Quantification of cephalomedullary nail fit in the femur using 3D computer modelling: a comparison between 1.0 and 1.5m bow designs.
BACKGROUND
The radius of curvature (ROC) misfit of cephalomedullary nails during anterograde nailing can lead to complications such as distal anterior cortical encroachment. This study quantified the anatomical fit of a new nail with 1.0-m ROC (TFN-ADVANCED(™) Proximal Femoral Nailing System [TFNA]) compared with a nail with 1.5-m ROC (Gamma3 Long Nail R1.5 [Gamma3]).


METHODS
We generated 63 three-dimensional models (48 female, 45 right femur) representing the cortical surfaces of the femora (31 Caucasian, 28 Japanese, and 4 Thai). The mean age of the specimens was 77 years (±8.1), and the mean height was 158.5 cm (±9.6). Utilizing a customized software tool, nail fit was determined from the total surface area of nail protrusion from the inner cortex surface and maximum distance of nail protrusion in the axial plane; the position of the distal nail tip within the canal was also determined.


RESULTS
Overall, TFNA had both a significantly smaller mean total surface area of nail protrusion (915.8 vs. 1181.6 mm(2); P < 0.05) and a mean maximum distance of nail protrusion in the axial plane (1.9 vs. 2.1 mm; P = 0.007) when compared with Gamma3. The mean total surface area of nail protrusion was significantly smaller with TFNA versus Gamma3 in both the Caucasian (P = 0.0009) and Asian (Japanese and Thai) samples (P = 0.000002); the mean maximum distance of TFNA protrusion was significantly smaller in Asians (P = 0.04), but not in Caucasians (P = 0.08). Most tip positions for both nail types were anterior, but TFNA had a higher number of center positions than Gamma3 (13 vs. 7) and a shift from the far anterior cortex to the center of the medullary canal (overall and in Caucasians). In Asians, the most prominent position was far anterior for both nails.


CONCLUSIONS
The 1.0-m ROC TFNA nail resulted in better fit than the 1.5-m ROC Gamma3 nail. Clinical trials and case studies should be conducted in the future to verify if these findings would also result in clinical improvements.
Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, QLD, 4059, Australia. b.schmutz@qut.edu.au.
Beat
B
Schmutz
Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, QLD, 4059, Australia.
Jayani
J
Amarathunga
DePuy Synthes, 1301 Goshen Parkway, West Chester, PA, 19380, USA.
Stanley
S
Kmiec
School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, 2 George Street, Brisbane, QLD, 4001, Australia.
Prasad
P
Yarlagadda
Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, QLD, 4059, Australia.|Trauma Services, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba, QLD, 4102, Australia.
Michael
M
Schuetz
D000368:Aged; D000369:Aged, 80 and over; D001858:Bone Nails; D003198:Computer Simulation; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008953:Models, Anatomic; D011474:Prosthesis Design; D017755:Prosthesis Fitting / Q000379:methods; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods
3D modelling; Cephalomedullary; Femur; Fracture fixation; Intramedullary nail; Nail fit