Abstract
Objectives
The shape of proximal femur is important for the selection of implant in total hip arthroplasty (THA). There are few reports about the shape of proximal femur. We analyzed preoperative and postoperative conditions of the proximal femurs of patients before and after total hip arthroplasty with computed tomography (CT) and evaluated the compatibility to the cementless stem.
Materials and Methods
We analyzed 65 hips of 63 patients (10 males and 53 females) who had THA between January 2008 and December 2010 in our hospital. We approximated the center of the femoral head as the center of the inscribed sphere in the femoral head. We defined the axis of proximal femur with the line between the centers of the circles located at 45 mm distal from lesser trochanter (LT) and at 90 mm proximal from LT. We measured the neck-shaft angle of femur, offset of femoral head, and diameter of bone-marrow cavity. After operation, we measured the distance between the stem surface and the edge of the femoral cortex (SF) at 10 mm proximal from LT to evaluate the compatibility of CT. We used PerFix HA cementless stem (Kyocera medical co., Osaka).
Results
The mean diameter of femoral head was 46.1 mm, neck-shaft angle was 128.9 degrees, horizontal offset was 33.5 mm, and vertical offset was 41.6 mm. The mean diameters of bone-marrow cavity were 20.8 mm at 10 mm proximal level from LT, 14.2 mm at 20 mm distal level from LT and 9.9 mm at 100 mm distal level from LT. The medial shape was curved within 40 mm distal point from lesser trochanter. The mean of SF was 3.4 mm (0–5.1mm) and SF values of 43 hips were less than 2.0 mm. The mean of CFI was 3.6.
Discussions and Conclusions
Several reports described about the shape of proximal femur on X-ray. However, it is inaccurate if we do not correct for the influence of anteversion angle of femur. For cementless stem, it is important to fit the medial area to the surface and the compatibility depends on the flare of the proximal femur.
