# Prosthesis Embodiment in Lower Extremity Limb Loss: A Narrative Review
## 2 Development of the Dimensions of Embodiment  
Surgical amputations of the lower extremity have been reported to have occurred as early as 31,000 years ago [8]. Since then, the role of surgical amputation has grown, and with it, the need for ever-improving prosthetic technology. The first documented example of the use of a lower extremity prosthesis dates back to the 15 th century BC, where an amputated right great toe was replaced with a prosthesis made of leather and wood. A significant driver of prosthetic evolution was the introduction of firearms in European warfare in the 16 th century, creating novel injury patterns, including blast injuries that created more extensive soft tissue damage, comminuted fractures, and wound contamination. As such, the incidence of lower-limb amputation increased during this time. To meet the needs of his patients with limb loss, French military surgeon [PERSON] not only helped refine the technique of lower extremity amputation, but he also hand-crafted artificial limbs for his amputees [8,9]. Although advances have been made in modern surgical techniques and prosthesis technologies, understanding how loss of a limb affects patient quality of life, functional status, and interactions with the prosthetic device continues to be a challenge for clinicians and scientists alike. Numerous patient-reported outcome measures (PROMs) have been used to evaluate the impact of lower-limb amputation and prosthesis use on compartmentalized measures focusing on mental health, chronic pain, and functionality [10,11]. However, there has been a recent push to uncover how a prosthesis affects not only the distinct mental and physical experiences and functions of a limb loss patient, but also a more holistic view of that patient's psychosocial perception of completeness: prosthesis embodiment. The rubber hand illusion [12] is the seminal paper that illustrates the powerful nature of embodiment. This paper intuitively identified the following three components of embodiment:  
1. Co-location, experienced as the volume in space where one feels their body is located. 2. Ownership, the experience of something being a part of the body. 3. Agency, the experience of authoring the actions of one's body, and the resulting outcomes. Coincidentally, Ref. [13] shows that the main factors that contribute to abandonment are
1. Lack of control of function. 2. Lack of sensation. 3. Comfort and fit issues when wearing, including the perceived weight of the device. And these factors correspond to the lack of prosthesis embodiment. Throughout the literature, measuring embodiment has been related to the use of upper-limb prostheses [3]. Here, the authors classify the measures as behavioral and physiological. Behavioral measures typically involve conscious judgments or voluntary actions, e.g., PROMs, while physiological measures assess subconscious processes without requiring participant input, e.g., measures of skin conductance, skin temperature, cortical imaging, etc. This distinction is made because behavioral measures capture subjective participant experience or perception, while physiological measures provide objective correlative data of the underpinning neurobiological processes. Despite the focus on upper limbs, there is one lower-limb specific measure of embodiment: [PERSON]'s prosthesis embodiment scale for lower extremity amputees (PEmbS-LLA) [14]. This test quantitatively validates the claim that the concept of the rubber hand can be applied to other regions of the body, including a parallel phenomenon in the lower limb known as the rubber foot illusion [15]. The first part of the test begins with the patient donning the prosthesis and then looking directly at the prosthesis for 60 s. The patient then responds with their level of agreement to the first eight questions in Table 1.  
In the second part of the test, patients walk for 30 s before answering the last two questions. The total score represents the patient's overall prosthesis embodiment.