Muller, Jacobus Hendrik
ENGLISH ABSTRACT: A methodology to facilitate analysis of dynamic subject-specific patellofemoral function is presented. An enhanced understanding of patellofemoral biomechanics will enable orthopaedic surgeons to identify the mechanisms responsible for imbalances in the joint stabilisers, while also providing objective information on which to base treatment methods. Dynamic patellofemoral function of three volunteers was simulated with a musculoskeletal computational model. The individuals underwent scans from which three-dimensional models of their patellofemoral joints were constructed. Skeletal muscles and soft tissue stabilisers were added to the skeletal models, after which subject-specific motion was simulated.
After trochlear engagement, the patellae of the volunteers followed a lateral path, whereas patella tilt was subject-specific. Comparison of the predicted tilt and mediolateral position values at 30 degrees knee flexion to in-vivo MRI values showed a mean accuracy of 62.1 % and 96.9 % respectively. The patellofemoral contact load . quadriceps tendon load ratio varied between 0.7 and 1.3, whereas the mediolateral load component . resultant load ratio ranged between 0 and 0.4. Both parameters. values were similar to previous findings. The medial patellofemoral ligament tension decreased with knee flexion, while the patellar tendon-quadriceps tendon ratio followed a similar trend to that of previous findings (varied between 0.4 and 1.2).
After induction of a tubercle osteotomy in the coronal plane, Volunteer One.s patella engaged the trochlear groove at an earlier knee flexion angle, while the patella of Volunteer Two only underwent a small medial displacement. Finite element analyses were employed to investigate the influence of the osteotomy on the patellofemoral pressure distribution. The mean pressure in Volunteer One.s patellofemoral joint was alleviated (17 % smaller) at all angles of flexion with the exception of 60 degrees (12 % greater). Pressure in Volunteer Two.s joint was alleviated at 30 and 45 degrees knee flexion (6 % smaller), while it was elevated (9.1 % greater) at other angles of flexion.
Two commercial patellofemoral prostheses were tested on the three Volunteers. joints in the virtual environment. Prosthesis Two delivered patella shift and tilt patterns similar to the baseline values. Patellar tendon tension was slightly greater after resurfacing, with the tensions elevated most with Prosthesis Two. Medial patellofemoral ligament tension was reduced most with Prosthesis Two, while lateral retinaculum tension was increased slightly. Prosthesis Two was the best candidate to reproduce patella kinematics, while the patellofemoral kinetics was largely independent from the type of prosthesis used. The prostheses performed worse for Volunteer Three, supporting the need for the development of patient-specific prostheses. Three validated subject-specific musculoskeletal models facilitated the analysis of the individuals. patellofemoral biomechanics. The technique can potentially be employed by orthopaedic surgeons to visualise the change that an osteotomy or patellofemoral arthroplasty might induce on an individual.s patellofemoral joint. This technique might aid in the development of a tool to assist biomedical engineers in the development of new patellofemoral prostheses. Most importantly, the outcome of surgical intervention may be predicted beforehand, and a treatment procedure may be tailored to optimally fit the patellofemoral biomechanics of that individual. AFRIKAANSE OPSOMMING: 'n Ondersoekmetode van die dinamiese gedrag van pasiënt-spesifieke patellofemorale gewrigte word beskryf. Indien die patellofemorale biomeganika beter verstaan word, kan ortopediese chirurge die meganismes wat verantwoordelik is vir oneffektiewe stabiliseerders identifiseer en behandeling op objektiewe bevindinge baseer. Die dinamiese patellofemorale funksie van drie vrywilligers is gesimuleer m.b.v. `n spier-skelet rekenaarmodel. Drie-dimensionele modelle van die individue se patellofemorale gewrig is gekonstrueer m.b.v. skanderings. Die skeletspiere en sagte ondersteuningsweefsel is tot die model toegevoeg, voordat vrywilliger-spesifieke beweging gesimuleer is.
Die knieskywe van die vrywilligers het `n laterale pad gevolg nadat dit die groef binnegetree het, met die tiltwaardes uniek vir elke vrywilliger. Vergelyking van die beraamde knieskyf mediolaterale tilt en posisies by 30 grade fleksie met in-vivo magnetiese resonansieskandering waardes het `n akkuraatheid van 62.1 % en 96.9 % respektiewelik getoon. Die patellofemorale kontaklas-kwadriseps seningspanning verhouding het gewissel tussen 0.7 en 1.3; asook die mediale komponent – resultante komponent patellofemorale kontaklas wat gewissel het tussen 0 en 0.4. Beide parameters se waardes was soortgelyk aan voorheen-gepubliseerde data. Die mediale patellofemorale ligamentspanning het afgeneem met fleksie. Die patella sening-kwadriseps seningspanning verhouding was soortgelyk aan vorige gepubliseerde waardes en het gewissel tussen 0.4 en 1.2.
Nadat 'n tuberkel-osteotomie in die koronale vlak aangebring is, het Vrywilliger Een se patella die femorale groef vroeër binnegetree. Vrywilliger Twee se patella het slegs `n mediale verskuiwing ondergaan. Eindige element analises is ingespan om die effek van die osteotomie op die spanningsverspreiding in die patellofemorale gewrig te ondersoek. Die gemiddelde spanning in Vrywilliger Een se gewrig was minder by alle hoeke van fleksie (17 % minder), met uitsondering van die spanning by 60 grade (12 % meer). Die spanning in Vrywilliger Twee se gewrig was minder by 30 en 45 grade (6 % minder), maar hoër by ander hoeke (9.1 % meer).
Twee kommersiële patellofemorale prosteses is getoets op die drie Vrywilligers d.m.v. die model. Prostese Twee het die knieskyf-kinematika die beste nageboots. Die patella-seningspanning was effens groter na die vervanging. Prostese Twee het gesorg vir die grootste toename. Die mediale patellofemorale ligamentspanning was die kleinste toe Prostese Twee gebruik is, maar dit het gesorg vir effense hoër laterale retinakulumlaste. Die analises het getoon dat Prostese Twee die beste kandidaat is om die korrekte kinematika te herbewerkstellig. Die kinetika daarteenoor was onafhanklik van die tipe prostese wat gebruik is. Geeneen van die twee prosteses was geskik vir Vrywilliger Drie nie, wat as motivering vir die ontwikkeling van pasiënt-spesifieke prosteses dien. Drie bekragtigde vrywilliger-spesifieke spier-skelet modelle het die analise van patellofemorale biomeganika bewerkstellig. Die tegniek het die potensiaal om ortopediste in staat te stel om die effek van `n osteotomie of patellofemorale vervanging te visualiseer. Die tegniek kan verder gebruik word deur biomediese ingenieurs in die vervaardiging van nuwe patellofemorale prosteses. Meer belangrik is die feit dat die resultaat van chirurgiese ingryping voorspel kan word en optimale behandelingsprosedures beplan kan word vir die patellofemorale biomeganika van `n individu. Please cite this item using this persistent URL
Doctoral Degrees (Mechanical and Mechatronic Engineering) 
Doctoral Degrees (High Performance Computing)