Nerve Entrapment Syndromes - Alistair Jepson 4/2/2002

ENTRAPMENTNEUROPATHIES

Probablyischaemic in origin

MEDIAN NERVE COMPRESSION

Pronator syndrome

Carpal tunnel syndrome

Pathology

- Proximal edge of the flexor retinaculum is the site of major compression of the median nerve(Phalen 1951, 1966 & Phalen and Kendrick 1957), however not the primarycause

- Phalen noted that flexion aggravated symptoms, c.f. extension, which was basis for his test (Phalen 1972) “ 60 seconds

- Flexion of wrist best test - Gellman H, Gleberman RH, Tan AM, Botte MJ. Carpal tunnelssyndrome: an evaluation of the provocative diagnostic test. JBJS 1986; 68-A:735

- Durkan described direct compression with thumb over the median nerve for 30 seconds “more specific (90%) and more sensitive (87%) “ Duran JA. A new diagnostic test for carpal tunnel syndrome. JBJS 1991; 73-A: 535

- Nerveconduction studies test: 90% sensitive and 60% specific

Epidemiology

- Occurs mostcommonly ages 30-60, 5F:1M

Aetiology

- Multiple causes& associations

- Malaligned Colles # (& extreme flexion &ulna deviation of immobilization post reduction)

- Oedema from infection/trauma

- Ganglion, lipoma or xanthoma

- Systemic conditions: Obesity, Diabetes, Thryoid dysfunction, Amyloidosis & Raynaud's disease

- Sleeping posture

- Trauma “ repetitive hand motion e.g. vibrating tools, typists

- Preganancy

- Aberrant muscles of forearm

- Acute thrombosis of median artery (ACUTE onset)

- Rheumatoid tenosynovitis

Treatment

- Kaplan SJ,Glickel SZ, Eaton RG. Predictive factors in the non-surgical treatment ofcarpal tunnel syndrome. J Hand Surg 1990; 15-B: 106

ULNARNERVE COMPRESSION

Guyon'scanal

- Felix Guyon(1861) published first description of canal at base of hypothenar eminence

- Roof: volar carpal ligament (relatively loose c.f.carpal tunnel)

- Lateral wall: hook of hamate to which volar carpallig attaches

- Medial wall: pisiform bone

- Contents: ulna a. & n. (divides in canal intodeep & superficial branches)

- Causes: often occupational “ repetitive blunt trauma; ganglions & lipomas common; #'s of hamate or ring/little finger MC's

Cubital tunnel syndrome

Pathophysiology:

- Chronic irritation of the nerve due to its superficial position initiates a vicious circle where inflammation & oedema reduce the natural longitudinal sliding, and further elbow flexion causesmicrostretching injuries in a fixated nerve, leading to extra-neural scarring. Fixed nerve has impaired intra-neural antero & retrograde microcirculation ('double crush syndrome')

- Nerve elongates 4.7 to 8mm with elbow flexion &intra-neural pressures exceed 200mmHg with elbow flexion & FCU contaraction(Bozentka CORR 1998; 351: 90-4)

- Resulting hypoxia from disturbances in localintra-neural microcirculation may cause ectopic impulse generation in axons,felt as tingling in digits. Permanant oedema may result in local demyelinationwith permanent symptoms & later degeneration of nerve fibres will result inmuscle wasting & loss of sensibility

Clinical tests:
1. Percussion/Tinels
2. Abnormal motility of nerve over medialepicondyle
3. +ve elbow flexion test ( ­ numbness with full elbow flexion &forearm supination)

Presence of intrinsic wasting warrants early surgery

Suggested causes of entrapment:

- Anatomy: arcade/ ligament of Struthers,medial intermuscular septum, the anconeus epitrochlearis (anomalous muscle),arcuate ligament of Osborne (forms roof of tunnel), aponeurotic band of FCU,hypertrophy of medial head of triceps

- Elbow pathology: osteophytes, synovitis,ganglia or lipomata assoc with elbow joint

- Nerve pathology: external compression 2 ° to subluxation of ulna n. acrossepicondyle

Suggested Mx:

- C onservative Mx: splintage in semi-flexedposition to keep nerve relaxed & to protect nerve from trauma, leading to reduced oedema “ night and/or day)

- Surgical decompression of ulnar nervealone

- Anterior transposition of nerve (subcutaneous or submuscular “ partial or complete undefined

- Medial epicondylectomy (partial orminimal

- [Fascial repairs to prevent nerve subluxation]

Few surgeons ever do internal neurolysis for ulnarnerve compression at elbow

Eversmann in Green believes that:

- Indications for ulnar nerve decompression alone: where symptoms well localized to elbow(+ve perussion over fibrous arcade of FCU) & at time of op narrowing of nerve seen at same point. Identify branches; epineurotomy acceptable if stillnarrowed after decompression but no internal neurolysis “ damages fragile B.S.;check no subluxation at end

- Indications for anterior transposition : subluxation of nerve, persistently positiveelbow flexion test, previous failed decompression, and anatomic lesions thatinterfere or impinge on nerve e.g. bony prominence, valgus deformity of elbow

- Follow 8cm proximally & through FCU distally(protect branches & blood vessels) +/- excision of medial intermuscularsection (must perform decompression along long length to avoid sharp edges)

1- Subcutaneous transposition: suture from anterior skin flap to medial epicondyle. Eaton et alis one technique described (uses a fasciodermal sling “ i.e. subcutaneous tissues secured to wide aponeurotic flap raised from superficial part of aponeurosis of medial epicondylar muscles)

2- Submuscular transposition: sharp dissection of CFO off medial epicondyle (leaving pronatorteres “ most lateral - if partial); bulky dressing; immobilize for 2/52 incast. Technique of Learmonth most commonly used. Good in thin pts & those who do heavy labour.

- Advantage of transposition “ gain length & if placed submuscular rich blood supply

- Problems: affecting vascularity, damage to branchese.g. to FCU, leaving new site of compression if the arcade of Struthers, medial intermuscular septum & flexor muscle mass are not mobilized adequately; more complex post-op (immobilization req'd); damage to medial brachial & antebrachial cutaneous nerves; weakness of flexor-pronator power