Inverse dynamics is a branch of biomechanical analysis that combines data obtained from kinetic and kinematic gait analyses to determine net muscular effort across joints. Traditional dynamics describes the production of motion from a prescribed, or known, force. Moment, torque, power, and work can be used to describe and evaluate objects in motion. However, in biological systems, the forces that initiate motion are often unknown or impossible to measure directly and can only be estimated by beginning with a known motion and solving for force by means of mathematical integration. The term inverse dynamics was coined to describe this process for estimating initiating forces in biological systems. Quantification of initiating forces in moving biological systems is important so that values for moment, torque, power, and work can be calculated to characterize motion.
Although the use of inverse dynamics in veterinary medicine is relatively novel, compared with its use in human medicine, numerous studies1–12 have been conducted to analyze the gait of various species of veterinary interest. Results of those studies1–12 have aided in the elucidation not only of the normal movement of animals, but also possible factors associated with the pathogenesis of musculoskeletal disease and injury. Investigators of many studies1–12 have described ground reaction forces (kinetic data) associated with both normal and abnormal gaits in species of veterinary interest as well as changes in joint angles and kinematic data for those species. These data can be combined and inverse dynamics used to more comprehensively describe the gait of a particular species.
In human medicine, inverse dynamics has been used to characterize many different motion patterns and compensatory gaits in patients with many different musculoskeletal disorders, especially those with arthritic or anterior cruciate ligament–deficient knee joints.13,14 This information can be used to verify gait-related movement patterns associated with particular injuries and help physicians modify treatment protocols. In veterinary medicine, CCL injury is analogous to anterior cruciate ligament injury in humans and occurs commonly in dogs. Veterinarians that treat dogs with CCL injuries would benefit from a better understanding of how affected dogs attempt to compensate for the injury and how various repairs affect gait. When considered separately, ground reaction force (ie, kinetic) and kinematic data are often insufficient to fully describe gait differences between affected individuals; however, when those data are combined with morphometric data for inverse dynamics analysis, significant gait differences between individuals may be identified.13,14 Inverse dynamics analysis can be used to evaluate pathological gaits so that treatment can be specifically designed and modified for affected patients, which should improve their response to treatment.
In some studies,15–17 kinematic data were obtained to assess gait changes in dogs with experimentally induced CCL injury that were and were not surgically repaired to evaluate how those dogs compensated for the injury and identify factors that could be useful for monitoring patient progress during recovery. Few investigators3–5,7,12,18 have used inverse dynamics to describe the motion of the canine pelvic limb, and investigators of only 1 study12 have used inverse dynamics to describe gait differences between dogs with and without arthritis of the stifle joint.
To our knowledge, only a few studies19–22 have been conducted to compare TPLO and LFS for stifle joint stabilization in CCL-deficient dogs, and none involved the use of joint kinetics to assess gait changes. Inverse dynamics requires morphometric data such as limb center of gravity, radius of gyration, and moment of inertia to calculate joint moments. Morphometric data are difficult to obtain by noninvasive and nonlethal methods and are likely to vary by breed. In fact, to our knowledge, only 1 study11 has been conducted in which morphometric data of dogs (Labrador Retrievers and Greyhounds) were obtained by noninvasive methods. The difficulty, time, and expense of obtaining morphometric data from live dogs is a potential obstacle to the application of inverse dynamics for gait analysis in veterinary medicine. Although a few studies23–26 have been conducted that involved the use of inverse dynamics to describe the 3-D movement of the canine pelvic limb, none involved dogs that had previously undergone a TPLO or LFS procedure, 2 commonly used procedures to stabilize CCL-deficient stifle joints. The purpose of the study reported here was to use an inverse dynamics method to evaluate the 3-D motion of the pelvic limb in clinically normal dogs and dogs with surgically induced CCL-deficient stifle joints that had undergone a TPLO or LFS procedure at least 3.5 years prior to the evaluation. The null hypothesis was that the 3-D gait characteristics would not vary significantly among the 3 groups of dogs.
Materials and Methods
Animals—The study protocol was approved by the University of Tennessee Institutional Animal Care and Use Committee. Twenty-five hound-type dogs (3 males and 22 females) were used in the study. The mean ± SD weight of the study dogs was 22.08 ± 1.88 kg (range, 17.9 to 26.1 kg). These dogs were part of an ongoing study and were grouped into 3 categories. The control group (n = 6) included clinically normal dogs that were free of gait, orthopedic, or neurologic abnormalities as determined by physical examination and did not have evidence of osteoarthritis in the caudal portion of the vertebral column, pelvis, or pelvic limbs as determined by radiographic examination. The other 2 groups consisted of dogs in which the CCL of 1 stifle joint had been surgically transected and immediately stabilized by means of a TPLO or LFS procedure. For each dog, the stifle joint selected for surgery was chosen in a random manner. The menisci were left intact during all procedures. The TPLO surgery was performed as described,27 and the mean ± SD time between the procedure and the initiation of the present study for the TPLO group (n = 13) was 4 ± 0.5 years. For the LFS procedure, the stifle joint was stabilized by the passage of 2 nylon sutures around the lateral fabella and through a hole created in the proximal aspect of the tibial tuberosity, and the mean time between the procedure and the initiation of the present study for the LFS group (n = 6) was 8 ± 0.5 years. Just prior to initiation of the present study, dogs in the TPLO and LFS groups underwent physical examination and radiographic evaluation of the caudal portion of the vertebral column, pelvis, and pelvic limbs. All dogs were clinically sound, and the only abnormality identified on radiographic evaluation was varying degrees of osteoarthritis in the CCL-deficient stifle joints. Following recovery from surgery, all dogs in the TPLO and LFS groups were allowed the same amount of leash-restricted activity and kept in a controlled kennel-type environment. The dogs in the control group were likewise housed.
Experimental protocol—Dogs were instrumented, and kinetic and kinematic data were simultaneously collected as described.26 Briefly, a 60-Hz, 4-camera, 3-D motion capture systema was used to collect kinematic data. A 1,000-Hz force platformb that was mounted in the center of and flush with a 10.68-m runway that was used to collect kinetic data, and a specialized computer software programc was used to process that data. Following a static calibration, each dog was trotted over the forceplate at a mean velocity between 1.7 and 2.1 m/s and a mean acceleration between −0.5 and 0.5 m/s2. For each limb evaluated, data were obtained for 5 valid trials. A valid trial was defined as a passage over the runway in which there was no aberrant movement of the subject's head or body in the calibrated space, the velocity and acceleration were within the established ranges, the fore and hind paws ipsilateral to the side being evaluated both struck the forceplate, and all tracking markers were visible by at least 2 cameras at all times.
Stance time was defined as the time between toe-on and toe-off as measured by the movement of the marker on the dorsal aspect of the foot in the sagittal plane. Ground reaction forces were normalized by the subject's body weight and reported as a percentage of body weight. The mediolateral, craniocaudal, and vertical components of the ground reaction force were assigned the values of x, y, and z, respectively. The same investigator (JFH) applied all the tracking markers to the dogs, and the same handler (RPM) trotted the dogs during all trials. A Cardan sequence (x-y-z) was used to compute 3-D angular kinematics. The conventions of 3-D angular kinematic variables were determined by use of a right-hand rule.
Data processing—Data were processed as described.26 Briefly, kinetic data were processed by custom software,c and kinematic data were processed by a motion analysis system.d Another software programe was used to synchronize the kinetic and kinematic data. The synchronized data were processed, computer models were created and analyzed, and reports were produced with commercially available software,f and those outputs were input into a customized computer programg to determine critical events and values for computed variables. Morphometric data for Labrador Retrievers, including each limb segment's (pelvis, femur, tibia, and foot) percentage of body weight and center of gravity, were obtained from a previous study5 and entered into the database of the 3-D softwaref used for the inverse dynamics calculations. This softwaref was also used to mathematically reconstruct and create virtual markers for the center of rotation of the hip, stifle, tibiotarsal (hock), and metatarsophalangeal joints as described.26
Joint angles, moments, and powers in the sagittal, frontal, and transverse planes during the stance phase of the gait cycle were determined as described.26 For all dogs, mean joint angular excursions, net joint moments, and net joint powers were determined and graphed in the sagittal, frontal, and transverse planes for the hock, stifle, and hip joints. Critical values such as the maximum and minimum values for each variable and areas under the curve for each graph were used for statistical comparisons.
Mean (95% confidence interval) curves of sagittal-plane angles (A, B, and C), moments (D, E, and F), and powers (G, H, and I) for the tibiotarsal (hock; A, D, and G), stifle (B, E, and H), and hip (C, F, and I) joints of adult hound-type dogs with clinically normal stifle joints (controls; n = 6; solid lines) and dogs with experimentally induced CCL-deficient stifle joint that were repaired by TPLO (n = 13; dotted lines) or an LFS procedure (n = 6; dashed lines) at a mean of 4 years and 8 years, respectively, before the evaluation. In panels A, B, and C, extension is represented as a positive slope and is defined as an increase in joint angle toward 180° between adjacent segments, and flexion is represented as a negative slope and is defined as a decrease in joint angle toward 0° between adjacent segments. In panels D and F, positive values indicate net flexor moments, whereas in panel E, positive values indicate net extensor moments. In panels G, H, and I, positive values indicate net concentric muscle contraction (ie, energy generation), whereas negative values indicate net eccentric muscle contraction (ie, energy absorption). For each set of 3 lines with the same pattern (solid, dotted, or dashed lines), the middle line represents the mean and the outside lines delimit the 95% confidence interval for the mean. The 95% confidence interval for the control group has been shaded to facilitate comparison of TPLO and LFS groups with the control group.
Citation: American Journal of Veterinary Research 75, 6; 10.2460/ajvr.75.6.554
Statistical analysis—For each dog in the control group, 1 pelvic limb was selected in a random manner for comparison with the surgically corrected limbs of dogs in the TPLO and LFS groups. Outcomes of interest were associated with the mean joint angle, net joint moment, and net joint power in the sagittal, frontal, and transverse planes for the hock, stifle, and hip joints. The Shapiro-Wilk test was use to assess whether the data for each outcome were normally distributed. When the data were not normally distributed, a logarithmic, square root, or rank transformation was used to normalize the distribution of the data before further analyses were performed. Each respective outcome was compared among the 3 groups by means of ANOVA. For each model, dog and group were included as independent variables. The Tukey method was used to adjust P values to avoid type I error inflation caused by multiple pairwise comparisons. Results were reported as the median and range for outcomes for which the data had to be transformed and least square mean ± SEM for outcomes for which the data were normally distributed. All analyses were performed with commercially available software,h and values of P < 0.05 were considered significant for all analyses.
Results
Sagittal plane dynamics—Values for outcomes of interest in the sagittal plane were summarized for the control, TPLO, and LFS groups (Table 1), and the mean joint angle and net joint moments and power in the sagittal plane for the hock, stifle, and hip joints for all 3 groups were graphed (Figure 1). Generally, pelvic limb movement patterns were consistent, with only small variations observed among all 3 joints for all 3 groups. The range of motion for the hock and stifle joints did not differ significantly among the groups. Although the hip joint was in continuous extension throughout the stance phase for all 3 groups, the contact angle of the hip joint for the TPLO group was significantly (P = 0.03) greater than that for the control group. Throughout hip excursion, the moment and power curves for all 3 groups were nearly identical.
Inverse dynamics variables in the sagittal plane for the tibiotarsal (hock), stifle, and hip joints of adult hound-type dogs that were clinically normal (control group; n = 6) or had experimentally induced CCL-deficient stifle joints that were repaired by TPLO (TPLO group; 13) or an LFS technique (LFS group; 6) at a mean of 4 years and 8 years, respectively, prior to the evaluation.
| Group | |||
|---|---|---|---|
| Joint and variable | Control | TPLO | LFS |
| Hock joint | |||
| Contact angle (°) | 167.05 (3.38) | 174.74 (2.30) | 171.66 (3.38) |
| Toe-off angle (°) | 182.94 (2.91) | 184.56 (1.98) | 180.06 (2.91) |
| Minimum angle (°) | 141.72 (3.17) | 148.62 (2.16) | 143.72 (3.17) |
| Excursion (°) | 35.50 (4.19) | 30.86 (2.85) | 32.25 (4.19) |
| Maximum extensor moment (Nm/kg) | −0.41 (0.06) | −0.52 (0.04) | −0.41 (0.06) |
| First maximum eccentric power (W/kg) | −2.51 (0.41) | −3.03 (0.28) | −2.75 (0.41) |
| Negative work (J/kg) | 0.12 (0.02) | 0.15 (0.015) | 0.14 (0.02) |
| Maximum concentric power (W/kg) | 2.11 (0.28) | 2.24 (0.19) | 1.94 (0.28) |
| Positive work (J/kg) | 0.11 (0.02) | 0.12 (0.01) | 0.09 (0.02) |
| Stifle joint | |||
| Contact angle (°) | 145.96 (3.44) | 144.4 (2.34) | 151.09 (3.44) |
| Toe-off angle (°) | 133.55 (3.55) | 129.52 (2.41) | 135.64 (3.55) |
| Minimum angle (°) | 127.49 (3.57) | 125.49 (2.43) | 130.07 (3.57) |
| Excursion (°) | 18.47 (1.54) | 18.91 (1.04) | 21.02 (1.54) |
| Maximum extensor moment (Nm/kg) | 0.31 (0.05) | 0.33 (0.04) | 0.32 (0.05) |
| Negative impulse (Ns/kg) | 0.002 (0 to 0.005) | 0.002 (0 to 0.013) | 0.001 (0.0005 to 0.002) |
| First maximum eccentric power (W/kg) | 0.48 (0.10) | 0.48 (0.07) | 0.60 (0.10) |
| First maximum concentric power (W/kg) | 0.40 (0.11) | 0.53 (0.07) | 0.37 (0.11) |
| Second maximum concentric power (W/kg) | 0.43 (0.10) | 0.39 (0.07) | 0.37 (0.10) |
| Positive work (J/kg) | 0.03 (0.01) | 0.03 (0.004) | 0.02 (0.01) |
| Negative work (J/kg) | 0.02 (0.01) | 0.02 (0.003) | 0.03 (0.01) |
| Hip joint | |||
| Contact angle (°) | 109.25 (2.60) | 117.73 (1.77)* | 112.63 (2.60) |
| Toe-off angle (°) | 130.58 (2.75) | 138.18 (1.87) | 132.03 (2.75) |
| Excursion (°) | 21.34 (1.11) | 20.44 (0.76) | 19.40 (1.11) |
| Maximum extensor moment (Nm/kg) | 0.32 (0.04) | 0.36 (0.03) | 0.26 (0.04) |
| Maximum flexor moment (Nm/kg) | 0.15 (0.03) | 0.15 (0.02) | 0.19 (0.03) |
| First maximum concentric power (W/kg) | 0.61 (0.12) | 0.68 (0.08) | 0.67 (0.12) |
| Positive work (J/kg) | 0.030 (0.01) | 0.04 (0.004) | 0.03 (0.01) |
| First maximum eccentric power (W/kg) | −0.39 (0.06) | −0.38 (0.04) | −0.35 (0.06) |
| Negative work (J/kg) | 0.02 (0.01) | 0.02 (0.003) | 0.02 (0.01) |
Values reported are least square mean (SEM) or median (range). The mean ± SD time between surgery and initiation of the present study was 4 ± 0.5 years for the dogs in the TPLO group and 8 ± 0.5 years for the dogs in the LFS group.
Within a row, value differs significantly (P < 0.05) from that for the control group.
Frontal plane dynamics—Values for outcomes of interest in the frontal plane were summarized for the control, TPLO, and LFS groups (Table 2), and the mean joint angle and net joint moments and power in the frontal plane for the hock, stifle, and hip joints for all 3 groups were graphed (Figure 2). In the frontal plane, the joint excursions were generally much smaller and the joint moments and powers were approximately one-fifth to one-tenth of the corresponding variables in the sagittal plane. The angle and motion of the hock joint did not differ significantly among the 3 groups.
Inverse dynamics variables in the frontal plane for the hock, stifle, and hip joints of the dogs in Table 1.
| Group | |||
|---|---|---|---|
| Joint and variable | Control | TPLO | LFS |
| Hock joint | |||
| Contact angle (°) | −4.32 (1.90) | −4.95 (1.29) | −6.01 (1.90) |
| Toe-off angle (°) | 3.07 (2.43) | 5.73 (1.65) | 4.23 (2.43) |
| Excursion (°) | 7.38 (2.00) | 10.68 (1.36) | 10.24 (2.00) |
| Positive impulse (Ns/kg) | 0.0008 (0.0002 to 0.02) | 0.005 (0.001 to 0.04) | 0.003 (0.0 to 0.02) |
| Negative impulse (Ns/kg) | 0.01 (0.006) | 0.02 (0.004) | 0.02 (0.006) |
| Maximum eccentric power (W/kg) | −0.19 (−0.29 to 0.04) | −0.09 (−1.15 to 0.03) | −0.15 (−0.61 to −0.07) |
| Maximum concentric power (W/kg) | 0.07 (0.10) | 0.21 (0.07) | 0.06 (0.10) |
| Stifle joint | |||
| Contact angle (°) | −2.46 (4.16) | 2.37 (2.82) | 0.70 (4.16) |
| Toe-off angle (°) | −3.66 (5.31) | 0.48 (3.6) | −1.37 (5.31) |
| Maximum angle (°) | −0.60 (5.70) | 7.62 (.87) | 3.52 (5.70) |
| Excursion (°) | 3.67 (1.53) | 7.41 (1.04) | 3.17 (1.53) |
| Maximum abductor moment (Nm/kg) | −0.06 (−0.079 to −0.021) | −0.14 (−0.41 to 0.18) | −0.12 (−0.29 to 0.02) |
| Maximum adductor moment (Nm/kg) | 0.001 (−0.03 to 0.19) | 0.01 (0.04) | 0.001 (−0.03 to 0.19) |
| Maximum concentric power (W/kg) | 0.03 (0.08) | 0.03 (0.05) | 0.26 (0.08)* |
| Positive work (J/kg) | 0.003 (0.0004 to 0.0133) | 0.008 (0.00 to 0.04) | 0.01 (0.0007 to 0.04) |
| Hip joint | |||
| Contact angle (°) | −4.04 (2.91) | −2.53 (1.98) | −3.45 (2.91) |
| Toe-off angle (°) | −12.69 (2.91) | −9.48 (1.98) | −8.51 (2.91) |
| Excursion (°) | 8.65 (2.53) | 7.67 (1.72) | 7.15 (2.53) |
| Maximum abductor moment (Nm/kg) | −0.05 (0.02) | −0.06 (0.01) | −0.05 (0.02) |
| Maximum concentric power (W/kg) | 0.08 (0.011 to 0.147) | 0.105 (−0.009 to 0.920) | 0.15 (0.026 to 0.55) |
| Positive work (J/kg) | 0.0039 (0.0001 to 0.0138) | 0.005 (0.00 to 0.065) | 0.008 (0.0002 to 0.039) |
See Table 1 for key.
For all 3 groups, the stifle joint was slightly adducted during the first half of the stance phase and then underwent slight abduction during the second half of the phase; however, the mean stifle joint angles and moments did not differ significantly among the groups. For the dogs of the control and LFS groups, the stifle joint had a net abductor moment during the initial 60% to 70% of the stance phase and then transitioned to a small net adductor moment for the remainder of the phase, whereas the stifle joint for the dogs of the TPLO group had a net abductor moment throughout the stance phase. The moments for the stifle joint were predominantly concentric in nature throughout the stance phase for all groups. The mean maximum concentric power of the stifle joint for the LFS group was significantly (P = 0.01) greater than that for the control group.
The hip joint was abducted throughout the stance phase in all 3 groups, and the abductors of the hip joint caused a net abduction moment and concentric contraction during most of the stance phase. The inverse dynamics of the hip joint did not vary significantly among the 3 groups.
Transverse plane dynamics—Values for outcomes of interest in the transverse plane were summarized for the control, TPLO, and LFS groups (Table 3), and the mean joint angle and net joint moments and power in the transverse plane for the hock, stifle, and hip joints for all 3 groups were graphed (Figure 3). In the transverse plane, the angular motions, moments, and powers for all 3 joints did not differ significantly among the 3 groups and were much smaller than the corresponding variables in the sagittal plane. For most dogs, the hock joint was in a slight internally rotated position at the beginning of the stance phase and underwent external rotation for most of the stance duration. The hock joint had a net external rotation moment for the first 60% to 80% of the stance phase, which was caused by concentric contraction of the joint's external rotators.
Inverse dynamics variables in the transverse plane for the hock, stifle, and hip joints of the dogs in Table 1.
| Group | |||
|---|---|---|---|
| Joint and variable | Control | TPLO | LFS |
| Hock joint | |||
| Contact angle (°) | 22.48 (11.47) | 1.69 (7.80) | 7.55 (11.47) |
| Toe-off angle (°) | 10.93 (10.32) | −6.01 (.008) | −2.93 (10.32) |
| Excursion (°) | 15.50 (2.65) | 11.40 (1.80) | 15.06 (2.65) |
| Maximum external rotation moment (Nm/kg) | −0.04 (0.01) | −0.08 (0.009) | −0.06 (0.01) |
| Maximum internal rotation moment (Nm/kg) | 0.027 (0.01) | 0.03 (0.007) | 0.007 (0.01) |
| Maximum external rotation power (W/kg) | −0.05 (−0.23 to 0.04) | 0.09 (−0.41 to 0.009) | −0.124 (−0.787 to 0.012) |
| Maximum internal rotation power (W/kg) | 0.10 (0.01 to 0.74) | 0.09 (0.00 to 0.46) | 0.11 (−0.018 to 0.257) |
| Stifle joint | |||
| Contact angle (°) | −2.99 (5.03) | 6.64 (3.42) | 11.61 (5.03) |
| Toe-off angle (°) | −7.80 (4.09) | 2.68 (2.78) | 3.63 (4.09) |
| Excursion (°) | 10.13 (2.91) | 10.04 (1.98) | 17.39 (2.91) |
| Maximum eccentric power (W/kg) | −0.02 (0.03) | −0.10 (0.02) | −0.11 (0.03) |
| Maximum internal rotation moment (Nm/kg) | 0.03 (0.009) | 0.05 (0.006) | 0.04 (0.009) |
| Negative work (J/kg) | 0.001 (0.002) | 0.005 (0.001) | 0.006 (0.002) |
| Hip joint | |||
| Contact angle (°) | −31.19 (8.21) | −24.41 (5.58) | −34.92 (8.21) |
| Toe-off angle (°) | −20.45 (8.31) | −9.92 (5.65) | −16.34 (8.31) |
| Excursion (°) | 10.74 (2.77) | 14.50 (1.88) | 18.57 (2.77) |
| Maximum external rotation moment (Nm/kg) | −0.07 (0.01) | −0.06 (0.009) | −0.08 (0.01) |
| Maximum eccentric power (W/kg) | −0.09 (0.03) | −0.11 (0.02) | −0.15 (0.03) |
| Maximum concentric power (W/kg) | 0.07 (0.03) | 0.09 (0.02) | 0.06 (0.03) |
See Table 1 for key.
Mean (95% confidence interval) curves of frontal-plane angles (A, B, and C), moments (D, E, and F), and powers (G, H, and I) for the hock (A, D, and G), stifle (B, E, and H), and hip (C, F, and I) joints of the dogs in Figure 1. In panels A, B, and C, positive values indicate angles with a net internal rotation. In panels D, E, and F, positive values indicate moments with a net internal rotation. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 75, 6; 10.2460/ajvr.75.6.554
Although none of the stifle joint variables varied significantly among the 3 groups, the stifle joints for the dogs in the control group began the stance phase at a nearly neutral angle, were externally rotated for the first half of the phase, and remained in that position for the second half of the phase, whereas the stifle joints for the dogs in the TPLO and LFS groups began the stance phase in an internally rotated position, were externally rotated for the first 50% to 60% of the phase, and then were internally rotated for the remainder of the phase. The internal rotators of the stifle joint underwent eccentric contraction during the initial portions of the stance phase, which was determined by a net internal rotation moment and negative power that indicated that those muscles lengthened and absorbed energy during the external rotation of the tibia.
For dogs of all 3 groups, the hip joint began the stance phase in an externally rotated position, was rotated internally for approximately the first 60% of the phase, and then remained in that position for the remainder of the phase. The hip joints of the dogs in the TPLO and LFS group were internally rotated to a greater extent throughout joint excursion than were the hip joints of the dogs in the control group, although the extent of hip joint rotation did not differ significantly among the 3 groups. The external rotators of the hip joint underwent predominantly eccentric contraction throughout joint excursion for most of the stance phase, although the dogs of the control group did have small changes in the eccentric and concentric activity of the external rotators of the hip joint throughout the stance phase that were not observed in the dogs of the TPLO and LFS groups.
Ground reaction forces—Vertical, breaking, and propulsion ground reaction forces and impulses were summarized for dogs in the control, TPLO, and LFS groups (Table 4). None of the mean ground reaction force variables varied significantly among the 3 groups of dogs.
Least square mean (SEM) vertical, breaking, and propulsion ground reaction forces for the pelvic limb of the dogs of Table 1.
| Group | |||
|---|---|---|---|
| Variable | Control | TPLO | LFS |
| Maximum vertical ground reaction force (N/kg) | 0.63 (0.03) | 0.64 (0.02) | 0.65 (0.03) |
| Vertical ground reaction force rate (N/s) | 7.75 (0.61) | 7.51 (0.41) | 7.88 (0.61) |
| Vertical ground reaction impulse (Ns/kg) | 0.08 (0.004) | 0.08 (0.003) | 0.08 (0.004) |
| Breaking ground reaction force (N/kg) | −0.04 (0.007) | −0.04 (0.005) | −0.05 (0.007) |
| Propulsion ground reaction force (N/kg) | 0.086 (0.007) | 0.084 (0.005) | 0.076 (0.007) |
| Breaking impulse (Ns/kg) | −0.003 (0.001) | −0.004 (0.0007) | −0.004 (0.001) |
| Propulsion impulse (Ns/kg) | 0.0045 (0.001) | 0.004 (0.0008) | 0.003 (0.001) |
See Table 1 for key.
Discussion
In the present study, kinetic, kinematic, and morphometric data were combined in an inverse dynamics method to describe the 3-D motion of the pelvic limb in clinically normal dogs (control group) and dogs with experimentally induced CCL-deficient stifle joints that were stabilized by means of TPLO (TPLO group) or an LFS technique (LFS group) at a mean of 4 and 8 years, respectively, prior to initiation of this study. Inverse dynamics variables were calculated in the sagittal, frontal, and transverse planes for each group of dogs and compared among the 3 groups. Of the variables compared, only 2 had significant differences among the groups; compared with dogs in the control group, the contact angle of the hip joint in the sagittal plane was greater for dogs in the TPLO group and the maximum concentric power of the stifle joint in the frontal plane was greater for dogs in LFS group. Although radiographic evaluation of the pelvic limbs of dogs in the TPLO and LFS groups revealed that all dogs had evidence of osteoarthritis in the CCL-deficient stifle joint, those dogs had similar gait characteristics as the dogs in the control group that had no radiographic evidence of pathology in the pelvis or pelvic limbs. Investigators of other studies15,19,21,22 have compared the short-term outcomes for dogs with CCL-deficient stifle joints that were repaired with TPLO with those for similar dogs that were repaired by an LFS technique. To our knowledge, the present study is the first to assess the 3-D motion of the pelvic limb in dogs that had a TPLO performed at a mean of 4 years prior to evaluation or an LFS technique performed at a mean of 8 years prior to evaluation by means of inverse dynamics and compare that motion with that of the pelvic limb in clinically normal dogs. The angles, moments, and powers of the hock, stifle, and hip joints in the sagittal plane were surprisingly similar among the 3 groups of dogs in the present study. For the dogs in the TPLO and LFS groups, the mean angles for the hock and hip joints were slightly more extended throughout the stance phase than were those for dogs in the control group, although the differences in extension among the 3 groups of dogs were not significant except for the hip joint angle at contact, which was significantly greater for dogs in the TPLO group, compared with that for dogs in the control group. These findings are similar to those of another study16 in which dogs were evaluated at 1, 3, and 6 months after CCL transection and repair. In that study,16 dogs with the CCL-deficient stifle joints walked with the stifle joint more flexed and the hip and hock joints more extended, compared with healthy dogs at a walk. Although the moments and powers of the stifle joint in the sagittal plane did not differ significantly among the 3 groups of dogs in the present study, the greater (albeit nonsignificant) extension of the hip and hock joints for dogs in the TPLO and LFS groups relative to that of the dogs in control group could have been the result of compensation for the altered function of the CCL-deficient stifle joint.
Variations in the stifle joint flexor moments in the sagittal plane during the initial 20% of the stance phase among the 3 groups of dogs in the present study were interesting and merit discussion even though they were not statistically significant. During this phase of the gait, the mean flexor moment impulse of the stifle joint for the dogs in the TPLO and LFS groups was increased from that for dogs in the control group. This slight change in the flexor moment for the dogs in the TPLO and LFS groups might indicate that muscles of the caudal aspect of the thigh in those dogs were attempting to stabilize the stifle joint at the point of impact. It would be interesting to study this area of the stifle joint moment curve at various times during recovery after surgical repair of a ruptured CCL. Investigators of another study12 reported that the flexor moment of the stifle joint was reduced in Labrador Retrievers with a recently ruptured CCL. Compared with the Labrador Retrievers of that study,12 the dogs of the present study had more extended hock and hip joints and the hock joint had a smaller excursion. The patterns for joint angles, moments, and power were similar between the Labrador Retrievers of the other study12 and hound-type dogs of the present study; however, the amplitudes of moment and power for the hock joint and the moments for the hip joint differed between the 2 studies. For the dogs of the present study, the flexor moment and the magnitude of the concentric power during the second half of the stance phase were both increased almost 2-fold, compared with those for the Labrador Retrievers of the other study.12
Mean (95% confidence interval) curves of transverse-plane angles (A, B, and C), moments (D, E, and F), and power (G, H, and I) for the hock (A, D, and G), stifle (B, E, and H), and hip (C, F, and I) joints of the dogs in Figure 1. See Figures 1 and 2 for remainder of key.
Citation: American Journal of Veterinary Research 75, 6; 10.2460/ajvr.75.6.554
In the present study, the only variable that differed significantly among the 3 groups of dogs aside from the hip joint angle in the sagittal plane at the onset of the stance phase was the maximum concentric power of the stifle joint in the frontal plane; the maximum concentric power of the stifle joint for the dogs of the LFS group was approximately 8.6 times that for the dogs in the control group. Although the motions and energy absorption and generation patterns in both the frontal and transverse planes were only a fraction of those observed in the sagittal plane, the difference of maximum concentric power between dogs in the LFS and control groups might indicate an altered or pathological gait for dogs with the CCL-deficient stifle joints20,24,25 and should be studied further. Interestingly, the dogs in both the TPLO and LFS groups had stifle joints that were more adducted, compared with the stifle joints of the control dogs, although the extent of that adduction was not significant. This finding is contrary to results of another study,24 in which the stifle joints of dogs 2 years after CCL transection were more abducted, compared with the stifle joints of clinically normal control dogs. It is difficult to compare the results of that study24 with those of the present study because the stifle joints of the dogs in the other study24 were not surgically stabilized and the time from CCL transection to evaluation differed between the 2 studies. Increased adduction of the stifle joint could cause more compression in the medial compartment of the joint. Interestingly, in the present study, the stifle joints for the dogs of the LFS group were adducted less than were the stifle joints for the dogs of the TPLO group, and we speculate that the presence of suture material and subsequent scar tissue on the lateral aspect of the joint for the dogs of the LFS group helped reduce the extent to which the stifle joint could be adducted. The TPLO procedure is designed to inhibit cranial translation of the tibia in the sagittal plane and should have minimal effect on movement of the stifle joint in the frontal and transverse planes. Although most of the variables evaluated did not vary significantly among the 3 groups of dogs in the present study, the differences in the motion of the pelvic limb in the frontal and transverse planes between dogs in the control group and dogs in the TPLO and LFS groups may be clinically relevant. For example, the hip joints of the dogs in the TPLO and LFS groups were maintained in a more adducted position, compared with the hip joints of the dogs in the control group. It is possible that the adduction of the hip joint in CCL-deficient dogs was a consequence of osteoarthritic changes commonly observed in the medial compartment of the stifle joint of those dogs.
Further analysis of the study data for the maximum concentric power of the stifle joint in the frontal plane revealed that the mean value for the dogs in the LFS group was heavily influenced by an extreme observation obtained from 1 of the 6 dogs in that group. The stifle joint of that dog had a consistent peak of concentric power, whereas the stifle joints for the other dogs in the LFS group had a small peak in concentric activity followed by a gradual decrease in power. Review of the videotapes and other trial data for that dog revealed no aberrant movement or extreme kinetic or kinematic measurements. This highlights a limitation of the small sample size of the LFS group; data from only 1 of 6 dogs greatly affected the mean value for the maximum concentric power of the stifle joint in the frontal plane for the LFS group and caused that value to differ significantly from the corresponding mean values for the control and TPLO groups. Another interpretation of this result is that the power calculation in the frontal plane has little information content, especially given that the magnitude of the power in the frontal plane is so much smaller than that in the sagittal plane.
Internal rotation of the stifle joint in the transverse plane was observed for the first half of the stance phase for all 3 groups of dogs in the present study. Although the extent of that rotation did not differ significantly among the 3 groups, there were small discrepancies in the waveforms for each group, which could be related to subtle changes in the arthritic or CCL-deficient stifle joints. Regardless, the results of this study suggested that motion of the surgically stabilized stifle joints was similar to that of the clinically normal stifle joints. However, these findings differ from those of another study,24 in which the stifle joints of dogs that underwent CCL transection without surgical stabilization were not internally rotated as much as those of clinically normal dogs.
Chailleux et al20 used a 3-D electromagnetic tracking system to describe the motion of the canine stifle joint immediately after TPLO or LFS surgery was performed on cadaveric pelvic limbs. In that study,20 the tibia of limbs that underwent TPLO or LFS surgery had increased external rotation, compared with the tibia of clinically normal control limbs, and the TPLO limbs had increased adduction, whereas the LFS limbs had increased abduction. It is difficult to compare the results of that study20 with those of the present study given the difference in elapsed time between surgery and evaluation for the 2 studies and the cadaveric versus in vivo nature of the pelvic limbs evaluated. Additional in vivo studies are needed to compare pelvic limb movement between dogs that underwent TPLO and those that underwent an LFS procedure immediately after surgery and beyond.
Ground reaction force is a major factor in the calculation of the moment and power across a joint. In the present study, ground reaction forces and the impulses (area under the curve) in the craniocaudal and vertical directions were compared and did not vary significantly among the 3 groups of dogs. To our knowledge, only 2 studies19,21 have been conducted in which ground reaction forces were measured in dogs following TPLO or an LFS procedure to stabilize the stifle joint subsequent to CCL rupture. In 1 study,21 mean peak vertical force at a walk did not differ significantly between dogs that underwent TPLO and those that underwent an LFS procedure at 6 months after surgery. In that study,21 only 7 of 64 (10.9%) dogs that underwent TPLO and 7 of 47 (14.9%) dogs that underwent an LFS procedure had returned to normal function at 6 months after surgery as determined by measurement of ground reaction forces and impulses, whereas in the present study, all dogs in the TPLO and LFS groups had returned to normal function, albeit at a mean of 4 and 8 years after surgery, respectively. It is possible that 6 months is an insufficient amount of time after stifle stabilization surgery for most dogs to attain normal function. Results of another study,19 in which dogs that underwent either TPLO or an LFS procedure were serially evaluated for 2 years after surgery, revealed that mean peak vertical force did not vary significantly between the 2 groups of dogs. Results of still other studies indicate peak vertical forces and impulses at a trot for dogs with surgically transected CCLs that were repaired by TPLO28 or an LFS procedure29 returned to values similar to presurgical values at 18 and 20 weeks after surgery, respectively. In an experimental model30 of stifle joint osteoarthritis that involved dogs with surgically transected CCLs that did not undergo stifle joint stabilization, ground reaction forces at a trot were determined to be a reasonable means to evaluate return to function after injury. The investigator of that study30 found that the peak vertical force of the affected limb of those dogs tended to plateau beginning at 10 months after CCL transection and changed very little up to 2 years after CCL transection.
The present study had several limitations. The small sample size, particularly for the control and LFS groups, reduced the power of the study and resulted in variable estimates that were extremely sensitive to outlier measurements. For example, we believe the reason that the mean maximum concentric power of the stifle joint in the frontal plane for the dogs in the LFS group was significantly greater than that for the dogs in the control and TPLO groups was because an extreme measurement obtained from 1 of the 6 dogs in the LFS group inflated that variable mean for that group. Evaluation of numerous measurements might have resulted in spurious associations being identified as statistically significant. Because of laboratory constraints and equipment availability, only 1 side of each dog could be evaluated during a trial, and it is unknown whether evaluation of study dogs over numerous days had any effect on the data collected. Serial radiographs of the pelvic limbs of the study dogs were not obtained to assess the progression of radiographic signs of osteoarthritis because such evidence is a poor predictor of a dog's ability to bear weight on the affected limb31; however, serial radiographic evaluation of the dogs in the TPLO and LFS groups might have been useful for detection of differences in the rate of progression of osteoarthritis in the stifle joint between the 2 groups.
In this study, discrete kinetic and kinematic variables were compared among the 3 groups of dogs, which resulted in a vast amount of data. Other methods such as such as principle component analysis,32 polynomial equations,33,34 Fourier analysis,16,35–37 and generalized indicator function analysis38 have all been successfully used to study gait waveforms, and use of those methods might have identified differences among the 3 groups of dogs that were undetectable by the discrete variable analysis used. Additionally, morphometric data for Labrador Retrievers obtained from another study5 were used for the inverse dynamics calculations for the hound-type dogs evaluated in the present study, and we are unsure how this may have affected our results. Although inverse dynamics calculations for human subjects often use morphometric data from a historic database for a population of limited-size, morphometrics vary greatly within species of veterinary interest, and breed-specific morphometric data would have provided more accurate inverse dynamics results. However, in inverse dynamics, morphometric data are required only for calculation of inertia, which has a very small effect on joint moment and power. Calculation of joint moments and powers are dependent primarily on ground reaction forces and the estimate of the center of rotation for the joint being evaluated. Finally, the dogs of the present study differed from dogs that typically develop CCL injury. It is unlikely that the relatively limited activity of study dogs mimicked that of active or working dogs in the general population. Moreover, the dogs in the TPLO and LFS groups underwent stifle joint stabilization immediately after CCL transection and did not have a period of stifle joint instability during which secondary osteoarthritis could develop as is typically observed in dogs with naturally occurring CCL disease. Although the postoperative recovery period for the study dogs was likely more controlled than that for most clinical patients, all of the dogs in the this study had similar housing and activity levels; therefore, it was reasonable to compare dogs in the control group with the dogs in the TPLO and LFS groups.
In the present study, inverse dynamics, a novel approach for analysis of gait biomechanics, was used to compare the 3-D motion of the pelvic limb among clinically normal dogs and dogs with experimentally induced CCL-deficient stifle joints that had been stabilized with a TPLO or LFS procedure at a mean of 4 and 8 years, respectively, prior to evaluation. Results indicated that the gait characteristics of dogs in the TPLO and LFS groups did not differ significantly, a finding that was similar to results of other studies15,19,21,22,24 and suggested that neither procedure was superior to the other. Furthermore, the gait characteristics for the dogs in the TPLO and LFS groups several years after stifle joint stabilization were generally similar to those of dogs in the clinically normal control group. Both the TPLO and LFS procedures successfully provided long-term stabilization of CCL-deficient stifle joints with minimal alterations to gait characteristics.
ABBREVIATIONS
| CCL | Cranial cruciate ligament |
| LFS | Lateral fabellar–tibial suture |
| TPLO | Tibial plateau leveling osteotomy |
Vicon Motion Systems Inc, Centennial, Colo.
American Mechanical Technology Inc, Watertown, Mass.
Acquire 7.3, Sharon Software Inc, Dewitt, Mich.
Peak Performance Technologies Inc, Centennial, Colo.
Combine, Sharon Software Inc, Dewitt, Mich.
Visual 3D, C-Motion Inc, Germantown, Md.
VB_V3D and VB_Tables, version 1.50, University of Tennessee, Knoxville, Tenn.
SAS, version 9.2, SAS Institute Inc, Cary, NC.
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