Structure and function of connective tissues and joints practice questions.

A javelin thrower rotates the humerus through a very large range during the cocking phase. Which classification of the glenohumeral joint accounts for that range?

• Ball-and-socket joint with three degrees of freedom
• Condyloid joint with two degrees of freedom
• Hinge joint with one degree of freedom
• Pivot joint that permits rotation about a single longitudinal axis

Answer: Ball-and-socket joint with three degrees of freedom

A ball-and-socket joint permits movement in all three planes, which is why the shoulder is the most mobile joint in the body. The mobility is bought at the cost of stability, so the shallow socket relies on the labrum, capsule and rotator cuff.

During a warm-up a swimmer performs progressively larger arm circles and the shoulder feels looser. Which change at the joint best explains the easier movement?

• The resting length of the joint capsule is shortened
• Synovial fluid becomes less viscous, so friction between the joint surfaces falls
• The articular cartilage is stiffened so that it resists compressive loading better
• Extra collagen fibres are laid down in the surrounding ligaments

Answer: Synovial fluid becomes less viscous, so friction between the joint surfaces falls

Synovial fluid is secreted by the synovial membrane; movement and the rise in joint temperature lower its viscosity, so the articular surfaces slide more easily. The fluid also nourishes the avascular articular cartilage by diffusion.

The menisci of the knee are made of fibrocartilage. Which function does this tissue perform for a footballer landing after a header?

• Secreting the fluid that lubricates the joint cavity
• Attaching the quadriceps group directly to the tibial tuberosity
• Producing the force that extends the knee on landing
• Spreading the compressive load over a wider joint surface

Answer: Spreading the compressive load over a wider joint surface

Fibrocartilage is dense and compressible, so the menisci deepen the tibial plateau and spread the impact force over a wider area, lowering the peak stress on the articular cartilage. Secretion of fluid is the job of the synovial membrane and force production the job of muscle.

After a second shoulder dislocation a rugby player is told that the glenohumeral joint capsule has been stretched. What does the joint lose as a result?

• The supply of synovial fluid, because the capsule rather than its lining secretes that fluid into the cavity
• Passive restraint at the end of range, so the humeral head can travel further out of the socket
• The ability of the articular cartilage to absorb compressive load when the arm is loaded
• The elastic energy that the rotator cuff tendons store during the cocking phase of a throw

Answer: Passive restraint at the end of range, so the humeral head can travel further out of the socket

The fibrous capsule joins the two bones and, with the glenohumeral ligaments it thickens into, brakes movement at the end of the range; once it is stretched that passive brake is gone and the joint depends on muscular control. The synovial membrane lining the capsule, not the capsule itself, secretes the fluid.

Which feature of a ligament allows a joint to move normally through its range while still being checked at the end of that range?

• Its collagen fibres lie in a slight wave that straightens under load
• It contains contractile fibres that actively shorten as the joint moves
• It is attached to bone at one end only and moves at the other
• It is made of elastic tissue and returns freely to its length

Answer: Its collagen fibres lie in a slight wave that straightens under load

The crimped collagen straightens out over the early part of the range, offering little resistance, and resists strongly once it is taut, which is what makes a ligament a check rather than a brake throughout. A ligament contains no contractile tissue and is anchored to bone at both ends.

Which type of cartilage forms the smooth surface covering the head of the femur where it articulates within the hip joint of a runner?

• Fibrocartilage
• Elastic cartilage
• Hyaline cartilage
• Calcified cartilage

Answer: Hyaline cartilage

Hyaline cartilage forms the articular surfaces of synovial joints and provides an extremely low-friction covering that spreads load. Fibrocartilage is the tougher tissue of the menisci and the intervertebral discs, where the demand is for load-bearing and shock absorption rather than a sliding surface.