Acetabular Rim Syndrome

Acetabular Rim Syndrome
Title: The Acetabular Rim Syndrome

Reference: Klaue, Durnin, Ganz, JBJS 73-B, No. 3, May 1991

Main Message

This is the first description of acetabular rim syndrome. It describes two types of acetabular dysplasia resulting in the “syndrome” – one being the incongruent oval shaped acetabulum which leads to tears in the limbus; the other being the congruent, spherical acetabulum with poor lateral coverage which leads to “fatigue fractures” of the acetabulum superolaterally.

Points of Interest

– tears of the limbus are associated with traumatic hip dislocations; their occurrence without trauma has been described only recently, and before this article there had been no explanation of their cause or relation to acetabular dysplasia.
Presentation
History – sharp groin pain; sensation of locking of the hip; sensation of giving way, going “dead”
– pain often relieved by “shaking out” the limb
– pain made worse with forced movements of adduction in combination with rotation in either direction
Physical – may be normal
– two painful maneuvers:
1. Passive flexion, adduction, internal rotation – brings the proximal and anterior part of the femoral neck into contact with the rim of the acetabulum at the point where the labrum is likely to be damaged, and exerts a shear force on the limbus at its attachment to the bony acetabular margin
2. Passive hyperextension, external rotation – “apprehension test” – brings upon the sensation of apprehension/instability or reproduces symptoms as the head is subluxed anteriorly

They reviewed 29 cases that were operated on and found either that the limbus was detached, or there was a separated bone fragment – “os acetabuli”. The limbic tear is akin to a bucket handle tear in the meniscus. Sometimes, a intra-osseous ganglia was identified. They either fixed the tear with sutures or excised the loose limbus – all their patients were doing well at the four year mark.

In the discussion, they identified two groups of radiologic features associate with abnormal loading:
Type I: Hips in which the acetabulum is shallow, lies more vertical than normal, and has a radius of curvature greater than that of the femoral head. Such joints are radiologically incongruent. These are potentially unstable hips and the labrum gets overstressed and tears.
Type II: Hips in which the acetabulum provides less than normal cover for the femoral head (short roof) and has a radius of curvature similar to that of the femoral head. Such joints are congruent. These are essentially stable hips, and the articular cartilage gets overstressed and a acetabular fatigue fracture occurs, rather than tearing of the labrum.

Thoughts….
Too early to know what the optimal surgical management of the damaged limbus or the detached bone fragment should be.

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