Eur J Plast Surg (1991) 14: 221-223 European 1 r ~ 1 • • Jourrlal of I ~ l a Q l r l d ' l

© Springer-Verlag 1991

Intraoperative electroneurography during median nerve decompression in carpal tunnel syndrome F.E. Sanner and C. Tizian

Department of Plastic, Reconstructive and Hand Surgery, Kliniken des Main-Taunus-Kreises, Lindenstrasse 10, W-6238 Hofheim am Taunus, FRG

Summary. In 17 patients with the diagnosis o f carpal tunnel syndrome, o r thodromic sensory nerve conduc t ion measurements dur ing l igament division and internal neu- rolysis were per formed wi thout the use o f a pneumat ic tourniquet . While l igament division led to an increase in conduc t ion velocity (p < 0.05; median increase 0.7 m/s), it did no t result in a significant change of the amplitude. Dur ing internal neurolysis, an increase o f the sensory nerve potent ia l ( p < 0 . 0 1 ; median increase 0.9 ~tV) and no significant change in conduc t ion velocity were ob- served. We conclude that internal neurolysis does no t cause a disrupt ion o f nerve funct ion dur ing the opera- tion.

Key words: Carpal tunnel syndrome - Internal neurolysis - Neurophys io logica l parameters

The s tandard t rea tment o f the carpal tunnel syndrome is the division o f the carpal ligament. In 1973, Curtis and Eversman [1] in t roduced internal neurolysis as an adjunct to l igament division alone to improve the neu- rological results after surgery in certain cases. Since then the p ro ' s and con ' s o f internal neurolysis have evoked considerable discussion. One of the arguments against internal neurolysis is the possibility o f fur ther damage to the intraneural vessels and microvascular circulation [9]. The aim of this s tudy was to look at the immediate effects o f l igament division and internal neurolysis. The circulation was mainta ined undis turbed, so that damage to the neural microvascula ture caused by the operative procedure would be detected in a change of the neu- rophysiological parameters .

Material and methods

Measurements of the orthodromic, sensible conduction velocity were performed on 17 patients with the clinically and electrophysio-

logically confirmed diagnosis of carpal tunnel syndrome. All opera- tions were carried out under brachial plexus block. According to the classification of Lundborg [6], 8 patients belonged to class 2b and 9 patients to class 3. The preoperative motor latencies (4.3-11.3 ms) were prolonged compared to age-related physiologi- cal values [5]. During the operative procedure no pneumatic tourni- quet was applied so that the blood circulation remained undis- turbed. Two monopolar needle electrodes were used as stimulation electrodes. The stimulation impulse had a duration of 0.2 ms, a voltage between 150 and 250 V, and was repeated once per second. The electrodes were applied as shown in Fig. 1. Intraoperative mea- surements were made before and after ligament division and after internal neurolysis. The indication for internal neurolysis (scar tis- sue encircling the nerve) was present in all 17 cases. In 3 cases where only epineural tissue was scarred, internal neurolysis was stopped after removal of the palmar part of the epineurium. In the other cases interfascicular fibrosis was present and an addition- al interfascicular neurolysis was performed (Fig. 2). The position of the electrodes was kept unchanged throughout the procedure and the distance was measured as depicted in Fig. 1. After averag- ing, the conduction velocity and the peak-to-peak voltage were determined. The skin temperature of the hand was more than 32 ° C in all cases. To determine whether a significant change of the pa- rameters in either direction had occurred, the Wilcoxon test was applied.

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Fig. 1. Intraoperative placement of electrodes

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Fig. 2. Technique of internal neurolysis as employed in this study

Results

During ligament division the conduction velocity in- creased significantly (p<0.05) with a range of 0.0- 3.0 m/s and a mean increase of 0.9 m/s. The mean value was 35.9 m/s preoperatively and 36.8 m/s after ligament division. The peak-to-peak voltage did not change signif- icantly.

During internal neurolysis the conduction velocity did not change significantly in either direction, while the peak-to-peak voltage increased in all cases (span: 0.1-1.67 gV; mean increase: 0.83 gV). The difference compared to the values before internal neurolysis was significant (p < 0.01).

Discussion

The arguments in favor of internal neurolysis are: 1. Intraneural fibrosis leads to an impairment of the intraneural blood circulation, nerve conduction [9], and axon transport [2]. 2. Furthermore it can impair the growth of regenerating axons. I f the median nerve after ligament division is still com- pressed by fibrous tissue encircling the fascicles, internal

neurolysis is indicated in order to improve blood circula- tion, nerve conduction, axon transport and the regenera- tion of axons. The arguments against internal neurolysis are: • Intraneural blood vessels could be destroyed by the procedure itself [9]. • Internal neurolysis could lead to a conduction block intraoperatively [13]. • Intrafascicular plexus could be destroyed [9]. • Internal neurolysis induces an inflammatory response that leads to the formation of new fibrous tissue in the long run, which again could lead to the same conse- quences as the scar tissue before nerve decompression [8].

While the latter point is still under discussion in the literature [7] our aim was to look at the intraoperative effects of internal neurolysis, especially at its effect on blood circulation.

To study nerve function we decided to measure the orthodromic sensible conduction velocity because of the high accuracy and sensitivity of this technique compared to measurement of the retrograde conduction velocity or the distal motor latency [4, 5, 10].

For interpretation of the results it is absolutely neces- sary to operate without creating a bloodless field. Thus the oxygen supply to the nerve and the temperature stay at a constant level [13].

The results of this study show that during internal neurolysis the amplitude increases significantly (p < 0.01) and that the conduction velocity is not changed in either direction. Since conduction velocity and peak-to-peak voltage are dependent on a certain blood supply to the nerve [3], internal neurolysis did not interfere with blood supply nor did it impair nerve function mechanically. Internal neurolysis even led to a slight increase in peak- to-peak voltage intraoperatively. An increase in peak-to- peak voltage reflects an increase in the numbers of con- ducting axons, and an increase in conduction velocity reflects an improved function of the fastest subgroup of neurons [12]. Since there was only a slight increase in nerve function, there is only a small amount of nerve fibres with an acutely reversible conduction block (Class 1 according to the Sunderland classification). This means that improvement of nerve function after surgery for the carpal tunnel syndrome is a long-term process in patients with advanced carpal tunnel syndrome. The objectives for operative treatment of the carpal tunnel syndrome are: • Relief of pain, • Prevention of chronic nerve injury, and • Improvement of nerve regeneration and nerve func- tion.

In our opinion a satisfactory result cannot be achieved in all cases by ligament division alone. In cases without or with only little postoperative improvement of nerve function one of the following situations could be the reason:

• Incomplete ligament division • Double crush lesion [11]

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• The nerve les ion has p r o c e e d e d to a p o i n t where on ly a f ib rous b a n d is left [9] • The nerve has the po ten t i a l to regenera te bu t con- s t r ic t ing f ib rous t issue is impa i r i ng nerve func t ion and nerve regenera t ion .

In the la t te r case in te rna l neuro lys i s is indica ted . Our resul ts have shown an i m p r o v e m e n t o f nerve func t ion in t raopera t ive ly . Thus this s tudy has p r o v e d tha t it is wrong to assume tha t p e r f o r m i n g an in te rna l neurolys is o f the m e d i a n nerve at the wr is t level leads to an impa i r - m e n t o f nerve func t ion in t r aopera t ive ly , e i ther mechan i - cally or by d a m a g e to the neura l mic rovascu la tu re .

We believe tha t in te rna l neuro lys i s is a useful ad junc t to ca rpa l tunne l surgery a n d shou ld be e m p l o y e d in any case where cons t r ic t ing ep ineura l f ibrosis is present .

References

1. Curtis R, Eversmann W (1973) Internal neurolysis as an adjunct to the treatment of the carpal-tunnel syndrome. J Bone Joint Surg [Am] 55 : 733-741

2. Dahlin L, Sj6strand J, McLean W (1986) Graded inhibition of retrograde axonal transport by compression of rabbit vagus nerve. J Neurol Sci 76:221-230

3. Fullerton P (1963) The effect of ischemia on nerve conduction

in the carpal tunnel syndrome. J Neurol Neurosurg Psychiatry 26 : 385-397

4. Holmgren H, Rabow L (1987) Internal neurolysis or ligament division only in carpal tunnel syndrome, 2. A 3 year follow-up with an evaluation of various neurophysiological parameters for diagnosis. Acta Neurochir (Wien) 87:44-47

5. Ludin H, Tackmann W (1979) Sensible Neurographie. Thieme, Stuttgart, pp 146-149

6. Lundborg G (1988) Nerve injury and repair. Churchill Liv- ingstone, Edinburgh London Melbourne New York, pp 116- 117

7. Mackinnon S, Dellon A (1988) Surgery of the peripheral nerve. Thieme, New York, pp 131-140

8. Rydevik B, Lundborg G, Nordberg C (1973) Intraneural tissue reactions induced by internal neurolysis. Scand J Plast Reconstr Surg 10 : 3-8 Sunderland S (1987) Nerves and nerve injuries. Churchill Liv- ingstone, Edinburgh London New York, pp 499-504 Tackmann W, Kaeser H, Magun H (1981) Comparison of orthodromic and antidromic sensory nerve conduction velocity measurements in the carpal tunnel syndrome. J Neurol 224:257-266 Upton A, McComas A (1973) The double crush lesion in nerve entrapment syndromes. Lancet II: 359-362 Williams H, Terzis J (1976) Single fascicular recordings: an intraoperative diagnostic tool for the management of peripheral nerve lesions. Plast Reconstr Surg 57:562-569 Yates S, Hurst L, Brown W (1981) Physiological observations in the median nerve during carpal tunnel surgery. Ann Neurol 10 : 227-229

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