Content uploaded by Mostafa H. El Dafrawy
Author content
All content in this area was uploaded by Mostafa H. El Dafrawy on Nov 24, 2018
Content may be subject to copyright.
Type of Anchor at the Proximal Fusion Level Has a Significant
Effect on the Incidence of Proximal Junctional Kyphosis and Outcome
in Adults After Long Posterior Spinal Fusion
Hamid Hassanzadeh, MD, Sachin Gupta, BA, Amit Jain, MD, Mostafa H. El Dafrawy, MD,
Richard L. Skolasky, ScD, Khaled M. Kebaish, MD*
Department of Orthopaedic Surgery, The Johns Hopkins University, 601 N. Caroline Street, Baltimore, MD, 21287, USA
Received 24 October 2012; revised 19 March 2013; accepted 23 May 2013
Abstract
Study Design: Retrospective review.
Objectives: To compare the incidence of proximal junctional kyphosis (PJK) and the clinical, radiographic, and functional outcomes in
adults undergoing long posterior spinal fusion with transverse process hooks versus pedicle screws at the uppermost instrumented vertebrae.
Summary of Background Data: Proximal junctional kyphosis often occurs after instrumented long spinal fusion. Although there have
been numerous studies of PJK development in adolescents with idiopathic scoliosis, few studies have focused on adults.
Methods: This study reviewed data on 47 consecutive adult patients who underwent long spinal fusion (five or more levels) with hooks or
screws at the uppermost instrumented vertebrae, from 2004 through 2009, and had 2-year radiographic and clinical follow-up. The hook
group (20 patients) and screw group (27 patients) were similar in terms of age, gender, and levels fused. Proximal junctional kyphosis was
defined as a sagittal Cobb angle of at least 10between the lower end plate of the uppermost instrumented vertebrae and the upper end plate
of the 2 immediately superior vertebrae, and at least 10of progression from the previous measurement. The groups’ radiographs,
complications, and functional outcomes (Scoliosis Research Societye22 Patient Questionnaire and the Oswestry Disability Index) were
compared using Hotelling’s t
2
test (significance, p !.05).
Results: Comparing immediate postoperative and final follow-ups, none of the 20 patients in the hook group versus 8 of 27 patients in the
screw group (29.6%) developed PJK (p 5.01). There were no statistical differences between groups in major or minor complications rates.
At final follow-up, patients with hooks had significantly higher functional scores than those with screws (p !.05), and patients with PJK
had significantly lower functional scores in all Scoliosis Research Societye22 Patient Questionnaire domains except satisfaction.
Conclusions: Transverse process hooks were associated with a lower incidence of PJK and higher functional scores than pedicle screws.
Ó2013 Scoliosis Research Society.
Keywords: Adult scoliosis; Proximal junctional kyphosis; Transverse process hooks; Pedicle screws; Posterior instrumentation and fusion
Introduction
With advances in surgical techniques and instrumenta-
tion of the spine, surgeons can tackle increasingly complex
spinal deformities and obtain better curve correction and
spinal balance. However, junctional problems above and
below spinal fusions continue to be a major challenge,
especially in the adult population. Proximal junctional
kyphosis (PJK) has been commonly observed after instru-
mented long spinal fusion [1-10]. Although there have been
numerous studies focusing on PJK development in the
adolescent idiopathic scoliosis (AIS) population [2,3,5-9],
few studies have focused on adults [1,4,10]. In the latter
Author disclosures: HH (none); SG (board membership with FOSA;
consultancy for DePuy, Medtronic, Osteotech; royalties from DePuy;
stock/stock options from Johnson & Johnson, Pfizer, Proctor and Gamble,
Pioneer); AJ (none); AHE (none); RLS (grant from DePuy Spine); KMK
(consultancy for DePuy Spine, K2M; grants from DePuy Spine, K2M;
stock/stock options from K2M; travel/accommodations/meeting expenses
from DePuy Spine).
*Corresponding author. Khaled M. Kebaish, MD, c/o Elaine P. Henze,
BJ, ELS, Medical Editor and Director, Editorial Services, Department of
Orthopaedic Surgery, The Johns Hopkins University/Johns Hopkins Bay-
view Medical Center, 4940 Eastern Avenue, #A665, Baltimore, MD
21224-2780, USA. Tel.: (410) 550-5400; fax: (410) 550-2899.
E-mail address: ehenze1@jhmi.edu (K.M. Kebaish).
2212-134X/$ - see front matter Ó2013 Scoliosis Research Society.
http://dx.doi.org/10.1016/j.jspd.2013.05.008
Spine Deformity 1 (2013) 299e305
www.spine-deformity.org
group, the estimates of PJK incidence have varied from
20% [10] to 39% [4].
Proximal junctional kyphosis development has been
attributed to several causes. Rhee et al. [8] proposed that
the disruption of the posterior tension band with posterior
surgery, the posterior compression forces from proximal
constructs, and the decrease in thoracic kyphosis might all
promote PJK. In a human cadaveric study, Anderson et al.
[11] tested loss of thoracic motion segment flexion stiffness
after sequential anchor placement techniques at the poste-
rior uppermost instrumented vertebrae (UIV). They re-
ported that the more dissection that is done at the UIV, the
more destabilization occurs.
Because the placement of different constructs requires
varying degrees of dissection, and the constructs themselves
can potentially exert different magnitudes of compressive
forces, some studies have focused on how construct type
influences PJK development [2,6]. In the AIS group, studies
have compared hook, hybrid, and pedicle screw constructs in
terms of causing PJK [2,6]. In a study of 410 patients with
AIS, Kim et al. [6] found that patients with pedicle screw
instrumentation had a significantly higher incidence of
PJK than those with hook-only instrumentation. Recently,
Helgeson et al. [2] reported that change in proximal kyphosis
was significantly greater with pedicle screw constructs than
with hook-only and hybrid constructs. They also found
a trend toward a decrease in proximal kyphosis in constructs
with all-pedicle screws, except hooks at the most ceph-
alad segment.
To the authors’ knowledge, however, no studies of the
adult population have focused primarily on the role of
constructs in influencing PJK incidence in adults. Although
2 studies reported on the incidence of PJK in adult patients
and analyzed associated risk factors, those authors com-
mented only incidentally on the role of the constructs, and
their findings were in opposition: Kim et al. [4] reported
that instrumentation type at the UIV has a role, whereas
Yagi et al. [10] reported that it did not influence PJK
development. However, based on the results of those
studies, it is still unclear whether construct choice at the
proximal anchor site influences PJK in the adult patient.
The purpose of this study was to compare the incidence
of PJK and the clinical, radiographic, and functional
outcomes in adults undergoing long posterior spinal fusion
with transverse process (TP) hooks versus pedicle screws
at the UIV. The hypotheses were that instrumentation with
TP hooks at the UIV would be associated with a lower
incidence of PJK and that patients who did not develop
PJK would have higher functional outcome measures.
Materials and Methods
Study groups
After the study received approval from The Johns Hopkins
University Institutional Review Board, 52 consecutive adult
patients were identified from a prospectively accrued cohort
who underwent long fusions with TP hooks from 2004
through2009(Figs. 1 and 2) or pedicle screws at the UIV
(Fig. 3) and pedicle screws at the remaining levels. All
surgeries were performed by the senior author.
Inclusion criteria for the study were: age 20 years or more
at the time of surgery, spinal deformity (scoliosis, kyphosis,
or kyphoscoliosis) treated with instrumentation involving 5
or more spinal levels, upper cephalad fusion level between
T2 and T5, instrumentation at the UIV with pedicle screws
or TP hooks, and complete clinical and radiographic follow-
up for a minimum of 2 years. Five patients who had
incomplete clinical or radiographic data were excluded. The
mean follow-up in the TP hook group was 2.8 years (range,
2.0e4.9 years), and the average follow-up in the screw group
was 5.7 years (range, 3.7e7.3 years).
Patient characteristics
The study population consisted of 47 patients: 20 (17
women and 3 men) in the TP hook group and 27 (22
women and 5 men) in the pedicle screw group. The
difference in proportion of women was not statistically
Fig. 1. Long, standing radiographs of a patient with kyphoscoliosis who
underwent posterior spinal instrumentation using a hookescrew construct
at UIV. (A) Postoperative anteroposterior view. (B) Postoperative lateral
view.
300 H. Hassanzadeh et al. / Spine Deformity 1 (2013) 299e305
significant between groups (p 5.75). The TP hook and
pedicle screw groups were not significantly different in
terms of mean age at surgery or race: mean age at surgery,
46 years (range, 22e78 years) versus 51 years (range,
20e78 years), respectively (p 5.24); and 1 black patient
and 19 white patients versus 1 black patient and 26 white
patients, respectively. In the TP hook group, 9 patients had
scoliosis, 7 had kyphosis, and 4 had kyphoscoliosis. In the
pedicle screw group, 14 patients had scoliosis, 6 had
kyphosis, and 7 had kyphoscoliosis. The mean American
Society of Anesthesiologists physical classification index
was 2.3 (range, 2e3) for the TP hook group and 2.4 (range,
2e4) for the pedicle screw group; the difference was not
statistically significant (p 5.57).
Surgical technique for hook insertion at UIV
Exposure was carried to the level of the distal end of
the respective spinous process, while preserving the inter-
spinous ligaments at the proximal and distal segments, with
minimal dissection of the paraspinal muscles. A blunt
Lamina Finder device (DePuy Synthes Spine, Raynham,
MA) was used to prepare the insertion point on the trans-
verse process, ensuring that the hook blade was immediately
lateral to the lateral edge of the pedicle. An important point
was to also ensure that the hook was of sufficient size so that
it was able to latch to the entire TP without potentially
weakening the TP or causing it to break.
Surgery characteristics
In the TP hook group, an average of 13.5 levels were fused
(range, 9e17 levels); T3 to S2 were the most commonly
fused levels. In the pedicle screw group, an average of 13
levels were fused (range, 9e18 levels); T4 to S2 were the
most commonly fused levels. The difference in the number of
levels fused was not statistically significant (p 50.43).
All patients were fused from the proximal thoracic spine
to the lumbar spine (Table 1 shows the uppermost instru-
mented vertebrae for both groups). The average operative
time for the TP hook and pedicle screw group was 459
minutes (range, 305e584 minutes) and 456 minutes (range,
305e570 minutes), respectively; the difference was not
statistically significant (p 5.92). The average blood loss
for the TP hook and pedicle screw group was 2,375 mL
(range, 700e5,000 mL) and 2,513 mL (range, 800e6,500
Table 1
Distribution of the uppermost instrumented vertebrae in each group.
Uppermost instrumented
vertebrae
Transverse process hook
group, n
Pedicle screw
group, n
T1 11
T2 62
T3 10 6
T4 214
T5 14
Fig. 3. Long, standing radiographs of a patient with kyphoscoliosis who
underwent posterior spinal instrumentation using a screws-only construct
at UIV. (A) Postoperative anteroposterior view. (B) Postoperative lateral
view.
Fig. 2. Hookescrew construct on a sawbones model. (A) Anteroposterior view. (B) Lateral view. (C) Hookescrew implants.
301H. Hassanzadeh et al. / Spine Deformity 1 (2013) 299e305
mL), respectively; the difference was not statistically
significant (p 5.74). The mean intraoperative packed red
blood cell transfusion in the TP hook and pedicle screw
group was 4.3 units (range, 0e12 units) and 4.0 units
(range, 0e10 units), respectively; the difference was not
statistically significant (p 5.79). The mean intraoperative
autologous blood transfusion from the cell-saver in the TP
hook and pedicle screw group was 556 mL (range, 0e1,500
mL) and 615 mL (range, 0e3,000 mL), respectively; the
difference was not statistically significant (p 5.72).
Measurements
Proximal junctional kyphosis was defined using the
definition of Glattes et al. [1]. Establishing PJK requires
meeting the following 2 criteria: 1) a proximal junction
sagittal angle of at least 10between the lower end plate of
the UIV and the upper end plate of the vertebrae 2 levels
above the UIV; and 2) at least 10of progression in the
proximal junctional sagittal angle from baseline. To deter-
mine the incidence of PJK, the anteroposterior and lateral
standing long cassette radiographs were reviewed and the
following parameters were measured using the Cobb
method: thoracic curve angle, lumbar curve angle, kyphosis
angle, lordosis angle, coronal plumb line, and sagittal
plumb line. These parameters were measured in a standard
fashion, as noted in the previous literature [12-14].
In terms of clinical outcome, the records of all patients
were reviewed to identify perioperative complications,
which were then tabulated and divided into major and
minor categories [15].
Functional outcome was measured by the Scoliosis
Research Societye22 Patient Questionnaire (SRS-22) and
the Oswestry Disability Index (ODI) surveys, which were
administered to all patients preoperatively, postoperatively,
and at final follow-up.
Statistical analysis
The data were analyzed using SAS 9.3 software (SAS
Institute, Inc., Cary, NC). Power analysis was performed in
the following manner: Based on the literature, a PJK rate
after use of pedicle screws was assumed to be 25% in the
adult population [4,10]. The hypothesis was that the rate of
PJK development after use of hooks at the UIV would be
15%. Based on an alpha of 0.5 and a beta of 80%, 21
patients in each group were needed to have sufficient power
to be able to detect a difference in rate of PJK development.
Statistical significance was assigned at p !.05 for all
analyses. Hotelling’s t
2
test was used to compare contin-
uous parameters, and the chi-square test was used to
compare categorical parameters.
Results
PJK development
Between the immediate postoperative and final follow-
up stages, PJK developed in none of the 20 patients in
the TP hook group and in 8 of the 27 patients in the pedicle
screw group (29.6%); the difference was statistically
significant (p 5.023) (Table 2). Of the 8 patients who
developed PJK, 2 required revision surgery. Of those 2, 1
required extension of the instrumentation to C5, and 1
required extension of the instrumentation to C6.
Table 2
Preoperative and postoperative spinal curve characteristics.
Parameter Spinal Deformity Correction
Transverse process hook group Pedicle Screw Group
Preoperative,
mean (range)
Postoperative follow-up,
mean (range)
Final follow-up,
mean (range)
Preoperative,
mean (range)
Postoperative follow-up,
mean (range)
Final follow-up,
mean (range)
Thoracic curve, 52 (18e72) 17 (3e39) 19 (4e39) 35 (2e68) 13 (1e51) 12 (1e51)
Lumbar curve, 41 (23e71) 24 (9e33) 23 (4e34) 41.5 (2e76) 15 (4e52) 13.5 (1e49)
Kyphosis, 53 (17e126) 42 (23e75) 48.5 (27e81) 46 (24e81) 41 (20e73) 56 (24e81)
Lordosis, 53 (26e88) 47 (26e65) 54.5 (33e78) 53.5 (23e94) 51 (31e65) 54.5 (31e79)
Proximal junctional
kyphosis,
4.5 (0e17) 11 (1e21) 7.5 (2e23) 5 (1e21) 12 (1e37) 20.5 (1e52)
Coronal plumb
line, cm
1.3 (0e11) 1.6 (0e4.7) 1.7 (0e4.2) 1 (0e11) 1 (0e3) 1.2 (0e2.2)
Sagittal plumb
line, cm
1.8 (0e17.5) 5.4 (0e17) 0.5 (0e5.7) 4 (0e29) 4.5 (0e10.5) 3 (0e15.3)
Table 3
Major complications.
Complication Transverse process
hook group, n
Pedicle screw
group, n
Epidural hematoma 11
Mesenteric ischemia 10
Pneumothorax 10
Proximal junctional fracture 01
Fracture at L1 01
Sacral fracture 01
Pseudarthrosis 01
Acute renal failure 01
Pneumonia 01
Pleural effusion 01
Deep wound infection 01
Total 39
302 H. Hassanzadeh et al. / Spine Deformity 1 (2013) 299e305
Between the preoperative and final follow-up stages, 2
of 20 patients in the TP hook group (10%) and 13 of 27
patients in the pedicle screw group (48.1%) developed PJK;
the difference was statistically significant (p 5.008). The
average proximal junctional sagittal angle was 6.35
10.19in the TP hook group and 22.0413.86in the
pedicle screw group; the difference was statistically
significant (p !.0001).
Perioperative complications
In the TP hook group, there were 3 major (Table 3) and
13 minor complications, and in the pedicle screw group,
there were 9 major and 13 minor complications. There were
no statistical differences between groups in major (p 5.15)
or minor (p 5.25) complications.
Functional outcome
Both the TP hook and pedicle screw groups had
a significant improvement in all 5 SRS-22 domains and in
the ODI, comparing preoperative to postoperative values
and comparing preoperative with final follow-up values
(p !.01). However, patients in the TP hook group had
significantly better functional outcome measures in all 5
SRS-22 domains and in the ODI than did the pedicle screw
group (Table 4): pain subscore (p !.0001), self-image
subscore (p !.0001), activity subscore (p !.0001),
mental health subscore (p !.0001), satisfaction subscore
(p !.0001), and ODI (p 5.0002). When the functional
outcome scores of patients with and without PJK were
compared (Table 5), those with PJK had significantly lower
scores in all SRS-22 domains except satisfaction, and
significantly higher ODI scores.
Discussion
The authors compared the use of TP hooks and pedicle
screws at the UIV and found that TP hooks were associated
with a significantly lower incidence of PJK, no difference
in the clinical outcomes (such as blood loss, transfusion
requirements, and major and minor complications, etc), and
better functional outcomes.
The significantly lower incidence of PJK associated with
TP hooks may be the result of several factors. First, the
surgical approach when using TP hooks is often less
extensive proximally than pedicle screws. In placing the
hooks, there is less risk of violating the facet joint proximal
to the UIV. As such, the ligament complex and the capsule
of the supra-adjacent facet are not violated. Anderson et al.
[11] reported that the supraspinous and interspinous liga-
ment complex were probably the most important structures
that needed to be preserved during dissection for the UIV
anchor preparation for avoiding PJK. In the placement of
pedicle screws, these structures may be compromised.
Second, the TP hooks provide a softer landing and
probably produce less mechanical stress on the level above.
Rhee et al. [8] postulated that the posterior compression
forces resulting from proximal constructs may contribute to
PJK development. The TP hooks are better than pedicle
screws in this regard. Furthermore, the TP hooks do not
violate the vertebral body, and therefore avoid the problem
of compression fractures at the UIV. The authors hypothe-
size that these factors may also partially account for the
reduction in blood loss that was observed with the use of TP
hooks in the current study.
Glattes et al. [1] was the first group to study PJK in adult
patients with spine deformity. They defined PJK as a junc-
tional sagittal angle of 10or more at baseline and at least
Table 5
Comparison of Scoliosis Research Societye22 Patient Questionnaire and
Oswestry Disability Index functional outcome characteristics between
patients with and without PJK at final follow-up.
Variable Proximal junctional
kyphosis
No proximal
junctional kyphosis
p
Pain 2.69 4.01 !.01
Image 1.86 3.58 !.01
Activity 2.80 3.49 !.01
Mental health 2.74 3.54 !.01
Satisfaction 3.52 3.94 .086
Oswestry
Disability Index
43.40 20.41 !.01
Table 4
SRS-22 and ODI functional outcome characteristics at preoperative, postoperative, and final follow-up stages.
Outcome measure Transverse process hook group Pedicle screw group
Preoperative,
points (mean
[range])
Postoperative follow-up,
points (mean
[range])
Final follow-up,
points (mean
[range])
Preoperative,
points (mean
[range])
Postoperative follow-up,
points (mean [range])
Final follow-up,
points (mean
[range])
SRS-22
Pain 1.8 (0.9e2.4) 4 (2.8e4.6) 4.3 (3.4e4.8) 1.7 (0.3e3.1) 3.4 (2.6e4.5) 3.2 (2.6e4.3)
Self-image 1.8 (0.5e3.4) 3.6 (2.2e4.7) 4.2 (2.6e5.3) 2.1 (0.9e3) 2.8 (2.0e3.9) 2.4 (1.2e3.6)
Activity 2.4 (1e3.3) 2.9 (2.5e3.3) 3.6 (3e4.1) 2.4 (1.7e3) 2.9 (2.4e3.2) 3.1 (2.5e3.7)
Mental health 1.7 (1.2e2.6) 2.1 (1.6e2.4) 3.8 (3.2e4.1) 1.8 (1.1e2.5) 1.8 (1.5e2.2) 3 (2.3e3.3)
Satisfaction 1.6 (0e4.1) 2.7 (2.3e3.4) 4.3 (3.5e5.5) 1.2 (0.1e4.5) 2.1 (1.5e2.7) 3.4 (2.3e4.6)
ODI 76 (52e90) 31 (11e63) 18 (8e38) 72 (48e90) 42 (12e58) 32 (0e54)
SRS-22, Scoliosis Research Societye22 Patient Questionnaire; ODI, Oswestry Disability Index.
303H. Hassanzadeh et al. / Spine Deformity 1 (2013) 299e305
a10
progression [1]. Other groups subsequently adopted
this definition [4,10], as did the authors in the current study.
Glattes et al. [1] reported that patient characteristics and
instrumentation techniques were not associated with
development of PJK. However, as they pointed out, their
study was not powered to find a difference in PJK devel-
opment between pedicle screws and hook constructs.
Other investigators have also attempted to explore the
relationship between the upper instrumented vertebral
construct type and PJK development. In a study of 161
patients, Kim et al. [4] reported a difference in PJK
development between patients with all-pedicle screw
constructs and those with use of hooks proximally and
pedicle screws distally or only hooks. However, in their
study, the difference was not shown when an adjustment for
age was made. In a study of 157 adult patients by Yagi et al.
[10], UIV instrumentation did not differ between the PJK
and non-PJK groups. However, neither of those studies had
the primary goal of comparing hook and screw constructs
in their ability to cause PJK, and the data presented in their
work represented a subgroup analysis from a study with
a different primary goal.
The current data are consistent with those of studies in
the AIS literature that directly compare hook and screw
constructs. Helgeson et al. [2] found a trend toward
a decrease in proximal kyphosis in constructs with hooks at
the UIV (18 patients) compared with the group treated with
all pedicle screws (37 patients). As part of their study, they
also redefined PJK as any increased postoperative kyphosis
of 15or more, and found the incidence of PJK to be 8.1%
in the all-screw group and 5.6% in the group with proximal
hooks and distal screws. Similarly, in a study of 410
patients with AIS, Kim et al. [6] found a difference between
hook-only and thoracic pedicle screw instrumentation (p 5
.029). However, they did not find a difference between
pedicle screws and constructs with proximal hooks and
distal screws. In that study, the researchers did not distin-
guish among laminar, TP, and pedicle hooks. This consid-
eration is important because their use of the UIV may have
led to varying degrees of ligamentous and soft tissue
disruptions. In the current study, TP hooks were chosen for
use because they result in less soft tissue damage. The
current hook group was associated with 3 major compli-
cations and the screw group was associated with 9 major
complications; although the difference in complication rate
was not significant, the absolute difference in number of
patients who developed major complications cannot be
attributed only to the type of instrumentation at the most
cephalad segment.
The functional outcome measures in this study have
several important implications. First, there was a significant
difference at final follow-up between the TP hook and
pedicle screw groups in all 5 SRS-22 domains and in the
ODI. Kim et al. [6] reported SRS-24 outcome scores of PJK
and non-PJK patients and found no difference at the 2-year
postoperative follow-up. However, they did not look at the
difference in functional outcomes scores stratified by
construct type. Similarly, other studies reporting functional
outcome measures have found no difference between PJK
and non-PJK patients [1,4,10]. The proposed explanation
for this finding included the following: 1) Junctional
kyphosis may not always lead to discomfort for the patient;
and 2) the SRS-24 instrument may not be sensitive in
detecting the change in adult deformity patients. However,
the current study found meaningful differences in func-
tional outcomes on the basis of instrumentation type.
This study had some limitations. Because it was
a retrospective review, complete radiographic follow-up
could be achieved for only 47 patients. In addition, there
was heterogeneity in the diagnostic categories: Patients
with scoliosis, kyphosis, and kyphoscoliosis were included.
Furthermore, it is possible that over a longer follow-up
time, new trends may emerge that could not be detected
within the time frame of this study. However, there is strong
evidence in the literature that in most cases, PJK presents
during the first 2 years after surgery [16]. There is also
a possibility that over the course of the study, the primary
surgeon may have improved in surgical technique, which
may have led to potentially better outcomes for the TP hook
group. Despite its limitations, however, this study was able
to show a significant difference in PJK development
between patients who received TP hooks and those who
received pedicle screws at the UIV.
At the UIV, the use of TP hooks leads to a lower inci-
dence of PJK and is associated with higher patient satis-
faction than the use of pedicle screws. This finding may be
the result of 1) the decreased amount of damage to the
ligaments complex and the capsule of the supra-adjacent
facet; and 2) a less rigid construct. A prospective
randomized controlled study with longer follow-up that
compares the 2 instrumentation types is needed.
References
[1] Glattes RC, Bridwell KH, Lenke LG, et al. Proximal junctional
kyphosis in adult spinal deformity following long instrumented poste-
rior spinal fusion: incidence, outcomes, and risk factor analysis.
Spine (Phila Pa 1976) 2005;30:1643e9.
[2] Helgeson MD, Shah SA, Newton PO, et al. Evaluation of proximal
junctional kyphosis in adolescent idiopathic scoliosis following
pedicle screw, hook, or hybrid instrumentation. Spine (Phila Pa
1976) 2010;35:177e81.
[3] Hollenbeck SM, Glattes RC, Asher MA, et al. The prevalence of
increased proximal junctional flexion following posterior instrumen-
tation and arthrodesis for adolescent idiopathic scoliosis. Spine (Phila
Pa 1976) 2008;33:1675e81.
[4] Kim YJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis
in adult spinal deformity after segmental posterior spinal instrumen-
tation and fusion: minimum five-year follow-up. Spine (Phila Pa
1976) 2008;33:2179e84.
[5] Kim YJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis
in adolescent idiopathic scoliosis following segmental posterior
spinal instrumentation and fusion: minimum 5-year follow-up. Spine
(Phila Pa 1976) 2005;30:2045e50.
304 H. Hassanzadeh et al. / Spine Deformity 1 (2013) 299e305
[6] Kim YJ, Lenke LG, Bridwell KH, et al. Proximal junctional kyphosis
in adolescent idiopathic scoliosis after 3 different types of posterior
segmental spinal instrumentation and fusions: incidence and risk
factor analysis of 410 cases. Spine (Phila Pa 1976) 2007;32:2731e8.
[7] Lee GA, Betz RR, Clements III DH, et al. Proximal kyphosis after
posterior spinal fusion in patients with idiopathic scoliosis. Spine
(Phila Pa 1976) 1999;24:795e9.
[8] Rhee JM, Bridwell KH, Won DS, et al. Sagittal plane analysis of
adolescent idiopathic scoliosis. The effect of anterior versus posterior
instrumentation. Spine (Phila Pa 1976) 2002;27:2350e6.
[9] Wang J, Zhao Y, Shen B, et al. Risk factor analysis of proximal junc-
tional kyphosis after posterior fusion in patients with idiopathic scoli-
osis. Injury 2010;41:415e20.
[10] Yagi M, Akilah KB, Boachie-Adjei O. Incidence, risk factors and clas-
sification of proximal junctional kyphosis: surgical outcomes review of
adult idiopathic scoliosis. Spine (Phila Pa 1976) 2011;36:E60e8.
[11] Anderson AL, McIff TE, Asher MA, et al. The effect of posterior
thoracic spine anatomical structures on motion segment flexion stiff-
ness. Spine (Phila Pa 1976) 2009;34:441e6.
[12] O’Brien MF, Kuklo TR, Blanke KM, et al. The Spinal Deformity
Study Group radiographic measurement manual. Memphis (TN):
Medtronic Sofamor Danck; 2004.
[13] Angevine PD, Kaiser MG. Radiographic measurement techniques.
Neurosurgery 2008;63:40e5.
[14] Kuklo TR. Radiographic evaluation of spinal deformity. Neurosurg
Clin N Am 2007;18:215e22.
[15] Glassman SD, Hamill CL, Bridwell KH, et al. The impact of perio-
perative complications on clinical outcome in adult deformity
surgery. Spine (Phila Pa 1976) 2007;32:2764e70.
[16] Kim HJ, Lenke LG, Shaffrey CI, et al. Proximal junctional kyphosis as
a distinct form of adjacent segment pathology after spinal deformity
surgery: a systematic review. Spine (Phila Pa 1976) 2012;37:S144e64.
305H. Hassanzadeh et al. / Spine Deformity 1 (2013) 299e305
