Can Calcium Phosphate Bone Cement Aid In Hallux Valgus Repair?

Author(s): 
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.

A Step-By-Step Guide To The Surgical Procedure

The integration of the calcium phosphate cement into the surgical procedure for metatarsal osteotomy-type bunionectomies is as follows.
After resecting an appropriate amount of bone from the distal aspect of the first metatarsal and preparing the void in the medullary canal, start preparing the OsteoVation calcium phosphate cement. The preparation period involves one minute of mixing followed by a few minutes for filling the syringe.
Distract the osteotomy to expose to the shaft of the medullary canal. Using a blunt, 14-gauge needle, fill the void with the OsteoVation bone cement. The use of a needle allows one to deliver the calcium phosphate cement in a directed and controlled manner.
Once the cement is in, continue the procedure with K-wire fixation. Following a five-minute setting period, proceed with compression screw fixation and stabilization. At this point, the
cement has hardened sufficiently to allow screws to gain a sufficient hold into the material. After checking the alignment of first ray and that the patient has achieved range of motion, avoid movement of the site to allow the cement to cure further and create a strong interface with the bone.

A Closer Look At The Post-Op Results

The clinical results after utilizing OsteoVation in osteotomy-type hallux valgus repairs have been remarkable. I have used OsteoVation in conjunction with these procedures on over 150 patients.
Typically, patients who undergo osteotomy-type hallux valgus repair are in a cast or walker boot for six to eight weeks. With OsteoVation, my patients are out of the walker boot in approximately two weeks and in an athletic or supported sport sandal within three weeks. Furthermore, female patients are back in low-heeled casual shoes at six weeks and dress shoes by 10 to 12 weeks.They are reporting minimal pain and I have observed significantly less swelling.
I believe we can directly attribute these results to a strong bone/cement interface and the creation of a stable osteotomy site with the calcium phosphate cement. The OsteoVation bone cement essentially functions as a grout in the medullary canal that prevents intraosseous hematoma formation.
As a result of the strong interface and stable osteotomy, as well as a reduction in postoperative edema, I can be more aggressive in achieving early range of motion of the first MPJ complex.This in turn facilitates even less swelling, greater range of motion and a shorter recovery period.

In Conclusion

As a result of the mechanical similarity of OsteoVation calcium phosphate bone cement to natural bone, calcium phosphate cement provides skeletal stabilization and is able to sustain compressive loads when one uses it to fill voids within the medullary canal of the first metatarsal.The hallux valgus repair procedure is not hindered in any way as surgeons may use the material in conjunction with internal fixation devices, screws, pins and plates.
The use of calcium phosphate cements removes the risk of potentially harmful complications resulting from polymeric cements, autogenous iliac crest grafts and cadaveric cancellous bone chips. This is due, in part, because the carbonated apatite which the calcium phosphate bone cement converts into is an osteoconductive biomaterial that remodels itself via normal cell-mediated activity and is ultimately replaced by living host bone.
The use of a calcium phosphate bone void filler cement to supplement internal and external fixation devices is effective in maintaining the reduction of deformities by providing increased stabilization, and ultimately a better clinical outcome.

Dr. Zang is a Diplomate of the American Board of Podiatric Surgery and a Fellow of the American College of Foot and Ankle Surgeons.

Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons, and is board certified in foot and ankle surgery. Dr. Burks practices in Little Rock, Ark.

For a related article, see “How To Treat Severe Bunions” in the August 2005 issue of Podiatry Today.

 




References:

1. Myerson MS, et al. Staged arthrodesis for salvage of the septic hallux metatarsophalangeal joint. Clin Orthop Relat Res. (307):174-181, 1994.
2. Willert HG, et al. Osteolysis in alloarthroplasty of the hip.The role of bone cement fragmentation. Clin Orthop Relat Res. (258):108-21, 1990.
3. Goodman S.Wear particulate and osteolysis. Orthop Clin North Am. 36(1):41-8, 2005.
4. Larsson S. Cement augmentation in fracture treatment. Scand J Surg. 95(2):111-8, 2006.
5. Muehrcke DD, et al. Calcium phosphate cements to control bleeding in osteoporotic sternums. Ann Thorac Surg. 84(1):259-61, 2007.
6. Coughlin MJ, et al. Hallux valgus and first ray mobility.A prospective study. J Bone Joint Surg Am. 89(9):1887-98, 2007.
7. Yetkinler DN, et al. In vitro and In vivo evaluation of two calcium phosphate cements. Orthopaedic Research Society Transactions. 29:1520, 2004.
8. Lin, J et al. Improved flexural strength of a novel craniomaxillofacial cement. Orthopaedic Research Society Transactions. 30:1029, 2005.
9. Frankenburg EP, et al. Biomechanical and Histological Evaluation of a Calcium Phosphate Cement. J Bone Joint Surg Am. 80:1112-24, 1998.

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