Does using autograft bone chips achieve consistent bone ingrowth in primary TKA?

Abstract

Background: Cementless fixation remains controversial in TKA due to the challenge of achieving consistent skeletal attachment. Factors predicting durable fixation are not clearly understood, but we presumed bone ingrowth could be enhanced by the quantity of host bone and application of autograft bone chips.

Questions/purposes: We asked: (1) Did the amount of bone ingrowth exceed the amount of periprosthetic and host bone with the addition of autograft bone chips? (2) Did the amount of bone ingrowth increase with implantation time? And (3) did osteolysis along the porous-coated interface and screw tracts progress with implantation time?

Methods: We measured the amount of bone in the porous-coated, periprosthetic, and host bone regions in 19 postmortem retrieved cementless primary total knee implants. The amount of bone in apposition to the implant surface, and alternatively lysed bone, was analyzed radiographically to assess the progression of osteolysis.

Results: While bone ingrowth tended to be less than periprosthetic and host bone in all three components, it was only significantly less in the patellar component. Bone ingrowth increased in all three components over time, but progression of osteolysis did not.

Conclusions: Even after long-term followup, the amount of bone ingrowth did not surpass host bone levels, suggesting the amount of a patient's host bone is a limiting factor in the amount of bone ingrowth achievable for this cementless design. It remains unknown whether compromised osteopenic bone could achieve the amount of bone attachment necessary to provide durable fixation over time.

Fig. 1A–C

Gross photographs show (A) the patellar component, (B) tibial component with its asymmetrical design, and (C) femoral component of the Natural-Knee^® System and porous-coated surfaces.

Fig. 2

The image shows high-resolution contact radiographs of 3-mm-thick sections from the right patella of one of the donors used to measure the ABI. This patellar implant had been in situ for 84 months and had a high percentage of bone in apposition to the porous-coated interface (original magnification, ×1).

Fig. 3A–C

BSE images illustrate the three regions used for analysis of bone ingrowth: (A) porous-coated region, (B) periprosthetic region, and (C) host bone region (original magnification, ×40). The periprosthetic interface region was in direct apposition to the porous-coated interface, whereas the host bone was 3 mm from the porous-coated interface.

Fig. 4A–B

(A) A gross radiograph and (B) high-resolution contact radiograph from the same specimen show projection effects inherent with gross radiography, making detailed regional observations difficult but showing the superior detail with high-resolution contact radiographs.

Fig. 5A–C

High-resolution contact radiographs of the (A) femur, (B) tibia, and (C) patella show the regions used for reporting osteolysis (Table 4).

Fig. 6A–F

Graphs show (A, C, E) the mean bone percent in each region (porous-coated ingrowth [PC], periprosthetic interface [PP], and host bone [HB]) and (B, D, F) the mean ABI data as they vary over time of implantation for each of the components: (A, B) patella, (C, D) tibia, and (E, F) femur.

Fig. 7A–D

(A, C) Full-sized and (B, D) detailed gross images taken from the bilateral patellas of Donor 12 show differences in wear patterns in the patellas of the same patient. (A, B) The left patella was implanted for 238 months (> 19 years) and showed extensive delamination of the surface with edge damage. (C, D) The right patella was implanted for 239 months and showed extensive metal back edge wear with metallosis.