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Hope After Hip Surgery

Byline: Andrea Salzman, MS, PT

Our patient spent one month in bed trying to ward off pain. He finally decided to have the hip surgery his doctor had suggested a year ago. The doctor warned that he had three months of plain hard work ahead of him. But his rehab might not be quite as tough as it sounds.

Why? You've got access to a pool and you know how to use it. Your patient can receive the best therapy can offer: both on land and in the water.

In water, a skilled therapist can allow postoperative patients to perform activities impossible on land. In fact, its unique properties make it difficult and clinically impractical to achieve a similar environment on land. Those properties are as follows:

• Buoyancy. Archimedes' principle states that "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 the body's movement.

It all depends on the position of the patient's body. The body has elements that tend to sink (dense muscle) and elements that tend to float (fatty tissue and air-filled lungs). This tendency to float counterbalances gravity and supports the body, resulting in an apparent reduction in weight. This reduction in weight can relieve 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, offsetting any deconditioning effects of immobility. Even better, this reduced 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 submerging the body deeper into the water. Static (standing) immersion at the level of the anterior superior iliac spine (ASIS) reduces weight 40 percent to 56 percent of normal.

But you must be careful: All bets are off when the patient moves. During slow walking, patients must be immersed to the clavicle to reduce weight bearing to 50 percent, and during fast walking, patients must be immersed deeper than the xiphosternum to reduce weight by 50 percent.

• 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. This reduces edema in the lower extremities (by providing graduated pressure at greater depths), offsets blood pooling in the lower extremities (and thus reduces the risk for postoperative clotting) and provides a desensitization effect (by constantly stimulating phasic receptors). This means postoperative patients 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 causes a resistance to flow. Water is more viscous than air. Therefore, 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, which creates additional resistance to movement.

Remember, the postoperative patient has probably 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 (perhaps even sacrificing additional Golgi tendon organs and muscle spindles to the surgeon's blade). It seems likely that movement in water can offer patients exaggerated input from the environment, perhaps enhancing proprioception.

• Flow. When an object moves through fluid, pressure increases in the front of an object, combined with reduced pressure in the back. The water, therefore, moves from an area of high pressure to an area of lower 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 percent of movement impedance. Surprisingly, the bow wave (the positive pressure in front of the object) is only responsible for 10 percent of the impedance.

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

• Refraction. This is the prism effect that's evident when one looks 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 the patient and provider. A patient's limbs seem distorted (bent away), and items seem high and to the right, thus making visual feedback and monitoring more difficult. For the postoperative patient, refraction may be used therapeutically. For instance, while immersed, a patient with a habitual visual method of joint placement (i.e., 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. Thermal energy (heat) is exchanged between water and the body and between air and the body.

Energy exchange between a submerged body and the water occurs through convection and conduction. Thermal energy also is 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.

Depending on the population using the facility, therapeutic pools are generally heated to between 92 F and 97 F. Immersion in water warmer than the skin will raise superficial tissue temperature, which creates a palliative effect. Immersion in thermoneutral water will produce a generalized relaxation effect similar to that experienced with swaddling or bundling of a body part.

Even though the water is an ideal environment to tackle many problems inherent in the postoperative population, you must be aware of the following considerations:

1. If the patient is uncomfortable or anxious in water, muscular bracing and splinting may worsen pain.

2. If the patient has undergone total hip replacement surgery with a posterior approach, take extreme caution to avoid contraindicated positions (hip internal rotation, adduction and flexion above 90 degrees). The freedom of movement in water may allow the patient to perform movements he shouldn't. If the patient has a surgical suture site or an open wound, a decision must be made about when to allow him in the pool. This decision is based on a risk to benefit ratio. If the patient's skin is in danger of maceration, or if the wound is draining, you must have 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's little risk involved in taking the patient into the pool. If the patient is immersed, thoroughly dry (via "patting" not rubbing) the surgical site after immersion.

When designing an aquatic therapy program for this population, be sure to take these other points into consideration.

• Start any new patient in water that's no deeper than he can comfortably stand in. Fear can contribute to muscle guarding, which can increase pain.

• Provide equipment for buoyancy-assistance so the patient doesn't require the assistance of the therapist to feel safe.

• Be sure to 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 gradually to prevent delayed-onset muscle soreness or hip dislocation.

• Increase weight bearing progressively by moving the patient to shallow water to return him to functional (land-based) status as soon as feasible.

• Make sure the water temperature is at least 93 F (thermoneutral) for pain palliation.

• Don't neglect aerobic conditioning; a strong relationship exists between aerobic exercise and pain palliation. But remember, the target heart rate zone for aquatic exercise is at least 12 to 17 beats per minute lower than its land-based counterpart.

If you've never worked with this patient population, don't set unrealistic goals. Realize that exercise in water can be a powerful tool to rehabilitate hip dysfunction. Among the goals are:

• Rehabilitate traumatized tissues by ap.plying graded and progressively more taxing stresses on injured tissue

• Improve strength, flexibility, posture (upright stance through terminal hip extension) and ability to perform ADLs

• Prevent contractures, muscle atrophy and loss of cardiovascular fitness immediately after surgery

• Decrease fatigue and complaints of pain.

Remember, you cannot place patients in the water simply because you believe in the "power of the pool." You must demonstrate through documentation that you have a solid rationale for placing the patient in the water following surgery. These reasons (known collectively as the "beneficial effects" of aquatic therapy) should be listed in the assessment section of your documentation.

As therapists who work in the water, you can offer the best of both worlds to patients after hip surgery. If you have expertise in the aquatic environment, you see the possibilities intrinsic to buoyancy, viscosity, turbulence and pressure. The universe expands: Patients have air and water and can integrate effort with ease.

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Read more research on aquatic therapy and hip surgery here: Liebs, Thoralf R., et al. "Multicenter randomized controlled trial comparing early versus late aquatic therapy after total hip or knee arthroplasty." Archives of physical medicine and rehabilitation 93.2 (2012): 192-199.

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