To examine the potential role of central bone grafting as a method of preventing femoral head collap

1
To examine the potential role of central bone
grafting as a method of preventing femoral head
collapse in an animal model of Legg Calve Perthes
disease.

• E Conroy, P Connolly, D McCormack.
• Department of Orthopaedic Surgery, Childrens
  University Hospital, Temple Street, Dublin 1,
  Ireland.

Radiological Changes
Assessment and analysis
Introduction
Late onset Legg Calve Perthes Disease (LCPD) is
associated with the development of a stiff,
painful hip during teenage years and the onset of
osteoarthritis in early adulthood2,5. (Fig 1)The
poor potential for remodelling of the collapsed
femoral head results in an aspherical incongruent
hip joint at skeletal maturity. Containment, the
cornerstone of treatment in LCPD, does not confer
the benefits to older children because of their
reduced ability to remodel. The two most
important prognostic factors for children
developing LCPD are age of onset and shape of
femoral head at skeletal maturity. Of these only
the shape of the femoral head is potentially
modifiable.
The rabbits were euthanised at four week
intervals post operatively and the femoral head
collapse was assessed using the Head Deformity
Score. (Figure 5). This scoring system combined
radiological and macroscopic changes and the
results were assessed using ANOVA, t- test and
Fishers test. Each femoral head was assessed
histologically to determine presence of avascular
necrosis and any possible growth disturbance or
chondrolysis resulting from drilling through the
growth plate into the central column of the
femoral head.
Normal
Smartset Bone Cement
Control
Bone Source
Vitoss Scaffold
Macroscopic Changes
Hypothesis
Summary
We hypothesised that by buttressing the central
column of the femoral head we could provide a
scaffold that would prevent the collapse of the
lateral column.
Bone source
Vitoss Scaffold
Control
Smartset Bone Cement
Figure 2 Intraoperative picture exposing femoral
head
Drilling through the physis into the central
column of the epiphyses did not cause a growth
disturbance or chondrolysis at the articular
surface of the femoral. We have shown that
buttressing the central column may improve the
congruency at skeletal maturity. The small
numbers used in the study prevent any statistics
from being significant but our treated groups did
have a better femoral head shape than the control
groups.
Figure 1 Late onset LCPD Left Hip with severe
lateral column collapse
Aims
Figure 4 Insertion point for drill on
third trochanter
Our aim was therefore to prevent lateral column
collapse by modifying the shape of the femoral
head and produce a more congruent spherical joint
at skeletal maturity. Severe Lateral column
collapse is associated with the poorest prognosis
1.
Methods
Late onset LCPD has detrimental consequences for
the affected femoral head. Severe epiphyseal
collapse in the absence of any remodelling
potential results in a painful stiff, incongruent
joint and early development of osteoarthritis2,.
Modification of the shape of the femoral head
before severe collapse occurs is the only
alterable parameter for these children4. We have
demonstrated that drilling through the physis
does not cause a growth disturbance or
chondrolysis and buttressing the central column
has a small but positive effect on the shape of
the femoral head. In our unit we have buttressed
the central column of a femoral head affected by
late onset LCPD and six months later there has
been no further collapse.( Pre operative
radiograph -figure 1, post op radiograph -figure
10)
Development of an animal model Twenty New
Zealand White rabbits were randomised into a
control group of eight rabbits and a treatment
group of 12 rabbits. (Figure 2) The treatment
group was further subdivided into three groups
each receiving a different buttressing material.
The rabbits were operated on at 18 weeks of age
and monitored to determine the shape of the
femoral head at skeletal maturity. Induction of
avascular necrosis General anaesthetic was
induced using a combination of medetomidine
(0.5mg/kg) and Ketamin (25 mg/kg) and this was
reversed with antimepazole (1mg/kg) at completion
of the procedure. The rabbits were placed in the
left lateral position allowing access to the
right femoral head. The rabbits were given
preoperative analgesia- Carprofen (5mg/kg) and
antibiotic - Enrofloxacin (5mg/kg). Through an
anterolateral approach to the right hip a partial
capsulotomy was performed. The ligamentum teres
was transected to allow subluxation of the
femoral head.(Figure 3) A double ligature was
placed around the femoral neck disrupting the
ascending cervical vessels supplying the femoral
head. Central column drilling The twelve
rabbits in the treatment group had a further
procedure that involved drilling the central
column of the femoral head from a point on the
large third trochanter n the lateral aspect of
the proximal femur. (Figure 4) The depth of the
drill piece was meticulously measured to allow
accurate drilling of the central column. Central
column buttressing The central column was then
buttressed with one of three substances -
Smartset HV Bone Cement (Depuy Inc, Johnson and
Johnson, Canada) Vitoss Scaffold - synthetic
cancellous bone void filler (Orthovita Inc) Bone
Source Hydroxyapatite cement (Stryker),
Figure 10 6 months post central column
buttressing
Figure 3 Study design


Figure 5 Head Deformity Score 3
References

• 1. Herring JA, Kim HT, Browne R.
  Legg-Calve-Perthes Disease. Part I
  Classification of Radiographs with Use of the
  Modified Lateral Pillar and Stulberg
  Classifications. J Bone Joint Surg 2004 86A
  2103-2120.
• 2. Ippolito E, Tudisco C, Farsetti P. Long term
  prognosis of Legg Calve Perthes disease
  developing during adolescence. J Paediatr Orthop
  1985 5 652-6.
• 3. Rowe SM, Chung JY, Moon ES, Jung ST, Lee
  HJ, Lee JJ. The effects of subluxation of the
  femoral head with avascular necrosis in growing
  rabbits.J Pediatr Orthop. 2004 Nov-Dec24(6)645-5
  0.
• 4. Stuhlberg, Salter The natural course of
  Legg Calve LCPD and its relationship to
  degenerative arthritis of the hip Long term
  follow up study. Orthop Trans 1105,1977.
• 5. Salter RB, Thompson GH. Legg Calve LCPD. The
  prognostic significance of the subchondral
  fracture and a two-group classification of the
  femoral head involvement. Journal Bone and Joint
  Surgery 1984, 66 a 961-966

Figure 6 Average Results of Head Deformity Score