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Knee extensor injuries usually occur from three different mechanisms: quadriceps tendon tear, patellar tendon tear, and patellar fracture. Extension may be limited by any disruption of these three. Patients with a history of trauma, other systemic conditions, steroid injections, or fluoroquinolone use are predisposed to tendon disruptions.
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Quadriceps tendon ruptures are the most common extensor failure and are more often seen in the elderly. Forced flexion during quadriceps contraction may cause rupture; patients may experience sudden buckling and pain. The patella is inferiorly displaced with proximal patellar tenderness and swelling. A soft tissue defect at the distal aspect of the quadriceps is often apparent.
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Patellar tendon rupture occurs in the younger, more active population and results in proximal displacement of the patella with inferior pole tenderness and swelling. Patellar fractures may be transverse (most common), comminuted, or vertical. They may be caused by direct trauma or because of high eccentric tension forces. Tenderness, swelling, and sometimes a palpable defect are typically present. Exam will reveal weakness of knee extension against gravity. Patients with complete tears will not be able to extend their knee.
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Management and Disposition
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Lateral radiographs may help distinguish between the two tendon injuries. Patients demonstrating either partial or complete tendon ruptures can be discharged with their knee in extension and follow-up with orthopedics. Care must be taken to differentiate between a bipartite patella and a fracture. Nondisplaced and displaced patellar fractures should receive splinting in full extension and orthopedic referral.
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