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An 18-year-old male presents 1 week after sustaining a patella dislocation while playing football. He says that he fell awkwardly and noticed a deformity to his kneecap. He was able to reduce the patella with his hand and walk after the reduction. He now presents with swelling and significant pain when flexing his right knee. Sunrise view X-ray (Figure 1) shows a reduced patella located centrally within the trochlea groove and a small avulsion type fracture off the medial patella.
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The patient presents with swelling and pain after a patella dislocation. Given his swelling and X-ray findings, an MRI should be ordered to rule out an osteochondral defect and injury to the medial patellofemoral ligament (MPFL). A traumatic patella dislocation can break off an osteochondral fragment, generally off the lateral femoral condyle as the patella dislocates laterally. An osteochondral fragment can break off and float around the knee causing symptoms of a loose body. Symptoms include recurrent effusions and mechanical symptoms of catching or locking of the knee. The incidence of loose body formation after patella dislocation was found to be 22% in one study.1
MPFL disruption may occur in up to 96% of patients who sustain a traumatic patella dislocation. The MPFL is the primary soft tissue stabilizer to lateral dislocation of the patella. The MPFL also helps the patella stay located centrally within the trochlea during knee flexion. MRI is the study of choice to determine if the MPFL is intact after a traumatic patella dislocation with a sensitivity of 85% and an accuracy of 80%. The standard of care for patella dislocations with MPFL disruption and without an OCD lesion is nonoperative treatment. Conservative treatment is usually successful with redislocation rates ranging from 15% to 44%.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 Orthopedics for Physician Assistants (JOPA).
References
- Farr J, Covell DJ, Lattermann C. Cartilage lesions in patellofemoral dislocations: Incidents/locations/when to treat. Sports Med Arthrosc Rev. 2012;20:181-186.
- Amin NH, Lynch TS, Patel RM, Patel N, Saluan P. Medial patellafemoral ligament reconstruction. JBJS Rev. 2015;3.
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