Abstract
Background
In total hip arthroplasty (THA), the importance of preserving muscles is widely recognized; therefore, muscle-sparing approaches are widely used. Recently, we reported that there are bony impressions, that we called the obturator attachment (OA), on the greater trochanter that indicate the insertions of the short external rotator tendons. In this study, we used a three-dimensional (3-D) template to evaluate damage to the insertions of the short external rotator muscles during a femoral procedure.
Methods
We investigated 12 hips in 10 patients who underwent THA. Preoperative CT imaging of the hip was performed, and 3-D reconstruction of the greater trochanter was used to visualize the bony impressions that indicate the insertions of the obturator internus and externus muscles (Fig 1A). We performed preoperative 3-D templating of two different femoral prosthesis (flat tapered-wedge stem: J-Taper, cylindrical straight stem: PerFix910) and then evaluated the extent of damage to the OA during the stem placement (Fig 1B, 1C). The extent of damage to the OA was classified using the following scale: grade 0, no damage of the insertion area; grade 1, less than 1/3; grade 2, equal to or more than 1/3–2/3; grade 3, equal to or more than 2/3; grade 4, complete.
Results
The attachment area of the obturator internus tendon was damaged in 9 hips (7 hips: grade 1, 2 hips: grade 2) using J-Taper and all hips (8 hips: grade 2, 4 hip: grade 3) using PerFix910. The attachment area of the obturator externus tendon was not damaged in any hip using J-Taper but was damaged in 5 hips (5 hips: grade 1) using PerFix910.
Conclusions
The tendon insertion site for the obturator internus was more likely to be damaged by rasping or reaming. The tapered-wedge type stem was considered to be superior to the straight, cylindrical stem for preserving the tendon insertions on the greater trochanter.
Fig.1 Three-dimensional reconstructed images of the left greater trochanter, after removal of the femoral head. A: The deep depression in the anterior part of the trochanteric fossa (blue area) indicates the insertion of the obturator internus, and the posterior depression in the trochanteric fossa (red area) indicates the insertion of the obturator externus. B: Preoperative 3-D templating of the J-taper (Kyocera, Kyoto, Japan) was performed. The insertion area of the obturator internus was damaged (Grade 1), while the insertion area of the obturator externus was not damaged. C: Preoperative 3-D templating of the PerFix910 (Kyocera, Kyoto, Japan) was performed. The most of the insertion area of the obturator internus was damaged (Grade 3), while the insertion area of the obturator externus was not damaged. Oi = obturator internus, Oe = obturator externus, Lt = lessor trochanter, Sup = superior, and Ant = anterior.
