21: VEPTR Opening Wedge Thoracostomy for Congenital Spinal Deformities

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Procedure 21 VEPTR Opening Wedge Thoracostomy for Congenital Spinal Deformities

Examination/Imaging

image Patients are evaluated for curve flexibility, head decompensation, truncal decompensation, and trunk rotation.

image Resting respiratory rate is measured and compared with normative values. An elevated rate suggests the child has occult respiratory insufficiency. The lips are examined for cyanosis. The fingers are examined for clubbing, a sign of chronic respiratory insufficiency, and the percentile normal weight for age is determined. When the work of breathing is excessive, children are often underweight.

image Thoracic function resulting from chest wall expansion is assessed by the thumb excursion test (Campbell et al, 2004).

image The examiner’s hands are lightly placed on each side of the patient, around the lateral base of the thorax, with the thumbs in back pointing upward medially, equidistant from the spine (Figure 21-1). The patient breathes spontaneously, and rib cage motion carries the thumbs outward away from the spine. Greater than 1 cm of thumb motion away from the spine is normal and is graded as a +3 thumb excursion test; 0.5 to 1 cm is a +2 thumb excursion test; less than 0.5 cm motion is +1; and no thumb excursion with respiration is graded +0.

image Causes of abnormal thumb excursion test include extensive fused ribs or the distortion of rib hump. Absent chest wall motion is a sign of thoracic insufficiency syndrome (TIS), because the rib cage cannot aid the diaphragm in expanding the lung during normal respiration.

image Radiographs should include anteroposterior (AP) and lateral films of the entire spine, including the entire rib cage and the pelvis. These are assessed for Cobb angle, space available for the lungs, and head and truncal decompensation (Figure 21-2). Space available for the lungs is determined by the ratio of the height of the concave lung from the middle of the most proximal rib to the top of the hemidiaphragm compared with the height of the convex lung measured in the same fashion. Head decompensation is measured from the center sacral line to the middle of C7, and truncal decompensation is measured from the midthorax at T6 to the center sacral line.

image Supine lateral bending radiographs are used to determine curve flexibility and apex of rib cage constriction on the concave side of the curve (Figure 21-3, arrow). In cases of thoracic kyphosis, a cross-table lateral radiograph of the spine with a bolster at the apex of the curve is included to assess for flexibility.

image Cervical spine films, with flexion/extension laterals, are performed to assess for cervical spine abnormalities and instability.

image Computed tomography (CT) scans of the chest and spine are performed, unenhanced, at 0.5-cm intervals from T1 to the sacrum, to assess for three-dimensional spine and rib cage abnormality. Thoracic rotation from rotation of the spine into the convex hemithorax with loss of lung volume is the angle between the sagittal plane of the spine and the sternum (Figure 21-4). To minimize radiation exposure, the scan should be performed at pediatric settings, with appropriate milliamperage and pitch angle.

image Fluoroscopy of the diaphragm or ultrasonography is performed to document normal function. Dynamic lung magnetic resonance imaging (MRI), if available, also can be used to assess diaphragm function.

image MRI of the entire spinal cord is performed to assess for spinal cord abnormalities.

Examination Pitfalls

Progressive thoracic insufficiency syndrome, the prime FDA indication for VEPTR treatment, is difficult to define by standard radiographic assessment, because it is a dynamic condition. Thoracic insufficiency syndrome is the inability of the thorax to support normal respiration or lung growth (Campbell et al, 2004), and the presence of either component enables the diagnosis of TIS. The disabled thorax, such as seen in a child with fused ribs, cannot expand the lung with chest wall motion on the involved side; so, normal biomechanical respiration is not possible. The same thorax, if unable to grow properly because of the rib cage constriction due to rib fusion, also has the second component of TIS.

TIS does not mean a child requires oxygen support. Pediatric patients needing oxygen, continuous positive airway pressure, or ventilator support have respiratory insufficiency, which means the respiratory mechanism is unable to provide physiologic oxygenation for the needs of the patient. Respiratory insufficiency may be due to intrinsic disease of the lungs and/or severe thoracic disability from volume depletion deformity (Campbell et al, 2003a) or abnormal thoracic function. Occult respiratory insufficiency syndrome in children with early TIS may be masked by an increase in respiratory rate, or adaptive behavior through reduction in activity levels for age. End-stage TIS almost always has associated respiratory insufficiency syndrome.

Surgical Anatomy

image Proximally, the common insertion of the middle and the posterior scalene muscle on the first and second ribs is identified. The brachial plexus and the artery lie immediately anterior to this (Figure 21-5). It is an important landmark, because the neurovascular bundle is just anterior. The safe zone for VEPTR proximal rib cradle attachment is posterior to the scalene muscles, extending from the second through the fourth ribs. Attachment anterior to the scalene muscles or posterior on the first rib endangers the neurovascular bundle.

image Absent ribs in the exposure are identified by palpating the flail area. These are commonly associated with dysraphism of the spine, and care should be taken to avoid violating the spinal canal in the dissection. The preoperative CT scan commonly identifies bony defects in the canal. Figure 21-6 shows the CT scan of an infant with a spinal dysraphism with the meningocele extending up to the medial border of the scapula that was poorly appreciated on radiographs. In surgery, the scapula was gently retracted upward and the rhomboid muscles dissected just adjacent to the edge of the scapula so that the dura was not injured.

Positioning

Portals/Exposures

Procedure

Step 1: Insertion of Superior Rib Cradle for the Hybrid VEPTR

image After exposure is completed, the level of the insertion of the superior rib cradle is located. This is based on radiographic evidence and confirmed by locating the first rib by palpation and counting ribs downward. The superior cradle should be placed at the proximal end of the rib cage constriction, which is commonly proximal to the apex of the congenital spinal curve. The site is marked by cautery, just lateral to the tips of the transverse processes.

image A 1-cm portal for insertion of the superior cradle is made by cautery at the correct level in the midportion of the intercostal muscle or the fibrous adhesion between ribs, just adjacent to the tip of the transverse processes.

image Another portal, 5 mm wide, is placed superiorly for the upper portion of the superior cradle, called the cradle cap. If a standard cradle cap is used, then approximately 1 cm of distance should separate the inferior and superior portals for the rib cradle. If an extended cradle is used to surround more bone or even two ribs, then a 1.5-cm distance is needed.

image A curved Freer elevator is then inserted through an intercostal incision into the inferior portal, pointed proximally, and is used to strip away the combined pleura/periosteum from the anterior surface of the rib, carefully creating a soft tissue tunnel up to the superior portal without damaging the neurovascular bundle. Next, a second Freer elevator is inserted into the superior portal and touched to the tip of the inferior Freer elevator in order to verify that a continuous soft tissue tunnel has been developed (Figure 21-12).

image The trial for the device is then inserted into the inferior and the superior portals to enlarge the soft tissue tunnel.

Step 2: Opening Wedge Thoracostomy

image The opening wedge thoracostomy is then performed at the center of the thoracic constriction. This is identified on plain AP radiographs, especially on the bending films, where there is an area of frank constriction of fused ribs or narrowed intercostal spaces.

image In a rib fusion mass of three or four ribs, in general, an opening wedge thoracostomy through the center is recommended.

image The line of the thoracostomy is first marked by cautery at the correct level along the groove between fused ribs.

image The opening wedge thoracostomy is begun anteriorly where the ribs begin to separate, where there is usually fibrous tissue or an intercostal muscle interval that gradually narrows to a groove in the fused bone posteriorly (Figure 21-14).

image Once this fibrous tissue or muscle has been lysed by Bovie cautery, a no. 4 Penfield elevator is inserted, pointing posteriorly along the line of the thoracostomy to be created, to strip away the pleura and periosteum for a distance of 2 cm. Then a Kerrison rongeur or Midas Rex bone cutter (Medtronic, Minneapolis, Minn.) is used to cut medially along the groove through the bone, with the Penfield elevator protecting the underlying soft tissues. This step is repeated until the tip of the transverse processes is reached.

image The thoracostomy should also extend anteriorly to the costochondral junction.

image If there is fibrous adhesion between ribs or intact intercostal muscle close to the center of the fused mass, the thoracostomy is preferentially placed there. In this case, the intercostal muscle or fibrous tissue is incised by cautery, with a right-angle clamp elevating the muscle to minimize damage to the underlying pleura.

image Once the thoracostomy interval through bone, fibrous tissue, or intercostal muscle is complete, an AO bone spreader is inserted between the ribs to gradually widen the thoracostomy interval, with lengthening of the concave hemithorax and indirect correction of the scoliosis (Figure 21-15).

image The interval medial to the transverse processes should open easily, but if there is dense fibrous tissue, this is gently probed with a Freer elevator to lyse it, with care taken not to enter the spinal canal.

image If bone is present medial to the tips of the transverse processes along the interval, it must be resected.

image The fused rib is exposed carefully with a Freer elevator, with resection by a rongeur. A 1-cm wide channel is cut down to the vertebra. Care must be taken not to violate any anomalous segmental arteries exiting through the rib fusion mass. Within 1 cm of the spine, the remaining bone is removed by a curved curette, using it to disarticulate the remaining medial portion of the fused rib.

image The AO bone spreader is removed, and a VEPTR rib retractor is placed to further enlarge the opening wedge thoracostomy.

image With a small moist sponge on a clamp, the pleura is then mobilized by rolling it down from the underlying periosteum of the ribs, both proximally and distally, from the line of the opening wedge.

Step 2 Pearls

The superior cradle is tilted medially at insertion because of the oblique position of the rib of attachment, but with successful hemithorax deformity correction through thoracostomy, it gradually assumes a position parallel to the longitudinal axis of the body, with transverse orientation of its rib of attachment.

If the area of rib fusion on the concave side of the curve is greater than four ribs, a second, or even third, thoracostomy must be performed to completely correct the deformity, with at least two rib thicknesses between thoracostomies.

It is important to use a soft tissue–sparing technique in performing the thoracostomy and inserting rib cradles. Stripping the periosteum over the ribs to facilitate exposure may devascularize the ribs and result in later absorption.

Small rents in the pleura (less than 2 cm) are not serious and do not need repair. Larger tears are patched with Surgisis (Cook, Bloomington, Ind.) bioabsorbable membrane.

Chest tubes are usually placed only if there is a “leak” from a visceral pleural tear of the lung or large quantities of pleural fluid are expected postoperatively.

If the gap of the opening wedge thoracostomy needed to correct the constricted hemithorax is greater than 3 to 4 cm in width, the patient may develop a clinically flail chest. This is addressed by a centralization transport procedure (Campbell et al, 2004) in which a section of two fused ribs, either above or below the opening wedge thoracostomy, is osteotomized free through a second opening wedge thoracostomy and rotated centrally. With the large gap of the first opening wedge thoracostomy stabilized by the centralization transport, the risk of clinical flail chest is minimized.

Alternatively, additional rib-to-rib VEPTRs may also be added anterolaterally to stabilize the flail area of the chest wall. These devices should not extend more proximal than the third rib because of proximity of the brachial plexus.

Step 3: The Hybrid VEPTR

Step 4: Implantation of the Hybrid VEPTR

Step 5: Hybrid VEPTR Attachment to Pelvis by Dunn-McCarthy Hook over Iliac Crest

image If there are inadequate posterior elements of the posterior spine for attachment of the VEPTR hybrid spine hook, such as in myelomeningocele or dysraphism in congenital scoliosis, distraction is achieved by bypassing the spine and attaching the VEPTR hybrid lumbar extension rod to the iliac crest through a Dunn-McCarthy hook placed on top of the iliac crest.

image A longitudinal 6-cm skin incision is made over the iliac crest on the side of the lumbar hybrid extension and carried down to the dorsal fascia, just lateral to the posterior superior iliac spine. The apophysis at the junction of the middle and posterior thirds of the iliac crest is exposed.

image Using cautery, the hip abductors are released over the bony part of the iliac crest just below the apophysis and reflected laterally with a Cobb elevator to create a pocket for the outer portion of the Dunn-McCarthy hook within the central third of the iliac crest (Figure 21-18).

image A transverse incision is made in the middle of the apophysis with equal amounts of cartilage above and below. The interval is widened with Crigo elevators, and a tract is created over the anterior cortex of the iliac crest. The sacroiliac joint should be just medial to the tract. This is confirmed by placing a Crigo elevator through the apophyseal incision of the crest and then shifting the instrument to touch the lateral edge of the sacroiliac joint (Figure 21-19). The Dunn-McCarthy hook is then inserted through the incision.

image Once the hook is in place, a 1 Prolene suture is placed through the apophysis and around the hook to help acutely immobilize the hook. A bone cap forms over the hook within 4 weeks of surgery.

Step 6: Addition of Second Rib-to-Rib VEPTR

Step 7: Closure

Step 7 Pearls

To aid closure, the combined skin and muscle flaps are grasped with dry laparotomy sponges and then stretched toward the middle of the exposure. This is usually adequate to enable overlap of the skin edges.

If desired, a catheter for infusion of local anesthesia can be placed under the flaps.

If there is a pleural rent greater than 3 to 4 cm, this can be patched with a bioabsorbable membrane, such as Surgisis, sutured with absorbable sutures around the periphery of the pleura.

To gain further closure, it is useful to undermine the muscle layers by cautery in both the superior and inferior flaps.

If during closure signs of acute thoracic outlet syndrome are seen upon decreased signal on the pulse oximeter as well as change in the upper extremity spinal cord monitoring, then closure is relaxed. Tracings and pulse oximeter signals usually return to normal.

Persistent loss of somatosensory evoked potentials tracings/pulse oximeter signal, indicating significant brachial plexus compression with elevation of the fused first and second ribs, may require acute partial resection of the first and second rib under the brachial plexus to relieve the obstruction if relaxation of distraction does not improve the findings. A trough in the fused ribs can be cut lateral to the rib cradle to allow passage of the neurovascular bundle without weakening the construct (Figure 21-24). This can be done through the thoracotomy incision, but also can be accomplished later through an axillary approach.

Postoperative Care and Expected Outcomes

image Patients are kept in the intensive care unit for observation for approximately 3 to 5 days.

image Extubation is usually possible 48 to 72 hours after surgery.

image Pain control is addressed with intravenous morphine and oral codeine.

image Subcutaneous catheters for local anesthesia are usually removed in 48 hours.

image Chest radiographs are taken on a daily basis for 3 to 4 days.

image Although minimal blood loss is usually encountered during the actual procedure, the risk of requiring transfusion is approximately 50% because of continued oozing beneath the flaps. The hematocrit and hemoglobin should be checked daily for several days. The author’s institution transfuses children in order to maintain a hematocrit of 30%, to maintain good oxygen-carrying capacity.

image The Jackson-Pratt drains are removed when each one has an output of only 20 mL or less over a 24-hour period.

image Chest tubes are removed when drainage has decreased to 1 mL/kg/day.

image Postoperative radiographs are performed after all drains are removed. This includes weight-bearing AP and lateral films of the entire spine, including the chest.

image Usually a large pleural effusion is seen on radiograph; this is normal. This procedure acutely enlarges the thorax while the underlying lung remains of normal size; so the additional volume is filled by pleural effusion. This effusion will slowly be replaced by the enlarging lung over a period of 3 to 6 months after surgery.

image Prophylactic intravenous (IV) antibiotics are used for 7 days for implants, 3 to 5 days for replacement procedures, and 2 days for expansion procedures.

image Expected outcomes of treatment of fused ribs and congenital scoliosis include an average reduction in curvature of 25 degrees, improvement in the space available for the lungs to an average of 80% (Campbell et al, 2003b), and an average 7% increase in length of unilateral unsegmented bars with growth in height of the thoracic spine (Campbell and Hell-Vocke, 2003). The percent of normal vital capacity at follow-up is most favorable for those patients treated by VEPTR opening wedge thoracostomy at age 2 years or younger, and least favorable in those patients older than age 2 years at the time of VEPTR surgery, with a history of prior spine fusion (Campbell et al, 2003b).

Expansion of the Devices