Eur Spine J (1993) 1 :222-225 European Spree Journal 9 Springer-Verlag1993 Cervical spine locking plate: in vitro biomechanical testing Stephen A. Smith, Ronald W. Lindsey, Brian J. Doherty, Jerry W. Alexander, and Jessie H. Dickson Center for Spinal Disorders, Department of Orthopaedic Surgery, BaylorCollegeof Medicine, Houston, Texas, USA La plaque cervicale verrouill~e (CSLP): essais biom~caniques en laboratoire R~sumd. La plaque cervicale verrouillde destinde aux ostdosynthdses du rachis cervical infdrieur a encore rd- cemment fait l'objet d'une approbation clinique crois- sante, mais jusqu'g ce jour il n'y a pas eu de travaux rap- portant les propridtds biomdcaniques de cet implant en laboratoire. Afin de ddterminer ces propridtds, 5 rachis cervicaux humains provenant de cadavres frais out dtd soumis 5 des tests de flexion et de torsion physiologiques, mends en trois dtapes: dtape 1: rachis intact, dtape 2: rachis ddstabilisd, dtape 3: rachis prdalablement ddstabilisd instrumental par une plaque cervicale verrouillde (CSLP). Les spdcimens de l'dtape 3 ont dtd dgalement soumis/a des mouvements de grande amplitude angulaire afin d'dvaluer la soliditd de la fixation. En flexion, le d@lace- ment moyen des processus 6pineux a 6td de 1,21 mm l'dtape 1, de 3,19ram ta l'dtape 2 et de 1,37 mm ~ l'Etape 3. La rigidit6 moyenne 5 la torsion a 6td de 2,86 Nm/degr6 5 la premidre dtape, de 1,82Nm/degr6 ~ la deuxidme et de 2,20 Nm/degrd ~ la troisidme. A l'dtape 3, les grands ddplacements angulaires ont abouti ~ un ddplacement de vis chez deux spdcimens; il n'y a cependant pas eu de ddmontage de plaque. Sur les moddles gravement dd- stabilisds, la plaque CSLP a restaurd Ia stabilitd 5 la flexion mais pas celle ~tla rotation. Ceci suggdre la ndcessitd d'un moyen d'immobilisation ou de fixation suppldmentaire pour rdtablir la stabilitd 5 la rotation pendant la phase de consolidation osseuse. Mots-elds: Rachis cervical - Fixation antdrieure - Bio- mdcanique - Plaque - Stabilitd Summary. The AO cervical spine locking plate (CSLP) for anterior subaxial fixation was recently received in- creasing clinical acclaim, yet to date the in vitro mechan- ical properties of this implant have not been reported. To determine the in vitro biomechanical properties of this device, five fresh human cadaver cervical spines were subjected to nondestructive testing in flexion and torsion Correspondence to: Ronald W. Lindsey,M. D., Departmentof Or- thopaedic Surgery,BaylorCollegeof Medicine, 6550Fannin, Suite 2625, Houston, TX 77030, USA in three stages: stage 1: intact spine; stage 2: destabilized spine; stage 3: destabilized spine with CSLP. Stage 3 specimens were also subjected to large angular displace- ment testing to assess the integrity of the fixation. In flexion, mean spinous process displacement was 1.21 mm for stage 1, 3.19 mm for stage 2, and 1.37 mm, for stage 3. Mean torsional stiffness was 2.86Nm/degree in stage 1, 1.82Nm/degree in stage 2, and 2.20Nm/degree in stage 3. Large angular displacement testing in stage 3 resulted in screw loosening from the bone in two specimens; no screw plate loosening occurred. In our severely destabiliz- ed in vitro model, the CSLP restored flexion stability but not rotational stability. This suggests that supplemented bracing or fixation may be required to restore torsional stability. Key words: Cervical spine - Anterior fixation - Biome- chanics - Plate - Stability Over the past three decades, anterior cervical discectomy and fusion has become a well-accepted method for the treatment of certain cervical disc disorders. Anterior cervical fusion (ACF) for the treatment of many acute fractures and/or dislocations of the cervical spine has also become the standard for care [2, 3]. However, ACF without internal fixation has occasionally been compli- cated by further destabilization of an already unstable spine [4, 5, 17, 21]. Attempts at external support the aug- ment this technique in the form of a Minerva cast or halo device have not always provided adequate immobiliza- tion [6], while their use limits patient mobility and access to the chest, abdomen, or pelvis if additional diagnosis or therapeutic measures are required. The concept of direct anterior internal fixation of the cervical spine has been advocated by several authors [8, 9]. In 1970, Orosco and Llovet [15] first described the use of a small fragment plate for anterior fixation of the cervical spine, and by the end of 1975 the AO cervical spine plate (H-plate) had been fully developed. Numer- ous clinical reports followed on the use of these plates and this prompted the development of other implants (e.g., the Caspar plate) of similar design [7, 8, 16]. How-