Open Wounds at the Wrist
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:
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1- First layer corresponds to the bones
2- Second layer corresponds to the capsule and ligaments
3- 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 wrist wounds indicate the skin is breached, the wound contaminated and exposure with potential injury of deeper structuresis a possibility. Depending on the mechanism of injury, the wounds can occur after sharp lacerations from a knife or saw injuries, a crushing injury,an avulsion injury or any combination of the above type of injuries.
Open wounds are classified as superficial when they remain above the level of the deep which covers the tendons, muscles, major nerves and arteries in the wrist. A superficial wound can involve the skin, subcutaneous tissue (fat) and the superficial vessels or nerves. All wounds demand immediate assessment and treatment by a specialistto avoid the risk of injection and confirm the exact tissue injured for a treatment plan to be instituted timely. The degree of contamination, the extent and the severity of the injury must be documented and addressed promptly in an emergency approach, usually the same day of injury. A superficial wound and laceration can be cleaned and sutured after a hand specialist has been made aware of the extent of the injury and an appropriate treatment plan formulated. Tetanus is updated if it has been longer than 10 years since receiving a tetanus shot or if the wound is dirty, then the tetanus is updated if it has been five years since receiving a tetanus shot. This is to avoid the risk of acquiring gas gangrene that can be deadly. The use of oral antibiotics for one week after a repair is commonly used as a prophylaxis to avoid the risk of infection. Special splints are applied after the procedure for comfort and protection. The injured extremity must be elevated to at least heart level to avoid swelling which can cause moderate pain, cut off the blood supply and delay wound healing.
The treatment of superficial wounds 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 any major cutaneous nerves that run superficially in the subcutaneous tissue. The repair should be done within a week after injury.
A deep open wound 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 determine if surgery is done the night of injury or within one week of injury. Some patients present with severe contamination, uncontrollable bleeding, presence of a foreign body (glass, metal fragments), a pulseless extremity, an open fracture or open joint requiring immediate care the night of injury.
Thorough knowledge of the hand anatomy and microsurgical techniques is key in dealing with thesekind of injuries that frequently involve multiple structures. These injuries require a specialty trained hand surgeon knowledgeable of the variety of tissues that need repair. An orthopedic surgeon or plastic surgeon that has not done a fellowship in the area of hand surgery is not qualified to repair these complex injuries.
Tendons are the continuation of muscles responsible for joint mobility and strength. When a laceration involves more than 30 -50% of the tendon diameter, there is significant loss of tension resistance and a risk of tendon triggering or a delayed complete rupture. It is important to explorethe wound to accurately to determine the severity and types of tissues injured. Tendon repairs take approximately 6 weeks to heal and regain about 80 % of their original strength in approximately 10 weeks and up to 95 % of their original strength at final healing. There are several techniques for tendon repairs using different types of sutures and suturing techniques that will determine the level of initial strength the repair possesses and the amount of active or passive motion that can be done safely to avoid tendon ruptures during the time healing is occurring.
Tendons lacerated about the wrist should be repaired with sufficiently strong techniques to permit early mobilization. When there is tissue loss creating a large defect on the tendon, tendon grafts or tendon transfers will be required to regain preinjury function. A repaired or reconstructed tendon will require initial protection in a splint for the first four to six weeks. A hand therapy program for tendon repair will initially focus on techniques to control pain, decrease swelling/edema, initiate and increase protected tendon gliding, advancing to differential tissue plane gliding that avoids scarring which limits motion and decreases the final functional outcome.
Nerves have a spectrum of injury that has been classified according to theinjury severity into 5 Grades known as Sunderland Grades I through V. Grade I and II are the most benign and will recover function within weeks on injury without the need for surgery. Grades IV and V represent a severe injury demanding surgical intervention for function to be recovered. Grade III has variableoutcomes requiring careful evaluation if surgery is to be performed.
Once a nerve is repaired, the axon must re-grow from the point where the injury occurredto the end organ it innervates. In addition, if the final target organ is a muscle, there is only a certain amount of time available for the nerve to reach the target organ and allow the muscle to remain viable. If this does not happen within that time frame, the muscle dies and function will never recover for those muscles. This time frame is about six months after a nerve injury. Sensory nerves can have a more prolonged time frame to reinnervate their sensory end organs which is believed to be as long as several years.
Vessels are the pipes where the blood flows through and supplies oxygen and other nutrients to the multiple tissues in the body. Tissue survival depends directly on sufficient blood supply provided by the arteries. The vessels that bring the blood back to the heart are called veins. At the level of the wrist there are two main arteries that supply most of the blood in the hand. Two main venous systems exist but when injured or occluded, new veins can grow as long as the hand has at least one sufficient vein for outflow. If either the radial or ulnar artery is injured, the intact artery can maintain sufficient blood supply to keep the tissues in the hand alive. When the two main arteries of the wrist and hand have been transected, it is imperative to re-establish blood flow in a timely fashion to prevent tissue death.
Nerve and Vessel (arteries and veins) lacerations about the wrist require of microsurgical techniques for repair that involve the use of magnification (loupes/ microscope), special fine instruments called jeweler instruments for the handling of the tissue and very fine suture not visible to the naked eye. Microsurgical techniques require specialized training in hand and microsurgery.
A nerve repair takes approximately 2- 4 weeks for the new axons (nerve fibers) to cross the line of repair and subsequently advances at a pace of approximately 1 mm per day. Therefore, if a nerve laceration occurred at 10 cm proximal to the final target organ, it will take approximately 100 days plus 30 more days to cross the repair site or 130 days to reach the final target organ after repair. The outcome for nerve repair is influenced by technical factors that depends on surgeon competence (tension free repair, proper fascicular alignment, appropriate bed), age (age less than 35 years hasa better prognosis), general health status and smoking habits amongst others.
The average percentage of success in small vessel repair is 95- 97 %. Patients that have had a vessel repaired through microsurgical techniques may have to remain in the hospital for 5 days on blood thinners, appropriate temperature control, extremity elevation, fluid maintenance, immobilization, and the avoidance of caffeine products and chocolates to increase the success of the repair. Therapy geared towards nerve repairs will include various modalities such as nerve glide exercises, desensitization, neuromuscular re-education, bio-feedback, functional electric stimulation, sensory re-education, strengthening and splinting as indicated.