The present study utilizes finite element analysis in order to simulate a surgical operation in the treatment of a hallux rigidus case, as designed and developed by Episurf Medical AB (Stockholm, Sweden). The surgical intervention includes an initial cheilectomy as well as an insertion of an orthopedic implant. The goal of the study was to evaluate the current concept of the medical intervention as it is manifested today, as well as to give design suggestions as how to further improve the pre-planning of the surgery. MRI-images of the first metatarsophalangeal joint in the hallux was collected from a patient suffering from hallux rigidus, and used in order to build case-specific geometrical images to be used in the FE analysis. The simulation was setup as to simulate a normal motion in the first metatarsophalangeal joint during a normal gait pattern. The first simulation was conducted without any intervention, while the second was conducted after a pre-determined operation plan in accordance with the surgical operation that Episurf Medical AB wants to perform. The results was then compared and analyzed in order to determine the post-surgical effects that such an operation could have on the patient. A third and final simulation was then performed, by using optimization algorithms in order to make suggestions to the pre-planned cheilectomy shape, as well as orientation of the implant. Two parameters were being investigated in order to assess the surgical intervention as designed by Episurf Medical AB; the contact stress on the articular side of the metatarsal head, and the strain on the implant shaft. The current manifestation of the cheilectomy did not reduce the contact stress compared to the untreated condition, as the implant failed to be a load baring surface due to the two dimensional nature of which it is conceived. Instead, the contact surface area is reduced and positioned medial and lateral to the implant head. The optimization algorithm could reduce the maximum contact stress significantly, from 295MPa and 400MPa in the treated and untreated conditons respectively, to 160MPa after the optimization algorithm. It became clear that the angle of the cheilectomy as well as the orientation of the implant angle has an incriminating effect on the post-operative results. However, the shape of the cheilectomy as well as the design of the implant would need to be revised in future embodiments, as the current concept failed to provide joint with a new articulating surface. Further development of the models formulated in this thesis is advised, as well as validating the findings with clinical data. / Den aktuella studien använder finita elementmetoden i syfte att simulera en kirurgisk operation som har utvecklats av Episurf Medical AB (Stockholm, Sverige) för att behandla ett hallux rigidus fall. Det kirurgiska ingreppet utgörs av en inledande cheilectomi,  som sedan följs av att operera in ett ortopediskt implantat. Målet med studien var att utvärdera det nuvarande konceptet för det medicinska ingrepp så som den är uttänkt idag, samt att ge designförslag för hur man ytterligare kan förbättra planeringen av operationen. MR-bilder av den första metatarsalleden i stortån samlades in från en patient som lider av hallux rigidus, som användes sedan för att bygga patient specifika geometriska bilder för att användas i FE-analysen. Simuleringen var modellerad för att simulera en normal rörelse i första metatarsofalangealleden under en normal gångcykel. Den första simuleringen genomfördes utan något ingripande, medan den andra genomfördes efter en förutbestämd operationsplan i enlighet med det kirurgiska ingreppet som Episurf Medical AB vill utföra. Resultaten jämfördes sedan och analyserades för att bestämma de resultaten som en sådan operation skulle kunna innebära för patienten postoperativt. En tredje och sista simulering utfördes sedan, med hjälp av optimeringsalgoritmer för att ge förslag på förbättringar för den förplanerade cheilectomin, samt orienteringen av implantatet. Två parametrar undersöktes för att bedöma det kirurgiska ingrepp som designats av Episurf Medical AB, kontaktbelastningen på artikulära sidan av metatarsalhuvudet, och påfrestningen på implantatet. Den nuvarande utformningen av cheilectomin minskade inte kontaktbelastningen jämfört med det obehandlade tillståndet, då implantatet inte vart belastat på grund av den tvådimensionella profilen i dess utformning. Optimeringsalgoritmen kunde minska den maximala kontaktbelastningen markant, från 295MPa i den behandlade och 400MPa i den obehandlade simuleringarna, till 160MPa efter optimeringsalgoritmen. Det blev tydligt att vinkeln på cheilectomin samt orienteringen av implantatet har en avgörande betydelse för det postoperativa resultatet. Dock skulle formen på cheilectomin liksom designen av implantatet behöva revideras i framtida utformningar, då det nuvarande konceptet inte lyckades att ge leden en ny ledyta. Vidareutveckling av de modeller som utvecklats i avhandlingen rekommenderas, samt att validera resultaten med annan kliniska data.

[Truncated abstract] Measuring the kinematics of joints and implants following orthopaedic surgery is important since joint motion directly influences the functional outcome of the patient and the longevity of the implant. Radiostereometric Analysis (RSA) has been used to assess the motion over time of various joints and implant designs following corrective orthopaedic and joint replacement surgery for more than 20 years in more than 10,000 patients around the world. While the use of RSA reduces the risk of implanting potentially inferior prostheses on a large scale, conventional methodological procedures are based on the acquisition of static, stereographic x-ray images that are not suitable for measuring skeletal kinematics in a dynamic manner. The purpose of this thesis was to design, validate and test a novel technique for dynamically assessing the skeletal motion of human subjects using RSA and single-plane digital x-ray video fluoroscopy. The validation procedure utilised two in-vitro phantom models of human joints capable of simulating normal kinematic motion. These phantom models were supplied with realistic spatial displacement protocols derived from cadaveric specimens. The spatial positions of a series of tantalum markers that were implanted in each skeletal segment were measured using RSA. Skeletal motion was determined in x-ray fluoroscopy images by minimising the difference between the markers measured and projected in the single image plane. Accuracy was determined in terms of bias and precision by analysing the deviation between the applied displacement protocol and measured pose estimates. ... The RSA and low dose single-plane fluoroscopy technique developed, validated and tested in this thesis is capable of dynamically measuring the kinematics of any joint in the human body, following the implantation of small metallic markers in the surrounding bone during corrective orthopaedic surgery. The kinematics of joints with replacement prostheses, such as the total knee replacement (TKR), can be analysed in addition to the kinematics of joints without replacement prostheses, such as the sacroiliac joint. The technique may be used in the future on groups of human subjects enrolled in controlled trials that are designed to analyse the kinematics of the shoulder, spine, hip, knee, patella or ankle joints for the purposes of quantitatively comparing the kinematics of different prosthesis designs and various corrective orthopaedic procedures.