Author's Reply

We read the letter by Drs. Lorenz, Illingworth, and Fu about our recent article with attention. We thank them for their comments that add complementary information to our work as they describe the diagnosis of partial anterior cruciate ligament (ACL) ruptures. This was not, however, the purpose of our article. As readers most certainly will have observed, our article was mainly based on the histologic evolution of such ruptures, which have been very accurately described by Murray et al.,1 but was never clearly identified during arthroscopic examination in the context of ACL reconstruction in humans. Such retraction of the posterolateral (PL) bundle may account for the difference in the percentage of lesions observed in our 2 series.

In our experience, an incomplete ACL rupture is suspected in the presence of a delayed firm endpoint, with a differential laxity of less than 6 mm. Certain studies carried out on cadavers, such as that by Furman et al.,2 suggest that the Lachman and anterior drawer tests in isolated PL bundle tears are positive and negative, respectively, whereas the opposite is found for isolated anteromedial (AM) bundle tears. Other studies have reported more moderate results and underline the difficulty of obtaining a reliable diagnosis.3, 4 We believe it might be inappropriate to transpose the results of these cadaveric studies to the clinical examination of our patients. We lack both an objective means of evaluation of such laxity and a sufficient population in our clinical series to be able to describe these 2 distinct clinical pictures accurately. Stating that, on the one hand, an isolated PL bundle rupture results in a positive pivot-shift test result and that, on the other hand, an isolated AM bundle rupture results in a positive Lachman test and a negative anterior drawer remains to be shown. It is difficult to establish a correlation between the pivot-shift test and a specific type of ACL rupture, probably because of the difficulty in definitely ruling out associated peripheral lesions having occurred during injury and having healed on patient follow-up examination, even under general anesthesia.

Concerning the radiologic workup, and particularly magnetic resonance imaging, we obviously acknowledge that the radiologists we collaborate with may not be quite as skilled as the radiologists on Dr. Fu's team. However, the presence of bleeding in the ACL fibers makes interpretation very difficult and only rarely allows for a precise distinction of the 2 bundles. To our knowledge, no study ever established a correlation between the magnetic resonance imaging aspect of the ACL and the biomechanical quality of the identified bundles.

Clinical examination, imaging, and arthroscopic exploration are fundamental elements orienting toward incomplete ACL rupture. Dr. Fu and his colleagues wrote a perfect description of all these steps. However, we believe it is impossible to definitely rule out the absence of lesions on the seemingly healthy bundle, even if appearing appropriately tensed on arthroscopic examination. Maybe we should talk about incomplete rupture and partial reconstruction with a quantity of preserved native fibers. We perform such a reconstruction in our cases of incomplete ruptures to increase graft revascularization and proprioception.5 We are currently studying a series of 50 patients with a 2-year follow-up who underwent isolated PL reconstruction with preservation of the continuous AM bundle, even when stretched. Clinical and differential laxity results are satisfactory, and more importantly, no graft rupture has been observed to date.

The objective of our article was to draw the attention of surgeons to the fact that the PL bundle retracts and may disappear several months after the injury. Therefore extreme vigilance and attention should be paid to this bundle's tibial insertion so as not to miss the diagnosis. As many surgeons do, we routinely use the AM portal to properly visualize the femoral insertion of the ACL and, with more difficulties, its tibial insertion.

We wish to thank Drs. Lorenz, Illingworth, and Fu once more for their most interesting letter, and we hope our clarifications have helped them understand the purpose of our article.