Assessment of the medial collateral ligament as an intra-operative anatomical landmark for tibial plateau levelling osteotomy.

OBJECTIVES: To determine whether the medial collateral ligament can be a reliable intra-operative anatomical landmark for rotation of the tibial plateau in the tibial plateau levelling osteotomy (TPLO) procedure, thus providing a tibial plateau rotation equal to that obtained using standard preoperative measurements. METHODS: Tibial plateau levelling osteotomy procedures were performed on pelvic limbs (n = 42) from canine cadavers with or without a history of cranial cruciate ligament deficiency. The rotation of the proximal fragment was performed such that the orientation of the fibres of the medial collateral ligament were aligned parallel to the caudal tibial cortex at the location of the osteotomy. Statistical analysis was performed to evaluate the difference between calculated rotation to achieve a postoperative tibial plateau angle of five degrees and the actual rotation achieved by aligning the medial collateral ligament and caudal tibial cortex. RESULTS: The rotation performed by alignment of the medial collateral ligament fibres with the caudal tibial cortex resulted in a significantly greater rotation than the calculated movement required to achieve a postoperative angle of five degrees. The mean over-rotation was 2.1 ± 1.73 mm. CLINICAL SIGNIFICANCE: Use of the medial collateral ligament alignment with the caudal tibial cortex will reliably result in over-rotation of the tibial plateau and should not be used as an intra-operative guideline for tibial plateau rotation during TPLO procedures.

Evaluation of compression generated by self compressing Orthofix bone pins and lag screws in simulated lateral humeral condylar fractures.

A simulated lateral humeral condylar fracture was created in each of the 52 humeri collected from 26 dogs. One humerus from each pair was stabilized with a 2.0 mm cortical bone screw which was inserted in lag fashion. The other humerus from each pair was stabilized with a 2.2 mm threaded diameter Orthofix pin inserted across the condyle. Prior to each repair, an antirotational K-wire was placed and then the Pressurex Sensitive film was inserted in the osteotomy site in order to determine the compressive pressure (MPa), compressive force (KN), and area of compression (cm(2)) achieved during fixation. The maximum insertional torque achieved before stripping was measured for each implant. The mean compression generated by insertion of a 2.0 mm lag screw was 20.36 +/- 1.51 MPa compared to 18.88 +/- 1.76 MPa generated by a 2.2 mm Orthofix pin (p < 0.003). The mean area of compression generated by insertion of a 2.0 mm lag screw was 2.39 +/- 1.29 cm(2), compared to 1.16 +/- 0.84 cm(2) generated by insertion of a 2.2 mm Orthofix pin (p < 0.0001). The mean compressive force (compression x area compressed) generated by insertion of a 2.0 mm lag screw was 4.96 +/- 2.90 Kn, compared to 2.20 +/- 1.65 Kn generated by insertion of a 2.2 mm Orthofix pin (p < 0.0001). The mean insertion torque to failure for the lag screws was 0.49 +/- 0.07 NM, compared to 0.91 NM +/- 0.18 NM generated by the Orthofix pins (P < 0.0001). Both repair methods are likely to be acceptable for the repair of similar fractures in small breed dogs.