Performance evaluation of pelvic symphyseal implants
The pelvis is a ring-like structure of bones at the lower end of the trunk. Strong connective tissues join the pelvis bones to the large triangular bone (sacrum) at the base of the spine. On each side, there is a hollow cup (acetabulum) that serves as the socket for the hip joint. The pelvic ring is made up of three bones and several ligaments. The pubic symphysis is the anterior ligament that keeps the pelvic ring intact. Pelvic ring disruptions are commonly caused by car and motorcycle accidents. Roughly one quarter of the people that die in car accidents sustain pelvic fracture. Around one half of the deaths caused by high speed motorcycle or pedestrian-automobile accidents sustain a disrupted pelvic ring.[1] These accidents cause high impact force to the pelvis. Impact to the pelvis can cause one or more of the bones to break along with the tearing of ligaments that keep the pelvic ring intact.
The pubic symphysis is essential in the stability of the pelvic ring. Without an intact pubic symphysis, the pelvic ring is compromised and small forces can cause bones or other ligaments to fail. Pelvic ring failures occur in three main modes: anteroposterior compression, lateral compression, and vertical shear injuries. Pubic symphysis tearing is typically associated with all three modes of failure. Thus there is a great need to find a method that would properly simulate an intact pubic symphysis so that the body can repair itself and the patient can regain a high quality of life.
Before new prosthetics can be designed, for this injury the properties of the system need to be found. Analysis of the currently available prosthetics can also aid in developing new designs by finding their limitations. Study of the pelvic ring will ultimately lead to a prosthetic that can adequately mimic the pubic symphysis long enough for the body to repair itself. This project deals with evaluation of two types of prosthesis for pubic symphysis; the locking plate and the compression plate.
The displacement characteristics across pubic joint with intact pubic symphysis in reaction to load through femur is first measured using micron-resolution LVDTs. Then the symphysis is cut artificially and the implants are placed. Then the displacement characteristics across the pubic joint is again measured.
Initial results show that both the implants are inferior to their performance characteristics when compare to pubic symphysis. However, the characteristics of locking plate is slightly better than the compression plate.
Testing of Displacement across illiac joint with implant in placeĀ
TTU, Mechanical Engineering Dept., 7th and Boston, Lubbock, TX 79409
(806) 742-3563