Abstract
Acetabular component malposition is the cause of half of all cases of recurrent hip dislocation. Intraoperative xrays after component insertion are helpful, yet it is certainly more useful to know the exact component position before final component insertion. The current study reviews results of acetabular component positioning using surgical navigation.
A prospective study of acetabular component positioning using surgical navigation was conducted in 22 hips of 21 patients. The technique involves insertion of a dynamic reference frame onto the pelvis during the surgical exposure and the acquisition of AP fluoroscopic views of each hip. Using the Fluoronav software and the ION surgical navigation system (Medtronics, Louisville, Colorado) a virtual horizontal line was then drawn between the teardrops. Acetabular component abduction was then aimed for 41 degrees. Component abduction was measured intra-operatively during component insertion by measuring the angle between the acetabular insertion handle and the virtual horizontal line between the teardrops. Post-operative xrays were analyzed for acetabular component abduction angle.
Using surgical navigation and aiming for 41 degrees of abduction resulted in post-operative cup positions averaging 40.8 degrees (range 37 to 44 degrees). These results show dramatically improved accuracy as compared to 85 acetabular component inserted without navigation showing a mean abduction of 42.8 degrees but with a range of 25 to 59 degrees. Frame placement and image acquisition required about 10 minutes. All intra-operative imaging after component insertion in complex cases was unnecessary. Having the dynamic reference frame in place also allowed assessment of pelvic position during surgery. Pelvic orientation varied greatly between patients on the operating table from about 12 degrees abducted to 12 degrees adducted. Further, pelvic orientation varied during surgery.
Surgical navigation allows extremely accurate positioning of the acetabular component at the time of total hip replacement surgery with an accuracy far greater than any study of acetabular component positioning reported in the literature. The pelvis is typically not orthogonal to the operating table during total hip arthroplasty and its position varies widely between patients and in the same patient during the procedure. Since acetabular component malposition represents the cause of half of all cases of recurrent dislocation, surgical navigation has been shown to directly address and potentially eliminate the problem of acetabular component malposition.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
