[Osseous reconstruction of the patella with screwed autologous graft in the course of repeat prosthesis of the knee].

PURPOSE OF THE STUDY

The aim of this study was to propose an original way of solving the infrequent but difficult problem of a thin patellar remnant. After removal of the loose patellar button of a knee prosthesis, several options are available: patellectomy should be avoided because of unpredictable results; patelloplasty may be the solution if bone quality is too poor and can allow for its improvement with time; recementing a new implant needs the remaining patella to be thick enough (more than 10 millimeters).

MATERIAL AND METHODS

We advised reconstruction with an autologous monocortical iliac bone graft, harvested from the medial cortex of the anterior iliac wing, and shaped to accommodate for the patellar remnant. Its cancellous surface is opposed to the roughened patellar bone to which it is fixed by four 1.5 mm cortical screws (the heads of which are countersunk). Any defect will be filled with cancellous chips. The patellar button can then be cemented. Two cases with a long follow-up (5 years) are shown: one is a "typical" indication of isolated patellar loosening 16 years after implantation of a GSB total knee prosthesis, in a 91 year old woman. The other one illustrates the salvage of a "patellectomized" multi-operated knee, in which a trochlear implant was used as a first step, then 4 years later the patellar pseudarthrosed remnant was reconstructed.

DISCUSSION

Indications of this technique are obviously rare: the patellar remnant should be thinner than 10 mm, in one piece (or easy to rebuild with the graft), the bone should allow a good purchase of the screws and the extensor apparatus should be in continuity. The first cases seem encouraging, as no secondary fracture or non-union has been seen at five years follow-up. The bone-cement lucency seems to be due to cementing on a cortical surface, but did not increased. Autologous bone has been favoured to increase the chances of union in a poor quality bed. It has the drawback of a second approach to harvest the bone at the iliac wing, where it is not always flat. The surgeon must "cheat" to get as flat a surface as possible for cementing. The loss of quadriceps is so troublesome that Buechel has proposed autologous grafting inside the patellar tendon and Bakay has used a mushroom-shaped allograft. Finally, we should like to advise against too much thinning of the patella to try and gain a few more degrees of flexion in total knee replacement: think of revision!

CONCLUSION

We think this technique may be helpful in patellar loosening, as an other way of solving this problem.