Hydrotherapy After Total Knee Arthroplasty

Total knee arthroplasty (TKA) is one of the most successful treatments for end-stage knee osteoarthritis. Despite excellent long-term outcomes, many patients experience postoperative pain, reduced knee mobility and difficulty walking during the first weeks after surgery. A 2025 randomized controlled trial compared hydrotherapy after total knee arthroplasty with photobiomodulation therapy (PBMT) and standard physiotherapy to determine which approach best supports recovery.

Why hydrotherapy is beneficial after knee replacement

Early rehabilitation following knee replacement aims to reduce pain, restore knee range of motion and improve walking ability. However, pain and swelling often limit how much patients can comfortably exercise on land.

Hydrotherapy offers a supportive rehabilitation environment where buoyancy reduces weight-bearing, warm water promotes relaxation and hydrostatic pressure may help reduce postoperative swelling. These properties allow patients to begin functional exercises earlier while moving with greater confidence.

Study design

Ninety patients undergoing unilateral total knee arthroplasty were randomly assigned to one of three rehabilitation programmes:

• Hydrotherapy combined with standard physiotherapy
• Photobiomodulation therapy (PBMT) combined with standard physiotherapy
• Standard physiotherapy alone

The hydrotherapy group completed supervised aquatic exercise sessions three times per week for 12 weeks in a therapeutic pool maintained at 33–35°C. Sessions included range of motion exercises, balance training, functional movements and progressive strengthening using water resistance. Outcomes were assessed after six and twelve weeks.

Key findings

Both hydrotherapy and PBMT produced significantly better outcomes than standard physiotherapy alone. However, each treatment demonstrated a different recovery profile.

Greater improvements in knee mobility

Hydrotherapy produced the largest improvements in knee flexion throughout the rehabilitation programme.

After 12 weeks:

• Hydrotherapy improved knee flexion to an average of 122°
• PBMT improved knee flexion to 113°
• Standard physiotherapy reached 105°

These findings indicate that hydrotherapy was particularly effective at restoring knee range of motion during recovery.

Better functional mobility

Functional mobility was measured using the Timed Up and Go (TUG) test.

Patients receiving hydrotherapy achieved the greatest improvements, demonstrating faster walking, improved transfers and better overall mobility than both comparison groups.

The authors concluded that hydrotherapy translated increased knee mobility into meaningful improvements in daily function.

Significant pain reduction

Pain decreased significantly in all three groups.

At six weeks, PBMT produced slightly greater early pain relief than hydrotherapy. By twelve weeks, however, both treatments continued to demonstrate significantly lower pain levels than standard physiotherapy alone.

This suggests that PBMT may be particularly valuable during the early postoperative phase, while hydrotherapy provides sustained improvements throughout rehabilitation.

Improved quality of life

Patients receiving hydrotherapy reported significantly higher scores on the Knee Injury and Osteoarthritis Outcome Score (KOOS), including improvements in:

• Pain
• Physical function
• Knee-related quality of life

Hydrotherapy consistently achieved the highest scores across all KOOS domains after twelve weeks.

Why exercising in water works

Several properties of water contribute to successful rehabilitation after knee replacement surgery.

Buoyancy reduces joint loading

Water supports body weight, allowing patients to practise walking and functional exercises with less stress on the new knee joint.

Warm water promotes comfortable movement

The therapeutic pool temperature of 33–35°C helps relax muscles, reduce stiffness and improve comfort during exercise.

Hydrostatic pressure may reduce swelling

Water pressure provides gentle compression around the knee, which may assist in reducing postoperative oedema while improving movement confidence.

Water resistance strengthens muscles

Natural resistance during movement strengthens the muscles surrounding the knee while avoiding the high-impact forces associated with land-based exercise.

Clinical implications

This randomized controlled trial demonstrates that hydrotherapy after total knee arthroplasty is an effective addition to standard physiotherapy.

The authors suggest that rehabilitation may benefit from a phase-specific approach:

• PBMT may be most valuable during the early postoperative phase when pain control is the primary goal.
• Hydrotherapy appears particularly effective during the following weeks, when restoring knee mobility, walking ability and functional independence becomes the focus.

Combining both interventions at different stages of rehabilitation may further optimise patient outcomes, although additional research is needed to confirm this approach.

Conclusion

This randomized controlled trial demonstrates that hydrotherapy after total knee arthroplasty significantly improves knee range of motion, functional mobility and knee-related quality of life compared with standard physiotherapy alone.

While photobiomodulation therapy provided greater early pain relief, hydrotherapy delivered superior functional recovery by twelve weeks. These findings support the integration of hydrotherapy into comprehensive rehabilitation programmes following total knee replacement surgery.