Abstract Magnetic resonance imaging (MRI) is a well-established imaging modality for disorders of the musculoskeletal system. The distinguishing advantages of MRI are absence of ionizing radiation, excellent tissue contrast and the ability to use any arbitrary imaging plane. MRI can also be used as a guidance method for various percutaneous procedures. The purpose of this study was to evaluate the feasibility of MRI guidance for musculoskeletal biopsies and therapeutic bone drillings. A 0.23 tesla open configuration MRI scanner with an interventional optical guidance system was used. 172 percutaneous biopsies performed using MRI guidance were reviewed to define the safety and accuracy of the guidance method. The value of fine needle aspiration biopsy (FNAB) as a supplementary diagnostic procedure for core biopsy was also evaluated. The overall diagnostic accuracy of MRI-guided biopsy was 0.95, sensitivity 0.91, and specificity 0.98. The diagnostic accuracy of histological biopsy alone was 0.93, sensitivity 0.89, and specificity 0.98, and accuracy for FNAB alone was 0.85, sensitivity 0.80, and specificity 0.90. MRI guidance was deemed feasible and accurate and fine needle biopsy a useful supplement. The feasibility and safety of MRI-guided retrograde drilling of osteochondritis dissecans of the knee were evaluated by analysing ten procedures. All the lesions were successfully located and reached without complications. All patients experienced pain alleviation and follow-up MRI showed ossification in all. The feasibility and safety of MRI-guided retrograde drilling of osteochondritis dissecans of the talus were assessed by evaluating four procedures. Technical success was achieved in all cases and no complications were reported. All patients experienced some clinical benefit, although the changes in the pathological imaging findings were subtle. The feasibility and safety of MRI-guided core decompression for avascular necrosis of the femoral head were assessed by analysing twelve such procedures. The patients quantified their symptoms before and after the procedure. All procedures were successful without complications. All patients with low-stage disease benefited from the procedure. MRI guidance seems accurate, safe and technically feasible for the therapeutic bone drillings studied. / Tiivistelmä Magneettikuvaus (MK) on vakiintunut tuki- ja liikuntaelimistön sairauksien kuvantamismenetelmä. Sen erityispiirteitä ovat ionisoivan säteilyn puuttuminen, erinomainen kudoskontrasti sekä mahdollisuus saada kuvia mielivaltaisesta leiketasosta. Magneettikuvausta voidaan myös käyttää ohjausmenetelmänä useiden perkutaanisten toimenpiteiden yhteydessä. Tämän tutkimuksen tarkoitus oli selvittää MK-ohjauksen käyttökelpoisuus tuki- ja liikuntaelimistön neulanäytteenottojen ja hoidollisten luuporausten ohjausmenetelmänä. Tutkimuksessa käytettiin 0.23 teslan avomagneettia, jossa oli lisäksi optinen ohjausjärjestelmä. MK-ohjauksen turvallisuuden ja tarkkuuden selvittämiseksi tutkittiin 172 perkutaanista MK-ohjattua neulanäytteenottoa. Myös paksuneulanäyteen yhteydessä otetun ohutneulanäytteen antama lisäarvo arvioitiin. MK-ohjatun neulanäytteenoton kokonaistarkkuus oli 0.95, herkkyys 0.91 ja spesifisyys 0.98. Pelkän histologisen näytteenoton vastaavat tunnusluvut olivat 0.93, 0.89 ja 0.90 ja pelkän ohutneulanäytteen tunnusluvut olivat 0.85, 0.80 ja 0.90. Magneettikuvaus todettiin käyttökelpoiseksi ja tarkaksi ohjausmenetelmäksi ja ohutneulanäyte hyödylliseksi lisätoimenpiteeksi. MK-ohjauksen turvallisuutta ja soveltuvuutta polven osteokondriitin poraushoitoon arvioitiin kymmenen toimenpiteen perusteella. Kaikkiin kohteisiin osuttiin, eikä komplikaatioita ilmennyt. Kaikkien potilaiden kipu helpottui ja seurantakuvauksissa nähtiin luutumista. MK-ohjauksen turvallisuutta ja soveltuvuutta telaluun osteokondriitin poraushoitoon arvioitiin neljän toimenpiteen perusteella. Toimenpide onnistui teknisesti kaikissa tapauksissa, eikä komplikaatioita esiintynyt. Kaikki potilaat hyötyivät jonkin verran, mutta poikkeava kuvalöydös muuttui vain vähän. MK-ohjatun reisiluun pään avaskulaarisen nekroosin poraushoidon turvallisuutta ja soveltuvuutta arvioitiin kahdentoista toimenpiteen perusteella. Potilaat määrittivät oireensa numeerisesti ennen ja jälkeen toimenpiteen. Kaikki toimenpiteet onnistuivat, eikä komplikaatioita esiintynyt. Toimenpiteestä hyötyivät kaikki potilaat, joilla oli varhaisvaiheen tauti. Magneettikuvaus vaikuttaa tarkalta, turvalliselta ja teknisesti soveltuvalta ohjausmenetelmältä tutkittujen terapeuttisten luuporausten yhteydessä.

Bone drilling is a major part of orthopaedic surgery performed during the internal fixation of fractured bones. At present, information related to drilling force, drilling torque, rate of drill bit penetration and drill bit rotational speed is not available to orthopaedic surgeons, clinicians and researchers as bone drilling is performed manually. This research demonstrates that bone drilling force data if recorded in-vivo, during the repair of bone fractures, can provide information about the strength/quality of the bone. Drilling force does not give a direct measure of bone strength; therefore it has been correlated with the shear strength and screw pullout strength to determine the efficacy in estimating the bone strength. Various synthetic bone material densities and animal bones have been tested to demonstrate the use of drilling force data. A novel automated experimental test rig, which enables drilling tests, screw insertion and screw pullout tests to be carried out in a controlled environment, has been developed. Both drilling and screw pullout tests have been carried out in a single setting of the specimen to reduce the experimental errors and increase repeatability of the results. A significantly high value of correlation (r² > 0.99) between drilling force & shear strength and also between drilling force & normalised screw pullout strength in synthetic bone material was found. Furthermore, a high value of correlation (r² = 0.958 for pig bones and r² = 0.901 for lamb bones) between maximum drilling force & normalised screw pullout strength was also found. The result shows that drilling data can be used to predict material strength. Bone screws are extensively used during the internal fixation of fractured bones. The amount of screw been tightened is one of the main factor which affects the bone-screw fixation quality. Over tightening of screw can result into the loss of bone-screw fixation strength, whereas under tightening can result in the screw loosening. Therefore, optimum tightening of the screw is important to achieve the maximum bone-screw fixation strength. At present, optimum tightening of the screw is entirely dependent upon the skill and judgment of the surgeon, which is predominantly based on the feel of the screw tightening torque. Various studies have been reported in the literature to develop an algorithm to set an optimum tightening torque value to be used in surgery. A method which is based on the use of rotation angle of the screw while tightening, rather than using screw insertion/tightening torque, to optimise the bone-screw fixation strength is proposed in this research. The effectiveness of the proposed method has been successfully demonstrated on the synthetic bone material using the designed test rig. The optimum angle for the tested screw was found to be 120° which is equivalent to 33% of the screw pitch.