Can Calcium Phosphate Bone Cement Aid In Hallux Valgus Repair?

Kerry Zang, DPM

Over the years, hallux valgus repair has evolved from simple bunionectomies to complex and multiple osteotomies. The keys to a successful outcome are the realignment of the structural abnormalities and a stable postoperative environment.The former is important for proper function and the latter facilitates the healing process.
With this in mind, let us take a closer look at the potential benefits of utilizing calcium phosphate bone cement (OsteoVation, OsteoMed Corp.) for filling voids in metatarsal osteotomy-type bunionectomies to achieve a favorable surgical outcome.
Surgeons have used polymeric cement spacers, such as polymethylmethacrylate (PMMA), to help salvage failed metatarsophalangeal joint (MPJ) surgery but primarily as a means of antibiotic drug delivery.1
While the polymeric cement offered structural support of the osteotomy site, Myerson, et al., never intended to allow it to remain on site. While the use of PMMA is common, researchers have observed that it can elicit an inflammatory foreign body
reaction.2,3 After allowing three to five weeks for full elution of the antibiotics, patients required a second surgery to replace the PMMA spacer with an osteoconductive autogenous iliac crest bone graft.

What Are The Advantages To Bioactive Cements?

In looking for an alternative to polymeric cements such as PMMA, surgeons are currently applying bioactive calcium phosphate-based cements in a variety of indications ranging from craniomaxillofacial reconstructions and sternectomies to distal radius fractures.4,5 These biomaterials are an attractive alternative to PMMA because they cure into an osteoconductive carbonated apatite, which happens to be the same mineral component of bone.
Calcium phosphate cements are also preferable over the current practice of filling voids with autogeneous iliac crest grafting and/or cadaveric cancellous bone chips.They require no secondary
surgical sites and do not pose a potential risk for disease transmission.6
Furthermore, calcium phosphate cements hold in place the necessary internal fixation devices, such as screws and pins, and provide a platform to stabilize the osteotomy site. For all these reasons, calcium phosphate cements are expected to provide an environment for faster and more predictable healing.
These biomaterials have several notable characteristics that make them especially useful in hallux valgus repair when one utilizes metatarsal shaft osteotomies. The viscous yet pliable consistency of the cement allows one to place it within the osseous void. Surgeons can also use it to fill even small voids, crevices and defects.
This particular calcium phosphate bone cement, OsteoVation, hardens insitu approximately 10 minutes after placement. The subsequent stable platform, along with surgical hardware, contributes to the structural integrity of the osteotomy site.Approximately 80 to 95 percent of the cement converts from a calcium phosphate-based material to a carbonated apatite within 12 hours after placement. It reaches its maximum mechanical strength after a 24-hour period of postimplantation.7,8
Furthermore, in an in vivo study performed by Frankenburg, et al., mechanical tests revealed that a comminuted fracture of canine distal tibia treated with calcium phosphate cement reached nearly 100 percent of its original torsional strength by
eight weeks.9 No fibrous tissue was present between the bone and the cement, nor was there any acute inflammatory foreign body response. Histological evaluation revealed direct bone apposition to the cement and rapid restoration of the cortex. The resulting carbonated apatite was a biocompatible, osteoconductive material that remodeled via normal osteoclastic cell-mediated activity and was replaced, in time, by the host bone.

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