Working Diagnosis:
Sexually transmitted chlamydia trachomatis infection resulting in reactive arthritis with a concurrent osteochondral defect of the knee

Treatment:
The patient was initially treated with indomethacin. After testing positive for Chlamydia, he was treated with doxycycline for one week.

Outcome:
The patient's symptoms improved significantly with treatment. A nonoperative approach was taken as the OCD lesion was currently stable and not felt to be the cause of his symptoms. He was started on a home exercise rehabilitation program with plans for ongoing follow-up.

Author's Comments:
Reactive arthritis is an inflammatory non-infectious or sterile arthritis typically following an gastrointestinal infection such as Salmonella or urogenital infection such as Chlamydia. Patients typically present with an asymmetric oligoarthritis, usually of the knees, one to four weeks following the inciting infection. The diagnosis is clinical based on the pattern of findings and exclusion of other forms of arthritis. The pathogen cannot be cultured from the affected joints but may be identified from other sources. Initial treatment of the triggering infection with antibiotics along with NSAIDs is recommended. Intra-articular and/or systemic glucocorticoids can be considered if resistant to NSAIDs. Symptoms typically remit in six to twelve months. It can continue despite treatment in some patients. It is important to keep reactive arthritis on the differential for acute knee pain and remember to take a sexual history despite presentation to the sports medicine clinic and abnormal findings on radiographs.

Editor's Comments:
The finding of an osteochondral lesion, while important and requiring follow-up and further treatment, was a red herring in this case. The migrating nature of the pain and swelling and lack of an injury history suggested another etiology. Reactive arthritis is considered a spondyloarthopathy, an inflammatory condition that involves a genetic predisposition and includes ankylosing spondylitis and psoriatic arthritis among other conditions. It has been classically taught as a triad syndrome of "can't see (uveitis), can't pee (urethritis), and can't climb a tree (arthritis)." Two out of three were reported in this case. The sports physician must remain on the lookout for non-injury causes of symptoms.

References:
1. Buchanan WW, Kean CA, Rainsford KD, Kean WF. Spondyloarthropathies and arthritis post-infection: a historical perspective. Inflammopharmacology. 2023 Sep 7. doi: 10.1007/s10787-023-01331-9. Epub ahead of print. PMID: 37676415.

2. Carlin E, Flew S. Sexually acquired reactive arthritis. Clin Med (Lond). 2016 Apr;16(2):193-6. doi: 10.7861/clinmedicine.16-2-193. PMID: 27037393; PMCID: PMC4952977.

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