Mechanical Strength of the Proximal Tibia Following Total Knee Arthroplasty: A Cadaveric Study of Resection Depth and Bone Density.

BACKGROUND: Tibial component failure has been a problem in total knee arthroplasty, it is still undetermined how tibial resection depth affects the strength to support a tibial component. This study examined the relationship between the resection depth and the bone density and the mechanical strength to support the tibial component. MATERIALS AND METHODS: Eight matched pairs of fresh, frozen cadaver lower legs were imaged with computed tomography to assess the bone density. A right tibia was resected at minimum resection level and a left tibia was resected at deep resection level. After the tibial component was implanted with cement on each tibia, it was loaded on a materials testing load frame to measure the stiffness and the load to failure. RESULTS: The average bone density at the minimum resection level of the tibia was significantly higher than at deep level (p=0.0003). The average stiffness and load to failure of the proximal tibia were 1105 N/mm (range 889 to 1303 N/mm) and 5626 N (range 3360 to 9098 N). There was no statistical correlation between tibial resection depth and the axial stiffness (p=0.4107) or the load to failure (p=0.1487). CONCLUSIONS: Although the bone density at a minimum resection level was higher than that at a deep level, the strength to support the tibial component was not statistically higher at a minimum cutting level than at a deeper cutting level proportionally. Surgeons may not need to minimize a proximal tibial bone resection to maintain a stronger support for a tibial component.

Primary Stability in Cementless Rotating Platform Total Knee Arthroplasty.

Highly porous ingrowth surfaces have been introduced into tibial tray fixation to improve long-term survivorship in cementless total knee arthroplasty. This study was designed to evaluate the effect of porous ingrowth surface on primary stability in the implanted cementless tibial component. Three tibial tray designs possessing sintered bead or roughened porous coating ingrowth surfaces were implanted into a foam tibia model with primary stability assessed via digital image correlation during stair descent and condylar liftoff loading. Follow-up testing was conducted by implanting matched-pair cadaveric tibias with otherwise identical trays with two iterations of ingrowth surface design. Trays were loaded and micromotion evaluated in a condylar liftoff model. The sintered bead tibial tray exhibited slightly lower micromotion than the roughened porous coating in stair descent loading. However, no significant difference in primary stability was observed in condylar liftoff loading in either foam or cadaveric specimens. Cementless tibial trays featuring two different iterations of porous ingrowth surfaces demonstrated both good stability in cadaveric specimens with less than 80 microns of micromotion and 1 mm of subsidence under cyclic loading. While improved ingrowth surfaces may lead to improved biological fixation and long-term osteointegration, this study was unable to identify a difference in primary stability associated with subsequent ingrown surface design iteration.