Case of implant failure following osteosynthesis for an intertrochanteric femoral fracture using a carbon fiber intramedullary nail

Abstract

Carbon fiber-reinforced polyetheretherketone (CFR-PEEK) materials are radiolucent and produce fewer metallic artifacts during radiological examinations, making them a subject of growing interest as osteosynthesis materials in the field of orthopedics. However, clinical reports on carbon intramedullary nails are still limited, and there are few reports on postoperative complications. The present case report describes a 55-year-old female patient who sustained an unstable intertrochanteric fracture of the left femur and underwent open reduction and internal fixation using a CFR-PEEK intramedullary nail. Ultimately, within just 6 months after the initial surgery, varus deformity developed at the fracture site, resulting in failure of the junction between the intramedullary nail and the lag screw, and necessitating revision surgery involving total hip arthroplasty.

Introduction

Open reduction and internal fixation (ORIF) using intramedullary nails is a widely used surgical treatment for intertrochanteric femoral fractures, and numerous excellent treatment outcomes have been reported [1, 2]. The primary materials used for intramedullary nails are generally metallic materials such as titanium alloys and stainless steel. Meanwhile, in recent years, Carbon fiber-reinforced polyetheretherketone (CFR-PEEK) have also been gaining attention as osteosynthesis materials [3, 4]. However, there are few reports on postoperative complications. In this report, we present a case in which an implant failure occurred following ORIF using a carbon intramedullary nail for an intertrochanteric femoral fracture, necessitating total hip arthroplasty (THA).

Case

A 55-year-old woman fell and was diagnosed with a left intertrochanteric femoral fracture of type 1, group 4 according to the Evans classification [5] (Figs 1 and 2). In response, ORIF using CFR-PEEK intramedullary nail (Medicarbo hip nail system, b-itec, Kakamigahara, Japan) was performed (Figs 3 and 4). Two weeks after the initial surgery, displacement of the greater trochanter occurred (Fig. 5), and an additional osteosynthesis was performed (Fig. 6A). However, varus deformity of the femoral head gradually progressed even after the second surgery (Fig. 6B and C). The patient was referred to our hospital 6 months after the initial surgery for further examination and treatment. The patient had difficulty bearing weight, was walking with crutches at the time. The Modified Harris Hip Score (HHS) was 22 points. Imaging findings showed nonunion at fracture site and varus deformity of the femoral head, raising suspicion of implant failure. The system used in this case was designed such that the angle between the nail and lag screw is 56°, but images taken at the time of admission showed this angle had changed to 91° (Fig. 7). It was determined that THA should be performed, as early postoperative rehabilitation was considered beneficial.

The surgery began with a lateral approach. Upon dissection down to the subfascial layer, a dark gray substance was observed diffusely distributed (Fig. 8) and several carbon fragments measuring a few millimeters in size were also noted. A dark gray substance was removed as thoroughly as possible. Bone union was not observed, and all implants, including those in the femoral head and neck, were removed. Significant wear was observed in the lag screw hole (Fig. 9A) and at the interface between the lag screw and the nail (Fig. 9B). THA was performed using a cementless cup and a cemented long stem (G7 acetabular system and CMK stem, Zimmer Biomet, Warsaw, IN, USA) (Fig. 10). Postoperative therapy included full weight-bearing from the day after surgery. Two years after surgery, the Modified HHS improved to 78 points, and the patient able to walk independently.

Discussion

CFR-PEEK exhibits superior fatigue resistance, and it has been reported that its elastic modulus is similar to that of bone [6, 7]. Furthermore, because CFR-PEEK is radiolucent, it produces fewer metallic artifacts on plain radiographs and computed tomography (CT), making it easier to evaluate the reduction status of the fracture site and bone union [8]. Reports on the use of CFR-PEEK intramedullary nails for humeral fractures and CFR-PEEK plates for distal femoral fractures indicate bone union rates of 91%–100%, demonstrating their clinical utility [9]. Furthermore, a systematic review comparing CFR-PEEK intramedullary nails and those made of titanium in patients impending fractures due to metastatic bone tumors that the complication rates and implant failure rates were generally equivalent between the two [7]. On the other hand, regarding reports on CFR-PEEK intramedullary nail failure, Pala et al. reported that among 17 cases with impending pathological fractures of the femur, implant failure occurred in two cases [10]. Furthermore, there have been reports of CFR-PEEK intramedullary nails in the humerus failing after extensive tumor resection [11]. However, these reports on fractures relate to pathological fracture in metastatic bone tumors or surgery following tumor resection, and are likely influenced by factors such as the extent of tumor infiltration and resection; therefore, they are considered to have little relevance to general fractures. Takashima et al. reported a high bone union rate of 95% in 20 cases of intertrochanteric femoral fractures treated with CFR-PEEK intramedullary nails, but noted that nonunion was observed in one case of an unstable fracture [12].

In the present case, postoperative CT images revealed that the posterolateral fragment of the trochanter had not been adequately reduced and was posteriorly displaced. Furthermore, it was confirmed that the nail had been inserted from the fracture site, suggesting that the initial fixation was inadequate. It is believed that, under unstable biomechanical conditions where bone union had not yet been achieved, loading on the femoral head likely generated persistent varus stress, resulting in stress concentration at the junction between the intramedullary nail and the lag screw. Ultimately, within 6 months after the initial surgery, the lag screw hole had significantly worn down and expanded, resulting in a fracture.

In a study using a finite element model, CFR-PEEK intramedullary nails distribute stress more evenly throughout the implant compared to titanium, thereby reducing stress shielding in the proximal femur. However, they also noted that the internal stress was higher than that of titanium, and that peak stress was localized around the lag screw hole [13]. Additionally, Fragomen et al. state that because CFR-PEEK intramedullary nails possess high elasticity due to its carbon fiber polymer composition, they may allow for considerable movement, which may increase the risk of delayed union or nonunion [14]. The limitations of this case report include the fact that it does not compare the biomechanical properties regarding wear and damage when CFR-PEEK surfaces come into contact with one another to those of metals such as titanium. Based on previous reports of poor outcomes and this case, CFR-PEEK intramedullary nails are useful for stable fractures; however, the risk of failure may increase in cases of unstable fractures or when reduction is inadequate. At present, careful patient selection and ensuring initial stability through precise reduction techniques are considered crucial.

Acknowledgements

The authors would like to thank Mr. Nick Pollifrone for his assistance in editing the English version of this manuscript.

Conflicts of interest

None declared.

Funding

None declared.

Ethics approval

Informed written consent was obtained from the patient for publication of this case report and accompanying images.

References