A finite element analysis of two novel screw designs for scaphoid waist fractures

Варга, П.; Zysset, Philippe; Schefzig, Philip; Unger, Ewald; Mayr, Winfried; Erhart, Jochen

doi:10.1016/j.medengphy.2015.11.006

Cited by 18 publications

(17 citation statements)

References 27 publications

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“…In our test set up we did not take shear forces perpendicular to the scaphoid longitudinal axis into consideration as it was done in Varga´s finite element study [ 29 ]. Torque results also could have been dependent on the depth of potting of the proximal and distal poles of the scaphoid into the negative forms of the scaphoid and sample holder.…”

Section: Limitations Of This Studymentioning

confidence: 99%

Rotational Stability of Scaphoid Osteosyntheses: An In Vitro Comparison of Small Fragment Cannulated Screws to Novel Bone Screw Sets

et al. 2016

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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.

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Section: Limitations Of This Studymentioning

confidence: 99%

Rotational Stability of Scaphoid Osteosyntheses: An In Vitro Comparison of Small Fragment Cannulated Screws to Novel Bone Screw Sets

et al. 2016

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“…It is entirely intraarticular and covered with articular cartilage which limits the availability of the fixation techniques. [5,6,15] Advances in implant technology, such as the development of new screws and scaphoid plate designs providing compression, have significantly reduced the rates of scaphoid nonunion. Despite the range of these new techniques and implants used, the search for a more stable method for scaphoid bone fixation continues.…”

Section: Discussionmentioning

confidence: 99%

Single versus double screw fixation for the treatment of scaphoid waist fractures: Finite element analysis and preliminary clinical results in scaphoid nonunion

et al. 2020

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This study aims to compare the single versus double screw fixation of scaphoid waist fractures using finite element analysis, and to present the preliminary clinical results of double screw fixation in a consecutive series of patients with scaphoid nonunion. Patients and methods: A transverse scaphoid waist fracture (Herbert type B2) model was fixed with either single or double cannulated compression screws. Displacement and rotation of the fragments were performed using three-dimensional finite element analysis in three different wrist positions. A retrospective review was performed on 13 male patients (mean age 31.6±12.8 years; range, 17 to 64 years) who underwent double screw fixation for an established scaphoid nonunion in our clinic between January 2015 and December 2017. Assessment of union was established with serial plain radiographs in eight patients and with wrist computed tomography in five patients. Clinical evaluation was performed using the Mayo wrist score and visual analog scale (VAS). Results: In all wrist positions, the displacement of the fracture gap in double screw fixation in all planes (x, y, and z) was less than in single screw fixation. Similarly, rotation of the fracture fragments around the longitudinal axis of the scaphoid was lower in double screw fixation. Complete union was obtained in all patients. The mean time to union was 5±0.75 months (range, 4 to 6 months). The mean VAS was 0.8±0.9 (range, 0 to 3). Mayo wrist score was 91±6.9 (range, 80 to 100) at the final follow-up. Conclusion: Double-screw fixation technique may be a solution to reduce the rate of scaphoid nonunion in unstable type B2 scaphoid fractures or nonunion.

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“…A relatively large body of work has evaluated the role of FE modeling in clinical fracture fixation scenarios. For example, Ramlee et al reviewed two external fixators with an FE model and their effects on subtalar dislocation reduction, similarly, Varga et al reviewed the use of compression screws in scaphoid fracture fixation and the effects these have on interfragmentary forces and again fracture reduction. Both of these studies among others (e.g., Ref …”

Section: Discussionmentioning

confidence: 99%

Biomechanics of two external fixator devices used in rat femoral fractures

Osagie

Kaufmann

Blunn

et al. 2019

Journal Orthopaedic Research

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The use of external fixators allows for the direct investigation of newly formed interfragmentary bone, and the radiographic evaluation of the fracture. We validated the results of a finite element (FE) model with the in vitro stiffness' of two widely used external fixator devices used for in vivo analysis of fracture healing in rat femoral fractures with differing construction (Ti alloy ExFix1 and PEEK ExFix2). Rat femoral fracture fixation was modeled using two external fixators. For both constructs an osteotomy of 2.75 mm was used, and offset maintained at 5 mm. Tufnol, served as standardized substitutes for rat femora. Constructs were loaded under axial compression and torsion. Overall axial and torsional stiffness were compared between the in vitro models and FE results. FE models were also used to compare the fracture movement and overall pattern of von Mises stress across the external fixators. In vitro axial stiffness of ExFix1 was 29.26 N/mm AE 3.83 compared to ExFix2 6.31 N/mm AE 0.67 (p Ã < 0.05). Torsional stiffness of ExFix1 was 47.5 Nmm/˚AE 2.71 compared to ExFix2 at 19.1 Nmm/˚AE1.18 (p Ã < 0.05). FE results predicted similar comparative ratios between the ExFix1 and 2 as the in vitro studies. FE results predicted considerably larger interfragmentary motion in the ExFix2 comparing to ExFix1. We demonstrated significant differences in the stiffness' of the two external fixators as one would expect from such variable designs; yet, importantly we validated the utility of an FE model for the analysis and prediction of changes in fracture mechanics dependent on fixator choice. ß

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A finite element analysis of two novel screw designs for scaphoid waist fractures

Cited by 18 publications

References 27 publications

Rotational Stability of Scaphoid Osteosyntheses: An In Vitro Comparison of Small Fragment Cannulated Screws to Novel Bone Screw Sets

Rotational Stability of Scaphoid Osteosyntheses: An In Vitro Comparison of Small Fragment Cannulated Screws to Novel Bone Screw Sets

Single versus double screw fixation for the treatment of scaphoid waist fractures: Finite element analysis and preliminary clinical results in scaphoid nonunion

Biomechanics of two external fixator devices used in rat femoral fractures

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