Peripheral Nerve Injuries of the Elbow, Forearm, and Hand - Medical ...

Chapter 6Peripheral Nerve Injuries of the Elbow, Forearm, and HandJacqueline J. Wertsch and Anne Zeni HochUpper limb peripheral nerve problems are seen inboth the "couch potato" and the athlete. Nerves arevulnerable to stretch, angulation, direct or indirecttrauma, or chronic irritation from overuse or overload.! Nerve problems in the elbow, forearm, wrist,and hand region are not that surprising consideringthe complex biomechanics of the upper limb. Thereis increasing understanding of the importance ofnerve movement during upper limb range ofmotion, which can involve various amounts ofelbow flexion/extension, forearm pronation/supination,wrist ulnar/radial deviation, wrist flexion/extension, and finger movements. In addition to thecomplex movements that can occur in the distalupper limb, there are also many muscles with complexfascial structures. In view of the high level ofmuscular activity in the athlete, it is surprising thatperipheral nerve injuries are reportedly relativelyuncommon. 2 This chapter reviews peripheral nerveinjuries and entrapments that have been recognizedin the elbow, forearm, and hand for both athleteand nonathlete.Median Nerve Syndromescarpal tunnel syndrome (CTS). Because CTS is socommonly known, many are quick to assume thatany numbness or weakness in the thumb or indexfinger is due to CTS.4 Other potential sites of mediannerve problems must be considered startingproximally from the neck level all the way distallyto the hand (Fig. 6.1). Potential sites of nerve injuryor entrapment in the neck or shoulder region arebeing covered in other chapters.medial cutaneous nerveof forearm--1 Arcade of Struthers'--1 Retrocondylar groove'--1 Cubital tunnel'flexor carpi ulnaris--1 Lower cervical root '--1 Brachial plexus'The median nerve contains nerve fibers from C5 toTl spinal nerves with contributions from upper,middle, and lower trunks of the brachial plexus. 3The most widely known median nerve problem isdeep ulnar motor branchJ.J. Wertsch (IBJ)Department of Physical Medicine and Rehabilitation,Medical College of Wisconsin, Milwaukee, WI, USAFig.6.1 Sites of entrapment for the median nerveV. Akuthota, S.A. Herring (eds.), Nerve and Vascular Injuries in Sports Medicine,DOI 10.1007/978-0-387-76600-3_6, © Springer Science+Business Media, LLC 200975

76In the antecubital region the most widely recognizedanatomic sites of potential median nerveentrapment include the ligament of Struthers, lacertusfibrosus, pronator teres muscle, and sublimisarch of the flexor digitorum superficialis muscles. 4Ligament of StruthersThe ligament of Struthers is a rare anatomic structure,being noted in only I % of upper limbs. 3 Thisligament has been described as extending from ananomalous humeral bony spur to the medial epicondyle.The bony spur cannot always be seen onradiographs. s Most individuals who have a ligamentof Struthers are asymptomatic, and mediannerve compromise occurs only with some other contributingfactor or trauma. 3 . S - 9 Diagnosis can bedifficult. The patient may complain of pain in thewrist or medial forearm and paresthesias in theindex or long finger.S, IO,11 The pain may be exacerbatedwith full extension of the elbow or supinationof the forearm such as the follow-through phase ofpitching. 9 , II Because the brachial artery accompaniesthe median nerve, attenuation of the pulse withprovocative maneuvers may be clinically observed. 4Needle electromyography (EMG) may help defineabnormalities in median-innervated muscles in theforearm. Because a diagnosis of a median nerveentrapment by a ligament of Struthers would berare, consultation with a specialist in upper limbperipheral nerves is recommended early in the considerationof this diagnosis.J.J. Wertsch and A.Z. Hochmedian nerve distribution. 13 Unfortunately, variationsin symptoms and signs are common, 14 andsurgical outcomes are not convincing that the anatomicproblem is the static relation of the mediannerve and the pronator teres musc le. i S' 16 0 t h erstructures in the area (e.g., lacertus fibrosus andsublimis arch of the flexor digitorum superficialismuscles) need to also be considered in the presenceof antecubital median nerve problems. 16 Even anaberrant fibrous component of the flexor carpiradialis originating from the ulna can compromisethe median nerve at this level. ? Physical examinationmaneuvers to detect the pronator syndromedescribed by Spinner are discussed in a previouschapter.Axonal changes should be evident on needleEMG if there is median nerve entrapment. A cleardiagnosis of proximal forearm median nerveentrapment would then be preferred over the termnonspecific pronator syndrome. Other causes ofproximal forearm symptoms (e.g. , focal muscle orfascia injuries) should be specifically diagnosed andnot lumped together as pronator syndrome. Use ofthe term pronator syndrome is discouraged in favorof a specific diagnosis including possible dynamicconditions in which the nerve is compressed onlyduring sports activities. Clarity of diagnosis helps toguide management. In the athlete with possibledynamic proximal forearm median nerve compression,technique modification may be helpful alongwith rest and splinting. 13 This syndrome is seen insports that require repetitive, forceful pronationand gripping. I ?, 18 Most commonly seen in throwers,pronator syndrome has been reported in weightliftmg,. arc h ery, tenms, . arm wrest l' mg, an d rowmg. . 19 ,- ?0Pronator SyndromeIn 1951 , Seyffarth l 2 described median nerve entrapmentby the pronator teres muscle. In the antecubitalarea the median nerve passes between the twoheads of the pronator teres muscle and then underthe edge of the flexor digitorum sublimis muscle.The nerve can be trapped by either of these musclesor compromised by the overlying lacertus fibrosusfrom the biceps tendon. The term "pronator syndrome"has been used by many for a clinical pictureof diffuse forearm pain and paresthesia in the distalAnterior Interosseous NerveThe anterior interosseous nerve CAIN), the largestbranch of the median nerve, arises from the mediannerve soon after it passes between the two heads ofthe pronator teres and under the flexor digitorumsublimis muscle. The AIN innervates three forearmmuscles: the flexor pollicis longus, the radial part ofthe flexor digitorum profundus, and the pronatorquadratus. Because the AIN does not have anycutaneous representation, it is often considered to

6 Peripheral Nerve Injuries of the Elbow, Forearm, and Handbe a pure motor nerve. This is technically not truebecause sensory fibers from the wrist radiocarpal,radioulnar, intercarpal, and carpometacarpal jointstravel in the AIN. 2 1 ,22 Injury to the terminal branchof the AIN can be the source of persistent, dullaching volar wrist pain, which may be diagnosedby local block of the terminal AIN branch.As early as 1918, Tinel recognized an isolated"neuritis" of the AIN branch of the mediannerve.23 Anterior interosseous nerve syndrome(AINS) was described in 1952 by Kiloh andNevin? 4 They reported two cases that were spontaneousand recovered without treatment. Fearn andGoodfellow 25 reported the first case of surgicallytreated AIN with discovery of a fibrous band compressingthe AIN in the region of the pronator teres.Although often described in earlier literature asidiopathic and spontaneous, AINS can have manycauses including bone injuries, antecubital vascularprocedures, metastasis, accessory muscles, andfibrous bands.23 Consideration should always begiven to the possibility of neuralgic amyotrophy orParsonage Turner syndrome presenting with AINweakness. 26 ,27 Careful clinical examination isneeded to ensure there are no other sites of muscleweakness, such as serratus anterior scapularwmgmg.With AINS, the typical history is acute onset ofthumb and index finger weakness. The patient mayhave noted difficulty using a fork, tearing out acheck, or picking up a cup. There are no sensorycomplaints. Clinical examination reveals an inabilityto flex the terminal phalanges of the thumb andindex finger. Because of this weakness, the patientis unable to form an "0" (Fig. 6.2), also called theOK sign. This abnormal pinch is quite constantand characteristic of the anterior interosseousnerve syndrome. 23 AINS can be confirmed onEMG examination. Needle EMG reveals abnormalitiesin the three muscles supplied by the AINwith normal examination results of other muscles.Sensory nerve conduction studies are normal.Clinical management depends on the etiology ofthe AINS.Internal topography is an important issue forthe AIN. Fascicular groups remain localizedwithin the median nerve for long distances?8,29Because these fascicles are on the posterior aspect,a humeral supracondylar fracture may damage theAIN fibers of the median nerve. 3D Thus, this much77Fig. 6.2 Typical pinch sign with flattening of index pulp and classic palsy of the anterior interosseus nerve. From Planche ret al. 50 Copyright Elsevier 1996. Used with permission

78more proximal partial median nerve injury maypresent just like an AIN problem with weaknessconfined to anterior interosseous innervated muscles3 ! ,32 A partial median nerve injury at the antecubitallevel presenting as pseudo-AINS has beenreported. 33Carpal Tunnel SyndromeThe most frequently diagnosed peripheral nerveentrapment in the general population is carpal tunnelsyndrome (CTS). In the athletic population, somebelieve that "the proximal forearm is the more usualanatomic location of median nerve impairment."!Sports involving repetitive wrist flexion and extensionsuch as gymnastics or prolonged grip withcycling may cause more cases of CTS than othersports. !8,34 CTS is frequently noted in wheelchairathletes. 2 ! Krivickas and Wilbourn,2 in a study of333 athletes, found that 24 of the 28 median neuropathycases were CTS. It is of interest that only 6 oftheir 24 patients with CTS were symptomatic. Collinset al. 35 reported CTS frequently in rowers and bicyclistssecondary to hand position. In a separate retrospectivereview, Krivickas and Wilbourn 36 studied180 athletes from 27 different sports. They found43 athletes to have median neuropathies. 25 out ofthese 43 athletes were asymptomatic.The carpal tunnel is an osseofibrous structure.The lunate, capitate, and trapezoid are the floor; thepisiform and hamate are medial; and the navicularand trapezium are lateral. The roof is the transversecarpal ligament, a portion of the volar carpalligament(flexor retinaculum). Ten structures passthrough the carpal tunnel: four flexor digitorumtendons, four flexor superficialis (or sublimes) tendons,the flexor pollicis longus tendon, and themedian nerve. 3 CTS can be caused by anythingthat either decreases the size of the canal (e.g.,thickening of the flexor retinaculum) or increasesthe volume of the contents (e.g., tendonitis).Carpal tunnel syndrome is often described withthe classic presentation ofparesthesias in the thumband index and long fingers that increases with activity.It is important to note if the paresthesias areepisodic or constant, the exacerbating or remittingactivities, and if there is nocturnal worsening. It isJ.j. Wertsch and A.Z. Hochimportant to distinguish the individual describingnightly burning intense paresthesias (dysesthesias)from the individual reporting episodic hand tingling.The time course can also be revealing, withan acute presentation perhaps preceded by years ofepisodic symptoms. The patient may report that thehand feels clumsy, especially noting difficulty withfine motor activities such as buttoning a shirt. Proximalsymptoms with discomfort and aching may bereported, especially in the extensor mass region.Physical examination may reveal sensorychanges in the median innervated digits. Themotor examination may reveal weakness of palmarabduction, although this requires attention to commonextrinsic substitution patterns that would beexpected. During a careful clinical examination,abductor pollicis brevis weakness is quite sensitivein those with CTS 3 A Phalen test can be quite helpfulwith details of how long the paresthesia lasts(less than 20 seconds would be expected) and whatdigit develops the paresthesias (most commonly thelong finger). Tapping over the median nerve at thewrist to elicit a Tinel sign is commonly done.Because the carpal tunnel is tightest at its distalend, tapping in the palm at the distal end of thetransverse ligament may increase the yield of theTinel testing for CTS. 3Unfortunately, CTS has come to be associatedwith any hand numbness, and other causes of handnumbness may not be considered. Another unfortunatereality is that many physicians still believe thatthere is a high false-negative rate for nerve conductionstudies in CTS. This was perhaps true in theearly days before careful temperature control andshort segment transcarpal studies?9 Now, nerveconduction studies, including paired transcarpalstudies, are considered by many to be the gold standardfor CTS diagnosis. Nerve conduction studiesfor CTS would include both median and ulnar studiesto make sure there is no diffuse slowing. Bothsensory and motor studies should be done. Theshort segment paired trans carpal study would beconsidered the most sensitive test. 8 Paired digitalsensory and paired motor studies would also bedone. "Mapping" should be done when the motorstudies are inconsistent with the sensory studies.Mapping simply implies moving the E I (previouslyreferred to as the active electrode) location and canbe important for avoiding false-positive median

6 Peripheral Nerve Injuries of the Elbow, Forearm, and Handmotor studies. 37 Hsu et al. reported an isolatedmedian mononeuropathy in the palm of an amateurgolfer. 38Radial NerveThe radial nerve is the largest peripheral branch ofthe brachial plexus. It receives contributions fromthe cervical roots C5- 8 and is derived from theposterior cord of the brachial plexus. In the axilla,the radial nerve is posterior to the axillary arteryand superficial to the subscapularis muscle and tendonsof the latissimus dorsi and teres major. Theradial nerve travels between the long and medialheads of the triceps, continuing to the spiral grooveof the humerus.Proximal Radial Nerve EntrapmentThe term "high radial nerve lesions" has been usedin the past for radial nerve lesions proximal to thedivision in the forearm into the posterior interosseousnerve and superficial radial sensory branch. 39The classic "honeymooners" spiral groove radialneuropathies have wrist and finger extension weakness.Distal interphalangeal (DIP) joint extension isusually preserved owing to the mechanical effect ofthe intact median and ulnar innervated intrinsicmuscles. 39 Compression of the radial nerve by thelateral head of the triceps muscles following strenuousmuscular effort has been described. I ,21 ,32,34This site is distal to the branches innervating thetriceps and anconeus muscles, both of which wouldbe expected to be spared clinically and on needleEMG studies. Compression of the radial nerve bythe long head of the triceps has also beenreported. 22 ,32,34 Compression or injury in the spiralgroove may be seen in activities that require forcefuladduction of the shoulder, as seen in gymnastics 17and wrestling. 4o Activities that require forcefulextension of the elbow against resistance, such asthrowing (e.g., discus, javelin, baseball) are associatedwith high radial nerve entrapment. 18, 19,41"Runner's radial palsy," an unusual and distinctentity that presents with numbness in the distalforearm and dorsum of the hand of runners whokeep their elbow acutely flexed while running, isanother example of a high radial nerve lesion. Thenerve in this injury is compressed between thehumerus and triceps. Treatment is altering the runningposition, resulting in complete resolution ofsymptoms. 42Forearm Radial Nerve EntrapmentThe radial nerve innervates the brachioradialis andextensor carpi radialis longus distal to the spiralgroove. In the lateral antecubital region, the radialnerve lies between the brachialis and brachioradialismuscles and passes over the annular ligament of theradius. In the proximal forearm, the radial nervebifurcates into a sensory branch and a motorbranch, the posterior interosseous nerve (PIN).The PIN usually innervates the extensor carpi radialisbrevis and sends several branches to the supinatorprior to going through the arcade of Frohse. Asthe PIN emerges from the supinator, it supplies themuscles in the extensor forearm, including theextensor digitorum communis, extensor digitiquinti, extensor carpi ulnaris and the deeper muscles(abductor pollicis longus, extensor pollicislongus and brevis, extensor indicis proprius). Similarto the AIN, the PIN terminates at the wrist, withseveral sensory branches innervating the carpaljoints. 43Historically, radial tunnel syndrome and supinatorsyndrome have both been described. 44 Theradial tunnel syndrome remains a somewhat controversialdisorder, while the supinator syndrome iscurrently more clearly called posterior interosseousnerve syndrome (PINS). They differ in their clinicalpresentations, with the radial tunnel syndromeoften described as "resistant tennis elbow" becauseit presents with pain as its primary feature whereasPINS characteristically has painless weakness.Radial Tunnel SyndromeIn 1972, Roles and Maudslel 5 introduced the term"radial tunnel syndrome." The radial tunnel was79

80described as extending from where the radial nervepierces the lateral intermuscular septum to wherethe PIN enters the supinator muscle. Radial tunnelsyndrome presents with lateral elbow pain. Objectivemotor or sensory loss in the distribution of theradial nerve would not be expected.When evaluating a patient for radial tunnel syndrome,the main differential diagnosis to consider islateral epicondylitis, or "tennis elbow." Physicalexamination findings may help differentiate thetwo. With radial tunnel syndrome there is painupon palpation of the extensor forearm musclemass a few centimeters distal to the lateral epicondyle,whereas with lateral epicondylitis the point ofmaximum tenderness is at the lateral epicondyle. 10Resisted supination is more painful with radial tunnelsyndrome. lo Three characteristic findings aredescribed for radial tunnel syndrome: pain uponpalpation of the extensor forearm muscle massabout the radial head; pain in the forearm uponresisted supination; and lateral elbow pain withresisted elbow, wrist, and long finger extension. 39The initial treatment is rest for both radial tunneland lateral epicondylitis, followed by stretching andstrengthening. 46Radial tunnel syndrome is often seen in thoseathletes who repetitively pronate and supinate andin those who are stressed in wrist extension, as inweightlifting, bowling, rowing, discus, racquetsports, swimming, and golf. 18,19,47 Roles andMaudsley thought that radial tunnel syndromemimics and may coexist with lateral epicondylitisin up to 10% of patients. 45 Werner found an 8%coincident lesion in 203 patients. 48Posterior Interosseous Nerve SyndromeThe classic presentation of PINS is painless weaknessof the wrist and finger extensors without sensoryimpairment. Wrist extension weakness generallyis not complete owing to sparing of the extensorcarpi radialis longus (ECRL), which receives innervationfrom the main radial nerve before the PINbranch. The characteristic radial deviation duringattempted wrist extension is explained by the imbalanceof a strong direct radial-innervated ECRLwith weak PIN-innervated extensor carpi ulnarisJ.J. Wertsch and A.l. Hoch(ECU). Weakness of finger extension would alsobe expected. Weakness of the brachioradialis andsuperficial radial sensory impairment would notsupport a PINS but, instead, suggests a higherradial nerve lesion. Electrodiagnostic studies shouldbe done to confirm and grade the PINS. Denervation,motor unit changes, and recruitment abnormalitieswould be expected proportional to the clinicalweakness. Surgical treatment IS oftennecessa ry. 39Cheiralgia paresthetica refers to isolated injury ofthe superficial sensory branch of the radial nerve.Numerous etiologies have been described, includingdirect trauma, fibrosis from hemorrhage, handcuffs,and pressure (from tight watchbands, a cast, tightwristbands, tape, archery guards, gloves). 17,49 Directtrauma may be responsible for this syndrome in contactsports such as hockey, football, and lacrosse. 50Ulnar NerveThe ulnar nerve receives contributions from C8 andTl nerve roots and is the distal continuation of themedial cord of the brachial plexus (Fig. 6.3). Nobranches arise from the ulnar nerve in the arm. Theulnar nerve goes under the arcade of Struthers,which is the mid-arm band of fascia connecting thedeep investing fascia of the anterior and posteriorcompartments of the arm. Proximal to the arcade ofStruthers the nerve is freely mobile. In the area ofthe arcade, the nerve travels from the anterior toposterior compartments of the arm.At the elbow, the ulnar nerve travels between themedial epicondyle and the olecranon in the retrocondylargroove. The superior edge of the medialepicondyle is an interesting site where the ulnarnerve has a fairly tight curve as it comes posteriorlytoward the retrocondylar groove. This site shouldbe carefully examined with inching nerve conductionstudies when evaluating idiopathic ulnar neuropathies.Continuing distally, the nerve passesbetween the two heads of the flexor carpi ulnaris(FCU), passing under the humeroulnar aponeuroticarcade, which along with the underlying bone andligaments form the cubital tunnel. The ulnar nervecontinues in the forearm resting on the flexor digitorum profundus (FDP) and covered by the FCU.

6 Peripheral Nerve Injuries of the Elbow, Forearm, and Handbiceps brachi muscleproximal end ofpronator teres muscle--l Lacertus fibrosus 1--l Pronator teres I--1 Sublimis arch Iflexor digitorum sublimis muscleanterior interosseous nervemain median nerve--1 Median sensory digital branches IFig.6.3 Sites of entrapment of the ulnar nerveAt the wrist, the ulnar nerve enters the handthrough Guyon's canal, which is bound mediallyby the pisiform and laterally by the hook of thehamate. In the hand, the ulnar nerve divides into asuperficial branch and a deep branch. The superficialbranch innervates the palmaris brevis anddivides into the palmar digital sensory branches.The deep ulnar motor branch supplies all otherulnar innervated hand muscles. The dorsal ulnarcutaneous (DUC) nerve branch comes off themain ulnar nerve 5- 10 cm proximal to the wrist,but the DUe can be identified as an independentbundle for some distance proximal. 28 This anatomicfeature explains the clinical observation that theDUe nerve is quite sensitive to proximal ulnarproblems.The ulnar nerve exists in a dynamic relation withanatomic structures in the elbow region. 5t Withextension, the nerve becomes redundant within theretrocondylar groove; with flexion, the medialligament of the elbow bulges into the floor of theretrocondylar groove. Elbow flexion tightens thehumeral ulnar arcuate ligament over the ulnarnerve, decreases the volume in the cubital tunnel,and elongates the ulnar nerve from its previouslyslack position. With extreme elbow flexion, themedial head of the triceps can exert a posteriorforce on the nerve. Partial or complete subluxationof the ulnar nerve occurs in up to 16% of the population.52 A subluxing ulnar nerve is rarely of anyclinical significance.Proximal Ulnar NeuropathiesEpisodic paresthesias in the ring and little fingersare a common human experience, similar to legparesthesia noted with leg crossing. The dynamicnature of ulnar paresthesias is vastly underappreciatedand in need of much more research. Thepatient with a proximal ulnar neuropathy has apersistent sense of decreased sensation in the ulnardigits, hypothenar region, and dorsal ulnar hand.The forearm should not have any numbness. Thereis no elbow pain. There may be a sense of weaknessin the hand. Patients may report difficulty gettingobjects out of their pockets because their little fingergets caught on the pocket edge (Wartenberg sign).On clinical examination there may be impairedsensation in the ulnar nerve distribution. The motorexamination may reveal ulnar intrinsic muscleweakness with preserved median intrinsic musclestrength. The ulnar innervated palmaris brevis musclecan be important to examine by looking for thepresence or absence of palmaris brevis hypothenarskin wrinkling. ThiS is a fairly reliable physical findingin significant ulnar neuropathies and shouldalways be included as either a pertinent positive ornegative finding. A positive Froment sign is seenwith ulnar neuropathies owing to the median innervatedflexor pollicis longus attempting to compensatefor the weak ulnar intrinsic muscles. The Wartenbergsign with the little finger hanging out in anabducted position can also been seen in ulnar neuropathies,reflecting the misbalance of the weakulnar interossei muscles and the intact radial innervatedextensor muscles. 53 Although both the Fromentsign and the Wartenberg sign are indicative ofulnar neuropathy, neither identifies the site of thelesion. 54 The Tinel sign over the ulnar nerve should81

82be interpreted with caution because it has beennoted to be present in more than 80% of asymptomaticnormal people. 6 ,54Although an ulnar neuropathy at the elbow isfrequently considered first in patients presentingwith "ulnar" seJ?sory symptoms, a broad differentialdiagnosis must be considered, including cervicalradiculopathy, medial cord brachial plexopathy,or even vascular or visceral problems. 55 It is widelyrecognized clinically that even patients with CTSmay present with "ulnar" sensory symptoms. 56The role of electrophysiologic data in the evaluationof suspected ulnar neuropathies has been thesubject of many publications. Parameters that havebeen utilized have included motor, mixed nerve, andsensory conduction velocity of the elbow segment;comparison of the elbow segment velocity to that ofan adjacent nerve segment; inching; change in thesize or configuration of the compound muscleaction potential or sensory nerve action potentials;and the pattern of needle examination abnormalitiesin ulnar-supplied muscles. 57 When interpretingulnar nerve conduction studies, it should be rememberedthat the exact site where the cubital begins canbe extremely variable. In a patient in whom theulnar amplitude may appear to drop at the "belowelbow" site, this may simply reflect a proximal originof the cubital tunnel and should not be misinterpretedas a conduction block. Further work isneeded on all ulnar techniques to examine repeatability,correlation to clinical features, and outcomes.Current research efforts are exploringrefinements of inching, the usefulness of includingthe dorsal ulnar cutaneous study, and the role of E2(previously referred to as the referenceelectrode).57,58The act of throwing is often responsible for ulnarnerve involvement at the elbow in athletes. Tremendousforces develop at the elbow with angular velocitiesup to 7000° Is. 18 Studies have shown that theposition of elbow flexion and wrist extension createsa threefold increase in ulnar nerve pressure in thecubital tunnel; when the upper extremity is placed inthe cocking position of a throw, the pressureincreases to six times the resting pressure. 59 Biomechanically,several processes cause an elevation ofpressure. The arcuate ligament lengthens withelbow flexion until the proximal edge becomes tautat 90° of flexion. At the same time, the ulnarJ.J. Wertsch and A.Z. Hochcollateral ligament relaxes and may bulge inward,potentially decreasing the space available to thenerve. 60 During elbow flexion, the ulnar nerve hasbeen shown to elongate an average of 4.7 mm. I ,51All of these factors can contribute to athletes' symptoms.lobe and colleagues believe that throwersdevelop a progressive flexion valgus deformitywith attenuation of the ulnar collateral ligament. 6 IThis exacerbates the athletes' symptoms by increasingthe magnitude of the tensile forces already atwork.Cubital tunnel syndrome is found more often inthe throwing athlete but can be seen in the recreationalskier, weightlifter, and racquet sport enthusiast.62 There has been a case report of cubital tunnelsyndrome involving a cross-country skier. Themechanism of injury was the extension and pronationrequired for poling. 63Distal Ulnar NeuropathiesUlnar neuropathy at the wrist and hand is uncommon.31 ,64,65 Reported etiologies have includedganglion cysts, ulnar artery thrombosis, carpal fractures(especially the hamate), anomalous muscles,and repetitive trauma or direct pressure. 1,65 In theathlete, the most widely known cause is pressurefrom handlebars seen in bicyclists (Fig. 6.4). 1,66The Guyon canal, or ulnar tunnel, is the depressionbetween the pisiform and the hook of thehamate. It is different from the carpal tunnel inthat the roof is quite thin, there are no tendons inthe Guyon canal, and there are vascular structuresincluding the ulnar artery and its associated veins 67Problems that can occur with the ulnar nerve distallyin the wrist have been classified by Shea amdMcClain. 31 Type I has involvement of all parts ofthe nerve including the hypothenar muscles, thedeep ulnar motor branch to the ulnar intrinsic muscles,and the ulnar digital sensory fibers. Type IIinvolves only the deep ulnar motor branch. Type IIIinvolves only the superficial ulnar sensory branches.Unfortunately, this classification scheme does notinclude the branch to the palmaris brevis muscle.This motor branch initially travels with the ulnardigital sensory fibers as the superficial branch of theulnar nerve. Clinicians are increasingly aware of this

6 Peripheral Nerve Injuries of the Elbow, Forearm, and Hand 83Fig.6.4 Mechanism of injury for cyclist's palsy. From Plancher et al. so Copyright Elsevier 1996. Used with permissionunusual anatomy and finding it useful to check forpalmaris brevis wrinkling with little finger abductionin all cases of suspected ulnar neuropathl 5To evaluate possible distal ulnar nerve problemsbeyond a detailed history and physical examination,electro diagnostic studies can be helpful. An initialpaired transcarpal study should be done to rule out apossible CTS presentation with ulnar sensory symptoms.56 Ulnar digital sensory studies should be doneboth orthodromically and antidromically to avoid misinterpretationof an interosseous far field motorresponse as a prolonged digital sensory response.Ulnar motor studies can be done by recording overthe hypothenar muscles or any of the ulnar intrinsicmuscles. 57 Caution is urged during interpretation ofulnar motor studies, however, as the E2 is always activeand is a significant factor that can affect not onlyamplitude and waveform shape but even latency. 58Needle EMG of many ulnar intrinsic muscles, includingboth volar and dorsal interossei, are often needed tolocalize a true distal ulnar neuropathy.65Isolated entrapment of the DUC nerve has beenreported 68 and should be considered in any patientpresenting with ulnar hand sensory symptoms. TheDUC passes between the flexor carpi ulnaris and theulna to pierce the fascia in the distal forearm. Itappears vulnerable to irritation by fast repetitiveforearm pronation and concomitant wrist flexion .Isolated entrapment of the DUC was initiallyreported in a grocery store clerk who had to passobjects over a static universal product code (UPC)reader; the disorder was thus named "pricer palsy. "68The technology improvement to wand-type UPCreaders makes this less likely to occur currently, butisolated DUC entrapment should still be consideredin those involved in sports activities with a lot offorearm/wrist repetitive movements.Digital NervesInjury to the digital nerves is often the result ofrepetitive trauma over the palm or digits. Themost common example, described by Dobynset a1. 69 in 1972, is the bowler's thumb. The termbowler's thumb describes an injury to the ulnardigital sensory nerve to the thumb caused by direct

84J.J. Wertsch and A.Z. Hochchain elements rather than the vulnerable elbow.Although the evidence is unclear, ergonomic correctionsin the individuals engaged in desk work mayalso help reduce pressures within the carpal tunneland around the elbow.Special EquipmentFig.6.S Compression of the ulnar digital nerve of the thumbin bowler's thumbtrauma from the edge of the thumb hole of a bowlingball (Fig. 6.5). The radial digital nerve of theindex finger is similarly at risk in racquet sports.?O.?1Digital nerve symptoms can be seen in baseball,handball, gymnastics, and the martial arts. I? Thechronic nature of the injury was demonstrated byBuckhout and Warner, who showed that digitalnerve involvement in handball players occur inthose with more than 2 years or 200 hours ofplay.72TreatmentFocal neuropathies of the elbow, forearm, and handcan all be treated similarly. After diagnosis andseverity of neuropathy is elucidated and underlyingconditions are addressed, a typical treatment algorithmcan be applied.Activity ModificationFirst, activity modification should be considered.For example, in bicyclists experiencing ulnar neuropathyat the wrist or carpal tunnel syndrome, thehand/wrist position should be modified so excessivepressure does not occur. Reducing repetitive loadson nerves at their tethering points has also beenadvised. Overhead athletes can be rehabilitated togenerate kinetic forces through proximal kineticEquipment can sometimes be used to reduce external/internalpres~ures and splint joints so nerves arenot stretched. For ulnar neuropathies at the elbow,pads (e.g. , hockey elbow pads) or splints can be usedto prevent the elbow joint from fully flexing andavoid maximum stretch of the ulnar nerve. Paddedbicycling gloves are also thought to reduce externalpressures on ulnar and median nerves at the wrist.Wrist splints (carpal tunnel braces), particularly inthe neutral position, have also been shown to helpup to 30% of individuals with CTS achieve significantsymptom reduction.?3MedicationMedications have been used empirically to treat variousneuropathies. Antiinflammatory drugs, neuropathicmedications, diuretics, and various analgesicshave been used with mixed success. There is no goodliterature on the use of nonsteroidal antiinflammatoriesas monotherapy for CTS and little literaturefor other neuropathies. Vitamin B6 (pyridoxine) hasbeen used for CTS, but theoretically it should onlyhelp individuals with concomitant peripheral neuropathy.Injected corticosteroids are relatively frequentlyused for CTS but not other neuropathies.Bland concluded that 70% of CTS patients significantlyimprove with carpal tunnel corticosteroidinjection, but 50% relapse within 1 year. 73SurgerySurgical release can be utilized to treat various neuropathies.Carpal tunnel release surgery is commonand appears to "cure" CTS in at least 75% of individuals.73 Open and endoscopic carpal tunnel release

6 Peripheral Nerve Injuries of the Elbow, Forearm, and Handcan be performed for recalcitrant and severe CTScases. Endoscopic surgery may be appealing to athletesas it offers a faster recovery time. However,individuals should be cautioned that endoscopicmethods are not as well studied as others, and complicationprofiles are not as clear owing to incompleteexposure and transection of the transverse carpalligament.Ulnar nerve surgery about the elbow is alsofrequently performed for recalcitrant ulnar neuropathies.Surgery may include release and decompression(e.g. , in cases where the ulnar nerve appears to beentrapped distal to the elbow at the humeroulnaraponeurotic arcade) or an anterior transposition andmedial epicondylectomy (e.g., in cases where ulnarneuropathy occurs at the ulnar groove). 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