Oral and Poster Presentations / Journal of Biomechanics 43S1 (2010) S23–S74 S51

coated with HA, modular metaphyseal stem (S-ROM, De Puy). We

used a porous cup without HA in these patients. Metal on poly and

ceramic on ceramic were the most frequently used bearings. Metal

on metal was used in the last 4 years, monoblock cups rather than

modular ones for young and active patients.

Results: Six of the stems were revised at latest follow up. Three

patients becomed infected and were finally revised with a two stage

protocol. Two patients had an early dislocation requiring revision

with a modular stem and one patient suffered a periprosthetic

fracture requiring revision with a Wagner stem. The rest of

the stems were classified as well integrated, with no signs of

radiological loosening or subsidence at latest follow-up (1–10 years,

mean 7.5 years). Radiolucent lines or bone atrophy around proximal

Gruen zones 1 and 7 were observed in 10% of the stems, all well

osseointegrated.

Discussion: The promising results produced by HA-coated femoral

prostheses have been repeated in the younger patient. Cemented

hip arthroplasty may not be the “gold standard” for patients younger

than 55 years6. Several studies with uncemented prostheses report

survivorships over 95% at 15 years2,7. Some of the theoretical

problems remain unsolved but have not demonstrated, so far, any

deleterious influence in the performance of the implants8. These

are HA resorption and long-term stability, osteolısis and granuloma

that are occasionally observed in the proximal zones, and difficulty

removing a well integrated HA-coated stem. Our experience only

allows us to assure that extraction of a fully HA coated stem requires

a transfemoral approach. The rest of the problems are not expected

to occur before the second decade of implant life and are not a

major concern in the literature. An additional advantage of HA

coatings is that bioactive fixation may seal the whole interface and

block the migration of wear debris, limiting osteolısis or granuloma

formation derived from particle disease to proximal areas.

Reference(s)

[1] Meding JB, Galley MR, Ritter MA. (2010) High Survival of Uncemented

Proximally Porous-coated Titanium Alloy Femoral Stems in Osteo-

porotic Bone CORR 468:441–447.

[2] Wangen H, Lereim P, Holm I, Gunderson R, Reikeras O. (2008) Hip

arthroplasty in patients younger than 30 years: excellent ten to 16-year

follow-up results with a HA-coated stem. International Orthopaedics

(SICOT) 32:203–208.

[3] Capello WN, D’Antonio JA, Feinberg JR, Manley MT (2003) Ten-year

results with hydroxyapatite-coated total hip femoral components in

patients less than fifty years old. A concise follow-up of a previous

report. J Bone Joint Surg Am 85:885–889.

[4] Reikeras O, Gunderson RB (2003) Excellent results of HA coating on a

grit-blasted stem: 245 patients followed for 8–12 years. Acta Orthop

Scand 74:140–145.

[5] Yates P, Serjeant S, Rushforth G, Middleton R. (2006) The Relative

Cost of Cemented and Uncemented Total Hip Arthroplasties. Journal

of Arthroplasty 21.

[6] Delaunay C, Migaud H. (2007) Primary total hip arthroplasty in the

younger and active patient. European instructional course lectures.

EFFORT. The British Editorial Society of Bone and Joint Surg 8:134–

145.

[7] Hallan G, Lie SA, Furnes O, Engesaeter LB, Vollset SE, Havelin LI. (2007)

Medium- and long-term performance of 11516 uncemented primary

femoral stems from the Norwegian arthroplasty register. J Bone Joint

Surg [Br] 89-B:1574–80.

[8] Reikeras O, Gunderson RB. (2007) Excellent results with femoral

revision surgery using an extensively hydroxyapatite-coated stem:

59 patients followed for 10–16 years. Acta Orthopaedica 77:1, 98–103.

S-54

Can Joint Realignment Surgery Reveal Mechanically Regulated

Signals that Influence Pain and Pathology in Humans?

D.J. Mason1,3, G. Whatling1,3, R.S. Kotwal2,3, K. Brakspear1,3,

H. Roberts1,3, C. Wilson1,3, R. Williams2,3, J. Sultan2,3, C. Holt1,3.1Cardiff University, Cardiff, UK; 2University Llandough Hospital,

Cardiff, UK; 3Arthritis Research UK Biomechanics and Bioengineering

Centre, UK

Introduction: The neurotransmitter glutamate transmits mechan-

ical signals in bone [1] and activates glutamate receptors and

transporters, in various joint tissues [2]. Glutamate receptor

activation influences inflammatory, degenerative and nociceptive

pathways in arthritic joints [2]. Thus glutamate signalling is a

mechanism whereby mechanical load can directly influence joint

pathology and pain. To investigate whether mechanical loading

through joints alters glutamatergic signaling, we have investigated

glutamate signalling in the subchondral bone of patients undergoing

High Tibial Osteotomy (HTO) surgery. HTO is performed to realign

the forces through the knee by removal of a wedge of bone from

the tibia and stabilisation with a plate. We have compared gene

expression pre and post joint realignment surgery and correlated

this to the predicted changes in forces within the joint.

Methods: RNA was extracted from medial/lateral and ante-

rior/posterior tibial drill hole sites from HTO (n=5). RNA was

reverse transcribed and RT-PCR performed for a housekeeping gene

GAPDH, glutamate transporters (EAAT-1, EAAT1ex9skip), glutamate

receptors (NR2A and KA1), osteocalcin, osteoprotegerin and RANKL.

For each of these preoperative samples, the gene expression was

correlated to the distribution of forces through the knee predicted

by standing radiographs. For one patient, both pre and post-

operative bone samples were obtained and correlated to adduction

moments and forces at the knee, computed from a motion analysis

of level gait.

Results: Good quality RNA was obtained from drill hole bone

cores removed during HTO surgery. GAPDH, osteocalcin, EAAT-1,

EAAT1ex9skip, NR2A, KA1, OPG and RANKL mRNA expression was

detected in HTO bone cores. In one patient, where HTO reduced

loading in the medial compartment, comparison of gene expression

in pre and post HTO bone cores revealed differential expression of

EAAT1ex9skip and KA1. This differential mRNA expression may be

due to the altered loading through the joint.

Discussion: We have shown that glutamate transporters and

receptors are expressed in human subchondral bone. Activation of

these receptors and transporters by the increased synovial fluid

concentrations of glutamate released in arthritis will influence

pathology and nociception. Glutamate transporter mRNA expression

varies after HTO, consistent with our original discovery of this

transporter as mechanically-regulated in bone [1]. Glutamatergic

signals provide a direct mechanism linking mechanical loading

through the joint to pathology and pain in arthritis.

Acknowledgements: This work is funded by Arthritis Research UK

Reference(s)

[1] Mason DJ, et al. (1997). Bone 20 (3):199–20.

[2] Flood S, et al. (2007). Arthritis and Rheumatism 56(8):2523–2534.

S-55

Bone Quality Dictates Implant Healing in Cementless Total

Hip Arthroplasty

H.T. Aro, N. Moritz, J.J. Alm, S. Timlin. Turku University Hospital and

University of Turku, Finland

In cementless total hip replacement (THR), osteoporosis may

jeopardize the achievement of immediate press-fit stability and

adversely affect early implant incorporation. Our study was aimed

to characterize implant healing in female patients with low

systemic bone mineral density (BMD) compared with those with

normal BMD. Primary stem stability and the time point of stem