Morphometric analyses of the body and the branches of the normal third interosseous muscle (suspensory ligament) in Standardbreds

Suspensory ligament or interosseous muscle? Histology of the interosseous muscle of South American Camelids

The interosseous muscles (IOM) have evolved to largely collagenized structures in many large grazers, including South American Camelids (SACs). SACs include lama (Lama glama), alpaca (Vicugna pacos), guanaco (Lama guanicoe) and vicuna (Vicugna vicugna). This study reports on a comparative histomorphological evaluation of the IOM in these four species. First, a descriptive qualitative analysis of the tissue composition within the physiological IOM clearly demonstrates that the IOM of all SAC species is predominantly tendinous. However, we can always find a small amount of striated muscle fibres supporting the claim that the term "interosseous muscle" should be preferred over the denomination "suspensory ligament". Second, we quantify the ratio of muscle tissue (MTr) occupying the cross-sectional area (CSA) of 80 limbs at three levels and examine it in relation to limb, sample localization and species. Values for MTr are highest at the middle level, ranging from 0.4% to 15.2% with a mean of 3.4% ± 3.2%. We also detect notable amounts of muscle tissue at the distal sample level in the area of the branches of the IOM. Of all SACs, alpacas present the highest MTr. Lamas have a significantly larger MTr than guanacos. These results suggest the influence of domestication and/or physical activity on the muscle tissue content of the IOM of SACs. Amounts and distribution of muscle, adipose and lose connective tissue vary greatly for each sample localization and within individuals of one species. This may complicate the interpretation of MRI images of SACs' IOM for diagnostic purposes.

Non-weight bearing ultrasonographic examination allows the diagnosis of longitudinal fiber disruption (split) in equine suspensory ligament branches not visible on weight bearing examination

When evaluating suspensory ligament branch splits, there is a discrepancy between high field MRI findings and weight bearing ultrasonographic imaging characteristics. In this descriptive and retrospective case series, ultrasonographic examination was performed on suspensory ligament branches with the limbs in weight bearing and non-weight bearing positions. Suspensory ligament branch splits were defined as linear regions of decreased echogenicity when imaged with the limb in a weight bearing position that increased in size and became anechoic with the limb in a non-weight bearing position. This appearance was considered an indication of pathologic change in the branch. A total of 62 suspensory ligament branches were included in the study from 37 horses, with 14 partial splits, 11 intrasubstance splits, and 14 complete splits of which two had extension of fetlock synovial fluid and synovial membrane through the split. Recheck ultrasonographic examinations performed in eight horses up to 14 months following the initial examination demonstrated persistence of the split in two horses, partial resolution in five horses, and complete resolution in one horse. Ultrasonographic examination using the non-weight bearing approach proved valuable for increasing the lesion conspicuity as compared to the weight bearing images. Certain abnormalities, such as longitudinal fiber disruption (split) in suspensory ligament branches may only be evident when imaged non-weight bearing. The use of this technique provides a more accurate representation of lesion severity and allows for monitoring over time. A longitudinal study is necessary to determine the clinical relevance of suspensory ligament branch splits.

Subclinical Ultrasonographic Abnormalities of the Suspensory Ligament Branches Are Common in Elite Showjumping Warmblood Horses

Background: There is limited information concerning the ultrasonographic appearance of suspensory ligament branches (SLB) in sports horses. Publications exist on clinical injuries that lead to loss of training days and retirement, but not on the appearance of SLBs in high level showjumping Warmbloods.

Objectives: To demonstrate the prevalence of subclinical SLB abnormalities in regularly competing high-level showjumpers; to grade each branch 0–3; compare forelimb vs. hindlimb and medial vs. lateral SLBs; subjectively assess periligamentous fibrosis; measure cross sectional area (CSA) and to gather competition follow-up data.

Study Design: Prospective cross-sectional study using ultrasonograms.

Methods: Sixty elite showjumping Warmbloods without recent history or clinical signs of SLB desmopathy were examined ultrasonographically. Eight static images of each SLB were acquired in transverse and longitudinal sections, anonymised and stored. Images were then assessed and graded by two experienced blinded clinicians based on a published ordinal scale (grade 0–3). A branch score was assigned based on the most severe grade of any image slice in each branch series. SLB cross-sectional area measurement was obtained from each SLB using the transverse image proximal to insertion.

Results: The frequency of grade 2 (moderate) ultrasonographic abnormalities was high. Combined data showed a prevalence of 58% (554/960) grade 2 SLBs. Interobserver agreement was good (kappa = 0.65). Periligamentous fibrosis was over represented in hindlimbs (64%). Combined observer data showed there was no statistical difference in branch scores based on limb or laterality. Follow-up over 12 months revealed only two horses were excluded from competition due to SLB injury.

Main Limitations: Sample size was small. Images were obtained in static mode, limbs were not clipped of hair, lameness evaluation was under FEI veterinary inspection and not performed by the authors and follow-up evaluation was from FEI competition records and communication only, and was limited to 1 year.

Conclusions: Regularly competing elite showjumping Warmbloods have a high prevalence of subclinical SLB ultrasongraphic abnormalities, which may not contribute to causing lameness, poor-performance or be viewed entirely negatively at prepurchase examination. Judicious interpretation of moderate severity SLB abnormalities is advised due the low incidence of clinical injury demonstrated during the 1 year follow-up.

The equine forelimb suspensory ligament exhibits a heterogeneous strain pattern under tensile load

Objectives: To determine if regional variations in strain patterns occur within the suspensory ligament under tensile load. Local increases in strain may put certain regions of the suspensory ligament at risk and may explain the poor healing and high recurrence rates associated with suspensory branch injuries.

Methods: The suspensory ligament and its bone attachments were isolated from each of 10 adult equine cadaveric forelimbs and radiodense reference beads were inserted throughout the length of the ligament. Specimens were attached to a custom fixture secured to a materials testing system. Radio-graphs were acquired at 50, 445, 1112, and 2224 N of applied tensile load. Changes in distances between the beads in each region of the suspensory ligament were measured and the regional strain was calculated. Significant differences were determined using a repeated-measures analysis of variance.

Results: The suspensory ligament exhibited significant differences in regional strain (p <0.001). The distal branches of the suspensory ligament had significantly greater strains than the proximal (p = 0.025) and mid-body (p = 0.002) regions. The mid-body of the suspensory ligament also exhibited local strain variation, with the distal mid-body having significantly higher strains than the proximal mid-body (p = 0.038).

Clinical significance: The equine suspensory ligament demonstrates a heterogeneous strain pattern during tensile loading, with the distal regions exhibiting significantly more strain than the proximal region. The nonhomogenous strain pattern could explain the regional difference in injury and re-injury rates.

Tissues from equine cadaver ligaments up to 72 hours of post-mortem: a promising reservoir of stem cells

Background

Mesenchymal stem cells (MSCs) harvested from cadaveric tissues represent a promising approach for regenerative medicine. To date, no study has investigated whether viable MSCs could survive in cadaveric tissues from tendon or ligament up to 72 hours of post-mortem. The purpose of the present work was to find out if viable MSCs could survive in cadaveric tissues from adult equine ligaments up to 72 hours of post-mortem, and to assess their ability (i) to remain in an undifferentiated state and (ii) to divide and proliferate in the absence of any specific stimulus.

Methods

MSCs were isolated from equine cadaver (EC) suspensory ligaments within 48–72 hours of post-mortem. They were evaluated for viability, proliferation, capacity for tri-lineage differentiation, expression of cell surface markers (CD90, CD105, CD73, CD45), pluripotent transcription factor (OCT-4), stage-specific embryonic antigen-1 (SSEA-1), neuron-specific class III beta-tubulin (TUJ-1), and glial fibrillary acidic protein (GFAP). As well, they were characterized by transmission electron microscope (TEM).

Results

EC-MSCs were successfully isolated and maintained for 20 passages with high cell viability and proliferation. Phase contrast microscopy revealed that cells with fibroblast-like appearance were predominant in the culture. Differentiation assays proved that EC-MSCs are able to differentiate towards mesodermal lineages (osteogenic, adipogenic, chondrogenic). Flow cytometry analysis demonstrated that EC-MSCs expressed CD90, CD105, and CD73, while being negative for the leukocyte common antigen CD45. Immunofluorescence analysis showed a high percentage of positive cells for OCT-4 and SSEA-1. Surprisingly, in absence of any stimuli, some adherent cells closely resembling neuronal and glial morphology were also observed. Interestingly, our results revealed that approximately 15 % of the cell populations were TUJ-1 positive, whereas GFAP expression was detected in only a few cells. Furthermore, TEM analysis confirmed the stemness of EC-MSCs and identified some cells with a typical neuronal morphology.

Conclusions

Our findings raise the prospect that the tissues harvested from equine ligaments up to 72 hours of post-mortem represent an available reservoir of specific stem cells. EC-MSCs could be a promising alternative source for tissue engineering and stem cell therapy in equine medicine.

Characterization of collagen fibrils after equine suspensory ligament injury: an ultrastructural and biochemical approach

Suspensory ligament (SL) injuries are an important cause of lameness in horses. The mechanical properties of connective tissue in normal and pathological ligaments are mainly related to fibril morphology, as well as collagen content and types. The purpose of this study was to evaluate, using biochemical and ultrastructural approaches, the alterations in collagen fibrils after injury. Eight Warmblood horses with visible signs of injury in only one forelimb SL were selected and specimens were examined by transmission electron microscope (TEM). Collagen types I, III and V were purified by differential salt precipitation after collagen extraction with acetic acid containing pepsin. TEM revealed abnormal organization as well as alterations in the diameter and shape of fibrils after SL injury. The bands corresponding to types I, III and V collagen were assessed by densitometry after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Densitometric analysis indicated that the proportions of type III and type V collagen were higher (P < 0.001) in damaged tissues compared with normal tissues with a mean increase of 20.9% and 17.3%, respectively. Concurrently, a decrease (P < 0.001) in type I collagen within damaged tissues was recorded with a mean decrease of 15.2%. These alterations could be the hallmark of a decrease in the tissue quality and mechanical properties of the ligament. The findings provide new insight for subsequent research on tissue regeneration that may lead to the development of future treatment strategies for SL injury.