How cervical and cervicothoracic scoliosis influence the atlantoaxial joint.

INTRODUCTION: Children with cervical or cervicothoracic congenital scoliosis are limited in their ability to compensate for the main curve of the deformity because there are only a few mobile segments in their cervical spine. Over the years, we have frequently observed coronal atlantoaxial dislocation (CAAD) in a lateral direction (from left to right or vice versa) in these patients. It was anticipated that CAAD might compensate for the horizontal position of the head, and it is hypothesized that CAAD depends on the degree of scoliotic deformity. Thus, the aim of our study was to investigate whether there is a correlation between CAAD and scoliosis parameters in these patients. METHODS: Retrospective analysis was performed based on CAT scans and preoperative X-rays of patients with cervical and cervicothoracic scoliosis with an apex between C4 and T6. Seventeen patients, with a mean age of 7.25 years, who were 9 girls and 8 boys, and who were treated between 2006 and 2022 were included. Cobb`s angle of the main curve (CA-MC), Cobb`s angle of the secondary curve (CA-SC), and T1-, C2- and UEV (upper end vertebra) tilt were measured on whole-spine radiographs in the standing position. The CAAD was measured via coronal CAT scan reconstruction and defined as the difference in the distances of the lateral masses to the midline of the axis. Pearson`s linear correlation coefficients (r) were determined using SPSS to evaluate correlations between CAAD and the measured parameters. p < 0.05 indicated statistical significance. RESULTS: CAAD toward the convex region in patients with scoliosis was typically observed; the mean CAAD was 3 mm ± 3.7 mm. The mean CA-MC was 46° ± 13°, the mean CA-SC was 16° ± 9.6°, the mean T1 tilt was 17° ± 8.8°, the mean C2 tilt was 9°± 8.8°, and the mean UEV tilt was 24° ± 7.2°. There was a strong linear correlation between CAAD and CA-MC (r = 0.784, p < 0.001), C2 tilt (r = 0.745; p < 0.001), and UEV tilt (r = 0.519; p = 0.033). There was no correlation between CAAD and either CA-SC or T1 tilt. DISCUSSION: Children with cervical or cervicothoracic scoliosis tend to have a CAAD toward the convexity of the scoliosis that correlates to CA-MC, C2-tilt, and UEV-tilt. CAAD may be seen as a compensatory mechanism to keep the head in a horizontal position. Severe or progressive CAAD may result in destruction of the atlantoaxial joint, including severe complaints, thus necessitating close follow-up and possibly early surgical treatment. Moreover, CAAD might be a useful additional radiographic parameter to be checked in future scoliosis studies.

Melorheostosis of the cervical and cervicothoracic spine: review of the literature and presentation of 3 new cases.

Melorheostosis is a rare dysplastic bone disease that usually affects long bones at the upper or lower limbs. It is rarely seen at the spine and very rarely located at the cervical spine. To the best of our knowledge, there are currently 6 cases of melorheostosis described at the cervical spine. Here, we give an overview of the current literature of spinal melorheostosis with respect to number of cases and skeletal distribution, aetiology, radiographic appearance, symptoms and treatment. Finally, we describe 3 new clinical cases with manifestation of melorheostosis at the cervical spine and the cervicothoracic junction.

The effect of posterior compression of the facet joints for initial stability and sagittal profile in the treatment of thoracolumbar fractures: a biomechanical study.

PURPOSE: Surgical treatment of thoracolumbar A3-fractures usually comprises posterior fixation-in neutral position or distraction-potentially followed by subsequent anterior support. We hypothesized that additional posterior compression in circumferential stabilization may increase stability by locking the facets, and better restore the sagittal profile. METHODS: Burst fractures Type A3 were created in six fresh frozen cadaver spine segments (T12-L2). Testing was performed in a custom-made spinal loading simulator. Loads were applied as pure bending moments of ± 3.75 Nm in all six movement axes. We checked range of motion, neutral zone and Cobb's angle over the injured/treated segment within the following conditions: Intact, fractured, instrumented in neutral alignment, instrumented in distraction, with cage left in posterior distraction, with cage with posterior compression. RESULTS: We found that both types of instrumentation with cage stabilized the segment compared to the fractured state in all motion planes. For flexion/extension and lateral bending, flexibility was decreased even compared to the intact state, however, not in axial rotation, being the most critical movement axis. Additional posterior compression in the presence of a cage significantly decreased flexibility in axial rotation, thus achieving stability comparable to the intact state even in this movement axis. In addition, posterior compression with cage significantly increased lordosis compared to the distracted state. CONCLUSION: Among different surgical modifications tested, circumferential fixation with final posterior compression as the last step resulted in superior stability and improved sagittal alignment. Thus, posterior compression as the last step is recommended in these pathologies.

The Feasibility of C1-C2 Screw-rod Fixation in the Children 5 Years of Age and Younger.

BACKGROUND: Atlantoaxial fixation is technically challenging in younger children. The C1-C2 screw-rod fixation technique is established for adults but limited data about the clinical and radiographical outcome for the treatment of children with 5 years of age or younger is available. METHODS: All files of children who were consecutively treated for spinal disorders were reviewed. Inclusion criteria for further evaluation were: 0 to 5 years of age at initial procedure; detailed surgical report of a posterior C1-C2 fusion with mass lateral and pedicle screw-rod fixation as described by Harms; a minimum clinical and radiographical follow-up of 24 months. The postoperative and last follow-up computed tomography scan and radiographs were used to assess the positioning and stability of the C1-C2 screw-rod construct. RESULTS: Eleven patients (3 boys) with a mean age of 46 months (range: 8 to 66 mo) fulfilled inclusion criteria and were evaluated retrospectively. The mean clinical and radiographical follow-up was 79 months (range: 24 mo to 170 mo). The diagnosis was atlantoaxial rotatory dislocation (4 cases), C1-C2 instability with subluxation (3 cases), atlantoaxial dislocation and os odontoideum (1 case), type II odontoid fracture (1 case), traumatic odontoid epiphysiolysis (1 case), and traumatic rupture of the transverse ligament with C1 subluxation (1 case). Intraoperatively and postoperatively no new neurovascular or vascular complication occurred. C1 lateral mass screws were placed correctly in all cases. Twenty-two C2 pedicle screws were placed correctly (85.7%), and 3 screws showed penetration of the pedicle wall (14.3%). No implant revision, implant failure, and pseudarthrosis were noted. Loss of correction was noted in 1 patient with unilateral C1-C2 fixation and a repeated dorsal fusion procedures were performed. A repeat procedure for implant removal and segmental release was performed in 3 patients to increase the axial rotation of the head. CONCLUSIONS: The C1-C2 screw-rod fixation is a safe technique that achieves solid fixation of the atlantoaxial complex in young children with various disorders. The technique preserves the joint and allows for segmental release via implant removal.

The Effect of Cervicodorsal Hemivertebra Resection on Head Tilt and Trunk Shift in Children With Congenital Scoliosis.

BACKGROUND: Congenital scoliosis due to hemivertebra of the cervicodorsal spine is a rare disorder. It might be accompanied by impaired cosmetic appearances such as head tilt and trunk shift. Little is known about the effect of correction of the major curve on head tilt and trunk shift in children. The purpose of this study was to assess radiographic changes of head tilt and trunk shift following posterior hemivertebra resection (PHVR). METHODS: Retrospectively, all children who underwent PHVR at the cervicodorsal spine (C6-Th6) with pedicle screw fixation with a minimum radiographic follow-up of 1 year were identified for further assessment. A total of 5 radiographic parameters were assessed on preoperative, postoperative, and final follow-up radiographs. (1) Head tilt was defined as the angle between the horizontal line and the line through both molars of the maxillary, (2) trunk shift as the angle between the line of the center of C7 to the sacrum and the central sacral vertical line, (3) Cobb angle was used to assess the major curve, (4) cranial, and (5) caudal compensatory curvature. RESULTS: Seven boys and 10 girls with a mean age of 9.0 years at surgery were evaluated. The mean radiographic follow-up was 89.5 months (range: 12 to 166 mo). The mean head tilt reoriented from 6.9 to 1.9 degrees (P<0.001); trunk shift improved from 4.3 to 2.5 degrees after surgery (P=0.100). There was a significant correlation between head tilt and trunk shift on preoperative and postoperative radiographs (P=0.030/0.031). The major curve, and compensatory curvatures were all significantly corrected (P<0.001). Head reorientation was significantly influenced by patient age at surgery. Repeated procedures due to decompensation of the compensatory curvature were performed in 2 cases. CONCLUSIONS: PHVR and pedicle screw fixation is an effective treatment for patients with congenital scoliosis. Surgery achieves a significant correction of the major curve and reorientation of the head postoperatively, and till the last follow-up. LEVEL OF EVIDENCE: Level IV.

[Biomechanical compensatory mechanisms of hips and spine : The essentials for spine and hip surgeons]. / Biomechanische Kompensationsmechanismen der Hüftgelenke und der Wirbelsäule : Das Wesentliche für Wirbelsäulen- und Hüftchirurgen.

Spinal alignment changes with age and degeneration. Different compensatory mechanisms of the spine are necessary to preserve spinal balance. The capacity of compensation of the spine decreases with age. Thus, the pelvis and the lower limbs become involved in the compensatory mechanism. Concomitant osteoarthritis of the hip could impair this capacity. The biomechanical principles of compensation are described with respect to planning reconstructive hip and spine surgery.

[Diagnostics and treatment of cervical spine trauma in pediatric patients : Recommendations from the Pediatric Spinal Trauma Group]. / Diagnostik und Therapie von Verletzungen der Halswirbelsäule im Kindesalter : Empfehlungen der AG Wirbelsäulentrauma im Kindesalter.

BACKGROUND: Severe cervical spine injuries in children under the age of 17 years are rare. Recommendations or even guidelines for the diagnostics and treatment of such injuries in children are currently not available. OBJECTIVE: The aim of the study was to formulate recommendations for diagnostics and treatment of injuries of the cervical spine in pediatric patients. MATERIAL AND METHODS: First, a search of primary and secondary literature on the topic complex of diagnostics and treatment of cervical spine injuries in children was carried out. An appropriate internal literature database was defined and maintained. Second, within the framework of 9 meetings from April 2017 to December 2019 the members of the Pediatric Spinal Trauma Group of the Spine Section of the German Society for Orthopaedics and Trauma (DGOU) systematically formulated recommendations for the diagnostics and treatment of injuries of the cervical spine in pediatric patients by a consensus process. RESULTS: Recommendation for the diagnostics and treatment for injuries of the cervical spine could be formulated for three age groups (age group I: 0-6 years; age group II: 7-9 years; age group III: 10-16 years). The diagnostic and therapeutic principles known from adult patients suffering from injuries to the cervical spine cannot be easily transferred to pediatric patients. CONCLUSION: Injuries to the pediatric spine are rare and should be treated in specialized spine centers. Pediatric patients with a stable cardiopulmonary status should undergo magnetic resonance imaging (MRI) if a spinal trauma is suspected. Classification systems and therapeutic recommendations for injuries to the cervical spine known from adult patients could also be used for adolescent patients. This is not possible for children under the age of 10 years. Only few classification systems exist for this age group. Basic principles of the treatment of spinal trauma in children is the restoration of spinal stability and correct anatomical relationships as well as the protection of all neural structures.

Iatrogenic Intracranial Hypotension after Surgery of Adolescent Idiopathic Scoliosis due to a Misplaced Screw within the Thoracic Thecal Sac.

We present the case of a postoperative intracranial hypotension due to a misplaced intrathecal screw. Although typical symptoms such as orthostatic headache were present immediately after surgery, diagnosis was hidden until 20 years later, resulting in a disastrous clinical course.

Atlantoaxial Rotatory Dislocation: Delayed Diagnose Will Result in More Invasive Treatment Options.

PURPOSE: The atlantoaxial joint represents the most mobile joint complex within the spine, secured by ligaments and capsules. Integrity of the atlantoaxial joint is crucial with respect to the mobility of the head and the upper spine. Atlantoaxial rotatory dislocation is the most common type of injury within this joint in children and is characterized by a typical position of the head (cock robin position). Nevertheless, this type of injury is frequently overlooked. The purpose of the current study was threefold. First, the characteristics of the patients with atlantoaxial dislocation were identified. Next, we checked if the time to treatment did influence the type of treatment. Finally, we checked if the age of the child at the time of treatment influenced the type of treatment. METHODS: Forty-four children, who were treated consecutively due to atlantoaxial dislocation at a single spine center between September 1993 and October 2018, are analyzed retrospectively regarding age, sex, symptoms, etiology, time to diagnosis, time to treatment, and outcome. RESULTS: Forty-four children (30 girls, mean age 8.9 years) were included in the study. The cock robin head position was found in all of them, but neurological deficits were not found in any of them. In 21 patients, dislocation was caused by previous infection (Grisel's syndrome), whereas in 19 patients, dislocation was due to minor trauma. In 4 cases, etiology remained unknown. Mean time to sufficient treatment was 178 days. Eighteen patients received closed reduction and immobilization after 57 days at mean. Open reduction followed by temporary fixation was done in 12 patients after a mean time gap of 188 days. Bony atlantoaxial fusion was necessary in 14 children, who were diagnosed after 319 days on average. Invasiveness of treatment was dependent on the time delay between development of dislocation and treatment; a significant difference was found between invasiveness of treatment and time to treatment (Kruskal-Wallis test, p < 0,05). Moreover, older children were treated significantly more often with fusion than younger ones (χ 2, p = 0,002). CONCLUSION: Young girls are predisposed to incur an atlantoaxial rotatory dislocation, which usually occurs due to minor trauma or infection. The cock robin position is characteristic, but neurological deficits are not common. There is a need for early and sufficient treatment because delayed treatment necessitates more invasive treatment, thus leading to a complete loss of function of the most mobile joint within the spine. Finally, older children are predisposed to more invasive treatment strategies.

Degenerative Cervical Myelopathy: A 7-Letter Coding System That Supports Decision-Making for the Surgical Approach.

OBJECTIVE: To validate with a prospective study a decision-supporting coding system for the surgical approach for multilevel degenerative cervical myelopathy. METHODS: Ten cases were presented on an internet platform, including clinical and imaging data. A single-approach (G1), a choice between 2 (G2), or 3 approaches (G3) were options. Senior and junior spine surgeons analyzed 7 parameters: location and extension of the compression of the spinal cord, C-spine alignment and instability, general morbidity and bone diseases, and K-line and multilevel corpectomy. For each parameter, an anterior, posterior, or combined approach was suggested. The most frequent letter or the last letter (if C) of the resulting 7-letter code (7LC) suggested the surgical approach. Each surgeon performed 2 reads per case within 8 weeks. RESULTS: G1: Interrater reliability between junior surgeons improved from the first read (κ = 0.40) to the second (κ = 0.76, p < 0.001) but did not change between senior surgeons (κ = 0.85). The intrarater reliability was similar for junior (κ = 0.78) and senior (κ = 0.71) surgeons. G2: Junior/senior surgeons agreed completely (58%/62%), partially (24%/23%), or did not agree (18%/15%) with the 7LC choice. G3: junior/senior surgeons agreed completely (50%/50%) or partially (50%/50%) with the 7LC choice. CONCLUSION: The 7LC showed good overall reliability. Junior surgeons went through a learning curve and converged to senior surgeons in the second read. The 7LC helps less experienced surgeons to analyze, in a structured manner, the relevant clinical and imaging parameters influencing the choice of the surgical approach, rather than simply pointing out the only correct one.

Comparison of bioresorbable and titanium plates in cervical spinal fusion: early radiologic and clinical results.

STUDY DESIGN: This is a prospective, randomized, and controlled study, approved by the local ethical committee of Saarland (Germany), no. 209/06. OBJECTIVE: The aim of this study was to compare clinical results, segmental motility, magnetic resonance imaging (MRI) compatibility, and change of the bone density of a cervical spine segment that was treated with either bioresorbable or titanium plates in single level. SUMMARY AND BACKGROUND DATA: Anterior cervical discectomy and fusion including plate fixation is an accepted technique for treatment of symptomatic degenerative disc disease. Titanium plates have been used but cause imaging artifacts. Radiolucent bioresorbable plates and screws were developed to reduce the imaging artifacts associated with titanium. METHODS: Forty patients with single level cervical radiculopathy were randomized to anterior discectomy and fusion with bioresorbable plate (19 patients, study group) or titanium plate (18 patients, control group). Follow-up used a visual analog scale (VAS) with regard to brachial pain and Neck Disability Index (NDI) for neck pain. Radiostereometry was performed immediately postoperative and after 6 weeks, 3, and 6 months. MRI of the cervical spine was obtained immediately postoperatively at 3 and 6 months to assess hematoma, infection, and swelling. Computed tomography of the operated cervical spine segment was performed to assess bone density, expressed in Hounsfield units. RESULTS: Three-dimensional analysis of segmental motion (medio-lateral, cranio-caudal and anterior-posterior) did not reveal any statistical difference between both groups at any time postoperatively (P>0.05). Fusion rate and speed evaluated on Radiostereometric analysis and computed tomography of cervical spine segment were similar in both groups. MRI of cervical spine did not show any pathology, especially hematoma and infection. The VAS and NDI did not differ between both groups after 6 months (P>0.05). CONCLUSIONS: Anterior plate fixation by using a bioresorbable plate has the same fusion progress and stability as titanium. During the study, no complications like soft tissue swelling and infection occurred.

Changes in Swallowing After Anterior Cervical Discectomy and Fusion With Instrumentation: A Presurgical Versus Postsurgical Videofluoroscopic Comparison.

Purpose: The purpose of this study was to explore the impact of anterior cervical discectomy and fusion (ACDF) with anterior instrumentation on swallowing function and physiology as measured on videofluoroscopic swallowing studies. Method: We retrospectively analyzed both functional measures (penetration-aspiration, residue) and physiological/anatomical measures (hyoid excursion, posterior pharyngeal wall thickness) in a series of 17 patients (8 men, 9 women, mean age 54 years). These measures were extracted from calibrated 5-ml boluses of thin radio-opaque liquids on both pre-ACDF and post-ACDF videofluoroscopies, thus controlling for individual variation and protocol variation. Results: After ACDF surgery, we found significant within-subject worsening of Penetration-Aspiration Scale (Rosenbek, Robbins, Roecker, Coyle, & Wood, 1996) scores, vallecular (but not piriform sinus) residue, superior (but not anterior) hyoid excursion, and posterior pharyngeal wall thickness. Results are discussed in the context of previous literature. Conclusions: ACDF surgery can affect both physiological/anatomical and functional measures of swallowing. Future research should expand to other biomechanical and temporal variables, as well as greater bolus volumes and a wider array of viscosities and textures.

Effectiveness of cemented rescue screws for anterior cervical plate fixation.

OBJECT: Among the various ways to optimize the fixation of bone implants is to use bone cement, for example, in a total hip prosthesis. No data exist, however, concerning the effectiveness of cemented rescue screws for anterior cervical plate fixation. The aim of this study was to investigate whether cemented rescue screws increase fixation strength in comparison with uncemented standard screws. METHODS: Six cervical spine segments (C4-7) were explanted during routine autopsy studies from fresh human cadavers. Bone mineral density (BMD) was measured for each vertebral body (VB) using quantitative computerized tomography scanning, and 24 VBs were dissected from the segments. Two initial pilot holes were drilled into each VB parallel to the sagittal plane. Based on their BMD, the specimens were assigned to one of two groups in which torque and pullout force were tested. The test was begun with standard screws and was repeated with cannulated slotted rescue screws into which bone cement was injected. The mean values of peak torque and pullout forces resulting from the left and right measurements were used for statistical analysis. A t-test was performed to determine the effect of screw type on peak torque and pullout force. Moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force for each type of screw. The mean insertional peak torque was 67.1 N/cm for the standard screw and 102.6 N/cm for the cemented screw (p < 0.05). The mean pullout force was 526.9 N for standard osteoporosis screws and 531.5 N for cemented screws (p > 0.05). The effect of increased holding strength as measured by peak torque and pullout force was more pronounced in the presence of low bone density. CONCLUSIONS: Cemented rescue screws that have been inserted into a fatigued pilot hole in the cervical VB strengthen the screw-bone interface compared with the strength initially conferred by a standard screw.

C1-C2 Instrumentation According to Harms/Goel in Case of Vertebral Artery below the Arch of C1: A Case Report.

Study Design Case report. Background and Study Aims For stabilizing surgery of the atlantoaxial region, a precise evaluation of the course of the vertebral artery (VA) is essential to avoid vessel injury and life threatening complications. In patients with aberrant VA course, an appropriate way for fusion needs to be found. This article presents a case of an unusual VA course and illuminates the importance of surgical planning with computed tomography angiography identifying VA variations at the atlantoaxial region. Case Report A 71-year-old woman with atlantoaxial arthrosis had a VA variation (persistent first intersegmental artery). She underwent C1-C2 posterior fixation according to Harms/Goel using the typical entry points, requiring VA dissection in caudal direction. The postoperative clinical as well as radiographic result was excellent. Angiography 6 months postoperatively showed the VAs below the C1 screws with normal blood flow. Conclusions Placement of C1 screws in a patient with a persistent first intersegmental VA is possible. Careful VA dissection is the key step for safe screw placement, screw anchoring, and clinical success.

Resection of a Hemivertebra Within the Craniocervical Junction.

STUDY DESIGN: Case report on resection of a hemivertebra at the craniocervical junction. OBJECTIVE: To describe technique and result of a hemivertebra resection within the craniocervical junction (axis). SUMMARY OF BACKGROUND DATA: To our knowledge, this is the first report on a transoral and posterior hemivertebra resection at C2. METHODS: A 42-year-old patient presented with coronal imbalance due to a hemivertebra at C2. Correction was performed by a combined anterior (transoral) and posterior approach with hemivertebra resection and compression instrumentation. RESULTS: The postoperative course was uneventful. The radiographs showed a complete correction of the deformity with a perfect clinical result. CONCLUSION: Hemivertebra resection at the craniocervical junction can be performed safely with good clinical and radiographical outcome. LEVEL OF EVIDENCE: 4.

Initial stability of cervical spine fixation: predictive value of a finite element model. Technical note.

The purpose of this study was to generate a validated finite element (FE) model of the human cervical spine to be used to analyze new implants. Digitized data obtained from computerized tomography scanning of a human cervical spine were used to generate a three-dimensional, anisotropic, linear C5-6 FE model by using a software package (ANSYS 5.4). Based on the intact model (FE/Intact), a second was generated by simulating an anterior cervical fusion and plate (ACFP) C5-6 model in which monocortical screws (FE/ACFP) were used. Loading of each FE model was simulated using pure moments of +/- 2.5 Nm in flexion/extension, axial left/right rotation, and left/right lateral bending. For validation of the models, their predicted C5-6 range of motion (ROM) was compared with the results of an earlier, corresponding in vitro study of six human spines, which were tested in the intact state and surgically altered at C5-6 with the same implants. The validated model was used to analyze the stabilizing effect of a new disc spacer, Cenius (Aesculap AG, Tuttlingen, Germany), as a stand-alone implant (FE/Cenius) and in combination with an anterior plate (FE/Cenius+ACFP). In addition, compression loads at the upper surface of the spacer were investigated using both models. As calculated by FE/Intact and FE/ACFP models, the ROM was within 1 standard deviation of the mean value of the corresponding in vitro measurements for each loading case. The FE/Cenius model predicted C5-6 ROM values of 5.5 degrees in flexion/extension, 3.1 degrees in axial rotation (left and right), and 2.9 degrees in lateral bending (left and right). Addition of an anterior plate resulted in a further decrease of ROM in each loading case. The FE/Cenius model predicted an increase of compression load in flexion and a decrease in extension, whereas in the FE/Cenius+ACFP model an increase of graft compression in extension and unloading of the graft in flexion were predicted. The current FE model predicted ROM values comparable with those obtained in vitro in the intact state as well as after simulation of an ACFP model. It predicted a stabilizing potential for a new cage, alone and in combination with an anterior plate system, and predicted the influence of both loading modality and additional instrumentation on the behavior of the interbody graft.

Anterior cervical plate fixation: biomechanical effectiveness as a function of posterior element injury.

OBJECT: The primary goal of this study was to determine if the stabilization provided to the spine by anterior cervical fixation with plating (ACFP) was dependent on the degree of posterior element injury. The secondary goal was to evaluate the effectiveness of additional posterior screw/rod stabilization in these injuries. METHODS: Following ACFP with interbody bone graft and stepwise transection of the posterior ligaments and facets at C5-6, eight fresh-frozen human C4-7 spine segments were loaded using pure moments of +/- 1.5 Nm in flexion-extension, axial rotation, and lateral bending in the intact state. Posterior screw/rod fixation was performed after complete ligamentous destruction and complete removal of the facets. Repeated-measures analysis of variance and pairwise Student-Newman-Keuls tests were used to detect changes in the range of motion (ROM) and neutral zone (NZ). Statistical significance was assumed at a 95% level. Significant increases in ROM occurred in each loading direction after transection of the capsular ligaments (p < 0.001) and again following facetectomy (p < 0.001) compared with the ACFP condition. Additional posterior fixation resulted in a significant decrease in ROM in all loading directions (p < 0.001). There was a significant increase in NZ for complete ligamentous destruction compared with ACFP (p < 0.05) and facetectomy compared with ACFP (p < 0.05) for flexion-extension. In lateral bending, a significant increase in NZ was found for facetectomy compared with ACFP (p < 0.05). CONCLUSIONS: Capsular ligaments and articular facets are important structures in limiting three-dimensional vertebral motion in the presence of an anterior plate. Supplementary posterior fixation does reduce motion for all injury conditions.

Insertion torque and pullout force of rescue screws for anterior cervical plate fixation in a fatigued initial pilot hole.

OBJECT: The purpose of this study was to investigate whether thicker-core-diameter screws increase fixation strength in the cervical spine. METHODS: Bone mineral density (BMD) was determined for each vertebral body (VB) obtained in six human C4-7 segments. Based on their BMD, the specimens were assigned to one of two groups in which torque and pullout force were tested. Two initial pilot holes were drilled into the VBs and tests were first performed using a standard screw. The test was repeated using a thicker rescue screw inserted into the same initial pilot hole. The mean value of peak torque and pullout force resulting from the single left/right measurements was used for statistical analysis. A t-test was performed to determine the effect of screw design on peak torque and pullout force. Moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force. Mean insertional peak torque for the standard screw was 82.1 N/cm and that for the rescue screw was 47.6 Ncm (p < 0.001). There was a strong correlation between insertional peak torque and BMD for both standard screws (r = 0.71, p = 0.02) and rescue screws (r = 0.59, p = 0.07). The mean pullout force for standard screws was 464.7 N, whereas it was 164.5 N for rescue screws (p < 0.001). There was a strong correlation between pullout force and BMD for both standard (r = 0.75, p = 0.0081) and rescue screws (r = 0.7, p = 0.025). CONCLUSIONS: Uncemented rescue screws that have been inserted into a fatigued hole in the cervical VB do not strengthen the screw-bone interface compared with the strength initially conferred by a standard screw.