The Wrist I. Anatomy. III. Wrist Radiography Typical wrist series: Lateral Oblique

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1 The Wrist I. Anatomy The wrist is a complex system of articulations comprising 27 articular surfaces among the radius, ulna, carpus, and metacarpals. It is generally agreed that the wrist is comprised of four joints: the distal radioulnar joint (DRUJ), the radiocarpal joint, the midcarpal joint and the carpometacarpal joints. The carpus is arranged as two rows of eight bones. The proximal row consists of (from radial to ulnar side) the scaphoid, lunate and triquetrum bones. The pisiform bone is a sesamoid bone located within the tendon of the flexor carpi ulnaris. The distal carpal row is comprised of (from radial to ulnar side) the trapezium, trapezoid, capitate and hamate bones. Each carpal bone is tethered to its neighbor by an interosseus ligament. The proximal row consists of the scapholunate and lunotriquetral interosseus ligaments. The interosseus ligaments of the distal row rarely fail clinically and, therefore, will not be addressed in this article. Other ligaments tether the ulnar carpus to the ulna (ulnolunate and ulnotriquetral ligaments) and the radial carpus to the radius (radioscapholunate ligaments). Finally, added to these are the ligamentous components of the TFCC, such as the volar and dorsal radioulnar ligaments and the ulnar collateral ligament. II. Biomechanics The principle movements of the wrist include wrist extension, flexion, radial deviation, ulnar deviation, supination and pronation. The normal range of motion about the wrist as 80 of flexion, 70 of extension, 20 of radial deviation and 30 of ulnar deviation. The bony structures of the DRUJ provide very little inherent stability. Both intrinsic and extrinsic structures offer most of the support at the DRUJ. The triangular fibrocartilage complex (TFCC) gives the major intrinsic support. The TFCC comprises ligamentous and cartilaginous structures on the ulnar side of the wrist, situated between the ulna and the ulnar carpus. Extrinsic contributors include the pronator quadratus, interosseous membrane, and flexor and extensor carpi ulnaris tendons. At the ulnocarpal joint and the DRUJ, TFCC injuries may result in instability. III. Wrist Radiography Typical wrist series: PA Lateral Oblique

2 Optional = Scaphoid view (AP with ulnar deviation)

3 1. Fat Pads- there are two primary fat pads to bear in mind in the wrist: pronator quadratus and scaphoid fat pads. Normally in both of these areas, you may see small fat pads. With injuries, such as fracture, these fat pads will be larger and more convex. This will give subtle clues to the presence of fractures. The scaphoid fat pad is a collection of fat between the radial collateral ligament and the extensor pollicis brevis and the abductor pollicis longus. An abnormal fat pad is seen with fractures (scaphoid, distal radius or trapezium) in this area in ~ 85-90%. 2. Angles and Measures- there are a number of indices at the hand and wrist that may aid the clinician in reading xrays. Many of these indices are not well studied in terms of their accuracy in diagnosis of orthopedic injuries. Some of them, however, may be more useful to the family physician in the diagnosis of wrist sprains and fractures. For example, the use of the scapholunate gap and angle may allow for quick assessment of wrist instability (sprain). A wrist sprain can involve the scapholunate ligament. This more common sprain may result in characteristic changes on xray. The classic increase in scapholunate gap (normal < 2 mm, abnormal > 4 mm) on AP views and abnormally high S-L angle (normal ) on lateral views may be appreciated. A S-L angle > 60 is termed a DISI phenomenon. This term is used to describe the characteristic biomechanics of the carpal bonesthe proximal row (esp. lunate) is extended; the term DISI, dorsal intercalated segmental instability. Another xray finding is a positive ring sign seen on AP views. As the scaphoid continues to extend, the appearance of the scaphoid seen end-on, resembles a round bone, with a whitish (sclerotic) border. This gives a characteristic "ring" appearance. Over time, the S-L gap increases until the capitate is seen trying to wedge itself between the scaphoid and the lunate. The extreme of this is what is termed a SLAC lesion (scapholunate advanced collapse). Another type of wrist sprain involves stretch or tear of the lunotriquetral ligament. Lunotriquetral dissociation causes the proximal row (esp. lunate) to flex causing the typical VISI phenomenon seen on lateral views. With VISI instability (S-L angle < 30 ) the lunate is in flexion. The S-L gap is typically not widened.

4 3. Ulna variance. On AP views, the ulna may appear shorter or longer than the radius. This depends somewhat on the position of the wrist, but with most wrists, the ulna is from 2 mm below to 4 mm above the radius. Ulna negativity refers to an ulna that is below the radius, while ulna positivity refers to the ulna appearing above the radius. Therefore, normally, the ulna is between +4 to -2. The importance of this relates to the idea that the amount of force transmitted through each bone of the forearm changes as the ulnar variance changes. In addition, the amount of ulna negativity or positivity reflects the thickness of the TFCC (triangulofibrocartilage complex). The TFCC is a complex on the ulnar side of the wrist akin to the meniscus of the knee. A number of studies demonstrate an inverse relationship between the thickness of the TFCC and the likelihood of a TFCC tear. The TFCC does not show up well on xray, so this would assist the clinician in expediting the diagnosis. In addition, an ulna that is significantly ulna positive has a higher chance of abutting the lunate over time and may produce degenerative changes to the lunate (cystic and sclerotic changes) that may be symptomatic. This is termed ulnar impaction syndrome (OA). IV. Wrist Injuries A. Tendons 1. Wrist tendinitis is common. Tendinitis occurs primarily with extensor and flexor carpi ulnaris (ECU, FCU), the other extensor tendons and the thumb tendons (abductor pollicis longus, extensor pollicis brevis). a. Hx- Mechanism is repetitive action (overuse) of these tendons. Patient will also describe pain with activity. Common in carpenters, tailors, using screwdrivers, turning knobs, etc. b. PE- Pain to palpation and resisted motion. Generally demonstrates full ROM. c. Xrays- not indicated unless acute trauma or unresponsive to initial treatment. If xrays obtained, may demonstrate specific calcifications along the tendon. d. Rx- RICE, NSAID's; If continued pain consider P.T or.splint

5 2. DeQuervain's tenosynovitis- inflammation of tendons and tendon sheaths of the abductor pollicis longus and extensor pollicis brevis as they course over the radial styloid. Usually dominant hand. a. Hx- Mechanism = repetitive thumb abduction and extension. Overuse. b. PE- tender to palpation tendons over radial styloid; + finkelstein s test: Finkelstein s test: Ask patient to grasp his/her own thumb; examiner passively deviates the wrist in ulnar direction. Positive test is pain at radial styloid. c. Dx- H&P, rarely need xrays. d. Rx- RICE, NSAID s; if continued pain use P.T. and Universal thumb splint. Injected steroids if recalcitrant pain. B. Ligament Injuries 1. Scapholunate sprains: The disruption of the scapholunate ligaments is the most common type of wrist ligament injury. Mechanism = FOOSH. PE- + Watson s scaphoid shift test; +TTP dorsum of the wrist on radial side and midline. Watson s scaphoid shift test The distal scaphoid will translate dorsally with ulnar deviation of the wrist. The intact scapholunate ligaments allow smooth transition of the distal scaphoid. With scapholunate disruption, the scaphoid will click into position. A click indicates tear to scapholunate ligaments and is a + test. May be difficult to perform in the acute injury due to pain. Dx- Xrays may demonstrate a wide gap between the scaphoid and lunate (normal gap <2 mm) and increased scapholunate angle ((normal o ). MRI useful if questions of concomitant scaphoid fx. Rx- acute injury usually treated with short arm cast x 4-8 weeks; PRICES. Consider surgery if continued Sxs or xray changes (increased widening of the gap, collapse of the capitate between the scaphoid and lunate). 2. TFCC injuries: the TFCC, as stated previously, is a complex located at the ulnar side of the wrist. It is the meniscus of the dorsal, ulnar wrist. Hx- mechanism is either acute tear of the TFCC with FOOSH vs repetitive tear with overause/degeneration. Common in gymnasts, hockey, racquet sports. PE- + TTP of the dorsal ulnar wrist; + ulnar grind test. Ulnar grind test- pain with ulnar deviation of the wrist. This pain is localized to the ulnar side of the wrist. Some authors advocate rotation of the wrist while you ulnarly deviate the wrist (in a figure-of-eight motion).

6 Dx- xrays help r/o other causes of pain. MRI may be helpful, though false negative rates are still high Consider MR-arthrogram for best results. Rx- Definitive treatment of TFCC tears remains controversial. Acute tears may require cast immobilization for 4-6 wks; chronic tears may require PRICES, PT. If continued pain, consider surgery. C. Nerve entrapment 1. Carpal tunnel syndrome (CTS)- most common nerve entrapment in the body. Carpal tunnel made up of carpal bones dorsally, and the transverse carpal ligament volarly. Typical age is years; women: men 3:1. Associated with pregnancy, DM and RA. Association of CTS with computer use not definitively seen. The median nerve provides sensory to and thumb abduction. Hx- Entrapment of the median nerve causes pain, paresthesias in the volar hand, wrist and forearm (even to the shoulder). The distribution of these sxs is quite variable and not always consistent with this exact diagram. Common with repetitive motion, worse with wrist flexion (which decreases the size of the carpal tunnel). Worse at night with altered sleep patterns. PE- Tinel s test (tap on volar wrist) positive for paresthesias/pain in median nerve distribution. Phalen s test (60 seconds of bilateral wrist flexion to 90 o ) positive for paresthesias/pain in median nerve distribution. Thenar atrophy is late sign. No clinical exam finding accurately predicts positive EMG result. Dx- H&P; Xrays not helpful for CTS but may rule out other causes of sxs; Note: EMG = current diagnostic standard, but has drawbacks. It can be used, especially to r/o radicular cause of pain (neck OA or HNP). Some third party payers require it before compensating claims. EMG pitfalls: EMG + in 45% Sx patients; EMG 33% negative in clinically certain cases of CTS; EMG + 20% ASx subjects. Rxo Activity modification (avoid vibratory machines, etc.); NSAID still recommended despite info below. o Volar cock-up wrist splints at night can be helpful. Duration unclear. Some data to suggest full-time brace (vs nocturnal) provides greater improvement of sx. o Oral meds- NSAID s, B6, diuretics- variable to no benefit demonstrated. o Oral steroids- variable results, but better than other oral meds, not as good as injected steroids at 8 and 12 weeks. o Steroid injx: there is strong evidence of benefit up to 80% (though recurrence can

7 occur). If recalcitrant pain despite these measures, REFERRAL to ortho. o Surgery relieves sxs in up to 85%. Sxs resolve before resolution of EMG changes. No clinical or test results accurately predict recovery from CTS release. Surgery especially helpful for severe entrapment on EMG, or thenar atrophy or motor weakness (even with normal EMG). 2. Ulnar tunnel syndrome Much less common than CTS. The ulnar nerve is compressed at the site of the ulnar tunnel (Guyon s canal). The ulnar tunnel is enclosed by the palmar ligament. The artery, vein and nerve pass thru the tunnel. No tendon passes thru the tunnel. Scar, fibrosis or repetitive compression will produce classic Sxs. The ulnar nerve produces sensory innervation to the fifth digit and the ulnar side of the fourth digit. Motor function includes the muscles of the hypothenar eminence, the interossei and some of the lumbricals. Hx- often occupational exposure or cyclist palsy. Mechanism = repetitive stress to the hypothenar eminence. PE- variable exam. May see weakness with finger flexion and abduction. Must rule out ulnar nerve dysfunction from the elbow (more common site of ulnar nerve compression). Dx- EMG helpful in localizing the site of compression (proximal vs distal). Xrays + MRI of C-spine may assist with Dx of HNP or OA at neck and C8-T1 nerve root problems. Rx- usually nonsurgical. Avoidance of activity; protective gloves; surgical explration if continued Sxs (months). D. Bones 1. Scaphoid Fracture a. Mech = fall on outstretched hand with wrist in hyperextension. Typically requires more wrist extension and force to create scaphoid fx than distal radius fx. b. Classification - Proximal pole (30%), waist (most common, 50-60%), distal pole and tubercle (the latter two combined account for 10% of all scaphoid fx). Vasculature often enters from the distal pole, running proximally. Fractures, therefore, of the proximal pole are at risk (30%) for avascular necrosis. This phenomenon is immediate in onset, but may take 1-2 months to become visible on xray. PE = pain in anatomic snuffbox and/or palmarly. Decreased ROM. Radiology - AP, lateral; oblique and scaphoid (AP in ulnar deviation) views can be helpful. If negative, repeat at 2-4 weeks or obtain further testing. Diagnosis requires high

8 clinical suspicion. If tenderness and negative radiography, treat as if fx. Also, some evidence that MRI may add needed support for the presence of scaphoid fracture. In addition, MRI of the wrist will yield info about other structures of the wrist, such as scapholunate ligaments, etc. Rx- if undisplaced fx, rx with thumb spica cast (wrist in slight radial deviation). The reported duration of casting depends upon the location of fracture (as explained in the table below: Location of Fracture Distal Pole Waist Proximal Pole Duration of Casting 6-8 weeks 8-12 weeks weeks There is continued debate whether regarding cast length and duration. Some authors utilize a long arm thumb spica cast initially (for about 2-6 weeks), then switch to a short arm thumb spica for the until fx line healed radiographically. If continued pain or evidence of avascular necrosis/nonunion at 12 weeks, referral to surgeon is appropriate. If displaced fx referral to surgeon for screw placement. 2. Distal Radius a. Colles Fracture (distal radius with dorsal angulation): Fall on outstretched hand in hyperextension. PE with obvious "silver fork" deformity, edema and ecchymosis. Beware coexistent ulnar fracture, distal radioulnar joint (DRUJ) subluxation/dislocation, median nerve palsy and referred injury. Xray consistent with above. Assess follow-up xrays at 2-4 weeks for delayed displacement, angulation, shortening of radius and callous formation. Treatment as below: Undisplaced, minimal angulation: short arm cast (with wrist in slight flexion and ulnar deviation) for 4-6 weeks. Mild displacement/angulation > 5 mm loss of radial height, and >10 o dorsal tilt of distal radius (normal wrist has ~ o of volar tilt): long arm cast while maintaining traction. Manipulation via distraction and volarly directed force. Obtain post-manipulation xrays. Consider weekly xrays for 3-4 weeks if manipulation required. If difficult to maintain anatomic reduction, REFER to surgeon. Some authors advocate referral of any fx requiring manipulation. Moderate-to-severe displacement/angulation or associated injuries (DRUJ dislocation, median nerve palsy, etc.), REFER to surgeon. b. Smith's Fracture (distal radius with volar angulation) AKA reverse Colles: Mech = fall on back of flexed hand. Much less common than Colles fx. Xrays demonstrate volar

9 angulation. If fx line is transverse (type I), treatment with short arm cast for 4-6 weeks. c. Torus and Greenstick Fractures- also check for concomitant ulnar injuries. Treatment the same as above. REFER large displacements and angulation (> o ). Expect quicker healing in this pediatric age group than with fractures above. d. Radial Styloid Fracture- AKA Chauffeur's fracture: when cars were first made, many required hand crank in front of the car/engine to start. kick-back on hand crank to start engine struck forearm)- minimal displacement, angulation = cast immobilization. REFER for displacement, angulation. Note- consider short-arm thumb spica cast in the above situations if significant pain with thumb movements, and long-arm thumb spica cast if significant pain with supination/pronation movements.

10 WRIST REFERENCES Brydie A, Raby N. Early MRI in the management of clinical scaphoid fracture. Brit J Radiol. 76: , Darcy CA, McGee S. Does this patient have carpal tunnel syndrome? The rational clinical examination. J Am Med Assoc. 283(23): , Gerritsen A, dekrom M, Struijs A, et al. Conservative treatment options for carpal tunnel syndrome: a systematic review of randomized controlled trials. J Neurol. 249:272-80, Goodyear-Smith F, Arroll B. What can family physicians offer patients with carpal tunnel syndrome other than surgery? A systematic review of the nonsurgical management. Ann Fam Med. 2(3): , Gutierrez, G. Office management of scaphoid fractures. Phys and Sports Med. 24(8):60-70, Massy-WestroppN, Grimmer K and Bain G. A systematic review of the clinical diagnostic tests for carpal tunnel syndrome. J Hand Surg. 25A(1):120-7, Morgan RL, Linder MM. Common wrist injuries. Am Fam Phys.. 55(3):857-68, Retig A. Athletic injuries of the hand. Part 1: Traumatic injuries of the wrist. Am J Sports Med. 31(6): , Retig A. Athletic injuries of the hand. Part 1: Overuse injuries of the wrist, traumatic injuries of the hand. Am J Sports Med. 32(1): , Viera AJ. Management of carpal tunnel syndrome. Am Fam Physician. 68(2): , 2003.