Muscles To Target In Hip Osteoarthritis

Hip osteoarthritis is very common amongst an elderly population. There are many researches looking at the causes, the process and even potential (conservative, pharmacological and operative) treatment of osteoarthritis. However, how the muscles of the hip are affected is not as clearly understood.

Why is this important? We as clinicians are involved in the pre-operative and post-operative rehabilitation of patients. Therefore, it is vital for us to understand which muscles are weak, how best to strengthen them and which muscles are overactive, and therefore do not require strengthening.

Muscle Synergy Around The Hip

When looking at the muscles synergy around the hip, we can separate superficial muscles (Gluteal max (GM), tensor fascia lata (TFL) from those in the deep system. These include the gluteus medius (G.MED), gluteal minimus (G.MIN), quadratus lumborum and piriformis.

There is research suggesting that increase adduction activity increases compressive forces through the hip. Therefore, it may make hip osteoarthritis symptoms worse. What this suggests, is that in generic home exercise programmes, exercises to strengthen adduction ought to be avoided.

The notion that the gluteus max acts like 2 separate muscles carrying out two different movements has also come about. This is due to its attachment and insertion site; the upper portion of the GM muscle (UGM) arises from the posterior iliac crest. However, the lower portion of the GM muscle (LGM) arises from the inferior sacrum and upper lateral coccyx. This causes the UGM to act primarily as a hip abductor. It will not play a role in hip extension unlike the LGM, which is predominately a hip extensor. Both portions externally rotate the femur.

The results showed muscle wastage in the LGM of the affected hip but not the UGM. This is when comparing muscle wastage of patients with unilateral hip osteoarthritis. On the unaffected side the UGM experienced hypertrophy. Hypertrophy can be explained by compensation with offloading the painful side. This leads to increase weight bearing on the unaffected side. Commonly enough, unilateral osteoarthritis tends to develop into bilateral osteoarthritis.

How Does Bilateral Osteoarthritis Develop?

There is a proposed theory that excessive abduction can also lead to bilateral hip osteoarthritis, due to the increase compressive loading. This is to explain the development of bilateral osteoarthritis. Therefore, routine hip abduction exercise for osteoarthritic patients targeting the superficial UGM may not be beneficial.

The emphasis is moving more towards strengthening hip extensors (LGM) and the deep abductors G.MED, G.MIN and piriformis over superficial hip abductors (UGM). The deep muscles of the hip are believed to have a part in absorbing ground reaction forces at heel strike during gait. The inabilty of these muscles to do this effectively may explain the degenerative process and pain of the hip joint, causing hip osteoarthritis.

There have also been suggestions that post-total hip arthro-plasty in patients with hip osteoarthritis and GM plays a vital role in preventing surgical implants from loosening, and hastens the recovery. When looking at the energy transfer and mitochondria function of a diseased osteoarthitic hip, GM appeared to show greater deterioration of the intracellular energy transfer processes. The authors of this study concluded that arthroplasty undertaken before development of the grade 3 osteoarthritie may improve greater post surgically as there would be fewer changes at a cellular level to the muscle.

A following article will demonstrate useful hip strengthening exercises and stretches.

References:

1. Grimald, A., Richardson,C.,Durbridge,G. Donnelly, W., Darnell, C., Hides, J (2009) The association between degenerative hip joint pathology and size of the gluteus maximus and tensor fascia lata muscles, Manual therapy
2. Eimre, M., Puhke, R., Alev, K., Seppet, E., Sikkut, A., Peet, N., Kadaja, L., Lenzner, A., Haviko, T., Seene, T., Saks, V.A., Seppet, E.K., (2006) Altered mitochondrial apparent af?nity for ADP and impaired function of mitochondrial creatine kinase in gluteus medius of patients with hip osteoarthritis, Am J Physiol Regul Integr Comp Physiol 290: R1271–R1275