Big Head Technology
The bearing surface is all important.
Demands of the modern patient have changed. They wish to be informed and desire cutting edge technology rather than to accept standard, conventional treatment.
The young patient with a higher activity profile wishes to have a stable hip joint without restriction and is therefore well suited to a big head metal on metal articular bearing surface shown in the x–ray below:
This is the choice of implant for fracture neck of femur and avascular necrosis as a consequence of a Revision Hip Replacement (RHR) procedure. The size of the femoral head is tailored to the patients’ socket size.
Once the surgeon has decided on a big femoral head to articulate with the acetabular cup then the choice is either a metal on metal or ceramic on ceramic.
These new big head bearing surfaces are exceptionally smooth and have a low coefficient of friction. The frictional forces are dependant on the surface roughness and the chemical composition of the material. The technological advances in bearing materials have reduced wear, and should result in an increased longevity of the hip joint.
At the same time the low wear bearing surface eliminates the use of a ‘soft’ socket articular surface such as polyethylene, and therefore eliminates polyethylene debris, which initiates bone resorption (osteolysis). However new crossed linked polyethylene has reduced the wear of this material but still continues to function as a low friction bearing surface suitable for patients with lower activity demands.
An even lower wear surface is a ceramic on ceramic articulation. New ceramics such as Biolox have reduced crack propagation and fracture potential. The head size can be increased to 36mm when articulating with an average sized socket.
The future is ‘hard’ big head technology. This may include ceramic on metal and diamond coated surfaces, as well as nanoceramic coatings
The aim is for longevity of the artificial hip joint with unrestricted activity — hip joint stability and the elimination of dislocation.
Neck or Metaphyseal Hip Replacements (‘Stubbies’)
These hip designs are still experimental at present. A number of bone conserving hip joints are being developed at present and are being used in controlled clinical trials. The preclinical tests such as mechanical fatigue tests, finite element analysis and photoelastic techniques are used to design a bone conserving hip that can be effective and have the excellent long term outcomes of some of the conventional Total Hip Replacements.
Appointments
To make an appointment e–mail Sue Misir, secretary to Mr Evert Smith, or telephone:
- 0117 907 4228 (private)
- 0117 959 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.