Regional Patellar Tendon Strain in the Short- and Long-term After ACL Reconstruction Using Bone-Patellar Tendon-Bone Autograft

Background: Anterior cruciate ligament reconstruction (ACLR) often involves harvesting a bone-patellar tendon-bone (BPTB) autograft. How graft harvest affects tendon strain across the 3 distinct regions (medial, lateral, and central) is not known. Purpose: To (1) quantify strain in the 3 regions of the patellar tendon during 60% of maximum voluntary isometric contraction (MVIC) in 90 degrees of knee flexion and (2) assess how effort level in 2 different knee joint angles (60 degrees and 90 degrees) impacts strain in the medial and lateral regions of the patellar tendon, in 2 cohorts of patients after ACLR using a BPTB autograft (one group <24 months after surgery and another group >= 24 months after surgery). Study Design: Descriptive laboratory study. Methods: Effort levels ranging from 20% to 100% of MVIC were performed at 90 degrees and 60 degrees of knee flexion on an isokinetic dynamometer, with simultaneous ultrasound imaging of tendon length to calculate regional strain. Linear mixed-effects models were used to evaluate regional strain at 60% of MVIC in 90 degrees of knee flexion. The fixed effects of percentage of MVIC, joint angles, and time from surgery groups on patellar tendon strain were evaluated using separate models for the medial and lateral regions. Results: Fourteen participants in the short-term group (7.5 +/- 1.9 months from surgery) and 15 participants in the long-term group (71.5 +/- 16.5 months from surgery) were included. At 60% of MVIC in 90 degrees of knee flexion, the short-term group demonstrated lower patellar tendon strain than the long-term group regardless of region (P < .01). The central region also had lower strain than the medial and lateral regions regardless of group (both P < .01). Finally, the rate at which strain increased with increasing effect levels differed between time from surgery groups in both medial and lateral regions. Conclusion: The short-term group had lower strain in all regions of the patellar tendon after ACLR using BPTB autograft. The medial and lateral regions showed varying strain based on time from surgery and effort level. Varying knee joint angles and effort levels for graft site rehabilitation may have to be considered to target specific regions of the patellar tendon. Clinical Relevance: Clinicians should consider the time elapsed since surgery and the manipulation of knee angle as factors that can exert varying levels of strain on different regions of the patellar tendon after ACLR. Accelerating quadriceps strengthening to enhance strain distribution across the patellar tendon to promote tendon healing may be of benefit for optimizing postsurgery rehabilitation.