Why the "first time" deserves extra attention
It often happens in the clinic: an adolescent reports "my kneecap popped out" during a sprint or a change of direction, then "it went back in," and now the knee is swollen. The X-ray shows no obvious fractures, and the temptation is to dismiss it as a single episode, destined to resolve with rest and physical therapy.
The problem is that the first dislocation, especially in pediatric age, can leave intra-articular "traces" that we risk not seeing with X-rays alone.
Today we analyze this article
Reed JM, et al. Frequency of Adjunctive MRI Findings on First-Time Patellar Dislocations in Pediatric Patients: A Systematic Review. Am J Sports Med. 2026 Jan 9. DOI: 10.1177/03635465251383851. PMID: 41508815.
PubMed: https://pubmed.ncbi.nlm.nih.gov/41508815/
DOI: https://doi.org/10.1177/03635465251383851
What MRI typically finds after the first dislocation
The authors collected and synthesized 12 pediatric studies with MRI after a first episode. The "pooled" frequencies of findings are difficult to ignore:
- MPFL injury (the ligament that medially stabilizes the patella): complete rupture 47% and partial 41%.
- Osteochondral damage (cartilage and/or bone): 50%.
- Intra-articular loose bodies: 34%.
- As for location, when the lesion is isolated, it more often involves the medial facet of the patella compared to the lateral femoral condyle.
These numbers do not mean that "everyone needs surgery." They mean that a not insignificant proportion of patients may have elements that change management (for example: free fragments, osteochondral fractures, indications for different protection/immobilization, or simply more accurate counseling on the risk of recurrence).
A (generic) clinical scenario that explains the purpose of MRI
An athletic boy, swollen knee after the "first time," negative X-ray, gradually recovers. Then, weeks later, episodes of locking or a pinpoint "mechanical" pain appear during stairs/squats. At that moment, an MRI is often rushed to understand if there is a fragment or an osteochondral lesion. If we had done it earlier, we would have set up a more straightforward path from the beginning (and with less uncertainty for the family).
What really changes in practice
This review pushes towards a simple concept: the first dislocation should not be treated "blindly." The pragmatic approaches, depending on resources, are two:
- More liberal early MRI, especially if there is significant hemarthrosis/swelling, marked pain, locking, or suspicion of an osteochondral lesion.
- Or selective MRI with rigorous criteria, knowing however that the probability of associated findings is high and that "wait and see" is not always the most efficient choice.
Limitations to remember (without discarding the message)
This is a review of heterogeneous studies: MRI timing, selection criteria, and definitions vary. This can influence the percentages. But even with this caution, the signal remains robust: MRI often finds something clinically relevant.
Disclaimer: informational content, does not replace an individual specialist evaluation.
Reference
Reed JM, et al. Am J Sports Med. 2026. DOI: 10.1177/03635465251383851. PMID: 41508815.
