You are in: eMedicine Specialties > Orthopedic Surgery > HAND AND UPPER EXTREMITY Intrinsic Plus HandArticle Last Updated: Nov 16, 2005AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Jessica Gillespie, MD, Staff Physician, Department of Surgery, Division of Plastic Surgery, Southern Illinois University School of Medicine Jessica Gillespie is a member of the following medical societies: Phi Beta Kappa Coauthor(s): Bradon J Wilhelmi, MD, Endowed Leonard Weiner, MD, Professor and Chief of Division of Plastic Surgery, Residency Program Director, University of Louisville School of Medicine Editors: Michael S Clarke, MD, Clinical Associate Professor, Department of Orthopedic Surgery, University of Missouri-Columbia School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Thomas R Hunt III, MD, John D Sherrill Professor of Surgery, Director, Division of Orthopedic Surgery, Surgeon in Chief, UAB Upper Extremity Fellowship, UAB Highlands Hospital, University of Alabama at Birmingham School of Medicine; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Harris Gellman, MD, Consulting Surgeon, Broward Hand Center, Voluntary Clinical Professor of Orthopedic Surgery and Plastic Surgery, Departments of Orthopedic Surgery and Surgery, University of Miami School of Medicine Author and Editor Disclosure Synonyms and related keywords: intrinsic plus position, safe position for hand splinting, hand immobilization, hand stiffness, intrinsic contractures, hand deformity, hand disability, intrinsic muscle contracture, intrinsic tightness test, intrinsic plus test INTRODUCTIONSection 2 of 10
  Intrinsic plus position The intrinsic plus position is otherwise known as the safe position for hand splinting. The hand can be immobilized in this position for long periods of time without developing as much stiffness as would occur if the digits were positioned differently. In the intrinsic plus position, the metacarpophalangeal (MP) joints are flexed at 60-70°, the interphalangeal (IP) joints are fully extended, and the thumb is in the fist projection. The wrist is held in extension at 10° less than maximal. Why intrinsic plus is the safe position In the safe position, the MP joints are in flexion and the IP joints are in full extension. The MP joints recover well from flexion, and the IP joints recover well from extension based on differences in the shape of the metacarpal head, volar plate, and collateral ligament anatomy. The metacarpal head is uniquely shaped in that it is ovoid in the sagittal plane, and it widens from the dorsal to the volar dimension. The collateral ligaments are eccentrically mounted dorsal to the axis of rotation of the MP joint. This anatomy causes variable degrees of tightness on the collateral ligaments based on the position of the joint by a camlike effect. When the joint is in extension, the collateral ligaments are lax. In flexion, the collateral ligaments span a greater distance and are tight (see Images 1-2). In addition, the MP joint is also curved in 2 planes to permit abduction, adduction, and rotation, as well as flexion and extension in an abbreviated ball and socket configuration. In flexion, bone surface area contact is greater than in extension, producing a more stable joint (see Image 1). Proximal IP (PIP) joint collateral ligaments originate close to the axis of rotation, providing a smaller change in length with joint position and providing lateral stability. The PIP joint ranges in only 1 plane, and its trochlear shape also adds to its lateral stability (see Image 2). ProblemContracture of the interosseous, lumbrical, or hypothenar muscles causes the fingers to stiffen and the hand to become deformed and functionally disabled. FrequencyThe frequency of intrinsic plus hand is not known. EtiologyExcessive immobilization, trauma, inflammation, infection, tumor, central nervous system disease, and joint destruction are all causes of joint stiffness and intrinsic contractures. Decreased blood supply to the hand as a result of injury or primary disease of the vessels of the upper extremity is a leading cause of intrinsic muscle contracture. PathophysiologyEdema is the initial response to any insult to the hand and leads to adverse sequelae. Joint stiffness develops as intra-articular hematoma and fluid accumulate within the synovial space, distending the capsule. Increased fluid content within the articular capsule and collateral ligaments effectively shortens these structures, favoring extension. The fluid in the joint space also serves to hydraulically drive the MP joints into extension (see Image 1). In extension, the joint is able to accommodate this increased fluid capacity. As the MP joints extend, the flexor tension on the IP joints increases and the extensor tension decreases. This causes the PIP and DIP joints to flex. The resultant late deformity is the intrinsic negative (or minus) hand, consisting of MP joint extension, IP joint flexion, thumb adduction, and wrist flexion. With injury, checkreins form at the IP joints (see Image 4). Checkreins are collagenous bands connecting the lateral sides of the proximal volar plate to the assembly lines on the volar lateral surfaces of the phalanx. Assembly lines are the 2 ridges along the volar lateral surfaces of the phalanx to which are attached volar ligamentous structures such as the flexor sheath, Cleland and Grayson ligaments, and the oblique retinacular ligaments of Landsmeer. The volar plate pocket behind the MP volar plate is smaller than at the IP joint, and checkreins do not develop at the MP joint (see Image 4). Compartment syndrome is the usual cause of posttraumatic intrinsic contractures due to edema and ischemia. Hematoma and edema fill the interosseous muscle compartment and are trapped by the firm dorsal and volar interosseous fascia. Capillary compression and venous stasis adds to the congestion. As the edema subsides, fibrosis develops. Compressive circular dressings can also impede venous drainage and lead to the development of myostatic contractures in the interossei. Finally, muscle necrosis and fibrosis may ensue with cases of severe and prolonged deep-space edema of the hand. ClinicalThe most common test used to test for intrinsic contracture is the intrinsic tightness test. The examiner holds the MP joints in extension while passively flexing the IP joints. While holding the MP joints in flexion, the IP joints are then passively flexed. If IP joint flexion is blocked or lessened when the MP joint is in extension compared to when it is in flexion, the result is positive and there is tightness of the intrinsic muscles. In contrast, if extensor contracture is present at the PIP joint, then PIP joint flexion is greater with MP joint extension. INDICATIONSSection 3 of 10
See Treatment, Surgical therapy, below. RELEVANT ANATOMYSection 4 of 10
Brief anatomy and function of the intrinsic and lumbrical muscles The intrinsic musculature, composed of the interossei and the lumbrical muscles, acts on the hand to flex the MP joints and extend the IP joints. The interossei also act to abduct and adduct the fingers. There are 7 interosseous muscles divided into 4 dorsal and 3 volar interossei. These muscles lie on either side of the metacarpals. The dorsal interossei are abductors, whereas the ventral interossei are adductors. Each dorsal interosseous muscle, except the one lying on the ulnar side of the middle finger, has 2 muscle heads. The superficial head originates most dorsally and inserts by way of a medial tendon onto the lateral tubercle at the base of the proximal phalanx. Therefore, the superficial head abducts and weakly flexes the proximal phalanx. The deep head of the dorsal interosseous muscle forms a lateral tendon or lateral band at the base of the proximal phalanx. These lateral bands are joined by the lateral slips of the extensor tendon to form the conjoined lateral band at the level of the PIP joint. The conjoined lateral bands on either side of the finger then join at the distal end of the middle phalanx to form the terminal extensor tendon. The terminal tendon inserts onto the base of the distal phalanx and serves to extend it. Each lateral band at the level of the middle of the proximal phalanx sends off fibers, which arch dorsally to join each other on the dorsum of the finger. These fibers flex the proximal phalanx. Oblique (spiral) fibers also originate from the lateral bands more distally and insert onto the lateral tubercles at the base of the middle phalanx. These oblique fibers extend the middle phalanx. Therefore, the deep head of the dorsal interosseous muscle acts to flex and weakly abduct the proximal phalanx and extend the middle and distal phalanges. The volar interossei each only have one muscle head and form the ulnar lateral band of the index finger and the radial lateral band of the ring and little finger. The hypothenar muscles function similarly to the interossei for the small finger. The abductor digiti quinti function is similar to the superficial head of a dorsal interosseous muscle. The flexor digiti quinti brevis functions similarly to the deep head of a dorsal interosseous muscle, forming the ulnar lateral band. The opponens digiti quinti is a third hypothenar muscle that serves to flex and supinate the fifth metacarpal. The lumbrical muscles arise from the flexor digitorum profundus tendons in the palm and join the radial lateral band at the middle of the proximal phalanx. The lumbricals extend the PIP and DIP joints and assist in flexing the MP joints. Volar plate anatomy Architectural differences exist between the volar plates of the MP and IP joints. The MP volar plate is composed of crisscrossing bands of fibers that collapse like an accordion on flexion and expand with extension. The IP volar plate is a more rigid cartilaginous structure that does not collapse but glides with movement. It is attached to the proximal phalanx only by the proximal checkrein ligaments; therefore, the rigid IP volar plate can slide proximally and distally with joint motion to protect the joint (see Image 3). CONTRAINDICATIONSSection 5 of 10
In some circumstances, the intrinsic tightness test may not be reliable in diagnosing intrinsic contracture. IP joint stiffness and capsular or intra-articular adhesions can mask underlying intrinsic muscle tightness. In these situations, IP joint flexion may be decreased regardless of the position of the MP joint. WORKUPSection 6 of 10
Imaging Studies
TREATMENTSection 7 of 10
Medical therapyAny injury to the hand can lead to intrinsic contracture. Early recognition is essential. Efforts must be directed at decreasing edema in the injured hand. Limb elevation is crucial, and care must be taken to avoid applying compressive dressings such as ace wraps or restrictive circular casts. If these conservative measures fail or if the surgeon notices persistent swelling and pitting edema, increasing median nerve hypesthesia, or poor capillary refill, a quantitative measurement of intracompartmental pressure may be obtained. Surgical therapyEarly and acute trauma: interosseus and adductor compartment release When increased intracompartmental pressures do not respond quickly to conservative measures, the interosseous compartments should be released promptly. Most patients also require release of the adductor pollicis and carpal tunnel. When flexion of the MP joints is limited, Kirschner (K)–wires should be used to fix the MP joints in 60° of flexion to stretch the collateral ligaments. Late and mild posttraumatic intrinsic contracture: distal intrinsic release Patients with mild intrinsic muscle contracture may be able to open and close their fingers normally, but they may have persistent limited flexion at the PIP joint several months after an injury to the hand or wrist. These patients often have little to no MP flexion contracture but limited PIP flexion. In these instances, the edema of the hand causes the collateral ligaments to swell and tighten. Although the intrinsic contracture is mild, the swollen and tight collateral ligaments resist stretching, and the MP joints are not pulled into flexion. The results of the intrinsic tightness test are positive. For these patients, distal intrinsic release is recommended. In this procedure, the lateral bands and oblique fibers of the distal third of the proximal phalanges are resected. Postoperatively, the MP joints are splinted in extension (neutral) position for 3 weeks. The IP joints are ranged in active and passive flexion/extension exercises to avoid relapse of the deformity. Dynamic splinting in the MP extension splint, otherwise known as the reverse knuckle-bender splint, is useful in this period. Late posttraumatic intrinsic contracture with MP and PIP joint contractures: muscle slide/release With more severe ischemic contracture of the interossei and lumbricals, flexion contracture occurs at the MP joints and an extension contracture occurs at the IP joints. With extensive edema of the hand, the contracted interossei overcome the resistance of the tightened collateral ligaments and pull the proximal phalanx into flexion. Secondary changes may include contraction of the volar plate and collateral ligaments of the PIP joints. The results of the intrinsic tightness test are positive, and the deformity of the hand is severe. Extensive release of the dorsal aponeurosis is necessary to correct severe intrinsic muscle contractures that involve both the MCP and PIP joints. Muscle slide may be used if the interossei are fibrotic and tight but have retained some contractility. With more severe ischemic damage, the interossei are often necrotic and nonfunctional. Proximal intrinsic release is indicated, and the lateral tendons of all interossei, including the abductor digiti quinti tendon, are resected at the level of the MP joints. The volar plate is also freed of any attachments at the base of the proximal phalanx, and the accessory collateral ligaments may be resected at their insertion into the volar plate. K-wires may be inserted obliquely through the MP joints to maintain them in maximal extension. If passive PIP joint flexion is still incomplete with the MP joints in extension, the lateral bands are resected at the distal half of the proximal phalanx. Postoperatively, the MP joints are kept in extension for about 3 weeks. After this time, the K-wires are usually removed. Passive and active flexion/extension of the PIP joints should begin on the first postoperative day. Spastic contracture of the interossei: muscle slide Patients with cerebral palsy, central nervous system disease, or stroke may have spastic contracture of the interossei causing disability. Often, intrinsic muscle spasticity is masked by extrinsic muscle spasticity and is elucidated several weeks after the patient undergoes release of extrinsic muscle spasticity. After extrinsic release, the patient's hand assumes the intrinsic plus position due to its intrinsic contractures. The goal of treatment in these patients is not to remove the tightened muscles but to weaken them. This can be accomplished by means of muscle slide. Muscle slide is accomplished via a dorsal approach to protect the palmar blood supply to the intrinsic muscles. The metacarpal origins of all interossei are released subperiosteally. The tendons of the abductor digiti quinti and the flexor digiti quinti brevis are also usually transected as described by RJ Smith in 1975. The MP joints are then extended and the PIP joints are flexed, allowing the muscles to advance distally. The hand is then splinted in this claw position for a period of 3 weeks. OUTCOME AND PROGNOSISSection 8 of 10
The prognosis for each patient is variable and depends on the severity of the contracture and the underlying cause of the contracture. The surgeon's objective is to restore structure and function to the contracted hand. The ultimate goal is to provide the patient maximal comfort and functional independence. MULTIMEDIASection 9 of 10
REFERENCESSection 10 of 10
Article Last Updated: Nov 16, 2005 | |||||||||||||||||||||||||||||||||
