Dystrophic scoliosis

https://www.wheelessonline.com/bones/scoliosis-in-neurofibromatosis/

https://pubmed.ncbi.nlm.nih.gov/8175817/

Dysplastic type: (dystrophic)

Short, sharply angulated curve which involve only few vertebra;

Associated w/:

Neural foramina enlargement
Rib penciling
Kyphosis;
Vertebral body scalloping
Dural ectasia
Soft tissue masses;

Treatment: of Dysplastic Scoliosis;

One can expect relentless progression that is refractory to bracing;

Surgical fusion is therefore required;

w/ scoliosis alone: posterior arthrodesis (w/ internal fixation);
w/ associatted kyphosis there is increases risk of paraplegia & pseudo-arthrosis following surgery;

Anterior fusion combined w/ posteiror instrumentation & fusion is indicated when kyphosis > 50 deg or scoliosis is > 80 deg

General

Caused by mutations in the tumour suppressor NF1 gene.
Scoliosis is the most common bony abnormality associated with NF1,

numbers

Patient Demographics and Deformity:

The mean age of patients at surgery ranged from 7 to 22 years,

99.7% being under 18.

The mean preoperative coronal Cobb angle was 75.2°, with an average correction of 40.3° achieved.

Natural History

Dystrophic scoliosis often results in kyphoscoliosis and spontaneous subluxation in severe untreated cases.

It can progress significantly; one study reported a mean progression rate of 8.1° per year for coronal Cobb angle and 11.2° per year for sagittal Cobb angle.
Unlike idiopathic scoliosis, even mild to moderate curves (<40°) can progress after skeletal maturity, and severe curves progress more rapidly.
Predictors of progression include vertebral body scalloping, apical vertebral rotation greater than 11°, early onset, and larger curves

Pathophysiology of NF1 dystrophic scoliosis

Tumour Burden and Mass Effect:

NF1 is caused by mutations in the tumour suppressor NF1 gene.
Spinal tumours are reported in 1.5% to 24% of NF1 patients.

Patients with dystrophic scoliosis have a higher incidence and greater tumour burden.

Spinal tumours in NF1 are

Intraforaminal (56%)
Intradural extramedullary (33%)
Intramedullary (6%)

Paraspinal neurofibromas are specifically associated with

increased apical vertebral rotation
rotatory subluxation.

Tumour growth and mass effect can lead to osseous changes, contributing to the dysplastic features.

For instance, extensive plexiform neurofibromas encasing the retroperitoneal cavity and extending intradurally can be observed in patients with severe lumbar kyphoscoliosis.
In patients with extensive tumour burden (circumferential involvement), tumour resection is crucial for exposing the spine and aiding in spinal deformity correction.

Plexiform neurofibromas can be unpredictably vascular, making meticulous hemostasis vital during surgery to manage high-volume blood loss.

Dural Ectasia:

Dural ectasia, an abnormal expansion of the thecal sac with increased cerebrospinal fluid (CSF) space, is reported in up to 29% of NF1 patients with dystrophic scoliosis.

This is a higher incidence compared to 11% in those with nondystrophic scoliosis.

It is associated with dysmorphic bony findings such as vertebral body scalloping and wedging.
Chicken or egg

There is some controversy as to whether dural ectasia is caused by abnormally high hydrostatic pressure, or if it simply represents the filling of the spinal canal as independent osseous changes occur.

Dural ectasia can pose significant challenges during surgery, with an increased risk of CSF leaks during decompressions or osteotomies, and potential for postoperative complications like wound complications and meningitis.

Abnormal Bony Metabolism:

Dysregulated bony metabolism in NF1 patients is thought to contribute to de novo pathological bone remodelling independently of external elements like tumours or dural ectasia.
This suggests an inherent problem with bone formation and remodelling in NF1.

Management

Conservative

Eg: corrective bracing
Generally ineffective, with curves often progressing despite their use, even in mild to moderate cases.
One study showed significant curve progression in patients who wore a brace for at least 12 months, leading to the conclusion that bracing was of "no value" in dystrophic scoliosis treatment.

Surgical

is complex due to factors such as tumour burden, dural ectasia, poor bone quality, dysplastic pedicles, and the severity of the deformity.
Early intervention for moderate curves. Some surgeons suggest that all moderate curves with dystrophic features warrant surgical intervention, regardless of skeletal maturity or curve extent. Many studies in the review reported surgical outcomes for dystrophic scoliosis patients with curve thresholds of 20° to 35° and greater.
Growth-friendly constructs can be considered for early-onset, skeletally immature patients with large dystrophic curves, though outcomes are mixed and definitive fusion is often preferred if possible.
Indication for surgery

When NF1 scoliosis become dystrophic there is a need for surgery even without curve progression

Monitor this by close CT scan as xray can miss dystrophic changes
When patient develop dystrophic changes and curve progression, it will be too late as there wont be pedicles for pedicle fusion purposes.

Moderate to Severe Curve Progression:

Curve thresholds of 20° to 35° and greater.
Irrespective of the patient's skeletal maturity or the extent of the curve.
Dystrophic scoliosis is characterised by an early onset and rapid progression, often leading to kyphoscoliosis and spontaneous subluxation in severe untreated cases.

Tumour-Related Neurological Compromise:

Resection of intraspinal (foraminal, extradural, and/or intradural) tumours is primarily indicated if

they cause neurological deficits OR
Place the patient at risk for neurological compromise following deformity correction.

In cases of extensive tumour burden, tumour resection is also essential to adequately expose the spine and aid in deformity correction.

Consideration for Early-Onset Cases:

In early-onset, skeletally immature patients with large dystrophic curves, growth-friendly constructs can be considered, though outcomes are varied, and definitive fusion is often preferred if feasible.
Aim of growth friendly rods to slow curvature progression until patient is old enough for lung and pedicle maturation for definitive fusion.

Growth friendly rods have diminishing returns i.e. second growth rod extension will likely not improve curve progression much.

Even mild to moderate curves (< 40°) can progress after skeletal maturity, and severe curves progress more rapidly.

Deformity management

Surgical techniques

Variety of approaches: Varied

Posterior-only
Combined anterior-posterior
Growth-friendly surgery.

Growing rods

Associated with higher rates of implant-related complications, reoperation, and lower curve correction rates in some comparisons with fusion

Fixation techniques

Pedicle screws offer the greatest control, reliability, and rigidity.
However, dysplastic pedicles are a significant challenge, making pedicle screw placement difficult or impossible.
Pedicle dysplasia can lead to high rates of malpositioned screws (20% to 30%), even with navigation guidance.
Hybrid constructs are often necessary due to dysplastic pedicles, combining pedicle screws where amenable with hooks (laminar, pedicle, transverse process), laminar bands, and wires at severely dysplastic levels.
High implant density is crucial for optimal correction and to decrease the loss of correction, regardless of the specific implants used.

High-Grade Osteotomies

Low rate of high-grade osteotomies: Only 0.9% of patients in the reviewed studies underwent vertebral column resection (VCR). This is surprisingly low given the rigidity and severity of many dystrophic curves.
Reasons for low VCR use may include the steep learning curve, difficulty in achieving adequate fixation at the curve apex, the presence of dural ectasia, and differing surgical goals (stabilisation vs. aggressive correction).
Feasibility: Despite being technically demanding, VCR can be performed in carefully selected patients with dystrophic scoliosis, as highlighted by case reports demonstrating significant kyphotic and coronal correction.

Tumour Resection

Common occurrence: Up to 58% of NF1 patients have spinal nerve sheath tumours, with a higher incidence and burden in those with dystrophic scoliosis.
Necessity for exposure and correction:

In cases of extensive tumour burden (e.g., circumferential involvement, plexiform neurofibromas), tumour resection is essential to expose the spine and facilitate deformity correction.

Challenges:

Plexiform neurofibromas can be unpredictably vascular, making meticulous haemostasis crucial to manage potentially high-volume blood loss, especially in paediatric patients.

Neurological compromise:

Resection of intraspinal tumours is primarily indicated if they cause neurological deficits or pose a risk of neurological compromise following deformity correction.

Outcome

Complications:

Non-neurological complications

occurred in 14.0% of patients, primarily dural tears and wound infections.
The rates varied significantly between studies (0% to 72%).

Postoperative neurological deficit rate

Immediate 2.1%
Permanent neurological deficit rate was 1.2%

Spinal cord injuries were more likely to result in permanent deficits than nerve root injuries.

These rates are surprisingly low compared to other severe paediatric deformities, potentially indicating underreporting or less aggressive surgical approaches.

Revision Surgery:

A high rate of revision surgery (21.5%) was observed,
Due to

Implant-related complications such as rod fractures, pseudarthrosis, and junctional failures.

Presented as loss of correction in both sagittal and coronal planes commonly occurred at follow-up.

Patient-Reported Outcomes Measures (PROMs)

Generally showed improvement in mental health, self-image, and activity domains following surgery.

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