MicroStrain Pattern Analysis of the Canine Patellar Tendon Following a Tibial Plateau Leveling Osteotomy

This study investigates the change in strain patterns of the canine patellar tendon following a Tibial Plateau Leveling Osteotomy (TPLO). The TPLO is a procedure used to minimize anterior tibial translation in canines following a cranial cruciate rupture. A noted clinical deficiency randomly seen with the TPLO is an inflammation of the patellar tendon. In some instances, the inflammation results in material damage resulting in a calcification of the tendon and in worst cases, a fracture of the patella.

In order to investigate the strain patterns, four fresh frozen canine cadaver stifles were used. The cadavers were mounted for stabilization and a motor was attached to the patella to simulate the quadriceps contraction. Tendonous material is not ideal for direct measurement of strain; therefore, a rectangular rubber section was attached to the anterior patella and the insertion of the quadriceps femoris complex of the anterior tibial crest. A strain gage was then applied to the center of the rubber aligned axially with the line of applied force. The stifle was put through a simulated extension using the motor attached to the patella. A controlled intact knee was used as the baseline for all four specimens, independently. Following the control data acquisition, a simulated cranial cruciate rupture was performed and the strain values collected in the same manner. Finally, the TPLO was performed. Two specimens used an 18 mm biradial saw, whereas, the other two used a 24 mm biradial saw. Five measurements of strain were recorded for the control, a simulated ruptured cranial cruciate, and 0, 2, 4, 6, 8, 10, 12, and 14 mm of tibial plateau rotation following a TPLO.

It was found that there is a statistically significant increase in strain experienced by the patellar tendon following a TPLO at nearly every angle of rotation for both cuts. Whereas, a simulated ruptured cranial cruciate ligament resulted in no statistically significant difference in 3 out of 4 of the samples. Strain values increased by as much as 96 and 81 percent for the 18 mm cut at 8 mm of rotation and the 24 mm cut at 12 mm of rotation, respectively.

This study will provide a basis for improvements to be made with respect to the TPLO. Further research may result in a more concise and clinically relevant data set that will continue the advancement of this common surgical technique.