Antimicrobial implants and bone allografts: new uses for old antibiotics

1.1 A historical perspective Bone grafting is the procedure whereby missing bone is replaced with material from either the patient’s own body (autograft), that of a donor (allograft) or with synthetics. The use of exogenous materials to reconstruct skeletal defects is not a new concept. Artiﬁcial, synthetic or natural substitutes, in the form of gold and silver plates and pieces of coconut shell, were found in cranial defects within prehistoric skulls [1]. As a matter of fact, bone was the second-ever transplanted tissue, with tooth being the first. While it is possible that these procedures were performed even earlier, the first documented bone transplantation was performed in 1668 by the Dutch surgeon Job van Meek’ren, who described the filling of a bony defect in a soldier’s cranium with a piece of skull from a dog [2, 3]. In 1879, some two hundred years later, Sir William MacEwen introduced allografting in a 4-year-old boy when he successfully replaced the proximal two thirds of a humerus with bone procured from other patients [4]. In 1915, Fred Albee, MD described autologous bone grafting where he used part of a patient’s tibia for spinal fusion. Bone grafting continues to be used extensively in medicine today. Even though the basic principles of bone transplantation have not changed significantly, the materials and techniques used have evolved tremendously. Multiple bone substitutes have been characterized over the last 50 years, the unique fibrous and mineral composite nature of bone is difficult to recreate, making bone allograft the most successful substitute. 1.2 Bone grafting in orthopaedics Orthopaedic and spine surgeons are frequently faced with bone defects that are unlikely to heal by simple fixation. Thus, bone grafting is commonly used in orthopaedics and maxillofacial surgery, particularly in cases of revision total joint arthroplasty, trauma, spine fusion and treated bone infections[5-12]. Moreover, the frequency of spine (and more often lumbar) arthrodesis surgery has grown substantially over the past decade [13] with approximately half of all bone grafting procedures performed today being related to spine fusion [14]. Typically the surgeon will remove the damaged disc and any arthritic areas, and place a bone graft between the vertebrae where it eventually fuses to the surrounding vertebrae stopping abnormal motion [15]. Over time, nerve function is restored therefore relieving pain, numbness, tingling and weakness. In orthopaedic oncology, bone grafts are also used extensively. Fortunately, prognosis has greatly improved in recent years thanks to enhanced imaging techniques, adjuvant chemotherapy and radiotherapy, leading to more successful limb-saving surgeries. Once bone tumors are resected, the use of large allografts in combination with fixation devices is the state of the art for reconstruction [16]. Femoral or acetabular bone loss is often seen after failure of total hip arthroplasties (THA), which account for approximately 10% of THA’s performed in the United States each year [18], making the restoration of bone loss of paramount importance to provide structural stability for the new components. [19] Thus, bone grafting has become a crucial part of both primary as well as revision total joint arthroplasty where maintaining proper alignment of the implants and establishing a stable bone-implant interface can be very challenging [17]. As a matter of fact, re-establishment of the bone stock is so critical that guidelines have been published to guide the surgical team in preoperative planning solely based on bone loss [20]. Selection of the proper bone graft from the vast variety of available graft constructs is then determined which is typically based on size, location, biology of the defect and whether structural support is desired.