The effect of obturator externus in enhanced posterior soft tissue repair of total hip replacement

Objective To investigate anatomic feature of obturator externus and the region of hip joint capsule covered by it and to probe hip stabilization offered by obturator externus in hip flexion and internal rotation.Methods Ten adult cadaver pelvises were used.Following dissection and measurement,ten left hips were used for obturator externus experiment.After touching and understanding obturator externus in hip flexion and internal rotation,the distance of femoral head cartilage side exceeding acetabular labrum in exposed obturator externus region was measured in hip flexion 30°、60°、90°and internal rotation 15°adding to different hip flexion angle.Ten left hips were used for hip joint capsule experiment.Following dissection,the average thickness of every part of the posterior hip joint capsule was measured and the ischiofemorale ligament was observed.Results Obturator externus was the unique muscle tightly sticking to posteroinferior parts of hip joint capsule.In hip flexion and internal rotation,obturator externus was expanded and pushed by femoral head.The extent of expansion and push increases following hip flexion angle's increase.In the same flexion angle,the extent of expansion and push on internal rotation was greater than that of non-rotation.The thickness in the posterior hip joint capsule was ununiformity.Two weaker parts located at obturator externus region,ischiofemorale ligament trunk did not go through obturator externus region.Obturator externus region of hip capsule was weaker than other region.Conclusion Obturator externus is the unique dynamic sustain muscle to posteroinferior parts of hip joint capsule.Obturator externus and the region of hip joint capsule covered by it mainly are main factor which prevent femoral head from dislocation in hip flexion and internal rotation condition.But this region of hip joint capsule is weaker.So obturator externus should not be ignored in enhanced posterior soft tissue repair of total hip replacement. Key words: Arthroplasty; replacement; hip; Muscle; skeletal; Joint capsule