Introduction: The success of total knee arthroplasty (TKA) is dependent on many factors. Postoperative extremity and component alignment are important determinants of outcome and longevity and malalignment results in higher failure rates. Computer-assisted (CAS) navigation devices were developed to improve implant positioning but their use increases the complexity of the surgery. The aim of this study is to assess the radiological outcome of conventional techniques versus CAS for TKA performed by an expert and other group performed by a beginner in CAS.

Methods: 90 patients patients with knee arthritis were prospective randomized into 3 groups: CAS performed by an expert, CAS performed during the learning curve and conventional technique (manual instrumentation) performed by an expert. Preoperative and postoperative clinical examinations were performed at four weeks, six months, and one year by an independent physician who was blinded to the surgical technique. Preoperative and postoperative radiographic measurements of the anterior-posterior mechanical axis and the sagittal tibial and femoral axes were evaluated by an observer who was blinded to the surgical technique. The Knee Society Scoring System was used to asses clinical and functional outcomes. All variables were analysed for differences between the groups either by Student’s t-test or the Mann-Whitney U test.

Results: There was no differences in implant positioning between the CAS groups. The mechanical axis of the leg was significantly better in the two CAS groups (96%, within +/−3° varus/valgus) compared with the conventional Group (78%, within +/− 3° varus/valgus). The frontal and sagittal alignment of the femoral component and the frontal tibial alignment were also more precise in the CAS groups. Improvement occurred in the Knee Society scores up to one year post-operatively and was similar for the three groups. No significant difference between the groups could be found at any time point in the study, with the mean difference being 3.5 points (95% CI;18.6 to 13.6).

Conclusions: We have not shown differences in the precise positioning of implants during the learning curve in computer-assisted total knee arthroplasty. Computer-assisted total knee arthroplasty gives a better correction of alignment of the leg and orientation of the components compared with the conventional technique. Potential benefits in the long-term outcome and functional improvement require further investigation.

Introduction and purpose: To assess the diagnostic usefulness of MRI to diagnose ACL lesions using quantitative instead of qualitative parameters.

Materials and methods: A retrospective study was made of the MRIs of a group of 50 patients with an athroscopically confirmed ACL tear and a control group of 50 patients with meniscal lesions and with an arthroscopic confirmation that they had a normal ACL. Multiple MRI findings were studied in order to evaluate their sensitivity and Specificity to detect an ACL lesion. Special emphasis was placed on 3 quantitative parameters, including a simplified method to measure the angle between the ACL and the tibial plateau.

Results: Using 45° as a cutoff value, the ACL/tibial plateau angle yielded a sensitivity and Specificity of 100%. With a 0° cutoff value, the angle together with Blumensaat’s line showed a sensitivity of 90% and a Specificity of 98%. With a cutoff value of 115°, the PCL angle showed a sensitivity of 70% and a Specificity of 82%

Conclusions: The quantitative parameters studied are valuable to predict ACL lesions and can increase both the sensitivity and Specificity of MRI images. The ACL/ tibial plateau angle can be measured easily using a single MRI image and can be regarded as the best clue to diagnose ACL lesions.