Open Wounds in the Hand
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: 1- Trapezium, 2- Trapezoid, 3- Capitate, 4 Hamate, and in the proximal row starting on the thumb side the 5- Scaphoid, 6- Lunate and 7- Triquetrum. 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
Open wounds at the hand imply the disruption of the skin with exposure of deeper structures. Depending on the mechanism of injury, these wounds can present as sharp lacerations, a crush component that if severe enough will tear the skin apart, a pulling force (avulsion), shearing and saw injuries that will produce a sharp or a ragged edge on the tissues depending on the thickness of the saw. Any combination of the above type of injuries can happen.
Open wounds can be classified as superficial when they remain above the level of the deep fascia, which is a whitish looking, well defined envelope covering the tendons, muscles, deep nerves and arteries. A superficialwound can involve the skin, subcutaneous tissue (fat) and superficial vessels or nerves. All wounds demand immediate assessment and treatment by a trained hand surgeon to correctly identify the injured structures. A superficialwound can be treated in an emergency room setting and a hand specialist contacted to discuss a clear treatment plan. The patient should then be seen by a hand specialist for further evaluation and recommendation. Tetanus is updated if it has been longer than 10 years since receiving a tetanus shot or if the wound is a dirty wound, then the tetanus is updated if it has been five years since receiving a tetanus shot. This is to avoid the danger of acquiring gas gangrene that can be deadly. The use of oral antibiotics for one week after a repair is used as a prophylaxis to avoid the risk of infection. Special splints are applied after the procedure for comfort or protection. The injured extremity must be elevated to at least heart level to avoid swelling of the limb that can cause moderate pain, cut off the blood supply and delay wound healing.
Some of these cases will require urgent exploration, debridement (surgical cleaning that is deeper and more thorough than a regular wash out in the emergency room), and repair of superficial nerves. This should be done as soon as possible within a week time from injury. Some of these cases may require only close observation for the wounds to appropriately heal if the physical exam indicates that the tendons, nerves and vessels are intact.
A deepwound can involve the above mentioned structures and a number of deep tendons, muscles, nerves and arteries. The degree of contamination, the extent and severity of the injury will demand different urgency of treatment that only a qualified health care professional can appropriately assess. Emergency treatment of a deep wound can receive initial cleaning by a emergency health care professional, and any bleeders can be controlled at that time by gentle pressure or by direct suturing and the laceration can be closed after a thorough preliminary assessment has been done and a hand specialist has been contacted to discuss appropriate definitive treatment recommendations. Many of these injuries can be referred to a hand specialist for further evaluation and recommendations in an URGENT within a one week time. At ROC, however, we also offer emergency treatment of the injury if the patient is ready to proceed with surgery and has the appropriate medical clearance to have the surgery performed.
Some patients may present with severe contamination, incontrollable bleeding, presence of a foreign body (glass), a pulseless extremity (that is at the highest risk for loosing tissue), open joint or other associated injuries like an open fracture that demand EMERGENT surgical care the moment it presents. In these cases the patients need to be stabilized, the hand specialist needs to be contacted immediately to communicate the emergent need of attention and organize appropriate routes and locations for triage of the patient or the patient can present directly to ROC where a hand specialist is always present.
Treatment
Thorough knowledge of anatomy, hand and microsurgical techniques is the key in dealing with open hand injuries that frequently involve multiple structures. This is why training in a specialized hand fellowship program for one year to be a certified hand surgeon is vital for the best possible outcomes to be obtained.
The treatment of an open wound begins with obtaining a clear history to determine the lacerating instrument, the position of the arm and hand during the laceration, the direction and depth of the laceration. The exam will point to the injured tissue and the history will provide the direction the wound should be extended during exploration. The cleaning of the wound, repair of muscle, artery and tendon is done best with the use of magnifying glasses called loupes in a bloodless field by the use of a tourniquet. The improved magnification allows for more accurate determination of the injured and contaminated tissue allowing an accurate repair. From the wrist to the finger tips, the use of a microscope permits the most accurate repair of all tissue structures, particularly the arteries, veins and nerves.
Tetanus is updated if it has been longer than 10 years since receiving a tetanus shot or if the wound is a dirty wound, then the tetanus is updated if it has been five years since receiving a tetanus shot. This is to avoid the danger of acquiring gas gangrene that can be deadly. The use of oral antibiotics for one week after a repair is used as a prophylaxis to avoid the risk of infection. Special splints are applied after surgery for protection and prevent certain movements the patient might inadvertently do. The injured extremity after sugery must be elevated to at least heart level to avoid swelling of the limb that causes moderate pain, cut off the blood supply and delay wound healing. Depending on whether the wound is superficial or deep and the association of other injuries, your surgeon at ROC will elaborate a treatment plan. Please refer to the section on Tendon, Nerve and Vessel Injuries or Fractures to review the pertinent information if you wish to learn more about it.