Sports Medicine: Just the Facts

findings. A description of the components of an EDX

evaluation will be provided.

• EDX are divided into nerve conduction studies(NCS)
  and needle examination(NE). The NE is also referred
  to as electromyography(EMG).


• The purpose of the information presented in this chap-
  ter will be to provide the clinician a basis of ordering
  and understanding proper EDX reports.

ANATOMY

• Electrodiagnostic studies evaluate the peripheral
  nerve system or lower motor neuron pathway.


• The peripheral nervous system includes both the
  afferent sensory pathway and the efferent motor path-
  way.

SENSORY (AFFERENT) PATHWAY

• Cutaneous receptors →sensory axons →pure sen-
  sory or mixed nerves →nerve plexus (e.g., brachial
  plexus, lumbosacral plexus) → cell bodies in the
  dorsal root ganglion (usually within intervertebral
  foramina) → dorsal roots synapse in dorsolateral
  spinal cord.


• NCS of pure sensory and mixed nerves evaluate this
  aspect of the peripheral nervous system.

MOTOR (EFFERENT) PATHWAY

• Anterior horn cell (spinal cord) →spinal nerves →
  divide into ventral and dorsal rami. Ventral rami →
  nerve plexus →peripheral motor nerve →neuromus-
  cular junction →muscle. Entire pathway is referred to
  as a motor unit.
  
  
  • NCS of the pure motor and mixed nerves evaluate this
    aspect of the peripheral nervous system.
  
  
  • Motor units are evaluated during needle EMG with
    voluntary muscle activation.
  
  
  
  

PATHOPHYSIOLOGY OF

NERVE INJURY

• Peripheral nerves can either be myelinated or
  unmyelinated.


• Myelinated fibers have nodes of Ranvier, which facilitate
  saltatory (jumping) conduction along the nerve fiber.


• NCS evaluate the fastest conducting fibers—usually A
  alpha myelinated fibers.


• Peripheral nerve injury is categorized by injury to the
  myelin alone or to the axon.

SEDDON CLASSIFICATION

•Divides peripheral nerve injury into neurapraxia,

axonotmesis, neurotmesis (Table 19-1).

NEURAPRAXIA

• Neurapraxia is focal conduction slowing or focal con-
  duction block. Myelin is injured; yet, the nerve fibers
  remain in axonal continuity. This results in impaired
  conduction across the demyelinated segment; how-
  ever, impulse conduction is normal in the segments
  proximal and distal to the injury.


• Demyelination is mostly seen with focal nerve entrap-
  ments, e.g., carpal tunnel syndrome. It may also occur
  in peripheral polyneuropathies as either a patchy
  process (e.g., Guillain-Barre syndrome) or a diffuse
  process (e.g., diabetic peripheral neuropathy).

112 SECTION 2 • EVALUATION OF THE INJURED ATHLETE

TABLE 19-1 Classification of Nerve Pathophysiology

TYPE PATHOLOGY EDX CORRELATION PROGNOSIS

Neurapraxia Myelin injury CV slowing across segment Recovery in weeks
DL prolonged across segment
Loss or amplitude proximal but not distal
NE normal

Axonotmeses Axonal injury with endoneurium intact Loss of amplitude distal and proximal Longer recovery
NE show spontaneous activity
NE shows abnormal voluntary motor units

Neurotmeses Severance of entire nerve No waveform with proximal or distal stimulation Poor recovery
NE shows spontaneous activity
NE shows no recruitable motor units

ABBREVIATIONS: CV =conduction velocity; DL =distal latency; NE =needle examination