MR diagnosis of meniscal tears of the knee: analysis of error patterns

PURPOSE

Despite high accuracy of magnetic resonance imaging (MRI) for diagnosing meniscal tears, MR findings do not always agree with surgical findings. We performed a blinded, retrospective study to analyze the nature and frequency of errors in the MR diagnosis of meniscal tears.

MATERIALS AND METHODS

Medical records of 100 consecutive patients who underwent MR and arthroscopy of the knee at our institution were reviewed. Twelve patients underwent prior meniscal surgery. Twenty-three patients had 27 discrepancies between MR and surgical findings. These were independently reviewed by two additional musculoskeletal radiologists in a double blinded fashion. Original incorrect diagnoses were categorized as either unavoidable, interpretation error or equivocal for meniscal tear.

RESULTS

MR accuracy was 88% for the medial and 85% for the lateral meniscus. Of 27 incorrect MR diagnoses, 12 (44%) were unavoidable, 10 (37%) equivocal and 5 (19%) interpretation errors. Of the 67 medial meniscal tears, 12 (18%) were missed. Eight (67%) of these 12 were categorized as equivocal, including three postoperative menisci. Of 30 lateral tears, 12 (40%) were missed, 7 (58%) of which were categorized as unavoidable. Of these 12, 11 (92%) showed fraying of the inner edge, which was shaved at arthroscopy (n = 8) or had stable tear treated conservatively (n = 3). There were three false-positive diagnoses, all occuring in the lateral meniscus, two of which were unavoidable and one interpretation error.

CONCLUSION

Of all missed lateral meniscal tears, most are unavoidable and related to confusion between what represents fraying and what represents a tear. Unavoidable false-positive diagnoses are infrequent and may be related to incomplete arthroscopic evaluation. Subtle or equivocal findings still make MR diagnosis difficult, even for experienced radiologists.

Arthroscopically assisted reduction and internal fixation of tibial plateau fractures: report of twenty cases

The purpose of this study was to evaluate the results of arthroscopically assisted reduction and internal fixation of tibial plateau fractures. We report on 20 patients with 20 fractures with a mean follow-up time of 39 months (27-64 months). All fractures were evaluated according to the Schatzker classification. Under arthroscopic guidance, the fractures were reduced and associated intra-articular lesions were addressed appropriately. For split fractures a limited lateral approach, or the joystick technique, was used. Depression fractures were reduced with the aid of an anterior cruciate ligament (ACL) tibial guide. Postoperatively, immediate mobilisation and continuous passive motion was encouraged. A hinged brace provided stability and the patients were not allowed to bear weight for at least six weeks. According to the Rasmussen grading system, 18 out of 20 patients scored an excellent (15 patients), or a good (3 patients) result. One patient had a fair result. The only poor result we noted was caused by the fact that we were unable to reduce the fracture arthroscopically and had to perform an arthrotomy. We experienced no complications due to the arthroscopic procedure.