Proximal tibial fracture following anterior cruciate ligament reconstruction surgery: a biomechanical analysis of the tibial tunnel as a stress riser.

PURPOSE: This is the first biomechanical study to examine the potential stress riser effect of the tibial tunnel or tunnels after ACL reconstruction surgery. In keeping with literature, the primary hypothesis tested in this study was that the tibial tunnel acts as a stress riser for fracture propagation. Secondary hypotheses were that the stress riser effect increases with the size of the tunnel (8 vs. 10 mm), the orientation of the tunnel [standard (STT) vs. modified transtibial (MTT)], and with the number of tunnels (1 vs. 2). METHODS: Tibial tunnels simulating both single bundle hamstring graft (8 mm) and bone-patellar tendon-bone graft (10 mm) either STT or MTT position, as well as tunnels simulating double bundle (DB) ACL reconstruction (7, 6 mm), were drilled in fourth-generation saw bones. These five experimental groups and a control group consisting of native saw bones without tunnels were loaded to failure on a Materials Testing System to simulate tibial plateau fracture. RESULTS: There were no statistically significant differences in peak load to failure between any of the groups, including the control group. The fracture occurred through the tibial tunnel in 100 % of the MTT tunnels (8 and 10 mm) and 80 % of the DB tunnels specimens; however, the fractures never (0 %) occurred through the tibial tunnel of the standard tunnels (8 or 10 mm) (P = 0.032). CONCLUSIONS: In the biomechanical model, the tibial tunnel does not appear to be a stress riser for fracture propagation, despite suggestions to the contrary in the literature. Use of a standard, more vertical tunnel decreases the risk of ACL graft compromise in the event of a fracture. This may help to inform surgical decision making on ACL reconstruction technique.

Injectable hydrogel induces regeneration of naturally degenerate human intervertebral discs in a loaded organ culture model.

Low back pain resulting from disc degeneration is a leading cause of disability worldwide. However, to date few therapies target the cause and fail to repair the intervertebral disc (IVD). This study investigates the ability of an injectable hydrogel (NPgel), to inhibit catabolic protein expression and promote matrix expression in human nucleus pulposus (NP) cells within a tissue explant culture model isolated from degenerate discs. Furthermore, the injection capacity of NPgel into naturally degenerate whole human discs, effects on mechanical function, and resistance to extrusion during loading were investigated. Finally, the induction of potential regenerative effects in a physiologically loaded human organ culture system was investigated following injection of NPgel with or without bone marrow progenitor cells. Injection of NPgel into naturally degenerate human IVDs increased disc height and Young's modulus, and was retained during extrusion testing. Injection into cadaveric discs followed by culture under physiological loading increased MRI signal intensity, restored natural biomechanical properties and showed evidence of increased anabolism and decreased catabolism with tissue integration observed. These results provide essential proof of concept data supporting the use of NPgel as an injectable therapy for disc regeneration. STATEMENT OF SIGNIFICANCE: Low back pain resulting from disc degeneration is a leading cause of disability worldwide. However, to date few therapies target the cause and fail to repair the intervertebral disc. This study investigated the potential regenerative properties of an injectable hydrogel system (NPgel) within human tissue samples. To mimic the human in vivo conditions and the unique IVD niche, a dynamically loaded intact human disc culture system was utilised. NPgel improved the biomechanical properties, increased MRI intensity and decreased degree of degeneration. Furthermore, NPgel induced matrix production and decreased catabolic factors by the native cells of the disc. This manuscript provides evidence for the potential use of NPgel as a regenerative biomaterial for intervertebral disc degeneration.

Risk of glove perforation with arthroscopic knot tying using different surgical gloves and high-tensile strength sutures.

PURPOSE: To examine the risk of glove tears associated with arthroscopic knot tying using 4 commonly used high-tensile strength sutures and 2 different types of gloves. METHODS: We analyzed 2 different surgical latex glove types (0.24-mm-thick powder-free and 0.32-mm-thick powdered) for perforation after arthroscopic knot tying with 4 different high-tensile strength sutures: Hi-Fi (ConMed Linvatec, Largo, FL), Ultrabraid (Smith & Nephew, Memphis, TN), FiberWire (Arthrex, Naples, FL), and Orthocord (DePuy Mitek, Raynham, MA). All knots were tied by a double-gloved single surgeon. Twelve trials of 4 knots each were performed for every glove-suture combination. All gloves were analyzed for perforation by a blinded evaluator using visual inspection, hydro-insufflation, and electroconductivity. RESULTS: The overall incidence of glove perforation was 3.4% and was detectable only by the electroconductivity method; the other 2 methods did not detect any perforations. There was a statistically significantly higher rate (P < .001) of perforations in the 0.32-mm powdered gloves (6.8%) compared with the 0.24-mm powder-free gloves (0%). Perforation of the inner glove occurred 5.7 times more frequently than perforation of the outer glove. However, simultaneous perforation of both the inner and outer gloves did not occur in any set. The Hi-Fi suture was involved in 6 perforations compared with 4 for FiberWire, 3 for Ultrabraid, and 0 for Orthocord. CONCLUSIONS: Double gloving provides an adequate surgical barrier between the surgeon and the patient during arthroscopic knot tying with high-tensile strength sutures as indicated by the low incidence of glove perforations in our study in an in vitro biomechanical evaluation. There were no instances of simultaneous perforation of both the inner and outer gloves. All perforations occurred only in the thicker (0.32-mm) powdered gloves. CLINICAL RELEVANCE: Glove tears and finger lacerations have been reported with the use of high-tensile strength sutures during arthroscopic shoulder surgery, thereby raising a concern for safety and disease transmission. This study addresses these concerns by evaluating the risk of glove tears during arthroscopic knot tying.

Investigating Commercial Filaments for 3D Printing of Stiff and Elastic Constructs with Ligament-Like Mechanics.

The current gold standard technique for treatment of anterior cruciate ligament (ACL) injury is reconstruction with autograft. These treatments have a relatively high failure and re-tear rate. To overcome this, tissue engineering and additive manufacturing are being used to explore the potential of 3D scaffolds as autograft substitutes. However, mechanically optimal polymers for this have yet to be identified. Here, we use 3D printing technology and various materials with the aim of fabricating constructs better matching the mechanical properties of the native ACL. A fused deposition modeling (FDM) 3D printer was used to microfabricate dog bone-shaped specimens from six different polymers-PLA, PETG, Lay FOMM 60, NinjaFlex, NinjaFlex-SemiFlex, and FlexiFil-at three different raster angles. The tensile mechanical properties of these polymers were determined from stress-strain curves. Our results indicate that no single material came close enough to successfully match reported mechanical properties of the native ACL. However, PLA and PETG had similar ultimate tensile strengths. Lay FOMM 60 displayed a percentage strain at failure similar to reported values for native ACL. Furthermore, raster angle had a significant impact on some mechanical properties for all of the materials except for FlexiFil. We therefore conclude that while none of these materials alone is optimal for mimicking ACL mechanical properties, there may be potential for creating a 3D-printed composite constructs to match ACL mechanical properties. Further investigations involving co-printing of stiff and elastomeric materials must be explored.

Fibular fixation as an adjuvant to tibial intramedullary nailing in the treatment of combined distal third tibia and fibula fractures: a biomechanical investigation.

OBJECTIVE: Distal third tibia fractures have classically been treated with standard plating, but intramedullary (IM) nailing has gained popularity. Owing to the lack of interference fit of the nail in the metaphyseal bone of the distal tibia, it may be beneficial to add rigid plating of the fibula to augment the overall stability of fracture fixation in this area. This study sought to assess the biomechanical effect of adding a fibular plate to standard IM nailing in the treatment of distal third tibia and fibula fractures. METHODS: Eight cadaveric tibia specimens were used. Tibial fixation consisted of a solid titanium nail locked with 3 screws distally and 2 proximally, and fibular fixation consisted of a 3.5 mm low-contact dynamic compression plate. A section of tibia and fibula was removed. Testing was accomplished with an MTS machine. Each leg was tested 3 times; with and without a fibular plate and with a repetition of the initial test condition. Vertical displacements were tested with an axial load up to 500 N, and angular rotation was tested with torques up to 5 N*m. RESULTS: The difference in axial rotation was the only statistically significant finding (p = 0.003), with fibular fixation resulting in 1.1 degrees less rotation through the osteotomy site (17.96 degrees v. 19.10 degrees ). Over 35% of this rotational displacement occurred at the nail-locking bolt interface with the application of small torsional forces. CONCLUSION: Fibular plating in addition to tibial IM fixation of distal third tibia and fibula fractures leads to slightly increased resistance to torsional forces. This small improvement may not be clinically relevant.

Cadaveric device-injected very high-viscosity cement during vertebroplasty.

INTRODUCTION: Cement extravasation during vertebroplasty (VP) is the most commonly reported complication. Cement viscosity is considered the single most important predictor of the risk of extravasation. Certainly, injecting high-viscosity cement (HVC) is difficult to utilize in real practice. We invented a new device capable of injecting high-viscosity with ease and at a distance to avoid radiation. The aim of this study is to confirm the efficacy and safety of the new device on cadaveric vertebrae. METHODOLOGY: A 126 osteoporotic vertebral bodies were harvested from cadavers. Eighty vertebrae were included in the study. Computer-randomization software was used to allocate specimens over two main groups, Conventional VP and New Device. Both groups were further subdivided into two subgroups; high-viscosity and low-viscosity. A custom device was used on each vertebra to induce a compression fracture. RESULTS: Injecting HVC was associated with a lower leakage volume compared with low-viscosity cement. HVC was associated with no leakage into the spinal canal. It was also associated with a low incidence of vascular extravasation (P < 0.001). The mean volume of cement leakage in the low-viscosity group was 0.23 and 0.15 cc, for the Conventional VP and New Device, respectively. In both groups, the most common site for leakage was the vertebral end plate, which was exhibited more in the low-viscosity group (71.5%) compared with the high-viscosity group (42.5%). The preset target amount of cement to be injected was reached in 99% of the time when injecting HVC with the New Device, compared with 62% using the Conventional VP. In both groups, there was no correlation between the amount of cement injected and the amount of leakage. CONCLUSION: The new device is capable of injecting HVC easily, with a lower incidence of cement leakage. It also minimized the risk of radiation exposure to the surgeon.

Biomechanical comparison of a unique locking plate versus a standard plate for internal fixation of proximal humerus fractures in a cadaveric model.

BACKGROUND: Newer internal fixation devices with a locking mechanism between the plate and the screw have recently been released. The efficacy of these plates in the proximal humerus has yet to be fully described. There is a need to compare the biomechanical properties of efficacy of plate fixation with or without locking screws for surgery of two-part proximal humerus fractures. Multiple-plane locking plate and cloverleaf plate designs were tested to determine their ability to maintain fixation on the humeral head. METHODS: Eight matched pairs of cadaveric shoulders with 7-millimeter osteotomy defects at the surgical neck simulating two-part fractures of the proximal humerus were loaded to failure in thirty degrees of glenohumeral abduction. One side was repaired with a proximal humerus locking plate and the other with a cloverleaf plate. The rotator cuff musculature was then loaded via a servo-hydraulic testing machine under displacement control to simulate the deforming forces present in vivo. FINDINGS: The average maximum load to failure was greater in proximal humerus locking plates than in cloverleaf plates (876 versus 712; P=0.04). INTERPRETATION: In the cadaveric, two-part proximal humerus fracture model that was created, the locking plate displayed significantly greater holding power of the humeral head. Clinical relevance is unproven but may be manifested in vivo as improved early range of motion exercises and functional outcome.

Does Balloon Kyphoplasty Deliver More Cement Safely into Osteoporotic Vertebrae with Compression Fractures Compared with Vertebroplasty? A Study in Vertebral Analogues.

Study Design A biomechanical and radiographic study using vertebral analogues. Objectives Kyphoplasty and vertebroplasty are widely used techniques to alleviate pain in fractures secondary to osteoporosis. However, cement leakage toward vital structures like the spinal cord can be a major source of morbidity and even mortality. We define safe cement injection as the volume of the cement injected into a vertebra before the cement leakage occurs. Our objective is to compare the amount of cement that can be safely injected into an osteoporotic vertebra with simulated compression fracture using either vertebroplasty or balloon kyphoplasty techniques. Methods Forty artificial vertebral analogues made of polyurethane with osteoporotic cancellous matrix representing the L3 vertebrae were used for this study and were divided into four groups of 10 vertebrae each. The four groups tested were: low-viscosity cement injected using vertebroplasty, high-viscosity cement injected using vertebroplasty, low-viscosity cement injected using balloon kyphoplasty, and high-viscosity cement injected using balloon kyphoplasty. The procedures were performed under fluoroscopic guidance. The injection was stopped when the cement started protruding from the created vascular channel in the osteoporotic vertebral fracture model. The main outcome measured was the volume of the cement injected safely into a vertebra before leakage through the posterior vascular channel. Results The highest volume of the cement injected was in the vertebroplasty group using high-viscosity cement, which was almost twice the injected volume in the other three groups. One-way analysis of variance comparing the four groups showed a statistically significant difference (p < 0.005). Conclusions High-viscosity cement injected using vertebroplasty delivers more cement volume before cement leakage and fills the vertebral body more uniformly when compared with balloon kyphoplasty in osteoporotic vertebrae with compression fractures.

Effects of osteogenic protein-1 on distraction osteogenesis in rabbits.

In this study we tested the effect of locally applied osteogenic protein 1 (OP-1) on distraction osteogenesis in rabbits. Seven days after tibial osteotomy, distraction was started at a rate of 0.25 mm per 12 h for 3 weeks. At the end of the distraction period, OP-1 was injected at the site of osteotomy. Four different dosages were tested (0, 80, 800, or 2000 microg; eight rabbits per dose group). Rabbits were sacrificed 3 weeks later, and histologic, densitometric, and biomechanical parameters were assessed. No significant differences were found between groups for any parameter. To explain why this approach was only modestly successful, the expression of BMP receptor protein in the newly formed tissue was analyzed by immunohistochemistry. Strong expression of BMP receptor IA, IB, and II was found during the early distraction phase, but not during later stages of the process. Thus, it appears that the lack of receptor protein in the target tissue impairs the effect of OP-1 given at the end of the distraction period. Possibly, OP-1 could be more useful when applied early in the distraction phase.

Physiological loading can restore the proteoglycan content in a model of early IVD degeneration.

A hallmark of early IVD degeneration is a decrease in proteoglycan content. Progression will eventually lead to matrix degradation, a decrease in weight bearing capacity and loss of disc height. In the final stages of IVD degradation, fissures appear in the annular ring allowing extrusion of the NP. It is crucial to understand the interplay between mechanobiology, disc composition and metabolism to be able to provide exercise recommendations to patients with early signs of disc degeneration. This study evaluates the effect of physiological loading compared to no loading on matrix homeostasis in bovine discs with induced degeneration. Bovine discs with trypsin-induced degeneration were cultured for 14 days in a bioreactor under dynamic loading with maintained metabolic activity. Chondroadherin abundance and structure was used to confirm that a functional matrix was preserved in the chosen loading environment. No change was observed in chondroadherin integrity and a non-significant increase in abundance was detected in trypsin-treated loaded discs compared to unloaded discs. The proteoglycan concentration in loaded trypsin-treated discs was significantly higher than in unloaded disc and the newly synthesised proteoglycans were of the same size range as those found in control samples. The proteoglycan showed an even distribution throughout the NP region, similar to that of control discs. Significantly more newly synthesised type II collagen was detected in trypsin-treated loaded discs compared to unloaded discs, demonstrating that physiological load not only stimulates aggrecan production, but also that of type II collagen. Taken together, this study shows that dynamic physiological load has the ability to repair the extracellular matrix depletion typical of early disc degeneration.

Topical application of complement C3 in collagen formulation increases early wound healing.

BACKGROUND: The complement system is composed of bactericidal and hemolytic proteins that increase capillary leakage and inflammatory cell migration. The role of complement C3 to augment wound healing has not yet been studied. METHODS: We examined the effects of topical complement C3 formulation at two concentrations (10 and 100 nM) on the rat surgical skin incision model. Skin was examined for maximal breaking strength and sectioned for histological examination. Fibronectin and collagen I content were measured using western blot analysis. RESULTS: There was a statistically significant 74% increase in maximum wound strength with the topical application of 100 nM of C3 at day 3 (850 ± 138 g) when compared to the control rats (490 ± 57 g). Histological correlation was seen with an increased inflammatory cell and fibroblast infiltration in treated wounds as compared to control rats as early as 3 days post-wounding. Western blots revealed increased fibronectin and collagen I levels in C3 treated wounds. CONCLUSIONS: Topical application of complement C3 in collagen formulation to skin wounds significantly increases wound healing as early as 3 days after wounding. This is correlated with increased inflammatory cell recruitment and the subsequent early fibroblast migration and increased collagen deposition and organization in wounds.

Complements c3 and c5 individually and in combination increase early wound strength in a rat model of experimental wound healing.

Background. Complements C3 and C5 have independently been shown to augment and increase wound healing and strength. Our goal was to investigate the combinatorial effect of complements C3 and C5 on wound healing. Methods. Each rat served as its own control where topical collagen was applied to one incision and 100 nM of C3 and C5 in collagen vehicle was applied to the other incision (n = 6). To compare between systemic effects, a sham group of rats (n = 6) was treated with collagen alone on one wound and saline on the other. At day 3, the tissue was examined for maximal breaking strength (MBS) and sectioned for histological examination. Results. There was a statistically significant 88% increase in MBS with the topical application of C3C5 when compared to sham wounds (n < 0.05). This was correlated with increased fibroblast and collagen deposition in the treated wounds. Furthermore, there appeared to be an additive hemostatic effect with the C3C5 combination. Conclusions. The combination of complements C3 and C5 as a topical application drug to skin wounds significantly increased wound healing maximum breaking strength as early as 3 days.

The effects of topical collagen treatment on wound breaking strength and scar cosmesis in rats.

BACKGROUND: Topical application of collagen has been suggested to enhance wound healing; however, its long-term effect on wounds has not been studied in a rat model. HYPOTHESIS: Topical application of collagen type I will not facilitate incision healing or cosmesis in rats up to 28 days postwounding. METHODS: The effects of bovine collagen type I (6 mg/mL) on the rat surgical paired skin incision model were examined. Each rat served as its own control in which topical collagen was applied to one incision while normal saline (0.9%) was applied to the other incision. Rats were euthanized three (n=6), seven (n=6) and 28 (n=5) days after wounding. Tissue harvested from each time point was examined for maximal breaking strength, and for biochemical and histological analysis. RESULTS: There were no statistically significant differences (ie, P<0.05) in maximum wound breaking strength between the collagen- and saline-treated wounds at all time points. Histological analysis revealed a similar infiltration of inflammatory cells and fibroblasts in the wound edges of all incisions when matched with time of wounding. Western blot analysis revealed no differences in fibronectin or collagen I content in all wounds in each rat. CONCLUSIONS: The topical application of collagen did not facilitate wound healing from three to 28 days in the rat wound model.

HISTORIQUE: L'application topique de collagène améliorerait la guérison des plaies. Cependant, on n'a pas étudié son effet à long terme sur les plaies d'un modèle de rat. HYPOTHÈSE: L'application topique de collagène de type I ne facilitera pas la cicatrisation ou l'esthétique d'une incision chez les rats jusqu'à 28 jours après la formation de plaies. MÉTHODOLOGIE: Les auteurs ont examiné les effets du collagène bovin de type I (6 mg/mL) sur un modèle de double incision cutanée chez des rats. Chaque rat était son propre sujet témoin, car du collagène topique était appliqué sur une incision, et une solution physiologique normale (0,9 %), sur l'autre. Les rats étaient euthanasiés trois (n=6), sept (n=6) et 28 (n=5) jours après la création des plaies. Les auteurs ont prélevé des tissus à chacun de ces moments et les ont examinés pour établir leur résistance maximale à la rupture et pour procéder à une analyse biochimique et histologique. RÉSULTATS: Il n'y a pas de différence statistiquement significative (c'est-à-dire P<0,05) quant à la résistance maximale à la rupture des plaies traitées au collagène et de celles traitées au moyen d'une solution physiologique à l'un de ces trois moments. L'analyse histologique a révélé une infiltration similaire des cellules inflammatoires et des fibroblastes dans les lèvres de la plaie de chacune des incisions par rapport au moment de création de la plaie. Le transfert de Western n'a révélé aucune différence dans le contenu en fibronectine ou en collagène I des plaies de chaque rat. CONCLUSIONS: L'application topique de collagène ne facilite pas la cicatrisation des plaies au bout de trois à 28 jours dans un modèle de plaies chez les rats.

Accelerated wound healing with topical application of complement C5.

BACKGROUND: Delayed-healing traumatic, surgical, and chronic wounds can be detrimental to patients and the health care system. The authors set out to investigate the effects of complement C5, a naturally occurring chemotactic cytokine, on wounds. METHODS: The authors examined the effects of complement C5 on the rat paired skin incision model. Each rat served as its own control where topical collagen was applied to one incision and 100 nM of C5 in collagen vehicle was applied to the other incision. Rats were killed on days 3 (n = 6), 7 (n = 6), and 28 (n = 5) after wounding. RESULTS: There was a statistically significant, 65 percent increase in maximum wound breaking strength with the topical application of C5 at day 3 (p < 0.01). The increase persisted to 14 percent at 7 days after wounding (p < 0.05). When compared with the sham group, the C5-treated wound strength increased by 83 percent at day 3 and 64 percent at day 7. There was no change in breaking strength at 28 days. Western blot analysis demonstrated a significant increase in collagen and fibronectin content in the C5-treated wounds. CONCLUSIONS: Topical application of C5 to skin wounds significantly increases wound healing maximum breaking strength as early as 3 days and up to 7 days after wounding. C5 accelerated wound healing by at least 4 days in the first week of wounding. This was correlated with an increase in vascular permeability, increased inflammatory cell recruitment, subsequent fibroblast migration, and increased collagen deposition.

Development of a bioreactor for axially loaded intervertebral disc organ culture.

Whole disc organ culture is needed for preclinical testing of biological repair of the degenerate intervertebral disc. Such organ culture is hampered by two major limitations: first obtaining adequate nutrition though the calcified cartilage endplates adjacent to the vertebral bone, and second by loss of tissue integrity if the endplates are removed from the discs. In this work we utilize a recently described technique for whole disc isolation that overcomes these problems, by removal of vertebral bone and the adjacent calcified portion of the endplate, and the construction of a bioreactor that permits long-term viability of these discs in loaded organ culture. The bioreactor consists of a culture chamber in which the disc can be dynamically loaded in a uniform manner. The culture chamber is large enough to accommodate discs up to 60 mm in diameter, and so is amendable to study both bovine and human discs. The discs are loaded in the culture chamber by upper and lower platens, which conform to the shape of the remaining cartilaginous endplate and permit fluid flow across its surface. The bioreactor is able to load the disc under a variety of conditions ranging from static to dynamic and from physiological to pathological, and monitor induced changes in disc height. To date, bovine caudal discs have been maintained viable in the bioreactor for up to 4 weeks without any appreciable loss of disc height under physiological cyclic load and, in principle, could be maintained in such a manner for several months. Such long-term organ culture is essential for studying biological repair of the disc.

Rapid intraoperative zygoma fracture imaging.

BACKGROUND: A fractured zygoma frequently results in an aesthetically displeasing facial asymmetry. Open reduction and internal fixation may accurately realign the facial skeleton but often with undesirable sequelae. The authors' objective was to develop a precise technique of intraoperative zygoma fracture imaging using a C-arm to permit anatomical fracture realignment while reducing the extent of skeletal exposure required. The simplicity and accessibility of this method should allow its widespread clinical application. METHODS: First, using a model skull, the relative positions of the C-arm required to adequately depict zygoma projection, width, arch contour, and zygoma rotation were defined. Second, diverse zygoma fracture types were created in six cadaver heads with a Mini Bionix machine and were repaired using C-arm guidance; accuracy was confirmed with postoperative computed tomography. Third, after defining optimal operating room setup, the accuracy in a clinical case was assessed. RESULTS: Two C-arm views were defined. The zygoma projection view (C-arm at 70 to 90 degrees to the skull's coronal plane) allows visualization of projection, width, and contour. The rotation view (C-arm at 70 to 90 degrees to the skull's sagittal plane) allows visualization of zygoma rotation. Postoperative computed tomographic imaging confirmed anatomical repair in all cases. Average operating room duration was less than 30 minutes, with operating room times decreasing progressively. CONCLUSIONS: The authors have developed an accurate technique of intraoperative zygoma fracture imaging and reduction guidance. This technique may decrease the risks of open access by potentially limiting direct skeletal exposure to buttresses where skeletal stabilization is required. In addition, this method is simple, can be learned and used rapidly, and is readily accessible.

Evaluation of quantitative magnetic resonance imaging, biochemical and mechanical properties of trypsin-treated intervertebral discs under physiological compression loading.

PURPOSE: To investigate the influence of targeted trypsin digestion and 16 hours compression loading on MR parameters and the mechanical and biochemical properties of bovine disc segments. MATERIALS AND METHODS: Twenty-two 3-disc bovine coccygeal segments underwent compression loading for 16 hours after the nucleus pulposus (NP) of each disc was injected with a solution of trypsin or buffer. The properties of the NP and annulus fibrosus (AF) tissues of each disc were analyzed by quantitative MRI, biochemical tests, and confined compression tests. RESULTS: Loading had a significant effect on the MR properties (T(1), T(2), T(1rho), MTR, ADC) of both the NP and AF tissues. Loading had a greater effect on the MR parameters and biochemical composition of the NP than trypsin. In contrast, trypsin had a larger effect on the mechanical properties. Our data also indicated that localized trypsin injection predominantly affected the NP. T(1rho) was sensitive to loading and correlated with the water content of the NP and AF but not with their proteoglycan content. CONCLUSION: Our studies indicate that physiological loading is an important parameter to consider and that T(1rho) contributes new information in efforts to develop quantitative MRI as a noninvasive diagnostic tool to detect changes in early disc degeneration.

Double pedicle screw instrumentation in the osteoporotic spine: a biomechanical feasibility study.

STUDY DESIGN: A biomechanical feasibility test. OBJECTIVE: To assess the overall feasibility, safety, and mechanical effectiveness of an intrapedicular double-screw construct in the thoracolumbar spine. SUMMARY OF BACKGROUND DATA: The bony purchase of the pedicle screw fixation is often not strong enough in elderly patients with osteoporosis. Our hypothesis was that the elliptical cross-section of the pedicle would allow the insertion of 2 smaller diameter pedicle screws resulting in a bony purchase superior to the standard single-screw technique. METHODS: Thirty-six double-screw constructs (5mm diameter AOUSS and 5 mm Schanz screw) and 36 standard single pedicle screws (6mm diameter AOUSS screw) were placed. Screw pullout, multiaxial flexibility, and axial failure load testing was performed. RESULTS: Visual inspection, palpation, and radiograph confirmed that there were no pedicle breaches. In the double-screw group, all but 2 constructs had ideal direction. Pullout strength of the double-screw construct was no different than that of the single-screw construct. However, stiffness increased considerably in all testing modes. Axial load to failure, adjusted for bone mineral density, and dimensional variation, also increased. All differences were statistically significant except for axial rotation that was only marginally significant. CONCLUSIONS: The double-screw construct appears feasible and safe in the thoracolumbar spine. In this study, the new technique demonstrates a mechanical advantage over the standard single-screw technique. Further in vitro cadaveric safety studies with better adapted instrumentation are needed before the technique can be widely recommended.

Square-lashing technique in segmental spinal instrumentation: a biomechanical study.

Sublaminar wires have been used for many years for segmental spinal instrumentation in scoliosis surgery. More recently, stainless steel wires have been replaced by titanium cables. However, in rigid scoliotic curves, sublaminar wires or simple cables can either brake or pull out. The square-lashing technique was devised to avoid complications such as cable breakage or lamina cutout. The purpose of the study was therefore to test biomechanically the pull out and failure mode of simple sublaminar constructs versus the square-lashing technique. Individual vertebrae were subjected to pullout testing having one of two different constructs (single loop and square lashing) using either monofilament wire or multifilament cables. Four different methods of fixation were therefore tested: single wire construct, square-lashing wiring construct, single cable construct, and square-lashing cable construct. Ultimate failure load and failure mechanism were recorded. For the single wire the construct failed 12/16 times by wire breakage with an average ultimate failure load of 793 N. For the square-lashing wire the construct failed with pedicle fracture in 14/16, one bilateral lamina fracture, and one wire breakage. Ultimate failure load average was 1,239 N For the single cable the construct failed 12/16 times due to cable breakage (average force 1,162 N). 10/12 of these breakages were where the cable looped over the rod. For the square-lashing cable all of these constructs (16/16) failed by fracture of the pedicle with an average ultimate failure load of 1,388 N. The square-lashing construct had a higher pullout strength than the single loop and almost no cutting out from the lamina. The square-lashing technique with cables may therefore represent a new advance in segmental spinal instrumentation.

Atlantoaxial fusion using anterior transarticular screw fixation of C1-C2: technical innovation and biomechanical study.

This study is an attempt to describe a new technique for anterior transarticular screw fixation of the atlantoaxial joints, and to compare the stability of this construct to posterior transarticular screw fixation with and without laminar cerclage wiring. Nine human cadaveric specimens were included in this study. The C1-C2 motion segment was instrumented using either anterior transarticular screws (group 1), posterior transarticular screws alone (group 2), or posterior screws with interlaminar cerclage wires (group 3). Using an unconstrained mechanical testing machine, the specimens were tested in rotation, lateral bending, and flexion-extension using nondestructive loads of +/-2 N m. The specimens were also tested in translation using nondestructive loads of +/-100 N. All values for the three groups with regards to anterior-posterior displacement, rotation, and lateral bending were similar as determined using a Kruskal-Wallis rank sum test with a significance level of p<0.05. The only significant difference was registered in flexion-extension where the cerclage wire added some strength to the construct. Anterior transarticular screw fixation of the atlantoaxial spine has several advantages over posterior fixation techniques, and is as stable as posterior transarticular fixation in all clinically significant planes of motion. The addition of posterior interlaminar cerclage wiring further improves resistance to flexion-extension forces. Anterior transarticular screw fixation of the atlantoaxial joint is a useful technique for achieving C1-C2 stabilization.