Anatomy, Shoulder and Upper Limb, Hand Anatomical Snuff Box

Article Author:
Sasha Hallett
Article Editor:
John Ashurst
Updated:
9/12/2018 9:28:50 PM
PubMed Link:
Anatomy, Shoulder and Upper Limb, Hand Anatomical Snuff Box

Introduction

The anatomical snuffbox is a surface anatomy feature described as a triangular depression on the dorsum of the hand at the base of the thumb. The anatomical snuffbox is visible with ulnar deviation of the wrist and extension and abduction of the thumb. Its name was derived from using the depression as a means of placement for the inhalation of powdered tobacco, otherwise known as dry snuff, and was first described in the medical literature in 1850. However, the anatomical snuffbox was not introduced into anatomy textbooks until the early 1900s when it was described by Germain Cloquet and Marie Francois Bichat.

Anatomically, the anatomical snuffbox is bordered medially by the tendons of the muscle named the extensor pollicis longus, and laterally by the tendons of the muscles named the extensor pollicis brevis and the abductor pollicis longus. The floor of the anatomical snuffbox is formed by the scaphoid bone and trapezium bone of the wrist, as well as the tendons of the muscle named the extensor carpi radialis longus and the muscle named the extensor carpi radialis brevis. The base of the first metacarpal bone can be palpated distally, and the styloid process of the radius can be palpated proximally. Contained within the anatomical snuffbox are the radial artery, the superficial branches of the radial nerve, and the cephalic vein.

Structure and Function

The anatomical snuffbox is merely a surface anatomy characteristic and functions in context with other anatomical features. By knowing the boundaries of and contents of the anatomical snuff box, a healthcare provider can generate a differential diagnosis when a patient complains of pain in the area. For example, tenderness to palpation in the anatomical snuffbox after a fall on an outstretched hand is indicative of a scaphoid fracture and would require further testing, including radiologic x-rays, to accurately make the definitive diagnosis. Knowledge of the contents of the anatomical snuffbox will also aid the healthcare provider in those patients with difficult vascular access because both the radial artery and the cephalic vein lie within this area.

Blood Supply and Lymphatics

Although the anatomical snuffbox does not have its own blood supply, several vessels course through the boundaries of this surface anatomy feature. Both the cephalic vein and radial artery lie within the anatomical snuffbox. However, the branches of the radial artery are the most discussed in the practice of medicine due to their supply of the scaphoid bone. Direct branches from the radial artery supply 80% of the proximal scaphoid through intraosseous retrograde flow through the articular foramina, while the remainder is supplied via the volar scaphoid branches of the radial artery that enter at the distal pole. Avascular necrosis of the scaphoid bone commonly occurs due to the unique flow found in the anatomical snuffbox to the scaphoid bone.

Nerves

The superficial nerve branches of the radial nerve that reside within the anatomical snuffbox can be rolled over the tendon of the muscle named the extensor pollicis longus. The tendon of this muscle serves as the medial border of the anatomical snuffbox.

Muscles

The anatomical snuffbox is bordered medially by the tendons of the muscle named the extensor pollicis longus, and laterally by the tendons of the muscles named the extensor pollicis brevis and the abductor pollicis longus. The floor of the anatomical snuffbox is partially formed by the tendons of the muscle named the extensor carpi radialis longus and the muscle named the extensor carpi radialis brevis.

Physiologic Variants

Through anatomical research, multiple variations of the tendons of the anatomical snuffbox have been discovered. Both the extensor pollicis longus and the abductor pollicis longus have been shown to have not only numerous tendon slips but also different areas of insertion. This is clinically significant because it may predispose an individual patient to the development of tendinopathy of either the extensor pollicis longus or the abductor pollicis longus. Surgical management, if needed, would also be affected because of these numerous variations in tendon location.

Through similar cadaveric research, multiple variations have been noted in the location of the cephalic vein and the radial artery. Clinically this is important because intravenous access can be obtained in the anatomical snuffbox and inadvertent arterial puncture may cause a pseudo-aneurysm, arterial occlusion, or hematoma.

Surgical Considerations

The superficial branch of the radial nerve is the third most common peripheral nerve injury and will cause an area of paresthesia over the dorsum of the first web space on the hand. Surgeons should be aware of its varied location within the anatomical snuffbox to avoid injury.

Clinical Significance

The anatomical snuffbox is clinically significant when there is pain with palpation within its boundaries. Scaphoid fractures account for two-thirds of all carpal bone fractures and are commonly misdiagnosed. The most common form of injury is when a patient falls onto an outstretched hand when it is pronated and deviated ulnarly. The hallmark of anatomic snuffbox tenderness is highly sensitive for scaphoid fractures but lacks specificity. Due to the lack of specificity, those with snuffbox tenderness should undergo radiographic studies of the wrist. Those with initial negative imaging can be managed with either a thumb spica short armed splint or advanced imaging by MRI or CT to determine if a fracture exists. Given the unique blood flow to the scaphoid, fracture location is important in determining treatment options to prevent avascular necrosis of the bone.

De Quervain tenosynovitis is a second diagnosis that is clinically significant in relation to the anatomical snuffbox. De Quervain tenosynovitis is a stenosing tendinopathy that affects the first dorsal compartment, which includes the muscle named the abductor pollicis longus and the muscle named the extensor pollicis brevis, both of which are lateral borders of the anatomical snuffbox. Diagnosis can be made based on a thorough history and physical examination. History may include repetitive hand motions in which repeated radio-ulnar deviation occurs. Patients will typically present with pain or swelling over the dorsal aspect of the wrist with associated aggravation of symptoms with the forced resistance of the thumb. Treatment typically includes conservative therapy with NSAIDs, corticosteroids, physical therapy, or splinting in a thumb spica splint. Surgery is reserved for refractory symptomology.