A 59 yo male presents after fall from standing with right knee pain.  Pt describes feeling a "pop" and notes that his knee is visibly distorted after the fall.  An x-ray is shown.  What's the diagnosis?   Scroll down for answer. 

Answer:  Quadriceps/patella tendon rupture

Mecahnism:  fall onto flexed knee or forceful contraction of quadriceps

Presentation:  pain, swelling, deformity, inability to extend the knee or maintain extension against gravity

• Patella tendon rupture usually in age <40

• quadriceps tendon rupture usually in age >40

X-ray

• patella tendon rupture: superior dislacement of patella or "patella alta"
• quadricepts tendon rupture: inferior displacemtn of pateall or "patella baja"

Management

• Complete tear - orthopedic consultation in ED for surgical repair
• Incomplete tear (intact extensor mechanism) - knee immobilizer, crutches, follow-up orthopedics within one week

Bonus points: bony structure posterior to the knee on this x-ray = fabella

References:

Bengtzen, RR, Glaspy, JN, Steele, MT. "Knee Injuries." Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 8eEds. Judith E. Tintinalli, et al. New York, NY: McGraw-Hill, 2016, pg 1857-1864.?