The Role of the Transverse Arch in Progressive Collapsing Foot Deformity.

BACKGROUND: The transverse arch (TA) has recently been shown to significantly increase the intrinsic stiffness of the midfoot when coupled with the medial longitudinal arch (MLA). Progressive collapsing foot deformity (PCFD) is a complex deformity that ultimately results in a loss of stiffness and collapse of the MLA. The role of the TA has not been investigated in patients diagnosed with this disorder using weightbearing CT (WBCT).Therefore, this study aims to answer the following questions: (1) Is the curvature of the TA decreased in PCFD? (2) Where within the midfoot does TA curvature flattening happen in PCFD?

METHODS: A retrospective review of weightbearing CT images was conducted for 32 PCFD and 32 control feet. The TA curvature was assessed both indirectly using previously described methods and directly using a novel measurement termed the transverse arch plantar (TAP) angle that assesses the angle formed between the first, second, and fifth metatarsals in the coronal plane. Location of TA collapse was also assessed in the coronal plane.

RESULTS: The TAP angle was significantly higher in PCFD (mean 115.2 degrees, SD 10.7) than in the control group (mean 100.8 degrees, SD 7.9) ( P  < .001). No difference was found using the calculated normalized TA curvature between PCFD (mean 17.1, SD 4.8) and controls (mean 18.3, SD 4.0) ( P  = .266). Location of collapse along the TA in PCFD was most significant at the second metatarsal and medial cuneiform.

CONCLUSION: The TA is more collapsed in PCFD compared to controls. This collapse was most substantial between the plantar medial cuneiform and the plantar second metatarsal. This may represent a location of uncoupling of the TA and MLA.

LEVEL OF EVIDENCE: Level III, retrospective case control.