Comparison of Cervical Stabilization with Transpedicular Pins and Polymethylmethacrylate versus Transvertebral Body Polyaxial Screws with or without an Interbody Distractor in Dogs.

OBJECTIVE: The main aim of this study was to compare the biomechanical properties of caudal cervical vertebral stabilization using bicortical transpedicular pins with polymethylmethacrylate (PMMA) versus transvertebral body polyaxial screws and connecting rods with or without an interbody distractor. STUDY DESIGN: Ten canine cervical vertebral columns (C2-T3) were used. Four models (intact, transvertebral body polyaxial screw with interbody distractor [polyaxial + distractor], transvertebral body polyaxial screw without interbody distractor [polyaxial - distractor] and bicortical transpedicular pins/polymethylmethacrylate [pin-PMMA]) were applied to C6-7 sequentially on the same specimens. Angular range of motion (AROM) in the form of flexion and extension was measured at C4-5, C5-6 and C6-7 in all groups. RESULTS: Treated vertebral specimens had significantly less AROM than unaltered specimens. There was no significant difference in AROM between the experimental groups at C6 and C7. Angular range of motion ratio in flexion-extension was 80.8, 72.7 and 78.3% for polyaxial + distractor, polyaxial - distractor and pin-PMMA groups, respectively, which were less than the intact group. There was no significant increase in the range of motion of the adjacent vertebrae after stabilization. CONCLUSION: Stabilization obtained with transvertebral body polyaxial screws was comparable to that from the well-established bicortical pins/PMMA construct. Association of an intervertebral distractor did not change AROM of the polyaxial screw constructs.

Post mortem evaluation of spinal cord and protruded intervertebral discs in dogs without neurological abnormalities / Avaliação post mortem da medula espinhal e de discos intervertebrais protrusos em cães sem alterações neurológicas

The aim of this study was to verify the presence of protrusion of the intervertebral disc (IVD) causing compression of the spinal cord and/or roots of cauda equina in 30 dogs above seven years of age with no evidence of previous neurological abnormalities. After the occurrence of death or euthanasia, a laminectomy was performed from C2 to the sacral vertebra to verify the presence of IVD protrusions. The protruded IVD were macroscopically graded according to the Thompson scale, and the corresponding spinal cord segment was histologically analyzed for nervous tissue compression. Of the 30 dogs, twelve (40%) presented disc protrusion, and of these 12 dogs, seven (58%) presented more than one protruded disc. Disc protrusion was observed in 3.2% (25/780) of all IVD evaluated. Of the six chondrodystrophic dogs, five (83%) presented disc protrusion. Of the 24 nonchondrodystrophic dogs, seven (29%) presented IVD protrusion. The site that showed the highest frequency of protrusion was L4-L5 (6/25) followed by the L6-L7 region (3/25) and C6-C7 (3/25). Only two of the medullary segments evaluated showed histological changes, with presence of focal lymphocytic infiltration and multifocal mild hemorrhage in the gray matter. Under the conditions of this study, 40% of dogs older than seven years old showed IVD protrusions without showing neurological signs, with no abnormality of the nervous tissue in 92% of the evaluated segments. Thus, the protrusion of the IVD in some dogs, can only be a finding of no clinical relevance.(AU)

O objetivo do presente estudo foi verificar a presença de protrusão do disco intervertebral (DIV) causando compressão da medula espinhal e/ou raízes da cauda equina em cadáveres de cães, sem histórico de alterações neurológicas. Para isso, após a ocorrência de óbito ou realização de eutanásia em 30 cães com mais de sete anos de idade, sem histórico de alterações neurológicas, foi realizada a laminectomia entre C2 até a vértebra sacral para verificar a presença de protrusões do DIV. Os DIV protrusos foram graduados macroscopicamente quanto à degeneração segundo a escala de Thompson, e o segmentos medular correspondente à localização da compressão foi analisado microscopicamente em busca de lesões compressivas ao tecido nervoso. Quarenta por cento dos cães (12/30) apresentaram protrusão do DIV, e destes, 58% (7/12) apresentavam mais de um DIV protruso. A protrusão estava presente em 3,2% (25/780) de todos os DIV avaliados. Cães de raças condrodistróficas apresentaram protrusões em 83% dos casos (5/6) e raças não condrodistróficas em 29% (7/24). O local que apresentou maior frequência de protrusão foi L4-L5 (6/25), seguido da região L6-L7 (3/25) e C6-C7 (3/25). Apenas dois segmentos medulares avaliados na histopatologia apresentaram alterações, com presença de infiltrado linfoplasmocitário focal e hemorragia discreta multifocal na substância cinzenta. Nas condições do presente estudo, 40% dos cães com mais de sete anos de idade apresentaram protrusões do DIV sem que houvesse sinais neurológicos, com normalidade do tecido nervoso em 92% dos segmentos avaliados. Assim, a protrusão do DIV, em alguns cães, pode ser apenas um achado sem relevância clínica.(AU)