The Role Of Articular Surface Fibrous Layer In The Genesis Of Traumatic Temporomandibular Joint Ankylosis:An Experimental Study

Part 1: Preserving the fibrous layer of the mandibular condyle reduces the risk of ankylosis in a sheep model of intracapsular condylar fracture Purpose: The aim of this experimental study was to investigate the role of the fibrous layer of the condylar head in the formation of temporomandibular joint(TMJ)ankylosis in a sheep model of intracapsular condylar fracture.Materials and Methods: Six growing Xiao-wei Han sheep were used in the study,and bilateral TMJ surgery was performed for each sheep.On the left TMJ,sagittal fracture of the condyle,removal of the fibrous layer of the condylar head,excision of 2/3 of the disc,and removal of the fibrous zone of the glenoid fossa,were performed.On the right TMJ,the same surgical management was performed,except that in each sheep the fibrous layer of the condylar head was preserved.Three sheep were sacrificed at 1 month postoperatively,and the other 3 sheep were sacrificed at 3 months postoperatively.One day before sacrifice,the maximum mouth opening vertically and body weight were measured.The TMJ complexes were examined by histological evaluation.Results: Fibrous ankylosis was observed on the left side of 3 sheep at 1month postoperatively,and 2 of 3 sheep at 3 months postoperatively.Fibro-osseous ankylosis was achieved on the left side of 1 sheep at 3 months postoperatively.On the right TMJ,the main postoperative histological findings included condylar fracture healing,topical rupture or exfoliation of the fibrous layer of the condyle,and the fissure between the fibrous layer and the proliferative zone of the condyle.However,no evidence of ankylosis was observed.The scores of TMJ ankylosis for the right side were significantly lower than that of the left side at different time points(P < 0.05).Conclusion: This study demonstrated that the presence of the fibrous layer of the condylar head prevented the development of TMJ ankylosis in a sheep model of intracapsular condylar fracture.Part 2: Removal of the articular fibrous layers with discectomy leads to traumatic temporomandibular joint ankylosis Purpose: The aim of this experimental study was to investigate whether the direct damage of the articular fibrous layers without condylar fracture,combined with discectomy,was enough to induce temporomandibular joint(TMJ)ankylosis.Materials and Methods: Eight growing Xiao-wei Han sheep were used in the study,and bilateral TMJ surgery was performed for each sheep.On the left TMJ,the excision of the lateral 2/3 of the disc and the removal of the fibrous layers of the condylar head and the glenoid fossa,were performed.On the right TMJ,only the lateral 2/3 of the disc was excised.Four sheep were sacrificed at 1 month postoperatively,and the other 4 sheep were sacrificed at 3 months postoperatively.One day before sacrificethe,body weight was measured.The TMJ complexes were examined by histological evaluation.Results: Fibrous ankylosis was achieved on the left side of the 2 of 4 sheep,and fibro-osseous ankylosis in the other 2 sheep at 1 month after surgery.Fibro-osseous ankylosis developed on the left side of 4 sheep at 3 months postoperatively.On the right TMJ,the main postoperative histological findings included topical crack or exfoliation of the fibrous layer of the condyle,the multiple fissures and the chondrocyte differentiation of the proliferative zone of the condyle,the thickening proliferative zone,and the proliferation of the articular facet of the glenoid fossa with the chondrocytic cluster in the fibrous layer.However,no evidence of ankylosis was observed.The scores of TMJ ankylosis for the right side were significantly lower than that of the left side at different time points(P < 0.05).Conclusion: This study demonstrated that removal of the articular fibrous layers with discectomy can lead to traumatic TMJ ankylosis.