The junction between the ilium, ischium and pubis in the human acetabulum, known as the acetabular point,17
has been shown to be consistently represented by the indentation between the superior and the anterior lobe of the cloverleaf-shaped acetabular fossa in adults.16
The fact that the anterior groove identified in this patient originated from the same area reinforces our belief, reported previously, that it represents the remnant of incomplete iliopubic fusion of the triradiate cartilage.13
Arthroscopy also clearly identified an ilioischial groove, corresponding to the indentation between the superior and the posterior lobes of the acetabular fossa. The only other report of incomplete posterior fusion known to the authors, which describes the complete separation of the outer and inner parts of a bipartite acetabulum with a subluxed femoral head, also associated it with severe hip dysplasia.18
Despite extensive literature being available on premature acetabular fusion,19–25
our report is one of only three existing reports of incomplete acetabular fusion, and the only report of a patient with both iliopubic and ilioischial grooves.
The functional integrity of this irregularly shaped acetabulum had been interrupted on this occasion by femoroacetabular impingement, a labral tear and a partial ligamentum teres tear.
Regardless of the significance of this rare anatomical variant, special attention needs to be paid when interpreting such a finding during MRI or hip arthroscopy. It is difficult, but important, to distinguish the finding from an intra-articular lesion, as this could result in overtreatment. Given the limitations of conventional radiography and MRI with or without arthrography26–28
, this case highlights the diagnostic efficacy of hip arthroscopy in revealing the otherwise undetectable lesions at an early stage.13 14
- If identified, this condition should not be treated as pathological but as a rare variant.
- This variant suggests some independence between the component parts of the epiphysis during acetabular development.
- The diagnostic efficacy of hip arthroscopy enables identification of such subtle anatomical variants, whereas conventional radiography and MRI arthrography frequently do not.