Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Nakhon Pathom, Thailand.
Int Orthop. 2013 Jun;37(6):1141-5. doi: 10.1007/s00264-013-1870-0. Epub 2013 Apr 2.
Unstable posterior fracture-dislocation of the hip is determined by the wall defect or acetabular fracture index. The unstable hip is a result of inadequate posterior acetabular coverage of the femoral head from the posterior acetabular wall fracture. In order to measure total posterior acetabular coverage of the femoral head and avoid using the contralateral acetabulum as a calculation reference, the posterior acetabular arc angle of the femoral head was measured to assess stability of posterior fracture-dislocation of the hip.
Using coronal computed tomography (CT) scan of the normal contralateral acetabulum at the level of the widest acetabular diameter and thinnest medial wall of 60 acetabular fractures, posterior acetabular arc angles of the femoral head in intact, 20 % and 50 % defects of posterior acetabular walls were measured. The angles were measured from the acetabular centre to the thinnest medial wall and to the top, inner cortex of 80 % and 50 % posterior acetabular walls.
Average intact, 80 % and 50 % posterior acetabular walls were 33.82 ± 4.30, 26.88 ± 3.33 and 16.91 ± 2.15 mm which corresponded to 92.25 ± 11.34, 77.42 ± 10.04 and 50.63 ± 6.58° of posterior acetabular arc angles of the femoral head. The intraclass correlation coefficient (ICC) of the measurements including correlation of conversion of posterior acetabular wall depths to posterior acetabular arc angles of the femoral head were more than 0.82 and 0.89.
The measurement technique of posterior acetabular arc angle of the femoral head has strong reliability. Therefore, stable or unstable posterior fracture-dislocation of the hip can be determined in terms of more than 77 degrees or less than 50 degrees of posterior acetabular arc angles of the femoral head instead of less than 20 % or more than 50 % posterior acetabular wall defect.
髋关节后不稳定骨折脱位由壁缺损或髋臼骨折指数决定。不稳定髋关节是由于后髋臼壁骨折导致股骨头后髋臼覆盖不足所致。为了测量股骨头的总后髋臼覆盖，并避免使用对侧髋臼作为计算参考，测量了股骨头的后髋臼弧角，以评估髋关节后骨折脱位的稳定性。
使用 60 例髋臼骨折患者在髋臼最宽直径和最薄内侧壁层面的对侧正常髋臼的冠状位 CT 扫描，测量完整、后髋臼壁 20%和 50%缺损的股骨头后髋臼弧角。从髋臼中心到最薄的内侧壁以及 80%和 50%后髋臼壁的顶部、内皮质测量角度。
平均完整、80%和 50%后髋臼壁分别为 33.82±4.30、26.88±3.33 和 16.91±2.15mm，对应股骨头后髋臼弧角为 92.25±11.34、77.42±10.04 和 50.63±6.58°。包括将后髋臼壁深度转换为股骨头后髋臼弧角的相关性在内的测量的组内相关系数（ICC）均大于 0.82 和 0.89。
股骨头后髋臼弧角的测量技术具有很强的可靠性。因此，髋关节后不稳定骨折脱位可以根据股骨头后髋臼弧角大于 77 度或小于 50 度来确定，而不是根据后髋臼壁缺损小于 20%或大于 50%来确定。
