In vitro efficacy of a 0.2% polyhexamethylene biguanide-impregnated gauze dressing against pathogenic bacterial isolates found in horses.

OBJECTIVE: To determine the ability of 0.2% polyhexamethylene biguanide (PHMB)-impregnated gauze to inhibit the growth of bacteria isolated from equine infected sites. STUDY DESIGN: In vitro study. METHODS: Nine bacterial isolates were obtained from cultures submitted from equine patients presenting with penetrating injuries of the hoof (n = 4), septic osteitis (n = 1), synovial sepsis (n = 1), wounds (n = 2), and incisional infection following laparotomy (n = 1). Two standardized strains were also included. A standard inoculum of each isolate was placed on 12 Muller-Hinton agar plates. Squares (2.5 cm × 2.5 cm) of 0.2% PHMB-impregnated (n = 6) and nonimpregnated control gauze (n = 6) were placed on inoculated agar plates. Bacterial growth under each gauze square was assessed after a 24-h incubation period and areas of inhibition were measured to a standardized scale, using image-processing software. Mean ± SD growth inhibition (%) using 0.2% PHMB-impregnated gauze was compared to the nonimpregnated gauze for each isolate using Student's t test (p < .05). RESULTS: The 0.2% PMHB-impregnated gauze inhibited the growth of Staphylococcus spp. (n = 4) by 33%-83.1% and that of Escherichia coli spp. (n = 4) by 6.5%-37%. There was no inhibition of growth of Pseudomonas aeruginosa or either Enterococcus spp. CONCLUSION: The 0.2% PHMB-impregnated dressing tested here inhibited the growth of staphylococcal and E. coli isolates, but the magnitude of inhibition varied between strains. CLINICAL RELEVANCE: These results justify in vivo studies to evaluate the ability of the dressing to reduce the bacterial growth of common equine bacterial pathogens in clinical practice.

The efficacy of core decompression for steroid-associated osteonecrosis of the femoral head in rabbits.

Although core decompression (CD) is often performed in the early stage of osteonecrosis of the femoral head (ONFH), the procedure does not always prevent subsequent deterioration and the effects of CD are not fully clarified. The aim of this study is to evaluate the efficacy of CD for steroid-associated ONFH in rabbits. Twelve male and 12 female New Zealand rabbits were injected intramuscularly 20 mg/kg of methylprednisolone once and were divided into the disease control and CD groups. In the disease control group, rabbits had no treatment and were euthanized at 12 weeks postinjection. In the CD group, rabbits underwent left femoral CD at 4 weeks postinjection and were euthanized 8 weeks postoperatively. The left femurs were collected to perform morphological, biomechanical, and histological analysis. Bone mineral density and bone volume fraction in the femoral head in the CD group were significantly higher than in the disease control group. However, no difference in the mechanical strength was observed between the two groups. Histological analysis showed that alkaline phosphatase and CD31 positive cells significantly increased in the males after CD treatment. The number of empty lacunae in the surrounding trabecular bone was significantly higher in the CD group. The current study indicated that CD improved the morphological properties, but did not improve the mechanical strength in the femoral head at early-stage ONFH. These data suggest the need for additional biological, mechanical strategies, and therapeutic windows to improve the outcome of early-stage steroid-associated ONFH.

Safety of Releasing the Volar Capsule During Open Treatment of Distal Radius Fractures: An Analysis of the Extrinsic Radiocarpal Ligaments' Contribution to Radiocarpal Stability.

PURPOSE: The contribution of the extrinsic radiocarpal ligaments to carpal stability continues to be studied. Clinically, there is a concern for carpal instability from release of the volar extrinsic ligaments during volar plating of distal radius fractures in which the integrity of the dorsal ligaments may be unknown. The primary hypothesis of this study was that serial sectioning of radiocarpal ligaments would lead to progressive ulnar translation of the carpus. METHODS: We studied the stabilizing roles of the radioscaphocapitate (RSC), short radiolunate (SRL), long radiolunate (LRL), and dorsal radiocarpal (DRC) ligaments. We sequentially sectioned these ligaments in 2 groups of 5 matched pairs and measured the motion of the scaphoid and lunate with the wrist in passive neutral alignment, radial deviation, ulnar deviation, and simulated grip. Displacement of the lunate in the radioulnar plane was used as a surrogate for carpal translation. The groups differed only by the order in which the ligaments were sectioned. RESULTS: In the intact state, the lunate translated ulnarly during simulated grip and radial deviation, whereas radial translation, relative to its position under resting tension, was observed during ulnar deviation. With serial sectioning, the lunate displayed increased ulnar translation in all wrist positions for both groups 1 and 2. The magnitude of ulnar translation exceeded 1 mm after sectioning the LRL plus RSC along with either the DRC or the SRL. CONCLUSIONS: Sectioning of either the DRC or SRL ligaments along with release of the RSC and LRL ligaments leads to notable although minimal (<2 mm) ulnar lunate translation. CLINICAL RELEVANCE: Isolated sectioning of individual radiocarpal ligaments, such as for visualization of the articular surface of the distal radius, leads to minimal ulnar translation. Because prior clinical work found no clinical complications after volar capsule release, it is posited that translation less than 2 mm creates subclinical changes in carpal mechanics.

Rotational Stability of Scaphoid Waist Nonunion Bone Graft and Fixation Techniques.

PURPOSE: Rotational instability of scaphoid fracture nonunions can lead to persistent nonunion. We hypothesized that a hybrid Russe technique would provide improved rotational stability compared with an instrumented corticocancellous wedge graft in a cadaver model of scaphoid nonunion. METHODS: A volar wedge osteotomy was created at the scaphoid waist in 16 scaphoids from matched-pair specimens. A wedge was inset at the osteotomy site or a 4 × 16-mm strut was inserted in the scaphoid and a screw was placed along the central axis (model 1). The construct was cyclically loaded in torsion until failure. The screw was removed and the proximal and distal poles were debrided. A matching wedge and packed cancellous bone graft or an 8 × 20-mm strut was shaped and fit inside the proximal and distal pole (model 2). A screw was placed and testing was repeated. RESULTS: In the first model, there was no significant difference in cycles to failure, target torque, or maximal torque between the strut graft and the wedge graft. Cycles to failure positively correlated with estimated bone density for the wedge graft, but not for the strut graft. In the second model, the strut graft had significantly higher cycles to failure, greater target torque, and higher maximal torque compared with the wedge graft. The number of cycles to failure was not correlated with estimated bone density for the wedge or the strut grafts. CONCLUSIONS: The hybrid Russe technique of inlay corticocancellous strut and screw fixation provides improved rotational stability compared with a wedge graft with screw fixation for a cadaver model of scaphoid waist nonunion with cystic change. CLINICAL RELEVANCE: The hybrid Russe technique may provide better rotational stability for scaphoid waist nonunions when the proximal or distal scaphoid pole is compromised, such as when there is extensive cystic change, when considerable debridement is necessary, or with revision nonunion surgery.

Drilling Energy Correlates With Screw Insertion Torque, Screw Compression, and Pullout Strength: A Cadaver Study.

INTRODUCTION: To determine whether drilling energy correlates with bone mineral density (BMD), maximum insertion torque (MIT), maximum screw compression, and pullout strength (POS). METHODS: Ten cadaver tibias were used for testing. Unicortical pilot holes were drilled and the drilling energy measured. Drill site bone quality was determined with microcomputed tomography. Drill holes were randomly assigned to POS or MIT testing using 3.5-mm cortical screws engaging only the near cortex. Pearson correlation coefficients were calculated to determine the relationship between drilling energy, BMD, POS, MIT, and maximum screw compression. RESULTS: Drilling energy was correlated with BMD (P < 0.001). Compared with BMD, drilling energy had a better correlation with MIT, maximum screw compression, and POS. Maximum screw compression also correlated with MIT (P = 0.012). CONCLUSIONS: Drilling energy better correlates with MIT, maximum screw compression, and POS compared with BMD in cadaver cortical bone. Dynamically measuring drilling energy may help inform the orthopaedic surgeon as to the quality of the bone before insertion of implants.

The effects of varenicline on lumbar spinal fusion in a rat model.

BACKGROUND CONTEXT: Smoking is detrimental to obtaining a solid spinal fusion mass with previous studies demonstrating its association with pseudoarthrosis in patients undergoing spinal fusion. Varenicline is a pharmacologic adjunct used in smoking cessation which acts as a partial agonist of the same nicotinic receptors activated during tobacco use. However, no clinical or basic science studies to date have characterized if varenicline has negative effects on spinal fusion and bone healing by itself. PURPOSE: Our study's aim was to elucidate whether varenicline affects the frequency or quality of posterolateral spinal fusion in a rodent model at an endpoint of 12 weeks. STUDY DESIGN: Randomized control trial. PATIENT SAMPLE: Fourteen male Lewis rats randomly separated into two experimental groups. OUTCOME MEASURES: Manual palpation of fusion segment, radiography, µCT imaging, and four-point bend. METHODS: Fourteen male Lewis rats were randomly separated into two experimental groups undergoing L4-L5 posterior spinal fusion procedure followed by daily subcutaneous injections of human dose varenicline or saline (control) for 12 weeks postsurgery. Spine samples were explanted, and fusion was determined via manual palpation of segments by two independent observers. High-resolution radiographs were obtained to evaluate bridging fusion mass. µCT imaging was performed to characterize fusion mass and consolidation. Lumbar spinal fusion units were tested in four-point bending to evaluate stiffness and peak load. Study funding sources include $5000 OREF Grant. There were no applicable financial relationships or conflicts of interest. RESULTS: At 3 months postsurgery, 12 out of 14 rats demonstrated lumbar spine fusion (86% fused) with no difference in fusion frequency between the varenicline and control groups as detected by manual palpation. High-resolution radiography revealed six out of seven rats (86%) having complete fusion in both groups. µCT showed no significant difference in bone mineral density or bone fraction volume between groups in the region of interest. Biomechanical testing demonstrated no significant different in the average stiffness or peak loads at the fusion site of the varenicline and control groups. CONCLUSION: Based on the results of our rat study, there is no indication that varenicline itself has a detrimental effect on the frequency and quality of spinal fusion.

The Effect of Mesenchymal Stem Cell Sheets on Early Healing of the Achilles Tendon in Rats.

Bone marrow-derived mesenchymal stem cells (BMSCs) have potential to accelerate flexor tendon healing and allow for earlier rehabilitation. The ideal BMSC construct and delivery method to the repair site remains unknown. We investigated the efficacy of interposed scaffold-free BMSC sheets on early Achilles tendon healing in rats. BMSCs were isolated from the femora and tibias of male Sprague-Dawley rats aged 8-12 weeks and BMSC sheets were produced on temperature-responsive culture dishes. Ninety-five male Sprague-Dawley rats aged 8-12 weeks were utilized. A bilateral Achilles tendon repair model was created. One side was randomly selected, and the tendon was repaired with the interposed BMSC sheet (BMSC group). The other side was repaired without BMSCs (control group). The bilateral tendons were harvested at 5, 6, 7, 10, and 14 days postoperatively for biomechanical analysis, measurement of the gene expression level of tendon markers scleraxis and tenomodulin by real-time polymerase chain reaction, and histological evaluation. The BMSC group had significantly higher maximum load to failure and stiffness at 5 and 6 days compared with the control group. Moreover, the BMSC group showed significantly increased gene expression of scleraxis and/or tenomodulin at all timepoints. The cross sectional areas in the BMSC group were significantly larger at 5, 6, and 14 days. However, hematoxylin and eosin staining of the central part of the repair site revealed no significant differences at all timepoints. These results suggest that the increased biomechanical strength afforded by BMSC sheet implantation into tendon repair sites may allow for the earlier onset of rehabilitation and improved clinical outcomes in flexor tendon surgery. Impact Statement We investigated the efficacy of interposed bone marrow-derived mesenchymal stem cell (BMSC) sheets on early Achilles tendon healing in rats. The tendons repaired with BMSC sheets revealed significantly increased mechanical strength compared with the control repairs (without the BMSC sheet) at 5 and 6 days. These data reveal that BMSC sheet implantation into tendon repair sites may allow for earlier onset of rehabilitation and improved clinical outcomes in flexor tendon surgery.

The Effect of Oral Contraceptive Hormones on Anterior Cruciate Ligament Strength.

BACKGROUND: Women are 2 to 9 times more likely to experience an anterior cruciate ligament (ACL) injury than men. Various hormones including relaxin, progesterone, and estrogen influence ACL strength. Oral contraceptives (OCs) alter these hormone levels; however, studies have yet to comprehensively compare different OCs' effects on the ACL. HYPOTHESIS: OCs with increased progestin-to-estrogen ratios will (1) increase ACL collagen expression, (2) decrease ACL matrix metalloproteinase expression, and (3) increase ACL strength. STUDY DESIGN: Controlled laboratory study. METHODS: Untreated female rats were compared with rats treated with 1 of 5 clinically used OCs: norethindrone (NE) only, NE plus ethinylestradiol (EE), etynodiol diacetate (ED) plus EE, norgestimate (NG) plus EE, and drospirenone (DS) plus EE. Doses were scaled from human doses to account for differences in bioavailability and body weight, and OCs were administered daily via oral gavage for 4 rat estrous cycles (20 days). A total of 36 rats were then sacrificed (6 rats/group). ACLs underwent biomechanical testing to assess ACL strength, stiffness, and maximum load before failure. ACL specimens were also isolated for quantitative real-time polymerase chain reaction analysis to assess collagen, matrix metalloproteinase, and relaxin receptor-1 expression. RESULTS: While the primary structural property of interest (ACL maximum load before failure) was not significantly improved by OC treatment, the main material property of interest (ACL strength) in rats treated with NE only, DS + EE, ED + EE, and NE + EE was significantly increased compared with untreated controls (P = .001, P = .004, P = .004, and P = .04, respectively). The order from strongest to weakest ACLs, which was also the same order as the highest to lowest progestin-to-estrogen ratios, was groups treated with NE only, DS + EE, ED + EE, NE + EE, and lastly NG + EE. Higher ratio formulations also increased the expression of type I collagen (P = .02) and decreased the expression of matrix metalloproteinase-1 (P = .04). CONCLUSION: OC formulations with higher progestin-to-estrogen ratios may be more protective for the ACL than formulations with lower ratios. CLINICAL RELEVANCE: OC formulations with high progestin-to-estrogen ratios may benefit female athletes by reducing their ACL injury risk by decreasing the effects of relaxin on the ACL.

Biomechanical comparison of bone-screw-fasteners versus traditional locked screws in plating female geriatric bone.

OBJECTIVES: To biomechanically compare plated constructs using nonlocking bone-screw-fasteners with interlocking threads versus locking screws with traditional buttress threads in geriatric female bone. METHODS: Eleven matched pairs of proximal and distal segments of geriatric female cadaveric tibias were used to create a diaphyseal fracture model. Nonlocking bone-screw-fasteners or locking buttress threaded screws were applied to a locking compression plate on the anterolateral aspect of the tibia placed in bridge mode. Specimens were subjected to incrementally increasing cyclic axial load combined with constant cyclic torsion. Total cycles to failure served as a primary outcome measure, with failure defined as 2 mm of displacement or 10 degrees of rotation. Secondary outcome measures included initial stiffness in compression and torsion determined from preconditioning testing and overall rigidity as determined by maximum peak-to-peak axial and rotational motion at 500 cycle intervals during cyclic testing. Group comparisons were made using paired Student's t-tests. Significance was set at p < 0.05. RESULTS: Bone-screw-fastener constructs failed at an average of 40,636 ± 22,151 cycles and locking screw constructs failed at an average of 37,773 ± 8433 cycles, without difference between groups (p = =0.610). Total cycles to failure was higher in the bone-screw-fasteners group for 7 tibiae out of the eleven matched pairs tested. During static and cyclic testing, bone-screw-fastener constructs demonstrated increased initial torsional stiffness (7.6%) and less peak-to-peak displacement and rotation throughout the testing cycle(p < 0.05). CONCLUSIONS: In female geriatric bone, constructs fixed with bone-screw-fasteners incorporate multiplanar interlocking thread geometry and performed similarly to traditional locked plating. These novel devices may combine the benefits of both nonlocking and locking screws when plating geriatric bone.

The Role of Anterior Capsular Laxity in Hip Microinstability: A Novel Biomechanical Model.

BACKGROUND: Hip microinstability is an increasingly recognized source of hip pain and disability. Although the clinical entity has been well described, the pathomechanics of this disease remain poorly understood. PURPOSE/HYPOTHESIS: The purpose of this study was to determine the role of capsular laxity in atraumatic hip microinstability. Our hypothesis was that cyclic stretching of the anterior hip capsule would result in increased hip range of motion and femoral head displacement. STUDY DESIGN: Controlled laboratory study. METHODS: In this study, 7 hip specimens met inclusion criteria (age, 18-46 years). Specimens were stripped of all soft tissue, aligned, cut, and potted by use of a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation while rotating about the mechanical axis of the hip. A motion tracking system was used to record hip rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing was conducted at baseline, after venting, and after capsular stretching. RESULTS: With the hip in anatomic neutral alignment, cyclic stretching of the anterior hip capsule resulted in increased hip rotation ( P < .001). Femoral head displacement significantly increased relative to the vented state in the medial-lateral ( P < .001), anterior-posterior ( P = .013), and superior-inferior ( P = .036) planes after cyclic stretching of the anterior hip capsule. CONCLUSION: The anterior hip capsule plays an important role in controlling hip rotation and femoral head displacement. This study is the first to display significant increases in femoral head displacement through a controlled cyclic stretching protocol of the anterior hip capsule. CLINICAL RELEVANCE: This study is directly applicable to the treatment of atraumatic hip microinstability. The results quantitatively define the relative importance of the hip capsule in controlling femoral head motion. This allows for a better understanding of the pathophysiological process of hip microinstability and serves as a platform to develop effective surgical techniques for treatment of this disease.

Contributions of the Capsule and Labrum to Hip Mechanics in the Context of Hip Microinstability.

BACKGROUND: Hip microinstability and labral pathology are commonly treated conditions with increasing research emphasis. To date, there is limited understanding of the biomechanical effects of the hip capsule and labrum on controlling femoral head motion. PURPOSE/HYPOTHESIS: The purpose of this study was to determine the relative role of anterior capsular laxity and labral insufficiency in atraumatic hip microinstability. Our hypotheses were that (1) labral tears in a capsular intact state will have a minimal effect on femoral head motion and (2) the capsule and labrum work synergistically in controlling hip stability. STUDY DESIGN: Controlled laboratory study. METHODS: Twelve paired hip specimens from 6 cadaveric pelvises (age, 18-41 years) met the inclusion criteria. Specimens were stripped of all soft tissue except the hip capsule and labrum, then aligned, cut, and potted using a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation, while rotating about the mechanical axis of the hip. Labral insufficiency was created with a combined radial and chondrolabral tear under direct visualization. A motion tracking system was used to record hip internal-external rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing variables included baseline, postventing, postcapsular stretching, and postlabral insufficiency. RESULTS: When comparing the vented state with each experimental pathologic state, increases in femoral head motion were noted in both the capsular laxity state and the labral insufficiency state. The combined labral insufficiency and capsular laxity state produced statistically significant increases (P < .001) in femoral head translation compared with the vented state in all planes of motion. CONCLUSION: Both the anterior capsule and labrum play a role in hip stability. In this study, the anterior hip capsule was the primary stabilizer to femoral head translation, but labral tears in the setting of capsular laxity produced the most significant increases in femoral head translation. CLINICAL RELEVANCE: This study provides a physiologic biomechanical assessment of the hip constraints in the setting of hip microinstability. It also sheds light on the importance of the hip capsule in the management of labral tears. Our study demonstrates that labral tears in isolation provide minimal changes in femoral head translation, but in the setting of a deficient capsule, significant increases in femoral head translation are seen, which may result in joint-related symptoms.

The effects of a functionally-graded scaffold and bone marrow-derived mononuclear cells on steroid-induced femoral head osteonecrosis.

Osteonecrosis of the femoral head (ONFH) is a debilitating disease that may progress to femoral head collapse and subsequently, degenerative arthritis. Although injection of bone marrow-derived mononuclear cells (BMMCs) is often performed with core decompression (CD) in the early stage of ONFH, these treatments are not always effective in prevention of disease progression and femoral head collapse. We previously described a novel 3D printed, customized functionally-graded scaffold (FGS) that improved bone growth in the femoral head after CD in a normal healthy rabbit, by providing structural and mechanical guidance. The present study demonstrates similar results of the FGS in a rabbit steroid-induced osteonecrosis model. Furthermore, the injection of BMMCs into the CD decreased the osteonecrotic area in the femoral head. Thus, the combination of FGS and BMMC provides a new therapy modality that may improve the outcome of CD for early stage of ONFH by providing both enhanced biological and biomechanical cues to promote bone regeneration in the osteonecrotic area.