Arnaud Germaneau1, Tanguy Vendeuvre2, Alexandre Delmotte3, Samuel D'Houtaud4, Cyril Brèque5, Louis Petureau6, Pascal Doumalin6, Jean-Christophe Dupré6, Fabrice Brémand6, Philippe Maxy7, Jean-Pierre Richer8, Philippe Rigoard2. 1. Institut Pprime UPR 3346, CNRS - Université de Poitiers - ISAE-ENSMA, France; Spine & Neuromodulation Functional Unit, Department of Neurosurgery, CHU Poitiers, PRISMATICS Lab, Poitiers, France. Electronic address: arnaud.germaneau@univ-poitiers.fr. 2. Institut Pprime UPR 3346, CNRS - Université de Poitiers - ISAE-ENSMA, France; Spine & Neuromodulation Functional Unit, Department of Neurosurgery, CHU Poitiers, PRISMATICS Lab, Poitiers, France. 3. Spine & Neuromodulation Functional Unit, Department of Neurosurgery, CHU Poitiers, PRISMATICS Lab, Poitiers, France; Centre du Rachis de la Sauvergarde, 69009 Lyon, France. 4. Spine & Neuromodulation Functional Unit, Department of Neurosurgery, CHU Poitiers, PRISMATICS Lab, Poitiers, France; Service de Neurochirurgie Clinique, La Rochelle, France. 5. Institut Pprime UPR 3346, CNRS - Université de Poitiers - ISAE-ENSMA, France; ABS Lab, Université de Poitiers, France. 6. Institut Pprime UPR 3346, CNRS - Université de Poitiers - ISAE-ENSMA, France. 7. Medtronic, Medtronic International Trading Sarl, Tolochenaz, Switzerland. 8. ABS Lab, Université de Poitiers, France.
Abstract
BACKGROUND: Occipito-cervical fusion can be necessary in case of cranio-cervical junction instability. Proximal stabilisation is usually ensured by bi-cortical occipital screws implanted through one median or two lateral occipital plate(s). Bone thickness variability as well as the proximity of vasculo-nervous elements can induce substantial morbidity. The choice of site and implant type remains difficult for surgeons and is often empirically based. Given this challenge, implants with smaller pitch to increase bone interfacing are being developed, as is a surgical technique consisting in inverted occipital hook clamps, a potential alternative to plate/screws association. We present here a biomechanical comparison of the different occipito-cervical fusion devices. METHODS: We have developed a 3D mark tracking technique to measure experimental mechanical data on implants and occipital bone. Biomechanical tests were performed to study the mechanical stiffness of the occipito-cervical instrumentation on human skulls. Four occipital implant systems were analysed: lateral plates+large pitch screws, lateral plates+hooks, lateral plates+small pitch screws and median plate+small pitch screws. Mechanical responses were analysed using 3D displacement field measurements from optical methods and compared with an analytical model. FINDINGS: Paradoxical mechanical responses were observed among the four types of fixations. Lateral plates+small pitch screws appear to show the best accordance of displacement field between bone/implant/system interface providing higher stiffness and an average maximum moment around 50 N.m before fracture. INTERPRETATION: Stability of occipito-cervical fixation depends not only on the site of screws implantation and occipital bone thickness but is also directly influenced by the type of occipital implant.
BACKGROUND: Occipito-cervical fusion can be necessary in case of cranio-cervical junction instability. Proximal stabilisation is usually ensured by bi-cortical occipital screws implanted through one median or two lateral occipital plate(s). Bone thickness variability as well as the proximity of vasculo-nervous elements can induce substantial morbidity. The choice of site and implant type remains difficult for surgeons and is often empirically based. Given this challenge, implants with smaller pitch to increase bone interfacing are being developed, as is a surgical technique consisting in inverted occipital hook clamps, a potential alternative to plate/screws association. We present here a biomechanical comparison of the different occipito-cervical fusion devices. METHODS: We have developed a 3D mark tracking technique to measure experimental mechanical data on implants and occipital bone. Biomechanical tests were performed to study the mechanical stiffness of the occipito-cervical instrumentation on human skulls. Four occipital implant systems were analysed: lateral plates+large pitch screws, lateral plates+hooks, lateral plates+small pitch screws and median plate+small pitch screws. Mechanical responses were analysed using 3D displacement field measurements from optical methods and compared with an analytical model. FINDINGS: Paradoxical mechanical responses were observed among the four types of fixations. Lateral plates+small pitch screws appear to show the best accordance of displacement field between bone/implant/system interface providing higher stiffness and an average maximum moment around 50 N.m before fracture. INTERPRETATION: Stability of occipito-cervical fixation depends not only on the site of screws implantation and occipital bone thickness but is also directly influenced by the type of occipital implant.
Authors: Filippo Migliorini; Alice Baroncini; Yasser El Mansy; Valentin Quack; Andreas Prescher; Max Mischer; Johannes Greven; Markus Tingart; Jörg Eschweiler Journal: BMC Musculoskelet Disord Date: 2021-03-06 Impact factor: 2.362