Trigger Finger (Stenosing Tenosynovitis): This condition is characterized by the tendon sheath becoming inflamed and narrowing, causing the tendon to catch or lock as it moves through the sheath, leading to the finger locking up. The ring finger is one of the most common fingers affected by this condition.

Dupuytren's Contracture: A condition where one or more fingers become permanently bent in a flexed position, often affecting the ring finger. It's caused by thickening of the palmar fascia.
Flexor Tendon Injury: An injury to the flexor tendons, which are responsible for bending the fingers, could lead to locking or inability to bend the finger.
Arthritis (Osteoarthritis or Rheumatoid Arthritis): Both forms of arthritis can cause stiffness, pain, and limited mobility in the fingers, potentially leading to a sensation of locking.

Infection (Septic Arthritis or Osteomyelitis): Although less common, an infection in the joint or bone of the finger can cause severe pain, swelling, and limited mobility, which might be mistaken for locking.
Tumor (Benign or Malignant): A tumor in the finger, though rare, could cause mechanical obstruction or nerve compression leading to locking or inability to move the finger.
Neurological Conditions (e.g., Peripheral Neuropathy): Certain neurological conditions can affect the nerves controlling the muscles of the hand, leading to weakness or paralysis of the finger.

Ganglion Cyst: A non-cancerous lump that can develop on the wrist or finger, potentially causing pressure on the tendons or nerves, leading to locking or limited mobility.
Scleroderma: A chronic disease characterized by deposition of collagen, leading to thickening and hardening of skin and connective tissue, which can affect the fingers and cause limited mobility.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, potentially leading to joint hypermobility or instability that might be perceived as locking.