Pedal bone density, strength, orientation, and plantar loads preceding incipient metatarsal fracture after charcot neuroarthropathy: 2 case reports.

STUDY
DESIGN: Case report.
BACKGROUND: Charcot neuroarthropathy is a progressive, noninfective, inflammatory destruction of bones and joints leading to foot deformities and plantar ulceration. Though individuals with Charcot neuroarthropathy typically have low areal bone mineral density, little is known regarding changes in volumetric bone mineral density (vBMD), bone geometry, joint malalignment, and biomechanical loads preceding fracture. CASE DESCRIPTION: Two women, aged 45 and 54 years at the onset of an acute, nonfracture Charcot neuroarthropathy event, received regular physical therapy with wound care and total-contact casting. Both enrolled in a larger research study that included plantar pressure assessment and quantitative computed tomography at enrollment and 3, 6, and 12 months later. The women sustained mid-diaphyseal fifth metatarsal fracture 10 to 11 months after enrollment. Quantitative computed tomography image-analysis techniques were used to measure vBMD; bone geometric indices reflecting strength in compression, bending, and cortical buckling; and 3-D bone-to-bone orientation angles reflecting foot deformity. OUTCOMES: Fifth metatarsal mid-diaphyseal vBMD decreased during offloading treatment from 0 to 3 months, then increased to above baseline levels by 6 months. All geometric strength indices improved from baseline through 6 months. Plantar loading in the lateral midfoot increased preceding fracture, concomitant with alterations in bone orientation angles, which suggest progressive development of metatarsus adductus and equinovarus foot deformity. DISCUSSION: Fractures may occur when bone strength decreases or when biomechanical loading increases. Incipient fracture was preceded by increased loading in the lateral midfoot but not by reductions in vBMD or geometric strength indices, suggesting that loading played a greater role in fracture. Moreover, the progression of foot deformities may be causally linked to the increased plantar loading. LEVEL OF EVIDENCE: Prognosis, level 4.