[A prospective study of the outcome of anterior laxity of the knee after anterior cruciate ligament reconstruction with procedures using two different patellar tendon grafting methods].

PURPOSE OF THE STUDY

The aim of this study was to evaluate postoperative evolution of anterior laxity, in order to know at what time the elongation of the reconstructed anterior cruciate ligament (ACL) begins to develop after surgery, and if there were any correlations with recuperation of knee flexion or extension. The second purpose of this study was to compare two series of patients operated on by two different procedures for a long standing ACL rupture.

MATERIAL AND METHODS

Two series of patients were compared: group I (60 cases), had an ACL reconstruction using a free autologous patellar tendon graft with a bone-to-bone fixation, supplemented by an external extra-articular plasty with a strip of quadricipital tendon as a direct prolongation of the graft of the patellar tendon and patella itself. "Mac InJones", and group II (50 cases), had a reconstruction with a similar transplant, but still attached on the tibia and with a fibrous fixation through the femoral condyle and the Gerdy's tubercule (modified "Marshall-Mac Intosh"). Anterior laxity was measured using two instrumented methods; first, Medmetric knee arthrometer (KT-1000), before and after operation, then each month later during the first 6 months and yearly. On the other hand, a personal stress X-ray protocol (at 20 degrees of flexion and with application of a 9 kg load at the distal part of the thigh), was made before operation, 6 months later, and yearly during 8 years. The laxity of both medial and lateral compartments of the knee were separately measured. Laxity was studied in parallel with the recuperation of knee flexion and extension during a rehabilitation program without any limitation in both directions.

RESULTS

During a period of 3 months, the laxity was arthrometrically inferior to the normal knee in the two groups, and appeared progressively. Laxity was independent from early recuperation of full range of flexion and extension. The elongation of the reconstructed ligament was showed to develop during the first 6 months and less during the following 6 months. Better results were found for group I during the earliest period with the Medmetric arthrometer, but there was no difference between both groups after 1 year and 2 years. With dynamic radiography, laxity was higher than indicated by KT-1000, and results were better for group I. Laxity was stabilized after one year and the results were still good after 8 years.

DISCUSSION

KT-1000 showed a great interest for measurement of the compliance index (difference between laxity at 89 newtons and 69 newtons of traction), and can be used without any inconvenient for patients. Stress radiographs may be used for yearly controls. The radiographic method had better accuracy than KT-1000 and gave precise laxity measurements of the medial and lateral compartments of the knee. The laxity of the medial compartment showed to have a good prognostic value.

CONCLUSION

Evolution of laxity is more favourable in group I with bone-to-bone ligament fixation. Recovering early and complete flexion and extension is not prejudicial for the ligament. Laxity developed between 3 and 6 months and less between 6 and 12 months. KT-1000 is able to detect laxity during early postoperative period. Dynamic radiographs are more precise to control laxity year after year. Informations concerning the two compartments of the knee are of great interest to compare different procedures and to improve new surgical techniques.