Patients with painful knee conditions often present with hip muscle weakness. This weakness can lead to, and perpetuate, knee problems. Diminished strength causes movement impairments that can lead to pathology, functional limitations and disablement. In some cases, this hip muscle weakness is not caused by simple disuse and muscle shrinkage (atrophy). Hip weakness may be caused by an inhibitory mechanism that limits the force output of a muscle. The inhibition is reflexive and is in response to pain or joint dysfunction. Joint mobilization/manipulation can quickly reduce pain and improve joint function, possibly decreasing inhibition and increasing strength. Joint mobilization/manipulation may facilitate strength recovery. By restoring strength sooner, the patient may avoid the deleterious effects of prolonged muscle weakness and achieve quicker or better outcomes.

Patients with knee pain often present with hip muscle weakness. Hip muscle weakness can cause faulty hip mechanics that contribute to adverse knee joint kinematics. The gluteus maximus is the largest hip muscle and its primary actions are extension and external rotation of the hip joint. Gluteus muscle weakness was associated with varied knee injuries, including patellofemoral pain syndrome, iliotibial band syndrome and anterior cruciate ligament (ACL) sprains. In 2 systematic reviews that have assessed subjects with anterior knee pain, the authors found strong evidence for impaired hip extensor muscle strength and activation. In a prospective cohort study, weak hip external rotation strength was associated with the development of anterior knee pain and the hip strength further diminished after pain started. There is evidence supporting gluteal muscle strengthening for the management of anterior knee pain. Some authors argue that gluteal muscle weakness may be caused by muscle inhibition and not simple disuse atrophy. This reflexive muscle inhibition is neural-mediated and driven by pain or joint dysfunction. Joint mobilization/manipulation reduces pain and improves joint function and may help maximize strength by reducing inhibition. Yerys et. al. (2002) demonstrated that hip joint mobilization caused an immediate 14% increase gluteus maximus strength and Makofsky (2007) found an immediate 17% increase in gluteus medius strength after hip joint mobilization. Both of these studies, however, used asymptomatic subjects and their results may not translate to symptomatic patients. Chilibeck (2011) found an immediate 14% increase in hip extension strength, and 12% in hip abduction, after lumbar spine thrust joint manipulation. This study also used an asymptomatic sample. In addition, thrust joint manipulation is used less frequently in physical therapy practice compared to nonthrust joint mobilization. The scientific objective for this research is to assess the effect of spine and hip joint mobilization on hip muscle strength in patients with knee pain.

The study aims to answers the following questions:

1. Does hip joint mobilization immediately improve hip muscle strength in patients with knee pain?
2. Does spinal joint mobilization immediately improve hip muscle strength in patients with knee pain?
3. Does hip or spinal joint mobilization create a greater improvement on hip muscle strength in patients with knee pain?

This pilot, prospective clinical trial will use a randomized clinical trial design. The primary dependent variable is isometric muscle strength, measured in pounds, an interval level of measurement. Muscle strength will be determined by the maximum voluntary contraction (MVC) and measured by an electronic hand-held dynamometer. Hand-held dynamometric muscle testing has demonstrated good intrarater reliability and validity when compared to Biodex dynamometry. Although there is no established minimal clinically important change (MCID) score for strength testing, some authors have suggested a 10% change in strength to be clinically significant. Pain will be measured at the ordinal level with the numeric pain rating scale (NRPS). Investigators will recruit subjects from routine clinical practice within the NYULMC-CMC. The outcomes variables (isometric muscle strength and strength) will be measured before and after the intervention at the initial evaluation visit. After these measures are obtained, the participation in the study is complete. There is no follow-up.

Inclusion Criteria:

1. Age18-75
2. Referred to out-patient physical therapy for evaluation/treatment of a knee condition
3. Agreed to be in the study and signed the informed consent document

Exclusion Criteria:

1. Presence of any medical 'red flags' suggestive of pain that is not of musculoskeletal origin
2. Osteoporosis or recent fracture of the hip or spinal joints
3. Spinal or hip joint surgery or prosthesis
4. Spinal instability (Grade II spondylolithesis or greater), spondyloarthritides, or severe spinal misalignment
5. Nervous system disease or disorder
6. Pregnant