Tensile properties in collagen-rich tissues of Quarter Horses with hereditary equine regional dermal asthenia (HERDA).

REASONS FOR PERFORMING STUDY: Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive disorder of Quarter Horses characterised by skin fragility. Horses with HERDA have a missense mutation in peptidyl-prolyl cis-trans isomerase B (PPIB), which encodes cyclophilin B and alters folding and post translational modifications of fibrillar collagen. OBJECTIVES: The study aimed to test the hypothesis that tendons, ligaments and great vessels, which, like skin, are rich in fibrillar collagen, will also have abnormal biomechanical properties in horses with HERDA. STUDY DESIGN: Ex vivo biomechanical study comparing horses with and without a diagnosis of HERDA. METHODS: Forelimb suspensory ligament, superficial and deep digital flexor tendons; withers, forelimb and abdominal skin; the main pulmonary artery and the aortic arch were harvested from 6 horses with HERDA and 6 control horses without the HERDA allele. Tissues were distracted to failure. Tensile strength (TS), elastic modulus (EM) and energy to failure (ETF) were compared. RESULTS: Horses with HERDA had significantly lower TS and EM in tendinoligamentous tissues and great vessels, respectively. The TS, EM and ETF were significantly lower in skin from horses with HERDA. Differences in TS and ETF were more extreme at the withers than at the forelimb or abdomen. CONCLUSIONS: Tendinoligamentous tissue, great vessels and skin are significantly weaker in horses with HERDA than in horses lacking the PPIB mutation, substantiating that diverse tissues with high fibrillar collagen content are abnormal in HERDA and that the HERDA phenotype is not limited to the integument.

A cryogenic clamping technique that facilitates ultimate tensile strength determinations in tendons and ligaments.

OBJECTIVE: To describe the use of a cryogenic clamp of novel design for tensile strength testing of tendinous and ligamentous tissues with inherently high tensile strength. METHODS: Inexpensive, easily machined steel clamps were manufactured to facilitate rapid insertion into a standard wedge-screw grip apparatus installed on a testing system with a control system attached. The deep digital flexor tendon (DDFT) of six horses was trimmed to a uniform dumbbell shape and secured in clamps using partial submersion in liquid nitrogen for approximately 45 seconds and immediately tested. Approximate time between removal from liquid nitrogen and failure of tendon was four minutes. RESULTS: Failure was achieved in all tendons tested in a region approximating a midpoint between the clamps. Ultimate failure loads of up to 6745 N were achieved without slippage of the tissue from the grips. The ultimate tensile strength of the normal equine DDFT determined in this study was 111.82 ± 11.53 N/mm2, and the stress versus grip-to-grip elongation plots for our equine DDFT were representative of a standard non-linear elastic curve obtained in similar studies. CLINICAL SIGNIFICANCE: We present a low cost device for quantifying physical properties of specimens with high connective tissue concentrations and inherent high tensile strength. Results of this study indicate that this device provides a practical alternative to other more costly methods of adequately securing larger tendons and ligaments for tensile strength testing.

Zonal dermal separation: a distinctive histopathological lesion associated with hyperelastosis cutis in a Quarter Horse.

This case report describes a distinctive deep cutaneous lesion in a 1-year-old Quarter Horse filly with hyperelastosis cutis. The horse had a typical clinical presentation of hyperelastic skin associated with a 6-month history of cutaneous wounds that developed following minor cutaneous trauma. Punch biopsies of skin from the affected horse were thinner than similar biopsies from an age- and breed-matched control. Significant microscopic lesions were not seen in cutaneous punch biopsies stained with haematoxylin and eosin and Masson's trichrome stains, but the ultrastructure of the dermis from the affected horse was characterized by variation in collagen fibre diameter and loose packing of collagen fibres within bundles. The horse was euthanized and necropsied, and full-thickness sections of skin were collected and examined microscopically. Affected skin was of normal thickness; however, the deep dermis contained a distinctive horizontal linear zone in which separation of collagen bundles resulted in the formation of large empty cleft-like spaces between the upper and lower regions of the deep dermis. We suggest the term 'zonal dermal separation' for this microscopic lesion. Incisional full-thickness skin biopsies should be taken in suspected cases of equine hyperelastosis cutis because punch biopsies may not obtain enough deep dermis to adequately represent pathological change in the skin of horses with this disorder.

Papillomatous pastern dermatitis with spirochetes and Pelodera strongyloides in a Tennessee Walking Horse.

Papillomatous digital dermatitis is a common disease in cattle. The pastern dermatitis observed in a horse shared many of the gross characteristics of papillomatous digital dermatitis in cattle. Lesions included a mixture of proliferative and erosive changes, with a verrucose appearance in some areas. Microscopic similarities included pseudoepitheliomatous and papillomatous epidermal hyperplasia with hyperkeratosis, spongiosis of the epidermis, and intraepidermal spirochetes. The horse was also concurrently infected with Pelodera strongyloides. Papillomatous digital dermatitis in cattle is associated with poor husbandry practices. The environment of the affected horse was heavily contaminated with urine, manure, and other organic debris. Verrucous pododermatitis of horses may be the same as or similar to bovine papillomatous digital dermatitis, and these conditions have similar etiologies.

The response of cancellous and cortical canine bone to hydroxylapatite-coated and uncoated titanium rods.

Because of the recent trend in total hip arthroplasty to achieve direct contact of the endoprosthesis with cortical bone, comparison of bone apposition from cortical bone and cancellous bone was performed. The response of cortical and cancellous bone to hydroxylapatite was also compared. Implants in cortical bone demonstrated a higher interface shear strength and more bone apposition than those in cancellous bone over all time periods tested. Hydroxylapatite coating increased the interfacial shear and bone apposition in cortical bone at all time periods and in both the 3- and 6-week cancellous bone models. The potential effect of stress shielding (and subsequent bone resorption) by femoral stems ingrown with cortical bone is discussed.

Subsidence of an uncemented canine femoral stem.

Factors contributing to subsidence were analyzed by radiographic evaluation and mechanical testing of 36 canine cadaver femora during and after insertion of an uncemented porous-coated femoral stem and by radiographic evaluation of 35 canine total hip arthroplasties. Mean percentage of canal fill in immediate postoperative radiographs, and percentage of canal fill at midimplant and distal implant locations, were accurate predictors of subsidence. Force required to implant the femoral stem was strongly correlated with force required for implant subsidence. Femoral morphology and percentage of canal fill at the middle and distal sites were accurate predictors of subsidence. Implants in femora with a stovepipe morphology (canal flare index less than or equal to 1.8) were six times more likely to subside than implants in femora that had a normal appearance (canal flare index 1.8 to 2.5), and 72 times more likely to subside than implants in champagne-fluted femora (canal flare index greater than or equal to 2.5). Femora with more than 85% mean, middle, or distal canal fill were less likely to subside.

Inhibition of equine complement activity by polysulfated glycosaminoglycans.

The ability of polysulfated glycosaminoglycans (PSGAG) to inhibit the complement cascade was evaluated. The role of complement in inflammation and infection has been well documented. Inhibition of the complement cascade by PSGAG could explain why intra-articularly administered PSGAG diminish diarthrodial joint inflammation and potentiate septic arthritis in horses. Hemolytic complement testing was performed to evaluate the effect of PSGAG on the equine classical and alternate pathways of complement, using rabbit erythrocytes as the target cells. Concentration of PSGAG between 0.2 mg/ml and 0.6 mg/ml significantly (P less than 0.05) inhibited equine complement in dose-related fashion. Further increase in complement inhibition was not observed at PSGAG concentration greater than 0.6 mg/ml. Difference was not apparent in the extent of inhibition of complement from each of the 4 horses tested. Polysulfated glycosaminoglycans appeared to inhibit the classical and alternate complement pathways equally, indicating possible effect on complement components common to both pathways. Heat inactivation of complement function completely inhibited (P less than 0.01) the hemolytic activity of the serum from all horses.