Effects of third fragment size and displacement on non-union of femoral shaft fractures after locking for intramedullary nailing

BackgroundThe femoral shaft fractures with large fragments makes anatomical reduction challenging and often results in non-union. In some studies, the degree of fragment displacement was reported to have affected non-union, but the association between the one fragment size and degree of displacement has not been fully clarified. Therefore we performed a retrospective study to assess: (1) the more influential factor of non-union: the degree of fragment displacement, or the fragment size? (2) the non-union rates according to different sizes and degrees of displacement.HypothesisThe degree of displacement is the more potent factor of non-union than the third fragment size in femoral shaft fractures.Patients and methodsWe assessed retrospectively 64 cases, which could be followed up for longer than one year. Fragments were divided according to the length of their long axis into three groups: group A (0–3.9 cm), (n = 21); group B (4–7.9 cm), (n = 22); group C (8 cm or more), (n = 21). Fragment displacement was also assessed in the proximal (P) or distal (D) end to the nearest cortex of the femoral shaft, and divided into the following groups: group P1 (n = 44) or D1 (n = 47), (0–9 mm); group P2 (n = 10) or D2 (n = 11), (10–19 mm); group P3 (n = 7) or D3 (n = 3), (20–29 mm); and group P4 (n = 3) or D4 (n = 3), (30 mm or more).ResultsThe bone union rate was 86% in the small (less than 8 cm) fragment groups and 71% in the large (8 cm or more) fragment group (P = 0.046). With respect to the degree of displacement, the union rate was lower (P = 0.001) and the average union time was longer (P = 0.012) in the 20 mm or more group for both the proximal fragment part and the distal fragment part (P = 0.002, P = 0.014). A logistic regression analysis underlined the displacement in the proximal site (OR: 0.298, 95% CI: 0.118–0.750) as in the distal site (OR: 0.359, 95% CI: 0.162–0.793) as a larger effect on union rate than the fragment size that as no effect in logistic regression (OR 3.8, 95% CI: 0.669–21.6).ConclusionNon-union develops significantly more frequently in femoral shaft fractures with fragments 8 cm or longer or when the displacement in the proximal area is 20 mm or greater and 10 mm or greater in the distal area during the intramedullary nailing procedure. Regarding union rate, the degree of displacement has more influence than the third fragment size in femoral shaft fractures.Level of evidenceIV, retrospective cohort study.