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 r emoval procedure, a fact that could make them particularly suitable fo r 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 absorb able fixation devices, polyglycolide pins and screws were implanted th rough the articular surface of the intercondylar portion of the bone i n adult animals. The polymer was known to have a degradation time of a pproximately 20 weeks. At follow-up times of 3-48 weeks, the restorati on of the tissue components was examined histomorphometrically and mic roradiographically. The intact contralateral femur served as an intern al control. The first signs of degradation of the implants were seen a t 6 weeks. The mean fractional osteoid formation surface of the bone t rabeculae within the sample fields showed significantly increased valu es until 6 weeks but thereafter approached the level of the control fe mur. In the 36-week and 48-week specimens, the polyglycolide had been absorbed and the intra-articular entrance of the implant channel had b ecome filled either with firm whitish tissue resembling mature articul ar cartilage or with soft undifferentiated mesenchymal tissue only. Go od restoration of the trabecular bone architecture corresponding to th e original subchondral bone was a prerequisite for the regeneration of the articular cartilage. The causes of the dichotomous pattern of res toration could not be identified, but possibly it represented a normal biologic variation. Since instability associated with fracture fixati on, not an issue of this study, could affect the quality of tissue res toration, the present findings call for caution if large-diameter abso rbable devices are to be inserted through articular surfaces in clinic al practice.