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nerves and provide a denervated recipient bed for subsequent reinnervation via a mechanism similar to
[52]
TMR . Feasibly, these nerve/muscle units could also be used to form a neural interface with a myoelectric
[53]
prosthesis, but current studies have been limited to animal models thus far . The main benefit of RPNI is
its surgical efficiency because the time consuming process of identifying appropriate recipient motor nerves
is omitted. At our institution, we employ RPNI as a backup to TMR in unstable patients or when donor
nerves are limited due to scar burden or other unfavorable patient pathology.

Finally, the vast majority of the surgical experience with TMR in the lower extremity is in trauma or
oncologic patients. These patients represent a different cohort than the majority of amputees, who suffer
from limb loss secondary to diabetes and vascular disease and are much more likely to experience
longstanding pre-amputation neuropathy. One of the main unanswered questions is whether TMR is
effective for pain relief and prevention in the diabetic vasculopath. We seek to answer this question in the
near future at our institution.

OSSEOINTEGRATION
Background
While TMR offers the potential for markedly improved prosthetic control, the control benefits of the
technique can only be realized if the prosthetic is actually used. While this seems to be an obvious pre-
requisite, at least 35% of upper limb amputees completely abandon use of their prostheses due to socket-
[54]
related limitations or discomfort . Lower limb amputees use their prostheses more consistently, but
frequently must endure pain or soft tissue problems to maintain their mobility. In addition, a substantial
cohort of patients with limb loss have residual limbs that are too short to be candidates for a conventional,
socket-based prosthesis. Even in limbs sufficiently long enough to be fit with a socket, the cylindrical
shape of most transhumeral and transfemoral amputations presents challenges with regard to suspension
and rotation control that plague conventional liner and socket systems. The additional support straps or
harnesses required to adequately support the device further limit range of motion and impart additional
difficulty with donning and doffing of the prosthetic. Likewise, efforts to overcome the intrinsic design
flaw of socket-based strategies frequently employ closed suction environments and/or occlusive liners that
[55]
predispose to irritation, breakdown, and soft tissue infection .
Direct skeletal attachment of extremity prostheses through OI of a percutaneous implant offers a means
to circumvent the limitations imposed by the conventional liner and socket fitting strategy [Figure 5]. OI
obviates the need to bear weight or control the prosthetic device through a soft tissue intermediary. This
translates into enhanced suspension, finer control, greater ease of use, reduced energy expenditure, and
increased range of motion in the immediate proximal joint [56-58] .

In addition, OI offers a pathway to successful prosthetic use even in the setting of an insufficient soft tissue
envelope or skeletal length that precludes fitting of a socket. In this way, OI expands the reconstructive
possibilities and maximizes rehabilitative potential following limb loss.

OI of percutaneous implants for attachment of major limb prostheses has been in limited clinical use for nearly
30 years. The concept of placing titanium implants into living bone was first introduced by Bothe et al.
[59]
in 1940. However, the clinical potential of implanted titanium was not fully realized until Per Ingvar
Branemark made the serendipitous discovery of bony in-growth while using titanium chambers to study
[60]
bone microcirculation in a rabbit model . The process, which Branemark described as “osseointegration”,
served as the foundation for use of titanium implants in dental restoration. OI was first adapted for
use in major limb amputees by Rickard Branemark, an orthopedic surgeon and the son of Per Ingvar
Branemark, with the first procedure performed in a bilateral transfemoral amputee in 1990 . Leveraging
[61]