Blog Topic: Growing Rod Constructs
for Patients with Neuromuscular Scoliosis
12-31-2022
This talk was presented
at the International Pediatric Orthopaedic Symposium in Orlando, Florida last
November 2022. My topic was to talk on
patients with neuromuscular scoliosis (NMS) who were less than 8 years of age,
presenting the argument to do Growing Rod (GR) surgeries, instead of performing
a Posterior Spinal Fusion (PSF). My opponent was Dr. Nick Fletcher from
Children’s Healthcare of Atlanta, who provided a nice counter-argument presentation
for PSF in this patient population.
My side of the debate was
an easy one for me to support, specifically to support GR surgeries. I will present the slides of the talk and
give some additional information.
The diagnosis of NMS
lumps together a wide variety of neuromuscular diagnoses, from cerebral palsy
to spina bifida to spinal muscle atrophy, just to name just a few. With these different neuromuscular diseases
come a wider variety of medical comorbidities, such as cardiac (heart),
pulmonary (lung), and endocrine issues which can impact surgery and the
recovery from surgery. When compared to
idiopathic, syndromic, and congenital scoliosis patients, neuromuscular
patients are by far the most challenging group of patients.
In NMS the impact on
the child can be broken down into two broad groups, orthopaedic and
medical. One main musculoskeletal
problem we see in NMS is difficulty in sitting, which can be called “imbalance”,
because the pelvis is tipped. When the
patient tries to get their bottom onto the seat of their wheelchair they lean
severely to the left or the right.
The other main problem we see in NMS is back pain when
patients are sitting. The bigger the scoliosis, and the more the pelvis is
tipped the higher, the chance of having pain when sitting. This can be a significant problem preventing
the children to sit in a car seat, be upright in school and/or be unable to travel
any significant distances.
The last bullet point on this slide is about T1-S1 distance,
which is a quantitative measurement of the distance from the shoulders to the
pelvis. The longer this distance is, the
greater potential lung volume will be.
However, we don’t often know how much distance a single child will need to
have no pulmonary problems (pneumonias, shortness of breath, etc…) in
adolescence and adulthood. Also, we
don’t know the growth potential for any one child. What we do know is that, in general, children
with neuromuscular disease do not grow as much as the family history (height of
parents and siblings) may predict.
So if a child has NMS, and is less than or under 8 years of
age and needs surgery, how do we know if a child should undergo GR or PSF
surgery? We know the data to support either surgery, over the other, is
poor. The main reason is we don’t know
how much T1-S1 distance a child needs at the end of growth or how much
potential T1-S1 growth any child may have….. so we need to have discussions,
between the surgeon and family/caregivers about the two options, and their
benefits, risks, and potential complications.
As indicated on the slide, we need to discuss:
1.
Number of procedures a family/caregiver is
willing to have the child undergo.
2.
The tolerance of complications, such as implant
breakage, implant pull-out and infection.
3.
The ability of the family/caregivers to be able
to deal with complications and need for hospitalizations and procedures,
sometimes with short notice.
4.
The amount of T1-S1 distance a patient may need
5.
The patient’s pulmonary (lung) status, such as
need for supplemental oxygen, tracheostomy or use of a ventilator to breath.
For each child/family/caregiver there is a unique situation
for each item #1-#5….and varying degrees.
These discussions can take many months or years to come to a
decision. Each child and decision is
unique.
This slide presents a published study from the Pediatric
Spine Study Group on the use of GR in NMS.
81% of patients achieved a T1-S1 distance of 18 cm, which is the minimum
distance currently believed to be sufficient for asymptomatic pulmonary
function though there is scant data to support this position.
Not every scoliosis needs surgery right away. Here is a 9
year old girl with CP. In the first
picture on the left there is severe scoliosis of 81 degrees and pelvic obliquity
(tipped pelvis) of 28 degrees (away from being level). Move to the third picture from the left and
you see there is kyphosis of 76 degrees (high end of the normal range is 50
degrees). So this young lady has a
severe kypho-scoliosis, a combination of both deformities. This magnitude of deformity typically ends up
getting surgery, however see the 2nd from the left and the 4th
from the left pictures and you see how flexible she is! The scoliosis goes down to 45 degrees and the
kyphosis down to 28 degrees! Based on
this information we can treat nonsurgically with bracing and wheelchair
modifications. Eventually she will need PSF
surgery but it will be just one surgery….and not several!
The goals for surgery mirror the topics which should be part
of preoperative discussions:
1.
Improve pelvic obliquity
2.
Improve scoliosis and/or kyphosis
3.
Increase T1-S1 distance
4.
No complications. It is important to point out
GR constructs will have more complications than PSF due to the nature of the GR
constructs (stiff metal, relatively flexible spine) and the need to convert
these patients to a final, definitive at or near the end of skeletal growth.
5.
Durable; minimal reoperations. To this point,
traditional growing rods (TGRs) will need more surgeries than
magnetically-controlled growing rods (MCGRs).
This is because the MCGRs can be lengthened in the office without
sedation, while TGRs need to be lengthened in the OR under general anesthesia
(about every 6 months). Hence we try
very hard to place MCGR, but sometimes patients size and deformity prevents us
from placing them, and we have to place TGRs.
The correction forces of GRs is demonstrated on this slide.
A car jack, which lifts a car off the ground, has two points it is distracting
against, the ground and the car. In GRs
we need to establish two point to distract against, and these need to be over the
area of the spine deformity in order to correct the deformity. So there are two foundations which need to be
created:
1.
Cranial (Upper)
2.
Caudal (Lower)
Cranial fixation points can be ribs or the spine.
Caudal fixation points can be spine, iliac crest or the
sacrum-pelvis
Cranial or upper fixation point option are the ribs, and
there are many of them on each side of the chest. After using them for many years, it appears
these are likely a better option than the spine in children under 7 years of
age. When these are used 3-4 ribs should be used for each rod, to minimize the
occurrence of the rib hooks pulling through the ribs.
This slide demonstrates two points of interest: the use of
spine fixation (pedicle screws) cranially and the use of only one rod.
#1: The use of
spine fixation appears more successful in patients over 7-9 years of age,
versus patients over 9 years of age. In the older patients, the grip strength
of the screws is more reliable, due to the ability to maintain bony fixation. If the fixation is UNBALANCED (upper vs.
lower) then the end with weaker fixation is more likely to fail. This is important when the caudal (below)
fixation is in the iliac crests or sacropelvis, as this is a very strong
fixation method. Therefore, in this case the BALANCED fixation is sacropelvic
fixation caudally, and 6 pedicle screws used at the cranial side creating BALANCED
fixation.
If the lower foundation is to the spine, then the cranial
fixation with 4 screws may be sufficient.
By fixating short of the pelvis, a lot of the normal body/trunk motion
is dissipated by the lumbar spine below the spine fixation.
#2: The use of
two rods is stronger than using one rod.
However, the use of one rod is occasionally necessary because the spinal
deformity may prevent safe placement of two rods. A child with low body mass, and hence low
muscle mass may not allow a rod on the convex side. The other situation is in the spinal deformity
with significant kyphosis, called kyphoscoliosis, which can preclude a rod on
the convex side, especially a magnetically-controlled growing rod.
The caudal foundation options are presented here. If the fixation can stop short of the pelvis,
onto the spine, this is preferred. The
risk of a surgical site infection is lower if pelvic fixation can be avoided.
If fixation needs to go to the pelvis, such as the pelvis is
very tipped at an angle, then all methods of fixation are reasonable to
use.
Here are the three main types of pelvic fixation
The left picture shows the use of a Dunn-McCarthy or “S”
hook. This device rests on the top of
the iliac crest and was popularized by Dr. Robert Campbell with the VEPTR
device.
The middle picture is another method of iliac crest fixation
called pelvic saddles.
The right picture is sacropelvic fixation using pedicle
screw at bilateral L5 and bilateral S1 and bilateral iliac screws. This is a very strong, rigid method of
fixation.
The choice of fixation method depends on multiple factors,
such as patient age, diagnosis, deformity type, and surgeon training and
experience.
As mentioned two rods are stronger than one, so we typically
try to put in two rods.
Another obvious statement is to use bigger rods (5.5 mm vs.
4.5 mm) as they have a lower fracture rate.
What type of rods should be used? In general, the use of
magnetically-controlled growing rods is preferred as this minimizes the number
of surgical procedures. However, the use
of traditional growing rods may be necessary due to the patient size and type
of spinal deformity.
In conclusion, it is important to have shared
decision-making. Ideally, the decision
of growing rods vs. posterior spinal fusion is one, which usually occurs over
multiple office visits. Both approaches
are reasonable and the complications, potential outcomes and need for future surgical
procedures are the main drivers of the decision.
