Hip resurfacing can only be considered a viable alternative to THA if it can be reasonably taught to surgeons and subsequently performed with an acceptable risk of complications. Legitimate concern has been raised that given the more technically demanding nature of hip resurfacing, the rate of complications may be unacceptably high. The goal of this report was to describe the early experience with metal-on-metal hip resurfacing, following FDA approval of the first device in the United States, with a focus on the risk of early post-operative complications, associated treatment and any demographic associations with these complications.
One of the limitations of this study is the inclusion of a large number of surgeons with varying levels of experience with hip surgery. However, the use of such a mixed population of surgeons may provide a better estimate of what the “average” orthopaedic surgeon can expect [4
]. Further, no radiographs were reviewed as part of this study. However, the early complications that we sought to identify should not have been hampered by the lack of a radiographic review. Furthermore, because complete 1 year data were not available for all 540 cases, the results reported here represent the minimum and the actual rate may have been higher if followup on all patients had been received. What remains unknown is if the risk of hip resurfacing is associated with a higher risk of complications than standard THA. Because this study was observational and not randomized, this critical question remains unanswered.
The most commonly reported complication of hip resurfacing is femoral neck fracture. Femoral neck fracture has been associated with both technical error and patient-related factors, including advanced age, female gender, and decreased bone density (Table ) [3
]. A femoral neck fracture was seen in 2% of cases in this series with 6 months followup, which is similar to the 1.46% rate reported in the largest known series to date [21
] and far lower than the rate of 7.2% reported in one series focusing on the learning curve associated with the procedure [18
]. Consistent with prior literature, patient-related factors (notably age and female gender) seem to have been important in the occurrence of this complication with three of the cases being in women who were older than 55 years of age, five being in men older than 55 years of age, and nine of the 10 occurring in patients who were either female or older than 55 years of age. Both surgeons and patients should be aware of the importance of patient selection when deciding on hip resurfacing as opposed to conventional THA. Although the seriousness of this complication cannot be overemphasized, the popularity of cementless femoral reconstruction in the United States has been associated with an increased risk of periprosthetic femoral fracture in association with conventional THA [6
Reported femoral neck fracture rates following metal-on-metal hip resurfacing
Nine nerve injuries were reported in this series, for a rate of 1.7%, with six of the nine occurring among the surgeons’ first 10 cases. In one of the largest published series to date, the risk of nerve palsy was 16 of 1000 (1.6%) [14
], which is similar to the risk noted in this report. In a report of 230 BHRs followed for a mean of 5 years, five nerve palsies were noted (2.2%; two sciatic, two femoral, one common peroneal) with all recovering at the most recent evaluation [12
]. Schmalzried et al. [20
] estimated the risk of nerve palsy at approximately 1% after standard THA, although other large series have estimated the risk is lower, at approximately 0.2% [10
]. Retention of the femoral head in resurfacing arthroplasty complicates exposure, and the higher risk of nerve injury associated with hip resurfacing may be attributable to difficulties in gaining adequate exposure of the acetabulum. In addition, retraction of the femoral head anteriorly may directly compress the femoral nerve during exposure. Given the higher risk reported in this study and other reports, it may be prudent to fully release the hip capsule and gluteus maximus tendon insertion to ease exposure and limit forceful retraction.
A purported benefit of resurfacing arthroplasty of the hip is a decreased risk of dislocation; however, eight dislocations were noted in this study (1.8%). Although this number appears high, it is important to note four of the dislocations were seen on the recovery room radiographs and have not resulted in recurrent instability. Given the complete capsulotomy recommended for hip resurfacing, it is possible a dislocation might occur when neuraxial anesthesia results in lower extremity paralysis. Several other series have reported no dislocations after hip resurfacing [2
], although in one series of 1000 patients, the risk of dislocation was 0.9% [14
], which is the same rate we found if the recovery room dislocations are excluded. Two of the dislocations in the present report were managed with early revision surgery, one for a vertically placed acetabular component indicating the importance of appropriate acetabular component placement, even when a large-sized femoral head is used. In one large series of 19,680 conventional THAs performed at a tertiary care center, the incidence of dislocation was 1.8% at 1 year and 7% at 25 years [24
] indicating the risk of dislocation may be lower with hip resurfacing, even when performed by surgeons with minimal prior experience in the technique. Several studies [11
] demonstrate the risk of dislocation after conventional THA is related to surgical experience and thus with increased familiarity with the technique, the risk of dislocation with hip resurfacing would be expected to decrease as well.
Results from the Australian Hip Registry suggest that although the overall rate of early revision is higher as a whole, in target populations (males and patients younger than 55 years of age), the early revision rate is the same as conventional THA [7
]. There were 14 early revisions in this study (3% of the hips with followup of at least 1 year), which is similar to what has been reported in the Australian Registry [7
] for hip resurfacing (2.8%), albeit at a shorter time to followup.