RESTORATION OF TISSUE-COMPONENTS AFTER INSERTION OF ABSORBABLE FRACTURE FIXATION DEVICES OF POLYGLYCOLIDE THROUGH THE ARTICULAR SURFACE - AN EXPERIMENTAL-STUDY IN THE DISTAL RABBIT FEMUR

Absorbable implants for fracture fixation do not require a secondary removal procedure, a fact that could make them particularly suitable for intra-articular fixation, provided the degree of regeneration of the articular surface is acceptable. To determine the restoration pattern in distal rabbit femurs after the intra-articular insertion of absorbable fixation devices, polyglycolide pins and screws were implanted through the articular surface of the intercondylar portion of the bone in adult animals. The polymer was known to have a degradation time of approximately 20 weeks. At follow-up times of 3-48 weeks, the restoration of the tissue components was examined histomorphometrically and microradiographically. The intact contralateral femur served as an internal control. The first signs of degradation of the implants were seen at 6 weeks. The mean fractional osteoid formation surface of the bone trabeculae within the sample fields showed significantly increased values until 6 weeks but thereafter approached the level of the control femur. In the 36-week and 48-week specimens, the polyglycolide had been absorbed and the intra-articular entrance of the implant channel had become filled either with firm whitish tissue resembling mature articular cartilage or with soft undifferentiated mesenchymal tissue only. Good restoration of the trabecular bone architecture corresponding to the original subchondral bone was a prerequisite for the regeneration of the articular cartilage. The causes of the dichotomous pattern of restoration could not be identified, but possibly it represented a normal biologic variation. Since instability associated with fracture fixation, not an issue of this study, could affect the quality of tissue restoration, the present findings call for caution if large-diameter absorbable devices are to be inserted through articular surfaces in clinical practice.