gms | German Medical Science

Problem: Biophysical stimuli may be an effective therapy to counteract age-related changes in bone structure, which affect the osseointegration and thus, the primary stability of implants used in joint replacement or fracture fixation. The influence of controlled mechanical loading on osseointegration was investigated using an in vivo device implanted in the distal lateral femur of twelve male rabbits.

Methods: Compressive loads (1 MPa, 1 Hz, 50 cycles/day, 4 weeks) were applied to a porous titanium foam cylindrical implant (5 mm diameter, 2 mm length, 74% porosity, 565 µm mean void intercept length) and the underlying cancellous bone, while the contralateral limbs served as unloaded controls. The amount of bone impacted into the implant during surgery and the basal mineral apposition rate was determined at time zero in two rabbits. A scanning electron microscope with a backscattered electron detector was used to quantify the amount of bone ingrowth and periprosthetic bone in undecalcified sections. The histological characteristics of bone ingrowth and periprosthetic bone were also compared between implants that had undergone loading and bilateral unloaded control implants. A mixed effects model was used to account for the correlation of the outcome measures within rabbits.

Results and conclusion: Backscattered electron imaging indicated that the amount of bone ingrowth was significantly greater in the loaded limb (21±4%) compared to the unloaded control limb (15±5%, p=0.03). The amount of underlying cancellous periprosthetic bone was not significantly different between the loaded (29±8%) and unloaded control limb (25±9%, p=0.37). Fluorescent microscopy indicated that there was no significant difference in the mineral apposition rate of the bone ingrowth or periprosthetic bone measured in the loaded compared to the control limb. Although there was an increased amount of bone ingrowth in the loaded implants, histological analysis demonstrated that the quality of osseointegration was similar. Newly formed woven bone was observed in direct apposition to the coatings in both loaded and unloaded implants. These data indicate that cyclic mechanical loading significantly enhanced the amount of cancellous bone ingrowth into a porous titanium foam implant. These results suggest that biophysical therapy should be further investigated to augment current treatments to enhance long-term cementless fixation.