In cases when conservative treatment has failed in the management of hip osteoarthritis several surgical options are available. Hip arthroscopic debridement, proximal femoral osteotomies and hip arthrodesis have all in all a small role to play in the management of an arthritic hip.
TOTAL HIP REPLACEMENT (THR) has evolved over the last 50 years as the 'gold standard', and seems the ideal way of treating any disorder causing joint destruction. It has become one of the most commonly performed elective surgical procedures in the developed world: well over 75,000 THR are undertaken in the UK every year.
Sir John Charnley revolutionised the management of the arthritic hip with the development of the low-friction arthroplasty (LFA) of the hip. His major contributions to the evolution of the hip replacement remain up-to-date.
THR reproducibly alleviates pain and restores joint mobility while providing joint stability. The indications for THR include pain, loss of mobility, severe stiffness and instability in the presence of joint destruction. As the hip is a 'ball and socket' joint, both the acetabulum (socket), and the proximal femur (ball) have to be replaced.
There is a wide variety of implants available both for primary and revision Total Hip Arthroplasty. Depending on the mode of fixation to the bone, implants can be cemented or un-cemented (cementless).
Cement is a grout, not a glue, and fixation is achieved by a mechanical interlock in the bony interstices. Cement can be antibiotically unloaded and it produces high local concentration of antibiotics in the operative area, thus reducing the incidence of infection. Polymethyl methacrylate (PMMA) is the most common acrylic cement in use in orthopaedic practice.
Un-cemented implants have become more popular over the past two decades. Fixation depends on osseointegration between the implant and the underlying bone. It is important to have initial press-feet stability to allow ingrowth into the surface of the implant. To accelerate bone ongrowth and improve the long-term fixation of the prosthesis, bio-active surface coatings have been applied (plasma spray, hydroxyapatite, titanium mesh...). New implants have been designed with new materials such as trabecular metal (tantalum).
Total Hip Replacement can therefore be fully cemented (when both the femoral and acetabular components are fixed with PMMA), cementless (when both components are un-cemented) and hybrid (when one of the components is cemented and the other not).
The most common combination of bearing surfaces remains metal (femoral head) with polyethylene (acetabulum), but metal on metal surfaces are also used (hip resurfacing), and ceramic on ceramic have become more popular in the last decade as new ceramic material has a low wear rate and has much improved fracture toughness.
Careful evaluation and assessment of the patient is required prior to undergoing surgery. Age of the patient, quality of bone, soft tissue condition, presence of muscle weakness and lifestyle have to be taken into consideration in order to select the appropriate type of implant, the surgical approach and the post-op physiotherapy regime of the patient.
Although THR is a very successful procedure, complications do occur. Patients are often elderly; some have rheumatic diseases, and many have comorbidities (cardiopulmonary, COPD, diabetes, anticoagulation...). Complications can be divided into intra-operative (fracture of the femur or acetabulum, sciatic or femoral nerve damage, vascular injury...) and post-operative (DVT, dislocation, infection, heterotopic bone formation...).
HIP RESURFACING (Resurfacing Arthroplasty) has become popular in the last 20 years. The principle of bone conservation, stability and enhanced range of motion seems very attractive, mainly in young and active patients seeking a THR.
The NICE (National Institute for Health and Care Excellence) has issued some guidance and advice on hip resurfacing which summarises pros and cons of the procedure.
Technically a very demanding operation where minimal malalignment of the implants can seriously limit the function and longevity of the implant. Resurfacing is not suitable for all hips: bone stock must be carefully assessed as the rate of failure and femoral neck fracture is higher in women and in the presence of osteoporosis in the proximal femur.
When appropriate patient selection and careful surgical technique has taken place long-term survival of the resurfacing implants matches those of conventional THR.
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