Interventional procedure overview of vertebral body tethering for idiopathic scoliosis in children and young people

Indications and current treatment

Scoliosis causes the bones of the spine to twist or rotate so that the spine curves sideways. Scoliosis curves most commonly happen in the upper and middle back (thoracic spine). It can also develop in the lower back and, occasionally, happens in both the upper and lower parts of the spine.

Idiopathic scoliosis is the most common type of scoliosis. It is a progressive condition, and its exact cause is unknown. There are 3 types of idiopathic scoliosis: infantile idiopathic scoliosis, juvenile idiopathic scoliosis and adolescent idiopathic scoliosis.

Treatment of idiopathic scoliosis depends on a number of factors, including age, severity and location of the spinal curve, and the pattern and progression of the curve. In many cases, idiopathic scoliosis is mild (a curve of less than 25^°) and does not need treatment other than close monitoring and physical therapy. For moderate scoliosis (a curve between 25^° and 45^°) and severe scoliosis (a curve greater than 45^°), treatment includes casting, bracing and surgery (such as spinal fusion and growing rods).

What the procedure involves

Vertebral body tethering is a nonfusion spinal treatment for idiopathic scoliosis. The aim is to preserve the flexibility of the spine and modulate its growth on the concave and convex sides, so slowly correcting the scoliosis.

In this procedure, under general anaesthesia, screws are placed into each vertebra at the convex side of the spine. The screws are connected by a flexible cord. Tension is then applied to the cord to partially correct and tether the convex side of the spine and so restrict its growth. Thoracic tethers are usually done through a thoracoscopic or open approach and lumbar tethers need a mini-open approach. After surgery, the cord continues to restrict growth on the convex side while allowing faster growth on the concave side, so potentially producing further correction of the scoliosis.

The technique exploits a known reaction of bone to being stretched or being compressed. This response is known as the Heuter–Volkmann law and notes that bone growth increases when stretched and decreases when compressed. In scoliosis this response can be used on a curved spine if the bones still have significant growth potential.

Outcome measures

The Cobb angle is used to quantify the magnitude of spinal deformities, especially in the case of scoliosis, on plain radiographs. Scoliosis is defined as a lateral spinal curvature with a Cobb angle of 10^° or more. A Cobb angle can also aid kyphosis or lordosis assessment in the sagittal plane. Overall, if a greater than 10^° change in Cobb angle is measured, it is 95% likely to represent a true difference.

The normal ranges of motion for the thoracic spine include 30^° of rotation and 50^° of kyphosis. The normal lumbar ranges of motion include 60^° of flexion, 25^° of extension, and 25^° of lateral or side bending.

Pulmonary function tests measure how well the lungs work and include tests that measure lung volume, capacity and air flow, such as:

If the FVC and FEV1 are equal to or greater than 80% of the reference value, the results are considered normal. The normal value for the FEV1/FVC ratio is 70% (and 65% in persons older than age 65). When comparing with the reference value, a lower measured value corresponds to a more severe lung abnormality.

The Risser classification is used to grade skeletal maturity based on the level of ossification and fusion of the iliac crest apophyses. It is primarily in planning corrective surgery for scoliosis, consisting of stage 0 to 5:

The Sanders maturity scale gives a measure of progression of ossification and predicts the curve acceleration phase of growth.

The EOSQ-24 is a validated questionnaire to measure the caregiver perspectives of health-related quality of life and burden of care of patients with early-onset scoliosis. It includes 24 items across 12 domains (general health, pain/discomfort, pulmonary function, transfer, physical function, daily living, fatigue/energy level, emotion, parental impact, financial impact, child satisfaction and parental satisfaction). Each domain is scored from 0 to 100, with lower scores indicating greater disability.

The SRS-22 questionnaire is used to assess health-related quality of life in patients with scoliosis. It includes 22 items distributed among 5 domains (pain, self-image, function/activity, mental health, and satisfaction with management). Each item is scored from 1 (worst) to 5 (best).

The SF-36 questionnaire is a measure of health status to determine the impact of interventions. It includes 36 items across 8 domains (physical functioning, physical role limitations, bodily pain, general health perceptions, energy/vitality, social functioning, emotional role limitations, and mental health). Each domain is scored from 1 to 100, with a higher score indicating a better health status.