Accuracy of radiographic determination of the posterior femoral wall integrity in anterior cruciate ligament reconstruction.

OBJECTIVE: To evaluate the accuracy of radiographs in determining integrity of the posterior femoral cortex following ACL reconstruction.
METHODS: Fifty adult volunteers undergoing primary arthroscopic transtibial ACL reconstructions were prospectively enrolled into this study. Plain radiographs and fine-cut CT of the operative knee were obtained post-operatively. Three blinded orthopaedic surgeons were asked to measure the distance from the femoral tunnel to the posterior cortex on lateral radiographs. Inter/intra-observer reliabilities were assessed with the interclass correlation coefficient. The true measurement of the posterior wall was determined on CT. For each, a measurement was made at the aperture, 5 mm, and 10 mm along the tunnel. Plain radiographic measurements were compared to the CT measurement of back wall using a paired t-test.
RESULTS: All measurements made on the lateral radiograph were significantly different from those from the respective CT scans for each surgeon (p < 0.0001) at all points. When radiographic measurements were compared to CT at the level of the intra-articular aperture, 29 subjects showed violation of the posterior cortex, with only one being identified on plain films. At 5 mm, 7 subjects demonstrated posterior cortical violation, and none were identified on lateral radiographs. The posterior cortex remained intact in all cases at 10 mm.
CONCLUSION: Lateral radiographs of the knee are insufficient for evaluation of the posterior cortical integrity following primary ACL reconstruction. Direct visualization of the femoral tunnel remains the gold standard for evaluation of the posterior wall and may be supplemented by CT scan if there remains concern over graft fixation.