Purpose of the study: The objectives of this study were to measure tension force usually applied to the transplant and analyze its impact on postoperative laxity and joint mobility.

Material and methods: This was a prospective consecutive study. Inclusion criteria were: isolated tear of the anterior cruciate ligament (ACL) more than three months earlier, healthy contralateral knee, radiological anterior drawer measurements (Telos 20 kg) both pre and postoperatively, follow-up greater than six months. ACL reconstruction was achieved with a free bone-tendon-bone patellar transplant using the blind technique. A dynometer was used to measure the traction force applied by the operator using the «usual» method for the tibial fixation. The force applied (2, 4, 6, 9, or 11 kg) was recorded by the assistant and was maintained constant while screwing. Variables studied were: tension force applied to the transplant by four different operators, mobility of the two knees, differential laxity pre and postoperatively (L0 and L1) and relative gain in laxity (real gain/ideal gain).

Results: The study included 22 patients, mean age 26 years. Mean tension force applied was 7.68 kg and varied from 7.3 to 8.1 for each operator. Mean extension and flexion deficit compared with the healthy side was 1.6° and 3° respectively. There was no correlation between loss of mobility and tension applied. Mean laxities (L0 and L1) were 9.2 and 5.4 mm respectively. Mean minimal differential laxity (< 5 mm) was obtained for tension forces of 4 to 6 kg. There was no correlation between tension and L1. The relative gain was greater in the knees with tension at 6 kg. But there was no correlation between these two variables.

Discussion: This study provides the only available data on tension forces applied in routine practice. This tension does not appear to have an impact on the final joint mobility. It would appear however tht laxity would be minimal for tension forces to the order of 7 kg. These data are in agreement with reported in the literature were it is recommended to apply tension to the order of 1.5 to 7 kg.

Conclusion: It would not appear that measuring the force applied to the implant during the tibial fixation provides useful information for routine practice. The force applied in routine practice appears to give the best gain in stability without limiting joint mobility.