Stabilization

Keywords : Spinal fusion Donor site

Bone Grafts Recipient site

Autograft Osteoinduction

Allograft Osteoconduction

Callus Instrumentation

Stabilization procedure of the spine is usually synonymous to "spinal fusion" of the diseased segment of the anatomy. Trauma, congenital defects, infection, tumors and ageing can create instability to spine segments that can compromise the spinal cord and its roots or simply produce severe recalcitrant pain. By fusing and stabilizing the affected segments the desired results are often achieved.

The most common way of fusing the spine is choosing the appropriate "donor site" of the body where we can harvest bone grafts. The pelvis, the fibula and the rib are usually good sources of autografts. Autografts are the preferred choice because they come from the same patient and rejection is uncommon. However they require a separate surgical site for the donor source. It is sometimes limited especially in children.

Cadaveric grafts if available are called allografts. Tubular bones like the humerus, femur and tibia are good allografts. From the word itself it comes from dead donors. It requires special processing to reduce rejection from the "recipient site." It has to be specially stored in special freezers. When large segments are needed, cadaveric allografts are very useful. It requires special handling making it a bit expensive.

Autografts and allografts induce osteoinduction and osteoconduction to fuse the desired segments we want to treat. Osteoinduction is the capacity of the graft to stimulate the stem cells of our own body to produce "callus" or new bone formation. Osteoconduction is the capability of bone grafts to bridge the callus by acting as biologic templates or mesh to achieve fusion from one bone segment to another.

"Allografts"

"Autografts"

The iliac crests of the pelvis is the most frequent source of bone grafts. It is the favorite donor site of many surgeons because of its accessibility during posterior spine surgery. The quality of bone taken from this area produces very good spinal fusion. The only drawback is a separate surgical dissection to harvest the autografts.

Spinal fusion can be done as a stand-alone procedure. Bone grafts are placed over bony structures of the spine so that the callus would fuse segments of the spine. In cases where there is gross instability and when correction has to be done, surgeons might suggest adding spine implants loosely termed by many as "instrumentation." Latter are metallic implants or composite materials that secure spine segments rigidly.

Stand-alone Fusion

Instrumented Fusion

Spinal fusion is usually done either over the anterior column or the posterior column. There are cases when your surgeon might have to suggest doing both anterior and posterior spinal fusion. Posterior fusion involves applying your bone grafts over the facets and transverse processes. Anterior fusion involves doing discectomy and inserting bone grafts in-between vertebral bodies to fuse the segments. Various combinations of stand-alone or instrumented techniques can be performed to suite specific spine problems of patients.

Posterior fusion

Posterior and Anterior fusion

Posterior fusion

Posterior and Anterior

fusion

A.

B.

A. Shows a long segment bone graft spanning an area where a vertebrectomy was performed. The bone graft is stabilized by a plate and screw system. B. Shows a titanium cage filled with cancellous bone graft. Titanium cages are sometimes used if long segment bone grafts are not available and if we need maximum strength to span a vertebrectomy. Plates and screw systems are also utilized to stabilize titanium cage mesh.

In certain conditions, stabilization by bone grafting has to be augmented with spine implants to maintain corrections of deformities. Bone grafts would usually undergo a stage whereby its intrinsic properties weaken significantly because it looses its blood supply from where it was taken or harvested. During this critical stage of weakness, spine implants prevent the possibility of collapse.