Abstract
Purpose
There are some concerns about doing hip resurfacing arthroplasty in ONFH due to bone defect which can cause mechanical weakness of femoral component and highly active young age of patients which can cause high wear rate and failure rate. The purpose of this study is to verify the HRA is safe procedure in ONFH in the aspect of mechanical and biological issue.
Materials and Methods
Between December 1998 and May 2005, 185 hips of 169 patients underwent MoM HRA using Birmingham Hip Resurfacing System® at single center. 166 hips (26 hips of female, 140 hips of male) of 144 patients have been reviewed for at least 7 years after MoM HRA. Mean follow-up period was 101.8 (84–178) months. Their mean age at the time of operation was 37.7(16–67) years old. Clinically, Harris hip scores (HHS), UCLA activity scores and range of motion were evaluated. Radiologically, the extent of necrotic area in preoperative MRI and radiolucency around implants, narrowing of retained neck, impingement, stress shielding, and heterotopic ossification were evaluated in the serial anteroposterior and groin lateral radiographs of hip. Complications were defined as joint dislocation, infection, implant loosening, femoral neck fracture and pseudotumor. Failure was defined as revision arthroplasty due to the complications.
Results
The extent of necrotic area in preoperative MRI was average 37.6 (13.3–65)%. Clinically, average HHS was improved from 81.7 points to 98.5 points at last follow-up. Average UCLA activity score at last follow-up was 9.0 points. Range of motion at last follow-up was very satisfactory. There was no patient with severe pain around hip joint. Radiologically, radiolucency was shown around acetabular component in 2 cases (1.2%) and around stem of femoral components in 3 cases (1.8%). Fracture of femoral neck was seen in 1 case(0.6%). Moderate narrowing changes of retained femoral neck were noticed in 4 cases (2.4%). Impingement was seen in 12 cases (7.2%). We found only 1 case of osteolysis at Gruen zone III of acetabulum. Heterotopic ossification was found in 5 cases (3.0%). There was no case with hip dislocation, infection or pseudotumor. Revision surgeries after the primary resurfacing arthroplasty were performed in 4 cases (2.4%). Three hips were revised to the conventional total hip arthroplasty (THA) because of loosening of acetabular component and femur neck fracture. One case of femoral component loosening was revised to THA using big metal head with retained acetabular component.
Conclusions
MoM HRA in ONFH demonstrates good survivorship in average 101.8 months follow-up study. Most of patients show excellent clinical results with high level of activity postoperatively. Prevalence of complications is extremely lower than concern including the allergic reaction to the metal ion. There was no mechanical failure related to bone defect due to ONFH. This results suggests that MoM HRA in ONFH less than 50% of extent of necrosis can be justified.
