Instantaneous center of rotation in the canine femorotibial joint: Ex vivo assessment of a tool to evaluate joint stabilization surgeries.

Cranial cruciate ligament rupture is a common cause of femorotibial joint instability in the dog. Numerous techniques including several tibial osteotomies have been described for stabilization, but there is no current consensus on the best method. The instantaneous center of rotation (ICR) can aid investigations of pathological joint movement, but its use is problematic in the femorotibial joint due to combined rotation and translation during flexion and extension. Using fluoroscopic images from an earlier cadaveric study of canine joint stability, an interpolation method was used to create repeatable rotational steps across joint situations, followed by least squares approximation of the ICR. The ICR in intact joints was located mid-condyle but displaced significantly (P < 0.001) proximally following cranial cruciate ligament transection and medial meniscal release. Individual joints appear to respond differently to destabilization. Triple tibial osteotomy partially restored ICR location during early movement from flexion to extension. Joint instability significantly altered the proportions of rolling and gliding movement at the joint surface (P < 0.02), which triple tibial osteotomy partially improved. While triple tibial osteotomy restores joint stability ex vivo and clinically, normal biomechanics of the joint are not restored. The methods described here may prove useful for comparison of osteotomy techniques for stabilization of the cranial cruciate ligament deficient femorotibial joint in dogs.

Geometric modelling of error sources for tibial plateau levelling osteotomy in the dog.

Tibial plateau levelling osteotomy is widely performed for stabilization of cranial cruciate ligament deficient stifles in dogs. A wide range of postoperative tibial plateau angles around the target angle has been reported. The main aim of this study was to investigate if osteotomy placement could explain this range. Landmarks were derived from 50 tibial radiographs by five observers and used to define osteotomy placement and correction angles for simulation. Observer-specific osteotomy locations with mean landmark data were used to simulate planning errors, and simulated malpositioning of the osteotomy at 5 mm and 10 mm from the ideal location was used to simulate surgical errors. The tibial plateau midpoint was used as the ideal centre of the osteotomy in this model. Planning errors mostly arose from tibial plateau misidentification, with osteotomy centre locations dispersed up to 2.4% of tibial length from ideal. Malpositioning of the osteotomy resulted in variable changes in tibial plateau angle. Synthesis with historical data suggested such changes are likely limited in magnitude in tibiae with a mechanical axis length over 140 mm, but will be greater in smaller dogs and with steeper tibial plateaus. In medium to large breed dogs, our findings indicate osteotomy inaccuracy alone cannot explain the reported postoperative ranges in tibial plateau angles. Other error sources such as rotational inaccuracies or shifts during implant placement may be more significant. Surgeons should exercise additional caution when operating small and miniature breeds due to the much larger potential for clinically significant errors in these smaller dogs.

Geometric modelling of CORA-based levelling osteotomy in the dog.

Centre of rotation of angulation (CORA)-based levelling osteotomy (CBLO) is a recent addition to surgical procedures for stabilization of the cranial cruciate ligament-deficient canine stifle joint. Careful identification of the CORA location preoperatively and use of this location intraoperatively are required to ensure accurate correction of the tibial plateau angle. Limited data are available regarding the magnitude and source of potential errors during planning and execution of CBLO. A geometric model enabling isolation of various error sources is described. Landmarks were derived from tibial radiographs (n = 50) by 5 observers and used to define proximal and distal anatomical axes for simulation of CBLO. Observer-specific CORA locations with mean landmark data were used to assess planning errors, and simulated malpositioning of the CORA at 10 mm from the ideal location was used to assess surgical errors. Planning errors result mainly from tibial plateau misidentification, with CORA locations dispersed up to ±10 mm proximodistally from ideal (95% confidence). Malpositioning of the CORA during surgery causes equal and opposite changes in tibial plateau angle (TPA) and anatomical-mechanical axis angles, and varying degrees of translation and limb length changes. The magnitude of these changes is dependent on initial TPA and limb length, with smaller dogs and steeper tibial plateaus resulting in larger errors. Optimal planning and execution are required to achieve the planned outcome of CBLO. The main source of error in our simulation is identification of the tibial plateau. While both pre- and intraoperative errors influenced TPA, based on our geometric model the effect in larger dogs may not be clinically significant. If distalisation of the CORA is required during surgery, compensation of the CORA angle to maintain the target TPA is possible.