Comparison of the fixation ability of headless compression screws and locking plate for metacarpal shaft transverse fracture

Metacarpal shaft fractures are common hand fractures. Although bone plates possess strong fixation ability, they have several limitations. The use of headless compression screws for fracture repair has been reported, but their fixation ability has not been understood clearly.This study aimed to compare the fixation ability of locked plate with that of headless compression screw for metacarpal fracture repair.A total of 14 artificial metacarpal bones (Sawbones, Vashon, WA, USA) were subjected to transverse metacarpal shaft fractures and divided into 2 groups. The first group of bones was fixed using locked plates (LP group), whereas the second group was fixed using headless compression screws (HC group). A material testing machine was used to perform cantilever bending tests, whereby maximum fracture force and stiffness were measured. The fixation methods were compared by conducting a Mann-Whitney U test.The maximum fracture force of the HC group (285.6 ± 57.3 N, median + interquartile range) was significantly higher than that of the LP group (227.8 ± 37.5 N; P < .05). The median of the HC group was 25.4% greater. However, no significant difference in stiffness (P > .05) was observed between the HC (65.2 ± 24.6 N/mm) and LP (61.7 ± 19.7 N/mm) groups.Headless compression screws exhibited greater fixability than did locked plates, particularly in its resistance to maximum fracture force.

Fractured coracoid process with acromioclavicular joint dislocation: A case report

RATIONALE

Coracoid processes (CPs) fracture with acromioclavicular (AC) joint dislocation are extremely rare. This combined injury has brought many challenges to surgeons, and the mechanism underlying the injury is still not fully understood. There is no clear consensus on its treatment.

PATIENT CONCERNS

Here, we describe a CP fracture with AC joint dislocation in a middle-aged manual worker.

DIAGNOSIS

Radiographs showed a fracture of the base of the CP and a third-degree AC joint separation.

INTERVENTIONS

The patient was treated surgically with open reduction and internal fixation of the AC joint by LCP clavicle hook plate, and the CP was fixed with a 3.5 mm diameter cannulated screw.

OUTCOMES

Three months after the operation, shoulder function was completely restored, and the affected shoulder had full mobility with no tenderness. Plain film radiography showed anatomical indications of the healing of these combined injuries.

LESSONS

Although AC joint dislocation with CP fractures is extremely rare in adults, it is important to remind and remember that this possibility exists. In unclear cases, special radiographic films and CT are necessary. Surgical treatment of AC joint dislocation with CP fractures can provide solid stability and restore normal shoulder function with an excellent prognosis.

Three-Dimensional Printed Porous Titanium Screw with Bioactive Surface Modification for Bone-Tendon Healing: A Rabbit Animal Model

The interference screw fixation method is used to secure a graft in the tibial tunnel during anterior cruciate ligament reconstruction surgery. However, several complications have been reported, such as biodegradable screw breakage, inflammatory or foreign body reaction, tunnel enlargement, and delayed graft healing. Using additive manufacturing (AM) technology, we developed a titanium alloy (Ti₆Al₄V) interference screw with chemically calcium phosphate surface modification technology to improve bone integration in the tibial tunnel. After chemical and heat treatment, the titanium screw formed a dense apatite layer on the metal surface in simulated body fluid. Twenty-seven New Zealand white rabbits were randomly divided into control and additive manufactured (AMD) screw groups. The long digital extensor tendon was detached and translated into a tibial plateau tunnel (diameter: 2.0 mm) and transfixed with an interference screw while the paw was in dorsiflexion. Biomechanical analyses, histological analyses, and an imaging study were performed at 1, 3, and 6 months. The biomechanical test showed that the ultimate pull-out load failure was significantly higher in the AMD screw group in all tested periods. Micro-computed tomography analyses revealed early woven bone formation in the AMD screw group at 1 and 3 months. In conclusion, AMD screws with bioactive surface modification improved bone ingrowth and enhanced biomechanical performance in a rabbit model.

The implant density does not change the correction rate of the main and the accompanying curves: A comparison between consecutive and intermittent pedicle screw constructs

OBJECTIVE

The aim of this study was to evaluate the clinical outcomes and the coronal correction rate of the main and accompanying curves of adolescent idiopathic scoliosis (AIS) corrected with pedicle screws inserted consecutively or intermittently.

METHODS

The prospectively collected data of 60 patients (8 men and 52 women; mean age: 14.6±2.5 years) who underwent corrective surgery for AIS between January 2010 and December 2015 were reviewed retrospectively. Two groups were constituted according to the pedicle screw construct type: consecutive pedicle screw construct (CPSC) and intermittent pedicle screw construct (IPSC) groups. The preoperative, early postoperative, and 24-month follow-up radiographs and the Scoliosis Research Society-22 (SRS-22) scores were reevaluated. The Cobb angle of the main and accompanying curves, the correction rate, and the flexibility of the curves were calculated.

RESULTS

The mean preoperative Cobb angles were 57.03° and 57.46°, the mean postoperative Cobb angles were 14.93° and 14.4°, and the mean correction rates were 76.22% and 75.31% in IPSC and CPSC groups, respectively (p>0.05). The preoperative and postoperative accompanying curve magnitudes and correction rates were similar (p>0.05). These radiographic outcomes were also consistent with the SRS-22 scores.

CONCLUSION

Both the pedicle screw constructs had satisfactory outcomes following the surgery, which were confirmed by both the SRS-22 scores and radiographs taken perioperatively and at follow-ups. The IPSC and CPSC groups did not demonstrate a significant change in the correction rate of the main and minor or major accompanying structural and nonstructural curves, and also in the SRS-22 scores.

LEVEL OF EVIDENCE

Level III, Retrospective comparative study.

3-Dimensional printing templates guiding versus free hand technique for cervical lateral mass screw fixation: A prospective study

OBJECTIVE

In this randomized, single blind and controlled study, the feasibility and precision of 3-dimensional printing templates for cervical lateral mass screw insertion was evaluated.

METHODS

A total of 6 patients (72 screws), who were diagnosed with cervical spondylotic myelopathy (CSM) and developmental cervical spinal stenosis, were randomly divided into A and B two groups. All subjects underwent modified posterior surgery with using cervical lateral mass screws insertion (C4-C6). Group A underwent surgeries with screw insertion assisted by the guidance of 3-dimensional printing templates and Group B underwent surgeries with screw insertion by freehand. The criteria of the accuracy of screw placement were set as the main evaluation indicators.

RESULTS

There was no significant difference between the 2 groups in age, improvement rate of JOA, operation time and blood loss. According to Bayard's criteria, 32 screws (88.9%) were described as "acceptable" in group A and 22 screws (61.1%) were described as "acceptable" in Group B (P < 0.05). Based on our criteria, the "excellent and good" rate of screws was 83.3% in group A and 47.2% in Group B, respectively (P < 0.05). The precision of screws' location in Group A was superior to that in Group B.

CONCLUSIONS

3-Dimensional printing screw insertion templates may achieve (1) comprehensive visualization of the cervical vertebrae and lateral mass and the individual surgical planning using the 3-dimensional model preoperatively. (2) increasing the accuracy of cervical lateral mass screw insertion.

Safe zones of the maxillary alveolar bone in Down syndrome for orthodontic miniscrew placement assessed with cone-beam computed tomography

The aim of this study was to quantify the available maxillary alveolar bone in a group of individuals with Down syndrome (DS) to determine the best areas for orthodontic miniscrew placement. The study group consisted of 40 patients with DS aged 12-30 years. We also selected an age and sex-matched control group. All measurements were performed on cross-sectional images obtained with cone-beam computed tomography. The selected areas of interest were the 4 interradicular spaces between the distal wall of the canine and the mesial wall of the second molar, in both maxillary quadrants. We measured the vestibular-palatine (VP) and mesiodistal (MD) dimensions to depths of 3, 6 and 9 mm from the alveolar ridge. We also measured the bone density in the same interradicular spaces of interest to 6 mm of depth from the alveolar crest. VP measurements were longer in the more posterior sectors and as the distance from the alveolar ridge increased. MD measurements also increased progressively as the distance from the alveolar ridge increased. In general, both the VP and MD measurements in the DS group were similar among the male and female participants. As age increased, the MD distance increased, while the VP distance decreased. The VP distance was ≥6 mm in at least 75% of the DS group in practically all assessed interdental spaces. The MD distance was ≥2 mm in at least 75% of the DS group only between the first and second molar, to 9 mm of depth from the alveolar ridge. The safe area for inserting orthodontic miniscrews in DS patients is restricted to the most posterior and deepest area of the maxillary alveolar bone.

Improvement of osteogenesis by a uniform PCL coating on a magnesium screw for biodegradable applications

A polymer coating as polycaprolactone (PCL) is applied to improve the initial corrosion resistance of biodegradable magnesium. In addition, plasma electrolytic oxidation (PEO) is performed to increase adhesion between the polymer and the metal. However, when a complex-shaped material such as a screw is implanted in a bone, the surface coatings are locally damaged, and the protective role of the coating is not sufficiently maintained. In this study, the optimal conditions for producing a polymer coating on a screw were determined by varying the concentration of the PCL and the coating cycles, and were examined in vitro and in vivo. Among various the PCL coating conditions of 2∼6 cycles with 5∼7 wt.% concentrations, the 6 wt.% + 4 cycles group was applied uniformly to the screw thread. In the case of the non-uniform PCL layers, oxides and gases were present between the Mg and the PCL layer because internal magnesium corrosion and the layer peel off. The 6 wt.% + 4 cycles group had a high corrosion resistance due to the low wear on the thread. Denser and thicker bone formed around the PCL-coated screw in rat femur. This difference was due to the high corrosion resistance, which provided sufficient time for bone healing and promoting new bone growth.

Cancellous Screws Are Biomechanically Superior to Cortical Screws in Metaphyseal Bone

Cancellous screws are designed to optimize fixation in metaphyseal bone environments; however, certain clinical situations may require the substitution of cortical screws for use in cancellous bone, such as anatomic constraints, fragment size, or available instrumentation. This study compares the biomechanical properties of commercially available cortical and cancellous screw designs in a synthetic model representing various bone densities. Commercially available, fully threaded, 4.0-mm outer-diameter cortical and cancellous screws were tested in terms of pullout strength and maximum insertion torque in standard-density and osteoporotic cancellous bone models. Pullout strength and maximum insertion torque were both found to be greater for cancellous screws than cortical screws in all synthetic densities tested. The magnitude of difference in pullout strength between cortical and cancellous screws increased with decreasing synthetic bone density. Screw displacement prior to failure and total energy absorbed during pullout strength testing were also significantly greater for cancellous screws in osteoporotic models. Stiffness was greater for cancellous screws in standard and osteoporotic models. Cancellous screws have biomechanical advantages over cortical screws when used in metaphyseal bone, implying the ability to both achieve greater compression and resist displacement at the screw-plate interface. Surgeons should preferentially use cancellous over cortical screws in metaphyseal environments where cortical bone is insufficient for fixation. [Orthopedics.2016; 39(5):e828-e832.].

Prototype of a Silicon Nitride Ceramic-Based Miniplate Osteofixation System for the Midface

OBJECTIVE: The favorable properties of silicon nitride (Si3N4) ceramics, such as high mean strength level and fracture toughness, suggest biomedical use as an implant material. Minor reservations about the biocompatibility of Si3N4 ceramics were cleared up by previous in vitro and in vivo investigations.

STUDY DESIGN AND SETTING: A Si3N4 prototype mini-fixation system was manufactured and implanted for osteosynthesis of artificial frontal bone defects in 3 minipigs. After 3 months, histological sections, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans were obtained. Finite element modeling (FEM) was used to simulate stresses and strains on Si3N4 miniplates and screws to calculate survival probabilities.

RESULTS: Si3N4 miniplates and screws showed satisfying intraoperative workability. There was no implant loss, displacement, or fracture. Bone healing was complete in all animals. The formation of new bone was observed in direct contact to the implants. The implants showed no artifacts on CT and MRI scanning. FEM simulation confirmed the mechanical reliability of the screws, whereas simulated plate geometries regarding pullout forces at maximum load showed limited safety in a bending situation.

CONCLUSIONS: Si3N4 ceramics show a good biocompatibility outcome both in vitro and in vivo. In ENT surgery, this ceramic may serve as a biomaterial for osteosynthesis (eg, of the midface including reconstruction the floor of the orbit and the skull base). To our knowledge, this is the first introduction of a ceramic-based miniplate-osteofixation system. Advantages compared with titanium are no risk of implantation to bone with mucosal attachment, no need for explantation, and no interference with radiologic imaging. Disadvantages include the impossibility of individual bending of the miniplates.

Impact of screw location and endplate preparation on pullout strength for anterior plates and integrated fixation cages

BACKGROUND CONTEXT

Numerous integrated fixation cages (IFCs) have recently been introduced to the market with "zero-profile" designs that incorporate screw fixation through the vertebral endplate. It is unclear whether differences in bone quality and quantity in this insertion location may affect fixation compared with screws used in traditional anterior plate (AP) fixation. Moreover, endplate preparation for IFC implantation may affect fixation strength.

PURPOSE

This study aimed to compare pullout strength of screws used in IFCs with screws used for AP implantations.

STUDY DESIGN

A biomechanical cadaveric study.

METHODS

T12 and L1 vertebrae from 13 human cadaver spines were prepared for pullout testing. End plates in T12 vertebrae were scraped according to surgical practice for fusion procedures. Conversely, endplates in L1 vertebrae were kept intact (unscraped). Integrated fixation cage screws were implanted at a 45° angle into the endplate and AP screws were implanted horizontally into the same vertebral body. Pullout testing was performed on all screws, and peak pullout force (PPF) and work were compared between groups to determine fixation strength. In addition, micro-CT imaging was used to assess bone quantity and quality parameters such as trabecular bone volume fraction, endplate and anterior cortex thickness at screw insertion location, endplate mineralization, and anterior cortex mineralization.

RESULTS

Peak pullout force for IFC screws (176±68 N) with scraped endplates was similar (p=.26) to AP screws (192±84 N). However, PPF for IFC screws (231±75 N) with unscraped endplates was significantly greater (p<.01) than AP screws (176±50 N). Peak pullout force for IFC screws with scraped endplates was significantly lower (p=.03) than IFC screws with unscraped endplates. Scraped endplates group (0.17±0.05 mm) were thinner (p=.05) than unscraped endplates (0.21±0.06 mm) by approximately 40 µ on average.

CONCLUSIONS

These data indicate that IFC and AP screws exhibited similar fixation behavior when the endplate is prepared according to common surgical practices. However, endplate scraping reduces endplate thickness by 20% on average, resulting in a decrease in fixation strength when compared with the unscraped endplates and provides bounds for IFC screw fixation strength.

The new shank construct of lag screw improves the maximum compression force for internal fixations: preliminary results

OBJECTIVE

The treatment of osteoporotic intra-articular fractures with AO lag screws remained challenging due to insufficient compression. Several strategies to improve the compressive ability of lag screws have been evaluated. However, the effect of the shank construct on the compressive ability of lag screw has never been explored. The aim of this study was to determine the effect of a shank construction the compressive ability of lag screw for different bone mineral densities (BMDs).

MATERIALS AND METHODS

Three synthetic cancellous bone blocks were used for this study, including 0.12 g/cc, 0.16 g/cc, and 0.20 g/cc. 24 pilot holes with 3.2 mm diameters were drilled equably in each block. An AO lag screw and a combined lag screw with the newly designed compound shank construct were inserted through the custom-designed measuring device into a pilot hole by hand until failure, and the maximum compressive force (CMAX) was determined.

RESULTS

Among three densities specimens CMAX of the combined lag screw was significantly higher than that of the AO lag screw (p < 0.001), and the mean CMAX difference value of the two screws in a specimen increased as the BMD increased. The CMAX of two screws increased as the BMD increased (p < 0.001), and the amplification of the CMAX generated by the combined lag screw was higher than that generated by the AO lag screw when the BMD increased.

CONCLUSIONS

The newly designed compound shank construct improves the compressive ability of lag screws independent of the BMD.

Clinical comparative analysis on unstable pelvic fractures in the treatment with percutaneous sacroiliac screws and sacroiliac joint anterior plate fixation

OBJECTIVE

To investigate clinical efficacy of unstable pelvic fractures in the treatment with percutaneous sacroiliac screws and sacroiliac joint anterior plate fixation.

PATIENTS AND METHODS

64 patients with unstable pelvic fractures were selected in the hospital from January 2008 to June 2011, and were randomly divided into two groups.(32 patients with sacroiliac anterior plate fixation as the control group, and another 32 patients with percutaneous sacroiliac screw internal fixation as the observation group). The perioperative period clinical indicators, postoperative Matta score, postoperative Majeed function score of all patients were compared and analyzed.

RESULTS

The operation time, intraoperative blood loss, wound total length, postoperative fever time, duration of hospitalization in the observation group were significantly less than those in the control group. The complication rate (3.1%) in the observation group was lower than that in the control group (21.9%). The rate of Matta score excellent (96.9%) in the observation group was higher than that in the control group (81.2%) after the treatment. The rate of Majeed function score excellent (93.8%) in the observation group was significantly higher than that in the control group (75%) after the treatment.

CONCLUSIONS

Percutaneous sacroiliac screw internal fixation in the treatment of unstable pelvic fractures has less injury, less bleeding, less pain and rapid recovery which is a safe and effective minimally invasive operation method. The clinical curative effect of percutaneous sacroiliac screw internal fixation is better than anterior plate fixation for the treatment of sacroiliac joint. The full preparation before the surgery and patients with positive can substantially reduce the occurrence of complications rate.

Biomechanical analysis of a new expandable vertebral body replacement combined with a new polyaxial antero-lateral plate and/or pedicle screws and rods

PURPOSE

Restoration of the anterior spinal profile and regular load-bearing is the main goal treating anterior spinal defects in case of fracture. Over the past years, development and clinical usage of cages for vertebral body replacement have increased rapidly. For an enhanced stabilization of rotationally unstable fractures, additional antero-lateral implants are common. The purpose of this study was the evaluation of the biomechanical behaviour of a recently modified, in situ distractible vertebral body replacement (VBR) combined with a newly developed antero-lateral polyaxial plate and/or pedicle screws and rods using a full corpectomy model as fracture simulation.

METHODS

Twelve human spinal specimens (Th12-L4) were tested in a six-degree-of-freedom spine tester applying pure moments of 7.5 Nm to evaluate the stiffness of three different test instrumentations using a total corpectomy L2 model: (1) VBR+antero-lateral plate; (2) VBR, antero-lateral plate+pedicle screws and rods and (3) VBR+pedicle screws and rods.

RESULTS

In the presented total corpectomy defect model, only the combined antero-posterior instrumentation (VBR, antero-lateral plate+pedicle screws and rods) could achieve higher stiffness in all three-movement planes than the intact specimen. In axial rotation, neither isolated anterior instrumentation (VBR+antero-lateral plate) nor isolated posterior instrumentation (VBR+pedicle screws and rods) could stabilize the total corpectomy compared to the intact state.

CONCLUSIONS

For rotationally unstable vertebral body fractures, only combined antero-posterior instrumentation could significantly decrease the range of motion (ROM) in all motion planes compared to the intact state.

Frame stability and anatomical QA in radiosurgery

OBJECTIVES

The aim of the study was to analyze whether the fixation of the stereotactic frame is stable and whether the location of the treated target coincides with its anatomical location during Gamma Knife(®) surgery (GKS).

MATERIALS AND METHODS

Stereotactic MR examinations using the same high-resolution MRI protocol were performed before and after GKS in 18 consecutive patients. The stereotactic (x,y,z) coordinates for three different anatomical landmarks were independently defined three times in each study for each landmark of the images taken before and after GKS by two of the authors, resulting in a total of 648 coordinate definitions.

RESULTS

The uncertainty in the readings of the coordinates for the anatomical landmarks was of the same magnitude as the difference in the coordinates before and after GKS in all but one patient. The differences in this one case were due to MR distortion and not to repositioning of the frame. The difference in the coordinates before and after treatment was not affected by the removal of one of the frontal fixation screws in one of the patients.

CONCLUSIONS

The stereotactic frame position is stable and does not move.

Pedicle screw instrumentation in adolescent idiopathic scoliosis (AIS)

INTRODUCTION

Pedicle screw instrumentation in AIS has advantages of rigid fixation, improved deformity correction and a shorter fusion, but needs an exacting technique.

MATERIALS AND METHODS

The author has been using the K-wire method with intraoperative single PA and lateral radiographs, because it is safe, accurate and fast. Pedicle screws are inserted in every segment on the correction side (thoracic concave) and every 2-3 on the supportive side (thoracic convex). After an over-bent rod is inserted on the corrective side, the rod is rotated 90° counterclockwise. This maneuver corrects the coronal and sagittal curves. Then the vertebra is derotated by direct vertebral rotation (DVR) correcting the rotational deformity. The direction of DVR should be opposite to that of the vertebral rotation. A rigid rod has to be used to prevent the rod from straightening out during the rod derotation and DVR. The ideal classification of AIS should address all curve patterns, predicts accurate fusion extent and have good inter/intraobserver reliability. The Suk classification matches the ideal classification is simple and memorable, and has only four structural curve patterns; single thoracic, double thoracic, double major and thoracolumbar/lumbar. Each curve has two types, A and B. When using pedicle screws in thoracic AIS, curves are usually fused from upper neutral to lower neutral vertebra. Identification of the end vertebra and the neutral vertebra is important in deciding the fusion levels and the direction of DVR. In lumbar AIS, fusion is performed from upper neutral vertebra to L3 or L4 depending on its curve types.

CONCLUSIONS

Rod derotation and DVR using pedicle screw instrumentation give true three dimensional deformity correction in the treatment of AIS. Suk classification with these methods predicts exact fusion extent and is easy to understand and remember.

Accuracy of freehand fluoroscopy-guided placement of C1 lateral mass and C2 isthmic screws in atlanto-axial instability

BACKGROUND

The C1 lateral mass and C2 isthmic stabilization, as introduced by Goel and Laheri and by Harms and Melcher, is a well-known fixation technique. We present the clinical and radiographic results with freehand fluoroscopy guided C1 lateral mass and C2 isthmic fixation in a consecutive series of 28 patients, evaluating the accuracy of screw placement.

METHODS

Twenty-eight consecutive patients suffering from post-traumatic and other C1-C2 instability were operated on between 2001 and 2010. Indications for surgery were: trauma (n = 21 cases), os odontoideum (n = 1), cranio-verterbal malformation (n = 1), and arthritis (n = 3) and idiopathic instability (n = 2). C1 lateral mass and C2 isthmic screws were placed according to the usual anatomical landmarks with lateral fluoroscopy guidance. All patients underwent a postoperative CT scan. The extent of cortical lateral or medial breach was determined and classified as follows: no breach (grade A), 0-2 mm (grade B), 2-4 mm (grade C), 4-6 mm (grade D), more than 6 mm (grade E). Grade A and B screws were considered well positioned.

RESULTS

A total of 56 C1 lateral mass and 55 C2 isthmic screws were placed. Accuracy of screw placement was as follows: 107 grade A (96.4%), four grade B (3.6%), and no grade C, D or E. Clinical and radiological follow-up showed improvement in symptoms (mainly pain) and stability of the implants at the end of the follow-up.

CONCLUSIONS

Freehand fluoroscopy-guided insertion of C1 lateral mass and C2 isthmic screws can be safely and effectively performed.

Factors affecting the accurate placement of percutaneous pedicle screws during minimally invasive transforaminal lumbar interbody fusion

We retrospectively evaluated 488 percutaneous pedicle screws in 110 consecutive patients that had undergone minimally invasive transforaminal lumbar interbody fusion (MITLIF) to determine the incidence of pedicle screw misplacement and its relevant risk factors. Screw placements were classified based on postoperative computed tomographic findings as "correct", "cortical encroachment" or as "frank penetration". Age, gender, body mass index, bone mineral density, diagnosis, operation time, estimated blood loss (EBL), level of fusion, surgeon's position, spinal alignment, quality/quantity of multifidus muscle, and depth to screw entry point were considered to be demographic and anatomical variables capable of affecting pedicle screw placement. Pedicle dimensions, facet joint arthritis, screw location (ipsilateral or contralateral), screw length, screw diameter, and screw trajectory angle were regarded as screw-related variables. Logistic regression analysis was conducted to examine relations between these variables and the correctness of screw placement. The incidence of cortical encroachment was 12.5% (61 screws), and frank penetration was found for 54 (11.1%) screws. Two patients (0.4%) with medial penetration underwent revision for unbearable radicular pain and foot drop, respectively. The odds ratios of significant risk factors for pedicle screw misplacement were 3.373 (95% CI 1.095-10.391) for obesity, 1.141 (95% CI 1.024-1.271) for pedicle convergent angle, 1.013 (95% CI 1.006-1.065) for EBL >400 cc, and 1.003 (95% CI 1.000-1.006) for cross-sectional area of multifidus muscle. Although percutaneous insertion of pedicle screws was performed safely during MITLIF, several risk factors should be considered to improve placement accuracy.

Anterior and posterior vertebral column resection for severe and rigid idiopathic scoliosis

A total of 16 patients with severe and rigid idiopathic scoliosis treated by anterior and posterior vertebral column resection (APVCR) were retrospectively reviewed after a minimum follow-up of 2 years. The indication for APVCR was scoliosis more than 90° with flexibility less than 20%. The radiographic parameters were evaluated, and clinical records were reviewed. All patients underwent APVCR with posterior pedicle screw instrumentation in a two-stage surgery. The rib hump was reduced from 7.2 cm preoperatively to 1.8 cm at final follow-up (75% correction). Preoperative curves ranged from 93° to 110° Cobb angle. Coronal plane correction of the major curve averaged 67% with an average loss of correction of 1.4%. The apical vertebral translation of the major curve was corrected by 63.5%. The preoperative coronal imbalance of 0.9 cm (range 0-2.4) was improved to 0.8 cm (range 0.1-1.7) at the most recent follow-up. The preoperative sagittal imbalance of 1.0 cm (range -3.1 to 4.6) was improved to 0.9 cm (range -2.6 to 3.0) at the most recent follow-up. Complications were encountered in four patients. One patient required ventilator support for 12 h after anterior surgery. Malposition of one pedicle screw was found in one patient. Malposition of titanium mesh cage happened to two patients. There were no neurological complications, deep wound infections or pseudarthrosis. APVCR is an effective alternative for severe and rigid idiopathic scoliosis.

Polymethylmethacrylate augmentation of the pedicle screw: the cement distribution in the vertebral body

Many studies have proven that the polymethylmethacrylate (PMMA) augmentation of the pedicle screw can significantly increase stiffness and strength of spinal fixation. Some major complications have also been reported. However, there are no reports discussing cement distribution and its morphology in the osteoporotic vertebral body, which is critical in the analysis of the biomechanical strength of the pedicle screw and the risk of cement leakage after pedicle screw augmentation. In this study, we used computed tomography (CT) to evaluate the cement distribution in the osteoporotic vertebral body after PMMA augmentation of a pedicle screw and to analyze the factors leading to cement leakage. Two groups of patients were studied. Group A consisted 25 osteoporotic patients (mean age of 73 years) with spinal instrumentation who had a total of 145 pedicle screws and cement augmentation with biopsy needles. Group B consisted of 23 osteoporotic patients (mean age of 74.6 years) with spinal instrumentation who had a total of 125 cannulated pedicle screws with cement augmentation. All patients had CT evaluation of the cement distribution in the vertebral body after the surgery. The cement distribution in the vertebrae was divided into four zones in the axial CT view: anterior one-third, middle third, and posterior third of vertebral body, and the pedicle. The morphology of the cement distribution around the pedicle screw was defined as scattered type or concentrate type. The leakage pattern was divided to anterior-lateral, posterior-lateral, and canal leakage. The correlations among bone mineral density (BMD), the cement leakage rate, and cement distribution morphology were also analyzed. The results showed that most augmented pedicle screws had cement extension into three of the four zones of the vertebral body (66.3%), followed by two zones (20%), all four zones (11.5%), and only one zone (2.2%). Overall, 123 screws (84.8%) in Group A and 108 screws (86.4%) in Group B had cement concentrate type distribution. The cement leakage rate in Group A is 18.3% and 13.6% in Group B. Patients with a BMD <0.6 g/cm(2) had significantly higher rates of cement leakage and tended toward a scattered cement distribution. There was only one patient who had a symptomatic leakage (sciatica) in Group B. We concluded that the cement distribution after pedicle screw augmentation with biopsy needle or cannulated screw technique was mostly localized in three zones of the vertebral body, and patients with lower BMD had a higher risk of cement leakage and scattered cement distribution.

Pedicle screw-based dynamic stabilization of the thoracolumbar spine with the Cosmic-system: a prospective observation

OBJECT

The objective of the study was to generate prospective data to assess the clinical results after dynamic stabilization with the Cosmic system (Ulrich Medical).

PATIENTS AND METHODS

Between April 2006 and December 2007, 103 consecutive patients were treated with Cosmic for painful degenerative segmental instability +/- spinal stenosis. The preoperative workup included radiological (MRI and myelography/CT) and clinical parameters (general/neurological examination, visual analogue scale (VAS), Oswestry disability index (ODI), SF-36, Karnofsky (KPS)). At pre-defined intervals (at discharge, 6 weeks, 3 months, 6 months, 12 months, and yearly) the patients were reevaluated (X-ray/flexion/extension, neurological status, VAS, ODI, SF-36, KPS, and patient satisfaction). Data were collected in a prospective observational design.

RESULTS

Data collection was completed in 100 of 103 operated patients (mean follow-up, 15 +/- 0.6 months). Dynamic stabilization was performed as first-tier surgery in 43 cases and as second-tier therapy in 60 cases. Additional decompression was performed in 83 cases. Dynamic stabilization led to significant reduction of back pain-related disability (ODI pre-op, 51 +/- 1%; post-op, 21 +/- 1%) and improvement of pain (VAS pre-op, 65 +/- 1; post-op, 21 +/- 2), mental/physical health (norm-based SF-36: mental pre-op, 44; post-op, 48; physical pre-op, 41; post-op, 46), and mobility (KPS pre-op, 70 +/- 1; post-op, 82 +/- 31). Early reoperation was necessary in 12 patients (n = 3 symptomatic misplaced screws, n = 8 CSF pseudocele, rebleeding, or impaired wound healing, n = 1 misjudged instability/stenosis in adjacent segment). Reoperations within the follow-up period were necessary in another 10 patients due to secondary screw loosening (n = 2), persistent stenosis/disk protrusion in an instrumented segment (n = 3), symptomatic degeneration of an adjacent segment (n = 6), or osteoporotic fracture of an adjacent vertebra (n = 1), respectively. Patient satisfaction rate was 91%.

CONCLUSIONS

Dynamic stabilization with Cosmic achieved significant improvement of pain, related disability, mental/physical health, and mobility, respectively, and a high rate of satisfied patients. A reoperation rate of 10% during follow-up seems relatively high at first glance. Comparable data, however, are scarce, and a prospective randomized trial (spondylodesis vs. dynamic stabilization) is warranted based on these results.

Radiological and clinical outcome of screw placement in adolescent idiopathic scoliosis: evaluation with low-dose computed tomography

Posterior corrective surgery using "all pedicle screw construct" carries risk of neurovascular complications. The study aims were to assess the screw placement in patients with adolescent idiopathic scoliosis using CT with low-radiation dose, and to evaluate the clinical outcome in patients with misplaced pedicle screws. CTs of 49 consecutive patients (873 screws, 79% thoracic) were retrospectively evaluated by two independent radiologists. A new grading system was developed to distinguish between lateral, medial and anterior cortical perforations, endplate perforation and foraminal perforation. The grading system is based on whether the cortical violation is partial or total rather than on mm-basis. The overall rate of screw misplacement was 17% (n = 149): 8% were laterally placed and 6.1% were medially placed. The rates of anterior cortical, endplate and foraminal perforation were 1.5, 0.9, and 0.5%, respectively. Lateral cortical perforation was more frequent in the thoracic spine (P = 0.005), whereas other types of misplacement including medial cortical perforation were more frequent on the left and the concave side of scoliotic curves (P = 0.002 and 0.003). No neurovascular complications were reported. The association between the occurrence of screw misplacement and the Cobb angle was statistically significant (P = 0.037). Misplacements exceeding half screw diameter should be classified as unacceptable. Low-dose CT implies exposing these young individuals to a significantly lower radiation dose than do other protocols used in daily clinical practice. We recommend using low-dose CT and the grading system proposed here in the postoperative assessment of screw placement.

Retrieval analysis on dental implants biointegration phases

This study was developed for evaluating the possible causes of losing primary stability of dental implants and to find possible associations between implant designs or implant surface treatment and the quality of surrounding bone tissue. There have been evaluated five CP (Commercial Products) titanium dental implants having different shapes and surface morphology. All the implants have been extracted between three and six month from insertion time due to the loosening of primary stability. The lost during three to six months of the primary stability for the dental implants evaluated at the interface was attributed to blood supply deficiency of the surrounding bone in case of the implants inserted in the anterior-lateral and lateral mandible bone, on implant surrounding bone with consecutive necrosis without leaving the possibility of normal healing both for the maxilla and the mandible, or to prosthetic load deficiency by applying forces out of the implant axis.

A clinical comparison of screw and suture fixation of anterior cruciate ligament tibial avulsion fractures

BACKGROUND

Screw and suture fixations are the most commonly used methods of fixation in treatment of anterior cruciate ligament tibial avulsion fractures. Even though a few biomechanical studies have compared the stability of the 2 fixation techniques, a clinical comparison has not yet been reported.

HYPOTHESIS

The authors hypothesized that both fixations would be identical in all studied clinical outcome measures at a minimum 2-year follow-up.

STUDY DESIGN

Cohort study; Level of evidence, 3.

MATERIALS AND METHODS

Thirty-three patients treated with either screw fixation (16 patients) or suture fixation (17 patients) within 1 month of the anterior cruciate ligament tibial avulsion fracture (type II or III) without associated ligamentous injury were included. All patients were evaluated at a minimum 2-year follow-up in terms of Lysholm knee scores and return to preinjury activities. Knee stability was compared based on the Lachman test and stress radiography.

RESULTS

No significant differences were found between the 2 groups in terms of average Lysholm knee scores (91.7 in the screw group and 92.7 in the suture group, P = .413) at follow-up. All patients except 2 (1 in each group) returned to preinjury activity levels. However, flexion contractures (5 degrees to 10 degrees) were found in 3 patients in the screw group and 2 patients in the suture group without significant intergroup difference. Stabilities based on the Lachman test and instrumented stress radiography were also similar between the 2 groups at follow-up. However, 2 patients in the screw group and 1 in the suture group showed more than 5 mm laxity compared with the contralateral knee on stress radiographs.

CONCLUSION

Both the screw and suture fixation techniques for the anterior cruciate ligament tibial avulsion fracture produced relatively good results in terms of functional outcomes and stability without any significant differences. However, some patients in both groups showed residual laxity or flexion contractures.

Comparison of ventral corpectomy and plate-screw-instrumented fusion with dorsal laminectomy and rod-screw-instrumented fusion for treatment of at least two vertebral-level spondylotic cervical myelopathy

The objective of the article is to verify the hypothesis that the dorsal multilevel laminectomy and rod-screw-instrumented fusion (DLF) for multilevel spondylotic cervical myelopathy (MSCM) is less strenuous for patients, and less prone to perioperative complications, than ventral multilevel corpectomy and plate-screw-instrumented fusion (VCF), while clinical outcome is comparable. One hundred and three successive patients were treated for at least two vertebral-level MSCM, 42 of them by VCF and 61 by DLF. The two patients groups were retrospectively compared. VCF patients were slightly younger than DLF patients (62.5 +/- 10.61 years versus 66 +/- 12.4 years, P = 0.012). In VCF patients, a median of 2 (2-3) corpectomies and in DLF patients a median of 3 (2-5) laminectomies were performed. In VCF patients, surgery lasted longer than in DLF patients (229 +/- 60 min versus 183 +/- 46 min, P < or = 0.001). Between the VCF and the DLF patients groups, no significant difference was found in perioperative complications (e.g. hardware failure rates of 16.7% in VCF and of 6.6% in the DLF patients) and mortality rates. The postoperative outcome, as assessed by the postoperative change of the Nurick scores, the change of neck pain, the patients' satisfaction, and the change of the subaxial Cobb angle of the spine did not differ between the two patients groups. However, when comparing the postoperative Nurick scores directly, VCF patients fared somewhat better than DLF patients [median of 2 (0-5) versus 3 (1-5), P = 0.003]. The hypothesized advantages of DLF over VCF in the surgical treatment of at least two vertebral-level MSCM could not be confirmed in this retrospective study. A prospective randomized study is warranted to clarify this issue.

Locking plates increase the strength of dynamic hip screws

INTRODUCTION

Failure of a dynamic hip screw (DHS) fixation leads to decreased mobility of the patient and frequently to a decrease in general health. The most common mode of failure of a DHS is cut out of the lag screw from the femoral head. The second most common mode of failure is lift-off of the plate from the femur. The aim of this laboratory-based experimental study was to determine whether a DHS secured to an osteoporotic femur with a locking screw plate would provide a stronger construct than the standard DHS plate.

METHOD

The standard DHS design was compared to a DHS with fixed angle locking screws holding the DHS plate to the femur. Standard dynamic compression plates (DCP) and locking compression plates (LCP) were attached to synthetic, osteoporotic bone. A load was applied to replicate the forces occurring following the fixation of unstable, intertrochanteric hip fractures. A bracket on the proximal end of the plate replicated the lag screw in the femoral head. The constructs were cyclically loaded by a screw-driven material-testing machine and the number of cycles before failure occurred was determined.

RESULTS

The mean number of cycles to failure for the locking plate construct was 2.6 times greater than for the standard screw construct (285 versus 108 cycles, respectively p=0.016).

CONCLUSION

A dynamic hip screw with fixed angle locking screws would reduce the risk of DHS failure. A locking screw DHS would be particularly useful in patients with osteoporotic bone, and in patients with less stable fracture configurations.

Mechanical properties of 18 different AO bone plates and the clamp-rod internal fixation system tested on a gap model construct

OBJECTIVE

To compare the stiffness and strength of AO bone plates (DCP, LC-DCP, VCP, RCP, and LP) and the Clamp-Rod Internal Fixation System (CRIF).

STUDY DESIGN

In vitro.

SAMPLE SIZE

12 individual implants of 18 plate dimensions and four sizes of CRIF, each corresponding to 2.0, 2.4/2.7, 3.5, or 4.5 mm screw sizes.

METHODS

Implant-constructs of each plate and CRIF were created using Canevasit rods as a bone substitute in an unstable gap fracture model. Six implant-constructs of each type were tested under single cycle four-point bending loading, and six were tested under single cycle torsional loading until permanent plastic deformation occurred.

RESULTS

Torsional stiffness and yield load of the DCP were always significantly greater than the CRIF within the same group. Bending properties of the 2.0 DCP were not significantly different to the 2.0 CRIF. The 2.7 DCP had significantly higher bending values than the 2.7 CRIF. The bending stiffness of the 3.5 DCP and 4.5 DCP was significantly less than their CRIF counterparts. While the bending yield load of the 3.5 DCP was significantly greater than the 3.5 CRIF, the bending yield load of the 4.5 DCP was significantly less than the 4.5 CRIF.

CONCLUSION

A weakness was found in the torsional resistance of the CRIF constructs compared to the DCP constructs.

CLINICAL SIGNIFICANCE

Bone holding power and applied screw torque should be considered when using the CRIF system in clinical application.

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.

Segmental polymethylmethacrylate-augmented pedicle screw fixation in patients with bone softening caused by osteoporosis and metastatic tumor involvement: a clinical evaluation

OBJECTIVE

Instrumentation of the osteoporotic spine may result in bone failure because of pedicle screw loosening and pullout. A clinical evaluation of a novel fenestrated bone tap used in pedicle screw augmentation was performed to determine the performance and safety of this technique.

METHODS

Over a 2.5-year period, the clinical and radiographic results of 119 consecutive patients who underwent instrumented arthrodesis were reviewed. Of these patients, 23 had bone softening secondary to osteoporosis and/or metastatic spinal tumor involvement. These patients underwent surgical decompression and spinal instrumentation.

RESULTS

Six patients (26%) had metastatic spine disease (squamous cell lung carcinoma, renal cell carcinoma, bladder carcinoma, breast, prostate, and uterine adenocarcinoma); five patients (22%) had a degenerative spondylolisthesis; and 12 patients (52%) had burst fractures, eight as a result of benign causes and four as a result of metastatic disease. Four (17%) patients underwent revision surgery of previous pedicle screw failure resulting from bone softening and pseudarthrosis. A total of 98 levels were fused using 158 polymethylmethacrylate-augmented screws. None of the patients experienced operative death, myocardial infarction, hypoxemia, intraoperative hypotension, radiculopathy, or myelopathy. Asymptomatic anterior cement extravasation was observed in nine patients (39%). There was one asymptomatic polymethylmethacrylate pulmonary embolus and one wound infection. There was no significant relationship between cement extravasation and the quantity used, levels augmented, or location (P > 0.05). There were no construct failures.

CONCLUSION

Polymethylmethacrylate-augmented pedicle screw fixation reduces the likelihood of pedicle screw loosening and pullout in patients with osteoporosis requiring instrumented arthrodesis.

Screw fixation via diploic bone paralleling to occiput table: anatomical analysis of a new technique and report of 11 cases

Several types of posterior approaches have been adopted for occipitocervical fusion. Prior to this study, Foerater et al. in 1927 used a fibular strut graft in the site between the occiput and the lower cervical spine to achieve fusion. Since then, various techniques including wrings, Hartshill loop, AO reconstructive plate, and AXIS occipital plate were described and used widely. As far as we know, all these techniques involve the screw placement vertical to the diploic bone; however none has ever addressed the feasibility of screw placement in occiput parallelling to the diploic bone. In our study, 30 dry specimens of human occiputs were measured manually using vernier calipers and protractors. The intradiploic screw was first supposed to be inserted inferiorly to the superior nuchal line (SNL) prominence. The entry point located at the superior edge of the SNL prominence. Afterward, the measurements of extracranial occiput in SNL area on midline and bilateral 15 mm to the midline saggital-cutting planes of the occiput were conducted. The thickness of the occipital bone at the location of SNL prominence, the entry point, the exit point and the screw orientation were measured, respectively. Afterward, 11 patients with craniocervical malformation were treated surgically using this alternative and their X-ray radiographs and CT scans were evaluated postoperatively. The data showed that the occipital at the site of SNL prominence was the thickest. The thickest point was external occipital protuberance (EOP), which was up to 14 mm. The thickness decreased gradually from the site of SNL to the superior border of surgical decompressed area. The actual length of screw channel was about 26 mm. The mean thickness for safe screw insertion ranged from 5.73 to 14.14 mm. A total of 22 intraocciput screws parallel to diploic bone were placed precisely, without injury to the cerebral and inner occipital venous sinus. The results confirm that occiput is available for holding intraocciput screw paralleling to diploic bone.

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.

Evidence-based medicine analysis of all pedicle screw constructs in adolescent idiopathic scoliosis

STUDY DESIGN

: Focus paper.

OBJECTIVE

: To evaluate the current evidence-based medicine (EBM) literature in the use of pedicle screw constructs in patients with adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND

: EBM has evolved over the past 20 years to provide a framework for the evaluation of therapy and the application of that assessment to a particular patient or a disease. Application of EBM analysis to spinal instrumentation, and specifically to pedicle screw constructs, is challenging.

METHODS

: Cochrane database, Ovid Medline, and PubMed were searched using the terms "pedicle screws" and "adolescent idiopathic scoliosis." The reference list of the major papers by authors Lenke, Suk, and Kim were hand searched. Relevant articles were retained if they described a pedicle screw construct to correct AIS or compared pedicle screw constructs with another technique. Articles that did not have patients with adolescent idiopathic scoliosis in their subject groups or did not use pedicle screws as a part of their deformity correction were excluded from the study.

RESULTS

: Based on the search strategy described above, 40 articles met the inclusion criteria and were selected for review in this manuscript. Of these, 32 studies are retrospective reviews including 2 studies that do not define their data collection technique. Six studies have a prospective study design, 1 is a case report, and 1 is a cadaveric study.

CONCLUSION

: In the absence of evidence from randomized trials, surgeons must rely on the best available information to guide patient management decisions. Although there have been many publications on the topic of all pedicle screw constructs in AIS, evidence regarding the advantage of all pedicle screw constructs remain limited to case series, biomechanical studies, and expert opinions.

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.

Complications of fixed infrared emitters in computer-assisted total knee arthroplasties

Background

The first stage in the implant of a total knee arthroplasty with computer-assisted surgery is to fasten the emitters to the femur and the tibia. These trackers must be hard-fixed to the bone. The objectives of our study are to evaluate the technical problems and complications of these tracker-pins, the necessary time to fix them to the bone and the possible advantages of a new femoral-fixed tracker-pin.

Methods

Three hundred and sixty seven tracker-pins were used in one hundred and fifty one computer-assisted total knee replacements. A bicortical screw was used to fix the tracker to the tibia in all cases; in the femur, however, a bicortical tracker was used in 112 cases, while a new device (OrthoLock) with percutaneous fixation pins was employed in the remaining 39.

Results

Technical problems related to the fixing of the trackers appeared in nine cases (2.5%). The mean surgery time to fix the tracker pin to the tibia was 3 minutes (range 2–7), and 5 minutes in the case of the femoral pin (range: 4–11), although with the new tool it was only three minutes (range 2–4) (p < 0.001). No complications were observed with this new device.

Conclusion

The incidence of problems and complications with the fixing systems used in knee navigation is very small. The use of a new device with percutaneous pins facilitates the fixing of femoral trackers and decreases the time needed to place them.

C-arm assessment of cervical pedicle screw: screw coaxial fluoroscopy and oblique view

STUDY DESIGN

Oblique view and screw coaxial fluoroscopy were used to assess cervical pedicle screw position in human cadaveric spine, results of which were compared with those of direct visual inspection by an anatomist.

OBJECTIVES

To determine whether clinicians can detect misplaced cervical pedicle screws with accurate sensitivity and specificity using conventional C-arm equipment.

SUMMARY OF BACKGROUND DATA

In the cervical region, pedicle screws have not been used so popularly as in lumbar or in thoracic regions. The reasons are related to the risk of inserting screw in small pedicle. So far, no method has been studied to assess the position of cervical pedicle screw during the operation.

METHODS

Ten human cadavers were prepared for this study. Headed and nonheaded pedicle screws were inserted bilaterally from C3-C7. Using C-arm oblique and screw coaxial fluoroscopy, the depth of penetration was recorded in 2-dimension scale (superoinferior and mediolateral direction) by 6 different observers. The vertebrae were all harvested, and the penetration depth was recorded by an anatomist under direct visualization. The accuracy of C-arm measurements was analyzed. The results of nonheaded and headed screws also were compared.

RESULTS

A total of 98 pedicle screw positions were finally enrolled into the study. The oblique view can verify screw position with the sensitivity of 86.1% and specificity of 64.5%. Coaxial fluoroscopy had a sensitivity of 89.8% and a specificity of 56.9% in superoinferior direction. Mediolaterally coaxial fluoroscopy had a sensitivity of 70.0% and a specificity of 51.3%.

CONCLUSION

C-arm assessment of pedicle position has acceptable accuracy. With C-arm swing motion of the coaxial fluoroscopy, headed screws were also inspected without any difference as nonheaded screws. Measurements for superoinferior direction showed better sensitivity than those for mediolateral direction, which are supposed to be related to be elliptical shape and thin lateral margin of cervical pedicle.

Direct Repair of Multiple Levels Lumbar Spondylolysis by Pedicle Screw Laminar Hook and Bone Grafting: Clinical, CT, and MRI-Assessed Study

INTRODUCTION

A prospective analysis of 6 cases with multiple-level spondylolysis treated by direct repair with pedicle screw laminar hook is presented. The objective of the study was to evaluate the clinical outcome, plain radiographs, computed tomography (CT) scan, and magnetic resonance imaging to demonstrate the result of direct repair in the treatment of multiple-level spondylolysis.

MATERIALS AND METHODS

Ten patients with multiple-level spondylolysis of lumbar spine were treated with segmental pedicle screw hook fixation and autogenous bone graft. Four patients had lost follow-up. Six patients were followed up for a minimum of 2 years (mean 34.3 mo, range 24 to 55 mo). Patient's average age was 22 years old (range from 20 to 25 y old). All lytic defects were bilateral and located at 2 different lumbar vertebras (levels). CT scans and MR images were obtained at the latest follow-up postoperatively to assess the healing of the bony defects and the adjacent disc conditions. Fusion was considered to be presented when trabecula across the lytic defect was detected.

RESULTS

The union rate was 87% (21 pars/24 pars) on plain radiographs and 75% (18 pars/24 pars) on CT scans. Follow-up magnetic resonance imaging of lumbar spine showed no disc degeneration. All patients were satisfied (either excellent or good) with the postoperative outcomes.

CONCLUSIONS

Direct repair of multiple-level spondylolysis by pedicle screw laminar hook and autogenous bone graft would be the alternative of treating patients with persistent back pain after 6 months of conservative treatment The favorable clinical outcome was correlated with bony healing rate in this series.

Complications of thoracic pedicle screws in scoliosis treatment

STUDY DESIGN

A retrospective study.

OBJECTIVE

To analyze complications with thoracic pedicle screws in scoliosis treatment at our Department over a 3-year period (1999-2001).

SUMMARY OF BACKGROUND DATA

The use of pedicle screws remains controversial for thoracic scoliosis for fear of complications.

METHODS

A total of 115 consecutive patients who underwent posterior fusion using 1035 transpedicular thoracic screws were reviewed. All patients presented a main thoracic scoliosis with a mean Cobb angle of 75.4 degrees (range, 60 degrees -105 degrees ). For thoracic screw placement, a mini-laminotomy technique was used, inserting a spatula inside the vertebral canal to palpate the borders of the pedicle. Postoperative CT scan was used in 25 patients (21.7%) to study a total of 311 screws, when the screw position was questionable.

RESULTS

An independent spine surgeon retrospectively reviewed medical records and radiographs of the patients, at a mean follow-up of 4 years. There were 18 screws misplaced (1.7%) in a total of 13 patients (11.3%). Screw malposition was symptomatic only in 1 patient (pleural effusion and fever) and asymptomatic in the other 12 cases (10.4%). Other complications included intraoperative pedicle fractures in 15 patients (13%), dural tears (without neurologic complications) in 14 cases (12.1%), and superficial wound infections in 2 (1.7%). Another operation for screw removal was performed in 5 patients (4.3%), due to pleural effusion (in 1 case), asymptomatic late lateral loosening of a malpositioned screw (in 1), and the possible future risks related the intrathoracic screw position despite the lack of any symptoms (in 3). Two cases (1.7%) were retreated due to wound infection, without removing instrumentation. There was no loss of correction at follow-up.

CONCLUSIONS

The thoracic pedicle screw placement in scoliosis patients requires utmost caution. The mini-laminotomy technique was beneficial in increasing safety of the procedure with an acceptable incidence of complications.

Cortical screw pullout strength and effective shear stress in synthetic third generation composite femurs

BACKGROUND

The use of artificial bone analogs in biomechanical testing of orthopaedic fracture fixation devices has increased, particularly due to the recent development of commercially available femurs such as the third generation composite femur that closely reproduce the bulk mechanical behavior of human cadaveric and/or fresh whole bone. The purpose of this investigation was to measure bone screw pullout forces in composite femurs and determine whether results are comparable to cadaver data from previous literature.

METHOD OF APPROACH

The pullout strengths of 3.5 and 4.5 mm standard bicortical screws inserted into synthetic third generation composite femurs were measured and compared to existing adult human cadaveric and animal data from the literature.

RESULTS

For 3.5 mm screws, the measured extraction shear stress in synthetic femurs (23.70-33.99 MPa) was in the range of adult human femurs and tibias (24.4-38.8 MPa). For 4.5 mm screws, the measured values in synthetic femurs (26.04-34.76 MPa) were also similar to adult human specimens (15.9-38.9 MPa). Synthetic femur results for extraction stress showed no statistically significant site-to-site effect for 3.5 and 4.5 mm screws, with one exception. Overall, the 4.5 mm screws showed statistically higher stress required for extraction than 3.5 mm screws.

CONCLUSIONS

The third generation composite femurs provide a satisfactory biomechanical analog to human long-bones at the screw-bone interface. However, it is not known whether these femurs perform similarly to human bone during physiological screw "toggling."

Percutaneous Pedicle Screw Instrumentation for Temporary Internal Bracing of Nondisplaced Bony Chance Fractures

OBJECTIVE AND IMPORTANCE

Although many patients with unstable Chance fractures can heal in an external brace, others will require internal stabilization. Short-segment minimally invasive internal bracing of a Chance fracture offers the rigidity and patient compliance of internal bracing with minimal tissue disruption. This technique has not yet been described.

CLINICAL PRESENTATION

A healthy 16-year-old female and 21-year-old male sustained classic nondisplaced Chance fractures. They were both neurologically intact.

TECHNIQUE

An image-guided Jamshidi needle was used to percutaneously place K-wires to direct percutaneous pedicle screws. Freehand percutaneous passing of rods to connect the pedicle screw heads on each side created a short-segment construct.

CONCLUSIONS

Minimally invasive internal bracing of nondisplaced bony Chance fractures is an option for selected neurologically intact patients unable to tolerate external bracing.

Early Failure of Bioabsorbable Anterior Cervical Fusion Plates

STUDY DESIGN

Case report with forensic failure analysis.

OBJECTIVE

To determine the failure modes of 3 explanted 70:30 PLDLA Mystique (Medtronic Sofamor Danek, Memphis, TN) graft containment plates retrieved from revision surgery for early device failure.

SUMMARY OF BACKGROUND DATA

To reduce the problems of stress-shielding and radiopacity associated with metallic systems, bioabsorbable polymers have been used in anterior cervical discectomy and fusion procedures. Degradation of mechanical properties in vivo is a major concern when using bioabsorbable systems. Three of 6 patients who underwent anterior cervical discectomy with instrumented fusion, using Mystique graft containment systems experienced early failure requiring revision to alternate hardware.

METHODS

Devices were retrieved after failure and analyzed by light microscopy and environmental scanning electron microscopy. Simulations were performed with an unused plating system to induce damage for comparison with the retrieved devices. A detailed case review was performed to identify possible sources of extraordinary loading or damage.

RESULTS

One plating system failed at 6 weeks postimplantation due to fatigue fracture of the screws. Crack initiation sites were identified at the interface of the thread root and mold line of the screw. Another plating system failed at 16 weeks postimplantation due to the coalescence of radial microcracking between holes in the plate, leading to catastrophic failure of the plate. The final plating system failed during the implantation surgery, when the screw fractured in torsion.

CONCLUSIONS

Stress concentrations at the screw head-shaft interface and thread-shaft interface reduce the fatigue performance of bioabsorbable screws. Hydrolysis of the polymer may also play a role in the reduction of resistance to crack initiation and propagation.

Posterior spinal shortening for paraparesis following vertebral collapse due to osteoporosis

STUDY DESIGN

Retrospective case series.

OBJECTIVES

To assess the efficacy of posterior spinal shortening for paraparetic patients following vertebral collapse owing to osteoporosis, especially on instrumentation loosening.

SETTING

Department of orthopaedic surgery, Jichi Medical University Hospital and Omiya Medical Center in Japan.

METHODS

The clinical records and radiographs of 13 patients with paraparesis following vertebral collapse owing to osteoporosis treated with posterior spinal shortening were retrospectively reviewed to evaluate the usefulness of this method. Assessment of the clinical course was done by direct examination in all cases. Ambulatory ability was divided into four categories.

RESULTS

Upon final observation, nine cases were able to walk with a cane or crutch, one case remained in gait training, two cases remained unable to stand and one case with urinary incontinence improved in urinary function. In one case, paralysis deteriorated. Vertebral compression fracture of the end vertebrae that were fixed occurred in three cases complicated with rheumatoid arthritis.

CONCLUSION

The posterior spinal shortening can be a choice for treating delayed paraparesis following vertebral collapse owing to osteoporosis.

An innovative broken pedicle screw retrieval instrument

OBJECTIVE

To introduce a new broken pedicle screw fragment retrieval instrument, and evaluate its clinical viability and effectiveness.

METHODS

Following basic retrieval contrivance of broken pedicle screws described in literature, a new retrieval instrument was designed and developed; introducing its mechanism, technical components, and use. This innovative apparatus proved successful not only in saw bone and cadaver trials but in 10 clinical cases as well.

RESULTS

This particular unique instrument successfully retrieves broken pedicle screw fragments through original passage backing out the screw with preservation of pedicle integrity while maintaining pedicle biomechanics. No complications were observed.

CONCLUSIONS

With solid scientific theoretical planning and experimentation, the new retrieval instrument design proved clinical practicality and efficacy.

Intermediate Screws in Short Segment Pedicular Fixation for Thoracic and Lumbar Fractures

To determine the effect of adding pedicle screws at the level of a burst fracture (intermediate screws) on the stiffness of a short segment pedicle fixation, an in vitro biomechanical study was carried out. Six fresh-frozen pig lumbar spine specimens were used. The flexibility of the intact specimens was examined in flexion, extension, lateral bending, and torsion. An unstable burst fracture model was created by the dropped-mass technique. The unstable spine specimens were instrumented with pedicle screws. The flexibility was tested again with and without intermediate screws. The addition of intermediate screws provided a smaller range of motion in flexion-extension (P<0.001), torsion (P<0.001), and lateral bending (P=0.014). The slopes of the load displacement curves increased in flexion (P<0.001), extension (P=0.003), lateral bending (P=0.003), and torsion (P=0.006), signifying a decrease in flexibility. The addition of intermediate screws at the level of a burst fracture significantly increases the stiffness of a short segment pedicular fixation.

Double insurance atlantoaxial fixation

BACKGROUND

An alternative technique of atlantoaxial fixation is described, which combines the trans-articular method of fixation described by Magerl in 1982 and the interarticular technique described by us in 1988.

METHODS

Between January 2001 and January 2005, 18 patients underwent the discussed method of fixation at the Department of Neurosurgery at King Edward VII Memorial Hospital in Mumbai, India. Fifteen patients had congenital craniovertebral anomaly and 3 patients had posttraumatic atlantoaxial instability. Fourteen patients had basilar invagination with "fixed" atlantoaxial dislocation, and 4 patients had mobile and reducible atlantoaxial dislocation. The mean follow-up period was 22 months (range, 3-50 months).

RESULTS

Successful atlantoaxial stabilization was achieved in all patients and was documented with dynamic radiography. There was no incidence of implant rejection. There were no neurological, vascular, or infective complications.

CONCLUSION

The described method of atlantoaxial fixation that incorporates the advantages of the 2 currently more frequently used techniques of lateral mass fixation could be an alternative method of fixation.