Introduction

No substitute has been proven to be better than autograft. Bone is formed by stem cells, and most arrive in the circulation and migrate to an injured surface of bone, attach, and begin to form bone.

The contribution of stem cells in the graft is thought to be small, but the scaffold of bone and its contained growth factors is ideal for the formation of new bone. William Macewen of Glasgow proved the ability of bone graft to regenerate a humerus, and this followed an exemplary series of studies and research.¹

Circulating monocytes also migrate through the endothelium of adjacent capillaries and become either alternatively activated (AA) macrophages or, under the influence of receptor activator of nuclear factor-кβ (RANK), osteoclasts. These three cell types are the basis of repair, bone regeneration, and remodeling.

The early hematoma forming around an injured bone surface (whether the result of your osteotomy or a fracture) immediately contains stem cells.² These multiply rapidly in the hematoma and are in the right place to contribute to healing.

Of note, only the first bleeding from an injured bony surface provides these cells, so the initial hematoma is particularly precious; it should not be thrown away but should be used to amalgamate your bone graft or mix into bone graft substitutes.

The osteoblasts are particularly sensitive to the mechanical environment.

Stability is defined as the maintenance of reduction and correlates with strength. Stiffness is a distinctly different parameter from strength and in fracture or osteotomy fixation is defined as the rigidity of the construct.

Osteoblasts are evolved for a rigid environment with cyclic strains of less than 1% to 2% of their length.

It is particularly useful for graft to be packed tight, for early callus to be bulky, and to limit cyclic movements or a rigid plate be applied while an osteotomy or cancellous fracture is healing.

Weight bearing is good for the maintenance of bone and muscle and the prevention of deep vein thrombosis, but the biological plate of callus or the internal or external fixation must be able to sustain these loads, otherwise weight-bearing loads will need to be limited.

Flexible fixation and early cyclic movements are appropriate for the bulky callus formation needed in diaphyseal fractures.³

This external callus is rarely needed in the metaphysic or epiphysis where there is sufficient bulk and well vascularized cancellous bone that will allow rapid union. John Charnley took biopsies at 6 weeks following knee arthrodesis to prove that union is achieved in this time.⁴

Taking Autograft

Cancellous Graft

Before surgery, and even if the possibility is remote, explain to your patient that he or she may need a bone graft and that this will be taken from the iliac crest.

It is useful to know if the patient always sleeps on one side, as you should warn the patient that the donor site will be tender for some time.

When possible, a small sandbag behind the hip is useful.

Prepare the area of the iliac crest with antiseptic, and use adherent paper drapes with an adherent plastic sheet to prevent the drapes from moving around while you are operating on the knee.

Use a skin incision that ends 2 cm from the anterior superior iliac spine to avoid cutting the lateral cutaneous nerve of the thigh. This happens in 10% of cases, and it is of note that in 10% of cases the nerve passes through the bone of the iliac crest.

If there is no spinal anesthetic, it is useful to infiltrate bupivacaine or a similar long-acting anesthetic in the tissues around your incision at this time to prevent painful stimuli reaching the brain.

Cut the fibers of gluteus maximus as they arise from the lip of the iliac crest.

Hemostasis will be needed at the posterior part of your incision.

Use a saw to cut the outer table of the iliac crest and then a broad osteotome to lift a lid. This exposes the cancellous layer (see Fig. 15-1, A-C).

FIGURE 15-1 A, Exposure of the iliac crest. A slice of the iliac crest has been raised by an oscillating saw, although a sharp osteotome is an alternative. B, Exposure of the iliac crest. Cadaver image. C, Section through A-A’. Skin and deep fascia have been incised and the iliac crest osteotomized to expose the internal cancellous bone.

Use a sharp, long-handled curette to remove cancellous bone from between the cortical sheets (Fig. 15-2).

FIGURE 15-2 The cancellous bone has been removed in scoops using a suitable sharp spoon.

Keep the hematoma that gathers in the wound with your graft.

Corticocancellous Strips

Expose the iliac crest as explained earlier. Use the saw to make an initial vertical cut, and then use a narrow and thin osteotome or chisel to cut thin vertical strips. A hammer is actually safer for controlling the instrument, as it avoids plunging that can occur if an osteotome is pushed by hand (see Fig. 15-3, A-B). The saw can also be used to cut the strips.

FIGURE 15-3 A, The ilium has been more widely exposed by stripping off the origin of gluteus maximus. Retractors are holding the muscle down. A sharp osteotome is being used to cut strips of corticocancellous graft. B, Cadaver image of the harvest of corticocancellous grafts.

Tricortical Graft

Expose the iliac crest as descried, and then strip all periosteum from the bone to be taken; otherwise it will not expand in the months and years following incorporation. Macewen described periosteum as the limiting membrane of bone. He undertook many studies on bone and was the first person to use allograft successfully.¹

Use a saw to cut an accurately sized block including both inner and outer walls of the iliac crest. There is a risk of herniation through the iliac crest, so for large blocks of bone greater than about 4 × 4 cm I would advise suturing a suitable membrane such as one used for inguinal hernia repair across the inner table to reduce this risk.

For closure after harvest of the different bone grafts described earlier in the text, follow these steps:

• Close the lid earlier raised by suturing the inserting fibers of external oblique to the gluteus maximus origin (Fig. 15-4).

• Place a suction drain outside the lid. If placed inside the bone, it will simply extract fresh blood in large volumes.

• Consider using a local anesthetic catheter for continuous infusion, as bone donor sites are very painful.

FIGURE 15-4 Closing the muscle fascia will restore the iliac crest and maintain a normal contour. Place a drain outside this layer; otherwise excessive amounts of blood can be aspirated. Consider wound infiltration with a local anesthetic or place a catheter or a pump that can provide a continuous infusion of local anesthetic under the control of the patient.

Percutaneous Techniques

Small amounts of graft are taken most conveniently and with less postoperative pain using systems such as the Precision Bone Grafting System (Kaltee Pty Ltd, Edwardstown, SA, Australia) (see Fig. 15-5). A small incision is made over the iliac crest 2 cm posterior to the anterior superior iliac spine. A trocar and cannula is provided as means of excluding soft tissues.⁵

Figure 15-5 The Precision Bone Grafting System allows a percutaneous collection of small grafts. The cannula protects surrounding muscle and a circular handle (not shown) allows the graft to be cut. The blunt trocars provide a means of removing the plugs of graft. Made by Kaltec, www.kaltec.com.au.

Attach the large circular handle to the hollow mill of appropriate diameter, and direct it downward and inward in the plane of the pelvis.

It is useful to have a plastic model of the pelvis in theatre if you are unsure of the plane of the pelvis. Alternatively, slip a spike-type retractor down the outer table of the pelvis to ensure the correct orientation.

Rotatory movements of the mill will allow the device to advance and graft to be obtained.

Take care not to plunge the device into the pelvis.

Allograft: Fresh Frozen

Allograft bone will carry a small risk of infection, despite all the screening measures used. All nonautologous graft does, however, carry the advantages of avoiding the complications of an autologous graft.⁶

Allograft: Freeze-Dried Graft

This may be useful as a filler or expander of cancellous graft, but it is weak. Better and stronger bone graft substitutes are now available. Porous or solid hydroxyapatite can be used depending on the strength required.

Autogenous Osteochondral Grafts

These can be taken as Mosaic or the longer OATS plugs (see Chapters 5 and 6). Different systems are available, but choose a device that allows insertion without impaction of the cartilage.

Apoptosis of chondrocytes results from high impaction forces. Apoptosis also follows blunt cutting of the edges, so it is important to use sharp instruments on cartilage edges that will remain.

Bone can be replaced, as well as overlying cartilage loss, with these techniques.

Allograft: Osteochondral Graft

Those grafts require careful harvesting and regulatory control. It is possible to keep 67% of cells alive for 44 days if the graft is kept sterile.⁸ Alternatives include freezing of the graft in sequential steps with increasing concentrations of antifreezing agents such as dimethyl sulfoxide (DMSO). This provides greater flexibility in timing of procedures and can also maintain a high proportion of viable chondrocytes. Close liaison with a tissue bank is necessary for these options.

Bone Graft Substitutes

These are numerous in composition, and handling has greatly improved. Table 15-1 lists only a selection.

TABLE 15-1 Examples of Bone Graft Substitutes

There are few reports of histology or of clinical trials against autogenous bone graft demonstrating successful incorporation of bone graft substitutes, but even the simple calcium sulphate is in widespread use.

We use Allogran-N for load bearing in impaction grafting,⁷ geneX for tibial, and femoral tensegrity osteotomies,⁹ and for cultured stem cells in nonunion.¹⁰ Stimulan is used with added antibiotic for chronic osteomyelitis.

Autologous bone graft is now only used for osteochondral defects in combination in autologous chondrocyte implantation.