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Objectives and questions: Plantar plate lesions are a common cause of metatarsophalangeal joint (MTPJ) pain, but diagnosing their severity is challenging. Ultrasonography (US) and cone-beam CT (CBCT) offer complementary advantages: US enables static and dynamic soft tissue assessment, while CBCT precisely locates the MTPJ's center of rotation. This study aimed to evaluate the diagnostic performance of US and CBCT for plantar plate lesions.

Material and methods: Eighteen cadaveric specimens (36 plantar plates, 18 second and 18 third MTPJ) were independently examined by a musculoskeletal radiologist and an orthopedic surgeon. US classified plantar plates using the echographic Borne’s classification and measured Lachman test drawer. CBCT measured the dorsal translation of the MTPJ’s center of rotation. An independent orthopedic surgeon performed cadaveric dissection, recording lesions according to the cadaveric Coughlin’s classification (gold standard). Coughlin stages were compared to US and CBCT findings, and ROC curves were plotted for quantitative variables to assess diagnostic performance in determining the presence or absence of plantar plate lesions.

Results: Interobserver reliability was poor for Borne’s classification (K=0.11) and the Lachman test (ICC=0.4; p=0.003) for US, but good for CBCT’s dorsal translation measurement (ICC=0.69; p<0.001). Of the plantar plates, 2.8% were Coughlin stage 3, 5.6% stage 2, 19.4% stage 1, and 72.2% had no lesions (stage 0). There was no significant association between Borne’s and Coughlin’s classifications (p=0.055). Lachman’s drawer significantly increased between Coughlin stages 0 and 1 (p=0.02) but not between stages 1 and 2 or 3. The Lachman test had an AUC of 0.81, with a >2.5 mm drawer showing 70% sensitivity and 80.8% specificity. CBCT showed no significant difference in dorsal translation between Coughlin stages 0 and 1 (p=0.84) but a significant increase between stages 1 and 2 or 3 (p=0.004).

Discussion and conclusions: CBCT demonstrated better interobserver reliability than US, indicating that US should be performed by trained musculoskeletal radiologists. The Lachman test on US effectively diagnosed minor plantar plate lesions, while CBCT’s dorsal translation measurement differentiated minor from major lesions. A drawer >2.5 mm on the Lachman test suggests a plantar plate lesion.