Crosnier, Emilie A

Gill, Richie

Miles, Anthony W

Ramoutar, Darryl

OPUS

        Citation for published version:Ramoutar, D, Crosnier, EA, Gill, R & Miles, AW 2014, 'Assessment of head displacement and disassembly forcewith increasing assembly load at the modular head/trunnion junction of a total hip replacement prosthesis' Paperpresented at 15 EFORT Congress 2014, London, UK United Kingdom, 4/06/14 - 6/06/14, .Publication date:2014Document VersionEarly version, also known as pre-printLink to publicationUniversity of BathGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 07. Dec. 2019ResultsThe pull-off/disassembly forces increased significantly with assembly load;the statistical different between the three groups was p = 0.007 (KruskalWallis) (Fig. 3).The maximum head displacement on the trunnion was significantly differentbetween the 2 kN group and the other two groups. No difference wasobserved between the 4 kN and 6 kN groups (p = 0.89) (Fig. 5).0.00.51.01.52.02.53.03.54.04.55.02 kN 4 kN 6 kNPull-off Force (kN)Assembly Loadp = 0.029p = 0.029p = 0.029Pull-off ForceAssessment of Head Displacement and Disassembly Force with Increasing Assembly Load at the Modular Head/TrunnionJunction of a Total Hip Replacement ProsthesisDN Ramoutar*, EA Crosnier**, HS Gill**, AW Miles***Nottingham University Hospitals, Nottingham, UK. **University of Bath, Bath, UKIntroductionThe femoral components commonly used in total hip arthroplasty aremodular. They require a secure connection between the head and trunnion,a factor that is influenced by the impaction force used by the surgeon atassembly. There is no standard protocol for the assembly of modular headsonto femoral stems. Manufacturing guidelines and surgical practice varywidely.The aim of this study was to assess the effect of assembly force on thestrength of the head-trunnion interface and to measure the initialdisplacement of the head on the trunnion with different assembly forces.Materials and MethodsTwelve JRITM Furlong HAC stems and head (size 28S) were used for thisstudy. The stems were mounted in a custom rig on a materials test machine(Model 3367, Instron) and a pre-calibrated laser (optoNCDT 1302-20, Micro-Epsilon) sensor was used to measure the head displacement (Fig. 1).Fig. 2: Assembly and Pull-off TestFor statistical analyses, a Kruskal Wallis test was used to determine if anysignificant differences existed amongst the three groups of samples in termsof maximum head displacement and pull-off force. The Mann-Whitney U testwas then used to compare pairs of groups to determine the significantdifferences between them.Discussion & ConclusionsThe increase in assembly load resulted in a higher pull-off force. Anassembly force of at least 2.5 kN was required to overcome the frictionalforces needed to engage the head on the trunnion. Assembly loads belowthis threshold were insufficient to achieve full seating of the head and hencecoupling between the two components. The results presented are applicableto JRI Furlong HAC stems, however similar patterns would be expected withcomparable implant designs.Fig. 3 – Pull-off force (kN) for each assembly load group (Mann-Whitney U). 0501001502002502 kN 4 kN 6 kNAssembly Loadp = 0.057p = 0.029LoadMaximum Head Displacement (µm)Pull-offPull-off rate: 0.008 mm/sMeasuring:Pull-off forceLaserAssemblyLoading rate: 0.05 mm/sMeasuring:Head DisplacementLaserDirection of head motionLaser target Micro-Epsilon Laser SensorDistance measuredHeadRing to hold headLaserStemFig. 1: Test Set-upThe heads were assembled on the stems with the Instron at a constant rateof 0.05 kN/s (ISO7206-10:2003). The implants were divided into threegroups. Each group was assembled with a different peak assembly load: 2kN, 4 kN and 6 kN. Levels of applied load and head displacement wererecorded during assembly.A pull-off test was then performed using the Instron at a constant rate of0.008 mm/s (ISO7206-10:2003) and the disassembly force was recorded(Fig. 2).Fig. 5 – Maximum head displacement for each assembly load (Mann-Whitney U). 0 2 4 6 8 10 12-250-200-150-100-500-6-4-202Head Displacement (µm)Load (kN)Time (s)2.0kN4.0kN6.0kNDuring assembly, almost no head displacement was seen until a suddenchange in displacement of about 150 µm corresponding to a spike of 2.5 kNin the loading profile (Fig. 4). A more gradual change in displacement wasthen observed up to the peak assembly force. This was not seen with the 2kN group.Fig. 4 – Load and head displacement for each assembly load groupReferences: 1. Heiney et al. Arch Orthop Trauma Surg 2009; 129: 793-7962. Rehmer et al. Clin Biomech 2012; 27: 77-83Corresponding Author: darryl.ramoutar@doctors.org.ukNottingham University Hospitals, Nottingham, NG7 2UH, UKHead clamped in Instron adaptor2.5 kN Spike

Assessment of head displacement and disassembly force with increasing assembly load at the modular head/trunnion junction of a total hip replacement prosthesis

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Assessment of head displacement and disassembly force with increasing assembly load at the modular head/trunnion junction of a total hip replacement prosthesis

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