[Replacement of the anterior cruciate ligament by a PET prosthesis (Trevira extra-strength) as a salvage procedure in chronically unstable previously operated knee joints. Intermediate to long-term results of a clinical study].

Thirty-one salvage cases of chronically unstable previously operated knees were stabilized by an anterior cruciate ligament prosthesis of polyethyleneterephthalate (Trevira hochfest) and additional repair of concomitant lesions. The patients were followed up at yearly intervals. For the final follow-up after 4.4 years 27 patients could be evaluated clinically, radiologically and by several scores. The pre-operative Lysholm score was 59.8 (+/- 16.7). It was raised significantly by the operation to 75.4 (+/- 18.9) after 1 year, but then gradually decreased to 71.4 (+/- 19.6) at the final examination. Similar values were reached for the other scores (OAK, IKDC, VAS). The degree of activity (as estimated by the Tegner activity scale) increased from 2.0 (+/- 2.1) to 3.1 (+/- 1.9). Pre-operative anterior translation revealed a side-to-side difference of 7.5 (+/- 3.4) mm. The stability, which was restored by the operation, gave way a little in the first 2 years up to a side-to-side difference of 2.1 (+/- 2.5) mm, but then remained constant and was measured 2.3 (+/- 2.9) mm after 4.4 years. On the whole, the patients gained a significant improvement from the operation in all investigated parameters. Major complications included 5 ruptures of the synthetic ligament (1 by material fatigue), 1 avulsion of a staple, 1 supracondylar fracture due to 3 closely located staples, 4 cases of arthrofibrosis and 1 case of chronic knee irritation. The gradual deterioration of the operated knees within the follow-up period is mainly caused by the pre-existing chronic degenerative changes, which progress in spite of a sufficient stabilization of the central pivot.