Generic Joint Anatomy

The joint is the point at which two bones connect and joints are of value to the piano teacher solely as potentialities for movement.
Question: What is the probability that movement can originate from this joint?
The essential feature in any joint is the sliding of one surface over another and any such form of movement produces considerable friction.
In healthy joints this is reduced by the interposition of "two membranes", called synovial membranes ^[1] (one for each articulating surface), between the bony surfaces, and by the constant moistening of these membranes by an albumen^[2] like substance known as the synovial fluid. This acts as a lubricant, and permits an easy, noiseless sliding of the two articulating surfaces.
Joined to the sides of the two bones, near their ends, and extending from one bone-head to the other (arc ligaments) consisting of connective tissue. These ligaments, although they arc plastic, so that they do not interfere with the movements at the joint, are nevertheless strong and inelastic. These ligaments are strong and inelastic. Strength and inelasticity are necessary if the ligaments are to fulfill their physiological function, which is the holding of the ends of the bones within the articulating cavity. If this normal range of movement be exceeded by tearing the ligaments, a dislocation of the joint may follow.

Since these inelastic ligaments must permit considerable natural movement at the joint , they cannot also serve to hold the bones in place during the range of natural movement. In these positions they surround the joint loosely, and only function actively when the movement reaches its physiological limit, at which position one of the ligaments (on the extended side) is fully stretched, and thus, being inextensible, makes further movement impossible, unless the ligament is torn (as in a "sprain"). The function of holding the ends of the bones fully together falls to the muscles controlling movement at the joint and more indirectly, to fat and fleshy parts of the body surrounding the joint.

The particular action of the muscles is discussed in the module on Muscles and Muscular action. For the present it will suffice to point out that the muscles are "stabilizers" of the joint. The latter is always surrounded by at least two sets of muscles: 1) the one performing movement in a direction opposite to that of the other. In a normal condition every muscle exerts a certain constant degree of pull, and this simultaneous pull on both sides of the joint presses one bone surface more or less firmly upon the other, making possible an immediate response to a nerve stimulus.^[3] Through the analysis of joint-structure we open the doorway of information to the effect of the 1) choice of fingering and, to some extent, control of tone.

[1]synovial membranes:The synovial membrane (also known as the synovial stratum, synovium or stratum synoviale) is a specialized connective tissue that lines the inner surface of capsules of synovial joints and tendon sheath.

[2]albumen (noun). [L. < albus, white] 1) the white of an egg, 2) the nutritive protein substance in germinating plant and animal cells.

[3]synovia: [Modern Latin: coined by Paracelsus < ?] the clear, albuminous lubricating fluid secreted by the membrances of joint cavities, tendons sheaths, etc. - synovial adj.

[4] nerve stimulus: 1) The movement of action potential along a nerve fiber in response to a stimulus (such as touching the keyboard). (2) The relaying of a coded signal that travels along a nerve cell membrane to an effector, such as muscle, gland or another nerve cell.