An exploratory study of relationships among morphological and mechanical properties of the patellar tendon and patient-reported outcomes after ACLR using BPTB autograft.

PURPOSE: Patellar tendon structural and mechanical properties undergo significant remodelling after anterior cruciate ligament (ACL) reconstruction (ACLR) using a bone-patellar tendon-bone (BPTB) autograft. Tendon properties have been described at different time points after surgery, but their relationship to patient-reported outcome measures (PROMs) is unclear. The purpose of this investigation was to assess how patellar tendon structure relates to PROMs after ACLR using BPTB autograft. METHODS: Thirty-four individuals with unilateral ACLR using a BPTB autograft participated in this secondary exploratory analysis. At time points 1, 3-4, and 6-9 months after surgery, PROMs were completed and tendon properties (cross-sectional area [CSA], thickness, shear modulus, and viscosity) were assessed using B-mode ultrasound imaging and continuous shear wave elastography. Simple linear regressions evaluated the relationship between Limb Symmetry Index of tendon properties (LSI, [involved ÷ uninvolved] × 100) at each time point and PROM scores at the 6-9-month time point. Multiple regressions assessed associations between involved limb tendon properties at all three time points and PROMs at 6-9 months, adjusting for age, sex, body mass index (BMI), and time from surgery. R 2 values for simple linear regressions and R 2 change values for multiple regressions were interpreted with an alpha level of 0.05. RESULTS: Shear modulus LSI at 1 month was negatively correlated with Anterior Cruciate Ligament-Return to Sport after Injury (ACL-RSI) scores at 6-9 months (p = 0.022, R 2 = 0.225, β  = -0.20). Viscosity LSI at the 3-4 month time point was positively correlated with Tampa Scale of Kinesiophobia (11-item) (TSK-11) scores at 6-9 months (p = 0.016, R 2 = 0.197, β  = 0.06). Thickness LSI at 6-9 months was positively correlated with Knee Outcome Survey-Activities of Daily Living Scale (KOS-ADLS) scores at 6-9 months (p = 0.031, R 2 = 0.156, β  = 0.03). When involved limb patellar tendon properties and covariates were considered, no significant relationships with PROM scores were observed (p = 0.120-0.960). CONCLUSION: Limb symmetry in tendon properties, but not involved limb properties alone, was associated with PROMs 6-9 months after ACLR using BPTB autograft. This suggests that limb symmetry of tendon properties may relate to self-reported recovery. LEVEL OF EVIDENCE: Level II.