Abstract
Purpose
Short metaphyseal fitting femoral stems convey stress to proximal femur and have no distal fixation. They have advantages in that there is no thigh pain and no bone loss due to stress shielding, but there is a concern for weakened fixation. So the authors evaluated whether short metaphyseal fitting femoral stems, which have only metaphyseal and no diaphyseal fixation, can acquire sufficient stability.
Materials & methods
39 cases of 36 patients who undervent uncemented total hip arthroplasty with DePuy ProximaTM (Johnson & Johnson orthopaedics, New Milton, UK) short metaphyseal fitting femoral stems from August 2009 to September 2011 were retrospectively evaluated. There were 19 male and 20 female cases. The mean follow-up period was 35.8(21.8∼49.2) months. Harris hip scores, WOMAC scores, UCLA scores, and presence of femoral pain were evaluated to assess clinical outcome. Femoral radiolucency in coronal and sagittal views of the hip, femoral stem loosening, and displacement was measured to evaluate radiological outcome. Distance between femoral stem and cortical bone was also measured to assess the relationship with radiolucency and loosening according to degree of contact.
Results
Harris hip score before and after operation was 49.8(37–59) and 96.0(71–100) on average. WOMAC score improved from 44.1(31.9–56.3) to 91.8(62.3–100)after operation. UCLA activity score improved from 3.8(2–5) to 7.5(4–9) after operation. When assessed with 1mm as the standard, radiolucent line was shown in 5 cases(12.8%). When the area around the stem was divided into 5 sections, there were 3 cases in which radiolucent line was observed in all 5 sections, 1 case in which radiolucent line was found in only section 4, and 1 case in which radiolucent line was found only in section 5. There was 1 case(2.6%) that required revision THA due to femoral stem loosening. Femoral radiolucency and loosening on coronal and sagittal views increased with greater distance between femoral stem and cortical bone (p=0.002).
Conclusion
In uncemented total hip arthroplasty with short metaphyseal fitting femoral stem, it is important to fill the femoral metaphyseal medullary cavity completely with the femoral stem. Therefore, there is severe loss of cancellous bone at proximal femur. Stability varies with differing degree of contact between femoral stem and proximal femoral cortical bone observed on postoperative coronal and sagittal views. When short metaphyseal fitting femoral stems are used, adequate early fixation can be achieved only with understanding of such characteristics as well as sufficient proficiency of the operator.
