Abnormal gait. The limp is due partly to the restriction of movement in the joint, and partly to an antalgic gait (p. 25); i.e. walking so that the load on the hip joint is reduced. The limp is usually observed by other people rather than the patient but a few are more worried by the limp than anything else.

Patients with osteoarthritis of the hip are ideal subjects for the clinical section of final medical examinations, and it is only the most foolhardy student who will attend the examination without being able to examine the hip easily and confidently.

Movements. The technique of examination is described on p. 24. Examination will usually show apparent shortening of the affected limb and a fixed flexion deformity detectable by Thomas’ test (p. 25).

Osteoarthritic hips show characteristic radiological changes (Fig. 24.1).

Osteoarthritis of the hip begins with fibrillation of the articular surface and the formation of wear particles. The wear particles are swept to the side of the joint where they irritate the synovium and are responsible for some of the patient’s pain and the formation of osteophytes.

As the disease progresses, articular cartilage is lost, subchondral bone is exposed and the bone surfaces become eburnated (Fig. 24.2). Grooves form in the joint surfaces and the hip is gradually converted from a ball and socket into a roller bearing. Later, cysts form in the bone and the femoral head may collapse.

If conservative measures fail, joint replacement is the only effective treatment. Rheumatoid patients do well because their activity is limited by disease elsewhere and also because they are generally lightweight.

Aseptic techniques. Meticulous asepsis in an operating enclosure with ultraclean air changed continuously and impervious operating gowns with individual exhaust systems for expired air (Fig. 24.9) can reduce the infection rate to 0.2%, but the operations may also be done in a standard operating theatre.

Prophylactic antibiotics used in a standard operating theatre will produce a similar infection rate to the operating enclosure. A regimen of flucloxacillin 500 mg started with the premedication and continued for three doses is effective. If the patient is allergic to penicillin, vancomycin may be used.

Combining antibiotics with a clean air enclosure can reduce the infection rate still further.

Catheterization. Inserting catheters immediately after operation runs the risk of infection. If it cannot be avoided, catheterization should be done gently with complete sterility and covered with an appropriate antibacterial drug.

Cross-infection. Patients with clean joint replacements should not be nursed in the same ward as those with abscesses, colostomies or open infection.

Some surgeons prefer to hold the hip in abduction by placing a wedge-shaped pillow between the patient’s thighs for 2 days. This is particularly helpful if a Charnley hip prosthesis with a small femoral head has been used.

The suction drains are usually removed after 2 days, when the patient may sit out of bed. They should not sit in a low chair because this flexes the hips beyond 90° and can, in some circumstances, cause the hip to dislocate. Most patients should mobilize the next day with a frame and be walking reasonably with elbow crutches, ready for discharge, after 4–5 days. By then the patients should be able to climb stairs and be able to cope with many activities of daily living.

Between 6 and 12 weeks after the operation most patients have little pain from their hip and an improved range of motion that allows them to resume normal activities. However, heavy work, especially lifting and jumping, should be avoided indefinitely in case it stresses the bone–cement interface.

Not all hip replacements are successful and it is estimated that between 0.5% and 1% of all hip prostheses in position fail each year because of infection or loosening (Fig. 24.10).

Early infection around a total hip replacement almost invariably leads to failure and special care is needed to avoid infection at the time of operation.

Late infection can also occur later via the bloodstream from infections in the urinary tract or elsewhere.

The organisms responsible for infection around total hip replacements include many normally regarded as non-pathogenic, e.g. Staphylococcus epidermidis. The explanation is unknown but it may be that these bacteria flourish in the unusual tissue that surrounds prosthetic materials (glycocalyx), or that the minute amount of metallic salts leaving the prostheses inhibits macrophage activity.

Treatment of loosening. Replacement of the loose component with another may be successful, but the operation is more difficult and less reliable than a primary hip replacement. Excision arthroplasty may be needed (Fig. 24.11) as a salvage procedure.

Other complications include fracture of the components (Fig. 24.12), dislocation (Fig. 24.13) and excessive new bone formation (Fig. 24.14).

Isotope scan. Technetium-99m scans show areas of activity in both loosening and infection and a gallium or indium scan may show areas of infection (Fig. 24.15).

Aspiration. Aspiration of the fluid around the prosthesis is helpful if a bacterium is retrieved but a sterile aspirate does not exclude infection. This procedure should be done with full sterile precautions in the operating theatre.

Replacing (revising) a hip replacement is more difficult than the original procedure. Technical problems include dissecting through tissue that has abnormal anatomy. Dense scar tissue may contain the femoral and sciatic nerves.

Removing the prosthesis and the bone cement is difficult. Bone cement is harder than bone and the femur may be split as the cement is removed from the depth of the shaft. There is likely to be such extensive bone loss in both the femur and acetabulum that the standard prostheses do not fit.

Care must be taken to be as certain as possible that the wound is not infected. Tissues can be examined by Gram staining during the procedure but a negative finding does not exclude infection. If it seems likely that infection is present, it is wise to remove all foreign material, irrigate thoroughly, pack the wound with antibiotic-impregnated beads and close it. Antibiotics should be given systemically for at least 8 weeks, by which time any residual infection should be under control. The new prosthesis can then be inserted at a second operation.

Before total hip replacement was available, femoral osteotomy was commonly done to realign the femur so that the load was taken by a different area of bone (Fig. 24.16). In this respect, the operation was similar in principle to moving an area of worn carpet away from the door. Osteotomy also affects the venous drainage of bone, and perhaps allows microfractures to heal.

Results of osteotomy are satisfactory in about 75% of patients 2 years after operation, but many have pain relief for much longer. The operation is indicated for younger patients who are unsuitable for total hip replacement. Acetabular rotational osteotomies work in the same way.

Excision arthroplasty was developed by Girdlestone as a primary procedure for osteoarthritis and is still known as Girdlestone’s operation. The hip joint is replaced with a fibrous ankylosis and is similar to Keller’s operation and other excision arthroplasties.

The operation converts a painful but stable joint into one that is unstable but less painful. The limb is shortened but function of the limb is improved. Today, the operation is done as a salvage procedure for failed total hip replacement and not as a primary procedure.

Arthrodesis of the hip leaves a solid hip that will last a lifetime and is indicated for gross destruction of the hip in a young patient, e.g. after a motorcycle accident (Fig. 24.17). The alternative operation in such a patient is a total hip replacement, which is doomed to failure in a young and active adult.

The operation has the advantage that an arthrodesis can be revised to a total hip replacement but hip replacement can only be revised to another hip replacement or excision arthroplasty.

Arthrodesis also has the disadvantage that the movement lost at the hip is made up for by excessive movement of the lumbar spine and the knee, which then become worn and present problems of their own.

Surface replacement arthroplasty, in which both joint surfaces were replaced but the femoral shaft left intact, was comparable with a mould arthroplasty. The operation was introduced in the 1980s but the results were poor and it became obsolete. New designs of such prostheses are promising (see Fig. 24.5 and Fig. 24.8).

Protrusio acetabuli is a strange condition for which no cause is known (Fig. 24.18). The medial wall of the acetabulum becomes paper-thin and the head migrates medially. The result is a hip that is virtually ankylosed in the neutral position.

Treatment. Untreated, the patient loses both rotation and abduction and in effect has bilateral hip arthrodesis. No treatment is effective except joint replacement.

Ankylosing spondylitis causes stiffness of the spine and large weight-bearing joints, including the hip. The HLAb27 gene is often found in association with this condition.