Kyphosis refers to the normal apical-dorsal sagittal contour of the thoracic and sacral spine. Normal kyphosis is defined as a Cobb angle of 20-40° measured from T2 to T12.[1, 2]
As a pathologic entity, kyphosis is an accentuation of this normal curvature. Many potential etiologies of kyphosis have been identified. Kyphosis can occur as a deformity solely in the sagittal plane, or it can occur in association with an abnormality in the coronal plane, resulting in kyphoscoliosis. Although pathologic kyphosis can affect the cervical and lumbar spine as well the thoracic spine, cervical and lumbar involvement is uncommon; any kyphosis in these areas is abnormal.
Kyphosis can cause pain and potentially lead to neurologic deficit and abnormal cardiopulmonary function.
The pathophysiology of kyphosis depends on the etiologic factor. The exact cause of Scheuermann disease is still imprecisely defined. Scheuermann postulated that the condition resulted from avascular necrosis of the apophyseal ring. Other theories include histologic abnormalities at the endplate, osteoporosis,[3] and mechanical factors that affect spinal growth.[4] A Danish study demonstrated an important genetic component to the entity.[5]
Postural kyphosis is present when accentuated kyphosis is observed without the characteristic 5° of wedging over three consecutive vertebral segments that defines Scheuermann kyphosis.[6] This is felt to be due to muscular imbalance leading to the round-back appearance of these individuals.
When focal kyphosis occurs after a fracture, more height is lost in the anterior aspect than in the posterior aspect; this is the typical fracture pattern. The angulation can increase as the fracture heals, placing pressure on the spinal cord. Patients with fractures have historically been treated with laminectomy alone, especially in the thoracic spine, and they often had progressive kyphosis at the fracture site.[7, 8]
Postinfectious kyphosis occurs in a manner similar to that just described. Mechanical integrity of the anterior column is lost as a consequence of the infectious process. Bending forces then accentuate the normal sagittal contour.
Many potential causes of kyphosis have been described.[9] Scheuermann disease and postural round back are often identified in adolescents.[10, 11, 12] Congenital abnormalities, such as failure of formation or failure of segmentation of the spinal elements, can cause a pathologic kyphosis. Autoimmune arthropathy, such as ankylosing spondylitis, can cause rigid kyphosis to develop as the spinal elements coalesce.
Kyphosis can also develop as a result of trauma, a spinal tumor, or an infection. Iatrogenic causes of kyphosis include the effects of laminectomy and irradiation, which lead to incompetence of the anterior or posterior column. Finally, metabolic disorders and dwarfing conditions can lead to kyphosis.
This article focuses on kyphosis due to Scheuermann disease and postural, postinfectious, posttraumatic, or iatrogenic etiologies.
Results of surgical correction vary, depending on the etiology of the deformity.
Malcolm et al reviewed 48 patients and achieved a deformity correction rate of 26% and at least partial pain relief in 98% of patients with posttraumatic kyphosis with anterior and/or posterior fusions.[7]
Lehmer et al studied 38 patients who underwent a single-stage closing wedge procedure to treat posttraumatic and postlaminectomy kyphosis.[13] They obtained a mean correction of 35° with three pseudarthroses. Eight of 14 preoperative neurologic deficits improved, and 76% of the patients treated said they would undergo the surgery again if needed.
Kostuick achieved fusion in 36 of 37 patients receiving anterior-only fusion.[14] Pain significantly improved in 78%, and three of eight patients with paraparesis improved.
Outcomes in Scheuermann kyphosis are similar to those just presented, though the amount of correction achieved may not be correlated with pain relief.
In a series of patients who were treated with a posterior Harrington rod, all had pain relief. However, 16 of 22 lost correction.[15]
Lowe and Kasten used posterior instrumentation to achieve a mean correction of 85° down to 43°.[16]
With anterior-posterior and posterior-only surgery, Speck and Chopin gained an average deformity correction of 40%, and 28 of 45 patients were pain-free.[17] However, four patients had infections, nine lost more than 10° of correction, and one had Brown-Sequard syndrome postoperatively.
Investigators have evaluated advanced techniques, such as osteotomies and new instrumentation. Bridwell et al reported a series of 33 patients treated with pedicle subtraction osteotomy for sagittal imbalance.[18, 19] The C7 plumb line improved from 16.6 cm positive to 1.7 cm. Pain and Oswestry disability indexes significantly improved. Eight patients had pseudarthrosis, and one had a wound infection. No permanent neurologic injuries occurred.
Video-assisted thoracoscopic release followed by posterior arthrodesis has been successful. In one study, deformity correction was 84.8° to 45.3° in patients with thoracic kyphosis associated with Scheuermann disease.[20] Mean loss of correction was 1.6°, and one hook pulled out. No cases of junctional kyphosis were observed.
In a retrospective study, anterior-posterior correction was compared with posterior-only instrumentation with all pedicle screws.[21] The posterior-only group had significant improvement in terms of blood loss, correction of deformity, and number of complications.
Patients with a symptomatic kyphosis often present with axial back pain. They may also be concerned about the cosmesis of their rounded back.
Patients with kyphosis should be carefully questioned about and examined for neurologic problems, especially myelopathy. Difficulty with gait and hyperreflexia should prompt further investigation of the kyphosis.
A 10- to 42-year, natural-history study of Scheuermann disease revealed that patients, as compared with a control group, tended to have increased back pain.[22] However, they were not more likely than the control group to take pain medication, to have sedentary jobs, or to lose motion of the spine. The investigators found no differences in educational level, absenteeism, self-consciousness, or reports of numbness in the legs. Of interest, restrictive lung disease was observed in patients with a curve greater than 100°.
Standard laboratory results should be evaluated whenever surgical intervention is being considered. The laboratory workup should include determination of a complete blood count (CBC), coagulation studies, and routine chemical analyses.
Autodonation of blood can be recommended to the patient in anticipation of the need for intraoperative transfusion.
In patients with a known or suspected infectious etiology, the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level should be measured to help identify a potential infection or to help track the progress of treatment.
Before a major operation, the patient's nutritional status might also be checked, because it considerably influences a patient's ability to heal.
Radiographs are crucial both for diagnosing kyphosis and for planning treatment.
The most useful radiographs are upright posteroanterior (PA) and lateral images of the entire spine. These views enable the reviewer to assess the sagittal balance of the entire spine and to determine whether a scoliosis is present. (See the image below.)
View Image
Preoperative lateral radiograph of patient with 85° thoracic deformity secondary to Scheuermann kyphosis.
Measurements are made on radiographs by using the standard Cobb technique for scoliosis, which has been adapted to the measurement of kyphosis. Thoracic kyphosis is measured from T1 to T12, though the upper thoracic vertebral endplates are often difficult to see.
Normal measurements for thoracic spine vary widely, but the accepted definition of normal according to the Scoliosis Research Society is 20-40°. A plumb line dropped from C7 should pass through or just anterior to S1 on a lateral full-length image. This technique helps in assessing and quantifying the patient's overall sagittal alignment.
Radiographs obtained with the patient in a supine lateral hyperextension position over a bolster can be used to determine the flexibility of the curve. This information is useful in surgical planning. A flexible curve is best corrected with posterior-only fusion, whereas an anterior-only or combined anterior-posterior procedure may be needed for a stiff curve. A curve that corrects to 50° or less on hyperextension can be treated with posterior-only fusion.[23, 15] Postural kyphosis is rarely more than 60°, and it should correct to normal with hyperextension.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) can be a useful adjunct in planning treatment for patients with kyphosis. If a neurologic abnormality is present, MRI may aid in localizing impingement on neural structures.
If surgery is being planned for the treatment of postinfectious kyphosis, MRI helps in planning an anterior approach with regard to the amount of resection needed (if any) to remove diseased bone.
Ensuring the adequacy of bone density is imperative when surgical correction of kyphosis is being considered. Correction of the kyphosis relies on instrumentation to reduce the spine, and considerable forces are placed on the instrumentation-bone interface. Osteopenic bone can predispose to loss of correction over time, if the instrumentation cuts through the relatively less dense vertebrae.
If a patient's bone density is in question, bone densitometry can be perform to quantify it. Efforts should be made to a patient's improve bone density before and following surgery. When bone density is poor, the surgeon must usually increase the number of points of fixation to reduce the stress at each point.
Indications for treatment of kyphosis include unremitting pain, neurologic changes, progression of deformity,[24] and cosmesis.[4] 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 kyphosis greater than 75°, kyphosis greater than 65° with pain, and an unacceptable appearance of the trunk.[25]
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 if the patient's neurologic status changes, if the condition progresses, if the kyphosis is 30° or more, or if the loss of anterior vertebral height is more than 50%.[26]
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 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.
Medical therapy for kyphosis consists of exercise, medication, and bracing.[24] Physical therapy, which usually consists of extension-focused activities, may be of some benefit; however, this has not been proved.[25, 27]
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[28] ; 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.[29] Bradford et al reported modest success in treating adults with a brace, with some correction of their deformities.[15]
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.
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.[30] 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.[31]
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.
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.[9] Some recommend anterior diskectomy and fusion with Smith-Peterson osteotomy to decrease the pseudarthrosis rate.[18, 19]
Pedicle-subtraction osteotomy involves relatively aggressive resection of a wedge of bone, including posterior elements, the pedicles, and the vertebral body.[32]
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 have described the uise of posterior vertebral column resection with 360º osteosynthesis to reduce kyphotic deformity.[33, 34]
As kyphosis becomes notably sharp and/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.[35] Procedures involving the anterior column are usually followed by posterior instrumentation and fusion.
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.[23]
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.[36]
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.[37, 38] Recommended correction should not exceed 50%, to prevent junctional kyphosis at the ends of the fusion.[16]
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.[9]
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 than the upper lumbar roots are.[39] 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.[18, 19] 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.[40] 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.
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. With hooks, multiple claws on each side are usually recommended.
Some surgeons have applied thoracic pedicle screws to spread the force throughout each vertebra that receives instrumentation. 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.[9, 41, 42]
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.
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.[43]
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.
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, and, if identified, the cause 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.[40] Blood losses put 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.[44] Other risk factors in long fusions to treat scoliosis include age greater than 55 years,[45] thoracolumbar kyphosis greater than 20°, and fusion of more than 12 levels.[46]
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.[16]
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. Maximizing the patient's nutritional status before surgery can also help reduce the risk of infection.
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 strut (if any), or for the lack of adequate fusion mass.[47]
Postoperative measurements of the C7 plumb line should be at or within a few centimeters of S1.
R Carter Cassidy, MD, Associate Professor of Orthopedic Surgery, University of Kentucky College of Medicine
Disclosure: Received income in an amount equal to or greater than $250 from: Johnson and Johnson.
Coauthor(s)
William O Shaffer, MD, Orthopedic Spine Surgeon, Northwest Iowa Bone, Joint, and Sports Surgeons
Disclosure: Received royalty from DePuySpine 1997-2007 (not presently) for consulting; Received grant/research funds from DePuySpine 2002-2007 (closed) for sacropelvic instrumentation biomechanical study; Received grant/research funds from DePuyBiologics 2005-2008 (closed) for healos study just closed; Received consulting fee from DePuySpine 2009 for design of offset modification of expedium.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Chief Editor
Jeffrey A Goldstein, MD, Clinical Professor of Orthopedic Surgery, New York University School of Medicine; Director of Spine Service, Director of Spine Fellowship, Department of Orthopedic Surgery, NYU Hospital for Joint Diseases, NYU Langone Medical Center
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Medtronic, Nuvasive, NLT Spine, RTI, Magellan Health<br/>Received consulting fee from Medtronic for consulting; Received consulting fee from NuVasive for consulting; Received royalty from Nuvasive for consulting; Received consulting fee from K2M for consulting; Received ownership interest from NuVasive for none.
){kind=link}