Scoliosis is a broad term encompassing multiple pathologies with different etiologies. Patients may range from the infant with congenital deformity, to the adolescent with idiopathic scoliosis, to the elderly patient with severe degenerative scoliosis. Treatment must be tailored to individual circumstances and the pathoanatomy of each deformity. Various coronal reduction techniques have been described and will be discussed within this article. While scoliosis is generally considered a deformity in the coronal plane, often deformity is present in the sagittal and axial planes also. Treatment of these deformities can require osteotomies or vertebral column resections, techniques further discussed in accompanying articles.
Key points
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Multiple reduction/realignment techniques have been described for treating coronal plane deformity.
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Rigid deformities may require anterior release or osteotomies before correction.
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Each deformity is unique and requires a tailored approach, often combining several techniques.
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Minimizing complications from spinal reconstructions requires adequate preoperative planning and attention to detail in the perioperative period.
Advances in technology, such as segmental pedicle screw instrumentation, have dramatically increased the number and effectiveness of realignment and reduction techniques for the treatment of coronal spinal deformity. Historically, distraction–compression was the primary technique used to correct coronal curvature. However, employing this technique has deleterious effects on sagittal alignment, and it is rarely used as the sole maneuver to correct spinal deformity today. Other techniques, including cantilever bending, in situ bending, translation, derotation, direct vertebral rotation, and vertebral column resection have been described and are more commonly employed today. Each patient’s spinal deformity is unique; therefore spinal realignment must be individualized and employ a combination of techniques. The treatment of coronal deformity often requires substantial spinal reconstruction and involves significant risk of complications. Minimizing complications requires attention to detail in planning, positioning, and in perioperative management.
Coronal correction concepts
The correction of spinal malalignment requires the application of appropriate forces counter to the direction of the deformity. All reduction strategies employ one or more of the following forces. Distraction of the vertebrae may be employed to address the concavity of the curve but also results in kyphosis in the sagittal plane. Compression is best applied over the convexity of the curve and results in increased lordosis in the sagittal plane. Other forces that can be applied in correction include the application of cantilever forces, translation or reducing the vertebra to a straight construct, tilting, and derotation or applying force in the axial plane to correct rotational deformity.
The use of these forces requires a spine with some degree of flexibility. In certain cases, applying these forces will not result in adequate reduction due to the rigidity of the deformity. In other cases, previous operations may have led to arthrodesis of the spine in the deformed state. In these cases, the principles of rigid and revision surgery are applied. These include anterior releases designed to increase flexibility of a rigid curve, or osteotomies, including smith-petersen, pedicle subtraction, or vertebral column resection, which offer varying degrees of sagittal and coronal plane correction.
Coronal correction concepts
The correction of spinal malalignment requires the application of appropriate forces counter to the direction of the deformity. All reduction strategies employ one or more of the following forces. Distraction of the vertebrae may be employed to address the concavity of the curve but also results in kyphosis in the sagittal plane. Compression is best applied over the convexity of the curve and results in increased lordosis in the sagittal plane. Other forces that can be applied in correction include the application of cantilever forces, translation or reducing the vertebra to a straight construct, tilting, and derotation or applying force in the axial plane to correct rotational deformity.
The use of these forces requires a spine with some degree of flexibility. In certain cases, applying these forces will not result in adequate reduction due to the rigidity of the deformity. In other cases, previous operations may have led to arthrodesis of the spine in the deformed state. In these cases, the principles of rigid and revision surgery are applied. These include anterior releases designed to increase flexibility of a rigid curve, or osteotomies, including smith-petersen, pedicle subtraction, or vertebral column resection, which offer varying degrees of sagittal and coronal plane correction.
Procedures and techniques
Historically, scoliosis was treated with the principles of correction pioneered by Harrington. Fig. 1 demonstrates this technique. Distraction is applied to the concave side, and compression is applied over the convex side. Reduction is not segmental, but the technique can correct lateral and angular displacement. The technique does not correct rotational deformity and places high stress on the spine and instrumentation. Furthermore, the application of a straight rod reduced thoracic kyphosis and reduced lumbar lordosis, resulting in flat back deformity and sagittal spinopelvic malalignment. Subsequently, many patients required revision surgeries, which entailed complex osteotomy procedures to correct the iatrogenic sagittal plane deformity. Fig. 2 demonstrates such a case in which attempted coronal realignment resulted in thoracolumbar junction kyphosis, necessitating revision. Attention to detail in all planes is required to avoid long-term complications.
With the advent of segmental instrumentation, other techniques have been described to affect coronal reduction with less deleterious effects in the sagittal plane. First described by Luque, translational reduction involves the placement of a contoured rod, during which each segment is brought toward the rod. Fig. 3 demonstrates this technique. In general, the proximal and distal ends of the rod are provisionally placed. After this, each vertebral segment is reduced to the construct. This technique is useful in correcting lateral and rotational deformity. Proper contouring of the rod allows for the maintenance of physiologic lumbar lordosis and thoracic kyphosis. Translation, however, places high stress on the bone/implant interface, and there are limits to reduction before implants fail, either by loss of fixation (loosened screw), failure (instrumentation fracture), or failure to maintain correction.
In situ bending is another method for obtaining coronal correction. Fig. 4 demonstrates this technique. In this method, the rod is shaped and fixed to the spine. The deformity is then corrected by bending the rod to the desired shape with in situ bending tools. This method provides for correction of lateral deformity. Again, this technique results in high stress on the instrumentation and bone. With titanium rods, multiple bends can lead to increased rod notching and structural weakening of the rod with associated risk of rod fracture.
Segmental rod translation applies the techniques of translation in a segmental fashion. Again, the rod is contoured to the appropriate shape with care taken to address the physiologic contours of the sagittal plane. As opposed to the translation techniques describe previously, the rod is secured at 1 end only. Each segment is brought to the rod, and the deformity is reduced at each segment, leading to a realigned spine ( Fig. 5 ). A benefit of this approach is that less stress is applied to the instrumentation and bone, as the reduction is gradual and controlled. In addition, lateral and rotational components of deformity can be readily addressed.
Related posts:
Clinical and Radiographic Evaluation of the Adult Spinal Deformity Patient
Spinal Deformity Surgery
Classifications for Adult Spinal Deformity and Use of the Scoliosis Research Society–Schwab Adult Spinal Deformity Classification
Spinal Osteotomies for Rigid Deformities
Treatment Algorithms and Protocol Practice in High-Risk Spine Surgery
Management of High-Grade Spondylolisthesis
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