Patellar tendon rupture is a relatively uncommon but disabling disruption of the knee extensor mechanism, most commonly seen in males under 40 years of age during athletic activities involving a violent eccentric quadriceps contraction against a flexed knee. [1-2] The incidence in the general population is approximately 0.68 per 100,000 person-years, though substantially higher (6 per 100,000) in active military populations. [3] It accounts for roughly 5% of all extensor mechanism injuries and is six times less common than patellar fracture. [2][4] The diagnosis is often clinically straightforward but is frequently missed in the emergency department, leading to delayed repair and worse outcomes. [2][5]
1. History
- Mechanism: Sudden forceful eccentric quadriceps contraction against a flexed knee — typically during jumping, landing, stumbling, or a fall [1]
- Ask about the specific activity at the time of injury (sports, stairs, fall from height)
- Acute onset of anterior knee pain with a "pop" or tearing sensation
- Immediate inability to walk or bear weight on the affected leg
- Inability to straighten the knee or perform a straight leg raise
- Prior history of patellar tendinopathy ("jumper's knee"), prior knee injections, or chronic knee pain — rupture often represents the final stage of degenerative tendinopathy [1]
- Medication history: corticosteroids (local or systemic), fluoroquinolones [6-7]
- Systemic disease history: SLE, chronic renal failure, diabetes, rheumatoid arthritis [1][8]
2. Alarm Features
- Complete inability to extend the knee against gravity — hallmark of complete rupture [1][5]
- Palpable gap in the infrapatellar region
- High-riding patella (patella alta) visible or palpable [5]
- Bilateral rupture (rare but associated with systemic disease — SLE, CKD, steroid use) [8]
- High-energy mechanism (direct blow) — 75% of these have associated intra-articular injuries (ACL tear, meniscal tear) [9]
- Open wound over the tendon (open extensor mechanism injury)
- Neurovascular compromise distally (rare, but assess)
3. Medications
- Contributors to rupture:
- Systemic or local corticosteroids — weaken tendon collagen [1][8]
- Fluoroquinolones (ciprofloxacin, levofloxacin) — associated with tendon degeneration and rupture [6]
- Anabolic steroids
- Anastrozole — case reports of bilateral extensor mechanism rupture [7]
- Acute pain management:
- NSAIDs or acetaminophen for analgesia
- Opioids as needed for severe pain in the ED
- Avoid: Intra-articular or peritendinous corticosteroid injection in the acute setting
4. Diet
- No specific acute dietary triggers
- Adequate protein intake is important for tendon healing postoperatively
- Ensure adequate vitamin D and calcium — deficiency may impair musculoskeletal healing
- Hydration is standard perioperative care
5. Review of Systems
- Musculoskeletal: Prior knee pain, tendinopathy, contralateral knee symptoms (bilateral rupture risk)
- Rheumatologic: Joint pain, rash, oral ulcers, photosensitivity (SLE), morning stiffness (RA)
- Renal: History of CKD, dialysis (associated with tendon weakening)
- Endocrine: Diabetes, thyroid disease, hyperparathyroidism
- Medications: Steroid use, fluoroquinolone use
- Constitutional: Fever, weight loss (if concern for underlying systemic disease)
6. Collateral History and Family History
- Witnesses to the mechanism of injury (sports trainers, bystanders)
- Prior athletic level and functional demands — critical for surgical planning
- Family history of connective tissue disorders (Ehlers-Danlos, osteogenesis imperfecta) [10]
- History of SLE, rheumatoid arthritis, or renal disease in the family
- Social context: occupation, athletic goals, ability to comply with prolonged rehabilitation
7. Risk Factors
- Age <40 years (peak incidence), though 43% occur in patients over 40 [1][11]
- Male sex — 91–98% of cases [3][11]
- Overweight/obesity — mean BMI ~28.7 kg/m² in patellar tendon rupture cohorts; worse prognosis with BMI >25 [4][11]
- Chronic patellar tendinopathy ("jumper's knee") — rupture is often the end-stage [1][4]
- Jumping sports (basketball, volleyball) and high-demand activities [6]
- Systemic diseases: SLE, CKD, diabetes mellitus, rheumatoid arthritis, hyperparathyroidism [1][8]
- Medications: Corticosteroids, fluoroquinolones [6-7]
- Black race — higher relative rate ratio (9.21× vs White) in military data [3]
- Age 35–44 — highest risk bracket in military populations [3]
- Prior knee surgery or patellar tendon harvest (e.g., ACL reconstruction)
8. Differential Diagnosis
- Quadriceps tendon rupture — more common in patients >40; palpable gap is suprapatellar; patella baja on radiograph (vs. patella alta) [2][12]
- Patellar fracture — 6× more common than tendon ruptures; bony tenderness, crepitus, visible on X-ray [2]
- Tibial tubercle avulsion — skeletally immature patients; pain/swelling at tibial tuberosity; risk of compartment syndrome [13]
- Patellar sleeve fracture — pediatric patients; cartilaginous avulsion may be radiographically occult [13]
- ACL rupture — hemarthrosis, instability, positive Lachman; can coexist (18% of patellar tendon ruptures) [9]
- Patellar dislocation/subluxation — lateral displacement, apprehension test positive, medial retinacular tenderness
- Meniscal tear — joint line tenderness, mechanical symptoms; can coexist [9]
- Partial patellar tendon tear — may retain some active extension; diagnosis may require ultrasound or MRI
9. Past Medical History
- Prior episodes of patellar tendinopathy or "jumper's knee"
- Previous corticosteroid injections around the knee
- Prior knee surgery (especially patellar tendon autograft harvest for ACL reconstruction)
- History of SLE, CKD, diabetes, RA, hyperparathyroidism [1][8]
- Osgood-Schlatter disease (pediatric patients) [10]
- Osteogenesis imperfecta or connective tissue disorders [10]
- Prior fluoroquinolone use
10. Physical Exam
- Inspection: Swelling, ecchymosis over the anterior knee; high-riding patella (patella alta) — the patella may appear visibly displaced superiorly [5]
- Palpation: Palpable gap or defect in the infrapatellar tendon substance — pathognomonic [1][5]
- Active extension test: Inability to perform a straight leg raise or actively extend the knee against gravity — the single most important exam finding [1-2][12]
- Partial tears may retain some extension but with an extensor lag
- Hemarthrosis is common
- Assess retinacular integrity — if intact, some active extension may be preserved, masking a complete tear
- Compare to contralateral knee for patellar height
- Neurovascular exam of the distal extremity
- Assess for associated ligamentous instability (Lachman, anterior drawer) especially with high-energy mechanisms [9]
11. Lab Studies
- Routine labs are generally not required for isolated traumatic rupture
- If bilateral rupture or atraumatic mechanism, consider:
- BMP/CMP (renal function — CKD association)
- ANA, anti-dsDNA, complement levels (SLE screening) [8]
- ESR/CRP (inflammatory markers)
- Calcium, phosphorus, PTH (hyperparathyroidism)
- HbA1c (diabetes)
- Uric acid (gout — rare association)
- Preoperative labs as indicated (CBC, BMP, coagulation studies, type and screen)
12. Imaging
- First-line: Bilateral lateral knee radiographs
- Patella alta (high-riding patella) is the hallmark finding — compare to the contralateral knee [1][5]
- Insall-Salvati ratio >1.2 suggests patella alta (sensitivity 84%, specificity 79%) [14]
- Focal intratendinous radiolucency — a newer sign with 82.5% sensitivity and 95.2% specificity [14]
- May show avulsion fragments from the inferior pole of the patella or tibial tuberosity
- Ultrasound: High-resolution, dynamic evaluation; differentiates partial from complete tears; readily available at bedside (point-of-care) [8][15]
- MRI: Gold standard for soft tissue characterization; indicated when diagnosis is equivocal, to assess partial vs. complete tear, or to evaluate for associated intra-articular injuries (ACL, meniscus) [15-16]
- Complete rupture shows increased T2 signal intensity with tendon discontinuity [16]
- Recommended especially with high-energy direct impact mechanisms (75% have associated intra-articular injuries) [9]
- Imaging is often unnecessary when clinical findings are unequivocal (palpable gap + inability to extend + patella alta) [17]
13. Special Tests
- Insall-Salvati ratio (patellar tendon length : patellar length on lateral radiograph) — ratio >1.2 indicates patella alta [14]
- Caton-Deschamps ratio and Blackburne-Peel ratio — alternative patellar height measurements [14]
- Point-of-care ultrasound (POCUS): Can rapidly confirm tendon discontinuity at the bedside in the ED [8][15]
- Straight leg raise test: Inability = complete extensor mechanism disruption
- Extensor lag test: Partial tears may show a lag (inability to fully extend from a flexed position)
14. ECG
- Not routinely indicated for isolated patellar tendon rupture
- Obtain if planning procedural sedation or if the patient has cardiac risk factors/comorbidities
- Standard preoperative ECG per institutional protocol if surgical repair is planned
15. Assessment
Patellar tendon rupture is a clinical diagnosis made by the triad of: (1) palpable infrapatellar gap, (2) inability to actively extend the knee/perform SLR, and (3) patella alta on lateral radiograph. [1][5] The injury typically results from the final stage of chronic degenerative tendinopathy precipitated by an acute eccentric load. [1]
- Complete ruptures require surgical repair — this is not a conservative-management injury [12][17]
- Partial tears with intact active extension may be managed nonoperatively in select cases, though high-grade partial tears often warrant surgery [12]
- Delayed diagnosis is the most common pitfall — easily missed in a busy ED, especially with partial tears or when hemarthrosis/swelling obscures the palpable gap [2][5]
- Complications to consider: Quadriceps atrophy, knee stiffness, rerupture (3–7.5%), infection, patellofemoral symptoms [3][17-18]
- Associated intra-articular injuries occur in ~30% of patellar tendon ruptures overall and 75% with high-energy mechanisms (ACL tears 18%, meniscal tears 18%) [9]
16. Treatment Plan
Initial stabilization (ED)
- Immobilize the knee in full extension with a knee immobilizer or long-leg posterior splint
- Ice, elevation, analgesia (NSAIDs ± opioids)
- Non-weight-bearing or protected weight-bearing with crutches
- Urgent orthopedic consultation — early repair is critical [1][5]
Surgical repair (definitive treatment)
- All complete ruptures require surgical repair [12][17][19]
- Ideally performed within days to 2–3 weeks of injury; outcomes decline with delay [1][4]
- Transosseous (bone tunnel) repair: Traditional gold standard — Krackow sutures through the tendon secured via patellar bone tunnels [12][20]
- Suture anchor repair: Smaller incision, less dissection; significantly lower rerupture rate (0% vs 7.5%) compared to transosseous in one large cohort [18]
- Augmentation (cerclage wire, suture tape, or graft) is commonly used, especially for mid-substance tears, compromised tissue, or chronic ruptures [12][19-20]
- Augmented primary repair has the best outcomes for acute tears (~2% failure rate) [19]
Postoperative rehabilitation
- Immediate protected weight-bearing in a knee immobilizer locked in extension [12][17]
- Early passive ROM (safe-zone flexion) initiated within the first 1–2 weeks; avoid active extension initially [12]
- Progressive flexion: 45° for weeks 1–3, 90° by weeks 3–6, then unrestricted [21]
- Full active ROM and concentric strengthening program after 6 weeks [12]
- Return to running ~9 months; return to pre-injury sport level ~12–18 months [4][20]
- 75–94% of patients return to sport; 83% at pre-injury level [3-4]
17. Disposition
- Discharge from ED with knee immobilizer in full extension, crutches (NWB or TDWB), and urgent orthopedic follow-up within 3–7 days [5]
- Admission criteria:
- Open injury or associated vascular injury
- Bilateral rupture requiring urgent bilateral repair
- Polytrauma or inability to safely mobilize
- Need for same-day/next-day surgical repair based on orthopedic assessment
- Orthopedic consultation in the ED is warranted for all complete ruptures to establish a surgical timeline [2][5]
- Partial tears with intact active extension may be managed with immobilization and close outpatient follow-up, though orthopedic referral remains essential
18. Follow Up / Return Precautions
- Orthopedic follow-up within 3–7 days if not repaired acutely — delay worsens outcomes [1][5]
- Return precautions for patients discharged from the ED:
- Increasing pain, swelling, or inability to keep the knee immobilized
- Signs of compartment syndrome (severe pain with passive stretch, paresthesias, pallor)
- Wound complications if post-surgical (redness, drainage, fever)
- Expected recovery course:
- 6 weeks: progressive ROM and strengthening
- 3–6 months: functional activities
- 9–12 months: return to running
- 12–18 months: return to pre-injury sport level [4][20]
- Prognosis is worse with age >40, BMI >25, and delayed repair [1][4]
- Long-term complications include quadriceps atrophy, knee stiffness, patellofemoral symptoms, and rerupture (3–7.5%) [3][17-18]
- Patient counseling: Emphasize that this is a surgical injury requiring timely repair; compliance with immobilization and rehabilitation is critical for optimal outcomes
References
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2. Adult Native Knee Extensor Mechanism Ruptures. — Pengas IP, Assiotis A, Khan W, Spalding T. Injury. 2016.
3. Incidence and Risk Factors of Acute Patellar Tendon Rupture, Repair Failure, and Return to Activity in the Active-Duty Military Population. — Fredericks DR, Slaven SE, McCarthy CF, et al. The American Journal of Sports Medicine. 2021.
4. Return to Sport After Early Surgical Repair of Acute Patellar Tendon Ruptures. — Beranger JS, Kajetanek C, Bayoud W, Pascal-Mousselard H, Khiami F. Orthopaedics & Traumatology, Surgery & Research : OTSR. 2020.
5. Patellar Tendon Ruptures. — Enad JG. Southern Medical Journal. 1999.
6. Answer to Last Month's Radiology Case and Image: Bilateral Patellar Tendon Rupture. — Riojas RA, Folio L. Military Medicine. 2009.
7. Knee Extensor Mechanism Repairs: Standard Suture Repair and Novel Augmentation Technique. — Meyer Z, Ricci WM. Journal of Orthopaedic Trauma. 2016.
8. Bilateral Patellar Tendon Rupture on Lupus Undergoing Corticosteroids: A Case Report. — El Ouali Z, Nassar K, Bassa E, et al. BMC Musculoskeletal Disorders. 2020.
9. Intra-Articular Knee Injuries in Patients With Knee Extensor Mechanism Ruptures. — McKinney B, Cherney S, Penna J. Knee Surgery, Sports Traumatology, Arthroscopy : Official Journal of the ESSKA. 2008.
10. Acute Traumatic Rupture of the Patellar Tendon in Pediatric Population: Case Series and Review of the Literature. — Ali Yousef MA, Rosenfeld S. Injury. 2017.
11. Extensor Mechanism Injuries of the Knee: Demographic Characteristics and Comorbidities From a Review of 726 Patient Records. — Garner MR, Gausden E, Berkes MB, Nguyen JT, Lorich DG. The Journal of Bone and Joint Surgery. American Volume. 2015.
12. Repair of Quadriceps and Patellar Tendon Tears. — Danaher M, Faucett SC, Endres NK, Geeslin AG. Arthroscopy : The Journal of Arthroscopic & Related Surgery : Official Publication of the Arthroscopy Association of North America and the International Arthroscopy Association. 2023.
13. Acute Knee Injuries in Children and Adolescents: A Review. — MacDonald J, Rodenberg R, Sweeney E. JAMA Pediatrics. 2021.
14. Focal Intratendinous Radiolucency: A New Radiographic Method for Diagnosing Patellar Tendon Ruptures. — Ng JP, Cawley DT, Beecher SM, et al. The Knee. 2016.
15. Extensor Apparatus of the Knee: Anatomy and Injury Patterns. — Flores D, Atinga A, Beaulieu C, Alaia EF, Probyn L. Skeletal Radiology. 2026.
16. MR Imaging of Injuries of the Extensor Mechanism of the Knee. — Yu JS, Petersilge C, Sartoris DJ, Pathria MN, Resnick D. Radiographics : A Review Publication of the Radiological Society of North America, Inc. 1994.
17. Quadriceps and Patellar Tendon Ruptures. — Lee D, Stinner D, Mir H. The Journal of Knee Surgery. 2013.
18. Operative Treatment of Acute Patellar Tendon Ruptures. — O'Dowd JA, Lehoang DM, Butler RR, Dewitt DO, Mirzayan R. The American Journal of Sports Medicine. 2020.
19. Reconstruction Techniques and Clinical Results of Patellar Tendon Ruptures: Evidence Today. — Gilmore JH, Clayton-Smith ZJ, Aguilar M, Pneumaticos SG, Giannoudis PV. The Knee. 2015.
20. Management of Acute Midsubstance Patella Tendon Rupture: Current Concepts and Clinical Narrative Review. — Di Stefano MT, Young M, Corvi M, et al. JBJS Reviews. 2025.
21. Primary Repair of Patellar Tendon Rupture Without Augmentation. — Marder RA, Timmerman LA. The American Journal of Sports Medicine. 1999.