Austin Moore’s Prosthesis
It’s Relevance Today
Vi d N i Gi i h Y tik
Girish Yeotikar A j W dh
Arjun Wadhwani i
Department Of Orthopaedics
Choithram Hospital & Research Centre, Indore, India
Why AMP – Disput ?
• Improper technique
• Design of Implant
• Design of instruments
• No long term data from Indian scene
• THR – dominated
• Failures / revisions – THR – Rethinking ?
• All successful long standing AMP develop
hypertrophy of the bone all around.
• Osteolysis seen early in failed AMP within
• All successful l
f l long standing THR d
t di develop
some osteolysis of the bone.
• Osteolysis in THR seen late and damge
becomes a problem
• Mechanical loading altering the
mechanostat of bone after implant surgery
decides the future of surgery
• Proximal fixation at or above the level of
lesser trochanter save the “disuse
cancellization of cortical bone” in the
• Proximal fixation of the implant is crucial in
the success of the surgery.
• A tight fixation gives mechanical stability
and allow the grafts in the fenestration to
consolidate making it a self locking
• Thi prevents over-loading of calcar – no
This t l di fl
subsidence, no loosening, no failure.
• Frost HM Strain and other mechanical
influences on bone strength and
maintenance Curr Opin Orthop Orthop.
• Bone loading - Bone strength
• Bone modeling – hypertrophy / normal
• Bone remodeling – hypotrophy / atrophy
g yp py py
Bone modeling by drifts
(A) An infant’s long bone with its original size
and shape shown i solid li
dh h in lid line. T k
To keep it shape
as it grows in length and diameter, modeling
d ift move it surfaces in tissue space as th
its f i ti the
dashed lines suggest. Formation drifts make
and control new osteoblasts t build some
d tl t bl t to b ild
surfaces. Resorption drifts make and control
new osteoclasts to remove bone from other
t l tt b f th
A different drift pattern can correct the fracture
malunion in a child The cross-sectional view to the right
child. cross sectional
shows the endocortical as well as the periosteal drifts
that do the correction.
(C) How the drifts in B would move the whole segment
to the reader’s right. Changing the anatomy in that way
reader s right
reduces the bone’s bending moments; it does not
eliminate bending but it does limit it Drifts are created
when and where they are needed, and they include
capillaries, precursor and supporting cells, and some
wandering cells. They are multicellular entities in the
same sense as renal nephrons, and they usually act to
minimize peak b
ii i k bone strains
BMU – Renal Nephron
Bone remodeling BMUs. Top row: an activation event on a bone
surface at (A) makes a packet of bone resorption begin
(B) and then its osteoclasts are replaced by osteoblasts at (C)
The BMU makes and controls the new osteoclasts and
osteoblasts that do this. Second row: this emphasizes the
amounts of bone resorbed (E) and formed (F) by completed
BMUs. Third row: in these ‘‘BMU graphs’’ (G) shows a small
excess of formation over resorption. ( ) Equalized resorption and
p (H) q p
formation as on haversian surfaces and in ‘‘conservation-mode’’
BMU – Renal Nephron
(I) A net deficit of formation, as in disuse-mode
remodeling of endocortical and trabecular bone. Bottom
row: these ‘‘stair graphs’’ show the effects of a series of
BMUs of the kind immediately above on the local bone
‘‘bank.’’ BMUs are created when and where they are
needed and include a capillary, precursor and supporting
cells, and some wandering cells. They are multicellular
entities in the same sense as renal.
Strain in Cemented stems
• Adaptive changes in the femur after
implantation of an Austin Moore
SB Murphy, PS Walker and AL Schiller
J Bone Joint Surg Am. 1984;66:437- 443.
• The calcar and proximal regions are
understrained because much of the loads
and moments are transferred to the bone
around the distal half of the stem.
• The broad proximal collar provides good
resistance to axial force, whereas the distal half
of the stem may carry little axial load. The varus
moment on the stem is counteracted by forces at
the medial part of the calcar and the distal tip, in
a more concentrated manner than in a
t td th i
cemented stem. The radiographic appearance
around uncemented stems suggests bone
hypertrophy in the whole proximal area,
especially medially, and local thickening at a
p y y, g
point level with the tip of the prosthetic stem.
More than 1 300 Austin Moore
hemiarthroplasties have been reviewed in the
literature with no reports of fracture of the
stem. Results from our finite-element analysis
indicate that with good calcar collar support
that, calcar-collar support,
the stresses in the stem are small because
the stem portion of the prosthesis and the
bone are uncoupled and, consequently, do not
share the resultant bending moment of the
head and abductor forces.
Calcar – Collar Support
If the stem is coupled to the bone so that the
resultant bending moment is shared, high stresses
in the stem are predicted; such stresses are
inconsistent with the complete absence of fractures
of these prostheses. The results of the finite-
element analysis further showed that loss of calcar-
collar support with proximal fixation through the
fenestrations resulted in high stresses in the stem
and stress shielding of the proximal medial cortex.
Calcar – C ll S
The uncoupled prosthesis also may be modeled with
a free-body diagram as a three-force member loaded
at the head, stem tip, and in the proximal region. With
this model it can be shown that the reaction force of
the stem tip, and thus the peak bending stress in the
stem increases as calcar-collar support is decreased
calcar collar decreased.
If there is no calcar-collar support, proximal support
must be provided by some combination of integration
of bone in the fenestrations and wedging due to the
lateral-medial taper of the device..
Stresses on Stem
Stresses in the stem are largest when there is no
wedging, b t hi h stresses d
di but high t develop i th
l in the
cancellous bone in the fenestrations. When there
is wedging stresses in the stem can be low but
stresses in the supporting cancellous bone can
be high; additional proximal support through the
g; p pp g
fenestrations substantially reduces these bone
Stresses on Stem
. Ifreduced stresses in the
cancellous bone are indicative of a
stable device, these mechanisms
indicate that fractures of the Austin
Moore prosthesis have not occurred
in normally loaded hips because
load was transferred primarily either
through the collar or by wedging,
with additional support at th
ith dditi l t t the
Painful AMP two primary reasons
• Inadequate Proximal Fixation
– Loose Prosthesis
– Subsidence of the prosthesis
–LLoss of varus alignment i th canal
f li t in the l
• Acetabular cartilage erosion
Inadequate Proximal Fixation
• Not under our control
– Wide canal
• U d our control
– Faulty operative technique
– Over reaming by improper Rasp
– Improper selection of Implant
Effect of neck resection on torsional stability of cementless total hip replacement.
Whiteside LA White SE, McCarthy DS
LA, SE DS.
Biomechanical Research Laboratory, St. Louis, Missouri, USA.
Loosening of the femoral component in total hip
arthroplasty commonly results from inadequate
resistance to torsional loads We evaluated 20 adult
human cadaver femora to determine the effect of
different neck-resection levels on torsional resistance of
the femoral component. All specimens were prepared for
fixation with the Impact modular total hip replacement.
Each femoral diaphysis was overreamed 2 mm to
achieve only proximal fixation. The specimens were then
di id d i t groups of fi and i l t were i
f five d implants inserted
with the precision press-fit technique.
Without distal fixation, the femoral
component is highly dependent on p
p gy p proximal
geometry for resistance to torsional loading.
Preserving the femoral neck p
g provides an
effective means of resistance. Maintaining
the entire femoral neck most effectivelyy
reduces miromotion at low loads, but
maintaining the midshaft area of the femoral
neck appears to most effectively control
micromotion at higher torsional loads.
Resection below the midshaft of the neck
markedly decreases the torsional load-
bearing capacity of the proximal femur.
Primary positive calcar collar contact reduced the
incidence of calcar resorption. Sufficient cementation
of the medullary canal significantly reduced the
incidence of calcar resorption, as did neutral and
valgus positioning of the femoral component.
Loosening of the acetabular component occurred
more often in the group with calcar resorption. Middle-
aged patients and men were more prone t develop
d ti t d to d l
resorption of the calcar. Calcar resorption may be
influenced by surgical technique Alteration of the
operative technique is recommended, with emphasis
on correct valgus or neutral p
g position of the femoral
component, a positive calcar-collar contact, and
Tips T i k
Ti & Tricks
• Pre operative
Pre-operative assessment of the Canal
• Proper neck cut.
A id comminuting C l
i ti Calcar F Femoris.
• Save at least 1cm of neck at Calcar
• Insert canal finder from Piriformis Fossa
• In wider canal avoid use of rasp
Tips T i k
Ti & Tricks
• Select proper Implant which will fill the
proximal femur without increasing
• Use a artery forcep in the prosthesis
proximal hole ( originally for extraction) for
rotation control during insertion.
Tips T i k
Ti & Tricks
• Impaction grafting:
– The most important area is the medial side near
calcar. Graft should be inserted when nearly half of
the prosthesis has gone inside.
– Fill the fenestrations of the prosthesis with bone
grafts as the prosthesis advances in to the canal
– The color of the implant should not over-hang on the
– If done properly, it should rest on the neck and will
compress the grafts.
Intra operative error during implantation of the
uncemented Austin Moore prosthesis is relatively
common The error rates between junior doctors
and consultants were not significantly different.
Austin Moore hemiarthroplasty is a technically
demanding operation; the prosthesis is difficult to
Greater selectivity should be exercised when
considering this prosthesis for management of
femoral neck fractures.
(1)Inadequate length of the neck remnant (≤12
mm)-measured from the superior margin of the
lesser trochanter to the resection margin at the
calcar femorale If an inadequate neck
remnant was identified on postoperative
radiographs the neck length from the lesser
trochanter to the level of the fracture on
preoperative radiographs was also measured
(2) Inadequate calcar seating (>1 mm)-measured
from the medial prosthetic collar to calcar A
prosthesis collar seated on the medial calcar was
recorded as zero
(3) Difference in prosthetic head size compared
with the contralateral normal femoral head using g
circular overlays-a diameter of prosthesis up to 2
mm larger to account for articular cartilage was
considered satisfactory. If the contralateral
femoral head was not suitable for analysis (due to
disease or previous prosthetic replacement), the
ipsilateral femoral head on p p
radiographs was used for assessment of the
pp p prosthetic head size.
(4) Intra-operative periprosthetic fracture- fracture
classification was conducted using the Vancouver
147 patients were treated with the unipolar
uncemented Austin Moore prostheses over the
time period: 128 (87%) had surgery performed by
relatively junior doctors 14% by senior medical
officers, 57% by training registrars, and 17% by
principal house officers; 19 (13%) were
performed by a consultant surgeon.
84 errors in implantation were identified in 71
patients; only 76 (52%) had no errors in
implantation while 52 (35%) had one error 17
(12%) had 2 errors, and
2 (1.4%) had 3 errors
(1 4%) errors.
1: Injury. 2002 Jun;33(5):419-22.
Austin Moore hemiarthroplasty: technical aspects and their effects on outcome, in patients with fractures of the neck
p y p ,p
Orthopaedic Department, Peterborough District Hospital, Peterborough PE3 6DA,
In order to determine which technical aspects of the Austin Moore hemiarthroplasty
procedure affect the outcome, we reviewed 243 patients with a non-pathological
intracapsular femoral neck fracture who had, Austin Moore uncemented
hemiarthroplasty The immediate post operative X rays were assessed for
hemiarthroplasty. post-operative X-rays
alignment of the prosthetic stem, calcar seating, length of the neck remnant,
leg length discrepancy and size of the head, compared with the contralateral femur.
All patients were followed-up for 1 year. Significant pain at 1 year and/or revision
of the prosthesis for loosening were considered as unfavourable outcomes.
Inadequate calcar seating was significantly associated with pain and revision
of the prosthesis (P = 0.04 and 0.01, respectively). Length of the neck remnant
was also significantly associated with these two outcomes (P = 0 05 and 0 023
respectively). Difference in head size was associated with pain, but not with
loosening (P = 0.01 and 0.08, respectively). The rest of the parameters were not
significantly associated with the outcome. We recommend that when inserting an
Austin Moore hemiarthroplasty, particular attention must be paid to the seating of
the collar of the prosthesis on the calcar and correct choice of head size.
Injury. 2004 Oct;35(10):1020-4.
C t ca ad o og ca a a ys s a te ust
Critical radiological analysis after Austin Moore hemiarthroplasty.
oo e e a t op asty
Yau WP, Chiu KY.
Department of Orthopaedic Surgery, The University of Hong Kong, Queen Mary
Hospital, No. 102, Pokfulam Road, Hong Kong, PR China. email@example.com
The aim of this study is to investigate the causes of prosthesis loosening in patients
treated with Austin Moore hemiarthroplasty (AMA). The clinical and radiological
outcomes were documented in a quantitative manner after 7 years follow-up of 144
patients. At the time of final follow-up, 52 patients had died and 48 patients were lost
to follow-up, leaving a total of 44 patients for analysis. Immediate post-operative
X-rays were studied for the initial alignment of prosthesis, the fit of the prosthesis
and the degree of osteoporosis. X-rays on latest follow-up were studied for evidence
of loosening. All patients were assessed clinically with the hip score of hospital for
special surgery. It was found that hip pain was significantly related to subsidence
and pivoting of the prosthesis (P = 0.014 and 0.035, respectively).
Significant increase in subsidence was noted if the stem of prosthesis was not fitting
well within the shaft of femur (P = 0.006). When the patient was younger than
73 years old at the time of operation, there was more subsidence of the prosthesis at
the final follow-up (P = 0.001). It was concluded that the fill of AMA within the shaft
of femur should be greater than 70% to avoid early loosening Relatively younger
patients with acute fracture of the neck of femur should be treated by methods other
than cementless AMA.
•Injury. 2004 Oct;35(10):1020-4.
Critical radiological analysis after Austin Moore hemiarthroplasty.
Yau WP, Chiu KY
It was concluded th t th fill of AMA within th shaft of
l d d that the f ithi the h ft f
femur should be greater than 70% to avoid early
loosening Relatively younger patients with acute
fracture of the neck of femur should be treated by
methods other than cementless AMA.
•Injury. 2002 Jun;33(5):419-22.
Austin Moore hemiarthroplasty: technical aspects and their effects on outcome, in
patients with fractures of the neck of femur.
Sharif KM, Parker MJ.
Sh if KM P k MJ
Inadequate calcar seating was significantly associated
with pain and revision of the p
p prosthesis ( = 0.04 and
0.01, respectively). Length of the neck remnant was also
significantly associated with these two outcomes (P =
0.05 and 0.023, respectively). Difference in head size
was associated with pain, but not with loosening
J Trauma. 2001 Jul;51(1):84-7.
The effect of intramedullary corticocancellous bone plug for hip hemiarthroplasty.
Kligman M, Zecevic M, Roffman M.
Application of a corticocancellous bone plug in uncemented
hip hemiarthroplasty for treatment of femoral neck fractures
p p y
can decrease the incidence of early thigh pain in the first 6
Scand J Surg. 2002;91(4):357-60.
The long-term results of Lubinus interplanta hemiarthroplasty in 228 acute femoral neck
fractures. A retrospective six-year f ll
ft t ti i follow-up.
Isotalo K, Rantanen J, Aärimaa V, Gullichsen E.
The Lubinus prosthesis has a greater CCD (caput collum
diaphyse) angle and a longer stem compared to Thompson and
Moore implants. The need for resection of calcar cortex is also
limited. These biomechanical facts may explain the good long-
term results of Lubinus hemiarthroplasty.
Loading of the calcar leading to Neck over hang & absorption
Reinforcement of the
After One year
Ideal Prosthesis Fitting
F moderately wide canal
For d l id l
2 Correct sitting over calcar
3. Correct Varus setting
4. Three point fixation
For Narrow canal the junction
below the fenestrations is too much
angulated Needs a straight stem
Intra-operative error during AMP
hemiarthroplasty J of Ortho Surgery
• 147 patients were treated with th unipolar uncemented
ti t t t d ith the i l td
Austin Moore prostheses over the time period: 128
(87%) had surgery p
) g y performed by relatively j
y y junior
• doctors-14% by senior medical officers, 57% by training
registrars, and 17% by principal house officers; 19 (13%)
were performed by a consultant surgeon
• 84 errors in implantation were identified in 71 patients;
only 76 (52%) had no errors in implantation, while 52
y ( ) p ,
(35%) had one error, 17 (12%) had 2 errors, and
• 2 (1.4%) had 3 errors.
• G H hospital U K
• 188 patients
Infection 4 5%
I f ti 4.5%
Journal of injury - 2001
AOSJ - 1991 June
quality of life
185 patients – average 80 yrs
4% deep infection
1% prostr sio
2% loosening of prosthesis
5 yrs -- > 60% mortality in both groups
Half of pts & most of the controls able to
AMP was well fixed
Could not be removed
Locking / Mamman’s plate
“Don’t throw away the AMP
Don t AMP”
Says Marcus R ER.E.
From University hospital of Cleveland Ohio
(journal of A th l t 2002)
(j l f Arthroplasty
7% died(3 months) 11% died
HHS Avg 75(26 mon) 78 Avg
(55 to 92) (60 to 94)
must be paid to the
seating of collar of
th prosthesis on
the calcar & correct
choice of head size.
Method is very easy to
Cost effective, well
tolerated by aged
154 AMP for 10 yrs
At 3yrs 46% community
35% non functional
Men had better than women
H i hi score -- 69 – 55yrs
59 – 10yrs
Failure rate -- > 5 yrs – 6 5%
10 yrs – 7.7%
Revision rate -- > 5 yrs - 4.5 %
10 yrs – 5.2%
A case of THR done 14 Years ago
N th CUP showing d f
h i deformation ti
No complaints A.M.P. 16 years ago.
• In our setup AMP serves purposeful
satisfactory function in elderly
• Average ortho surgeon can perform
this surgery comfortably in average
• Pl th surgery b f
Plan the before h d & ask
for appropriate stem width according
t femoral canal.
• Carefully reaming in narrow
• No reaming in Osteoporotic
• Use bone grafts from femoral
head for calcar reinforcement
• Always fill the fenestrations
with bone grafts.
ith b ft
• AMP is time tested implant and results are
• THR, cemented bipolar has got their own
, p g
indications, & they are also not free from serious
• AMP is Cost effective,
• Bone cement can be used as last option.
• Further improvement in the implant design is
22 years old Male
AMP working since then
THR - fail
• Material failure
• Friction failure
• Cement di
C t disease
• Design failure
• Particle disease
• Material failure
• Mechanical failure - Mechanostat
Proxima – Depuy
a conservative metaphyseal implant
Information contained and transmitted by this presentation is
based on personal experience and collection of cases at
Choithram Hospital & Research centre, Indore, India, during last
It is intended for use only by the students of orthopaedic surgery.
yy p gy
Views and opinion expressed in this presentation are personal
Depending upon the x-rays and clinical presentations, viewers
can make their own opinion.
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