Approach Considerations
Indications for treatment of kyphosis include the following:
Indications for surgical treatment of Scheuermann kyphosis have changed fairly substantially; however, precise indicators have not been elucidated.
Authors from early clinical series simply cited pain and deformity as reasons to perform fusion. Proposed indications more specific than these are as follows [38] :
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Kyphosis greater than 75°
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Kyphosis greater than 65° with pain
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Unacceptable appearance of the trunk
Other possible indications in severely affected patients are problems with balance while sitting and skin problems due to pressure at the apex of the deformity.
Surgical intervention for posttraumatic kyphosis is recommended in the following circumstances [39] :
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The patient's neurologic status changes
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The condition progresses
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Kyphosis is 30° or more
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Loss of anterior vertebral height exceeds 50%
Contraindications for surgical treatment of kyphosis include a clinically significant cardiopulmonary risk and medical unfitness for surgery.
As surgical implants and techniques have improved, so have the results of surgery. Patient safety should be the foremost goal of the treating physician. Future prospective trials will help in defining the best way to care for patients with clinically significant sagittal imbalances.
Nonoperative Therapy
Medical therapy for kyphosis consists of exercise, medication, and bracing. [40] Physical therapy, which usually consists of extension-focused activities, may be of some benefit; however, this has not been proved. [38, 41]
Medications used to treat discomfort associated with kyphosis should be limited to nonsteroidal anti-inflammatory drugs (NSAIDs) and, possibly, muscle relaxants. Narcotics should be avoided for long-term treatment of pain associated with kyphosis.
If a patient has an active infection, such as diskitis or vertebral osteomyelitis, appropriate antibiotics based on culture results should be started as soon as possible.
In some skeletally immature patients with Scheuermann kyphosis, bracing is effective [42] ; however, the correction obtained may diminish as patients approach and pass skeletal maturity.
Sachs et al found that treatment with a Milwaukee brace improved deformity in 76 of 120 (63%) patients who wore the brace regularly; brace treatment seemed to be least effective when the curve was more than 74° at the beginning of treatment. [43] Bradford et al reported modest success in treating adults with a brace, with some correction of their deformities. [18]
Surgical Options
Careful surgical planning is crucial for successful operative treatment of kyphosis. The goals of surgery are to correct the deformity and to remove any neural compression, if present.
The age of the patient choosing surgery should play a role in the planned correction. Aging causes an increase in kyphosis naturally, and some advocate limiting the planned correction in older patients in order to minimize mechanical complications. [44]
Correction of the deformity can be done via an anterior, a posterior, or a combined anterior-posterior approach. Posterior surgery is most commonly described and performed. Posterior arthrodesis for kyphosis can be an extensive operation, with many spinal segments typically included in the fusion mass. [45] This procedure is most helpful for long, sweeping, flexible curves. In cases of rigid deformity, osteotomies can be performed to improve the correction. Combined anterior-posterior surgery may be required for severe deformities. [46]
Smith-Peterson osteotomy, pedicle-subtraction osteotomy, and vertebral-column resection
Specific osteotomies are aggressive facetectomies at each level, Smith-Peterson osteotomy, pedicle-subtraction osteotomy, and vertebral-column resection. Two-level osteotomies (eg, pedicle-subtraction osteotomy plus Smith-Peterson osteotomy) for correction of severe kyphosis from ankylosing spondylitis have been described.
Smith-Peterson osteotomy involves wedge-shaped resection of posterior elements from the pedicles of the superior vertebra to those of the inferior vertebra. When closed posteriorly, the spine hinges on the disk space; therefore, an open, mobile disk is crucial to the success of this procedure. The osteotomy can be performed at one or multiple levels, if necessary. This permits significant correction, with approximately 1 mm of resection yielding 1° of lordosis. [11] Some recommend anterior diskectomy and fusion with Smith-Peterson osteotomy to decrease the pseudarthrosis rate. [21, 47, 48]
Pedicle-subtraction osteotomy involves relatively aggressive resection of a wedge of bone, including posterior elements, the pedicles, and the vertebral body. [49, 50]
Vertebral-column resection entails removal of posterior elements, the vertebral body, and adjacent disk material. Because of the destabilizing effect of this resection, both anterior and posterior fixation are often required. Dreimann et al described the use of posterior vertebral-column resection with 360º osteosynthesis to reduce kyphotic deformity. [51, 52]
As kyphosis becomes notably sharp or focal, increasingly aggressive techniques are required for correction. Cho et al demonstrated that the corrections per segment were 10.7° for Smith-Peterson osteotomy and 31.7° for pedicle-subtraction osteotomy. [53] Procedures involving the anterior column are usually followed by posterior instrumentation and fusion. Vertebral column resection yielded up to 63% improvement in deformity at 5 years in a medium-term study. [54]
Although having a correction “target” is important in preoperative planning, it is often difficult to assess the correction intraoperatively. The lumbar pelvic angle, a portion of the T1-pelvic angle (TPA), may be useful in this regard and also seems to correlate with patient satisfaction. [55]
Zhong et al investigated the use of a two-level pedicle-subtraction osteotomy in comparison with a one-level pedicle-subtraction osteotomy plus a Smith-Peterson osteotomy for severe kyphosis. [56] The two-level pedicle-subtraction osteotomy was useful, especially in cases of a fixed kyphosis, such as that due to ankylosing spondylitis.
Anterior surgery
Anterior surgery can include single or multiple diskectomies to increase the flexibility of the spine, followed by a posterior arthrodesis. The transthoracic approach allows decompression of the neural elements before the spine is corrected with posterior instrumentation. Anterior-only fusion is most useful for treating relatively short and focal kyphosis, such as posttraumatic or postinfectious kyphosis. [24]
A consecutive series of 48 patients were treated for severe deformity with either anterior diskectomy and posterior fusion or vertebral-column resection and followed for at least 2 years. In this case series, the vertebral-column resection group had better correction but also more blood loss, longer operating times, and longer hospital stays. Patient-reported outcome scores were similar in the two groups. [57]
A novel technique for single-curve scoliosis may also be used to correct kyphosis. The bone-on-bone technique involves an anterior-only approach to perform complete annulectomy and diskectomy at each level in the Cobb angle of the deformity. Then, using sequential compression along two rods, which are affixed with a staple and two screws in each vertebral level, the surgeon brings the bony endplates into immediate contact. Substantial correction can be achieved in this manner. [58]
A technique called anterior-column restoration relies on multiple lateral interbody fusions to release the anterior longitudinal ligament and realign the spine. This is often followed by an open posterior fusion. Possible benefits of this technique over posterior-only bony resection may include less blood loss and dural manipulation and excellent sagittal plane correction; however, further study is needed. [59]
Operative Therapy
Preparation for surgery
Patients with kyphosis may have subtle neurologic abnormalities that are easily missed during examination. Magnetic resonance imaging (MRI) of the affected area can help in determining whether decompression is necessary before instrumentation and correction of the deformity.
Selection of the fusion level is important. The proximal level is usually the most cranial vertebra rotated into the kyphosis. In the distal aspect, the fusion is commonly extended to the last lordotic segment; however, some have advocated using the sagittal stable vertebra to determine the distal fusion level. [60, 61] Recommended correction should not exceed 50%, so as to prevent junctional kyphosis at the ends of the fusion. [19]
Operative details
The spinal cord and its roots are at risk during correction of kyphosis, especially when the canal is stenotic or when the cord is tethered at the apex of the kyphosis. In these situations, consideration should be given to performing anterior decompression before the posterior arthrodesis. The cord is also at risk for ischemia if blood flow is altered with the change in spinal alignment. [12]
Manipulation of the spinal cord, especially during osteotomies in the thoracic spine, should be avoided. Evidence suggests that the lower lumbar roots are vulnerable during pedicle-subtraction osteotomy, more so than the upper lumbar roots are. [47] Careful attention should be paid to the removal of posterior bone and ligament, which may buckle into the canal as the osteotomy is closed.
Thorough central decompression is recommended to help prevent neurologic compromise. Subluxation of the spine can also occur when an osteotomy is being closed; therefore, intraoperative radiography is essential to facilitate rapid identification and correction of subluxation.
Neural monitoring may help identify correctable neurologic injury before the case is concluded. Monitoring of somatosensory and motor evoked potentials can be helpful in detecting reversible neural injury (eg, from stretching during correction of deformity or improper placement of devices). However, neural monitoring may not be useful with isolated root injuries. [21, 22] A wake-up test can also be performed to assess the patient's gross motor function after the deformity is corrected.
Blood loss can be clinically significant during correction of kyphosis, especially if anterior procedures and large osteotomies are being performed. [62] Bleeding should be controlled at every step of the operation to keep overall loss to a minimum. Clinically significant blood loss can cause hypotension and potentially injure the spinal cord, myocardium, or retina. Intraoperative blood-loss mitigation techniques include preoperative autodonation, decreasing abdominal pressure, and use of antifibrinolytic drugs. [63, 64, 65]
In terms of intraoperative considerations related to instrumentation, it is important to ensure that the substantial cantilever force applied to the spine with posterior instrumentation is spread over multiple levels. In the thoracic spine, sublaminar wires, hooks, or screws can be used. Pedicle screws in multiple sites will spread the force throughout the construct. Pedicle screws are also useful with aggressive osteotomies, which tend to destabilize the spine. Segmental fixation increases the surgeon's control over the coronal plane, where a deformity can coexist with a sagittal deformity. [11, 66, 67]
In the lumbar spine, pedicle screws are most often used for the reasons just mentioned. Osteoporosis should be addressed with multiple points of posterior fixation, and a low threshold should be maintained for performing concomitant anterior fusion. This approach may help prevent implant pull-out or postoperative collapse and loss of correction.
Intervertebral instrumentation can be useful in increasing the fusion rate and improving deformity correction. Numerous procedures exist for placing an interbody spacer, often filled with osteoconductive matrix, into the spine. These spacers can be placed from the back (transforaminal lumbar interbody fusion, posterior lumbar interbody fusion), from the side (extreme lateral interbody fusion, oblique lumbar interbody fusion), or from the front (anterior lumbar interbody fusion).
Aggressive correction of the spine can be achieved with vertebral-column resection. In a review of adult and pediatric patients with severe deformities who underwent a vertebral-column resection, the correction at final follow-up was in the range of 53-61%, and improvements were noted on patient-reported outcome measures, despite a 56% complication rate. [54]
Postoperative Care
Patients usually require clinically significant pain medication after undergoing correction of kyphosis, especially extensive procedures. The amount of narcotics given should be carefully titrated because the drugs may cause ileus, atelectasis, or difficulty in mobilizing the patient after surgery.
Because blood losses can be substantial, patients should be monitored for anemia. Electrolytes should be checked as well, given that notable fluid shifts are common in the perioperative period.
Careful postoperative neurologic examination is important for identifying any changes from the patient's preoperative status. [68]
Complications
Possible complications of treatment range from superficial wound infection to complete neurologic injury. The nervous system is at risk with correction because of direct manipulation, traction, or compression resulting from the altered anatomy of the spine. In addition, blood flow to the cord or roots can be impeded. Reported complication rates are quite high, in the range of 40-90%. [32, 69]
Neurologic changes are most often transient. However, if a new deficit is identified postoperatively, transience cannot be assumed. Imaging of the spine should be done to identify any reversible cause of the deficit; if a cause is identified, it should be addressed rapidly. Removing the fixation and allowing the kyphosis to settle may help relieve cord compromise.
Intraoperative blood loss can be clinically significant. [62] Loss of blood puts the patient at risk for transfusion, hypotension, ischemia to critical tissues, and potentially death. Therefore, careful attention to blood loss is essential.
Mechanical complications are possible as well. Pseudarthrosis can occur, especially with long fusions, inadequate support of the anterior column, and fusions at the thoracolumbar junction. [70] Other risk factors in long fusions to treat scoliosis include age greater than 55 years, [71] thoracolumbar kyphosis greater than 20°, and fusion of more than 12 levels. [72]
Implant failure can lead to loss of correction, especially at the proximal portion of the instrumentation. Patients with osteoporosis are at somewhat increased risk of implant failure or even fracture at levels contiguous with the fusion mass.
In some individuals, posterior instrumentation can be prominent and cause discomfort. Overcorrection of the deformity (>50%) and inadequate selection of fusion levels can predispose a patient to junctional kyphosis at the proximal and distal extent of the fusion mass. [19, 73]
Proximal junctional failure is a junctional kyphosis that requires additional surgery. It occurs in 1-5% of all adult spinal deformity procedures. Failures can be due to disk or ligament issues, failure of the bone, or failure at the bone-implant interface. [74]
Postoperative wound infections can be superficial or deep. As with any surgical procedure, use of prophylactic antibiotics and sterile technique are imperative to lower the incidence of postoperative wound infection. Optimizing the patient's nutritional status before surgery can also help reduce the risk of infection.
In a 2-year postsurgery review of a series of 324 patients, there was a significant improvement in radiographic parameters and a corresponding improvement in pain scores, Oswestry Disability Index (ODI), and Scoliosis Research Society (SRS) scores. [75] Patients with leg pain before surgery continued to have more pain postoperatively than those who did not have preoperative leg pain, despite significant improvement in both groups.
An overall assessment of patient frailty may be an important predictor of risk of complication risk. A validation study of a prior database review identified criteria that assigned people to not-frail, frail, and significantly frail categories and reviewed their postoperative complications and length of stay. [76] As frailty increased, so did the complication rate: 65% for the not-frail group, 78% for the frail group, and 92% for the significantly frail group. Hospital length of stay also increased with frailty. [76]
Long-Term Monitoring
Standing posteroanterior (PA) and lateral full-length radiographs of the spine should be obtained as soon as possible after surgery and serially for follow-up. Full-length scoliosis films obtained yearly allow evaluation of the patient's curve over time.
Comparison of the postoperative and follow-up images with the preoperative images helps in defining the amount of correction achieved and in determining if correction is being lost over time. Loss of correction should prompt a careful evaluation for implant pull-out or breakage, for subsidence of an anterior implant (if any), or for lack of adequate fusion mass. [77]
A large review of adult spine deformity patients at least 2 years after surgery identified implant-related complications (eg, implant pull-out or rod breakage) in 32%, and over half of those required an additional operation. These complications negatively affected patient function, as reflected on patient-reported outcome measures. [78]
Postoperative measurements of the C7 plumb line should be at or within a few centimeters of S1.
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Preoperative lateral radiograph of patient with 85° thoracic deformity secondary to Scheuermann kyphosis.
