Anterior cruciate ligament reconstruction: MR imaging signs of anterior knee laxity in the presence of an intact graft.

PURPOSE: To determine the accuracy of secondary magnetic resonance (MR) imaging signs of anterior cruciate ligament (ACL) insufficiency in predicting clinical anterior translational knee laxity, in the presence of an intact graft, after ACL reconstruction. MATERIALS AND METHODS: Institutional review board approval was obtained, and the requirement to obtain informed consent was waived. Fifty-two patients with ACL reconstruction and no injury to the contralateral knee were included. Three patients with visible ACL graft tears at MR imaging were excluded. All patients underwent MR imaging of the affected knee, functional assessment with use of the International Knee Documentation Committee (IKDC) score, and arthrometric testing of both the affected and uninjured knee. A side-to-side difference of more than 3 mm at 133 N was considered to be indicative of knee laxity. Two radiologists independently evaluated all MR images for seven signs of anterior knee laxity. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) were calculated for each MR imaging sign. RESULTS: Ten patients demonstrated knee laxity at arthrometric testing. Patients with knee laxity at arthrometric testing had significantly lower IKDC scores (P < .03). Sensitivities for all signs were low (0%-50%). Anterior translation of the tibia of more than 7 mm, a posterior cruciate ligament (PCL) angle of less than 100°, and a PCL curvature ratio of more than 0.39 demonstrated high specificity (range, 82%-90%). Uncovering of the posterior horn of the lateral meniscus and the posterior femoral line had a specificity of 97%-100% and a sensitivity of 0%. All signs had a low PPV and high NPV for laxity. All MR imaging signs demonstrated near-perfect interobserver agreement. CONCLUSION: Although MR imaging signs of knee laxity in the presence of an intact ACL graft have a high specificity, the low PPV means that MR imaging is of little value in predicting anterior knee laxity as demonstrated with mechanical testing.

Anterior cruciate ligament reconstruction grafts: MR imaging features at long-term follow-up--correlation with functional and clinical evaluation.

PURPOSE: To assess the presence of increased intrasubstance signal intensity within anterior cruciate ligament (ACL) grafts and to assess whether such signal intensity changes are correlated to clinical assessments of graft instability and patient function 4-12 years after ACL reconstruction. MATERIALS AND METHODS: Ethical permission and written informed patient consent were obtained. The study was HIPAA compliant. Forty-seven patients were included and underwent 1.5-T magnetic resonance (MR) imaging of the knee that was treated surgically. Signal intensity characteristics of the ACL graft were evaluated on sagittal intermediate-weighted and sagittal and axial T2-weighted fast spin-echo MR images. The amount of signal intensity change, femoral and tibial graft tunnel position, and orientation of ACL graft in the coronal plane were assessed. Objective index of graft stability or laxity was performed with arthrometric testing, and subjective function was assessed by using International Knee Documentation Committee (IKDC) scoring. RESULTS: Increased intrasubstance graft signal intensity was found in 70 % (33 of 47) and in 64% (30 of 47) of patients on intermediate-weighted MR images and T2-weighted MR images, respectively. When present, intrasubstance graft signal intensity changes involved less than 25% of the maximal cross-sectional area of the graft in 70% (23 of 33) of cases on intermediate-weighted acquisitions and in 70% (21 of 30) of cases on T2-weighted acquisitions. No significant association was seen between graft signal intensity changes on intermediate-weighted and T2-weighted images and IKDC score (P = .667 and .698, respectively), arthrometric testing (P = .045-.99), and time since surgery (P = .592 and .610, respectively). CONCLUSION: Small amounts of increased intrasubstance graft signal intensity on intermediate- and T2-weighted images can be seen after ACL reconstruction at long-term follow-up of 4 years or longer and do not necessarily correlate with findings of joint instability or functional limitations in patients after ACL repair.