1 Introduction

Distal femur fractures have an annual incidence of 4.5 per 100,000 population, primarily in patients over 70 years, often resulting in mortality rates as high as 25 % at 1 year.^1–4 Early mobilization is crucial but challenging due to poor bone quality and complex fracture patterns.^2,5 Recently, two main strategies have been employed: retrograde intramedullary nailing and open reduction internal fixation (ORIF) with locked plating, each with distinct biomechanical advantages.⁶ Studies show similar union rates (up to 90 %) and outcomes for both, but neither allows immediate weight-bearing.^7,8

Efforts have been made to develop fixation methods supporting early weight-bearing.^9,10 Examples include dual plating and retrograde intramedullary nailing combined with plate fixation, both showing promising results with immediate weight-bearing.^11,12 Additionally, industry advancements have led to pre-fabricated nail and locking washer constructs designed to combine the load-sharing benefits of intramedullary nails with the improved fixation of locked plating. This case report discusses three patients with distal femoral fractures, all treated by a fellowship-trained orthopaedic traumatologist. They underwent femur retrograde intramedullary nailing using the DePuy Synthes RFN-Advanced™ Retrograde Femoral Nailing System (RFNA) (DePuy Synthes, Raynham, MA, USA). This system enables a locking screw to pass through the nail and locking attachment washer (LAW), designed to increase fixation strength. The patients experienced screw migration involving these locking screws engaging the washer and nail. This report aims to illustrate implant complications, outline their management and follow-up, and explore potential mechanisms for screw migration.

2 Case report

2.1

2.1 Case 1

A 66 year old female presented after a ground level fall with a 2mm poke hole wound over the anterior aspect of the knee with a left distal femur supracondylar fracture with intercondylar extension (Fig. 1). She received expedient antibiotic prophylaxis and was taken in a timely fashion to the operating room.

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Fig. 1 Radiographs of Case 1, including injurying films, intraoperative fluoroscopy, and subsequent screw migration in follow up.

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The intercondylar fracture was reduced anatomically and secured with a 7.3mm cannulated screw to achieve rigid compression of the articular surface. A transpatellar approach to the distal femur was performed, and a retrograde femur nail with locking washer was placed to achieve fixation according to the manufacturer's guidelines. A 5.0 interlocking screw was placed medially, and once the distal femoral washer was applied laterally, two additional 5.0 locking screws were placed through the washer and through the nail providing further fixation. Three additional 3.5 cortical locking screws were utilized. The nail was further locked with a lateral to posteromedial screw placed through the extramedullary jig. All nails in this report were locked proximally. A gram of vancomycin powder was placed along the implant and wounds were closed. Patient was made toe touch weight bearing postoperatively.

At 8 weeks, radiographs showed maintained implant and fracture alignment and she was progressed to 50 % partial weight bearing. At 12 weeks she had a palpable prominence on the lateral aspect of her knee. Radiographs showed migration of the distal 5.0 nail-washer locking screw with otherwise maintained alignment and interval callous formation. Patient underwent removal of the screw and there was noted to be a small hematoma and chronic inflammatory tissue. Infection was ruled out.

At 4 weeks after hardware removal (approximately 4 months after index procedure), the proximal 5.0 nail-washer locking screw migrated. Patient was asymptomatic and subsequent radiographs showed no interval change in screw position, and decision was made in discussion with the patient to leave the implant unless it becomes symptomatic.

2.2

2.2 Case 2

A 70 year old female presented after a motor vehicle collision requiring extrication with a left distal femur supracondylar fracture with significant comminution and intercondylar extension (Fig. 2). A transpatellar approach was utilized and a retrograde femur intramedullary nail with locking washer was placed. Two 5.0 locking screws were placed through the washer and the nail as well as 3.5 cortical screws locking into the washer. A gram of vancomycin powder was placed onto the implant. Patient was made toe touch weight bearing postoperatively.

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Fig. 2 Radiographs of Case 2, including injurying films, intraoperative fluoroscopy, and subsequent screw migration in follow up.

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The patient had an otherwise standard postoperative course. At her 12 week follow up patient reports she still had significant pain in her knee especially with ambulation. She was progressed to approximately 50 % protected weight bearing. Radiographs showed maintained fracture alignment with minimal callous formation, and migration of the distal 5.0 nail-washer locking screw. At this time CT scan was obtained, demonstrating a partial non-union. Patient was maintained with partial weight bearing and after shared decision making with the patient, she followed up in 4 weeks for repeat radiographs demonstrating further screw migration. Patient was now symptomatic and screw palpable.

At this time patient was taken back to the operating room to manage her partial non-union and painful implant due to screw backout. The screw was removed and the fracture site was bone grafted with cancellous bone chips and demineralized bone matrix putty. A 5.0 screw was placed through the lateral washer and nail for revision fixation of the fracture. Infection was ruled out. A gram of vancomycin powder was placed along the graft site. Patient progressed well post operatively, and 1 year after the revision procedure patient was healed radiographically and clinically.

2.3

2.3 Case 3

A 66 year old female presented after a ground level fall with a left distal femur supracondylar fracture with intraarticular extension (Fig. 3). Patient was medically optimized and taken to the operating room in a timely fashion. A transpatellar approach was utilized and a retrograde femur intramedullary nail with locking washer was placed. Two 5.0 locking screws were placed through the washer and the nail as well as 3.5 cortical screws locking into the washer. Patient was made 50 % partial weight bearing postoperatively.

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Fig. 3 Radiographs of Case 3, including injurying films, intraoperative fluoroscopy, and subsequent screw migration in follow up.

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Her postoperative course was uncomplicated, and at her 8 week follow up appointment she was doing well and progressed to weight bearing as tolerated with a walker. Her HbA1c went down to 8, and continued to improve to 6.2 at 12 weeks. At this time she developed prominence on the lateral aspect of her left knee with associated pain. Radiographs showed maintained fracture alignment with migration of the distal 5.0 nail-washer locking screw.

Patient was taken back to the operating room and the distal screw was removed. It was noted that the screw and threads were all intact; however, some soft tissue appeared to be interposed in the washer which may have altered the locking mechanism. A new screw was placed. Infection was ruled out. Patient was continued as weight bearing as tolerated with walker postoperatively. At one year following final procedure, patient was radiographically and clinically healed and walking unassisted.

3 Discussion

Distal femoral fractures can be challenging injuries and the utilization of intramedullary nailing alongside plate fixation has shown promising results enabling earlier weight bearing. While this innovative system provides promise, the screw migration observed resulted in increased morbidity. A case series by Minhas et al. also described screw migration associated with the use of this implant. Out of 27 patients at their institution, 8 patients experienced screw migration, one of which included a screw in the locking washer.¹³ We postulated several potential causes and categorized them into patient, device, and surgeon factors.

Examining patient factors, our patients shared common characteristics (Table 1). They were predominantly older females with diabetes. Although diabetes is known to affect healing, only one patient had significantly elevated HbA1c, which was subsequently managed. Patient 1 had multiple comorbidities, including ESRD and immunosuppressant use from a renal transplant, potentially impeding healing. Two patients had extensive smoking histories, a known cause of delayed healing. Additionally, two patients had a BMI over 40kgm2, associated with increased complications and potential for delayed or non-union.¹⁴ Post-operative weight-bearing status was relatively consistent, with two patients toe-touch weight-bearing and one at 50 % partial weight-bearing (patient with lower BMI). These factors suggest potential challenges in bone healing, with one patient experiencing partial non-union requiring bone grafting and revision. It is worth noting that another patient at our institution with a periprosthetic distal femoral fracture also experienced minimal screw migration at 6 weeks postoperatively. This patient, a morbidly obese female, was not included in this report as the screw migration was minimal, and the fracture healed without requiring revision. However, her characteristics offer insights, suggesting that delayed bone healing could lead to prolonged micromotion, potentially causing screw migration.

Regarding implant-related factors, no obvious causes were found. In all cases, the distal locking screws, passing through the washer plate and the nail, migrated. The distal-most screw migrated in all three patients, and one also had proximal screw migration, on average within 12 weeks. To enable migration, there must be sufficient force to overcome the interface between the locking screw and the locking plate. Intraoperatively, torque limiters are used to secure the screws, and an extramedullary jig helps align the locking washer with the nail. It's possible for slight misalignment to occur or the torque required for proper seating exceeds the limiter's capacity. These issues could lead to increased micromotion and subsequent screw migration. Another factor to consider is galvanic corrosion due to the use of different materials (titanium and stainless steel), however the screw's carbon coating is designed to mitigate this. Additionally, this screw and nail may experience increased mechanical loads, although there are no available manufacturer biomechanical studies to confirm this at the time of this review.

Furthermore, surgeon experience and technique must be considered. Surgeon training and comfort with managing distal femoral fractures are important to consider, noting that both our surgeons are fellowship trained orthopaedic traumatologists. As mentioned previously, one of our surgeons expressed concern regarding possible soft tissue interposition at this junction during the revision. Despite the screw feeling well-seated with the torque limiter, even a small amount of tissue might play a role.

In conclusion, fixation of complex distal femoral fractures with an intramedullary nail and plate combination is a helpful tool in the management of these injuries. This novel system is promising, but not free of risk and potential for increased morbidity. While there is not a clear etiology for the screw migration observed in this report, it is likely due to increased micromotion at this interface. We must consider patient factors that could result in delayed fracture healing, implant factors that may lead to compromise of this screw-washer interface, and surgeon factors. Further studies should be performed to evaluate the biomechanical loads experienced by the screw with this combination, and strategies developed to mitigate this complication.

Financial support and sponsorship

None.

Informed consent

The patients were informed that data concerning the case would be submitted for publication and provided consent.

Ethics

The authors of the study have read the publisher's code of ethics and confirm adherence to these standards.

Funding

This study received no funding.

Patient consent statement

Consent was obtained from each patient for inclusion in this case report. Patient's were informed that the details of their case including the history of their injury, their characteristics including age and comorbidities, and clinical course would be included for publication. Patients were also informed images of their radiographs would also be included. There is no inclusion of patient identifiers as described by HIPAA.

Should the journal wish to obtain the formal consents, these can be provided, but are not listed here per the submission instructions from the Journal's “Guide for Authors”.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Daniel K. Haddad: Investigation, Visualization, Writing – original draft, Writing – review & editing. Jared Sain: Investigation, Visualization, Writing – original draft, Writing – review & editing. Sergei Pushilin: Conceptualization, Investigation, Project administration, Supervision, Writing – review & editing. Carlos A. Sagebien: Conceptualization, Investigation, Project administration, Supervision, Writing – review & editing.