Does radiographic location ensure precise anatomic location of the femoral fixation site in medial patellofemoral ligament surgery?

PURPOSE: To correlate the location of the medial patellofemoral ligament femoral fixation site in knees suffering a chronic lateral patellar instability, by using radiographic references and by using the most important anatomic reference point (i.e. the adductor tubercle) identified by means of 3-dimensional (3D) surface reconstructions by computed tomography (CT) imaging.

METHODS

Thirty consecutive knee 3D-CT examinations at 0º of knee extension were obtained from patients (20 females, 10 males; median age of 23.5 years; range, 14-48 years) treated for chronic lateral patellar instability with at least two documented patellar dislocations. For each knee, three virtual 7-mm-diameter femoral tunnels were created. One of the tunnels used an anatomic fixation landmark (anatomic fixation), while the other two used established radiologic methods. We calculated the percentage of the anatomic tunnel covered by the tunnel created according to the method described by Schoettle, and the percentage of the anatomic tunnel covered by the tunnel created according to the method described by Stephen. These percentages were compared using paired Student's t test.

RESULTS

The percentage of anatomic tunnel area covered by the femoral tunnel created using Schoettle's method was 36.7 ± 25.2 %. When using Stephen's method, the percentage of overlap with the anatomic femoral tunnel was 25.5 ± 21.5 %. There were no significant differences between the two radiographic methods (n.s.).

CONCLUSION

None of the standard radiographic methods allowed a precise anatomic femoral placement. Conventional radiographic identification of the femoral graft placement site is only an approximation and should not be the sole basis for femoral attachment location.

LEVEL OF EVIDENCE: IV.