No abstract

No abstract

BackgroundThe current standard of care for operative repair of scaphoid fractures involves reduction and internal fixation with a single headless compression screw. However, a compression screw in isolation does not necessarily control rotational stability at a fracture or nonunion site. The single screw provides rotational control through friction and bone interdigitation from compression at the fracture site. We hypothesize that osteosyntheses with novel bone screw sets (BSS) equipped with anti-rotational elements provide improved rotational stability.MethodsStability of osteosynthesis under increasing cyclic torsional loading was investigated on osteotomized cadaveric scaphoids. Two novel prototype BSS, oblique type (BSS-obl.) and longitudinal type (BSS-long.) were compared to three conventional screws: Acutrak2®mini, HCS®3.0 and Twinfix®. Biomechanical tests were performed on scaphoids from single donors in paired comparison and analyzed by balanced incomplete random block design. Loading was increased by 50 mNm increments with 1,000 cycles per torque level and repeated until a rotational clearance of 10°. Primary outcome measure was the number of cycles to 10° clearance, secondary outcome measure was the maximum rotational clearance for each torque level.FindingsBSS-obl. performed significantly better than Acutrak2®mini and HCS® (p = 0.015, p<0.0001). BSS-long. performed significantly better than HCS® (p = 0.010). No significant difference in performance between BSS-obl. and BSS-long. (p = 0.361), between BSS obl. and Twinfix® (p = 0.50) and BSS long. and Twinfix® (p = 0.667) was detected. Within the torque range up to 200 mNm, four of 21 (19%) BSS-long. and four of 21 (19%) BSS-obl. preparations showed early failure. The same loading led to early failure in four (29%) Twinfix®, seven (50%) Acutrak2®mini and 10 (71%) HCS® of 14 screw samples, respectively.ConclusionsFor both BSS and to a lesser extent for Twinfix® (as dual-component screw), higher rotational stabilities were identified in comparison to single component headless compression screws.

The aim of this study was to measure the magnitude and direction of forces and torque within osteotomized scaphoids within cadaveric wrists during grasping movement of the hand. The mechanical contributions of clinically relevant individual wrist-crossing tendon groups were investigated. Wrists of eight forearms were immobilized in the sagittal, transverse, and coronal plane on a fixation device with unhindered axial gliding. The scaphoid was osteotomized and the fragments stabilized using an interlocking nail. The nail served as a sensor for measurement of inter-fragmentary forces orthogonal and torque around the sensor axis. Thus, torque and cantilever forces were measured which originated between the fragments through co-contraction through the activity of wrist-crossing tendons. Grasping movement of the hand induced a mean maximum torque of 0.038 ± 0.051 Nm and a force of 4.01 ± 1.71 N on the scaphoid. The isolated activation of thumb tendons resulted in a torque of 9.9 E ± 7.7 E Nm and a force of 1.42 ± 0.49 N. Despite immobilization of the wrist, grasping movement of the hand caused substantial forces and torque within the osteotomized scaphoid bone in varying directions and severity among different specimens. These factors may contribute to the development of nonunions and malunions in unstable scaphoid fractures through interfragmentary micromotion. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1734-1742, 2016.

Screw osteosynthesis using headless compression screws has become the accepted gold standard for the surgical treatment of scaphoid fractures. Optimal screw specifications remain controversially discussed. We aimed to investigate the influence of bone model composition on screw stability tests using headless compression screws in different scaphoid fracture models. We conducted pull-out tests using Acutrak2 ® mini, HCS ® , HKS ® , HBS ® , Herbert/Whipple ® and Twinfix ® screws. To imitate cortical and cancellous bone, two-layer polyurethane (PU) models with two distinct densities were produced. The cylinders were cut at different positions to replicate fracture localisations at increasing distances. The maximum pull-out force required to achieve up to 1 mm of pull-out distance (N to 1 mm) was measured. Acutrak2 ® mini and HCS ® followed by Twinfix ® showed the greatest average pull-out forces. N to 1 mm was, on average, greater in the cortico-cancellous model than in the cancellous cylinder with the Acutrak2 ® mini and the Herbert/Whipple ® screws, while it was the least with the HBS ® and the Twinfix ® screws; there were also differences between the HCS ® and HKS ®. There were no differences between the different fracture simulations in the synthesis strength using either the HKS ® or HBS ®. The pull-out forces of the HCS ® and Twinfix ® remained high also in simulations with the smaller screw base fragments. Varying imitations of cancellous and cortico-cancellous bone and fracture localisation reveal important information about the ex vivo strength of screw syntheses. The grip of the cortical structure should be used with the screws that fit more firmly in cortico-cancellous bone.