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Simulation driven pre-operative planning for the treatment of hallux rigidus: A novel concept of implant assessment
KTH, School of Technology and Health (STH), Medical Engineering.
2013 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

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.

Abstract [sv]

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.

Place, publisher, year, edition, pages
2013. , 53 p.
Series
Trita-STH, 2013:98
Keyword [en]
Biomechanics, Implant assessment, Hallux rigidus, FEM.
National Category
Medical Materials Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-127909OAI: oai:DiVA.org:kth-127909DiVA: diva2:646620
External cooperation
Episurf Medical AB
Subject / course
Medical Engineering
Educational program
Master of Science - Medical Engineering
Presentation
2013-06-13, 205, Alfred Nobels alle 10, Huddinge, 15:16 (English)
Supervisors
Examiners
Available from: 2013-10-24 Created: 2013-09-09 Last updated: 2013-10-24Bibliographically approved

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