Adult spinal deformity can be principally divided into problems of the sagittal plane, problems of the coronal plane, and problems with both planes. The sagittal plane divides the body vertically into left and right sides. The coronal plane is also called the frontal plane and divides the body front (anterior) and back (posterior). See Figure 1 below.
Scoliosis, kyphosis, and sagittal imbalance are types of spinal deformity. Scoliosis is a three-dimensional deformity that affects the coronal, sagittal, and axial planes. Most people think of it as principally being a coronal plane deformity. The coronal plane deformity is represented on Anterior/Posterior (AP) or Posterior/Anterior (PA) spine x-rays (radiographs). Kyphosis and sagittal imbalance represent the sagittal plane. Sometimes patients will have co-existent sagittal problems such as spondylolisthesis.
The causes of spinal deformity are multifold. As stated, some deformities are idiopathic with superimposed degenerative changes and others are de novo lumbar curves. A deformity with an idiopathic etiology (cause) is initially precipitated by idiopathic scoliosis. With time and aging, the discs involved in the deformity undergo degenerative changes.
For instance, in a lumbar curve, the majority of the lumbar deformity will quite commonly exist between the 11th thoracic and 3rd lumbar vertebrae (T11-L3). If the patient had a surgery as a teenager, the surgery would probably have been an anterior fusion and instrumentation from T11 to L3. Left untreated, by age 45 or so, the lumbar curve would develop a rotatory subluxation (one vertebra slides off another vertebra in both the coronal and axial planes) at L3-L4 with degenerative changes, a fixed tilt at L4-L5, and degenerative changes at L5-S1. The surgery often requires fusion down to the sacrum.
Indications for Spine Surgery
Progressive deformity, increased back and leg pain or particular concern about the magnitude of the deformity is the tidemark for surgical treatment. Certain developments trigger surgical treatment intervention, such as sagittal or coronal imbalance, spinal stenosis, or increased pain.
Adult scoliosis differs from teenage scoliosis. With adult scoliosis, decisions about surgical treatment are based on a combination of factors that are considered by both the surgeon and the patient. In teenage scoliosis, the severity of the curve (degree of abnormal curvature) is often the main determining factor.
Types of Spine Surgery
In most cases, thoracic curves can be treated with a one-stage posterior fusion and instrumentation.
At times, lumbar curves with substantial degeneration are best treated with fusion to the sacrum, usually anterior and posterior. Posterior surgery includes bone grafting and fixation down to the sacrum and pelvis. Anterior surgery depends on the circumstances and may involve the lower two to four segments of the spine or all the lumbar segments. Of late, our preference is the use of large trapezoidal mesh cages with bone morphogenic protein (BMP) sponges. The extent of the surgery is dependent on many factors.
Recent Surgical Advancements
- Most recent advancements include improved fixation techniques to provide anterior column support in the distal (lower) lumbar spine and sacropelvic (sacrum/pelvis) regions. We have found that bicortical (a type of screw) S1 fixation and bilateral iliac fixation with screws measuring 60-70mm in length and 7.0 to 7.5mm in diameter provide excellent fixation of the sacrum and pelvis. Many failures have been noted when the sacral screws are not protected by iliac screws.
- Options for anterior column support include either femoral rings (a type of bone graft) or large trapezoidal mesh cages.
- Bone morphogenetic protein (BMP) plays an important role in these surgeries. Most common in anterior surgery (especially in the middle and lower lumbar spine), 8-12mg of BMP is applied to each level and to the cages. However, bone graft is not used. BMP is also used:
- Posteriorly - If surgically addressing a lumbar curve using posterior fusion and instrumentation from T11 to the sacrum, solely local bone graft (no iliac harvesting) and BMP may be used. This is considered "off label" use of BMP.
- Anteriorly - If surgically addressing the lower three to four levels, BMP sponges may be used to eliminate harvesting additional iliac bone graft. The use of BMP and cages at more than one level is considered “off label.”
Many patients who undergo revision surgeries may have already had their ilium (iliac crest, hip bone) harvested on one or both sides. BMP helps to eliminate the need to take additional iliac bone and reduces morbidity (post-operative complications).
At this time, BMP's track record for anterior use is understood better than it is for posterior use. The best knowledge suggests that 8-12mg of BMP is needed for each anterior level and perhaps 40mg for each posterior level.
Benefits to Patients and Their Surgeons
It is hoped that advancements in treatment will improve outcomes and reduce the incidence of pseudarthrosis (failed fusion), surgical time, blood loss, pain, and complications.
Special types of catheters and IVs benefit both patients and surgeons. Some patients do not have all of their surgery performed in one day. In fact, it is not uncommon for certain types of surgeries to be done five days apart. When this is the case, subclavian lines or multiple lumen subclavian catheters can be used to provide 24-hour access to a central vein (called central venous access). Intravenous nutrition helps to reduce complications associated with weight loss between surgeries.
The incidence of pneumonia, deep venous thrombosis, and deep wound problems is low. Bowel immobility is the biggest problem a patient may encounter between surgeries. A great deal of information has been learned and experience gained in the use of multiple lumen subclavian catheters and parenteral nutrition (providing nutrition and calories through an intravenous line).
Anticipated Future Developments
- Forecasted research will provide a better understanding of when patients can simply be treated with an anterior distal (lower) lumbar procedure as opposed to treating all of the lumbar segments anteriorly. The anterior distal lumbar approach provides better exposure of L4-L5 and L5-S1 and does not disrupt the rib cage or diaphragm. The anterior procedure to treat all of the lumbar segments requires a chest/stomach incision called a thoracoabdominal approach and is more invasive.
- There is more to learn about BMP, its limitations, and its applications. Spine surgeons are optimistic that the cost of BMP will eventually decline, making it a more affordable option.
- Advancements in the development of smaller implants would benefit patients and surgeons. Implants need to be strong with components of elasticity and plasticity. But, if an implant is too large or bulky, it can make it difficult to decorticate (roughen) the bed under the instrumentation and the implant may be felt beneath the skin.
- In addition, a multicenter study is underway to gather information about the treatment of adult spinal deformity. This study, launched by the Spinal Deformity Study Group, will culminate in a database of information to help establish treatment guidelines and principles involving types of adult spinal deformity.