PART VIII
HAND
CHAPTER 70 FUNCTIONAL ANATOMY AND PRINCIPLES OF UPPER EXTREMITY-SURGERY
KATE W. NELLANS AND KEVIN C. CHUNG
INTRODUCTION
This chapter presents the common elements in the evaluation and conduct of hand surgery.
FUNCTIONAL ANATOMY
Hand and Digits
The thumb is a unique and specialized digit with tremendous mobility and strength, essential for power and precision grips. Painful arthritis at the carpometacarpal (CMC) joint can be crippling, and laxity at the metacarpophalangeal (MCP) joint of the thumb can prevent a strong oppositional grip because of joint instability. The mobility of the CMC joints of the index through small fingers increases toward the ulnar aspect of the hand. Angulated fractures are generally better tolerated, therefore, in the ulnar digits because of compensatory motion.
The MCP joints of the index through the little fingers have little tolerance for stiffness because the arc of motion for the fingers starts at the MCP joints. Motion at the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints also contributes to making a fist, but stiffness is better tolerated in these joints, particularly the DIP joints because stability, rather than mobility, is more important in the terminal joints. Rotational or angular deformities are not tolerated because they may lead to scissoring of the fingers by interfering with the motion of the adjacent normal finger, or catching on pockets and clothing.
The forces acting across these joints include both static constraints (collateral ligaments, joint capsules, and volar plates) and tendons that create dynamic compression through movements. The volar plate of the MCP, PIP, and DIP may be involved in dislocations, both prior to and following reduction (Chapter 81). For dorsal MCP dislocations, if the deformity is accentuated in an attempted reduction, the volar plate may have become interposed in the joint, necessitating open reduction in the operating room. If the volar plate is disrupted during dorsal dislocation of the PIP joint, the lateral bands may subluxate dorsally over time, causing hyperextension at the PIP and flexion at the DIP, known as a “swan-neck” deformity (Figure 70.1). Another common finger deformity is the boutonniere deformity. This occurs when the insertion of the central slip on the dorsal middle phalanx and the triangular ligament are disrupted, causing the lateral bands to subluxate volarly. The PIP joint becomes flexed, and the DIP hyperextends (Figure 70.2).
Most flexion and extension of the fingers and wrist results from forearm-based muscle groups, innervated far proximally. Finely controlled movements, however, use the intrinsic musculature of the hand (muscles that arise in the hand), which includes the thenar and hypothenar muscle groups, the adductor pollicis, lumbrical, and interosseous muscles. More distal nerve lacerations or compressive pathologies affect these intrinsic muscles without deficits in the other flexors and extensors (Chapters 74 and 77).
Wrist
The wrist consists of eight carpal bones grouped in two rows with restricted motion between them and is the most complex joint in the body. The term “wrist” is used to include any of these numerous articulations. Normal flexion/extension motion is 90°/70°, but an 80° arc provides good function.1 Reduction in hand pronation is well tolerated if one has a functional shoulder to compensate, whereas loss of supination is not as easily tolerated.
The distal radioulnar joint is unique in that the ulna makes no direct contact to the carpal bones and is connected to the radius through the triangular fibrocartilage complex (TFCC). Eighty percent of the forces through the arm are dispersed by the carpal articulation with the radius. Static restraints to the movements at the radiocarpal joint include the tough, strong volar capsular ligaments, as well as less stout dorsal capsular ligaments. Incising the volar capsular ligaments to assess articular congruity when performing an ORIF (open reduction and internal fixation) of a distal radius fracture is discouraged, because this can lead to instability.
Movements between the carpal rows are biomechanically complex. The lunate is an intercalated segment sandwiched between the scaphoid and the triquetrum which follows the bone to which it is still attached. Dorsal tilt occurs when the scapholunate ligament is torn because the scaphoid flexes and the lunate must extend with the triquetrum (resulting in a dorsal intercalated segment instability) (Figure 70.3). A more rare condition occurs when the lunotriquetral ligament is disrupted, leaving the scapholunate ligament is intact, resulting in flexion of the lunate with the scaphoid (resulting in a volar intercalated segment instability) (Chapter 81).
Wrist and finger motions are the result of combined actions and firing of multiple muscle groups. For example, wrist flexion requires a balanced flexion of both the flexor carpi ulnaris and flexor carpi radialis to prevent deviation in one direction or the other. The finger flexors and the median nerve run through the carpal tunnel, which is covered by the transverse carpal ligament connecting the hamate and the pisiform ulnarly to the scaphoid and trapezium radially (Chapter 77). The median nerve is susceptible to compression in carpal tunnel syndrome and when dorsally displaced distal radius fractures increase the pressure at the carpal tunnel. The extensors of the wrist and hand are grouped into six tightly bound fibro-osseous compartments (Chapter 78). Stenosis or tenosynovitis can develop due to the restricted spaces and movements, commonly resulting in De Quervain syndrome at the first dorsal compartment, or intersection syndrome at the crossover of the first on the second compartment tendons (Chapter 79).
FIGURE 70.1. A swan-neck deformity of the middle and ring fingers, resulting from dorsal subluxation of the lateral bands, and leading to a fixed hyperextension at the PIP joint and flexion at the DIP joint.
PRINCIPLES OF UPPER EXTREMITY SURGERY
Acute Injuries
Emergency room management of patients with hand injuries includes an assessment of other, life-threatening injuries. One should always remember the expression “life over limb.” A severely mangled hand may attract attention, but the patient must be assessed in sequence to verify that all life-threatening conditions are treated first. Attempting to “tie off” a bleeding vessel in the emergency room is not recommended, because hemorrhage can usually be controlled with elevation and direct pressure. A blood pressure cuff may be inflated above the systolic blood pressure to control bleeding, but should not be left in place for longer than necessary, 90 minutes at most, to prevent ischemic reperfusion injuries.
Injuries that require urgent operative intervention include limb-threatening ischemia, most open fractures, pressure injection injuries, or active bleeding in the setting of a coagulopathy.For amputated digits, hypothermia (wrapped in moist gauze inside a plastic bag and placed on ice) will reduce the metabolic by-products that damage the tissue and improve the likelihood of a successful replant (see Chapter 83). Pressure injection injuries may appear innocuous on presentation, but in cases of caustic materials such as paint or cleaning solutions can lead to tissue necrosis and possible loss of the digit if not recognized and appropriately debrided.
FIGURE 70.2. A boutonniere deformity of the right ring and little fingers has resulted from a volar subluxation of the lateral bands, leading to fixed flexion at the PIP joint and hyperextension at the DIP joint.
Most displaced fractures should be reduced into a more anatomic position in the emergency room prior to splinting to decrease tension on the soft tissues or to achieve definitive reduction if the fracture is to be treated nonoperatively. Closed reduction requires an understanding of the bony anatomy and the muscular and tendinous attachments that serve as the deforming forces. A knowledge of the intact ligaments, soft tissues, and bony anatomy for a particular fracture will help in the realignment of any displaced fracture fragments into an improved position using ligamentotaxis (Figure 70.4). Splinting options are discussed later in this chapter.
Whether in the emergency department or in the office, a proper history should include hand dominance, the time course of the problem (acute injury versus gradual onset), and a patient’s level of functioning and difficulty with activities of daily living. A pianist with a tendon laceration may have different needs and expectations than an elderly patient with a distal radius fracture.
Physical Examination. The physical examination of the hand begins with general inspection for edema, bruising or discoloration, deformities of the digits, or previous scars. Wounds are inspected for infection, surrounding skin viability, and proximity to major neurovascular structures. Nerve laceration may not always be evident in the initial survey. Range of motion (ROM) of the digits and wrist helps guide further evaluation. When assessing motion, a concurrent evaluation of rotational deformities, gross instability, or laxity may be completed. Occasionally, a full assessment of ROM is limited by pain, and local blocks may help further assess injuries, but these should not be performed before a full sensory examination is conducted, including two-point discrimination. A strength assessment should be comprehensive, and areas of concern carefully evaluated to, for example, distinguish mechanical weakness (i.e., torn or lacerated tendon) from a more proximal nerve injury resulting in muscle denervation.
FIGURE 70.3. AP and lateral wrist x-rays of dorsal intercalated segment instability (DISI). A. Scapholunate widening is shown in the AP view with an arrow. B. The dorsally tipped lunate is outlined with white dots in the lateral view.
Radial and ulnar pulses at the wrist are typically palpable when systolic blood pressures are above 80 mmHg. The pulses of individual digital arteries are assessed with a Doppler probe, although the finger is usually adequately perfused if one digital artery is patent. In most individuals, the ulnar artery provides most of the blood flow to the fingers via the superficial palmar branch, forming a connection with the superficial branch of the radial artery. The Allen test assesses the competency of the ulnar artery to perfuse the hand by occluding both arteries, exsanguinating the hand with a tight fist, and then releasing the ulnar artery and looking for full perfusion to the fingers. The radial artery terminates in the deep palmar arch after circling around the dorsal aspect of the CMC joint of the thumb, supplying blood flow to the thumb and index finger via the princeps pollicis.
Adequate sensation of the digits is necessary for practical use of the hand. Proximal denervation may be assessed by knowing the autonomous sensory zones of the radial nerve (first dorsal web space), median nerve (volar aspect of index fingertip), and ulnar nerve (volar tip of the small fingertip). For injuries in the palm or fingers, two-point discrimination distal to the laceration can be tested with a paperclip bent into a 5 mm gap. A Tinel sign may indicate an injured nerve with regenerating axons.
Radiographic Evaluation. Most acute hand injuries require radiographic assessment. Imaging generally begins with standard x-ray evaluation. Specifically, an injury to a single digit requires a true anterior–posterior view of the finger, including the MCP, PIP, and DIP joints. A lateral film must include the condyles of the distal, proximal, and middle phalanx, without other fingers obscuring the digit in question. The thumb has a unique orientation and requires oblique views to obtain adequate views of the interphalangeal (IP), MCP, and CMC joints. A hand series is most useful for suspected metacarpal injuries, whereas a wrist series is required to assess distal radius fractures.
Part of the art of assessing hand injuries is a concise and accurate description of the fracture pattern seen on the x-rays (Chapter 75). Eponyms help describe common fracture patterns, but should not be used if there is an abnormal component to the fracture, because this leads to confusion and misunderstanding. The bone and location of the fracture is stated (e.g., base of the thumb metacarpal or midshaft proximal phalanx of the ring finger) and specific mention is made if it extends into the joint (e.g., intra-articular distal radius fracture). The angulation of the fracture apex (dorsal or volar), as well as the fracture pattern (transverse versus oblique), with comment on the comminution or displacement of the fragments should be described because this aids in assessing whether nonoperative treatment is possible. For example, describing a fracture as a “Colles fracture” is less helpful than saying, “apex volar, intra-articular, distal radius fracture with dorsal comminution and 30° of dorsal tilt, significant shortening and loss of inclination, with an associated ulnar styloid fracture.” Such a description immediately conveys that this is an unstable fracture unlikely to hold the reduction and requires operative reduction and fixation.
FIGURE 70.4. A technique for closed reduction of a metacarpal neck fracture using knowledge of the important anatomical structures to successfully reduce the malalignment using ligamentotaxis.
Advanced imaging, such as computerized tomographic (CT) scans, magnetic resonance imaging (MRI), and magnetic resonance (MR) arthrograms, are helpful to better define certain conditions and injuries (CT for suspected carpal fractures or intra-articular distal radius fracture, MRI for soft-tissue tumors, or MR arthrograms for suspected TFCC injuries), but should not replace X-rays as the first line of imaging.
IMMOBILIZATION TECHNIQUES
For mobile structures such as the hand and wrist, splinting and immobilization following injury or surgery is often a difficult balance between healing and stiffness. In general, immobilization of fractures above and below the joint is recommended, and immobilization following a soft-tissue injury can prevent excessive tension on the repair. Intrinsic positioning for the hand reduces stiffness by fully extending the joint capsules of the wrist in slight extension, the MCPs in near full flexion, and the IPs in full extension.
FIGURE 70.5. A sugar-tong splint can be useful for distal forearm and wrist injuries, especially when it is important to control pronation, supination, flexion, and extension.
Two basic types of splints are used to immobilize injuries based on their locations. A cast or other circumferential immobilization is used with caution in acute injuries because swelling could result in a compartment syndrome. A sugar-tong splint is most useful for distal forearm and wrist injuries where both flexion/extension and pronation/supination need to be controlled (Figure 70.5). Three-point cast molding with pressure at the apex of the fracture, as well as molding proximal and distal to the fracture opposite of the fracture apex, can be used to help maintain a reduction. An ulnar gutter splint can immobilize metacarpal and phalangeal fractures, while leaving the thumb and two other fingers free to allow for pinch-type movements (Figure 70.6).
Preoperative Planning
For elective surgical cases, the operating room staff should have preference cards listing the specific preferences of the surgeon, including positioning and draping, instrument trays, special implants for fractures, and dressing and immobilization materials. For more complex fractures and combined-type injuries where multiple major structures are damaged, the reconstructive principles serve as a framework for guiding operative steps (Table 70.1).
FIGURE 70.6. The ulnar gutter splint works to immobilize metacarpal and phalangeal fractures, while leaving the thumb and two other fingers free for pinch movements.
The equipment necessary for upper extremity surgery, especially if bony work is required, must be addressed in advance of the case. Intraoperative imaging with a mini C-arm is indispensable for fracture work, especially for fractures that may be amenable to closed reduction and fixation. If vascular repair is anticipated, use of the microscope is required. Depending on the fracture and injury, the options for plates and screw are numerous and should be considered in advance. Additional equipment beyond a basic hand tray may include drills, Kirschner wires (K-wires), or bone reduction clamps.
Operative Principles
Nearly all routine hand surgery cases require an arm table with the patient’s arm abducted 90°, allowing the surgeons to be seated around the table. The hand can be pronated and supinated in this position, giving access to both the dorsal and volar aspects of the hand and wrist. The use of perioperative antibiotic coverage administered prior to the incision remains controversial for short (<2 hour) soft-tissue procedures because there is no evidence that the benefits outweigh the risks. Generally, for procedures involving implants or bony work and for those lasting more than 2 hours, antibiotics are used and redosed throughout the course of the surgery as needed based on the drug’s half-life properties.2
Anesthesia. Local blocks are covered in Chapter 71, but are extremely useful for hand surgery to prevent the need for general anesthesia. For most routine hand cases, a local block with a small amount of sedation is adequate. Regional anesthesia, such as interscalene blocks, with or without general anesthesia, provides complete muscle relaxation and is helpful to reduce initial pain pathways. However, in trauma cases where monitoring for compartment syndrome is required postoperatively, a long-acting block may mask the symptoms and prove dangerous.
Tourniquet. Hand and wrist procedures are facilitated by a tourniquet. Essentially a blood pressure cuff, the tourniquet prevents arterial flow in the arm, leaving the operative field nearly bloodless. An upper arm tourniquet (either sterile or non-sterile) should be used for the elbow, forearm, and wrist work. It is important to exsanguinate the arm before inflation to empty the compliant venous system. Generally, a tourniquet 100 mmHg greater than the patient’s systolic pressure is sufficient to prevent surgical field bleeding. One must be careful to monitor the time a tourniquet has been in place, because anything over 90 to 120 minutes increases the risk for a reperfusion injury, resulting from the buildup of toxic metabolites in the arm.3 For hand and finger work, a forearm tourniquet may be used that is more comfortable for the patient. In the emergency room setting, a finger tourniquet may be used, but requires vigilance to remove it before the dressing is placed because the patient will not detect an ischemic finger when the finger is anesthetized. We typically place a clamp on the finger tourniquet to remind us to remove it.
FIGURE 70.7. A Bruner incision of the finger into the palm. This incision technique is useful to decrease the likelihood of contracture formation.
Incisions. When considering incisions in the hand, care should be taken not to cut across flexion creases to prevent the development of scars which will contract and limit motion. The dorsal aspect of the hand has thinner, more mobile skin and longitudinal incisions can generally be used. Zigzag incisions allow access to structures in the volar finger and palm. The common incision techniques, known as Bruner incisions, are diagonal incisions between flexion creases that serve to create a series of short broad-based opposing flaps (Figure 70.7).
Closure of hand incisions and wounds is generally accomplished with a single layer of interrupted nylon sutures. Vertical mattress sutures help evert the skin edges. If a laceration crosses a skin crease, a Z-plasty is considered to prevent contractures.
Postoperative Principles
Dressings following surgical procedures are highly dependent on surgeon preference. Directly over the surgical site, a non-occlusive yet adherent dressing, such as petroleum-impregnated gauze, is placed. Layers of dry gauze or “fluffs” may be used to cushion the incision and absorb any bleeding from the surgical site. Most importantly, any circumferential dressings are placed loosely to prevent a tourniquet effect. Splint immobilization for most operatively repaired fractures is advised and may be useful for soft-tissue procedures to prevent tension on the incision with movement, especially if the incision crosses a joint.
Perhaps most important is the benefit of elevation on swelling, a point that cannot be overemphasized with the patient. Careful attention to elevation while sleeping and in a sling can minimize swelling that leads to pain, wound problems, finger stiffness, and longer recovery times. The role of postoperative oral antibiotics in routine elective soft-tissue procedures (i.e., carpal tunnel release, trigger finger release, etc.) remains controversial with no clear benefit. Injuries or surgeries involving open fractures or other bony work warrant 24 hours of perioperative IV antibiotic coverage.
References
1. Ryu J, Cooney WP III, Askew LJ, An KN, Chao E. Functional ranges of motion of the wrist joint. J Hand Surg. 1991;16(3):409-419.
2. Rizvi M, Bille B, Holtom P, Schnall SB. The role of prophylactic antibiotics in elective hand surgery. J Hand Surg. 2008;33(3):413-420.
3. Wilgis E. Observations on the effects of tourniquet ischemia. J Bone Joint Surg Am Vol. 1971;53(7):1343.