Effect of Tibial Plateau Leveling Osteotomy on Femorotibial Contact Mechanics and Stifle Kinematics STANLEY E. KIM, BVSc, ANTONIO POZZI, DMV, MS, Diplomate ACVS, SCOTT A. BANKS, PhD, BRYAN P. CONRAD, MEng, and DANIEL D. LEWIS, DVM, Diplomate ACVS Objective—To evaluate the effects of tibial plateau leveling osteotomy (TPLO) on femorotibial contact mechanics and 3-dimensional (3D) kinematics in cranial cruciate ligament (CrCL)-deficient stifles of dogs. Study Design—In vitro biomechanical study. Animals—Unpaired pelvic limbs from 8 dogs, weighing 28–35 kg. Methods—Digital pressure sensors placed subjacent to the menisci were used to measure femoro- tibial contact force, contact area, peak and mean contact pressure, and peak pressure location with the limb under an axial load of 30% body weight and a stifle angle of 1351. Three-dimensional static poses of the stifle were obtained using a Microscribe digitizing arm. Each specimen was tested under normal, CrCL-deficient, and TPLO-treated conditions. Repeated measures analysis of variance with a Tukey post hoc test (Po.05) was used for statistical comparison. Results—Significant disturbances to all measured contact mechanical variables were evident after CrCL transection, which corresponded to marked cranial tibial subluxation and increased internal tibial rotation in the CrCL-deficient stifle. No significant differences in 3D femorotibial alignment were observed between normal and TPLO-treated stifles; however, femorotibial contact area remained significantly smaller and peak contact pressures in both medial and lateral stifle com- partments were positioned more caudally on the tibial plateau, when compared with normal. Conclusion—Whereas TPLO eliminates craniocaudal stifle instability during simulated weight bearing, the procedure fails to concurrently restore femorotibial contact mechanics to normal. Clinical Relevance—Progression of stifle osteoarthritis in dogs treated with TPLO may be partly the result of abnormal stifle contact mechanics induced by altering the orientation of the proximal tibial articulating surface. r Copyright 2009 by The American College of Veterinary Surgeons INTRODUCTION R ECENT DEVELOPMENTS in the surgical treat- ment of cranial cruciate ligament (CrCL) insuffi- ciency in dogs have introduced an innovative and clinically successful concept of imparting functional, or dynamic, stability to CrCL-deficient stifles. 1 By altering the conformation of the proximal tibia, stifle biomechan- ics can be modified so that stability is no longer depen- dent on what is normally one of the major stabilizing structures of a dog’s stifle: the CrCL. 1 Cranial tibial sub- luxation during stance phase of gait is the predominant feature of CrCL-deficient stifle kinematics, caused by a cranially directed femorotibial shear force termed cra- nial tibial thrust. 2–4 Tibial plateau leveling osteotomy (TPLO), currently one the most commonly performed surgical procedures for the treatment of CrCL insuffi- ciency, is purported to eliminate cranial tibial thrust by Presented in part at the Veterinary Orthopaedic Society Conference, Big Sky, MT, March 2008, and the American College of Veterinary Surgeons Symposium, San Diego, CA, October 2008. Address reprint requests to Dr. Antonio Pozzi, DMV, MS, Diplomate ACVS Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610. E-mail: pozzia@vetmed.ufl.edu. Submitted January 2008; Accepted June 2008 From the Department of Small Animal Clinical Sciences, Department of Mechanical and Aerospace Engineering, and Department of Orthopaedics and Rehabilitation, College of Veterinary Medicine, University of Florida, Gainesville, FL. r Copyright 2009 by The American College of Veterinary Surgeons 0161-3499/08 doi:10.1111/j.1532-950X.2008.00470.x 23 Veterinary Surgery 38:23–32, 2009