Re-fracture after Osteosynthesis of Femoral Shaft Fracture in Osteopetrosis

Abstract

This study presents a case report of a 54-year-old female patient with osteopetrosis who experienced re-fracture after undergoing osteosynthesis for a femoral shaft fracture. The patient visited our emergency department for a right distal femur fracture. The patient had undergone surgery for a right femoral shaft fracture six years prior to this visit, at which time osteopetrosis was diagnosed at another medical facility. Following three years of postoperative care, successful osteosynthesis was achieved, and the surgical implant was removed. The re-fracture occurred at the site of the previous screw fixation which had not healed sufficiently. We performed an open reduction and internal fixation. We concluded that, during fracture surgery in patients with osteopetrosis, caution should be exercised as technical challenges like thermal injury may arise due to the hardness of the bone. Furthermore, careful evaluation is necessary when considering implant removal because of increased recurrent fracture risk.

Osteopetrosis, also known as marble bone disease, is a rare and heterogeneous group of inherited bone dysplasia characterized by diminished osteoclast activity¹⁾. Due to reduced bone resorption, this condition results in increased bone density. Increasing the susceptibility to fractures, osteopetrosis is well known for rendering bones more brittle. Several studies have reported difficulties in surgical treatment. However, in osteopetrosis cases, there is still ambiguity regarding fracture healing and the optimal timing for implant removal.

The aim of this study is to present a case report of a 54-year-old female patient with osteopetrosis who experienced a re-fracture post-osteosynthesis for a previous femoral shaft fracture. Through this case, we aim to discuss the challenges related to bone union and implant management in osteopetrosis. Ethical committee approval was received from the Institutional Review Board of Bucheon St. Mary’s Hospital, The Catholic University of Korea (approval No. HC21ZISI0137). We obtained prior written informed consent from the patient.

CASE REPORT

A 54-year-old female patient visited our emergency room for right thigh pain which developed without any traumatic history during yoga class. She underwent surgery for a right femoral shaft fracture six years previously and was diagnosed with osteopetrosis at another hospital.

After reviewing the patient’s medical records and radiographs from previous surgeries, it was determined that six years ago, a femoral shaft fracture occurred following a slip (Fig. 1A). Initially, the surgical team attempted a retrograde intramedullary nailing, but it was unsuccessful due to the sclerotic nature of the bone. Therefore, during the surgery, the surgical team altered their treatment plan and opted to stabilize the fracture using a plate (Fig. 1B). After three years, successful osteosynthesis was achieved, and the implant was subsequently removed (Fig. 1C). Prior to the emergency department (ED) visit, the patient did not experience any subjective symptoms following the removal of the implant for three years.

Fig. 1.

The initial X-ray revealed a fracture of right femoral shaft accompanied by the characteristic sclerotic features of the entire femur due to osteopetrosis (A). The fracture was fixed by plate and successful osteosynthesis was achieved (B). The implant was subsequently removed (C). The X-ray of the emergency department visit revealed a fracture of the right distal femur (D) and incomplete healing of the screw removal defect (arrows). Traces of intramedullary reaming from the previous surgery (arrowheads) were identified. An open reduction and internal fixation were performed using an anatomical plate and only cortical screws (E).

An X-ray obtained during the ED visit revealed a fracture of the right femoral shaft (Fig. 1D), accompanied by the characteristic sclerotic features of the entire femur due to osteopetrosis. The fracture observed on this occasion manifested in the distal region of the previous fracture. Moreover, evidence of a broken screw, incomplete healing of the screw removal defect, and traces of intramedullary reaming from the previous surgery were identified.

We performed an open reduction and internal fixation using an anatomical distal femur plate and screws. The fracture occurred at the site of the previous screw fixation, which had not healed sufficiently (Fig. 2). We observed a dense medullary structure due to osteopetrosis, as well as evidence of thermal injury from previous reaming for the retrograde intramedullary nail. Due to the femur deformity, the plate needed to be bent. Drilling proved to be extremely challenging and time-consuming, taking an average of 10 to 15 minutes per screw. The drilling site was irrigated with normal saline to prevent thermal injury. The use of locking head screws was initially attempted for a few holes, but the screw heads broke due to the dense bone structure. Consequently, we opted to use only cortical screws (Fig. 1E).

Fig. 2.

The fracture occurred at the site of the previous screw fixation, which had not adequately healed (arrows). A dense medullary structure due to osteopetrosis and evidence of thermal injury from a previous reaming for the retrograde intramedullary nail (arrowheads) were observed.

In microscopic analysis, a pronounced irregularity was observed in the thickened bony trabeculae, concomitant with the presence of hyaline cartilages (Fig. 3). The discernible reduction in marrow spaces is indicative of osteoclast dysfunction, a pivotal factor contributing to the observed histological changes.

Fig. 3.

Microscopic findings show thick irregular bony trabeculae with hyaline cartilages and reduced marrow spaces (H&E stain, ×40).

Two years after surgery, successful bone union was achieved. Although the initial plan was to retain the implant to mitigate the risk of re-fracture, concerns arose regarding potential infection in the vicinity of the implant during follow-up. Consequently, the implant was instead removed three years after surgery.

DISCUSSION

Osteopetrosis is well-known for rendering bones more brittle, increasing the susceptibility to fractures. The femur is the most commonly affected site for fractures in individuals with osteopetrosis²⁾. Conservative treatments such as plaster casts and traction have shown favorable clinical outcomes; however, they often require a longer hospitalization period^3-5). Considering this extended hospital stay, surgical treatment can be a preferable option for managing fractures in patients with osteopetrosis. Several authors have reported on the technical difficulties encountered during surgery due to the increased hardness of bone in patients with osteopetrosis^2,6,7). In this case report, plate fixation required a significant amount of time to achieve due to the excessive heat generated during screw drilling. Drilling took approximately 5 to 10 minutes per screw, and inserting the locking screws was challenging due to stripping in the hexagonal recess of the screw head. To address these technical difficulties, previous studies suggest that the use of a new drill bit and avoiding the use of locking screws can be viable options^2,8).

Notably, the thermal injury induced during the initial attempt at intramedullary nail fixation, which occurred five years ago, has not resolved (Fig. 1). Thermal injuries can impede fracture healing and increase the subsequent fracture risk at the affected site. Therefore, every effort must be made to avoid thermal injury during surgery. Although attempts at intramedullary nail fixation have been reported in patients with osteopetrosis⁹⁾, careful surgical planning is necessary to address any potential technical difficulties. For fracture fixation, an anatomical locking plate can serve as a suitable surgical option¹⁰⁾. However, in this particular case, the structural femoral deformation caused by osteopetrosis prevented a proper fit of the anatomical locking plate. It is crucial to carefully select the appropriate implant before surgery and prepare for potential bone deformities.

It has been previously reported that bone formation after fractures is relatively normal in patients with osteopetrosis¹⁾. However, due to osteoclast dysfunction , abnormal bone resorption can occur, which can prolong the fracture healing time⁴⁾. Landa et al.¹¹⁾ reported that, due to pathologic bone remodeling, patients who have osteopetrosis are predisposed to fracture nonunion. Yiğit et al.¹²⁾ reported that fracture union was delayed in nine pediatric osteopetrosis cases and the risk of post-operative infection was high. Amit et al.¹³⁾ reported a high complication rate, including nonunion (12%), infection (12%), and hardware failure (29%), following surgical treatment of fractures in patients with osteopetrosis.

Currently, there is no consensus on the optimal timing for implant removal in cases of osteopetrosis. In this case, the implant was removed three years after the initial fracture. However, even though two years had passed since the removal of the implant, a re-fracture occurred at the screw insertion site during stretching without any significant trauma. It is thought that unresolved tensile forces at the screw site caused the re-fracture to occur. While long bones in osteopetrosis are known to withstand compressive forces well, they are vulnerable to tensile forces due to their excessive strength. de Palma et al.¹⁾ also suggested that re-fractures can occur due to stress concentration at the site where screws were removed in osteopetrotic bone. Therefore, the decision to remove the implant in patients with osteopetrosis should be carefully evaluated.

In conclusion, as technical challenges may arise due to the hardness of the bone, caution should be exercised during fracture surgery in patients with osteopetrosis. Moreover, following implant removal, there is a risk of recurrent fractures due to diminished bone formation at the screw site. Therefore, careful evaluation is necessary when considering implant removal.

Funding Statement

Funding No funding to declare.