• Edward Allen, James Houston, Raymond M Smith, and Alex J Trompeter.
• Royal Sussex County Hospital, Brighton & Sussex University Hospitals NHS Trust, Eastern Road, Brighton, United Kingdom. Electronic address: edward.allen9@nhs.net.
• Injury. 2023 Aug 1; 54 (8): 110873110873.

IntroductionBoth mechanical and biological theories have been proposed in the development of non-union. The mechanical theory suggests that a high strain environment in a fracture will predispose it to non-union. While in simple fractures and wedge fractures there are only one and two primary fracture planes respectively, in multi-fragmentary fractures there are many and a non-union may form along any of the original fracture lines, however the plane which experiences the highest strain is at 45O - the shear plane. We hypothesise that in multi-fragmentary fractures the initial fracture line that most often fails to unite will tend towards the plane with the highest strain.Objectives1) Define the mean non-union angle in a cohort of multi-fragmentary tibial and femoral fractures. 2) In wedge-like fractures within the cohort, define and compare the mean angle of initial fracture planes which go on to form a non-union to those that unite 3) In comminuted fractures within the cohort, define the mean non-union angle DESIGN: Retrospective cohort study SETTING: Level-1 trauma centre METHODOLOGY: Fractures were categorised into wedge-like and comminuted. A published technique was utilised to measure fracture and non-union angles. In wedge-like fractures, united and non-united initial planes were compared. In comminuted fractures only the mean non-union angle was defined. Demographic patient data was also collected.Results183 non-unions were screened, 68 patients were included. The mean non-union angle was 56°(SD 18) across all fractures. In wedge-like fractures the mean non-union angle was 59°(SD 18). In comminuted fractures the mean non-union angle was 50°(SD 19). Non-united initial fracture planes in wedge-like fractures showed a peaked distribution about a mean of 58° while united fracture planes were distributed at the extremities of the range.ConclusionsIn patients with multi-fragmentary fractures resulting in non-union, the mean tibial non-union angle was 52° while the mean femoral non-union angle was 65°. In wedge-like fractures, non-unions occurred more commonly than appropriate union in fractures between 41°-80°. The non-union angle is closer to 45° in comminuted fractures than in wedge-like fractures. These results support the mechanical theory that strain from the shear plane is an important factor in the formation of non-unions.Level Of EvidencePrognostic level 3.Copyright © 2023 Elsevier Ltd. All rights reserved.

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