A morphological study on the human obturator externus muscle with reference to anomalous muscle and anomalous fasciculus originating from the obturator externus muscle.

To elucidate the essential nature of the human obturator externus muscle (OE), the gross anatomy of the anomalous muscle and anomalous fasciculus originating from this muscle as well as the posterior division of the obturator nerve (P) were examined in 73 thighs of 45 Japanese adult cadavers. The investigation of anomalous muscle and anomalous fasciculus was effected by observation of the supernumerary muscular branch and supernumerary muscular twig from the P. The anomalous muscle occurring between the adductor brevis muscle (AB) and adductor minimus muscle (AMi) (37/73 thighs; 50.7%) and the anomalous fasciculus fused to the posterior surface of the AMi (18/73 thighs; 24.7%) were detected. It was demonstrated by the course of the P and the suppling nerve, that the OE was divided into its superior fasciculus (or fasciculi) (SF) and main belly by the P, moreover the anomalous muscle originated from the former and the anomalous fasciculus from the latter. Presumably, in the process of ontogeny, the SF of the original OE retained its original morphology (23/73 thighs; 31.5%), a part of the SF was converted to anomalous muscle (27/73 thighs; 37.0%), the entire SF was converted to anomalous muscle (10/73 thighs; 13.7%), and the entire SF underwent retrogression and disappeared (13/73 thighs; 17.8%). The presence (50/73 thighs; 68.5%) or absence (23/73 thighs; 31.5%) of piercing of the OE by the P seemed to depend upon the circumstances surrounding the morphological change in the SF. The original OE was considered to occur as an OE pierced by the P not possessing any supernumerary muscular branch or twig. Actually, the original OE was confirmed to occur with a low frequency (15/73 thighs; 20.5%). It was inferred that the original OE readily underwent variation in the process of ontogeny due to the influence of the obturator nerve. The segmental composition of the obturator nerve was considered not to be involved in the morphological change in the OE.

A quantitative anatomic characterization of the quadrilateral surface for periacetabular osteotomy.

The periacetabular osteotomy described by Ganz et al is used widely, and includes an outward osteotomy from the quadrilateral surface. Because intraarticular extension of the osteotomy can complicate the Ganz osteotomy, it is important to image the margin of the hip. To prevent this complication, and to do this procedure more safely, 32 hemipelves from cadavers were used in the current study. Some landmarks were selected that can be clarified on the quadrilateral surface during the periacetabular osteotomy. The acetabulum was hollowed out using an acetabular reamer of the same size as each femoral head, and the margin of the penetrated hole through the acetabulum was determined using these landmarks. The posterior margin of the hip is located approximately 2 cm anterior to the sciatic notch. The anatomic guidepoint for the osteotomy of the ischium averaged 14 mm inferior to the distal margin of the hip. By clarifying the margin of the hip presumed on the quadrilateral surface in this way, the periacetabular osteotomy can be done more safely, without causing complications such as intraarticular chisel penetration.

Vascular anatomy for rotational acetabular osteotomy: cadaveric study.

Rotational acetabular osteotomies are performed to correct dysplastic hips in young adults. However, there is a potential risk of intrapelvic vascular injury. To define the relation of these vascular structures to the bone around the acetabulum, we measured the distance and direction from the anteroinferior iliac spine to the external iliac artery and from the base of the superior pubic ramus to the obturator artery in 34 cadaveric hemipelves (17 male, 17 female; 19 left, 15 right). The distance to the external iliac artery was significantly shorter in females (average 31.7 mm) than in males (average 38.2 mm); and the distance to the intrapelvic entry portal of the obturator canal, through which the obturator artery passes, was significantly shorter in females (average 27.2 mm) than in males (average 33.4 mm). In addition, the external iliac artery was located significantly more ventral and closer to the anteroinferior iliac spine in right hemipelves than in left hemipelves. The intrapelvic entry portal of the obturator canal was located more caudodorsal to the base of the superior pubic ramus in females than in males. Care should thus be taken during surgery in light of our findings.