Big Head Technology
Demands of the modern patient have changed. They wish to be informed of innovations and cutting edge technology.
The young patient with a higher activity profile requires a stable hip joint without restriction.
With big femoral heads, the choice is either a metal on metal, ceramic on ceramic or ceramic on metal bearing surface. The large head simulates the patient's own femoral head and so feels natural in function, while also increasing stability which in turn reduces the risk of dislocation.
These new big head bearing surfaces are exceptionally smooth and have a low coefficient of friction. The technological advances in bearing materials have resulted in reduced wear and this should, therefore, give an increased longevity of the hip joint.
However it should be noted that big head metal on metal THRs are being 'abandoned' by the surgeons in the UK. Audited results ranged from 21% revision rate at 4 years to 49% at 6 years for the ASR XL device. Other devices were shown to have higher revision rates at around 12-15% at 5 years.
Debris is generated from any bearing surface and increased wear of the metal on metal bearing surfaces has been noted. Wear and/or corrosion have now also been identified at the trunnion-taper junction between the metal head and the stem. Cobalt and Chromium ion levels may be elevated and may initiate pain.
This group of patients' radiographs may show loosening and osteolysis. Ultrasound and MRI scans may show fluid collections, cystic and/or solid masses. Patients with pain should be investigated appropriately.
The use of large diameter metal on metal bearings in primary total hip replacement should be carefully considered and possibly avoided.
Revision procedures can be complicated if there is significant soft tissue damage and may require specialist reconstruction techniques for revision hip surgery.
This is in contrast to the use of conventional polyethylene which is restricted to socket/liners with small heads to reduce the frictional torque and thus reduce polyethylene debris. New cross linked polyethylene may reduce wear in patients with lower activity demands. However, some manufacturers have used crossed linked polyethylene with larger heads. This may be possible with vitamin E polyethylene used as a cemented cup or as a liner within the acetabular shell.
The aim is for longevity of the artificial hip joint with unrestricted activity — hip joint stability and the elimination of dislocation.
To make an appointment e–mail Sue Misir, secretary to Mr Evert Smith, or telephone:
- 0117 907 4228 (private)
- 0117 323 5194 (NHS)
For an NHS appointment your GP will need to refer you. How?
Evert Smith is an Orthopaedic Surgeon in whom I have absolute faith and confidence.
Bob Gibbons, 2007.