›Patellar tendon composed of type I collagen fibers
›Tensile strength dependent on collagen crosslinks and fibrillar organization
›Enthesis at inferior patellar pole is the most common rupture site
›Degenerative tendinopathy pathway
›Chronic repetitive microtrauma leads to collagen fiber disorganization
›Tendinosis (mucoid degeneration, fibrocartilaginous metaplasia) reduces tensile strength
›Rupture represents terminal event in cumulative tendinopathy
›75-98% of ruptured tendons show pre-existing degenerative changes histologically
›Acute eccentric overload mechanism
›Violent eccentric quadriceps contraction against flexed knee
›Tensile load exceeds remaining tendon capacity
›Sudden catastrophic failure at weakest point
›Anatomical vulnerability
›Inferior patellar pole enthesis
›Watershed zone of poor vascularity predisposes to degeneration
›Stress concentration at bone-tendon interface
›Mid-substance tears
›Less common than pole avulsions
›More common in younger high-energy trauma patients
›Tibial tuberosity avulsion
›Rare in adults; more common in skeletally immature patients
›Systemic disease mechanisms
›SLE and corticosteroid use
›Immune complex deposition in tendon vessels causing ischemia
›Corticosteroids impair collagen synthesis and promote proteolysis
›CKD and renal osteodystrophy
›Secondary hyperparathyroidism weakens bone-tendon interface
›Tendon calcifications and degeneration
›Fluoroquinolone tendon toxicity
›Inhibition of tenocyte proliferation and matrix metalloprotease upregulation
›Direct disruption of collagen fibril structure
Therapeutic Considerations
›Surgical vs nonoperative outcomes
›Complete tear management
›All complete patellar tendon ruptures require surgical repair
›Nonoperative management of complete tears leads to poor functional outcomes
›Quadriceps strength deficit, chronic extensor lag, and disability
›Repair timing and outcomes
›Acute repair (within 2-3 weeks): best functional outcomes
›Delayed repair (6-12 weeks): requires more extensive mobilization
›Chronic repair (>3 months): graft augmentation or reconstruction required
›Return-to-sport data
›75-94% of patients return to sport after surgical repair
›83% return to pre-injury athletic level
›Return-to-running approximately 9 months; pre-injury sport 12-18 months
›Surgical technique evidence
›Suture anchor vs transosseous technique
›Suture anchor: rerupture rate 0% vs 7.5% for transosseous in one large cohort
›Both techniques yield similar functional scores (IKDC, Lysholm, Tegner)
›Augmentation reduces failure rate to approximately 2%
›Augmentation rationale
›Protects repair during early healing
›Recommended for mid-substance tears, poor tissue quality, and chronic ruptures
›Complications
›Rerupture rate
›3-7.5% with transosseous technique
›Reduced with suture anchor repair
›Quadriceps atrophy
›Universal after repair; responds to rehabilitation
›Knee stiffness
›Risk reduced with early passive ROM protocol
›Patellofemoral symptoms
›Altered patellar tracking post-repair
›Infection
›Surgical site infection risk
›Higher with diabetes, immunosuppression
›Prognostic factors
›Favorable prognosis
›Acute repair within 2 weeks
›Age under 40
›No systemic disease
›BMI under 25
›Unfavorable prognosis
›Delayed repair
›Age over 40
›BMI over 25
›Systemic disease (SLE, CKD, diabetes)
›Prior corticosteroid exposure