Rheumatoid arthritis (RA) is a systemic inflammatory disorder characterized by persistent synovitis that typically appears symmetrically in numerous joints, particularly in the lesser toe and finger joints. Many researchers have reported a prevalence of forefoot deformities in adults with chronic RA of up to approximately 90% [[1], [2], [3]]. Many rheumatoid forefoot deformities frequently cause painful deformities that interfere with standing and walking [4,5]. Rheumatoid forefoot deformities are a combination of hallux valgus, digitus quintus varus, spread foot, overlapping, and metatarsophalangeal (MTP) joint dorsal subluxation. MTP joints are the main sites affected by RA [[6], [7], [8]]. Pain due to forefoot deformities is often the chief complaint. Therefore, rheumatoid forefoot deformities are considered to be the main therapeutic targets.

Surgical procedures are usually performed in cases of severe deformity or persistent pain after conservative treatments [9,10]. Symptomatic plantar callosities or bunions are the main reason for surgical treatment of rheumatoid forefoot deformities. However, clinical symptoms do not always correlate with the severity of articular destruction, which makes identifying indications for operation more complex.

There are two main surgical procedures: Resection arthroplasty and joint-preservation surgery, however there is no clear indication for performing either surgery [10,11]. The degree of joint destruction is an important factor for surgical treatment. Generally, resection arthroplasty is performed when articular destruction is severe. Recently, joint-sparing surgery has been reported in patients with controllable RA and has been applied in cases without severe articular destruction. Indications for joint-sparing surgery have been recommended on the basis of Larsen grades [12,13]. However, Larsen's criteria, based on bone condition, do not always reflect the remaining joint function, as they are influenced by multiple factors, such as cartilage, joint congruity, and subluxation. It is important to accurately assess the degree of joint destruction when considering surgical treatment and selection of a surgical procedure.

Radiography and computed tomography (CT) are commonly used to evaluate residual joint surfaces. Radiographic evaluation of the joint in the AP view by radiography does not always correlate with articular cartilage integrity. In addition, CT does not allow cartilage evaluation, and the problem of radiation exposure arises. There are no previous reports evaluating the severity of joint destruction pathologically in relation to the affected area and the severity of radiographic MTP joint subluxation, although the pattern of MTP joint subluxation or dislocation varies in each case. If the pattern of dislocation is related to the degree of joint destruction, it may be useful in determining the surgical indications and decision making for which metatarsal head of the lesser toes should be resected or preserved.

Hence, the hypothesis of this study was that the affected region and severity of MTP joint subluxation are correlated with the severity of articular destruction. The purpose of the present study is to elucidate the relationship between the severity of joint dislocation/subluxation in the lesser toes and the severity of joint destruction in rheumatoid forefoot deformities.