Bone Grafts for Back Surgery

One of the basic components for a spinal fusion surgery is a bone graft. Bone grafts are used to stimulate bone healing and to offer support to the spine by filling gaps between two vertebrae (spinal bones). Thousands of bone grafting orthopedic procedures are performed in the United States each year.

Why use a bone graft?

The most common reason to use a bone graft is for promotion of bone healing. The graft works as a “fertilizer” that speeds up the healing process. When bone is placed around a fracture or fusion site, chemicals from the bone stimulate the bone to heal. The graft is removed from the patient’s own body, so living osteocytes (bone cells) survive and continue making new bone when transferred.

Another reason for using a bone graft is for structure. Pieces of bone can be utilized to fill in gaps between two vertebrae, which gives the spine support. The surgeon may have to remove a portion of disc or vertebra due to degeneration or damage. The bone graft then is placed in the area to hold the spine together. Over time, the bone graft is remodeled and replaced by new bone growth.

How is the bone graft obtained?

Bone taken from the patient is called an autograft, whereas bone taken from another person or a cadaver is called an allograft. With the autograft procedure, the surgeon harvests the bone right before the spinal fusion surgery. A small incision is made over the hip (iliac crest), and the surgeon surgically removes a small piece of the bone to be used.

With the allograft procedure, the bone is removed from a donor and placed in a bone bank. The bone bank then will sell the allograft to the hospital where your surgery is to be performed. The allograft does not contain living cells, but it does have the same chemicals that stimulate the growth of new bone. The surgeon can add a bone-growing protein to the site to improve bone healing.

When is the allograft preferred?

A donor graft (allograft) is useful when the surgery requires more bone graft that the patient’s body can supply. Many major spinal fusion surgeries require a lot of bone graft, so the surgeon may use allograft material along with the autograft.

Does artificial bone graft exist?

Yes, and some options include:

• Sea coral – Derived from the ocean, sea coral has been used in clinical studies as a bone graft substitute.
• Electrical current – This helps with bone growth, so during the first weeks following surgery, the doctor may use an electrical stimulation device.
• Demineralized bone matrix (DBM) – This is a type of allograft developed from cadaver bones. The calcium of the bone is removed and turned into a gel, putty, or sheet, which is added to improve fusion.
• Bone morphogenic protein (BMP) – This is additional material that is added to enhance bone growth at the fusion site. Background

What determines the bone graft choice?

The surgeon will choose a bone graft based on the goal of achieving a successful fusion. The tree most important properties are osteoinductivity, osteoconductivity, and osteogenicity. Osteoinductivity is the ability of the bone graft to develop into new cells that differentiate into osteocytes and osteoblasts, which produce new bone. Osteoconductivity is the ability to allow bone vascularization and growth within the graft. Finally, osteogenicity is the presence of bone cells that maintain bone growth.

Iliac crest harvest has been considered the “gold standard” at producing successful arthrodesis of the lumbar spine but is also associated with many donor-site morbidities. Many alternatives have been used to avoid iliac crest harvest, including autologous bone from other donor sites, allogeneic bone, ceramics, and recombinant human bone morphogenetic proteins (rhBMPs). This review will highlight the properties and preparations of these graft types and their potential complications and reported clinical efficacy.

Methods

A Medline search was conducted via PubMed by use of the following terms in various combinations: lumbar fusion, freeze-dried allograft, fresh-frozen allograft, autograft, iliac crest, demineralized bone matrix, rhBMP-2, rhBMP-7, scoliosis, bone marrow aspirate, HEALOS, coralline hydroxyapatite, beta tricalcium phosphate, synthetic, ceramics, spinal fusion, PLF, PLIF, ALIF, and TLIF. Only articles written in English were assessed for appropriate material. Related articles were also assessed depending on the content of articles found in the original literature search.

Conclusions

Although iliac crest remains the gold standard, reported success with alternative approaches, especially in combination, has shown promise. Stronger evidence with limited sources of potential bias is necessary to provide a clear picture of their clinical efficacy.

Resources

Vaz K, Verma K, Protopsaltis T, et al. (2010). Bone grafting options for lumbar spine surgery: a review examining clinical efficacy and complications. SAS Journal, 4(3), 75-86.