Benjamin J. Ahern

Preclinical animal models in single site cartilage defect testing: a systematic review.

OBJECTIVE Review the literature for single site cartilage defect research and evaluate the respective strengths and weaknesses of different preclinical animal models. METHOD A literature search for animal models evaluating single site cartilage defects was performed. Variables tabulated and analyzed included animal species, age and number, defect depth and diameter and study duration. Cluster analyses were then used to separate animals with only distal femoral defects into similar groups based on defect dimensions. Representative human studies were included allowing comparison of common clinical lesions to animal models. The suitability of each species for single site cartilage defect research and its relevance to clinical human practice is then discussed. RESULTS One hundred thirteen studies relating to single site cartilage defects were reviewed. Cluster analysis included 101 studies and placed the murine, laprine, ovine, canine, porcine and caprine models in group 1. Group 2 contained ovine, canine, porcine, caprine and equine models. Group 3 contained only equine models and humans. Species in each group are similar with regard to defect dimensions. Some species occur in multiple groups reflecting utilization of a variety defect sizes. We report and discuss factors to be considered when selecting a preclinical animal model for single site cartilage defect research. DISCUSSION Standardization of study design and outcome parameters would help to compare different studies evaluating various novel therapeutic concepts. Comparison to the human clinical counterpart during study design may help increase the predictive value of preclinical research using animal models and improve the process of developing efficacious therapies.

Orthopedic Infections in Equine Long Bone Fractures and Arthrodeses Treated by Internal Fixation: 192 Cases (1990–2006)

OBJECTIVE To determine the rate of postoperative infection (POI) for internal fixation repaired equine long bone fractures and arthrodeses and identify associated risk factors. STUDY DESIGN Case series. ANIMALS Horses (n=192) with fracture repair of the third metacarpal and metatarsal bones, radius, ulna, humerus, tibia, and femur, or arthrodesis with internal fixation. METHODS Medical records (1990-2006) were reviewed for signalment, anatomic location, fracture classification and method of repair, technique and surgical duration, bacterial species isolated, postoperative care, onset of POI, and outcome. RESULTS Of 192 horses (171 [89%] closed, 21 [11%] open fractures), 157 (82%) were discharged from the hospital. Infection occurred in 53 (28% horses), of which 31 (59%) were discharged. Repairs without POI were 7.25 times more likely to be discharged from the hospital. Closed fractures were 4.23 times more likely to remain uninfected and 4.59 times more likely to be discharged from the hospital compared with open fractures. Closed reduction and internal fixation was associated with a 2.5-fold reduction in rate of POI and a 5.9 times greater chance for discharge from the hospital compared with open reduction and internal fixation. Females had a strong trend for increased POI when compared with colts and stallion but not geldings. CONCLUSIONS Overall rate of POI was 28%. Fracture classification, method of repair, gender, and surgical duration were significant risk factors.

Evaluation of equine peripheral blood apheresis product, bone marrow, and adipose tissue as sources of mesenchymal stem cells and their differentation potential

OBJECTIVE To evaluate effects of apheresis on mesenchymal stem cells (MSCs) and compare those MSCs with MSCs obtained from adipose tissue or bone marrow (BM). SAMPLE POPULATION Samples obtained from 6 adult horses. PROCEDURES Samples of blood from a peripheral vein, adipose tissue, and BM aspirate were obtained from each horse. Samples were processed via apheresis of blood and techniques reported elsewhere for adipose tissue and BM. Cultures were maintained until adherence and subsequently were subjected to differentiation protocols to evaluate adipogenic, osteoblastogenic, and chondrogenic potential. RESULTS Apheresis product had a significantly higher mononuclear percentage, higher platelet count, and lower RBC count, compared with values for peripheral blood. No cell adherence to the tissue culture plates was detected for the apheresis product. Adherence was detected for 6 of 6 adipose-derived and 4 of 6 BM-derived samples. Variations in efficiency were detected for differentiation of adipose- and BM-derived cells into adipocytes, chondrocytes, and osteoblasts. CONCLUSIONS AND CLINICAL RELEVANCE Apheresis was able to concentrate mononuclear cells and reduce RBC contamination. However, the apheresis product was unable to adhere to the tissue culture plates. In matched horses, adipose- and BM-derived MSCs were capable of producing lipids, glycosaminoglycan, and mineral. The BM was vastly superior to adipose tissue as a source of MSCs with osteoblastogenic potential in matched horses. Additional studies will be necessary to optimize apheresis techniques for horses before peripheral blood can be considered a suitable source for multipotential cells for use in cell-based treatments.

Comparison of the analgesic properties of transdermally administered fentanyl and intramuscularly administered buprenorphine during and following experimental orthopedic surgery in sheep

OBJECTIVE To evaluate the analgesic properties of transdermally administered fentanyl and IM administered buprenorphine in sheep undergoing unilateral tibial osteotomy. ANIMALS 20 mature sheep. PROCEDURES Fentanyl patches (n = 15 sheep) or placebo patches (5 sheep) were applied 12 hours before sheep underwent general anesthesia and a unilateral tibial osteotomy. Buprenorphine was administered to the placebo group every 6 hours commencing at time of induction. Signs of pain were assessed every 12 hours after surgery by 2 independent observers unaware of treatment groups. RESULTS There were no differences in preoperative and intraoperative physiologic data between the 2 groups. Sheep treated with fentanyl required less preoperative administration of diazepam for sedation and had significantly lower postoperative pain scores, compared with those treated with buprenorphine. No complications associated with the antebrachium at the site of patch application were detected. CONCLUSIONS AND CLINICAL RELEVANCE Under the conditions of this study, transdermally administered fentanyl was a superior option to IM administered buprenorphine for alleviation of postoperative orthopedic pain in sheep. This information can be used to assist clinicians in the development of a rational analgesic regimen for research and clinical patients.

Surgical complications of the equine upper respiratory tract.

Upper respiratory abnormalities are common performance-limiting problems in horses. The complications of various treatment methods, including laryngoplasty surgery, sinus surgery, intermittent dorsal displacement of the soft palate, laser surgery, and tracheal disorders, are discussed.

Pharmacokinetics of fentanyl administered transdermally and intravenously in sheep

OBJECTIVE To investigate the pharmacokinetics of fentanyl administered transdermally and IV in sheep. ANIMALS 21 adult female sheep. PROCEDURES Fentanyl was administered IV to 6 healthy sheep. Transdermal fentanyl patches (TFPs) were applied to 15 sheep 12 hours prior to general anesthesia and surgery. Seria blood samples were collected for 18 hours after IV injection and 84 hours after TFP application. Fentanyl concentrations were quantified via liquid chromatography-mass spectrometry, and pharmacokinetic values were estimated. RESULTS All sheep completed the study without complications. Following a dose of 2.5 g/kg administered IV, the half-life was 3.08 hours (range, 2.20 to 3.36 hours), volume of distribution at steady state was 8.86 L/kg (range, 5.55 to 15.04 L/kg), and systemic clearance was 3.62 L/kg/h (range, 2.51 to 5.39 L/kg/h). The TFPs were applied at a mean dose of 2.05 g/kg/h. Time to maximum plasma concentration and maximal concentration were 12 hours (range, 4 to 24 hours) and 1.30 ng/mL (range, 0.62 to 2.73 ng/mL), respectively. Fentanyl concentrations were maintained at >0.5 ng/mL for 40 hours after TFP application. CONCLUSIONS AND CLINICAL RELEVANCE IV administration of fentanyl resulted in a short half-life. Application of a TFP resulted in stable blood fentanyl concentrations in sheep.

Mechanical evaluation of the equine laryngoplasty.

OBJECTIVES Mechanical evaluation of the equine laryngoplasty. STUDY DESIGN Experimental. ANIMAL POPULATION Cadaveric cricoid (n=36) and arytenoid (46) cartilages. METHODS Arytenoid and cricoid cartilage specimens were embedded for testing. Suture material (2 Ethilon, 5 Ethibond, or 5 Fiberwire) was inserted simulating laryngoplasty procedures. Constructs were evaluated in single or cyclic loading. Single cycle tests recorded load at failure and stiffness. Cyclical tests recorded displacement after 10,000 cycles. ANOVA and t-tests were used (significance P<.05). RESULTS The arytenoid Ethibond (241.10+/-47.67 N) constructs were stronger in single cycle than Ethilon (133.85+/-27.89 N) and Fiberwire (142.67+/-32.40 N). The cricoid Ethibond (220.39+/-49.11 N) constructs were stronger than Ethilon (171.93+/-21.19). The stiffness of Ethilon constructs was lower in both the arytenoid and cricoid compared with Ethibond and Fiberwire. The arytenoids failed at a lower load than the cricoids for Ethilon and Fiberwire but not Ethibond constructs. In cyclic testing complete failure of either cartilage did not occur. Arytenoid Ethibond constructs (0.43+/-0.21 mm) had less distraction than Ethilon (0.92+/-0.41 mm) and a trend for less compared with Fiberwire (0.83+/-0.43 mm; P=.0513). Cricoid Ethibond constructs (0.45+/-0.18 mm) had less distraction compared with Ethilon (1.04+/-0.30 mm) and Fiberwire (0.97+/-0.45 mm). CONCLUSIONS Ethibond was superior to Ethilon and Fiberwire constructs in vitro. CLINICAL RELEVANCE Abduction loss after laryngoplasty is a common complication. The results of this study suggest that the use of Ethibond should minimize abduction loss after surgery relative to the other materials tested.

In vitro mechanical testing of an alternate laryngoplasty system (ALPS) for horses.

OBJECTIVE Mechanical evaluation of a novel alternate laryngoplasty system (ALPS). STUDY DESIGN Experimental. ANIMAL POPULATION Cadaveric horse larynges (n = 10). METHODS Arytenoid and cricoid cartilages were embedded for testing. A novel laryngoplasty system consisting of a metallic anchor, 2 stands of #2 suture material, and a metallic button were evaluated. A traditional laryngoplasty using a single strand of #5 Ethibond was evaluated in parallel. Constructs were evaluated in cyclic testing oscillating from 30 to 50 N for 3600 cycles. Constructs subsequently underwent a single cycle to failure. Distraction during cyclic testing was recorded. Load at failure and stiffness were calculated from single-cycle failure testing. RESULTS There was no difference in mean arytenoid single-cycle load-to-failure for the Ethibond (206.9 ± 13.1 N) constructs compared with ALPS (220.6 ±17.1 N) constructs (P = .486). In the cricoid under single-cycle testing, the ALPS (236.0 ± 23.4 N) constructs were significantly stronger than the Ethibond (161.5 ± 12.2 N) constructs (P = .013). The combined distraction was significantly greater for Ethibond (6.29 ± 1.24 mm) constructs compared to the ALPS (3.43 ± 0.28 mm) constructs (P = .033). CONCLUSIONS The ALPS construct was stiffer and at least as strong as the traditional laryngoplasty construct in single cycle failure in both the arytenoid and cricoid cartilages. Combined distraction was significantly reduced using the ALPS compared to the traditional laryngoplasty in vitro under cyclic testing.

In vitro biomechanical comparison of a 4.5 mm narrow locking compression plate construct versus a 4.5 mm limited contact dynamic compression plate construct for arthrodesis of the equine proximal interphalangeal joint.

OBJECTIVES To compare the in vitro biomechanical properties of a 4.5 mm narrow locking compression plate (PIP-LCP) with 2 abaxially located transarticular screws and a 4.5 mm limited contact dynamic compression plate (LC-DCP) with 2 abaxially located transarticular screws using equine pasterns. STUDY DESIGN Experimental. Paired in vitro biomechanical testing of 2 methods for stabilizing adult equine forelimb PIP joints. ANIMAL Adult equine forelimbs (n = 8 pairs). METHODS Each pair of PIP joints were randomly instrumented with either a PIP-LCP or LC-DCP plate axially and 2 parasagitally positioned 5.5 mm transarticular screws. The proximal aspect of the proximal phalanx (P1) and the distal aspect of the middle phalanx (P2) were embedded to allow for mounting on a mechanical testing machine. Each construct was tested in both cyclic and subsequently single cycle to failure in 4-point bending. The displacement required to maintain a target load of 1 kN over 3600 cycles at 1 Hz was recorded. Maximum bending moment at failure and construct stiffness was calculated from the single cycle to failure testing. RESULTS In cyclic testing, significantly more displacement occurred in the LC-DCP (0.46 ± 0.10 mm) than for the PIP-LCP (0.17 ± 0.11 mm) constructs (P = .016). During single cycle testing there was no significant difference in the bending moment between the LC-DCP (148.7 ± 19.4 N m) and the PIP-LCP (164.6 ± 17.6 N m) constructs (P = .553) and the stiffness of the LC-DCP (183.9 ± 26.9 N mm) was significantly lower than for the PIP-LCP (279.8 ± 15.9 N/mm) constructs (P = .011). All constructs failed by fracture of the bone associated with the transarticular screws and subsequently bending of the plates at the middle hole. CONCLUSIONS Use of the PIP-LCP resulted in a stiffer construct of the same strength as the LC-DCP in vitro using this 4-point bending model.

Evaluation of a Fiber Reinforced Drillable Bone Cement for Screw Augmentation in a Sheep Model—Mechanical Testing

We evaluated the mechanical properties of a novel fiber reinforced calcium phosphate at time zero and after 12 weeks in vivo using a sheep long bone osteotomy model. Time zero data were obtained and compared by pullout testing of 4.5 mm bone screws from bone proper and overdrilled defects of 4.5 and 8 mm diameter. Defects were augmented with: polymethylmethacrylate (PMMA), calcium phosphate, and fiber reinforced calcium phosphate using cadaveric sheep tibiae. Twelve‐week data were obtained from explanted tibiae of sheep that underwent unilateral tibial osteotomy surgery repaired with a locking compression plate. The most distal hole was overdrilled to 4.5 or 8 mm diameter, filled with fiber reinforced cement, drilled, tapped and a 4.5 mm screw was placed. Screw holding strength at t= 0 was significantly higher for reinforced when compared to nonreinforced cement, but not different from bone or PMMA in 4.5 mm defects. There was no difference in pullout strength for the 8 mm defect data. After 12 weeks fiber reinforced pullout strength increased by 45% and 8.9% for 4.5 and 8 mm defects, respectively, when compared to t= 0 testing. Fiber reinforced calcium phosphate bone cement can be drilled and tapped to support orthopedic hardware for trauma applications. Clin Trans Sci 2010; Volume 3: 112–115