Abstract
Purpose
To determine if minimally invasive surgery (MIS) for primary hip replacement surgery increases the risk of long term aseptic loosening as predicted by implant micromotion measured with radiostereometric analysis (RSA).
Method
Ninety patients undergoing primary THA for osteoarthritis (exclusion criteria: post-traumatic arthritis, rheumatoid arthritis, hip dysplasia, previous hip infection) were randomized to undergo THR surgery utilizing the standard direct lateral approach (n=45; 24 male; age=58 yrs; BMI=27) or MIS via a one-incision direct lateral approach using specific instrumentation (n=45; 23 male; age=55; BMI=29). Uncemented acetabular and femoral (ProfemurZ) components were used with ceramic on ceramic bearings. The femur was marked with 9 tantalum beads placed in the greater trochanter, lesser trochanter, and femoral shaft distal to the tip of the prosthesis. Post-operative care was be standardized according to the care maps at our institution. Primary outcome measure was femoral stem MTPM (maximum total point motion) measured using Model-based RSA. Stereo supine X-rays were taken before weight bearing and 3, 6, and 12 months postoperatively. At the same time intervals Harris Hip Score, Oxford-12, WOMAC, and SF36 questionnaires were administered. Rates of infection, dislocation and revision were recorded.
Results
Nine patients were lost to follow-up (4 due to missing post-op exams; 5 did not have enough beads placed during surgery). Ten patients were revised (2 due to failure of the ceramic femoral head; 8 due to long (38.5 mm) neck fractures at 17–30 months postop). There were no differences between groups for all outcome measures. Mean MTPM at 24 months was 3.0mm (SD=2.0mm) for the MIS group and 2.9mm (SD=2.1mm) for the standard group.
Conclusion
No difference between groups at one year indicates MIS for uncemented primary THR through a direct lateral approach does not appear to negatively affect stability of the femoral stem. However, there was a high rate of femoral neck fracture in the study cohort that was not related to micromotion or treatment group that indicates a problem with the design of the titanium alloy modular femoral neck.
