Association Between Pronation External Rotation IV Fracture Pattern and Regional Bone Density.

Introduction: Throughout the musculoskeletal system, fracture patterns and subsequent healing rely partly on bone density. In the foot and ankle, bone density has been shown to play a role in supination and external rotation fracture patterns. Adding to previous research, this investigation examines the association between bone density and trimalleolar versus trimalleolar equivalent fracture patterns following pronation and external rotation injuries using computed tomography (CT)-derived Hounsfield units (HU).

Methods: A retrospective chart review was conducted among patients without a history of fracture or osteoporosis who sustained a PER IV fracture. Demographic data were collected. Fractures were separated between PER IV equivalent and fracture groups. CT-derived HU was assessed at the distal tibia and fibula. Density was compared between PER IV equivalent and fracture groups and among posterior malleolar fracture patterns.

Results: Seventy-five patients met the selection criteria, with 17 comprising the equivalent group and 58 in the fracture group. There were 38 type 1, 9 type 2, and 11 type 3 posterior malleolus fractures. The ankle bone density of the PER fracture equivalent group (331.98 ± 65.71HU) was greater than the PER fracture group (281.61 ± 76.99HU; P = .008). A statistically significant difference in tibial bone densities among equivalent and all PER fracture types (P = .01) with the equivalent group (331.98 ± 65.71HU) maintaining a greater tibial bone density than the type 2 posterior malleolus fracture group (252.35 ± 57.33HU; P = .009).

Conclusion: Higher bone density was associated with PER IV equivalent fractures; however, there was no density difference among posterior malleolus fracture types. When presented with PER IV fractures, consider fixation that addresses a lower bone density.

Level of evidence: III.