A 16 yo female presents with knee pain after her knee was struck by another player during a soccer game.  She holds her knee in flexion, there is impressive hemarthrosis and patellar deformity.  She is neurovascularly intact and there is no skin tenting or laceration.  X-ray is shown.  What's the diagnosis?  Scroll down for answer.

Answer:  Patellar dislocation

• Most common in young athletes
• Mechanism: twisting of extended knee with foot externally rotated, or a direct medial blow - causes disruption in the medial restraint of patella (medial patellofemoral ligament)
• Reduction: with hip and knee in partial flexion to relax quadriceps, slowly extend the knee with gentle medial directed pressure on the laterally displaced patella; patella is felt sliding back into the intercondylar fossa of the femur
• Contraindications to bedside reduction (call ortho): superior, horizontal or intercondylar dislocation, or associated femur/tibia fracture
• Post reduction: knee immobilizer, weight bearing with crutches, follow-up with orthopedics and physical therapy
• Long term complications: patellar instability (recurrent dislocations), osteoarthritis

References:

Tsai, Chun-Hao et al. “Primary Traumatic Patellar Dislocation.” Journal of Orthopaedic Surgery and Research 7 (2012): 21. PMC. Web. 21 Aug. 2018.

“Chapter 87. Patellar Dislocation Reduction” Emergency Medicine Procedures, 2e Ed. Eric F. Reichman. New York, NY: McGraw-Hill, 2013