Musculoskeletal · Orthopedic Trauma
The facts most likely to be tested
Quadriceps tendon rupture typically occurs in patients older than 40 years with a history of eccentric loading of the knee while the foot is planted.
The classic physical exam finding is a palpable defect or sulcus located superior to the patella.
Patients present with an inability to actively extend the knee against gravity or maintain a straight leg raise.
The patella baja (low-riding patella) sign is a pathognomonic radiographic finding caused by the loss of the superior tethering force of the quadriceps tendon.
Risk factors include chronic systemic disease such as diabetes mellitus, chronic renal failure, hyperparathyroidism, or long-term corticosteroid use.
Magnetic resonance imaging (MRI) is the gold standard diagnostic modality to confirm the diagnosis and assess the extent of the tendon tear.
Surgical repair is the definitive treatment of choice for complete ruptures to restore the extensor mechanism of the knee.
Vignette unlocked
A 55-year-old male with a history of end-stage renal disease presents to the emergency department after feeling a 'pop' in his right knee while stepping off a curb. On physical examination, he has significant swelling and tenderness at the superior pole of the patella. He is unable to perform an active straight leg raise. A lateral knee radiograph reveals a low-riding patella. A palpable defect is noted just above the patella.
What is the most likely diagnosis?
Quadriceps tendon rupture
The patient's inability to perform a straight leg raise combined with a palpable defect superior to the patella and radiographic evidence of patella baja is diagnostic for a quadriceps tendon rupture.
Full handout
High yield triage
Etiology / Epidemiology
Occurs primarily in patients >40 years old with tendinopathy or systemic disease (e.g., diabetes, CKD).
Clinical Manifestations
Presents with inability to extend the knee and a palpable defect above the patella.
Diagnosis
MRI is the gold standard for confirming the extent of the tear.
Treatment
Surgical repair is required for complete ruptures, ideally within 7-10 days.
Prognosis
Full recovery requires 6-12 months of physical therapy; quadriceps atrophy is a common complication.
Full handout
Epidemiology & Etiology
Most common in males >40 years old following a sudden eccentric contraction of the quadriceps. Underlying chronic tendinopathy is a major predisposing factor. Systemic conditions like hyperparathyroidism, diabetes mellitus, and chronic kidney disease weaken the tendon structure.
Pertinent Anatomy
The quadriceps tendon attaches the four quadriceps muscles to the superior pole of the patella. Rupture results in a loss of the extensor mechanism of the knee. The retinaculum may remain intact, potentially allowing for limited active extension.
Pathophysiology
The injury typically occurs during a fall on a flexed knee or sudden deceleration. The tendon fails at the osteotendinous junction due to degenerative changes or acute overload. Complete rupture leads to proximal retraction of the quadriceps muscle belly.
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 against gravity. A sulcus sign or palpable gap is often felt superior to the patella. Inability to bear weight is a universal red flag.
Diagnosis
Physical exam is diagnostic if a gap is palpable and extension is absent. MRI is the gold standard to differentiate partial from complete tears and assess retraction. Radiographs may show patella baja, indicating a loss of the superior tethering force.
Treatment
Complete ruptures require surgical repair to restore the extensor mechanism. Surgery should be performed within 7-10 days to prevent muscle retraction and scarring. Delayed repair leads to significantly worse functional outcomes. Post-operative management involves a knee immobilizer in full extension.
Prognosis
Most patients regain near-full range of motion with aggressive rehabilitation. Quadriceps atrophy is the most frequent long-term complication. Return to pre-injury activity levels typically takes 6-12 months.
Differential Diagnosis
Patellar tendon rupture: palpable defect inferior to the patella with patella alta
Patellar fracture: tenderness directly over the bone with bony crepitus
Quadriceps strain: preserved ability to perform a straight leg raise
Prepatellar bursitis: localized swelling without loss of extension
Septic arthritis: systemic symptoms like fever and elevated inflammatory markers