Femoral neck fractures in young adults only comprise 2–3% of all femoral neck fractures and often result from high-energy trauma ^[1]. Studies have shown an association between these fractures in young adults and high incidences of osteonecrosis and non-union [2-7]. Fixation strategies in young patients emphasize anatomic reduction, preserving blood supply, and stable fixation to reduce complications. Classic fixation methods include closed reduction and percutaneous pinning (CRPP) with cannulated screws and sliding hip screw (SHS). Complication rates after CRPP and SHS remain high, with studies showing the incidence of osteonecrosis at 14.3%, malunion at 7.1%, and implant failure at 9.7%, with complications correlated with increasing Pauwel’s angle ^[8]. The Femoral Neck System™ (FNS) (Fig. 1) is a fixation device that aims to reduce varus collapse risk, increase mechanical and rotational stability compared to CRPP, and decrease incision size and incidence of lateral thigh pain compared to SHS [9-12]. While the FNS aims to combine the benefits of CRPP and SHS while eliminating the challenges associated with each, reported outcomes from in vivo studies are limited. Recent meta-analyses comparing the FNS to other fixation strategies have reported favorable union rates and relatively low complication rates, including rare instances of implant failure. However, few reports have detailed the specific modes of failure or the intraoperative challenges that may arise during revision surgery ^[13,14]. We report a case of FNS implant failure in a young patient with a femoral neck fracture occurring within 1 year of surgery. The patient consented to the publication of her case.

An active 21-year-old female sustained a right basicervical femoral neck fracture after being struck by a golf cart. She was treated at another institution using the FNS with an additional partially threaded headless screw (Fig. 2a and b). Seven months post-operatively, she developed progressive, atraumatic right hip pain with an inability to ambulate. She presented to our institution for evaluation. Radiographs demonstrated a right femoral neck non-union with implant failure through the bolt and antirotation screw at the level of the plate barrel aperture (Fig. 3a and b). She was consented for revision surgery with intertrochanteric valgus osteotomy and blade plate fixation.

The patient had no relevant past medical history and no history of tobacco use. Her body mass index was 24 kg/m². A non-union workup was non-contributory, and to our knowledge, there were no pre-existing risk factors for non-union. For the procedure, her previous lateral incision was used, and the FNS plate was easily visualized (Fig. 4a). The locking screw was removed from the plate, and the plate was removed with the head of the broken antirotation screw and a piece of the broken bolt. Proximal fragments of the broken lag screw and bolt remained in the femoral head (Fig. 4b), which were challenging to remove without causing further damage to the femoral head and neck. To remove the broken bolt, a threaded Steinmann pin was inserted manually into the bolt fragment, and the pin and bolt were extracted together. For the broken antirotation screw, a small core trephine was placed over the broken fragment to resect it along with a small core of surrounding bone from the femoral head and neck (Fig. 4c). Extracting the failed FNS was technically demanding, required sacrificing tenuous bone stock, and added approximately 60 min to the total operative time. The intact partially threaded headless screw was removed without difficulty after FNS removal.

Next, a 20° intertrochanteric valgus closing wedge osteotomy and blade plate insertion was performed. An articulating tensioning device was used to maximize compression at the osteotomy site. Fluoroscopy revealed an acceptable position of all implants (Fig. 5a and b). Post-operatively, she underwent a supervised return-to-activity protocol consisting of partial (50%) weight-bearing with crutches for 8 weeks, following by gradual return to full weight-bearing with physical therapy over 2 weeks thereafter.

She has been followed for 18 months post-operatively. At the most recent follow-up, she has returned to full weight-bearing, along with competitive swimming and daily bicycling without pain. Radiographs demonstrate intact and appropriately positioned implants with completely healed non-union and osteotomy sites (Fig. 6a and b). She has a 2 cm limb length discrepancy, for which she uses a shoe lift.

We describe a case of FNS implant failure involving the antirotation screw and femoral head bolt, including a challenging removal and revision. It is important to alert surgeons to this failure mode, as it may impact pre-operative planning and implant selection. A multicenter case series of 125 patients treated with the FNS reported 2 cases (1.6%) of implant failure, but the failure sites were not specified ^[15]. In seven studies involving 473 FNS cases, no implant breakage was noted [16-22]. Several reports of FNS compromise exist in the FDA MAUDE database, though these often lack critical details and are not peer reviewed ^[23]. In this report, failure of both the bolt and the antirotation screw occurred where they exit from the plate barrel. In an analysis of SHS failure, the bending forces of the lag screw, analogous to the FNS bolt, increase along the implant from proximal to distal and reach a maximum at its intersection with the plate barrel ^[24]. In this case, that intersection occurred at, or very near, the patient’s fracture. Consequently, the shear forces at the fracture were concentrated near the point of maximal bending stress of the implant, likely contributing to failure at that location. Further, the bolt has an aperture on its superior surface, allowing for the antirotation screw to fit near its intersection with the plate barrel, which may have weakened the bolt and contributed to its failure at this level. The antirotation screw failed at the screw notch, placed at the same level as the end of the plate barrel, where the narrow caliber proximal third of the screw meets the larger caliber portion of the remaining screw. Biomechanically, this change in cross-sectional diameter may generate an area of stress concentration, which may have contributed to its failure at this location. In our case, the failed components were returned to the manufacturer for safety reporting in accordance with institutional protocol. We do not have access to a retrieval lab, and we did not receive a formal report or failure analysis from the manufacturer. In future cases, consultation with an implant retrieval laboratory may provide further insight into the failure mechanism and should be considered. In addition, no histopathological or advanced imaging analysis was performed on the resected bone. Such assessments may help characterize the biological integrity of bone at the failure site and its potential contribution to healing outcomes or implant performance. Beyond implant design, the patient’s non-union resulted in prolonged reliance on and loading of the implant. In a study of non-geriatric patients with femoral neck fractures treated with the FNS, the mean time to union was 2.86 months ±0.77, with 2 patients developing non-union ^[18]. Reported non-union rates for patients treated with FNS range from 1 to 10% [15,17,18,20-22]. Known risk factors for femoral neck non-union include high fracture angle (i.e., Pauwels Type III), initial fracture displacement, and inadequate reduction [2,25-29]. This patient had a displaced fracture (Garden IV) with a fracture angle of 48°, near the cut-off for a Pauwels Type III (50°). Of note, original injury films and intraoperative imaging from the index surgery were unavailable, limiting full assessment of reduction quality and fracture characteristics. However, initial post-operative imaging revealed a slight residual fracture gap inferomedially, which may have limited compression (Fig. 2a). Therefore, in a healthy patient without risk factors for non-union, the initial and non-anatomic reduction may have contributed to non-union and implant failure. While the fracture was reduced in slightly more valgus, post-operative imaging, as well as the operative report, revealed no evidence of implant malposition or mechanical error. Although it is not possible to confirm whether the implant was fully tightened at the time of surgery, the simultaneous failure of both the antirotation screw and bolt at the non-union site suggests fatigue loading as the likely mechanism. In a study of femoral neck non-union, 7 of 9 cases of non-union in patients with fixed-angle devices occurred in the setting of uncontrolled collapse and loss of bone stock ^[30]. Interestingly, in this case, there was relatively well-preserved bone stock and minimal femoral neck shortening along the line of the FNS bolt. In biomechanical studies, the FNS has performed similarly to SHS and superior to cannulated screws [9-11,31,32]. However, a single study found that cannulated screws have better biomechanical stability in fractures with non-anatomic reductions ^[33]. In clinical studies, the FNS has shown lower complication rates compared to cannulated screws and similar outcomes to SHS ^{[16,18,19,21]}. Compared to a SHS, the FNS is reported to be less invasive with a smaller incision, shorter operative time, and less blood loss ^[12]. High rates of non-union can be expected when treating displaced femoral neck fractures, and surgeons who use the FNS device should be aware of the possibility that this device could fail in the manner we describe, should non-union occur, rendering implant removal difficult [34-36]. We recognize that this report describes a single patient experience, which precludes generalizations about overall device reliability, and we do not suggest the FNS is uniquely failure-prone; any device can fail in a non-union under mechanical stress. However, this failure mode presented unusual technical challenges during revision, particularly in comparison to more commonly used constructs, which surgeons should be aware of during surgical planning. The need for trephination to extract the broken antirotation screw and the use of a threaded Steinmann pin to retrieve the broken bolt added complexity and required careful preservation of limited bone stock. These technical demands alone prolonged the surgery by approximately 60 min. The resulting bone loss and surgical burden underscore the importance of considering potential revision implications during implant selection, especially in fractures with relatively high complication rates, such as displaced femoral neck fractures. This consideration is particularly salient in young, active patients, where implant durability, the demands of high-impact activity, and the feasibility of future revisions are critical concerns. Studies have highlighted that younger patients with femoral neck fractures face a unique treatment dilemma—balancing the need for stable fixation against the long-term risk of mechanical failure and reoperation, including conversion to arthroplasty ^[37,38]. Beyond technical complexity, revision procedures following femoral neck implant failure can impose substantial healthcare and societal costs. Studies have shown that revision surgery after failed internal fixation is associated with significantly higher overall costs and resource utilization compared to primary fixation or arthroplasty ^[39]. While we did not quantify cost in this case, the surgical demands and resource intensity of osteotomy and blade plate fixation underscore the importance of pre-operative planning and appropriate implant selection to minimize the risk and burden of revision. In addition, while our patient achieved a full return to activity, we did not obtain standardized functional outcome scores, such as the Harris hip score or SF-36 during follow-up. Incorporating validated outcome measures in future case reports and studies would strengthen objective assessments of recovery.

We present a case of FNS failure involving both an antirotation screw and a bolt at the plate barrel aperture in a young patient with non-union. Revision required extensive effort and sacrifice of bone stock. As the FNS is a relatively new implant for treating femoral neck fractures, orthopedic surgeons should be aware of this failure mode and the associated challenges during revision. While our patient demonstrated a full functional recovery with over 18 months of follow-up, describing this mode of failure may inform manufacturers and surgeons of potential failure during implant design or selection and serve as a basis for future comparative studies in this population.

While the FNS offers theoretical advantages in femoral neck fracture fixation, rare failure at the junction of the antirotation screw and bolt near the plate barrel can significantly complicate revision surgery. This case emphasizes the need for careful implant selection, especially in young patients at risk for non-union, and highlights the importance of pre-operative planning for potential implant removal. Recognizing and reporting such failures can guide future design improvements and surgical decision-making.