Ito, Naoaki2023-10-092023-10-092023https://udspace.udel.edu/handle/19716/33455Prevalence of anterior cruciate ligament (ACL) injury and subsequent reconstruction surgery (ACLR) exceeds 200,000 cases a year, impeding young athletes’ participation in sports and long-term knee joint health. The bone-patellar tendon-bone (BPTB) autograft is one of the most common graft types used in the United States and is harvested from the central third of the patellar tendon. Harvesting a graft from the already injured knee, however, comes with a cost. Quadriceps weakness, a key factor to address in rehabilitation after ACL injury, is more profound when compared to other graft types that do not involve the extensor mechanism. Anterior knee pain, especially with kneeling, is also more prevalent due to the additional surgical insult. Such graft site morbidities early after ACLR may exacerbate the already elevated rates of post-traumatic knee osteoarthritis (OA) observed after ACL injury. Recovery of the graft site patellar tendon’s morphology and mechanical properties may in part explain graft site morbidities. The course of recovery of the patellar tendon, its relationship with clinical outcomes, and its influence on movements such as walking gait have been seldom studied. Objectives of this project were to investigate the changes in patellar tendon structure after BPTB graft harvest, assess the influence of tendon structure on clinical outcomes after ACLR, and to investigate whether neuromuscular deficits of the quadriceps are reflected during gait and persist from BPTB graft harvest. We aimed to fulfill our objectives through the following specific aims. ☐ Aim 1: Establish the healing trajectory of the patellar tendon after BPTB autograft harvest. • Aim 2a: Examine the associations between patellar tendon morphology and mechanical properties with clinical and functional outcomes after ACLR using BPTB autograft. • Aim 2b: Evaluate the prognostic value of patellar tendon structure early after BPTB graft harvest to predict clinical and functional outcomes at later stages in rehabilitation. • Aim 3a: Identify deficits in quadriceps neuromuscular function during gait after ACLR using BPTB autograft compared to alternative graft types 5 months after ACLR. • Aim 3b: Determine whether quadriceps neuromuscular function during gait improves from 5 months to 24 months after ACLR using BPTB autograft. ☐ In aims 1 and 2, we collected patellar tendon structure and clinical data from patients after ACLR using BPTB at three critical timepoints (1-month, 3-4 months, 6-9 months) during rehabilitation. Aim 1 characterized the healing trajectory of both morphological (cross-sectional area, thickness, and length using B-mode ultrasound) and mechanical (shear modulus and viscosity using continuous shear wave elastography) properties in the medial, lateral, and central (graft site) regions of the patellar tendon. Through this aim we learnt that there is initial hypertrophy in the patellar tendon after graft harvest, which is most exaggerated in the central third, followed by a uniform reduction in size over the course of rehabilitation reflecting remodeling of the tendon. Tendon elongation was also seen in all three regions, with the medial and lateral region staying elongated over the course of rehabilitation and the central region shortening, likely attributed to bony healing at the graft site. Findings in mechanical properties were less clear. Viscosity was higher in the medial compared to the central and lateral regions primarily in the uninvolved limb, but a more uniform viscosity was observed in the involved limb. The viscosity in the involved limb also reduced over time in all three regions. Shear modulus was greater in the involved compared to uninvolved limb across all three regions initially after surgery, and shear modulus reduced from 1 month to 3-4 months, but only in the central region. Findings from this aim provide clinicians with a reference point for the expected healing trajectory of the patellar tendon after graft harvest. ☐ In aim 2, patellar tendon structural measures collected in aim 1 were used to predict quadriceps function (strength and inhibition) and patient reported outcome measures (Knee Outcome Survey – Activities of Daily Living Scale [KOS-ADLS] and International Knee Documentation Committee 2000 [IKDC]). Through this aim we learnt that patellar tendon hypertrophy early on after surgery is a major predictor of quadriceps strength later in rehabilitation. Presenting with greater cross-sectional area was also predictive of less quadriceps inhibition 3-4 months after ACLR. High viscosity at the 3-4 month timepoint, when the remodeling phase of tendon healing takes place, was predictive of quadriceps strength later on. By 6-9 months from surgery, patients with more symmetrical thickness, or likely better remodeled tendons, also demonstrated better quadriceps strength index. No structural variables were predictive of patient reported outcome measures. Findings from aim 2 support the use of ultrasound imaging to quantify patellar tendon structure early after ACLR as an early prognostic biomarker for quadriceps function. ☐ In aim 3, we quantified quadriceps neuromuscular function during walking gait in athletes after ACLR using BPTB autograft and compared them against those with grafts that did not insult the extensor mechanism. Quadriceps neuromuscular function was quantified using the extensor latency metric which measures the delay in peak external knee flexion moment (measured via motion capture and inverse dynamics) from peak quadriceps activation (measure via electromyography) during the weight acceptance phase of gait. Athletes were followed up 5 and 24 months after ACLR to assess whether BPTB autograft specific quadriceps neuromuscular deficits persist. Athletes after ACLR using BPTB autograft walked with longer latency in their involved limb compared to those who received alternative graft types. No changes in latency were seen, indicating that prolonged extensor latency persisted from rehabilitation until 2 years after surgery when most athletes were actively participating in sport. Neuromuscular changes identified in this aim may in part explain the elevated rates of developing post-traumatic OA after ACLR using the BPTB autograft compared to alternative graft types. Prolonged extensor latency may also influence knee biomechanics during other activities than gait, by impeding efficient control of the knee joint. This aim outlined how patellar tendon graft harvest may impede knee function for a prolonged period of time after ACLR. Early intervention to promote better healing of the graft site tendon may be necessary to preserve and recover neuromuscular function of the quadriceps after ACLR using BPTB autograft. ☐ This dissertation revealed the healing trajectory and influence of patellar tendon graft harvest over the course of rehabilitation. The influence of graft harvest was also shown to influence gait biomechanics 2 years after ACLR when athletes are commonly back to participating in their sport. Work from this dissertation supports the use of B-mode ultrasound early after ACLR to quantify healing of the patellar tendon, and to possibly implement treatments for those who may benefit from targeted interventions. Patellar tendon graft site morphology guided care may optimize recovery of quadriceps function, and possibly subsequent alterations in movement patterns such as gait and the development of post-traumatic knee OA. Future studies will investigate the impact of implementing an imaging guided graft site tendon loading protocol to investigate if we can optimize our current care to improve overall outcomes after ACLR using BPTB autograft.Anterior cruciate ligamentAutograftUltrasound imagingBone-patellar tendon-boneKnee osteoarthritisACL injuryThesis1410956762https://doi.org/10.58088/njk7-f4862023-09-20en