Infection is a leading cause of total joint arthroplasty failure. Current preventative measures incorporate antibiotics into the poly (methyl methacrylate) (PMMA) bone cement that anchors the implant into the natural bone. With bacterial resistance to antibiotics on the rise, the development of alternative antibacterial materials is crucial to mitigate infection. Borate bioactive glass, 13–93-B3, has been studied previously for use in orthopedic applications due to its ability to be incorporated into bone cements and other scaffolds, convert into hydroxyapatite (HA)-like layer, and enhance the osseointegration and antibacterial properties of the material. The purpose of this study is to better understand how glass composition and change in surrounding pH effects the composite’s antibacterial characteristics by comparing the incorporation of 30% wt/wt 13–93-B3 glass and pH neutral borophosphate bioactive glass into PMMA bone cement. We also aim to elucidate how HA-like layer formation on the cement’s surface may affect bacterial adhesion. These studies showed that 13–93-B3 incorporated cements had significant reduction of bacterial growth surrounding the composite beyond 24 h of exposure when compared to a neutral borate bioactive glass incorporated cement (p < 0.01) and cement only (p < 0.0001). Additionally, through soaking cement composites in simulated body fluid and then exposing them to a bioluminescent strand of staphylococcus aureus, we found that the presence of a HA-like layer on the 13–93-B3 or pH neutral glass incorporated cement disks resulted in an increase in bacterial attachment on the composite cement’s surface, where p < 0.001, and p < 0.05 respectively. Overall, our studies demonstrated that borate bioactive glass incorporated PMMA bone cement has innate antimicrobial properties that make it a promising material to prevent infection in total joint arthroplasties.

Osteosarcoma and other types of bone cancers often require bone resection, and backfill with cement. A novel silorane-based cement without PMMA's drawbacks, previously developed for dental applications, has been reformulated for orthopedic use. The aim of this study is to assess each cement's ability to elute doxorubicin, maintain its potency, and maintain suitable weight-bearing strength.The silorane-based epoxy cement was synthesized using a platinum-based Lamoreaux's catalyst. Four groups of cement were prepared. Two PMMA groups, one without any additives, one with 200 mg of doxorubicin. Two silorane groups: one without any additive, one with doxorubicin, added so that the w% of drug into both cements were equal. Pellets 6 × 12 mm were used for testing (ASTM F451). n=10. Ten pellets from each group were kept dry. All others were placed into tubes containing 2.5 mL of PBS and stored at 37 °C. Elution from doxorubicin-containing groups were collected every day for 7 days, with daily PBS changeout. Antibiotic concentrations were determined via HPLC. Compressive strength and compressive modulus of all groups were determined for unsoaked specimens, and those soaked for 7 and 14 days. MTT assays were done using an MG63 osteosarcoma cell line.Both cements were able to elute doxorubicin over 7 days in clinically-favorable quantities. For PMMA samples, the incorporation of doxorubicin was shown to significantly affect the compressive strength and modulus of the samples (p<0.01). Incorporation of doxorubicin into silorane had no significant effect on either (p>.05). MTT assays indicated that doxorubicin incorporated into the silorane cement maintained its effectiveness whereas that into PMMA did not. At the dosing used, both cements remained above the 70 MPa.Both PMMA and silorane-based cements can deliver doxorubicin. Doxorubicin, however, interacts chemically with PMMA, inhibiting polymerization and lowering the chemotherapeutic's effectiveness.

We developed a novel silorane-based biomaterial (SBB) for use as an orthopedic cement. SBB is comprised of non-toxic silicon-based monomers, undergoes non-exothermic polymerization, and has weight-bearing strength required of orthopedic cements. We sought to compare the antibiotic release kinetics of this new cement to that of commercially available PMMA bone cement. We also evaluated each material's inherent propensity to support the attachment of bacteria under both static and dynamic conditions. One gram of either rifampin or vancomycin was added to 40g batches of PMMA and SBB. Pellets were individually soaked in PBS. Eluate was collected and tested daily for 14 days using HPLC. Compressive strength and modulus were tested over 21 days. Bioassays were used to confirm the bioactivity of the antibiotics eluted. We measured the growth and maturation of staphylococcus aureus (SA) biofilm on the surface of both PMMA and SBB disks over the course of 72 hours in a static well plate and in a dynamic biofilm reactor (CDC Biofilm Reactor). N=4 at 24, 48, and 72 hours. A luminescent strain of SA (Xen 29) was employed allowing imaging of bacteria on the discs. SBB eluted higher concentrations of vancomycin than did PMMA over the course of 14 days (p<0.001). A significant 55.1% greater day 1 elution was observed from SBB. Silorane cement was able to deliver rifampin in clinically favorable concentrations over 14 days. On the contrary, PMMA was unable to deliver rifampin past day 1. The incorporation of rifampin into PMMA severely reduced its mechanical strength (p<0.001) and modulus (p<0.001). Surface bacterial radiance of PMMA specimens was significantly greater than that of SBB specimens at all time points (p<0.05). The novel silorane-based cement demonstrated superior antibiotic release and, even without antibiotic incorporation, demonstrated an innate inhabitation to bacterial attachment and biofilm.

The basilar thumb joint is the joint second most commonly affected by osteoarthritis (OA) in the hand. Evaluation of dorsal subluxation of the thumb during a functional task such as key pinch could help assess OA risk. The objectives of this study were to determine the best imaging angle for measuring thumb dorsal subluxation during key pinch and to compare subluxation to corresponding OA grades on the Eaton-Glickel, Outerbridge, and ICRS scales. Eleven cadavers cadveric forearm specimens were rigged to simulate key pinch. A mobile c-arm captured AP view images of the hand, and rotating in 5° increments toward the ulnar aspect of the arm up to 60°. Dorsal subluxation was measured on each image and compared to determine which angle captured maximum subluxation. The resulting best imaging angle was used for comparisons between dorsal subluxation of the thumb and OA grades for the basilar thumb joint. The max subluxation was in the AP view for most specimens. There was a significant correlation between subluxation and the Eaton-Glickel grade (p=0.003, R2 = 0.779), but not with either Outerbridge grades (p=0.8018) or ICRS grades (p=0.7001). Dorsal Our results indicate that dorsal thumb subluxation during key pinch should be measured in the A-P view of the forearm/handhand view. Dorsal thumb subluxation during key pinch had a significant correlation with the Eaton-Glickel radiographic measure of OA but not with more accurate visual classifications of OA.

Commentary The attempt to identify real advantages of surgical treatment over conservative treatment for lumbar herniation has spurred a continuing series of studies over the last 40 years. Despite varying in population, size, study design, treatment techniques, and patient condition, most studies have had very similar findings: that surgery provides faster pain relief, with improved scores, at earlier time points. However, in almost all studies, those differences decrease with time and vanish after 1 or 2 years. The article by Bailey et al. contains valuable information for surgeons considering prompt surgical intervention for chronic lumbar disc herniation rather than a more common nonoperative treatment regimen prior to possible surgery. In undertaking this randomized controlled trial (RCT) using intention-to-treat analysis, the authors took advantage of a feature of the Canadian health-care system with its inherent waiting periods of >6 months, which limited the ability of patients in the nonoperative group to cross over to surgery in the early periods of the study. Nevertheless, this study recorded 24 crossover events: 2 early events, 12 events between 6 and 12 months, and 10 events by 2 years. In addition, 8 patients in the surgery cohort did not have surgery. In the first 6 months, crossover events were indeed low. However, with the increasing number of crossover events after 6 months and then more after 12 months, the unique advantage in study design between this RCT, undertaken in Canada, and previously published RCTs appears to vanish. In contrast to several other prior studies mentioned by the authors, this study showed evidence of advantages of prompt discectomy rather than additional nonoperative treatment over the longer term of 2 years as well as at 1 year after treatment group assignment. Under close scrutiny, the differences at 1 year and earlier do appear to be meaningful, but the differences at 2 years are not substantial and do not refute the findings of most other related studies: that the difference between groups decreases over time, becoming clinically unimportant by 2 years. The interpretation of many published studies is made difficult by statistical methodology and metrics that are not readily familiar to most surgeons, but it is important to look deeper before accepting an author’s conclusions at face value. In their paper, the authors use and recognize a minimal clinically important difference (MCID) in the patient-reported outcome measures. Based on a study by Lauridsen et al., Bailey et al. chose 2 as the MCID for their leg pain score, meaning that any difference of <2 is recognized as not clinically meaningful1. However, the authors report the mean difference between treatment groups in their primary outcome measure, leg pain, to be 1.3, well below their acknowledged MCID, indicating that the difference is not clinically important even though it might be significantly different. The MCID can be determined in many ways with use of different methods, so perhaps the value of 2 is off-base2. Copay et al. compared several different ways of determining the MCID with use of similar data on similar outcome measures3. They found the best estimates to be 4.9 for the SF-36 physical component summary (PCS) score, 1.6 for leg pain, and 1.2 for back pain. Although the SF-36 PCS score reported by Bailey et al. is just above Copay’s proposed MCID (5.3 vs. 4.9) indicating clinical importance, the mean differences found by Bailey et al. for leg pain and back pain were both lower than Copay’s proposed MCIDs, indicating differences that are clinically unimportant. So what can we conclude? Although the results of the study by Bailey et al. offer strong evidence for a difference in outcome measures at 6 and 12 months as previously reported4, there was a very marginal or clinically unimportant difference between Bailey’s groups at 2 years. Additionally, readers should always be wary of the very real placebo effect in studies such as this, in which no blinding of patients or surgeons has been accomplished. Based on these considerations, the authors’ conclusion that “microdiscectomy is superior” at 2 years may be just a little bold. The choice to undertake surgery or nonoperative treatment prior to potential surgery should not be taken lightly, even for patients with chronic conditions, because surgery entails risks. The overall surgical complication rate at 2 years reported by Bailey et al. was 15% (with at least one surgery-related adverse event occurring in 12 of 80 patients who underwent surgery). The rate in a previously reported meta-analysis was similar, at 12.5% for open microdiscectomy5. An RCT design, as used by Bailey et al., selects patients blindly for assignment to one treatment or another and reports the results as means for each cohort. Physicians, however, should never blindly choose treatment based solely on what appears to be best for the average patient but should rely instead on a range of available information about individual patients, including pain level, function, mental state, length of symptoms, and above all, patient preference. It may be informative that, even in a socialized medical environment, 40 of the 64 patients initially assigned to the nonoperative treatment group did not go on to have surgery within the time frame of the study even though they could have easily done so at 6 months without cost. The guidance suggested by Legrand et al.6, that the best approach is to “let the patient choose between treatments,” remains valid. Those authors recommended that patients be informed that surgery does not modify the long-term outcome but can speed up recovery, at the expense of potential complications, most of which are reversible6.

PURPOSE:To compare knot and loop characteristics of commonly used high-strength tapes and high-strength round sutures.METHODS:Twenty tied 30-mm loops were prepared for using suture-knot combinations of 4 common arthroscopic knots or a hand-tied surgeon's knot and 7 sutures. Two tapes (BroadBand, SutureTape) and three no. 2 sutures (MaxBraid, FiberWire, DynaCord) were compared. Two additional larger tape sutures (FiberTape, PermaTape) not commonly tied arthroscopically were included in the hand-tied group. Each suture-knot combination was evaluated for loop integrity (single load to a specified elongation), knot security (plastic loop deformation with cyclic testing), loop security, and knot volume. Data were compared using analysis of variance followed by Tukey-Kramer post hoc tests.RESULTS:BroadBand and SutureTape demonstrated superior loop integrity compared to most no. 2 suture-knot combinations. FiberTape (430.48 ± 89.00 N) and PermaTape (545.16 ± 95.09 N) required significantly greater force to undergo 3 mm of displacement than all other hand-tied sutures (P < .001). All suture-knot configurations demonstrated significant plastic deformation (cyclic elongation) over 1000 cycles (P < 0.001). DynaCord displayed the best loop security except when paired with the Duncan loop. Overall, BroadBand and SutureTape had lower knot volumes compared to all other sutures.CONCLUSION:This study exhibits the ability of narrow tape sutures to provide reliable tissue apposition and fixation in multiple suture-knot configurations, while decreasing the potential adverse effects accompanying knot prominence. Generally, BroadBand and SutureTape demonstrated an ideal balance of mechanical characteristics to achieve the optimal suture-knot construct among those tested. Dynacord displayed superior loop security and performed best among round sutures. PermaTape and FiberTape showed greater loop integrity, albeit to the detriment of loop security and knot volume.CLINICAL RELEVANCE:When securing a rotator cuff repair construct with a knot, one should have a basic understanding of the mechanical properties of the suture and knot being used to provide the best possible repair. This study will provide information about the mechanical characteristics of commonly used high-strength tape suture knots and loops to help determine what knot type may provide the best overall construct.

ABSTRACT IMPACT: This study will answer key questions that spine surgeons have regarding techniques used in cement augmentation of vertebral compression fractures and will ultimately advance patient care for such injuries. OBJECTIVES/GOALS: The objective of this study is to determine if a difference exists in load-bearing characteristics and load-to-fracture between injecting cement anteriorly prior to screw placement versus cement augmentation via fenestrated pedicle screws. We also expect differences in load-to-failure characteristics between different cement volumes. METHODS/STUDY POPULATION: This study will be performed in a bioengineering laboratory that has access to a Materials Testing System (MTS). Eight cadaveric specimens will be selected from our stock after pre-screening via CT for inclusion and exclusion criteria. The levels T8-L1 will be dissected from the vertebral column along with any soft tissue structures. The vertebral bodies will be potted in an epoxy mold. From each spine, there are 2 groups of three. One vertebral body from each spine will serve as an internal control, one will be augmented with cement via a cannula and then instrumented with a non-fenestrated screw and the third will be instrumented will a fenestrated screw and then augmented with cement. After appropriate curing time, repeat CT imaging will be completed. The specimens will then be loaded to failure and the results analyzed. RESULTS/ANTICIPATED RESULTS: We hypothesize that we will see a better anterior spread with the cannula/non-fenestrated screw method as compared to the fenestrated screw. The reason being is that we would expect the fenestrated screw to experience more cement extruding from the fenestration rather than being directed anteriorly. We believe a better anterior spread of the cement will lead to a greater load-bearing capacity for the vertebral body. We also believe that a difference will exist in load-to-failure testing with the two volumes being tested, though we cannot predict to what a degree this difference will be impactful as there have been few studies prior looking at this. DISCUSSION/SIGNIFICANCE OF FINDINGS: This study is significant because it will aid in determining the optimal technique to implement in the setting of vertebral compression fractures. This will lead to improved patient care as well as a greater understanding of the instrumentation used in such procedures. The results will lay the groundwork for future research on this procedure.

To evaluate knot security, loop security, and knot size of suture tape and suture wire. The single load to failure (LTF) and cyclic loading of one arthroscopic knot (Samsung Medical Center [SMC]) and one hand-tied knot (surgeon’s knot) using two suture tapes (Broadband-[BB], Suture Tape-[ST]) and two No. 2 suture wires (MaxBraid-[MB], FiberWire-[FW]). A third tape (FiberTape-[FT]), not commonly tied arthroscopically, was included in the hand-tied group. Ten samples for each suture-knot combination were evaluated for knot security, loop security, and knot volume. Data were compared with analysis of variance and the Tukey post-hoc test and considered significant at P < 0.05. In single LTF testing, FT was stronger than any other suture-knot configuration. With surgeon’s knots, BB was stronger than MB and FW, while ST was superior to FW. With cyclic loading, BB and ST had less cyclic elongation than MB and FT in the hand-tied group. Among surgeon’s knots, loop elongation was smallest in BB. FT had the largest loop elongation among all configurations. No significant differences detected among SMC-knot configurations in single LTF, cyclic testing, and loop elongation. Measuring hand-tied knots, FW had greater knot volume than BB and ST, and MB was larger than ST. Excluding FT, surgeon’s knots were smaller than SMC-knots. Among SMC-knots, BB was bulkier than ST and MB. FT had largest knots overall. FT had the best knot security, but the poorest loop security and largest knot volume. With surgeon’s knots, BB had better knot security than both suture wires; ST also bested FW. Hand-tied BB, ST, and MB knots were stronger than their SMC-knot counterparts. BB demonstrated the best loop security among hand-tied knots; no differences were seen between surgeon’s and SMC-knots. Thinner tape designs (BB, ST) had smaller knots than wire designs when tied with surgeon’s knots, but not with SMC-knots.

Borate bioactive glass 13-93B3 converts into an osteoconductive hydroxyapatite-like material in a liquid medium. In this study, 13-93B3 was incorporated into a commercial PMMA (poly(methyl methacrylate)) bone cement, and the conversion of the glass into a precipitate in solution was investigated with scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared (spectroscopy)-attenuated total reflection, and micro-Raman spectroscopy. Glass particles of 5, 33, and 100 mu m diameter were each mixed with the PMMA cement to create 20, 30, and 40% glass-loaded composites. Precipitate formation was found to be a calcium-deficient apatite partially substituted with magnesium ions that resembles native bone material and would ideally encourage bone growth better than stoichiometric hydroxyapatite. Composites of bone cement and 13-93B3 show promise as a means of encouraging bone attachment to the surface of the bone cement.

Study designBiomechanical evaluation of woven polyester tethers.ObjectivesTo quantify changes in tether elongation, stiffness, and failure characteristics after cyclic loading.Summary of background dataLigamentous augmentation is gaining interest as a technique to prevent proximal junctional kyphosis (PJK) in adult spinal fusions. There are a lack of data regarding the effects of cyclic loading on polyester tether mechanical properties. Tether stretch may lead to loss of stabilization and increased risk of tether failure. Biomechanical data are needed to determine the effects of cyclic loading on tether integrity.MethodsTesting was done in two materials: (1) a synthetic cortical bone composite to determine baseline mechanical properties, and (2) nine cadaveric L1 spinous processes. 5 mm woven polyester tethers were looped through 2.5 mm holes drilled in each material. First, five tethers were tested directly to failure in the synthetic bone to establish baseline failure properties. Next, tethers were tested at one of the three cyclic load ranges [5%, 25%, and 50% (n=5 each) of baseline failure] for 1000 cycles and then loaded to failure. Cadaveric tests were done at the 25% range and compared to synthetic bone tests at the same range. Cadaveric failure tests were classified as either tether failure or spinous process bone failure.ResultsGreater cyclic loading range had a significant effect on tether loop elongation, increased stiffness, and decreased ultimate tensile force. Among the cadaveric failure tests, 56% resulted in tether failure and the remaining 44% resulted in bone failure.ConclusionsPolyester tethers stretch significantly when loaded to physiological ranges. Anticipation of tether stretch may be an important consideration for a tethering strategy to prevent PJK. Improved understanding of tether material properties can provide guidance for the evaluation of clinical outcomes associated with techniques to reduce the risk of PJK caused by ligamentous laxity.Level of evidenceBiomechanical study.

Laxity of the anterior oblique ligament (AOL) and/or the dorsoradial ligament (DRL) are believed to contribute to the progression of osteoarthritis in the trapeziometacarpal joint through increased dorsal subluxation. Stress radiographs during functional tasks, such as key pinch, can be used to evaluate such joint instability. Cadaveric experiments can explore joint contact pressures as well as subluxation under varying conditions, to gain knowledge about joint mechanics. The disturbance of supporting tissues, such as the joint capsule, during experiments may affect the recorded stability of the joint. To evaluate potential effects of opening the joint capsule and severing the AOL, eleven cadaveric specimens were rigged to simulate key pinch. An anteroposterior (AP) radiograph of the hand was recorded for each specimen while intact, after partially opening the joint capsule and after sectioning the AOL. First metacarpal subluxation levels were compared between the intact joint, partially open joint capsule, and sectioned AOL. Neither opening the joint capsule nor cutting the AOL had a statistically significant effect on metacarpal subluxation. The results indicate that partially opening the joint capsule has a negligible effect on joint mechanics and support recent studies that postulate that the AOL plays a less substantial role in preventing subluxation.

Bone cement is used extensively in orthopedics to anchor prostheses to bone and fill voids. Incorporating bioactive glass into poly(methyl methacrylate) (PMMA)-based bone cement could potentially improve its effectiveness for these tasks. This study characterizes the mechanical and degradation properties of composites containing PMMA-based bone cement and particles of borate bioactive glass designated as 13-93B3. Glass particles of size 5, 33, and 100 μm were mixed with PMMA bone cement to create composites containing 20, 30, and 40 wt % glass. Composites and a bone cement control were soaked in phosphate-buffered saline. Compressive strength, Young's modulus, weight loss, water uptake, solution pH, and ionic concentrations were measured over 21 days. The compressive strengths of composites decreased over 21 days. Average Young's moduli of the composites remained below 3 GPa. Weight loss and water uptake of specimens did not exceed 2 and 6%, respectively. Boron concentrations and pH of all solutions increased over time, with higher glass weight fractions leading to higher pH values. Results demonstrated that the composite can sustain glass degradation and ionic release without compromising short-term mechanical strength.

Objectives The objective of this study was to characterize the effect of rifampin incorporation into poly(methyl methacrylate) (PMMA) bone cement. While incompatibilities between the two materials have been previously noted, we sought to identify and quantify the cause of rifampin's effects, including alterations in curing properties, mechanical strength, and residual monomer content. Methods Four cement groups were prepared using commercial PMMA bone cement: a control; one with 1 g of rifampin; and one each with equimolar amounts of ascorbic acid or hydroquinone relative to the amount of rifampin added. The handling properties, setting time, exothermic output, and monomer loss were measured throughout curing. The mechanical strength of each group was tested over 14 days. A radical scavenging assay was used to assess the scavenging abilities of rifampin and its individual moieties. Results Compared with control, the rifampin-incorporated cement had a prolonged setting time and a reduction in exothermic output during polymerization. The rifampin cement showed significantly reduced strength and was below the orthopaedic weight-bearing threshold of 70 MPa. Based on the radical scavenging assay and strength tests, the hydroquinone structure within rifampin was identified as the polymerization inhibitor. Conclusion The incorporation of rifampin into PMMA bone cement interferes with the cement's radical polymerization. This interference is due to the hydroquinone moiety within rifampin. This combination alters the cement's handling and curing properties, and lowers the strength below the threshold for weight-bearing applications. Additionally, the incomplete polymerization leads to increased toxic monomer output, which discourages its use even in nonweight-bearing applications.

INTRODUCTION:The objective of this study was to evaluate the effect of ultrasound frequency and treatment duration on antibiotic-impregnated polymethylmethacrylate (PMMA) antibiotic elution rates and mechanical strength.METHODS:Two batches of PMMA were prepared: one with five grams of vancomycin powder and one without. Each batch was divided into two frequency groups: kHz and MHz. Each frequency group was divided into two duration groups: two minutes and ten minutes. Elution samples were measured daily using flow injection analysis. After one week of elution, ultrasound treatments were done daily until each group's average concentration fell below those of non-ultrasound control groups. After elution testing, compression testing determined mechanical properties. Paired t-tests were used to compare daily elution amounts to baseline values. Univariate ANOVAs were used to test for effects of both frequency and treatment duration on antibiotic elution amounts and on mechanical properties.RESULTS:All ultrasound treatments resulted in significant increases in antibiotic elution. Frequency and duration had significant effects of increasing antibiotic elution (p < 0.001). The kHz group produced significantly greater antibiotic elution than the MHz group (p < 0.001). The 10-minute duration produced significantly greater antibiotic elution than the two-minute duration (both p < 0.001). Frequency and duration did not have significant effects on yield stress (p = 0.841 and p = 0.179, respectively). Frequency had a significant effect (p = 0.024) on modulus, but duration did not (p = 0.136).CONCLUSIONS:Ultrasound frequency and treatment duration significantly affect antibiotic elution from PMMA which may be helpful for treatment of periprosthetic joint infections during revision arthroplasty.

STUDY DESIGN:Biomechanical study.OBJECTIVES:Compare effects of four spinous process (SP) tether looping methods on segmental flexion range of motion (ROM), intervertebral disc (IVD) pressures, and peak tether forces.SUMMARY OF BACKGROUND DATA:SP tethering has been gaining interest as a prophylactic technique to prevent PJK caused by ligamentous laxity in ASD corrective surgery. Several SP tether looping methods have been proposed; however, there is no consensus on appropriate technique. No study has investigated the effect of the tether looping method on segmental biomechanics.METHODS:Nine T1-T4 cadaveric motion segments were tested to 5 Nm of flexion-extension. The uppermost instrumented vertebra (UIV) was located at T3 using standard pedicle screws and fusion rods. A crosslink (CL) was placed inferior to the pedicle screws. A 5-mm polyester tether was looped under the CL at UIV and through holes drilled at the base of UIV + 1 and UIV + 2 SPs. Biomechanical measurements included flexion ROM, IVD pressure, and peak tether forces at UIV/UIV + 1 and UIV + 1/UIV + 2. An untethered test was used for baseline values. Tethered tests included one single-level (SL) method and three double-level (DL) methods: common (CM), chained (CH), and figure-8 (F8).RESULTS:SL yielded significant reductions in flexion ROM at UIV/UIV + 1 (p = .001) and in IVD pressure at UIV/UIV + 1 (p = .007). Choice of DL method had a significant effect on flexion ROM at UIV/UIV + 1 (p = .004) but not at UIV + 1/UIV + 2 (p = .14). Choice of DL method also had a significant effect on IVD pressure at UIV/UIV + 1 (p < .001) but not at UIV + 1/UIV + 2 (p = .311). CM produced the greatest reductions in flexion ROM and IVD pressure, with the lowest peak tether forces among the DL methods.CONCLUSION:Tether looping method significantly alters segmental biomechanics. Tethering with the CM method to UIV + 2 allows for reductions in loads acting on the UIV + 1 SP and posterior ligaments.LEVEL OF EVIDENCE:Level V, biomechanical study.

Introduction Forefoot strike has been advocated for many runners because of the relatively lower impact and push-off forces compared to a heel strike. The purpose of this study was to explore the ability of mature (> 30 years old), experienced runners to transition from a heel foot strike to a forefoot strike when first introduced to barefoot running on a treadmill. We hypothesized: 1) mature runners who heel strike while wearing traditional training shoes would persist in heel striking immediately following a switch to barefoot, 2) mean shoe heel-to-toe drop would be significantly greater in runners who persist in heel striking when running barefoot compared to those who transition to a forefoot strike pattern, and 3) there would be a significant decrease in heel striking in the barefoot condition as running speeds increased. Methods This was a controlled crossover laboratory study. Thirty-three experienced runners (average 23.4 miles per week) with an average age of 45.6 years were recruited for this study. The participants first ran in their standard running shoes and subsequently barefoot. A motion capture system was utilized to detect and analyze any transition from heel strike to forefoot strike made by study participants. Results Of the 26 participants who were classified as heel strike runners in their running shoes, 50% (13/26, p = 0.001) transitioned to forefoot strike when changing from running in shoes to running barefoot. Conclusions The injuries associated with transition from standard running shoes to barefoot running or minimalist shoes may be influenced by the persistence of heel striking in mature runners. Older experienced runners may have limited ability to transition from heel to forefoot striking when first introduced to barefoot running. Mature runners should be cautious when beginning a minimalist shoe or barefoot running regimen.

STUDY DESIGN:Biomechanical evaluation of cadaver functional spinal units (FSUs).OBJECTIVES:Demonstrate the effect of increasing spinous process (SP) tether pretension on FSU flexion range of motion (ROM), intervertebral disc (IVD) pressure, and SP force. Quantify SP tether pull-out forces and relate them to SP forces generated at maximum flexion.SUMMARY OF BACKGROUND DATA:There has been recent interest in the use of SP tethering for prophylactic treatment of proximal junctional kyphosis (PJK). There is currently no consensus on standard tethering technique and no biomechanical data on the effect of tether pretension.METHODS:Nine T11-T12 FSUs were tested to 5 Nm of flexion-extension bending. A strain gauge was applied at the base of the T11 SP to measure force. Two custom pressure sensors were inserted into the anterior and posterior thirds of the IVD. Motion kinematics were measured by a motion capture system. An untethered test was done to describe baseline behavior. A 5-mm polyester tether was looped through holes drilled at the base of each SP and pretensioned to five different pretensions ranging from 0 to 88 N. Following ROM testing, specimens were dissected into individual vertebra and then SP pull-out testing was done at each level.RESULTS:Increasing pretension significantly reduced flexion ROM, reduced IVD pressures, and increased SP force. All pretensions, including the minimum, significantly reduced flexion ROM. SP pull-out forces were significantly greater than SP forces generated at maximum flexion.CONCLUSIONS:Tether pretension significantly affects segmental FSU biomechanics. Pretension should be considered an integral factor in the overall success of a tethering strategy. Efforts should be made to control and record pretension intraoperatively.LEVEL OF EVIDENCE:Level V, biomechanical study.

Summary StatementA porcine model using Yucatan minipigs was found to be very promising for the investigation of healing around transcutaneous osseointegrated implants. Pigs demonstrated surprising ...

Introduction: Local delivery of antibiotics using bone cement as the delivery vehicle is an established method of managing implant-associated orthopedic infections. Various fillers have been added to cement to increase antibiotic elution, but they often do so at the expense of strength. This study evaluated the effect of adding a borate bioactive glass, previously shown to promote bone formation, on vancomycin elution from PMMA bone cement.Methods: Five cement composites were made: three loaded with borate bioactive glass along with 0, 1, and 5 grams of vancomycin and two without any glass but with 1 and 5 grams vancomycin to serve as controls. The specimens were soaked in PBS. Eluate of vancomycin was collected every 24 hours and analyzed by HPLC. Orthopedic-relevant mechanical properties of each composite were tested over time.Results: The addition of borate bioactive glass provided an increase in vancomycin release at Day 1 and an increase in sustained vancomycin release throughout the treatment period. An 87.6% and 21.1% increase in cumulative vancomycin release was seen for both 1g and 5g loading groups, respectively. Compressive strength of all composites remained above the weight-bearing threshold of 70 MPa throughout the duration of the study with the glass-containing composites showing comparable strength to their respective controls.Conclusion: The incorporation of borate bioactive glass into commercial PMMA bone cement can significantly increase the elution of vancomycin. The mechanical strength of the cement-glass composites remained above 70 MPa even after soaking for 8 weeks, suggesting their suitability for orthopedic weight-bearing applications.

BACKGROUND CONTEXT Spinous process (SP) tethering is gaining interest as a prophylactic technique to alleviate load concentrations and reinforce the posterior ligament complex (PLC) at the uppermost instrumented vertebra (UIV) to reduce the risk of developing proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgeries. Consensus has yet to be established on appropriate technique and there is a lack of biomechanical data to provide initial guidance. While multiple SP looping methods have recently been proposed, no study has evaluated the effect of tether looping method on segmental biomechanics. PURPOSE We sought to evaluate the effects of four tether looping methods on segmental biomechanics at UIV, UIV+1, and UIV+2. We hypothesized that the different looping methods would result in significant differences in flexion range-of-motion (ROM), intervertebral disc (IVD) pressures, and peak tether loop tensions. STUDY DESIGN/SETTING Biomechanical study. OUTCOME MEASURES Flexion ROM, IVD pressure, peak tether tension. METHODS Nine T1–T4 cadaveric motion segments were tested in flexion–extension bending to 5 Nm using a pure-moment testing machine. UIV was located at T3 using standard pedicle screws and rods. A rod crosslink (CL) was placed inferior to the pedicle screws. Motion of UIV, UIV+1, and UIV+2 was recorded using a motion capture system. IVD pressure was measured at UIV/UIV+1 and UIV+1/UIV+2 using custom pressure probes. A 5 mm braided polyester suture was used for tethering. The tether was looped under the CL at UIV, and through holes drilled at the base of UIV+1 and UIV+2 SPs. Tether tension was measured using custom in-line tension sensors for each independent loop. An untethered test was used for baseline values. Tethered tests included one single level (SL) and three double level (DL) tests: (1) SL, a single tether from CL at UIV to UIV+1 SP, (2) DL Common (CM), a tether from CL at UIV to UIV+1 SP and another tether from CL at UIV to UIV+2 SP, (3) DL Chained (CH), a tether from CL at UIV to UIV+1 SP and another tether from UIV+1 SP to UIV+2 SP, and (4) DL Figure-Eight (F8), a single tether from CL at UIV to UIV+1 SP and UIV+2 SP in a woven figure-eight loop. Loops were pretensioned to 22N before each test. RESULTS The SL method resulted in significant reductions in flexion ROM at UIV/UIV+1 (p=.001) but not at UIV+1/UIV+2 (p=.052). SL also yielded significant reductions in IVD pressure at both UIV/UIV+1 (p=.007) and UIV+1/UIV+2 (0.002). The choice of DL method had a significant univariate effect on flexion ROM reduction at UIV/UIV+1 (p=.004) but not at UIV+1/UIV+2 (0.14). The choice of DL method also had a significant univariate effect on IVD pressure reduction at UIV/UIV+1 (p<.001) but not at UIV+1/UIV+2 (p=.311). Maximum tether tensions occurred at the uppermost tethered level for DL methods. CM yielded the greatest reductions of flexion ROM and IVD pressures with the lowest peak tether tensions compared to CH or F8. CONCLUSIONS The use of different tether looping methods significantly alters the tether's effect on segmental biomechanics. double level techniques provide greater reductions in flexion ROM and IVD pressures; however, they yield greater tether tensions at the uppermost tethered level compared to SL. CM produced the best results for improved segmental stability. The transfer of peak SP loading to superjacent levels may provide benefits in protecting the UIV+1 SP and the PLC. New understanding in the effect of looping methods may provide improved ability to reduce PJK caused by ligamentous laxity. Spinous process (SP) tethering is gaining interest as a prophylactic technique to alleviate load concentrations and reinforce the posterior ligament complex (PLC) at the uppermost instrumented vertebra (UIV) to reduce the risk of developing proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgeries. Consensus has yet to be established on appropriate technique and there is a lack of biomechanical data to provide initial guidance. While multiple SP looping methods have recently been proposed, no study has evaluated the effect of tether looping method on segmental biomechanics. We sought to evaluate the effects of four tether looping methods on segmental biomechanics at UIV, UIV+1, and UIV+2. We hypothesized that the different looping methods would result in significant differences in flexion range-of-motion (ROM), intervertebral disc (IVD) pressures, and peak tether loop tensions. Biomechanical study. Flexion ROM, IVD pressure, peak tether tension. Nine T1–T4 cadaveric motion segments were tested in flexion–extension bending to 5 Nm using a pure-moment testing machine. UIV was located at T3 using standard pedicle screws and rods. A rod crosslink (CL) was placed inferior to the pedicle screws. Motion of UIV, UIV+1, and UIV+2 was recorded using a motion capture system. IVD pressure was measured at UIV/UIV+1 and UIV+1/UIV+2 using custom pressure probes. A 5 mm braided polyester suture was used for tethering. The tether was looped under the CL at UIV, and through holes drilled at the base of UIV+1 and UIV+2 SPs. Tether tension was measured using custom in-line tension sensors for each independent loop. An untethered test was used for baseline values. Tethered tests included one single level (SL) and three double level (DL) tests: (1) SL, a single tether from CL at UIV to UIV+1 SP, (2) DL Common (CM), a tether from CL at UIV to UIV+1 SP and another tether from CL at UIV to UIV+2 SP, (3) DL Chained (CH), a tether from CL at UIV to UIV+1 SP and another tether from UIV+1 SP to UIV+2 SP, and (4) DL Figure-Eight (F8), a single tether from CL at UIV to UIV+1 SP and UIV+2 SP in a woven figure-eight loop. Loops were pretensioned to 22N before each test. The SL method resulted in significant reductions in flexion ROM at UIV/UIV+1 (p=.001) but not at UIV+1/UIV+2 (p=.052). SL also yielded significant reductions in IVD pressure at both UIV/UIV+1 (p=.007) and UIV+1/UIV+2 (0.002). The choice of DL method had a significant univariate effect on flexion ROM reduction at UIV/UIV+1 (p=.004) but not at UIV+1/UIV+2 (0.14). The choice of DL method also had a significant univariate effect on IVD pressure reduction at UIV/UIV+1 (p<.001) but not at UIV+1/UIV+2 (p=.311). Maximum tether tensions occurred at the uppermost tethered level for DL methods. CM yielded the greatest reductions of flexion ROM and IVD pressures with the lowest peak tether tensions compared to CH or F8. The use of different tether looping methods significantly alters the tether's effect on segmental biomechanics. double level techniques provide greater reductions in flexion ROM and IVD pressures; however, they yield greater tether tensions at the uppermost tethered level compared to SL. CM produced the best results for improved segmental stability. The transfer of peak SP loading to superjacent levels may provide benefits in protecting the UIV+1 SP and the PLC. New understanding in the effect of looping methods may provide improved ability to reduce PJK caused by ligamentous laxity.