Abstract
Background
Femoral neck fractures (FNF) are one of the most common fractures, with a projected increase in incidence with population growth and ageing. The Femoral Neck System (FNS) launched in 2019 was developed specifically for fixation of FNF with the purported advantages of providing both angular and rotational stability. We report our experience with the FNS and evaluate its effectiveness and associated complications.
Methods
A retrospective case series of 50 patients who underwent surgical fixation for FNF from August 2020 to October 2021 using the FNS in two Singapore tertiary institutions with at least 2 years follow-up were included. Clinical data (patients’ demographics, fracture classification, intra-operative and post-operative complications) were reviewed. Radiological analysis assessed the pre- and immediate post-operative garden alignment index (GAI) and presence of femoral neck shortening at 3 months.
Results
The mean age was 63.5 years (SD 16.9, range 26–92). Five (10 %), 34 (68 %) and 11 (22 %) were ASA 1, 2 and 3 respectively. Twenty-four (48 %), 16 (32 %), 4 (8 %), and 6 (12 %) patients sustained Garden's 1, 2, 3 and 4 FNF respectively. The mean operative duration was 66.2 min (SD 20.5) and length of stay was 6.9 days (SD 4.6).The post-operative improvement in garden alignment index (GAI) was a mean of 9.1° (p < 0.001) on lateral view. The mean femoral neck shortening was 1.97 mm (SD 5.3) at 3 months. There were no intra-operative complications. Post-operatively, 1 (2 %) patient required blood transfusion, 1 (2 %) patient had implant cut-out and non-union managed non-operatively, 2 (4 %) patients developed avascular necrosis and required revision to total hip replacements. There were two (4 %) cases of 1-year mortality.
Conclusion
The FNS achieved good outcomes with low rates of complications. The promising results justify its continued use and further evaluation in comparison to other devices.
Keywords: Hip fractures, Femoral neck fractures, Femoral neck system, Asian, Outcomes
1. Introduction
Femoral neck fractures (FNF) are one of the most common fractures, with a projected increase in incidence with population growth and ageing. The worldwide incidence is expected to increase to 6.26 million by 2050,1 with up to 21 million persons living with hip fracture related disability in the next 40 years.2 This places a significant burden on our healthcare system,3 thus emphasizing the importance of optimization of hip fracture management and improving clinical outcomes.
The surgical treatment of FNF depends on patient demographics, fracture pattern and stability. Hip preservation surgery with internal fixation is preferred in younger patients, whereas this option is mostly reserved for valgus impacted or stable FNF in the older population. Internal fixation is traditionally performed using the cannulated cancellous screws (CCS) or a sliding hip screw (SHS).
The Femoral Neck System (FNS; DePuy Synthes, Raynham, MA) was developed specifically for the fixation of FNF, with FDA approval obtained in 2018. Similar to the SHS implant, it is able to provide fixed-angle stability with a cylindrical bolt and locking plate, and allow controlled fracture collapse with repeated weight bearing of the hip joint. Its purported advantages include a less invasive approach compared to the SHS, that provides both angular and rotational stability with the additional built-in anti-rotation screw.4,5
Multiple biomechanical studies have shown non-inferiority of the FNS in comparison to the SHS/CCS constructs.4,6,7 In addition, clinical studies have demonstrated other advantages including reducing operative time, fluoroscopy exposure, and better fracture healing.8, 9, 10, 11
The existing studies have provided outcomes with a minimum follow-up period of 12 months. However, there is paucity of data with longer-term outcomes. We report our experience with the FNS with a minimum of 2 years follow-up and evaluate its effectiveness and associated complications.
2. Methods
A multi-centre study involving two tertiary institutions in Singapore was conducted. All patients who underwent surgical fixation with the FNS for FNF from August 2020 to October 2021 were included. All patients had a minimum of 2 years follow-up.
A retrospective review of the patients' medical records was performed. Clinical data including the age, sex, race, smoking status, American Society of Anaesthesiologists (ASA) score and serum vitamin D levels were recorded. Details of the injury including the mechanism, side, and radiographical Garden's classifications were noted. The operative duration, length of hospital stay, blood transfusion requirements, and other post-operative complications (such as avascular necrosis, non-union, implant cut-out, need for revision surgery, mortality) were reviewed. Radiological analysis performed by trained Orthopaedic surgeons assessed the pre- and immediate post-operative garden alignment index (GAI) and presence of femoral neck shortening 3 months post-operatively10 (Fig. 1). Pre- and post-operative home and community ambulatory status were also compared.
Fig. 1.
Radiographical assessment and calculation of femoral neck shortening comparing immediate and 3 months post-operative radiographs.
Categorical variables were expressed in percentages and continuous variables as means (standard deviations). The Wilcoxon signed rank test was used for the statistical evaluation of the radiological outcomes pre- and post-operatively as they were not normally distributed. The level of significance was set at 0.05. Subgroup analysis in patients with undisplaced and displaced FNFs were performed. We utilized Microsoft Excel 2010 (Microsoft Corp., Redmond, WA) and Statistical Package for the Social Sciences Version 23.0 (SPSS Inc, Chicago, II) for compilation of data and statistical analysis, respectively. The study was performed in accordance with the ethical standards of both institutional research committees.
3. Results
A total of 50 patients were included in the study. Table 1 demonstrates the patient characteristics. The mean age was 63.5 years (SD 16.9, range 26–92). There were 26 females (52 %) and 24 males (48 %). Thirty-seven (74 %) were of Chinese ethnicity, 7 (14 %) Malay, 4 (8 %) Indian, and 2 (4 %) of other ethnicities. Five (10 %), 34 (68 %) and 11 (22 %) were ASA 1, 2 and 3 respectively. Smoking was prevalent in 10 (20 %) patients. Serum Vitamin D levels was 25.1 ng/mL on average (SD 9.0, range 9.1–57.6).
Table 1.
Patient characteristics.
| Characteristic | n/Mean | %/SD (range) |
|---|---|---|
| Age (years) | 63.5 | 16.9 (26–92) |
| Gender | ||
| Male | 24 | 48 |
| Female | 26 | 52 |
| Race | ||
| Chinese | 37 | 74 |
| Malay | 7 | 14 |
| Indian | 4 | 8 |
| Others | 2 | 4 |
| Smoker | ||
| Yes | 10 | 20 |
| No | 40 | 80 |
| ASA | ||
| 1 | 5 | 10 |
| 2 | 34 | 68 |
| 3 | 11 | 22 |
| Vit D (ng/mL) | 25.1 | 9.0 (9.1–57.6) |
| MOI | ||
| Fall | 46 | 92 |
| Others | 4 (2 RTA; 2 exercise workout) | 8 |
| Side | ||
| Left | 26 | 52 |
| Right | 24 | 48 |
| Garden's classification | ||
| 1 | 24 | 48 |
| 2 | 16 | 32 |
| 3 | 4 | 8 |
| 4 | 6 | 12 |
| Length of stay (days) | 6.9 | 4.6 (2–30) |
| Operative duration (min) | 66.2 | 20.5 (39–130) |
| Blood transfusion | ||
| Yes | 1 | 2 |
| No | 49 | 98 |
Falls was the main cause of injury in 46 (92 %) patients, with 2 (4 %) from road traffic accidents, and 1 (2 %) from injury during an exercise workout. Left FNF occurred in 26 (52 %) patients, and right FNF in 24 (48 %). The mean operative duration was 66.2 min (SD 20.5, range 39–130) and mean length of hospital stay was 6.9 days (SD 4.6, range 2–30). Twenty-four (48 %), 16 (32 %), 4 (8 %), and 6 (12 %) patients sustained Garden's 1, 2, 3 and 4 FNF respectively. Table 2 demonstrates the proportion of Garden's 1 to 4 and undisplaced or displaced FNF in patients <65 and ≥ 65 years old.
Table 2.
Garden's classification and displacement of FNF in patients <65 and ≥ 65 years.
| Age (years) | Garden's Classification |
|||
|---|---|---|---|---|
| 1 | 2 | 3 | 4 | |
| <65 (n = 21) | 8 (38.1 %) | 3 (14.3 %) | 4 (19.0 %) | 6 (28.6 %) |
| ≥65 (n = 29) |
16 (55.2 %) |
13 (44.8 %) |
0 |
0 |
| Undisplaced FNF (n=40) | Displaced FNF (n=10) | |||
| <65 (n = 21) | 11 (52.4 %) | 10 (47.6 %) | ||
| ≥65 (n = 29) | 29 (100 %) | 0 | ||
The pre- and post-operative garden alignment index (GAI) and 3-months femoral neck shortening are detailed in Table 3. Overall, the post-operative difference in GAI was a mean of 2.2° (p = 0.12) on AP view, and improved 9.1° (p < 0.001) on average on lateral view. The mean femoral neck shortening was 1.97 mm (SD 5.3) at 3 months. Subgroup analysis for undisplaced and displaced FNFs are demonstrated in Table 3.
Table 3.
Radiological indices pre- and post-operatively.
| Radiological outcomes | All (n = 50) |
Undisplaced FNF (n = 40) |
Displaced FNF (n = 10) |
|
|---|---|---|---|---|
| Mean ± SD | ||||
| Garden alignment index (AP) (°) | Pre-operative | 167.0 ± 14.0 | 170.3 ± 9.0 | 153.8 ± 21.9 |
| Post-operative | 164.8 ± 8.1 | 165.7 ± 7.9 | 161.2 ± 8.4 | |
| Difference | 2.2 | 4.6 | 7.4 | |
| P-value | 0.117 | 0.008 | <0.001 | |
| Garden alignment index (lateral) (°) | Pre-operative | 165.8 ± 10.5 | 167.8 ± 8.3 | 158.0 ± 15.0 |
| Post-operative | 174.9 ± 8.1 | 176.2 ± 7.2 | 169.9 ± 10.2 | |
| Difference | 9.1 | 8.4 | 11.9 | |
| P-value | <0.001 | 0.20 | 0.005 | |
| Femoral neck shortening (mm) | Difference | 1.97 ± 5.31 | 1.18 ± 4.56 | 5.14 ± 7.04 |
Pre-operatively, 41 patients were home ambulant without aid, 5 ambulant with walking stick/quad-stick, and 4 ambulant with walking frame. Post-operatively, the home ambulatory status remained status quo for 38 patients, whereas 12 patients required increased aids (Table 4). Pre-operatively, 40 patients were community ambulant without aid, 5 ambulant with walking stick/quad-stick, and 4 ambulant on wheelchair. Post-operatively, the community ambulatory status remained status quo for 37 patients, whereas 13 patients required increased aids (Table 3). In patients <65 years old, all 10 patients who sustained displaced FNF returned to ambulation without aids at home and in the community post-operatively. Three of 11 patients who sustained undisplaced FNF had required escalation from no aids to use of walking stick at home and in the community post-operatively.
Table 4.
Pre- and post-operative home and community ambulatory status.
| All (n = 50) |
Undisplaced FNF (n = 40) |
Displaced FNF (n = 10) |
|||||
|---|---|---|---|---|---|---|---|
| Ambulatory status | Pre-operative (n/%) | Post-operative (n/%) | Pre-operative (n/%) | Post-operative (n/%) | Pre-operative (n/%) | Post-operative (n/%) | |
| Home ambulation | No aids | 41 (82) | 30 (60) | 31 (77.5) | 20 (50) | 10 (100) | 10 (100) |
| Walking stick/Quad-stick | 5 (10) | 12 (24) | 5 (12.5) | 12 (30) | 0 | 0 | |
| Walking frame | 4 (8) | 7 (14) | 4 (10) | 7 (17.5) | 0 | 0 | |
| Wheelchair | 0 | 1 (2) | 0 | 1 (2.5) | 0 | 0 | |
| Community ambulation | No aids | 40 (80) | 28 (56) | 30 (75) | 18 (45) | 10 | 10 |
| Walking stick/Quad-stick | 5 (10) | 11 (22) | 5 (12.5) | 11 (27.5) | 0 | 0 | |
| Walking frame | 0 | 0 | 0 | 0 | 0 | 0 | |
| Wheelchair | 5 (10) | 11 (22) | 5 (12.5) | 11 (27.5) | 0 | 0 | |
There were no intra-operative complications. Post-operatively, 1 (2 %) patient required blood transfusion, 1 (2 %) patient had implant cut-out and non-union managed non-operatively, 2 (4 %) patients developed avascular necrosis and required revision to total hip replacements. There were two (4 %) cases of 1-year mortality.
The single case of implant cut-out and non-union occurred in a 90-year-old Chinese male who had sustained a valgus impacted right FNF following a fall. His serum vitamin D was 14 ng/mL, with known osteoporosis (BMD T score of the hip −3.3) previously on Alendronate from 2018 to 2019. Treatment was however stopped upon discussion with his primary care physician given his age. Pre-morbidly he was home and community ambulant without aids. The pre- and post-operative radiographs are shown in Fig. 2. The immediate post-operative radiographs (Fig. 2B) demonstrate suboptimal implant positioning with tip apex distance of 36.4 mm. The GAI on AP and lateral views were 163° and 178° respectively. He was kept non-weight bearing on the right lower limb for 6 weeks and progressed to full weight-bearing thereafter. The implant cut-out and non-union was noted at his 6 months follow-up (Fig. 2D) with no reported falls prior. He has been wheelchair bound post-operatively with minimal pain on transfers. Decision was made for non-operative treatment after extensive discussion with the patient and family members.
Fig. 2.
Case of implant cut-out and non-union. (A) Pre-operative radiograph (B) Immediate post-operative radiograph (C) 6 weeks post-operative radiograph (D) 6 months post-operative radiograph demonstrating implant cut-out and non-union.
The first case of avascular necrosis occurred in a 49-year-old Chinese male who had sustained a displaced FNF following a road traffic accident. His serum Vitamin D was 23.5 ng/mL, with no underlying osteoporosis. Pre-morbidly he was home and community ambulant without aids. The pre- and post-operative radiographs are shown in Fig. 3. Pre-operative radiographs demonstrate a Pauwel's angle of 75° (Fig. 3A). The immediate post-operative radiographs demonstrate adequate reduction of the fracture with restoration of the medial calcar, GAI and native neck shaft angle (Fig. 3B). However, the 3 months post-operative radiographs show an 18.7 mm femoral neck shortening (Fig. 3C), and the development of femoral head avascular necrosis changes on the 10 months post-operative radiographs (Fig. 3D). The patient had persistent right hip pain, and underwent conversion to total hip replacement.
Fig. 3.
First case of femoral head avascular necrosis. (A) Pre-operative radiograph (B) Immediate post-operative radiograph (C) 3 months post-operative radiograph (D) 10 months post-operative radiograph demonstrating femoral head lucencies suggestive of avascular necrosis.
The second case of avascular necrosis occurred in a 65-year-old Chinese female who had sustained a valgus impacted FNF following a fall. Her serum Vitamin D was 40 ng/mL, with BMD T score of the hip −2.2 and T score of the spine 0.6. Pre-morbidly she was home and community ambulant without aids. The pre- and post-operative radiographs are shown in Fig. 4. She had initially progressed well post-operatively, requiring quad-stick for ambulation. However, 6 months post-surgery, she experienced an acute sharp pain in the right proximal thigh after an episode of bending forwards to don her pants. She was wheelchair bound due to the pain. A computed tomography scan was performed which demonstrated healing of the neck of femur fracture and collapse of the femoral head (Fig. 4D). She underwent conversion to total hip replacement.
Fig. 4.
Second case of femoral head avascular necrosis. (A) Pre-operative radiograph (B) Immediate post-operative radiograph (C) 3 months post-operative radiograph (D) 6 months post-operative radiograph and computer tomography scan demonstrating femoral head collapse.
4. Discussion
To the best of our knowledge, this is the first study to report the clinical outcomes and complications of the FNS with a minimum of 2 years follow-up. The overall failure rate for FNS in the treatment of FNF in our series was 6 % in 2 years. The present study showed that FNS is a safe and effective option for the treatment of FNF in a variety of patients of varied ages and fracture classifications.
Post-operative failure of surgical fixation of FNF could be due to avascular necrosis, fracture non-union, implant cut out or implant aseptic loosening. These complications contribute to post-operative morbidity and increase in healthcare costs for patients. The innovative and design advancements in surgical implants aim to minimize these complications and requires thorough evaluation of its effectiveness. Failure rates of the SHS or CCS in literature vary from 16 to 30 % after 6–24 months.2,12,13 However, recent outcome studies of FNS demonstrated much lower rates of failure.14, 15, 16 Kenmegne et al.14 performed a retrospective comparative study between FNS (n = 56) and CCS (n = 58) in non-geriatric FNF with a follow-up period of 12–36 months. There was a statistically significant difference in complication rates (non-union, AVN, aseptic screw loosening) between the FNS group (8.93 %) and CCS group (24.13 %). Yan et al.15 similarly reported the retrospective outcomes of younger patients treated with FNS (n = 22) and CCS (n = 27) with a minimum follow-up of 12 months. There were 0 cases of non-union, AVN and cut out in the FNS group compared to 4 cases of these complications in the CCS group. A systematic review and meta-analysis by Jiang et al.16 also showed significantly lower occurrences of AVN and implant cut out with FNS compared to CCS (OR = 0.27; 95 % CI, 0.08 to 0.83; P = 0.02; OR = 0.28; 95 % CI, 0.10 to 0.82; P = 0.02 respectively).
On the contrary, recent case series published in 202217 and 202318 which included geriatric FNF, the failure rates are higher than those reported by Kenmegne et al.14 and Yan et al.15 Stassen et al.17 had an overall failure rate of 17.6 % (11.8 % AVN, 5.8 % implant cut-out) after 1 year follow-up in a population with mean age of 63 years. Stegelmann et al.18 reported a 11.4 % failure rate (4.7 % cut-out, 3.8 % non-union, 1.9 % peri-implant fracture, 1.0 % AVN) after a minimum of 1 year follow-up in 105 patients with a mean age of 77.2 years (range 46–95). The present study had 1 case of non-union and implant cut out (2 %), and 2 cases of avascular necrosis requiring conversion to total hip replacements (4 %). The overall failure rate of 6 % after 2 years falls below the lower limit of average failure rates in FNF fixations in existing literature. We are unable to perform analysis for risk factors for failure as it would be underpowered.
Konrad et al.19 compared the clinical results of the 1-hole FNS (n = 113) with the 2-hole DHS (n = 108). The rate of cut out (FNS 12.4 % vs DHS 10.2 %, p > 0.05) showed no difference between the groups. Logistic regression showed that poor blade position (ie. not positioned center–center or inferior–center) was the only significant predictor for cut out and increased the risk by factor 7. High age was not a significant predictor of implant failure. In our single case of non-union and implant cut out, the blade position was suboptimal with a TAD of 36.4 mm, where the blade position was placed too anteriorly.
While studies have attempted to identify risk factors for avascular necrosis of the femoral head following surgical fixation of FNF, there is no real consensus. Biologically, AVN occurs following a disruption to the retinacular vessels which are crucial for the vascular supply of the femoral head.2 A systematic review and meta-analysis by Xu et al.20 included a total of 17 case-control studies with 2065 patients included. The main risk factors identified include Garden classification of 3 or 4 (ie displaced), or retained implants. In our 2 cases of AVN, the first case occurred in a displaced FNF (Garden 4) with high pauwel's angle, whereas the second case involved a valgus impacted Garden 1 FNF. With the limited number of AVN cases in our series, we are unable to make any conclusions regarding the underlying risk factors.
The major strength of this study is that it is the first to report outcomes of the FNS with 2 years follow-up. All types of fractures and age groups were included as per the manufacturers intended use, including Garden 1 to 4 FNF. Additionally, this is the first outcome study to include ambulatory status as a surrogate for clinical outcomes. One of the limitations of this study include a small sample size. This is because of the novelty of the implant (where usage of FNS started in 2020 in our institutions) and the intention to report 2 year outcomes and complications. Secondly, only objective outcomes were used in the current study, with no patient reported outcome scores evaluated. However, this is the first study to evaluate ambulatory status pre- and post-operatively as a surrogate marker of clinical outcomes. Thirdly, due to the low numbers of fixation failures in our cohort, assessment of risk factors for failures cannot be performed. However, this suggests that the overall failure rates of the FNS is low. Lastly, a control or comparison group would further enhance the reliability of results.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Ethical statement
The study was performed in accordance with the ethical standards of both institutional research committees (2021/01058).
Guardian/patient’s consent
There was no need for guardian/patient's consent as waiver of consent was obtained.
CRediT authorship contribution statement
Chloe Xiaoyun Chan: Conceptualization, Data curation, Formal analysis, Methodology, Project administration, Writing – original draft, Writing – review & editing. Joshua Ian Lim: Data curation, Formal analysis, Methodology, Writing – original draft. Amritpal Singh: Supervision, Validation, Writing – review & editing. Diarmuid Murphy: Supervision, Validation, Writing – review & editing. Yongsheng Chen: Supervision, Validation, Writing – review & editing.
Declaration of competing interest
The authors have no conflicts of interest to declare.
(Unable to edit and save the Conflict of Interest Form provided in the link in the portal)
Acknowledgements
Not applicable.
Contributor Information
Chloe Xiaoyun Chan, Email: chloe.chan@mohh.com.sg.
Joshua Ian Lim, Email: joshuaianlim14@gmail.com.
Amritpal Singh, Email: amritpal_singh@nuhs.edu.sg.
Diarmuid Murphy, Email: diarmuid_murphy@nuhs.edu.sg.
Yongsheng Chen, Email: yongsheng_chen@nuhs.edu.sg.
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