Journal of Musculoskeletal Trauma

Original Article

Multiple blocking screws reduce peak stress in a smaller-diameter tibial nail to a level similar to that in a canal-filling nail: a comparative finite element analysis: Jungtae Ahn, Se Lin Jeong, Gu-Hee Jung; Received July 22, 2026 Accepted September 10, 2026 Published online October 13, 2026; DOI: https://doi.org/10.12671/jmt.2026.00255 [Epub ahead of print]

Abstract PDF: Background
Cortical contact at the medullary isthmus permits cortical load sharing and constrains nail motion, and is considered important for stable intramedullary nailing. Blocking screws may provide the latter function. This finite element analysis examined whether adding multiple blocking screws to a smaller-diameter nail would reduce peak nail stress to a level similar to that of a canal-filling construct.
Methods
Three configurations were modeled in a tibia with a 5-mm diaphyseal defect at the isthmus: an 11-mm canal-filling nail (model A), an 8-mm nail alone (model B), and an 8-mm nail with four 3.5-mm blocking screws positioned circumferentially (model C). An 800-N static axial load was applied at a medial-to-lateral ratio of 3:2 with the distal end fixed. Total deformation and von Mises stresses in bone, nail, and screws were analyzed using a linear elastic, small-deformation formulation.
Results
Maximum total deformation was 5.60, 33.33, and 18.82 mm in models A, B, and C, respectively, occurring at the proximal tibia in all models. Peak nail stress in model B was 891.9 MPa, slightly exceeding the assumed 880-MPa yield threshold, whereas peak stresses were similar in models A (272.9 MPa) and C (265.8 MPa). Screw stress was asymmetric: 57.9 and 58.2 MPa in the posterior and medial screws versus 3.2 and 6.8 MPa in the lateral and anterior screws, indicating differential mechanical engagement of the blocking screws.
Conclusions
Under the single static loading condition evaluated, four circumferential blocking screws reduced the peak nail stress of a smaller-diameter nail to a level similar to that of a canal-filling nail. Total deformation nevertheless remained approximately 3.4 times that of the canal-filling construct, and peak bone stress differed between constructs. The asymmetric screw-stress distribution was consistent with differential mechanical engagement of the blocking screws. Mechanical equivalence was not established for outcomes other than peak nail stress. Level of evidence: Not applicable.

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