Analysis of torque stability and cement penetration using a stemless rimmed cemented tibial component in cadaveric tibia

Loosening of the tibial component continues to be a major cause of failure in cemented total knee arthroplasty. Much of the cement applied to the device does not penetrate evenly into the trabecular bone due to cement leakage along the outer margins of the component during implantation which may ultimately translate into compromised fixation. Achieving uniform penetration to 3 - 4 mm has presented a challenge with current implants. A new stemless rimmed cemented tibial component (SRCTC) was designed featuring a 3 mm rim patterned in the perimeter shape of the Zimmer Natural Knee II (NKII) tibial baseplate and the elimination of the antirotational stem extending from the center. The purpose of the 3 mm rim was to provide a cement well that limits outer margin leakage, promotes uniform cement penetration, and is 80% shorter in profile than the NKII implant. The goal of this thesis was to compare the SRCTC s rotational stability, cement containment, and cement penetration characteristics against those of the NKII. Six pairs of cadaveric tibia with similar demographics were implanted with the SRCTC and NKII and subjected to torsonial testing. Specimens were sectioned and analyzed using backscattered electron microscopy and image analysis software. Tibias implanted with the SRCTC had on average significantly more trabecule in the cement mantle (p=0.02) and those trabecule were closer to the underside of the implant (p=0.06). No significant differences between the two implants were noted following torque testing (p=0.42). The means of cement penetration depth along the length of the implant (p=0.18) and at the perimeter (p=0.13) differed, but were also not significant. The SRCTC s rim limited cement extrusion during implantation for all tibial pairs, potentially reducing the threat of third body wear following implantation. Comparable levels of rotational stability and cement penetration depths for an 80% shorter implant may be an asset to future minimally invasive surgical procedures. Future studies may incorporate axial loads to replicate tibial forces experienced in vivo. Lever-out mechanical testing may also provide further insight into the posterior and anterior stability of the SRCTC implant versus other implants containing stems like the NKII.