Austin Moore’s Prosthesis It’s Relevance Today

Vi d N i Gi i h Y tik A j W dh iVinod Naneria Girish Yeotikar Arjun WadhwaniConsultants

Department Of OrthopaedicsDepartment Of OrthopaedicsChoithram Hospital & Research Centre, Indore, India

Why AMP – Disput ?Why AMP Disput ?

• Improper technique• Design of Implantg p• Design of instruments• No long term data from Indian sceneNo long term data from Indian scene• THR – dominated • Failures / revisions THR Rethinking ?• Failures / revisions – THR – Rethinking ?

Question?Question?

• All successful long standing AMP developAll successful long standing AMP develop hypertrophy of the bone all around.

• Osteolysis seen early in failed AMP within• Osteolysis seen early in failed AMP within months.All f l l t di THR d l• All successful long standing THR develop some osteolysis of the bone.

• Osteolysis in THR seen late and damge becomes a problem

AnswerAnswer

• Mechanical loading altering theMechanical loading altering the mechanostat of bone after implant surgery decides the future of surgerydecides the future of surgery.

• Proximal fixation at or above the level of lesser trochanter save the “disuselesser trochanter save the disuse cancellization of cortical bone” in the calcar regioncalcar region.

The philosophyThe philosophy

• Proximal fixation of the implant is crucial inProximal fixation of the implant is crucial in the success of the surgery.

• A tight fixation gives mechanical stability• A tight fixation gives mechanical stability, and allow the grafts in the fenestration to consolidate making it a self lockingconsolidate, making it a self-locking device.Thi t l di f l• This prevents over-loading of calcar – no subsidence, no loosening, no failure.

MechanostatMechanostat

• Frost HM Strain and other mechanicalFrost HM. Strain and other mechanical influences on bone strength and maintenance Curr Opin Orthopmaintenance. Curr Opin Orthop. 1997;8:60–70.

-----------------------------------------------------------• Bone loading - Bone strength • Bone modeling – hypertrophy / normal• Bone remodeling – hypotrophy / atrophyg yp p y p y-----------------------------------------------------------

Bone modeling by drifts

(A) An infant’s long bone with its original size d h h i lid li T k it hand shape shown in solid line. To keep its shape

as it grows in length and diameter, modeling d ift it f i ti thdrifts move its surfaces in tissue space as the dashed lines suggest. Formation drifts make

d t l t bl t t b ildand control new osteoblasts to build some surfaces. Resorption drifts make and control

t l t t b f thnew osteoclasts to remove bone from other surfaces.

(B) A different drift pattern can correct the fracture malunion in a child The cross-sectional view to the rightmalunion in a child. The cross sectional view to the right 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 wayto the reader s right. Changing the anatomy in that way reduces the bone’s bending moments; it does not eliminate bending but it does limit it Drifts are createdeliminate 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

i i i k b t iminimize peak 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)(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. (H) Equalized resorption and p ( ) q pformation as on haversian surfaces and in ‘‘conservation-mode’’remodeling.

BMU Renal NephronBMU – 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 ofrow: 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 arebank. 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 stemsStrain in Cemented stems

• Adaptive changes in the femur afterAdaptive changes in the femur after implantation of an Austin Moore prosthesisprosthesisSB Murphy, PS Walker and AL SchillerJ Bone Joint Surg Am. 1984;66:437- 443.

• The calcar and proximal regions are understrained because much of the loads

fand moments are transferred to the bone around the distal half of the stem.

Un-cemented stemsUn cemented stems

• The broad proximal collar provides goodThe 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

t t d th ia more concentrated manner than in a cemented stem. The radiographic appearance around uncemented stems suggests bonearound uncemented stems suggests bone hypertrophy in the whole proximal area, especially medially, and local thickening at a p y y, gpoint level with the tip of the prosthetic stem.

More than 1 300 Austin MooreMore than 1,300 Austin Moore hemiarthroplasties have been reviewed in the literature with no reports of fracture of theliterature, with no reports of fracture of the stem. Results from our finite-element analysis indicate that with good calcar collar supportindicate that, with good calcar-collar support, the stresses in the stem are small because the stem portion of the prosthesis and thethe stem portion of the prosthesis and the bone are uncoupled and, consequently, do not share the resultant bending moment of theshare the resultant bending moment of the head and abductor forces.

Calcar – Collar Support

If the stem is coupled to the bone so that the

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 p ;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 stemfenestrations resulted in high stresses in the stem and stress shielding of the proximal medial cortex.

C l C ll S tThe uncoupled prosthesis also may be modeled with

Calcar – Collar Support

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 ofthis 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 decreasedstem, increases as calcar collar support is decreased. If there is no calcar-collar support, proximal support must be provided by some combination of integration y gof 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 d i b t hi h t d l i thwedging, but high stresses develop in the

cancellous bone in the fenestrations. When there is wedging stresses in the stem can be low butis 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 gfenestrations substantially reduces these bone stresses

Stresses on Stem

. If reduced stresses in the cancellous bone are indicative of acancellous bone are indicative of a stable device, these mechanisms indicate that fractures of the Austinindicate 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,

ith dditi l t t thwith additional support at the fenestrations

Painful AMP- two primary reasonsPainful AMP two primary reasons

• Inadequate Proximal Fixation• Inadequate Proximal Fixation– Loose Prosthesis

C l b ti– Calcar absorption– Subsidence of the prosthesis

L f li t i th l– Loss of varus alignment in the canal

• Acetabular cartilage erosion

Inadequate Proximal FixationInadequate Proximal Fixation

• Not under our controlNot under our control– Elderly

Osteoporotic– Osteoporotic– Wide canal

U d t l• Under 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 DSWhiteside LA, White SE, McCarthy 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 adultresistance to torsional loads. We evaluated 20 adult human cadaver femora to determine the effect of different neck-resection levels on torsional resistance ofdifferent 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 f fi d i l t i t ddivided into groups of five and implants were inserted with the precision press-fit technique.

Without distal fixation, the femoral component is highly dependent on proximal p g y p pgeometry for resistance to torsional loading. Preserving the femoral neck provides an g peffective means of resistance. Maintaining the entire femoral neck most effectively yreduces miromotion at low loads, but maintaining the midshaft area of the femoral gneck appears to most effectively control micromotion at higher torsional loads. gResection below the midshaft of the neck markedly decreases the torsional load-ybearing capacity of the proximal femur.

Primary positive calcar collar contact reduced thePrimary positive calcar-collar contact reduced the incidence of calcar resorption. Sufficient cementation of the medullary canal significantly reduced theof 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-

d ti t d t d laged patients and men were more prone to develop resorption of the calcar. Calcar resorption may be influenced by surgical technique Alteration of theinfluenced by surgical technique. Alteration of the operative technique is recommended, with emphasis on correct valgus or neutral position of the femoral g pcomponent, a positive calcar-collar contact, and improved cementation

Proximal FixationTi & T i kTips & Tricks

• Pre-operative assessment of the CanalPre operative assessment of the Canal.• Proper neck cut.

A id i ti C l F i• Avoid comminuting Calcar Femoris.• Save at least 1cm of neck at Calcar• Insert canal finder from Piriformis Fossa• In wider canal avoid use of raspIn wider canal, avoid use of rasp.

Proximal FixationTi & T i kTips & Tricks

• Select proper Implant which will fill theSelect proper Implant which will fill the proximal femur without increasing comminutioncomminution.

• Use a artery forcep in the prosthesis proximal hole ( originally for extraction) forproximal hole ( originally for extraction), for rotation control during insertion.

Proximal FixationTi & T i kTips & Tricks

• Impaction grafting: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 canalgrafts, as the prosthesis advances in to the canal.

– The color of the implant should not over-hang on the calcar.

– If done properly, it should rest on the neck and will compress the grafts.

Intra operative error during implantation of theIntra-operative error during implantation of the uncemented Austin Moore prosthesis is relatively common The error rates between junior doctorscommon. The error rates between junior doctors and consultants were not significantly different. Austin Moore hemiarthroplasty is a technicallyAustin Moore hemiarthroplasty is a technically demanding operation; the prosthesis is difficult to implant wellimplant well. Greater selectivity should be exercised when considering this prosthesis for management ofconsidering this prosthesis for management of femoral neck fractures.

(1)Inadequate length of the neck remnant (≤12 mm)-measured from the superior margin of themm)-measured from the superior margin of the lesser trochanter to the resection margin at the calcar femorale If an inadequate neckcalcar femorale. If an inadequate neck remnant was identified on postoperative radiographs the neck length from the lesserradiographs, the neck length from the lesser trochanter to the level of the fracture on preoperative radiographs was also measuredpreoperative radiographs was also measured.

(2) Inadequate calcar seating (>1 mm)-measured from the medial prosthetic collar to calcar Afrom the medial prosthetic collar to calcar. A prosthesis collar seated on the medial calcar was recorded as zerorecorded as zero.

(3) Difference in prosthetic head size compared with the contralateral normal femoral head using gcircular overlays-a diameter of prosthesis up to 2 mm larger to account for articular cartilage was g gconsidered satisfactory. If the contralateral femoral head was not suitable for analysis (due to y (disease or previous prosthetic replacement), the ipsilateral femoral head on preoperative p p pradiographs was used for assessment of the appropriate prosthetic head size. pp p p(4) Intra-operative periprosthetic fracture- fracture classification was conducted using the Vancouver gsystem.

147 patients were treated with the unipolar uncemented Austin Moore prostheses over theuncemented Austin Moore prostheses over the time period: 128 (87%) had surgery performed by relatively junior doctors 14% by senior medicalrelatively junior doctors-14% by senior medical officers, 57% by training registrars, and 17% by principal house officers; 19 (13%) wereprincipal house officers; 19 (13%) were performed by a consultant surgeon. 84 errors in implantation were identified in 7184 errors in implantation were identified in 71 patients; only 76 (52%) had no errors in implantation while 52 (35%) had one error 17implantation, while 52 (35%) had one error, 17 (12%) had 2 errors, and 2 (1 4%) had 3 errors2 (1.4%) had 3 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 , pof femur.Sharif KM, Parker MJ.Orthopaedic Department, Peterborough District Hospital, Peterborough PE3 6DA,UK. khalidsharif@doctors.org.uk@ gIn order to determine which technical aspects of the Austin Moore hemiarthroplastyprocedure affect the outcome, we reviewed 243 patients with a non-pathologicalintracapsular femoral neck fracture who had, Austin Moore uncemented hemiarthroplasty The immediate post operative X rays were assessed forhemiarthroplasty. The immediate post-operative X-rays were assessed for 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 023was 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.

Critical radiological analysis after Austin Moore hemiarthroplasty.C t ca ad o og ca a a ys s a te ust oo e e a t op astyYau WP, Chiu KY.Department of Orthopaedic Surgery, The University of Hong Kong, Queen MaryHospital, No. 102, Pokfulam Road, Hong Kong, PR China. peterwpy@hkucc.hku.hkThe aim of this study is to investigate the causes of prosthesis loosening in patientsThe aim of this study is to investigate the causes of prosthesis loosening in patientstreated with Austin Moore hemiarthroplasty (AMA). The clinical and radiological outcomes were documented in a quantitative manner after 7 years follow-up of 144patients. At the time of final follow-up, 52 patients had died and 48 patients were lostto 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 forof 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 atthe 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 youngerof 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 l d d th t th fill f AMA ithi th h ft fIt 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 acuteloosening. 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.Sh if KM P k MJSharif KM, Parker MJ.

Inadequate calcar seating was significantly associated with pain and revision of the prosthesis (P = 0.04 and p p (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 uncementedhip hemiarthroplasty for treatment of femoral neck fractures p p ycan decrease the incidence of early thigh pain in the first 6 months.

Scand J Surg. 2002;91(4):357-60.The long-term results of Lubinus interplanta hemiarthroplasty in 228 acute femoral neck f t A t ti i f llfractures. A retrospective six-year follow-up.Isotalo K, Rantanen J, Aärimaa V, Gullichsen E.

The Lubinus prosthesis has a greater CCD (caput collumThe 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

Impaction Grafting Reinforcement of theReinforcement of the Calcar Femoris

After One yearDay One

After One year

Tight Femoral CanalThree Point Fixation

Proximal Fixation

10 years follow up came with # Tr10 years follow up came with # Tr.

Proximal Fixation

14 years PO

Broken stem Not a Failure

Proximal FixationProximal Fixation

Broken Stem –Broken Stem –Not a Failure20 years FUy

Bone in the fenestration

A broken stem is not a failure

Too Much Valgus Too Mush Varus

S b idSubsidenceNo proximal Fixation

Subsidence

Ideal Prosthesis FittingF d l id lFor moderately wide canal1.Correct offset2 Correct sitting over calcar2.Correct sitting over calcar3. Correct Varus setting4. Three point fixationp

For Narrow canal the junction below the fenestrations is too much angulated Needs a straight stemangulated, Needs a straight stem

Intra-operative error during AMPhemiarthroplasty J of Ortho Surgeryhemiarthroplasty.J. of Ortho Surgery

Weinrauch, P

147 ti t t t d ith th i l t d• 147 patients were treated with the unipolar uncementedAustin Moore prostheses over the time period: 128 (87%) had surgery performed by relatively junior ( ) g y p y y j

• doctors-14% by senior medical officers, 57% by training registrars, and 17% by principal house officers; 19 (13%) were performed by a consultant surgeonwere 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.

Burminghum StudyBurminghum Study

• G H hospital U KG.H.hospital U.K.• 188 patients

I f ti 4 5%Infection 4.5%Dislocation 3.4% Loosening 3.4%

Journal of injury - 2001Journal of injury 2001

AOSJ - 1991 JuneAOSJ 1991 Junequality of life

185 ti t 80185 patients – average 80 yrs

7% dislocation

4% deep infection

1% prostr sio1% prostrusio

2% loosening of prosthesis

5 yrs -- > 60% mortality in both groups

Half of pts & most of the controls able toHalf of pts & most of the controls able to move independently.

Peri-prosthetic fracture

AMP was well fixedCould not be removedLocking / Mamman’s plateLocking / Mamman s plate

“Don’t throw away the AMP”Don t throw away the AMP

Says Marcus R ESays Marcus R.E. From University hospital of Cleveland Ohio(j l f A th l t 2002)(journal of Arthroplasty 2002)

AMP Bipolar7% died(3 months) 11% diedHHS Avg 75(26 mon) 78 AvgHHS Avg.75(26 mon) 78 Avg

(55 to 92) (60 to 94)

Particular attentionParticular attention must be paid to the pseating of collar of th th ithe prosthesis on the calcar & correctthe calcar & correct choice of head size.

Method is very easy toMethod is very easy to be learnt.

Cost effective, well tolerated by agedtolerated by aged patients

German article

154 AMP for 10 yrsAt 3yrs 46% community

ambulanceambulance

10% household10% household

35% non functionalambulance

Men had better than women H i hi 69 5Harris hip score -- 69 – 5yrs

59 – 10yrsFailure rate -- > 5 yrs – 6 5%Failure rate -- > 5 yrs – 6.5%

10 yrs – 7.7%Revision rate -- > 5 yrs - 4.5 %y

10 yrs – 5.2%

A case of THR done 14 Years ago N th CUP h i d f tiNow the CUP showing deformationNo complaints A.M.P. 16 years ago.Awaiting Revision?Awaiting Revision?

SummarySummary • In our setup AMP serves purposefulIn our setup AMP serves purposeful

satisfactory function in elderly individualsindividuals

• Average ortho surgeon can perform this surgery comfortably in averagethis surgery comfortably in average set-up.Pl th b f h d & k• Plan the surgery before hand & ask for appropriate stem width according t f l lto femoral canal.

Summary

• Carefully reaming in narrow femoral canal.

• No reaming in Osteoporotic bonebone.

• Use bone grafts from femoral head for calcar reinforcementhead for calcar reinforcement

• Always fill the fenestrations ith b ftwith bone grafts.

ConclusionsConclusions• AMP is time tested implant and results areAMP is time tested implant and results are

satisfactory.• THR, cemented bipolar has got their own , p g

indications, & they are also not free from serious complications.

• AMP is Cost effective, • Bone cement can be used as last option.• Further improvement in the implant design is

recommended.

22 years old Male22 years old MaleFracture N/FAVN 1998AMP working since then

THR - failTHR fail

• Material failureMaterial failure• Friction failure

C t di• Cement disease• Design failure• Particle disease• Material failureMaterial failure• Mechanical failure - Mechanostat

Proxima – Depuya conservative metaphyseal implantp y p

Proximal Fixation

Well fixed AMP Proxima DePuy

AMP Still working

“Don’t throw away y

th AMP”the AMP”

DISCLAIMER

Information contained and transmitted by this presentation is based on personal experience and collection of cases atbased on personal experience and collection of cases at Choithram Hospital & Research centre, Indore, India, during last 25 years.It is intended for use only by the students of orthopaedic surgery. y y p g yViews and opinion expressed in this presentation are personal opinion.Depending upon the x-rays and clinical presentations, viewers can make their own opinioncan make their own opinion.For any confusion please contact the sole author for clarification.Every body is allowed to copy or download and use the material best suited to him I am not responsible for any controversiesbest suited to him. I am not responsible for any controversies arise out of this presentation.For any correction or suggestion please contactnaneria@yahoo.com@y