Cams and pincer impingement are distinct, not mixed: the acetabular pathomorphology of femoroacetabular impingement.
BACKGROUND
Many impinging hips are said to have a mix of features of femoral cam and an overcovered acetabulum causing pincer impingement. Correction of such a mixed picture by reduction of the cam lesion and the acetabular rim is the suggested treatment.


OBJECTIVE
We therefore asked two questions: (1) Is the acetabulum in cam impingement easily distinguishable from the pincer acetabulum, or is there a group with features of both types of impingement? (2) Is version or depth of socket better able to distinguish cam from pincer impingement?


METHODS
We analyzed the morphologic features of the acetabulum and rim profile of 20 normal, healthy hips, 20 with cams and 20 with pincers on CT. Pelvises were digitized, orientated to the best-fit acetabular plane, and a rim profile was plotted.


RESULTS
Cam hips were shallower than normal hips, which in turn were shallower than pincer hips (84 degrees +/- 5 degrees versus 87 degrees +/- 4 degrees versus 96 degrees +/- 5 degrees, respectively). The rim planes of cam, normal, and pincer hips had similar version (23 degrees, 24 degrees, 25 degrees), but females were 4 degrees more anteverted than males.


CONCLUSIONS
We concluded cam and pincer hips are distinct pathoanatomic entities. Cam hips are slightly shallower than normal, whereas pincers are deeper.


CONCLUSIONS
Before performing surgery for cam-type femoroacetabular impingement, surgeons should consider measuring the acetabular depth. The cam acetabulum is shallower than normal and may be rendered pathologically shallow by acetabular rim resection leading to early joint failure.
Cobb
Justin
J
Department of Orthopaedics, Imperial College, Charing Cross Hospital, London W6 8RF, UK. j.cobb@imperial.ac.uk
Logishetty
Kartik
K
Davda
Kinner
K
Iranpour
Farhad
F
D000077:Acetabulum / Q000473:pathology* / Q000601:surgery; D001175:Arthrography; D004839:Epiphyses, Slipped / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D005260:Female; D005270:Femur Head / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D006621:Hip Joint / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies