Findings
The radiographs demonstrate a very subtle fleck of bone adjacent to the lateral facet of the right patella. This is only appreciated on the Merchant view. MRI demonstrates a small fluid cleft adjacent to the bone fragment and moderate edema in the underlying lateral aspect of the patella. These findings are present about the lateral patella retinacular attachment to the patella. Slight irregularity of the lateral retinaculum at the patellar attachment.
Diagnosis: Lateral Patellar Retinaculum Sleeve Avulsion
An entity we as a group had not seen and one that is extremely limited in its discussion in the literature. The only case reports are described in the pediatric population. This is thought to relate to violent contraction of the quadriceps during sprinting but again is limited in its understanding.
Conservative, nonoperative treatment seems to be successful but again information about treatment is limited. Probably most critical is in the pediatric population when a patient comes in with lateral knee pain following sprinting if subtle or no findings are identified on the radiograph, this entity should be entertained with the thought to obtain MRI for further evaluation.
References
Murphy, M., Withers, K., & Koh, E. (2017). Pediatric Lateral Patellar
Retinacular Sleeve Avulsion. Journal of Orthopaedic & Sports Physical Therapy, 47(10), 815. https://doi.org/10.2519/jospt.2017.6616