In the case of pain with extension of the thumb, this is typically caused by inflammation and irritation of the thumb tendons
that run under a tunnel-like band of tissue called the first extensor compartment retinaculum on the thumb side of the wrist. This tissue holds the thumb tendons close to the wrist or radius bone when you extend your thumb. Repeated rubbing of the tendons under the retinaculum can result in pain with movements of the thumb or wrist. This condition may be called deQuervain’s tenosynovitis
If there iscatching, “popping,” or locking located where the thumb joins the hand while the thumb is bent or extended, that could be a condition called trigger thumb. Pain is typically present on the palm side the thumb. Triggering with thumb flexion, such as with pushing a button on the phone, results from the flexor tendon becoming inflamed under the tunnel, called the first pulley, that the tendon passes through as it moves from the hand into the thumb. The pulley holds the tendon close to the bone.
In both deQuervain’s tenosynovitis and trigger thumb, the tendons run through a synovial sheath that serves as a lubricant that helps the tendon glide during motion. The tendon has a thin lining called tenosynovium. This lining may thicken in these conditions, making the tendon thicker. The sheath has a confined area and does not change in size. When the tendon or tendon lining traveling through the sheath becomes enlarged, the tendons get caught in the tunnels (retinaculum or pulley), which causes pain, triggering, or even locking.
Weakness, cramping, or muscle ache occurs from thumb muscle fatigue. The muscle can even spasm and shake. If the blood flow to the muscle is limited from the position you are holding the device, then the area will cramp initially and then ache for a few days as it recovers. Carpal tunnel syndrome
or cubital tunnel syndrome
numbness in the thumb or pinky may also be the cause of numbness in your thumb from how you are holding your wrist or your elbows while using the device.