A cadaveric biomechanical study comparing the ease of femoral nail insertion: 1.0- vs 1.5-m bow designs
Anatomic fit of intramedullary nails was suggested by previous studies to improve significantly when the nail radius of curvature (ROC) is closer to the average femoral anatomy. However, no attempt has been made to investigate the impact of different ROC designs on the nail insertion process. Therefore, this biomechanical study quantitatively compared the ease of insertion between femoral intramedullary nails with a 1.0-m and a 1.5-m bow radius.
Materials and methods
Long TFN-ADVANCED™ (TFNA, 1.0 m ROC) and Proximal Femoral Nail Antirotation nails (PFNA, 1.5 m ROC) were implanted pairwise into seven paired cadaver femora. All bones were reamed 1.5 mm larger than the nail diameter. Using a material testing machine, intramedullary nailing was then performed stepwise with 20-mm steps and a 10-mm/s insertion rate, and force was measured. The nail deformation caused by the insertion was assessed through 3D computer models built from pre- and post-nailing CT scans. The ease of insertion between TFNA and PFNA nails was quantified in terms of insertion force, insertion energy and nail deformation.
There was no significant difference in the peak force generated during nailing between TFNA and PFNA nails (P = 0.731). However, the force measured at the end of insertion (P = 0.002) was significantly smaller in TFNA nails compared to PFNA nails. After implantation, TFNA nails showed significantly smaller deformation when compared to PFNA nails (P = 0.005, both ends aligned). Furthermore, less energy was required to insert TFNA nails; however, the difference was not significant (P = 0.25).
Compared to PFNA nails, a significant decrease in insertion force and nail deformation was found at the end of insertion for TFNA nails. Results suggest that TFNA having a 1.0-m ROC is easier to insert for the set of femora used in this study compared to PFNA with a 1.5-m ROC.
KeywordsFemur Intramedullary nail Nail insertion Biomechanical test Radius of curvature (ROC) Insertion force Nail deformation
The authors would like to acknowledge and thank Mr. Dieter Wahl from AO Research Institute for his excellent support during the nail insertion test.
Compliance with ethical standards
Conflict of interest
B. Schmutz has received an industrial scholarship from DePuy Synthes Australia.
The study was approved by the internal institutional board.
- 4.Collinge CA, Beltran C (2013) Does modern nail geometry affect positioning in the distal femur of elderly patients with hip fractures? A comparison of otherwise identical intramedullary nails with a 200 versus 150 cm radius of curvature. J Orthop Trauma 27:299–302. doi: 10.1097/BOT.0b013e318283f231 CrossRefPubMedGoogle Scholar
- 7.Harper MC, Carson WL (1987) Curvature of the femur and the proximal entry point for an intramedullary rod. Clin Orthop Relat Res 220:155–161Google Scholar
- 9.Koval KJ (2007) Intramedullary nailing of proximal femur fractures. Am J Orthop (Belle Mead NJ) 36:4–7Google Scholar
- 13.Karakaş HM, Harma A (2008) Femoral shaft bowing with age: a digital radiological study of Anatolian Caucasian adults. Diagnostic Interv Radiol 14:29–32.Google Scholar
- 15.Synthes D (2016) TFN-ADVANCED™ proximal femoral nailing system: surgical technique. http://synthes.vo.llnwd.net/o16/LLNWMB8/USMobile/Synthes North America/Product Support Materials/Technique Guides/DSUSTRM06140109_2_TFNA_TG.pdf. Accessed 21 Jul 2016
- 16.Blauth M, Finkemeier CG (2015) TFN-Advanced Proximal Femoral Nailing System (TFNA). AOTK Syst Innov 1:4–10. https://issuu.com/aofoundation/docs/tk_news_2015_11_hires?e=5253115/31551614. Accessed 28 Mar 2017
- 20.Disegi J (2008) Implant materials. Titanium—6% Aluminum—7% Niobium. https://www.scribd.com/document/235706163/Implant-Materials-Titanium-6-Aluminum-7-Niobium. Accessed 28 Mar 2017
- 21.Disegi J (2009) Implant materials. Wrought Titanium-15% Molybdenum. doi: 10.1016/S0091-6749(00)70134-5
- 22.Synthes D (2016) PFNA. Proximal femoral nail antirotation: Surgical Technique. http://synthes.vo.llnwd.net/o16/LLNWMB8/INTMobile/Synthes International/Product Support Material/legacy_Synthes_PDF/DSEM-TRM-0714-0120-3_LR.pdf. Accessed 21 Jul 2016
- 23.INSTRON (2017) 2525 Series Drop-Through Static Load Cell. http://www.instron.us/en-us/products/testing-accessories/load-cells/static/2525-series-drop-through/2525-806. Accessed 23 Feb 2017