Musculoskeletal · Knee Injuries
The facts most likely to be tested
Patellar tendon rupture typically occurs in patients under 40 years old following a forced eccentric contraction of the quadriceps.
The classic physical exam finding is an inability to perform an active straight leg raise due to loss of the extensor mechanism.
Physical examination reveals a palpable defect inferior to the patella and patella alta on clinical inspection.
Radiographic imaging often demonstrates patella alta (high-riding patella) on the lateral knee view.
Patellar tendon rupture is strongly associated with systemic conditions such as systemic lupus erythematosus (SLE), rheumatoid arthritis, and chronic kidney disease.
Fluoroquinolone antibiotic use and corticosteroid injections are significant iatrogenic risk factors for tendon weakening and subsequent rupture.
The definitive treatment for a complete patellar tendon rupture is urgent surgical repair to restore the extensor mechanism.
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A 35-year-old male presents to the emergency department after feeling a 'pop' in his right knee while jumping for a basketball. He reports immediate pain and an inability to bear weight. On physical examination, there is a palpable gap inferior to the patella, and the patella appears superiorly displaced. The patient is unable to perform an active straight leg raise against gravity. He has a history of systemic lupus erythematosus managed with chronic oral prednisone.
What is the most appropriate next step in management?
Urgent surgical repair
The patient presents with the classic triad of a palpable defect, patella alta, and inability to perform a straight leg raise, confirming a complete patellar tendon rupture which requires surgical intervention to restore the extensor mechanism.
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Etiology / Epidemiology
Occurs primarily in patients <40 years old with tendinopathy or systemic disease.
Clinical Manifestations
Classic inability to extend the knee against gravity with a palpable defect.
Diagnosis
MRI is the gold standard; plain radiographs show patella alta.
Treatment
Surgical repair is mandatory; do not delay to prevent retraction.
Prognosis
Full recovery takes 6-12 months; quadriceps atrophy is a common complication.
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Epidemiology & Etiology
Typically affects active individuals under 40, often secondary to chronic patellar tendinopathy. Systemic risk factors include chronic corticosteroid use, diabetes mellitus, and rheumatoid arthritis. It is frequently associated with a sudden, forceful eccentric contraction of the quadriceps.
Pertinent Anatomy
The patellar tendon connects the inferior pole of the patella to the tibial tubercle. It is the primary stabilizer for knee extension. Disruption results in the loss of the extensor mechanism.
Pathophysiology
Rupture occurs when the force applied to the tendon exceeds its tensile strength. This often happens during a jump or landing with the knee in a flexed position. The resulting loss of the extensor mechanism leads to patella alta as the quadriceps pulls the patella superiorly.
Clinical Manifestations
Patients report a popping sensation followed by immediate pain and swelling. The hallmark is the inability to perform a straight leg raise or actively extend the knee. A palpable defect is often felt inferior to the patella. Red flag: misdiagnosis as a simple knee sprain leads to permanent functional loss.
Diagnosis
Physical exam reveals a high-riding patella, known as patella alta. Plain radiographs are the initial imaging choice to rule out avulsion fractures. MRI is the gold standard for confirming the diagnosis and assessing the extent of the tear.
Treatment
Complete ruptures require urgent surgical repair to restore the extensor mechanism. Delayed surgery (>2 weeks) leads to tendon retraction and poor outcomes. Post-operative management involves a knee immobilizer in full extension followed by a structured physical therapy protocol.
Prognosis
Most patients regain full range of motion, but quadriceps atrophy is common. Failure to regain full extension is a major long-term complication. Return to sports typically requires 6-12 months of rehabilitation.
Differential Diagnosis
Quadriceps tendon rupture: patella baja and defect superior to the patella
Patellar fracture: tenderness directly over the bone with visible fracture line on X-ray
Patellar dislocation: patella displaced laterally with spontaneous reduction or visible deformity
Prepatellar bursitis: localized swelling without loss of extensor mechanism
Tibial tubercle avulsion: common in adolescents; fracture visible on imaging