Ankylosing Spondylitis: Deformity Management

MANAGEMENT

Treating Ankylosing Spondylitis is a delicate task that can be frustrating to the sufferer and the physician. Lifestyle changes at times are required and ill habits such as smoking, which is a detriment to individuals with AS, (2) need to be eliminated. Options do exist to manage the horrific manifestations of AS which need to be addressed and sought to benefit the patient's quality of life and provide beneficial long–term results.

Medication

Presently, there is no cure for AS. However, the earlier AS is diagnosed the more optimum results will be obtained from medicinal therapy. Conservative treatment is carried out by the use of nonsteroidal anti–inflammatory drugs (NSAIDs). NSAIDs help reduce pain, stiffness, and discomfort by reducing the inflammatory activity. A large array of NSAIDs are available, but preference and outcome varies between individuals. Although Indomethacin, (7) Naproxen, (45<) and Phenylbutazone (7) may be preferred among AS sufferers, Sulfasalazine, (13, 17) Diclofenac, Fenoprofen calcium, and Salicylates have also shown efficacy in relieving symptoms of AS. It should be noted that Salicylates and aspirin are usually initially sought to relieve symptoms of AS, but sufferers tend to depart from this medication and seek other more potent routes as mentioned above. (7, 18) Furthermore, a majority of NSAIDs have a tendency to cause gastrointestinal bleeding, ulcers, and other adverse reactions; whereas, new Cox 2 inhibitors do not.

Although the entire purpose of medication to treat AS is to reduce stiffness and pain in sufferers, optimal improvement can be grasped with daily exercise or physical therapy techniques. Exercise coupled with medication could lead to beneficial results because inflammation is reduced and the body is not exposed to long periods of rest allowing fusion to fix the spine in a maladaptive position. Increasing the body's range of motion always is beneficial and could hinder or prevent poor posture.

Indications for Surgery

The surgical route is sought when excruciating pain overwhelms the patient, neurologic deterioration develops, a decrease in horizontal gaze, medication is not helpful, and when spinal deformity is excessive to the point that it inhibits daily activity and increases the risk of trauma. Although, surgical intervention to rectify deformity of the spine as a result of AS is a potentially harmful and delicate procedure, it could provide a beneficial outcome for the patient by decreasing their pain, increase their function and mobility, and soften physical embarrassment. Since the natural progression of the disease varies between individuals, a suggested timeline for operative management depends upon the severity of the spinal deformity and the distress and obstruction of daily function.

Age, sex, occupation, location of the pronounced deformity, deterioration of quality of life, severity of spinal deformity, appropriateness of the operation, and postoperative rehabilitation are all are factors that need to be assessed for operative treatment. Spinal deformity can be measured by the chin–brow technique. This method measures the angle produced by a line drawn from the brow to the chin intersecting the vertical axis. The physician should periodically assess the chin–brow measurement to establish a baseline and monitor progressive spinal changes. Obviously, the greater the angle the more pronounced spinal deformity exists and indication for operative intervention should be sought.

Treatment of Thoracolumbar Deformity

Correction for a pronounced spinal kyphotic deformity has been investigated since the 1940s. Operative procedures of the spine to correct AS need to be conscious of the vital structures that surround the spinal column, but primarily the spinal cord and neural roots. Therefore, many seek to decrease the pronounced spinal deformity of AS in the lumbar region primarily at the end of the spinal cord to avoid compression and at L2/L3 or L3/L4 where the descending aorta bifurcates and is more manageable decreasing the risk of rupture. Also, dealing with the thoracic region could lead to less beneficial results because of its involvement with the rib cage and attached costovertebral joints that may be affected by operative measures, and the presumably narrow spinal canal that could increase the risk of cord compression. However, AS patients with flexed contracture of the hip joints should first undergo a bilateral hip arthroplasty before seeking spinal correction. Nevertheless, AS patients with pronounced thoracolumbar deformity should seek correction in the lumbar region (Fig. 3); whereas, AS patients with increased thoracic kyphosis and an intact lumbar lordosis should seek thoracic correction. Therefore, particular attention needs to be given to the vertebral level that will be responsible for the new shape of the spine.

Smith–Petersen, Larson, & Aufranc Approach – Introduction of the Lumbar Osteotomy

Correction of spinal deformity is primarily accompanied through lumbar osteotomy. As a result of this procedure, relordosation is accomplished and kyphotic deformity is decreased throughout the spine. Although, there have been numerous accounts detailing operative techniques to correct kyphosis, the use of internal instrumentation, depth of osteotomy and approach, and use of bone graft are evolving. Nevertheless, vertebral osteotomy to correct spinal deformity in AS sufferers was first introduced by Smith–Petersen, Larson, and Aufranc in 1945. (38)

The technique by Smith–Petersen et al provided the foundation for possible routes in correcting pronounced kyphosis in AS. Smith–Petersen et al presented five cases of lumbar monosegmental or multisegmental posterior osteotomy. Osteotomy location was determined by the less ossified segment (s) on radiographic evaluation that would render greater manipulation ease. This procedure begins with the patient in the prone position under general anesthesia. An incision is made in the midline including at least three vertebral levels of interest at the lumbar region. The spinous processes involved (L1–L2 and L3) are excised as well as ones directly above and below. Retraction of muscle attachments from the spinous processes and laminae is carried out. The ligamentum flavum is removed and by use of an osteotome a V–shaped wedge osteotomy at a 45 degree angle from the frontal plane is accomplished through the superior articular processes of the inferior vertebra and the inferior articular processes of the superior vertebra (Fig. 4 A,B). (38) Bone graft from the excised spinous processes is inserted between the lamina for support and as an anchor to achieve desired lordosis. Closing the osteotomy is achieved by manual means or by raising the head and foot of the operating table to meet the desired spinal curvature (Fig. 5). The patient is then closed and a plaster shell is applied for four to six weeks. Afterwards, the patient is instructed to remain in a plaster jacket for one year. All five patients, in the original report, tolerated the procedure fairly well and were ambulatory and reported little to no pain. It should be noted that in the report by Smith–Petersen et al, a sixth case was also mentioned, but it involved an individual who underwent lumbar and thoracic osteotomies whose outcome objectively did not improve.

Introduction of the Two Staged Approach –Anterior & Posterior

One of the main concerns of operative procedures to correct spinal deformity of AS is to establish a desired curvature and allow it to remain so postoperatively. However, if the desired spinal correction was not obtained other avenues were sought. La Chapelle in 1946 (26) reported on posterior vertebral osteotomy with anterior intervertebral disc bone graft insertion. La Chapelle recommended a similar procedure as Smith–Petersen et al, but removed laminae with local anesthesia and included a second stage two to three weeks after the first operative osteotomy with general anesthesia. Although laminectomies in AS patients, whose lumbar muscles are weakened or atrophied, could pose threat of spondylolisthesis, LaChapelle believed that an intact ossified posterior longitudinal ligament would prevent such a risk. In the second stage, under general anesthesia, the patient is placed in a left lateral decubitas position and a transverse abdominal incision is carried out at the level of the umbilicus. After retraction of the peritoneum and obvious structures the lumbar spine is viewed and displacement of the aorta and inferior vena cava is accomplished. The intervertebral disc is excised and packed with autologous bone graft in a desired amount to obtain curvature while not excising the posterior longitudinal ligament. Afterwards, the patient is stabilized in a plaster spica for three months and a plaster jacket for six months. Ambulation is slowly accomplished beginning after four weeks.

In 1959, Herbert (22) performed a similar approach as La Chapelle, but resected the neural arches in a T–shaped posterior osteotomy to avoid spinal cord compression in the event subluxation occurred. Herbert chose the location of the posterior osteotomy by determining the least ossified intervertebral disc. Herbert also performed a second stage osteotomy as La Chapelle, but sectioned the corresponding intervertebral disc to promote collapse and to achieve deformity correction.

Internal Metallic Instrumentation

Internal stabilization to correct for fixed lumbar deformity in AS was first reported by Briggs et al in 1947. (6) Briggs et al postulated a monosegmental posterior closed wedge osteotomy, with essential disruption of the anterior longitudinal ligament and bilateral intervertebral foraminotomy to correct for lumbar kyphosis. The osteotomy Briggs et al implemented consisted of a wedge removal of the adjacent spinous processes, superior articular processes, and a portion of the pedicle. Location of the osteotomy was determined by a radiographic evaluation of the greater ossified anterior longitudinal ligament. Rupture of the anterior longitudinal ligament intraoperatively by manual pressure was shown to facilitate in reestablishing physiologically correct lumbar lordosis. However, in the event the anterior longitudinal ligament did not break, a curved Wilson plate was applied on the right lateral surface of the involved spinous process. Furthermore, a plate was also implemented in preventing vertebral spondylolisthesis due to the instability a ruptured anterior longitudinal ligament might impose on the vertebrae.

Further accounts of internal metallic fixation were also reported by Lichtblau and Wilson in 1956 (32) and Law in 1959, 1962, and 1969. (28–30) Law's reports of surgical correction of AS kyphotic deformity were the largest of his time. In 1952, Law reported his experience with monosegmental osteotomy at L2–L3 utilizing the Smith–Petersen et al technique in (30) patients. (28) Law avoided rupture of the anterior longitudinal ligament and implemented prolonged external plaster cast fixation to promote bone consolidation. In the following years, 1959, (28) 1962, (29) and 1969, (30) Law reported the outcome of 100, 110, and 120 patients respectively. However, since 1959 Law applied wire loops and metal plates around the spinous process for increased internal stability and to decrease postoperative external immobilization wear. Although Law presented a large sample of kyphotic correction, his mass experience and reports also noted a 10% risk of death associated with surgical intervention.

Simmons in 1977 (37) was the first to use Harrington compression system for correction of AS thoracic deformity. Simmons presented a case of a 38–year–old female with 116 degrees thoracic kyphosis at T2–T11 with anterior spondylodiscitis at T8–T9. The patient presented a sharp angular kyphosis with accompanying skin breakdown at kyphotic proximity, restricted pulmonary capability, shortness of breath, and a degree of subluxation at C1–C2. The patient was first placed into a halo–femoral traction for three weeks in which her thoracic kyphosis reduced to 68 degrees. Surgical intervention was then performed via a transthoracic approach and Harrington compression instrumentation was appropriately applied which reduced her thoracic kyphosis to 50 degrees. At 2 ½ years status post, the patient managed to maintain her newly constructed thoracic curve and presented no signs of neurologic compromise.

Simmons, also reported his experience with surgical intervention for lumbar AS deformity with posterior wiring to maintain corrected spinal curvature. Simmons, utilizing the Smith–Petersen et al technique, performed a monosegmental posterior osteotomy with osteoclasis of the anterior longitudinal ligament in 19 patients under local anesthesia and positioned laterally. Simmons selected the site of the main deformity to perform an osteotomy. His preference was reported as L3–L4, but his results showed osteotomies at L2–L3 in eight patients, L3–L4 in eight patients, and L4–L5 in three patients. He used 20 gauge stainless steel wires to loop through holes in adjacent spinous processes in relation to the osteotomy. His procedure achieved a deformity correction of 30–60 degrees and an average of 47 degrees. As a result of the operation, no mortalities occurred as well as no signs of permanent neurologic deficit.