The purpose of this study was to compare clinical and radiological outcomes of the first 191 fully porous-coated hip resurfacing arthroplasties with 96 hybrid hip resurfacing arthroplasties performed during the same period at a minimum 2-year follow-up to evaluate the initial fixation of uncemented femoral resurfacing components. The results of this study indicate that fully porous-coated femoral resurfacing components can routinely achieve reliable fixation and provide similar initial results as have been achieved with cemented fixation. Long-term results are needed to determine which type of fixation is superior for the femoral hip resurfacing component.
Surgeons have debated the relative value of cemented versus uncemented fixation in total hip arthroplasty (THA) for the last few decades. Because orthopedic surgeons have come to a general consensus on the superiority of uncemented fixation, uncemented fixation has virtually replaced cemented fixation in stemmed THAs in the United States. Most acetabular components that are used today are of the uncemented type, as are about 80% of femoral stems. This trend is occurring in Canada and Europe as well.
Hip resurfacing arthroplasty (HRA) has become an accepted alternative to stemmed THA in the last decade for young active patients wishing to return to a high level of activity, including impact sports. In modern metal-on-metal HRAs, hybrid fixation (uncemented acetabular and cemented femoral components) has been adopted as the standard. Many studies have demonstrated successful early and midterm outcomes with survivorship rates of up to 97%. In contemporary HRAs, cement technique has been shown to be quite variable and difficult to control. Increasing cement thickness may cause more thermal necrosis and a higher risk of stress shielding. Excess cement under the femoral component may result in leaving the femoral component incompletely seated; this extends the femoral neck, leaving uncovered reamed bone, and increases the risk of fracture. Also, the mechanical properties of the cement may result in an increasing rate of aseptic loosening over time. Our results at the midterm (average 5.6 years) follow-up of the Corin (Corin, Cirencester, Gloucestershire, UK) Food and Drug Administration Investigational Device Exemption study of hybrid HRAs have demonstrated that cement fixation failure is the most common source of failure at a rate of 3%, accounting for half of all failures.
Because of the superior results of bone ingrowth implants in stemmed THA, it may be logical to also apply uncemented fixation techniques to femoral resurfacing components. Several studies have reported positive clinical outcomes of contemporary metal-on-metal HRAs using nonporous uncemented fixation methods on both the femoral and the acetabular side. We hypothesized that the clinical results of bone ingrowth type uncemented fixation on the femoral side in HRA should be equal to, if not superior to, cemented fixation at early follow-up. The purpose of this study was to report our 2-year clinical and radiological follow-up of the first modern fully porous-coated (uncemented) hip resurfacing prosthesis and to compare these results with those of hybrid hip resurfacing prostheses manufactured by the same company.
Material and methods
The senior author (T.P.G) implanted the first fully porous-coated metal-on-metal Recap and Magnum combination hip resurfacing prosthesis (Biomet, Warsaw, IN, USA) in March 2007 ( Fig. 1 ). The Biomet uncemented femoral hip resurfacing component has a full coating of titanium plasma spray under the entire undersurface of the femoral component, excluding the stem. The porous coating is identical to that present on the Magnum acetabular component and numerous other Biomet products. There are no other changes from the cemented version of the Recap device. The cemented Recap femoral component, used in the control group, has a grit blast cobalt chrome surface. The same instrumentation was used for both versions, which is designed to allow a 0.5-mm gap for cement and a press fit for the uncemented version. The Magnum acetabular component, used in both groups, has a full porous plasma spray titanium coating and 4 small radial splines. These implants and their instrumentation were described in detail in a previous publication. Use of either the cemented or fully porous-coated Recap femoral component together with the Magnum acetabular component for an HRA procedure constitutes an off-label use in the United States; however, these implants are approved for total hip resurfacing in most other countries. Consent was obtained from each patient.
For the first year (from March 2007–February 2008), the manufacturer could not keep pace with the surgeon’s demand for the fully porous-coated femoral implant. Implant type used in each individual case was therefore determined by the availability of the uncemented implant at the time of surgery. The decision regarding fixation type was made during the operation at the time of femoral preparation. If an uncemented femoral component of the correct size was available, it was used; otherwise, the cemented version was used. There was no supply limit of the cemented version. All the fully porous-coated and hybrid HRAs performed by the senior author during this period of time were included in this study. The surgical technique was the same for both groups, with exception of the fixation method on the femoral side.
All patients younger than 65 years who were otherwise candidates for THA and who had less than one-third of their femoral head bone stock missing and who had enough acetabular wall integrity to fix a screwless acetabular component were offered HRA (occasionally, older patients were accommodated if they insisted on HRA). It is not our practice to select patients for HRA based on implant size, gender, diagnosis, and presence of cysts or deformity.
There are no additional selection criteria for the type of femoral fixation ( Table 1 ). No cases of uncemented femoral fixation were abandoned because of a failure to achieve adequate initial fixation or for any other reason. All cases had a tight initial press fit by manual testing, and none failed to seat at the desired level (within 1–2 mm of the trial position). In the cemented components, only the undersurfaces of the component, but not the stems, were cemented. In both groups, cysts were treated in the same manner: grafting with platelet concentrate and acetabular reamings. No attempts were made to remove any femoral component (either type) after it was implanted. No patients scheduled for HRA were converted to THA intraoperatively for any reason.
| Fully Porous-Coated | Hybrid | P Value | |
|---|---|---|---|
| Surgical Date | March 2007–February 2008 | March 2007–February 2008 | — |
| Number of hips | 191 | 96 | — |
| Number of patients | 182 | 90 | — |
| Age at surgery (y) | 50 ± 8 (range: 28–73) | 52 ± 8 (range: 21–68) | .08 |
| Weight (kg) | 84.6 ± 16.2 (range: 49.50–132.75) | 84.6 ± 18.0 (range: 51.3–167.5) | .93 |
| Body mass index | 27 ± 4 (range: 19–43) | 28 ± 4 (range: 18–43) | .48 |
| T score (Bone mineral density) | 0.3 ± 1.6 (range: −2.2–5.2) | 0 ± 1.19 (range: −2.1–2.8) | .10 |
| Gender | .06 | ||
| Women | 50 (27%) | 35 (39%) | — |
| Men | 132 (73%) | 55 (61%) | — |
| Side | .32 | ||
| Left | 92 (48%) | 53 (55%) | — |
| Right | 99 (52%) | 43 (45%) | — |
| Diagnosis | .46 | ||
| Osteoarthritis | 133 (70%) | 74 (77%) | — |
| Dysplasia | 31 (16%) | 14 (15%) | — |
| Posttrauma | 8 (4%) | 1 (1%) | — |
| Avascular Necrosis | 12 (6%) | 4 (4%) | — |
| Others | 7 (4%) | 3 (3%) | — |
By March 2010, all 191 cases in 182 patients who received the porous femoral component as well as the 96 cases in 90 patients implanted with the cemented femoral component reached their minimum 2-year follow-up. One patient (1 hip) in the control group died due to causes not related to his hip at the age of 57 years. Because we had his 2-year follow-up, this patient was still included in the study.
The posterior minimally invasive vascular sparing surgical approach using a 4-inch incision was used in both groups. Platelet concentrate was used. A multimodal pain management program in combination with spinal anesthesia was used. A comprehensive blood management program was used that resulted in complete avoidance of any transfusion. Both groups were allowed weight bearing immediately after the surgery and advanced to impact sports after 6 months if desired. Patients were encouraged to proceed at their own pace using crutches for 1 to 2 weeks and then a cane for 1 to 2 weeks. They were encouraged to walk 1 mile daily without a support device by 6 weeks. No formal physical therapy was used after hospital discharge. Celebrex was used for 2 weeks postoperatively to avoid heterotopic ossification.
There were no statistical differences between the demographic characteristics in the 2 groups in terms of average age, weight, BMI, T score (bone mineral density), gender, side, and diagnosis (see Table 1 ). This confirms that similar comparison groups were created by this nonstandard method of patient selection.
Postoperative follow-up visits were requested at 6 weeks, 1 year, 2 years, and every other year thereafter and entered into our prospective database. Because 77% of the patients came from out of the state where the senior author practices, they were given 3 options to generate the clinical scores. They could answer the questionnaire related to their Harris Hip Score (HHS); visual analog scale (VAS) of pain score; pain location; and University of California, Los Angeles (UCLA) activity score during an office visit (32%), on an online database (55%), by mail (11%), or through a phone interview (2%). Radiographs were reviewed at each follow-up interval, but the latest radiographic review was used as a basis for this report. 76% of patients had complete follow-up information at a minimum of 2 years.
In this study, the null hypothesis for all comparisons between the 2 groups was that the evaluated parameter of the fully porous-coated group was the same as that of the hybrid group. The significance level α was set as 0.05. The statistical difference between numerical variables, including patient demographic information and clinical outcomes, was evaluated and compared between these 2 groups with the use of independent 2-sample student t tests. The statistical differences between categorical variables, including gender, operational side, and intraoperative complications, were also calculated and compared between these 2 groups based on χ 2 tests. The null hypothesis for all longitudinal comparisons within 1 group was that the evaluated preoperative parameter was the same as the postoperative outcomes. The comparisons between preoperative and postoperative HHSs in the same group were evaluated with the use of paired t tests. Kaplan-Meier curves were calculated to evaluate the survivorship rates of the 2 groups using revision of any component as the end point. The log-rank analysis was used to test the hypothesis that the survival functions between these 2 groups were the same. The data collection and analyses were performed with the use of OrthoTrack (Midlands Orthopaedics, p.a., Columbia, SC, USA) and JMP (SAS, Cary, NC, USA). The institutional review board approval was obtained for this study.
Results
There was no difference in the survivorship rates between the 2 groups ( P = .92). Specifically, there was no difference of the femoral complication rate. The femoral revision rate was 1% for femoral neck fracture and 1% for other early femoral failure in both groups. In both groups, Kaplan-Meier survivorships were the same: 97.8% using revision for any component as the endpoint, 97.8% using any failure of the femoral component as the endpoint, and 100% using any failure of the acetabular component as the endpoint at 3-year follow-up postoperatively ( Fig. 2 ).
In the study group, 4 of the 191 hips (2%) required a revision of the femoral component. Two were revised because of femoral neck fractures (1%) at 1-month (59-year-old man) and 2-months (63-year-old man) follow-up and 2 because of femoral failure (osteonecrosis) (1%) at 10-months (50-year-old man) and 12-months (60-year-old) follow-up. In the control group, 2 of the 96 hips (2%) were revised: 1 was revised because of a femoral neck fracture (1%) (43-year-old woman) at 3 months postoperatively and 1 because of femoral failure (osteonecrosis) (1%) (31-year-old man) at 28 months postoperatively. All 6 revisions were isolated femoral revisions converting the resurfacing to a jumbo bearing metal-on-metal uncemented stemmed THA.
Other hip-related complications were seen in 2 of the 191 hips (1%) in the study group and 4 of the 96 hips (4%) in the control group ( P = .22). In the study group, 1 hip dislocation (55-year-old man) was treated with closed reduction, but the hip was functioning well at the latest follow-up. One acetabular component appeared to be shifted in 1 hip before the 6-week follow-up (56-years-old man) postoperatively and remained stable at the latest follow-up of 2 years. The patient was functioning well at final follow-up. In the control group, 2 dislocated hips (both men, 44 and 46 years old) were treated with closed reductions. One deep infection with Pseudomonas (68-year-old woman) was cured with an open subcutaneous debridement and a 6-week course of intravenous antibiotics. The patient remains free of infection at the final follow-up of 2 years. One patient (68-year-old woman) suffered an abductor tear 4 months postoperatively that eventually healed after a platelet concentrate injection. All patients with complications were doing well at the latest follow-up visit.
There were no statistical differences in the average femoral component size, average blood loss, average hospital stay, and operation time between the study group and the control group ( Table 2 ). The minimum duration of follow-up was 2.1 years for both groups ( Table 3 ). In the control group, 1 patient had died (1 hip) due to causes unrelated to his hip surgery after 2 years of follow-up. At his 2-year follow-up, the patient’s HHS was 97, UCLA score was 7/10, and VAS pain score on normal days and on worst days were both equal to 0. The clinical outcomes, including preoperative and postoperative HHSs and VAS scores, were summarized for both groups (see Table 3 ). The postoperative HHSs were significantly improved compared with their preoperative HHSs in both groups ( P <.001).
| Fully Porous-Coated | Hybrid | P Value | |
|---|---|---|---|
| Hospital Stay (d) | 3 ± 1 (range: 2–7) | 3 ± 1 (range: 2–5) | .9 |
| Operation Time (min) | 116 ± 21 (range: 80–220) | 117 ± 15 (range: 90–169) | .9 |
| Blood Loss (mL) | 263 ± 100 (range: 75–550) | 246 ± 96 (range: 50–550) | .18 |
| Femoral Component Size (mm) | 51 ± 4 (range: 40–60) | 50 ± 3 (range: 44–56) | .22 |
| Fully Porous-Coated | Hybrid | P Value | |
|---|---|---|---|
| Period of Follow-Up (y) | 2.4 ± 0.2 (range: 2.1–3.0) | 2.6 ± 0.3 (range: 2.1–3.0) | <.001 a |
| Preoperative Information | |||
| HHS | 57 ± 13 (range: 22–83) | 54 ± 13 (range: 21–81) | .07 |
| Postoperative Information | |||
| HHS | 94 ± 9 (range: 55–100) | 96 ± 6 (range: 70–100) | .25 |
| UCLA Score | 8 ± 2 (range: 2–10) | 7 ± 2 (range: 3–10) | <.001 a |
| VAS Regular Day | 1 ± 1 (range: 0–7) | 1 ± 1 (range: 0–7) | .48 |
| VAS Worst Day | 2 ± 2 (range: 0–10) | 2 ± 2 (range: 0–9) | .89 |
| Femoral Radiolucency | 0 (0%) | 0 (0%) | 1 |
| Incomplete Acetabular Radiolucency | 2 (1%) | 0 (0%) | .55 |
| Number of Complications b | 2 (1%) | 4 (4%) | .22 |
| Number of Failures | 4 (2%) | 2 (2%) | 1 |
| Deceased | 0 | 1 | .33 |
Related posts:
Comparison of Functional Results of Hip Resurfacing and Total Hip Replacement: A Review of the Literature
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A Prospective Metal Ion Study of Large-Head Metal-on-Metal Bearing: A Matched-Pair Analysis of Hip Resurfacing Versus Total Hip Replacement
Complications After Metal-on-Metal Hip Resurfacing Arthroplasty
The Future of Hip Resurfacing
A Prospective Metal Ion Study of Large-Head Metal-on-Metal Bearing: A Matched-Pair Analysis of Hip Resurfacing Versus Total Hip Replacement
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