Superolateral wear of the acetabulum / Author’s reply
I read with interest the topic for debate in the March 1998 issue by Murray and O’Connor entitled `Superolateral wear of the acetabulum’. I agree that flexion and extension occur about a transverse axis and that internal rotation about a vertical axis during the stance phase will shift the site of maximum sliding velocity slightly laterally. I wonder if this is the most important reason for changing the axis of rotation laterally and distally. This can only happen with adduction of the leg or with a fixed leg in the stance phase due to a drop of the contralateral hip with some degree of Trendelenburg gait. I suggest that this could cause a much more superolateral redirected wear component than any rotation of the hip during the gait cycle.
This is supported by the finding of a slight Trendelenburg gait pattern in patients after total hip replacement. Analysis of adduction and abduction in patients after total hip replacement would appear to give a more likely explanation of the consistent superolateral wear patterns.
S. EHRENDORFER, MD Vienna, Austria.
Murray DW, O’Connor JJ. Superolateral wear of the acetabulum. J Bone Joint Surg [Br] 1998;80-B:197-200.
Author’s reply: Sir,
I am pleased that our article has generated some debate and that Dr Ehrendorfer agrees that a combination of extension and internal rotation causes the axis of rotation to pass laterally and distally and therefore could contribute to superolateral wear.
He suggests that the Trendelenburg gait after total hip replacement is the main cause of superolateral wear. Although a Trendelenburg gait may contribute to superolateral wear it does not explain why this is associated with higher wear rates than superomedial wear. With a Trendelenburg gait the loads across the hip are likely to be lower than normal, and therefore the wear rate in a superolateral direction would actually be lower not higher. It is for this reason that I do not think that a Trendelenburg gait is the most important cause of superolateral wear.
D. MURRAY, FRCS
Nuffield Orthopaedic Centre Oxford, UK.
Copyright British Editorial Society of Bone & Joint Surgery Sep 1998
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