[Osteosynthesis of tibial valgus osteotomies by goniometric CH-N external fixator]

The authors present technique and results of a new external fixator, the < < goniometric > > external fixator CH-N for osteosynthesis of high tibial osteotomy for arthritic varus knee deformity on 86 kness (75 patients).

86 knees in varus deformity with degenerative arthritis of the medial compartment (56 females and 16 males - age 63 +/-8 years) were treated for 5 years (1989-1993) by high tibial osteotomy stabilized by a < < goniometric > > external fixator CH-N.

Clinical results were 65,9 per cent excellent, 17, 1 per cent good, 11,8 per cent fair and 5,2 per cent poor 1 year after osteotomy (86 cases analyzed), changing in 60 per cent excellent, 22,3 per cent good, 9, 1 per cent fair and 8,5 per cent at 3 years follow-up (61 cases). Radiological results were: - The preoperative mechanical axis of 13 degrees +/- 5 degrees in varus transformed to 4 degrees +/- 2 degrees in valgus at consolidation and to 2,5 degrees +/- 3 degrees in valgus at one year follow-up. At 3 years follow-up we founded a new loss of correction of 1 degree (mean) in 22 per cent of cases (61 cases). - Subchondral density decreased in 91 per cent of cases (86 cases) one year after and in 82 per cent of cases, 3 years after the osteotomy (61 cases). - In 12 per cent of cases we found a decrease of the overcorrectional angle of the varus deformity 1 year after, and in 22 per cent of cases 3 years after. Two cases needed total knee arthroplasty 4 years after ostcotomy. - Postoperatively, in 86 per cent of cases we did not found increase in both clinical and radiological (pathological) findings of the patellofemoral joint one year after, and in 75 per cent of cases 3 years after.

The principle of this special < < goniometri > > external fixator is based on the < < goniometric > > central joint in the frontal plane, this allows to guide the screws during osteotomy in the predesigned position and to control the correction during and after the procedure, in contrary to the others current system either internal or external. Any faulty correction can be modified. With its distal screwing axis, it allows axial dynamization. There are only some but not serious incoveniences due to the application of pins (temporary neuromuscular problems and pin-track infections.