Question

28 y.o. male felt his left knee "pop" after landing from a jump while playing basketball. Knee exam revealed limited knee extension. X-ray is shown. Diagnosis?

Answer

Answer: Patella Alta secondary to Patellar tendon rupture

• Mechanism is knee flexion combined with forceful contraction of the quadriceps
• Swelling, patellar tenderness, and limited extension of knee
• Radiographs are helpful in diagnosis when using the Insall-Salvatti ratio (see below)
  • This ratio is the patellar length (PL) (in cm) divided by the distance between inferior pole of the patella and tibial tuberosity (PT)
  • Insall-Salvatti ratio PL/PT =1 is normal; <0.8 is predictive of tendon rupture

References

• Insall J, Salvati E. Patella position in the normal knee joint. Radiology 1971;101:101
• Sibley T, Algren D, Ellison S. Bilateral patellar tendon ruptures without predisposing systemic disease or steroid use: a case report and review of the literature. American Journal of Emergency Medicine 2012; 30: 261.e3-261.e

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