Sports Medicine: Just the Facts

67 NERVE ENTRAPMENTS OF THE

LOWER EXTREMITY

Robert P Wilder, MD, FACSM

Jay Smith, MD

Diane Dahm, MD

INTRODUCTION

• Neurological conditions currently account for 10 to
  15% of all exercise-inducted leg pain among runners
  (Smith and Dahm, 2001; McCluskey and Webb, 1999;
  Massey and Pleet, 1978).


• Among runners, most nerve entrapments occur at or
  below the knee. In order of decreasing frequency,
  common nerves affected include the interdigital nerve
  (interdigital or Morton’s neuroma), the fir st branch of
  the lateral plantar nerve (FB-LPN), medial plantar
  nerve (MPN), tibial nerve (TN), peroneal nerve deep
  and superficial portions(DPN and SPN), sural nerve
  (SN), and saphenous nerve (Smith and Dahm, 2001;
  Schon and Baxter, 1990).
  •Nerve entrapment produces neuropathic pain,
  described as a diffuse, aching, burning discomfort,
  often accompanied by tingling and cramping.
  Numbness is less common. Neuropathic pain classi-
  cally occurs in the nerve distribution distal to the
  injury site (Smith and Dahm, 2001).
  •However, symptoms may affect only a portion of the
  distal nerve, and may also radiate proximally (called
  the Valleix phenomenon) (Lau and Daniels, 1999).
  Symptoms usually occur during and shortly after run-
  ning, although some syndromes include components
  of rest and nighttime pain (e.g., tarsal tunnel syn-
  drome).


• Examination findings include tenderness over the
  affected site and a positive percussion sign (Schon,
  1994; Baxter, 1993). The percussion sign, or Tinel’s
  sign, involves percussion along the length of the
  nerve. Neuropathic pain reproduction with palpation
  or percussion suggests the possible level of the lesion
  (Downey and Barrett, 1999; Henderson, 1948).


• Motor or sensory deficits may be subtle requiring
  focused examination.


• Double crushinjuries, in which a proximal nerve
  injury renders the distal portion of the nerve more sus-
  ceptible to insult, have been reported in the lower limb
  (Upton and McComas, 1973; Sammarco, Chalk, and
  Feibel, 1993).


• The majority of entrapment neuropathies are
  diagnosed clinically, with supportive imaging and

electrodiagnostic(EDX) testing. EDX testing is

only occasionally positive, but is useful to exclude

alternative neurological conditions (Park and Del

To r o, 1998).

COMMON NERVE ENTRAPMENT

SYNDROMES

INTERDIGITAL NEUROMA (MORTON’S

NEUROMA)

DEFINITION

• Interdigital neuromas commonly affect the third web
  space, but may rarely affect the second or fourth web
  spaces.

ANATOMY, PATHOPHYSIOLOGY, ANDRISKFACTORS

• At the level of the matatarsal heads, the interdigital
  nerve passes under (superficial) to the intermetatarsal
  ligament. During push off, forceful toe dorsiflexion
  may compress and stretch the nerve beneath the inter-
  metatarsal ligament (Baxter, 1993). A tumorous mass
  may develop just distal to the intermetatarsal liga-
  ment.


• Risk factors include prolonged walking or running
  (especially during push-off), squatting, use of high-
  heeled shoes, or the demi-pointe in ballet (Smith and
  Dahm, 2001).


• Hyperpronation dorsiflexes the third metatarsal rela-
  tive to the fourth, exposing the nerve to injury (Schon
  and Baxter, 1990). Hallux valgus or a hypermobile
  first ray may lead to callus formation, increasing
  intermetatarsal pressures. Metatarsophalangeal joint
  (MTJ) synovitis may cause local edema and interdig-
  ital nerve compression (Schon, 1994). Soft soled
  shoes or a heel lift may cause symptoms due to
  increased toe dorsiflexion.

SYMPTOMS ANDSIGNS

• Neuropathic pain between the third and fourth toes,
  increased with running, walking, toe dorsiflexion, and
  squatting. Burning/cramping is common, as is night
  pain.
  •Tenderness in the intermetatarsal space. Provocative
  testing includes squeezing the metatarsals together
  during palpation (metatarsal squeeze test) with distal
  radiating neuropathic pain. A click (Mulder’s click)
  may result as the neuromasubluxes from between the
  metatarsals (Schon and Baxter, 1990). A web space
  sensory deficit is occasionally seen, but no motor
  deficit is expected to occur along the purely sensory
  nerve.

396 SECTION 4 • MUSCULOSKELETAL PROBLEMS IN THE ATHLETE