Far cortical locking versus standard locking screw fixation in simulated femoral fractures: A biomechanical meta-analysis

Robert S. Bullock; John G. Coury; Brendan Liakos; Eric G. Huish

doi:10.1016/j.jor.2024.09.013

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61 (); 43-46

doi:

10.1016/j.jor.2024.09.013

Far cortical locking versus standard locking screw fixation in simulated femoral fractures: A biomechanical meta-analysis

Robert S. Bullock, John G. Coury, Brendan Liakos , Eric G. Huish

Valley Consortium for Medical Education, 1400 Florida Ave Suite 200, Modesto, CA, 95350, USA

⁎Corresponding author: Brendan Liakos. BrendanJLiakos@gmail.com

Received: 2024-8-19, Accepted: 2024-9-13, Published: 2024-9-16

Professor P K Surendran Memorial Education Foundation

Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Far cortical locking (FCL) is a concept of locking plate fixation with reduced stiffness and symmetric micromotion to improve callus formation. The goal of our study was to review biomechanical data evaluating FCL plate and screw fixation versus standard locking (SL) plate and screw fixation by analyzing studies of cadaveric and synthetic bone models to draw biomechanical conclusions.

Biomechanical studies that compared FCL and SL plate fixation for simulated femoral fractures were reviewed for construct stiffness, load to failure, axial motion at the near and far cortices, and the difference between near and far cortical axial motion to demonstrate motion symmetry.

FCL decreased stiffness by 1.069 kN/mm compared to SL (95 % CI 0.405 to 1.732, p = 0.002). FCL demonstrated greater axial motion than SL in the near cortex by 0.425 mm (95 % CI 0.359 to 0.491, p < 0.001) and in the far cortex by 0.456 mm (95 % CI 0.378 to 0.534, p < 0.001). FCL resulted in symmetric motion with no significant difference between far and near cortices with the far cortex displacing 0.347 mm more than near (95 % CI -0.038 to 0.731, p = 0.78). SL resulted in asymmetric motion favoring the far cortex by 0.270 mm (0.096–0.443, p = 0.002). Construct strength was not significantly different with FCL load to failure 0.367 kN greater than SL (95 % CI -0.762 to 1.496, p = 0.524).

FCL screw fixation in femoral fractures achieves the goals of reducing construct stiffness and promoting more symmetric axial motion while maintaining construct strength. These results support the overall biomechanical goals of far cortical locking and should encourage investigation into its effects on clinical and radiographic outcomes.

Keywords

Far cortical locking

Distal femur

Supracondylar femur

Nonunion

Biomechanical

(FCL)

(SL)

1 Introduction

Non-union following locking plate fixation can be an unfortunate complication of surgical intervention, seen in the treatment of comminuted distal femur fractures in geriatric trauma patients.^1–11 Previous literature has identified shorter working length, increased construct rigidity, stainless steel implants, and specific constructs that utilize purely locking screws as modifiable variables that may lead to non-union.¹¹^,¹² Construct rigidity and lack of interfragmentary motion may lead to impaired fracture healing of the near cortex,¹³ though several techniques have been developed to improve delayed union, non-union, and hardware failure rates. It has been shown in previous studies that standard lateral locking (SL) plate constructs in distal femur fractures leads to an asymmetric formation of callus, favoring medial cortex callus formation over the lateral.¹⁴ Multiple techniques have been used to reduce this rigidity, such as increased plate-to-bone offset or utilization of an elastic screw suspension within the plate to provide screw-plate micromotion.^16–19 A novel technique was presented in 2009 by Bottlang et al., termed far cortical locking (FCL), in which diaphyseal screws are partially threaded to individually engage the far cortex, with a smooth shaft to prevent purchase in the near cortex, while utilizing a standard locking head to engage the plate. This provides the near cortex-screw interface flexibility to enhance interfragmentary motion.²⁰ A similar technique has been previously studied by creating a near cortical oval slot in which the locking screw does not directly thread into the near cortex, allowing for greater axial motion.²¹^,²² Since the advent of far cortical locking screws, there have been several biomechanical studies performed to evaluate their altered construct stiffness. With only far cortical thread purchase, the effects on construct strength or load to failure are also of interest. The purpose of this study was to perform a systematic review and meta-analysis of studies which used non-biological models, including cadaveric and synthetic bones, to draw biomechanical conclusions regarding stiffness, interfragmentary motion, and construct strength between FCL and SL plate and screw fixation.

2 Materials and methods

Institutional Review Board approval #20–317 was granted for this project by the San Joaquin General Hospital IRB. Systematic review was performed according to PRISMA guidelines. On June 10, 2020, a Pubmed database search was performed with the following terms: (far cortical locking or dynamic locking) AND (biomechanic or biomechanics or biomechanical) AND (femur or femoral or supracondylar). This search resulted in 17 articles. Two authors then screened these 17 articles for inclusion or exclusion using Abstrackr software (Brown, Providence, RI). Inclusion criteria were biomechanical studies that directly compared stiffness, strength, and axial interfragmentary motion between partially threaded FCL screw and SL screw and plate fixation on cadaveric or surrogate femoral bone models with applied axial load. All articles were screened and any conflicts were resolved by a fourth author. Eligible articles must have included direct measurements with standard deviations of the primary outcomes for final analysis.

2.1

2.1 Included studies

Four studies met eligibility criteria for final comparison and contributed to each primary outcome.²⁰^,^23–25 One study compared 22 cadaveric supracondylar femoral fractures,²³ while the other three studies compared a total of 32 composite diaphyseal femoral fractures (Sawbones Worldwide, WA).²⁰^,²⁴^,²⁵ One of the composite models created Vancouver B periprosthetic fractures distal to a cemented stem.²⁵ All fracture models included gaps to simulate comminution. The included studies varied in the plate material used, with two studies using stainless steel and two using titanium plates. To note, two of the studies reported using 4.5 mm thick plates with a width of 17.5 mm, whereas the other two studies did not report on plate sizes.

2.2

2.2 Statistical analysis

Meta-analysis was performed using OpenMeta[Analyst] (Brown, Providence, RI) to evaluate the following primary outcomes comparing FCL and SL fixation: axial stiffness (kN/mm), near cortex axial motion (mm), far cortex axial motion (mm), and load to failure (N). In addition, a comparison between near and far cortical axial motion was performed within the FCL group and within the SL group to signify symmetric versus asymmetric axial interfragmentary motion. Statistical significance was set at P < 0.05.

3 Results

Results of each study are presented in Table 1. FCL decreased overall construct stiffness by a mean of 1.069 kN/mm (95 % CI 0.405 to 1.732, p = 0.002). FCL demonstrated greater axial motion than SL on the near cortex by 0.425 mm (95 % CI 0.359 to 0.491, p < 0.001) and on the far cortex by 0.456 mm (95 % CI 0.378 to 0.534, p < 0.001). FCL resulted in symmetric motion with no significant difference between far and near cortex motion, favoring the far cortex by 0.347 mm greater than near cortex (95 % CI -0.038 to 0.731, p = 0.78). SL resulted in asymmetric motion favoring the far cortex by a significant difference of 0.270 mm (0.096–0.443, p = 0.002). The load to failure was not significantly different between FCL and SL fixation, with FCL showing 0.367 kN higher load to failure (95 % CI -0.762 to 1.496, p = 0.524).

Table 1 Included studies with relevant results and statistical analysis.

# Femora	Bottlang (2009)		Doornink (2011)		Henschel (2017)		Moazen (2013)		P Value
	10 Surrogate		22 Cadaveric		10 Surrogate		12 Surrogate
	FCL	SL	FCL	SL	FCL	SL	FCL	SL
Axial stiffness (kN/mm)	2.26 ± 0.08	2.94±0.13	3.70±1.2	5.90±1.5	1.13±0.10	3.00±0.36	0.46±0.06	0.55±0.05	p = 0.002
Near motion (mm)	0.51±0.08	0.02±0.01	0.57±0.09	0.10±0.04	0.50±0.06	0.10±0.02	0.60±0.10	0.30±0.10	p < 0.001
Far motion (mm)	0.59±0.10	0.05±0.02	0.63±0.11	0.19±0.09	0.75±0.07	0.37±0.04	1.60±0.10	1.10±0.20	p < 0.001
Near vs far motion	86 %	40 %	90 %	53 %	67 %	27 %	38 %	27 %	P = 0.78 (FCL) p = 0.002 (SL)
Load to failure (kN)	5.5±0.20	5.9±0.20	5.3±1.10	4.9±1.60	–	–	6.1±0.92	4.7±1.07	p = 0.524

4 Discussion

This is the first meta-analysis of available biomechanical data comparing FCL and SL screw and plate fixation in femoral fractures. FCL has been evaluated in several additional biomechanical studies that did not meet inclusion in this meta-analysis. In a previous study, Gardner et al. examined the effect of disengaging the near cortex and standard fully threaded locking screws via drilling of near cortical slots. The result of this study demonstrated a reduction in the axial and torsional stiffness without screw loosening or loss of reduction, shown in both normal and osteoporotic bone models.²¹^,²²

Habet et al. compared bicortical locking and non-locking screws, far cortical locking (FCL), and near cortical unicortical locking screws across various bridging lengths. While no significant difference in axial displacement was observed, the study did identify a notable increase in shear displacement in the FCL group.²⁶ Despite its relevance, their study was excluded from our review due to the absence of reported standard deviations required for meta-analysis. Nevertheless, it raises questions about the shear forces associated with the FCL technique, which may warrant further investigation.

Methods similar to FCL are currently under animal and biomechanical examination. One such method involves the use of silicone sleeves surrounding the plate-screw locking mechanism. This construct, known as "active plating," allows for micromotion that translates directly to the fracture site.^16–19 Preliminary research has shown that this technique can reduce construct stiffness and produce symmetric callus formation when compared with standard locked (SL) plating.

In theory, FCL plating should increase axial motion, contributing to greater symmetry in callus formation compared to SL plating. Previous animal studies have demonstrated this increased symmetry and callus volume, suggesting FCL as a viable alternative to SL plating.²⁷ While concerns about decreased stiffness leading to early failure have been raised, our study found no statistically significant difference between FCL and SL constructs.

Recently, a prospective cohort study looked at 20 patients with distal femur fractures, who received lateral plates with all diaphyseal near cortices over-drilled. No incidents of non-union, loss of reduction, or hardware failure were reported.²⁸ While our study provides good evidence for the utility of FCL technique, future prospective clinical data will help to either validate FCL technique or identify any previously unreported limitations.

4.1

4.1 Limitations

There are several limitations to this meta-analysis. The number of included biomechanical studies is only four, with a total of 54 femora put through biomechanical testing. Though statistical significance was found, a greater sample size could result in additional findings. Three out of four included papers utilized composite femora, with one article using cadaveric specimens, therefore the application of this testing may not resemble en vivo biomechanical properties. Finally, the variation between diaphyseal and metaphyseal simulated femoral fractures also contributes to the heterogeneity of the included biomechanical studies. These biomechanical studies also only give information at time zero. No conclusions about healing, biomechanical changes due to callous formation, or fatigue failure can be made.

5 Conclusions

Our review of the current data indicates that far cortical locking (FCL) effectively reduces construct stiffness and promotes more symmetric axial interfragmentary motion, all while maintaining construct strength. Importantly, no significant differences were observed in load-to-failure tests in biomechanical simulations of femoral fractures. These findings align with the biomechanical objectives of FCL and should motivate further research into its impact on clinical and radiographic outcomes.

Funding

This study and its authors did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Funding statement

The authors do not report any external funding received for the completion of this study.

Ethical statement

This study was performed ethically, with IRB approval via the San Joaquin General Hospital IRB. The IRB approval number is #20–317.

Consent statement

No patient/guardian consent was necessary for this study as it was a systematic review and meta-analysis of studies that did not include protected patient information.

Author statement

Listed below are the primary contributions provided by each author involved in this meta-analysis and manuscript., Robert S Bullock, DO, MBA, Project conceptualization, data curation, formal analysis, investigation, methodology, project, administration, resources, supervision, validation, visualization, writing original draft of manuscript, John G Coury, DO, Data curation, formal analysis, investigation, methodology, validation, visualization, review and, editing of manuscript, Brendan J Liakos, DO, Writing-review & editing, Validation, Eric G Huish, DO, Data curation, formal analysis, investigation, methodology, project administration, resources, software, supervision, validation, visualization, review and editing of manuscript.

Declaration of competing interest

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

References

Koso R., Terhoeve C., Steen R.G., et al . Healing, nonunion, and re-operation after internal fixation of diaphyseal and distal femoral fractures: a systematic review and meta-analysis. Int Orthop. 2018;42(11):2675-2683.
[Google Scholar]
Ehlinger M., Ducrot G., Adam P., et al . Distal femur fractures. Surgical techniques and a review of the literature. Orthopaed Traumatol Surg Res. 2013;99(3):353-360.
[Google Scholar]
Anakwe R.E., Aitken S.A., Khan L.A., . Osteoporotic periprosthetic fractures of the femur in elderly patients: outcome 2682 International Orthopaedics (SICOT) (2018) 42:2675–2683 after fixation with the LISS plate. Injury. 2008;39(10):1191-1197.
[Google Scholar]
Are locking constructs in distal femoral fractures always best? A prospective multicenter randomized controlled trial comparing the less invasive stabilization system with the minimally invasive dynamic Condylar screw system. J Orthop Trauma. 2016;30(1):e1-e6.
[Google Scholar]
Kayali C., Agus H., Turgut A., . Successful results of minimally invasive surgery for comminuted supracondylar femoral fractures with LISS: comparative study of multiply injured and isolated femoral fractures. J Orthop Sci. 2007;12(5):458-465.
[Google Scholar]
Markmiller M., Konrad G., Sudkamp N., . Femur-LISS and distal femoral nail for fixation of distal femoral fractures: are there differences in outcome and complications? Clin Orthop Relat Res. 2004;426:252-257.
[Google Scholar]
LCP versus LISS in the treatment of open and closed distal femur fractures: does it make a difference? J Orthop Trauma. 2016;30(6):e212-e216.
[Google Scholar]
Smith T.O., Hedges C., MacNair R., et al . The clinical and radiological outcomes of the LISS plate for distal femoral fractures: a systematic review. Injury. 2009;40(10):1049-1063.
[Google Scholar]
Kao F.C., Tu Y.K., Su J.Y., et al . Treatment of distal femoral fracture by minimally invasive percutaneous plate osteosynthesis: comparison between the dynamic condylar screw and the less invasive stabilization system. J Trauma. 2009;67(4):719-726.
[Google Scholar]
Hanschen M., Aschenbrenner I.M., Fehske K., et al . Mono-versus polyaxial locking plates in distal femur fractures: a prospective randomized multicentre clinical trial. Int Orthop. 2014;38(4):857-863.
[Google Scholar]
Wang M.T., An V.V.G., Sivakumar B.S., . Non-union in lateral locked plating for distal femoral fractures: a systematic review. Injury. 2019;50(11):1790-1794.
[Google Scholar]
Rodriguez E.K., Zurakowski D., Herder L., et al . Mechanical construct characteristics predisposing to non-union after locked lateral plating of distal femur fractures. J Orthop Trauma. 2016;30(8):403-408.
[Google Scholar]
Uhthoff Hans K., Poitras Philippe, et al . Internal plate fixation of fractures: short history and recent developments. J Orthop Sci. 2006;11:118-126.
[Google Scholar]
Lujan T.J., Henderson C.E., Madey S.M., et al . Locked plating of distal femur fractures leads to inconsistent and asymmetric callus formation. J Orthop Trauma. 2010;24(3):156-162.
[Google Scholar]
Tsai S., Fitzpatrick D.C., Madey S.M., et al . Dynamic locking plates provide symmetric axial dynamization to stimulate fracture healing. J Orthop Res. 2015;33(8):1218-1225.
[Google Scholar]
Capanni F., Hansen K., Fitzpatrick D.C., Madey S.M., Bottlang M., . Elastically suspending the screw holes of a locked osteosynthesis plate can dampen impact loads. J Appl Biomech. 2015;31(3):164-169.
[Google Scholar]
Bottlang M., Tsai S., Bliven E.K., et al . Dynamic stabilization of simple fractures with active plates delivers stronger healing than conventional compression plating. J Orthop Trauma. 2017;31(2):71-77.
[Google Scholar]
Bottlang M., Tsai S., Bliven E.K., et al . Dynamic stabilization with active locking plates delivers faster, stronger, and more symmetric fracture-healing. J Bone Joint Surg Am. 2016;98(6):466-474.
[Google Scholar]
Bottlang M., Doornink J., Fitzpatrick D.C., et al . Far cortical locking can reduce stiffness of locked plating constructs while retaining construct strength. J Bone Joint Surg Am.. 2009;91(8):1985-1994.
[Google Scholar]
Gardner M.J., Nork S.E., Huber P., et al . Stiffness modulation of locking plate constructs using near cortical slotted holes: a preliminary study. J Orthop Trauma. 2009;23(4):281-287.
[Google Scholar]
Gardner M.J., Nork S.E., Huber P., et al . Less rigid stable fracture fixation in osteoporotic bone using locked plates with near cortical slots. Injury. 2010;41(6):652-656.
[Google Scholar]
Doornink J., Fitzpatrick D.C., Madey S.M., et al . Far cortical locking enables flexible fixation with periarticular locking plates. J Orthop Trauma. 2011;25(Suppl 1):S29-S34.
[Google Scholar]
Henschel J., Tsai S., Fitzpatrick D.C., et al . Comparison of 4 methods for dynamization of locking plates: differences in the amount and type of fracture motion. J Orthop Trauma. 2017;31(10):531-537.
[Google Scholar]
Moazen M., Mak J.H., Jones A.C., et al . Evaluation of a new approach for modelling the screw-bone interface in a locking plate fixation: a corroboration study. Proc Inst Mech Eng H. 2013;227(7):746-756.
[Google Scholar]
Habet N., Elkins J., Peindl R., et al . Far cortical locking fixation of distal femur fractures is dominated by shear at clinically relevant bridge spans. J Orthop Trauma. 2019;33(2):92-96.
[Google Scholar]
Bottlang M., Lesser M., Koerber J., et al . Far cortical locking can improve healing of fractures stabilized with locking plates. J Bone Joint Surg Am. 2010;92(7):1652-1660.
[Google Scholar]
Galal S., . Dynamic locked plating for fixation of distal femur fractures using near- cortical over-drilling: preliminary results of a prospective observational study. J Clin Orthop Trauma. 2017;8(3):215-219.
[Google Scholar]