Tuesday, January 10, 2023

 Blog Topic: Neuromuscular Scoliosis: Use of Magnetically-Controlled Growing Rods



In the second-to-last blog post the concept of using Magnetically-Controlled Growing Rods (MCGR) was presented for treatment of NeuroMuscular Scoliosis (NMS). In that post the different cranial/upper and the caudal/lower foundations were discussed briefly, and the reasons for why we choose one type over another.  In this post the use of proximal screws and distal pelvic fixation will be presented.


Below is a 7 year old female with cerebral palsy and NMS.  Her parents have noticed she is curving her body more, is having more difficulty with sitting, and is not tolerating sitting for very long periods of time which makes travel and school participation very difficult.


Because this 7 year old girl had a progressive, severe spinal deformity which is impacting her quality of life, we entered into shared-decision making with parents around surgical options.  So, what are our goals of surgery?

#1: Correct spinal deformity

#2: Improve sitting

#3: Improve sitting intolerance/pain

#4: Permit vertical growth of the spine

The only way to address all 4 of these goals is to use a “growth-friendly” instrumentation, which is to use either a distraction-based construct or Shilla Growth Guidance Construct.  My present preference is to use a distraction-based construct in neuromuscular patients, though I am using Shilla Growth Guidance Constructs more and more.


The below radiographs demonstrate the flexibility of the spine deformity.  The Supine image is done with the patient lying on their back, simply taking gravity off the spine.  The Push Supine is also done laying down, but then there are two individuals using lead gloves to create three-point push on the body/spine to further improve the spine deformity. This Push Supine significantly corrects the deformity, and gives us a good idea of what type of correction will be obtained in surgery.  Hence, for this patient a distraction construct will provide good correction.


After the decision was made to use a distraction-based construct, the next step is to decide what type of actuator or lengthening mechanism can be used.  If the kyphosis is rigid on the lateral radiograph (far right radiograph, above) then we may not be able to use a magnetically-controlled growing rod, and use a traditional growing rod (TGR).  The downside to TGRs is the need for surgically lengthening in the operating room every 6 months.  However, if the kyphosis is flexible, then we can be fairly reassured that we can place a magnetically-controlled growing rod.  The below radiograph is a lateral radiograph, with the patient lying on a bolster, which causes the spine to hyperextend and if the spine if flexible the kyphosis will significantly improve.  As you see in the below radiograph, this spine has a very flexible kyphosis.


A magnetically-controlled growing rod construct, 2 rods, were placed from the cranial foundation of pedicle screws T2-T3-T4 down to two S-hooks on top of the iliac wings. As mentioned 2 blog posts ago, the cranial (top) foundation can be hooks on ribs or screws on the spine.  The placement of T2-T3-T4 pedicle screws, in this case, nice balances the very strong pelvic fixation of two iliac S-hooks.  The decision to use these S-hooks, rather than L5-S1-Iliac screws, was made to preserve the fixation points for the definitive fusion at, or near, the end of skeletal growth.



As you see above the growing rods nicely improves the oblique pelvis (left radiograph to the 2nd from left radiograph) and scoliosis.  The 2nd two radiographs on the right demonstrates the improvement of the kyphosis.


Three years after surgery (below) the spine deformity remains nicely corrected.


So how much did we lengthen the magnetically-controlled growing rods? The below pictures show the rods immediately after surgery and then at the 3 years after surgery time point.  The area identified in red is a distraction of 48 mm!


More to come on growing rods….

Tuesday, January 3, 2023


Blog Topic: Recent Publication on Anterior Vertebral Body Tethering (AVBT) Compared with Posterior Spinal Fusion for Major Thoracic Curves: A Retrospective Comparison by the Harms Study Group




Study Cohort: Thoracic Idiopathic Scoliosis patients who underwent Anterior Vertebral Body Tethering (AVBT) with minimum 2-year follow-up after surgery and propensity matched to Posterior Spinal Fusion (PSF) patients from Harms Study Group multicenter database.

237 AVBT patients (thoracic curve tethered only) vs. 237 PSF patients

Propensity matched using: age, preoperative thoracic curve magnitude, sex, and grouped Risser sign

All but one AVBT were Lenke 1 or 2


Measures: Compared preoperatively and at >/= 2-year follow-up.

               Radiographic data

               Clinical data

               Scoliosis Research Society 22-Item Questionnaire (SRS-22)




Preoperatively AVBT patients:

1.3 years younger (p<0.001) than PSF group

Triradiate cartilage were open in 59% (vs. 19% in PSF)

Smaller preoperative curves (5 degrees; p<0.001) than PSF group

               More Lenke 1 curves (81%) vs. PSF (64%)


Postoperatively AVBT patients:

               21 degrees correction from preop (44% correction) vs. PSF 33 degrees (62% correction)

               1 degree improvement from initial postop to final vs. 4 degrees worsening for PSF.

Residual thoracic curve

<35 degrees in 76% (vs. 97% for PSF)

Improvement of Angle of Trunk Rotation: 6 degrees (preop to postop) vs. 9 degrees (PSF)


LIV: T10-L3 vs. PSF T10-L4; on average PSF was 1 level longer than AVBT




AVBT broken tethers documented in 20%

Secondary surgeries:

               AVBT: 46 procedures in 38 patients (16%)

               PSF: 4 procedures in 3 patients (1.3%)


SRS-22: AVBT group with less improvement in pain and self-image


Secondary, more stringent propensity matching:

               AVBT improved 22 degrees (preop to postop) and PSF 33 degrees

               Revision rate: AVBT 10% vs. PSF 2%



Study Problems and Issues:

No reporting of Lumbar Modifiers. This can impact the outcomes of AVBT and PSF.

No power analysis was reported.

Despite primary propensity matching, the two groups were statistically different for age and curve magnitude.

There were separate cohorts analyzed in the study which is confusing. It can be assumed by the reader the more stringent propensity-matching was done primarily, and was likely underpowered, so there were few significant findings. Hence a less stringent propensity-matching analysis was performed and is the bulk of the statistical findings.

“Angle of trunk rotation” was not defined but could be assumed to be from a scoliometer measurement.

No report on how missing data was handled statistically

No Sanders grading (only Risser grades)

Minimum follow-up 2 years and mean follow-up 2.2 years +/-0.5 (which means some patients did not reach two-year follow-up).  This is a very short follow-up for AVBT and longer follow-up will likely demonstrate high tether breakage, loss of correction and higher reoperation rate.


Take-away message:

               In this short follow-up study, Posterior Spinal Fusions (PSFs) when compared to Anterior Vertebral Body Tethering (AVBT) of the thoracic spine:

Better corrected the deformity (+11 degrees coronal, +3 degrees rotational)

Were instrumented with 1 more vertebral level distally

5-12 times lower reoperation rate

               Had 21% more patients with a thoracic curve less than 35 degrees

               Reported better improvement in pain and self-image


This information needs to be discussed before surgery to achieve shared decision-making.  Both procedures correct the deformity but due to the short length of follow-up the use of AVBT in this patient population should be approached with caution.