Total hip replacement is one of the most common and effective orthopaedic operations and overall has one of the highest quality of life improvements of all medical interventions. Many, mostly elderly, people have a very good outcome with their hip replacement surgery but this can hide the potentially large numbers of sub-optimal outcomes where the person’s function is limited by incomplete rehabilitation.
An osteoarthritic hip joint is likely to cause a degree of pain and disability for a year or more before the person comes to operation. This period of difficulty can cause influential changes in the tissues around the hip which can be relevant in the postoperative period. Pain and weakness can make us use our joints less, avoiding pushing them to the ends of their movement, a process which gradually reduces the joint’s range of motion. Adaptive shortening occurs in the hip’s ligaments, as the structures shorten in response to the fact that the joint is not being put through its full range any more in the normal daily pattern.
Weakness of a muscle or muscle group is the consequence of stiffness and pain interfering with the normal function of a joint. Weight bearing while the body is in motion is the function of the hip joints and they allow us to perform functional activities such as climbing the stairs, getting up from a chair, walking and running. To do these activities against the weight of the body and the force of gravity they are provided with the largest and most powerful muscles in the body. Weakness which develops in this muscle group can be disabling and compromise independence.
The pelvis is controlled in a lateral direction by the abductor muscles of the hip, part of the gluteal muscle group, and a lack of strength in these muscles inhibits normal gait. The abductor muscles of the leg which is supporting the weight of the body must hold the pelvis level and even raise the opposite side slightly to facilitate carry through of the other leg. Without their support the pelvis will drop on the unsupported side and cause a loss of balance to that side which is only countered by a lean of the body to the other in an effort to regain balance and prevent falling. This is called a Trendelenberg gait.
The hip joint is exposed to abnormal forces in the Trendelenberg gait and the spine has to make repeated sideways movements each step to prevent overbalancing. In this kind of gait there is no strengthening of the hip abductor muscles so the abnormality remains. The pain and the weakness of the hip extensor muscles means that the person does not fully extend their leg behind them in each walking step, leading to a shortened and less efficient gait. Maintaining mobility becomes more and more of a challenge and can, in the absence of physiotherapy rehabilitation, lead to their hip replacement doing less well than hoped.
Patients typically have impaired balance and coordination even before they have their joint replacement operation, with some improvement occurring as the hip’s function moves more towards normal after the joint has been replaced and the mechanical function of the hip is restored towards normal. Other impairments usually include the sense of joint position sense, an important ability the lack of which compromises balance and makes falling more likely.
Physiotherapists assess a patient’s hip function and ability to get through their normal daily work, looking at the deficiencies in the joint so they can plan the rehabilitation. Noting the gait of the patient will be the first thing in the assessment, moving on to checking movements of the hip, knee and spine to check for any restrictions due to joint stiffness. An abnormal gait can be habitual and the physiotherapist will analyse and correct the gait pattern towards normal.
Hip joint range of movement is not promoted due to dislocation risk, but the physiotherapist will assess the joint’s muscle power and the ability of the patient to balance and sense where their hip is. The patient will be given a rehabilitation programme by the physiotherapist which will include hip muscle strengthening, joint mobilisation, gait correction and balance work. Rehabilitation can improve the outcome of hip joint replacement.
