Use of resorbable implants for symptomatic cervical spondylosis: experience on 16 consecutive patients

AIM

The aim of this study was to evaluate the results of a consecutive series of 16 patients affected by degenerative cervical spondylosis and operated on by anterior cervical discectomy and fusion (ACFD) by means of anterior bioresorbable plate and screws. Further, the authors compared the results in these patients with a series of 13 patients also affected by degenerative cervical spondylosis in whom arthrodesis was obtained by means of cages without plates.\

METHODS

The series included 8 males and 8 females aging from 37 to 69 years, operated from June 2003 to September 2004. They showed signs of cervical myelopathy, radiculopathy or both. The ACDF was performed with the insertion of dense cancellous allograft and application of anterior bioresorbable plate and screws (group A). The group B series included 9 males and 4 females aging from 50 to 77 years, all affected by the same pathology of group A patients and operated on in the same period of time. In these cases the ACDF was followed by the insertion of cages without anterior plates.

RESULTS

The retrospective analysis of our series showed lack of soft tissue reaction, with safeguarding of the vertebral body and disc space height. The degree of alignment of the cervical spine was also preserved, with a good rate of fusion and a good clinical outcome in both series of patients.

CONCLUSION

The use of a cervical plate increase stability and rate of fusion when added to the interbody device; while the use of a metallic plate may be responsible for several shortcomings, a resorbable plate may overcome these problems.

Complication avoidance in 116 dynamic-plated single-level anterior corpectomy and fusion

Complications arising over a 6-year interval after 116 single-level anterior corpectomy/fusions (ACF) using iliac crest autograft and dynamic ABC plates were sequentially evaluated. Patients averaged 45 years of age (52 females and 64 males). Preoperative magnetic resonance and computed tomography studies documented adjacent 2-level disease/retrovertebral extension. Single level ACF (eg, C5-C7) used iliac crest autograft and dynamic ABC plates (Aesculap, Tuttlingen, Germany). Patients underwent dynamic x-ray and 2D-computed tomography evaluations 3, 4.5, 6, and up to 12 months postoperatively until fusion was documented by 2 independent radiologists. Patient were followed an average of 3.2 years (minimum 1 y). Three patients undergoing surgery in the first year of the study exhibited plate/graft extrusion (1 to 3 wk) or pseudarthroses (2 to 6 mo); subsequent improvements in surgical technique eliminated these complications in the last 5 years of the study. Inadequate bracing (4 mo on average) over the first 2 years was presumed responsible for 2-delayed strut fractures requiring secondary surgery (6 mo, and 2 y/Lupus/steroids) and 5 managed nonsurgically had 3 to 6 months of additional bracing. The routine addition of 6 weeks of cervicothoracic orthoses bracing in the latter 4 years of the study eliminated these strut fractures. Of interest, only 1 patient developed symptomatic adjacent level disease requiring a laminectomy (C6, C7) and posterior fusion (C2-T2) 5 years later. Complications observed in the first 2 years of a study involving 116 single-level dynamic-plated ACF were largely eliminated by introducing more prolonged bracing and improved surgical techniques for the study's last 4 years.

Screw pull-out force is dependent on screw orientation in an anterior cervical plate construct

Two common justifications for orienting cervical screws in an angled direction is to increase pull-out strength and to allow use of longer screws. This concept is widely taught and has guided implant design. Fixed versus variable angle systems may offer strength advantages. The purpose of our study is to test the influence of screw orientation and plate design on the maximum screw pull-out load. Variable and fixed angle 4.0 x 15 mm and 4.0 x 13 mm self-tapping screws were used to affix a Medtronic Atlantis cervical plate to polyurethane foam bone samples (density 0.160/cm). This synthetic product is a model of osteoporotic cancellous bone. The fixed angle screws can only be placed at 12 degrees convergent to the midline and 12 degrees in the cephalad/caudal ("12 degrees up and in") direction. Three groups were tested: (1) all fixed angle screws, (2) variable angle, all screws 12 degrees up and in, (3) variable angle, all screws 90 degrees to the plate. Plate constructs were pulled off with an Instron DynaMight 8841 servohydrolic machine measuring for maximum screw pull-out force. There was no difference between group 1, fixed angle (288.4 +/- 37.7 N) (mean +/- SD) and 2, variable angle group (297.7 +/- 41.31 N P< or =0.73). There was a significant increase in maximum pull-out force to failure for the construct with all screws at 90 degrees (415.2+/-17.4 N) compared with all screws 12 degrees "up and in" (297.4 +/- 41.3 N, P< or =0.0016). Group 3 done with 13 mm screws, showed a trend toward better pull-out strength, compared to group 2 w/15 mm screws (345.2 +/- 20.5 vs. 297.4 +/- 41.3, P< or =0.06). In this plate pull-out model, screw orientation influences maximum force to failure. When all 4 screws are 90 degrees to the plate the construct has the greatest ability to resist pullout. Fixed angle designs show no advantage over variable angle. These findings are contrary to current teaching.

Bicortical screw fixation of distal fibula fractures with a lateral plate: an anatomic and biomechanical study of a new technique

One of the potential drawbacks of lateral plating of distal fibula fractures is less than satisfactory fixation of unicortical screws commonly placed in the distal fragment to avoid implant penetration of the ankle joint. This study examines the anatomy of the distal fibula, proposes new techniques for bicortical screw fixation and radiographic evaluation of screw placement, and compares pullout strength of unicortical versus bicortical screws in this area. Sixteen pairs of human cadaver feet were used in this study. It was found that a large percentage of the surface area of the distal fibula is nonarticular and that the distal fibula could be divided into 3 zones with distinct anatomic features. Zone I is defined as the distal most 1.5 cm of the fibula, zone II is the next 1 cm of fibula proximal to zone I, and zone III is defined as the fibula above the ankle joint, starting at just over 2.5 cm proximal to the tip of the fibula. We determined a safe corridor for bicortical screw placement by means of a lateral plate in each zone. An improved radiographic view is described for confirmation of extraarticular screw placement. Screw pullout testing was performed on 8 pairs of fresh-frozen human cadaver fibulas. In both zone I and zone II, the bicortical screw fixation was significantly stronger than the unicortical screw fixation. In zone I, the average pullout strength for the bicortical screw fixation was 2.3 times higher than the unicortical screw fixation. In zone II, the average pullout strength for the bicortical screw fixation was 3.3 times higher than the unicortical screw fixation. This study shows that not only is bicortical screw placement in the distal fibula technically feasible, but it is also biomechanically stronger than unicortical placement in this area.

Correlation of cervical endplate strength with CT measured subchondral bone density

Cervical interbody device subsidence can result in screw breakage, plate dislodgement, and/or kyphosis. Preoperative bone density measurement may be helpful in predicting the complications associated with anterior cervical surgery. This is especially important when a motion preserving device is implanted given the detrimental effect of subsidence on the postoperative segmental motion following disc replacement. To evaluate the structural properties of the cervical endplate and examine the correlation with CT measured trabecular bone density. Eight fresh human cadaver cervical spines (C2-T1) were CT scanned and the average trabecular bone densities of the vertebral bodies (C3-C7) were measured. Each endplate surface was biomechanically tested for regional yield load and stiffness using an indentation test method. Overall average density of the cervical vertebral body trabecular bone was 270 +/- 74 mg/cm3. There was no significant difference between levels. The yield load and stiffness from the indentation test of the endplate averaged 139 +/- 99 N and 156 +/- 52 N/mm across all cervical levels, endplate surfaces, and regional locations. The posterior aspect of the endplate had significantly higher yield load and stiffness in comparison to the anterior aspect and the lateral aspect had significantly higher yield load in comparison to the midline aspect. There was a significant correlation between the average yield load and stiffness of the cervical endplate and the trabecular bone density on regression analysis. Although there are significant regional variations in the endplate structural properties, the average of the endplate yield loads and stiffnesses correlated with the trabecular bone density. Given the morbidity associated with subsidence of interbody devices, a reliable and predictive method of measuring endplate strength in the cervical spine is required. Bone density measures may be used preoperatively to assist in the prediction of the strength of the vertebral endplate. A threshold density measure has yet to be established where the probability of endplate fracture outweighs the benefit of anterior cervical procedure.

New rod-plate anterior instrumentation for thoracolumbar/lumbar scoliosis: biomechanical evaluation compared with dual-rod and single-rod with structural interbody support

STUDY DESIGN

A new rod-plate anterior implant was designed to provide plate fixation at the cephalad and caudal-end segments of a 5-level anterior spine construct. Biomechanical testing was performed on calf spines instrumented with 5-segment anterior scoliosis constructs. OBJECTIVES.: To analyze the initial and post-fatigue biomechanical performance of the new implant, and compare it to an anterior dual-rod construct and a single-rod construct with interbody cages.

SUMMARY OF BACKGROUND DATA

Using single-rod anterior instrumentation for thoracolumbar and lumbar scoliosis, an unacceptable incidence of loss of correction, segmental kyphosis, and pseudarthrosis has been reported. Inadequate construct stiffness due to early postoperative bone-screw interface failure, especially at cephalad and caudal-end vertebrae, has been implicated as the cause of these complications.

METHODS

Thirty calf spines were instrumented over 5 segments with: (1) single-rod augmented with rod-plate implants, (2) dual-rod construct, and (3) single-rod with titanium mesh cages. Stiffness in flexion-extension and lateral bending modes was determined initially and post-cyclical loading by measuring segmental range of motion (ROM). Post-fatigue screw pullout tests were also performed.

RESULTS

In lateral bending, the caudal-end segmental ROM for rod-plate construct was 54% less than single-rod with cages construct (P < 0.05), with no difference between rod-plate and dual-rod constructs. In flexion-extension, the rod-plate construct showed 45% to 91% (initial test) and 84% to 90% (post-fatigue) less ROM than the single-rod with cages construct (P < 0.001). Again, there was no difference between rod-plate and dual-rod constructs at the cephalad and caudal-end segments. Post-fatigue screw pullout strengths of the rod-plate construct were significantly greater than those of the dual-rod and single-rod with cages constructs (P < 0.05).

CONCLUSIONS

The rod-plate construct was significantly stiffer and provided greater stability of bone-screw interface than the single-rod with cages construct. It achieved similar stiffness and improved bone-screw interface stability compared to dual-rod construct.

An In Vitro Biomechanical Comparison Between Prototype Tapered Shaft Cortical Bone Screws and AO Cortical Bone Screws for an Equine Metacarpal Dynamic Compression Plate Fixation of Osteotomized Equine Third Metacarpal Bones

OBJECTIVES

To compare biomechanical properties of a prototype 5.5 mm tapered shaft cortical screw (TSS) and 5.5 mm AO cortical screw for an equine third metacarpal dynamic compression plate (EM-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones.

STUDY DESIGN

Paired in vitro biomechanical testing of cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation.

ANIMAL POPULATION

Adult equine cadaveric MC3 bones (n=12 pairs).

METHODS

Twelve pairs of equine MC3 were divided into 3 groups (4 pairs each) for (1) 4-point bending single cycle to failure testing, (2) 4-point bending cyclic fatigue testing, and (3) torsional single cycle to failure testing. An EM-DCP (10-hole, 4.5 mm) was applied to the dorsal surface of each, mid-diaphyseal osteotomized, MC3 pair. For each MC3 bone pair, 1 was randomly chosen to have the EM-DCP secured with four 5.5 mm TSS (2 screws proximal and distal to the osteotomy; TSS construct), two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws in the remaining holes. The control construct (AO construct) had four 5.5 mm AO cortical screws to secure the EM-DCP in the 2 holes proximal and distal to the osteotomy in the contralateral bone from each pair. The remaining holes of the EM-DCP were filled with two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws. All plates and screws were applied using standard AO/ASIF techniques. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P<.05.

RESULTS

Mean 4-point bending yield load, yield bending moment, bending composite rigidity, failure load and failure bending moment of the TSS construct were significantly greater (P<.00004 for yield and P<.00001 for failure loads) than those of the AO construct. Mean cycles to failure in 4-point bending of the TSS construct was significantly greater (P<.0002) than that of the AO construct. The mean yield load and composite rigidity in torsion of the TSS construct were significantly greater (P<.0039 and P<.00003, respectively) than that of the AO construct.

CONCLUSION

The TSS construct provides increased stability in both static overload testing and cyclic fatigue testing.

CLINICAL RELEVANCE

The results of this in vitro study support the conclusion that the EM-DCP fixation using the prototype 5.5 mm TSS is biomechanically superior to the EM-DCP fixation using 5.5 mm AO cortical screws for the stabilization of osteotomized equine MC3.

Fatigue Analysis of Plates Used for Fracture Stabilization in Small Dogs and Cats

OBJECTIVE

To evaluate the fatigue life of stacked and single, veterinary cuttable plates (VCP) and small, limited contact, dynamic compression plates (LC-DCP).

STUDY DESIGN

In vitro biomechanical study.

METHODS

Fracture models (constructs; n = 8) were assembled for each of 6 groups all with 8-hole plates: 2.0 mm LC-DCP; 2.4 mm LC-DCP; single 1.5/2.0 mm VCP; stacked 1.5/2.0 mm VCP; single 2.0/2.7 mm VCP; and stacked 2.0/2.7 mm VCP. Plate(s) were secured to 2 polyvinylchloride pipe lengths, mounted in a testing system with a custom jig, and subjected to axial loading (10-100 N) for 1,000,000 cycles at 10 Hz or until failure. Differences in number of cycles to failure among groups were compared. Failure mode was determined.

RESULTS

All LC-DCP and single VCP constructs failed before 1,000,000 cycles. Stacked 2.0/2.7 mm VCP constructs withstood 1,000,000 cycles without failure. ANOVA and Fisher's least significant difference tests demonstrated significantly more cycles to failure for the stacked 1.5/2.0 mm VCP and stacked 2.0/2.7 mm VCP compared with the single 1.5/2.0 mm VCP, single 2.0/2.7 mm VCP, 2.0 mm LC-DCP, or 2.4 mm LC-DCP. Constructs that failed did so through a screw hole adjacent to the gap.

CONCLUSION

Stacked VCP constructs have greater fatigue lives than comparably sized LC-DCP or single VCP constructs. Plates with 2.4 mm screws were not significantly different from the comparable construct with 2.0 mm screws.

CLINICAL RELEVANCE

Although these data reveal that stacked VCP create a superior construct with respect to cyclic fatigue, surgeons must decide whether this is a clinical advantage on a case-by-case basis.

Surgical treatment of spondylodiscitis in the cervical spine: a minimum 2-year follow-up

Cervical spine spondylodiscitis is a rare, but serious manifestation of spinal infection. We present a retrospective study of 20 consecutive patients between 01/1994 and 12/1999 treated because of cervical spondylodiscitis. Mean age at the time of treatment was 59.7 (range 34-81) years, nine of them female. In all cases, diagnosis had been established with a delay. All patients in this series underwent surgery such as radical debridement, decompression if necessary, autologous bone grafting and instrumentation. Surgery was indicated if a neurological deficit, symptoms of sepsis, epidural abscess formation with consecutive stenosis, instability or severe deformity were present. Postoperative antibiotic therapy was carried out for 8-12 weeks. Follow-up examinations were performed a mean of 37 (range 24-63) months after surgery. Healing of the inflammation was confirmed in all cases by laboratory, clinical and radiological parameters. Spondylodesis was controlled radiologically and could be achieved in all cases. One case showed a 15 degrees kyphotic angle in the proximal adjacent segment. Spontaneous bony bridging of the proximal adjacent segment was observed in one patient. In the other cases the adjacent segments radiologically showed neither fusion nor infection related changes. Preoperative neurological deficits improved in all cases. Residual neurological deficits persisted in three of eight cases. The results indicate that spondylodiscitis in cervical spine should be treated early and aggressive to avoid local and systemic complications.

Eyebrow Surgery: The Supraciliary Craniotomy: Technical Note

OBJECTIVE:

Many approaches have been recommended for the surgical treatment of anterior and middle cranial fossa lesions. The frontobasal approach and its many modifications have been proposed and developed for such situated lesions. An alternative approach is the frontolateral craniotomy through a supraciliary skin incision.

METHODS:

This minimally invasive technique, a 2.5 × 3.0 cm craniotomy, just above the eyebrow through a supraciliary incision, is a simple but elegant modification of the traditional approach to the anterior cranial fossa.

RESULTS:

A step-by-step description of the approach is offered in this report to facilitate a clear understanding of the lesions treatable with this minimally invasive technique.

CONCLUSION:

The supraciliary frontolateral keyhole craniotomy is a minimally invasive cosmetic approach that provides excellent exposure to a variety of intracranial lesions. This approach cannot be used for all intracranial pathologies, but is recommended for many anterior and middle cranial fossa lesions.

Comparison of the biomechanical stability of dense cancellous allograft with tricortical iliac autograft and fibular allograft for cervical interbody fusion

Several choices are available for cervical interbody fusion after anterior cervical discectomy. A recent option is dense cancellous allograft (CS) which is characterized by an open-matrix structure that may promote vascularization and cellular penetration during early osseous integration. However, the biomechanical stability of CS should be comparable to that of the tricortical iliac autograft (AG) and fibular allograft (FA) to be an acceptable alternative to these materials. The purpose of this study was to compare the initial biomechanical stability of CS to that of AG and FA in a one-level anterior cervical discectomy and interbody fusion (ACDF) model. Twelve human cervical spines (C3-T1) were loaded in six modes of motion and evaluated under three conditions: (1) intact, (2) after ACDF using CS, AG, and FA in alternating sequences, and (3) after ACDF with anterior plating. Three reflective markers were placed on the adjacent vertebral bodies. Intervertebral motion was measured with a video-based motion-capture system (MacReflex, Qualisys, Sweden). Torques were applied to a maximum of 2.0 N m. The range-of-motion and neutral-zone values measured in each loading mode were compared. No graft material displayed significant differences in biomechanical stability in any of the tested loading modes, suggesting that the initial stability of CS is comparable to that of AG and FA. Anterior cervical plating significantly increased biomechanical stability in all modes.

Biomechanical analysis of posterior fixation techniques in a 360 degrees arthrodesis model

STUDY DESIGN

A biomechanical study to assess the ability of posterior fixation techniques to stabilize a functional spine unit (FSU) after insertion of an anterior load-sharing device.

OBJECTIVE

The objective of this study is to compare various posterior fixation techniques in combination with an anterior load-sharing implant.

SUMMARY OF BACKGROUND DATA

Pedicle screws and translaminar facet screws have been shown to improve the stiffness of an FSU in combination with an anterior load-sharing device. No published studies, to our knowledge, have compared translaminar facet screw fixation versus bilateral and unilateral pedicle screw fixation used with an anterior load-sharing device.

METHODS

Ten cadaveric FSUs were potted using methylmethacrylate and attached to a spine simulator mounted to an MTS Mini-Bionix testing machine. The simulator was configured to control compressive loading, axial torque, flexion, extension, and lateral bending. Each specimen was tested in the intact state and following the application of each of four stabilization techniques: custom cage alone, cage plus translaminar facet screw fixation, cage plus unilateral pedicle screw and plate fixation, and cage plus bilateral pedicle screw and rod fixation with transverse coupling. Compressive stiffness and total range of motion (ROM) between +/-8 Nm of torque were extracted from the raw data.

RESULTS

Each fixation method decreased ROM in torsion, flexion-extension, and lateral bending compared with the intact state. Unilateral pedicle fixation offered less stability than either of the other posterior fixations in all modes of testing except axial loading, where it was equivalent. Translaminar facet screw fixation was equivalent to bilateral pedicle screws in all modes tested.

CONCLUSIONS

Using a load-sharing interbody implant, translaminar facet screws are equivalent to bilateral pedicle screws in resisting motion in all three planes. Translaminar facet screws and bilateral pedicle screws offer greater stabilization in all three planes compared with unilateral pedicle screws and a single plate.

Sarcoma of the proximal portion of the tibia in a dog 5.5 years after tibial plateau leveling osteotomy

Osseous neoplasia was identified in the proximal portion of the tibia and distal portion of the femur in an 11.75-year-old spayed female German Shepherd Dog. A tibial plateau leveling osteotomy, followed by application of a metal plate, had been performed on the affected limb 5.5 years earlier. Areas of osteolysis and periosteal proliferation were seen radiographically, with an intense area of osteolysis directly beneath the metal plate. Histologically, the tumor was identified as a poorly differentiated sarcoma. Extracellular and intracellular debris was seen histologically, and energy-dispersive x-ray analysis confirmed that this debris was metallic. On visual examination, areas of the underside of the metal plate that had been in contact with bone had a dull, roughened appearance, and scanning electron microscopy of these areas revealed multiple corrosion pits. The plate was strongly magnetic, suggesting that it contained ferrite, and metallographic examination of the plate revealed substantial differences in the chemical makeup of various parts of the plate. Microstructure analysis revealed that the plate consisted of an austenite matrix with a large fraction of ferrite. The plate was determined to be a cast 316L stainless steel implant, but it did not meet American Society for Testing Materials standards for implant-grade materials. The possibility that implant corrosion might have played a role in tumor development is of concern; however, a definitive association was not established.

Comparison of stiffness and failure load of two cervical spine fixation techniques in an in vitro human model

OBJECTIVE

Recently, an unpaired threaded cage has been introduced as a fusion device for the cervical spine. No biomechanical comparison of a stand-alone single interbody threaded cage to a standard plated Smith-Robinson construct has been reported. Accordingly, an in vitro biomechanical comparison of a single threaded cylindrical interbody fusion cage versus a plated Smith-Robinson cervical discectomy and fusion construct was conducted to establish whether a single cylindrical interbody cage in the cervical spine would perform mechanically as well as a plated structural interbody graft.

METHODS

Six fresh-frozen human cadaveric cervical spines were used for biomechanical testing. Flexion-extension and load-to-failure testing were performed on two single-level discectomy and interbody fusion constructs from each specimen.

RESULTS

Initial range of motion (ROM) was significantly greater for the specimens implanted with a cage than specimens implanted with a structural graft and plate (9.1 degrees +/- 3.7 degrees vs 5.8 degrees +/- 2.4 degrees ; P = 0.040). Initial stiffness in flexion in caged specimens was significantly less than in plated specimens (0.7 +/- 0.3 vs 0.9 +/- 0.3 Nm/ degrees ; P = 0.028). Cage specimens also failed at a significantly lower load than plated specimens (9.8 +/- 3.5 vs 15.8 +/- 4.1 Nm; P = 0.0104).

CONCLUSIONS

This study demonstrates that a plated Smith-Robinson cervical discectomy and fusion construct provides greater stiffness and failure load and reduced ROM across operated levels than a single interbody cage construct. Although clinical success may not directly correlate with biomechanical data, these results raise concern regarding the use of a single threaded interbody cage as a stand-alone device for cervical interbody fusion.

Biomechanical comparison of transarticular facet screws to lateral mass plates in two-level instrumentations of the cervical spine

STUDY DESIGN

In vitro biomechanical comparison of transarticular facet screws to lateral mass plates in two level instrumentations of the cervical spine.

OBJECTIVE

Lateral mass plates are costly, and screw placement is difficult. Facet screws have never been tested as an alternative in the cervical spine. This biomechanical study compared cervical transarticular facet screws to lateral mass plates in two-level instrumentations of human cadaveric cervical spines.

SUMMARY OF BACKGROUND DATA

Translaminar facet screws have been shown to have similar biomechanical performance to pedicle screw fixation in the lumbar spine, especially in flexion. They have proven to be fast, safe, and effective, with authors reporting 94% to 100% fusion rates in single-level lumbar fusions. However, a biomechanical comparison of transarticular facet screws to lateral mass plates in cervical spine instrumentations has not been reported.

METHODS

Thirteen human cadaveric cervical motion segments (C2-C4, C5-C7) were tested before and after instrumentation, with either transarticular facet screws or lateral mass plates, in flexion, extension, lateral bending, and torsion. Specimens were subjected to six cycles under a load of 2 Nm.

RESULTS

Both fixation systems significantly reduced range of motion (ROM) and increased stiffness compared with the intact state in flexion, extension, lateral bending, and torsion. There were also no significant differences between the facet screws and plates in any of the four directions. To compare the two systems, ROM of each was analyzed relative to the uninstrumented state. Flexion was 0.26 (or 26% of the intact state) for the transarticular facet screws versus 0.20 for the lateral mass plates (P = 0.34), extension was 0.10 versus 0.07 (P = 0.43), lateral bending was 0.17 versus 0.15 (P = 0.52), and torque was 0.25 versus 0.38 (P = 0.12). Load to failure testing failed to indicate any differences between the two methods of fixation because all the specimens failed elsewhere.

CONCLUSION

This study proves that transarticular facet screws and lateral mass plates are equivalent in two-level instrumentations of the cervical spine. This is the first biomechanical study to test transarticular facet screws in this context.

Anterior correction of cervical spine lordosis using an adjustable depth tap: technical note

OBJECTIVE

In cases of multilevel anterior cervical spine decompression where intervening vertebral bodies need to be incorporated into the anterior plate construct, it may be difficult to apply the plate flush against the entire anterior cortical surface of the spine segment. Some have suggested using the levering property of bicortical screws to "pull" the body against the plate. Others have recommended contouring the anterior cervical plate with a plate bender. The objective of this work was to describe a novel technique using the adjustable depth tap provided in the Atlantis plating system for achieving cervical spine alignment against the lordotic plate after multilevel anterior decompression.

METHODS

We describe an illustrative case of a 14-year-old girl with complex cervical spine fractures after trauma. We used the 4.0-mm adjustable depth tap in the Atlantis plating system to lever the C4 body against the premachined lordotic plate.

RESULTS

Cervical lordosis and anterior cervical plate placement were accomplished after multilevel anterior cervical decompression with the use of an adjustable depth tap.

CONCLUSIONS

Bicortical screw placement and plate bending have drawbacks in trying to apply the anterior cervical plate firmly to the anterior surface of the cervical spine. We describe a new and safe technique of using an adjustable depth tap for achieving that same goal without any obvious drawbacks.

Anterior-Only Stabilization of Three-Column Thoracolumbar Injuries

OBJECTIVE

The optimal treatment of "unstable" thoracolumbar injuries remains controversial. Studies have shown the advantages of direct anterior decompression of thoracolumbar injuries along with supplemental posterior instrumentation as a combined or staged procedure. Others have also shown success in decompression as a single-stage anterior procedure, largely limited to two-column (anterior and middle) injuries. A retrospective review of all available clinical and radiographic data was used to classify unstable three-column thoracolumbar fractures according to the Association for the Study of Internal Fixation (AO) classification system. This was conducted to evaluate the efficacy of stand-alone anterior decompression and reconstruction of unstable three-column thoracolumbar injuries, utilizing current-generation anterior spinal instrumentation.

METHODS

Between 1992 and 1998, 40 patients underwent anterior decompression and two-segment anteriorly instrumented reconstruction for three-column thoracolumbar fractures. Retrospective review of all available clinical and radiographic data was used to classify these unstable injuries according to the AO classification system, evaluating for neurologic changes, spinal canal compromise, preoperative and postoperative segmental angulation, and arthrodesis rate.

RESULTS

According to the AO classification system, there were 24 (60%) type B1.2, 10 (25%) type B2.3, 5 (12.5%) type C1.3, and 1 (2.5%) type C2.1 three-column injuries. Preoperative canal compromise averaged 68.5% and vertebral height loss averaged 44.5%. There were no cases of neurologic deterioration, and 30 (91%) patients with incomplete neurologic deficits improved by at least one modified Frankel grade. Mean preoperative segmental kyphosis of 22.7 degrees was improved to an early mean of 7.4 degrees (P < 0.0001). At latest follow-up, angulation had increased by an average 2.1 degrees but maintained significant improvement from preoperative measurements (P < 0.0001). There was one early construct failure due to technical error. Thirty-seven of the remaining patients (95%) went on to apparently stable arthrodesis.

CONCLUSIONS

Current types of anterior spinal instrumentation and reconstruction techniques can allow some types of unstable three-column thoracolumbar injuries to be treated in an anterior stand-alone fashion. This allows direct anterior decompression of neural elements, improvement in segmental angulation, and acceptable rates of arthrodesis without the need for supplemental posterior instrumentation.

Treatment of complex tibial plateau fractures using the less invasive stabilization system plate: clinical experience and a laboratory comparison with double plating

BACKGROUND

Bicondylar tibial plateau fractures are complex injuries, historically associated with high complication rates. The purpose of this study was: 1) to evaluate the clinical use L.I.S.S plating system for stabilization of bicondylar tibial plateau fractures. 2) To compare the biomechanics of this plating system with a double plate construct.

METHODS AND MATERIALS

Thirty-eight patients who sustained a complex tibial plateau fracture (OTA type 41C) at one of three level-one trauma centers were stabilized using the Less Invasive Stabilization System (L.I.S.S.). The cohort of patients was evaluated clinically and radiographically for outcomes at a mean 15 months. In phase 2 of this study a model of a bicondylar tibial plateau fractures was made in six matched pairs of embalmed, human tibia and randomized to fixation with either a L.I.S.S plate or a standard double plate construct. The tibias were then subjected to an axial cyclic load of 500N for 10 cycles (3Hz) to approximate 2 months in vivo and displacements measured.

RESULTS

Thirty-six of /38 (95%) patients united at 4 months after surgery with no loss of fixation nor infection. Two patients underwent prophylactic autogenous bone grafting for bone loss and united by 3 months postgrafting. Significant loss of knee range of motion (<90) was seen in five patients.Biomechanically, no differences in permanent inferior displacement of the medial fragment were found in initial axial loading and after 10 cycles between the two plate constructs. However, when loaded to 500N the L.I.S.S plate construct demonstrated almost twice the displacement of the medial fragment compared with the dual plate construct. No specimen lost fixation during cycling.

CONCLUSION

The L.I.S.S plating system provides stable fixation of complex bicondylar tibial plateau fractures allowing early range of knee motion with favorable clinical results.

A retrospective review of cervical corpectomy: indications, complications and outcome

BACKGROUND

Cervical corpectomy is a common spinal surgery procedure used to decompress the spinal cord in numerous degenerative, traumatic and neoplastic conditions. The aim of this study was to investigate the indications, complications and outcomes in past cervical corpectomy cases at one centre.

METHOD

72 patients who underwent cervical corpectomy between February 1992 and June 2001 were retrospectively investigated.

FINDINGS

The indications for this operation were degenerative spondylitic disease (26 cases; 36.1%), trauma (18 cases; 25%), tumour (11 cases; 15.3%), infection (10 cases; 13.9%), and ossification of the posterior longitudinal ligament (7 cases; 9.7%). Thirty-seven patients (51.4%) underwent one-level corpectomy, and 35 (48.6%) underwent two-level corpectomy. Autografts were used in 13 cases (18.1%) and allografts were used in 59 cases (81.9%). Anterior plate-screw fixation was performed in all cases. There were 31 postoperative complications in 15 (20.8%) patients. Twelve of the complications were surgical, 5 were graft-related, 7 were plating-related, and 7 were medical. Solid bony fusion was achieved in 65 (92.9%) of the 70 surviving patients. The mean follow-up time was 23.4 months. An overall favourable outcome was achieved in 88% of cases.

CONCLUSION

The outcomes in this series indicate that cervical corpectomy is an effective method for treating traumatic lesions, degenerative disease, tumours and infectious processes involving the anterior and middle portions of the cervical spine.

New material for Nuss procedure

The Nuss procedure for pectus excavatum repair has been considered an acceptable method in terms of its decreased invasiveness and excellent cosmetic results. Although a steel bar is usually used for elevating the sternum, we used a titanium alloy plate for pectus excavatum repair for the first time. The characteristics of this plate are that 1) it comes out translucently on X-rays, 2) MRI examination is possible because titanium will not be magnetized, and 3) it is possible to go through the security checkpoint at the airport without setting off the metal detector. Furthermore, the titanium alloy is highly elastic, which reduces complications such as dislocation, and it excels in the conformity to organization. Patients who have received the Nuss operation are forced to somewhat limit their daily life for two or three years until the bar is removed. A plate made from titanium alloy resolves this problem because of its material and it is thought to be an ideal candidate for elevating the sternum during the Nuss operation.

Reconstruction of a large post-traumatic cranial defect with a customized titanium plaque

The treatment of serious cranial defects has always been a fascinating and controversial issue for craniofacial surgeons and in the last years many solutions have been proposed. One of the most effective method is a personalized titanium plaque prepared by processing anatomical data obtained with a CAT of the patient. A case of wide cranial defect on the left fronto-parietal region in a 56-year-old man treated with a personalized titanium plaque obtained by processing the data of a spiral CAT of the skull is described. No complications were observed in the postoperative course and follow-up after 6 moths showed that the patient was in good general condition.

Distractive flexion injuries of the subaxial cervical spine treated with anterior plate alone

The clinical and radiographic effect of anterior plate fixation alone was evaluated in 36 consecutive patients with distractive flexion (DF) injuries in the lower cervical spine. Mean follow-up time was 15 months. The aim of the present study was to determine whether anterior plate fixation alone provides sufficient stability when treating DF injuries in the cervical spine. Solid union was seen in 6 of 6 patients with stage 1 injury and in 15 of 17 patients with stage 2 injury. In the patients with stage 3 injury, 7 of 13 of the anterior fixations failed. These failures occurred mainly among the patients with severe neurologic injuries. We believe these findings substantiate the use of anterior plate alone for DF injuries at stage 1 and 2 but disqualify anterior plate fixation alone for DF injuries at stage 3, with neurologic injury present.