Parameters and functional analysis of the deep epaxial muscles in the thoracic, lumbar and sacral regions of the equine spine.

The epaxial muscles produce intervertebral rotation in the transverse, vertical and axial axes. These muscles also counteract the movements induced by gravitational and inertial forces and movements produced by antagonistic muscles and the intrinsic muscles of the pelvic limb. Their fascicles are innervated by the dorsal branch of the spinal nerve, which corresponds to the metamere of its cranial insertion in the spinous process. The structure allows the function of the muscles to be predicted: those with long and parallel fibres have a shortening function, whereas the muscles with short and oblique fibres have an antigravity action. In the horse, the multifidus muscle of the thoracolumbar region extends in multiple segments of two to eight vertebral motion segments (VMS). Functionally, the multifidus muscle is considered a spine stabiliser, maintaining VMS neutrality during spine rotations. However, there is evidence of the structural and functional heterogeneity of the equine thoracolumbar multifidus muscle, depending on the VMS considered, related to the complex control of the required neuromuscular activity. Osteoarticular lesions of the spine have been directly related to asymmetries of the multifidus muscle. The lateral (LDSM) and medial (MDSM) dorsal sacrocaudal muscles may be included in the multifidus complex, the function of which is also unclear in the lumbosacral region. The functional parameters of maximum force (Fmax ), maximum velocity of contraction (Vmax ) and joint moment (M) of the multifidus muscles inserted in the 4th, 9th, 12th and 17th thoracic and 3rd and 4th lumbar vertebrae of six horses were studied postmortem (for example: 4MT4 indicates the multifidus muscle that crosses four metameres with cranial insertion in the T4 vertebra). Furthermore, the structural and functional characteristics of LDSM and MDSM were determined. Data were analysed by analysis of variance (anova) in a randomised complete block design (P ≤ 0.05). For some muscles, the ordering of Vmax values was almost opposite to that of Fmax values, generally indicating antigravity or dynamic functions, depending on the muscle and VMS. The muscles 3MT12, 3ML3 and 4ML4 exhibited high Fmax and low Vmax values, indicating a stabilising action. The very long 7MT4 and 8MT4 multifidus had low Fmax and high Vmax values, suggesting a shortening action. However, some functional characteristics of interest did not fall within these general observations, also indicating a dual action. In summary, the results of the analysis of various structural and functional parameters confirm the structural and functional heterogeneity of the equine thoracolumbar multifidus complex, depending on the VMS, regardless of the number of metameres crossing each fascicle. To clarify the functions of the equine multifidus muscle complex, this study aimed to assess its functional parameters in thoracolumbar VMSs with different movement characteristics and in the MDSM and LDSM muscles, hypothesising that the functional parameters vary significantly when the VMS is considered.

Structural and functional characteristics of the thoracolumbar multifidus muscle in horses.

The multifidus muscle fascicles of horses attach to vertebral spinous processes after crossing between one to six metameres. The fascicles within one or two metameres are difficult to distinguish in horses. A vertebral motion segment is anatomically formed by two adjacent vertebrae and the interposed soft tissue structures, and excessive mobility of a vertebral motion segment frequently causes osteoarthropathies in sport horses. The importance of the equine multifidus muscle as a vertebral motion segment stabilizer has been demonstrated; however, there is scant documentation of the structure and function of this muscle. By studying six sport horses postmortem, the normalized muscle fibre lengths of the the multifidus muscle attached to the thoracic (T)4, T9, T12, T17 and lumbar (L)3 vertebral motion segments were determined and the relative areas occupied by fibre types I, IIA and IIX were measured in the same muscles after immunohistochemical typying. The values for the normalized muscle fibre lengths and the relative areas were analysed as completely randomized blocks using an anova (P ≤ 0.05). The vertebral motion segments of the T4 vertebra include multifidus bundles extending between two and eight metameres; the vertebral motion segments of the T9, T12, T17 and L3 vertebrae contain fascicles extending between two and four metameres The muscle fibres with high normalized lengths that insert into the T4 (three and eight metameres) vertebral motion segment tend to have smaller physiological cross-sectional areas, indicating their diminished capacity to generate isometric force. In contrast, the significantly decreased normalized muscle fibre lengths and the increased physiological cross-sectional areas of the fascicles of three metameres with insertions on T9, T17, T12, L3 and the fascicles of four metameres with insertions on L3 increase their capacities to generate isometric muscle force and neutralize excessive movements of the vertebral segments with great mobility. There were no significant differences in the values of relative areas occupied by fibre types I, IIA and IIX. In considering the relative areas occupied by the fibre types in the multifidus muscle fascicles attached to each vertebral motion segment examined, the relative area occupied by the type I fibres was found to be significantly higher in the T4 vertebral motion segment than in the other segments. It can be concluded that the equine multifidus muscle in horses is an immunohistochemically homogeneous muscle with various architectural designs that have functional significance according to the vertebral motion segments considered. The results obtained in this study can serve as a basis for future research aimed at understanding the posture and dynamics of the equine spine.

Adaptive functional specialisation of architectural design and fibre type characteristics in agonist shoulder flexor muscles of the llama, Lama glama.

Like other camelids, llamas (Lama glama) have the natural ability to pace (moving ipsilateral limbs in near synchronicity). But unlike the Old World camelids (bactrian and dromedary camels), they are well adapted for pacing at slower or moderate speeds in high-altitude habitats, having been described as good climbers and used as pack animals for centuries. In order to gain insight into skeletal muscle design and to ascertain its relationship with the llama's characteristic locomotor behaviour, this study examined the correspondence between architecture and fibre types in two agonist muscles involved in shoulder flexion (M. teres major - TM and M. deltoideus, pars scapularis - DS and pars acromialis - DA). Architectural properties were found to be correlated with fibre-type characteristics both in DS (long fibres, low pinnation angle, fast-glycolytic fibre phenotype with abundant IIB fibres, small fibre size, reduced number of capillaries per fibre and low oxidative capacity) and in DA (short fibres, high pinnation angle, slow-oxidative fibre phenotype with numerous type I fibres, very sparse IIB fibres, and larger fibre size, abundant capillaries and high oxidative capacity). This correlation suggests a clear division of labour within the M. deltoideus of the llama, DS being involved in rapid flexion of the shoulder joint during the swing phase of the gait, and DA in joint stabilisation during the stance phase. However, the architectural design of the TM muscle (longer fibres and lower fibre pinnation angle) was not strictly matched with its fibre-type characteristics (very similar to those of the postural DA muscle). This unusual design suggests a dual function of the TM muscle both in active flexion of the shoulder and in passive support of the limb during the stance phase, pulling the forelimb to the trunk. This functional specialisation seems to be well suited to a quadruped species that needs to increase ipsilateral stability of the limb during the support phase of the pacing gait. Compared with other species, llama skeletal muscles are well suited for greater force generation combined with higher fatigue resistance during exercise. These characteristics are interpreted as being of high adaptive value, given the llama's habitat and its use as a pack animal.

Arteries of the hindfoot of the llama (Lama glama).

The objective of this study was to describe the arterial distribution of the hindfoot of the llama (Lama glama). Ten adult llamas, preserved in 6% formalin solution at 0 degree C, were dissected. The arterial system was perfused with a solution of 14% coloured plaster; the venous system was perfused with a solution of 17% coloured industrial gelatin. Angiographies were also obtained. In the llama, the arterial distribution is of the saphenous type and this simple sort of irrigation could be used as a didactic model. The caudal branch of the saphenous artery divides into the small lateral plantar artery and the larger medial plantar artery, which continues as the plantar common digital artery III, and it is the main blood supply of the hindfoot. The dorsal pedal artery is underdeveloped and the perforating tarsal artery does not exist in this species. The plantar common digital artery III divides into the plantar proper digital II, III and IV. Branches from the plantar proper digital artery III supply the digits. We compared the arterial distribution of the hindfoot of the llama with that of other domestic animals including the one-humped camel (Camelus dromedarius).

Non satellite veins in the pelvic limb of the llama (Lama glama).

The objective of this study was to determine the major differences in the venous system of the pelvic limb of the llama (Lama glama) and that of other mammals, including humans. Eight adult llamas, preserved by means of 6% formalin solution at 0 degrees C, were dissected. The venous system was perfused with a solution of 17% coloured industrial gelatin. Two venous systems are recognised, superficial and deep. The veins of the deep system follow the same course as the arteries, except for two important veins located in the femoral, popliteal and crural regions. A more voluminous vein than the femoral originates in a venous tripod in the proximal part of the femoral canal and forms an anastomosis with the femoral vein distally. The popliteal vein gives off an expansion located along the popliteal region. In the leg, it continues with a vein that accompanies the tibial nerve and forms an anastomosis distally with the medial saphenous vein. The described venous distribution represents an interesting complement to the medial saphenous, popliteal and femoral veins, being more important than the last one for its volume. In the thigh it would correspond to the deep femoral vein as in humans and dogs; the homology in the popliteal and leg regions is too difficult because it probably corresponds to the caudal tibial vein of the human, the caudal branch of the medial saphenous vein, and the satellite vein of the tibial nerve in the horse.

Irrigación de la rodilla y pierna de la llama (lama glama) / Knee and leg irrigation of the llama (lama glama)

Dado el escaso material bibliográfico existente y la poca profundidad en sus detalles, se estudiaron las regiones de la rodilla y pierna hasta el nivel de la articulación tarsocrural, describiéndose las relaciones y las estructuras irrigadas. Se utilizaron 7 cadáveres conservados de llamas, en solución de formol al 6 por ciento, a 0ºC y perfundidos por vía arterial con yeso al 14 por ciento y por vía venosa con gelatina industrial al 17 por ciento. Por la forma de la distribución arterial en esta especie, podemos clasificarla como de tipo safeno, suministrando la arteria safena la mayor parte de la irrigación en caudal de la pierna y casi la totalidad del pie. Presenta una rama dorsal distal proveniente de la arteria safena, no presente en los animales domésticos, y la arteria comitans del nervio tibial es semejante a la del equino. La irrigación de la articulación de la rodilla es completa; la arteria media de la rodilla cursa hacia la fosa intercondílea. La arteria tibial craneal es la continuación de la arteria poplítea, cursando en el tercio medio y proximal de la pierna, por la celda lateral, desde que alcanza el espacio interóseo; la arteria tibial caudal es de escaso desarrollo

La irrigación arterial del muslo de la llama (Lama glama) / Arteries of the thigh of the llama (Lama glama)

Se trabajó con 5 cadáveres conservados en solución de formol al 6 por ciento a 0ºC y perfundidos por vía arterial con yeso al 14 por ciento y gelatina industrial al 17 por ciento por vía venosa. Se realizaron disecciones con instrumental standard. La Lacuna vasorum está relacionada con las dos cabeza del M. sartorius; en la salida del Trigonum femorale, sólo un tenue anillo de Fascia fija la A. femoralis al Femur. Sus dos primeras colaterales son las Aa, circumflexa ilum superficialis y circumflexa femoris lateralis; la primera puede tener un origen atípico desde la A. iliaca externa; la segunda de ellas, emite los R. ascendens y descendens y, éste último da el R. transversus. La A. profunda femoris está ausente, emitiendo separadamente el Troncus pudendoepigastricus y la A. circumflexa femoris medialis; ésta se origina directamente de la A. femoralis con su tercera colateral, emitiendo los R. obturatorius, profundus, ascendens, transversus y acetabularis. La emergencia de la A. saphena del Trigonum femorale se da a la altura de la inserción distal del M. pectineus; la A. caudalis femoris media surge en este nivel, y proximal a éstas, se origna la A. caudalis femoris proximalis. Al A. saphena emite el R. articularis genus. En la salida del Trigonum femorales, emerge la A. caudalis femoris distalis, la cual pasa por un tenue anillo de Fascia que fija la arteria al Femur. La A. genus descendens se origina en el mismo nivel o ligeramente en distal de esta última. Cuando la A. circumflexa ilum superficialis tiene un origen atípico de la A. iliaca externa, parece reemplazar a la A. iliacofemoralis que presentan algunos individuos. Consideramos a esta especie como un interesante modelo didáctico por poseer una distribución arterial completa

[Anatomo-functional consideration of an aponeurosis on the caudal radiocarpus in the tiger, lion and domestic cat (Panthera tigris, Panthera leo and Felis catus)]. / Consideraciones anatomofuncionales de una aponeurosis radiocarpiana caudal en tigre, leon y gato domestico (Panthera tigris, Panthera leo y Felis catus).

This study describes a strong aponeurosis on the caudal surface of the antebrachium, between the Mm. Flexoris and the M. pronator quadratus. This aponeurosis has not been experimentally validated. By dissection and macroscopic examination of formaldehyde-prepared material, and experimental surgical transection of the structure in F. catus, the aponeurosis is described and its functional capacity is determined. The origin of the aponeurosis is the Facies caudalis, Margo medialis of the Radius and distal Ulna and inserts on the Crista transversa of the Radius and the Ligg. radiocarpeum palmare and ulno-carpeum palmare, and a strong Pars radialis. Its disposition is similar to that of the supernumerary M. anterior radialis brevis in humans. Surgical transection of the aponeurosis in F. catus resulted in hyperextension of the Manus and a decrease in the Carpus in its weight-bearing ability. These findings indicate the anatomico-functional importance of the aponeurosis in providing support to the claws.