Are new implants for patellar fractures reasonable? A biomechanical comparison of intramedullary locking nails versus tension-band osteosynthesis

Patellar fractures are predominantly treated surgically by open reduction and internal fixation using classic tension band osteosynthesis. Biomechanical testing was conducted to examine transverse patellar fracture stabilization using locked intramedullary nail systems in comparison to classic tension band osteosynthesis. Twenty-four Sawbones® with transverse patellar fractures type AO 34-C1.1 were divided equally into three test groups. Three principles for fracture stabilization were used: classical tension band osteosynthesis and newly developed locked intramedullary double nail- and single nail- prototypes. Knee motion (0°/0°/90°) was simulated in a dynamic test set-up using a “single muscle model” by applying tensile forces up to 300 N. The widening and the symmetry of the fracture gap were investigated over 1000 motion cycles using a video-optical system. The significance level was set at α = 0.05 for all statistical evaluations using the Bonferroni–Holm corrected unpaired unilateral t-test and mixed ANOVA with post-hoc Tukey test. The fixation principles showed different maximum fragment displacements of M = 2.04 ± 0.67 mm using classical tension band osteosynthesis, M = 1.34 ± 0.74 mm using intramedullary single nail system and M = 0.55 ± 0.31 mm using intramedullary double nail system. There was a statistically significant change in width of the fracture gap in flexed knee position comparing tension band osteosynthesis and double nail system (p = 0.0015) and comparing single nail and double nail system (p = 0.02). Furthermore, the tension-band osteosynthesis showed a significantly greater divergence from symmetry in the fracture gap compared to both intramedullary treatment methods (p < 0.001). Prototypes of locked intramedullary nail systems showed comparable fixation results for transverse patellar fractures compared to tension band wiring. They showed more symmetrical fracture gap openings during biomechanical testing and offered significantly higher stability to the fragments.