UMEM Educational Pearls

Title: What's the Diagnosis? By Michael Allison

Posted: 2/5/2012 by Haney Mallemat, MD (Updated: 8/28/2014)
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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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