To review, this is a 34 year-old man with left knee pain after fall onto bilateral knees.
Questions and Answers:
1) What is the injury?
This is a nondisplaced transverse patellar fracture, the most common kind, usually caused by direct trauma. Patellar fractures can be displaced or nondisplaced (like this one), comminuted, or vertical. They can also be avulsion fractures caused by axial strain from the quadriceps tendon, pulling off the superior portion of the patella.
2) What are possible associated physical exam findings?
Most commonly patients will have pain with palpation, knee effusion, and limited range of motion. There may be a palpable defect if the fracture is displaced. It is critical to test whether the extensor mechanism of the knee is intact by having the patient perform a straight leg raise, as this will affect management.
Inability to perform straight leg raise indicates a through-and-through injury to the extensor mechanism of the quadriceps-patella apparatus. If pain limits the exam of the extensor mechanism, consider injecting the joint with lidocaine.
If there is an overlying laceration or significant abrasion, the joint should be evaluated for traumatic arthrotomy by saline load test: inject saline with a small diluent of methylene blue into the joint and watch for extravasation from the injury site.
3) What are the next steps in management of this injury?
Nondisplaced, closed fractures with intact extensor mechanisms can be managed with a knee immobilizer, weight bearing as tolerated, and follow up with orthopedics in one-to-two weeks to begin physical therapy. Fractures displaced more than 3mm or with disruption of the extensor mechanism should receive the same emergent treatment, but will need earlier referral to orthopedics for ORIF (next 3-4 days). Severely comminuted fractures may need surgical debridement of the small pieces and repair of the quadriceps and patellar tendons, while open patellar fractures are treated in the usual fashion, with irrigation and antibiotics in the emergency department, followed by an emergent washout by orthopedics in the operating room.
Scolaro, John, Joseph Bernstein, and Jaimo Ahn. "In Brief: Patellar Fractures." Clin Orthop Relat Res 469.4 (2011): 1213-215.
Glaspy, John and Steele, Mark. Knee Injuries. In: Tintinalli JE et al. Tintinalli Emergency Medicine 7th ed. New York: McGraw-Hill; 2011:1856-1864.