Blog Topic:          ApiFix MID-C                                                                  5-25-2021

 

Non-fusion technologies for the treatment of scoliosis in the growing patient, has garnered increasing interest from patients and surgeons over the last 10 years.  The advantages have been touted as being a minimally invasive procedure, rapid postoperative recovery, faster resumption of normal activities, less postoperative pain and preservation of more spine motion, when compared to spinal fusions. 

 

The first system used for Anterior Vertebral Body Tethering (AVBT) was the Zimmer Biomet Dynesys system.  This system was originally designed for use in adult patients and in the posterior spine, and was used in an off-label/unlabeled manner in the anterior spine in the growing patient.  This was the precursor system to their current system which achieve FDA approval for use on the anterior spine in growing patients in August 2019.  The pluses and minuses of this surgical treatment has been previously posted on this blog, so I will refer those interested to scroll back through the blog to those posts (May 2017, November 2017, January 2018 x 2, and February 2018).

Another growth modulation system, the ApiFix Minimally Invasive Deformity Correction (MID-C) system, was also approved in August 2019.  Unlike the AVBT system, there was no similar device which could be used in the U.S. prior to the FDA approval.  Most of the clinical experience with this system, which was used for FDA approval, was from outside the U.S.  This means there is much less clinical experience with this device, when compared to AVBT, in the U.S.

As opposed to the AVBT system, which is placed on the front of the spine and compresses the convex side of the curve, the MID-C system is placed posteriorly and distracts on the convex side of the curve.

As you see above, there are two pedicle screws on the top and one at the bottom.  The mechanism is in the middle, which ratchets apart with bending. 

 

At present the current indications for the use of the ApiFix MID-C are:

               Lenke 1 (thoracic) or 5 (lumbar) curve patterns

               35-60 degrees coronal deformity

               SB to </= 30 degrees

               T5-T12 < 55 degrees

 

 

 

The surgical technique looks similar to a posterior spinal fusion, due its skin incision.  However there is not as much dissection or blood loss, so recovery is faster

 

At present the MID-C and AVBT have similar indications

 

To learn more about ApiFix MID-C:

https://apifix.com/patients-families/adolescent-idiopathic-scoliosis/

 

 

 

Blog Topic           What is the Sanders Maturity Scale for bone age?              5-23-2021

 

In the last blog post we discussed the Risser sign, a classic method to estimate bone age to predict the amount spinal growth remaining in adolescents with scoliosis.  As you see from the last diagram in that post, the Risser sign doesn’t show up until AFTER the peak height velocity. 

So why does this matter?

The faster the spine grows, the greater the risk of significant progression of the scoliosis.  The fastest time of spine growth is in the first 3 years of life (see below diagram, area in light red).

 

But the second fastest time of spine growth is during the pubertal growth phase (see below, area in light green box), and is one we call the “Peak Height Velocity”.

Using the graph above, spine growth is fairly constant between 6 and 11 years of age.  It is helpful to know before the growth acceleration occurs so we can have discussions with families about the risk of progression and the need for various types of treatment.  Bracing is a commonly used technique, but it works better in smaller, more flexible curves and it mainly tries to prevent progression, not improve the deformity.  If you want prevent curve progression, then bracing needs to be started prior to the pubertal growth spurt.

As you see below, the Sanders Maturity Scale has three more stages than Risser, and all of them are earlier making estimation of risk more precise.

If we extrapolate the lines (below) you can better appreciate how the Sanders Maturity Scale helps identify spine growth earlier than the Risser sign

 

 

To assess the Sanders Maturity Scale the hand is used, so a single hand radiograph/x-ray needs to be obtained.  It doesn’t matter which hand.

If we order a hand radiograph/x-ray it’s because we want to get a better idea of the person’s bone age so we can have more precise discussions about progression risks and treatment.

 

 Blog Topic           What is Bone Age? Why does it matter for treatment of scoliosis?    5-9-2021

 

What is bone age?

Bone age is a method to determine the skeletal maturation level of a growing person.  The younger the bone age, the more growth is ahead of them.

Why not just use someone’s chronologic age?

The chronologic age of a growing individual, which is calculated from their birth date to now, does not accurately estimate the maturation of their bones.  We all know people who are “early bloomers” and “late bloomers”, those young men who started shaving in 7^th grade vs. those who kept growing until they started college.  There is wide variation in bony maturation and growth when we look at someone’s chronologic age.

Why does bone age matter?

We can get much more precise when we look at the actual bones, and their growth plates, to get a better idea of someone’s future growth.  Remember, the more growth a person with scoliosis has remaining the greater the likelihood the scoliosis will worsen, and faster growth (during the pubertal growth phase) usually means faster progression (worsening).  So better knowing how much growth is in the future helps plan treatment more precisely.

How do you tell how old are someone’s bones?

Radiographs/x-rays are used.  Many different parts of the body have been used for determination of bone age, from the calcaneus (heel bone) to the olecranon (elbow) to the humerus (shoulder) and the hand. Classically, spine surgeons have use the Risser sign, which grades the iliac crest (hips) growth plates.  Since this part of the body is seen on spine radiographs/x-rays it doesn’t require any additional imaging. See below image, the iliac crests are at the blue arrows.

 

Where does someone look for the Risser sign?

The iliac bones (above, blue arrows), and there are two of them, one on the left and one on the right side of the pelvis.  The sit on each side of the sacrum and look like Mickey Mouse ears.

              

How is the Risser sign determined?

The Risser sign is from 0 to 5 (see below).  The iliac apophysis (a growth center for the iliac crest) is a thin strip of bone that forms on top of the iliac crests.  If there is no bone visualized on the plain radiographs/x-rays then it is called a Risser 0.  The strip of bone keeps growing back to cover the entire iliac crest (Risser 4), and then fuses to the iliac crest (Risser 5).  Once the Risser 5 stage is reached the patient has completed skeletal growth.

               Risser Sign

               Stage                    Description

0                                     Bony iliac apophysis not yet visible

1                                     Initial (<25%) ossification of the iliac apophysis

2                                     From 25% to 50% ossification of the iliac apophysis

3                                     From 50% to 75% ossification of the iliac apophysis

4                                     More than 75% ossification of the iliac apophysis

5                                     Iliac apophysis fuses to the iliac crest

 

 

 

Below is an example of a Risser 1-2 sign.  See the very small amount of bone on the outside part of the iliac crest (on the right side just below the “300” on the radiograph/x-ray).

 

The below graph demonstrates the velocity of growth, with year “zero” being the time of peak growth velocity.  As you look to the right, after menarche occurs, then Risser sign 1 occurs, almost a full year after peak growth velocity. This is a weakness of the Risser sign, it doesn’t identify the peak growth velocity, as it only occurs after it has happened.

 

To deal with this the Sanders grade was developed by Dr. Jim Sanders, the Chair of Orthopaedics at the University of North Carolina. 

Next blog post a better way to estimate skeletal age will be presented: The Sander grading system.

 

Blog Post: Idiopathic Scoliosis – Lumbar (5CN Curve Pattern)                     5-9-2021

 

14 year old female with progressive, painful thoracolumbar curve

Highly athletic, three sport athlete.  She has tried physical therapy for 3 months but has not helped decrease the intensity or frequency of her back pain.

Participating in her sports is becoming difficult and is having back pain which is interfering with normal activities she does day-to-day.

She has a 49 degree thoracolumbar curve and a very small 16 degree thoracic curve

She is almost fully grown (Risser 4)

 

 

On sidebending radiographs the 49 degree thoracolumbar curve decreases to 21 degrees.  The main thoracic 16 degree curve decreases to only 6 degrees.

 

 

The next question is: how should the scoliosis be treated?

A summary of important points about this patient:

               Physical therapy was tried but did not help.

               She is nearly fully grown, very little spinal growth remains

               Only has one curve to treat, the 49 degree thoracolumbar curve

               A curve greater than 40 degrees in the thoracolumbar region is very likely to continue to get                                  worse over time, even when she is done growing.

 

What are the treatment options:

               Nonsurgical:

Physical Therapy: can help with back pain in some patients.  However, for this patient she has tried physical therapy and didn’t get any decrease in her back pain.  So this is not a good option for her

Bracing: due to her being almost fully grown bracing will not be of any lasting benefit, so this also is not a good option.

 

               Surgical:

                              Growth modulation surgeries, such as Vertebral Body Tethering or ApiFix: Since she doesn’t have any significant growth remaining these devices will hold the curve straighter for awhile.  However it is important to remember these devices will fatigue and break of pull off the bone.  Since there isn’t much growth remaining the spine will then collapse back to the preoperative curve position.  So these are not good options for this patient.

                              Spine fusion: this can be done by either fusing the front (anterior) or the back (posterior) of the spine.  Over the last 15 years there has been a shift toward most of these being done only to the back of the spine, called a posterior spinal fusion.  This shift has occurred due to surgeons’ adoption of pedicle screws for fixation.  There is now little difference in outcomes between anterior and posterior spinal fusions for these thoracolumbar curves.

 

 

After discussion with the patient and her family the decision was to proceed with a posterior spinal fusion.  For thoracolumbar curves we can do a limited, short fusion and for this patient means going from the T10 vertebra down to the L3 vertebra.  The radiographs below are from 3 days after surgery, notice the shoulders are tilted, with the right shoulder being higher.

 

 

You can see the shoulders are level in the preoperative radiographs but the right shoulder is higher after surgery.  Why? There are two reasons.  First, when the thoracolumbar curve is corrected it is lengthening more the right than the left side of the spine. Second, there is a small thoracic curve above the fusion.  So if the right side of the spine is lengthened more than the left side and there is a slight curve to the right, this means the right shoulder will be elevated after surgery.

 

 

Since the curve above the fusion is so flexible we expect the upper curve to straighten, and at the one year postoperative visit her shoulders are now level.

 

 

As you see below the main thoracic curve slowly straightens and the shoulder become level!

 

 

This case highlights that it takes some time, up to one year after surgery for the body to rebalance itself and straighten curves and balance shoulders.

 

Blog Post: Idiopathic Scoliosis                                                         5-6-2021

Below is a 16 year old female with idiopathic scoliosis, who is otherwise healthy.

She noticed gradual development of waist asymmetry and a right rib prominence in the back.  She was have daily back pain with athletics and having pain while in school.

The below radiographs/x-rays demonstrate she has a 71 degree right thoracic curve and a left lumbar curve of 45 degrees.  On the side radiograph/x-ray she has a normal amount of rounding or kyphosis, at 40 degrees.

In general curves over 50 degrees, in this age group and diagnosis are surgical candidates.  When larger curves are present, like the above 71 degree curve, it is recommended to have surgery. 

But why?  

1. Worsening of the curve. It is generally accepted, based on several long-term studies, that curves over 50 degrees will very slowly progress (get worse) over time, around 0.5 to 1.0 degrees per year.  This may not sound very impressive, but if we calculate the future decades of life on top of what curve magnitude is at present, the deformity can become very large.  

In the above radiograph/x-ray there is a 71 degree curve, and if  there is a 5-10 degree increase every decade then she could have a 86 to 101 degree curve when she gets to her late 30's.  However, it is important to remember that not all patients will have curve worsening, but the average patient will.  

Surgery will correct the scoliosis and prevent it from recurring.

2. Pain.  As the curve magnitude increases the back pain usually gradually increases in severity, from mild to severe, and can progress from occasional to frequent.  In addition, the pain can go from occurring just during strenuous athletic activities to basic activities, like going to school and walking.  Studies have reported the average patient with surgically treated scoliosis has some back pain, but less than in patients, with the same size curves, whose scoliosis was not surgically treated.

Surgery helps mitigate pain now and in the future.

3. Body Asymmetry. Smaller curves cause less body asymmetry, larger one cause more body asymmetry.  This can be seen in shoulders being uneven, having a rib prominence in the back and the front, waistline being uneven, and body shift.  

Surgery 3-dimensionally improves the body position to be as close to normal as possible.

In previous blog posts we have shown growth modulation surgeries of Vertebral Body Stapling and Vertebral Body Tethering (VBT).  In a upcoming post the newest technique on the block, ApiFix, will be discussed.  However both VBT and ApiFix are not recommended for curves greater than 65 degrees.  In addition, there must be adequate growth remaining to get the spine to grow straighter.  The case in this post is mostly done growing, so again, neither VBT nor ApiFix are good treatment options.

So for the case in this post, the recommended surgery is a Posterior Spinal Fusion (PSF).  There is no maximum curve size for a PSF.  

Surgical planning is crucial for optimal results from a PSF.  Before surgery flexibility radiographs (below) help plan what to fuse and how to perform the surgery.  The below x-rays/radiographs show her biggest curve goes from 75 to 43 degrees, which is a normal amount of flexibility in a 16 year old female.

For this case the decision was to perform T3 to L1 fusion, meaning the top or upper vertebra to fuse is T3 and the bottom or lowest vertebra is L1.  The selection of which levels to fuse is only the first step in surgical planning.  There are many, many more steps to get the surgery right!

Two things to notice:

1. We did not put two screws at every vertebral level. It is never necessary to put two screws in each vertebra in a fusion.  More screws takes more time during surgery, creates more blood loss, increases the risk of a screw being placed incorrectly, and increases the cost of surgery.  Meticulous planning of screw placement optimizes surgical correction.

2. In a PSF the bigger curve is always fused.  Fusion, or partial fusion, of smaller curves is frequently not needed.  Fusions should always be a short as possible, yet be able to achieve the goals of surgery.

 The outcome from this surgery demonstrates the typical correction and balance patients have after surgery.

Congenital Spine Dislocation               5-3-2021

Congenital dislocation of the spine (CDS) is a rare congenital malformation due to failure of the spine and the spinal cord to develop at a single spinal level. 

The patient may be completely neurologically intact or, in severe cases, may not have any muscle function or sensation below the level of the dislocation.

It is potentially the most serious form of congenital kyphosis or scoliosis with an abrupt single-level displacement of the spinal canal.  See the below x-rays of an 18 month old female, who was noticed to have a “bump” on her back, at the red arrow.  

She was moving her legs normally and was felt to have normal sensation in her legs.  The red arrow points to the T12 vertebra which does not sit under the T11 vertebra (orange arrow).

The right side X-ray shows how the upper spine (thick green line) does not line up with the lower spine (thick red line)

When lying down the T12 vertebra does not move under the T11 vertebra…..it is dislocated.

On the below CT scan cuts the red arrows point to the dislocation, with T12 sitting too far back.

The below MRI cut nicely shows how the spinal cord is draped over the posterior T12 vertebra.  It is easy to see if the dislocation gets worse the spinal cord will get more compressed and deformed, which would then cause problems with muscle function and sensation in the legs and cause bowel and bladder incontinence (inability to control).

To correct the dislocation, the T12 vertebra needed to be completely removed, and once it was the spine was very mobile and allows T11 get appropriately lined up with the L1 vertebra.  Because there was a space between T11 and L1 a cage (yellow arrows) was put between them to add to stability and put the spinal cord at the correct length. 

Four pedicle screws were placed above and below the removed T12 vertebra and were locked down.  To make sure this area heals solidly, and permanently a bone graft was placed in the cage in the front and also in the back of the spine.

In the below slide the patient is now 6 weeks after surgery.  It is easy to see the improvement of the spine alignment back to normal.  Because the bone is soft at this age we kept her in a brace for 6 months to protect the surgery.

Here she is now 8 year out after surgery.  She has normal spinal alignment and normal function of her spinal cord.  Her long-term prognosis is for a normal life.