In revision hip surgery, large bone defects and bone stock loss in the pelvis remain a critical problem. The more severe the bone loss of the peri-acetabular structure, the less chance there is of creating long term stability.
Bone graft (including impaction bone grafting), polyethylene cups, plates and screws, and mesh, as well as multi-holed jumbo acetabular shells/cups, have all been used to treat major bone defects following mechanical failure of a total hip replacement.
Jumbo cups made with cobalt chrome alloy have been the workhorse for revision hip surgery over the past two decades. However, acetabular shells made with porous metals are now being used. The pores in the metal mimic coral and are of a size appropriate for increased bone in-growth. Canine model studies have confirmed rapid bone in-growth and early vascularity.
Porous metals are highly bio-compatible and at the same time they are strong, flexible and impart high friction. These metals may be either pure tantalum or pure titanium.
The enhanced surface roughness which is due to the macro texture of these metals provides initial primary stability. Porous metals are unique in that they also have ‘nano scale’ roughness, which allows bone cells to interact with the surface, thus initiating bone cell (osteoblast) adhesion. Fixation can be further enhanced with multiple screw holes in the shells.
Porous metal shells thus provide the patient with a chance for long-term fixation in the face of considerable bone stock loss. Porous metal augments can also be used for the reconstruction of crevices, large defects and pelvic discontinuity. This reduces the need for bone graft.
Early clinical results are encouraging and at present there have been no mechanical failures or any evidence of migration of the shells in the pelvis. Now E-Poly liners can be cemented into the shell to provide the patient with an excellent bearing surface as well.
Given the massive stride forward in materials and designs, the prediction is that porous metals will become the gold standard for complex acetabular revision hip surgery.
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.