A case of subchondral insufficiency fracture of the knee potentially caused by mediolateral knee laxity without structural abnormalities

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BACKGROUND: Meniscal injury and/or extrusion have been indicated as causes of subchondral insufficiency fracture (SIFK). However, mediolateral knee laxity has not been discussed as a risk factor. This is a case report of SIFK potentially caused by mediolateral laxity in the absence of a meniscal disorder. CASE PRESENTATION: A 59-year-old male patient presented with SIFK in the medial femoral condyle without meniscal injury or extrusion. Tibial condylar valgus osteotomy (TCVO) was performed, and the preoperative total mediolateral laxity of 8° in extension and 6° in 80° flexion decreased to 6° and 4°, respectively, two years postoperatively. Moreover, the magnetic resonance images revealed no bone marrow lesions, and the knee injury and osteoarthritis outcome score improved from 61.4 to 79.7. CONCLUSION: A case of SIFK with mediolateral laxity, without meniscal disorder, was successfully treated by TCVO, indicating knee laxity as a potential risk factor for SIFK.