JBJS - 2026-08-20 - Journal Article
The Articular Dislocation Angle of the First Metatarsophalangeal Joint: Its Conception, Measurement Method, and Role in Hallux Valgus.
Guo M, Liu F, Gan Y, Yang F
Topics
Key Takeaway
ADA contribution to HVA increases from 43.3% in mild to 69.3% in severe hallux valgus, establishing the geometric identity HVA = DMAA + DASA + ADA across all severity grades.
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Summary
This study introduces the articular dislocation angle (ADA) to quantify first MTPJ subluxation and defines its geometric relationship to HVA, DMAA, and DASA using weight-bearing radiographs and CT in 70 HV feet. ADA contribution to HVA rose progressively from 43.3% (mild) to 52.6% (moderate) to 69.3% (severe), while DMAA and DASA contributions declined with severity. Radiographs showed excellent agreement with CT for DMAA but systematically underestimated DASA by 5.1°–7.8°, with the discrepancy worsening with disease severity.
Key Limitation
The formula HVA = DMAA + DASA + ADA is validated only cross-sectionally without outcome data confirming that ADA-guided surgical selection improves correction or reduces recurrence.
Original Abstract
BACKGROUND
First metatarsophalangeal joint (MTPJ) subluxation or dislocation represents a common yet unquantified pathological feature in hallux valgus (HV). In this study, we introduce the concept of the articular dislocation angle (ADA), defined as the angle between a line perpendicular to the proximal articular surface of the proximal phalanx and a line perpendicular to the distal articular surface of the first metatarsal, to quantitatively evaluate the degree of joint subluxation or dislocation. Using the ADA concept, this study quantitatively investigated the relationships between HV-related angular parameters (hallux valgus angle [HVA], distal metatarsal articular angle [DMAA], distal articular set angle [DASA], and ADA), thereby precisely delineating the pathological deformity components contributing to HV.
METHODS
We measured HVA, DMAA, DASA, and ADA on weight-bearing radiographs of 70 feet (52 patients) with HV to investigate their interrelationships and quantify their respective contributions to HV. The mean patient age was 58 years, 63 feet were in female patients, and all patients were Asian. Additionally, by comparing DMAA and DASA measurements obtained from weight-bearing radiographs versus computed tomography (CT) scans, we systematically evaluated the accuracy of measurements on weight-bearing radiographs.
RESULTS
Radiographic data demonstrated that the relationship HVA = DMAA + DASA + ADA held true across all HV severity grades. Quantitative analysis revealed a progressive increase in the ADA contribution with increasing disease severity (mild: 43.3%; moderate: 52.6%; severe: 69.3%), while DMAA and DASA contributions showed corresponding decreases (DMAA: 40.7%, 38.1%, 28.1%, respectively;
DASA
16.0%, 9.3%, 2.5%). Comparative analysis indicated excellent agreement between CT and weight-bearing radiographs for DMAA measurements, whereas radiographs systematically underestimated DASA values versus CT (mean differences: mild, -5.1°; moderate, -5.4°; severe, -7.8°), with the discrepancy magnitude increasing with disease severity.
CONCLUSIONS
ADA provides an accurate quantitative assessment of first MTPJ subluxation or dislocation severity. The introduction of the ADA establishes a clear geometric relationship among HVA, DMAA, and DASA, formulated as: HVA = DMAA + DASA + ADA. Preoperative application of this formula allows effective assessment of the pathological components contributing to HV, thereby assisting surgeons in developing appropriate surgical strategies.
LEVEL OF EVIDENCE
Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.