.004). Inclination: No significant difference between the two techniques although less outliers (safe zone) with TAL.
O'Neill et al55 Freehand, modified Mechanical Alignment Guide (MAG) or digital inclinometer-assisted cup insertion techniques (n = 270) Postoperative radiographic cup inclination as measured by target to apparent operative inclination (AOI 35° ± 2.5°) Digital inclinometer technique achieved AOI target in 88% versus 71% of MAG versus 51% Freehand.
Statistically significant differences between:
Freehand versus inclinometer groups (P < 0.001)
Freehand versus MAG (P < 0.001)
Digital inclinometer versus MAG (P < 0.023).
THA = total hip arthroplasty, LLD = leg length discrepancy

The remaining seven RCTs reported no significant differences and made the following comparisons: sequential versus simultaneous bilateral THA; removal versus retention of subchondral bone plate for cemented cups in two trials; cup insertion with or without inclinometer; the use of abductor shuck versus trans-osseous pins (a level-caliper system using trans-osseous periacetabular and femoral pins as two fixed points) versus patella electrocardiogram leads to measure intraoperative leg length; plasma-rich platelets versus no plasma-rich platelet in bilateral THA; and autologous impaction bone grafting versus traditional technique in cementless THA (Appendix 1).

Skin Closure, Drain, and Postoperative Care

There were 13 RCTs in this group with 2287 patients included. Only one RCT (7.7%) reported significant findings. Rui et al56 compared staples versus absorbable subcuticular suture for skin closure at a 3-month follow-up in 165 patients. They reported no infections in sutures group versus 2 superficial infections (2.4%) in the staples group. A statistically significant difference was observed in favor of the suture group for time to dry surgical incisions (4.8 versus 5.0 days, P = 0.028), hospital stay (6 versus 12, P < 0.001), and cost saving $82.2 per case. Although shorter surgical time to use staples (24.7 versus 357.7 seconds, P < 0.001), no difference was observed in patients' satisfaction. However, two additional RCTs made similar comparisons and reported no significant difference between staples and sutures (Appendix 1).

Four RCTs evaluated the use of surgical drain postoperatively comparing it to no drain and reported no significant differences in their measured outcomes. Different postoperative care instructions were also evaluated in six RCTs with no significant differences including weight-bearing status after cementless THA (unrestricted versus protected) across four RCTs and hip precautions after the posterolateral approach in two RCTs (Appendix 1).

Discussion

In this study, we provide a comprehensive overview of 312 RCTs in primary THA. The total number of patients included in those RCTs was 34,020. The most important finding is that only 19.5% of trials reported significant differences between the intervention and the control groups for the outcome measures used by those trials.

Different surgical approaches were evaluated in 72 trials, the largest subgroup of trials, with ∼93% reporting no significant differences in their reported outcomes. This evidence supports surgeons' preference based on their familiarity with a particular approach that allows adequate exposure to perform THA safely acknowledging that each surgical approach has its own pros and cons. The majority of modern THA cementless acetabular components are hemispheric press-fit with improved modular liner congruity and fixation. Furthermore, the use of HXLPE liners seems to have substantially reduced wear rate and osteolysis. This was a consistent finding in a large number of RCTs included. Fixation of THA and stem designs, once fiercely debated topics, are covered by a variety of RCTs with no clear advantage of the comparators. Forty-six RCTs evaluated various designs of femoral stems, both cemented and cementless, with similar clinical outcomes reported at short to medium term. Here lies one of the limitations of RCT evidence where long-term survivorship data, most pertinent to stem survivorship, are lacking.

In total, 60 RCTs compared different bearing surfaces including metal-on-metal bearings that have consistently shown raised levels of metal ions and the familiar mode of failure of this particular bearing. The evidence reviewed equally supports the use of metal-on-PE, CoC, and ceramic-on-PE bearings; the latter is further supported by emerging long-term survivorship and registry data.3,57 Clinical outcomes of hip resurfacing were evaluated in 20 trials in comparison with THA, and functional outcomes were similar at short- to medium-term follow-ups. Trials of navigation techniques show no difference in clinical outcomes although some reported significant differences in radiological outcomes, particularly cup positioning, and a long-term follow-up is needed to see whether this leads to improved clinical outcomes. Finally, skin closure techniques, use of drains, and postoperative weight-bearing status or hip precautions were evaluated in a small number of trials with no significant differences.

Evidence derived from RCTs is based on highly selective populations in a tightly controlled settings and deemed to have the highest reliability. However, most RCTs are short or medium term as obtaining a long-term follow-up is complicated by cost, co-intervention, loss to follow up, and postrandomization variables.58 Long-term observational studies and data registries, despite their inherent limitations, prove more practical in evaluating long-term outcomes of THA such as survivorship and reoperations and provide a pragmatic overview of clinical practice.5961 In its 16th annual report, the UK's national joint registry has collated data for over 1 million primary THA with up to a 15-year follow-up. Ceramic-on-polyethylene bearings performing particularly well and the overall revision rates after primary THA have reduced over the last 10 years after the peak of metal-on-metal bearings.57 Similar trends have been reported in other national registries and long-term follow-up studies3; the RCTs included in this study support those findings.

Patient-reported outcome measures (PROMs) play an important role in evaluating interventions in terms of outcomes that matter to patients and widely used in clinical research.62 The majority of trials included in this study used PROMs (Oxford Hip Score, Harris Hip Score, WOMAC) as a primary or secondary measure. A number of studies have demonstrated a ceiling effect of those PROMS where a considerable proportion of patients score the best/maximum or worst/minimum score, making the measure unable to discriminate between subjects at either extreme of the scale.63,64 However, more recent registry-based observational studies have demonstrated that population-wide data do not exhibit a ceiling or floor effect of these PROMs.65 Others have found only weak-to-moderate correlation between PROMs and patient satisfaction.66 The International Society of Arthroplasty Registries PROMs working group acknowledges the variation in the specific PROMs used and does not make specific recommendations about which PROMs to use in arthroplasty registries.67 PROMs are used in many registries to support quality assurance and provide information on value-based care. However, in the context of RCTs, they may not detect the marginal effects of the evaluated interventions.

This is the first study to undertake a comprehensive overview of RCTs in THA. We do, however, acknowledge limitations to its findings. We did not calculate the treatment effect of individual trials with significant statistical findings and whether this correlated with clinically measurable effects. Furthermore, the quality of reporting trials was not addressed as this aspect falls outside the scope of this study. However, reporting bias or publication bias in clinical research is a known phenomenon where data from trials with negative findings are not publicized, and so they remain inaccessible.68 The prospective registration of trials and public access to study data via results databases had been introduced to minimize the impact reporting bias.69 The true scale of this bias in the clinical literature is unclear. However, ∼80% of published RCTs in THA reported no significant differences “negative trials,” which may indicate that there is no tendency to overestimate the efficacy and underestimate the risks of the interventions evaluated in those trials.

To conclude, THA is a successful and durable operation that has helped millions of patients worldwide. The early failures encountered in the 1970 to 1980s had been largely addressed in the 1990s and the early 2000s with improved metallurgy and manufacturing processes. The RCT evidence presented indicates that for the vast majority of patients, a standard conventional THA with a surgical approach familiar to the surgeon using standard well-established components and highly cross-linked polyethylene leads to satisfactory clinical outcomes. This evidence also offers arthroplasty surgeons the flexibility to use the standard and cost-effective techniques and achieve comparable outcomes. Future trials should also focus on preoperative interventions to improve clinical outcomes, an area that is currently lacking in THA trials.

Appendix 1 Trials With No Significant Findings

-
Category Studies
Surgical approach Brismar 2018, Nistor 2017, De Anta-Díaz 2016, Restrepo 2010, Zomar 2018, Mjaaland 2015, Brun 2019, Taunton 2018, Barrett 2019, Bon 2019, Rykov 2017, Zhao 2017, Cheng 2017, Christensen 2015, Taunton 2014, Barrett 2013, Widman 1999, Morris 2013, Rosenlund 2017, Rosenlund 2016, Ji 2012, Witzleb 2009, Stevenson 2017, Shitama 2009, Speranza 2007, Ogonda 2005, Dienstknecht 2014, Reichert 2018, Tan 2019, Krych 2010, Pagnano 2009, Pagnano 2008, Abdel 2017, Sershon 2017, Hu 2012, Goyal 2017, Khan 2012a, Khan 2012b, Pace 2008, Ouyang 2018, Horwitz 1993, Tarasevicius 2011, Tarasevicius 2010, Tarasevicius 2006, Chiu 2000, Chimento 200, Lawlor 2005, Kim 2006, Meneghini 2008, Wohlrab 2008, Mazoochian 2009, Meneghini 2009, Della Valle 2010, Müller 2010, Pospischill 2010, Varela-Egocheaga 2010, Yang 2010, Foucher 2011, Goosen 2011, Martin 2011, Müller 2011, Dienstknecht 2013, Greidanus 2013, Varela-Egocheaga 2013, Petridis 2014, Biau 2015, Repantis 2015
Fixation Wykman 1991, Laupacis 1993, Rorabeck 1996, Kim 2002, Mulliken 1996, Grant 2005
Cement Jeffery 1997, Nivbrant 2001, Digas 2004, Digas 2005, Nelissen 2005, Digas 2006, Hallan 2006, Husby 2010, Van Der Voort 2016, Meinardi 2016, van IJperen 2018
Stem Rasquinha 2004, Lachiewicz 2008, McCalden 2010, Hutt 2014, Marston 1996, Nivbrant 1999, Thien 2010, Kadar 2011, Ström 2006, Johnston 2001, Karachalios 2004, Healy 2009, Simpson 2010, Nysted 2011, Bennett 2014, Miyatake 2015, Van Oldenrijk 2017, Meding 1997, Meding 1999, Settecerri 2002, Ciccotti 1994, Kärrholm 1994, Incavo 1998, Yee 1999, Yoon 2007, Camazzola 2009, Kärrholm 2002, MacDonald 2010, Baad-Hansen 2011, Sandiford 2014, Gielis 2019, von Roth 2014, Salemyr 2015, Freitag 2016, Kim 2016, Koyano 2017, Schilcher 2017, Ferguson 2018, Samy 2019, Laupacis 2002, Hjorth 2016, Pitto 1999
Head sizes Lee 2014, Lindalen 2015, Howie 2016, van der Veen 2019
Cup design Flivik 2005, Digas 2006, Bjørgul 2010, Baad-Hansen 2011, Angadi 2012, Pakvis 2012, Ullmark 2012, Veldstra 2012, Naudie 2013, Broeke 2013, Ayers 2015, Blakeney 2015, Salemyr 2015, Wegrzyn 2015, Minten 2016, Gallen 2018.
Polyethylene Engh 2006, García-Rey 2008, Ayers 2009, Geerdink 2009, McCalden 2009, Jonsson 2015, Salemyr 2015, Nebergall 2017, Shareghi 2015, Devane 2017, Teeter 2017, Galea 2019
Bearing surfaces Amanatullah 2011, Atrey 2018, Bascarevic 2010, Beaupre 2013, Beaupre 2016, Borgwardt 2017, Cai 2012, Capello 2005, Capello 2005, Capello 2008, D'Antonio 2002, D'Antonio 2005, Hamilton 2010, Ise 2009, Jassim 2015, Kadar 2011, Kim 2013, Lewis 2010, Lombardi 2010, Morison 2014, Nikolaou 2012, Pitto 2008, Sonny 2005, Vendittoli 2007, Zerahn 2011, Zhou 2006
Metal-on-metal THA Lombardi 2001, Brodner 2003, MacDonald 2003, Jacobs 2004, Lombardi 2004, Nygaard 2004, Grübl 2006, Vendittoli 2006, Dahlstrand 2009, Engh 2009, Garbuz 2010, Hailer 2011, Malviya 2011, Weissinger 2011, Zijlstra 2011, Hanna 2012, Schouten 2012, Desmarchelier 2013, Tiusanen 2013, Vendittoli 2013, Zagra 2013, Engh 2014, Gustafson 2014, Zijlstra 2014, Ando 2015, Briggs 2015, Gofton 2015, Engh 2016, Dahlstrand 2017, Schouten 2017
Hip resurfacing Vendittoli 2006, Girard 2006, Girard 2008, Lavigne 2010, Smolders 2010, Vendittoli 2010, Jensen 2011, Petersen 2011, Costa 2012, Penny 2012, Wang 2012, Penny 2013a, Lorenzen 2013, Gerhardt 2015, Tice 2015, Bisseling 2015, Costa 2018, Tao 2018, Gerhardt 2019.
Navigation Kalteis 2006, Parratte 2007, Hart 2008, Sendtner 2011, Reininga 2013, Gurgel 2014, Lass 2014, Weber 2014, Renkawitz 2015, Parratte 2016, Sariali 2016, Weber 2016.
Technique Bhan 2006, Flivik 2006, Vendittoli 2007, Rice 2014, Flivik 2015, Qu 2016, Rutherford 2019
Closure, drains, and postoperative care Livesey 2009, Buttaro 2015, Walmsley 2005, Cheung 2010, Horstmann 2012, Kleinert 2012, Ström 2007a, Ström 2007b, Wolf 2010, Dietz 2019, Peters 2019, Thien 2007

References

1. Laupacis A, Bourne R, Rorabeck C, et al. The effect of elective total hip replacement on health-related quality of life. J Bone Joint Surg Am 1993;75:1619-1626.
2. Charnley J: Arthroplasty of the hip. A new operation. Lancet 1961;1:1129-1132.
3. Evans JT, Evans JP, Walker RW, Blom AW, Sayers A: How long does a hip replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. Lancet 2019;393:647-654.
4. Porter M, Armstrong R, Howard P, Porteous M, Wilkinson JM: Orthopaedic registries—the UK view (National Joint Registry): Impact on practice. EFORT Open Rev 2019;4:377-390.
5. Altman DG, Schulz KF, Moher D, et al.: The revised CONSORT statement for reporting randomized trials: Explanation and elaboration. Ann Intern Med 2001;134:663-694.
6. Evidence-Based-Medicine-Working-Group: Evidence-based medicine: A new approach to teaching the practice of medicine. JAMA 1992;268:2420-2425.
7. Prescott RJ, Counsell CE, Gillespie WJ, et al.: Factors that limit the quality, number and progress of randomised controlled trials. Health Technol Assess 1999;3:1-143.
8. McCulloch P, Taylor I, Sasako M, Lovett B, Griffin D , Randomised trials in surgery: Problems and possible solutions. Bmj 2002;324:1448-1451.
9. Matar HE, Platt SR: Overview of randomised controlled trials in orthopaedic research: Search for significant findings. Eur J Orthop Surg Traumatol 2019;29:1163-1168.
10. Moher D, Liberati A, Tetzlaff J, Altman DG: Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement. PLoS Med 2009;6:e1000097.
11. Lefebvre C, Manheimer E, Glanville J, Chapter 6: Searching for studies, in Higgins JPT, Green S, eds: Cochrane Handbook for Systematic Reviews of Interventions. The Cochrane Collaboration, 2011. Accessed May 15, 2020.
12. Hamilton WG, Parks NL, McDonald JF, Pfefferle KJ: A prospective, randomized study of surgical positioning software shows improved cup placement in total hip arthroplasty. Orthopedics 2019;42:42-47.
13. Takada R, Jinno T, Miyatake K, et al.: Supine versus lateral position for accurate positioning of acetabular cup in total hip arthroplasty using the modified Watson-Jones approach: A randomized single-blind controlled trial. Orthop Traumatol Surg Res 2019;105:915-922.
14. Moon JK, Kim Y, Hwang KT, Yang JH, Kim YH: The incidence of hip dislocation and suture failure according to two different types of posterior soft tissue repair techniques in total hip arthroplasty: A prospective randomized controlled trial. Int Orthop 2018;42:2049-2056.
15. Takada R, Jinno T, Miyatake K, et al.: Direct anterior versus anterolateral approach in one-stage supine total hip arthroplasty. Focused on nerve injury: A prospective, randomized, controlled trial. J Orthop Sci 2018;23:783-787.
16. Kruse C, Rosenlund S, Broeng L, Overgaard S: Radiographic cup position following posterior and lateral approach to total hip arthroplasty. An explorative randomized controlled trial. PLoS One 2018;13:e0191401.
17. Corten K, Bourne RB, Charron KD, Au K, Rorabeck CH: Comparison of total hip arthroplasty performed with and without cement: A randomized trial. A concise follow-up, at twenty years, of previous reports. J Bone Joint Surg Am 2011;93:1335-1338.
18. Corten K, Bourne RB, Charron KD, Au K, Rorabeck CH: What works best, a cemented or cementless primary total hip arthroplasty?: Minimum 17-year followup of a randomized controlled trial. Clin Orthop Relat Res 2011;469:209-217.
19. Koessler MJ, Fabiani R, Hamer H, Pitto RP: The clinical relevance of embolic events detected by transesophageal echocardiography during cemented total hip arthroplasty: A randomized clinical trial. Anesth Analg 2001;92:49-55.
20. Visser CP, Eygendaal D, Coene LN, Tavy DL: Comparative prospective trial of 3 intramedullary plugs in cemented total hip arthroplasty. J Arthroplasty 2002;17:576-578.
21. Freund KG, Herold N, Røck ND, Riegels-Nielsen P: Poor results with the shuttle stop: Resorbable versus nonresorbable intramedullar cement restrictor in a prospective and randomized study with a 2-year follow-up. Acta Orthop Scand 2003;74:37-41.
22. Schauss SM, Hinz M, Mayr E, Bach CM, Krismer M, Fischer M: Inferior stability of a biodegradable cement plug. 122 total hip replacements randomized to degradable or non-degradable cement restrictor. Arch Orthop Trauma Surg 2006;126:324-329.
23. Wembridge KR, Hamer AJ: A prospective comparison of cement restrictor migration in primary total hip arthroplasty. J Arthroplasty 2006;21:92-96.
24. Berger RA, Seel MJ, Wood K, Evans R, D'Antonio J, Rubash HE: Effect of a centralizing device on cement mantle deficiencies and initial prosthetic alignment in total hip arthroplasty. J Arthroplasty 1997;12:434-443.
25. Tanzer M, Kantor S, Rosenthall L, Bobyn JD: Femoral remodeling after porous-coated total hip arthroplasty with and without hydroxyapatite-tricalcium phosphate coating: A prospective randomized trial. J Arthroplasty 2001;16:552-558.
26. Luites JW, Spruit M, Hellemondt GG, Horstmann WG, Valstar ER: Failure of the uncoated titanium ProxiLock femoral hip prosthesis. Clin Orthop Relat Res 2006;448:79-86.
27. Howie DW, Holubowycz OT, Middleton R: Large femoral heads decrease the incidence of dislocation after total hip arthroplasty: A randomized controlled trial. J Bone Joint Surg Am 2012;94:1095-1102.
28. Faris PM, Ritter MA, Keating EM, Thong AE, Davis KE, Meding JB: The cemented all-polyethylene acetabular cup: Factors affecting survival with emphasis on the integrated polyethylene spacer: An analysis of the effect of cement spacers, cement mantle thickness, and acetabular angle on the survival of total hip arthroplasty. J Arthroplasty 2006;21:191-198.
29. Stilling M, Rahbek O, Søballe K: Inferior survival of hydroxyapatite versus titanium-coated cups at 15 years. Clin Orthop Relat Res 2009;467:2872-2879.
30. Geerdink CH, Grimm B, Ramakrishnan R, Rondhuis J, Verburg AJ, Tonino AJ: Crosslinked polyethylene compared to conventional polyethylene in total hip replacement: Pre-clinical evaluation, in-vitro testing and prospective clinical follow-up study. Acta Orthop 2006;77:719-725.
31. Engh CA Jr, Hopper RH Jr, Huynh C, Ho H, Sritulanondha S, Engh CA Sr: A prospective, randomized study of cross-linked and non-cross-linked polyethylene for total hip arthroplasty at 10-year follow-up. J Arthroplasty 2012;27(8 suppl):2-7.e1.
32. Hopper RH Jr, Ho H, Sritulanondha S, Williams AC, Engh CA Jr: Otto Aufranc Award: Crosslinking reduces THA wear, osteolysis, and revision rates at 15-year followup compared with noncrosslinked polyethylene. Clin Orthop Relat Res 2018;476:279-290.
33. Martell JM, Verner JJ, Incavo SJ: Clinical performance of a highly cross-linked polyethylene at two years in total hip arthroplasty: A randomized prospective trial. J Arthroplasty 2003;18(7 suppl 1):55-59.
34. Glyn-Jones S, McLardy-Smith P, Gill HS, Murray DW: The creep and wear of highly cross-linked polyethylene: A three-year randomised, controlled trial using radiostereometric analysis. J Bone Joint Surg Br 2008;90:556-561.
35. Thomas GE, Simpson DJ, Mehmood S, et al.: The seven-year wear of highly cross-linked polyethylene in total hip arthroplasty: A double-blind, randomized controlled trial using radiostereometric analysis. J Bone Joint Surg Am 2011;93:716-722.
36. Glyn-Jones S, Thomas GE, Garfjeld-Roberts P, Gundle R, Taylor A, McLardy-Smith P, Murray DW: The John Charnley award: Highly crosslinked polyethylene in total hip arthroplasty decreases long-term wear: A double-blind randomized trial. Clin Orthop Relat Res 2015;473:432-438.
37. Broomfield JA, Malak TT, Thomas GE, Palmer AJ, Taylor A, Glyn-Jones S: The relationship between polyethylene wear and periprosthetic osteolysis in total hip arthroplasty at 12 years in a randomized controlled trial cohort. J Arthroplasty 2017;32:1186-1191.
38. Calvert GT, Devane PA, Fielden J, Adams K, Horne JG: A double-blind, prospective, randomized controlled trial comparing highly cross-linked and conventional polyethylene in primary total hip arthroplasty. J Arthroplasty 2009;24:505-510.
39. Mutimer J, Devane PA, Adams K, Horne JG: Highly crosslinked polyethylene reduces wear in total hip arthroplasty at 5 years. Clin Orthop Relat Res 2010;468:3228-3233.
40. Langlois J, Atlan F, Scemama C, Courpied JP, Hamadouche M: A randomised controlled trial comparing highly cross-linked and contemporary annealed polyethylene after a minimal eight-year follow-up in total hip arthroplasty using cemented acetabular components. Bone Joint J 2015;97-b:1458-1462.
41. Scemama C, Anract P, Dumaine V, Babinet A, Courpied JP, Hamadouche M: Does vitamin E-blended polyethylene reduce wear in primary total hip arthroplasty: A blinded randomised clinical trial. Int Orthop 2017;41:1113-1118.
42. Rochcongar G, Buia G, Bourroux E, Dunet J, Chapus V, Hulet C: Creep and wear in vitamin E-infused highly cross-linked polyethylene cups for total hip arthroplasty: A prospective randomized controlled trial. J Bone Joint Surg Am 2018;100:107-114.
43. Kim YH: Comparison of polyethylene wear associated with cobalt-chromium and zirconia heads after total hip replacement. A prospective, randomized study. J Bone Joint Surg Am 2005;87:1769-1776.
44. von Schewelov T, Sanzén L, Onsten I, Carlsson A, Besjakov J: Total hip replacement with a zirconium oxide ceramic femoral head: A randomised roentgen stereophotogrammetric study. J Bone Joint Surg Br 2005;87:1631-1635.
45. Vendittoli PA, Rivière C, Lavigne M, Lavoie P, Alghamdi A, Duval N: Alumina on alumina versus metal on conventional polyethylene: A randomized clinical trial with 9 to 15 years follow-up. Acta Orthop Belg 2013;79:181-190.
46. Atrey A, Ward SE, Khoshbin A, et al.: Ten-year follow-up study of three alternative bearing surfaces used in total hip arthroplasty in young patients: A prospective randomised controlled trial. Bone Joint J 2017;99-b:1590-1595.
47. Penny JØ, Varmarken JE, Ovesen O, Nielsen C, Overgaard S: Metal ion levels and lymphocyte counts: ASR hip resurfacing prosthesis vs. standard THA: 2-year results from a randomized study. Acta Orthop 2013;84:130-137.
48. Honl M, Dierk O, Gauck C, et al.: Comparison of robotic-assisted and manual implantation of a primary total hip replacement. A prospective study. J Bone Joint Surg Am 2003;85:1470-1478.
49. Lim SJ, Ko KR, Park CW, Moon YW, Park YS: Robot-assisted primary cementless total hip arthroplasty with a short femoral stem: A prospective randomized short-term outcome study. Comput Aided Surg 2015;20:41-46.
50. Bargar WL, Parise CA, Hankins A, Marlen NA, Campanelli V, Netravali NA: Fourteen year follow-up of randomized clinical trials of active robotic-assisted total hip arthroplasty. J Arthroplasty 2018;33:810-814.
51. Bose WJ: Accurate limb-length equalization during total hip arthroplasty. Orthopedics 2000;23:433-436.
52. Stocks GW, O'Connor DP, Self SD, Marcek GA, Thompson BL: Directed air flow to reduce airborne particulate and bacterial contamination in the surgical field during total hip arthroplasty. J Arthroplasty 2011;26:771-776.
53. Small T, Krebs V, Molloy R, Bryan J, Klika AK, Barsoum WK: Comparison of acetabular shell position using patient specific instruments vs. standard surgical instruments: A randomized clinical trial. J Arthroplasty 2014;29:1030-1037.
54. Meermans G, Van Doorn WJ, Koenraadt K, Kats J: The use of the transverse acetabular ligament for determining the orientation of the components in total hip replacement: A randomised controlled trial. Bone Joint J 2014;96-b:312-318.
55. O'Neill CKJ, Hill JC, Patterson CC, Molloy DO, Gill HS, Beverland DE: Reducing variability in apparent operative inclination during total hip arthroplasty: Findings of a randomised controlled trial. Hip Int 2018;28:234-239.
56. Rui M, Zheng X, Sun SS, et al.: A prospective randomised comparison of 2 skin closure techniques in primary total hip arthroplasty surgery. Hip Int 2018;28:101-105.
57. National Joint Registry for England, Wales, Northern Ireland and the Isle of Man: 16th Annual Report 2019. 2020. https://reports.njrcentre.org.uk/Portals/0/PDFdownloads/NJR%2016th%20Annual%20Report%202019.pdf.
58. Herbert RD, Kasza J, Bø K: Analysis of randomised trials with long-term follow-up. BMC Med Res Methodol 2018;18:48.
59. Lübbeke A, Silman AJ, Prieto-Alhambra D, Adler AI, Barea C, Carr AJ: The role of national registries in improving patient safety for hip and knee replacements. BMC Musculoskelet Disord 2017;18:414.
60. Pugely AJ, Martin CT, Harwood J, Ong KL, Bozic KJ, Callaghan JJ: Database and registry research in orthopaedic surgery: Part 2: Clinical registry data. J Bone Joint Surg Am 2015;97:1799-1808.
61. Inacio MC, Paxton EW, Dillon MT: Understanding orthopaedic registry studies: A comparison with clinical studies. J Bone Joint Surg Am 2016;98:e3.
62. Siljander MP, McQuivey KS, Fahs AM, Galasso LA, Serdahely KJ, Karadsheh MS: Current trends in patient-reported outcome measures in total joint arthroplasty: A study of 4 major orthopaedic Journals. J Arthroplasty 2018;33:3416-3421.
63. Marx RG, Jones EC, Atwan NC, Closkey RF, Salvati EA, Sculco TP: Measuring improvement following total hip and knee arthroplasty using patient-based measures of outcome. J Bone Joint Surg Am 2005;87:1999-2005.
64. Garbuz DS, Xu M, Sayre EC: Patients' outcome after total hip arthroplasty: A comparison between the Western ontario and McMaster Universities index and the oxford 12-item hip score. J Arthroplasty 2006;21:998-1004.
65. Lim CR, Harris K, Dawson J, Beard DJ, Fitzpatrick R, Price AJ: Floor and ceiling effects in the OHS: An analysis of the NHS PROMs data set. BMJ Open 2015;5:e007765.
66. Halawi MJ, Jongbloed W, Baron S, Savoy L, Cote MP, Lieberman JR: Patient-reported outcome measures are not a valid proxy for patient satisfaction in total joint arthroplasty. J Arthroplasty 2020;35:335-339.
67. Rolfson O, Bohm E, Franklin P, et al.: Patient-reported outcome measures in arthroplasty registries report of the patient-reported outcome measures working group of the International Society of Arthroplasty Registries Part II. Recommendations for selection, administration, and analysis. Acta Orthop 2016;87(suppl 1):9-23.
68. Brassington I: The ethics of reporting all the results of clinical trials. Br Med Bull 2017;121:19-29.
69. McGauran N, Wieseler B, Kreis J, Schüler YB, Kölsch H, Kaiser T: Reporting bias in medical research—a narrative review. Trials 2010;11:37.
70. Kalteis T, et al.: Greater accuracy in positioning of the acetabular cup by using an image-free navigation system. Int Orthop 2005;29:272-276.
    71. Verdier N, et al.: EOS-based cup navigation: Randomised controlled trial in 78 total hip arthroplasties. Orthop Traumatol Surg Res 2016;102:417-421.
      72. Yamada K, et al.: Accuracy of Cup Positioning With the Computed Tomography-Based Two-dimensional to Three-Dimensional Matched Navigation System: A Prospective, Randomized Controlled Study. J Arthroplasty 2018;33:136-143.
        Copyright © 2020 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Orthopaedic Surgeons.