Archives of Orthopaedic and Trauma Surgery - 2026-04-06 - Journal Article
Are new implants for patellar fractures reasonable? A biomechanical comparison of intramedullary locking nails versus tension-band osteosynthesis.
Gercek N, Arand C, Glockner C, Nienhaus M, Gercek E, Hopf J, Rommens PM, Gruszka D
Topics
Key Takeaway
Intramedullary double nail fixation of transverse patellar fractures produced 73% less fragment displacement (0.55 mm) than tension-band osteosynthesis (2.04 mm) over 1,000 simulated knee flexion cycles.
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Summary
This study compared fragment displacement and fracture gap symmetry across three fixation constructs—classic tension-band osteosynthesis, intramedullary single nail, and intramedullary double nail prototypes—applied to AO 34-C1.1 transverse patellar fractures in synthetic bone models under 1,000 cycles of simulated knee motion (0–90°) with up to 300 N tensile load. The double nail system produced the least displacement (0.55 ± 0.31 mm) versus single nail (1.34 ± 0.74 mm) and tension-band (2.04 ± 0.67 mm), with statistically significant differences between double nail and both other constructs. Tension-band osteosynthesis also demonstrated significantly greater asymmetric fracture gap opening compared to both intramedullary systems (p < 0.001).
Key Limitation
Synthetic Sawbones models cannot replicate the comminution, bone quality variation, or soft tissue envelope of clinical patellar fractures, limiting direct translation of displacement values to in vivo performance.
Original Abstract
BACKGROUND
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.
METHODS
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.
RESULTS
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).
CONCLUSIONS
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.