Objective: To study the biomechanical effects and the clinical outcome of different internal fixation methods in treating posterior malleolus fractures.
Methods: (1) Biomechaniccal study of 18 pairs of posterior malleolus fracture models was conducted, in which all the cases were divided into 3 groups as I, II and III (n=12), according to different fracture degrees that included specimens with 1/4, 1/3 and 1/2 of articular facets fractured respectively; Each group was further divided into 2 subgroups as group A and group B. Group A was fixed with 2 steel half-thread tensile screws whose diameter was 4.0 mm; and group B was fixed with "T-shaped" steel distal-radius plates and 4 screws. The uploading experiment was carried out by settling the specimen on an experiment machine at its neutral position, and the data were collected and managed. (2) Clinical Applications: 31 cases with closed trimalleolar fractures were treated from 2009.1-2010.12 in our hospital, in which 14 with posterior malleolus fractures ≤ 2 5% of the capital diameter of the tibial plafond were fixed with screws, and 17 with posterior malleolus fractures >25% of the capital diameter of the tibial plafond were fixed with steel plates. Prospective cohort study of these cases were carried out. The outcome was assessed using a Leeds Scoring System.
Results: The mechanical fixation strengths of the plates for 1/4, 1/3 and 1/2 facets of posterior malleolus fractures were all higher than those of the screw groups [(4.10 ± 0.13) kN vs. (4.6 0 ± 0.27)kN, (3.20 ± 0.12)kN vs. (4.12 ± 0.14)kN and (1.98 ± 0.18)kN vs. (3.72 ± 0.18)kN, respectively, P<0.05]. For the clinical study ,the mean follow-up period was 12 months (6-18 months), all the cases acquired bone union, and the mean time for healing was 10 weeks ( 8-12 weeks). In the evaluation of therapeutic effects, we found that 28 cases were excellent and 3 good, which was 100% satisfying.
Conclusion: If only 1/4 of the posterior articular facet is involved, 2 screws are enough to supply the stability; but for the fractures involve more than 1/4 facet, the plate fixation supplies more stable fixation and is superior to simply screws.