Scoliosis in younger children is characterized by early onset and progressive worsening of the deformity, making it difficult to treat and one of the challenges of spinal surgery. Delaying the age of surgery through brace therapy has limited corrective effect and it is difficult for the child to adhere to the brace.
Adolescent patients with severe scoliosis can undergo orthopedic fusion surgery, which has less impact on their spinal development and cardiopulmonary function. However, in younger children with scoliosis, orthopedic fusion surgery significantly affects the development of the child’s spine and thorax, resulting in disproportionate trunk and lower extremities, which is difficult to accept; in children under 5 years of age, spinal fusion surgery can also affect the development and function of the patient’s heart and lungs. In addition, spinal mobility and function are inevitably affected after surgery, and the incidence of spinal degeneration in adjacent segments of the fused spine, especially the lumbar segment, adjacent segmental kyphosis, lower back pain, endophyte-related complications, and late onset infection is also higher. Therefore, some scholars in China and abroad have been trying to treat scoliosis in younger children with some non-fusion spine methods. At present, there are three major types of non-fusion surgery for scoliosis: 1) spinal growth valve technique; 2) vertical expandable prosthetic titanium rib (VEPTR) technique; and 3) anterior vertebral body U-nailing technique. The first two of them are delayed fusion techniques, and the latter is a complete non-fusion technique. Among them, the spinal growth valve technique is currently the most widely used non-fusion spine surgery in clinical practice.
1. History of the spinal growth valve technique
The first non-fusion internal fixation technique for scoliosis was recommended by Paul Harrington for scoliosis in younger children, and in 1977 Marchetti et al. first proposed the concept of “telescopic fusion”, in which an internal fixator is placed at the end of the scoliotic spine with limited fusion around the fixator to prevent prolapse or loosening. In 1984, Moe et al. reported initial results of subcutaneous placement of metal rods (Harrington rods or Moe rods) to control severe scoliosis in younger children, followed by the CD and TSRH techniques and their modifications. The Tandem technique uses a tubular connector to connect two short rods together (similar to a tie rod antenna), which are pulled out in opposite directions and secured with small screws during the lengthening procedure, which not only allows for periodic lengthening of the spine, but also reduces skin compression due to its smaller size compared to the Domino connector.
2. Indications for the spinal growth valve technique
The spinal growth valve technique is not limited by the type of scoliosis, and can be applied to patients of low age with various types of scoliosis, including idiopathic, congenital, and neuromuscular. Although there are no uniform indications, the majority of scholars agree that patients undergoing the spinal growth valve technique must meet three criteria: (1) significant longitudinal growth capacity of the spine; (2) scoliosis with a Cobb’s angle greater than 50° and progressive worsening; and (3) good flexibility of the scoliosis or good flexibility after release surgery. Because the spinal growth valve technique of bracing operation has a tendency to aggravate kyphosis, kyphotic deformity is a relative contraindication.
3. Technique of spinal growth valve operation
For the growth valve technique, general anesthesia is performed routinely with the patient in the prone position. The vertebrae above and below the internal fixation area are positioned according to the preoperative radiographs. A median skin incision of approximately 3 cm is made above the internal fixation zone, and the paravertebral muscles on both sides of the spine are peeled off to insert screws, pedicle hooks, or transverse process hooks into the vertebrae in the fixation zone. A metal rod of appropriate length is placed above and below the internal fixation area on each side of the spine, with one end of the rod attached to the nail or hook and the other end inserted subcutaneously. A median skin incision of approximately 3 cm in length is made at the joint of the two rods, and a domino connector or tubular connector is inserted into which the rods are inserted, braced on both the concave and convex sides of the scoliosis, and then the rods are locked in place. The rods and connectors are inserted into the muscle without exposing the posterior vertebral structures such as the laminae and articular processes. Thereafter, bracing is performed at 6- to 12-month intervals, and after the child has reached maturity, conventional internal spinal fusion fixation is performed.
4. Clinical results of the spinal growth valve technique
In 1984, Moe reported the preliminary results of 20 patients with scoliosis who underwent unilateral or bilateral spinal growth valve surgery. Of these, nine cases ultimately required spinal fusion surgery, five cases had internal fixation dislocation, and four cases had broken sticks. In the nine patients who ultimately underwent spinal fusion, the mean scoliosis Cobb’s angle was 58° before the first surgery, 40° immediately after surgery, and the scoliosis was stable at 43° after a mean follow-up of 15 months. percent). In contrast, the 11 patients who did not ultimately undergo fusion had a mean scoliosis Cobb’s angle of 70° before the first surgery and 38° at the most recent follow-up.Klemme et al. treated 67 pediatric scoliosis patients with the spinal growth valve technique and reported similar results. These authors concluded that non-fusion surgery for scoliosis is superior to traditional fusion surgery for internal spinal fixation in children with scoliosis who have significant growth potential in the spine.
In 2004, Thompson and Akbarnia concluded in a retrospective study of 28 patients undergoing growth valve surgery that in children with severe scoliosis, although both unilateral and bilateral growth valve techniques helped to control the progression of scoliosis and maintain the growth potential of the spine, the results of bilateral growth valves were significantly better than those of unilateral growth valves. Short-segment fusion of the parietal spine is not necessary in either growth valve technique.
In 2002, Miniero and Weinstein reported the results of spinal growth valve surgery in 11 children with low-grade scoliosis. During follow-up, the 11 patients underwent a total of 53 procedures and had 17 complications. Therefore, the authors concluded that although the subcutaneous growth valve technique is an option for progressive severe childhood scoliosis, its results may not be superior to direct single anterior or posterior spinal fusion internal fixation.
In 2004, Thompson and Poe-Kochert followed 47 patients after unilateral growth valve surgery and found that severe scoliosis in children often progressed rapidly, with more complications after unilateral growth valve surgery, a less than ideal patient profile, and a difficult spontaneous fusion of the spine during treatment.
In 2006, Prof. Qiu Yong followed up 21 children after spinal growth valve surgery and found that regardless of the type of single-rod lengthenable internal fixation device used, a good initial correction was obtained, but the lengthening effect decreased and the complication rate increased as the number of lengthenings increased, with nearly 3/4 of the children ultimately failing to complete the expected lengthening course. Taking into account the national situation, Professor Qiu suggests that single rod lengthenable internal fixation technique should be used with caution at present. Of course, lengthenable internal fixation is still a research direction for correction of scoliosis in younger children, especially for bilateral double-rod systems.
5. Disadvantages of the spinal growth valve technique
Although the spinal growth valve technique can effectively delay the aggravation of scoliosis and preserve some of the growth capacity of the spine, there are obvious disadvantages: (1) The spinal growth valve technique only fixes the upper and lower end vertebrae of scoliosis, and while preserving the growth capacity of the spine, it does not control the aggravation of scoliosis, especially the growth of the anterior spinal column, which can cause the “curvilinear effect The “curvilinear effect” can occur, especially in the anterior spine. (2) The spinal growth valve technique requires multiple lengthening surgeries, resulting in destruction of the vertebral periosteum and cortical bone, microhemorrhage and new bone formation, and the spine is prone to spontaneous fusion, which increases the stiffness of the spine and affects the growth capacity of the spine and the orthopedic effect of scoliosis. (3) The complication rate of internal fixation is high, and in many cases, the expected lengthening cannot be completed, which affects the treatment outcome. (4) Patients need to wear the brace for more than 22 hours a day after growth valve surgery, which brings inconvenience to their life.
6. Research progress
In order to reduce the complications associated with repeated surgical prolongation, Takaso et al. invented a remotely controllable lengthenable internal fixation device with a miniature built-in motor and an adjustable lengthening valve with a maximum outer diameter of 16 mm. This system has been successfully used in a canine scoliosis model. However, the size of the adjustable lengthening valve is too large and the micro-motor requires a separate incision into the abdominal cavity, which limits the clinical application of this technique.
In 2006, Burke et al. proposed a model of the ideal growth valve technique for the spine. He suggested that the ideal growth valve should, first, be made of a metal material with the same biomechanical properties as the bone and, second, grow as the spine grows, thereby correcting the deformity in a three-dimensional structure. He designed a growth valve structure with a shape matching the scoliosis, consisting of many unitary structures fused together with the same distance between the unitary structures as the intervertebral disc gap, each unitary structure consisting of a metal rod and an internal fixation, such as pedicle screws, pedicle hooks or transverse process hooks, which are fixed to the adjacent vertebrae of the scoliotic segment. Subject to spinal growth forces, the rods lengthen in a predetermined direction, thereby correcting the deformity. With this ideal growth valve technique, patients do not require periodic bracing and eventual fusion surgery, nor do they need to wear a brace or restrict their activities after surgery.
In conclusion, the spinal growth valve technique, especially the bilateral double rod system, is an important research direction for the correction of scoliosis in younger children, as it can effectively control the progression of scoliosis and preserve some of the growth capacity of the spine, but it should still be used with caution due to the need for multiple surgeries and the high complication rate. How to effectively avoid repeated multiple surgeries and failure of internal fixation remains a topic for future research on spinal growth valve technology.