Volume 25, Issue 11 , Pages 1203-1204, November 2009
Diagnosis of Isolated Posterolateral Bundle Tears of the Anterior Cruciate Ligament
Article Outline
To the Editor:
We would like to respond to the article by Sonnery-Cottet et al.1 entitled “Arthroscopic Identification of Isolated Tear of the Posterolateral Bundle of the Anterior Cruciate Ligament.” This well-written article describes the incidence of isolated posterolateral (PL) bundle tears and their clinical, radiologic, and arthroscopic diagnosis.
The authors observed that 8.6% of their cases had an isolated PL bundle tear. This rate is higher than what we have observed. In our most recent series of 431 patients who were prospectively evaluated at our clinic, only 7 (1.6%) had an isolated PL bundle tear. In addition, we found 12 isolated anteromedial (AM) bundle tears (2.8%). This discrepancy may be due to the fact that the authors did not examine the patients under anesthesia and did not use the AM portal to examine the anterior cruciate ligament (ACL) during arthroscopy. Therefore concomitant AM bundle lesions may have been missed. The definitive diagnosis of an isolated PL bundle tear is important because our surgical approach for an isolated PL bundle tear with symptomatic instability is augmentation of the PL bundle. The consequence of missing a concomitant AM bundle tear may be early failure of the PL bundle graft.
In general, our clinical pathway for evaluation and treatment of an ACL injury starts with the patient's history and examination in the office. The sense of instability and guarding during the pivot-shift test without a large side-to-side difference (<5 mm) in the anterior drawer and Lachman test is suspicious for a partial ACL tear.
The outpatient examination is followed by magnetic resonance imaging studies. Special coronal and sagittal oblique sequences in the long axis of the ACL are helpful in making the correct diagnosis.2 The appearance of a partial tear can vary between full intersection of the fibers up to discrete fraying and crumpling. Frequently, an increased signal intensity is seen in the torn bundle. The presence of a bone bruise on magnetic resonance imaging should be evaluated because it is suggestive of a complete ACL tear and will rarely be seen in the event of a partial tear.
The most important components of the examination process to diagnose a partial ACL tear are the preoperative examination with the patient under anesthesia and meticulous probing of the ACL with the arthroscope in the medial portal to allow for complete visualization of the femoral and tibial insertion sites.
Examination under anesthesia is essential because the findings for the anterior drawer test, the Lachman test, and the pivot-shift test are subtle in patients with a partial ACL tear and may not be appreciated in the awake patient. When comparing the affected knee and unaffected knee in the clinic, these slight differences might be missed. According to Furman et al.,3 the Lachman and anterior drawer tests in isolated PL bundle tears are positive and negative, respectively, whereas the opposite is found for isolated AM bundle tears. The pivot shift is often guarded by the patient during the office examination and might be the only sign for symptomatic isolated PL bundle lesions. This leads to the conclusion that if only 1 test is positive, then the chance of a partial ACL tear of the PL or AM bundle has increased.4
The visualization and probing of the ACL from an AM portal enable visualization of the entire medial wall of the lateral condyle.5 From this portal, concomitant proximal tears and partial intrasubstance tears of the AM bundle can be ruled out by meticulous probing of the ACL (Fig 1). Nonphysiologic lengthening of the AM bundle can also be detected from this position by probing the AM bundle for laxity while applying a force to translate the tibia anteriorly. Elongated PL bundles are best confirmed by using a probe to test tension in the PL bundle while internally rotating the tibia.
Figure 1.
Complete proximal ACL rupture: (A) view from lateral portal and (B) view from medial parapatellar portal. The whole medial wall of the lateral condyle can be evaluated. The probe comes from an additional medial portal. The proximal rupture zone can be clearly seen (arrows). (AM, anteromedial bundle; PL, posterolateral bundle; LFC, lateral femoral condyle; MFC, medial femoral condyle; PCL, posterior cruciate ligament.)
We enjoyed reading the article by Sonnery-Cottet et al.1 and hope that we have added some useful pearls from our own experiences that will help improve the diagnosis of isolated PL bundle tears.
References
- . Arthroscopic identification of isolated tear of the posterolateral bundle of the anterior cruciate ligament. Arthroscopy. 2009;25:728–732
- . Normal appearance and complications of double-bundle and selective-bundle anterior cruciate ligament reconstructions using optimal MRI techniques. AJR Am J Roentgenol. 2009;192:1407–1415
- . The anterior cruciate ligament (A functional analysis based on postmortem studies). J Bone Joint Surg Am. 1976;58:179–185
- . Partial rupture of the anterior cruciate ligament. Arthroscopy. 2006;22:1143–1145
- . Three-portal technique for anterior cruciate ligament reconstruction: Use of a central medial portal. Arthroscopy. 2007;23:325.e1–325.e5www.arthroscopyjournal.org
PII: S0749-8063(09)00790-7
doi:10.1016/j.arthro.2009.09.005
© 2009 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.
Refers to article:
- Author's Reply
- Arthroscopic Identification of Isolated Tear of the Posterolateral Bundle of the Anterior Cruciate Ligament , 12 March 2009
Volume 25, Issue 11 , Pages 1203-1204, November 2009
