Development of an augmented reality guided computer assisted orthopaedic surgery system

Previously held under moratorium from 1st December 2016 until 1st December 2021.This body of work documents the developed of a proof of concept augmented reality guided computer assisted orthopaedic surgery system – ARgCAOS. After initial investigation a visible-spectrum single camera tool-mounted tracking system based upon fiducial planar markers was implemented. The use of visible-spectrum cameras, as opposed to the infra-red cameras typically used by surgical tracking systems, allowed the captured image to be streamed to a display in an intelligible fashion. The tracking information defined the location of physical objects relative to the camera. Therefore, this information allowed virtual models to be overlaid onto the camera image. This produced a convincing augmented experience, whereby the virtual objects appeared to be within the physical world, moving with both the camera and markers as expected of physical objects. Analysis of the first generation system identified both accuracy and graphical inadequacies, prompting the development of a second generation system. This too was based upon a tool-mounted fiducial marker system, and improved performance to near-millimetre probing accuracy. A resection system was incorporated into the system, and utilising the tracking information controlled resection was performed, producing sub-millimetre accuracies. Several complications resulted from the tool-mounted approach. Therefore, a third generation system was developed. This final generation deployed a stereoscopic visible-spectrum camera system affixed to a head-mounted display worn by the user. The system allowed the augmentation of the natural view of the user, providing convincing and immersive three dimensional augmented guidance, with probing and resection accuracies of 0.55±0.04 and 0.34±0.04 mm, respectively.This body of work documents the developed of a proof of concept augmented reality guided computer assisted orthopaedic surgery system – ARgCAOS. After initial investigation a visible-spectrum single camera tool-mounted tracking system based upon fiducial planar markers was implemented. The use of visible-spectrum cameras, as opposed to the infra-red cameras typically used by surgical tracking systems, allowed the captured image to be streamed to a display in an intelligible fashion. The tracking information defined the location of physical objects relative to the camera. Therefore, this information allowed virtual models to be overlaid onto the camera image. This produced a convincing augmented experience, whereby the virtual objects appeared to be within the physical world, moving with both the camera and markers as expected of physical objects. Analysis of the first generation system identified both accuracy and graphical inadequacies, prompting the development of a second generation system. This too was based upon a tool-mounted fiducial marker system, and improved performance to near-millimetre probing accuracy. A resection system was incorporated into the system, and utilising the tracking information controlled resection was performed, producing sub-millimetre accuracies. Several complications resulted from the tool-mounted approach. Therefore, a third generation system was developed. This final generation deployed a stereoscopic visible-spectrum camera system affixed to a head-mounted display worn by the user. The system allowed the augmentation of the natural view of the user, providing convincing and immersive three dimensional augmented guidance, with probing and resection accuracies of 0.55±0.04 and 0.34±0.04 mm, respectively

Application of Engineered Porosity and Modified Effective Moduli to the Design of Orthopaedic Implants

Commercially available orthopaedic implants have a bending stiffness (flexural rigidity) that is at least 10 times greater than cortical bone. Effects of this stiffness mismatch have been extensively studied relative to total hip arthroplasty (THA). Clinical experience with THA has shown that stiffness mismatch is the primary cause of accelerated bone resorption due to the stress shielding, resulting in sub-optimal bone loading, aseptic loosening and inadequate bone support for a future revision implant. Attempts to incorporate design features that reduce the flexural rigidity of implants have yielded inconsistent results or failures due to biomaterial incompatibilities and practical manufacturing complications. The recent development of additive manufacturing (AM) processes allow the fabrication of closed-cell porous Ti or CoCr microstructures as a practical means of fabrication while reducing implant stiffness. The use of engineered porosity to modify flexural rigidity requires an ability to predict moduli from microstructural parameters. The literature is replete with different formulas which are often contradictory; existing equations relating porosity to effective moduli are generally interpretive and not predictive. This study applied finite element methods to three-dimensional porous structures with different arrangements of spheroidal voids. The resulting data show that the effective Young\u27s modulus varies linearly with &psi, the ratio of pore radius to center-to-center dimension, for a porosity range of 20 to 50%. In addition, the arrangement of spherical voids was found to have only a minimal effect on the resultant Young\u27s modulus. Predictive equations for Poisson\u27s ratio are second-order and dependent upon the void arrangement. The effect of changes in loading direction on moduli indicate that the three microstructures evaluated in this study are anisotropic, with anisotropy increasing with both ψ and volume porosity. The predictive equations developed in this study were validated with AM fabrication and testing of prototypical Ti6Al4V spinal rods. Constructs of a rhombohedral (FCC) pore arrangement with 30% porosity showed an effective reduction of ~ 50% in Young\u27s modulus. Predicted values for flexural rigidity fell within 95% confidence intervals for the tested porous Ti6Al4V constructs, confirming a design methodology with the potential of reducing the flexural rigidity, and resulting bone resorption, of orthopaedic implants

The History of Biomechanics in Total Hip Arthroplasty.

Biomechanics of the hip joint describes how the complex combination of osseous, ligamentous, and muscular structures transfers the weight of the body from the axial skeleton into the appendicular skeleton of the lower limbs. Throughout history, several biomechanical studies based on theoretical mathematics, in vitro, in vivo as well as in silico models have been successfully performed. The insights gained from these studies have improved our understanding of the development of mechanical hip pathologies such as osteoarthritis, hip fractures, and developmental dysplasia of the hip. The main treatment of end-stage degeneration of the hip is total hip arthroplasty (THA). The increasing number of patients undergoing this surgical procedure, as well as their demand for more than just pain relief and leading an active lifestyle, has challenged surgeons and implant manufacturers to deliver higher function as well as longevity with the prosthesis. The science of biomechanics has played and will continue to play a crucial and integral role in achieving these goals. The aim of this article, therefore, is to present to the readers the key concepts in biomechanics of the hip and their application to THA

ITAP: Clinical outcomes and implant design optimisation using numerical modelling

Redistribution of the flow of forces through the body, such as that after amputation and/or implantation of a skeletally anchored amputation prostheses, leads to bone remodelling. Periprosthetic bone resorption can destabilise skeletally anchored amputation prostheses. Therefore, implants that minimise bone resorption will achieve a more successful long term bone fixation. Bone remodelling outcome measures rely on implant design using mechanoregulatory bone remodelling theory. Mechanoregulation is implemented by functions that link a local mechanical stimulus to a local change in the structure or properties of bone material. This thesis uses the strain adaptive remodelling theory at the time of implantation with periprosthetic strain energy density as the outcome parameter. Clinical trial data was collected from a patient with a skeletally anchored amputation prostheses; The Intraosseous Transcutaneous Amputation Prosthesis (ITAP). The clinical trial ran from 2008 – 2019, the data was investigated for patterns between implant design and fixation success. This thesis reports trends in fixation success and bone change using a developed fixation success score. There was an ideal implant length to bone length ratio range and a straight, tapered stem with a flared bone collar growth shape were beneficial to fixation success. Conversely, one or more parameters associated with pressfit fixation were detrimental to fixation success. Results between the clinical and numerical data compared favourably; clinically, regions of periprosthetic bone growth were also observed by regions of high strain energy density in the finite element analysis and vice versa at the implant tip and osteotomy face. This thesis provides skeletally anchored amputation prostheses design guidelines that will minimise bone resorption when measured with strain energy density. Moreover, that future skeletally anchored amputation prostheses parameterised design can and should be used as a tool to assess bone fixation outcome in pre-clinical assessments

Radiostereometric analysis of initial femoral stem migration in cementless total hip arthroplasty of postmenopausal women : Exploring contributing factors in initial femoral stem migration

In cementless total hip arthroplasty (THA), femoral stems rely on the initial press‐fit fixation against the cortical bone to achieve osseointegration. In aging women, structural changes of the proximal femur may jeopardize the stem stability. Preoperative screening of bone quality and exploring the factors that cause stem migration may help in the selection process of patients for the use of cementless fixation techniques. Antiresorptive denosumab therapy might be efficient in preventing periprosthetic bone loss and reducing femoral stem migration in postmenopausal women. Sixty-five postmenopausal women with primary hip osteoarthritis (60 to 85 years old and Dorr A-type or B-type femur morphology) underwent cementless THA with implantation of a parallel-sided femoral component in a randomized double-blind placebo-controlled trial. The patients randomly received denosumab or a placebo 1 month before and 5 months after the surgery. The three-dimensional stem migration was measured using model-based radiostereometric analysis (RSA). Patient’s baseline characteristics, local and systemic bone mineral density (BMD) values measured by dual-energy X-ray absorptiometry (DXA), cortical-bone thicknes measured by pulse-echo ultrasonometry, surgery-related factors, and postoperative walking activity were examined for the association with stem migration. The accuracy and clinical precision of model-based RSA were comparable to those of marker-based RSA. Denosumab significantly decreased periprosthetic bone loss but did not reduce stem migration which occurred predominately during the first 3 months. DXA and pulse-echo ultrasonometry of the distal radius helped to identify patients at high risk of stem subsidence of more than 2 mm. Walking activity and local BMD dictated the direction and magnitude of stem rotation around y-axis. Femoral stem stability is sensitive to adequate bone stock. In postmenopausal women, stem migration is predominantly due to impaired bone quality. Inhibition of periprosthetic bone resorption did not prevent stem migration. Preoperative evaluation of the skeletal status is recommended for all postmenopausal women with hip osteoarthritis before scheduling cementless THA.Lonkan tekonivelen biologinen kiinnittyminen ikääntyvillä naisilla: varsiosan liikkeen radiostereometrinen analyysi Sementitön lonkan tekonivelleikkaus perustuu implantin biologiseen kiinnittymiseen. Kantavan varsiosan luutuminen edellyttää, että implantti saadaan leikkauksessa tukevasti paikoilleen kuoriluuta vasten. Tämän saavuttaminen voi olla vaikeaa naisilla, joille on kehittynyt vaihdevuosien jälkeen reisiluun kuoriluun ohentumista ja huokoistumista. Tästä johtuen on tärkeää selvittää ennen leikkausta potilaan luuston kunto. On myös arvioitava muita tekijöitä, jotka voivat lisätä varsiosan liikettä. Ennen leikkausta aloitettu luukatoa estävä lääkitys voi vahvistaa kuoriluuta ja näin parantaa varsiosan tukevuutta. Satunnaistettuun kliiniseen potilastutkimukseen osallistui 65 lonkan nivelrikkoa sairastavaa naispotilasta (keski-ikä 69 vuotta). Potilaille tehtiin sementitön lonkan tekonivelleikkaus. Ennen leikkausta aloitettiin luulääkitys (denosumabi), jonka tiedetään vahvistavan reisiluun kuoriluuta osteoporoosia sairastavilla naisilla. Potilaiden subjektiivista toipumista seurattiin kuvaavilla kyselykaavakkeilla ja myös objektiivisilla mittauksilla (kävelynopeus, kävelyaktiviteetti, luuntiheysmittaus, kuoriluun ultraäänimittaus ja luuaineenvaihdunnan merkkiaineet). Varsiosan kolmiulotteista liikettä seurattiin 3D-mallinnukseen perustuvalla radiostereometrisellä analyysillä. Menetelmän tarkkuus ja toistettavuus varmistettiin prekliinisessä kokeessa muoviluumalleilla. Lääkehoito esti reisiluun yläosan paikallisen luukadon varsiosan ympärillä, mutta se ei vähentänyt varsiosan painumista ja kiertymistä. Liikettä tapahtui ensimmäisten kuukausien aikana leikkauksesta. Varsiosat luutuivat ja hoitoryhmien välillä ei ollut eroa kliinisessä toipumisessa. Ennen leikkausta tehty ranteen kuoriluun paksuuden ultraäänimittaus (Bindex®) ja luuntiheysmittaus auttoivat tunnistamaan kohtalaisen hyvin ne potilaat, joille kehittyi varsiosan yli 2 mm painuminen leikkauksen jälkeen. Varsiosan kiertymisen suunta ja määrä heijastivat kävelyaktiivisuutta leikkauksen jälkeen. Tulokset vahvistivat aiempia tuloksia, että biologisesti kiinnittyvä lonkan tekonivelen varsiosa vaatii hyvää luuainesta. Luulääkkeellä (denosumabi) voidaan estää paikallista luukatoa, mutta luuresorption esto ei vähennä varsiosan alkuvaiheen liikettä. Luuston kunnon seulontaa suositellaan kaikille vaihevuosi-iän ohittaneille naisille, joille suunnitellaan sementitöntä lonkan tekonivelleikkausta

Impact of Ear Occlusion on In-Ear Sounds Generated by Intra-oral Behaviors

We conducted a case study with one volunteer and a recording setup to detect sounds induced by the actions: jaw clenching, tooth grinding, reading, eating, and drinking. The setup consisted of two in-ear microphones, where the left ear was semi-occluded with a commercially available earpiece and the right ear was occluded with a mouldable silicon ear piece. Investigations in the time and frequency domains demonstrated that for behaviors such as eating, tooth grinding, and reading, sounds could be recorded with both sensors. For jaw clenching, however, occluding the ear with a mouldable piece was necessary to enable its detection. This can be attributed to the fact that the mouldable ear piece sealed the ear canal and isolated it from the environment, resulting in a detectable change in pressure. In conclusion, our work suggests that detecting behaviors such as eating, grinding, reading with a semi-occluded ear is possible, whereas, behaviors such as clenching require the complete occlusion of the ear if the activity should be easily detectable. Nevertheless, the latter approach may limit real-world applicability because it hinders the hearing capabilities.</p

Probabilistic finite element analysis of the uncemented total hip replacement

There are many interacting factors affecting the performance of a total hip replacement(THR), such as prosthesis design and material properties, applied loads, surgical approach, femur size and quality, interface conditions etc. All these factors are subject to variation and therefore uncertainties have to be taken into account when designing and analysing the performance of these systems. To address this problem, probabilistic design methods have been developed.A computational probabilistic tool to analyse the performance of an uncemented THR has been developed. Monte Carlo Simulation (MCS) was applied to various models with increasing complexity. In the pilot models, MCS was applied to a simplified finite element model (FE) of an uncemented total hip replacement (UTHR). The implant and bone stiffness, load magnitude and geometry, and implant version angle were included as random variables and a reliable strain-based performance indicator was adopted. The sensitivity results highlighted the bone stiffness, implant version and load magnitude as the most sensitive parameters.The FE model was developed further to include the main muscle forces, and to consider fully bonded and frictional interface conditions. Three proximal femurs and two implants (one with a short and another with a long stem) were analysed. Different boundary conditions were compared, and convergence was improved when the distal portion of the implant was constrained and a frictional interface was employed. This was particularly true when looking at the maximum nodal micromotion. The micromotion results compared well with previous studies, confirming the reliability and accuracy of the probabilistic finite element model (PFEM). Results were often influenced by the bone, suggesting that variability in bone features should be included in any probabilistic analysis of the implanted construct.This study achieved the aim of developing a probabilistic finite element tool for the analysis of finite element models of uncemented hip replacements and forms a good basis for probabilistic models of constructs subject to implant position-related variability