This prospective single-center observational cohort study will evaluate the relationship between anterior knee pain and patellar tendon elasticity after infrapatellar tendon-split tibial intramedullary nailing. Adult patients undergoing standard tibial intramedullary nailing through an infrapatellar tendon-split approach will be enrolled after ethics approval. Patellar tendon elasticity will be assessed using shear-wave ultrasound elastography before surgery and during follow-up at 6 weeks, 3 months, and 6 months. Clinical outcomes will include anterior knee pain severity, patellofemoral function, tendon-related symptoms, and knee range of motion. Inter-rater reliability between two independent radiologists will also be evaluated.

Anterior knee pain is a frequent complaint after tibial intramedullary nailing, but the role of patellar tendon biomechanical changes remains unclear. The infrapatellar tendon-split approach may lead to tendon healing, remodeling, and fibrosis, which could alter tendon elasticity and contribute to persistent pain and functional limitation. This study aims to prospectively investigate whether changes in patellar tendon elasticity are associated with anterior knee pain after infrapatellar tendon-split tibial intramedullary nailing.

This is a prospective, single-center, non-interventional observational cohort study. Adult patients aged 18 to 65 years with unilateral tibial shaft or metaphyseal fractures treated with standard infrapatellar tendon-split tibial intramedullary nailing will be enrolled consecutively after institutional ethics approval. Only patients enrolled after ethics approval will be included in the registered cohort.

Patellar tendon elasticity will be measured using shear-wave ultrasound elastography at four predefined time points: preoperatively, 6 weeks, 3 months, and 6 months postoperatively. Ultrasound assessments will be performed according to a standardized protocol by two independent radiologists, and inter-rater reliability will be assessed. Additional ultrasound parameters will include tendon thickness on B-mode imaging and Doppler neovascularization.

Clinical outcomes will include anterior knee pain assessed with a visual analog scale, patellofemoral function assessed with the Kujala Anterior Knee Pain Scale, tendon-related symptoms assessed with the VISA-P questionnaire, pressure pain sensitivity, and active knee range of motion. The primary objective is to determine whether change in patellar tendon elasticity is associated with anterior knee pain at 6 months. Secondary objectives are to examine associations between tendon elasticity and functional scores, range of motion, tendon thickness, Doppler findings, and inter-rater measurement reliability.

Inclusion Criteria:

• Age 18 to 65 years
• Unilateral tibial shaft or metaphyseal fracture
• Planned treatment with infrapatellar tendon-split tibial intramedullary nailing
• Ability to complete baseline and follow-up assessments
• Written informed consent

Exclusion Criteria:

• Previous surgery on the same knee
• Previous patellar tendon rupture or known patellar tendon disorder
• Active inflammatory rheumatologic disease
• Chronic systemic corticosteroid therapy or long-term immunosuppressive treatment
• Significant peripheral neuropathy or advanced diabetic neuropathy
• Bilateral tibial fracture
• Additional major lower-extremity injury or surgery affecting assessment
• Inability to comply with scheduled follow-up visits

Adults with unilateral tibial shaft or metaphyseal fractures treated at Bagcilar Training and Research Hospital with standard infrapatellar tendon-split tibial intramedullary nailing will be enrolled prospectively after ethics approval.

Individual participant data will not be shared because this is a single-center study with a limited sample size and no predefined external data-sharing agreement. Only aggregate, de-identified study results will be reported in publications and presentations.