Side-to-side comparison of anatomical or functional parameters in the evaluation of unilateral pathologies of the knee joint is common practice. Generally, it is assumed that the contralateral joint provides “normal” anatomy and function and that within-subject side differences are less when compared with between-subject variability. This has advocated the use of side-to-side comparisons in a wide field of orthopaedic surgery. The aim of this study was to test the hypothesis that there are no significant differences in the morphometric knee joint dimensions between the right and the left knee of a human subject. Furthermore, it was hypothesized that side differences within subjects are smaller than inter-subject variability.

In 30 pairs of human cadaver knees the morphometry of the articulating osseous structures of the femorotibial joint, the cruciate ligaments, and the mensici were measured using established measurement methods. Morphometric data were obtained either using digital callipers, radiographs, contour gauges, or cross-sectiontal scans. Data were analysed for overall side differences using the Student t-test and Pearson’s correlation coefficient and the ratio between within-subject side differences and intersubject variability was calculated.

In three out of 71 morphometric dimensions there was a significant side difference, including the posterior tibial slope, the anatomical valgus alignment of the distal femur, and the position of the femoral insertion area of the ACL. In two additional parameters, including the cross-sectional area of the distal third of the ACL and PCL, within-subject side differences were larger than intersubject variability. In general, there was a positive correlation in morphometric dimensions between right and left knees in one subject.

This study confirmed a good correlation in the morphometric dimensions of a human knee joint between the right and the left side. Our data support the concept of obtaining morphometric reference data from the contralateral uninjured side in the evaluation of unilateral pathologies of the knee joint. The uninjured contralateral side rather than knee joint dimensions obtained from an uninjured subject should be used as a valid control in orthopaedic practice.