Evaluation of the clinical results in patients with symptomatic partial tears of the anterior cruciate ligament diagnosed arthroscopically

PURPOSE OF THE STUDY: The study presents a retrospective evaluation of clinical data and arthroscopic findings in a group of our patients with symptomatic knee instability due to a partial tear of the anterior cruciate ligament (ACL). MATERIAL AND METHODS: The group included 31 patients diagnosed with symptomatic partial ACL tears, i.e. an isolated tear of the posterolateral (PL) or the anteromedial (AM) bundle. The patients' average age was 26.5 years. A side-to-side difference in ventral knee laxity was assessed using the anterior drawer test and the Lachman test under general anaesthesia before arthroscopy was commenced; rotational knee laxity was evaluated by the pivot shift test. An objective evaluation of side-to-side ventral laxity differences in both knees was performed on the GNRB® arthrometer with an applied pressure of 134 N and 250 N in the conscious patient. During arthroscopic examination, findings on the two ACL bundles were recorded. RESULTS: All 31 patients were diagnosed with symptomatic partial ACL tears, of them 22 had a PL bundle lesion and nine had an AM bundle tear. All patients with PL bundle lesions only reported problems in association with pivot sports, and all patients with AM bundle tears had problems regardless of any sports activities. In all patients with isolated AM bundle tears, the lesion was located close to its femoral attachment. In the patients with PL bundle tears, femoral location was found in 68% and tibial location in 32% of the patients. In the patients with partial PL bundle lesions, + and ++ results in the pivot shift test were recorded in 32% and 68% of the treated patients, respectively. The Lachman test showed + and ++ results in 71% and 9% of the patients, respectively. The anterior drawer test had negative results in 87% and positive + results in 13% of the patients. The side-to-side difference on the GNRB arthrometer ranged from 0.4 to 2.3 mm at a pressure of 134 N and from 1.2 to 4.2 mm at 250 N in the patients with isolated PL bundle lesions. In the patients with AM bundle lesions, the results were as follows: pivot shift test, 89% negative. 11% positive +; Lachman test, 56% negative, 44% positive +; anterior drawer test, 89% +, 11% ++; GNRB test, 2.2 to 4.4 mm at 134 N, and 4.3 to 7.1 at 250 N. DISCUSSION: The diagnosis of partial ACL lesions, i.e., isolated tears of the AM or the PL bundle, requires accurate knowledge of knee anatomy and its biomechanics. In accordance with other authors our results showed that an arthroscopic examination of both bundles of the ligament as well as knee laxity evaluation under general anaesthesia are most essential for making the definite diagnosis in partial ACL tears. They also confirmed that, in isolated AM bundle lesions, ventral laxity is present more often particularly at a higher degree of knee flexion while, in PL bundle lesions, rotational laxity is more frequent and ranges from 0 to 30 degrees of knee flexion. CONCLUSIONS: To make the definite diagnosis of partial ACL tears, patient medical history, clinical knee examination including instability type and degree assessment under general anaesthesia and, most importantly, arthroscopic findings on both ACL bundles are necessary.