Abstract
We want to prove that you cannot make a good fitting stem of a THP before surgery because the resulting shape of the femoral cavity is set after all the tools have been introduced in the femur.
We are fully aware that fit and fill alone is not enough to obtain good fixation therefor all the investigated implants were plasma spray coated with HA.
We’ve investigated two groups of patients:
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Pre-operative group: custommade implant based on CT scans and manufactured before surgery The proximal part was size for size and coated with HA; the distal part is cylindrical (44 cases, followup from 1.6 years to 5.2 years)
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Per-operative group: custommade implants based on a mould of the femoral cavity in the proximal femur and manufactured during surgery. The prosthesis was size for size and the HA coating was applied on the proximal 1/3 of the implant. (13 cases, with a minimum followup 1 year).
The coating specifications for both groups were exactly the same.We’ve compared the Harris hip score for both groups and we’ve performed a radiolographical analysis.
Of the pre- operative group 6 protheses had to be revised.This results in a revision rate of 25 % which is not acceptable.In the peroperative group however, no revisions have been performed.
Radiografically the per-operative group showed much better results than then the pre-operative group.
The obtained results suggest that it is not only important to have a good bone growth initiator such as HA but the implant needs to be in close contact with the bone.This confirms the limited gap bridging capacity of HA which has been reported by several authors in the past. A close fit can only be obtained by designing and manufacturing the implant during surgery based on the actual size of the femoral cavity.
