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Arthrosis of the hip joint (coxarthrosis) and joint replacement

The most common cause of a hip joint disorder is increasing destruction of the joint cartilage, which can develop into arthrosis of the hip or coxarthrosis. A distinction is made between primary arthroses with largely unknown causes and secondary arthroses after certain basic disorders (congenital malformations, rheumatism, circulatory disorders, accidents or similar). The joint increasingly loses its fit, bony deposits are formed along the edges, and abrasion particles cause repeated pain. The loss of cartilage results in an increasing stiffening of the joint. At the same time, pains occurs, at first associated with initial movement after periods of inactivity and with stress, later also at night and at rest, resulting in an increasing limitation of the walking range and ultimately a reduction in quality of life.

 

ArthrosisX-ray of arthrosisThe arthrosis can be shown schematically and in the normal X-ray image; the narrowing of the joint cavity between hip and femur can be seen as an indirect indication of the loss of cartilage. The head of the joint and the socket are partially destroyed and no longer fit together well ("running on the rim").

Hip joint replacement: material and fixation

The time for surgery has come once all conservative treatment options (physiotherapy, balneotherapy, massage, pain medication) have been exhausted, the pain has become too strong, and the X-ray confirms arthrosis. For arthrosis of the hip joint, both the ball and the socket of the joint have to be replaced with an artificial joint, known as a total hip replacement (THR).

Continuous improvement in both surgical techniques and the quality of implants since the 1960s make this procedure one of the most common and most successful routine operations in orthopaedic surgery, with a total of about 400,000 operations a year in Europe as a whole.

The prosthesis is modelled on the actual human joint, i.e. it consists of a socket and a shaft, to which a ball head is fitted. The pre-operative planning sketch is used to specify the model size and fixation of the prosthesis, with full consideration of individual requirements (age, gender, shape of bone, body weight, etc. ).

Hip joint operation
Steps in the surgical implantation of an artificial hip joint

Three different fixation techniques are used in the implantation:

  • Cement-free endoprosthesis fixation:
    shaft and socket are ‘press-fit’ exactly into the bone.
  • Cemented endoprosthesis fixation:
    hip socket and shaft are fixed with a quick-hardening antibiotic bone cement. 
  • Hybrid endoprosthesis fixation:
    the socket is fixed cement-free, the shaft anchored using bone cement.

 

Standard cement-free prostheses
Standard cement-free prostheses
and sockets
X-ray image of a cement-free prosthesis
X-ray image of a
cement-free prosthesis

 

Over the last two decades, the noncemented version has steadily gained in importance as the standard procedure. Titanium implants, often equipped with special macro- or micro-structured surfaces, are particularly well suited for cement-free fixation because of their excellent integration into the bone. For this technique, only implants with an excellent track record worldwide are used.

Alternatively, the socket in a cemented prosthesis is made from polyethylene, the cemented shaft from a chrome-cobalt alloy. For this traditional approach, implants with many years of proven reliability are available.

An innovative approach includes short shaft prostheses and resurfacing options, thus preserving the otherwise resected femoral neck; these implants are supported by the upper part of the femur. The minimally invasive implantation spares the trochanteric ridge as well as the gluteal muscles, thus accelerating rehabilitation. While the short shaft prosthesis represents an attractive alternative to previous prostheses and also supports our minimally-invasive philosophy, resurfacing is mainly suitable for young patients. Common to both procedures is that they offer excellent options in case of later revisions.

 

Short shaft prosthesis Short shaft prosthesis with support in the proximal femur section while preserving the neck of the femur
(by kind permission of the company Zimmer)

Socket
Resurfacing to replace the socket while also preserving the femoral neck and part of the head.

 

Combinations of polyethylene/ceramic, ceramic/ceramic or metal/metal are used as slide bearings (slide components in direct contact with each other) between the socket and the artificial femoral head. The latest developments in slide bearings have optimized the abrasion behaviour of the components to the extent that many years of use are tolerated without almost no material abrasion.

 

Hip jointsTypical slide bearing combinations. such as metal-metal, ceramic-ceramic or metal-polyethylene.

Durability promises to be further improved by the use of navigation systems; similar to a GPS in vehicle navigation, these will allow to surgical steps and bone resections to be checked on the computer to ensure an optimal fit of the parts of the prosthesis, axis-accurate alignment and optimization of tendon tension. First studies have shown extended durability, a result that we can confirm from our extensive experience with navigation systems.

 

Hip joint operationNavigation systems similar to a GPS permit the optimal implantation of replacement hip joints, thus extending the durability of the prosthesis.

Aftercare

All endoprosthetic operations are exclusively performed on an in-patient basis. In order to ensure the best possible outcome of the operation, our patients are mobilized early with the help of physiotherapists; depending on the implantation technique used, patients can soon put weight on the treated leg. For cemented prostheses and normal wound healing, the treated leg can soon bear full weight. Partly cemented and cement-free implanted prostheses can for the first two weeks only be exposed to loads of 10 - 20 kg; after that, progression to full weight-bearing is soon possible.

Most patients stay in hospital for 10-14 days, generally followed by 2 weeks in a rehabilitation clinic. The progress of patients is documented through regular out-patient check-ups at close intervals; if necessary, mobilization therapy will be continued on an out-patient basis.

Joint replacement and sporting activities

Severe arthrosis of the hip joint comes with a significant limitation to sporting activities. Freedom from earlier complaints raises the desire in many patients to resume a certain level of sporting activities. There is international consensus that "low impact" activities such as cycling, swimming, sailing, diving, golf and bowling can be supported. Sports such as tennis, basketball and skiing are possible or advisable within limits, while contact sports such as football or rugby should be avoided unconditionally.