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R E S E A R C H Open Access
Surgical results with the use of Silicated
Calcium Phosphate (SiCaP) as bone graft
substitute in Posterior Spinal Fusion (PSF)
for Adolescent Idiopathic Scoliosis (AIS)
Nanjundappa S. Harshavardhana
1*
and Mohammed H H Noordeen
2
Abstract
Background: The gold standard iliac crest bone graft (ICBG) used to achieve arthrodesis in spinal fusions is not without
complications (donor-site morbidity, iliac wing fractures etc.…). Our objectives were to evaluate the role of silicated
calcium phosphate (SiCaP), an osteoconductive synthetic bone graft substitute in conjunction with locally harvested
autologous bone in achieving arthrodesis following posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS)
and report clinic-radiological results / adverse events with its use in a prospective single surgeon case series (Level of
evidence [LoE] IV) treated by low implant density index (IDI) constructs (i.e., IDI ≤1.5).
Methods: Thirty-five patients (8♂&2727♀) who underwent PSF and followed-up for a minimum of 2 years formed
thestudycohort.Themeanageatsurgerywas15years(range:11–21y)andpre-opCobbanglewas60°(range:40°–90°).
SiCaP mixed with locally harvested bone during exposure and instrumentation was laid over instrumented segments. The
average SiCaP used per patient was 32mls (range: 10–60mls). Radiographs were assessed for fusion at serial six monthly
follow-ups. All clinical adverse events and complications were recorded.
Results: The mean follow-up was 2.94 years (range: 2–4y). The post-op Cobb angle improved to 23° (range: 2°–55°) and
the mean in-patient stay was 7.72 days (range: 5–13d). The mean number of instrumented segments was 9.4
(range: 4–13) and implant density index (IDI) averaged 1.23 (range: 1.15–1.5). Radiographic new bone formation
was seen within 3 months in all cases. All patients (except two) were highly satisfied at minimum follow-up of
8 years. There were two complications warranting revision surgery (deep infection, and implant failure without
any evidence of pseudarthrosis). There were no SiCaP specific adverse events in any of the 35 patients.
Conclusion: SiCaP facilitated early bony consolidation in operated cohort of AIS patients treated by PSF. There were
no inflammatory reaction or other adverse effects associated with its use. SiCaP is a safe alternative to autologous iliac
crest bone graft with reduced complications, morbidity, faster recovery and similar infection/fusion rates reported in
the literature.
Keywords: Silicated Calcium Phosphate (SiCaP),Idiopathic Scoliosis (IS),Posterior Spinal Fusion (PSF),Bone Graft substitutes
* Correspondence: nharsha@outlook.com
1
Twin Cities Spine Center, 1111 S 8th St, Apt 214 N, Minneapolis 55404, MN,
USA
Full list of author information is available at the end of the article
© 2015 Harshavardhana and Noordeen.
Open Access
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reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the
Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://
creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Harshavardhana and Noordeen Scoliosis (2015) 10:27
DOI 10.1186/s13013-015-0051-x
Background
Adolescent Idiopathic scoliosis (AIS) is characterized
by a frontal plane deformity of the spine and its exact
etiology is unknown. Numerous theories are proposed
to explain its etiology and pathogenesis [1]. Cobb angle
is used to quantify and assess progression of deformity
on standard PA radiographs, which have a three-fold
reduced radiation to breast tissue than AP x-rays [2, 3].
Surgery is recommended and performed when the Cobb
angle is ≥50°. Surgery addresses the shoulder, flank asym-
metry and arrests progression of deformity. It also en-
hances self-esteem, improving body self-image, overall
appearance and quality of life [4].
The first reported use of instrumentation for scoli-
osis was by Harrington [5]. Emphasis on achieving
sound arthrodesis is attributed to JH Moe who recom-
mended facetal and inter-laminar fusion [6]. Autolo-
gous iliac crest bone graft (ICBG) is considered to be
gold standard in achieving arthrodesis for idiopathic
scoliosis [7]. Numerous studies have reported excessive
blood loss, iliac wing fractures, limited bone stock,
prolonged hospital stay, increased pain and donor site
morbidity with harvest and use of ICBG [8, 9]. Allo-
grafts and other synthetic bone graft substitutes are
commonly used to minimise the risks associated with
useofICBG.Thebiologicalproperties of allografts are
variable and greatly influenced by processing tech-
niques employed. Price reported 28 % pseudarthrosis
rates with use of allografts for spinal fusions in com-
parison to 12 % for ICBG [10].
Silicated calcium phosphate (SiCaP) is a synthetic and
porous bone graft substitute (ACTIFUSE™;ApaTech
and Baxter Ltd, Elstree, Hertfordshire; UK) that is man-
ufactured against highly controlled specifications mim-
icking the trabecular architecture of native cancellous
bone as granules. It is available for use in two sizes with
granule diameters of 1–2and2–5 mm. The silicate
substitute at 0.8 % concentration by its negative surface
charge significantly improves bone formation by in-
creasing vascularity to host bone [11]. Studies have also
demonstrated accelerated bone formation, enhanced
volume of new bone formed and consolidation with re-
modelling into mature bone in-vivo animal studies [12].
SicaP’s use is well-documented and reported for degen-
erative spinal disorders. No published literature exists
till date reporting its use in isolation (i.e., without mix-
ing with vertebral or bone marrow aspirate or ICBG) in
scoliosis surgeries and long spinal fusions. The purpose
of this prospective clinical study was to evaluate the
clinical and radiographic outcomes with its isolated as a
bone graft substitute in conjunction with locally har-
vested bone in AIS patients treated by posterior spinal
fusion (PSF) with low implant density index (IDI)
constructs.
Methods
Thirty five consecutive patients with AIS scheduled for
posterior spinal fusion at our institution were enrolled
into this prospective study against pre-determined strin-
gent inclusion criteria following a research and ethics
committee (REC) approval which were:
i. Age at surgery –at least 11 years
ii. Cobb angle of structural thoracic curve ≥50° and
that of thoraco-lumbar/lumbar curve ≥40°.
iii. Patients/parents & care givers signed a written
consent form voluntarily agreeing to participate in
the study.
The exclusion criteria included:
i. AIS treated by anterior or combined anterior +
posterior surgery
ii. Revision spinal surgeries and scoliosis secondary to
other etiologies (i.e., congenital/neuromuscular/
syndromic etc.…)
iii. Patients with known malignancy or local/systemic
infection
iv. Those who refused to provide consent to participate
in the study.
Information brochure about ACTIFUSE™was provided
to enrolled patients and all questions were convincingly
answered by the surgical team before their surgeries.
The senior author (MHHN) has devised a surgical algo-
rithm that identifies all AIS curves as three main curve
types (I-III). Each curve type is further sub-divided into
sub-type A & B depending on whether the convex
shoulder was higher or lower to inter-clavicular line thus
yielding six curve patterns that all AIS curves fitted into.
The definition of these three curve types with illustrative
line diagram is illustrated in Fig 1.
Surgical procedure
All patients underwent scoliosis correction by third gen-
eration instrumentation through a midline posterior
approach by means of a segmental all pedicle screws or
hybrid construct plus cobalt-chrome rod system. Three
instrumentation systems used were:-
a. Expedium Spine System (De-Puy Spine Inc.,
Raynham, Massachusetts, USA)
b. Synergy Spine Instrumentation (Interpore Cross
International, Irvine, California, USA).
c. K2M Spine Solutions (K2M Inc., Leesburg, Virginia,
USA)
After appropriate exposure of the spine by meticulous
subperiosteaal dissection and haemostasis, facetectomies
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 2 of 12
were performed. Cell saver and transfusion recycler was
used in all cases and intra-operative estimated blood loss
(EBL) was recorded as percentage of estimated blood
volume (EBV). Pedicle screws were instrumented in the
selected vertebrae after confirming the upper and lower
instrumented vertebrae (i.e., UIV and LIV) with intra-
operative fluoroscopy. Alternating convex and concave
pedicle screws were inserted into the vertebrae (i.e., each
vertebra had only one pedicle screw) except the end ver-
tebrae, which had bilateral pedicle screws in all 35
patients. The implant density index (IDI) was no more
than 1.5 in all cases. A pre-bent and appropriately con-
toured rod in sagittal plane was then inserted and
correction was accomplished by a combination of the
cantilever and translation manoeuvres. The convex
(right sided rod) was inserted first to aid in translation
and application of cantilever forces for correction. Finally,
direct vertebral rotation was performed to correct the
axial deformity. At the end of surgical correction, the spin-
ous processes were resected and outer cortices of laminae
were decorticated. 20–60mls of ACTIFUSE™(depending
on the no. of vertebral segments to be fused and quantity
of locally harvested bone) was mixed at 60:40 ratio (i.e.,
60 % of SiCaP and 40 % of autograft). The resulting com-
posite material was laid over the prepared bony bed across
the entire instrumented segment of the spine prior to the
closure to facilitate arthrodesis.
Postoperative care and rehabilitation
Swimming, Pilates and gentle stretching was encouraged
at 6 weeks onwards. Cycling and non-contact sports per-
mitted at 6 months postoperatively. Contact sports and
horse riding was prohibited for up to a year. None of the
patient wore any orthosis in the postoperative period.
Radiographic & statistical analysis
All patients had preoperative standardized long-cassette
erect PA and lateral radiographs. Supine side- bending
views were performed to assess flexibility of structural
and compensatory curves to aid decision-making in per-
forming a selective spinal fusion. The senior author has
devised a surgical algorithm and classified AIS into three
curve main types. This simplified surgical algorithm also
aided us in choosing fusion levels and was strictly ad-
hered to for all cases.
The curve characteristics of all patients as per the se-
nior author’s algorithm is summarised in Table 1. Serial
post-op radiographs were performed at the time of dis-
charge, 3, 6, 12 and 24 months post-op follow-up. The
radiographs were evaluated for instrumentation failure,
lucency around the screws, anchor pull-out or dislodge-
ment from its initially inserted position and for defects
in the fusion mass as indicators of pseudarthrosis by a
fellowship trained junior colleague with input from an
independent Consultant radiologist who was not in-
volved in the patients’treatment. Cobb angles of struc-
tural and compensatory curves were measured pre and
serial postoperative radiographs using the same vertebral
segments as preoperative x-rays. The degree of postoper-
ative curve correction and loss of correction with time
at final follow-up was diligently recorded. Pseudarthrosis
when present was recorded as definite or probable. A
definite non-union existed when proven by a CT scan
(on 1–2 mm fine-cut osteo window) and presence of
frank defect during revision surgery Pseudoarthrosis was
considered as probable when:
a. There was loss of correction by >10° in comparison
with immediate postop x-ray
b. Radiologically visible defect in the fusion mass
Fig. 1 The Noordeen AIS curve algorithm: Six curve patterns
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 3 of 12
Table 1 Results - Summary of perioperative parameters in all 35 patients
Patient
ID
Sex Age at
Sx
F/u in
mo
Levels
fused
Instrumented
Segments
IDI Actifuse wt.
in mls
Total Blood
loss (EBV)
Intra-op
BT
a
Post-op
BT
a
Pre-op
VAS
VAS at
Discharge
Final f/u
VAS
Complication Fusion Instrumentation
system
1001 F 21 48 T2-L1 11 1.18 40 0.2 0 0 2 1 1 None Good Synergy
1002 F 19 30 T3-L3 12 1.16 20 0.3 0 0 2 1 0 None Good Synergy
1003 M 19 30 T2-L2 12 1.16 40 0.4 0 0 1 0 0 None Good K2M
1004 F 14 30 T3-L1 10 1.2 20 0.25 0 0 1 0 0 None Good K2M
1005 F 14 48 T4-L2 10 1.2 20 0.35 0 0 0 0 0 None Good Synergy adult
1006 F 16 48 T3-L1 10 1.2 40 0.3 0 0 0 0 0 None Good K2M
1007 M 14 48 T3-L3 12 1.16 40 0.45 0 0 0 2 0 MRSA deep
infection
Good Synergy
1008 F 14 24 T3-L3 12 1.16 40 0.35 0 0 0 0 0 None Good Synergy
1009 F 12 48 T3-T11 8 1.25 40 0.25 0 0 2 1 0 None Good Synergy
1010 F 14 48 T3-T11 8 1.25 30 0.3 0 0 2 0 0 None Good Synergy
1011 F 13 36 T4-T10 6 1.33 20 0.2 0 0 2 0 0 None Good Synergy
1012 F 13 30 T2-T12 10 1.2 25 0.25 0 0 3 2 0 None Good K2M
1013 M 15 48 T3-L3 12 1.16 40 0.3 0 0 0 0 0 None Good K2M
1014 F 11 30 T2-T12 10 1.2 40 0.3 0 0 0 0 0 None Good K2M
1015 F 13 24 T3-L1 10 1.2 40 0.3 0 0 0 0 0 None Good K2M
1016 F 13 30 T2-L1 11 1.18 30 0.3 0 0 6 2 1 None Good Synergy adult
1017 M 15 30 T3-T11 8 1.25 30 0.25 0 0 2 1 0 None Good K2M
1018 F 14 48 T4-T12 8 1.25 30 0.25 0 0 3 1 1 None Good Synergy
1019 F 19 48 T2-L3 13 1.15 40 0.35 0 0 0 0 0 Right rod at T9 is
broken
Good K2M
1020 F 15 48 T2-L2 12 1.16 60 0.35 0 0 0 0 0 None Good K2M
1021 F 18 24 T4-L2 10 1.2 35 0.28 0 0 0 0 0 None Good Synergy adult
1022 F 12 24 T4-L2 10 1.2 40 0.3 0 0 3 1 0 None Good K2M
1023 M 16 24 T3-T11 8 1.25 40 0.25 0 0 2 1 0 None Good K2M
1024 F 20 24 T10-L3 5 1.4 20 0.25 0 0 0 0 0 None Good K2M
1025 F 13 24 T2-L2 12 1.16 30 0.3 0 0 0 0 0 None Good K2M
1026 F 20 24 T2-T12 10 1.2 20 0.3 0 0 0 0 0 None Good K2M
1027 F 14 24 T3-T12 9 1.22 20 0.25 0 0 3 1 0 None Good K2M
1028 F 14 48 T10-S1 8 1.25 40 0.2 0 0 8 5 2 None Good Expedium
1029 M 17 36 T3-L3 12 1.16 40 0.3 0 0 3 3 0 None Good K2M
1030 M 14 30 T4-L1 9 1.22 30 0.25 0 0 4 4 2 Unhappy with pain
relief
Good K2M
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 4 of 12
Table 1 Results - Summary of perioperative parameters in all 35 patients (Continued)
1031 M 15 36 T3-T11 8 1.25 20 0.22 0 0 5 3 2 Had low back pain
(NSAIDs)
Good K2M
1032 F 16 48 T11-L3 4 1.5 25 0.25 0 0 1 0 0 None Good K2M
1033 F 14 42 T4-T11 7 1.28 30 0.35 0 0 0 0 0 None Good K2M
1034 F 13 24 T4-T10 6 1.33 30 0.3 0 0 3 0 0 None Good K2M
1035 F 12 30 T4-T10 6 1.5 20 0.25 0 0 2 1 0 None Good K2M
a
BT blood transfusion
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 5 of 12
c. Persistent axial back pain of intensity severe to
warrant regular intake of pain-killers.
Thus collected clinico-radiological data was analysed
using statistical package for the social sciences v16 (SPSS
Inc. IBM Corp., U.S.A). Statistical significance was set at
p< 0.05.
Results
The study cohort comprised of 8 males and 27 females.
The mean age at diagnosis of AIS was 10.75 years
(range: 10 –16). The mean age at surgery was 15 years
(range: 11 –21 years). The most common curve pattern
at the time of surgery was structural main thoracic curve
(23 patients). Double structural curve and structural
thoraco-lumbar/lumbar curves comprised of nine and
three patients respectively. The mean preoperative curve
magnitude at the time of surgery was 60° (range: 40° –90°)
Perioperative parameters
The results of all perioperative parameters is sum-
marised comprehensively in Table 1. The average follow-
up was 2.94 years (range: 2–4y). The mean duration of
surgery was 148 min (range: 98–175 min). The VAS
score was reduced from 1.71 (range: 0–8) to 0.26 at
6 months post-op (range: 0–2). The mean no. of instru-
mented segments was 9.4 (range: 4–13) and implant
density index (IDI) averaged 1.23 (range: 1.15 –1.50).
The harvest from cell saver on recycling yielded an aver-
age of 95mls (range: 65–430mls). None of the 35 pa-
tients needed any postoperative blood transfusions.
Three different instrumentation systems were used in
the study population were: Expedium (1), Synergy (11)
and K2M (23). The mean amount of ACTIFUSE™used
was 32mls (range: 20–60mls)
Radiographic parameters
The immediate postop Cobb angle improved to 23.2°
(range: 9° –55°) and new bone formation was seen on
plain x-rays as early as 6 weeks in few patients. New
bone formation was seen in all cases by 3 months postop
follow-up radiographs. Loss of curve correction was seen
in 19 patients and remaining 16 had improvement in
final Cobb angle with time. The mean loss of Cobb angle
at end of study was 2.7° (range: 1°–5°). No patient in the
study group had loss of Cobb angle correction by more
than 10°. The radiographic parameters in all 35 patients
are summarized in Table 2. Case examples of senior
author’s algorithm with three curve types (I - III) show-
ing preoperative, immediate postoperative and final
follow-up x-rays of AIS treated by PSF and use of low
IDI construct (Figs 2, 3 and 4). Instrumentation system
had no effect on fusion rates though the numbers were
small for the three spinal implant systems used.
Complications
There were two adverse events in our case series:
Implant failure - Without any evidence of
pseudarthrosis in a 16 year old female. She
presented with a subcutaneously palpable implant
and mechanical pain at 25 months postoperatively
following a T3 –L4 PSF. Sound arthrodesis with
good fusion mass was seen on CT and at revision
surgery for exchange of broken rod The relevant
preoperative, postoperative radiographs and at the
time of revision surgery for right sided rod
breakage at 26 months from index surgery are
illustrated in Fig 5.
Late deep MRSA infection warranting removal of
all instrumentation at 47 months post-op in a
15 year old male. Sound arthrodesis was seen at the
time of implant removal and deep cultures grew
MRSA (Fig 6).
Discussion
We undertook a prospective clinical study to evaluate
the therapeutic efficacy of a novel synthetic osteocon-
ductive bone graft expander (SiCaP) for achieving arth-
rodesis in AIS surgeries. In this group of 35 patients, we
did not observe any inflammatory response or any other
adverse effects in both genders. We observed osteointe-
gration of SiCaP with native host bone as early as 6 weeks
and some evidence of radiographic fusion was seen in all
patients by 3 months post-op. The ACTIFUSE™granules
remained circumscribable on plain x-rays at 9 –12 months
and were fully integrated with host bone as solid fusion
mass by 24 months.
Radiographic assessment of spinal fusion by plain x-rays
is fraught with fallacies and may be inaccurate as they
more often tend to over-estimate solid fusion (i.e., false
negative for non-unions) [13]. Despite advances in im-
aging quality, radiographs at best are only two dimen-
sional and dynamic radiographs though helpful in ruling
out instability have their own limitations. The main short-
coming of dynamic x-rays includes measurement reliabil-
ity and disagreement between observers on permissible
motion [14]. Computed tomography (CT) is more sensi-
tive in detecting non-union and is investigation of choice
to confirm or rule out pseudarthrosis [15]. Three dimen-
sional CT reconstructions are helpful in planning revision
surgeries to address symptomatic pseudarthrosis. How-
ever enormous radiation exposure precludes its routine
use in asymptomatic patients and is reserved for patients
with persistent axial back pain and instrumentation fail-
ure. A single lumbar spine CT has the irradiation dose
equivalent to 240 chest radiographs [16]. Though Mag-
netic resonance imaging (MRI) is appealing owing to lack
of irradiation induced risks, its utility in assessing spinal
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 6 of 12
fusion is inferior to CT scans [17]. Further research is
needed to define the MR sequences and magnet strength
required to assess spinal fusion in presence of instrumen-
tation and its artifacts.
Lerner et al. compared the osteointegration properties of
beta-tricalcium phosphate (b-TCP) and silicated calcium
phosphate (SiCaP) as bone graft substitutes in PSF for
AIS. Unlike SiCaP, the b-TCP granules were observed
to dissolve rapidly (at 6 months) and underwent faster
degradation [18, 19]. Similar observations were made
by Muschik who reported b-TCP granules to be invis-
ible on radiographs at 8 ± 2 months postoperatively.
Table 2 Results - Summary of radiographic parameters of all 35 patients
Patient
ID
Levels
fused
AIS Curve Type
MHHN Algorithm
Pre-op
Cobb ^le
3 months f/u
Cobb ^le
Final F/U
Cobb ^le
Total loss of
Cobb ^le
Complication Radiographic
fusion
Instrumentation
1001 T2-L1 Type I 75 22 25 3 None Good Synergy
1002 T3-L3 Type II 73 & 61 38 & 25 26 & 31 −12 None Good Synergy
1003 T2-L2 Type I 56 27 20 −7 None Good K2M
1004 T3-L1 Type I 57 15 13 −2 None Good K2M
1005 T4-L2 Type I 78 37 30 −7 None Good Synergy
1006 T3-L1 Type I 56 22 20 −2 None Good K2M
1007 T3-L3 Type I 60 20 22 3 MRSA deep
infection
Good despite
deep infection
Synergy
1008 T3-L3 Type I 90 12 16 4 None Good Synergy
1009 T3-T11 Type II 80 & 55 35 & 38 40 & 21 5 None Good Synergy
1010 T3-T11 Type I 74 28 25 −3 None Good Synergy
1011 T4-T10 Type II 54 & 45 26 & 28 27 & 25 1 None Good Synergy
1012 T2-T12 Type I 64 18 16 −2 None Good K2M
1013 T3-L3 Type I 56 19 20 1 None Good K2M
1014 T2-T12 Type II 86 & 56 34 & 26 38 & 42 4 None Good K2M
1015 T3-L1 Type I 60 26 18 −8 None Good K2M
1016 T2-L1 Type I 60 22 20 −2 None Good Synergy
1017 T3-T11 Type II 53 & 38 34 & 37 29 & 31 −5 None Good K2M
1018 T4-T12 Type II 47 & 38 16 & 26 20 & 20 4 None Good Synergy
1019 T2-L3 Type II 68 & 65 32 & 35 30 & 32 2 Right rod
broken at T9
Good K2M
1020 T2-L2 Type I 57 20 16 −4 None Good K2M
1021 T4-L2 Type I 64 32 25 −7 None Good Synergy
1022 T4-L2 Type I 58 20 22 2 None Good K2M
1023 T3-T11 Type II 46 & 36 21 & 21 21 & 21 0 None Good K2M
1024 T10-L3 Type III 40 9 10 1 None Good K2M
1025 T2-L2 Type I 55 25 28 3 None Good K2M
1026 T2-T12 Type II 53 & 37 17 & 18 22 & 21 5 None Good K2M
1027 T3-T12 Type I 45 2 4 2 None Good K2M
1028 T10-S1 Type III 40 15 18 3 None Good Expedium
1029 T3-L3 Type I 60 16 18 2 None Good K2M
1030 T4-L1 Type I 55 20 22 2 Unhappy with
pain relief
Good K2M
1031 T3-T11 Type I 58 20 16 −4 Had low back
pain
Good K2M
1032 T11-L3 Type III 50 20 18 −2 None Good K2M
1033 T4-T11 Type I 50 18 15 −3 None Good K2M
1034 T4-T10 Type I 55 20 22 2 None Good K2M
1035 T4-T10 Type I 70 55 52 2 None Good K2M
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 7 of 12
This faster degradation of b-TCP produced inflammatory
response in an animal model [20]. Such an inflammatory
response would be detrimental for sound fusion as it can
trigger bone resorption. The end volume and quality of
such newly formed bone may have poor trabecular archi-
tecture and susceptible for breaks/fracture. The silicate
substitution at 0.8 % in ACTIFUSE™was observed to pro-
mote accelerated neovascularisation and bone apposition
with formation of normal trabecular architecture [11, 19].
It also significantly promoted bioactivity and facilitated
adaptive remodelling with better bony in-growths in com-
parison to hydroxyapatite (HA). We mixed SiCaP and lo-
cally harvested bone in 60:40 ratio prior to laying over the
instrumented area. Posterior decortication of laminae and
transverse processes exposes the bleeding cancellous bone
creating an ideal environment for new bone formation
facilitating linkage between native bone and bone graft
substitute. Korovessis observed that HA in combination
with local bone and bone marrow aspirates (BMA) did
not produce satisfactory arthrodesis in postero-lateral fu-
sion unlike SiCaP which produced consistent results and
good fusion mass in similar surgeries [21].
Lerner et al. used 20 –40mls of SiCaP mixed with lo-
cally harvested bone plus BMA from vertebral bodies in
21 patients who underwent posterior spinal fusion for AIS
[19]. BMA possess osteoinductive properties and the true
role of SiCaP in causing arthrodesis when mixed with
such an osteogenic agent cannot be determined defini-
tively/is questionable [22]. We did not use BMA in any of
our 35 patients in this series and all but one had good/ex-
cellent arthrodesis with similar quantities of SiCaP (aver-
age 32mls). This conclusively establishes that solid fusion
does happen with isolated use of SiCaP when mixed with
locally harvested bone in scoliosis surgeries.
Finally, the gold standard iliac crest bone graft
(ICBG) was associated with significant donor site mor-
bidity in adolescents that limited activities of daily liv-
ing (ADL) in at least 21 out of 87 patients observed by
Skaggs [9]. The mean VAS was 4 and up to 10 % were
on regular analgesics even at 4 years post-op from the
time of index surgery. They concluded that the true
dimensions of pain and suffering from other complica-
tions associated with ICBG was significantly under-
reported in published literature. All patients in our
series were pain-free except two and had stopped all
analgesics by 6 months post-op. Only 14 patients re-
ported mild pain/discomfort at 6 months and the mean
VAS score at final follow-up was 0.23 (range: 0 –2).
Fig. 2 Structural thoracic AIS (MHHN curve type I) in 16y/♀treated with PSF with 66 % correction showing pre-op, immediate post-op and 4 years
post-op radiographs
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 8 of 12
Fig. 4 Double structural AIS (MHHN curve type II) in 14.5y/♀treated with selective thoracic fusion (65 % correction) with f/u of 3.5 years showing
pre-op, immediate post-op and 3.5 years follow-up radiographs
Fig. 3 Double structural AIS (MHHN curve type II) in 15y/♀treated by PSF of both curves. 66 % and 50 % correction of main thoracic and
compensatory lumbar curves was achieved. The pre-op, immediate post-op and 2.5 years post-op radiographs are shown
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 9 of 12
Only two patients had moderate pain that warranted
intake of over the counter NSAIDs.
Implant density index refers to the number of fixation
anchors used to correct the scoliotic deformity. It is
defined as the ratio of number of fixation anchors to the
number of vertebral segments fused [23]. Larger the IDI,
better is the degree of Cobb angle correction and lesser
the loss of correction with time owing to superior fix-
ation and enhanced pull-out strength imparted by the
anchors. Constructs with IDI of <1.5 are considered to
be of lower implant density and many studies have ques-
tioned the need for bilateral screws in every vertebra for
AIS correction [24, 25]. There was negligible loss of
Cobb angle correction at final follow-up and was within
the measurement error (i.e., mean loss of correction was
2° [range: 1°–5°]) despite low IDI construct. One patient
with instrumentation failure had exploration of fusion
mass and exchange of broken rod for a prominent im-
plant was found to have sound fusion at the time of revi-
sion surgery (Fig 6).
The use of low IDI constructs yielded significant cost-
savings without any compromise in our clinical results.
The market price of 20mls of ACTIFUSE™is equivalent
to that of one pedicle screw. Utilizing the synthetic bone
graft substitute for the entire study cohort amounted to
the price of one and half pedicle screws (i.e., 30mls of
ACTIFUSE™= 1.5 pedicle screw in terms of cost) which
was more cost-effective in-comparison to a scenario
wherein one were to have used bilateral anchors at each
vertebral segment.
Our study was not without limitations. Firstly we did
not peform any power analysis to determine the number
of AIS cases treated by PSF that would be needed to de-
tect one pseudoarthrosis. Secondly we did not perform
CT scans in all patients to assess fusion and the role of
CT was confined only for evaluation of symptomatic
patients who had either instrumentation failure or per-
sistent pain. Ethical considerations and hazards of irradi-
ation of asymptomatic patients esp. in reproducible age
group was the main hurdle to the same. We would not
be surprised if any REC would approve such a study.
Thirdly two of our patients with persistent pain used
NSAIDs owing to intolerance to opioid based medica-
tions (severe itching in one and drowsiness in the other).
Fig. 5 Adverse event –Radiographs of AIS with right rod breakage at 25 months following T3 –L4 PSF
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 10 of 12
NSAIDs consumption and nicotine comsumption would
interfere would fusion rates (esp. in early phase of healing)
from many well documented clinical studies [26, 27]. Con-
sumption of nicotine (smoking/chewing) status was not
collected in any of our patients owing to the reluctance of
majority of teenagers to be upfront and disclose inviting
wrath from their parents/care-givers. And finally we did
not have a control group to evaluate the results of SiCaP
used PSF vs. controls who underwent PSF. The control
group would ideally be a age, curve severity and sex
matched AIS patients were operated by PSF with use of
ICBG. Performing such a prospective comparative study
(i.e., at least a LoE II if not a randomized controlled study)
is desired to truly determine the role of SiCaP in spinal
deformity surgeries. This would undoubtedly be grounds
for further research and this pilot study is a first step
towards that goal having established the safety profile of
SiCaP without any untoward adverse events with its
clinical use.
Conclusion
In conclusion, SiCaP’s use was safe and it produced a pre-
dictable sound arthrodesis without any adverse effects or
inflammatory response in all 35 patients in our series
treated by PSF. The surgical results were equivalent or su-
perior and consistent with published historical studies as-
sociated with use of gold standard ICBG. Use of SiCaP had
distinct advantages in minimising complications reported
with ICBG harvest. Use of low IDI instrumentation con-
structs was not associated with unacceptable (i.e., >10°) loss
of correction or increase in pseudarthrosis rates at 2 years.
There was substantial cost savings without any comprom-
ise in clinical outcomes.
Competing interests
NS Harshavardhana: No relationships.
Mohammed H H Noordeen: K2M - Consultant and, Ellipse Tech. Inc. –
Consultant and stock holder.
ApaTech & Baxter –Research funding.
Stryker spine –Research & educational support.
Authors’contributions
The two authors (i.e., NSH & MHHN) hereby declare that: We made substantial
contributions to conception, design acquisition of data, its analysis and
interpretation. We discussed with one another drafting the manuscript and
revising it critically for intellectual content and clinical merit. The senior author
(i.e., MHHN) gave final approval of the version to be published and NSH wrote
the manuscript draft. We take all the responsibility for the contents of this
publication and agree to be accountable for all aspects of the work in ensuring
that questions related to the accuracy or integrity of any part of the presented
and published work. Both authors read and approved the final manuscript.
Acknowledgements
The authors would like to acknowledge ApaTech & Baxter, U.K for research
support and educational aid/grant in undertaking this project.
Author details
1
Twin Cities Spine Center, 1111 S 8th St, Apt 214 N, Minneapolis 55404, MN,
USA.
2
Spinal Deformity Unit, Royal National Orthopaedic Hospital NHS Trust,
Brockley Hill-Stanmore, Middlesex HA7 4LP, UK.
Received: 17 March 2015 Accepted: 16 August 2015
Fig. 6 Late deep MRSA infection in a 15/♂showing pre-op and 47 months post-op x-rays (i.e., immediately prior to implant removal). Solid arthrodesis
was seen at implant removal and final x-rays 6 months post implant removal are depicted
Harshavardhana and Noordeen Scoliosis (2015) 10:27 Page 11 of 12
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