Re: SROM-THR lasts a lifetime (extremely long)

[Guest guest]

>I continue to be amazed at what I read from this group. The generalizations

>and the statements of fact are just preposterous,

>>5) All THRs (even BFH MoM) suffer from a problem called " proximal stress

>> shielding " . This causes bone at the top of (what's left of) your femur

>> to atrophy and weaken, which contributes to loosening of the stem.

So, what part of this statement gives you heartburn? Bone remodeling due

to stress shielding is generally accepted to be one of the two main

causes of loosening of conventional total hips (the other being

osteolysis due to polyethylene debris). If you actually read the

literature, you'll see that reducing stress shielding has been

one of the major (thus far unsolved) problems in the design of

conventional hip implants. I refer you to the

following, just in case you think I'm making this up:

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AAOS 1989 Annual Meeting Scientific Program, Paper No.381

" Stress Shielding and Micromotion in Cemented Total Hip Replacements

after Ten Years in Vivo " :

Stress transfer and micromotion with cemented femoral

components retrieved at autopsy were studied from 40 months to

17 years after surgery. A 100 pound spinal load was applied in

single-limb stance and stairclimbing configurations with a

simulated pelvis with abductor and extensor muscle simulations.

Marked strain reductions in the proximal femoral cortex were

observed in all femurs as late as 17 years. The range of the

ratio of proximal to distal medial axial strain measured 0.23

to 0.41. The maximum micromotion was 26 microns in the axial

direction and 90 microns in the transverse direction. The data

showed that proximal stress shielding persists ... for up to 17

years after implantation.

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AAOS 2003 Annual Meesting Poster Program, Poster No. P032, " The Effect

of Femoral Stem Size and Impaction Grafting on Proximal Femoral Stress

Shielding " :

Introduction: The purpose of this study was to determine the

extent of proximal stress shielding with varying femoral stem

diameters and to determine if impaction grafting can restore

physiologic loading. Methods: Measurement Group, Inc., strain

gauges were attached to the proximal surface of four research

composite femurs. Single-leg stance model was used to simulate

loading by applying one-half body weight (360 N) to the femoral

head and attaching a cable to simulate abductor forces.

Hemiarthroplasty was performed on each femur using Howmedica

long stem implant progressing from 15 mm diameter to 19 mm

diameter. Strains were measured for intact femurs and each stem

size. Impaction grafting was then utilized on each femur using

Stryker Osteonics #7 Restoration C-stem with bovine cancellous

bone. Results: Significant reduction in proximal surface

strains occurred following hemiarthroplasty and continued to

decline with increasing stem size. The percent reduction in

proximal surface strains of implants from intact to 15 mm

diameter was approximately 71% on anterolateral surface, 40% on

anteromedial surface, 57% on posterolateral surface, and 50% on

posteromedial surface. With a 19 mm stem diameter, the surface

strain reduction was 84% on anterolateral surface, 48% on

anteromedial surface, 64% on posterolateral surface, and 53% on

posteromedial surface. Impaction grafting demonstrated the

least reduction in strain with 41% on anterolateral surface,

30% on anteromedial surface, 31% on posterolateral surface, and

33% on posteromedial surface.

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_International Orthopaedics. 2003;26(5); pp299-302:

" A computed tomography assessment of femoral and acetabular bone changes after

total hip arthroplasty.

Schmidt R, Muller L, Kress A, Hirschfelder H, Aplas A, Pitto RP.

Orthopaedische Klinik mit Poliklinik, University of Erlangen, Waldkrankenhaus St

Marien, Rathsberger Str 57, D-91054 Erlangen, Germany.:

Using computed tomography-assisted (CT) osteodensitometry, we

studied the bone changes that occurred in 12 patients at 2

weeks and again at 1 year after total hip arthroplasty with

insertion of a press-fit acetabular cup and an uncemented

femoral tapered stem. There was a greater decrease in full bone

density (BD) lateral to the femoral stem when compared to the

medial side, at the proximal end of the femur this difference

was significant (-22.1% versus -16.2%)

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_Clinical Biomechanics_, July 2003;18(6);S53-8

Finite element analysis of the cervico-trochanteric stemless femoral prosthesis.

Tai CL, Shih CH, Chen WP, Lee SS, Liu YL, Hsieh PH, Chen WJ.

Department of Biomedical Engineering, Chung Yuan Christian University, Chungli

320, Taiwan, ROC.

Local bone loss after implantation of traditional stem-type

prostheses remains an unsolved problem during the long-term

application of total hip replacement. The stress shielding

effect and osteolysis were thought to be the two main factors

that result in local bone loss after prosthesis implantation.

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_Medical Engineering Physics. March 2002; 24(2): 109-14

" The influence of design parameters on cortical strain distribution of

a cementless titanium femoral stem. "

Gillies RM, Morberg PH, Bruce WJ, Turnbull A, Walsh WR.

Orthopaedic Research Laboratories, Dept of Orthopaedics, University of

New South Wales, Prince of Wales Hospital, High Street, Edmund Blackett

Building, Randwick 2031, NSW, Australia.

The strain distribution imposed on a femur following a total

joint replacement is an important factor, in proximal bone loss

due to stress shielding, and long term clinical success.

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This next one is particularly relevant, since it actually refers to the

SROM THR:

_Journal of Arthroplasty_, December 2001; 16(8 Suppl 1): 64-70

" Primary cementless total hip arthroplasty using a modular femoral

component: a minimum 6-year follow-up. "

Tanzer M, Chan S, CE, Bobyn JD.

Division of Orthopaedic Surgery, McGill University, and the Jo

Orthopaedic Research Laboratory, Montreal, Quebec, Canada.

mtanz@...

We evaluated 59 hips that underwent a primary total hip

arthroplasty using an S-ROM modular femoral component at a mean

follow-up of 101 months (range, 72-145 months). All cases

showed radiographic evidence of bone ingrowth, and there were

no femoral revisions for aseptic loosening. The hip

score improved from a mean of 40 preoperatively to 89 at final

follow-up. Some degree of proximal femoral disuse atrophy from

stress shielding occurred in 46 hips (78%), and some degree of

femoral osteolysis occurred in 25 hips (42%). Only additional

follow-up will reveal whether there is a consequence of both

types of proximal femoral bone loss.

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_Journal of Bone and Joint Surgery_. August 2001; 83(6); 921-9.

" Changes in proximal femoral strain after insertion of uncemented

standard and customised femoral stems. An experimental study in human

femora. "

Aamodt A, Lund-Larsen J, Eine J, Andersen E, Benum P, Husby OS.

Department of Orthopaedic Surgery, Trondheim University Hospital, Norway.

We have compared the changes in the pattern of the principal

strains in the proximal femur after insertion of eight

uncemented anatomical stems and eight customised stems in human

cadaver femora. During testing we aimed to reproduce the

physiological loads on the proximal femur and to simulate

single-leg stance and stair-climbing. The strains in the intact

femora were measured and there were no significant differences

in principal tensile and compressive strains in the left and

right femora of each pair. The two types of femoral stem were

then inserted randomly into the left or right femora and the

cortical strains were again measured. Both induced significant

stress shielding in the proximal part of the metaphysis, but

the deviation from the physiological strains was most

pronounced after insertion of the anatomical stems. The

principal compressive strain at the calcar was reduced by 90%

for the anatomical stems and 67% for the customised stems.

Medially, at the level of the lesser trochanter, the corresponding

figures were 59% and 21%.

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Der Unfallchirurg. July 2001;104(7)622-8

" Changes in bone density of the femur after cement-free implantation of

a modular hip prosthesis with a long shaft "

Andress HJ, von Ruckmann B, Zwonitzer R, Kahl S, Ringling M, Lob G.

Chirurgische Klinik und Poliklinik, Unfallchirurgie,

Ludwig-Maximilians-Universitat Munchen, Klinikum Grosshadern, Marchioninistrasse

15, 81377 Munchen. handress@...

Until now, no reports exist on the existence of femoral bone

loss after hip arthroplasty using long-stem cementless

prostheses in elderly patients. In a prospective evaluation the

amount of bone loss (stress-shielding) after implantation of a

long stem hip prosthesis in patients with femoral neck

fractures (group A) or pertrochanteric femoral fractures (group

was examined. Eleven patients (five from group A and six

from group were treated with a long-stem modular hip

prosthesis (MHP). Change of bone mass was evaluated using

quantitative computed tomographie (QCT) immediately following

and at six months (group A and and twelve months (group A)

after implantation of the prosthesis. Clinical results,

expressed with the modified Hip Score, and relative

changes of bone mass were compared with mean periprosthetic

bone mass of the femur after operation. After implantation of

the MHP, the maximum decrease of mean femoral bone mass was

19.1% at six months and 20.2% at twelve months for group A

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_Journal of Biomechanics_, August 2001;34(9): 995-1003

" A finite element analysis of hollow stemmed hip prostheses as a means

of reducing stress shielding of the femur. "

Gross S, Abel EW.

Medical Engineering Research Institute, University of Dundee, Scotland

DD1 4HN, Dundee, UK.

Stress shielding of the femur is known to be a principal factor

in aseptic loosening of hip replacements.

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_Journal of Biomechanics_, Dec 2000;33(12): 1655-62

" Analysis of a femoral hip prosthesis designed to reduce stress shielding. "

Joshi MG, Advani SG, F, Santare MH.

Department of Mechanical Engineering, University of Delaware, 19716,

Newark, DE, USA.

The natural stress distribution in the femur is significantly

altered after total hip arthroplasty (THA). When an implant is

introduced, it will carry a portion of the load, causing a

reduction of stress in some regions of the remaining bone. This

phenomenon is commonly known as stress shielding. In response

to the changed mechanical environment the shielded bone will

remodel according to Wolff's law, resulting in a loss of bone

mass through the biological process called resorption.

Resorption can, in turn, cause or contribute to loosening of

the prosthesis. The problem is particularly common among

younger THA recipients.

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Journal of Orthopaedic Research, July 1999; 17(4): 525-31.

" Reduced bone stress as predicted by composite beam theory correlates

with cortical bone loss following cemented total hip arthroplasty. "

Silva MJ, KL, on DD, Bragdon C, WH, Maloney WJ.

Department of Orthopaedic Surgery, Washington University School of

Medicine, St. Louis, Missouri, USA. silvam@...

Clinical and experimental evidence suggest that periprosthetic

bone loss following total hip arthroplasty is caused in part by

stress-shielding. Changes in bone stress in the proximal femur

following implantation can be estimated with use of composite

beam theory. We hypothesized that the degree of

stress-shielding predicted by beam theory correlates with the

magnitude of bone loss following cemented total hip

arthroplasty. We analyzed cross sections from the proximal

femur of 13 patients who had undergone unilateral cemented

total hip arthroplasty. A matching implant was inserted

contralaterally, and the cross-sectional properties of the

implant and bone and the bone density were determined. Bone

loss was calculated on the basis of differences between

contralateral (control) and ipsilateral (remodeled) sections

and correlated to several beam-theory parameters calculated

from the control sections: implant rigidity, bone rigidity,

ratio of implant to bone rigidity, and predicted decrease in

bone stress.

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_Journal of Biomechanical Engineering_ August 1997; 119(3): 228-31

" The predictive value of stress shielding for quantification of

adaptive bone resorption around hip replacements. "

Kuiper JH, Huiskes R.

Biomechanics Section, University of Nijmegen, The Netherlands.

The presence of a femoral hip stem changes local mechanical

signals inside the surrounding bone. In this study we examined

the hypothesis that the eventual loss of bone can be estimated

from the initial patterns of elastic energy deviation, as

determined in FE models of the intact bone and the operated

femur. For that purpose two hypothetical relations between

elastic energy reduction and resorption were investigated.

Their estimates of bone loss were compared to the results of

iterative computer simulations. Two kinds of FE model were

used, and in each stem stiffness and remodeling threshold (a

measure of " biological reactivity " ) were varied. Provided that

reasonable values of the remodeling threshold are assumed and

that the stem is firmly bonded to the bone, we found that the

difference between direct estimates and simulation models was 4

percent of bone loss. It is therefore concluded that initial

patterns of elastic energy deviation give a reasonable

indication of expected bone loss.

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_Journal of Biomechanics_ Apr-May 1993; 26(4-5): 369-82

" ESB Research Award 1992. The mechanism of bone remodeling and

resorption around press-fitted THA stems. "

Van Rietbergen B, Huiskes R, Weinans H, Sumner DR, TM, Galante JO.

Biomechanics Section, University of Nijmegen, The Netherlands.

A major problem threatening the long-term integrity of total

hip replacement is the loss of proximal bone often found around

noncemented stems in the long term. It is generally accepted

that 'stress shielding' is the cause for this problem: after

implantation of the prosthesis the surrounding bone is

partially 'shielding' from load carrying and starts to resorb.

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Happy now?

Steve