The aim of this study was to compare the primary fixation stability and initial fixation stiffness of two commonly used fixation techniques, the tension band wiring technique and interfragmentary screw fixation, with an innovative mini-screw fragment fixation system in a model of transverse fracture of the patella. It was hypothesized that the biomechanical performance of the fragment fixation system would not significantly differ from the loading characteristics of the two established methods currently investigated.

Materials and Methods: A standardized transverse patella fracture was induced in ninety-six calf patella and three different fixation methods, including the mod-ified tension band wiring technique, interfragmentary screw fixation, and the mini-screw fragment fixation system, were used for fragment fixation. Specimens were mounted to a loading rig which was integrated within a material testing machine. In each fixation group, eight specimens were loaded to failure at varying simulated knee angles of either 0° or 45°. Another eight specimens were submitted to polycyclic loading consisting of 30 cycles between 20 N and 300 N at a simulated knee angle of either 0° or 45°. The residual displacement between the first and the last cycle was recorded. Differences in the biomechanical performance between the three fixation groups were evaluated.

Results: With monocyclic loading, no significant differences between the three groups were observed in the parameters maximum load to failure and linear fixation stiffness. Specimens loaded at 45° showed significantly lower maximum failure loads and linear stiffness when compared with 0° knee angle. With polycyclic loading, no significant differences in the residual displacement were observed between the groups at 0° loading angle, while at 45°, residual displacement was significantly higher with tension band fixation when compared with interfragmentary screw fixation or the fragment fixation system.

Conclusion: This study confirmed that the biomechanical performance of the fragment fixation system was comparable to interfragmentary screw fixation and superior to the tension band wiring technique. As the fragment fixation system combines the advantages of providing interfragmentary compression with percutaneous pin insertion after closed reduction, we believe the fragment fixation system to be an adequate alternative in the osteosynthesis of transverse patella fractures.

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.