Wrist

Abstract

The wrist is anatomically complex and susceptible to a variety of injuries. Appropriate diagnosis and management of these injuries are imperative to prevent long-term morbidity. The next section will describe the intricate anatomic relationships of the carpal bones and adjacent neurovascular structures, assessment/treatment of various injury presentations, and advanced instruction regarding physical examination and radiographic evaluation.

Introduction

• Anatomic bridge from forearm to the hand.

• Assists in force transmission, helps generate and execute powerful/coordinated movements of the hand, and provides strict stabilization during performance of fine motor activities.

• Methodical approach is key to appropriately diagnosing and managing these fragile, yet often complex injuries.

Wrist (Carpal) Anatomy

• Formed by eight carpal bones, roughly arranged in two rows, with numerous ligamentous attachments that assist in maintaining stability and coordinating movement.

• Bony Anatomy :

  • 1. Proximal row (radial → ulna direction): scaphoid (spans both rows), lunate, triquetrum, and pisiform; only scaphoid and lunate articulate with the distal radius.

  • 2. Distal row : trapezium, trapezoid, capitate and hamate; these bones articulate with metacarpal bones of the hand (See Fig. 8.1).

• It is also composed of several joints:

  • 1. Distal radioulnar joint (DRUJ) : acts as a pivot point to generate forearm pronation/supination.

  • 2. Radio-carpal joint : region between radius and proximal carpal row; this articulation permits wrist flexion/extension and radial/ulnar deviation.

  • 3. Midcarpal joint : area between the two carpal rows; considered a “functional” rather than “anatomical” unit, as it does not contain an uninterrupted (“classic”) articular surface (See Fig. 8.2).

• Carpal Tunnel : fibro-osseous passageway on palmar aspect of the wrist; transmits median nerve and nine extrinsic flexor tendons to the hand. Median nerve compression can lead to paresthesias, pain, numbness, and/or weakness within its anatomic distribution (See Fig. 8.3).

• Guyon’s Canal : structural space created on ulnar aspect of the wrist that transmits ulnar artery/nerve from forearm to the hand (See Fig. 8.4).

• Extensor Tendon Compartments : dorsal side wrist tunnels that transport extrinsic extensor tendons to their digital insertion sites; tendons held firmly in place by extensor retinaculum and travel in synovial tendon sheaths to facilitate their excursion over dorsal wrist surface.

  Anatomic Snuffbox : triangular structural deepening on the radial/dorsal aspect of the hand; contains radial artery, cephalic vein, and dorsal cutaneous branch of radial nerve (superficial radial nerve). Borders accentuated with thumb extension .

• Lister’s Tubercle : palpable prominence on dorsal distal radius; serves as pulley for EPL tendon and reference landmark for wrist joint arthrocentesis (See Fig. 8.5a, b).

• Ulnar Styloid Process : distal ulna bony prominence that serves as attachment point for triangular fibrocartilage complex (TFCC); disruption may signal damage to TFCC, instability of DRUJ, or concomitant distal radius injury (See Fig. 8.6).

Wrist/Hand Blood Supply:

• Contains rich vascular network supplied by radial/ulnar arteries; these vessels branch to perfuse distal digits while also coalescing to form overlapping collateral circulation through formation of two major palmar arches.

  • 1. Superficial palmar arch : distal to deep arch; supplied predominately by ulnar artery.

  • 2. Deep palmar arch : supplied principally by deep branch of radial artery (See Fig. 8.7).

Figure 8.1

Carpal bones: A (scaphoid), B (lunate), C (triquetrum), D (pisiform), E (trapezium), F (trapezoid), G (capitate), H (hamate), 1 (radius), 2 (ulna). (Reprinted with permission from Dr. Jochen Lengerke. Retrieved from https://commons.wikimedia.org/wiki/File:Xray_hand_with_color.jpg)

Figure 8.2

Joints of the wrist. (Adapted with permission from https://commons.wikimedia.org/wiki/File:Gray336.png)

Figure 8.3

Carpal tunnel syndrome. (Reprinted from Blausen.com staff. Medical gallery of Blausen Medical 2014. WikiJournal of Medicine. 2014;1(2). doi:https://doi.org/10.15347/wjm/2014.010. ISSN 2002-4436. https://commons.wikimedia.org/wiki/File:Carpal_Tunnel_Syndrome.png. With permission from Bruce Blaus)

Figure 8.4

Guyon’s canal: labeled “Zone 1” floor (transverse carpal ligament), roof (palmar carpal ligament), ulnar border (pisiform), radial border (hook of hamate). (Reprinted from http://www.ehealthstar.com/anatomy/guyons-canal. With permission from Ehealthstar.com)

Figure 8.5

Lister’s tubercle: (a) surface anatomy, (b) skeleton. (b: Adapted from https://commons.wikimedia.org/wiki/File:Left_hand_dorsal_view_Arabic_YM.png with permission from Creative Commons License: https://creativecommons.org/licenses/by-sa/4.0/deed.en)

Figure 8.6

EPL and Lister’s tubercle: anatomic relationship. (Adapted from with permission from https://commons.wikimedia.org/wiki/File:Gray419.png)

Figure 8.7

Blood supply of the hand. (Reprinted with permission from https://commons.wikimedia.org/wiki/File:Gray1237.svg)

Clinical Assessment

• History:

  • Determine the timing/mechanism of injury, previous/associated injuries, loss of function (neuromotor/perfusion deficits), position of the wrist at time of injury, activities and/or motion(s) that alleviate/exacerbate patient discomfort, previous treatment, etc.

  • Be sure to document hand dominance, employment-specific requirements, and/or recreational /professional activity needs (e.g., surgeon, musician, etc.)

• Physical Examination:

  • Visual inspection-note evidence of swelling, ecchymosis, associated skin changes, and/or positional deformity.

  • Measure passive/active ROM (compare with contralateral wrist).

  • Palpate bony prominences (Lister’s tubercle, scaphoid tubercle, ulnar styloid, etc.) and any areas of communicated patient discomfort.

  • Assess overall appearance, temperature alterations/differences in handedness, pulse strength, digital capillary refill, and consider systemic disease that may affect healing and/or contribute to future potential complications (e.g., DM, peripheral vascular disease, etc.).

  • Evaluate potential neuromotor deficits and record results of overall strength, functional capacity, and neurologic assessment.

• Plain Radiographic Examination: (See Fig. 8.8a–c)

  • A. Carpal bone alignment: standard joint spacing is suggested when carpal bones are visualized in parallel when examined in profile; physical overlap can be suggestive of abnormal tilting, dislocation, and/or carpal fracture.

  • B. Carpal (Gilula) arcs: three smooth, continuous arcs should be identified on PA view.

    • I. First arc: outlines proximal surfaces of the scaphoid, lunate, and triquetrum.

    • II. Second arc: traces their distal surfaces.

    • III. Third arc: follows proximal curvatures of the capitate and hamate (See Fig. 8.9).

    • **An arc is disrupted if it cannot be traced smoothly and continuously; disruption is generally indicative of ligamentous tear and/or fracture. **

    • 1. First arc: radio-carpal row; disruption is suggestive of lunate dislocation.

    • 2. Second arc: mid-carpal row; disruption is suggestive of peri-lunate dislocation.

    • 3. Third arc: outlines proximal surface of distal carpal row.

Figure 8.8

Hand X-ray: (a) PA, (b) lateral, (c) oblique A–C. (Used with permission from http://www.wikiradiography.net/page/Hand+Radiographic+Anatomy)

Figure 8.9

Carpal arcs. (Reprinted from http://www.radiologyassistant.nl/en/p42a29ec06b9e8/wrist-carpal-instability.html. With permission from Robin Smithuis)

Selected Individual Bones

• A. Scaphoid (navicular): second largest carpal bone; most commonly fractured carpal bone.

  • Shape: changes with wrist movement; lengthens in extension/ulnar deviation, yet shortens with flexion/radial deviation, displaying a “signet ring” cortical appearance (See Fig. 8.10)

  • Contains three anatomic regions: proximal pole, distal pole (tubercle), and the waist (mid-portion that separates the two poles)

  • Functions as link across the mid-carpal joint, providing functional continuity between the proximal and distal carpal rows

  • Approximately 80% of its surface is covered in cartilage, leaving only a small area for arterial blood supply; this reduces its capacity for periosteal healing and leads to an increased risk of delayed, malunion, and/or nonunion.

  • Blood Supply:

    • 1. Dorsal carpal branch of radial artery: provides ~ 70–80% of vascular supply, entering slightly distal to scaphoid waist at the dorsal ridge; provides perfusion to proximal aspect of scaphoid in retrograde fashion

    • 2. Palmar and superficial palmar branches (scaphoid branches): enter at distal tubercle and accounts for remaining vascular supply (none of which reaches the proximal pole) (See Fig. 8.11).

      **Generally accepted that with proper treatment (immobilization), nearly 100% of tuberosity/distal third fractures and 80–90% of waist fractures will heal uneventfully; however, it has been reported that only 60–70% of proximal pole fractures heal free of complication(s).**

  • Injury Mechanism: Similar to distal radius fractures, a fall on an outstretched hand (FOOSH injury) transmits a large hyperextension force across the wrist joint; however, unlike distal radius fractures, scaphoid fractures are more common among young men, with a peak incidence in the second and third decades.

    • A. Extreme hyperextension locks scaphoid into the distal radial scaphoid fossa, with the capitate acting as a fulcrum for fracture generation.

    • B. “Punch” mechanism: involved metacarpal delivers a palmar-directed shear force across distal scaphoid.

      • Kinematic effect(s) of an “unstable” scaphoid fracture essentially describes a loss of functional continuity between the carpal rows.

  • Clinical Evaluation/Treatment: (See Figs. 8.12 and 8.13)

    • Anatomic snuffbox tenderness, described as “classic” physical finding, may be “overly sensitive” with false-positive results elicited through compression of superficial radial nerve; tenderness at the scaphoid tubercle is also quite limited in detecting scaphoid fractures when implemented in isolation.

    • Compression test: involves loading scaphoid via axial compression of the thumb along the line of the first metacarpal (See Fig. 8.13).

    • Preceding provocative maneuvers, along with “scaphoid series,” should minimize possibility of missing an acute scaphoid fracture.

      **Never Rely on Imaging Alone**

    • Estimated as much as 30% of all scaphoid fractures might not be detected on initial X-rays (even with perfect radiographic technique and an experienced physician interpreting the films).

      **Cortical disruption may not be radiographically evident in acute injury period**

      **Any clinical suggestion of fracture, despite negative imaging analysis, should prompt immobilization in thumb spica splint/cast**

      **If left untreated, there is a heightened risk of nonunion/AVN and associated future potential complications**

    • Based upon its high sensitivity/specificity, MRI is considered “gold standard” in diagnosis of occult scaphoid fractures; however, in many instances, MRI is neither practical nor available. Thus, adequate clinical follow-up and repeat imaging should lead to detection.

    • Average time for healing of non-displaced scaphoid fracture treated with immobilization, free of complication(s), is ~8 to 12 weeks.

    • Common post-traumatic complications include pain, arthritic degeneration, functional deficits, delayed union, malunion, and/or nonunion.

    • Preiser’s disease (scaphoid osteonecrosis): development of osteonecrosis (AVN) of scaphoid with no previous history of substantial trauma; etiology secondary to repetitive microtrauma and/or side effects of medications (e.g., steroids/chemotherapy) in conjunction with existing defective vascular perfusion; most commonly involves proximal pole.

• B. Lunate:

  • “Keystone” of proximal carpal row, yet most commonly dislocated carpal bone.

  • Isolated injuries are rare and often overlooked on routine imaging secondary to superimposed structures. Slightly oblique X-ray imaging may better delineate suspected fractures, or CT should be considered.

  • Shape: normally appears trapezoidal; if becomes tilted, can appear triangular (“piece-of-pie” sign), which may indicate ligamentous injury and/or potential dislocation (See Fig. 8.14a, b).

  • Lunate dislocation: radio-lunate articulation disrupted, as the residual carpus remains stable.

  • Peri-lunate dislocation: radio-lunate articulation is maintained, while the remaining carpus becomes displaced.

    **Lunate dislocation: can mimic peri-lunate dislocation, especially on PA projection –> lateral imaging is key to make this distinction.** (See Figs. 8.15a, b and 8.16)

    • A. Lunate Dislocation: Lunate tilted out, while capitate and residual carpus remains centered over radius.

    • B. Peri-lunate Dislocation: Lunate remains centered over distal radius, while capitate and remaining carpus are displaced.

      **Imaging Clues to Lunate Dislocation:

      • 1. PA: break in Gilula’s arc (smooth contour), lunate/capitate overlap, and/or lunate appears triangular (“piece-of-pie” sign).

      • 2. Lateral: loss of colinearity of radius, lunate and capitate (“spilled teacup” sign); capitate not positioned within distal articular cup of lunate.

      **Imaging Clues to Peri-lunate Dislocation:

      • A. PA View: disruption of expected smooth carpal arcs. Can also see “piece-of-pie” sign.

      • B. Lateral View: usually demonstrates dorsal peri-lunate dislocation (lunate maintains normal relationship to distal radius, while capitate and remaining carpus are displaced dorsally) (See Fig. 8.17a–c).

  • Injury mechanism: axial loading of the wrist in hyperextended/ulnar-deviated position.

  • Dislocation can occur through greater arc (bone), lesser arc (ligaments), and/or combination of both.

  • Sequence of injury: usually begins radially, with destabilization through body of scaphoid (fracture) and/or through scapho-lunate interval (pure dislocation); scaphoid bridges proximal and distal carpal rows; thus with dislocation between rows, the scaphoid must either rotate and/or fracture.

Figure 8.10

Scaphoid: (a) extension/ulnar deviation, (b) flexion/radial deviation (“signet ring” sign). (Reprinted from http://www.radiologyassistant.nl/en/p42a29ec06b9e8/wrist-carpal-instability.html. With permission from Robin Smithuis)

Figure 8.11

Blood supply of scaphoid: Majority of perfusion occurs in retrograde fashion in a distal to proximal direction. More proximal fractures thus have higher rates of nonunion due to a diminished blood supply. (Reprinted from http://morphopedics.wikidot.com/scaphoid-fractures with permission from Creative Commons License: https://creativecommons.org/licenses/by-sa/3.0/)

Figure 8.12

Locations to palpate scaphoid: (a) tubercle, (b) anatomical snuff box, (c) proximal pole

Figure 8.13

Scaphoid compression test: axial compression of the scaphoid

Figure 8.14

Lunate dislocation: PA clenched fist view; note the pie-shaped lunate and loss of parallelism. (Reprinted from http://www.radiologyassistant.nl/en/p42a29ec06b9e8/wrist-carpal-instability.html. With permission from Robin Smithuis)

Figure 8.15

Wrist and carpal alignment: note aligned axis of distal radius, lunate, and capitate. (Image reprinted with permission from Medscape Drugs & Diseases (http://emedicine.medscape.com/), 2017, available at: http://emedicine.medscape.com/article/397035-overview)

Figure 8.16

Lateral wrist X-ray: (a) normal alignment (yellow, radius; red, lunate; blue, capitate), (b) lunate dislocation – note the “spilled teacup” sign of the lunate. (Reprinted from http://www.emcurious.com/blog-1/2015/7/8/1ftadghymctqd2flw27ao4zwl1m6tb with permission from Creative Commons License: https://creativecommons.org/licenses/by/4.0/)

Figure 8.17

Peri-lunate dislocation X-ray: Lunate (yellow) remains centered over radius while capitate (blue) dislocates dorsally – scaphoid (red). (Used with permission from http://www.wikiradiography.net/page/Lunate+and+Perilunate+Dislocations)

Figure 8.18

Lunate reduction: (a) The wrist is extended with the thumb placed over the proximal palmar lunate “X” to maintain concavity-up alignment, while the remaining fingers provide an opposing force to the residual carpus. (b) While maintaining manual longitudinal traction and applying pressure to palmar lunate, gradually flex the wrist to reduce the capito-lunate joint (arrow)

Figure 8.19

Triquetrum: just distal to ulnar styloid

Figure 8.20

Triquetrum X-ray: (a) PA view, (b) lateral view. (a, b: Used with permission from http://www.wikiradiography.net/page/Triquetral+Fractures)

Figure 8.21

Triquetral fracture X-ray: (a) PA view, (b) lateral view, arrow points to pathognomonic dorsal chip fracture. (a, b: Used with permission from http://www.wikiradiography.net/page/Triquetral+Fractures)

Figure 8.22

Pisiform

Figure 8.23

Pisiform X-ray: (a) oblique view showing fracture (arrow), (b) carpal tunnel view (no fracture). (a: Used with permission from Northwestern University, Feinberg School of Medicine, Department of Emergency Medicine. b: Reprinted from Watanabe A, Souza F, Vezeridis PS, et al. Ulnar-sided wrist pain. II. Clinical imaging and treatment. Skeletal Radiol. 2010;39(9):837–857. With permission from Springer Nature)

Figure 8.24

Hamate

Figure 8.25

Scapho-lunate dissociation (arrow). (Used with permission from: http://www.wikiradiography.net/page/The+Terry-Thomas+Sign)

Figure 8.26

DRUJ injury: (a) PA view: distal radio-ulnar joint widening (arrowheads), (b) Lateral view: volar displacement of the distal ulna demonstrates subluxation of the DRUJ A. (Image reprinted with permission from Claire K Sandstrom, MD, University of Washington Medical Center and Harborview Medical Center, published by Medscape Drugs & Diseases (http://emedicine.medscape.com/), 2017, available at: http://emedicine.medscape.com/article/389069-overview; b: Used with permission from http://www.wikiradiography.net/page/Subluxation+of+the+distal+radioulnar+joint)

Figure 8.27

“Piano-key” test: stabilize the distal radius and apply an anterior-posterior force to the distal ulna

Definitive Treatment Options

• Closed reduction and splinting/casting: despite initial success, usually generates poor long-term outcomes, with many patients experiencing functional deficit and/or recurrent dislocation.

• Closed reduction and percutaneous pin fixation.

• Open reduction with ligamentous repair and/or percutaneous pin fixation.

  **CLOSED REDUCTION TECHNIQUE**

• Place upper extremity in longitudinal traction, with the elbow at 90 degrees of flexion for ~10–15 min.

• Add 5–10 lbs of additional traction if possible to heighten distraction forces.

• Dorsal peri-lunate dislocations are reduced through application of volar pressure to the carpus, with a counter-force applied to the lunate.

• Palmar flexion then allows for reduction of the capitate into the concavity of the lunate (See Fig. 8.18).

  **If closed reduction is achieved/verified, interim operative intervention is still generally necessary to achieve enduring carpal stabilization.**

  **If closed reduction cannot be obtained, the patient should be taken promptly to the OR for open reduction.**

• Damage to median nerve is the most common associated injury; however, the associated skin can also become ischemic from the impinging radius/carpus.

• Fractures: typically follow hyperextension injury (FOOSH mechanism). Avulsions of dorsal pole are common in scapho-lunate dissociations (SLD), while fractures of ulnar aspect of palmar pole are associated with peri-lunate dislocations.

Treatment/Outcome:

• Most lunate fractures can be treated conservatively with immobilization. However, all fractures require serial imaging, ideally consisting of advanced imaging (MRI) to more definitively assess healing/revascularization, as there is a high incidence of nonunion, osteonecrosis, and potential for carpal collapse

• Kienbock’s disease: (avascular necrosis lunate) probably no single cause – its origin may involve multiple factors (blood supply (arteries), blood drainage (veins), skeletal variations, and/or acute or repetitive trauma).

• C. Triquetrum: located on medial side wrist, just distal to TFCC; articulates with lunate through luno-triquetral ligament (See Figs. 8.19 and 8.20a, b)

  • Fractures: most common mechanism of injury involves an impingement shear-type fracture, with the ulnar styloid contacting the dorsal aspect of the triquetrum with the wrist in extension and ulnar deviation.

  • Physical examination generally reveals localized tenderness over dorsum of the wrist, just distal to the ulnar styloid.

  • Frequently, only seen as dorsal chip fracture on the lateral projection, as the pisiform generally obscures the triquetrum on the frontal view (See Fig. 8.21a, b).

  • Treatment/outcome: generally depends upon location and amount of fracture displacement.

  • Non-displaced/dorsal chip fractures ( non-articular injuries ) can usually be treated conservatively with immobilization (ulnar gutter splint/cast or volar splint).

  • Rarely, more displaced fractures (>1 mm) or injuries that remain symptomatic despite significant healing time may ultimately require fragment excision.

  • Triquetrium has abundant vascular supply, thus delayed/nonunion exceptionally rare.

• D. Pisiform: sesamoid bone contained within the flexor carpi ulnaris (FCU) tendon; increases the moment arm (torque force) of the FCU muscle at its tendon traverses over the pisiform surface.

  • Delineates ulnar border of Guyon’s canal, thus injuries to pisiform can also involve concomitant damage to ulnar nerve (See Fig. 8.22).

  • Fractures: most sports-related, but injury may also occur following FOOSH mechanism. Diagnosis: can be difficult and they are easily missed upon initial examination.

  • Detection may require special imaging views such as an ~20–45° oblique image (wrist in radial deviation/mild supination) or “carpal tunnel” view (See Fig. 8.23a, b).

  • CT may also be required for diagnosis of occult fractures.

  Treatment/outcome: Most fractures heal with conservative measures, and patients are often treated with splint/cast immobilization.

  • However, some patients will continue to experience chronic discomfort despite adequate healing time. This occurs secondary to accelerated degenerative changes and may eventually require surgical excision (usually associated with minor loss of grip strength).

• E. Hamate:

  • Roughly triangular-shaped bone composed of both a body and “hook-like” process projecting from its volar surface; situated in distal carpal row, at extreme ulnar border of wrist.

  • The “hook” serves as distal, lateral border of Guyon’s canal; thus injury may signal potential ulnar artery and/or nerve involvement (See Fig. 8.24).

  • Fractures: overall quite rare, with the body much less commonly injured than its accompanying “hook” (may require oblique images to demonstrate pathology).

  • Physical examination findings are generally non-specific and quite often absent. If symptoms are present, evaluation typically reveals discrete point tenderness over “hook,” diminished grip strength, and/or paresthesias in ulnar nerve distribution.

  • Two mechanisms that account for most “hook” fractures:

    • Repetitive microtrauma during sports activities (e.g., swinging clubs, bats, or racquets). Eventually leads to stress fracture development and often occurs in non-dominant hand.

    • Direct trauma during sport-specific activities, whereby equipment rests directly on hamate, with force directly transmitted to the bone.

  • Fracture of the “hook” most commonly occurs at or near its base.

  • Similar to pisiform fractures, a carpal tunnel view/CT may be necessary to diagnose injury, with excision reserved for prolonged symptomatic injuries (painful nonunion).

  • Treatment involves immobilization if discovered early, yet many injuries are initially overlooked; this leads to decreased healing potential based upon multifactorial contribution (fragment displacement, poor vascular supply, etc.).

  • Pearls:

    • A. Scapho-lunate (SL) dissociation (“Terry Thomas” sign): most common traumatic etiology of carpal instability; can occur in isolation or with wrist fractures.

      • Both the direction of traumatic force and the relatively weaker dorsal ligaments contribute to dorsal carpal displacement (FOOSH mechanism) (See Fig. 8.25).

  • Treatment:

    • 1. Acute Tears: patients with partial tears and no evidence of carpal instability may be treated conservatively with splint/cast immobilization; this is ineffective when carpal instability is present, as they require opposite directions of movement to maintain reduction (scaphoid requires wrist extension, while lunate requires wrist flexion).

    • 2. Chronic Tears: usually requires surgical intervention for symptomatic cases; degenerative soft tissue supporting structures are not commonly amenable to direct repair methods.

      • Without treatment, can lead to advanced SL collapse (SLAC wrist) and/or progressive, painful wrist arthritis.

      • Clenched fist view in ulnar deviation most effectively expands SL joint space, placing maximum stress on SL ligament; positive intercarpal widening is commonly referred to as “Terry Thomas” sign (>2 mm widening).

    • B. DRUJ instability: common cause of pain and limited ROM following distal radius fractures.

      • Encountered as component of Galeazzi fractures, ulnar styloid fractures, TFCC injuries, and ulnar impaction syndrome (See Fig. 8.26a, b).

      • Clinical findings suggestive of DRUJ instability:

        • Pain with pronation/supination of forearm (holding the wrist, not the hand).

        • Pain with lateral compression of radius against the ulna.

      • “Piano-key” test: fully pronate hand and stabilize distal radius; apply an anterior-posterior force on the ulna with the other hand. If the ulna displaces with little resistance (“like pressing a piano key”), DRUJ instability is present (See Fig. 8.27).

      • Treatment/prognosis: primary method to prevent chronic disability is anatomic reduction of distal radius, which often results in an “anatomically reduced” DRUJ.