Impact of lesion location on the progression of osteoarthritis in a rat knee model

To investigate how surgically created acute full‐thickness cartilage defects of similar size and location created on the medial versus lateral femoral condyle influence progression of spontaneous cartilage lesions in a rat model. Full‐thickness cartilage defects of 1 mm were surgically created on the medial or lateral femoral condyles on the right leg of 20 rats (n = 10/group). Ten rats served as controls. Spontaneous lesion progression on the ipsilateral and contralateral surfaces was examined using a high‐resolution digital camera along with H&E and Safranin‐O staining. Chondral defects were scored grossly and histologically. Control femur displayed no cartilage disruption. Surgically treated knees exhibited created and spontaneous cartilage defects with no evidence of healing unless subchondral bone was penetrated. Ipsilateral spontaneous lesions on the lateral condyle were significantly more severe on average (p = 0.009) compared to medial lesions on gross examination. Histological examination found contralateral lesions on the lateral surface following surgically created medial lesions to be more severe (p = 0.057) compared to contralateral lesions. A trend toward more susceptible chondral damage to the lateral condyle was observed following acute lesion creation on either medial or lateral condyles. Mechanisms behind this pattern of spontaneous lesion development are unclear, requring further investigation.