Total knee arthroplasty (TKA) with rotating-hinge components has several indications. Traditionally, this construct was utilized during a salvage procedure, including revision of an unstable total knee replacement in knees with incompetent or completely absent collateral ligaments1. However, there are a host of other indications for a rotating-hinge TKA construct, including oncologic reconstruction2-4, management of periprosthetic fracture5, and recurvatum6. Some authors have even recommended more liberal indications, including use in patients who are >75 years old with comorbidities that may affect the stability of a total knee replacement7.
While excellent immediate stability is achieved with a rotating-hinge TKA design, the historically high failure rate has tempered its use8. This failure rate is partially attributed to the forces transmitted to the bone-cement interface from the constrained nature of the construct, combined with the lack of rotation in many designs. Contemporary rotating-hinge prosthetic designs, compared with older designs without rotation that are usually analyzed in the literature, allow for rotation and thus decreased rates of aseptic loosening9-13. Furthermore, recent innovations in highly porous metaphyseal cones have provided another treatment option to minimize forces at the bone-implant interface and thus potentially decrease the rates of aseptic loosening14-16. However, the current literature is limited, as most series of TKAs with contemporary rotating-hinge designs of which we are aware have small patient numbers, heterogeneous indications, and short-term follow-up17-22.
The goals of the current study were to determine the clinical outcomes, survivorship, radiographic results, and complications associated with the use of contemporary rotating-hinge TKA constructs for nononcologic indications in a large cohort.
Materials and Methods
All patients who received a rotating-hinge total knee replacement for nononcologic indications at a single academic institution from 2002 to 2012 were included. Patients were identified through an institutional registry used to follow all patients who had undergone a primary or revision total joint arthroplasty at our institution since 1969. Clinical and radiographic follow-up was completed at 1 year, 2 years, 5 years, and then every 5 years thereafter. Patients who were unable to return for follow-up were mailed a questionnaire and were asked to return radiographic images. The minimum potential follow-up period was 2 years (range, 2 to 12 years), and the mean follow-up was 4 years (range, 0.1 to 12 years). Minimal potential follow-up was defined as the intended minimal time that could be elapsed from the time of surgery to the time of the study; the mean follow-up time, on the other hand, was calculated on the actual cohort of patients and ranged from 0.1 year (a patient underwent a new surgery after 1 month) to 12 years. Institutional review board approval and patient consent for participation were obtained prior to initiation of the study.
Patients were evaluated clinically on the basis of range of motion and Knee Society scores23. The end points of revision and reoperation were calculated using both the Kaplan-Meier approach (in which data on patients who died are censored) and also in terms of cumulative incidence (in which the competing risk of death is accounted for)24. Radiographic assessment for loosening was assessed via the Knee Society radiographic evaluation system on 3 views (anteroposterior, lateral, and patellar radiographs)25. Complications were documented for all patients.
We identified 408 TKAs performed with rotating-hinge components during this time period in 392 patients with a mean age of 69 years (range, 16 to 96 years) at the time of the index arthroplasty. Sixty-two percent (243 patients) were female, and the mean body mass index (BMI) was 32 kg/m2 (range, 16 to 64 kg/m2). Rotating-hinge TKA components were implanted in 74 primary procedures (18%) and 334 revision procedures (82%). The prosthetic designs that were used included the Howmedica Modular Rotating Hinge Knee System (240 knees; 59%), Zimmer NexGen RH Knee (128 knees; 31%), DePuy S-ROM Noiles Rotating Hinge Knee System (38 knees; 9%), and Biomet Finn Rotating Hinged Knee (2 knees; 0.5%). The patients had a mean of 2 previous knee procedures (range, 0 to 11 procedures).
The indications for a rotating-hinge TKA construct were previous infection in 144 knees (35%), which were managed with 2-stage reimplantation, and aseptic etiologies in 264 knees (65%). The latter etiologies included instability in 62 knees (15%); aseptic loosening in 55 knees (13%); periprosthetic fracture in 54 knees (13%); nonunion of a previous fracture in 19 knees (5%); mechanical failure in 16 knees (4%); arthrofibrosis in 15 knees (4%); malrotation in 14 knees (3%); neuropathic arthropathy in 9 knees (2%); poliomyelitis in 9 knees (2%); rheumatoid arthritis in 7 knees (2%); and rickets, extensor mechanism failure, dwarfism, and congenital dislocation in 1 knee (0.2%) each.
Preoperative bone loss was evaluated and classified according to the Anderson Orthopaedic Research Institute (AORI) system26. Preoperative classification was available for 343 knees (84%). Of those knees, 204 (50%) were classified as having AORI type-3 bone loss; 82 (20%), as having type-2B; 36 (9%), as having type-2A; and 21 (5%), as having type-1 bone loss (Table I).
In 46 knees (11%), nonstructural allograft was used, while structural allograft was used in 10 knees (2.5%). Starting in 2002, the senior authors (A.D.H. and D.G.L.) began utilizing metaphyseal cones (Trabecular Metal; Zimmer) instead of allografts. Such cones were utilized in 114 procedures (28%), with 41 (10%) in both the femur and the tibia, 38 (9.3%) in the femur only, and 35 (8.6%) in the tibia only.
Kaplan-Meier survivorship24 was calculated using revision for aseptic loosening, revision for any reason, and any reoperation as the end points. In addition, these outcomes were also analyzed by calculating the cumulative incidence, accounting for the competing risk of death. Cox proportional hazards regression analysis was performed to evaluate different risk factors that potentially influence failure, including age (<65 or ≥65 years), sex, BMI, type of surgery (primary or revision procedure), use of allograft (none, nonstructural, or structural), and use of cones (no or yes, as well as location [femur only, tibia only, or both femur and tibia]). BMI was studied as a continuous variable. The robust variance estimate was used in the Cox models to properly account for patients who had bilateral TKA.
In addition, postoperative Knee Society knee and functional scores were analyzed with respect to age (<65 or ≥65 years), sex, surgery type (primary or revision procedure), use of allograft (none, nonstructural, or structural), and use of cones (none, only femur, only tibia, or both femur and tibia) using generalized linear models with generalized estimating equations to account for the within-patient correlation because of bilateral involvement. The threshold of significance for all analyses was set at p < 0.05.
The mean Knee Society knee score improved significantly from 51 points (range, 1 to 95 points) preoperatively to 81 points (range, 13 to 100 points) postoperatively, and the mean Knee Society functional score improved from 26 points (range, 0 to 100 points) preoperatively to 36 points (range, 5 to 100 points) postoperatively; the differences were significant (p < 0.0001 for both).
The postoperative Knee Society knee scores were not significantly associated with age (<65 compared with ≥65 years; mean, 79 and 81 points, respectively; p = 0.3), sex (males compared with females; 81 points in both groups; p = 0.9), use of allograft (structural compared with nonstructural compared with none; 87, 78, and 81 points, respectively; p = 0.13), use of cones (yes compared with no; 81 and 80 points, respectively; p = 0.7), or the type of procedure (revision compared with primary surgery; 80 and 82 points, respectively; p = 0.6).
The postoperative Knee Society functional scores were significantly associated with age, with higher scores for patients who were <65 years old (mean, 45 compared with 32 points; p < 0.001). They were also significantly associated with sex, with higher scores for males (44 compared with 31 points; p < 0.001); surgery type, with higher scores for those who had revision than for those who had a primary procedure (38 compared with 27 points; p = 0.02); and the use of cones, with higher scores for those who had cones (any) compared with those who had none (47 compared with 33 points; p < 0.001). However, the differences in the mean postoperative Knee Society functional scores based on the use of allograft (comparison of structural, nonstructural, and none; 21, 45, and 35 points, respectively; p = 0.07) did not reach significance.
Of the 349 unrevised knee replacements in living patients, 13 (3.7%) had loosening of the components: 6 knees (1.7%) had loosening around both the femoral and tibial components; 4 (1.1%), around the tibial component only; and 3 (0.86%), around the femoral component only. Radiographic loosening was not significantly associated with age (≥65 versus <65 years) (odds ratio [OR] = 0.7; 95% confidence interval [CI], 0.2 to 2.2; p = 0.5). While the risk of radiographic loosening was higher after revision surgery (OR = 2.9; 95% CI, 0.4 to 22.7; p = 0.31) and in males (OR = 2.9; 95% CI, 0.9 to 9.2; p = 0.06), these did not reach significance.
In addition, the use of nonstructural allograft (compared with no allograft) was observed to have a protective effect against the risk of loosening, but this was not significant (OR = 0.3; 95% CI, 0.04 to 2.1; p = 0.22). No significant association with an increased risk of loosening was found for the use of structural allograft compared with no allograft (1 of 10 knees compared with 12 of 300 knees; OR = 3.6; 95% CI, 0.8 to 16.7; p = 0.11) or for the use of structural allograft compared with nonstructural allograft (1 of 10 knees compared with 0 of 39 knees; OR = 12.5; 95% CI, 0.4 to 357; p = 0.14).
Although the finding was not significant, the use of cones appeared to be protective against radiographic loosening, with the risk of loosening being lower in knees in which both tibial and femoral cones were used (OR = 0.37; 95% CI, 0.04 to 3.4; p = 0.38) and in knees in which tibial cones, femoral cones, or both were used (OR = 0.47; 95% CI, 0.1 to 2.2; p = 0.33).
At the most recent follow-up evaluation, there had been 59 revisions: 21 for deep periprosthetic infection, 11 for periprosthetic fracture, 10 for aseptic loosening, 10 for mechanical failure, 4 for extensor mechanism disruption, 2 for arthrofibrosis, and 1 for chronic patellar dislocation. The revisions had occurred at a mean of 2.4 years postoperatively.
In addition, 25 reoperations with maintenance of the rotating-hinge TKA components had been performed for deep periprosthetic joint infection (24 knees) and for dissociation of the prosthetic hinge (1 knee).
As such, the cumulative incidence of revision for aseptic loosening was 1.7% (95% CI, 0.3% to 3%) at 2 years and 4.5% (95% CI, 1.2% to 7.7%) at 10 years (Fig. 1). The cumulative incidence of revision for any revision was 9.7% (95% CI, 6.7% to 12.6%) at 2 years and 22.5% (95% CI, 16% to 29%) at 10 years (Fig. 2). The 10-year cumulative incidence of any reoperation was 10.5% (95% CI, 4.6% to 16%) (Fig. 3).
An age of <65 years at the time of the TKA with the rotating-hinge construct was associated with an increased risk of revision because of aseptic loosening (hazard ratio [HR] = 5.7; 95% CI, 1.4 to 20; p = 0.01). Male sex was not significantly predictive of revision (HR = 1.5; 95% CI, 0.9 to 2.5; p = 0.12) or reoperation (HR = 1.5; 95% CI, 0.7 to 3.3; p = 0.31). BMI did not significantly influence the rate of revision (HR = 1.02; 95% CI, 0.99 to 1.1; p = 0.15) or reoperation (HR = 1.0; 95% CI, 0.9 to 1.01; p = 0.09). Similarly, surgery type (that is, revision compared with primary procedure) was not significantly associated with the rate of revision (HR = 1.37; 95% CI, 0.7 to 2.9; p = 0.41) or reoperation (HR = 1.62; 95% CI, 0.5 to 5.4; p = 0.43).
In regard to allografts, the use of nonstructural allograft did not significantly influence the rate of revision (HR = 1.02; 95% CI, 0.5 to 2.2; p = 0.96) or reoperation (HR = 0.76; 95% CI, 0.2 to 2.9; p = 0.7). Similarly, the use of structural allografts was not significantly associated with the rate of revision (HR = 0.28; 95% CI, 0.02 to 4.7; p = 0.38) or reoperation (HR = 0.73; 95% CI, 0.04 to 13.3; p = 0.83). Survivorship analysis revealed a trend toward a lower risk of revision (HR = 0.69; 95% [CI] = 0.39 to 1.22; p = 0.20) and reoperation (HR = 0.51; 95% CI = 0.22 to 1.19; p = 0.12) in patients with metaphyseal cones, despite their use in the most severe of bone defects.
There were 22 intraoperative complications, which included periprosthetic tibial fracture in 9 knees, periprosthetic femoral fracture in 8 knees, periprosthetic patellar fracture in 2 knees, partial patellar tendon avulsion in 2 knees, and periprosthetic fracture of both the tibia and the femur in 1 knee. Fractures were treated in 8 knees (2%) with no additional fixation. In the remaining knees, treatment was with a cerclage cable (4 knees; 1%); screws, threaded Kirschner wire, and cerclage wire and impaction bone-grafting (2 knees [0.5%] each); and structural allograft with cerclage cables and conversion to a resection arthroplasty (1 knee [0.2%] each). The partial avulsion of the patellar tendon in 2 knees was repaired with sutures and augmentation with hamstring tendons.
Postoperative complications occurred in 44 patients (44 knees; 11%) at a mean of 0.8 year after surgery. These included delayed wound-healing in 12 knees (3%); decreased range of motion in 10 knees (2.5%); superficial wound infections in 5 knees (1.2%); periprosthetic tibial fracture in 4 knees (1%); episodes of patellar instability in 4 knees (1%); skin necrosis in 3 knees (0.7%); partial quadriceps tears in 2 knees (0.5%); and deep vein thrombosis, periprosthetic femoral fracture, periprosthetic patellar fracture, and peroneal nerve palsy in 1 knee (0.2%) each.
The use of a hinged TKA construct was historically considered as a salvage procedure in low-demand patients with severe ligamentous instability. This was primarily because of poor reported outcomes and high failure rates as a result of the high stresses placed on the bone-cement interface secondary to the lack of rotation of the central hinge5. With further development of the rotating portion of the hinge construct, the stresses around the bone-cement-prosthesis interfaces have decreased, improving both implant survivorship and patient satisfaction9-13. However, most series continue to be limited by small patient numbers and short-term follow-up, as well as heterogeneous cohorts that include oncologic patients. In our study, which we believe to be the largest series to date with long-term follow-up, we found a significant improvement in clinical outcomes and excellent survivorship free from revision for aseptic loosening with contemporary rotating-hinge constructs.
At the time of the most recent follow-up, patients had significantly improved mean Knee Society knee and functional scores. While the mean Knee Society functional score was modest compared with functional outcomes after primary TKA, this was likely due to the substantial comorbidities among this difficult cohort of patients. Our data are consistent with other published series that have found similar improvements in clinical outcome scores (Table II)5,9,11,13,27,28.
From a radiographic standpoint, the rate of aseptic loosening was found to be very low (3.7%) and in line with other series10-12,18,27,28. This is notable when considering the massive bone loss and substantial instability that often accompany this procedure.
The cumulative incidence of revision for aseptic loosening was excellent at 4.5% at 10 years. This highlights the substantial decrease in bone-cement-implant interface stresses, and thus aseptic loosening, through the rotating-hinge construct compared with older designs without the rotating hinge (Table II). When septic failures were considered, the cumulative incidence increased to 22.5% at 10 years. Nevertheless, these results are not surprising as the majority of these patients were poor hosts with numerous medical comorbidities. In addition, many of these patients had several prior operations (including many for infection), resulting in a very poor local tissue milieu. Our results are better than those in the study by Smith et al.9, who reported a 54% overall survivorship for rotating-hinge TKA components at 4 years, with 57% of failures being nonmechanical. While other studies also looked at survivorship, it is difficult to compare our results as most are limited by small patient numbers and heterogeneity of indications within the cohort9,24.
We hypothesized that the use of uncemented metaphyseal cones would minimize the rate of aseptic loosening as this decreases stress at the bone-cement-implant interfaces. While a significantly lower rate of aseptic loosening was not shown with the use of cones, there is a substantial bias in that cones were used for the most difficult knees that would have traditionally received an amputation or a distal femoral and proximal tibial replacement. As such, the knees in which cones were utilized were preferentially the worst of cases.
Limitations of the current study include its retrospective nature and the fact that many patients had numerous previous surgical interventions. However, this is somewhat mitigated by the large patient numbers and high rate of patient follow-up.
In conclusion, contemporary rotating-hinge TKA components provide long-term reliable and durable constructs, even in the most difficult situations where limb salvage (or joint reconstruction) seems futile. The rotating-hinge construct has a low rate of aseptic loosening, even at 10 years, having a cumulative incidence as low as 4.5%; in addition, metaphyseal cones seem to have a protective effect on the rate of aseptic loosening, especially if used in both tibia and femur. This is likely partially attributable to decreased interface stresses.
Unfortunately, septic failure continues to be the common mode of failure in this difficult revision cohort because of the high number of patient comorbidities and previous joint infections.
NOTE: The authors thank the staff of the Division of Biomedical Statistics and Informatics for their statistical expertise.
Investigation performed at the Department of Orthopedic Surgery and the Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, Minnesota
Disclosure: No outside source of funding was used for this study. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work (http://links.lww.com/JBJS/A8).
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