Biomechanical and wearability testing of novel legwear for variably limiting extension of the metacarpophalangeal joint of horses.

OBJECTIVE: To evaluate the ability of novel legwear designed to limit extension of the metacarpophalangeal joint (MCPJ) to redirect loading forces from the flexor apparatus during walk, trot, and canter on a treadmill and during unrestrained and restrained activity in a stall. ANIMALS: 6 adult horses without musculoskeletal disease. PROCEDURES: Legwear-derived force data were recorded under 4 conditions: inactive state (unlimited legwear extension) and 3 active (restrictive) states (mild, 30° extension; moderate, 20° extension; or maximum, 10° extension). Associations between peak legwear loads and torques among legwear states and treadmill gaits and stall activities were assessed. The hair coat and skin of the forelimbs were examined for any legwear-induced adverse effects after testing. RESULTS: During the treadmill exercises, moderate restriction of legwear extension resulted in significantly higher peak load and torque than mild restriction, and faster speeds (canter vs walk or trot and trot vs walk) yielded significantly higher peak load and torque. During in-stall activity, maximum restriction of legwear extension yielded significantly higher peak load and torque than moderate restriction. Unrestrained in-stall activity resulted in significantly higher peak load and torque than restrained activity. The legwear caused minimal adverse effects on the hair coat and skin of the forelimbs. CONCLUSIONS AND CLINICAL RELEVANCE: Findings suggested that the legwear variably reduced peak loads on the flexor apparatus. Extension of the MCPJ may be incrementally adjusted through the legwear such that return to activity may be controlled, and controlled return to activity is crucial for rehabilitating flexor apparatus injuries.

Kinematic and kinetic analyses of the gait of horses wearing novel legwear for variably limiting extension of the metacarpophalangeal joint.

OBJECTIVE: To investigate the effects of novel legwear designed to limit metacarpophalangeal joint (MCPJ) extension and redirect loading forces from the flexor apparatus through analyses of 2-D kinematic and kinetic data. ANIMALS: 6 adult horses without musculoskeletal disease. PROCEDURES: Horses were subjected to 4 treatments: control (no legwear), inactive legwear (unlimited legwear extension), and active legwear with mild (30°) and moderate (20°) legwear extension limitation. Two-dimensional kinematic data were collected for the right forelimb (FL) during walk and trot and from leading and trailing FLs during canter on a treadmill. Ground reaction force (GRF) data were collected from FLs during overground walk and trot. Peak MCPJ angle and angular velocity were calculated from kinematic data, and peak force and average loading rate were calculated from vertical GRF data during the stance phase of the gait. Interactions between gait and treatment were determined via ANOVA. RESULTS: Interactions between gait and treatment for peak MCPJ angle were significant. Significant reductions in MCPJ angle were noted between the control treatment and legwear with moderate extension limitation for trot and canter (leading and trailing FL) and between inactive legwear and legwear with moderate extension limitation for trot and leading FL during canter. Interactions among peak MCPJ angular velocity, peak vertical GRF, and average loading rate of the vertical GRF showed nonsignificance. CONCLUSIONS AND CLINICAL RELEVANCE: Significant reductions in MCPJ extension without significant alterations to peak vertical GRF suggested the legwear's ability to redistribute internal forces. Findings suggested that the legwear may be beneficial for horses rehabilitating from flexor apparatus injuries.

Effect of Fatigue on Equine Metacarpophalangeal Joint Kinematics-A Single Horse Pilot Study.

The objective was to validate a scientific method for characterizing equine metacarpophalangeal joint (MCPJ) motion in the nonfatigued and fatigued states using a single horse at trot, slow canter, and fast canter. One healthy Thoroughbred gelding exercised on a treadmill to exhaustion (fatigued state) (heart rate >190 BPM and blood lactate >10 mmol/L) while bilateral MCPJ angular data were acquired using electrogoniometry. Blood lactate and heart rate reflected transition from nonfatigued to fatigued states with increasing exercise duration and treadmill speed. Electrogoniometry consistently demonstrated: increase in mean MCPJ maximum extension angle with onset of fatigue; altered extension and flexion angular velocities with onset of fatigue; and increasing stride duration and decreasing stride frequency with onset of fatigue. The method allowed a preliminary but comprehensive characterization of the dynamic relationship between MCPJ kinematics and fatigue, prompting the need for multisubject studies that may enhance our ability to moderate exercise-related distal limb injury in equine athletes.

Three-dimensional kinematics of the equine metacarpophalangeal joint using x-ray reconstruction of moving morphology - a pilot study.

X-ray reconstruction of moving morphology (XROMM) uses biplanar videoradiography and computed tomography (CT) scanning to capture three-dimensional (3D) bone motion. In XROMM, morphologically accurate 3D bone models derived from CT are animated with motion from videoradiography, yielding a highly accurate and precise reconstruction of skeletal kinematics. We employ this motion analysis technique to characterize metacarpophalangeal joint (MCPJ) motion in the absence and presence of protective legwear in a healthy pony. Our in vivo marker tracking precision was 0.09 mm for walk and trot, and 0.10 mm during jump down exercises. We report MCPJ maximum extension (walk: -27.70 ± 2.78° [standard deviation]; trot: -33.84 ± 4.94°), abduction/adduction (walk: 0.04 ± 0.24°; trot: -0.23 ± 0.35°) and external/internal rotations (walk: 0.30 ± 0.32°; trot: -0.49 ± 1.05°) indicating that the MCPJ in this pony is a stable hinge joint with negligible extra-sagittal rotations. No substantial change in MCPJ maximum extension angles or vertical ground reaction forces (GRFv) were observed upon application of legwear during jump down exercise. Neoprene boot application yielded -65.20 ± 2.06° extension (GRFv = 11.97 ± 0.67 N/kg) and fleece polo wrap application yielded -64.23 ± 1.68° extension (GRFv = 11.36 ± 1.66 N/kg), when compared to naked control (-66.11 ± 0.96°; GRFv = 12.02 ± 0.53 N/kg). Collectively, this proof of concept study illustrates the benefits and practical limitations of using XROMM to document equine MCPJ kinematics in the presence and absence of legwear.

Mitral valve regurgitation and left ventricular dysfunction treatment with an intravalvular spacer.

Attempts at transcatheter treatment of mitral valve regurgitation have generally been modeled on proven surgical procedures such as leaflet repair, annuloplasty, or prosthetic valve implantation. We introduce a novel approach to directly reducing the regurgitant orifice: the mitral valve spacer, a balloon that attempts to reduce the regurgitant orifice.

Sustained volume retention in vivo with adipocyte and lipoaspirate seeded silk scaffolds.

Current approaches to soft tissue regeneration include the use of fat grafts, natural or synthetic biomaterials as filler materials. Fat grafts and natural biomaterials resorb too quickly to maintain tissue regeneration, while synthetic materials do not degrade or regenerate tissue. Here, we present a simple approach to volume stable filling of soft tissue defects. In this study, we combined lipoaspirate with a silk protein matrix in a subcutaneous rat model. Silk biomaterials can be tailored to fit a variety of needs, and here were processed silk biomaterials into a porous sponge format to allow for tissue ingrowth while remaining mechanically robust. Over an 18 month period, the lipoaspirate seeded silk protein matrix regenerated subcutaneous adipose tissue while maintaining the original implanted volume. A silk protein matrix alone was not sufficient to regenerate adipose tissue, but yielded a fibrous tissue, although implanted volume was maintained. This work presents a significant improvement to the standard approaches to filling soft tissue defects by matching biomaterial degradation and tissue regeneration profiles.

Core decompression of the equine navicular bone: an in vivo study in healthy horses.

OBJECTIVE: To determine the physiologic response of the equine navicular bone to core decompression surgery in healthy horses. STUDY DESIGN: Experimental in vivo study. MATERIALS: Healthy adult horses (n=6). METHODS: Core decompression was completed by creating three 2.5-mm-diameter drill channels into the navicular bone under arthroscopic control. The venous (P(V)), arterial (P(A)), articular (P(DIPJ)), and intraosseous pressures (IOP) were recorded before and after decompression drilling. Each IOP measurement consisted of a baseline (IOP(B)) and a stress test (intramedullary injection of saline solution, IOP(S)) recording. Lameness was assessed subjectively and using force plate gait analysis. Fluorochrome bone labeling was performed. Horses were euthanatized at 12 weeks. Navicular bone mineral density (BMD) was measured, and bone histology evaluated. RESULTS: Peak IOP (IOP(max)) after stress testing was significantly (P<.05) reduced immediately after core decompression; however, the magnitude of these effects was decreased at 3 and 6 weeks after decompression. A significant (P<.05) correlation existed between IOP(max) and BMD. No lameness was observed beyond the first week after surgery. Substantial remodeling and neovascularization was evident adjacent the surgery sites. CONCLUSION: Navicular bone core decompression surgery reduced IOP(max), and, with the exception of a mild short-lived lameness, caused no other adverse effects in healthy horses during the 12-week study period.

Core decompression of the equine navicular bone: an in vitro biomechanical study.

OBJECTIVE: To determine the effect of core decompression surgery and bone mineral density (BMD) on the mechanical properties of equine navicular bones. STUDY DESIGN: Experimental, in vitro study. SAMPLE POPULATION: Fore limb navicular bones (n=36 pairs) from sound 2-5-year-old horses with no radiographic abnormalities of the distal aspect of the forelimbs. METHODS: Navicular BMD was measured using dual energy X-ray absorptiometry. One randomly assigned navicular bone from each pair served as control. The contralateral test specimen was allocated to 1 of 6 treatment groups defined by drill bit size (3.2 versus 2.5 mm diameter) and by the number of drill channels (1, 2, or 3) created in the proximal border of the bone. Bones were then tested until failure in 3-point bending. Data were statistically analyzed using ANOVA and regression analysis. RESULTS: There were significant (P<.001) positive correlations between BMD and biomechanical data. A significant (P<.001) reduction in breaking strength was noted between intact and drilled bone pairs; however, the diameter and number of decompression channels did not significantly (P>.05) influence the extent of the reduction in mechanical strength. CONCLUSION: In vitro core decompression significantly decreases the breaking strength of the equine navicular bone.

Pararectal cystotomy for urolith removal in nine horses.

OBJECTIVE: To report outcome of horses after standing pararectal cystotomy for removal of uroliths. STUDY DESIGN: Case series. ANIMALS: Horses (n=9) with cystic calculi. METHODS: Medical records (December 1998-May 2007) of horses with cystic calculi that had standing pararectal cystotomy were reviewed. Signalment; urolith number, size, and type; surgical technique; sedation and analgesia protocols; intra- and postoperative complications and outcome were analyzed. RESULTS: Uroliths (mean diameter, 6.37 cm; median, 6 cm; range, 3-10 cm) were removed intact without need for fragmentation. Eight (89%) horses had no complications and 1 horse (11%) developed persistent drainage from the perineal incision and incisional healing was prolonged. The complications resolved after wound revision, and although cystoscopy showed absence of uroliths, the clinical signs associated with cystitis recurred. CONCLUSIONS: Cystic calculi can be removed safely in standing horses using a pararectal approach. The procedure was well tolerated and no serious complications were encountered. CLINICAL RELEVANCE: Pararectal cystotomy allows removal of cystic calculi in standing sedated horses. The technique may offer an economic advantage over approaches that require general anesthesia.

In vivo degradation of three-dimensional silk fibroin scaffolds.

Three-dimensional porous scaffolds prepared from regenerated silk fibroin using either an all-aqueous process or a process involving an organic solvent, hexafluoroisopropanol (HFIP), have shown promise in cell culture and tissue engineering applications. However, their biocompatibility and in vivo degradation have not been fully established. The present study was conducted to systematically investigate how processing method (aqueous vs. organic solvent) and processing variables (silk fibroin concentration and pore size) affect the short-term (up to 2 months) and long-term (up to 1 year) in vivo behavior of the protein scaffolds in both nude and Lewis rats. The samples were analyzed by histology for scaffold morphological changes and tissue ingrowth, and by real-time RT-PCR and immunohistochemistry for immune responses. Throughout the period of implantation, all scaffolds were well tolerated by the host animals and immune responses to the implants were mild. Most scaffolds prepared from the all-aqueous process degraded to completion between 2 and 6 months, while those prepared from organic solvent (hexafluoroisopropanol (HFIP)) process persisted beyond 1 year. Due to widespread cellular invasion throughout the scaffold, the degradation of aqueous-derived scaffolds appears to be more homogeneous than that of HFIP-derived scaffolds. In general and especially for the HFIP-derived scaffolds, a higher original silk fibroin concentration (e.g. 17%) and smaller pore size (e.g. 100-200microm) resulted in lower levels of tissue ingrowth and slower degradation. These results demonstrate that the in vivo behavior of the three-dimensional silk fibroin scaffolds is related to the morphological and structural features that resulted from different scaffold preparation processes. The insights gained in this study can serve as a guide for processing scenarios to match desired morphological and structural features and degradation time with tissue-specific applications.

Evaluation of technetium Tc 99m-labeled biotin for scintigraphic detection of soft tissue inflammation in horses.

OBJECTIVE: To evaluate the use of technetium Tc 99m-labeled EDTA-biotin monomer ((99m)Tc-EB1) as a scintigraphic imaging agent for soft tissue inflammatory lesions in horses. ANIMALS: 6 healthy adult horses. PROCEDURES: First (phase 1), the agent's safety and blood-tissue clearance and an appropriate imaging protocol were determined in 6 horses. Each horse was injected with (99m)Tc-EB1 (1.1 GBq, IV, once); images were acquired at intervals during the following 24-hour period. Subsequently (phase 2), inflammation was induced via injection of 200 mg (10 mL) of mepivacaine (0.4 mg/kg) into the right neck musculature and perineurally in the proximal palmar metacarpal region of the right forelimb of 2 horses. Six hours after mepivacaine injection, (99m)Tc-EB1 (2.2 GBq, IV, once) was administered; 8 hours after injection, comparative soft tissue images were acquired after administration of technetium (99m)Tc-hydroxymethylene diphosphonate ((99m)Tc-HDP; 7.4 GBq, IV, once). RESULTS: After injections of (99m)Tc-EB1, physical examinations, CBCs, and serum biochemical analyses revealed no abnormalities in any horse. Blood clearance of (99m)Tc-EB1 was rapid (A phase, 2.2 minutes; beta phase, 58 minutes). Soft tissue uptake of (99m)Tc-EB1 was immediate and persisted for as long as 4 hours after injection. At 6 hours after IM and perineural mepivacaine injections, mepivacaine-induced inflammation was detectable by use of (99m)Tc-EB1. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that (99m)Tc-EB1 is safe for use in horses and can identify soft tissue inflammation without concurrent uptake in bone. Compared with (99m)Tc-HDP administration, use of (99m)Tc-EB1 extended the duration of soft tissue scintigraphic image acquisition.

Surgical management of small intestinal incarceration through the gastrosplenic ligament: 14 cases (1994-2006).

OBJECTIVE: To determine prevalence, clinical findings, and long-term survival rate after surgery associated with incarceration of the small intestine through the gastrosplenic ligament (ISIGL) in horses. DESIGN: Retrospective case series. ANIMALS: 14 horses with ISIGL. PROCEDURES: Medical records of horses with ISIGL examined between January 1994 and December 2006 were reviewed. Signalment, initial physical examination findings, results of abdominal fluid analysis, and clinical laboratory values were recorded, along with surgical findings, including segment of incarcerated intestine and surgical procedures performed. Long-term survival data were obtained through client interviews. RESULTS: Clinical findings included small intestinal distention identified via rectal palpation (10/14 horses) or transabdominal ultrasonography (8/11), nasogastric reflux (4/14), and abnormal abdominal fluid (9/9). All horses required intestinal resection and anastomosis. Postoperative complications included adynamic ileus (5/14 horses), incisional infection (4/14), diarrhea (3/14), and laminitis (1/14). No breed or age predilection was detected, although geldings were at increased risk for ISIGL. Long-term survival rate was 79% (11/14 horses). CONCLUSIONS AND CLINICAL RELEVANCE: ISIGL was an uncommon cause of colicin this hospital population. With appropriate surgical intervention and postoperative management, the long-term prognosis for surgically treated horses was fair to good.

Use of bone morphogenetic proteins for augmentation of bone regeneration.

A large body of preclinical and clinical data now documents that recombinant BMPs can be used for skeletal regeneration in humans and animals. Recombinant human BMP-2 and BMP-7 have been approved for use in human patients with long-bone fractures and nonunions and in patients undergoing lumbar fusion or various maxillofacial and dental regenerative procedures. These products have also been made available for veterinary use.

Engineering adipose-like tissue in vitro and in vivo utilizing human bone marrow and adipose-derived mesenchymal stem cells with silk fibroin 3D scaffolds.

Biomaterials derived from silk fibroin prepared by aqueous (AB) and organic (HFIP) solvent-based processes, along with collagen (COL) and poly-lactic acid (PLA)-based scaffolds were studied in vitro and in vivo for their utility in adipose tissue engineering strategies. For in vitro studies, human bone marrow and adipose-derived mesenchymal stem cells (hMSCs and hASCs) were seeded on the various biomaterials and cultured for 21 days in the presence of adipogenic stimulants (AD) or maintained as noninduced controls. Alamar Blue analysis revealed each biomaterial supported initial attachment of hMSCs and hASCs to similar levels for all matrices except COL in which higher levels were observed. hASCs and hMSCs cultured on all biomaterials in the presence of AD showed significant upregulation of adipogenic mRNA transcript levels (LPL, GLUT4, FABP4, PPARgamma, adipsin, ACS) to similar extents when compared to noninduced controls. Similarly Oil-Red O analysis of hASC or hMSC-seeded scaffolds displayed substantial amounts of lipid accumulating adipocytes following cultivation with AD. The data revealed AB and HFIP scaffolds supported similar extents of lipid accumulating cells while PLA and COL scaffolds qualitatively displayed lower and higher extents by comparison, respectively. Following a 4-week implantation period in a rat muscle pouch defect model, both AB and HFIP scaffolds supported in vivo adipogenesis either alone or seeded with hASCs or hMSCs as assessed by Oil-Red O analysis, however the presence of exogenous cell sources substantially increased the extent and frequency of adipogenesis observed. In contrast, COL and PLA scaffolds underwent rapid scaffold degradation and were irretrievable following the implantation period. The results suggest that macroporous 3D AB and HFIP silk fibroin scaffolds offer an important platform for cell-based adipose tissue engineering applications, and in particular, provide longer-term structural integrity to promote the maintenance of soft tissue in vivo.

Matrix-mediated retention of in vitro osteogenic differentiation potential and in vivo bone-forming capacity by human adult bone marrow-derived mesenchymal stem cells during ex vivo expansion.

Mesenchymal stem cells (MSCs) represent an attractive cell source for tissue engineering applications, since they are readily isolated from adult bone marrow and have the ability to differentiate along multiple mesenchymal lineages, including osteogenic. Currently, utilization of MSCs for bone tissue engineering is limited because of the attenuation of their osteogenic differentiation potential and in vivo bone-forming capacity following ex vivo expansion on conventional tissue culture plastic (TCP). Previously, we demonstrated that a denatured type I collagen (DC) matrix promotes the maintenance of MSC in vitro osteogenic differentiation potential during ex vivo expansion in contrast to TCP. In this study, we further demonstrate that the maintenance of MSC osteogenic differentiation potential is primarily due to the ability of DC matrix to influence the retention of early passage osteogenic functions in late passage (LP) cells during ex vivo expansion, in contrast to solely enhancing attenuated LP cellular functions during osteogenic differentiation. Serum-associated factors played a significant role in influencing the retention of MSC osteogenic differentiation potential during expansion on the DC matrix. Significantly, the results show that although LP cells expanded ex vivo on TCP highly attentuate their in vivo bone-forming capacity, the expansion of MSCs on DC matrix preserves this ability as determined by histological, histomorphometric, and bone mineral density evaluations of MSC-seeded hydroxyapatite/tricalcium phosphate scaffolds following an 8-week implantation period within a heterotopic muscle pouch model. These findings provide further insight into the importance of matrix-mediated effects on MSC function and selective factors important in this process.

Mesenchymal stem cells and bone regeneration.

OBJECTIVE: To review the role of mesenchymal stem cells (MSC) in bone formation and regeneration, and outline the development of strategies that use MSC in bone healing and regeneration. STUDY DESIGN: Literature review. METHODS: Medline review, synopses of authors' published research. RESULTS: The MSC is the basic cellular unit of embryologic bone formation. Secondary bone healing mimics bone formation with proliferation of MSC then their differentiation into components of fracture callus. Bone regeneration, where large amounts of bone must form, mimics bone healing and can be achieved with MSC combined with strategies of osteogenesis, osteoinduction, osteoconduction, and osteopromotion. MSC based strategies first employed isolated and culture expanded stem cells in an osteoconductive carrier to successfully regenerate a critical segmental defect in the femur of dogs, which was as effective as autogenous cancellous bone. Because MSC appeared to be immunologically privileged, a study using mismatched allogeneic stem cells demonstrated that these cells would regenerate bone without inciting an immunologic response, documenting the possibility of banked allogeneic MSC for bone regeneration. A technique was developed for selectively retaining MSC from large bone marrow aspirates at surgery for bone regeneration. These techniques utilized osteoconductive and osteoinductive carriers and resulted in bone regeneration that was similar to autogenous cancellous bone. CONCLUSION: MSC can be manipulated and combined with carriers that will result in bone regeneration of critically sized bone defects. CLINICAL RELEVANCE: These techniques can be employed clinically to regenerate bone and serve as an alternative to autogenous cancellous bone.

Safety of, and biological and functional response to, a novel metallic implant for the management of focal full-thickness cartilage defects: Preliminary assessment in an animal model out to 1 year.

Focal full-thickness cartilage lesions of the human medial femoral condyle (MFC) can cause pain and functional impairment. Affected middle-aged patients respond unpredictably to existing treatments and knee arthroplasty may be required, prompting risk of revision. This study assesses the safety of, and biological and functional response to, a metallic resurfacing implant which may delay or obviate the need for traditional arthroplasty. The anatomic contour of the surgically exposed MFC of six adult goats was digitally mapped and an 11 mm diameter full-thickness osteochondral defect was created. An anchor-based Co-Cr resurfacing implant, matching the mapped articular contour, was implanted. Each goat's contralateral unoperated femorotibial joint was used as a control. Postoperative outcome was assessed by lameness examination, radiography, arthroscopy, synoviocentesis, necropsy, and histology up to 26 (n = 3) or 52 (n = 3) weeks. By postoperative week (POW) 4, goats demonstrated normal range of motion, no joint effusion, and only mild lameness in the operated limb. By POW 26 the animals were sound with only occasional very mild lameness. Arthroscopy at POW 14 revealed moderate synovial inflammation and a chondral membrane extending centrally across the implant surface. Radiographs at POWs 14 to 52 implied implant stability in the operated joints, as well as subchondral bone remodeling and mild exostosis formation in the operated and contralateral unoperated joints of some goats. By POW 26, histology revealed new trabecular bone abutting the implant. At POWs 26 and 52 MFC cartilage was metachromatic and intact in the operated and unoperated femorotibial joints. Proximal tibiae of some operated and unoperated limbs demonstrated limited subchondral bone remodeling and foci of articular cartilage fibrillation and thinning. The chondral membrane crossing the prosthesis possessed a metachromatic matrix containing singular and clustered chondrocytes. Our data imply the safety, biocompatibility, and functionality of the implant. Focal articular damage was documented in the operated joints at POWs 26 and 52, but lesions were much reduced over those previously reported in untreated defects. Expanded animal or preclinical human studies are justified.

The inflammatory responses to silk films in vitro and in vivo.

Silks have a long history of biomedical use as sutures. Silk can be purified, chemically modified to attach RGD sequences and processed into highly porous scaffolds for tissue engineering. We report biocompatibility studies of silk films (with or without covalently bound RGD) that were seeded with bone-marrow derived mesenchymal stem cells (MSC) and (a) cultured in vitro with human MSC or (b) seeded with autologous rat MSC and implanted in vivo. Controls for in vitro studies included tissue culture plastic (TCP; negative control), TCP with lipopolysaccharide (LPS) in the cell culture medium (positive control), and collagen films; controls for in vivo studies included collagen, PLA and TCP. After 9 h of culture, the expression of the pro-inflammatory Interleukin 1 beta (IL-1beta) and inflammatory cyclooxygenase 2 (COX-2) in human MSC were comparable for silk, collagen and TCP. After 30 and 96 h, gene expression of IL-1beta and COX-2 in MSC returned to the baseline (pre-seeding) levels. These data were corroborated by measuring IL-1beta and prostaglandin E2 levels in culture medium. The rate of cell proliferation was higher on silk films than either on collagen or TCP. In vivo, films made of silk, collagen or PLA were seeded with rat MSCs, implanted intramuscularly in rats and harvested after 6 weeks. Histological and immunohistochemical evaluation of silk explants revealed the presence of circumferentially oriented fibroblasts, few blood vessels, macrophages at the implant-host interface, and the absence of giant cells. Inflammatory tissue reaction was more conspicuous around collagen films and even more around PLA films when compared to silk. These data suggest that (a) purified degradable silk is biocompatible and (b) the in vitro cell culture model (hMSC seeded and cultured on biomaterial films) gave inflammatory responses that were comparable to those observed in vivo.

Occult subchondral osseous cyst-like lesions of the equine tarsocrural joint.

OBJECTIVE: To report the clinical signs, diagnosis, management, and outcome of horses with occult sub-chondral osseous cyst-like lesions of the tarsocrural joint. DESIGN: Retrospective study. ANIMALS: Twelve horses with subchondral osseous cyst-like lesions (SOCLs) in the tarsocrural joint. METHODS: Information about history, examination findings, diagnostic techniques, and surgical procedures as obtained from medical records. Outcome was determined by patient re-evaluation and telephone communication with the referring veterinarian, owner, or trainer. RESULTS: Horses were aged from 3 to 29 years. Lameness (2 weeks to 1 year) varied from moderate to severe. Synovial fluid analyses (9 horses) yielded changes consistent with suppurative inflammation and positive bacterial culture was obtained in 4 horses. Eight of 9 horses that had intra-articular analgesia had a dramatic reduction in lameness. No abnormalities were detected on tarsal radiographs in 10 horses. Scintigraphy identified foci of increased radiopharmaceutical uptake in the distal tibia or talus of all horses, and the lesion was further characterized by computed tomography in 7 horses. SOCLs were identified in the medial malleolus (5), intertrochlear groove of the talus (4), lateral malleolus (2), and distal intermediate ridge of the tibia (1). One horse was euthanatized, 6 horses had surgical debridement, and 5 horses were managed conservatively. Four horses treated surgically (67%) returned to soundness. Conservatively treated horses continued to exhibit lameness but 2 were sufficiently sound for light pleasure riding. CONCLUSIONS: Occult lesions of the tarsus not visible on radiographs can be detected by computed tomography and scintigraphy and may be a source of lameness. CLINICAL RELEVANCE: SOCL, possibly of septic origin, should be a differential diagnosis for persistent lameness localized to the tarsocrural joint without radiographic abnormalities. Surgical debridement of the lesions may offer the best prognosis for a return to athletic soundness.

Mechanical evaluation of a porous bone graft substitute based on poly(propylene glycol-co-fumaric acid).

A porous, resorbable polymer composite based on poly(propylene glycol-co-fumaric acid) (PPF) was mechanically evaluated in vitro for use as a bone graft substitute and fracture fixative. The test material created a dynamic system capable of initially providing mechanical integrity to bony voids and a degradative mechanism for ingrowth by native bone. The unsaturated polymer, PPF, was crosslinked in the presence of effervescent agents to yield a porous microstructure upon curing. An in vitro degradation study first assessed the temporal mechanical properties of the test material. This research was followed by an ex vivo study using a long-bone osteotomy model to characterize the mechanics of fixation. Results showed the initial compressive strength of the cross-linked PPF system was comparable to cancellous bone. The rate of strength loss was commensurate with the predicted mechanical recovery of healing bone with analogous results in a composite that comprised also 25% (by weight) autograft. Mechanical testing in the long-bone model demonstrated that PPF-based bone-graft substitute increased the flexural strength of K-wire stabilized osteotomies. These results suggest that this type of bone graft substitute may have clinical utility in the stabilization of complex tubular bone fractures.