Figure 1. Anteroposterior x-ray of the left knee
Figure 2. Lateral x-ray of the left knee
A 15-year-old adolescent presents to an urgent care facility with left knee pain from an injury earlier in the day. He was playing football when he tripped and struck his knee on a cement wall with a direct impact. He had difficulty bearing weight after the injury and has severe pain over the anterior knee. On physical examination, the patient has a small abrasion over the anterior patella and he is able to perform a straight leg raise. Anteroposterior and lateral x-rays are shown in Figures 1 and 2, respectively.
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The patella is the largest sesamoid bone in the body and has the quadriceps tendon attached proximally and the patella ligament attached distally.1,2 The quadriceps, patella, and patella ligament form the extensor mechanism of the knee.2 Disruption in any of these 3 structures may cause an inability to straight leg raise or bear weight on the knee. Patella fractures may be treated nonoperatively if the extensor mechanism is intact and there is less than 2 mm to 3 mm of articular step-off and less than 4 mm of fracture displacement.1,2 Nonoperative acute treatment includes weight-bearing as tolerated in a knee immobilizer or hinged knee brace locked in extension.2
Weight-bearing as tolerated is permitted in a knee immobilizer for 4 to 6 weeks as the extensor mechanism is not activated with the knee in extension.2 Any type of flexion, especially with weight-bearing, activates the extensor mechanism and creates forces through the patella that can displace the patella fracture. Initiation of range of motion should follow this period of immobilization.2
Magnetic resonance imaging (MRI) is rarely indicated in displaced fractures unless the patient is unable to perform a straight leg raise.2 Computed tomography (CT) is often ordered if the amount of fracture displacement is unclear.2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopaedics for Physician Assistants.
1. Schuett DJ, Hake ME, Mauffrey C, Hammerberg EM, Stahel PF, Hak DJ. Current treatment strategies for patella fractures. Orthopedics. 2015;38(6):377-84. doi:10.3928/01477447-20150603-05
2. Hargett DI, Sanderson BR, Little MTM. Patella fractures: approach to treatment. J Am Acad Orthop Surg. 2021;29(6):244-253. doi:10.5435/JAAOS-D-20-00591