# Prosthesis Embodiment in Lower Extremity Limb Loss: A Narrative Review
## 4 Results
### Ossoeintegration  
Ossoeintegration (OI) is a surgical procedure that can improve the prosthesis-residuum interface by directly anchoring a metal implant into the residual bone and then attaching the prosthesis to the metal implant through a transcutaneous connector through a small opening in the skin [62]. Bone integrates with the metal implant through bony ingrowth, fusing on a cellular level by forming connections between osteocytes and titanium oxide [25]. OI has been used for upper- and lower limb prostheses and compared to traditional socket prostheses has been shown to improve comfort [63], performance [64], use [65], and embodiment [23]. Today, there are three FDA-approved OI implant systems: Ossoeintegrated prostheses for the Rehabilitation of Amputees (OPRA), Integral Leg Prosthesis (ILP), and Ossoeintegrated Prosthetic Limb (OPL). OPRA was the first successful human OI implant system. It is implanted in a two-stage procedure: the first step is the attachment of a threaded titanium alloy bone implant and the second step is the coupling of a transcutaneous abutment to the implant and the creation of a stoma in the skin through which the abutment can protrude, where an external prosthesis can then be attached. Because OPRA is the most established of the OI implant systems, its effectiveness has been extensively studied, and OPRA is cost-effective for highly active amputees and is associated with a higher quality of life [8]. ILP and OPL consist of a stem similar to an intramedullary nail with a texture to promote bone ingrowth and a titanium niobium oxynitride surface to prevent adherence to the skin and promote gliding of the soft tissue. Retention is achieved by press-fit implantation, similar to hip arthroplasty, and the prosthesis is then mounted via a cone and screw system. Like OPRA, two stages are required to implant the ILP for use, while OPL requires only a single stage. With ILP, only 4 to 6 weeks are required between stages, unlike the 6 months required for OPRA. This results in a much shorter time between implantation and full-weight bearing, with only 2 to 3 months required after implantation of ILP and 3 to 18 months for OPRA [62]. Another method similar to the ILP and OPL in development is the Percutaneous Osseointegrated Prosthesis, which is shaped like a hip arthroplasty stem with a texture meant to promote bone ongrowth and features a niobium oxide abutment for soft tissue gliding. Compressive osseointegration, with the Compress(r) transcutaneous implant, is currently under investigation through a national FDA-approved clinical trial [66]. Designed into this device are integrated Belleville washers preloaded for 400, 600, or 800 pounds of axial force within the terminus of the residual femur. Through Wolff's law, it is hypothesized that such axial loading leads to bony hypertrophy of the femur terminus, thereby limiting loosening and bony resorption commonly seen with other non-compressive OI implants secondary to stress shielding. While patients are currently being enrolled, the first custom-designed compressive OI device was implanted at the University of Utah in 2012. Additional custom cases have been performed with published preliminary results [67]. By creating a stable, direct connection between the prosthesis and the user's skeletal system, OI dramatically enhances the user's sense of agency and control. This improvement is evidenced through measurements of more stable electromyographic (EMG) signals, indicating more efficient and controlled muscle activation patterns during prosthesis use [68]. Direct skeletal attachment also introduces biomechanical advantages that further enhance the user's experience and capabilities. Eliminating socket-related problems allows more physiological weight bearing, meaning that users can distribute forces through their residual limb in a way that more closely resembles the function of the natural limb [69].