VOL. 93-B, No. 1, JANUARY 201173
Repair of spondylolysis using compression
with a modular link and screws
N. A. Osei,
H. H. Noordeen
From the Royal
? F . Altaf, BSc(Hons), MRCS,
Specialist Registrar in Trauma
? N. A. Osei, FRCS(Tr & Orth),
? E. Garrido, MRCS, EBOT,
? M. Al-Mukhtar, MRCS,
Registrar in Orthopaedics
? H. H. Noordeen, MD,
FRCS(Orth), Consultant Spinal
Royal National Orthopaedic
Hospital, Brockley Hill,
Stanmore, Middlesex HA7 4LP ,
? C. Natali, BSc, FRCS(Orth),
Consultant Spinal Surgeon
? A. Sivaraman, FRCS(Orth),
Consultant Spinal Surgeon
Royal London Hospital,
Whitechapel, London E1 1BB,
Correspondence should be sent
to Mr F . Altaf; e-mail:
©2011 British Editorial Society
of Bone and Joint Surgery
J Bone Joint Surg [Br]
Received 23 February 2010;
Accepted after revision 23
We describe the results of a prospective case series of patients with spondylolysis,
evaluating a technique of direct stabilisation of the pars interarticularis with a construct that
consists of a pair of pedicle screws connected by a U-shaped modular link passing beneath
the spinous process. Tightening the link to the screws compresses bone graft in the defect
in the pars, providing rigid intrasegmental fixation. We have carried out this procedure on
20 patients aged between nine and 21 years with a defect of the pars at L5, confirmed on CT.
The mean age of the patients was 13.9 years (9 to 21). They had a grade I or less
spondylolisthesis and no evidence of intervertebral degeneration on MRI. The mean follow-
up was four years (2.3 to 7.3). The patients were assessed by the Oswestry Disability Index
(ODI) and a visual analogue scale (VAS). At the latest follow-up, 18 patients had an excellent
clinical outcome, with a significant (p < 0.001) improvement in their ODI and VAS scores.
The mean ODI score at final follow-up was 8%. Assessment of the defect by CT showed a
rate of union of 80%. There were no complications involving the internal fixation.
The strength of the construct removes the need for post-operative immobilisation.
A spondylolysis is a defect of the pars inter-
articularis. Usually there is a complete break in
the pars on one or both sides of the neural arch.
The condition is often asymptomatic, but may be
the cause of pain in the back. Free nerve end-
ings with nociceptive function have been iden-
tified in the area of the lysis by Schneiderman
et al.1 Neuropeptides which mediate in the sen-
sation of pain have been described at the site of
the defect by Eisenstein et al.2
The surgical management of symptomatic
spondylolysis or isthmic spondylolisthesis was
first described by Albee,3 Hibbs,4 and Bos-
worth et al5 using posterior fusion to stabilise
the defect by eliminating the movement seg-
ment. Cleveland, Bosworth and Thompson6
and Watkins7 described the technique of poste-
Kimura8 was the first to describe the direct
repair of the pars defect using an isolated bone
graft without instrumentation. Patients who
underwent this procedure had to remain
recumbent for a number of weeks, followed by
external immobilisation in a cast for up to six
months. Buck9 first described the technique of
direct repair by filling the gap in the defect
with iliac cancellous autograft and placing
screws directly through the defect itself.
A number of techniques have since been
described for direct repair of the defect, but
have been associated with complications such
as loosening and breakage of the internal fixa-
tion, technical difficulty, extensive muscle and
tissue dissection, and variable rates of consoli-
dation of the defect.
We describe a prospective case series evalu-
ating a technique of direct repair of the pars
stabilised with a construct consisting of a pair
of pedicle screws connected by a U-shaped
modular link passing beneath the spinous pro-
cess. Tightening the link to the screws
compresses the bone graft in the defect, provid-
ing rigid intrasegmental
technique was first described by the senior
Patients and Methods
Patients were selected who had chronic disabling
pain located in the lower back without sciatica,
which had been resistant to conservative treat-
ment for at least 12 months, including modifica-
tion of activity and a trial of bracing and
physiotherapy. All had defects in the pars at L5
on CT scans. Other inclusion criteria were the
absence of adjacent degenerative disc disease
confirmed by normal T2-weighted MRI, and no
more than a grade I spondylolisthesis.10
Of the 20 patients in this series, 12 were
male and eight were female, and nine had
grade I spondylolisthesis. There was one
74 F. ALTAF, N. A. OSEI, E. GARRIDO, M. AL-MUKHTAR, C. NATALI, A. SIVARAMAN, H. H. NOORDEEN
THE JOURNAL OF BONE AND JOINT SURGERY
smoker, who was male. The mean age of the patients was
13.9 years (9 to 21). None had a motor or sensory deficit.
Bony union of the pars was assessed by plain lateral
radiographs and CT scans in all patients. The clinical out-
come was evaluated using the Oswestry Disability Index
(ODI),11 and a visual analogue scale (VAS)12 with 0 repre-
senting no pain and 10 maximum pain), both pre-
operatively and at follow-up. Complications were also
Statistical analysis used the paired t-test and the Wil-
coxon’s signed-ranks test. Significance was set at p < 0.05.
Surgical technique. The patient is positioned prone. A mid-
line incision is made and the paraspinal musculature ele-
vated laterally to expose the lamina, the pars and the base
of the transverse process. Care is taken not to injure the
capsule of the facet joint. The defect in the pars is exposed
and the fibrocartilaginous element curetted. A burr is used
to decorticate the defect and the corresponding lamina and
transverse process. Anatomical landmarks and fluoroscopy
are then used to determine the starting point for the pedicle
screw. A starting hole is burred and a pedicle finder used to
enter the pedicle. The walls and floor are assessed with a
ball-tipped probe, and the hole is tapped and prepared for
a 5 mm pedicle screw. Bone graft is harvested from the iliac
crest, placed in the defect and impacted before insertion of
the screw. After placement of the screw, a rod is contoured
in a U-shape, placed just caudal to the spinous process,
deep to the interspinous ligament of the affected level, and
attached to each pedicle screw (Figs 1 and 2). When tight-
ened to the screws, the rod compresses the defects. It is
firmly fixed against the spinous process and the laminae,
which promotes compression of the graft in the defect and
stabilises the posterior arch.
Finally, fluoroscopic imaging (Fig. 3) confirms correct
placement of the screw and link. Post-operative instruc-
tions include the administration of intravenous antibiotics
until the wound is dry. The patient is mobilised without a
The mean follow-up was four years (2.3 to 7.3). None of
the patients was lost to follow-up. The mean in-patient stay
was three days (2 to 5). Post-operative complications
Photograph showing the construct in a model spine. The shaded lines
illustrate the location of the pars defects.
Photograph showing the construct in situ
from above. The rod is firmly fixed
against the spinous process and the lam-
inae, which promotes compression of
the graft in the defect and stabilises the
Anteroposterior radiograph show-
ing the construct at L5.
REPAIR OF SPONDYLOLYSIS USING COMPRESSION WITH A MODULAR LINK AND SCREWS 75
VOL. 93-B, No. 1, JANUARY 2011
included one superficial wound haematoma which did not
require evacuation, and two superficial wound infections
which responded to antibiotic treatment.
Bony union of the defect (Figs 4 and 5) occurred in 16 of
the 20 patients. Three of the four patients with nonunion
had a grade I spondylolisthesis. At the latest follow-up,
18 of the 20 patients had a significant (p < 0.001) improve-
ment in their ODI (Table I) and in their VAS scores com-
pared with the pre-operative levels. The mean ODI
improved from 54% (42 to 78) pre-operatively, denoting
severe disability, to 8% (0 to 42), indicating minimal dis-
ability. The mean VAS improved from 8.1 (6.5 to 10) pre-
operatively to 1.6 (0 to 8.2) after operation. The mean ODI
and VAS of the 16 patients with union of the defect was 3%
and 0.4 respectively, at final follow-up.
The two patients who did not have a significant improve-
ment in outcome had no evidence of union of the pars defect
on the CT scan. The other two patients with nonunion were
asymptomatic. Of the two patients who developed a symp-
tomatic nonunion, one was classified as having severe dis-
ability at follow-up. He was a smoker, and was offered a
further grafting procedure. The second patient was classified
as having moderate disability, was a non-smoker, and had
grade I spondylolisthesis. This patient had some subjective
improvement and wanted no further intervention.
No breakage or loosening of the internal fixation was
encountered, and none was removed.
The aetiology of spondylolysis remains unknown, but cur-
rent opinion is that there is an element of weakness which is
genetically determined, or a degree of dysplasia at the pars
interarticularis which renders it susceptible to the stresses
of normal activity, resulting in a stress fracture.
Lateral radiographs showing a) the pars defect at L5 pre-operatively and b) union of the pars
defect at six months post-operatively.
Lateral CT scans showing a) the pars defect at L5 pre-operatively and b) union of the pars defect at six
76 F. ALTAF, N. A. OSEI, E. GARRIDO, M. AL-MUKHTAR, C. NATALI, A. SIVARAMAN, H. H. NOORDEEN
THE JOURNAL OF BONE AND JOINT SURGERY
A minority of those affected need treatment and only a
few require surgery. Most patients considered for surgical
treatment have had the time for adjacent disc disease to
develop, or have a spondylolisthesis. Lumbosacral fusion is
the most common operation performed in these cases. For a
grade I or less spondylolisthesis, a direct repair of the pars
defect may be considered. This has the advantage of pre-
serving adjacent movement segments and dealing directly
with the anatomical defect responsible for any listhesis.
Buck9 initially carried out his technique of direct repair
in 16 patients. None developed nonunion, which was
assessed radiologically, but three patients had a poor out-
come. He suggested that this technique should only be used
in cases where the gap in the neural arch was < 3 mm to
4 mm. In 197913 he described a larger series of 75 patients,
88% of whom had a satisfactory result. The accurate place-
ment of the screw in this technique was found to be diffi-
cult, with a lengthy learning curve, and complications of
this procedure most commonly arose secondary to screw
loosening or misplacement.14
The Scott technique15 involved stabilisation of the loose
posterior arch by cerclage wiring of the transverse process
to the spinous process of the involved vertebra with fusion
of the defect. This technique requires greater surgical expo-
sure, with extensive stripping of the muscle in order to
expose the transverse process completely. Placement of the
wires under the transverse processes is difficult and can lead
to substantial bleeding. There is also a risk of injuries to the
nerve root. Several cases of wire breakage have been
reported.16 Salib and Pettine17 described a modification of
this technique that consisted of a tension band wire around
the posterior spinous process, with a screw in the pedicle.
The proposed advantages were that there was no need to
pass the wire around the transverse process, with its associ-
ated risk of injury to the nerve root, and the better anchor-
age of the wire using the pedicle screw. The strength and
linkage of wires and the diversion of the compression force
away from the graft mass are disadvantages. Songer and
Rovin18 described a small series in which the cerclage wire
was replaced by a cable passing underneath the lamina,
fixed on a pair of pedicle screws, in a technique that
requires specific instrumentation.
In 1984, Morscher, Gerber and Fasel19 described a new
repair technique that used a laminar hook positioned in the
defect and a compressive force placed upon it with a spring
held against a screw within the articular process. The
proposed advantages of this technique were that the fixa-
tion did not depend on the shape of the defect; it allowed
for maximal grafting of the defect; and it would exert a
compressive force across the lamina. Numerous problems
have been encountered with this technique, including diffi-
culty in screw placement, screw loosening20 and break-
age,21 and a high rate of failure. Tokuhashi and
Matsuzaki22 described a modified technique that stabilised
bone grafted to the pars defect with a pedicular screw, a
hook and a rod used in combination. They described signif-
icant relief of symptoms in six patients over a limited period
Kakiuchi23 used a variable-angle pedicle screw, a rod and
a laminar hook with bone graft placed across the defect.
The proposed advantage was fixation which was more
rigid. He reported resolution of symptoms in 13 of
16 patients and bony union in all at a mean follow-up of
Gillet and Petit24 described direct repair by placing
screws on the pedicles of the involved vertebra and
fixing the loose posterior arch with a solid rod bent into a
V-shape, taking purchase on the spinous process and lami-
nae. They achieved excellent results in six of ten patients,
with no complications.
In our series of 20 patients we achieved an excellent clin-
ical outcome in 18, with a mean follow-up of four years.
Union of the pars defect was achieved in 16 patients (80%).
Contradictory opinions have been reported as to the effect
of nonunion on outcome. According to Nicol and Scott,25
Debnath et al,26 Wu, Lee and Chen27 and Dai et al,28
patients with a pseudarthrosis have a poor or fair outcome.
However, Hefti, Seelig and Morscher,29 Johnson and
Thompson30 and Pellisé et al31 could not prove this rela-
tionship. In our series, of the four patients with a non-
union,32 two had a poor and two an excellent outcome.
The treatment of defects of the pars that appear cold on
a bone scan is associated with a higher rate of nonunion.32
Although the patients in our study did not have a pre-
operative bone scan, this may be a useful investigation to
identify the rate of nonunion in those patients who have a
cold lesion. Biomechanical studies may also be useful to
further evaluate the distribution of compressive forces
across the pars defect in our construct. Most
studies9,16,18,19,23 on spondylolysis have used plain radio-
graphs for the assessment of union, with its associated lim-
ited sensitivity.33 In our study we used CT imaging, which is
more sensitive and specific when used to assess union.33
This may give an impression of a higher rate of pseud-
arthrosis in our study as compared with other studies which
have used radiographs to assess union.
Some authors30,34,35 consider that a slight degree of
spondylolisthesis does not affect the outcome of patients
undergoing direct repair of the pars. Others36,37 carry out
direct repair of the pars in patients with a spondylolisthesis
of up to 25%. Jeanneret38 found no difference in outcome
Table I. Post-operative clinical assessment using the Oswestry
Excellent (minimal disability)
Good (moderate disability)
Fair (severe disability)
Poor (complete disability)
Very poor (bedbound)
0 to 20
21 to 40
41 to 60
61 to 80
81 to 100
REPAIR OF SPONDYLOLYSIS USING COMPRESSION WITH A MODULAR LINK AND SCREWS77 Download full-text
VOL. 93-B, No. 1, JANUARY 2011
between patients with a spondylolisthesis of between 0%
and 25%. In our series, nine of the 20 patients had grade I
spondylolisthesis, three of whom developed a nonunion of
Our patients were aged between nine and 21 years, with
no evidence of adjacent level disc disease on MRI, and
spondylolisthesis not greater than grade I. Numerous
authors have found that patients in the age range 20 to
30 years have worse results than younger patients.38-40 The
primary reason for this failure is thought to be associated
with the appearance of degenerative disc disease.
Our technique uses readily available instrumentation to
provide a strong construct. The bone graft in the pars defect is
not hindered by screws, allowing for high rates of union. Post-
operative recovery is made easier as the strength of the con-
struct removes the need for post-operative immobilisation.
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cial party related directly or indirectly to the subject of this article.
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