PROSTHESES FOR OTHER HIP OPERATIONS

Contents:

Gothenburg osseointegrated total hip (GOT)

THRUST PLATE TOTAL HIP

The first modern total hip prostheses, implanted by the English surgeon Philip Wiles, in 1938, had a short femoral component. The metal ball sat on a short shaft, which passed through the thighbone’s neck and was firmly anchored by a plate on the outside of the thighbone.

In 1978 two Swiss surgeons (Jacob and Huggler) constructed a similar total hip device. Their total hip had a femoral component with a “thrust plate”. The thrust plate was an oval metal plate resting on the femoral neck; the surgeon removed the diseased femoral head carefully before creating an even area for support of the thrust plate. The idea was that the body weight should pass through this trust plate directly onto the femoral neck and upper part of the thighbone, in theory at least. No bone cement is used.

Picture: Thrust plate total hip

The obvious advantage of this construction is that the marrow cavity of the thighbone is left intact. If this total hip device should fail and must be revised, the revision operation will be easy, say the authors, practically as simple as in hips never operated before.

On the other hand, this operation is more radical than the surface replacement; in that operation most of the femoral head is still retained.

Since its introduction on the market in 1980, the device has been redesigned two times, always a sign that something was wrong with the previous models.

In the January 2005, four Swiss surgeons presented results of 102 operations with the latest model of the thrust plate total hip (Buergi 2005). This model has been on the market since 1992. The patients were considerably improved by the operation, and the six years survival of the prosthesis was 96%. There were, however, 2% of postoperative infections.

There is a rather restricted number of Swiss, German, Indian, and Australian surgeons performing this total hip replacement. The total hip device is something between surface replacement and an ordinary total hip joint. The obvious candidate is a young patient. The authors recommend partial weight bearing for 6 weeks after surgery, a rather long period.

Reference:

Buergi ML et al.: Radiological Findings and Clinical Results of 102 Thrust-Plate Femoral Hip Prostheses: A Follow-up of 2 to 8 Years. J. Arthroplasty 2005; 20: 108-17

2 Prostheses for hemiarthroplasty

Hemi-arthroplasty means a half replacement joint operation. In some hip ailments, only the femoral head is damaged, whereas the hip socket (acetabulum) still has a healthy cartilage cover. This occurs in cases of the so called femoral head necrosis, e.g. after fracture of the femoral neck.

In these patients the surgeon may remove only the diseased femoral head and replace it with an artificial ball of the same dimensions. The artificial head then articulates with the healthy cartilage in the socket (acetabulum) of the hip joint.

Prosthesis for hemiarthroplasty of the hip joint

The ball component has equal diameter as the removed femoral head

Because the artificial ball articulates with the well preserved joint cartilage in the acetabulum (socket) of the hip joint, it should be the same size as the removed femoral head, usually between 45 -56 mm.

The large ball may be fixed rigidly to the stem of the hemiprosthesis - the monopolar prosthesis, or

the large ball may be hollow and articulate freely with the prosthetic shaft- the bipolar prosthesis.

Picture: Assembling bi-polar hip joint device (prosthesis).

Such bipolar hemiprosthesis is supposed to spare the cartilage in the hip socket because it moves on "two poles": one is movement against the joint cartilage, the other is against the small ball of the shaft component.

The bipolar hemiprosthesis has extra large metallic femoral heads with diameters between 48 to 60 mm. The extra large ball has two layers: the outer metal layer is articulating with the joint cartilage and the inner layer of polyethylene articulating with a conventional femoral ball. The stem of femoral component is identical with the stem of a conventional total hip prosthesis. The surgeon assembles the hemiprosthesis directly on the operation table.

The advantage of such bipolar hip hemi- prostheses is the possibility to change them easily to ordinary total hip prostheses when the patient has pain in the hemi-arthroplasty hip joint. This is often necessary, because the joint cartilage usually does not tolerate contact with the metal surface of the hemi-prosthesis.

Picture: Transforming hip hemi-arthroplasty into total hip joint

In these patients the surgeons only removes the extra large femoral head (A ). The shaft component is left in place (B). The surgeon has then only to insert a conventional cup component (C) and the himiprosthesis is transformed into a conventional total hip joint.

One special indication for the use of this prosthesis is the unstable total hip joint. Because of the large diameter of the femoral ball, the prosthesis for hemiarthroplasty of the hip joint is very stable in the acetabulum-under one condition: that the surgeon removes the cup component and uses a femoral ball that will fill entirely the bony socket.

After such operation, the resulting hemiarthroplasty is usually stable. The large femoral ball, however, articulates directly against the raw bone on the bottom of the acetabulum. These patients thus have stable hips but often also considerable pain.

In some centers surgeons designed special cups that will contain large ball diameters for patients with unstable, dislocating total hips. There is a lot of technical problems with construction of such total hips and not many patients have been operated on with such total hip prostheses.

For more information visit also the chapter Dislocation total hip

3

Surface replacement arthroplasty

is also called double-cup arthroplasty of the hip. In this operation only the diseased joint surfaces are removed and replaced by two thin spherical shells made from polyethylene, metal, or ceramic.

One shell replaces the surface of the socket, the other shell replaces the surface of the femoral head. In the modern double- cup hip arthroplasty both shells are made from metal and the fixation of the shells to the skeleton is cementless.

For more information see also the chapter Surface hip replacement

4

Gothenburg osseointegrated total hip arthroplasty

The Swedish orthopaedic surgeons working at Gothenburg University adapted the “osseointegration” fixation method used by dental surgeons and developed an entirely new model of “osseointegrated” total hip with special tools for "low-trauma" implantation. The fixation by osseointegration is different from fixation by ingrowth of bone tissue into the porous surface of a cementless total hip / knee. The surface of the Gothenburg’s osseointegrated total hip in not porous.

The osseointegrated total hip device is screwn carefully into the skeleton of the colum and into the hip socket.

In contrast with the cementless total hip models, the track for the threads on the surface of the osseointegrated total hip is carved into the skeleton with special very precise and very sharp instruments, It is believed that the bone tissue close to the windings of the total hip surface remains well nourished. It is believed that the precise instruments for cutting the way for the screw will not damage the circulation in the bone tissue, as is usual with "press fitting" of the cementless components.

The upper picture shows the schematic sketch, the lower picture shows the x-ray image of the new total hip model.

Carlsson LV et al: Stepvise introduction of a bone conserving osseointegrated hip arthroplasty.... Acta Orthoped 2006; 77: 559-66

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