What's the Diagnosis? By Dr. Abby Renko

A 45 y/o M with PMhx of HTN and ESRD on dialysis presents to the ED w/ knee pain after slipping at work. On exam, he is unable to extend his leg. An X-ray is done and shown below. What's the diagnosis? (scroll down for answer)



Answer: Quadriceps tendon rupture

  • At first glance, lateral XR does not show obvious deformity....however: you may notice calcifications just superior to the patella (representing retracted tendon) 
  • Quadriceps tendon ruptures tend to occur in individuals > 40, while patellar tendon ruptures occur more frequently in individuals < 40
    • Overall quadricep tendon ruptures are more common (risk factors- rheumatologic disease, renal failure, DM, chronic steroid use) 
  • High riding patella ("patella alta") on lateral films is more frequently seen in patellar tendon ruptures
  • Low riding patella ("patella baja") may be seen on lateral film with complete quadricep tendon tear (intact patellar tendon displaces patella inferiorly) 
  • Xrays may be normal!
  • In both injuries, classic exam finding is inability to extend the knee
    • You can often palpate a defect just above the patella in quadriceps tendon ruptures
  • Orthopedic consultation is always warranted for these cases
  • Remember-- always consider knee dislocation in any patient that has a severely injured knee that is unstable!
    • Dislocations typically occur traumatically, but can also occur spontaneously, especially in obese individuals 
    • They are a surgical emergency due to possible injury of the popliteal artery (ischemia risk) and peroneal nerve
    • Timely reduction is essential, with documentation of a neurovascular exam before and after reduction
    • Extemity should then be splinted with knee at 20 degrees of flexion to prevent re-dislocation




Bengtzen RR, Glaspy JN, Steele MT. Knee Injuries. In: Tintinalli JE, Stapczynski JS, et al., eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 8th ed. New York, NY: McGraw-Hill; 2016: (Ch) 274.