Summary

The patellar tendon graft site after bone-patellar tendon-bone autograft harvest for anterior cruciate ligament reconstruction initially heals larger after surgery and reduces in size over the course of rehabilitation.

Abstract

Introduction

Anterior cruciate ligament reconstruction (ACLR) in young athletes commonly involves bone-patellar tendon-bone autograft (BPTB) harvest from the surgical knee. Patients who receive BPTB grafts experience graft site morbidities such as more severe anterior knee pain and prolonged quadriceps weakness compared to those who receive other graft types. The role of incomplete tendon healing in the pathogenesis of graft site morbidities, or the presence of vascularization in tendons during the proliferation and remodeling of the graft site tendon is not well understood. Quantifying the healing trajectory of the patellar tendon may provide insight for future interventions to improve outcomes after ACLR. The purpose of this study was to present descriptive preliminary findings from an ongoing prospective cohort study on the healing trajectory of the patellar tendon after BPTB graft harvest over the course of rehabilitation after ACLR.

Methods

Data from 24 participants (12male | 12female, age:23±8years, body mass index:26±4) at three timepoints after ACLR, T1(1.3±0.3month, n=19), T2(3.4±0.3months, n=18), and T3(7.0±0.4months, n=9) are presented. Data collections are ongoing, and 5 participants enrolled starting at T2. The presence of blood flow in the tendon was dichotomized (yes/no) on clinical examination using doppler ultrasound. B-mode ultrasound was used to quantify patellar tendon morphology. Patellar tendon thickness was assessed in the involved limb over the graft site, and over the central third in the uninvolved patellar tendon. Patellar tendon cross-sectional area (CSA) was assessed at 50% length of the patellar tendon. The means were calculated and interpreted descriptively given the sample size and preliminary nature of the results.

Results

Vasculature was observed in 100% of the involved patellar tendons at T1(19/19) and T2(18/18), and 66.7% of participants at T3(6/9). In the uninvolved patellar tendon, vasculature was noted in only one participant at T2 and one different participant at T3. Patellar tendon thickness was greater in the involved versus uninvolved limb at all timepoints (Involved: T1=0.86±0.17cm, T2=0.81±0.18cm, T3=0.63±0.17cm, Uninvolved: T1=0.40±0.07cm, T2=0.39±0.07cm, T3=0.38±0.06cm). Tendon CSA was also greater in the involved versus uninvolved limb (Involved: T1=1.66±0.40cm2, T2=1.52±0.40cm2, T3=1.15±0.17cm2, Uninvolved: T1=0.86±0.15cm2, T2=0.86±0.17cm2, T3=0.82±0.11cm2). Both thickness and CSA in the involved patellar tendon also tended to reduce over the three timepoints.

Discussion

Vascularization of the tendon demonstrates the natural response in the healing of the surgical defect, possibly identifying the timeframe in which targeted interventions to promote tendon healing may be effective. Most participants had neovascularization for up to 7-months after surgery, but the variability in the time that the patellar tendon stays vascularized may play a role in the healing process. The tendon starts thicker and larger early after surgery, representing the proliferation phase of tendon healing. By 7-months, the thickness and CSA start to reduce from the remodeling process at the graft site tendon. Patellar tendon structure after BPTB graft harvest changes over the course of rehabilitation, and further analysis is necessary to establish the clinical implications. Continued research is needed to quantify the association between structural changes in the patellar tendon and outcomes after BPTB graft harvest to inform targeted interventions to prevent or mitigate graft site morbidities.