Sesamoid Subluxation in Hallux Valgus Deformity.

BACKGROUND: Whether sesamoid subluxation relative to the metatarsal head occurs in hallux valgus (HV) remains unestablished. Deep transverse intermetatarsal ligament (DTML) attenuation, which spans the lateral sesamoid to the second metatarsal head, may increase transverse motion and facilitate medial sesamoid subluxation with the first metatarsal. This study aims to compare the average second metatarsal head to lateral sesamoid (2MTLS) distance between HV and control patients, which is a proxy of DTML length. We hypothesize that HV patients demonstrate an increased 2MTLS distance.

METHODS: Sixty-eight patients were matched into 2 groups: 34 with HV and 34 without HV. Standardized preoperative weightbearing computed tomography scans were used to measure the 2MTLS distance, hallux valgus angle (HVA), intermetatarsal angle (IMA), first metatarsal pronation, and sesamoid station. The 2MTLS distance was anatomically measured from the lateral sesamoid to the second metatarsal head.

RESULTS: The 2MTLS distance was significantly greater in HV patients compared with controls (20.90 mm vs 18.56 mm, P < .001). Similarly, the HVA and IMA were increased in HV patients (P < .001). First metatarsal pronation and sesamoid station were significantly greater in HV patients (P < .001). The 2MTLS distance demonstrated a moderately positive correlation with sesamoid station (r = 0.36, 95% CI 0.06-0.60), HVA (r = 0.40, 95% CI 0.12-0.65), and IMA (r = 0.43, 95% CI 0.06-0.71) but was not correlated with first metatarsal pronation (r = -0.18). Inter- and intrarater reliability for the 2MTLS measurements were ICC = 0.911 (95% CI 0.858-0.944) and 0.958 (95% CI 0.933-0.974), respectively.

CONCLUSION: In HV patients, 2MTLS was significantly increased compared with controls. Additionally, as sesamoid station increased, the 2MTLS distance also increased. This challenges the long-standing view that the sesamoids remain anchored in HV and suggests the sesamoids subluxate. Clinically, this highlights the DTML's role as a restraint to first metatarsal medial deviation and suggests against sectioning the ligament during lateral release.

LEVEL OF EVIDENCE: Level III, retrospective cohort study.