Biomechanical Evaluation of Standard Versus Extended Proximal Fixation Olecranon Plates for Fixation of Olecranon Fractures.

Background: Small olecranon fractures present a significant challenge for fixation, which has resulted in development of plates with proximal extension. Olecranon-specific plates with proximal extensions are widely thought to offer superior fixation of small proximal fragments but have distinct disadvantages: larger dissection, increased hardware prominence, and the increased possibility of impingement. Previous biomechanical studies of olecranon fracture fixation have compared methods of fracture fixation, but to date there have been no studies defining olecranon plate fixation strength for standard versus extended olecranon plates. The purpose of this study is to evaluate the biomechanical utility of the extended plate for treatment of olecranon fractures. Methods: Sixteen matched pairs of fresh-frozen human cadaveric elbows were used. Of the 16, 8 matched pairs received a transverse osteotomy including 25% and 8 including 50% of the articular surface on the proximal fragment. One elbow from each pair was randomly assigned to a standard-length plate, and the other elbow in the pair received the extended-length plate, for fixation of the fracture. The ulnae were cyclically loaded and subsequently loaded to failure, with ultimate load, number of cycles, and gap formation recorded. Results: There was no statistically significant difference between the standard and extended fixation plates in simple transverse fractures at either 25% or 50% from the proximal most portion of the articular surface of the olecranon. Conclusion: Standard fixation plates are sufficient for the fixation of small transverse fractures, but caution should be utilized particularly with comminution and nontransverse fracture patterns.

Biomechanical Strength of Retrograde Fixation in Proximal Third Scaphoid Fractures.

Background: Current techniques for fixation of proximal pole scaphoid fractures utilize antegrade fixation via a dorsal approach endangering the delicate vascular supply of the dorsal scaphoid. Volar and dorsal approaches demonstrate equivalent clinical outcomes in scaphoid wrist fractures, but no study has evaluated the biomechanical strength for fractures of the proximal pole. This study compares biomechanical strength of antegrade and retrograde fixation for fractures of the proximal pole of the scaphoid. Methods: A simulated proximal pole scaphoid fracture was produced in 22 matched cadaveric scaphoids, which were then assigned randomly to either antegrade or retrograde fixation with a cannulated headless compression screw. Cyclic loading and load to failure testing were performed and screw length, number of cycles, and maximum load sustained were recorded. Results: There were no significant differences in average screw length (25.5 mm vs 25.6 mm, P = .934), average number of cyclic loading cycles (3738 vs 3847, P = .552), average load to failure (348 N vs 371 N, P = .357), and number of catastrophic failures observed between the antegrade and retrograde fixation groups (3 in each). Practical equivalence between the 2 groups was calculated and the 2 groups were demonstrated to be practically equivalent (upper threshold P = .010). Conclusions: For this model of proximal pole scaphoid wrist fractures, antegrade and retrograde screw configuration have been proven to be equivalent in terms of biomechanical strength. With further clinical study, we hope surgeons will be able to make their decision for fixation technique based on approaches to bone grafting, concern for tenuous blood supply, and surgeon preference without fear of poor biomechanical properties.

Total Disk Replacement Adjacent to a Multilevel Fusion in the Cervical Spine: A Biomechanical Motion Analysis.

OBJECTIVE: Cervical total disk replacement (TDR) has emerged as a motion-preserving alternative to anterior cervical diskectomy fusion (ACDF). Biomechanical studies have demonstrated that the TDR preserves motion at the diseased segment and minimizes motion and stress at adjacent segments compared with fusion. There has been growing interest in performing a TDR adjacent to a cervical fusion. The purpose of this study was to investigate the kinematics of a TDR after sequentially fusing adjacent segments. METHODS: Seven fresh-frozen human cadaveric cervical spine specimens from C1-T1 were used (average age, 56.2 ± 7.3 years). The effect on cervical flexion-extension motion, by instrumenting a TDR above or below a 1-, 2-, or 3-level fusion, was measured. The protocol consisted of taking fluoroscopic images of each cervical specimen obtained at maximal angular displacement in flexion and extension during force application. Cobb angles were measured on digital radiographs to determine flexion-extension range of motion (ROM). RESULTS: Segmental ROM of the C6-7 TDR in the unfused spine was 11.3° ± 1.9°. After performing a 3-level fusion at C3-6, the motion of the C6-7 TDR increased to 12.9° ± 1.3° (P = 0.33). ROM of the C2-3 TDR in the unfused spine was 5.0° ± 1.1°. After performing a 3-level fusion of C3-6, the C2-3 TDR segmental motion was 6.1° ± 1.3° (P = 0.09). CONCLUSIONS: Biomechanically performing a cervical TDR adjacent to a long-segment fusion did not subject the implant to significantly greater motion than when the TDR was instrumented alone.

The combination of tibial anterior translation and axial rotation into a single biomechanical factor improves the prediction of patient satisfaction over each factor alone in patients with ACL reconstructed knees.

PURPOSE: The purpose of this study was to identify biomechanical factors, in both reconstructed and healthy knees, that correlate with patient satisfaction after ACL reconstruction. METHODS: Seventeen patients who had undergone unilateral ACL reconstruction were reviewed 9 years post-op. Patients completed subjective questionnaires and underwent manual knee laxity testing (Lachman-Trillat, KT-1000, and pivot shift) and automated laxity testing. During automated testing, both legs were rotated into external rotation and then internal rotation until peak rotational torque reached 5.65 Nm. Load-deformation curves were generated from torque and rotation data. Features of the curves were extracted for analysis. Total leg rotation and anterior laxity during KT-1000 testing were combined into a single factor (Joint Play Envelope or JPE). Patients were divided into groups based on patient satisfaction scores (Group 1: Higher Satisfaction, Group 2: Lower Satisfaction, Group 3: Unsatisfied). Load-deformation curve features and manual laxity testing results were compared between groups 1 and 2 to determine which biomechanical factors could distinguish between the groups. Diagnostic screening values were calculated for KT-1000 testing, the pivot shift test, total leg rotation and JPE. RESULTS: During manual testing, no significant differences in biomechanical factors were found when comparing reconstructed knees in group 1 and group 2. When comparing the reconstructed and healthy knees within group 2, the reconstructed knees had a significantly higher displacement during the KT-1000 manual maximum test (p < 0.002). When considering the reconstructed knees alone, neither the result of the pivot shift test nor KT-1000 testing could distinguish between group 1 and group 2. During automated testing, there were no significant differences between the groups when comparing the reconstructed lower limbs. The healthy lower limbs in group 2 had more maximum external rotation (p < 0.02) and decreased stiffness at maximum external rotation (p < 0.02) when compared to the healthy lower limbs in group 1. Total leg rotation was unable to distinguish between group 1 and group 2. JPE could distinguish between group 1 and group 2 when considering the reconstructed limb alone (p < 0.02). All four diagnostic screening values for JPE were equal or higher than in the other criteria. JPE also showed the most significant correlation with patient satisfaction. CONCLUSIONS: Joint Play Envelope is an objective measure that demonstrated improved predictive value as compared to other tests when used as a measure of satisfaction in patients with ACL reconstructed knees.

The effect of capacitively coupled (CC) electrical stimulation on human disc nucleus pulposus cells and the relationship between CC and BMP-7.

PURPOSE: An in vitro study using human intervertebral disc nucleus pulposus cells to evaluate the effects of CC stimulation on disc-matrix macromolecule production. METHODS: Nucleus pulposus cells were cultured in alginate beads and treated with CC stimulation. The effect of BMP on CC stimulation of the cells was evaluated by applying a BMP blocker (noggin) or by applying additional BMP-7 to the culture. The mRNA levels of the disc extracellular matrix genes (collagen I, II, aggrecan) and BMPs were measured by real-time PCR. The protein levels of aggrecan, collagen II, and BMPs were determined by ELISAs and Western blots. Sulfated glycosaminoglycan (sGAG) content was assayed using the DMMB method. RESULTS: (1) CC stimulation upregulates the production of the disc-matrix macromolecular components: sGAG, aggrecan and collagen II; (2) CC stimulation increases the ratio of mRNA expression levels of collagen II to collagen I; (3) CC stimulation induces the expression of endogenous BMP-4 and BMP-7; (4) inhibition of BMP activity (using noggin) reduces CC-mediated upregulation of aggrecan and collagen II; (5) CC and BMP-7 act in synergy to increase the upregulation of disc-matrix macromolecules. CONCLUSION: CC stimulation upregulates the production of the intervertebral disc-matrix macromolecules aggrecan, collagen II, and sGAG by a mechanism involving BMPs. CC stimulation acts in synergy with BMP-7 to increase the upregulation of these disc-matrix macromolecules.

Is It "In" or "Out"? The Optimal Fluoroscopic Views for Intraoperative Determination of Proper Lateral Mass Screw Placement.

STUDY DESIGN: Cadaveric. OBJECTIVE: Determine optimal fluoroscopic views for detecting cervical lateral mass screw (LMS) violations. SUMMARY OF BACKGROUND DATA: Single plane intraoperative x-rays are commonly used but frequently inadequate due to its complex trajectory. Fluoroscopy can be taken in multiple planes, but the ideal fluoroscopic view to assess malposition is not known: depending on the view, any given screw may look "in" or "out." METHODS: C3-6 LMS were inserted in three cadavers. To evaluate neuroforaminal violation, LMS were inserted into the foramen with the tip penetrating the anterior cortex by 0, 2, and 4 mm. To assess facet joint violation, LMS were inserted toward the subjacent facet joint with the tip penetrating the anterior cortex by 0 and 2 mm. Fluoroscopic views were taken 0°, 10°, 20°, 30°, and 40° to the lateral plane. Views were independently evaluated by three blinded spine surgeons. RESULTS: Twenty-degree oblique view correctly identified a 2 mm penetration into the neuroforamen in 79%, and a 4 mm penetration in 86%, for a sensitivity of 83% and specificity of 90%. Thirty-degree view had lower sensitivity (76%) but slightly higher specificity (93%). Twenty-degree and 30° views were significantly more sensitive than the other views. Zero-degree view correctly identified a 2 mm penetration into the facet joint in 93%, for a sensitivity of 93% and specificity of 92%. Ten-degree view had lower sensitivity (72%) but higher specificity (100%). The 0° view was significantly more sensitive than the other views. CONCLUSION: Twenty-degree and 30° oblique views significantly provided the most sensitive assessment of LMS potentially violating the neuroforamen, whereas the 0° neutral lateral view significantly provided the most sensitive assessment of facet violations. The specificities were also high (in the 90% range) for these views. We recommend the use of these views intraoperatively when assessing proper placement of LMS fluoroscopically. LEVEL OF EVIDENCE: N/A.

High-intensity stretch treatment for severe postoperative adhesive capsulitis of the shoulder.

BACKGROUND: Some patients with postoperative adhesive capsulitis reach a plateau in their recovery with a standard protocol of physical therapy (PT), which puts them at risk for further surgical intervention. OBJECTIVES: We aimed to evaluate therapy for postoperative adhesive capsulitis of the shoulder in 2 groups of patients: (1) those who used a high-intensity stretch (HIS) device after reaching a plateau in their recovery with a standard protocol of traditional PT (PT+HIS) and (2) those who showed no plateau in their recovery with a standard protocol of traditional PT alone (PT only). METHODS: We retrospectively reviewed the records for 60 patients (51 males; mean age 46.7±12.6years) with postoperative adhesive capsulitis who received treatment between March 2007 and May 2010. Forward elevation and combined internal/external rotation at the initial postoperative visit and final visit were measured. The measurements from group 2 patients were used as an observational benchmark. RESULTS: The PT+HIS (n=42) and PT-only (n=18) patients did not differ in total follow-up time. Initial elevation was worse for PT+HIS than PT-only patients (22.1° lower, P=0.02), but the final elevation was equivalent. Initial rotation was worse for PT+HIS than PT-only patients (16.6° lower, P=0.04), but the final rotation was higher for PT+HIS patients (10.6° higher, P=0.04). Gains in elevation and rotation were greater for the PT+HIS than PT-only patients (P=0.04 and P=0.01). CONCLUSIONS: Patients with postoperative adhesive capsulitis of the shoulder who are unable to reach their PT treatment goals with a standard protocol of PT may benefit from the addition of HIS to their treatment regimen. HIS could be a valuable adjunct to PT for treating postoperative adhesive capsulitis in appropriate patients.

Improving Spanning-Knee External Fixator Stiffness: A Biomechanical Study.

The purpose of this study was to test and compare external fixator construct stiffness using pin-to-bar clamps or multipin clamps across 2 external fixation systems. Constructs were tested with 8-mm and 11-mm-diameter bar systems and pin-to-bar or multipin clamps. Three construct designs were tested: construct 1 with a single crossbar and pin-to-bar clamps, construct 2 with 2 crossbars and pin-to-bar clamps, and construct 3 with 2 crossbars and multipin clamps. The stiffness of each construct (N = 24) was tested using anterior-posterior bending. Two crossbars and pin-to-bar clamps resulted in the highest mean stiffness. Constructs with a single crossbar and pin-to-bar clamps had a similar average stiffness compared with constructs with 2 crossbars and multipin clamps. Pin-to-bar clamps with 2 crossbars result in stronger spanning-knee external fixators than constructs using multipin clamps.

Biomechanical effects of rotator interval closure in shoulder arthroplasty.

BACKGROUND: Subscapularis dysfunction remains a significant problem after shoulder arthroplasty. Published techniques have variable recommendations for placing a rotator interval closing suture in attempts to off-load the subscapularis repair site, the implications of which have yet to be examined in the literature. The goals of this study were to investigate the biomechanical benefit of the rotator interval closing suture on the subscapularis repair strength and to analyze the effect on shoulder range of motion. METHODS: Sixteen matched cadaveric shoulders underwent a subscapularis tenotomy and shoulder arthroplasty. The subscapularis tenotomy was repaired, and motion at physiologic torsional force was recorded. One of each matched pair was randomly assigned to receive an additional rotator interval closure suture. Each specimen then underwent a standardized cyclic loading with measurement of gap formation and load to failure. RESULTS: The rotator interval closing suture significantly increased the ultimate load to failure of the subscapularis repair (452 N vs. 219 N; P = .002) and decreased gap formation at the subscapularis repair site. Measurement of the shoulder motion showed no significant difference between shoulders with and without the rotator interval closing suture. DISCUSSION: We report the additional biomechanical benefit that the rotator interval closing suture provides to the subscapularis repair site after shoulder arthroplasty. This suture acts to improve the load to failure of the subscapularis repair and to decrease gap formation under cyclic load. Furthermore, it does not detrimentally affect shoulder external rotation or overall arc of rotation. Our findings support the application of this off-loading technique after subscapularis repair during shoulder arthroplasty.

A biomechanical comparison of 360° stabilizations for corpectomy and total spondylectomy: a cadaveric study in the thoracolumbar spine.

BACKGROUND: To date, there has been no adequate biomechanical model that would allow a quantitative comparison in terms of stability/stiffness between a corpectomy with the posterior column preserved and a total spondylectomy with the posterior column sacrificed. The objective of this study was to perform a biomechanical comparison of 360° stabilizations for corpectomy and total spondylectomy, using the human thoracolumbar spine. METHODS: Five human cadaveric thoracolumbar spines (T8-L2) were tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and left, and axial rotation to the right and left. This loading protocol was applied three times. Each specimen was tested intact, after corpectomy, and after total spondylectomy. The relative stiffness of each motion segment was determined for each test. RESULTS: There was no significant difference in stiffness after reconstruction of total spondylectomy versus corpectomy in our thoracolumbar model. Our construct consisted of an anterior cage and four-level pedicle screw instrumentation (two above and two below) and provided similar stiffness in both models. Despite the additional bone resection in a total spondylectomy versus corpectomy, the constructs did not differ biomechanically. Additionally, there was no significant difference in stiffness between the intact specimen and either reconstruction model. CONCLUSIONS: A classic corpectomy, which leaves the posterior column intact, is no better in terms of stability/stiffness than a total spondylectomy carried out using a shorter cage, followed by compression using posterior instrumentation.

The effect of hubbing on the pull-out strength of lateral mass screws in the cervical spine: a biomechanical experiment.

STUDY DESIGN: This was a cadaveric biomechanical experiment. OBJECTIVE: To compare the pull-out strength of polyaxial screws that are either hubbed or not hubbed when inserted into the lateral mass. SUMMARY OF BACKGROUND DATA: It has been shown in a study on pedicle screws in the thoracic spine that "hubbing" the head of the screw against the dorsal laminar cortex results in significantly lower pull-out strength of the screws. MATERIALS AND METHODS: Fifteen segments of the human cervical spine (from C3 to C7) were prepared. Polyaxial screws 3.5 mm in diameter were used. On one side screws 12 mm in length were inserted until the screw head touched the lateral mass; they were then turned 2.5 more times until they were fully hubbed (hubbed screws). On the other side screws 14 mm in length were inserted until the screw head just touched the lateral mass (nonhubbed screws). The 2 mm difference in length was to ensure that the screws were buried to the same length. All screws inserted into the lateral masses underwent tensile pull-out by applying a tensile force down the long axis of the screw. The difference in pull-out strength between the 2 groups was evaluated using a nonparametric paired test (the Wilcoxon signed rank test), which compared side to side on each vertebra. RESULTS: One specimen was excluded because of cement breakage during the biomechanical test. A total of 14 vertebrae were tested. Four vertebrae in the hubbed group showed small fractures or cracks around the screw hole after screw insertion. In a side to side comparison, the hubbed screws had significantly lower pull-out strengths as compared with the nonhubbed screws (P=0.033). CONCLUSIONS: Hubbing of lateral mass screws lowers the potential pull-out strength of the screws as compared with the pull-out strength of nonhubbed screws. Thus, hubbing of lateral mass screws, on the basis of the parameters applied in this study, is not recommended.

Two fixation methods for acromioclavicular joint reduction during coracoclavicular ligament reconstruction: a biomechanical analysis.

One specimen from each of six pairs of cadaveric shoulders underwent a semitendinosus coracoclavicular ligament reconstruction with a hook plate used for acromioclavicular joint reduction, while on the other specimen a polydioxanone (PDS) suture braid was utilized. Cyclical loading followed by maximal load-to-failure testing was performed. Displacement during cyclical loading, loads to 50% and 100% displacement, stiffness, and maximal load to failure were determined for all specimens. Results showed that the locking hook plate allowed significantly less displacement of the coracoclavicular interval during cyclical loading (3.41 vs. 9.67 mm, p = .0081) and withstood significantly higher loads before both 50% (225.5 vs. 107.7 N, p = .0197) and 100% displacement (410.6 vs. 240.1 N, p = .0077). The locking hook plate was found to be significantly stiffer than the PDS suture braid (28.2 vs. 18.4 N/mm, p = .0029), but there was no difference in maximal load to failure between the two fixation methods (hook plate, 434.4 N; PDS, 476.7 N; p = .76).

Comparison of screw trajectory on stability of oblique scaphoid fractures: a mechanical study.

PURPOSE: To determine whether a screw placed perpendicular to the fracture line in an oblique scaphoid fracture will provide fixation strength that is comparable with that of a centrally placed screw. METHODS: Oblique osteotomies were made along the dorsal sulcus of 8 matched pairs of cadaveric scaphoids. One scaphoid from each pair was randomized to receive a screw placed centrally down the long axis. In the other scaphoid, a screw was placed perpendicular to the osteotomy. Each scaphoid underwent cyclic loading from 80 N to 120 N at 1 Hz. Cyclic loading was carried out until 2 mm of fracture displacement occurred or 4,000 cycles was reached. The specimens that reached the 4,000-cycle limit were then loaded to failure. Screw length, number of cycles, and load to failure were compared between the groups. RESULTS: We found no difference in number of cycles or load to failure between the 2 groups. Screws placed perpendicular to the fracture line were significantly shorter than screws placed down the central axis. CONCLUSIONS: A perpendicularly placed screw provides equivalent strength to one placed along the central axis. CLINICAL RELEVANCE: Compared with a screw placed centrally in an oblique scaphoid fracture, a screw placed perpendicular to the fracture line allows the use of a shorter screw without sacrificing strength of fixation.

Bone morphogenetic protein-7 antagonizes tumor necrosis factor-α-induced activation of nuclear factor κB and up-regulation of the ADAMTS, leading to decreased degradation of disc matrix macromolecules aggrecan and collagen II.

BACKGROUND CONTEXT: Tumor necrosis factor-α (TNF-α) is a regulatory cytokine that can increase the activity of enzymes such as ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs), which degrade disc matrix. ADAMTS are enzymes that break down disc matrix and thereby mediate disc degeneration. Bone morphogenetic protein-7 (BMP-7), on the other hand, stimulates synthesis of the disc extracellular matrix and is a potential therapeutic molecule for the treatment of disc degeneration. However, the effects of BMP-7 on TNF-α and ADAMTS are unknown. PURPOSE: We investigated the effects of BMP-7 on the catabolic regulators such as TNF-α and ADAMTS and evaluated the molecular mechanism by which BMP-7 affects the catabolic regulators. STUDY DESIGN: This was an in vitro study in which we used human intervertebral disc cells cultured in alginate beads. METHODS: Human intervertebral disc cells were cultured in alginate beads, and treated with TNF-α, or TNF- α plus BMP-7, pharmacological inhibitor of ERK1/2 (U0126), p38 (SB203580), or NFκB (BAY 11-7082). The mRNA levels of target genes were measured by real-time polymerase chain reaction, and the protein levels were determined by the Western blots. The nuclear factor (NF)κB activity was analyzed by measured phosphorylation and nuclear translocation of the NFκB protein p65. RESULTS: TNF-α activated NFκB signaling and induced up-regulation of the catabolic regulators ADAMTS-4 and ADAMTS-5, contributing to degradation of the disc matrix macromolecules aggrecan and collagen II. BMP-7 antagonized the TNF-α-induced activation of NFκB protein p65 and blocked TNF-α-induced up-regulation of ADAMTS-4 and ADAMTS-5, leading to reversing TNF-α-mediated degradation of aggrecan and collagen II. Moreover, BMP-7 antagonized the TNF-α-induced activation of NFκB signaling by suppressing phosphorylation and nucleus translocation of NFκB protein p65. CONCLUSION: BMP-7 antagonizes TNF-α-induced activation of NFκB and up-regulation of ADAMTS, leading to decreased degradation of disc matrix macromolecules. These data indicate that BMP-7 has a dual mechanism of action on disc metabolism: (1) the previously well-described positive effect on disc matrix synthesis and (2) an anticatabolic effect that is described here. This understanding is important as BMP-7 is being considered for treatment of disc degeneration.

Microendoscopic lateral decompression for lumbar foraminal stenosis: a biomechanical study.

STUDY DESIGN: A biomechanical study. OBJECTIVE: How much of the facet joint and the pars interarticularis (PI) can be removed in microendoscopic lateral decompression (MELD) for lumbar foraminal stenosis (LFS)? SUMMARY OF BACKGROUND DATA: MELD is a surgical modality for patients with LFS. In severe degenerative cases, unilateral facet joint resection or unilateral removal of the lateral part of the PI are sometimes needed to decompress the nerve root adequately. METHODS: Twelve human lumbar motion segments were tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and left, and axial rotation to the right and left. This loading protocol was applied to each motion segment after MELD in 2 experiments: (1) unilateral graded facetectomy was performed in stages of 25%, 50%, 75%, and 100% using 3 segments of L3/L4 and 3 segments of L5/S1; (2) unilateral removal of the lateral part of the PI was performed in stages of 25%, 50%, 75%, and 100% using 3 segments of L3/L4 and 3 segments of L5/S1. The relative stiffness of each motion segments was determined each time. RESULTS: (1) Unilateral facet joint resection of >75% can lead to a significant reduction in stiffness in axial rotation at both L3/L4 and L5/S1. (2) Unilateral removal of 75% of the lateral part of the PI can lead to significant reduction in stiffness in right and left rotation at L3/L4 and in left rotation at L5/S1. (3) Unilateral removal of 100% of the lateral part of the PI can lead to a significant reduction in stiffness in right axial rotation at L5/S1. CONCLUSIONS: It would seem judicious to remove no >50% of the facet joint or the lateral part of the PI in order to prevent postoperative instability when using MELD for LFS.

Pedicle screws can be 4 times stronger than lateral mass screws for insertion in the midcervical spine: a biomechanical study on strength of fixation.

STUDY DESIGN: A biomechanical study. OBJECTIVE: To compare, in cervical vertebrae (C3-C6), the pullout strengths of pedicle screws and lateral mass screws after both types of screw had been subjected to a period of cyclic loading in 2 planes. SUMMARY OF BACKGROUND DATA: In posterior subaxial cervical fixation systems, screws are usually inserted into the lateral mass. As an alternative to lateral mass fixation, pedicle screw fixation became popular in the 1990s and was first used for lower cervical spine trauma cases. However, it is controversial as to whether lateral mass screw fixation in the upper-middle cervical spine offers as much biomechanical security as compared with pedicle screw fixation. METHODS: For each of the 32 vertebrae, 1 side was randomly chosen to receive a pedicle screw and the other side a lateral mass screw. The pedicle or lateral mass screws inserted into the first 16 vertebrae were cyclically loaded to simulate torsion and the remaining 16 vertebrae were cyclically loaded to simulate flexion/extension of the spine. At the end of the cyclic loading each screw was pulled out along its long axis. RESULTS: For the torsion group, the mean pullout strength of the pedicle screws was nearly 4 times greater than the mean pullout strength of the lateral mass screws (cf 762 N with 191 N). In contrast, the mean pullout strength of the pedicle screws in the flexion/extension group was only twice the mean pullout strength of the lateral mass screws (cf 571 N with 289 N). CONCLUSIONS: Not forgetting the potential risks of inserting pedicle screws in cervical vertebrae, pedicle screws are a better biomechanical choice than lateral mass screws for cervical fixation at the levels C3 through to C6.

The effect of pedicle screw redirection after lateral wall breach--a biomechanical study using human lumbar vertebrae.

BACKGROUND CONTEXT: Currently, pedicle screw segmental fixation of the spine is considered a standard of care for a number of conditions. Most surgeons employ a free-hand technique using various intraoperative modalities to improve pedicle screw accuracy. Despite continued improvements in technique, pedicle breach remains a frequent occurrence. Once a breach is detected intraoperatively, the most common corrective maneuver is to medially redirect the pedicle screw into the pedicle. To our knowledge, the biomechanical impact of medially redirecting a pedicle screw after a lateral pedicle breach has not been examined. PURPOSE: To compare the fixation strength of perfectly placed pedicle screws to the fixation strength of pedicle screws that were correctly placed after having been redirected (RD) following a lateral pedicle breach. STUDY DESIGN/SETTING: A biomechanical study using human lumbar vertebrae. METHODS: Ten fresh human lumbar vertebrae were isolated from five donors. Each vertebra was instrumented with a monoaxial pedicle screw into each pedicle using two different techniques. On one side, a perfect center-center (CC) screw path was created using direct visualization and fluoroscopy. A 6.0-mm-diameter cannulated tap and a pedicle probe were used to develop the pedicle for the 7.0-mm-diameter by 45-mm-long cannulated pedicle screw, which was placed using a digital torque driver. On the contralateral side, an intentional lateral pedicle wall breach was created at the pedicle-vertebral body junction using a guide wire, a 6.0-mm-diameter cannulated tap, and a pedicle probe. This path was then redirected into a CC position, developed, and instrumented with a 7.0-mm-diameter by 45-mm-long cannulated pedicle screw: the RD screw. For each pedicle screw, we assessed four outcome measures: maximal torque, seating torque, screw loosening, and post-loosening axial pullout. Screw loosening and axial pullout were assessed using an MTS machine. RESULTS: The biomechanical cost of a lateral pedicle breach and the requirement to redirect the pedicle screw are as follows: an overall drop of 28% (p<.002) in maximal insertion torque and 25% (p<.049) in seating torque, a drop of 25% (p<.040) in resistance to screw loosening, and a drop in axial pullout force of 11% (p<.047). CONCLUSIONS: Compared with a CC lumbar pedicle screw, an RD lumbar pedicle screw placed after a lateral wall breach is significantly weaker in terms of maximal insertional torque, seating torque, screw loosening force, and axial pullout strength. These significant decreases in biomechanical properties are clearly important when RD pedicle screws are placed at the cephalad or caudal end of a long construct. In this situation, augmentation of the RD screw is an option.

Arthroscopic repair of triangular fibrocartilage tears: a biomechanical comparison of a knotless suture anchor and the traditional outside-in repairs.

PURPOSE: To compare the biomechanical strength of a knotless suture anchor repair and the traditional outside-in repair of peripheral triangular fibrocartilage complex (TFCC) tears in a cadaveric model. METHODS: We dissected the distal ulna and TFCC from 6 matched cadaveric wrist pairs and made iatrogenic complete peripheral TFCC tears in each wrist. In 6 wrists, the TFCC tears were repaired using the standard outside-in technique using 2 2-0 polydioxane sutures placed in a vertical mattress fashion. In the other 6 wrists, we repaired the TFCC tears using mini-pushlock suture anchors to the fovea. The strength of the repairs was then determined using a materials testing machine with the load placed across the repair site. We loaded the repairs until a gap of 2 mm formed across the repair site, and then subsequently loaded them to failure. Thus, for each repair we obtained the load at 2-mm gap formation, load to failure, and mode of failure. RESULTS: At the 2-mm gap formation, the suture anchor repairs were statistically stronger than the outside-in repairs. For load to failure, the suture anchor repairs were also statistically stronger than the outside-in repairs. Failure in both techniques occurred most commonly as suture pull-out from the soft tissues. CONCLUSIONS: The all-arthroscopic suture anchor TFCC repair was biomechanically stronger than an outside-in repair. CLINICAL RELEVANCE: The suture anchor technique allows for repair of both the superficial and deep layers of the articular disk directly to bone, restoring the native TFCC anatomy. By being knotless, the suture anchor repair avoids irritation to the surrounding soft tissues by suture knots.

Link protein N-terminal peptide binds to bone morphogenetic protein (BMP) type II receptor and drives matrix protein expression in rabbit intervertebral disc cells.

Intervertebral disc (IVD) degeneration and associated spinal disorders are leading sources of morbidity, and they can be responsible for chronic low back pain. Treatments for degenerative disc diseases continue to be a challenge. Intensive research is now focusing on promoting regeneration of degenerated discs by stimulating production of the disc matrix. Link protein N-terminal peptide (LPP) is a proteolytic fragment of link protein, an important cross-linker and stabilizer of the major structural components of cartilage, aggrecan and hyaluronan. In this study we investigated LPP action in rabbit primary intervertebral disc cells cultured ex vivo in a three-dimensional alginate matrix. Our data reveal that LPP promotes disc matrix production, which was evidenced by increased expression of the chondrocyte-specific transcription factor SOX9 and the extracellular matrix macromolecules aggrecan and collagen II. Using colocalization and pulldown studies we further document a noggin-insensitive direct peptide-protein association between LPP and BMP-RII. This association mediated Smad signaling that converges on BMP genes leading to expression of BMP-4 and BMP-7. Furthermore, through a cell-autonomous loop BMP-4 and BMP-7 intensified Smad1/5 signaling though a feedforward circuit involving BMP-RI, ultimately promoting expression of SOX9 and downstream aggrecan and collagen II genes. Our data define a complex regulatory signaling cascade initiated by LPP and suggest that LPP may be a useful therapeutic substitute for direct BMP administration to treat IVD degeneration and to ameliorate IVD-associated chronic low back pain.

A novel low-molecular-weight compound enhances ectopic bone formation and fracture repair.

BACKGROUND: Use of recombinant human bone morphogenetic protein-2 (rhBMP-2) is expensive and may cause local side effects. A small synthetic molecule, SVAK-12, has recently been shown in vitro to potentiate rhBMP-2-induced transdifferentiation of myoblasts into the osteoblastic phenotype. The aims of this study were to test the ability of SVAK-12 to enhance bone formation in a rodent ectopic model and to test whether a single percutaneous injection of SVAK-12 can accelerate callus formation in a rodent femoral fracture model. METHODS: Collagen disks with rhBMP-2 alone or with rhBMP-2 and SVAK-12 were implanted in a standard athymic rat chest ectopic model, and radiographic analysis was performed at four weeks. In a second set of rats (Sprague-Dawley), SVAK-12 was percutaneously injected into the site of a closed femoral fracture. The fractures were analyzed radiographically and biomechanically (with torsional testing) five weeks after surgery. RESULTS: In the ectopic model, there was dose-dependent enhancement of rhBMP-2 activity with use of SVAK-12 at doses of 100 to 500 µg. In the fracture model, the SVAK-12-treated group had significantly higher radiographic healing scores than the untreated group (p = 0.028). Biomechanical testing revealed that the fractured femora in the 200 to 250-µg SVAK-12 group were 43% stronger (p = 0.008) and 93% stiffer (p = 0.014) than those in the control group. In summary, at five weeks the femoral fracture group injected with SVAK-12 showed significantly improved radiographic and biomechanical evidence of healing compared with the controls. CONCLUSIONS: A single local dose of a low-molecular-weight compound, SVAK-12, enhanced bone-healing in the presence of low-dose exogenous rhBMP-2 (in the ectopic model) and endogenous rhBMPs (in the femoral fracture model). CLINICAL RELEVANCE: This study demonstrates that rhBMP-2 responsiveness can be enhanced by a novel small molecule, SVAK-12. Local application of anabolic small molecules has the potential for potentiating and accelerating fracture-healing. Use of this small molecule to lower required doses of rhBMPs might both decrease their cost and improve their safety profile.