Conversion of Fused Hip to Total Hip Arthroplasty: Long-Term Clinical and Radiological Outcomes

BackgroundDespite promising results at the mid-term followup, several aspects of conversion of the fused hip to total hip arthroplasty (THA) remain controversial. The aim of this study was to evaluate clinical and radiological outcomes with a minimum 5-year followup in patients who underwent conversion of the fused hip to THA.MethodsFifty-seven patients (59 hips) were evaluated. The Harris Hip Score (HHS), range of motion (ROM), and the Visual Analogue Scale (VAS) were used to assess hip function and low back pain. Subjective satisfaction with surgery and the presence of the Trendelenburg sign was also evaluated. Radiological assessment was performed pre- and postoperatively to evaluate loosening and heterotopic ossification (HO).ResultsAfter a mean followup of 13.0 ± 6.2 years, HHS and VAS significantly improved from 46.0 ± 16.7 to 80.8 ± 18.8 and from 4.4 ± 1.5 to 2.1 ± 1.4 (both P < .001), respectively. Twenty-three patients (40.4%) had a positive Trendelenburg sign, and HOs were found in 29 cases (49.1%). An overall 29.8% complication rate was noted. Smoking habits and rheumatoid arthritis were predictive of Trendelenburg sign (P = .046 and P = .038, respectively). Implant survival rate as the end point was 98.7 ± 1.3% at 5 years, 92.4 ± 3.3% at 10 years, 82.1 ± 5.7% at 15 years, and 73.4 ± 8.0% at 20 and 25 years. A worse cumulative implant survival rate was noted in patients who underwent previous hip surgery, defined as any hip operation before fusion (P = .005).ConclusionConversion of the fused hip to hip arthroplasty provides high levels of hip functionality and satisfaction with surgery at long-term followup. An implant survival rate higher than 70% can be expected 25 years postoperatively.     

Curved-stem Hip Resurfacing

Hip resurfacing is an attractive concept because it preserves rather than removes the femoral head and neck. Most early designs had high failure rates, but one unique design had a femoral stem. Because that particular device appeared to have better implant survival, this study assessed the clinical outcome and long-term survivorship of a hip resurfacing prosthesis. Four hundred forty-five patients (561 hips) were retrospectively reviewed after a minimum of 20 years' followup or until death; 23 additional patients were lost to followup. Patients received a metal femoral prosthesis with a small curved stem. Three types of acetabular reconstructions were used: (1) cemented polyurethane; (2) metal-on-metal; and (3) polyethylene secured with cement or used as the liner of a two-piece porous-coated implant. Long-term results were favorable with the metal-on-metal combination only. The mean overall Harris hip score was 92 at 2 years of followup. None of the 121 patients (133 hips) who received metal-on-metal articulation experienced failure. The failure rate with polyurethane was 100%, and the failure rate with cemented polyethylene was 41%. Hip resurfacing with a curved-stem femoral component had a durable clinical outcome when a metal-on-metal articulation was used.     

Femoral-head vascularity after hip surface arthroplasty

Background  

Iatrogenic devascularization of the femoral head is as an area of concern following hip resurfacing arthroplasty, with probable implications on short-term failure and long-term survival of the implant.     

Limited range of motion of hip resurfacing arthroplasty due to unfavorable ratio of prosthetic head size and femoral neck diameter

Background and purpose?Hip resurfacing arthroplasty is being used more and more frequently. The small ratio in size between the resurfaced femoral head and the relatively thick femoral neck raises the question of whether the range of motion is sufficient, particularly with regard to the high mobility required by younger patients. We analyzed motion in a CAD model.

Methods?Three-dimensional CAD models of the natural hip were created from CT scans and 8 designs of hip resurfacing prostheses (head diameter between 42 mm and 54 mm combined with a hemispherical cup) were implanted in a virtual sense. We simulated 3 different leg positions and the range of motion was evaluated, considering five different implant positions.

Results?The range of motion of the hip resurfacing designs analyzed was far below the range of motion of stemmed total hip prostheses. None of the resurfacing prostheses provided flexion movements of 90° without impingement. The average range of motion of hip resurfacing arthroplasty was 31–48° below the range of motion of a stemmed total hip replacement with 32-mm head diameter.

Interpretation?The range of motion of the hip resurfacing designs examined was substantially less than that of a conventional total hip prosthesis. Since impingement of the femoral neck on the acetabular component increases the risk of neck fractures, of dislocation and of subsequent implant loosening, the design and position of the implant should be considered before using hip resurfacing arthroplasty as a standard treatment for younger patients.     

Frequent Femoral Neck Osteolysis With Birmingham Mid-head Resection Resurfacing Arthroplasty in Young Patients

Background

Mid-head resection total hip resurfacing arthroplasty was promoted as an alternative to traditional total hip resurfacing for patients with poor femoral head bone quality or abnormal femoral head morphology, because those patients are at high risk of failure with traditional total hip resurfacing. It is a large-headed metal-on-metal device that uses a short, bone-conserving stem. Good performance of the implant has been reported at short-term followup, but no information on the implant performance in the mid- or long-term is available.

Questions/purposes

In this study, we report (1) on the mid-term implant survivorship and hip scores in a single nondesigner surgeon series. Because of the occurrence of femoral neck osteolysis and pseudotumor in a subgroup of patients, we also investigated the following: (2) Were there any preoperative parameters that are associated with osteolysis? (3) Could we differentiate the osteolysis group from the others on the basis of implant component sizes, positions, and radiologic parameters? (4) Could we differentiate the osteolysis group from the others on the basis of metal ion levels?

Methods

Between 2006 and 2011, one surgeon performed a total of 49 Birmingham Mid-head Resection total hip resurfacing arthroplasties in 47 patients. The general indications for this procedure were young patients who were considered suitable for hip resurfacing arthroplasty but had avascular necrosis, large cysts, or severe deformity of the femoral head. Clinical followup including Oxford Hip Score (OHS) and UCLA hip scores were available preoperatively and at a mean of 6 years (range, 3–8 years) on all patients (100%), radiographic followup on 45 of 47 (96%), MRIs on 18 (38%), and metal ion levels on 37 (79%). Mean age at surgery was 50 years. Spearman’s correlation was used to test the association between femoral neck osteolysis and preoperative parameters, implant component sizes and positions, and blood metal ion levels.

Results

We found 100% survival. Patients’ median OHS was 46 of 48 (range, 35–48) and UCLA 8 of 10 (range, 4–10). However, 16% of the hips (seven of 45) demonstrated osteolysis in the femoral neck. Of the preoperative parameters, the osteolysis was associated with low weight (r = −0.337, p = 0.031) and to a lesser degree with female sex (r = 0.275, p = 0.067). Radiologically, the osteolysis was strongly associated with the presence of a pseudotumor on MRI (r = 0.663, p = 0.004). We could not differentiate the osteolysis group from the rest of the cohort on the basis of the implant sizes or radiographic implant component positions. The cohort’s median whole blood cobalt was 1.77 ppb (range, 0.18–10.27 ppb) and chromium 1.88 ppb (range 0.36–10.09 ppb). There was no difference in the metal ion levels between the osteolysis group and the rest of the cohort.

Conclusions

The high rate of silently developing femoral neck osteolysis associated with this implant is concerning and is expected to cause a high rate of failure at longer followup. We have instituted a program of annual clinical and radiologic followup for this group of patients. We have stopped implanting this device and recommend against its use.

Level of Evidence

Level IV, therapeutic study.     

Hip Resurfacing: A Single Surgeon U.S. Series With Minimum Ten-Year Follow-up

BackgroundMetal-on-metal hip resurfacing is an alternative to total hip arthroplasty (THA). The aim of this study was to determine implant survivorship, analyze patient-reported outcomes measures and to determine patient satisfaction for patients who underwent metal-on-metal hip resurfacing at a large US academic institution by a single surgeon with a minimum of 10-year follow-up.MethodsPatients who underwent hip resurfacing from September 2006 through November 2009 were included. Patient demographics and variables were collected from a prospectively maintained institutional database and patients completed an additional questionnaire with patient-reported outcomes measures.ResultsA total of 350 patients (389 hips) out of 371 (433 hips) with a minimum 10-year follow-up were successfully contacted (94.3% follow-up). Mean age was 53 years, 258 were male (73%). 377 out of 389 hips (96.9%) did not require additional surgery. Gender was significantly related to implant survivorship (males 99.0%, females 90.9%; P < .001). 330 patients (369 hips, 94.8%) were satisfied with their surgery. Males had higher proportion of satisfaction scores (P = .02) and higher modified Harris Hip Score (odds ratio = 2.63 (1.39, 4.98), P = .003). Median modified Harris Hip Score score for non-revised hips was 84.0 [80.0; 86.0] versus those requiring revision, 81.5 [74.0; 83.0], (P = .009).ConclusionAt a minimum 10-year follow-up, hip resurfacing, using an implant with a good track record, demonstrates 99.0% survivorship in male patients with an average age of 52 years. We believe that the continued use of metal-on-metal hip resurfacing arthroplasty in this population is justified by both positive patient reported outcomes and survivorship.     

Lack of radiographic loosening signs in a hip resurfacing that failed by stem fracture

Fracture of the femoral stem is a rare manifestation of femoral component loosening in hip resurfacing. The patient had undergone successful hip resurfacing 3 years prior to presentation, presenting with complaints of groin pain, but without radiographic evidence of loosening. At 6 years post-operatively, the patient again presented with groin pain. Radiographs demonstrated a mid-stem fracture. Analysis of the retrieved implant and resected femoral head following conversion to total hip arthroplasty indicated that component failure and fracture appeared to be secondary to failed fixation and implant loosening not related to osteonecrosis or acute femoral neck fracture. The case report highlights the difficulty in diagnosing femoral component loosening in hip resurfacing in the absence of gross implant subsidence or stem radiolucency.