Postmortem total knee replacement; cement, bone, and interface morphology

Bone volume fraction (BV/TV) has been shown to decrease as early as 3 month around the tibial tray in TKR.

Is there also changes at the tibial tray cement bone interface?

• Tibial tray sagittal sectioned every 10 mm with water cooled silicone carbide saw.
• Surfaces were polished and washed with water.
• High resolution images (6 microns/pixel) captured of each section.
• Cement, interdigitated bone, support bone (bone distal to cement), resorbed trabecular bone cavities (defined by cavities at distal cement that are smaller than 250 microns that appear like fossil trace of trabecular bone), and stem were masked by tracing in photoshop
• Divided section into parts:

peripheral tray - outside 5 mm of the tray

central tray - interior portion of tray not incluing the stem or keel

proximal stem/ keel - top 1/2 of the stem or keel

distalstem/ keel -bottom 1/2 of the stem or keel

• Areal measurements made in Image Pro of each part for each mask and then normalize by linear length of each part
• to calculate Contact Fraction, digitally grow resorb trabecular bone cavities, interdigitated, and support bone by 2 pixels.

Use boolean operation of each mask with cement, and measure area. Calculate length by dividing measures by 2 pixels length.

Each mask was divided by the appropriate linear length of each part.

• To calculate interdigitation length, the interdigitated cement was defined by a 2 mm rule. This was determined by traveling around the cement and connecting the outermost protrusion of bone within at most a 2 mm linear span.

This was also performed the same for the resorb trabecular cavities (original interdigitated cement)

Image Pro calculated the average, min and max thickness of the interdigitated cement for each part of the section.

• All parts were summed and then average for each section values.
• Sections were summed and then divided for values of medial vs lateral.
• All sections were summed and divided for average values for donor bones.

Dramatic Spatial and temporal changes at the Cement Bone Interface with postmortem TKR

Used tibial trays from postmortem specimens with varying implant time in service to examine the spatial and temporal changes

with the cement bone interface of the tibial tray.

Examine 7 specimens (6 postmortems, 1 lab prepared which represents time at surgery)

We hypothesis:

early and continual bone loss occurs around implant tibial tray,

substantial less loss of bone will occur at the distal stem/ keel than the tray.

most loss of bone will occur at the peripheral tray,

contact between the cement and the bone will be maintained over time,