Assessment of Various Measurement Methods to Assess First Metatarsal Elevation in Hallux Rigidus

BACKGROUND: While metatarsus primus elevatus (MPE) has been implicated in the development of hallux rigidus, previous studies have presented conflicting findings regarding the relationship between MPE and arthritis. This may be due to the variety of definitions for MPE and the radiographic measurement techniques that are used to assess it. Additionally, previous studies have only assessed elevation of the first metatarsal with respect to the floor or the second metatarsal, and not with respect to the proximal phalanx. The aim of this study was to examine the reliability of new radiographic measurements that consider the elevation of the first metatarsal in relation to the proximal phalanx, rather than in relation to the second metatarsal as previously described, to assess for MPE. In addition, we aimed to determine whether the elevation of the first metatarsal was significantly different in patients with hallux rigidus than in a control population. METHODS: A retrospective chart review was conducted from prospectively collected registry data at the investigators’ institution to identify patients with hallux rigidus (n = 65). A size-matched control cohort of patients without evidence for first metatarsophalangeal (MTP) joint arthritis was identified (n = 65). Patients with a previous history of foot surgery, rheumatoid arthritis, or hallux valgus were excluded. Five blinded raters of varying levels of training, including 2 research assistants, 1 senior orthopedic resident, 1 foot and ankle fellowship-trained orthopedic surgeon, and 1 attending musculoskeletal fellowship-trained radiologist, evaluated 7 radiographic measurements for their reliability in assessing for MPE in hallux rigidus and control groups. Four of the 7 were newly designed measurements that include the relationship of the first MTP joint. Inter- and intrarater reliability were calculated using intraclass correlation coefficients (ICCs) and categorized by Landis and Koch reliability thresholds. The measurements between the hallux rigidus and control populations were compared using an independent t test. RESULTS: Six of the 7 radiographic measurements were found to have substantial to almost perfect interrater reliability (ICC, 0.800-0.953) between all levels of training, except for the proximal phalanx–first metatarsal angle, which showed moderate reliability (ICC, 0.527). Substantial to almost perfect intrarater reliability (ICC, 0.710-0.982) was demonstrated by the measurements performed by research assistants. All 7 of the measurements taken by the musculoskeletal fellowship-trained radiologist demonstrated significant differences in first metatarsal elevation between the hallux rigidus and control populations, with the hallux rigidus group showing increased elevation (P < .001-.019). CONCLUSION: This study confirmed the reliability of 7 radiographic measurements used to assess for MPE, including 3 previously established and 4 newly described measurements. Observers across all levels of training were able to demonstrate reliable measurements. In addition, the measurements were used to show that patients with hallux rigidus were more likely to have MPE compared with patients without radiographic evidence for first MTP arthritis. These measurements could be used in future work to examine how the presence of MPE relates to the etiology and progression of hallux rigidus, and how it affects the results of operative treatment. LEVEL OF EVIDENCE: Level III, retrospective comparative study.