Treatment of the Unstable Paediatric Hip using a TransArticular Bioabsorbable Suture

1
Treatment of the Unstable Paediatric Hip using a
Trans-Articular Bio-absorbable Suture

• Michael K Dodds1,2, Philip A OConnor1, James
  Lee1, Damian McCormack1,2.
• 1. Department of Paediatric Orthopaedic Surgery,
  The Childrens University Hospital, Temple
  Street, Dublin
• 2. Department of Surgery, University College
  Dublin

Introduction
Radiographic analysis In vivo radiography was
performed at six, twelve and eighteen weeks of
age. Piglets were positioned supine, with their
hip joints held in full extension.

• Treatments for Developmental Dysplasia of the Hip
  (DDH) are well established and largely
  efficacious. However, there are exceptions where
  recurrent, recalcitrant subluxation and
  dislocation is seen in both DDH and dysplasias
  associated with neuromuscular conditions1,2.
  These patients remain a challenge to the
  paediatric orthopaedist.
• Trans-articular toggled cables and sutures have
  been used in the treatment of traumatic
  dislocations in dogs and larger animals and are
  well described3-6. The effect of their use in
  the skeletally immature hip or developmental
  dysplasia is not known.
• The purpose of this study is to assess the damage
  caused by such a surgical procedure on the
  immature porcine hip. Specifically
• Does the procedure lead to the formation of a bar
  across the proximal femoral physis?
• Does avascular necrosis of the proximal femoral
  epiphysis occur?
• Does the procedure result in articular
  chondrolysis?
• Whether the procedure adversely affects
  subsequent acetabular development.

R
R
4
5
Plain radiography at eighteen weeks of age,
post-mortem 5mm sections and histological
analysis revealed no evidence of local or diffuse
osteonecrosis. Histological sections did exhibit
thickened trabeculae in the right femoral
epiphysis suggesting an increase in osteoblast
activity. There was no radiographic or
histological evidence of physeal bar formation
(figures 4-6). There was no evidence of
chondrolysis of either articular surface. The
acetabular indices and acetabular dimensions were
not significantly different (Plt0.05) (figures 8
and 9) .
Figure 4. AP pelvic radiograph of pig 12 weeks
post-op. Arrow points to femoral drill
tunnel. Figure 5. Plain radiograph of 5mm
sections through left and right hips, drill
tunnel visible through right hip joint.
Histological procedure The proximal femora were
sectioned down their long axis through the plane
of the drill tunnel (figures 3 and 5).
Acetabular sections were taken through their
long-axis8 in line with the drill tunnel, with
corresponding sections taken through the
contralateral acetabulum. 5µm sections were
stained with Haematoxylin and Eosin and Safranin
O and fast green for inspection under light
microscopy.
Materials and methods
Experimental Design The study was approved by the
Institutional Ethics Committee and performed
under appropriate animal license. Six female
mixed-breed European pigs, aged 6 weeks were
used. Surgical procedures were carried out on the
right hind-limb, the left serving as a control.
Animals received a single dose of intravenous
oxytetracycline 50mg/kg to stain bone7. We
drilled up the femoral neck, across the hip
joint, breeching the medial pelvic wall. We then
passed a suture-anchor (Panalok RC Quick-Anchor
and size 2 Panacryl suture) through this tunnel,
engaging the anchor against the medial wall. The
suture was tied down to the lateral aspect of the
proximal femur, stabilizing the hip
concentrically in joint (figure 1a-c).
P
P
M
E
M
S
6(a)
6(b)
Figure 8. Maximum and minimum acetabular
dimensions at necropsy
Figure 9. Left and right acetabular index at 6,
12 and 18 weeks of age.
Figure 6. 5µm sections through proximal femoral
physis. (a) HE stain through centre of bone
tunnel, suture material still visible (S). (b)
Safranin O and fast green stain through periphery
of tunnel showing damage to physis though no
bridging osseous bar. (M) Metaphysis, (P) Physis
and (E) Epiphysis. Magnification x 40.
Conclusions
Statistical analysis Two-way analysis of variance
was performed to determine the differences in
acetabular indices, femoral head diameters and
acetabular dimensions. Differences were deemed
significant at Plt0.05. All data are presented as
the mean and standard deviation.
This study suggests that the immature hip is
remarkably resilient to the isolated surgical
insult described. Further work is needed to
determine the optimal implant material for this
procedure, whether synthetic or biological, and
to study the efficacy of the procedure in the
dysplastic subluxating hip.
Results
References
1(a)
1(b)
1(c)
Figure 1. Retrograde drilling of proximal femur
through the medial wall of pelvis (a).
Advancement of steel sheath across the joint (b),
and insertion of suture anchor (c).
In two of the six subjects, the suture-anchor
pulled out of the acetabulum and remained in the
joint space. In all other cases, the suture
broke at the femoro-acetabular interface
suggesting failure through cyclical shear
forces. Result are summarized in Table 1. There
was no significant difference in the size of the
ossific nuclei at eighteen weeks. The femoral
head sizes at necropsy were also similar and not
statistically significantly different (figure 7).

1. Coleman, S.S. The subluxating or wandering
femoral head in developmental dislocation of the
hip. J Pediatr Orthop, 1995. 15 p. 785-8. 2.
Wilkinson, J.A. and Sedgwick, E.M. Occult spinal
dysraphism in established congenital dislocation
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Gross specimen analysis The maximum and minimum
acetabular diameters were measured as described
by Greenhill et al.8, as were the femoral head
diameters (Table 1). Articular surfaces were
inspected for gross damage and evidence of
chondrolysis prior to preparation for
histological sectioning (figure 2).
3(a)
2
3(b)
Figure 2. Right and left femoral heads 12 weeks
post-operatively, note comparable sizes and
normal articular cartilage. Figure 3. 5 mm
sections of femoral head visualized under (a)
ultraviolet light post-operative bone growth
seen as darker bone around stained bone, and (b)
plain light drill tunnel now skewed as skewed
line as a consequence of post-operative
metaphyseal growth, note also intact proximal
femoral physis.
Figure 7. Histogram showing radiographic ossific
nucleus diameters (mean) at 6, 12 and 18 weeks of
age and actual size of femoral heads at necropsy.