The Association of Crista Volume With Sesamoid Position as Measured From 3D Reconstructions of Weightbearing CT Scans

Background: Malposition of the sesamoids relative to the first metatarsal head may relate to intersesamoid crista underdevelopment or erosion. Using 3-dimensional models created from weightbearing CT (WBCT) scans, the current work examined crista volume and its relationship to first metatarsal pronation and sesamoid station. Methods: Thirty-eight hallux valgus (HV) patients and 10 normal subjects underwent weightbearing or simulated WBCT imaging. The crista was outlined by the inferior articular surface, and a line was drawn to connect the lowest point of each sulcus on either side of the intersesamoidal crista throughout the length of the crista. The volume was calculated. Sesamoid station and first metatarsal pronation were calculated from the 3D reconstructions. The mean crista volumes between HV and normal patients were statistically compared, as were the crista volume and pronation angle between sesamoid stations. Results: The mean crista volume in HV patients was 80.10 ± 35 mm3 and in normal subjects was 150.64 ± 24 mm3, which differed significantly between the 2 groups ( P < .001). Mean crista volumes were found to be statistically significantly different between the sesamoid stations ( P < .001) with decreasing crista volumes significantly and strongly correlated with increasing sesamoid station ( r = −0.80, P < .001). There was no difference in the mean pronation angle between the 4 sesamoid stations ( P = .37). The pronation angle was not associated with crista volume ( P = .52). Conclusion: HV patients have lower mean crista volume than normal patients. Crista volume is correlated with sesamoid station. Pronation of the first metatarsal was not associated with crista volume. Clinical Relevance: Crista volume may offer an additional determinant for the severity of hallux valgus.

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

Background The Distal Metatarsal Articular Angle (DMAA) was previously described as an increase in valgus deformity of the distal articular surface of the first metatarsal (M1) in hallux valgus (HV). Several studies have reported poor reliability of this measurement. Some authors have even called into question its existence and consider it to be the consequence of M1 pronation resulting in projection of the round-shaped lateral edge of M1 head. Our study aimed to compare the DMAA in HV and control populations, before and after computer correction of M1 pronation and plantarflexion with a dedicated weightbearing CT (WBCT) software. We hypothesized that after computerized correction, DMAA will not be increased in HV compared to controls. Methods: We performed a retrospective case-control study including 36 HV and 20 control feet. In both groups, DMAA was measured as initially described on conventional radiographs (XR-DMAA) and WBCT by measuring the angle between the distal articular surface and the longitudinal axis of M1. Then, the DMAA was measured after computerized correction of M1 plantarflexion and coronal plane rotation using the α angle (3d-DMAA). Results: The XR-DMAA and the 3d-DMAA showed higher significant mean values in HV group compared to controls (respectively 25.9 ± 7.3 vs 7.6 ± 4.2 degrees, P < .001, and 11.9 ± 4.9 vs 3.3 ± 2.9 degrees, P < .001). Comparing a small subset of precorrected juvenile HV (n=8) and nonjuvenile HV (n=28) demonstrated no significant difference in the measure DMAA values. On the other hand, the α angle was significantly higher in the juvenile HV group (21.6 ± 9.9 and 11.4 ± 3.7 degrees; P = .0046). Conclusion: Although the valgus deformity of M1 distal articular surface in HV is overestimated on conventional radiographs, comparing to controls showed that an 8.6 degrees increase remained after confounding factors’ correction. Clinical Relevance: After pronation computerized correction, an increase in valgus of M1 distal articular surface was still present in HV compared to controls. Level of Evidence: Level III, retrospective case-control study.

Weightbearing CT Analysis of the Transverse Tarsal Joint During Eversion and Inversion

Background: Understanding of the movement and function of the transverse tarsal joint (TTJt) continues to evolve. Most studies have been done in cadavers or under nonphysiologic conditions. Weightbearing computed tomographic (WBCT) scans may provide more accurate information about the position of the TTJt when the hindfoot is in valgus or varus. Methods: Five volunteers underwent bilateral weightbearing CT scans while standing on a platform that positioned both hindfeet in 20 degrees of valgus and 20 degrees of varus. Each bone of the foot was segmented, and the joint surfaces of the talus, calcaneus, cuboid, and navicular were identified. The principal axes for each joint surface were determined and used to calculate the angles and distances between the bones with the foot in valgus or varus. Results: In the coronal plane, the angle between the talus and calcaneus rotated 17.1 degrees as the hindfoot moved from valgus to varus. The distance between the centers of the talus and calcaneus decreased 7.1 mm. The cuboid translated 3.9 mm medially relative to the calcaneus. There was no change in angle or distance between the cuboid and navicular. The navicular rotated 25.4 degrees into varus relative to the talus. Conclusion: The TTJt locking mechanism was previously thought to occur from the talonavicular and calcaneocuboid joint axes moving from parallel to divergent as the hindfoot inverts. The current data show a more complex interaction between the four bones that comprise the TTJt and suggests that the locking mechanism may occur because of tightening of the ligaments and joint capsules. Clinical relevance: This study uses weight bearing CT scans of healthy, asymptomatic volunteers standing on valgus and varus platforms to characterize the normal motion of the transverse tarsal joint of the foot. A better understanding of how the transverse tarsal joint functions may assist clinicians in both the conservative and surgical management of hindfoot pathology.