A new synthetic bone hemostasis material made of water-soluble alkylene oxide copolymers recently became commercially available [41]. The use of a water-soluble synthetic wax for bone hemostasis comprised of similar alkylene oxide copolymers was first described by Wang et al. [40]. These copolymers have a long history in the medical and pharmaceutical fields [13, 40]. They are considered inert because they are eliminated from the body unchanged without being metabolized [10, 16, 21]. Because these copolymers are hydrophilic, they stick well to wet surfaces and thus are well suited for bone hemostasis.

All procedures were approved by the Institutional Animal Care and Use Committee at the Medical University of South Carolina. Twenty-four female New Zealand White rabbits (2.75 ± 0.025 kg) were randomly assigned to one of three groups (n = 8 per group). Buprenorphine (0.02 mg/kg) was administered before surgery; the rabbits were anesthetized using 30 mg/kg ketamine, 5 mg/kg xylazine, and 1 to 3 mg/kg atropine intramuscularly and maintained on isoflurane after intubation. Surgery was performed using standard aseptic techniques. Animals from each group were included at each laboratory session with the same operators performing all surgeries. The rabbit’s right hind limb was shaved and the skin cleaned with a solution containing 7.5% povidone-iodine and 70% isopropyl alcohol. Without the use of a tourniquet, a 2.0-cm anteromedial incision was made to access the proximal tibia. A cortical window measuring 4 mm × 12 mm was created at the anteromedial facet of the proximal tibia using a 4.0-mm drill bit and a microoscillating saw under constant irrigation. In the study groups, 0.25 g of material was applied to the edges of the cortical bony defects. An inoculum of Staphylococcus aureus strain ATCC-29230 (2.5 × 10⁴ colony-forming units in 0.1 mL saline) was introduced into the intramedullary canal through the defect. The organisms had been grown overnight in tryptic soy broth at 37° C assuring confluent growth, washed twice in phosphate-buffered saline, and resuspended in a balanced salt solution. The plate count method was used to confirm consistent bacterial inoculum load for all defects. The wound was closed in layers using monofilament sutures and the incision was covered with sterile dressing. After surgery, the animals were given buprenorphine (0.02–0.05 mg/kg) as needed every 12 hours.

Four weeks after surgery, the animals were euthanized using an intravenous overdose of pentobarbital. Radiographs of the tibias were taken. The tibias were exposed through the original incisions under sterile conditions, and bone was swabbed for bacterial culture and typing. The tibias were harvested and cut into two segments using an oscillating saw through the center of the original cortical defect. The upper part of the bone explant was cultured. Cultures were grown overnight in 5 mL of tryptic soy broth media. A 1-mL aliquot of the culture was removed, centrifuged to remove the growth medium, and diluted by 10⁶ with phosphate-buffered saline. One milliliter of the diluted culture was plated on standard agar plates and colonies were counted after 24 hours. Growth was graded as follows: no growth; less than 20 colonies were graded light growth; 20 to 80 colonies were graded moderate growth; and more than 80 colonies were graded heavy growth.

The lower part of the tibial bone and surrounding soft tissue were fixed in 10% buffered formalin, decalcified, and processed for paraffin sectioning. Sections were examined microscopically after hematoxylin and eosin staining. Image scanning of sections was performed using a ScanScope XT System (Aperio Technologies Inc, Vista, CA) at ×20 magnification courtesy of the Tissue Procurement Core Laboratory (UCLA School of Medicine, Los Angeles, CA). All radiographs and sections were viewed independently by two observers (TW, XW) who were blinded to the results.

Cultures of the swabs and bone segments were positive for the inoculated strain of Staphylococcus aureus in 100% of the bone wax-treated specimens. In the polymer group and the control group, cultures from the animals with radiographic evidence of osteomyelitis were positive, and one additional animal of the six with normal radiographs in each group had a positive culture; five animals in each group had no evidence of infection.

In several animal studies, bone wax was shown to increase infection rates and impair the ability of bone to clear bacteria [22, 28, 31]. In a rabbit study, the cancellous bone of the iliac crest was inoculated with Staphylococcus aureus followed by placement of either bone wax or a steel rod. The authors concluded that bone wax impaired the ability of cancellous bone to clear the infection [22]. In a rat tibia model, the presence of bone wax reduced the amount of bacteria needed to produce Staphylococcus aureus osteomyelitis by a factor of 10,000 [28]. In a retrospective clinical study, infection rates after spinal surgery were assessed during a 3-month period [15]. Surgical site infections occurred in six of 42 cases (14.3%) in which bone wax was used and in only one of 72 cases (1.4%) in which it was not used.

There have been no clinical reports or in vivo studies published to date reporting complications or infections with the use of the polymer material evaluated in this study. One in vitro study involving one of the component polymers (poloxamer 188) showed coating silicone wafers with the polymer reduced bacterial adhesion and was more effective than iodine in reducing Staphylococcus epidermidis colony counts on silicone surfaces [25]. In our study, the use of the polymer material considerably reduced the infection rate compared with the use of bone wax, and it had no effect on the infection rate compared with the untreated controls.

The propensity to interfere with bone healing is a well-known property of bone wax [41]. In the 1924 edition of Carson’s Modern Operative Surgery, the use of bone wax is recommended not for bone hemostasis, but to prevent bone healing and to create a pseudarthrosis as part of an arthroplasty [39]. In various animal studies, bone wax subsequently was shown to inhibit osteogenesis and prevent bone union [2, 5, 8, 11, 12, 14, 19, 20, 29, 32, 36, 40]. Bone wax remains as a foreign body at the site of application indefinitely, and it is known to cause intense foreign body reactions characterized by giant cells, plasma cells, and fibrous tissue [3, 22, 28, 33, 34]. Similar findings also were reported in humans [8, 35, 37]. Bone wax is believed to interfere with osteogenesis, and osteoblasts have been shown to be absent in the presence of a thin layer of bone wax [2]. Suggested appropriate uses for bone wax are prevention of osteosynthesis and osteophyte formation [2, 35].

The inflammatory reactions to bone wax may be a source of postoperative pain. One report described seven patients with intractable pain after the use of bone wax in foot surgery [4]. Five of the patients were pain-free after the bone containing the inflamed bone wax was resected. Clinical reports describing adverse inflammatory reactions to bone wax are common [3–7, 9, 17, 23, 24, 26, 38]. Reactions consist mainly of pain and swelling, often exacerbated by infection.

The alkylene oxide copolymer material used by Wang et al. showed new bone grew within 10 days into a rat femur defect with the polymer and the untreated controls [40]. In contrast, the defects filled with bone wax showed no bone formation 48 days after implantation. The polymer material dissolved from the site of application within 24 to 48 hours, allowing the early phases of bone healing to occur [40]. The polymer material used in our study dissolves in the body and has been shown not to interfere with bone healing or cause inflammation in a sterile environment [41].