2/16/2023 0 Comments Ruffini endings![]() Postfixation was carried out with 1 % OsO 4 in 0.1 M buffer. The halves were cut into 5 mm thick slices and kept in the same solution for several hours. Then the ligaments were divided into proximal (femoral) and distal (tibial) halves and placed in 6% glutardialdehyde at 4☌ for 20 min. The knee joints of both legs were injected with 6% glutardialdehyde for in situ fixation prior to surgical removal of the ligaments. ![]() Five adult sheep were sacrificed with T61® (Hoechst, Frankfort, Germany) (a mixture of pentobarbital, d-tubocourarin, and a local anaesthetic made by Hoechst). With the approval of the animal research ethics committee of the University of Hamburg, the anterior cruciate ligaments of sheep were investigated using light and electron microscopy. Preliminary results have been published in abstract form (Halata and Wagner, 1995). This study is the first detailed electron microscopical investigation of nerve endings and mechanoreceptors in the ACL of sheep. The knee joint is easily accessible, and the anatomical situation is rather similar to that in man. In contrast, sheep are highly suited for such experimental procedures. However, small animals are known to have only very few corpuscular mechanoreceptors in the cruciate ligaments (Marinozzi et al., 1991). In order to optimise the therapy of ACL injuries, animal experimental studies are needed. Electrophysiological recordings from ACL receptors during movements of the knee joint were made by Krauspe et al. The first detailed electron microscopic findings of sensory nerve endings in the ACL were published by Halata and Haus ( 1989). ( 1987) based on light microscopic evidence. The presence of nerve endings in the human ACL was first reported by Schultz et al. The present study investigates the structure and distribution of mechanoreceptors and their innervation in the ACL using light and electron microscopy. Especially in case of wrong positioning or overload, they can trigger reflexes at the level of the spinal cord, adjusting the tone of skeletal muscle (Brand, 1986 Solomonow et al., 1987 Johansson et al., 1991a). Many authors agree that the ligaments do not serve solely mechanical functions but are “sensors” monitoring the position of the knee joint (Jackson, 1993 Ellaway et al., 1996). The concepts for the treatment of injured cruciate ligaments are still controversial (Haus, 1996). Especially ruptures of the anterior cruciate ligament (ACL) and their therapy are attracting the interest of traumatologists and orthopaedic surgeons. The number of sports injuries is steadily growing, causing increasing financial burden through treatment costs and sick leave. In traumatology, the knee joint has become a focus of interest. The most important function of the ACL is its mechanical function, but additional sensory functions must be considered triggering reflex mechanisms in case of extreme positioning or overload. They are known to function as rapidly adapting pressure receptors. The afferent myelinated axon has a diameter of 4–6 μm, and the nerve terminal is located in the centre of numerous layers formed by lamellated terminal glial cells and by a perineural capsule. Lamellated corpuscles (usually between 5 and 15) are found in the subsynovial connective tissue. ![]() Functionally, Ruffini corpuscles have been described as slowly adapting stretch receptors. These enter in bundles from the surrounding connective tissue at one open pole, pass through the length of the cylinder, and leave at the other pole. They consist of cylinders formed from perineural cells surrounding the afferent myelinated axons (diameters 4–5 μm) with enlarged nerve terminals anchored between collagen fibres. A ligament contains about 20 Ruffini corpuscles, which are mainly located in the subsynovial connective tissue. The corpuscles are seen subsynovially and between fascicles of connective tissue close to the attachment points of the ACL. Part of this group may be efferent autonomic fibres controlling local blood flow. In addition, FNE are also seen between fascicles of collagen fibres, often close to blood vessels. FNE have been reported to function as thermoreceptors and polymodal nociceptors. The afferent nerve fibres are either thin myelinated axons (Aδ) or C fibres with diameters of 1–2 μm. The FNE (more than 100) are found subsynovially. Three types of nerve endings are found: free nerve endings (FNE), Ruffini corpuscles, and lamellated corpuscles. This study examines the structure of sensory nerve endings in the sheep anterior cruciate ligament (ACL).
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