Allison M. Crone

The ankle and foot rely on a complex, coordinated interaction of numerous small bones and supporting soft tissues to produce efficient locomotion and weight bearing. Subtle osseous malalignments or insufficiency of tendons and ligaments can result in pain, instability and arthropathy. Although gross malalignment can be seen qualitatively, detecting subtle malalignment often requires standardized measurement on imaging studies with prescribed techniques. Moreover, stress imaging techniques, such as weightbearing or angular stress, are more often used in ankle/foot imaging compared with other lower extremity joints, which results in an added layer of complexity when performing measurements. In the ankle/hindfoot, quantitative assessment is most commonly used to detect and/or characterize ankle instability, calcaneal fractures and posterior tibialis tendon dysfunction. Furthermore, quantitative assessments of ankle arthroplasties may help diagnose device failure. In the midfoot, assessment of the tarsometatarsal joints can help detect subtle Lisfranc instability, while in the forefoot, quantitative characterization of hallux valgus is often used to guide surgical management. This review article is the last of a three-part series discussing measurements of the lower extremities and focuses on common measurements used in the foot and ankle, grouped by pathology, with attention to the imaging study of choice for each measurement, as well as the appropriate technique of measurement.

Although most imaging assessments are made qualitatively, quantitative measurements in orthopedic imaging are becoming more important in detecting subtle findings and assessing degrees of abnormality, which can help direct surgical management. In the knee, patellofemoral maltracking is a common cause of anterior pain, particularly in younger patients. Failure to recognize this pathophysiology may result in accelerated chondral loss and osteoarthritis (OA), and the imaging findings may be subtle. As a result, clinicians and radiologists have developed numerous measurements to detect and quantify patellofemoral alignment. Additional entities, such as femorotibial subluxation or angular abnormalities, may only be detected by using standardized measurements and can help detect ligamentous insufficiency or developmental malalignment, which can lead to instability and OA in the medial and lateral femorotibial compartments. Finally, the proper positioning and hardware selection for knee arthroplasty are critical to preventing early hardware failure and postsurgical pain. This review, which focuses on the knee, is the second in a three-part series discussing the appropriate imaging modalities on which to obtain specific lower extremity measurements as well as proper measurement techniques, grouped by pathology. Furthermore, the normal value or range of values according to current literature is reported, along with the significance of abnormal measurements.