Effectiveness and cost effectiveness of anterior versus posterior approaches for thoracolumbar fusion in adolescent idiopathic scoliosis: a systematic review protocol

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Abstract

Review question/objective

The objective of this review is to compare anterior versus posterior surgical approaches for instrumented thoracolumbar fusion in adolescent idiopathic scoliosis (AIS).

Review question/objective

The reviewers seek to critically evaluate available evidence to provide an evidence-based appraisal of the comparative safety, effectiveness and cost effectiveness of alternative surgical approaches for thoracolumbar spinal fusion in AIS.

Background

Scoliosis is a three-dimensional rotational deformity of the spine. The majority of cases present in childhood or adolescence have enigmatic aetiology and are therefore classified as idiopathic. The proportion of scoliosis diagnoses that can be attributed to a known cause is approximately 20% and these include congenital or neuromuscular disorders such as cerebral palsy, muscular dystrophy and spina bifida.

Background

Adolescent idiopathic scoliosis is typically asymptomatic in early years and then develops insidiously during early puberty, before the accelerated progression during later pubertal years of rapid growth. The spectrum of physical and psychological symptoms in AIS is diverse. In the extreme, children may be severely disabled with serious associated cardio-pulmonary co-morbidities and considerable psychological detriment due to their impaired quality of life.

Background

The age at which diagnosis and early detection are done has prognostic significance. In early onset idiopathic scoliosis (defined as diagnosed less than 10 years of age), almost 90% of curves progress from their original state, with the majority of these requiring surgery. In 2006, a community-based self-detection tool was implemented to aid early diagnosis of immature curves at a young age. The “forward bend test” was a popular component of this nationwide screening program. Other characteristic features that were observed included asymmetrical shoulders or scapulae, uneven hips or chest wall prominence.

Background

Quantification of curve severity is generally determined by radiographic calculation of curve dimensions. The Cobb angle is a standard method of curve size estimation measured on plain spine radiographs. Curves with a Cobb angle of <10° are considered spinal asymmetry within normal range and are not associated with any long-term sequelae.1 The prevalence of AIS with a Cobb angle ≥10° is approximately 3%, but only 10% of these require treatment1. Curves with Cobb angle >10° may be expected to progress approximately 1° per month during the adolescent growth spurt. The velocity of curve progression is difficult to predict and requires scheduled assessment on a biannual or annual basis.

Background

Non surgical options for management of AIS consist of conservative observation and bracing techniques. The orthosis brace is designed to act as a three point fixation buttress to attenuate curve progression during active skeletal growth. Braces are limited in that they frequently do not permanently correct the curve and, at best, prevent worsening of the curve, although this is controversial2. The definitive surgical management for AIS is instrumented spinal fusion and this usually offers effective, lifelong deformity correction.3-5 For patients with an immature spine and a Cobb angle >50°, the pathological curve would be expected to continue to deform the patient. Severe curves in young patients can lead to Thoracic Insufficiency Syndrome with the inability of the deformed thorax to support normal respiration or lung growth.

Background

Surgical technology for spinal deformity correction has been evolving for over 100 years.6 Initially the instrumentation was designed to halt progression; however, no correction of the deformity was achieved. Later, a hook-rod method was developed which allowed concave distraction and convex compression to achieve true correction. Since the introduction of strategically placed anchors, surgeons have been able to attain de-rotation of vertebrae and improve the three dimensional profile of the deformed spine6.

Background

The choice of either anterior or posterior operative approaches is influenced by the location and pattern of the scoliosis curve. An anterior approach is generally used for thoracic curves while a posterior approach is generally used for lumbar curves. Thoracolumbar curves generate an apex at the junction between thorax and lumbar regions and consensus for the best suited operative approach for these curves remains conjectural.

Background

Traditionally, an anterior approach has been used for thoracolumbar surgery in an attempt to reduce the number of vertebrae being fused especially in the lower lumbar spine where mobility is ideally maintained. However, more recently, the advent of pedicle screw fixation has allowed surgeons to achieve similar correction with shorter fusions from a posterior approach. This has set a new benchmark in scoliosis surgery and patient satisfaction.

Background

The decision to opt for an anterior or posterior approach for a thoracolumbar fusion is made with consideration of various approach related pros and cons in the context of each individual case and surgeon experience. Anterior instrumentation and fusion involves exposing the convex side of the spine via either a: 1) thoracotomy 2) flank incision, 3) combined thoracotomy and retroperitoneum exposing flank incision, or 4) thoracoscopy. Direct visualization of the curve allows the surgeon to shorten the convex side of the deformity.7 This is a fundamental difference to posterior instrumentation, which relies on a degree of distraction to gain correction. The reported merits of the anterior approach include: less blood loss, lower risk of infection and neurologic injury, fewer vertebral levels fused and no violation of the posterior paraspinal muscles.8 One approach related disadvantage is an increased degree of technical difficulty which can compromise mobilization of major blood vessels. There is also a risk of temporary or permanent damage to the diaphragm, with subsequent pulmonary co-morbidity.9

Background

The posterior approach involves the prone patient positioning, a long midline incision and then sharp dissection through erector spinae muscles to the exposed spinal vertebrae. Stainless steel, cobalt chrome or titanium hooks and rods or screws are commonly used in various combinations for instrumented fusion. Surgeons can contour the rods to individual curves at multiple vertebral segments. The introduction of posterior pedicle screws at individual segments has allowed surgeons in the last 20 years to gain increased control in correcting rotation, distracting and compressing the spinal curve due to the strength and security of fixation. In addition, the stability of segmental instrumentation (most vertebral levels are secured by implants) has allowed early mobilisation of the patient postoperatively without the need for external bracing.10

Background

The literature reflects largely comparable curve correction being achieved through both approaches. However, the number of fusion levels was significantly fewer with anterior fixation.11 The ease of the anterior approach, release and instrumentation seems to permit less required instrumentation to maintain comparable curve correction. In addition, the anterior approach has a lower infection rate12 and lower systemic metal ion levels.11 However, studies evaluating pulmonary function pre and postoperatively showed that patients undergoing posterior fusion had better measures of pulmonary function than the anterior group.12 Posterior approach is less technically complex5 (for most surgeons) and has a lower rate of revision surgery compared to thoracoscopic anterior approaches.13 Due to more levels being fused and the higher implant density required to maintain correction, the posterior approach is more expensive.14 A small number of studies have reported significant reductions in estimated blood loss with anterior surgery, while several studies have observed a reduction in operative time and length of hospital stay with posterior surgery.

Background

The justification of higher implant density in posterior approach, and therefore greater cost per instrumented fusion, remains to be proven. In addition, does the reported reduced operative time and length of stay in posterior surgery equate to a cost minimisation despite an initial higher implant cost?

Background

Overall, confusion exists in the understanding of whether one approach is more beneficial compared to the other. Due to the wide range of outcome measures that are relevant in this context, it is important to collate and synthesize the evidence for a broader and more transparent understanding of salient advantages and disadvantages.

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