Bones & Joints
his joint allows flexion and extension at the finger base and is the site where lumbricals exert MCP flexion while extending the PIP.
What is the metacarpophalangeal (MCP) joint?
These muscles produce the “duck hand” position via simultaneous MCP flexion and PIP extension.
What are the lumbricals?
Ulnar nerve injury at Guyon’s canal spares which intrinsic muscles due to crossover of its deep branch?
What are some thenar muscles (radial side of hand)?
Flexor tendons are prevented from bowstringing during flexion by which structures?
What are the annular and cruciate ligaments?
Carpal tunnel syndrome affects which nerve branches and why does sensation remain normal on the 5th digit?
Median nerve; 5th digit is supplied by the ulnar nerve, unaffected by carpal tunnel compression.
When forming a fist, the DIPs remain flexed while MCPs extend, creating the “claw hand.” Which muscles are non-functional to produce this?
What are the lumbricals?
Which hypothenar muscle contributes indirectly to thumb opposition during a spherical grasp?
What is opponens digiti minimi?
Radial nerve provides minimal palmar sensation. Name the area it does innervate on the palmar side.
What is the proximal lateral part of the thumb?
What anatomical difference distinguishes the palmar carpal ligament from the transverse carpal ligament in clinical terms?
Palmar carpal ligament is superficial and spans the wrist; transverse carpal ligament forms the carpal tunnel roof, critical in carpal tunnel syndrome.
Mallet finger results from disruption of which tendon structure, and why does PIP extension remain intact?
Lateral bands of the extensor tendon at the distal phalanx; middle band attaching to the middle phalanx remains intact.
Only the thumb has this single interphalangeal joint. What structural advantage does this confer for opposition?
What is the IP joint? It allows simpler hinge motion facilitating precise thumb-to-finger opposition.
When abducting all fingers simultaneously, which group of muscles is active, and what mnemonic helps you remember this?
What are the dorsal interossei? (Mnemonic: DAB = Dorsal ABduct)
Which nerve injury would produce a hand of Benediction when the patient tries to make a fist? Explain why.
What is median nerve injury? Loss of lateral two lumbricals prevents flexion at MCP of digits 2–3.
Which ligament must be cut during carpal tunnel release surgery?
What is the transverse carpal ligament (flexor retinaculum)?
Which hand arteries form a redundant circuit, explaining why isolated ulnar artery compression rarely causes ischemia?
Superficial and deep palmar arches.
In a patient with loss of PIP extension but intact DIP extension, which part of the extensor mechanism is likely damaged?
What is the central band (middle part of extensor hood attaching to middle phalanx)?
Which muscle prevents palmar bowstringing and enhances tension on the palmar aponeurosis, and how is its evolutionary function different in cats?
What is palmaris longus? In cats, it retracts the claws; in humans, it primarily tensions the palmar fascia.
Explain why ulnar nerve lesions can affect both hypothenar wasting and some thumb movements.
Because the deep branch of the ulnar nerve wraps around to innervate some thenar muscles, contributing to thumb adduction/opposition.
Explain why swelling in the flexor tendon sheath can cause trigger finger.
A nodule in the tendon cannot slide through annular ligament tunnels, causing a catching or locking phenomenon.
Why might partial median or ulnar nerve injuries produce unusual two-finger deformities?
Because lumbricals and interossei have mixed innervation; partial denervation selectively impairs some fingers.
Which hand joint’s instability is most likely to cause abnormal “intrinsic minus” positioning, and why?
What is the MCP joint? Because loss of lumbrical function allows MCP hyperextension while PIPs and DIPs flex.
Name the intrinsic hand muscles that receive dual innervation and explain the clinical significance in partial ulnar nerve lesions.
What are the lumbricals? Lateral two = median nerve, medial two = ulnar nerve; partial ulnar lesions spare lateral lumbricals, altering the claw hand pattern.
A patient has clawing of the 4th and 5th digits but normal sensation in the thumb, index, and middle. Which nerve is injured and at what location?
What is the ulnar nerve at the elbow or wrist (proximal to Guyon’s canal)?
Which ligamentous tunnel could compress the ulnar artery without significantly compromising hand perfusion, and why?
What is Guyon’s canal? Redundant blood flow from the superficial and deep palmar arches maintains circulation.
Explain the biomechanical role of palmaris longus and palmaris brevis in enhancing intrinsic hand muscle function.
Tension the palmar fascia/aponeurosis, stabilizing the palm to allow efficient contraction of intrinsic muscles for grip and opposition.