Purpose

Analyze whether high degrees of passive hyperextension of the knee (more than 5 degrees) was associated with a worse functional prognosis and greater risk of graft failure after primary ACL reconstructions with hamstrings tendon autografts.

Methods

This was a retrospective cohort study, designed to assess the functional outcome of patients undergoing primary ACL reconstruction with hamstrings tendon autografts. Patients operated from from June/2013 to June/18 were included. Inclusion criteria were: patients aged between 18 and 60 years old, with acute or chronic ACL injury, who underwent anatomical single-bundle intra-articular ACL reconstruction with autologous hamstrings autografts, with a minimum follow-up of 2 years. Patients with associated injuries that required additional surgical procedures, such as peripheral ligament reconstructions, posterior cruciate ligament reconstruction, osteotomy and cartilage procedures and patients that lost follow-up were not included for this evaluation. The following data were collected: patient demographic data (age and gender), time from injury to surgery, passive knee hyperextension, KT-1000 and pivot-shift, associated meniscus injury and treatment, contra-lateral knee ligament injury, intra-articular graft size, follow-up time, occurrence of graft failure and postoperative Lysholm knee scale and IKDC subjective form. Passive knee hyperextension was measured using a goniometer in the contralateral knee to minimize the effects of the ACL injury on the affected knee. A group of cases was formed containing all patients with passive knee hyperextension. A control group of the same size was selected by matching among the other patients. The matching was done using age (each patient in the case group was paired with a patient up to 5 years older or 5 years younger), gender, associated meniscal tear and contra-lateral knee injury. Physical examination parameters were not used to match patients as it could be influenced by the knee laxity of each patient. We also did not use Beighton classification for this study and only focused on the knee hyperextension parameters.

Results

A total of 336 patients were initially included in the study; 21 were excluded. From our cohort of 314 patients, 102 had more than 5 degrees of knee hyperextension. A control group of the same size (102) was selected by matching among the other 212 patients. Data from 204 patients were evaluated. Both groups were similar regarding all variables, with the exception of passive knee hyperextension that presented a median of 1 degree for the control group and 9 for the hyperextension group (p=<0.001). Follow up time was also higher in the hyperextension group by a mean difference of 3.3 months. We found a significant difference between the 2 groups in the incidence of graft failure and Lysholm knee scale (89.6 +/- 6.1 vs. 86.4 +/- 9.8); p=0.018). Graft failure occurred at an incidence of 2.9% in the Control group and 14.7% in the Case group (p=0.005).

Conclusion

The most important finding of this study is that patients that have a preoperative higher degree of knee hyperextension present a higher failure rate after an ACL reconstruction performed with hamstrings grafts than patients with less or no knee hyperextension.