Sandwich Allograft for Long-Bone Deformity Correction in Bone Dysplasia

The "sandwich allograft" technique is indicated for correction of long-bone deformity in patients with osteogenesis imperfecta (OI) or another bone dysplasia. The external press-fit created by the large surface area of the allograft provides circumferential stabilization and introduces normal collagen to the long-bone nonunion site. Split allografts sandwich around the bone to promote stability and healing and to correct the deformity. This technique addresses the main issues in treating nonunion sites in patients with OI. First, osteogenesis has plateaued at the nonunion site, and this technique is osteoconductive. Second, traditional fixation techniques are not effective, as plates and screws do not achieve good fixation in brittle bone, and the circumferential fit of the allograft provides a different means of stabilization. Finally, the allograft bone is structurally stronger than the host OI bone.

Careful patient selection and preoperative planning are critical to ordering allograft with the correct length and width, as well as the correct type of internal fixation. The nonunion site is exposed circumferentially, and the periosteum is elevated. In instances in which there is previous intramedullary fixation, the implant should be assessed for any migration or breakage, which would warrant removal. New intramedullary fixation is then performed to align the bone ends at the nonunion site. Fresh-frozen allograft was selected in the example case because it is thought to be more osteoinductive. The allograft is then halved longitudinally and its ends are contoured and trimmed. Allograft ends are also contoured to fit the fracture proximally and distally. The native bone is compressed at the nonunion as much as possible. The 2 allograft halves are then sandwiched on opposing sides of the nonunion site, surrounding the nonunion. They are held with use of a Verbrugge clamp and compressed with use of cortical screws. Finally, during closure, the previously elevated muscle envelope apposes the new construct.

Nonoperative treatment of OI varies with the severity of the disease and the functional status of the patient¹. Age should also be considered, as fractures occur most often in early childhood and fracture rates decline after the child reaches skeletal maturity². Discontinuing contact sports and performing physical therapy and rehabilitation can help to both avoid and treat fractures. Operative treatment includes the insertion of intramedullary rods for fracture treatment and deformity correction. Rigid plate constructs are typically avoided to prevent osseous resorption from the stress shielding³. However, the use of a unicortical locking plate has been shown to be an effective supplement to intramedullary rod fixation⁴.

Stabilization of fractures in patients with OI is challenging because of poor bone quality, which commonly results in nonunion. The traditional treatment of nonunion, which includes plates and screws, does not achieve good fixation in cases with brittle bone. This makes the allograft sandwich another treatment option with specific advantages for long-bone nonunion.

The allograft sandwich procedure can successfully treat nonunion in patients with OI. Puvanesarajah et al. treated 13 nonunions with the allograft sandwich technique, with 12 nonunions healing during the study period². The only nonunion for which treatment was unsuccessful did eventually show healing after 1 revision procedure. There were no infectious or neurologic complications reported in the cohort. Potential complications include refractures and screw prominence that may cause pain or irritation.

The procedure is most applicable to treating nonunion of long-bone fractures in patients with low bone quality related to underlying disorders such as OI.Preoperative radiographs must be thoroughly evaluated for the extent of the nonunion, state of the implant from any previous fracture interventions, and nearby anatomic structures that can make fixation techniques challenging.The allograft sandwich should cradle most of, if not fully encircle, the nonunion site.At least 4 cm of the proximal and distal ends of the nonunion should be covered.Apposition of the fracture site may be challenging if the native bone has a small diameter.

BMP = bone morphogenetic proteinIM = intramedullaryOI = osteogenesis imperfectaORIF = open reduction and internal fixation.