Stiffness and ultimate load of osseointegrated prosthesis fixations in the upper and lower extremity

Abstract

BackgroundTechniques for the skeletal attachment of amputation-prostheses have been developed over recent decades. This type of attachment has only been performed on a small number of patients. It poses various potential advantages compared to conventional treatment with a socket, but is also associated with an increased risk of bone or implant-bone interface fracture in the case of a fall. We therefore investigated the bending stiffness and ultimate bending moment of such devices implanted in human and synthetic bones.MethodsEight human specimens and 16 synthetic models of the proximal femora were implanted with lower extremity prostheses and eight human specimens and six synthetic humeri were implanted with upper extremity prostheses. They were dissected according to typical amputation levels and underwent loading in a material testing machine in a four-point bending setup. Bending stiffness, ultimate bending moment and fracture modes were determined in a load to failure experiment. Additionally, axial pull-out was performed on eight synthetic specimens of the lower extremity.ResultsMaximum bending moment of the synthetic femora was 160.6±27.5 Nm, the flexural rigidity of the synthetic femora was 189.0±22.6 Nm2. Maximum bending moment of the human femora was 100.4±38.5 Nm, and the flexural rigidity was 137.8±29.4 Nm2. The maximum bending moment of the six synthetic humeri was 104.9±19.0 Nm, and the flexural rigidity was 63.7±3.6 Nm2. For the human humeri the maximum bending moment was 36.7±11.0 Nm, and the flexural rigidity at was 43.7±10.5 Nm2. The maximum pull-out force for the eight synthetic femora was 3571±919 N.ConclusionSignificant differences were found between human and synthetic specimens of the lower and upper extremity regarding maximum bending moment, bending displacement and flexural rigidity. The results of this study are relevant with respect to previous finding regarding the load at the interfaces of osseointegrated prosthesis fixation devices and are crucial for the development of safety devices intended to protect the bone-implant interface from damaging loadings.

Transhumeral loading during advanced upper extremity activities of daily living

“…As a result, it is more useful to compare the loads herein to biomechanical investigations of periprosthetic fracture in the humerus. Welke et al has performed the only investigation that has examined fracture loads of a percutaneous OI stem placed in the diaphysis of cadaveric humeri [ 5 ]. In that investigation, the mean±SD bending failure load was found to be 36.7±11.0Nm.…”

“…European trials of percutaneous OI fixation in individuals with transhumeral amputation have employed torsional overload protection devices, and strict post-operative activity restrictions, to reduce the risk of periprosthetic fracture [ 3 ]. Yet only Welke et al have investigated the ultimate bending fracture load of a percutaneous OI device implanted in the diaphysis of cadaveric humeri [ 5 ]. Unfortunately, the forces and moments that the humerus withstands during daily activities are unknown.…”

In vitro and in silico methods for the biomechanical assessment of osseointegrated transfemoral prostheses: a systematic review

“…Experimental in vitro pull-out and push-out tests were performed at the time of in vitro implantation ( Welke et al, 2013 ; Jeyapalina et al, 2014 ; Barnes et al, 2019 ) and after 3-6-9-12 months ex vivo on sheep ( Jeyapalina et al, 2014 ). Micromotions were investigated both in vitro at the time of implantation ( Barnes et al, 2019 ), and through in silico simulated rehabilitation exercises ( Prochor and Anna Mierzejewska, 2019 ).…”

Upper extremity prosthetic selection influences loading of transhumeral osseointegrated systems

“…Drew & Taylor et al [ 22 ] tested a transhumeral porous coated implant for percutaneous OI attachment (DJO Surgical, Austin, Texas). Welke et al [ 26 ] tested an established cementless intramedullary stem (MUTARS Implantcast, Germany). * Overlap between failure and daily loading values …”

“…Though it is unlikely that these maximum daily loads will ever be imparted on the bone-implant interface with no stabilizing bone ingrowth, comparing these data to cadaveric time-zero mechanical testing represents an absolute worst-case condition. This comparison reveals an alarming overlap between daily loading and loads to failure of the bone-implant interface during the early post-operative period (Table 4) [22,26]. The range of axial pullout yield load (784.2-1818.1 N) [22] was at least 4.8x the maximum estimated axial force (161.9 ± 21.7 N).…”