PHYSICAL THERAPY EVALUATION FOR PATIENTS WITH KNEE OA
Like most conditions treated with physical therapy, OA is a heterogeneous condition, and patients with the same diagnosis may present very differently. It is critical that each patient be assessed using a variety of clinical, self-reported, and performance-based measures to ensure that the impairments, Physical examination Patients with knee OA have musculoskeletal impairments that worsen as the disease progresses. Muscle weakness, joint contractures, and joint pain are common among individuals with knee OA. Measuring these impairments in a standardized fashion is essential to assessing the efficacy of treatment or when benchmarking a person’s condition compared to normative values. Muscle strength Muscle weakness in individuals with knee OA is most notable in the quadriceps muscles, but also can affect other muscles of the lower extremity. In particular, the knee flexors, ankle plantarflexors, and hip abductors may be weak from disuse atrophy, altered walking patterns that unload the affected side, or joint pain (Alnahdi, Zeni, & Snyder-Mackler, 2012). Muscle weakness in the lower extremity can have negative implications on overall function. Several studies have shown that lower extremity muscle weakness is the primary predictor of poor physical function. People with weakness have difficulty climbing stairs, walking long distances, and are at a greater risk of falling (de Zwart et al., 2015). There are several valid and reliable methods to assess muscle strength in individuals with knee OA. The most common method of measuring quadriceps strength is using maximal isometric contractions on an electrodynamometer (Figure 5). Figure 5: Isometric Knee Extension Strength Measurement
activity limitations, and participation restrictions of each individual are identified. These findings will inform the patient-specific treatment plan, whether it be strengthening to reduce instability, stretching to normalize range of motion, modalities to reduce pain, or a combination. Hip abductors are commonly weak in individuals with knee OA, which is related to worse functional ability (Tevald et al., 2016). Therefore, it is important to measure the hip muscles in addition to the quadriceps. Standardized measures of hip abductor strength can be taken using electrodynamometers, but recent studies have shown that using hand-held dynamometers also can provide meaningful and reliable results (Alnahdi, Zeni, & Snyder-Mackler, 2014). One method of standardizing hip abductor strength testing in patients with OA is to position the patient side lying with the extremity to be tested facing toward the ceiling. A nonelastic strap is placed around the leg just proximal to the femoral epicondyles. The strap is secured to the table so that it is taut when the leg is abducted to neutral. A hand-held dynamometer is placed between the strap and the thigh. The patient is instructed to provide a maximal abduction effort by saying “Push your leg as hard as you can toward the ceiling.” The peak force can then be determined from the dynamometer, or torque can be calculated by measuring the length of the femur. This method has been found to be reliable in patients with knee OA and is shown in Figure 6 (Tevald et al., 2016). Figure 6: Isometric Hip Abductor Strength Measurement Note. From Western Schools, 2018. Plantarflexor weakness is common among older adults and can negatively impact walking ability (Anderson & Madigan, 2014). Evaluating plantarflexor strength using hand-held dynamometry is not useful or valid in older adults with knee pathology (Marmon, Pozzi, Alnahdi, & Zeni, 2013). Strength values from hand-held dynamometry of the plantarflexors are different from values acquired using electrodynamometers, which are considered the gold standard. Because the plantarflexors are a very powerful muscle, the strength of the examiner is likely the limiting factor in hand-held measures of plantarflexor strength. Other clinical methods of measuring plantarflexor strength can be used when an electrodynamometer is not available. The heel rise test for endurance is quick to perform and reliable when the patients are given standardized instructions (Silbernagel, Nilsson-Helander, Thomeé, Eriksson, & Karlsson, 2010). Using one leg at a time, the patient stands on a box that has an incline of 10 degrees. A metronome can be used to provide audio feedback so the patient can perform a heel rise at a rate of one every 2 seconds. The patient is instructed to perform heel rises until the frequency can no longer be maintained, or until the patient’s form changes and they cannot do a heel rise to the full height. The strength measure for this test is the total number of heel rises performed. As with the other measures, a symmetry index can be created by dividing the number by the value from the unaffected side, but these strength deficits may be bilateral, even if the patient has symptoms on only one side.
Setup for measuring maximal isometric contraction of the quadriceps on an electrodynamometer. The axis of the dynamometer should be located at the center of the knee joint, the resistance pad should be located just proximal to the ankle joint, and the arms should be placed across the chest. Note. From Western Schools, 2018. When using this method, it is important to document the knee joint angle at which the test was performed, which is commonly 90 or 75 degrees of knee flexion. Changing the knee flexion angle between testing sessions can change the amount of force produced by the muscle. As a result, the patient may appear to be getting stronger or weaker, but the only thing that changed was the position at which they were tested. The strength of the muscles can be measured in Newtons for force or in Newton-meters (or foot-pounds) for torque. The strength of the affected side can be divided by the strength of the nonaffected side to obtain a symmetry index; however, it is important to remember that many individuals have bilateral disease, so the nonaffected limb may not be normal.
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Book Code: PTNC1023
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