LAUSR

I READ with great interest the article by Fukui et al. (1) in the most recent issue of Skin Research and Technology on skin translation during hip motion. I believe this article addresses an interesting and important topic in skin biomechanics; however, the article leaves the reader with a number of unanswered questions, largely as a result of the movement choice for the experiment. It was surprising that the authors investigated the relationship between hip angle and thigh skin translations during the movement of pelvic sway, which is neither a passive movement nor an isolated active movement of the hip. With a purely passive movement such as assisted passive flexion/extension, steady-state skin translations could have been determined strictly due to changes in the joint angle. Then with an active movement such as walking or isolated active hip flexion/extension, skin translations could have been studied while taking into account joint angular changes, joint angular velocities, and deformations due to muscle vibrations during contractions and limb-ground impact (2). Comparing active and passive tests would then provide an indication of how thigh skin translates under different mechanical scenarios. Clinically, the results presented by Fukui et al. (1) are further complicated when considering the possibility that patients may have scarring or wounds that demonstrate different biomechanical properties from surrounding healthy skin (3). While Fukui et al. (1) made an attempt to ensure knee extension throughout the movement, it is important to consider the effects of knee angular change on thigh skin translation as well. For example, with a given change in hip angle relative to neutral, will thigh skin translations be similar regardless of whether the knee is extended or flexed? This could have important implications in the context of scar contractures where a joint may only operate within a restricted range of motion. While Fukui et al. (1) have made an important early contribution to this area of research, it is difficult to generalize these findings to a dynamic or clinical scenario at the present time based on the complexities described above.