Abstract
Interest on acetabular version arose from unstable developmental dysplastic hips. Initial studies and clinical observations described the dysplastic hip as being excessively anteverted.
The advent of computed tomography allowed further detailed analysis of the acetabulum in the axial plane, yet these studies failed to determine conclusively whether or not the dysplastic acetabulum is abnormally anteverted. Much controversy evolved from different methods of measuring and from the fact that a more anteriorly located acetabular deficiency results in excessive anteversion while a more posteriorly located deficiency in retroversion. It remains inconclusive to what extent acetabular dysplasia is due to a mal-orientation of an otherwise normal configured acetabulum or to a deficient acetabulum which is otherwise normally orientated. Furthermore, the acetabular opening spirals gradually from mild anteversion proximally to increasing anteversion distal to it and therefore render its measurement dependent from pelvic inclination and from the level of the transverse CT scan slice.
On an orthograde pelvic X-ray, both, pelvic inclination and rotation can be controlled. Therefore, acetabular version is best estimated from the relationship of the anterior and posterior acetabular rim to each other on an orthograde pelvic X-ray.
The main hip pathologies, acetabular rim overload and anterior femoro-acetabular impingement, both occur in the superior part of the acetabulum, the acetabular dome, and that’s where version is best measured. We called this version of the acetabular dome.
Interest on retroversion of the acetabular dome arose from analysis of complications such as persistent posterior subluxation after acetabular reorienting procedures. They resulted in the hypothesis that the site of acetabular deficiency may vary and be more posteriorly located in some cases resulting in a rather retroverted than anteverted acetabular dome.
In fact, retroversion of the acetabular dome was found to be a characteristic feature of specific hip disorders. A review of ten patients with posttraumatic premature closure of the triradiate cartilage before age 5 showed beside a bowed hemipelvis with lateralized and caudalized acetabulum a mean retroversion of the acetabular dome of 27°. A review of 14 patients suffering from proximal femoral focal deficiency with a functional hip joint revealed a mean retroversion of the acetabular dome of 24°. Typically this was accompanied by femoral retrotorsion and coxa vara.
Finally, bladder exstrophy, when treated without pelvic osteotomy, typically end up with externally rotated or retroverted acetabula (Sponseller, 1995) Even in DDH, retroversion of the acetabular dome has been shown to be a significant variation as 40 of 232 such acetabula showed to have a retroverted dome (Li, 2003).
Furthermore retroversion typically can result from pelvic osteotomy in childhood as 26 from 97 subjects, who underwent either Salter or Le Coeur osteotomy in childhood ended up with retroverted acetabular domes after closure of the pelvic bone growth plates. In the context of neuromuscular or genetic disorders, dysplastic hips also may have retroverted acetabular domes and may additionally be influenced from fixed spine deformities. Finally, retroverted acetabular domes may be found in otherwise non dysplastic hips.
The relevance of acetabular retroversion is both technical and clinical: First, it calls for a more individual approach to acetabular dysplasia because presence of retroversion will affect the manner in which corrective osteotomy will be done. Salter-like reorientation maneuvers will result in worsening the pre-existing posterior deficiency or acetabular rim overload and risk continued posterior subluxation or dislocation of a previously reduced hip (Lee, 1991). Second, anterior overcorrection of a primarily retroverted acetabula may necessitate a further intervention to remove bone from the anterior aspect of the acetabulum or anterior part of the femoral head-neck junction due to limited hip flexion (Crockarell 1999, Myers 1999). Third, evidence that the long-term effect of retroversion of the acetabular dome is harmful is increasing: An association between decreased acetabular anteversion and osteoarthritis was found as soon as 1991 (Menke, 1991) and the prevalence of retroversion among patients with idiopathic hip osteoarthritis has been found to be 20% versus 5% among the general population (Giori, 2003). Furthermore, decreased acetabular and femoral anteversion was found to be a major cause of altered rotation, hip pain and osteoarthritis (Tönnis, 1999). A positive impingement test was the key clinical finding (Reynolds,1999). This anterior impingement of the femoral head-neck junction against the border of the prominent anterior acetabular wall which over a long period of time may lead to fatiguing and destruction of the acetabular labrum and the adjacent cartilage is thought to initiate groin pain and early osteoarthritis. Finally, even for total hip replacement, severe retroversion of the acetabular dome will make surgery more difficult.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
