Slideshow
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112917_OrthoDx_Figure1
Anteroposterior X-ray.
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112917_OrthoDx_Figure2
Lateral X-ray.
A 22-year-old woman presents to the emergency department with left knee pain after a motor vehicle accident. Her left knee struck the dashboard during the accident, and it now hurts with any movement. On examination, she has tenderness to palpation and ecchymosis over the left patella. She has no deformity to the patella and is able to straight leg raise. Active knee extension increases her pain. Anteroposterior and lateral X-rays of the left knee show a non-displaced transverse patella fracture.
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Patella fractures most commonly occur from a direct impact injury such as a fall or motor vehicle accident. Patients who sustain a patella fracture from a dashboard injury must be examined for an ipsilateral hip injury to rule out dislocation or fracture. The extensor mechanism of the knee may be tested by putting a bump under the patient’s knee and having him or her place the knee in full extension against gravity. Inability to straight leg raise may indicate an extensor mechanism tear or tear of the quadriceps tendon and/or the medial and lateral retinaculum. Anteroposterior and lateral X-rays are routinely ordered in the evaluation of patella fractures. A patella baja “low riding patella” or a patella alta “high riding patella” seen on lateral X-ray may indicate a quadriceps and patella tendon rupture, respectively.1
Most non-displaced patella fractures have a transverse fracture pattern. With non-displaced fractures, the articular cartilage on the undersurface of the patella and the extensor mechanism usually remain intact so further imaging with CT or MRI is generally not necessary. Activities such as ambulation, walking up stairs, and bending down place displacing forces through the knee and should be avoided in patients with a patella fracture. Because the extensor mechanism is not activated in full knee extension, displacing forces can be eliminated with a knee immobilizer. The knee immobilizer locks the knee in extension and prevents quadriceps activation during weight bearing. Therefore, the treatment for non-displaced patella fractures includes weight bearing as tolerated with a knee immobilizer on at all times.1
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 Orthopedics for Physician Assistants (JOPA).
References
- Abbasi D. Patella fracture. Available at: https://www.orthobullets.com/trauma/1042/patella-fracture. Accessed on 11/28/2017.
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