Cranial cruciate ligament disease is one of the most common orthopedic problems in adult large-breed dogs.1,2 The prevalence of CCLD has gradually increased from 1.81% to 4.87% during the past 40 years.1 Controversies exist regarding the exact pathogenesis of CCLD, and little information has been published concerning preventive measures. Most CCL ruptures appear to occur secondary to progressive adaptive and degenerative changes attributable to repetitive microinjury.3 Risk factors for CCLD include an excessively steep tibial plateau, cranial angulation of the proximal portion of the tibia, and torsion of the distal portion of the femur.4 The combination of the TPA and FAA has been identified as the best method to discriminate limbs predisposed to CCLD from limbs not predisposed to CCLD in Labrador Retrievers, a breed predisposed to CCL deficiency.5
Gait analysis and inverse dynamics have greatly contributed to elucidating joint mechanics that predispose human female athletes to anterior cruciate ligament injury. Dominance of the quadriceps muscles over the hamstring muscle group and increased laxity of the knee joint were identified as factors that predisposed female athletes to knee joint injuries, which provided the basis for neuromuscular exercise programs.6–8 A dynamic imbalance in joint kinetics and kinematics around the stifle joint may also be present in dogs predisposed to CCLD. The peak stifle joint moment during the propulsion phase accounts for 30% of the total moment in Labrador Retrievers, compared with only 12% in Greyhounds (a breed at low risk for CCLD).9 Moreover, the amplitude of the net flexor muscle moment across the stifle joint, which is an active restraint to cranial tibial thrust, was more than twice as high in Greyhounds during the early stance phase, compared with the value in Labrador Retrievers.9 These results are encouraging because they support the concept that dynamic stifle joint instability may predispose Labrador Retrievers to CCLD. However, these results may also reflect differences in morphology between the 2 breeds.
In addition, 37% to 48% of contralateral limbs have CCL deficiency 10 to 17 months after initial diagnosis of unilateral CCLD.10,11 On the basis of the high incidence of contralateral rupture, the contralateral limb of dogs with unilateral CCLD may be considered predisposed. The limb mechanics of Labrador Retrievers with unilateral CCLD or that are free of orthopedic disease have been compared during trotting on the ground.12 Gait analysis revealed increased propulsive forces and vertical impulse and greater power generation by the muscles around the stifle joint in contralateral limbs, compared with results for orthopedically normal limbs. This greater mobilization of the extensor muscles of the stifle joint at pushoff during extension of the stifle joint may increase the cranial tibial thrust, which is a force believed to contribute to the pathogenesis of CCLD.13 However, because of the design of that previous gait mechanics study,13 predisposing factors could not be differentiated from compensatory behaviors secondary to unilateral CCLD.
Most gait analyses in dogs involve trials conducted on the ground. Compared with these analyses, analyses conducted via treadmills instrumented with force platforms allow continuous measurement of GRF generated by all limbs during successive foot strikes. The ability to control the belt speed on a treadmill improves the reliability and consistency of subject velocity and acceleration and reduces the variability of measurements, compared with these factors in trials conducted in dogs trotting on the ground.14–16 Analysis of gait while trotting on a treadmill has been extensively used for evaluating kinematics in humans and horses because the assessment can be performed in less space and with improved control of variables (velocity, surface, and positioning of cameras), compared with an assessment performed while trotting on the ground.
The objective of the study reported here was to identify gait characteristics during trotting on a treadmill in nonlame Labrador Retrievers classified as presumed predisposed or not predisposed to CCLD on the basis of the score of a radiographic combination of TPA and FAA. We hypothesized that an increased propulsive force and greater energy generation by the extensor muscles around the stifle joint would be identified in limbs classified as predisposed to CCLD (high TPA-FAA score [> −1.5]), compared with results for limbs presumed not predisposed to CCLD (low TPA-FAA score [≤ −1.5]).
Cranial cruciate ligament
Cranial cruciate ligament disease
Femoral anteversion angle
Ground reaction force
Joint reaction force
Tibial plateau angle
Vicon Motion Systems Inc, Lake Forest, Calif.
Bertec Corp, Columbus, Ohio.
MATLAB, MathWorks Inc, Natick, Mass.
Systat, version 11, Systat Inc, Richmond, Calif.
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