Biomechanical efficacy of calcium phosphate cement in augmentation and restoration of anterior cervical unicortical screw fixation / 中国矫形外科杂志

[Objective]To evaluate the biomechanical efficacy of calcium phosphate cement(CPC)in augmentation and restoration of anterior cervical unicortical screw fixation.[Method]Anterior cervical unicortical screw were fixed in the cervical vertebra(C_(3~6)),pull-out test and cyclic bending test was performed and anti-shear test after cyclic bending.[Result]The pull out strength(pos)of restoration group and augmentation group were significantly higher than that in the control group,the statistic difference was also significant(P

Comparisons of Unicortical and Bicortical Lateral Mass Screws in the Cervical Spine: Safety vs Strength

INTRODUCTION: The purpose of this study was to analyze the safety, pullout strength and radiographic characteristics of unicortical and bicortical screws of cervical facet within cadaveric specimens and evaluate the influence of level of training on the positioning of these screws. METHODS: Twenty-one cadavers, mean 78.9 years of age, underwent bilateral placement of 3.5mm AO lateral mass screw from C3-C6(n=168) using a slight variation of the Magerl technique. Intraoperative imaging was not used. The right side(unicortical) utilized only 14mm screws(effective length of 11mm) while on the left side to determine the length of the screw after the ventral cortex had been drilled. Three spine surgeons(attending, fellow, chief resident) with varying levels of spine training performed the procedure on seven cadavers each. All spines were harvested and lateral radiographs were taken. Individual cervical vertebrae were carefully dissected and then axial radiographs were taken. The screws were evaluated clinically and radiographically for their safety. Screws were graded clinically for their safety with respect to the spinal cord, facet joint, nerve root and vertebral artery. The grades consisted of the following categories: "satisfactory", "at risk" and "direct injury". Each screw was also graded according to its zone placement. Screw position was quantified by measuring a sagittal angle from the lateral radiograph and an axial angle from the axial radiograph. Pull-out force was determined for all screws using a material testing machine. RESULTS: Dissection revealed that fifteen screws on the left side actually had only unicortical and not bicortical purchase as intended. The majority of screws(92.8%) were satisfactory in terms of safety. There were no injuries to the spinal cord. On the right side(unicortical), 98.9% of the screws were "satisfactory" and on the left side(bicortical) 68.1% were "satisfactory". There was a 5.8% incidence of direct arterial injury and a 17.4% incidence of direct nerve root injury with the bicortical screws. There were no "direct injuries" with the unicortical screws for the nerve root or vertebral artery. The unicortical screws had a 21.4% incidence of direct injury of the facet joint, while the bicortical screws had a 21.7% incidence. The majority of "direct injury" of bicortical screws were placed by the surgeon with the least experience. The performance of the resident surgeon was significantly different from the attending or fellow(p<0.05) in terms of safety of the nerve root and vertebral artery. The attending's performance was significantly better than the resident or fellow(p<0.05) in terms of safety of the facet joint. There was no relationship between the safety of a screw and its zone placement. The axial deviation angle measured 23.5+/-6.6 degrees and 19.8+/-7.9 degrees for the unicortical and bicortical screws, respectively. The resident surgeon had a significantly lower angle than the attending or fellow(p<0.05). The sagittal angle measured 66.3+/-7.0 degrees and 62.3+/-7.9 degrees for the unicortical and bicortical screws, respectively. The attending had a significantly lower sagittal angle than the fellow or resident(p<0.05). Thirty-three screws that entered the facet joint were tested for pull-out strength but excluded from the data because they were not lateral mass screws per-se and had deviated substantially from the intended final trajectory. The mean pull-out force for all screws was 542.9+/-296.6N. There was no statistically significant difference between the pull-out force for unicortical(519.9+/-286.9N) and bicortical(565.2+/-306N) screws. There was no significant difference in pull-out strengths with respect to zone placement. CONCLUSION: It is our belief that the risk associated with bicortical purchase mandates formal spine training if it is to be done safely and accurately. Unicortical screws are safer regardless of level of training. It is apparent that 14mm lateral mass screws placed in a supero-lateral trajectory in the adult cervical spine provide an equivalent strength with a much lower risk of injury than the longer bicortical screws placed in a similar orientation.

Prognostic Factors of Locking Unicortical System in Internal Fixation for Cervical Spine Lesions

Although anterior cervical plate provide excellent fixation for anterior column, the potential risk for injury to spinal cord or soft tissue has been the reason why they have not gained universal acceptance. For this reason, anterior cervical locking plating systems were designed to avoid such surgical complications. The authors reviewed 98 patients who underwent anterior cervical fusion with anterior cervical locking unicortical system during the period of January 1995 to December 1997. Mean follow up period was 8.4months. Morscher plate placement was done in 24 and Orion plate was applied in 74. We compare the safety and efficacy of these tow plates. The two groups were comparable in demographic details, mean age(Morscher 41, Orion 47) average fusion level(Morscher 1.25, Orion 1.55) and fusion rate(Morscher 95.8%, Orion 100%). For comparison of hardware related complication, two patients(2.7%) showed screw loosening without without need for reoperation in Orion plate group. In Morscher plate group, 1 patient(4.1%) developed plate fracture and 1 patient (4.1%) developed screw loosening, but did not require delete(re) operation. Non-hardware related complications in Morscher group were seen in 2 patients(8.2%): one delete CSF leakage and the other being postoperative hematoma collection. In Orion plate group, complications were developed in 9 patients(12%): two nerve injuries(recurrent laryngeal and hypoglossal nerve), two CSF leakages, two wound infections, one postoperative hematoma collection, two donor graft site pains. Reoperations were done in two cases(2%) due to two postoperative hematoma collection one in Morscher plate group and one in Orion plate group. In one level fusion, longer operation time was required in Morscher plate group(217+/-93.7min) compared to Orion plate group(157+/-47min)(p<0.05). In this study two types of anterior cervical locking plate and screw system had good bony fusion and cervical stabilization with few instrument related complication. Moreover, allograft bone fusion with anterior cervical locking plate and screw system had good solid bony fusion without donor site morbidity. Instrument related complications were more common in Morscher locking plate and screw system.

The Efficacy of the Unicortical Screw in the Anterior Cervical Fusion of the Degenerative Cervical Spine Disease

Anterior cervical fusion without internal fixation destabilizes an already unstable spine and can result in tenuous bone graft stability and potential for incorporation. Anterior fusion of cervical spine with screw-plates is gaining in popularity in the management of anterior cervical spine instability. Eighty six cases that underwent anterior fusion with or without internal fixation and autogenous iliac bone graft were compared and analyzed. The pathologies included 40 cases of cervical disc disease, 43 of cervical spondylosis and 3 of ossification of posterior longitudinal ligament. Changes in the alignment of the total cervical spine and of the fused segment were evaluated in both groups. Dislodgement of the grafted bone, which was observed in 2 of 11 cases in the nonplate group, was not seen in the plate group. Hardware failure was developed in 3 of 24 cases in the bicortical group, but not in 51 cases in the unicortical group. Alignment of the cervical spine was corrected and relatively well manintained in the plate group compared with the nonplate group. We concluded that a unicortical screw fixation was superior than a bicortical screw and a fusion without plating system could not keep a cervical lordotic curve in the treatment of the degenerative cervical disease.

Anterior Cervical Fusion: A Retrospective Analysis of 152 Cases

Anterior cervical fusion has enjoyed an increasing acceptance and frequency of utilization in the treatment of symptomatic degenerative, traumatic, and neoplastic disorders. Since the introduction of plate systems, cervical fusion with fixation has become popularized. We present our experiences of 152 cases of cervical fusion in degenerative and traumatic lesions, focusing on their surgical results and complications, along with our opinions about the various plate systems we used. Between March 1993 and May 1996, 152 patients with symptomatic degenerative and traumatic cervical lesions between C3-4 and C7-T1 levels were treated with anterior cervical fusions. These patients were retrospectively studied according to their medical records and radiological studies. A comparison between various plate systems were also done. There were 110 men and 42 women, aged from 21 to 77 years. Mean follow up period was 17 months. Mean fused segments were 1.4. Various plate systems were used: Caspar plate system in 14 patients; Top plate in 102; Orion plate in 21; and none in 15. Dislodgement of bone graft, screw loosening, and fusion failure that required reoperation were occurred in 8 cases. None of them were initially treated with unicortical type screws. Asymptomatic esophageal perforation was developed in one case among them. In conclusion, anterior cervical fusion with screw plate system can be carried out with acceptable complication rate. Although relative follow up period was short, we concluded that the locking type screw plate system was superior than the classic bicortical screw system in their procedural simplicity, unnecessary penetration of posterior cortex, and elimination of the fear for the neurological complication.