A degenerative knee joint may cause pain while it is used, joint stiffness, swelling, weak muscles, and difficulty in walking, going up stairs, or getting up from a chair. Avoiding movement out of fear of pain may make one even weaker and less able to function. But exercise that is too difficult, or whose level is increased unsuitably, may also trigger the symptoms.
Hydrotherapy, or exercise in water, is another environment for training movement, strength, balance, and walking in selected patients. Buoyancy helps reduce the apparent weight when the body is in the water, while the resistance of the water changes the force used in moving, so it may make exercising easier. But water does not remove all the force on the knee joint or make rehabilitation free of risk.
Exercise is still the main treatment
Therapeutic exercise should be adjusted according to the symptoms, the function, the goals, and the accompanying diseases of each person. It may consist of increasing the strength of the muscles of the thigh and the hip, aerobic exercise, balance, gait training, and activities that are really used.
It is not necessary to wait until the pain has gone before beginning to exercise. There may be some discomfort when the programme begins, and the response should be used to determine the starting amount and the increase in level. If the pain is severe, increases continuously, or is still much worse after training, it should be assessed again.
The NICE guideline states that therapeutic exercise, information and support, as well as managing weight where suitable, are the main care for degeneration. In general it is diagnosed from the symptoms and the physical examination, and imaging is not needed as a routine, unless there are abnormal features or another disease is suspected (NICE (opens in a new tab))
What may exercise in water help with
Buoyancy and adjusting the load-bearing force
The degree of reduction of the load-bearing force changes according to the depth of the water and the posture of the body. The therapist can adjust the water level, the range of movement, the speed, and the external support in order to find a starting point that can be tolerated. The words "reduced load-bearing" are therefore more correct than "no impact".
Resistance and water pressure
Moving through water has a resistance that changes according to the speed, the surface area, and the direction, so it can be used to increase the level of the exercise. But the resistance of the water does not replace a strengthening plan whose amount can be measured.
Water pressure may change the distribution of fluid and make some people feel supported, but it should not be claimed that it treats inflammation or swelling in everyone. Warm water may help one feel more comfortable, but the temperature also changes the load on the heart and the blood vessels, so it must suit the health of the person and the guidelines of the facility.
What does the evidence say?
A systematic review of 2023 of 22 randomised trials, including 1,394 participants, found that exercise in water made the pain, the joint stiffness, and the function better immediately at the end of the treatment compared with no exercise, but found no significant difference between exercise in water and on land in these outcomes, and no study reported serious adverse events related to the treatment (PubMed (opens in a new tab))
A Cochrane review of 13 studies, 1,190 participants, found small short-term benefits for pain, impairment, and quality of life compared with the control group. Most participants had a degenerative knee or hip joint with symptoms at a slight to moderate level, so the results should not be extended to every stage or every accompanying disease (Cochrane (opens in a new tab))
These reviews studied several forms of exercise in water. They are not evidence specific to one clinic, pool, or model of underwater treadmill, and they do not confirm that training in water creates new cartilage, puts right the pattern of walking permanently, prevents falls, or is superior to a suitable programme on land.
How does an underwater treadmill differ from training in a pool?
An underwater treadmill makes it possible to train walking repeatedly at a set belt speed together with adjusting the water level. Some systems may be able to adjust the incline, the water current, or other resistance. These features depend on the equipment installed and must be checked clearly.
A treadmill is not automatically better than supervised training in a pool. The possible benefit is repeating a specific activity and being able to observe the walking more easily. The goal should be changes that can be measured, such as tolerance in walking, the quality of the step, strength, or confidence, which can be carried over to activities on land.
See further information about hydrotherapy with an underwater treadmill
A rehabilitation plan that increases in level
- Assess: confirm the clinical diagnosis, and review the pain, swelling, the range of the joint, strength, balance, walking, medicines, the skin, and the medical risks
- Set goals: choose functional outcomes, such as walking further, using stairs, or getting up from a chair
- Determine the starting amount: choose the water level, the exercise postures, the speed, the support, and the duration that the patient can tolerate
- Increase the level: gradually increase one or several variables, and add strengthening and activities on land
- Assess again: compare the symptoms and the function with the outcomes agreed; adjust or stop the training in water if there is no benefit
Hydrotherapy should not be the end point when the patient's goals are on land. Some people may continue exercising in water because they like it, while others use it temporarily before moving on to activities on land.
Medical treatment and imaging
Medicine, or injection, may be used together with exercise in some cases, but it is not a condition that every patient must receive before beginning rehabilitation. The choice depends on the symptoms, the contraindications, previous treatment, and shared decision-making.
NICE advises that when medicine is necessary, it should be used together with care that does not use medicine, using the lowest dose that works for the shortest period. It does not recommend hyaluronan injection into the joint for degeneration, and it states that corticosteroid injection may be used to reduce the symptoms in the short term, about 2–10 weeks, when other medicines have not worked or are not suitable, or in order to help participation in therapeutic exercise. The guidelines may differ according to the country and the situation of each person.
Ultrasound or other imaging may be useful when the character of the symptoms is abnormal, changes unexpectedly, or another disease is suspected. An image alone should not determine tolerance of exercise or the necessity of every kind of treatment.
Who may or may not be suitable?
Exercise in water may be considered when training on land is difficult because of pain, low tolerance of load-bearing, reduced capacity, limitations of balance, or fear of movement. Suitability also depends on safe access to the pool, and the ability to get into the pool, get out of the pool, and follow instructions.
Precautions or reasons to postpone the training may consist of:
- An open or discharging wound, contagious skin disease, or an infection that is still active
- Fever, vomiting, diarrhoea, or being unable to control continence
- Heart, lung, blood pressure, or metabolic disease that is not stable
- Great difficulty breathing, fainting, seizures that are not controlled, or another medical state that is not stable
- Being unable to get into or out of the pool safely with the help available
Immersion in water changes the load on the cardiac and respiratory systems. The doctor should assess readiness and the rules of the facility. A single general list of contraindications should not be used with everyone.
When should the knee be assessed further?
There should be an urgent assessment after a severe accident, being unable to bear weight, a hot red swollen joint, fever, suspicion of infection, an acutely locked knee, swelling increasing quickly, or a new swollen calf together with difficulty breathing.
If the symptoms are continuous so that the quality of life is greatly affected, the diagnosis and the choices of treatment should be reviewed. A referral for joint replacement surgery may be considered when pain, joint stiffness, reduced function, or deformity of the joint greatly affects life, and suitable care without surgery has not worked or is not suitable. Rehabilitation may still have a role before and after surgery.
Frequently asked questions
Is hydrotherapy good for a degenerative knee joint?
It may give small short-term benefits and be a tolerable choice of exercise for some patients, but it is not necessary or superior for everyone.
Does an underwater treadmill reduce the force on the knee joint?
Immersion in water reduces the apparent weight, but the degree of reduction depends on the depth, the posture of the body, the pattern of walking, the speed, and the factors of each person. The knee joint is not relieved of all force.
Can hydrotherapy replace exercise on land?
Some people may use water as part of long-term activity, but in general training on land is still needed when the goal is to go up stairs, walk outside the house, or do other daily routines on land.
If the knee hurts, should exercise be stopped?
It does not have to be stopped every time. There may be slight discomfort at a level that is acceptable, particularly in the initial period. But if the pain is severe or increasing, there is a lot of swelling, the knee is unstable, or the flare-up lasts a long time, the amount should be adjusted and it should be assessed again.
How many sessions are needed?
There is no fixed number of sessions. The frequency and the duration depend on the goals, the response, access, and the accompanying exercise. Progress should be judged from the symptoms and the function, not from completing a package that has been determined.