Recent Progress in Animal Studies of the Skin- and Bone-integrated Pylon With Deep Porosity for Bone-Anchored Limb Prosthetics With and Without Neural Interface

Abstract

Introduction The three major unresolved problems in bone-anchored limb prosthetics are stable, infection-free integration of skin with a percutaneous bone implant, robust skeletal fixation between the implant and host bone, and a secure interface of sensory nerves and muscles with a prosthesis for the intuitive bidirectional prosthetic control. Here we review results of our completed work and report on recent progress. Materials and Methods Eight female adult cats received skin- and bone-integrated pylon (SBIP) and eight male adult cats received SBIP-peripheral neural interface (PNI) pylon into the right distal tibia. The latter pylons provided PNI for connection between a powered sensing transtibial prosthesis and electrodes in residual soleus muscle and on residual distal tibial nerve. If signs of infection were absent 28-70 days after implantation, cats started wearing a passive prosthesis. We recorded and analyzed full-body mechanics of level and slope locomotion in five cats with passive prostheses and in one cat with a powered sensing prosthesis. We also performed histological analyses of tissue integration with the implants in nine cats. Four pigs received SBIPs into the left hindlimb and two pigs—into the left forelimb. We recorded vertical ground reaction forces before amputation and following osseointegration. We also conducted pullout postmortem tests on the implanted pylons. One pig received in dorsum the modified SBIPs with and without silver coating. Results Six cats from the SBIP groups had implant for 70 days. One cat developed infection and did not receive prosthesis. Five cats had pylon for 148 to 183 days, showed substantial loading of the prosthesis during locomotion (40.4% below presurgery control), and demonstrated deep ingrowth of skin and bone tissue into SBIP (over 60%). Seven of eight cats from the SBIP-PNI group demonstrated poor pylon integration without clinical signs of infection. One cat had prosthesis for 824 days (27 months). The use of the bidirectionally controlled prosthesis by this animal during level walking demonstrated increased vertical loading to nearly normal values, although the propulsion force was significantly reduced. From the study on pigs, it was found that symmetry in loading between the intact and prosthetic limbs during locomotion was 80 ± 5.5%. Skin-implant interface was infection-free, but developed a stoma, probably because of the high mobility of the skin and soft tissues in the pig’s thigh. Dorsal implantation resulted in the infection-free deep ingrowth of skin into the SBIP implants. Conclusions Cats with SBIP (n = 5) and SBIP-PNI (n = 1) pylons developed a sound interface with the residuum skin and bone and demonstrated substantial loading of prosthetic limb during locomotion. One animal with SBIP developed infection and seven cats with SBIP-PNI demonstrated poor bone integration without signs of infection. Future studies of the SBIP-PNI should focus on reliability of integration with the residuum. Ongoing study with pigs requires decreasing the extra mobility of skin and soft tissues until the skin seal is developed within the SBIP implant.

Electrical Stimulation of Distal Tibial Nerve During Stance Phase of Walking May Reverse Effects of Unilateral Paw Pad Anesthesia in the Cat

“…Female and male cats were housed separately in a single room of animal facilities at Georgia Tech and T3 Laboratories, respectively. Most of the surgical and experimental procedures have been described elsewhere (Jarrell et al, 2018;Klishko et al, 2021;Ollivier-Lanvin et al, 2011;Park et al, 2019;Pitkin et al, 2021;Prilutsky et al, 2011) and, thus, only briefly outlined here.…”

“…As part of another study on developing a powered sensing transtibial prosthesis integrated with the bone, skin, muscles, and peripheral nerves (Farrell, Prilutsky, Kistenberg, et al, 2014;Farrell, Prilutsky, Ritter, et al, 2014;Park et al, 2018;Pitkin et al, 2021), we also investigated one male cat (mass 4.7 kg). This animal was trained to walk overground inside a horizontal Plexiglass enclosed walkway with three force plates (Bertec) embedded in the walkway floor.…”

“…First, removal of somatosensory feedback by transtibial amputation is much more extensive than local paw anesthesia. In addition, the lack of ankle muscles in the prosthetic hindlimb reduces limb support and propulsion even with the powered prosthesis, whose power appeared to be limited (Pitkin et al, 2021). As a result, the contralateral limbs, as well as the ipsilateral forelimb, increased their contribution to weight support and propulsion as evident from the longer stance time and higher duty factor of the contralateral limbs (Figure 4d and 4f) and the greater pacing on the ipsilateral side (Figure 4g) as compared with the intact walking before surgery; see also (Jarrell et al, 2018).…”

Temporary Botulinum Immobilization of Residuum Muscles for Facilitation of the Initial Ingrowth of Skin to the Porous Skin and Bone Integrated Pylon in the Technology of Direct Skeletal Attachment: Large Animal Model

“…As the SBIP implants have been designed to encourage and enable deep skin permeation, there is a critical and vulnerable period-between implantation and full permeationthat requires methodological advances. Until the surrounding skin cells remodel within all of the implant's pores, special care to minimize the skin movements around the implant is required to protect the still non-occupied pores from bacterial infiltration (15)(16)(17). Minimizing skin movements during the initial period after transdermal implantation is especially important in the studies with large animals (pigs), since the activity of the massive musculature in the residuum and above may mechanically pull out the skin around the implant.…”

“…Our previous studies with pigs ( 18 ) showed that deep and sustainable ingrowth of skin into the porous cladding of the SBIP can be achieved after implantation into the pig’s dorsum. As to implantation into the residuum of the leg, the skin developed a stoma around the implant ( 15 , 17 ). There is an excess of the movable skin and soft tissues in the pig thigh; simple casting did not successfully immobilize the skin while the skin seal was developing.…”