Biomechanical effects of the transcondylar approach on the craniovertebral junction.
The transcondylar variation of the far-lateral, retrosigmoid approach is intended for pathologies in the anterolateral portion of the foramen magnum. That area is more clearly visualized when a fraction of the ipsilateral occipital condyle is removed. In this study, the biomechanical effect of this approach on occiput-C2 rotation was investigated. Our hypothesis was that the biomechanical characteristics are significantly altered following the transcondylar approach. Five human cadaveric upper cervical spine specimens (occiput-C7) were used in the study. Torsional moments were applied from zero to a maximum of 1.5 N m to the left and to the right using a mechanical testing machine. The resulting rotational motions of the O-C1, C1-2, and O-C2 segments were measured in the intact specimen and after a simulated right-sided transcondylar approach with resection of 2/3 of the condyle, confirmed by CT scanning and visual inspection. After the posterior two-thirds of the occipital condyle were removed, the neutral zone (NZ) increased 1.3° to the left and 2° to the right at C0-C1, and 7.4° to the left and 6.2° to the right at C1-2. The cumulative increase in NZ between O and C2 was 8.7° to the left and 8.2° to the right. The transcondylar approach also resulted in significant increases in range of motion (ROM) in axial rotation to both sides in all segments. ROM increased 2.8° to the left and 2.4° to the right between C0 and C1, 7.3° to the left and 5.4° to the right between C1 and C2, and 10.1° to the left and 7.8° to the right between CO and C2. Upon inspection, the area of the occipital condyle where the alar ligament attaches had been completely removed in three of the five specimens. Removing the posteromedial two-thirds of one occipital condyle alters the normal axial rotational movements of the craniovertebral junction on both sides. The insertion of the alar ligament can be inadvertently removed during condylar resection, and this could contribute to atlanto-axial instability. There is a biomechanical substrate to cranio-cervical instability following a transcondylar approach; these patients may need to be followed over several years to ensure it does not progress and necessitate occipito-cervical fusion.
DFV Neuro, São Paulo, Brazil.
Alberto C
AC
Cardoso
Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois.
Ricardo B V
RB
Fontes
Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois.
Lee A
LA
Tan
Department of Neurological Surgery, University of Florida, Gainesville, Florida.
Albert L
AL
Rhoton
Department of Neurosurgery, Asan Medical Center, University of Ulsan, Seoul, Korea.
Sung W
SW
Roh
Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois.
Richard G
RG
Fessler
D000368:Aged; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology*; D001269:Atlanto-Occipital Joint / Q000033:anatomy & histology*; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology
anatomy; articular; atlanto-axial joint; atlanto-occipital joint; foramen magnum; neurosurgery; range of motion