In individuals with chronic complete spinal cord injury, reduced lower-limb weight-bearing due to long-term manual wheelchair use, as well as neurological and vascular dysfunctions below the level of injury, contribute to the loss of bone mineral density [1]. Unfortunately, low bone mineral density is associated to reduced bone strength and increased risk of lower-limb fragility fracture in this population [1]. Wearable robotic exoskeletons are an emerging and rapidly progressing technology that has, among other things, the potential to significantly increase lower-limb weight-bearing (i.e., mechanical loading) in this population. Mechanical loading is an important factor influencing bone strength through the “mechanostat” principal [1]. Briefly, the forces exerted on bone tissue during mechanical loading trigger an anabolic state during which the osteocyte-lead bone formation surpasses the osteoclast-lead bone resorption—thus, strengthening bone [1]. Hence, research in overground exoskeleton-assisted walking programs has increased substantially recently as such interventions could potentially increase bone strength and, theoretically, reduce the risk of fragility fractures (and associated complications). However, reported cases of lower-limb fragility fracture during exoskeleton-assisted walking raise safety concerns for both rehabilitation clinicians and researchers [2,3,4].

To ensure that research on this novel technology can be conducted ethically and safely, there is a need to strike an optimal balance so that the potential benefits of exoskeleton-assisted walking programs outweigh their potential risks. To our knowledge, aside from a recent history of lower-limb fragility fracture and a demonstrated capability to tolerate static standing posture, there are currently no universally accepted criteria or manufacturer recommendations on how to safely engage individuals with low bone mineral density in exoskeleton-assisted walking programs [5]. Hence, rehabilitation researchers must rely on a trial-error process supported by their competencies, experience, and intuition to establish and progress walking program parameters, especially in terms of total walking time, number of steps, or distance traveled. Yet, very few studies involving exoskeleton-assisted walking have used cut-off values for bone mineral density threshold (i.e., hip or spine T-score < −2.0; total hip or femoral neck T-score < −3.5) to mitigate fragility fracture risk [6, 7]. Thus, this Perspective introduces a recently developed algorithm, based on bone mineral density, targeting the mitigation of fragility fracture risk in individuals with chronic spinal cord injury engaging in an overground exoskeleton-assisted walking program [8]. Ultimately, this paper aims to open a discussion and engage the clinical and scientific communities into the co-creation of a decisional algorithm, based on a consensus-building process, to assure patient safety as this novel technology continues to be studied and implemented.

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