Kinetics of individual limbs during level and slope walking with a unilateral transtibial bone-anchored prosthesis in the cat
Introduction
It is a common practice to use animal models to investigate biomechanical function, safety and efficacy of orthopedic and prosthetic implants, procedures and technologies for translation to human clinical practice. For example, ongoing animal studies on transcutaneous porous titanium bone implants (Farrell et al., 2014a, Farrell et al., 2014b, Fitzpatrick et al., 2011, Pitkin et al., 2009, Shelton et al., 2011) have aimed to reduce skin infection in individuals with bone-anchored lower limb prostheses (Branemark et al., 2014, Drygas et al., 2008, Tillander et al., 2010, Tsikandylakis et al., 2014), and ultimately to improve biomechanics of prosthetic locomotion. It is much less common, however, to translate successful developments in human biomechanics, orthopedic and prosthetic research to veterinary medicine to treat animals with limb loss. According to Mich (2014), the current dogma in veterinary medicine of quadrupedal pets (dogs and cats) is: “animals do great on 3 legs”. As a result, standard of care in veterinary medicine is amputation of the whole limb if a distal segment (e.g., foot) cannot be salvaged. This, in turn, leads to animal limited mobility, weight gain, break-down of a sound limb, chronic neck and back pain, and premature euthanasia (Mich, 2014, Mich et al., 2013). The method of direct attachment of a prosthesis to the residual limb, developed for people with limb loss, could be beneficial for veterinary practice.
Direct attachment of limb prosthesis to the residual bone using a transcutaneous solid titanium implant inside the medullary cavity has been used in individuals with limb loss since the 1990s (Branemark et al., 2001, Hagberg and Branemark, 2009, Jonsson et al., 2011, Van de Meent et al., 2013). Several advantages of bone-anchored limb prostheses over conventional socket-attached prostheses have been reported. Bone-anchored prostheses improve load transmission, eliminate skin problems caused by skin friction inside the socket (irritation, blisters, edema and dermatitis) (Hagberg and Branemark, 2009, Jonsson et al., 2011, Juhnke et al., 2015), and increase range of motion (Hagberg et al., 2005, Tranberg et al., 2011). Bone-anchored prostheses improve comfort and confidence of the users (Hagberg et al., 2008, Lundberg et al., 2011, Witso, E., Kristensen, T., Benum, P., Sivertsen, S., Persen, L., Funderud, A., Magne, T., Aursand, H.P., Aamodt, A., 2006) and permit easier donning and doffing of the prosthesis (Jonsson et al., 2011). In addition, bone-anchored prostheses improve perception of prosthesis loading, defined as osseoperception (Haggstrom et al., 2013a, Jacobs et al., 2000, Lundborg et al., 2006), lead to fewer clinical visits to the prosthetist (Haggstrom et al., 2013b), and result in improvement of walking mechanics (Frossard et al., 2013, Hagberg et al., 2005, Tranberg et al., 2011).
All these advantages of bone-anchored prostheses would be beneficial to quadrupedal animals with limb loss if animals choose to utilize a prosthesis on one leg over locomoting on three sound legs, as currently assumed in veterinary medicine (Mich, 2014). Although few case report studies have suggested that quadrupedal animals might utilize a unilateral distal bone-anchored prosthesis for walking (Farrell et al., 2014a, Fitzpatrick et al., 2011), no studies have been published that rigorously document whether quadrupedal animals systematically utilize unilateral transtibial prostheses during locomotion and how prosthetic locomotion is performed. The use of the prosthetic limb during quadrupedal locomotion might depend on which limb is missing (forelimb versus hindlimb) and on loading demands on the prosthetic limb. For example, during downslope walking at grade 50%, peak loading on the hindlimbs is reduced by ∼25% compared to 50%-upslope walking (Gregor et al., 2006, Prilutsky et al., 2011). Reduced loading on the prosthetic limb could prompt the animal not to utilize the prosthesis at all and to locomote on three legs instead.
Therefore, the aim of this study was to examined if and how cats utilize the limb with a bone-anchored passive transtibial prosthesis during downslope, level and upslope walking. We judged whether the animal used the prosthetic limb for locomotion based on the duty factor (the ratio of the stance phase duration over the cycle duration). We hypothesized that the duty factor will not be zero, i.e. the stance phase of the prosthetic limb would be present. If the first hypothesis was confirmed, one would expect a reduced loading of the prosthetic leg during locomotion as observed in people walking with a unilateral passive transtibial prosthesis (Barr et al., 1992, Fey et al., 2011, Segal et al., 2006). Therefore, if the animals would utilize quadrupedal gait with the prosthesis, we would test a second hypothesis that the ground reaction forces and work done by the prosthetic limb would be reduced compared to those of the sound limbs.
Section snippets
Methods
Full descriptions of the surgical and rehabilitative procedures, prosthesis and implant design, and data acquisition have been published previously (Farrell et al., 2014a) and only briefly described here. All experimental procedures were in agreement with the US Public Health Service Policy on Humane Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committees at both Georgia Institute of Technology and St. Joseph’s Translational Research Institute
Results
No signs of discomfort or pain were observed in the animals during the post-surgical pylon loading in weeks 6 through 10 (the absence of limb withdrawal) or during prosthetic use. Behavioral observations of the prosthesis use indicated that the cats engaged the prosthesis for standing, walking, and, occasionally, jumping.
Discussion
The results of the study supported the hypothesis that cats with a SBIP-attached unilateral transtibial prosthesis would use it for support during quadrupedal locomotion – the duty factor of the prosthetic limb exceeded zero and was in the range of 45.0–60.6% for all cats. Additionally, the prosthetic limb generated substantial normal GRF during level and slope walking post implantation. The second hypothesis that the GRF and work values produced by the prosthetic limb would be lower compared
Acknowledgements
This study was supported in part by DOD grant W81XWH-16-1-0791, NIH grants T32HD055180, R44HD057492 and R44HD090768, and NSF grant 0946809. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Institutes of Health, National Science Foundation or Department of Defense. We would like to thank Dr. Ashley Strong, Dr. Evan Goldberg and staff of the T3 Labs for their excellent veterinary
Conflict of interest statement
We certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.
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