Osteoarthritis (OA) of the knee affects between 5.4% and 38% of older adults and this prevalence is increasing as the population ages and becomes more obese. As health costs rise, it is important to have accurate and cost-effective methods to assess knee OA and the risk for OA. One risk factor for progression of knee OA is lower extremity (LE) frontal-plane malalignment. The first goal of this thesis was to assess the suitability of knee radiographs and LE photographs for the estimation of frontal-plane LE alignment. In the first study, several versions of the femoral shaft-tibial shaft (FS-TS) angle, assessed from knee radiographs, were compared to the hip-knee-ankle (HKA) angle, assessed from full-length radiographs. We concluded that the FS-TS angle is not a recommended substitute for the HKA angle, because the association between the two measures differs depending on alignment, OA severity and the method of determining the FS-TS angle. In the second study, the hip-knee-ankle angle determined from a pelvis-to-ankle photograph (HKA-P) was assessed for its ability to estimate the HKA angle. The HKA-P angle was reliable and highly correlated to the HKA. It therefore shows promise as an accurate and cost-effective assessment tool for the estimation of LE alignment. Commonly-used grading scales for the severity of knee OA seen on a radiograph emphasize just one feature of OA; therefore the second goal of this thesis was to assess the psychometric properties of the unicompartmental osteoarthritis grade (UCOAG), a composite scale which grades several features of OA in the tibiofemoral (TF) compartment. In the third and fourth studies, the reliability, validity and sensitivity to change of the UCOAG scale was assessed and compared to two commonly-used scales (Kellgren-Lawrence and Osteoarthritis Research Society International joint space narrowing). The UCOAG scale showed moderate to excellent reliability. All three scales demonstrated comparable validity and sensitivity to change. The UCOAG is therefore recommended for the assessment of OA severity and change over time. This research provides evidence for the use of accurate and cost-effective measures to assess LE alignment using photographs, and TF OA severity using radiographs, for clinical assessment and research purposes. / Thesis (Ph.D, Rehabilitation Science) -- Queen's University, 2013-09-26 13:21:06.097