Rock-back is a recognized TPLO complication yet its cause has not been elucidated. We propose that rock-back is affected by 1) osteotomy orientation with respect to the caudal tibial cortex (uphill, normal and downhill) and 2) plate inclination with respect to the caudal tibial cortex (straight and inclined). Tibial bone models were 3D printed from CT images of a ~25 kg dog. Models featured one of three osteotomies (uphill-75℗ʻ, normal-90℗ʻ, downhill-105℗ʻ) with a 1 mm interfragmentary gap. For each osteotomy, a 2.7 mm TPLO plate (DPS) was applied either parallel to or at a 20℗ʻ angle to a best fit line of the caudal tibial cortex, representing a worse-case scenario of plate inclination. Specimens were cyclically loaded to 400 N using a custom-built loading press. Electromagnetic sensors affixed to the tibial plateau segment and distal tibial crest were used to compare tibial plateau rock-back about the mediolateral axis and roll about the craniocaudal axis. Within each osteotomy group, rock-back was ~1.5 times greater with inclined than straight plates (p < 0.05), which was associated with an average difference of ~1.34℗ʻ ℗ł 0.4℗ʻ. Conversely, the orientation of the osteotomy had no effect on rock-back (p > 0.05). These findings suggest that our model can replicate rock-back, which likely results from an accentuated disruptive force couple generated by an inclined plate as compared to a plate placed parallel to the caudal tibial cortex. Standardization is recommended to align the plate parallel to the caudal tibial cortex, thus reducing the risk of rock-back.
Read
