CORR Insights®: Loss of Mechanical Ankle Function Is Not Compensated by the Distal Foot Joints in Patients with Ankle Osteoarthritis.

In kinematics and kinetics research, it is very difficult to model the ankle and foot segments. Doing so in a realistic way is important, because researchers believe these approaches might improve clinicians’ abilities to provide orthotic devices or surgery that can improve gait in patients with a variety of disabling conditions [10, 12]. Although the foot has historically been modeled as a single rigid segment, we know that this concept is not nuanced enough to give us the biomechanical information we need when studying human motion. Early representations of the foot as a rigid structure have recently been replaced with multisegment models that can estimate motion separately for smaller segments of the foot [10]. Similar to a motion analysis of the knee or other large joints, a kinematic analysis of the foot (and more generally, gait studies of the foot) is especially limited by challenges with marker placement. Externally placed optic markers on the surface of the skin are easy to use but can generate artifact errors associated with skin movement. Models using intracortical bone pins or cine-radiographic models are moreprecise, but have obvious disadvantages pertaining to their invasiveness and complexity. Movements in the sagittal plane occur mainly at the talocrural joint, and those in the transverse (horizontal) plane mainly occur around the rear of the foot or another axis, and these movements could be measurable. However, it is not easy to measure united subtalar-midfoothindfoot movements. Multisegment foot models are further challenged by decisions about the number of foot segments to include, which bony landmarks to use, how many optical markers to attach, and how to distribute those markers [10]. When the patient is wearing shoes, the situation is even more complicated [3]. We have little information to guide us regarding relevant measures of reliability such as intertrial, intersession, and interexaminer variability in multisegment kinematic analyses of the foot [6]. A systematic review found that many different foot models have been reported, but there is inadequate evidence to support their clinical use [7]. Several proposals for improvement have been made to overcome this situation, such as reporting standards for the transparency of methods or protocols for comparisons [1, 2, 9, 12]. Eerdekens et al. [8] give new insight into such topics with their recent article in this issue of Clinical Orthopaedics and Related Research. This group [8] performed a kinematic and kinetic study to evaluate movement of the ankle and foot segments, comparing patients with ankle osteoarthritis with those without this diagnosis. Participants underwent a three-dimensional (3-D) gait analysis, during which a multisegment foot model (the Rizzoli foot model [11]) was used to quantify the following variables in the ankle: the Chopart, Lisfranc, and first metatarsophalangeal joints during the stance phase of walking; joint This CORR Insights is a commentary on the article “Loss of Mechanical Ankle Function Is Not Compensated by the Distal Foot Joints in Patients with Ankle Osteoarthritis” by Eerdekens et al. available at: DOI: 10. 1097/CORR.0000000000001443. The author certifies that neither he, nor any members of his immediate family, has funding or commercial associations (such as consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writer, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons. M. Akai ✉, Graduate School, International University of Health and Welfare, 4-1-26 Akasaka,Minato-ku, Tokyo 107-8402, Japan, Email: akai-masami@iuhw.ac. jp M. Akai, Graduate School, International University of Health and Welfare, Tokyo, Japan