Patients in the control group scored higher on WOMAC function (p = 0.027) and Oxford scores (p = 0.009) (Table 4) than the MRS group. However, there were no differences in any of the other WOMAC components, the SF-12, satisfaction, or UCLA scores.
The immediate postoperative radiographs showed the femoral and acetabular components to be well positioned. The alignment of the femoral stems in the coronal plane was within 5° of neutral. The cups were positioned in 40° to 50° of abduction. At latest followup, there was a nonprogressive radiolucent line measuring less than 2 mm at Zone 3 of three acetabular components and at Zones 3, 4, and 5 of the stem of four femoral components. None of the implants were deemed radiographically loose.
Six MRS patients (17%) had a complication related to the index operation. The most common being instability, as three of 36 patients (8%) suffered at least one dislocation. Two of the three patients who had a dislocation had a nonconstrained liner at the time of the index procedure. The third patient had a constrained liner, but the constraining ring failed and the hip subsequently dislocated. The three patients underwent limited rerevision to a constrained variant, with a successful outcome. Further surgery was not required. Cup pullout was seen in one patient (3%), which occurred 3 years after the index surgery. The liner in this case was constrained. The patient underwent reconstruction of the acetabular component. Unfortunately, the patient developed a subsequent infection and eventually ended up with a nonfunctional resection arthroplasty. Infection was seen in one other patient (3%) who was successfully treated with débridement, implantation of an antibiotic depot around the implant, prolonged antibiotic therapy, and retention of the components. Progressive osteolysis and loosening of both the acetabular and femoral components were seen in one patient (3%). The patient was not medically fit to undergo any form of reconstruction and underwent revision to a nonfunctional resection arthroplasty.
Proximal femoral bone loss continues to be a challenging condition for the arthroplasty surgeon, which is compounded by the fact that most of these patients have already had multiple hip operations, have severe abductor and possible acetabular bone stock deficiency, and are commonly elderly with preexisting comorbidities. If substitution of the proximal femur is chosen as the preferred treatment, the options include the use of a proximal allograft-prosthetic composite or proximal femoral replacement such as a MRS. The use of a conventional modular revision stem is an option; however, reattachment of the abductor mechanism can be compromised and there are no long-term results reported for this type of reconstruction [3, 4]. We evaluated whether the quality of life improves for patients undergoing proximal femoral replacement using a segmental modular system for severe bone loss.
Our study is subject to certain limitations. First, the number of patients is relatively small because this procedure is uncommon even in a tertiary care center such as the one where the study was conducted. Second, many of the patients in the original sample were eventually lost to followup despite extensive efforts to locate them. We attribute this loss to followup to their already advanced age at the time of surgery (median age, 81 years). Third, there is disparity in the number of hip revisions between patients in the MRS group and patients in the control group. Patients in the MRS group were more likely to have had multiple revisions and were expected to have more deficient bone stock, compromised abductor mechanism, and decreased functional reserve, which makes our control group not the ideal comparison group (Fig. 3).
Our data suggest proximal femoral replacement using the MRS in patients with severe proximal femoral bone deficiency led to functional and quality-of-life improvements as measured by several validated scores. We believe this study is a valuable contribution to the literature, which is lacking in regard to quality-of-life assessment in MRS patients.
The degree of improvement in pain for MRS patients was comparable to that achieved after RTHA using a conventional hip revision system. However, the improvement in function, while present, was less dramatic than that observed in the control group. The control group fared better as measured by WOMAC function and Oxford scores. This might be, at least partially, due to the fact that MRS patients, on average, had undergone a larger number of prior revisions as noted above.
Radiographs were available for 31 MRS patients (86%), none of whom showed evidence of radiographic loosening at the time of latest followup. Our findings are consistent with those of the study of Parvizi et al. , which, like our study, had a small sample size (n = 48) and a minimum 2-year followup.
The most common complication reported after proximal femoral replacement was dislocation [14, 15, 18, 30]. In our study, three of the 36 patients (8.3%) had a dislocation. Likewise, dislocation occurred in six of 43 patients (14%) in one study , in three of 18 (16.7%) in another , and in two of four (50%) in another series . This degree of instability is higher than that encountered after RTHA using a conventional implant [1, 19] but is comparable to that seen after the use of an allograft-prosthesis composite .
Our data suggest the MRS is a reasonable option for hip salvage in the setting of severe proximal femoral bone loss. Patients treated with this implant had improvement in function and quality of life. Some authors have conducted studies describing the functional outcome after this kind of reconstruction [15, 23, 24], but none assessed the patients’ postoperative quality of life. Dislocation rates were high and we suggest using a constrained cup in all cases where there is adequate fixation of the acetabular shell.
We thank Daphné Savoy for her assistance in the preparation of this manuscript.
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