Abstract
Introduction
Recently used hip resurfacing systems remove bone, ream away the subchondral bone stock and reduce biomechanical properties of the femoral neck. Since much bone was removed from the head, the biomechanical properties decrease. The Onlay Resurfacing technique preserves complete bone stock and individual anatomy without any change in offset or leg length. To quantify the clinical outcome and adverse events a group receiving standard total hip arthroplasty was designed as control.
Methods
104 patients with primary osteoarthritis underwent hip onlay resurfacing. Mean aged 51 years, BMI 27,2. An onlay resurfacing system with a cemented femoral cup and a modular cementless acetabular component was used for resurfacing. The control group (n:104) got a standard cementless THA with a standard head size of 32 mm in diameter. All procedures were performed by one surgeon and the same minimal invasive antero lateral approach was used. An identical post-operation procedure with regards to rehabilitation, physiotherapy and medication was performed in both groups. The Harris Hip Score was designed as the primary criteria.
Results
In the Onlay Resurfacing group the HHS improved six weeks, six months and three years after surgery from 46 to 89, to 95 and 97 after three years. Compared to resurfacing the THA improved from 42 to 85, to 92 and 93 after three years. At six months and three years, the SF12 score (mental and physical) improved to normal in both groups.
One neck fracture and one aseptic loosening occurred in the onlay resurfacing group, one DVT and 1 dislocation were found in the control group. No implant failure in both groups and no difference in blood loss. The mean leg length after standard THA shows 0.4 mm lengthening in contrast to resurfacing without statistic significant difference.
Conclusion
Hip onlay resurfacing preserves maximal bone stock and provides excellent functional outcome. The outcome was better in the onlay resurfacing group compared to standard THA. Combined with minimal invasive surgery patients will be able to shorten the rehab phase significantly. Side effects such as luxation, instability and length differences were expected to appear less frequently but adverse events typically related to resurfacing such as neck fracture occur. Because of the modularity of the onlay resurfacing system, revisions of the femoral component could be done as a primary hip arthroplasty.
