Objective Given the ability of ultrasound imaging (USI) to depict tissue-specific morphological changes before the onset of pain and before the point of irreversible structural damage, USI could play a fundamental role in earlier detection and assessment of foot osteoarthritis (OA). The current guidelines require further refinement of anatomical landmarks to establish a standardized imaging procedure to improve the interpretability and reproducibility between studies evaluating the first metatarsophalangeal joint (MTPJ). The aims were to develop an USI acquisition procedure and grading system to examine OA features in the first MTPJ and to determine intra-examiner and inter-examiner reliability of a newly developed USI acquisition procedure.

Design Thirty participants with first MTPJ OA confirmed radiographically with the use of the La Trobe Foot Atlas were included. An experienced sonographer applied a newly developed USI procedure to examine the following features: joint effusion, synovial hypertrophy, synovitis, joint space narrowing, osteophytes, and cartilage thickness. A semiquantitative grading system was applied to all features. A continuous measure was also examined for osteophyte size, joint space narrowing, and cartilage thickness. To determine the intra-examiner and inter-examiner reliability, an experienced radiologist and sonographer applied the developed grading system to the images acquired from two imaging sessions. Intra-examiner and inter-examiner reliability were calculated using intraclass correlation coefficients (ICCs).

Results ICCs for intra-examiner between session reliability ranged from 0.58 to 0.92 for semiquantitative grading and 0.39 to 0.94 for continuous measures. Joint effusion and osteophytes achieved the highest intra-examiner reliability (ICC = 0.78–0.94). ICCs for session one inter-examiner reliability ranged from 0.61 to 1.0 for semiquantitative grading; all continuous measures had an ICC of 1. ICCs for session two inter-examiner reliability ranged from 0.55 to 1.0 for semiquantitative grading and 0.9 to 0.97 for continuous measures. Inter-examiner reliability was good for grading joint effusion (ICC = 0.55–0.62) and was excellent for all other USI features (ICC = 0.77–1.0).

Conclusion The USI acquisition procedure and grading system are reliable in evaluating first MTPJ OA features in participants with radiologically confirmed OA. The study will inform the methodological development of an ultrasound atlas for grading the degree of osteoarthritic change in the first MTPJ.