Magnetic resonance imaging measurement of the contralateral normal meniscus is a more accurate method of determining meniscal allograft size than radiographic measurement of the recipient tibial plateau.

PURPOSE: The purpose of this study was to develop and validate magnetic resonance imaging (MRI) scanning of the contralateral meniscus as a more accurate method of determining the needed size of a meniscal allograft than the traditional method of inferring meniscal size from radiographic measurement of the ipsilateral tibial plateau. METHODS: Tissue bank meniscal size records from the left and right knees of 500 meniscal donors were analyzed for symmetry. The menisci of 10 cadaveric knees were then sized indirectly via the radiographic tibial plateau method and directly via MRI and actual physical measurement. The MRI and radiographic methods were then compared. Statistical analysis was carried out to determine error rates for each imaging method by comparison to the physical meniscal measurements. RESULTS: Of the 500 pairs of menisci, 97% were found to be within 3 mm of each other in both the anterior-posterior and medial-lateral dimensions. In the cadaveric study MRI measurement predicted actual meniscal size significantly better than the radiographic tibial plateau method. CONCLUSIONS: Human knee menisci are bilaterally symmetric in size. Direct MRI measurement of the contralateral intact meniscus better predicts actual meniscal size than estimation of size indirectly from measurement of the tibial plateau on which it is located. We, therefore, propose contralateral MRI meniscal measurement as a new gold standard to size menisci before transplantation. LEVEL OF EVIDENCE: Level II, diagnostic study of consecutive patients with a universally applied gold standard.