The Assessment of First Metatarsal Rotation in the Normal Adult Population Using Weightbearing Computed Tomography

Abstract

Background: The importance of the rotational profile of the first metatarsal is increasingly recognized in the surgical planning of hallux valgus. However, rotation in the normal population has only been measured in small series. We aimed to identify the normal range of first metatarsal rotation in a large series using weightbearing computed tomography (WBCT). Methods: WBCT scans were retrospectively analyzed for 182 normal feet (91 patients). Hallux valgus angle, intermetatarsal angle, anteroposterior/lateral talus–first metatarsal angle, calcaneal pitch, and hindfoot alignment angle were measured using digitally reconstructed radiographs. Patients with abnormal values for any of these measures and those with concomitant pathology, previous surgery, or hallux rigidus were excluded. Final assessment was performed on 126 feet. Metatarsal pronation (MPA) and α angles were measured on standardized coronal computed tomography slices. Pronation was recorded as positive. Intraobserver and interobserver reliability were assessed using intraclass correlation coefficients (ICCs). Results: Mean MPA was 5.5 ± 5.1 (range, –6 to 25) degrees, and mean α angle was 6.9 ± 5.5 (range, –5 to 22) degrees. When considering the normal range as within 2 standard deviations of the mean, the normal range identified was −5 to 16 degrees for MPA and −4 to 18 degrees for α angle. Interobserver and intraobserver reliability were excellent for both MPA (ICC = 0.80 and 0.97, respectively) and α angle (ICC = 0.83 and 0.95, respectively). There was a moderate positive correlation between MPA and α angle (Pearson coefficient 0.68, P < .001). Conclusion: Metatarsal rotation is variable in normal feet. Normal MPA can be defined as less than 16 degrees, and normal α angle can be defined as less than 18 degrees. Both MPA and α angle are reproducible methods for assessing rotation. Further work is needed to evaluate these angles in patients with deformity and to determine their significance when planning surgical correction of hallux valgus. Level of Evidence: Level III, retrospective comparative study.

Distal Metatarsal Articular Angle in Hallux Valgus Deformity. Fact or Fiction? A 3-Dimensional Weightbearing CT Assessment

“…Our α angle values were slightly different from those reported by Kim et al 16 and Mahmoud et al 20 But the α angle values of our control group are close to those defined by Steadman et al 35 and Najefi et al 21 and those of our HV group are close to those reported by Conti et al 4…”

“…Two recent articles evaluated the mean α angle in a normal population. 21,35 It appears that the mean value in a control population is around 6 degrees in pronation. Therefore, 6 degrees may be a better correction target.…”

Association of First Metatarsal Pronation Correction With Patient-Reported Outcomes and Recurrence Rates in Hallux Valgus

“…3,6,12,18,28,29,41,46 However, other recent studies have demonstrated a wide range of first metatarsal pronation in patients without HV, which has called into question the clinical importance of the first metatarsal pronation deformity in HV. 31,36,48…”

Repeatability of Weightbearing Computed Tomography Measurement of First Metatarsal Alignment and Rotation

“…In radiographically normal patients, the mean MPA has been shown to be 5.4±5.0 degrees and mean alpha angle was 6.9±5.6 degrees. 19 Steadman et al showed the normal alpha angle to be 6.1±6.6 degrees. 28 Therefore, a change of the MDC95 for alpha angle and MPA between scans is going to be significant, and will alter the results.…”