Allograft Bone.

Allograft bone harvested from living or deceased donors as cancellous, or corticocancellous chips, has a wide application as an osteoconductive filler for metaphyseal defects typically at the proximal and distal end of the tibia (Table 49-1). McKee and coworkers⁹ report on a case series of six humeral nonunions treated with a combination of compression plate fixation and cortical onlay grafts. All six nonunions had united at a median of 3.4 months. Hornicek and coauthors¹⁰ report a series of nine humeral nonunions treated in a similar fashion; union was achieved in all patients at an average of 2.9 months. Haddad and researchers¹¹ report on a retrospective case series of 40 patients using cortical onlay strut grafts together with well-fixed prosthetic femoral stems; 39 of the 40 patients united. Herrera and investigators¹² report on distal radial fractures treated with external fixation and internal fixation together with cancellous bone grafts and concluded that allograft was a useful adjunct for treatment of unstable distal radial fractures. An article that prospectively compared autologous graft versus allograft, delivered at the Orthopaedic Trauma Association (OTA) in 2005, demonstrated that allograft was not equal to autograft. However, autograft did have associated donor morbidity.¹³ No Level I evidence supports corticocancellous allografts in reconstructive trauma surgery, but Level II and IV evidence does exist, as noted earlier.

Calcium Phosphate Synthetic Substitutes.

The calcium phosphate synthetic substitutes have been investigated as devices by the FDA and by industry over the last 8 years. Initial studies were done with critical defects in rats, sheep, and dogs. Subsequent biomechanical studies suggested that bioabsorbable calcium phosphate paste (α-BSM) in tibias was stronger than cancellous bone graft used to repair periarticular fractures¹⁴ (Fig. 49-1). Trenholm and coworkers¹⁴ illustrate that the initial stiffness was significantly better in the α-BSM group (calcium phosphate cement) as compared with autograft under a 1000-newton load. Russell and investigators¹ in a prospective, randomized, multicenter trial compared the treatment of subarticular bone defects in tibial plateau fractures with conventional autogenous iliac bone graft (AIBG) with α-BSM. One hundred nineteen acute closed tibial plateau fractures were prospectively enrolled, and randomization occurred at surgery with a 2:1 ration of the α-BSM to autogenous bone graft. Russell and investigators¹ found both a significant increase in graft-related adverse effects on the AIBG group, and a statistically significantly greater rate of articular subsidence in the 3- to 12-month period in the AIBG group (Fig. 49-2). Thus, Level I evidence supports the use of bioabsorbable calcium phosphate material, such as α-BSM, as the treatment of choice for subarticular defects in tibial plateau fractures.

FIGURE 49-1 Higher compressive strength of calcium phosphate bone substitute in a biomechanical study of tibial plateau fractures. α-BSM, subchondral defect filled with calcium phosphate bone substitute; cancellous bone, subchondral defect filled with cancellous bone chips; empty, repair of fracture with no filling of subchondral defect; solid, no defect in tibial plateau.

Adapted from Bajammal SS, Zlowodski M, Schmitz-Lelwicka AE, et al.: The use of calcium phosphate bone cement in fracture treatment: a meta-analysis of randomized trials. Hamilton, ON, McMaster University, 2007, unpublished.

FIGURE 49-2 Late collapse of the tibial plateau after fracture fixation using autogenous iliac bone graft (AIBG) to support the articular surface. A, Initial fixation of the Schatzker II fracture. B, Three months after surgery. C, Twelve months after surgery. D, Eighteen months after surgery, articular surface has collapsed after hardware removal at 1 year.

Three of these six studies in the meta-analysis by Bajammal and colleagues⁸ report significantly improved functional outcome scores with the use of calcium phosphate versus autograft, and in evaluating them separately, Chapman and researchers¹⁵ found a difference in functional repair in favor of the calcium phosphate group. Cassidy and investigators¹⁶ found significant greater scores representing better function in bodily pain, role physical, role emotional, social function, and mental health subdomains of the 36-Item Short Form Health Survey (SF-36). Zimmermann and colleagues¹⁷ found significantly better DASH (disability of the arm, shoulder, and hand) scores in distal radius fractures for the calcium phosphate group. Six of the studies also reported loss-of-reduction outcome, and calcium phosphate significantly reduced the incidence of loss of fracture reduction compared with controls.^{1,15,16,18–20} Thus, loss of fracture alignment was 48% less likely when calcium phosphate was used. For every 17 patients treated with calcium phosphate, one loss of fracture reduction could be prevented.⁸