Muscles of The Hand

There are 20 muscles in the hand. As junior doctor we must know the names of these muscles. They can be asked directly or indirectly in any competitive exams. They are:                                      

• Thenar group – 4 muscles
• Hypothenar group – 4 muscles
• Lumbricals – 4 muscles
• Palmar interossei – 4 muscles
• Dorsal Interossei – 4 muscles

We shall read about each group in detail in this blog.

Thenar Muscles

These group of muscles are supplied by the medial nerve.

• Abductor pollicis Brevis
• Flexor pollicis Brevis
• Opponens pollicis
• Palmaris brevis : Subcutaneous muscle, not included in hypothenar region.

Hypothenar Muscles

The hypothenar muscles are supplied by the ulnar nerve. They are 

• Abductor digiti minimi
• Flexor digiti minimi
• Opponens digiti minimi
• Palmaris brevis 

The Adductor pollicis Brevis is a deep muscle which is Supplied by deep branch of ulnar nerve.

Flexor pollicis Brevis and Opponens pollicis are hybrid muscles which re supplied by both median and ulnar nerve.

Lumbricals

There are 4 lumbricles. They originate from the Flexor digitorum profundus tendon laterally. FDP tendon Insertion is at the base of distal phalanx . The 1^st and 2^nd lumbricals are unipennate & 3^rd and 4^th lumbricals are bipennate

FDP is a hybrid muscle supplied by median and ulnar nerve. Therefore,  

•  1^st and 2^nd lumbricals supplied by median nerve. 
• 3^rd and 4^th lumbricals supplied by ulnar nerve.

Lumbricals cross the MCP joint anteriorly helps in flexion. And attach to proximal phalanx in dorsal digital extension helps in Interphalangeal extension. Function of lumbricals: flexion of MCP joints (Metacarpophalangeal joints) and Extension of IP (Interphalangeal joints)

8 interossei

There are 8 interosseus muscles. 

• 4 Palmar interossei → for adduction
• 4 Dorsal Interossei → for abduction
• PAD→Palmar for adduction
• DAB→Dorsal for abduction

The Middle finger has 2 dorsal interossei I.e., D2 and has no palmar interossei (in middle finger) I.e., P0.

The 4 Palmar interossei are Unipennate muscles and the 4 Dorsal Interossei are Bipennate muscles. The Palmar interossei helps in adding the fingers towards the middle finger i.e., adduction. The Dorsal interossei helps in spreading the fingers away from the middle finger i.e., abduction. The Nerve supply: Deep branch of ulnar nerve supplies 4 Palmar interossei and 4 Dorsal Interossei.

Clinical Tests 

We can test the Palmar Interossei by Taking a card and inserting it between the patient’s finger. We then ask the patient to hold the card and try to pull the card and you will find some resistance. Palmar interossei helps to hold the card, if it is weak the patient can’t hold the card. 

To Test Dorsal Interossei we Ask the patient to spread the fingers and you prevent that, you will feel the resistance. These are the tests to test the ulnar nerve.

12 muscles: 4 lumbricals, 4 Palmar interossei and 4 Dorsal Interossei. Helps in 2 functions: MCP flexion – folding knuckle joint and IP Extension.

Muscle of posterior forearm 

Extensor digitorum has its origin from lateral epicondyle and sends it four tendons to four fingers for extension. This muscle crosses wrist joint, MCP joint, PIP and DIP joint and causes extension in all joints.

Dorsal digital expansion (DDE) is the triangular modification of the insertion of the extensor digitorum tendon and keep receiving the insertion of few muscles as well. That results in extension of PIP and DIP joints. E.g., in middle finger DDE there is insertion of 2 dorsal interossei and lumbrical muscle

Claw Hand

Klumpke’s Palsy

Here the Lesion is pulling lower trunk of brachial plexus, due to which T1 root value is compromised distal hand muscles and the  lumbricals and interossei also gets compromised which causes CLAW HAND. Normally lumbricals and interossei are balancing the forearm muscles, if they are not working forearm muscles become more powerful and results in claw hand deformity. MCP JOINT unable to flex results in hyperextension of MCP joint  due to unopposed action of extensor digitorum tendon. IP joints unable extend and results in IP flexion deformity  due to unopposed action of Anterior forearm muscle like FDP and FDS. in conclusion there is MCP hyperextension + IP flexion which results in CLAW HAND.

Frequently Asked Questions

Q. Identify the function of the shown muscles in the diagram.

1. Flexion at IP joint
2. Extension at MCP joint
3. Flexion at MCP joint
4. Abduction at MCP joint

Answer: Flexion at MCP joint

Q: Which root is affected in klumpke’s paralysis?

Answer: T1

Q: Klumpke’s paralysis causes what clinically visual sign?

Answer: Claw hand

Q: What is the card test used for?

Answer: Palmar Interossei 

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