1-18 DEXA and Periprosthetic Loosening

8/14/2019 1-18 DEXA and Periprosthetic Loosening

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BONE REMODELING FOLLOWNG HIP FEMORAL ENDOPROSTHESIS

BYProfessor Hazem Abdel Azeem

Cairo University

March 2001


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Introduction

Factors affecting survivorship of femoral componentStress shielding and bone loss.

Bone mineral changes in the femora of implanted prosthesis.Inability of conventional radiography to adequatelyevaluate these change in its early stage.


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(A). The patient was revised with a 19.5-mm extensively porous coated cobalt-chromium alloy stem (B). At the 20-month follow-up, there was extensive thinning of the proximal cortical bone, but the patient was asymptomatic (C). Adapted from Sumner DR, Turner TM. Total hip revision surgery. New York: Raven Press, 1995.


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Contact radiographs of retrieved femora from a dog that had anextensively porous-coated titanium alloy stem implanted in theleft femur for 24 months, showing marked cortical bone loss in

the proximal medial region.


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Literature review of different

densitometry in THAAUTHOR PROSTHESIS CHANGE Follow-up

McCarthy et al Cemented (unspecified composition) 0 1 to 14 yr Cohen and Rushton Cemented (CoCr) -7% BMDb (Gruen zone 7)-8% BMDb (Gruen zone 2) 1 yr

Korovessis et al Cemented (CoCr) -16% BMD(ROI overlapping lesser trochanter) 1 mo-10 yr (mean, 2 yK ilgus et al Cement les s CoCr-ex tens ively porous -c oat ed -40% B MDc (m edial mean)-24% B MDc (lat eral mean) 2-5 yr K ilgus et al Cement les s CoCr-prox im ally porous -c oat ed -19% BM Dc (m edial m ean)-11% BM Dc (lat eral m ean) 2-6 y r

Sychterz and Engh Cementless CoCr-extens ively porous-coated -42% BMC (medial+lateral mean) 1.5-13.5 yr Hughes et al Cementless CoCr-proximal 5/8 porous-coated -34% BMD (proximal of Gruen zone 7) 45 mo

K oroves si s et al C em ent les s Ti 6A l7N b-g rit -blas ted s urfac e -24% B M D (R OI overlap pi ng les ser tro cha nt er) 1 m o-1 0 y r(m ea n, 2 y r K irat li et al Cem ent les s Ti6A l4V-prox im ally porous -c oat ed -24% BM D (RO Is enc om pas sing les ser t roc hant er) 2 y r Nakamura Cementless Ti6Al4V -23% BMDd (Gruen zone 7) 2 yr Nakamura Cementless Ti6Al4V -20% BMD (Gruen zone 7) 12-24 moNakamura Cementless Ti6Al4V -27% BMD (Gruen zone 7) 25-48 mosNakamura Cementless Ti6Al4V -45% BMD (Gruen zone 7) 49-84 moBryan et al Cementless Ti6Al4V-extens ively porous-c oated on AP surfac es -34% BMC (Gruen zone 7 9-10 yr

Caniggia et al Cementless Ti alloy with hydroxyapatite coating -23% BMD (proximal medial cortex) 4 moHughes et al Cementless Ti-proximal 3/8porous-coated -15% BMD (proximal of Gruen zone 7) 38 mo

Niinimki and Jalovara Cementless polyacetal resin with a steel core -40% BMD (Gruen zone 7) 7.5-9.5 yr


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AIM OF THE WORK

A trial to find out a method for assessmentof the effect of stress shielding acquired by

presence of the prosthesis in the upper endof the femur Objective study based on the deterioration

of the quality of the bone around the stem inrelation to time


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AIM OF THE WORK (Contd.)

Should this have impact ontechnical details of prosthesisdesign, cemented or cementlessand technique of cementing ??


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LIMITATIONS OF THE STUDY

Presence of pre-existing evidentosteoporosisElapse of two years as osteolysis will takeshare in process of bone lossPathological lesions in the upper end of thefemur


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Inclusion Criteria

Cases of femoral endoprosthesis in patients before age 50 (possibly not osteoporotic)Active patient (was back to work)Cemented or cementlessStandard stem sizes


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Material

39 patientsunilateral total hip arthroplastyfemoral component: 24 cemented and15 cementless.Cementless: extensive coating with HA


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Material (contd.)

Age distribution: range: 36 - 50 years.

Sex distribution: 18 males. 21 females.


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METHODS

Time of DEXA: 3, 6 and 12 months postoperative

Equipment use: a human DPZ-IQMeasurements made in the 7 zones of Gruen.Base line is the findings of the first

periprosthetic DEXA evaluation (3 months postoperative)


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METHODS (Contd.)

Percentage of loss is calculated from thefirst measurement spaced three monthly for two years (Osteolysis takes share after twoyears and may mix up with the process of local osteoporosis)


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Technical details include pic.

A base line densitometry study is done onthe contralateral un-operated side

The software allows positioning of the prosthesis simulator to deduce the value of the prosthesis on that side and gives a

standard value in the seven areas


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Technical details (contd.)include

pic.The software measures the bone densityaround the prosthesis on the affected side

Comparison between both sides gives thedeterioration rate caused by stress shieldingin every of the seven areas

In the second study, further loss isestimated the same way and so on


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The 7 Zones of Gruen


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The 7 Zones of Gruen

(Further Analysis)


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FOLLOW UP PERIOD

2 YEARS


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Results

The third postoperative month measurement was usedas the baseline.

There was bone loss from the third month onwards(16 percent per year in zone 7)Bone loss leveled between the 12th month and 2years.

Bone loss is not uniform, greatest decrease was seenin Gruens zone 7 (16%)Least in Zone 4 (4%)


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Example of Densitometry


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Covariate Factors of Bone LossSex: Women have significantly higher bone loss (more

pronounced in zone 7)

Implant-related difference: Implant size

More bone loss with bigger sizes

Cementing

Less bone loss with cementingFemoral fill Less loss with femoral fill


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Effect of Femoral Fill


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Discussion

Early bone loss cannot be identified by standard x-rays; hence value of densitometry.

Rapid bone loss occurs up to two years: 16% per year in area 7

Bone loss slows down after two years (Lit.)Resorption is greater with bulkier and stiffer devices, both in the metaphysis and diaphysis


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Discussion (Contd.)

Stress shielding is more effective on the proximal part of the femur especially the

medial sideStress shielding is less with cemented

prosthesis (wider surface contact)

Stress was higher in non-cemented prosthesis (the contact at maximum is 20%)


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Discussion (Contd.)

Stress shielding is taken off suddenly inzone 4 in cementless prosthesis. This may

allow fracture in this zone.Stress shielding may be graduated bycementing (transitional zone)


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Conlusion

DEXA gives better insight into boneremodeling early post-implantation

DEXA may help optimization of femoraldesign and better techniqueLong stem devices may be less beneficial with

more stress shielding.Cemented stems may be associated with less

bone loss and stress shielding.


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Conclusion (contd.)

No correlation as yet has been found between observed bone resorption and

clinical result.Method used permits a quantitativeapproach to bone remodeling to

differentiate between physiological changesand pathological bone loss

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1-18 DEXA and Periprosthetic Loosening