Current concepts in neuromuscular scoliosis
Lee S. Segal - USA
(Current Opinion in
Orthopaedics Current Opinion in Orthopaedics 2004, 15:439–446)
Sussman provided an excellent overview of
the treatment principles for patients with Duchenne muscular dystrophy (DMD)
and spinal deformity. The onset of spinal deformity is usually noted between
the ages of 11 and 13 years, which corresponds to the time most patients stop
walking and become full-time sitters. All children should be screened
because scoliosis develops in most patients with this condition. When the
scoliosis magnitude reaches 20 to 30°, spine fusion should be done without
delay. Nonoperative treatment for scoliosis, such as bracing, is not
recommended for patients with DMD. The spine deformity is not responsive to
nonsurgical modalities or preventable by them. Posterior spine fusion will not
result in marked loss of truncal height or crankshaft deformity, because there
is sufficient spinal growth in children with DMD by the time they are 10 or 11
years of age. With progression of the disease, the paraspinal muscles are
progressively replaced by stiff fibrofatty tissue. This results in the
dissection and exposure of the spine being more difficult, decreases flexibility
and the ability to achieve correction, and increases intraoperative blood loss.
The most notable complication from delaying surgical stabilization of the
spinal deformity is postoperative pulmonary problems. There is a greater risk
of postoperative pulmonary problems when the forced vital capacity (FVC) is
less than 35%. All patients require full cardiac and pulmonary evaluation
preoperatively. Posterior arthrodesis and instrumentation should extend
proximally to the upper thoracic spine (T2–T4), ensuring that thoracic kyphosis
is maintained and the center of mass of the head is forward. If this is not
maintained, patients lose head control because they often lose strength in
their neck flexor muscles while retaining strength in their neck extensors. The
lower level of fusion distal remains controversial. Some favor ending fusion at
L5, and others recommend extending it to the pelvis. Extension to the pelvis,
however, increases blood loss, surgical time, and the risk of complications,
especially with osteopenia of the pelvis. Sussman noted that patients who
undergo stabilization of the spine have improved quality of life, better
maintenance of pulmonary function, and a longer life span. Sengupta et al. evaluated
the distal extent of posterior spine fusion in their retrospective series of 50
patients at two different centers. With a minimum follow-up time of 3 years,
31patients underwent fusion to the pelvis and 19 to L5. In these 19 patients,
pedicle screws were used in the lumbar spine and sublaminar wires in the
thoracic spine. In a comparison of the two groups (pelvic vs L5), the
mean age was 14 versus 11.7 years, the mean Cobb angle was 48° versus
20°, the mean pelvic obliquity (PO) was 19.8° versus 9°, the mean
estimated blood loss was 4.1L versus 3.3 L, the mean length of stay was
11.7 versus 7.7 days, and the FVC was 44% versus 58%. The PO was
corrected and maintained in all but 2 patients with an initial PO greater than
20°. The authors concluded that lumbar instrumentation to L5 is adequate provided
that surgery is performed early, soon after the patient becomes wheelchair
bound, and with smaller preoperative curves and minimal PO. This selective
approach was complemented when surgery was performed in younger patients and
with the improvements made in spinal implants and techniques. Pedicle screw
fixation into three or more levels achieved a solid distal foundation, allowing
the spine to be upright, balanced, and without rotation. This allowed the PO to
be corrected and prevented its progression in these patients with a relatively
short life expectancy. This paper adds to the growing literature about and
controversy over the distal extent of fusion in DMD patients. Mubarak et al.
recommended fusion to L5 when the Cobb angles were less than 40° and
the PO was less than 10°. Alman and Kim noted progression of the PO in
84% (32/38) of patients with lumbar fixation only, but none in the group of
patients who underwent fusion to the pelvis. They recommended extending the
fusion to the pelvis in general, particularly when the apex of the curve is
below L1. However, they did recognize that sublaminar wire fixation may have
contributed to the failure of lumbar fixation in controlling PO. In a review
paper, Sussman noted an increased risk of postoperative pulmonary
problems when the FVC was less than 35%. In a retrospective series of 30
patients, Marsh et al. evaluated the risks of surgery in patients with
low FVC. Of the 30 patients, 13 had a FVC less than 30% of predicted values.
The postoperative lengths of stay were similar, and complication rates were
comparable to those in other series. The mean length of ventilator support was
comparable. The authors emphasized the importance of a multidisciplinary team
approach, and they supported the belief that DMD patients with a FVC less than
30% should not be denied posterior spine fusion for scoliosis for pulmonary
factors alone. Iannaccone et al. examined the role of malnutrition
in DMD patients undergoing spinal deformity correction. The authors identified nine
boys who lost more than 5% of their body weight within 12 months of surgery,
and they retrospectively compared this group with eight patients who gained
weight after posterior spine fusion and eight patients of comparable age who
did not undergo surgery and served as control individuals. The authors noted
that weight loss was associated with the loss of self-feeding. This was not
associated with loss of biceps strength. Possible factors contributing to this
include the decrease in neck range of motion or head control, lack of adequate
caregiving, and low cognitive function. One criticism of the paper was that the
authors did not evaluate the preservation of thoracic kyphosis. Alman et al.
analyzed the effect of steroid treatment and the development of scoliosis
in DMD. The mutation in the dystrophin gene in DMD decreases production of the
gene protein important in maintaining the integrity of the cell membrane, and
steroids have been shown to maintain the integrity of the cell membrane and
decrease the inflammation associated with myocyte cell death. In this
nonrandomized prospective cohort study, the authors compared 30 boys (aged
7–10, and still able to walk) treated with deflazacort (a derivative of
prednisone with decreased prevalence of side effects) with 24 boys who were not
treated (control group). Muscle strength and pulmonary function were evaluated,
and the two groups were matched for age and baseline pulmonary function. The
patients were monitored for a minimum of 5 years, and Kaplan-Meier analysis was
used to determine the risk of the development of scoliosis. Surgery was
performed in 15 of 24 patients in the control group and only 5 of 30 in the
treated group. This difference between the two groups was statistically
significant (P < 0.001). The authors thought that steroid treatment
slows the progression of scoliosis, but long-term evaluation is needed to
determine whether treatment prevents the development of scoliosis or merely
delays its onset. This study supports the hypothesis that the use of
corticosteroids improves the natural history in DMD and that the benefits may
be even more obvious when treatment is begun earlier in life.
Evolving Therapeutic Strategies for Duchenne Muscular Dystrophy: Targeting Downstream Events
Pediatric Research,
2004
JAMES G. TIDBALL
and MICHELLE WEHLING-HENRICKS - USA
E-mail: jtidball@physci.ucla.edu.