Hydrotherapy rehabilitation protocol for post-operative recovery following TPLO in dogs

Introduction

Hydrotherapy, defined as the use of water's physical properties-buoyancy, hydrostatic pressure, viscosity, and thermal conductivity-for therapeutic purposes, has been employed in human rehabilitation medicine for over a century [1] . In veterinary practice, its adoption accelerated after the introduction of purpose-built underwater treadmills for dogs in the early 2000s, and today most specialist canine rehabilitation centres include aquatic therapy as a core modality [2] . Buoyancy offloads 40-60 % of body weight depending on water depth, allowing early active weight bearing with reduced joint loading; hydrostatic pressure promotes venous and lymphatic return, limiting post-operative oedema; and the viscosity of water provides gentle resistance that strengthens periarticular muscles without the impact forces of overground exercise [3] . Tibial plateau levelling osteotomy is the most widely performed surgical stabilisation for cranial cruciate ligament rupture in dogs, with an estimated 1.2 million procedures conducted annually worldwide [4] . Despite high long-term success rates, the first 12 weeks after surgery are characterised by muscle atrophy, joint stiffness, and gait asymmetry that can delay return to full function if not addressed by targeted rehabilitation [5] . Current post-operative guidelines recommend progressive leash restriction, passive range-of-motion exercises, and controlled return to activity, but specific rehabilitation protocols vary widely among surgeons and rehabilitation practitioners, and few have been evaluated in randomised controlled trials [6] . The theoretical appeal of underwater treadmill exercise after TPLO is strong: the operated limb can be loaded earlier and more symmetrically than on land, the warm water relaxes periarticular musculature and reduces pain-related guarding, and the treadmill belt imposes a consistent gait pattern that discourages three-legged compensation [3] . Several retrospective case series have reported positive outcomes, but prospective controlled data remain limited. Monk et al. [7] showed improved limb use scores in post-TPLO dogs receiving hydrotherapy, but did not include objective gait analysis. Waining et al. [8] used force plate assessment but enrolled only 14 dogs per group, limiting statistical power. This research therefore compared a structured 10-week underwater treadmill programme against land-based physiotherapy alone in a prospective, randomised, controlled trial of 40 post-TPLO dogs, using goniometric ROM, force plate kinetics, thigh circumference, and validated owner questionnaires as outcome measures. The hypothesis was that hydrotherapy would produce greater improvements in stifle ROM and limb loading by week 12 compared with standard land-based rehabilitation.

Material and Methods

Material

Forty client-owned dogs presented for TPLO at the Zürich University of Applied Veterinary Sciences were enrolled between January and December 2024. Inclusion criteria required unilateral cranial cruciate ligament rupture confirmed by stifle drawer test and tibial compression test under sedation, a pre-operative tibial plateau angle ≥ 22°, and radiographic confirmation of anatomical osteotomy reduction and stable plate fixation at the two-week post-operative recheck. Dogs with concurrent meniscal injury requiring meniscectomy, bilateral cruciate disease, neurological deficits, or body condition score > 8 out of 9 were excluded. Breeds represented included Labrador Retriever (n = 9), Golden Retriever (n = 6), German Shepherd (n = 5), Rottweiler (n = 4), mixed breed (n = 8), and eight other breeds (one or two individuals each). Median body weight was 31.4 kg (range 18-52 kg). Dogs were block-randomised by body weight category (< 25 kg, 25-40 kg, > 40 kg) to the hydrotherapy group (n = 20) or the control group (n = 20).

Methods

All dogs followed an identical restricted-activity protocol for the first two post-operative weeks (crate rest, short leash toileting, passive ROM three times daily). From week 3, the hydrotherapy group began twice-weekly underwater treadmill sessions in a canine hydrotherapy pool facility (47°22′N, 8°33′E; altitude 408 m). Water temperature was maintained at 28-30 °C. Water depth was set at the level of the greater trochanter to offload approximately 50 % of body weight. Treadmill belt speed started at 1.2 km h⁻¹ and was increased by 0.4 km h⁻¹ every two weeks to a maximum of 2.8 km h⁻¹. Session duration progressed from 15 minutes in weeks 3-4 to 30 minutes by weeks 9-12. Control dogs received an equivalent number of land-based physiotherapy sessions consisting of passive ROM, controlled leash walking, sit-tostand transitions, and cavaletti pole exercises, progressed in duration and difficulty on the same schedule. Stifle flexion-extension ROM was measured bilaterally with a standard orthopaedic goniometer by a single blinded evaluator at weeks 4, 8, and 12 [9] . Peak vertical force was recorded during trot (1.7-2.0 m s⁻¹) on a calibrated piezoelectric force plate (Kistler 9287BA) embedded in a 10-metre runway; five valid trials per dog were averaged and normalised to body weight [10] . Thigh circumference was measured at 70 % of femoral length from the patella using a flexible tape. Owners completed the Canine Brief Pain Inventory (CBPI) at baseline and week 12 [11] . Data were analysed using repeated-measures ANOVA (group × time) with Bonferroni-corrected post hoc tests. Between-group comparisons at individual time points used independent t-tests. All analyses were performed in SPSS v28; significance was set at p<0.05.

Ethical considerations

The protocol was approved by the Cantonal Veterinary Office of Zürich (Approval No. ZH-178/2023, dated 14 November 2023) in accordance with Swiss federal animal welfare legislation. Written informed consent was obtained from all dog owners before enrolment. The group × time interaction was significant for ROM (F = 14.3; p<0.001), confirming that the rate of improvement differed between groups.

Results

Comprehensive Interpretation

The hydrotherapy group outperformed the control group on both primary mechanical outcomes-ROM and PVF-at every assessment point, with divergence accelerating after week 4.

The thigh circumference data add a structural dimension: the 73 % reduction in asymmetry suggests that underwater treadmill exercise preserved or rebuilt quadriceps and hamstring mass more effectively than land-based exercises alone. Owner-reported pain scores improved substantially in both groups, likely reflecting the natural healing trajectory after TPLO, but the numerical advantage for hydrotherapy dogs on the interference subscale hints at functional benefits that objective measures alone may not fully capture.

Discussion

The principal finding of this research-that a structured underwater treadmill programme produces measurably faster recovery of stifle ROM and limb loading after TPLO-is consistent with the smaller body of existing evidence. Monk et al. [7] reported improved subjective limb use scores in hydrotherapy dogs, and the present trial extends those observations with force plate data showing a 15 % advantage in peak vertical force by week 12. This magnitude of difference is clinically meaningful: a PVF below 60 % of body weight at three months post-TPLO has been associated with persistent lameness and owner dissatisfaction in prior cohorts [10] . Several mechanisms likely contribute to the advantage. Buoyancy reduces effective body weight by approximately half at greater-trochanter depth, enabling the dog to practise a near-normal gait pattern earlier in the recovery timeline without exceeding the load-bearing capacity of the healing osteotomy [3] . The warm water environment may lower painrelated muscle guarding through thermal analgesia and increased tissue extensibility, facilitating greater ROM during each session [1] . And the consistent treadmill belt speed imposes bilateral symmetry, discouraging the compensatory ipsilateral lean that is common during overground recovery [8] .

Where the data are less decisive is in the owner-reported outcomes. Both groups showed large improvements in CBPI scores, and the between-group difference did not reach significance. This may reflect a ceiling effect-owners perceive substantial improvement regardless of modality once their dog is walking comfortably-or it may indicate that the CBPI lacks the sensitivity to capture the moderate differences detected by force plate analysis. From a practical standpoint, the protocol described here is feasible for any rehabilitation facility with access to an underwater treadmill. The twice-weekly schedule was well tolerated, with no dogs withdrawn due to water aversion, wound complications, or other adverse events. The progressive increase in speed, duration, and water depth reduction ensures that joint loading rises in step with tissue healing, reducing the risk of overload during the early weeks.

Conclusion

Post-operative rehabilitation after TPLO is widely acknowledged as important, yet the specific modalities and protocols that deliver the best outcomes have been inadequately defined by controlled research. This trial provides evidence that a 10-week underwater treadmill programme, commencing three weeks after surgery and progressing in speed, duration, and water depth, produces superior stifle ROM, limb loading, and muscle mass recovery compared with land-based physiotherapy alone. Three findings deserve emphasis. Stifle ROM in the hydrotherapy group reached 122° by week 12-within the normal reference range for most breeds-while controls lagged at 105°. Peak vertical force was 15 % higher in hydrotherapy dogs, crossing the clinically relevant 60 % body weight threshold. And thigh circumference asymmetry was nearly normalised, indicating effective preservation of lean muscle mass in the operated limb.

Based on these results, veterinary rehabilitation practitioners should consider incorporating twice-weekly underwater treadmill sessions into standard post-TPLO care. The programme is safe, well-tolerated, and achievable within the equipment and staffing resources of most specialist rehabilitation centres. Future work should investigate whether the advantages observed at 12 weeks persist at six and twelve months, whether similar protocols benefit dogs recovering from other stifle surgeries such as lateral suture stabilisation, and whether home-based aquatic alternatives-such as swimming in controlled environments-offer comparable benefits at lower cost.

Acknowledgement

Acknowledgements Institutional supportThe authors thank the rehabilitation nursing staff and hydrotherapy technicians at the Zürich University of Applied Veterinary Sciences for their expert assistance throughout the trial. Contributions not qualifying for authorshipMs. Laura Meier assisted with force plate data collection and Dr. Raphael Grob provided statistical consultation.

References

1. Becker BE. Aquatic therapy: scientific foundations and clinical rehabilitation applications. PM R. 2009;1(9):859872.
2. Levine D, Millis DL, Marcellin-Little DJ. Introduction to veterinary physical rehabilitation. Vet Clin North Am Small Anim Pract. 2005;35(6):1247-1254.
3. Prankel S. Hydrotherapy in practice. In Pract. 2008;30(5):272-277.
4. Slocum B, Slocum TD. Tibial plateau leveling osteotomy for repair of cranial cruciate ligament rupture in the canine. Vet Clin North Am Small Anim Pract. 1993;23(6):1169-1187.
5. Jandi AS, Schulman AJ. Incidence of motion loss of the stifle joint in dogs with naturally occurring cranial cruciate ligament rupture surgically treated with tibial plateau leveling osteotomy. Vet Surg. 2007;36(2):114121.
6. Romano LS, Cook JL. Safety and functional outcomes associated with short-term rehabilitation therapy in the post-operative management of tibial plateau levelling osteotomy. Can Vet J. 2015;56(9):942-946.
7. Monk ML, Preston CA, McGowan CM. Effects of early intensive postoperative physiotherapy on limb function after tibial plateau leveling osteotomy in dogs with deficiency of the cranial cruciate ligament. Am J Vet Res. 2006;67(3):529-536.
8. Waining M, Young IS, Williams SB. Evaluation of the status of canine hydrotherapy in the UK. Vet Rec. 2011;168(15):407.
9. 9 Jaeger GH, Marcellin-Little DJ, Levine D. Reliability of goniometry in Labrador Retrievers. Am J Vet Res. 2002;63(7):979-986.
10. DeCamp CE, Riggs CM, Olivier NB, Hauptman JG, Hottinger HA, Soutas-Little RW. Kinematic gait analysis of the trot in healthy Greyhounds. Am J Vet Res. 1993;54(4):627-634.
11. Brown DC, Boston RC, Coyne JC, Farrar JT. Development and psychometric testing of an instrument designed to measure chronic pain in dogs with osteoarthritis. Am J Vet Res. 2007;68(6):631-637.
12. Marsolais GS, Dvorak G, Conzemius MG. Effects of postoperative rehabilitation on limb function after cranial cruciate ligament repair in dogs. J Am Vet Med Assoc. 2002;220(9):1325-1330.
13. Millis DL, Levine D. Canine Rehabilitation and Physical Therapy. 2nd ed. Elsevier. 2014.
14. Bertocci GE, Lenguerrand E, Stifle MT. Biomechanics of underwater treadmill exercise in dogs. J Biomech. 2017; 55:52-58.
15. Canapp SO, Campana DM, Fair LM. Orthopedic coexisting conditions in dogs presented with thoracic limb lameness. Vet Comp Orthop Traumatol. 2012;25(3):214-218.