USMLE Guide: Musculoskeletal Anatomy of the Hand

Introduction

The musculoskeletal anatomy of the hand is an essential topic for medical students preparing for the United States Medical Licensing Examination (USMLE). This guide aims to provide a comprehensive overview of the structures and functions of the hand, enabling students to answer related questions accurately.

I. Bones of the Hand

The hand consists of numerous bones that form its structure. These bones can be divided into three groups:

1. Carpals: There are eight carpal bones in the hand, including the scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate.
2. Metacarpals: There are five metacarpal bones, each corresponding to one finger. They are numbered from the thumb (first metacarpal) to the little finger (fifth metacarpal).
3. Phalanges: Each finger contains three phalanges, except for the thumb, which only has two. These phalanges are named proximal, middle, and distal.

II. Joints of the Hand

Various joints in the hand contribute to its mobility and dexterity. These joints include:

1. Carpometacarpal joints (CMC): Located at the base of each finger, these joints connect the metacarpals to the carpal bones.
2. Metacarpophalangeal joints (MCP): These joints link the metacarpals to the proximal phalanges and allow flexion, extension, abduction, and adduction movements.
3. Interphalangeal joints (IP): Found between the phalanges, these joints enable flexion and extension of the fingers.

III. Muscles of the Hand

The muscles of the hand are responsible for generating movements and controlling fine motor skills. Here are the key muscles:

1. Intrinsic Muscles: These muscles originate and insert within the hand. They include:
   • Thenar muscles: Located at the base of the thumb, they control thumb movements.
   • Hypothenar muscles: Situated at the base of the little finger, they control movements of the little finger.
   • Interosseous muscles: Found between the metacarpal bones, they control finger abduction and adduction.
   • Lumbrical muscles: Arise from the flexor digitorum profundus tendons and assist in finger flexion.
2. Extrinsic Muscles: These muscles originate outside the hand and extend into the hand through tendons. They include:
   • Flexor muscles: Located on the palm side, they flex the fingers.
   • Extensor muscles: Situated on the back of the hand, they extend the fingers.

IV. Nerves and Blood Supply

Nerves and blood vessels play a vital role in the hand's sensory and motor functions. Key nerves and blood vessels include:

1. Median nerve: Provides motor innervation to most of the muscles in the forearm and some hand muscles. It also supplies sensation to the palm and fingers.
2. Ulnar nerve: Innervates the intrinsic hand muscles responsible for fine motor movements. It provides sensation to the ulnar side of the hand and the little finger.
3. Radial nerve: Supplies the extensor muscles of the forearm and provides sensory innervation to the back of the hand.
4. Superficial palmar arch: Arises from the ulnar artery and supplies blood to the palm and fingers.
5. Deep palmar arch: Formed by the radial artery and provides blood to the deep structures of the hand.

Conclusion

Understanding the musculoskeletal anatomy of the hand is crucial for medical students preparing for the USMLE. This guide has provided an overview of the bones, joints, muscles, nerves, and blood vessels of the hand. By mastering this information, students will be well-equipped to answer related questions on the exam and apply it to clinical scenarios.