For patients recovering from hip surgery, aquatic therapy provides the perfect rehabilitation environment.

Your patient spent December trying to ward off pain in bed or in that comfortable (ugly) recliner. He finally decided to bite the bullet and have that hip surgery his doc had suggested a year ago. The doctor warned: “It’s going to be 3 months of just plain hard work.”

But you have an idea that rehab isn’t going to be quite as tough as it could be. Why? You’ve got a pool in your pocket and you know how to use it. Water offers a therapeutic environment, which can be harnessed by a skilled therapist to permit activities for the postoperative patient. The unique properties of water are both difficult and clinically impractical to achieve on land. Take a moment to examine these properties one by one.

Buoyancy

Archimedes’ principle states, “When a body is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of fluid displaced.” This upthrust, or buoyancy, can be used to provide either assistance or resistance to movement depending on the position of the patient’s body. This tendency to float counterbalances gravity and supports the body, resulting in an apparent reduction in weight.

This can provide relief from compressive forces on painful joints. It is, therefore, possible for the postoperative patient to stand, even walk, with reduced pain without external support or abnormal protective mechanisms in the water. Thus, the patient can initiate “normal” weight-bearing tasks, such as gait, transfers, and balance drills, immediately after surgery and offset any deconditioning effects of immobility or reduced movement.

Even better? This reduction in compression creates an environment in which weight    bearing and joint compression can be applied in a graded or progressive manner. Weight bearing may be systematically reduced by increasing the amount of the body submerged.

Static (standing) immersion at the level of the anterior superior iliac spine (ASIS) reduces weight to 40%–56% of normal. Be careful though, all bets are off when the patient moves. During slow walking, patients must be immersed to the clavicle to reduce weight bearing to 50%, and during fast walking, patients must be immersed deeper than the xiphisternum in order to reduce weight that much. 

Buoyancy can be used to create:

• A decrease in weight bearing through joints;

• A decrease in joint stress;

• A decrease in splinting or guarding of antigravity muscles;

• An increase in freedom of movement.

Hydrostatic Pressure

Pascal’s Law states that, “Fluid pressure is exerted equally on all surfaces of an immersed body at rest at a given depth.” In essence, hydrostatic pressure increases the pressure on the outside of an immersed standing body, resulting in:

• A reduction in edema in the lower extremities (by providing graduated pressure at greater depths);

• An offsetting of blood pooling in lower extremities (and thus a reduction in the risk for postoperative clotting);

• A desensitization effect (by constantly stimulating phasic receptors).

This means the postoperative patient can be relieved of some of the potential for swelling and clotting problems associated with surgery.

Viscosity

Viscosity is nothing more than the inherent friction that exists between molecules of a liquid, which cause a resistance to flow. Water is more viscous than air; thus, it takes more force to push through water molecules than to push through air molecules.

Additionally, the faster an object is pushed through the water, the more turbulence is created; this creates additional resistance to movement. Keep in mind that the postoperative patient has probably already lost a great deal of proprioception.

First, his joint has been worn down, perhaps to bone on bone and has lost its normal weight-bearing feedback capacity. Second, the joint is further traumatized by surgical intervention. It seems likely that movement in water can offer patients exaggerated input from the environment—perhaps resulting in enhanced proprioception.

When an object moves through a fluid, there is an increase in pressure in the front of the object combined with a reduction in pressure in the back. This results in the water wanting to move from an area of high pressure to an area of low pressure. The area of negative pressure is known as the wake. Eddy currents form in this wake and drag the object back. The negative pressure (or drag) behind a moving object (the wake) is responsible for 90% of the impedance of movement. The bow wave (positive pressure in front of the object) is only responsible for only 10% of the impedance. 

The principle of flow can be used therapeutically to increase or decrease the force necessary to push through the water. This property can be used to create a progressive resistive exercise program that is three-dimensional, velocity specific, and safe.

Refraction

Refraction is the prism effect that is evident when looking from an air medium to a water medium. Light bends when its rays move from a more dense to a less dense substance. Most of the “therapeutic” effects of refraction are negative. Refraction decreases depth perception and makes the pool seem shallower. It alters visual cues for both patient and provider. Patient’s limbs look distorted (bent away), and items seem high and to the right, thus making visual feedback and monitoring more difficult.

For the postoperative patient, it is possible to use refraction therapeutically. For instance, while immersed, a patient with a habitual visual method of joint placement (eg, someone who looks at his feet to walk) may be forced to use his proprioceptive system instead.

Thermal Shifts

At temperatures above “thermoneutral” (approximately 93°F at rest), body temperature increases due to the body’s reduced ability to dissipate heat through the skin. Energy exchange between a submerged body and the water occurs through both convection and conduction. Thermal energy is also exchanged between the body and the air through radiation and evaporation—methods that become more critical if the total body is immersed and the water temperature prevents heat dissipation from occurring during aquatic exercise. Therapeutic pools are usually heated between 92°–97°F.

Immersion in water warmer than the skin will result in a rise in superficial tissue temperature, which creates a palliative effect like that experienced during the therapeutic use of paraffin, Fluidotherapy, and moist heat. Additionally, immersion in thermoneutral water will produce a generalized relaxation effect similar to that experienced with swaddling or bundling of a body part. 

Special Considerations

Take a moment to examine the following to ensure you will provide the best care to your patients with hip conditions.

• If the patient is uncomfortable or anxious in water, the resulting mus- cular bracing and splinting may make pain worse.

• If the patient has undergone total hip replacement surgery with a posterior

approach, extreme caution must be taken to avoid contraindicated positions (hip internal rotation, adduction, and flexion above 90°).

The freedom of movement possible in water may allow the patient to perform movements that should not be performed.

• If the patient has a surgical suture site or an open wound, a decision must be made as to when to permit the patient in the pool. This decision is based on a risk-benefit ratio.

• If the patient’s skin is delicate and in danger of maceration, or if the wound is draining, there must be a very compelling reason (benefit) for taking the patient into the pool.

• If the wound is clean and healing and is covered with a bio-occlusive dressing, there is little risk involved in taking the patient into the pool, so the benefit does not have to be as great.

• If the patient is immersed, care must be taken to thoroughly dry the surgical site after immersion.

• If the patient is incontinent of bowel,

he must be on a bowel program before allowing him into the pool. Incontinence of urine is not a reason to disallow aquatic therapy.

 Designing Programs

There are many considerations when designing an aquatic therapy program for this population.

• Start any new patient in water that is no deeper than what he can com fortably stand. Remember that fear can contribute to muscle guarding, which can increase pain. Provide equipment for buoyancy assistance (such as an aqua-stick or a floatation barbell) so the patient does not require the therapist’s assistance to feel safe.

• Provide more warm-up time at the beginning of each treatment to allow injured/repaired joints to warm up (from the synovial fluid bathing the joint).

• Make sure you increase progressive resistive exercise (PRE) gradually to prevent delayed onset muscle soreness or dislocation of a new hip.

• Increase weight bearing progressively by moving the patient to shallower water to return the patient to functional (land-based) status as soon as it is feasible to do so.

• If at all possible, the water tempera- ture should be at least 93°F (thermoneutral) for pain palliation.

• Don’t neglect aerobic conditioning in this population as there is a strong relationship between aerobic exercise and pain palliation. However, you should always be sure the patient understands his target heart rate zone for aquatic exercise is a minimum of   12–17 beats per minute lower than its land-based counterpart. 

Goals for Aquatic Therapy

The therapist who is not familiar with working with patients who are post–hip surgery may set unrealistic goals. Goals that would be appropriate include:

• Rehabilitation of traumatized tissues by applying graded and progressively more taxing stresses on injured tissue;

• Improvement in strength or preven- tion of muscle atrophy;

• Improvement in flexibility or preven- tion of contractures;

• Improvement in posture;

• Improvement in ability to perform ADLs;

• Decrease in fatigability;

• Improvement in exercise tolerance;

• Improvement in work tolerance or duration;

• Prevention of loss of cardiovascular fitness immediately after surgery;

• Decrease in complaints of pain;

• Improvement in gait parameters;

• Improvement in balance, reaction time, and safety during ambulation;

• Prevention of lower extremity blood stasis or clots.

Benefits of Aquatic Therapy

Therapists cannot choose to place patients in the water simply because they believe in the “power of the pool.” It is important for therapists to demonstrate through documentation that they have a solid rationale for placing the postsurgical patient in the water. These reasons should be listed in the assessment section of any documentation.

For example, the therapist who evaluates a patient who is 15 days post total hip arthroplasty may choose to place the following statement in the initial evaluation: “The following hydrodynamic and thermal effects of immersion and immersed activity make aquatic therapy the treatment of choice for this patient:

• Application of weight-bearing in a graded or progressive manner;

• Promotion of synovial fluid bathing of joints decreases joint stiffness and pain;

• Promotion of circulation, which promotes healing of musculoskeletal injuries;

• Retardation of muscle atrophy and contractures, which may occur in the absence of exercise;

• Retardation of the loss in cardiovas- cular fitness, which often accompa- nies surgery;

• Increase in proprioceptive awareness during exercise and functional task simulation;

• Application of resistance in a graded or progressive manner;

• Promotion of stretch of scarred tissue (postsurgery);

• Assistance in limb movements against gravity (assisted by buoyancy);

• Reduction in joint compression forces during exercise;

• Decrease in muscle splinting and guarding from pain;

• Encouragement of socialization in a “normal” recreational environment.

Conclusion

As therapists who work in the water, you have the best of both worlds to offer patients with hip dysfunction. You see the possibilities inherent in gravity and delight in the possibilities intrinsic to buoyancy, viscosity, turbulence and pressure. The universe expands; you can offer your patients air and water, an integration of effort and ease.

Andrea Poteat Salzman, MS, PT, has received both the prestigious Aquatic Therapy Professional of the Year Award (Aquatic Therapy and Rehabilitation Institute) and the Tsunami Aquatic Therapy Award. She can be contacted at asalzman@aquaticnet.com.