Simulated bone remodeling around two types of osseointegrated implants for direct fixation of upper-leg prostheses

Abstract

Direct attachment of an upper leg prosthesis to the skeletal system by a percutaneous implant is an alternative solution to the traditional socket fixation. In this study, we investigated long-term periprosthetic bone changes around two types of fixation implants using two different initial conditions, namely immediate post-amputation implantation and the conventional implantation after considerable time of socket prosthesis use. We questioned the difference in bone modeling response the implants provoked and if it could lead to premature bone fracture. Generic CT-based finite element models of an intact femoral bone and amputated bone implanted with models of two existing direct-fixation implants, the OPRA system (Integrum AB) and the ISP Endo/Exo prosthesis (ESKA Implants AG) were created for this study. Adaptive bone-remodeling simulations used the heel-strike and toe-off loads from a normal walking cycle. The bone loss caused by prolonged use of socket prosthesis had more severe effects on the ultimate bone quality than adaptation induced by the direct-fixation implants. Both implants showed considerable bone remodeling; the titanium screw implant (OPRA system) provoked more bone loss than the porous coated CoCrMo stem (ISP implant). The chance of the peri-prosthetic bone fracture remained higher for the post-socket case as compared to the direct amputation cases. In conclusion, both direct-fixation implants lead to considerable bone loss and bone loss is more severe after a prolonged period of post-socket use. Hence, from a biomechanical perspective it is better to limit the post-socket time and to re-design direct fixation devices to reduce bone loss and the probability of peri-prosthetic bone fractures.

Effect of load on the bone around bone-anchored amputation prostheses

“…This is in agreement with a radiographic follow‐up of a patient cohort, where no bone resorption was observed in the zones distal to the implant, as well as no cortical thinning in this zone in the majority of cases . Further, this distal zone has not been considered in previous modeling of the implant system, where no countersinking of the implant was present which is likely to change the overall distribution of loads significantly, as the lever arm is lengthened, thereby altering the moment in flexion. The clinically retrieved sample in the current study showed a preserved bone height at distal level after 15 years in vivo.…”

Design features of implants for direct skeletal attachment of limb prostheses

“…To meet the existing challenges faced by DSA, the development of new designs and methodologies for reducing the associated risks continues. New challenges may arise with the promising use of the transcutaneous implants for neuromuscular control of the limb prostheses .…”

“…22,24,87,92 An additional concern for longevity of the bone-device bond is that after replacement surgery, the porosity of the cortical bone hosting the femur implant increases compared to the ipsilateral bone, potentially reducing cortical bone strength. 93,94 To meet the existing challenges faced by DSA, the development of new designs and methodologies for reducing the associated risks 95,96 continues. New challenges may arise with the promising use of the transcutaneous implants for neuromuscular control of the limb prostheses.…”

Micromotion and Push‐Out Evaluation of an Additive Manufactured Implant for Above‐the‐Knee Amputees

“…These procedures do not have the same socket‐related soft tissue issues, facilitate quick attachment of the amputee's prosthesis, transfer load directly to the residual femur, and enable osseoperception whereby the amputee can discern the type of surface they are walking on . Downsides to direct skeletal attachment include a risk of superficial and deep infection through the skin opening, a risk of femoral fractures, implant extraction, high proximal revision, and potential bone resorption due to stress shielding . Despite the variety of devices, it appears that many surgeons remain unhappy with the concept of a permanent percutaneous implant.…”

“…6 Downsides to direct skeletal attachment include a risk of superficial and deep infection through the skin opening, a risk of femoral fractures, implant extraction, high proximal revision, and potential bone resorption due to stress shielding. [13][14][15][16] Despite the variety of devices, it appears that many surgeons remain unhappy with the concept of a permanent percutaneous implant. Subcutaneous implants have been developed: in the 1960s Swanson et al 17 developed a mushroom-shaped silicone implant in an attempt to improve end bearing.…”