Biomedical Engineering Reference
In-Depth Information
Over the years, extensive research on socket design and interaction between bio-
logical tissue and synthetic components has been conducted [
74
]. This partly orig-
inated when Brånemark [
75
] showed that living bone could become so fused with
the titanium oxide layer of an implant that the two could not be separated without
fracture, which is basically known as “oseointegration”. Nowadays, this principle has
been used for the design of prosthetic limbs commonly referred as osseointegrated
prosthesis. These devices are anchored in the residual femur and protrude through
the skin and soft tissue which allows the prosthesis attachment to an abutment. Clin-
ical results show an improvement in the quality of life of patients with this type of
prosthesis [
76
].
Recent studies illustrated the danger of skeletal and implant fractures of osseoin-
tegrated prosthetic interfaces [
77
]. The main risk of such fractures not only arises
from torsional loads but also in the mechanical loosening by bending moments. Thus,
it is important to define thresholds of forces and bending moments during activities
of daily living and during highrisk situations such as falling, since approximately
half of the population with a lower extremity amputation experiences a fall at least
once a year.
The TExoPro cooperative was funded by the Bundesministerium für Bildung
and Forshung (BMBF AZ: 01EZ0775, Federal German Ministry of Education and
Research) in order to deal with the persistent issues of microbiological infection in
the percutaneous passage and possible bone-implant interface overloading. In this
context, it was important to investigate the loads in the region of the prosthesis in
activities of daily living and risk situations, more specifically during falling.
However, as direct measurement is not possible for obvious practical and ethical
reasons, the loads acting on the interface of osseointegrated fixation and attached
prosthesis were investigated in the present study with a multi-body simulation in dif-
ferent cases of falling. As mentioned at the beginning of this chapter, multi-body sim-
ulations (MBS) offer the possibility to determine loads of the musculoskeletal system
in a non-invasive manner allowing the investigation of cases like falling scenarios.
Due to the highly accessible situation of above-knee amputees it is feasible to
measure forces and moments directly at the prosthesis interface with a six degrees
of freedom strain-gauge based transducer. Therefore, a comparison of calculated
and measured data was also conducted to validate the numerical model prior to the
evaluation of falling scenarios. The aim of the study was to provide upper bounding
of loading conditions to serve as design parameters for a safety element in order to
prevent skeletal fractures and implant failure.
Validation of the multi-body simulation
Six subjects with one-sided above-knee amputation were fitted with a C-Leg (Otto
Bock Healthcare Gmb, Göttingen, Germany) exoprosthesis and a conventional
socket. Level walkingwas performed in the gait laboratory of the LBB-MHH. Kinetic
and kinematic data was recorded with a VICONmotion capturing system (8 cameras
