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Abstract

Introduction

Femoral neck fractures (FNF) represent a significant challenge in orthopedic practice, demanding prompt intervention to restore function and mobility in affected individuals. Numerous surgical interventions have been developed to address these fractures, including internal fixation with devices such as the Femoral Neck System (FNS, DePuy Synthes, Inc., West Chester, PA, USA). However, the optimal fixation system remains unclear. Understanding the postoperative outcomes associated with these interventions is crucial for optimizing patient care and informing treatment decisions.

Significance

This PRISMA-compliant systematic literature review evaluates the efficacy and safety of the Femoral Neck System relative to other operative treatment options. Clinical and safety outcomes included mortality, perioperative complications, postoperative complications at 1 year, and reoperation.

Results

A total of 117 studies with 68,567 patients with FNF treated with internal fixation were identified. Of these, thirteen included FNS as a treatment arm (1078 patients). Due to heterogeneity in study designs and populations, only the eleven studies that directly compared FNS to other operative treatments, and 2 non-comparative studies that treated with FNS were included in the systematic review. Seven of the eleven included studies had high risk of bias, 2 had moderate risk of bias, and 2 had low risk of bias. FNS groups had similar or significantly lower incidences of postoperative complications, reoperations, and mortality compared to cannulated screw, cancellous screw, or dynamic or sliding hip screw groups in all studies.

Conclusion

FNS can be a safe and effective operative treatment option for FNF. Safety outcomes and reoperation rates are comparable between patients treated with FNS and patients treated with cannulated screws, cancellous screws, and dynamic or sliding hips screws. Future prospective, controlled studies are needed to confirm the safety and efficacy of FNS relative to other operative treatment options.

Keywords

femoral neck fracture femoral neck system hip fracture dynamic screws

Introduction

Femoral neck fractures (FNF), the most common hip fracture,¹ are frequently treated with internal fixation, but complications frequently arise, which may require reoperation.² Recently, a new fixation device, Femoral Neck System (FNS, DePuy Synthes, Inc., West Chester, PA, USA) was launched for treatment of femoral neck fractures, including basilar, transcervical, and subcapital fractures, in adults and adolescents (age 12-21 years) in which the growth plates have fused or will not be crossed (Figure 1). FNS was developed to reduce complications and reoperations by increasing construct stability, reducing surgical invasiveness, and reducing the risk of lateral implant protrusion.³ The FNS design compensated for 15 mm of femoral neck shortening without lateral protrusion by a telescoping mechanism.³ Moreover, a single insertion handle allows for placement of the central bolt as well as the antirotation screw to reduce procedural complexity and enhance operational efficiency.³ The bolt is currently available in units of 5 mm and a technical note has reported a modified technique for improved control of the depth of the bolt.⁴

Figure 1.

Three dimensional models of the FNS device. Used with permission.

Mechanical testing of FNS with standardized foam models has indicated up to 40% increased rotational stability compared to a sliding hip screw (SHS), and a minimum of 150% more rotational stability compared to a 3 cannulated screw.^5,6 A biomechanical study in a cadaveric model found that FNS had comparable stability to dynamic hip screws paired with antirotation screws or blades and superior stability compared to 3 cannulated screws for treating femoral neck fractures.⁷ However, the relative safety and efficacy of FNS compared to other treatment options remain undetermined. Here, we report the results of a systematic literature review to evaluate safety and efficacy outcomes associated with FNS relative to traditional operative treatment options in femoral neck fractures resulting from any mechanism of injury.

Methods

Literature Search and Study Selection

This study adheres to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.⁸ The PRISMA checklist associated with this systematic review can be found in Supplemental Files 1 and 2. A protocol was prepared based on the PROSPERO protocol guidelines. The review was not registered. Searches of PubMed were completed using the Application Program Interface (API) in the AutoLit platform (Nested Knowledge, nested-knowledge.com). All study metadata and abstracts from the search results were also obtained via API. Searches of Cochrane Library and Embase databases were completed through their respective web interfaces and the results were uploaded to the AutoLit platform. Searches were restricted to studies published after January 1, 2012 to capture the previous decade of comparative treatments and cover the date that FNS came on the market in 2017. Search terms included the phrases “femoral neck fracture”, “femoral neck system”, “sliding hip screw”, “cannulated screw”, and “internal fixation”. The full search strings are available in Supplemental Table 1.

Identified studies were evaluated for inclusion in the systematic review. Study inclusion criteria included those reporting adult patients with femoral neck fracture treated with FNS. All mechanisms of injury were included. Exclusion criteria were studies that did not report patients treated with FNS, studies that did not report the outcomes of interest, studies that did not separate patient outcomes by intervention, studies with less than 5 patients, studies that did not relate to femoral neck fracture, studies not reporting interventions or outcomes of interest, and studies reporting on a subpopulation that could introduce bias, including studies that focused on patients with cancer, HIV, or Parkinson’s disease. In vivo/in vitro studies, symposium/conferences, qualitative review articles, letters of correspondence, in silico study/mathematical models, guideline articles, technical notes, editorial/opinion articles, meta-analyses or systematic reviews, secondary analyses, protocols, studies not written in English, or interim analyses were also excluded. The reference lists of identified articles were also screened for potentially relevant papers. Each study was screened by a single investigator.

Data Extraction

Data was extracted by a single investigator for each study and reviewed by 2 independent investigators. Patient characteristics included age and fracture stability (Garden classification). Procedure characteristics included length of operation, intraoperative blood loss, and length of hospital stay. Methods for measuring blood loss vary widely, potentially introducing heterogeneity into the data. Intraoperative blood loss was extracted as reported in the study. Clinical and safety outcomes included mortality, perioperative complications (deep vein thrombosis [DVT] and perioperative surgical site infection), postoperative complications at 1 year (avascular necrosis [AVN] of the femoral head, non-union, internal fixture loosening, postoperative surgical site infection, hematoma, iatrogenic fracture, and femoral neck shortening), and reoperation (unspecified, implant removal, or conversion to another treatment).

Risk of Bias

Risk of bias (RoB) was assessed for comparative studies using the Newcastle-Ottawa Scale.⁹ Criteria for rating a study as low, moderate, or high risk of bias were made based on the decision rules described by Sharmin et al,¹⁰ outlined in Supplemental Table 2. The RoB was completed independently by 2 reviewers with any disagreements adjudicated by a third reviewer.

Statistical Analysis

Due to heterogeneity in data and the limited number of multi-armed studies available that distinguished between patients with acute and delayed instrumentation, inferential statistics were not performed, and data are expressed as descriptive statistics only. Statistics are reported as counts and percentages, median (interquartile range (IQR)), or mean ± standard deviation (SD).

Results

Literature Search Results

Our searches identified 1674 individual studies. Of the identified studies, 1394 were excluded based on title and abstract review (see PRISMA flowchart in Figure 2). The remaining 271 articles underwent full-text review. Four articles were identified through expert recommendation, which also underwent full-text review. Nine articles did not have full texts available, and 259 articles were excluded for other reasons, while 108 studies reported a comparable intervention but did not report patients treated with FNS (see PRISMA flowchart in Figure 2). Due to heterogeneity in study designs and populations, only the 13 studies that included patients treated with FNS were included in the systematic review.^11-23 Results from all 117 studies reporting either FNS or a comparable intervention are summarized in Supplemental Tables 3-6. Of the 13 studies reporting FNS, all were retrospective cohort studies.^11-23 Three studies compared dynamic or sliding hip screws or cannulated screws to FNS,^16,17,20 2 studies had a single intervention of FNS with no comparator,^12,18 1 study compared dynamic or sliding hip screws or cancellous screws to FNS,²¹ 1 study compared dynamic or sliding hip screws to FNS,¹⁶ and 6 studies compared cannulated screws to FNS.^{13-15,19,22,23} Two studies were found to have low risk of bias,^19,23 2 had moderate risk of bias,^13,16 and 7 had high risk of bias.^{11,14,15,17,20-22} The 2 non-comparative studies were not included in the risk of bias (Supplemental Table 7)

Figure 2.

PRISMA study selection flowchart.

FNS vs Cannulated Screws

Study Characteristics

Seven studies compared FNS against cannulated screws.^{13-15,19,20,22,23} Of these, Vazquez et al²⁰ compared a third treatment such that head-to-head comparisons between FNS and cannulated screws were not made. Nibe et al¹⁵ and Zhang et al²² restricted study patients to ≥65 years old and Vazquez et al²⁰ reported outcomes in patients ≥75 years old. Hu et al restricted to patients under 60 years old.¹⁴ Zhang et al²² restricted their study to patients with AO31-B type fractures, which include Garden Type II, III, and IV, Zhou et al²³ reported only patients with Pauwels Type III fractures, and Vazquez et al²⁰ restricted their study to patients with Garden Type I and II fractures. Two studies did not apply fracture type or age-based selection criteria, but excluded pathological fractures.^13,19

Three studies did not specify mechanism of injury.^14,19,20 In He et al, the majority of fractures were caused by falls in both groups (63.6% [21/33] in patients treated with FNS and 69.4% [25/36] in patients treated with cannulated screws).¹³ In Nibe et al, the majority of fractures were caused by low-energy falls in both groups (88.0% [22/25] in patients treated with FNS and 81.5% [22/27] in patients treated with cannulated screws). The remaining fractures were caused by traffic accidents (8.0% [2/25] in patients treated with FNS only), other high-energy injuries (3.7% [1/27] in patients treated with cannulated screws only) or unknown causes (4.0% [1/25] in patients treated with FNS and 14.8% [4/27] in patients treated with cannulated screws).¹⁵ In Zhou et al, fractures were caused by traffic accidents or falls and pathological fractures were excluded.²³

Two studies had low risk of bias,^19,23 1 had moderate risk of bias,¹³ and 4 had high risk of bias.^14,15,20,22 Common sources of risk of bias were selection bias, lack of comparability between groups, and short follow-up. A summary of risk of bias assessments can be found in Supplemental Table 7.

Patient Baseline Characteristics

Patient baseline characteristics are presented in Supplemental Table 3. Across studies, the average age ranged from 47.6 ± 10.3¹³ to 85.0 ± 6.6²⁰ for patients with cannulated screws, and from 50.5 ± 8.5¹⁴ to 86.1 ± 4.6²⁰ for patients with FNS. No studies reported statistically significant differences in age between groups. Only Nibe et al¹⁵ and Zhou et al²³ did not present Garden classification. Except for Vazquez et al,²⁰ in which most injuries were Type I, most injuries were Type II or above. No study reported significant differences for Garden classification between groups. Most studies had follow-up periods >12 months, but Vazquez et al²⁰ had follow-ups from 1-6 months and Zhou et al²³ had follow-ups from 10-22 months. The longest follow-up period was a range of 14-24 months.¹⁹

Procedure Characteristics

Procedure characteristics are presented in Table 1. The average length of operation ranged from 40.9 ± 5.2²³ to 76.8 ± 13.1²² minutes for cannulated screws, and from 42.0 ± 13.0¹⁵ to 79.8 ± 26.4¹⁴ for FNS. Compared to cannulated screws, 2 studies reported lower mean operation time in patients treated with FNS,^15,22 but 1 study reported significantly higher mean operation time (Table 1).¹⁴ Four studies reported intraoperative blood loss, ranging from 23.7 ± 28.1¹⁴ to 47.3 ± 9.3 mL¹⁹ for cannulated screws and from 36.0 ± 25.0¹⁵ to 99.7 ± 52.7 mL²³ for FNS. Two studies reported significantly higher intraoperative blood loss in patients treated with FNS compared to cannulated screws, but both studies also reported that patients treated with FNS had lower incidence of complications, indicating that the difference in blood loss may not be clinically significant.^14,23 All but Hu et al¹⁴ and Nibe et al¹⁵ reported length of hospital stay. No studies reported significant differences in length of hospital stay between patients treated with FNS and cannulated screws. Studies that restricted study patients to ≥65 years old found that FNS had significantly lower operation time and no significant differences in intraoperative blood loss or hospital stay compared to cannulated screws.^15,20,22

Table 1.

Procedure Characteristics.

Study	Intervention	N	Length of Operation (minutes)	P value	Intraoperative Blood Loss (mL)	P value	Length of Hospital Stay (days)	P value	Reported Conclusions
He, 2021¹³	Cannulated screw	36	56.1 ± 12.5	0.062^a	--	--	4.8 ± 1.6	0.410^a	The interventions had no significant differences in procedural characteristics
He, 2021¹³	FNS (DePuy synthes)	33	49.9 ± 14.5	0.062^a	--	--	5.1 ± 1.9	0.410^a
Hu, 2021¹⁴	Cannulated screw	24	64.6 ± 18.6	0.031^a	23.7±28.1	<0.001^a	--	--	FNS had a higher length of operation and intraoperative blood loss
Hu, 2021¹⁴	FNS (DePuy synthes)	20	79.8 ± 26.4	0.031^a	69.5±50.5	<0.001^a	--	--
Nibe, 2021¹⁵	Cannulated screw	27	53 ± 21	0.032^a	41±40	0.58^a	--	--	FNS had a lower length of operation and intraoperative blood loss
Nibe, 2021¹⁵	FNS (DePuy synthes)	25	42 ± 13	0.032^a	36±25	0.58^a	--	--
Tang, 2021¹⁹	Cannulated screw	45	42 ± 11.9	0.590^b	47.3±9.3	0.284^b	4.8 ± 1.4	0.113^b	The interventions had no significant differences in procedural characteristics
Tang, 2021¹⁹	FNS (DePuy synthes)	47	52.4 ± 11.0	0.590^b	50.6 ± 10.6	0.284^b	5.5 ± 1.3	0.113^b
Vazquez, 2021²⁰	Cannulated screw	32	66.9 ± 25.4	<0.001^c	--	--	12.2 ± 6.2	0.131^d	FNS had a lower length of operation
	Dynamic or sliding hip screw	16	70.7 ± 20.0		--		12.4 ± 5.3
	FNS (DePuy synthes)	15	43.3 ± 10.1		--		10.3 ± 6.0
Zhang, 2022²²	Cannulated screw	36	76.81 ± 13.10	0.000^a	--	--	8.5 ± 1.95	0.082^a	FNS had a lower length of operation
Zhang, 2022²²	FNS (DePuy synthes)	33	60.00 ± 12.44	0.000^a	--	--	7.57 ± 2.39	0.082^a	FNS had a lower length of operation
Zhou, 2021²³	Cannulated screw	51	40.9 ± 5.2	0.122^a	30.27 ± 9.04	<0.001^a	5.3 ± 1.5	0.133^a	FNS had a higher intraoperative blood loss
Zhou, 2021²³	FNS (DePuy synthes)	30	42.8 ± 4.7	0.122^a	99.73 ± 52.73	<0.001^a	5.1 ± 1.3	0.133^a	FNS had a higher intraoperative blood loss
Niemann, 2022¹⁶	Dynamic or sliding hip screw	19	91.68 ± 23.96	<0.01^e	--	--	7.35 ± 3.43	0.94^e	FNS had a lower length of operation
Niemann, 2022¹⁶	FNS (DePuy synthes)	12	54 ± 26.1	<0.01^e	--	--	8 ± 5.27	0.94^e	FNS had a lower length of operation
Schuetze, 2022¹⁷	Dynamic or sliding hip screw	108	54.7 ± 17.4	<0.05^f	--	--	11.3 ± 6.8	<0.05^f	FNS had a lower length of operation and length of hospital stay
Schuetze, 2022¹⁷	FNS (DePuy synthes)	113	36.3 ± 11.6	<0.05^f	--	--	8.9 ± 4.3	<0.05^f
Xu, 2022²¹	Cancellous screw	51	49 (38-61)	<0.001^d	30 (20-45)	<0.001^d	3 (2-4)	<0.001^d	FNS had a lower length of operation, intraoperative blood loss, and length of hospital stay
	Dynamic or sliding hip screw	52	72 (55-88.75)		50 (30-50)		3.5 (3-6)
	FNS (DePuy synthes)	54	45 (40-59)		30 (20-50)		2 (2-4)
Cintean, 2021¹¹	FNS (DePuy synthes)	29	--	--	--	--	9.8 ± 3.8	<0.001^e	FNS had a lower length of hospital stay
Cintean, 2021¹¹	Hemiarthroplasty	34	--		--		15.1 ± 5.1
Non-comparative studies
Davidson, 2022¹²	FNS (DePuy synthes)	102	44 ± 14	--	51 ± 47	--	5.7 ± 3.9	--	No comparison between interventions
Stassen, 2021¹⁸	FNS (DePuy synthes)	34	Mean: 33 (95% CI: 29.3-36.9)	--	Mean: 34 (95% CI: 24.7-44.6)	--	4 ± 2.8	--	No comparison between interventions

Data are expressed as mean ± SD or median (IQR). “--” indicates no data reported.

^aIndependent-samples t test.

^bAnalysis unclear (either Mann-Whitney U test or independent-samples t test).

^cLinear regression.

^dKruskal-Wallis test.

^eMann-Whitney U test.

^fStatistical methods not clearly reported.

Patient Outcomes

Patient outcomes are presented in Table 2. No significant differences between FNS and cannulated screws were reported for non-union events,^13-15,19 loosening or failure of the internal fixture,^13,15,19 avascular necrosis,^14,19,23 deep vein thrombosis,^19,23 or mortality.^20,22 Hu et al¹⁴ found that significantly more cannulated screw patients experienced femoral neck shortening than FNS patients (9/24 vs 2/20, P = 0.04), but Zhang et al²² found no significant difference between groups (5/36 vs 2/33, P = 0.28). He et al¹³ found that 8.3% (3/36) of cannulated screw patients and 3.0% (1/33) of FNS patients experienced femoral neck shortening, but did not report a statistical analysis. Nibe et al¹⁵ found significantly more reoperations for cannulated screw patients than FNS patients (6/21 vs 0/25, P = 0.23). Three other studies reported incidence of reoperation,^20,22,23 but no other study reported a statistical analysis. Studies that restricted study patients to ≥65 years old found that FNS had significantly lower incidence of reoperation compared to cannulated screws, with no other significant differences.^15,20,22

Table 2.

Patient Outcomes.

Study	Intervention	N	Non-union	Internal Fixture Loosening/Failure	Other Postoperative Complications	Reoperation	Mortality	P values	Reported Conclusions
He, 2021¹³	Cannulated screw	36	5.6% (2/36)	8.3% (3/36)	Femoral neck shortening: 8.3% (3/36)	--	--	--	FNS had a lower incidence of overall complications (combining non-union, nail retreat, femoral neck shortening, and internal fixation cutout)
He, 2021¹³	FNS (DePuy synthes)	33	0.0% (0/33)	3.0% (1/33)	Femoral neck shortening: 3.0% (1/33)	--	--	--
Hu, 2021¹⁴	Cannulated screw	24	12.5% (3/24), P = 0.795	--	AVN: 12.5% (3/24), Femoral neck shortening: 4.54±2.75 mm37.5% (9/24)	--	--	AVN: P = 0.389^aFemoral neck shortening length: P = 0.005^bFemoral neck shortening incidence: P = 0.036^a	FNS had a lower degree of femoral neck shortening and a lower incidence femoral neck shortening, but no difference in incidence of non-union or AVN.
Hu, 2021¹⁴	FNS (DePuy synthes)	20	10.0% (2/20)	--	AVN: 5.0% (1/20)Femoral neck shortening: 2.40±1.81 mm10.0% (2/20)	--	--
Nibe, 2021¹⁵	Cannulated screw	27	18.5% (5/27)	7.4% (2/27)	--	Overall: 28.6% (6/21)Conversion to HA: 11.1% (3/27)Implant removal: 11.1% (3/27)	--	Non-union: P = 0.052^cOverall reoperation: P = 0.023^c	FNS had a significantly lower incidence of reoperation
Nibe, 2021¹⁵	FNS (DePuy synthes)	25	0.0% (0/25)	--	--	0.0% (0/25)	--	Non-union: P = 0.052^cOverall reoperation: P = 0.023^c	FNS had a significantly lower incidence of reoperation
Tang, 2021¹⁹	Cannulated screw	45	8.9% (4/45)	11.1% (5/45)	AVN: 6.7% (3/45)DVT: 0.0% (0/45)	--	--	Non-union: P = 0.430^aInternal fixture loosening/failure: P = 0.481^aAVN: P = 0.356^a	The interventions had no significant differences in patient outcomes
Tang, 2021¹⁹	FNS (DePuy synthes)	47	4.3% (2/47)	6.4% (3/47)	AVN: 2.1% (1/47)DVT: 0.0% (0/47)	--	--
Vazquez, 2021²⁰	Cannulated screw	32	--	--		3.1% (1/32)	9.4% (3/32)	Mortality: P = 0.585^c	The interventions had no significant differences in patient outcomes
	Dynamic or sliding hip screw	16	--	--	--	0.0% (0/16)	12.5% (2/16)
	FNS (DePuy synthes)	15	--	--	--	0.0% (0/15)	0.0% (0/15)
Zhang, 2022²²	Cannulated screw	36	--	--	Femoral neck shortening: 13.89% (5/36)	Implant removal: 13.89% (5/36)	0.0% (0/36)	Femoral neck shortening: P = 0.282^aImplant removal: P = 0.026^a	FNS had a lower incidence of implant removal
Zhang, 2022²²	FNS (DePuy synthes)	33	--	--	Femoral neck shortening: 6.06% (2/33)	Implant removal: 0.0% (0/33)	0.0% (0/33)		FNS had a lower incidence of implant removal
Zhou, 2021²³	Cannulated screw	51	--	--	AVN: 0.0% (1/51)DVT: 0.0% (0/51)	Conversion to HA: 3.9% (2/51)	--	--	FNS had a lower incidence of overall complications
Zhou, 2021²³	FNS (DePuy synthes)	30	--	--	AVN: 0.0% (0/30)DVT: 0.0% (0/30)	Conversion to HA: 3.3% (1/30)	--	--	FNS had a lower incidence of overall complications
Niemann, 2022¹⁶	Dynamic or sliding hip screw	19	--	--	AVN: 0.0% (0/19)Femoral neck shortening: 0.0% (0/19)Femoral neck shortening: 0.0% (0/12)	--	--	--	The interventions had no significant differences in patient outcomes
Niemann, 2022¹⁶	FNS (DePuy synthes)	12	--	--	AVN: 0.0% (0/12)	--	--	--
Schuetze, 2022¹⁷	Dynamic or sliding hip screw	108	--	10.2% (11/108)	Femoral neck shortening: 4.8±2.1 mm27.7% (30/108)Hematoma: 5.6% (6/108)Surgical site infection: 2.8% (3/108)	Conversion to THA: 8.3% (9/108)Implant removal: 1.9% (2/108)	0.9% (1/108)	Failure, hematoma, or infection: P = 0.479^dFemoral neck shortening: 0.455^dMortality: >0.05^d	The interventions had no significant differences in patient outcomes
Schuetze, 2022¹⁷	FNS (DePuy synthes)	113	--	12.4% (14/113)	Femoral neck shortening: 5.3±1.9 mm27.4% (31/113)Hematoma: 0.9% (1/113)Surgical site infection: 0.0% (0/113)	Conversion to THA: 11.5% (13/113)Implant removal: 0.9% (1/113)	3.5% (4/113)
Xu, 2022²¹	Cancellous screw	51	--	3.9% (2/51)	AVN: 0.0% (0/51)DVT: 0.0% (0/51)Femoral neck shortening: 1.9 mm (0.2-3.5)	--	--	Internal fixture loosening/failure: P = 1.000^cFemoral neck shortening: P = 0.452^e	The interventions had no significant differences in patient outcomes
	Dynamic or sliding hip screw	52	--	3.8% (2/52)	AVN: 0.0% (0/52)DVT: 0.0% (0/52)Femoral neck shortening: 2.0 mm (0.2-4.8)	--	--
	FNS (DePuy synthes)	54	--	5.6% (3/54)	AVN: 0.0% (0/54)DVT: 0.0% (0/54)Femoral neck shortening: 2.2 mm (0.4-4.1)	--	--
Cintean, 2021¹¹	FNS (DePuy synthes)	29	--	--	AVN: 0.0% (0/21)Femoral neck shortening: 3.3±4.5 mm, 100.0% (21/21)	Overall: 13.8% (4/29)Conversion to hemiarthroplasty: 10.3% (3/29)Removal of implant: 3.4% (1/29)	6.9% (2/29)	Mortality: P = 0.663^c	The interventions had no significant difference in patient outcomes
Cintean, 2021¹¹	Hemiarthroplasty	34	--	--	--	Overall: 8.8% (3/34)Conversion to HA: 2.9% (1/34)	8.8% (3/34)
Non-comparative studies
Davidson, 2022¹²	FNS (DePuy synthes)	102	1.0% (1/102)	1.0% (1/102)	AVN: 2.9% (3/102)	Conversion to THA: 8.8% (9/102)	0.0% (0/102)	--	No comparison between interventions
Stassen, 2021¹⁸	FNS (DePuy synthes)	34	--	5.9% (2/34)	AVN: 11.8% (4/34)	Conversion to THA: 17.6% (6/34)Implant removal: 5.9% (2/34)	0.0% (0/34)	--	No comparison between interventions

Data are expressed as mean ± SD, median (IQR), or % (n) unless otherwise indicated. “--“ indicates no data reported.

AVN = avascular necrosis; DVT = deep vein thrombosis; FNS = Femoral Neck System; HA = hip arthroplasty; THA = total hip arthroplasty.

^aChi-squared test of independence.

^bIndependent-samples t-test.

^cFisher's exact test.

^dStatistical methods not clearly reported.

^eKruskal-Wallis test.

FNS vs Dynamic or Sliding Hip Screw

Study Characteristics

Four studies compared FNS with dynamic or sliding hip screws.^16,17,20,21 Of these, Vazquez et al²⁰ and Xu et al²¹ compared a third treatment such that head-to-head comparisons between FNS and cannulated screws were not made. Three studies applied age-related inclusion criteria: Vazquez et al²⁰ (≥75 years old), Schuetze et al¹⁷ (≥50 years old) and Xu et al²¹ (<65 years old). Vazquez et al²⁰ and Xu et al²¹ restricted their studies to patients with Garden Type I and II fractures. Niemann et al¹⁶ and Schuetze et al¹⁷ excluded pathological fractures. No studies specified mechanism of injury. One study had moderate risk of bias¹⁶ and 3 studies had high risk of bias.^17,20,21 Common sources of risk of bias included selection bias, failure to account for imbalances in important patient characteristics between cohorts, short follow-up, and failure to properly adjust analyses for imbalances in follow-up periods between cohorts. A summary of risk of bias assessments can be found in Supplemental Table 7.

Patient Baseline Characteristics

Across studies, the average age ranged from 60.5 ± 17¹⁶ to 83.4 ± 7.3 years²⁰ for patients with dynamic or sliding hip screw, and from 60.7 ± 15.2²¹ to 86.1 ± 4.6 years²¹ for FNS patients. No study found significant differences in age between groups. Likewise, no study reported significant differences in Garden classification between groups. Follow-up periods ranged from 7.4 ± 3.4 days¹⁶ to 12-16 months.²¹ No study reported significant differences for follow-up periods between groups (Supplemental Table 3).

Procedure Characteristics

The average duration of operation ranged from 54.7 ± 17.4¹⁷ to 91.7 ± 24.0 minutes¹⁶ for dynamic or sliding hip screw patients, and from 36.3 ± 11.6¹⁷ to 54.0 ± 26.1 minutes¹⁶ for FNS patients. In each study, FNS had significantly shorter operation time than dynamic or sliding hip screws.^16,17,20,21 Only Xu et al²¹ reported on intraoperative blood loss; dynamic or sliding hip screws operations had significantly more blood loss than FNS (median, range: 50, 30-50 vs median, range: 30, 20-50; P < 0.01). Length of hospital stay ranged from 3-6²¹ to 12.4 ± 5.3 days²⁰ for dynamic or sliding hip screws and from 2-4²¹ to 10.3 ± 6.0 days²⁰ for FNS. Only Schuetze et al¹⁷ and Xu et al²¹ found significant differences for length of hospital stay between groups; in both cases, FNS patient stays were significantly shorter than dynamic or sliding hip screw patient stays (Table 1).

Patient Outcomes

No study reported incidence of non-union. No significant differences between FNS and dynamic or sliding hip screws were reported for loosening or failure of the internal fixure,^17,21 avascular necrosis,^17,21 deep vein thrombosis,²¹ femoral neck shortening,^16,17,21 hematoma or surgical site infection,¹⁷ reoperation,^17,20 or mortality^17,20 (Table 2).

FNS vs Other Comparators

Xu et al²¹ compared FNS with cancellous screws. The study excluded patients >65 years old who had Garden Type III or IV fractures or pathological fractures and did not specify mechanisms of injury. The study had a high risk of bias, primarily due to selection bias, failure to account for imbalances in important patient characteristics between cohorts, short follow-up, and failure to properly adjust analyses for imbalances in follow-up periods between cohorts. Xu et al²¹ used linear regression that included a third procedure such that head-to-head comparisons were not made, median operation time, blood loss, and length of hospital stay were lower for FNS than cancellous screws (Table 1). No differences in patient outcomes were reported between the FNS and cancellous screws (Table 2).

Cintean et al¹¹ compared FNS with hemiarthroplasty. The study did not apply age-based selection criteria and did not specify mechanisms of injury. The study had high risk of bias due to lack of comparability between the groups, short follow-up, and loss of patients to follow-up. There were no significant differences between groups for age, Garden classification, or follow-up period (Supplemental Table 3). Cintean et al¹¹ found that length of hospital stay was significantly shorter for FNS than hemiarthroplasty (Table 1), but did not find any differences in patient outcomes (Table 2).

Non-Comparative Studies

There were 2 non-comparative studies of FNS.^12,18 Davidson et al¹² excluded cases with pathological fractures and Stassen et al¹⁸ excluded patients with polytrauma. Neither study applied age-related selection criteria or specified mechanism of injury. The average age in both studies was 63 years. In both studies, more than half of the fractures were at or below Garden Type II. The mean follow-up periods were 7¹² and 6 months¹⁸ (Supplemental Table 3). Mean length of operations were 44¹² and 33 minutes.¹⁸ Mean intraoperative blood-loss was 51¹² and 34 mL.¹⁸ Average length of hospital stay was 5.7 ± 3.9¹² and 4.0 ± 2.8 days¹⁸ (Table 1). Davidson et al¹² reported 1.0% (1/102) non-union events and 1.0% (1/102) patients with loosening/failure of internal fixtures, while Stassen et al¹⁸ did not report on non-union events and reported 5.9% (2/34) patients with loosening or failure of internal fixtures. Avascular necrosis was reported in 2.9% (3/102)¹² and 11.8% (4/34)¹⁸ cases. Davidson et al¹² reported that 8.8% (9/102) of cases were converted to hemiarthroplasty while Stassen et al¹⁸ reported that 17.6% (6/34) were converted with another 5.9% (2/34) implants removed. Neither study reported any deaths^12,18 (Table 2).

Discussion

The results of our systematic literature review suggest that FNS can be safely and effectively used to treat FNF compared to other operative treatments. The majority of studies reported no significant difference in patient outcomes including non-union,^11,15,19 change in internal fixture loosening/failure,^17,19,21,22 postoperative complications,^11,16,17,23 reoperation,¹¹ and mortality,^11,17,20 with respect to the comparator device. Studies identified significantly better outcomes associated with FNS compared to cannulated screws, for reduced femoral neck shortening length and incidence,¹⁴ reduced incidence of reoperation,¹⁵ and lower incidence of implant removal.²² One study, a systematic review by Zhou et al, reported that FNS were associated with a significantly lower incidence of overall complications compared to those treated with cannulated screws.²³

The relative incidences of complications and mortality found in the thirteen studies reporting FNS are also comparable or lower than the incidences reported for comparators in the 104 comparator-only studies, supporting the conclusion that FNS is comparable to similar operative treatments. The 2 non-comparative studies found similar results when using FNS. These conclusions are also in line with previous systematic reviews comparing operative treatments, which have found that dynamic and sliding hip screws and cannulated cancellous screws are largely comparable with respect to safety outcomes.^24,25 Recently, another case series was published reporting outcomes in 12 patients after treatment with FNS, which found higher rates of complications compared to previously reported incidences for comparators.²⁶ A larger case series recently reported a high incidence of femoral neck shortening in patients treated with FNS, with no effect on fracture healing.²⁷ However, a recent comparative study found no difference in incidence of complications between patients treated for femoral neck fractures with FNS or cancellous screws, while patients treated with FNS had significantly better joint function,²⁸ and another comparative study found that FNS was more effective compared to a dynamic compression locking plate system.²⁹ Future comparative studies are need to confirm the relative incidence of complications in patients treated with FNS and address considerations such as long-term stability and mobility, which may have different priorities in different patient populations, depending on age and activity.

Factors other than implant choice impact revision and conversion rates and incidence of AVN, potentially explaining the low effect size between groups. The use of computed tomography scans or magnetic resonance imagery, rather than basic X-rays, may improve diagnostic accuracy by allowing physicians to visualize the fracture more clearly. Different imaging methods and protocols for when patients received imaging may have contributed to heterogeneity in reported incidence AVN between studies and among patients in individual studies. Better visualization may lead to more accurate classification of fracture displacement, informing treatment decisions.^30-32 Stable internal fixation is key to prevent non-union and allow for positive functional outcomes, especially in younger patients, who have higher functional demands³³ and a high rate reoperation and conversion to total hip arthroplasty.³⁴ Young patients with Pauwels Type III FNF specifically have increased likelihood of loss of reduction and non-union.³⁵ The use of adjunctive implants is currently uncommon, but combining established implants with other stabilizing measures may provide additional stability and improve patient functional outcomes, particularly in young patients with displaced fractures.^36-39

A simplified classification scheme of stable vs unstable may also improve treatment decision-making. Current guidelines suggest classifying fractures as non-displaced (Garden Type I or II) or displaced (Garden Type III or IV).⁴⁰ Both non-displaced and displaced fractures may be treated with internal fixation in younger patients,^33,41 but currently only non-displaced fractures are recommended to be treated with internal fixation in older patients.⁴⁰ However, Vazquez et al suggest that using implants, including FNS, cannulated screws, or dynamic or sliding hip screws, to treat displaced fractures in older patients can lead to positive safety outcomes and low rates of reoperation.²⁰

Reduction quality and implant placement were not consistently reported in the studies reviewed. Achieving excellent reduction, including open reduction if necessary, and using standardized intraoperative imaging to ensure correct implant placement can both lower the need for revision or conversion and lower the incidence of AVN.^42-44 Reduction quality and measures of implant placement should be assessed during treatment and reported in further studies to enable future analyses to accurately compare implants.

Limitations

The primary limitation of our review was the lack of prospective studies on patients treated with FNS, particularly the lack of RCTs. Heterogeneity in study design and patient and procedure characteristics prevented a broader meta-analysis, including studies that did not report use of FNS. This variability is likely due to heterogeneity in trauma patients, as well as differences in study designs. Many data elements were reported inconsistently, especially perioperative and postoperative complications. As mentioned above, methods for measuring blood loss varied widely, introducing heterogeneity into the data and precludes a definitive conclusion. Variations in fracture classification, patient age, follow-up time, mechanism of injury, and data collection methodologies between studies likely contributed to the heterogeneity of the results. Additionally, over half of the included studies had high risk of bias. Lack of comparability between cohorts was a common source of risk of bias, likely due to the heterogenous nature of trauma patient presentation. Finally, all but 1 study¹⁹ in this review did not have long enough follow-up for the outcomes of interest to occur, indicating a need for longer-term studies on FNF treatment with FNS to verify these findings.

Conclusions

FNS can be a safe and effective treatment for FNF, including in older patients, with published incidences of complications similar to comparable treatment options. Further studies are necessary to prospectively compare FNS to other operative treatments.

Supplemental Material

Supplemental Material - Evaluation of Post-Operative Outcomes of Femoral Neck Fracture Interventions: A Systematic Review

Supplemental Material for Evaluation of Post-Operative Outcomes of Femoral Neck Fracture Interventions: A Systematic Review by Erin Sheffels, Mariam Khalil, Kristen Hutchison, Nicole J. Hardy, Ranita Tarchand, John M. Pederson, Anjani Parikh, and Michael Blauth in Geriatric Orthopaedic Surgery & Rehabilitation

Supplemental Material

Supplemental Material - Evaluation of Post-Operative Outcomes of Femoral Neck Fracture Interventions: A Systematic Review

Supplemental Material

Supplemental Material - Evaluation of Post-Operative Outcomes of Femoral Neck Fracture Interventions: A Systematic Review

Footnotes

Acknowledgements

The authors acknowledge Superior Medical Experts and Nested Knowledge, Inc. for research and editorial assistance. The authors acknowledge Karl Holub, Stephen Mead, Jeffrey Johnson, and Darian Lehmann-Plantenberg for their design, development, and support of the Nested Knowledge meta-analytical software.

Author Contributions

ES contributed to the study design and drafted and revised the manuscript. MK, KH, and RT contributed to the data acquisition. NJH contributed to the study design and the acquisition and analysis of the data. JMP contributed to the study design, data analysis, and drafting and revision of the manuscript. AP and MB contributed to the conception and design of the study and the revision of the manuscript. All authors read and approved the final manuscript.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: ES is employed by and hold equity in Superior Medical Experts. JMP is employed by and hold equity in Superior Medical Experts and Nested Knowledge. MK and RT are employed by Nested Knowledge. KH is employed by Superior Medical Experts and Nested Knowledge. NJH is employed by and holds equity in Nested Knowledge. AP and MB are employed by Johnson & Johnson (JnJ) and own stock in the company.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is sponsored by Johnson & Johnson.

Ethical Statement

ORCID iDs

Erin Sheffels

Nicole J. Hardy

Supplemental Material

Supplemental material for this article is available online.

Appendix

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