Sports Medicine: Just the Facts

CHAPTER 19 • ELECTRODIAGNOSTIC TESTING 115

• Surface or needle electrodes placed into muscles to
  record EMG signals through multiple channels.


• Caution should be used in correlating EMG signal
  amplitude with muscle force because the relationship is
  not consistently linear (Basmajian and DeLuca, 1988).


• Has been used to assess the degree of muscle fatigue
  and biomechanics of sports activities (Feinberg,
  1999).


• The kinesiology of the running gait has been eluci-
  dated with EMG. The glueal muscles and hamstrings
  are more active in running than in walking, particu-
  larly at the termination of the swing phase in prepara-
  tion for foot strike. The quadriceps and posterior calf
  group also work during a greater percentage of the
  swing and stance phase during running than in walk-
  ing. The calf muscle group in particular becomes
  much more active as the speed of gait increases
  (Mann, 1995).


• Surface EMG can be used as a biofeedback technique
  in athletes to improve their sport specific biomechan-
  ics (i.e., training the use of the hip extensors).

INDICATIONS FOR EDX TESTING

• The utility of EDX testing in a given athlete may be
  estimated following a thorough history and physical
  examination, by a review of supplemental information
  (e.g., imaging studies), and through an appreciation
  for the chronology of the electrophysiologic changes
  that occur following nerve injury.


• Some useful generalizations about the indications for
  EDX studies are the following (Press and Young,
  1997):
  
  
  1. Establish and/or confirm a clinical diagnosis.
     a. EDX examination can rule in a suspected diag-
     nosis or rule out a competing diagnosis.
     b.EDX studies may alert the possibility of an
     unsuspected concomitant pathologic process
     (i.e., an athlete with tarsal tunnel syndrome with
     superimposed radiculopathy).
  
  
  2. Localize nerve lesions.
     a. Nerve injury localization often needs to be
     objectively confirmed prior to contemplating
     invasive or surgical treatment.
     b.An athlete presenting with plantar foot numb-
     ness and tingling may have a sciatic nerve
     lesion anywhere along the course of the nerve or
     its branches.
     c. EDX studies can be used to determine if the sci-
     atic nerve injury is occurring at the piriformis or
     at its terminal branches.
  
  
  3. Determine the extent and chronicity of nerve
     injuries.
  
  
  
  

a. Properly timed EDX studies can differentiate a

neuropraxic injury from axonal degeneration.

This may have a significant impact on the

aggressiveness of treatment for nerve injury.

b.The acuteness and chronicity of the nerve lesion

may also be assessed using fibrillation ampli-

tude and motor unit analysis, as well as clinical

history (Robinson and Stop-Smith, 1999; Kraft,

1990).

4. Correlate findings of anatomic studies.
   a. EDX studies are useful to correlate nerve func-
   tion to anatomic abnormalities.
   b.This may be particularly useful in the spine
   because disc herniations effacing nerve roots
   can be seen in asymptomatic individuals
   (Jensen et al, 1994).


5. Assist in prognosis and return to play.
   a. By determining the degree of nerve injury, the
   clinician can predict nerve function recovery.
   b.In general, neuropraxic injuries recover sooner
   than axonal injuries.
   c. CMAP amplitude measurements of weak mus-
   cles (compared with asymptomatic contralateral
   amplitude) can give an idea of the extent of neu-
   roproxia and of potential recovery.
   d. A side-to-side amplitude difference of greater
   than 50% is probably significant.
   e. However, EDX studies should not be the sine
   qua non for return to play because they may lag
   behind clinical recovery.
   f. The best determination of return to play remains
   the athlete’s functional performance in simu-
   lated sports activities (Feinberg, 1999).

LIMITATIONS OF EDX TESTING

• Electrodiagnostic testing is not a perfect test and
  should not be performed in every athlete with neuro-
  logic signs or symptoms.


• Some diagnoses are unequivocal and treatment should
  be initiated without delay (e.g., progressive neuro-
  logic deficits following a traumatic posterior knee dis-
  location, which should be treated emergently).


• When ordering EDX studies, the timing of findings
  should be kept in mind (Table 19-4).


• NE findings can take from 2 to 6 weeks to manifest.
  •With traumatic injuries, serial EDX studies, including
  an immediate study, may be helpful to thoroughly
  determine the degree of nerve injury.


• Relative contraindications to EDX include pacemaker
  (no Erb’s point stimulation), defibrillator, arteriove-
  nous fistula, open wound, coagulopathy, lym-
  phedema, anasarca, and pending muscle biopsy.