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Original Article

Cement augmentation in the proximal femur to prevent stem subsidence in revision hip arthroplasty with Paprosky type II/IIIa defects

Tsai, Shang-Wena,b; Chen, Cheng-Fonga,b; Wu, Po-Kueia,b; Chen, Chao-Minga,b; Chen, Wei-Minga,b,*

Author Information
Journal of the Chinese Medical Association: June 2018 - Volume 81 - Issue 6 - p 571-576
doi: 10.1016/j.jcma.2017.11.008

    Abstract

    1. Introduction

    Femoral bone defects remain a challenge when revising femoral components. The extent of the bone defect determines the surgical technique used. The Paprosky femoral bone loss classification system is normally used to guide decision making.1,2 Type II and III bone defects are more prevalent among patients who have undergone femoral component. Those two defects can be adequately treated using an extensively coated, diaphyseal locking stem1,2 Two types of cementless revision stems—a cylindrical, non-modular cobalt–chromium stem, and a tapered, fluted, modular titanium stem—are commonly used. For both types of stem, however, subsidence remains a frequently reported complication (incidence: range = 8.4–84%).3–15 A considerable loss of function because of prolonged weight-bearing restrictions and problem with leg-length discrepancies because of subsidence are major concerns. Therefore, many surgeons recommend a protective weight-bearing or non-weight-bearing program for six to eight weeks after surgery.3,5,7,8,11,14,15 However, early ambulation without weight-bearing restrictions and the prevention of stem subsidence remain goals to be achieved.

    We have developed a simple technique, which was to fill metaphyseal bone defects with antibiotic-loaded bone cement during revision with a cementless, extensively coated, diaphyseal locking stem. We hypothesized that patients who had been treated using this technique could be allowed to walk with a more aggressive weight-bearing program and would achieve good stem survival with minimal stem subsidence.

    2. Methods

    This retrospective study, conducted in a single medical center from May 2001 to June 2011, was approved by the Institutional Review Board (IRB #2016–07–004C). Paprosky classification used in clinical practice to determine the surgical method throughout the study period.1 All patients were operated on by the same senior attending physician involved in this study. The type of femoral bone defect was classified based on preoperative radiographs and intraoperative findings. For patients with Paprosky type II and IIIa bone defects, an extensively coated, diaphyseal locking stem was the selected implant. Impaction bone grafting technique was used for patients with Paprosky type IIIb and IV defects. Allograft prosthetic composite was an alternative option for Paprosky type IV cases. Megaprostheses were not used in the present study to revise femoral components.

    Forty patients with Paprosky type II and IIIa defects who had undergone revision of femoral components were enrolled. Surgical indications included aseptic loosening, two-stage reconstruction after resection arthroplasty for septic loosening, recurrent dislocation, and periprosthetic fracture. Patients with a tumor in the proximal femur or a follow-up of less than two years were excluded.

    The mean age of the 40 enrollees (27 men and 13 women) was 60.9 years (range: 39–85 years) (Table 1); mean operation time was 112 min (range: 70–163); Estimated blood loss was 960 mL (range: 500–1850); and the mean follow-up was 67.7 months (range: 24–149). Indications for index surgery were aseptic loosening (n = 29), two-stage reconstruction after resection arthroplasty for septic loosening (n = 7), recurrent dislocation (n = 2), and periprosthetic fracture (n = 2). A modified Hardinge approach was used in 36 patients. For the other four patients (three with a cemented stem and one with a cementless stem), a posterior approach with an extended trochanteric osteotomy was used because it was difficult to remove the stems. Cylindrical non-modular cobalt–chromium stems (Depuy AML®; Warsaw, IN, USA) were implanted in all 40 patients.

    T1-13
    Table 1:
    Demographic information of the enrolled patients.

    An extended trochanteric osteotomy was done to remove distal cement plugs or well-fixed stems.16 Before the femoral stems were implanted, any source that led to impingement, e.g., cement, neocortex, and soft tissue membrane, was removed from the canal. We anticipated obtaining a scratch-fit segment of healthy distal femoral diaphysis within five to seven cm. To avoid stem penetration of the nearby pedestal, the femoral canal was first prepared with the aid of a flexible reamer using a 2.5-mm ball-tipped reaming rod (Synthes, West Chester, PA, USA) and intraoperative fluoroscopy. This was followed by serial straight reaming of the femoral canal. In general, a better press-fit mechanism was obtained by under-reaming the femoral canal by 0.5 mm. A femoral trial was initially inserted to determine its optimal length and version. A mark was made on the intertrochanteric area as a reference for a subsequent femoral stem implantation. The femoral stem was implanted about one cm away from its designated position, after which the defect in the proximal femoral metaphysis and medial calcar area was filled with Vancomycin-loaded bone cement at the late-working phase. One gram Vancomycin were hand-mixed in each half a pack of 40 g cement polymer (Simplex® P cement, Stryker). The stem was then introduced to the designated position (Figs. 1 and 2). Cable or cerclage wire was reserved for patients with an intraoperative femur fracture, a greater trochanter fracture, or when extended trochanteric osteotomy was done.

    F1-13
    Fig. 1.:
    Case demonstration for a patient with Paprosky type II femoral defect. (A) Preoperative antero-posterior radiograph of the hip; (B) immediately postoperative, antero-posterior radiograph of the hip; (C) schematic drawing. Asterisks indicate the area of cement augmentation in the proximal femur; (D) the final follow-up 43 months after surgery.
    F2-13
    Fig. 2.:
    Case demonstration for a patient with Paprosky type IIIa femoral defect. (A) Preoperative antero-posterior radiograph of the hip; (B) immediately postoperative antero-posterior radiograph of the hip; (C) schematic drawing. Asterisks indicate the area of cement augmentation in the proximal femur; (D) the final follow-up 37 months after surgery.

    Thirteen patients who had undergone stem revision only was allowed to walk immediately without weight-bearing restrictions. Twenty-seven patients who had undergone revision total hip arthroplasty was allowed partial weight-bearing within 6 weeks after surgery in the consideration of acetabular reconstruction. Weight-bearing without restrictions was allowed thereafter. In general, all patients received prophylactic antibiotics for three to five days after surgery, til the removal of surgical drains. Patients were followed-up at two weeks, six weeks, three months, one year, and then annually after surgery. All patients enrolled in this study completed a minimum two-year follow-up.

    Component fixation was assessed through serial radiographs at each follow-up visit. Cementless femoral component fixation was assessed based on the criteria developed by Engh et al.17 The Harris hip scoring system was used to evaluate clinical results before and after surgery.18 Callaghan's method was used to measure the degree of subsidence.19

    Kaplan–Meier survival analysis was used to determine the survival of femoral stems. Our primary endpoint was femoral stem failure because of aseptic loosening, infection, or periprosthetic fractures that required additional revision surgeries. SPSS 20.0 (SPSS Inc., Chicago, IL) was used for all analyses.

    3. Results

    For the 40 patients who had undergone revision of femoral stems, the mean pre-operative Harris hip score was 29.0 (range: 17–39) and 76.0 (range: 55–91) for the latest follow-up. Common intraoperative and postoperative complications included greater trochanter avulsion fractures (n = 5; 12.5%), stem subsidence (n = 3; 7.5%), infection (n = 2; 5%), periprosthetic fracture (n = 1; 2.5%), dislocation (n = 1; 2.5%), and intraoperative femur fractures (n = 1; 2.5%). There were no thromboembolic events in the perioperative or early postoperative periods. There was no stem penetration, delayed wound healing, or acute infection, nor were there sciatic, femoral, or peroneal nerve injuries. At the latest follow-up visit, 36 cases were considered osseointegrated stable, and the other four were considered fibrous stable.

    Five patients with greater trochanter fractures were managed using cerclage wiring. Three stems that had subsided three, five, and 10 mm, respectively, were stabilized, using conservative management, in the 3rd, 1st, and 14th months. Two of these stems were determined “osseointegrated”, and the third was labeled “fibrous stable” at the last follow-up (Fig. 3). Cup and liner revisions were done for dislocated hip joints. Intraoperative femur fractures were managed using wiring, and a longer stem was used to bypass the fracture site. There were three femoral stem failures—two delayed infections and one periprosthetic Vancouver B2 fracture—during the follow-up (Table 2). Resection arthroplasty was done during the 49th and 38th months after surgery for patients with delayed infections. The patient with the periprosthetic Vancouver B2 fracture underwent revision long stem arthroplasty 32 months after surgery. Both five-year and 10-year survival rate for the femoral stem were 90.1%.

    F3-13
    Fig. 3.:
    Case demonstration for a patient with stem subsidence. (A) Preoperative antero-posterior radiograph of the hip; (B) immediately postoperative antero-posterior radiograph of the hip; (C) the final follow-up 61 months after surgery.
    T2-13
    Table 2:
    Patients with arthroplasty failures.

    4. Discussion

    The most important finding is that a more aggressive weight-bearing program with minimal stem subsidence and good implant survival is possible by filling the metaphyseal bone defect with antibiotic-loaded cement when revising the femoral components in Paprosky type II and IIIa defects.

    Subsidence is commonly reported as ranging from 8.4% to 84% after revision surgeries using either a cylindrical, non-modular cobalt–chromium stem or a tapered, fluted, modular titanium stem.3–15 Most subsidence occurs in the early postoperative period, and mainly within a year after surgery.4,8,12 Optimal press-fit greatly depends upon diaphyseal bone quality, which varies between patients. Therefore, stem subsidence would be expected to occur in patients with poor bone quality when they start weight bearing before adequate bony ingrowth. In the patients with significant subsidence, additional revision surgery might be indicated for instability or gait disturbance because of the length discrepancy.3–5,14,15 Subsidence greater than three mm is considered clinically significant.20,21 In the present study, the incidence of subsidence was as low as 7.5%, showing non-inferior results compared with literature about the use of extensively coated nonmodular femoral stems (Table 3). There was no significant instability, limping, or gait disturbance because of a leg length discrepancy in any of our patients. All three stems stabilized without progressive subsidence.

    T3-13
    Table 3:
    Complications of reported extensively porous-coated, cylindrical, non-modular cobalt–chromium stem.

    Common indications for further revision surgery include aseptic loosening, progressive stem subsidence, periprosthetic fracture, dislocation, and infection. Mid-term to long-term implant survival rate has been reported from 87% to 95.2%.5,10,11,15 Both the five-year and 10-year implant survival rates in our study were 90.1%, which was comparable. In addition, there were no aseptic loosening events of femoral stems, and all stems were considered stable.17

    Evaluating femoral defects is crucial for determining treatment strategies when revising femoral components. Outcomes may differ greatly with different inclusion criteria. We believe that a significant bone defect in the metaphysis will lead to unreliable bony ingrowth when revising femoral components. In other words, the Paprosky type I defect has not been classified throughout our practice. A scratch-fit segment in the diaphysis of five to seven cm is required for both axial and rotatory stability.22 However, the bone stock remaining in Paprosky type IIIb and IV defects is insufficient to fulfill the criteria. Therefore, impaction bone grafting, an allograft prosthetic composite, or a megaprosthesis instead of an extensively porous coated, diaphyseal locking stem was anticipated to meet the requirement.1,2 Outcomes in patients with Paprosky type II and IIIa defects should be discussed separately from those in patients with Paprosky type IIIb and IV defects, in which the femoral bone loss is more severe.

    Immediate weight-bearing without restrictions was the most important aim of this technique. It is crucial to develop a preoperative plan to achieve adequate length of scratch-fit and five mm under-reaming in femoral canal preparation for a solid primary fixation. The concept of using cement in the proximal femoral metaphysis was suggested by the allograft prosthetic composite, which was developed to introduce the cemented stem into the proximal femur allograft and cementless portion with adequate length of scratch-fit into the distal host bone.23 We hypothesized that using bone cement to fill the defect in the metaphysis would provide additional immediate stability and support in the axial and rotatory dimensions. Without cement pressurization, this technique is always convenient and less stressful for both the surgeon and the patient. Because of unreliable metaphyseal osseointegration after revising femoral components, using bone cement to fill the metaphyseal defect is theoretically reasonable and should not affect the long-term stability of the stem. A morcellized allograft or autograft is an alternative to using bone cement to fill the defect. However, there will be lack of osseointegration in the interface between the allograft and implant. Donor site morbidities and questionable cost-effectiveness with potential higher risk of deep infection in revision surgeries are limitations for using autografts. A five to seven-cm scratch-fit segment in the diaphysis remains of paramount importance to ensure long-term stability of the stem. Although other studies3–15 have reported inferior implant osseointegration, there was none in ours. In addition, removing the cement during re-revision surgery was easily done using an osteotome or a burr. Antibiotic-loaded bone cement has been approved by the FDA only for the second stage of a two-stage revision arthroplasty after all acute infection has been eliminated. It has not been approved for preventing deep periprosthetic infection in aseptic hip revisions24; there was, however, no acute surgical site infection in our series. Antibiotic-loaded bone cement for preventing acute surgical site infection, especially in aseptic hip revisions, warrants additional study. Furthermore, cement augmentation in the proximal femoral metaphysis to prevent subsequent polyethylene particles from entering the space in the proximal femur between the implant and the bone (the “seal off” effect) is an additional consideration for this design. Longer follow-ups are required to investigate this possibility. Yin et al. has reported a same technique in 41 revision surgeries using an extensively coated modular revision stem in conjunction with allograft reconstruction. Mean follow-up period was 5.2 years. There was no stem subsidence.25 We agreed with the authors' rationale that bone cement provides initial stability, but osseointegration of the distal stem is the key to a successful reconstruction.

    This study has several strengths: using a single type of femoral stem, all surgeries done by the same senior surgeon, and consistent weight-bearing and follow-up programs. The study also has some limitations: the sample was small, there were no long-term results, and it had no control group of patients who had undergone a revision of their femoral components with a cylindrical, non-modular cobalt–chromium stem, or a tapered, fluted, modular titanium stem, without cement augmentation. Further biomechanical study to validate additional axial and rotatory stability provided by the cement in the proximal metaphysis is required.

    In conclusion, an adequate length of scratch-fit segment and diaphyseal ingrowth remain of paramount importance when revising femoral components. To fill metaphyseal bone defects with antibiotic-loaded bone cement may be an alternative method in dealing with proximal femoral bone loss during a femoral revision.

    Acknowledgments

    We thank Bill Franke for the proof-reading of this manuscript.

    References

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    Keywords:

    Bone defect; Cement augmentation; Femur; Revision hip arthroplasty; Subsidence

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