Is the rotation of the femural head a potential initiation for cutting out? A theoretical and experimental approach

BMC Musculoskeletal Disorders

Bernd Füchtmeier³  Amir Andreas Al-Munajjed¹  Edgar Mayr²  Jochen Hammer¹  Michael Nerlich³  Lukas Prantl³  Samuel Bachmeier¹  Andreas Lenich⁴ 

[1] Biomechanic Research Regensburg, University of Applied Sciences Regensburg, Regensburg 93053, Germany;Department of Trauma Surgery, Klinikum Augsburg, Augsburg 86156, Germany;Department of Trauma Surgery, University of Regensburg, Regensburg 93053, Germany;Department of Trauma Surgery, Klinikum Rechts der Isar, Technical University of Munich, Munich 81675, Germany

关键词: cutting out;    center-center-position;    osteosynthesis;    proximal femur fractures;   

Others  :  1158553
DOI  :  10.1186/1471-2474-12-79

 received in 2010-09-19, accepted in 2011-04-22,  发布年份 2011

【 摘 要 】

Background

Since cut-out still remains one of the major clinical challenges in the field of osteoporotic proximal femur fractures, remarkable developments have been made in improving treatment concepts. However, the mechanics of these complications have not been fully understood.

We hypothesize using the experimental data and a theoretical model that a previous rotation of the femoral head due to de-central implant positioning can initiate a cut-out.

Methods

In this investigation we analysed our experimental data using two common screws (DHS/Gamma 3) and helical blades (PFN A/TFN) for the fixation of femur fractures in a simple theoretical model applying typical gait pattern on de-central positioned implants. In previous tests during a forced implant rotation by a biomechanical testing machine in a human femoral head the two screws showed failure symptoms (2-6Nm) at the same magnitude as torques acting in the hip during daily activities with de-central implant positioning, while the helical blades showed a better stability (10-20Nm).

To calculate the torque of the head around the implant only the force and the leverarm is needed (N [Nm] = F [N] * × [m]). The force F is a product of the mass M [kg] multiplied by the acceleration g [m/s²]. The leverarm is the distance between the center of the head of femur and the implant center on a horizontal line.

Results

Using 50% of 75 kg body weight a torque of 0.37Nm for the 1 mm decentralized position and 1.1Nm for the 3 mm decentralized position of the implant was calculated. At 250% BW, appropriate to a normal step, torques of 1.8Nm (1 mm) and 5.5Nm (3 mm) have been calculated.

Comparing of the experimental and theoretical results shows that both screws fail in the same magnitude as torques occur in a more than 3 mm de-central positioned implant.

Conclusion

We conclude the center-center position in the head of femur of any kind of lag screw or blade is to be achieved to minimize rotation of the femoral head and to prevent further mechanical complications.

【 授权许可】

   
2011 Lenich et al; licensee BioMed Central Ltd.

【 图 表 】

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