Bio-conjugation of platelet-rich plasma and alginate through carbodiimide chemistry for injectable hydrogel therapies.

Alginate is a highly tailorable, biocompatible polymer whose properties can be tuned to mimic the properties of native nucleus pulposus (NP) tissue. Platelet-rich plasma (PRP) is a highly accessible, inexpensive, and readily available mix of pro-regenerative factors. By functionalizing alginate with PRP, a mechanically optimized, bioactive alginate NP analogue may stimulate NP cells to proliferate and accumulate matrix over a longer period of time than if the PRP were solely encapsulated within the hydrogel. In this study, PRP was chemically bound to alginate using carbodiimide chemistry and mechanically, physically, and cytologically compared to plain alginate as well as alginate containing free-floating lyophilized PRP. The alginates were mechanically and physically characterized; PRP-conjugated alginate had similar mechanical properties to controls and had the benefit of retained PRP proteins within the hydrogel. Human nucleus pulposus cells (hNPCs) were seeded within the modified alginates and cultured for 14 days. Quantification data of glycosaminoglycans suggests that PRP-incorporated alginate has the potential to increase ECM production within the characterized alginate constructs, and that PRP-functionalized alginate can retain protein within the hydrogel over time. This is the first study to functionalize the milieu of PRP proteins onto alginate and characterize the mechanical and physical properties of the modified alginates. This study also incorporates hNPCs into the characterized PRP-modified alginates to observe phenotypic maintenance when encapsulated within the in situ gelling constructs.

Changes in the material properties of the shell during simulated aquatic hibernation in the anoxia-tolerant painted turtle.

Western painted turtles (Chrysemys picta bellii) tolerate anoxic submergence longer than any other tetrapod, surviving more than 170 days at 3°C. This ability is due, in part, to the shell and skeleton simultaneously releasing calcium and magnesium carbonates, and sequestering lactate and H+ to prevent lethal decreases in body fluid pH. We evaluated the effects of anoxic submergence at 3°C on various material properties of painted turtle bone after 60, 130 and 167-170 days, and compared them with those of normoxic turtles held at the same temperature for the same time periods. To assess changes in the mechanical properties, beams (4×25 mm) were milled from the plastron and broken in a three-point flexural test. Bone mineral density, CO2 concentration (a measure of total bone HCO3-/CO32-) and elemental composition were measured using microcomputed tomography, HCO3-/CO32- titration and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Tissue mineral density of the sampled bone beams was not significantly altered by 167-170 days of aquatic overwintering in anoxic or normoxic water, but bone CO2 and Mg were depleted in anoxic compared with normoxic turtles. At this time point, the plastron beams from anoxic turtles yielded at stresses that were significantly smaller and strains that were significantly greater than the plastron beams of normoxic turtles. When data from anoxic and normoxic turtles were pooled, plastron beams had a diminished elastic modulus after 167-170 days compared with those of control turtles sampled on day 1, indicating an effect of prolonged housing of the turtles in 3°C water without access to basking sites. There were no changes in the mechanical properties of the plastron beams at any of the earlier time points in either group. We conclude that anoxic hibernation can weaken the painted turtle's plastron, but likely only after durations that exceed what it might naturally experience. The duration of aquatic overwintering, regardless of oxygenation state, is likely to be an important factor determining the mechanical properties of the turtle shell during spring emergence.

Does Posterior Fixation of Partially Unstable Open-Book Pelvic Ring Injuries Decrease Symphyseal Plate Failure? A Biomechanical Study.

OBJECTIVE: Recent clinical study suggests an advantage to adding an iliosacral screw to the anterior fixation construct for anteroposterior compression type-2 (OTA/AO type 61-B1), partially unstable open-book pelvic ring injuries. Others have described stress examination to determine any required supplemental fixation. However, biomechanical studies investigating iliosacral fixation requirements for this injury are lacking. Our objective was to determine whether adding an iliosacral screw to symphyseal plate fixation decreases displacement in a well-defined open-book pelvic ring injury model. METHODS: An open-book pelvic ring injury was created in 10 human cadaveric pelves by unilaterally releasing the sacrospinous, sacrotuberous, and anterior sacroiliac ligaments plus transection of the pubic symphysis, approximating the classically described anteroposterior compression type-2 (APC-2) injury. Specimens were divided into 2 groups: (1) symphyseal plating and (2) plating plus an iliosacral screw. Using a standard bilateral stance model loaded at 550 N, displacement measurements were obtained at 210,000 and 500,000 cycles. RESULTS: Three specimens failed before 210,000 cycles because of technical errors and were excluded from analysis. For the remaining 7, there was no significant difference in displacement between the 2 groups, and none sustained implant failure. Post hoc analysis showed that a large sample size (45/group) would be required to detect any difference with 80% power, indicating a small effect size with limited clinical application. CONCLUSIONS: Adding an iliosacral screw to the symphyseal plate fixation does not provide improved biomechanical outcome in classically described APC-2 injuries. Clinically, stress examination may be useful to determine the need for supplemental posterior fixation in APC-2 injuries.

Characterization and restoration of degenerated IVD function with an injectable, in situ gelling alginate hydrogel: An in vitro and ex vivo study.

Intervertebral disc (IVD) degeneration is a naturally, irreparable process that causes loss in IVD hydration, cellularity, and, mechanical stability. Invasive surgical attempts to ease back pain and, radiculopathy have shown to cause increased degeneration along the rest, of the spine. Due to its highly tunable mechanical and degradation, properties, alginate is a viable option for a less-invasive injectable, repair for IVD degeneration. This study centers on the characterization, of in situ gelling alginate and subsequent injection into enzymatically, degraded motion segments., In situ gelation of 2% alginate (% w/v PBS) was performed using calcium, carbonate (CaCO3) and glucono-δ-lactone (GDL) and compared to, instantaneously gelled 2% alginate crosslinked with calcium chloride., After characterization of multiple molar concentrations, a ratio of, 60mM:120mM CaCO3:GDL was determined to have the most optimum properties, for injection. Enzymatically degraded bovine caudal motion segments were, injected with the optimized in situ gelling alginate and mechanically, loaded; injected motion segments were compared to intact specimens, degraded specimens, and specimens injected with 20% gelatin to, corroborate with previous ex vivo injection studies., Overall, injection of in situ curing 2% alginate into an enzymatically, and mechanically degraded IVD restores function via reduction of height, loss over long-term cyclic loading, is constrained within the disc with, no injection site leakage, and successfully fills all void spaces created, by chemonucleolysis with 1% collagenase-f. These findings, along with the, ability of alginate to be specifically tailored to support cell, viability, show promise for a tissue engineered injectable NP substitute for the reversal of disc degeneration.

Characterization of slow-gelling alginate hydrogels for intervertebral disc tissue-engineering applications.

Reversal of intervertebral disc degeneration can have a potentially monumental effect on spinal health. As such, the goal of this research is to create an injectable, cellularized alginate-based nucleus pulposus that will restore disc function; with the primary goal of creating an alginate gel with tailorable rates of gelation to improve functionality over standard CaCl2 crosslinking techniques. Gelation characteristics of 1% sodium alginate were analyzed over various molar concentrations of a 1:2 ratio of CaCO3:glucono-δ-lactone (GDL), with 10% CaCl2 as the control crosslinker. Alginate construct characterization for all concentrations was performed via ultimate and cyclic compressive testing over a 28day degradation period in PBS. Dehydration, swell testing, and albumin release kinetics were determined, and cytotoxicity and cell homogeneity tests showed promise for cellularization strategies. Overall, the 30 and 60mM GDL alginate concentrations presented the most viable option for use in further studies, with a gelation time between 10 and 30min, low hysteresis over control, low percent change in thickness and weight under both PBS degradation and swelling conditions, and stable mechanical properties over 28days in vitro.

Are Hook Plates Advantageous Compared to Antiglide Plates for Vertical Shear Malleolar Fractures?

This study was designed to evaluate the biomechanical properties of a hook plate (HP) vs an antiglide (AG) plate for supination-adduction (SAD)-ankle fractures. Identical polyurethane tibial models were obtained and vertical fractures were created. The fractures were stabilized with 1 of the following: one-third tubular plate in an AG fashion with 2 screws proximal to the fracture; an AG plate with an additional screw perpendicular to the vertical shear fragment (MAG), or an HP. Ten models were randomly assigned to each of the 3 groups. The constructs were tested in offset-axial loading and were evaluated for construct stiffness and load-to-failure. The MAG construct yielded better stiffness compared with the AG plate (P < .05) and the HP (P < .05). The plate stiffness of the HP construct compared with the AG was not significant (P = .350). In regards to load-to-failure, the difference between MAG and AG was 638 N, and MAG and HP was 530 N (both P < .05). The HP had a load-to-failure that was, on average, 108 N more than the AG but was not significant (P = .063). A one-third tubular plate in the MAG fashion provided a stable, strong construct for fixation of vertical shear medial malleolus fractures.

Supplemental S1 fixation for type C pelvic ring injuries: biomechanical study of a long iliosacral versus a transsacral screw.

BACKGROUND: A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unreliable for certain type C pelvic ring injuries. Insertion of a second supplemental iliosacral screw into the S1 or S2 vertebral body has been widely used. However, clinical fixation failures have been reported using this technique, and a supplemental long iliosacral or transsacral screw has been used. The purpose of this study was to compare the biomechanical effect of a supplemental S1 long iliosacral screw versus a transsacral screw in an unstable type C vertically oriented sacral fracture model. MATERIALS AND METHODS: A type C pelvic ring injury was created in ten osteopenic/osteoporotic cadaver pelves by performing vertical osteotomies through zone 2 of the sacrum and the ipsilateral pubic rami. The sacrum was reduced maintaining a 2-mm fracture gap to simulate a closed-reduction model. All specimens were fixed using one 7.0-mm iliosacral screw into the S1 body. A supplemental long iliosacral screw was placed into the S1 body in five specimens. A supplemental transsacral S1 screw was placed in the other five. Each pelvis underwent 100,000 cycles at 250 N, followed by loading to failure. Vertical displacements at 25,000, 50,000, 75,000, and 100,000 cycles and failure force were recorded. RESULTS: Vertical displacement increased significantly (p < 0.05) within each group with each increase in the number of cycles. However, there was no statistically significant difference between groups in displacement or load to failure. CONCLUSIONS: Although intuitively a transsacral screw may seem to be better than a long iliosacral screw in conveying additional stability to an unstable sacral fracture fixation construct, we were not able to identify any biomechanical advantage of one method over the other.

Locked versus standard unlocked plating of the symphysis pubis in a Type-C pelvic injury: a cadaver biomechanical study.

INTRODUCTION: The benefits of locked plating for pubic symphyseal disruption have not been established. The purpose of this biomechanical study was to determine whether locked plating offers any advantage over conventional unlocked plating of the pubic symphysis in the vertically unstable, Type-C pelvic injury. METHODS: In each of eight embalmed cadaver pelvis specimens, sectioning of the pubic symphysis in conjunction with a unilateral release of the sacroiliac, sacrospinous, and sacrotuberous ligaments and pelvic floor was performed to simulate a vertically unstable Type-C (Orthopaedic Trauma Association 61-C1.2) pelvic injury. The disrupted SI joint was then reduced and fixed using two 6.5mm cannulated screws inserted into the S1 body. Using a six-hole 3.5mm plate specifically designed for the symphysis pubis having both locked and unlocked capability, four pelvises were fixed with locked screws and four pelvises were fixed with standard unlocked bicortical screws. Both groups were similar based on a dual-emission X-ray absorptiometry evaluation (P=0.69). Each pelvis was then mounted on a servohydraulic materials-testing apparatus using a bilateral stance model to mainly stress the symphyseal fixation and was cycled up to 1 million cycles or failure, whichever occurred first. RESULTS: Five specimens experienced failure at the jig mounting/S1 vertebral body interface, occurring between 360,000 and 715,000 cycles. Frank failure of the anterior or posterior instrumentation did not occur. However, end-trialing diastasis of the initial pubic symphysis reduction was found in all pelvises. There were no differences between the groups with respect to this loss of symphyseal reduction (P=0.69) or average cycles to failure (P=1.0). CONCLUSION: Pubic symphyseal locked plating does not appear to offer any advantage over standard unlocked plating for a Type-C (OTA 61-C1.2) pelvic ring injury.

Locked plating of comminuted distal femur fractures: does unlocked screw placement affect stability and failure?

OBJECTIVES: Locked plates provide greater stiffness, possibly at the expense of fracture healing. The purpose of this study is to evaluate construct stiffness of distal femur plates as a function of unlocked screw position in cadaveric distal femur fractures. METHODS: Osteoporotic cadaveric femurs were used. Four diaphyseal bridge plate constructs were created using 13-hole distal femur locking plates, all with identical condylar fixation. Constructs included all locked (AL), all unlocked (AUL), proximal unlocked (PUL), and distally unlocked (DUL) groups. Constructs underwent cyclic axial loading with increasing force per interval. Data were gathered on axial stiffness, torsional stiffness, maximum torque required for 5-degree external rotation, and axial force to failure. RESULTS: Twenty-one specimens were divided into AL, AUL, PUL, and DUL groups. Axial stiffness was not significantly different between the constructs. AL and PUL demonstrated greater torsional stiffness, maximum torque, and force to failure than AUL and AL showed greater final torsional stiffness and failure force than DUL (P < 0.05). AL and PUL had similar axial, torsion, and failure measures, as did AUL and DUL constructs. All but 2 specimens fractured before medial gap closure during failure tests. Drop-offs on load-displacement curves confirmed all failures. CONCLUSIONS: Only the screw nearest the gap had significant effect on torsional and failure stiffness but not axial stiffness. Construct mechanics depended on the type of screw placed in this position. This screw nearest the fracture dictates working length stiffness when the working length itself is constant and in turn determines overall construct stiffness in osteoporotic bone.

Biomechanical comparison of standard iliosacral screw fixation to transsacral locked screw fixation in a type C zone II pelvic fracture model.

OBJECTIVES: Iliosacral screw fixation into the first sacral body is a common method for pelvic ring fixation. However, this construct has been shown to be clinically unreliable for the percutaneous fixation of unstable Type C zone II vertically oriented sacral fractures with residual fracture site separation. The objective of this study was to biomechanically compare a locked transsacral construct versus the standard iliosacral construct in a Type C zone II sacral fracture model. METHODS: A Type C pelvic ring injury was created in ten embalmed cadaver pelves by performing vertical osteotomies through zone II of the sacrum and the ipsilateral pubic rami. The sacrum was then reduced maintaining a 2 mm fracture gap. Five specimens were fixed using two 7.0-mm iliosacral screws into the S1 body; the other 5 were fixed using one 7.0-mm iliosacral screw and one 7.0-mm transsacral screw exiting the contralateral ilium with a nut placed on its end, creating a locked construct. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. Vertical displacements at 25,000; 50,000; 75,000 and 100,000 cycles and failure force were recorded for each pelvis. RESULTS: The locked transsacral construct performed significantly better than the iliosacral construct at all 4 measurement points (P = 0.009) and in force to failure (P value = 0.02). CONCLUSIONS: Fixation of unstable zone II sacral fractures using the combination of an iliosacral screw and a locked transsacral screw resists deformation and withstands a greater force to failure as compared to fixation with 2 standard iliosacral screws. This locked transsacral construct may prove advantageous, especially when a percutaneous technique is used for a Type C zone II vertically oriented sacral fracture injury pattern, which can result in residual fracture site separation.

A biomechanical comparison of one-third tubular plates versus periarticular plates for fixation of osteoporotic distal fibula fractures.

OBJECTIVES: The purpose of this study was to test the biomechanical properties of locking and nonlocking plates using one-third tubular and periarticular plate designs in an osteoporotic distal fibula fracture model. METHODS: Twenty-four cadaveric specimens, whose bone mineral densities were obtained using dual x-ray absorptiometry scans, were tested. The fracture model simulated an OTA 44-B2.1 fracture. The constructs included (1) nonlocking one-third tubular plate, (2) locking one-third tubular plate, (3) nonlocking periarticular plate, and (4) locking periarticular plate. The specimens underwent axial loading followed by torsional loading to failure. Statistical analysis was performed using Kruskal-Wallis testing and further analysis with Mann-Whitney testing. RESULTS: The periarticular plates had greater rotational stiffness compared with the one-third tubular plates (P = 0.04). The nonlocking plates had greater torque to failure than the locking plates (P = 0.01). The nonlocking one-third tubular plate had greater torque to failure than the locking one-third tubular plate (P = 0.03). No significant differences were found in any of the comparisons regarding axial stiffness. CONCLUSIONS: In biomechanical testing using an osteoporotic model of OTA 44-B2.1 fractures, periarticular plates were superior to one-third tubular plates in rotational stiffness only. Locking plates did not outperform their nonlocking counterparts. Periarticular plates should be considered when treating osteoporotic distal fibula fractures, but one-third tubular plates and nonlocking plates provide adequate fixation for these injuries.

Locked versus standard unlocked plating of the pubic symphysis: a cadaver biomechanical study.

OBJECTIVES: Although locked plating has been shown to have advantages for diaphyseal and metaphyseal fracture fixation, its benefits for pubic symphyseal disruption have not been established. With traditional plate fixation of the disrupted pubic symphysis, normal physiological symphyseal pelvic motion eventually results in plate breakage, screw breakage, and loosening of screws. A concern exists that common modes of locked plate construct failure could result in abrupt and complete loss of symphyseal fixation. The purposes of this study were to determine, using an open-book pelvic injury model, whether locked plating of the pubic symphysis 1) offers any advantage over standard unlocked plating; and 2) results in a potential increased risk of abrupt fixation failure. METHODS: Twelve osteopenic cadaver pelvic specimens were acquired and dual-energy x-ray absorptiometry scans were obtained to ensure uniformity of the specimens' bone density. Sacrospinous, sacrotuberous, and anterior sacroiliac ligaments were released and the symphysis pubis was transected to simulate a partially stable open book (AO/Orthopaedic Trauma Association 61-B3.1) injury. Using a six-hole 3.5-mm plate specifically designed for the symphysis pubis with the capability of fixation in locked or unlocked mode, six pelvises were fixed with locked screws and six pelvises were fixed standard unlocked bicortical screws. There was no significant difference between these 2 groups with regard to bone density (P = 0.47). Two equally osteopenic pelvic specimens from each fixation group were selected for the purpose of obtaining failure data and determining an acceptable load for trialing. Both specimens failed at 1985 N. The remaining 10 pelvises were then mounted on a materials testing apparatus using the bilateral stance model as described by Tile. In accordance with the failure data, each pelvis was stressed at 440 N for a total of one million cycles (equivalent to 6.5 months of daily walking) or until fixation failure. RESULTS: All pelvic specimens in both fixation groups completed one million cycles without plate or screw failure. However, diastasis of the initial pubic symphysis reduction was found in all pelvises (mean, 2.45 mm; range, 1.5-4.0 mm) regardless of fixation method. This loss of reduction was not significantly different between the 2 fixation groups (P = 0.914). CONCLUSIONS: No abrupt failures occurred in either plating group. Consequently, any fear of catastrophic (ie, abrupt and complete) failure of locked symphyseal plates appears to be unfounded for open-book injuries treated in patients with low bone density. However, minor loss of the symphyseal reduction was evident in all pelvises regardless of the fixation method. Therefore, locked plating of the pubic symphysis does not appear to offer any advantage over the standard unlocked technique for an AO/Orthopaedic Trauma Association 61-B3.1 partially stable open-book pelvic injury pattern in osteopenic bone.

A biomechanical comparison of trochanteric nail proximal screw configurations in a subtrochanteric fracture model.

OBJECTIVES: Historically, because of the magnitude of muscle forces exerted locally, as well as the commonly associated comminution, subtrochanteric fractures have been difficult to treat. Tencer et al found intramedullary nail fixation to be superior to lateral plate constructs in axial compression and combined bending. In addition, reconstruction-type intramedullary nails of more recent design have been shown to provide strength and stiffness superior to that supplied by the earlier antegrade intramedullary implants. A relatively new reconstruction nail, the DePuy VersaNail Troch Entry Nail (DePuy Orthopaedics, Inc., Warsaw, IN, USA), is unique in that it allows for two different proximal two-screw configurations: (1) the common parallel cephalomedullary arrangement and (2) a novel crossed-screw pattern. Our hypothesis was that the crossed-screw configuration would be as strong in axial loading as the cephalomedullary screw configuration. METHODS: Twenty composite femurs were instrumented using the DePuy VersaNail Troch Entry Nail in a subtrochanteric fracture model: 10 with the crossed proximal screw configuration and 10 with the traditional parallel screw configuration. These constructs were first loaded axially to calculate their stiffness and then axially loaded to failure. RESULTS: One specimen was rendered unusable for all calculations. Therefore, 19 constructs were evaluated: 9 parallel screw constructs, 10 crossed-screw constructs. The crossed-screw construct had a significantly higher stiffness than the parallel screw construct (347 +/- 73 N/mm and 261 +/- 42 N/mm, respectively; P = 0.01) and a significantly higher axial load to failure (2848 +/- 391 N vs. 2300 +/- 444 N; P = 0.01). CONCLUSIONS: This study shows that axial failure loads of the crossed-screw configuration were greater than those of the parallel screw configuration. Clinically, this provides the surgeon more options for stabilizing a subtrochanteric femur fracture. This decision may be made intra-operatively if necessary, facilitating fracture fixation and providing a stable construct.

Biomechanical comparison of polyaxial-type locking plates and a fixed-angle locking plate for internal fixation of distal femur fractures.

OBJECTIVES: To test the stability to axial loading of 2 new polyaxial locking screw-plate designs and analyze different angles of screw insertion. The noncontact bridging (NCB) polyaxial locking plate (Zimmer) and the POLYAX plate (DePuy) were compared with a fixed-angle less invasive stabilization system (LISS; Synthes). METHODS: Twenty-five synthetic femurs were divided into 5 groups and assigned fixation with the LISS plate (group I), POLYAX plate (groups IIA and IIB), or NCB plate (groups IIIA and IIIB). The polyaxial constructs were divided into parallel and crossed distal condylar screw configurations. Each construct was tested under axial loading and stressed to failure at a displacement rate of 5 mm/min with a preload of 100 N. Outcome measurements included stiffness, load to failure, peak force, and mode of failure. RESULTS: All LISS and POLYAX constructs failed by plastic deformation of the plate, whereas 9 of 10 NCB constructs failed by an intra-articular lateral condyle fracture. No failures occurred at the screw-plate interface in either polyaxial constructs. Load to failure of the LISS was 33% greater than the parallel POLYAX (P < 0.01) and 24% greater than the crossed POLYAX (P < 0.01). Load to failure of NCB (parallel and crossed) were 24% greater than the parallel POLYAX (P < 0.01 and P < 0.01, respectively) and 15% greater than the crossed POLYAX (P < 0.01 and P = 0.02, respectively). The POLYAX also had significantly lower stiffness and peak force compared with the LISS and NCB. There was no difference between the LISS and NCB with regard to stiffness, load to failure, and peak force. Parallel and crossed polyaxial constructs showed no difference in stiffness or failure loads. CONCLUSIONS: There were no failures of either polyaxial screw-plate interface despite large forces and screw angle did not affect the overall strength of these constructs, supporting the biomechanical soundness of both polyaxial device designs under axial loading. However, the POLYAX supported smaller loads compared with the LISS and NCB while under axial loading. In addition, the mode of failure of the NCB plate, creating an intra-articular fracture propagating from the distal posterior screw hole, may be of some concern. Additional testing is needed to determine the clinical importance of the demonstrated differences among these plate designs.

Observation unit admission as an alternative to inpatient admission for trauma activation patients.

BACKGROUND: At this 35 000 visits/year emergency department (ED) at a level one trauma centre, a trauma protocol was implemented for the ED observation unit. Data on all trauma observation unit admissions were then collected to evaluate for safety, efficiency and admission rates. METHODS: A retrospective chart review was performed of all trauma patients in the observation unit during a 14-month period. Exclusion criteria for observation unit admission included: abnormal vital signs, positive focussed abdominal sonography for trauma examination, abnormal ECG, abnormal chest radiograph, abnormal head computed tomography, Glasgow coma score less than 14, or multisystem trauma. RESULTS: 364 trauma patients were admitted to the observation unit. 84.6% were trauma II activations and 3.8% were trauma I activations. There were no deaths, intubations, loss of vital signs or other adverse events. The average length of stay was 12 h 46 minutes and 11.5% of patients were admitted to an inpatient unit. At 30-day follow-up, there were no significant missed injuries. CONCLUSION: The observation unit is a safe alternative to inpatient admission for the evaluation of the minimally injured trauma activation patient.

The effects of screw orientation in severely osteoporotic bone: a comparison with locked plating.

BACKGROUND: Techniques such as varying screw insertion angles and the use of locked plating have been shown to improve the strength of fixation in bone. The effects of these methods is less clearly understood in bone of exceedingly poor quality. METHODS: Forty plate-bone constructs were assembled and divided into four groups of ten. Perpendicularly placed screws were placed in one group, convergently placed crossing screws were placed in a second group, an oblique end screw was placed in a third group, and a fourth group utilized perpendicularly placed locking screws in a locking plate. All test subjects were mounted and loaded in cantilever bending to the point of failure. Stiffness, initial load to failure, and maximal load tolerated were all analyzed. FINDINGS: All four groups demonstrated evidence of failure at similar loads (21.8-26.1N). The locked group was able to tolerate significantly higher loads overall (37.3N, P=.044). All three non-locked groups demonstrated similar failure patterns and load to failure. Locking constructs demonstrated a distinctly different failure pattern. No significant differences were detected with regard to screw orientation and load to failure. The group with an oblique end screw was significantly less stiff than the other three constructs (P=.017). INTERPRETATION: In a severely osteoporotic model, failure in cantilever bending at low forces will take place regardless of fixation methods used. The mechanism of failure is different in locked constructs compared to traditional constructs. The added benefit of oblique screw placement observed in healthy bone is not observed in osteoporotic bone.

Biomechanical comparison of a 2 and 3 proximal screw-configured antegrade piriformis intramedullary nail with a trochanteric reconstruction nail in an unstable subtrochanteric fracture model.

OBJECTIVE: The objective of this study was to test the stiffness and ultimate load to failure of new intramedullary (IM) nail proximal screw configurations as compared to a trochanteric reconstruction nail. METHODS: Twenty-one synthetic composite femurs were mounted on a Material Testing System and tested in axial compression 5 times. The femurs had an 1 of 2 IM nail types inserted with 1 of 3 proximal screw configurations: a 3-screw configuration with 2 transverse screws and a screw angled into the femoral neck; a 2-screw design with a single transverse screw and a single screw angled into the femoral neck; 2 parallel screws angled into the femoral neck. There were 7 specimens in each group. An unstable fracture (OTA/AO 32-C3.2) was created. and the stiffness of these constructs was tested in compression 5 times. Each construct was then loaded to failure in compression. RESULTS: The 3-screw construct provided more axial stiffness (214 N/mm +/- 75) than either the 2-screw construct (123 N/mm +/- 32) or the trochanteric reconstruction nail (127 N/mm +/- 21) (P = 0.017 and 0.035 for 3-screw vs. 2-screw and recon respectively, P = 0.45 for 2-screw vs. recon). Load-to-failure testing demonstrated similarity among the different screw configurations (3-screw = 2230 N +/- 265, 2-screw = 2283 N +/- 260, Reconstruction nail = 2121 N +/- 156) (P = 1.0 all groups). CONCLUSIONS: The proximal 3-screw configuration provided more stiffness than either the 2-screw configuration or trochanteric reconstruction nail. The 2-screw configuration performed equally to a standard trochanteric reconstruction nail in stiffness testing. The ultimate loads to failure for the 3 tested constructs were not significantly different.

Mechanical properties of layered poly (ethylene glycol) gels.

Poly(ethylene glycol) (PEG) hydrogels have become a popular material for biomedical applications because of their versatility in use and design. As these gels are readily crosslinked under UV, microfabrication techniques have been investigated to manufacture complex three dimensional structures to better mimic the in vivo environment. This work investigated whether a layering technique to fabricate gels offered sufficient strength between the layers to perform similarly in mechanical testing to unlayered gels. Two mechanical tests were performed: tensile tests and peel tests. The tensile tests, which examined sample gels whose test sections were crosslinked for different durations, demonstrated no statistical differences in elastic modulus between sample and control gels. As expected, a statistical increase in the elastic modulus was found with increased PEG concentration. Comparison of the yield stress between samples and controls illustrated differences with total crosslinking duration, which may be due to the decreased molecular weight of the chains with decreased crosslinking time. In peel tests, no statistical differences of maximum peel force were found between samples and controls. However, an increase in the maximum peel force was found with increasing concentration of PEG. Overall, this study demonstrates that the layering process described for the PEG gels has minimal impact on the tested mechanical properties of the system. As mechanical properties are critical to the design of tissue engineered devices, these results demonstrate that this fabrication method may be appropriate for further study as a scaffold for complex cellular systems.

Cyclic mechanical strain alters tissue-factor activity in rat osteosarcoma cells cultured on a titanium substrate.

Tissue factor (TF), a transmembrane glycoprotein, plays a role in the initiation of blood coagulation at sites of vascular injury. Activated products of coagulation may then enhance inflammatory responses. The present investigation assesses the ability of rat osteosarcoma (UMR-106) cells cultured on titanium alloy (Ti6Al4V) to express differential surface TF activity in response to cyclic mechanical strain. Strains ranged from -2000 micro-strain to +2000 micro-strain, and durations from 5, 10, and 20 min per day over 5 days to 24 h continuous stimulation. ROS cells exhibited significant TF activity as demonstrated by the conversion of Factor X to Factor Xa. Strains of +2000 micro-strain with 5-20-min duration exhibited decreased TF activity with duration from 1.4E-04 nM/cell to 8.7E-05 nM/cell. Additionally, ROS cells stimulated with calcium ionophore (A23187) exhibited at least twice the activity of nonstimulated cells. Strains of +1340 micro-strain with 5-20-min duration exhibited an increasing trend with 4.15E-05 nM/cell to 7.38E-05 nM/cell. Strain direction had no significant effect on TF activity. Thus, both mechanical and chemical stimuli induce differential expression of TF activity by ROS cells cultured on Ti6Al4V, a phenomenon that may potentiate or regulate the inflammatory responses associated with the implantation of orthopedic biomaterials.

Neuroendocrine regulation of sexually dimorphic brain structure and associated sexual behavior in male rats is genetically controlled.

Steroid hormones, particularly 17beta-estradiol (E2), regulate the development and expression of neural structures and sexual behavior. Recently, we demonstrated that E2-regulated responses are controlled by quantitative trait loci. In this study, we quantified 1) volume of the sexually dimorphic nucleus (SDN) of the preoptic area (POA); 2) medial basal hypothalamic (MBH)-POA aromatase and 5alpha-reductase enzyme activities during prenatal development and in adults; 3) serum LH, testosterone, FSH, E2, prolactin (PRL), and corticosterone levels; 4) reproductive organ (i.e., testis and ventral prostate) weights; and 5) male mating behavior in Noble (NB/Cr) and Wistar-Furth (WF/NCr) rat strains to determine the genetic influence on the measured parameters. Maximal phenotypic divergence in male SDN-POA volumes was seen between NB/Cr versus WF/NCr and BDIX/Cr rats (among nine rat strains initially examined), with the average SDN-POA volume of NB/Cr male rats being significantly greater ( approximately 30%) than that of either WF/NCr or BDIX/Cr males. Subsequent experiments investigated WF/NCr versus NB/Cr male rats in further detail. Significantly higher MBH-POA aromatase activity was seen in adult WF/NCr versus NB/Cr males, while MBH-POA 5alpha-reductase rates were not significantly different (within or between sex) for the two rat strains assayed. Serum LH levels were significantly higher (by greater than sixfold) in WF/NCr versus NB/Cr males, whereas testis organ:body weight and ventral prostate:body weight ratios in WF/NCr versus NB/Cr males were significantly smaller (by approximately 6-fold for testis and approximately 1.5-fold for prostate values). Serum FSH levels were significantly higher (by twofold) in WF/NCr versus NB/Cr males. However, serum testosterone levels were not significantly different, whereas E2 levels were approximately twofold higher (but not significantly different) in WF/NCr versus NB/Cr animals. No significant differences were found in basal (i.e., nonstress) serum PRL or corticosterone levels between the WF/NCr and NB/Cr males. In male copulatory tests, NB/Cr males exhibited significantly more aggressive sexual behavior (e.g., in mounting, intromission, and ejaculation parameters) compared with WF/NCr males. Taken together, these findings indicate that WF/NCr males are, in general, low responders, whereas NB/Cr males are high responders to hormonal signals. The obtained data suggest that the correlative, phenotypic variation in SDN-POA volume (i.e., structure) and reproductive hormone patterns and mating behavior (i.e., function) of WF/NCr versus NB/Cr males is regulated by potentially E2-mediated mechanisms that are genetically controlled.