The assembled 3D model was imported using ABAQUS software (Simulia, Suresnes, France) to generate the finite element model. The screws were made of titanium alloy. The elastic modulus, Poisson ratio of titanium alloy and bone were performed as previously described. Tetrahedral 10-nodes elements (C3D10) was used to simulate cortical bone, cancellous bone, and hollow screw of the femur. The effect of gravity was considered negligible in the model. Frictional contact interactions between different parts of the model were assumed to exist. The internal cancellous bone and the cannulated screw thread of the femoral head were modeled using the common joint method. A friction coefficient of 0.3 was used to simulate the interface between the body and bone of the common hollow compression screw. The friction coefficient of the interaction between the fracture end fragments was set at 0.46. During the analysis, all nodes on the distal surface of the femur were constrained by 0 degrees of freedom to prevent rigid body movement. A load of 2100 N equivalent to three times the body weight was applied in the finite element model to introduce a force into the center of the femoral head. The force vector pointed laterally at an angle of 13° with the axis of the femoral shaft on the coronal plane and posteriorly at an angle of 8° with the shaft axis in the sagittal plane. A major strain of 0.9% was taken as the yield strain value above which the bone was susceptible to yielding in accordance with previously published data. Three parameters were used to capture the mechanical factors affecting the fixation stability and fracture healing of the five types of reduction and internal fixation, including the von Mises stress distribution and stress peak of the internal fixator, the displacement distribution of fracture fragments, and the principal strain of the femoral neck cancellous bone model. The distribution and maximum displacement of fracture fragments are the most critical factors to determine the stability of fracture reduction and fixation.
Differences in fracture block displacement were observed among the five reduction models. Inter-fragmentary motions were calculated as the displacements between the two nodes on the proximal end of the fracture gap on the coronal view. The anatomic reduction model showed the smallest displacement of a fractured block, and it was 0.388 mm. The displacement value in the positive 2 mm model was 0.547 mm, which was close to the values found in the anatomic reduction model. The maximum displacement in the negative 2 mm model (0.786 mm) was between the values of the positive 3 mm model (0.721 mm) and the 4 mm model (0.838 mm) [Figure 4].
The concept of the Gotfried reduction technique is to stabilize unstable sub-cephalic fractures. The primary mechanism is that positive buttress can provide better biomechanical stability. If excessive pressure is generated on the bone-screw interface due to sliding tension of the cannulated nail, the femoral head may be displaced (with the possibility of “cutting out”). The medial femoral cervical cortex is markedly thick, and positive buttress reduces the screw stress when incisions occur, possibly due to the provision of cortical-cortical contact. Under axial load, compared with the stress in the negative buttress model, the stress in the positive buttress 2 and 3 mm model screws were smaller. This is because positive buttress can dissipate some of the screw stress. The stress in the positive buttress 4 mm model screw was higher than that in the negative buttress model. This may be due to the inability of the positive buttress to provide cortical to cortical contact after displacement. Under the action of the axial load, the fracture clearance displacement in the anatomic reduction model is the smallest. The fracture clearance displacement in the positive buttress 2 and 3 mm models was smaller than the displacement in the negative buttress 2 mm model. The fracture clearance displacement in the 4 mm model with positive buttress was the largest. Therefore, the stability of the positive buttress model was the closest to the stability provided by the anatomic reduction model. The stability of the 2 mm model of negative buttress was between the ones of the 3 and 4 mm models of positive buttress. All the main strain areas of the femoral neck cancellous bone model were concentrated around the three nail holes. Excessive stress may result in deformation of the cancellous bone around the cannulated nail. This causes cutting of the screws. The results of this study also confirmed the mechanism of Gotfried reduction and provided a quantitative analysis of the positive buttress technology to a certain extent, which has a positive guiding significance for clinical research.
According to the results of this study, positive buttress was graded and set as positive reduction level I (shift 0–2 mm). Positive 3 mm buttress was more stable than negative 2 mm buttress, and it was set as positive reduction level II (displacement 2–3 mm). Positive 4 mm support reset had poor stability, and it was set as positive reset level III (displacement 3–4 mm). The reset above 4 mm was set as positive reset level IV (shift >4 mm). Therefore, when anatomic reduction cannot be achieved during surgical reduction, positive reduction level I can also provide relatively stable biomechanical effects. Positive reset level II is a relatively acceptable range. Positive reset level III is not recommended. Positive reset level IV should be avoided as much as possible.
This study was partially supported by a grant from the Zhejiang Medical Science Foundation of China (No. 2019KY682).
1. Unnanuntana A, Saiyudthong N. Outcomes of cerclage wiring to manage intra-operative femoral fracture occurring during cementless hemiarthroplasty in older patients with femoral neck fractures. Int Orthop
2019; [Epub ahead of print]. doi: 10.1007/s00264-019-04327-9.
2. Stockton DJ, Dua K, O’Brien PJ, Pollak AN, Hoshino CM, Slobogean GP. Failure patterns of femoral neck fracture
fixation in young patients. Orthopedics
2019; 42:e376–e380. doi: 10.3928/01477447-20190321-03.
3. Svenoy S, Westberg M, Figved W, Valland H, Brun OC, Wangen H, et al. Posterior versus lateral approach for hemiarthroplasty after femoral neck fracture
: early complications in a prospective cohort of 583 patients. Injury
2017; 48:1565–1569. doi: 10.1016/j.injury.2017.03.024.
4. Jo S, Lee SH, Lee HJ. The correlation between the fracture types and the complications after internal fixation of the femoral neck fractures. Hip Pelvis
2016; 28:35–42. doi: 10.5371/hp.2016.28.1.35.
5. Sassoon A, D’Apuzzo M, Sems S, Cass J, Mabry T. Total hip arthroplasty for femoral neck fracture
: comparing in-hospital mortality, complications, and disposition to an elective patient population. J Arthroplasty
2013; 28:1659–1662. doi: 10.1016/j.arth.2013.01.027.
6. Wang G, Tang Y, Wang B, Yang H. Minimally invasive open reduction combined with proximal femoral hollow locking plate in the treatment of Pauwels type III femoral neck fracture
. J Int Med Res
2019; 47:3050–3060. doi: 10.1177/0300060519850962.
7. Wang Y, Ma JX, Yin T, Han Z, Cui SS, Liu ZP, et al. Correlation between reduction quality of femoral neck fracture
and femoral head necrosis based on biomechanics. Orthop Surg
2019; 11:318–324. doi: 10.1111/os.12458.
8. Eamsobhana P, Keawpornsawan K. Nonunion paediatric femoral neck fracture
treatment without open reduction. Hip Int
2016; 26:608–611. doi: 10.5301/hipint.5000382.
9. Kwon HM, Lim S, Yang IH, Lee WS, Jeon BH, Park KK. Impact of renal function on the surgical outcomes of displaced femoral neck fracture
in elderly patients. J Clin Med
2019; 8:E1149doi: 10.3390/jcm8081149.
10. Gotfried Y, Kovalenko S, Fuchs D. Nonanatomical reduction of displaced subcapital femoral fractures (Gotfried reduction). J Orthop Trauma
2013; 27:e254–e259. doi: 10.1097/BOT.0b013e31828f8ffc.
11. Kazley JM, Banerjee S, Abousayed MM, Rosenbaum AJ. Classifications in brief: garden classification of femoral neck fractures. Clin Orthop Relat Res
2018; 476:441–445. doi: 10.1007/s11999.0000000000000066.
12. Xiong WF, Changm SM, Zhang YQ, Hu SJ, Du SC. Inferior calcar buttress reduction pattern for displaced feoral neck fractures in young adults: a preliminary report and an effective alternative. J Orthop Surg Res
2019; 14:70doi: 10.1186/s13018-019-1109-x.
13. Goffin JM, Pankaj P, Simpson AH, Seil R, Gerich TG. Does bone compaction around the helical blade of a proximal femoral nail anti-rotation (PFNA) decrease the risk of cut-out?: a subject-specific computational study. Bone Joint Res
2013; 2:79–83. doi: 10.1302/2046-3758.25.2000150.
14. Zhang H, Li J, Zhou J, Li L, Hao M, Wang K, et al. Finite element analysis
of different double-plate angles in the treatment of the femoral shaft nonunion with no cortical support opposite the primary lateral plate. BioMed Res Int
2018; 2018:3267107doi: 10.1155/2018/3267107.
15. Panteli M, Rodham P, Giannoudis PV. Biomechanical rationale for implant choices in femoral neck fracture
fixation in the non-elderly. Injury
2015; 46:445–452. doi: 10.1016/j.injury.2014.12.031.
16. Yang JJ, Lin LC, Chao KH, Chuang SY, Wu CC, Yeh TT, et al. Risk factors for nonunion in patients with intracapsular femoral neck fractures treated with three cannulated screws placed in either a triangle or an inverted triangle configuration. J Bone Joint Surg Am
2013; 95:61–69. doi: 10.2106/JBJS.K.01081.
17. Mitchell RJ, Kay AB, Smith KM, Murphy SB, Le DT. Early results of displaced femoral neck fragility fractures treated with supercapsular percutaneous-assisted total hip arthroplasty. Arthroplasty today
2019; 5:193–196. doi: 10.1016/j.artd.2019.02.003.
18. Li J, Wang M, Li L, Zhang H, Hao M, Li C, et al. Finite element analysis
of different configurations of fully threaded cannulated screw in the treatment of unstable femoral neck fractures. J Orthop Surg Res
2018; 13:272doi: 10.1186/s13018-018-0970-3.
19. Li J, Wang M, Zhou J, Han L, Zhang H, Li C, et al. Optimum configuration of cannulated compression screws for the fixation of unstable femoral neck fractures: finite element analysis
evaluation. BioMed Res Int
2018; 2018:1271762doi: 10.1155/2018/1271762.
20. Papachristos IV, Rankine J, Giannoudis PV. Hip arthrodiastasis combined with core decompression and diamond concept for postcollapse femoral head avascular necrosis. BMJ case Rep
2019; 12:e231081doi: 10.1136/bcr-2019-231081.
21. Dheenadhayalan J, Prasad VD, Devendra A, Rajasekaran S. Impaction bone grafting and valgus osteotomy - a technical trick for the treatment of femoral neck nonunions. J Orthop Trauma
2019; 33:e403–e408. doi: 10.1097/BOT.0000000000001564.
22. Siebenburger G, Helfen T, Biermann N, Haasters F, Bocker W, Ockert B. Screw-tip augmentation versus standard locked plating of displaced proximal humeral fractures: a retrospective comparative cohort study. J Shoulder Elbow Surg
2019; 28:1326–1333. doi: 10.1016/j.jse.2018.12.001.
23. Gardner MP, Chong AC, Pollock AG, Wooley PH. Mechanical evaluation of large-size fourth-generation composite femur and tibia models. Ann Biomed Eng
2010; 38:613–620. doi: 10.1007/s10439-009-9887-7.
24. Yin W, Xu Z, Sheng J, Zhang C, Zhu Z. Logistic regression analysis of risk factors for femoral head osteonecrosis after healed intertrochanteric fractures. Hip Int
2016; 26:215–219. doi: 10.5301/hipint.5000346.