Spine Model for Disc Replacement - Computational Biomechanics of the Musculoskeletal System - page 216

The PCM prosthesis (Figure 17.4) has two porous-surfaced Co-Cr endplates and a polyethylene
bearing surface attached to the endplate. The articulating surface of this device creates a larger
radius of articulation and increased translation.
Various cadaver and FEM studies to date have investigated biomechanical changes after
cervical TDR procedures. A simplified C3-C6 FE model (Sung 2006) with an elastomer-type
artificial disc was shown to reasonably restore the mobility of a spinal segment. It has been
reported that the ROM of a prosthesis implanted at C4-C5 was reduced by about 50% to 70%
during flexion, extension, and right lateral bending, whereas the ROM increased by about 18%
during axial rotation (Jirkova and Horak 2009). A recent in vitro experiment found that the ROM
was not statistically different between an implanted cervical spine and an intact one (Barrey
et al. 2009). It has been concluded that use of artificial disc prostheses did not alter the motion
patterns at either the instrumented level or adjacent segments compared with the harvested con-
dition, except in extension (DiAngelo et al. 2004).
Previous in vitro cervical spine studies analyzed the range of motion after one- and two-level
cervical arthroplasty versus arthrodesis and hybrid constructs (Cho et al. 2010). Cho's results dem-
onstrated that two-level arthrodesis decreases the entire ROM, whereas two-level arthroplasty
increases the entire ROM, and two-level arthroplasty does not significantly change the ROM at
the adjacent level. It has been highlighted that the operative-level ROM was preserved with one-
and two-level arthroplasty, whereas the ROM at the distal adjacent level increased by the greatest
amount after two-level arthrodesis (Cunningham et al. 2003).
Most previous biomechanical studies investigated the operative- and adjacent-level kinematic or
mechanical responses to single-level cervical disc arthroplasty. Few studies have qualified or ana-
lyzed fundamental biomechanical changes after multi-level cervical arthroplasty, which has seen a
recent surge in popularity.
Noticeable limitations remain with current models of spine arthroplasty. Improvements could
be made by incorporating (1) anisotropy of the bony structure; (2) proper prestress in muscles and
ligaments; (3) accurate properties for annulus fibrosus and nucleus pulposus; and (4) a spinal cord
and nerves.

FIgure 17.4 PCM prosthesis.