CONSOLIDATION OF CRANIOTOMY LINES AFTER RESORBABLE POLYLACTIDE AND TITANIUM PLATING - A COMPARATIVE EXPERIMENTAL-STUDY IN SHEEP

The consolidation process of craniotomy lines in a skeletally immature large mammal was studied. A traditional narrow titanium miniplate was compared with a 0.5-mm-thick, 12-mm-wide absorbable punched self-rein forced poly-L-lactide (SR-PLLA) plate, both fixed with titanium minisc rews over bilateral parietal 2.5-mm-wide stable transosseous craniotom ies on nine female sheep (16 to 20 months old). After 6, 12, 20, 52, a nd 104 weeks, cross-sectional histology, histomorphometry, and oxytetr acycline chloride fluorescence studies were done to compare the healin g process of the craniotomy lines and to study the biocompatibility an d the degradation process of the SR-PLLA plate. The consolidation patt ern supported the principle of guided tissue regeneration: under the w ide, resorbable plate osseous bridging proceeded evenly throughout the line, whereas titanium plating led to bulky, uneven growth in the bon e margins. All SR-PLLA-plated osteotomy lines had healed completely by 20 weeks, whereas none of the titanium-plated lines had consolidated during a follow-up of 1 year. The nonossified gaps were filled with de nse connective tissue. Histomorphometric analysis showed that osseous bridging proceeded significantly faster on the resorbable plate side c ompared with the titanium side (p < 0.001). The osteoid surface fracti on over the total trabecular surface was highest at 6 weeks, being 63 percent on the SR-PLLA side and only 36 percent on the titanium side. The oxytetracycline chloride fluorescence studies confirmed these find ings. After 52 weeks, there was no osteoid or oxytetracycline chloride fluorescence left as a sign of terminated ossification, even in the n onconsolidated titanium sides. Microscopic cracking of the plate was e vident at 12 to 20 weeks, and the first signs of active resorption wer e present at 52 weeks. After 2 years, the plate had disappeared and ti ny polylactide particles were being actively resorbed. The biocompatib ility of SR-PLLA and titanium was good, and no adverse cellular reacti ons to these materials were noted, except a clinical foreign body reac tion caused by loosened titanium miniscrews. A densely punched, 0.5-mm -thick self-reinforced PLLA plate seems to retain its integrity for a sufficiently long time to complete osseous healing of a 2.5-mm-wide cr aniotomy line in the sheep calvarial area. A thin, wide fixation plate enables superior healing, especially in osseous defects. The degradat ion process of the SR-PLLA plate begins within 1 year and is far advan ced after 2 years. By using absorbable SR-PLLA fixation plates instead of metallic plates, a subsequent operation for the removal of the imp lants can be avoided. SR-PLLA devices could thus be a potential additi ve or even alternative to metallic implants in craniofacial surgery.