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Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXIX | Pages 105 - 105
1 Jul 2012
FINITE ELEMENT STUDY OF AUGMENTED TOTAL KNEE REPLACEMENT
Brigstocke G Agarwal Y Bradley N Crocombe A
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Aim

The aim of this FE study was to analyse the comparative behaviour of cement and metal based augments in TKR and quantify the stresses within these different augments and underlying cancellous bone.

Materials and methods

A three-dimensional FE model was constructed from a CT scan of the proximal tibia using SIMPLEWARE v3.2 image processing software. The tibial component of a TKR was implanted with either a block or wedge-shaped augment made of either metal or cement. The model was axially loaded with a force of 3600N and testing was conducted with both evenly and eccentrically distributed loads.

Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXIX | Pages 59 - 59
1 Jul 2012
FINITE ELEMENT ANALYSIS OF CEMENT SHEAR STRESSES IN AUGMENTED TOTAL KNEE REPLACEMENT
Brigstocke G Agarwal Y Bradley N Frehill B Crocombe A
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Introduction

In complex primary and revision total knee replacement (TKR) the operating surgeon may encounter proximal tibial bone defects. The correct management of such defects is fundamental to both the initial stability and long-term survival of the prosthesis. Block or wedge-shaped metal augments are used to address some such type II unconstrained defects.

Aim

The aim of this finite element (FE) study was to assess the effects of block and wedge-shaped metal augments upon the shear stresses in the cement mantle at the bone-implant interface of an augmented TKR.

Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_III | Pages 300 - 300
1 Jul 2011
THE DEVELOPMENT OF A COMPUTER MODEL OF THE HUMAN ANKLE JOINT AND DETERMINATION OF OPTIMAL SCREW POSITIONING IN FLEXOR HALLUCIS LONGUS TENDON TRANSFER FOR CHRONIC TENDOACHILLES RUPTURE
Arastu M Partridge R Crocombe A Solan M
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Background: Neglected ruptures of the tendoachilles pose a difficult surgical problem. Intervening scar tissue has to be excised which cannot be repaired by end-to-end anastamosis. Several techniques for reconstruction of chronic ruptures have been described. The flexor hallucis longus (FHL) tendon transfer is considered advantageous over other tendon transfers. One disadvantage of FHL is it has limited excursion. There are no data to determine the optimal positioning of the FHL tendon to the calcaneum.

Materials and Methods: Two computer programmes (MSC.visualNastran Desktop 2002™ and Solid Edge® V19 were used to generate a human ankle joint model. This model is able to reproduce dorsi- and plantarflexion. Different attachment points of FHL tendon transfer to the calcaneum were investigated.

Results: The lowest muscle force to produce plantarflexion (single stance heel rise) was 1355N. Plantarflexion increased for a more anterior attachment point. The maximal plantarflexion was 33.4° for anterior attachment and 24.4° for posterior attachment. There was no significant difference in these figures when the attachment point was moved to either a medial or lateral position.

Clinical relevance: Optimal FHL tendon transfer positioning is a compromise between achieving plantarflexion for normal physiological function versus the force generating capacity and limited excursion of FHL. A more posterior attachment point is advantageous in terms of power. The range of motion is 10° less than when attachment is more anterior, the arc of motion (24.4°) is still physiological. We recommend that FHL is transferred to the calcaneum in a posterior position.