Biomechanical effects of hydrotherapy on canines.

February 23, 2023

A comparison of the dry and wet treadmill and its impact on stifle flexion during walk and at increased speeds in canines. By Rory Thirlby-Flynn


Cranial cruciate ligament ruptures have become one of the most prevalent orthopaedic conditions within the veterinary industry (Christopher, Beetem, & Cook, 2015), leading to the necessity of an efficient method of exercising the stifle joint. Hydrotherapy has solidified itself as a significant therapy modality within veterinary science (Tomlinson, 2012), utilising the properties of water (Torres-Ronda & I del Alcázar, 2014) to successfully rehabilitate a variety of different conditions throughout conservative and post-operative treatment.

Due to the known antagonistic muscle pairing throughout the canine pelvic limbs (Ellis et al., 2018), it can be suggested that loss of stifle flexion, which is commonly observed in cases of cranial cruciate ligament rupture (Jandi & Schulman, 2007), could lead to a cascading effect throughout the entirety of the hind quarters gait pattern, and if not managed, could result in damaging compensatory, thus destabilising the hock and hip, as demonstrated within humans by Shah (2008). As the hindlimb is the primary mover for a canine (Williams et al., 2008) a large amount of motion is dependent on fluid kinematics of the stifle and its corresponding joints, and as such it is essential to ensure the efficient exercise and management of the stifle joint, as shown in research on humans by Fleckenstein et al., (1988), which found that conditions that limited knee flexion, such as arthritis, caused accelerated hip joint damage.

An improvement of research surrounding the kinematics of a canine patient throughout hydrotherapy exercise can further demonstrate its impact on stifle movement, thus demonstrating whether it can make a true and reliable method of treating and managing several stifle-based conditions.


To assess hydrotherapy’s true effects, eight healthy canines had their stifle flexion measured by utilising markers on three key bony landmarks; the greater trochanter (Hip), patella, and hock. Each canine was walked for one minute on the dry treadmill, followed by a one-minute break before walking at an increased speed for thirty seconds. This was repeated for a wet treadmill at a water height of hip level. Stifle angles were measured using Dartfish gait analysis software.

Whilst walking on a dry and wet treadmill, a mean stifle flexion of 89.2o and 59.4o was observed, respectively. The differences between the averages for dry and wet treadmill stifle flexion angle gave a p value of 0.001 and a t value of 5.559. The increase speed for dry treadmill gave a mean stifle flexion of 93.2o. The differences between the averages for dry walk and dry increased speed stifle flexion angle gave a p value of 0.023 and a t value of -2.639. The increase speed for wet treadmill gave a mean stifle flexion of 56o. The differences between the averages for wet walk and wet increased speed stifle flexion angle gave a p value of 0.038 and a t value of 2.240. These results demonstrate that when water is introduced during a hydrotherapy session, then stifle flexion increases. Also, in a dry treadmill, when the speed was increased, stifle flexion decreased, however when speed was increased in a wet treadmill, stifle flexion increased.


These results can be interpreted in several ways to aid development of aspects of a rehabilitation plan, such as altering the method of exercise, with either wet or dry treadmill. As per the results, to increase stifle flexion, hydrotherapists can utilise the effect of water introduction, and it is suggested that this can cause a reduction in certain orthopaedic conditions such as cranial cruciate ligament rupture, as noted by previous studies (Pinna et al., 2021).

While the primary purpose of the research was to evaluate hydrotherapy’s application in range of motion-based conditions, the gained knowledge of how the limbs moved can also be applied to other aspects of canine rehabilitation such as muscle activation. Results by Griffon (2010) suggest that an increase in stifle flexion creates a greater contraction of the antagonistic muscle pairing with the hamstrings and quadriceps, and as demonstrated above, this increase in stifle flexion can be achieved with the introduction of water and increase of speed in water. Furthermore, the findings of Brown et al., (2020) showed that the kinematics of canine stifle flexion result in the hindlimb undergoing hip flexion, moving the quadriceps nearer to the canine’s torso and so being placed back down from a greater height, thus increasing the contraction of the bicep femoris’ tibial and calcaneal portions. This demonstrated increase of contraction for the named muscles would aid in limiting atrophy from occurrences of orthopaedic conditions such as cranial cruciate ligament rupture.

While every precaution was taken to ensure the reliability of the results, limitations were still present such as a relatively small sample size, as well as the reliability of the use of skin surface markers for making assumptions on joint angle locomotion.

Stifle conditions are one of the most prevalent orthopaedic injuries and diseases within veterinary medicine. This research set out to discover the effects of differing conditions of an aquatic treadmill on stifle range of motion, and it was discovered that flexion increased in a wet treadmill when compared to a dry treadmill. It was also demonstrated that in an increased speed dry treadmill the stifle flexion decreased, and when treadmill speed was increased in a wet treadmill the stifle flexion increased. To further develop the understanding of hydrotherapy’s application on stifle injuries, future research should consider a greater variety of speeds and depths within the treadmill, as well as evaluating more planes of motion, and implementing biomechanical analysis methods with a greater objectivity.


Brown, N. P., Bertocci, G. E., States, G. J. R., Levine, G. J., Levine, J. M., & Howland, D. R. (2020) Development of a canine rigid body musculoskeletal computer model to evaluate gait. Frontiers in Bioengineering and Biotechnology.

Christopher, S. A., Beetem, J., & Cook, J. L. (2015) Comparison of long-term outcomes associated with three surgical techniques for treatment of cranial cruciate ligament diseases in dogs. Veterinary Surgery. 42(3). 329-334.

Ellis, R. G., Rankin, J. W., & Hutchinson, J. R. (2018) Limb Kinematics, Kinetics and Muscle Dynamics During the Sit-to-Stand Transition in Greyhounds. Frontiers in Bioengineering and Biotechnology. 6(1). 162.

Fleckenstein, S. J., Kirby, R. L., & MacLeod, D. A. (1988) Effect of limited knee-flexion range on peak hip moments of force while transferring from sitting to standing. Journal of Biomechanics. 21(11). 915-918.

Griffon, D. J. (2010) A review of the pathogenesis of canine cranial cruciate ligament disease as a basis for future preventative strategies. Veterinary Surgery. 39(4). 399-409.

Jandi, A. S. & Schulman, A. J. (2007) Incidence of motion loss of the stifle joint in dogs with naturally occurring cranial cruciate ligament rupture surgically treated with tibial plateau leveling osteotomy: Longitudinal clinical study of 412 cases. Veterinary Surgery. 36(2). 114-121.

Pinna, S., Lanzi, F., & Tassani, C. (2021) The effects of cranial cruciate ligament rupture on range of motion in dogs. Veterinary Sciences. 8(1). 119.

Shah, N. (2008) Increasing Knee Range of Motion Using a Unique Sustained Method. North American Journal of Sports Physical Therapy. 3(2). 110-113.

Tomlinson, R. (2012) Use of canine hydrotherapy as part of a rehabilitation programme. The Veterinary Nurse.

Torres-Ronda, L. & i del Alcázar, X. S. (2014) The properties of water and their applications for training. Journal of Human Kinetics. 44(1). 237-248.

Williams, S. B., Wilson, A. M., Rhodes, L., Andrews, J., & Payne, R. C. (2008) Functional anatomy and muscle moment arms of the pelvic limb of an elite sprinting athlete: the racing greyhound (Canis familiaris). Journal of Anatomy. 213(4). 361-372.


1 comment

Jun 08, 2023
Paula Teal

I like to have seen what the results had been had the hydrotherapy been done in a pool and not a treadmill.

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