Background: Patients with anterior cruciate ligament reconstruction (ACLR) have demonstrated morphological and compositional changes in femoral articular cartilage. However, it is unclear how running biomechanics are associated with femoral cartilage thickness and composition for both ACLR patients and controls. Objectives: (1) to compare measures of femoral cartilage thickness and composition between ACLR patients and matched non-ACLR controls at resting, (2) to investigate how 30 minutes of running influences the aforementioned measures for ACLR patients and controls, and (3) to investigate relationships between running biomechanics and knee cartilage thickness and composition in ACLR patients and controls. Methods: Twenty ACLR patients (age: 23 ± 3 years; mass: 69.7 ± 9.9 kg; time post ACLR: 14.6 ± 6.1 months) and 20 matched non-ACLR controls (age: 22 ± 2 years; mass: 67.1 ± 10.9 kg) participated in the study. A running session required both groups to run for 30 minutes at a self-selected speed. Before and after running we measured femoral cartilage thickness via ultrasound imaging. An MRI session consisted of T2 mapping. Independent t-tests were used to examine differences in femoral cartilage thickness and T2 relaxation time at resting, and thickness changes following the run between the two groups. Pearson correlations were used to explore relationships between running biomechanics and femoral cartilage thickness and relaxation time at resting. Results: The ACLR group showed longer T2 relaxation times in three regions of the medial femoral condyle at resting compared with the control group (overall: 54.9 ± 14.2 vs. 39.3 ± 8.2 ms, P = 0.001; central: 51.2 ± 16.6 vs. 34.9 ± 13.2 ms, P = 0.006; posterior: 50.2 ± 10.1 vs. 39.8 ± 7.4 ms, P = 0.006). Following the run, the ACLR group showed greater deformation in the medial femoral cartilage than the control group (0.03 ± 0.01 vs. 0.01 ± 0.01 cm, P = 0.001). Additionally, the ACLR group showed significant negative correlations between resting T2 relaxation time in the central region of the medial femoral condyle and peak vGRF, and vertical impulse (r = -0.53, P = 0.013; r = -0.46, P = 0.041, respectively) during running. Conclusions: The ACLR group showed greater water content in medial femoral cartilage and greater deformation in medial femoral cartilage thickness following 30 minutes of running compared with the controls. In addition, the ACLR group demonstrated significant negative correlations between water content in medial femoral cartilage and vGRF. Our findings suggest that those who are at least 24 months post-ACLR have degraded cartilage composition and their cartilage is more sensitive to joint loading morphologically.

Abstract Osteoarthritis (OA) is a heterogenic joint disease significantly affecting the quality of life of a patient, causing pain and disability. OA causes degenerative changes to the structure and composition of articular cartilage and subchondral bone. Currently, effective treatments for OA are limited, partly due to limitations in defining the imaging biomarkers of early OA. Improvement of imaging modalities in OA research and clinical setup is a requirement for quantitating early OA-related tissue features. In the clinical and preclinical setup, computed tomography (CT) enables imaging of bone and, using specific contrast agents, articular cartilage. The aim of this study is to create and validate novel micro-computed tomography (μCT) methods to quantify OA-related features and modifications in articular cartilage and subchondral bone. Contrast-enhanced μCT methods for imaging the collagen (phosphotungstic acid (PTA) and phosphomolybdic acid (PMA)) and GAG (CA4+) content of the articular cartilage in vitro were validated against various reference methods measuring the biochemical composition of articular cartilage. To improve the μCT imaging of subchondral bone, grey-level co-occurrence matrix (GLCM) based analysis of sub-resolution features of subchondral bone was introduced. In addition, to test the translatability of the GLCM-based analysis to clinical resolution, sub-resolution features extracted from clinical cone-beam CT were validated against the subchondral bone morphometrics from the μCT. PTA showed stronger association with the collagen content of the articular cartilage compared to PMA. PTA was also associated with collagen content even in degraded articular cartilage. CA4+ distribution was found to accumulate in chondrons and surrounding areas, suggesting that it is a prominent contrast agent for high-resolution μCT studies of chondrocytes. The GLCM-based analysis of subchondral bone provided information on cellular structure from μCT images and trabecular bone micro-structures from clinical CT images. In conclusion, μCT imaging can provide quantitative information on the collagen content and chondrons of articular cartilage, as well as on osteocytes in subchondral bone. The methods presented here extend the tools for researchers to quantify osteochondral tissue modifications in OA. Furthermore, the developed image processing tools could be translatable to the clinical CT. / Tiivistelmä Nivelrikko on heterogeeninen niveltauti, joka huonontaa yksilön elämän laatua aiheuttaen kipua ja liikuntakyvyttömyyttä. Nivelrikko aiheuttaa nivelkudosten rappeumaa vaikuttaen mm. ruston ja rustonalaisen luun rakenteeseen ja koostumukseen. Nivelrikon kudosmuutosten kuvantamisen kehittäminen ja määrällinen tutkiminen taudin alkuvaiheissa tukisivat nykyisten nivelrikon hoitomenetelmien kehittämistä. Kliinisessä käytössä ja perustutkimuksessa, tietokonetomografia (TT) mahdollistaa luukuvantamisen ja varjoaineita käytettäessä myös rustokuvantamisen. Tämän väitöskirjan tavoitteena on esitellä ja validoida uusia mikrotietokonetomografia-menetelmiä (μTT) nivelrikon rusto- ja luumuutosten määrälliseen tutkimukseen. Varjoaineavusteisia μTT in vitro menetelmiä ruston kollageenin (fosfovolframihappoa (PTA) ja fosfomolybdeenihappoa (PMA)) ja GAG (CA4+) jakauman määrälliseen tutkimukseen validoitiin useilla eri ruston biokemiallista koostumusta mittaavilla vertailumenetelmillä. Rustonalaisen luun kuvantamista kehitettiin soveltamalla harmaasävyjen tekstuurianalyysiä, jolla pyrittiin tunnistamaan kuva-alkiota pienempiä luurakenteita. Rustonalaisen luun μTT-kuvien analyysien tulokset validoitiin synkrotronisäteilyyn perustuvan μTT:n avulla. Lisäksi tekstuurianalyysin soveltuvuutta testattiin kliinisen resoluution kartiokeilan TT-kuville. Kuvista analysoituja tekstuuriparametrejä verrattiin μTT:lla mitattuun todelliseen rustonalaisen luun rakenteeseen. Väitöskirjan tulokset osoittavat, että PTA on spesifimpi kollageenille testatuista varjoaineista ja sen jakauma on verrannollinen kollageenijakaumaan jopa rappeutuneessa nivelrustossa. GAG-spesifisen varjoaineen CA4+:n todettiin kerääntyvän myös kondroneihin, mikä viittaa siihen, että kyseinen varjoaine soveltuisi potentiaalisesti rustosolujen korkean resoluution μTT-tutkimuksiin. Rustonalaisen luun μTT-kuvista analysoitujen tekstuuriparametrien havaittiin olevan verrannollisia osteosyyttien tilavuusfraktion kanssa. Väitöskirjassa esitettyjen tulosten perusteella μTT-kuvantaminen tarjoaa kvantitatiivisen menetelmän nivelruston kollageenijakauman ja rustosolujen sekä rustonalaisen luun osteosyyttien tutkimuksiin. Väitöskirjassa esitetyt menetelmät laajentavat jo olemassa olevaa tutkimusmenetelmien kirjoa nivelrikon aiheuttamien nivelrusto- ja luumuutosten tutkimuksessa. Lisäksi kehitetyt kuva-analyysimenetelmät voivat tarjota tarkempaa tietoa kliinisestä TT:sta.