Second metatarsophalangeal joint dislocation in hallux valgus: a radiographic study using a two-dimensional coordinate system

Background Hallux valgus (HV) poses additional challenges when accompanied by second metatarsophalangeal (MTP) joint dislocation, often requiring complex surgical intervention. This study aimed to analyze HV feet with second MTP joint dislocation using a 2-dimensional coordinate system to better understand the anatomical structure of this condition. Methods Weightbearing foot radiographs of 49 HV feet with second MTP joint dislocation (group D), 68 HV feet without second MTP joint dislocation (group W), and 54 control feet (group N) were analyzed. A 2-dimensional coordinate system was used to map standardized points on radiographs into X and Y coordinates, which were compared across groups. Radiographic parameters measured included hallux valgus angle (HVA), intermetatarsal angle (IMA), second toe MTP angle (2MTPA), metatarsus adductus angle (MAA), great toe length, first metatarsal (MT1) length, second toe length, and second metatarsal (MT2) length. The 2MTPA was further analyzed based on the deviation direction (medial, neutral, or lateral). Results The proximal phalanx head of the third toe in groups D and W was lateral compared to group N (P <.05 and P <.001, respectively), while the distal point in group D was medial to group W (P <.001). The base of MT1 in group D was significantly medial compared to other groups (P <.001). Additionally, the distal point of the great toe in group D was significantly lateral compared to other groups (P <.01 and P <.001, respectively). Conclusions Patients with second MTP joint dislocation exhibited a proximally translated second toe, an adducted third toe, a medialized MT1 base, and a lateralized great toe tip. The M1/2 angle influenced dislocation direction: higher angles led to medial or neutral deviation, while lower angles caused lateral deviation. Radiographic coordinate mapping provided novel insights into foot anatomy in HV with second MTP joint dislocation, laying the groundwork for future research on anatomical risk factors and optimizing surgical approaches to improve patient outcomes.