Reconstructive Orthopedic Center

Hand Mass/Tumors

Normal Wrist Anatomy and biomechanics

The wrist is a biomechanically complex joint allowing the wrist to move in extension (up), flexion (down), radial deviation (towards the thumb), ulnar deviation (towards the small finger) and minimal degrees of rotation. Functionally the wrist’s primary role, like the shoulder and elbow, is to position the hand in space. This accurate positioning, allows the hand to perform a vast array of activities that range from skillful manipulation of fine objects to handling heavy objects, including supporting the entire body weight.
To understand the wrist we arbitrarily divide it into 3 layers:

First layer corresponds to the bones
Second layer corresponds to the capsule and ligaments
Third layer corresponds to the remaining soft tissues (tendons, muscles, nerves, vessels)

These three layers are covered by the skin which we will discuss below.
The first layer or bonylayer begins at the metacarpal bases distally (finger side), and extends towards the very end of the forearm bones proximally (elbow side). The bones comprising the wrist include the 5 metacarpal bases, 8 carpal bones (wrist bones) which are organized in 2 rows and the distal ends of the radius and ulna (forearm bones). From distal (finger side) to proximal (elbow side), these bones form the following joints:

The five carpo-metacarpal(CMC) joints, midcarpal joint, radiocarpal joint, ulnocarpal jointand thedistal radio-ulnar joint (DRUJ).

The First CMC joint is at the base of the thumb and articulates with the trapezium, a carpal wrist bone, shaped like a horse’s saddle, that permits a wide range of motion including thumb rotation of 120 degrees, distinguishing humans from other mammals. The First Metacarpal and Trapezium are supported by a strong set of ligaments that surroundthe joint (second layer) allowing stable, thumb opposition against the rest of the fingers. The ability to oppose the thumb is responsible for 40 % of the function generated by the hand. The CMC joints of the 2nd and 3rd digits have minimal motion secondary to short, taut ligaments that surround the joint at the 2nd (index) and 3rd (middle) metacarpals bases and the distal end of the carpal bones including the Trapezium,Trapezoid and Hamate bones. This unit serves as the stable foundation around which the thumb, ring and small finger metacarpals move around. The CMC joints of the ring and small fingers are formed by 4th and 5th metacarpals, capitate and hamate wrist bones. These joints are more mobile and together with the 1st metacarpal create a gutter or cup configuration in the palm of the hand that facilitates the gripping of instruments and small objects.

The carpal bones comprise 8 wrist bones that function as a unit by virtue of having limited motion between each other. Only 7 of the 8 carpal (wrist) bones play a significant functional role in wrist stability and mobility.
The 7 important bones are named starting at the distal row (finger side) and from the thumb side:

The Pisiform is the eighth bone but does not play a functional role, however, it can be a source of wrist pain when sustaining a fracture or as a consequence of degenerative arthritis in the pisotriquetral articulation. The carpal bones are almost entirely covered by cartilage and receive their limited blood supply through small vessel branches that enter the bones through little tunnels where the ligaments attach.
Just proximal to the carpal bones (elbow side) are the Radius and Ulna whose articular surfaces form a cup that complements the carpal bones. Together, they form the radiocarpal joint that serves to support the proximal carpal row in a functional ball and socket mechanism. The radius with a much larger articular surface to cradle the carpus, transfers about 80 % of the wrist load. The radius and ulna have a second joint that provides forearm rotation called the Distal Radio Ulnar Joint (DRUJ). The Triangular FibroCartilage Complex is a fibrous structure containing collagenous fibers (ligaments) embedded in a fibrocartilage matrix that complements the distal end of the radius and ulna to complete the cup configuration. The DRUJ provides a cushion between the carpus and the distal ulna and is considered the main stabilizer of the DRUJ. For full normal forearm rotation to occur, the DRUJ is complemented at the elbow by a joint called the proximal radio-ulnar joint (PRUJ).

The Second Layeris composed of the wrist ligaments, a complex intermingling of collagen fibers that join the metacarpals to the carpals and to the radius and ulna, creating stable, balanced wrist motion during our daily activities. These ligaments are taut structures embedded in a thin capsule that function to reinforce key areas of the wrist. Between the carpal bones, a deeper layer of ligaments, called the intra-carpal ligaments, allow a restricted amount of motion and is the reason that the carpal bones function as a unit. The shape and position of the carpal bones is critical for proper function and when injury occurs, it is of vital importance to re-establish the bone anatomic shapes if normal function is to be achieved.

The Third Layer is formed by the tendons, muscles, vessels and nerves.
The tendons about the wrist are divided into flexors (palmar side) and extensors (back hand side). The extensor tendons are in the back of the wrist and travel through 6 independent compartments having 9 of these tendons corresponding to finger motion and 3 tendons corresponding to wrist motion. Compartments 1 and 3 controls the thumb tendons, compartments 2 and 6 the wrist extensors and compartments 4 and 5 the finger extensors.

There are nine flexor tendons that travel through a fibro-osseous tunnel at the wrist called the carpal canal. It is formed by the carpal bones and the transverse carpal ligament. There are three tendons that flex the wrist but only one of these three, the flexor carpi radialis, travels in an independent wrist compartment in the carpal canal.

Radial Artery Ulnar Artery

The primary vessels or channels that supply blood to the hand while traveling across the wrist are the Radial and Ulnar Arteries. An arcade of smaller branches that interconnect the radial and ulnar arteriesare safety pathways that allow the continuation of blood flow if the radial and ulnar artery becomes occluded. The blood returns to the heart through the veins which are more prominent in the back of the hand and wrist. The major nerves about the wrist are the Median nerve that travels together with the 9 flexor tendons in the carpal tunnel, the Ulnar nerve that together with the ulnar artery travel through Guyon’s canal and the Radial nerve in the back of the forearm. Terminal smaller branches provide sensation to the superficial and deeper levels within the wrist.

Pathology

- The most frequent swelling or masses found at the hand and wrist level are ganglion cysts.
Ganglion cysts in the wrist are more frequent in women, but in the hand, ganglions form as a result of arthritis of the joints and this type of ganglion is called a mucous cyst. Ganglions are like a small balloon composed of the joint capsule, filled with a clear, colorless, gelatinous fluid that comes from the joint itself. They usually present with a single cavity but may contain multiple chambers. When ganglions occur, they usually come and go with activity but once present for more than four weeks, the likelihood of spontaneous resolution is unlikely. The reason is that the ganglion has a one way valve mechanism that allows for the fluid to come in from the jointbut makes it difficult for the fluid to return to the joint. 70 % of ganglions occur between the second and fourth decades of life, while in older age groups, they may be associated with osteoarthritis and the spurs around the joint are usually responsible for their formation. Ganglions are rarely seen in children and when present is usually due to ligamentous laxity. 60-70 % of the wrist ganglions occur on the back of the wrist over the scapholunate ligament and about 20 % are found in the front or volar side of the wrist over the scaphotrapezoid joint. The differential diagnosis of the dorsal wrist mass is abnormal muscles of the hand (extensor digitorum brevis manus), synovitis of the extensor tendons (found in patients with rheumatoid arthritis) and other masses like lipomas (fat tumors), venous aneurysms, giant cell tumors, or other soft tissue tumors.

Patients complain of pain that is aggravated with repeated use of the hand, and witness a localizedslow growing mass associated with mild aching and weakness about the area of its occurrence. On physical exam, cysts can be firm, smooth, rubbery, rounded, slightly fluctuant and at times tender. Cysts transmit the light of a penlight when in the dark. Usually cysts are fixed but may have slight mobility on exam and when a dorsal ganglion is present in the back of the wrist, it becomes more obvious when the wrist is bent (flexed). On occasion, patients will present with pain with maximal wrist extension, tenderness to palpation over the scapholunate joint but no obvious mass on inspection. This may represent an occult ganglion cyst and an MRI may be necessary for the diagnosis to be made. Ganglion cysts also arise from the tendon lining called tenosynovium and from the flexor or extensor sheaths by microdegeneration of this collagen substance.

When a ganglion is associated with an arthritic DIPJ(Distal InterPhalangeal Joint), it is called a Mucous Cyst, which is a pea-sized or smaller mass that is painful if struck. Individual patients and doctors without experience are sometimes tempted to drain it in the office. This is a mistake that will cause a sinus drainage and infection of the joint. When present, this is a surgical problem that needs to be addressed in the operating room. Other rigid masses in the region correspond to bony spurs of the arthritic joints and these do not have to be removed unless painful. Mucous cysts can create grooving of the nail plate (actual nail) when it extends far enough to reach the nail growth center called the germinal matrix of the nailbed.

Treatment

Non-operative treatment of wrist ganglions has been reported consisting of aspiration with or without steroid injections and short term splinting. In the best of the cases, only 30 to 50 % of cases are successfully treated. Technically, it is very challenging to aspirate the fluid even with a large needle because of the thickness of the fluid and also the larger the needle, the higher the risk of injury to the tendons, nerves or vessels during the procedure. Aspiration is also difficult because of collapse of the cyst and occlusion of the needle tip before complete aspiration of the fluid is accomplished. The most reliable procedure is surgical excision that can be done through a small incision at the site of the mass. In the fingers, the removal of the cysts and bony spurs cleaning the arthritic joint will result in good cosmesis and function. These procedures provide reliable outcomes with unlikely recurrence and complete resolution of symptoms and return to normal activities in most cases.

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