At the elbow the ulnar nerve may be compressed either in the retrocondylar groove or at the cubital tunnel. Optimal surgical therapy should be directed at the specific site of involvement. lntraoperative electroneurography per- formed in conjunction with 19 ulnar nerve explorations helped localize the precise site of compression. Of the primary procedures, abnormality was at the retrocondylar groove in 9, cubital tunnel in 4, both locations in 3, and at an unusual distal point in 1 ; 12 anterior subcutaneous transpositions, 4 cubital tunnel releases, and 1 distal decompression resulted. lntraoperative studies helped identify residual compression in two patients undergoing reexploration. Although routine electrodiagnosis may localize an ulnar neu- ropathy to the elbow, reliably separating retrocondylar from cubital tunnel compression is more difficult. Preoperatively, percutaneous serial short in- crement studies were more accurate than simple “inching” in predicting the site of compression.

MUSCLE & NERVE 11:75-81 1988

INTRAOPERATIVE

MANAGEMENT OF ULNAR NEUROPATHY AT THE ELBOW

WILLIAM W. CAMPBELL, MD, SlNGH K. SAHNI, MD, RHONDA M. PRIDGEON, MD, GHAZALA RIAZ, MD, and ROBERT T. LESHNER, MD

F o r many years electromyographers have wrestled with the dilemma of precise diagnosis and localiza- tion of ulnar neuropathies at the elbow (UNE), while surgeons have debated optimum operative man-

e surgeon must choose among several procedures held to benefit such pa- tients, including cubital tunnel release (CBTR), an- terior subcutaneous transposition, anterior sub- muscular transposition, and resection of the medial epicondyle. Results of ulnar nerve surgery are poorer than with other entrapment neuropathies, and only 6 0 4 0 % of operated patients benefit.33 Often there is only minimal improvement, and patients are oc- casionally plagued by painful postoperative par- e~thesias.~ The procedure performed generally de- pends on the preference and bias of the surgeon.I4 Rarely have surgeons attempted to base the choice of procedure on the clinical or electrodiagnostic

agement. ~,14,15,19,”7.30,56 T h

From the Departments of Neurology (Drs. Campbell, Pridgeon, Riaz, and Leshner) and Neurosurgery (Dr Sahni), Medical College of Virginia, Rich- mond, VA

Address reprint request to Dr. Campbell at Neurology (127), McGuire VAMC, 1201 Broadrock Rd , Richmond, VA 23249.

Received for publication January 23, 1986, revised manuscript accepted for publication December 23, 1986.

0148-639)(/1101/0075 $04.0017 0 1988 John Wiley & Sons, Inc.

characteristics of the lesion in an individual pa-

Because of the limitations of surface EMG in distinguishing the two primary UNE processes, cubital tunnel syndrome (CBTS) versus compres- sion in the retrocondylar (RTC) groove, we re- sorted to intraoperative electroneurography (IENG) in an attempt to better tailor each surgical proce- dure to the needs of the individual patient.

tient.2 1.24.29.34

MATERIALS AND METHODS

Nineteen patients underwent exploration of the ul- nar nerve at the elbow. Each was studied by routine electromyography preoperatively, including care- ful “inching” of the stimulator around the elbow, as described by Miller,23 in which the stimulator was moved along the nerve in several steps in search of focal points of abrupt change in amplitude or configuration of the compound muscle action po- tential (CMAP). There were 14 patients who under- went serial short increment studies (SSIS), mea- suring CMAP amplitude and latency with stimulation of successive 1 cm segments from well above to well below the elbow in an attempt at more precise lo- cali~ation.”.’~

Intraoperative electroneurography (IENG) was performed by direct bipolar epineural stimulation using 1 cm platinum needle electrodes (platinum

lntraoperative Electroneurography MUSCLE & NERVE January 1988 75

subdermal electrode, type E2, Grass Instrument Co., Quincy, MA) mounted on a wooden carrier for the first 14 patients. For the last 5 patients a custom made bipolar stimulator with a fixed 1 cm interelectrode distance was employed. Initially, op- erative studies were limited to direct epineural “inching,” with casual stimulation in search of areas of obvious conduction block or differential slowing. There were 16 patients studied by stimulation at 0.5-1.0 cm intervals from the most proximal to the most distal reachable limits of the dissection as de- scribed by Brown et aL5 Stimuli were delivered by a constant current stimulus isolation unit using a stimulus duration usually of 0.05 msec, rarely 0.1 msec, and stimulus intensity of 10-30 mA adjusted to a level just supramaximal for the nerve under study. Care was taken to avoid excessively supra- maximal stimulation because of the danger of distal migration of the effective cathode producing er- roneous latency determinations over the very short segments being examined.

Initially the hand was isolated from the sterile field and recording was done with ordinary disc electrodes; however, it proved more efficient to prep the entire extremity, including the hand, and to record with subcutaneous platinum needle elec- trodes. Grounding was accomplished with a saline- soaked cottonoid and a spring-mounted ground (TGP-36, The Electrode Store, Yucca Valley, CA) placed on the dorsum of the wrist. Preamplifiers were placed in a sterile plastic video camera cover (model 4001, Medical Dynamics Inc., Englewood, CO) and secured near the recording site. Phone tip connectors were placed directly through the camera cover; once placed they were not removed or adjusted, thereby maintaining sterility. There have been no complications from the presence of the electromyographer or his paraphernalia.

Recording was done with a TE-42 electromy- ograph (TECA Corporation, Pleasantville, NY) and permanent records committed to fiber optic paper. The compound muscle action potential (CMAP) was recorded from the abductor digiti quinti (ADQ) except for case 10, where recording was from the flexor carpi ulnaris (FCU) because of severe distal wallerian degeneration and lack of an elicitable re- sponse from the ADQ. The ulnar sensory nerve action potential (SNAP) was recorded via subcu- taneous platinum electrodes at the base of the small finger, referenced to the distal interphalangeal joint. When a SNAP was present, the CMAP and SNAP were recorded simultaneously from each stimula- tion site through a TECA AX62 averager expan- der. Latencies were measured with the latency in-

dicator dial set to the nearest 0.05 msec to the CMAP onset and to the SNAP onset and peak. CMAP amplitude was measured from baseline to peak. Values were measured and recorded by a techni- cian under the guidance of the electromyographer. Later perusal of the fiber optic recordings showed no significant deviations from the values obtained at operation. SNAP recording added little addi- tional information, and because of time limitations as well as frequent SNAP absence in our patients, this part of the examination was deleted after sev- eral procedures.

After the nerve was exposed, the position of the cubital tunnel was noted, tagged with a suture, and the distance from medial epicondyle to cubital tun- nel entrance measured. The FCU aponeurosis was then incised and the muscle belly opened distally by blunt dissection. With the nerve exposed, direct epineural stimulation was performed from as far proximally to as far distally as feasible. Cases dem- onstrating a focal change in latency or amplitude at the aponeurotic arch of the FCU underwent no further dissection, and the wound was closed. When a focal change in latency or amplitude occurred at or proximal to the medial epicondyle, the nerve was mobilized further and anterior subcutaneous transposition performed in the usual manner.

RESULTS

Of 19 cases, 9 proved to have K I C compression and received transposition, 4 had CBTS and were managed by simple CBTR, 3 had major conduction abnormalities at both locations and received trans- position (which requires division of the FCU apo- neurosis, an “incidental” CBTR), and 1 patient had focal conduction block deep within the FCU treated with local decompression. Two patients were undergoing reexploration because of poor out- comes from their original procedure. One had been transposed without adequate division of the FCU aponeurosis, a technical error, and had an acquired iatrogenic CBTS.‘ The other reoperated patient had previously been managed with simple cubital tunnel release, and the nerve was imbedded in dense scar tissue, the position of the original cubital tun- nel impossible to identify. Marked conduction ab- normalities were present from the tip of the medial epicondyle over the next 4 cm. External neurolysis and transposition were performed (Table 1).

In the first two primary, i.e., not reexploration, procedures (Table 1, cases 1 and 3), major con- duction block was easily demonstrated at the medial epicondyle in case 1 and at the cubitdl tunnel en-

MUSCLE & NERVE January 1988 76 lntraoperative Electroneurography

Table 1. Comparison of Preoperative and intraoperative electrodiagnosis

Case EMG diagnosis findings Procedure Preoperative Intraoperative

1 Nonlocalizing RTC AT 2 Nonlocalizing CBTS CBTR* 3 CBTS CBTS CBTR 4 Nonlocalizing RTC ATt 5 Nonlocalizing RTC AT 6 RTC = CBT CBT > RTC AT 7 CBTS CBTS CBTR + AT* 8 CBTS RTC = CBT AT 9 RTC RTC AT

10 CBTS CBTS CBTR 11 CBTS Focal conduction Local release

block 7 cm below medial epiconyle

12 RTC RTC = CBT AT 13 RTC RTC AT 14 CBTS CBTS CBTR 15 RTC RTC AT 16 RTC RTC AT 17 RTC CBTS CBTR 18 RTC RTC AT 19 RTC RTC AT

Note CBT, cubitai tunnel, CBTS, cubital tunnef syndrome, CBTR, cubital tunnel release, RTC, retrocondylar, AT, anterior (subcutaneous) transposition ‘Previously transposed with rnadequate Nexor carpi ulnaris release and poor outcome (iatrogenic CBTS) t Neuroma in continuity by pathology * Previous CBTR with poor outcome, dense scarring at surgery

trance in case 3 (Fig. 1) In case 4 no conduction block was present, leading us to perform short seg- ment stimulation as described by Brown et aL5 A dramatic latency change of 1.4 msec occurred over the 1 cm segment just proximal to the medial ep- icondyle, corresponding to a conduction velocity of 7 d s e c (Fig. 2). The operating microscope was then employed to perform external and limited internal neurolysis over the segment of greatest conduction abnormality, after which the nerve was transposed. Epineural biopsy demonstrated neuroma in con- tinuity. Figure 3 demonstrates both marked latency change and conduction block occurring at the cub- ital tunnel entrance. Local decompression and mi- croscopic neurolysis were performed; epineural bi- opsy again showed neuroma in continuity. Short segment studies were performed during all sub- sequent procedures, and the preoperative evalua- tion was expanded to include percutaneous SSIS as well.

I t is of course impossible to study normal nerve by direct epineural stimulation. Figure 4 demon- strates percutaneous SSIS in a normal control, stim- ulating the ulnar nerve proximal ( - ) to distal (+),

with “0” representing the level of the medial epi- condyle, while recording CMAP onset. Latency changes over successive 1 cm segments range from 0.05 to 0.25 msec. Analyzing segments of nerve proximal to the point of major conduction abnor- mality, deleting patients with known underlying neuropathy, allows approximation of the expected latency change of the CMAP onset over a 1 cm segment as encountered in the electrically hostile, time-pressured, temperature-uncontrolled envi- ronment of the operating theater. In 15 patients latency change over 52 such “normal” segments ranged from 0 to 0.4 msec, with a mean of 0.23 and a standard deviation of 0.1 msec. Thus the upper limit of expected latency change (mean + 2SD) over a 1 cm segment under these recording conditions is 0.43 msec.

DISCUSSION

The pathogenesis of UNE has been debated for many years, and imprecision in terminology has not furthered understanding. The term tardy ul- nar palsy was originally applied to cases of UNE occurring years after an elbow fracture.33 Over time

Intraoperative Electroneurography MUSCLE & NERVE January 1988 77

FIGURE 1. Case 3. Preoperative "inching" demonstrated conduction block distal to the medial epicondyle that was felt to represent cubital tunnel syndrome. lntraoperative direct epineural stimulation, recording from ADQ, easily demonstrated major focal conduction block at the cubital tunnel. A short incremant study was not necessary for localization. Arrow indicates proximal edge of cubital tunnel.

the term degenerated into a generic for any ulnar neuropathy at the elbow. Similarly, Feindel and Stratford have been subverted in their attempt to define a distinct subgroup of' U N E characterized by entrapment of the nerve by the aponeurosis joining the humeral and ulnar heads of' the flexor carpi ulnaris, which they termed cubital tunnel syn- drome (CX'BS) from the Latin cubit for elbow.':' Many authors now either explicitly o r implicitly use CHTS to refer to any UNE, as though the cubital tunnel referred to the subcutaneous passage of the llerve around the 1 , 1 ( 1 12.22.2b.:i5 One author- itative text refers to "this so-called cubital tunnel.":'.' In agreement with others, the term C B T herein refers only to the point where the ulnar nerve passes beneath the humeroulnar aponeurotic arcade join- ing the heads of the flexor carpi ulnaris.'.2:i,"'

T h e two surgical procedures in common use for UNE: are cubital tunnel release (CBTR), by simple division of the FCU aponeurosis and ante- rior subcutaneous transposition (AT). T h e trans-

position procctlure requires division of the FCU aponeurosis to mobilize the nerve, and some sur- geons contend that the salutory effects of A T are diie to the incidental <:H?'K.':'."" Keviewing surgery for UNE:, Kengachary states that "the variety of operative approaches used . . . is in itself a testi- mony to the poor understanding of tardy ulnar p a l ~ y . " ~ ' Although some find simple CBTK

others co~iltl detect no signifi- cant difference in results o f A 1 versus (:R~I'K'"' o r found a slight trend for patients treated only wit.h CU'TK to do worse'.'" Clinical criteria to guide the choice of' procedure have been proposed."."".' Vaiiderpool et al. used clinical and operative find- ings to .judge the likely cause of UNE: and tailor the ensuing operation: of 40 patients, 2 1 received CB'I'K, 17 had AT. and 2 had release o f a persistent epitrochleoancone~is Transposition car- ries inherent disadvantages: a loiiger iiicision, a more extensive dissection, and remo\~al of the nerve from its anatomical bed with potential sacrifice of' small

1!1.2-1.:'1 .:'I;

78 lntraoperative Electroneurography MUSCLE & NERVE January 1988

Position 5msec msec

10 40

r'i. 10 00

9 90

9 10

8 4c

7 00

6 90

6 8 5

6 80

6.60

FIGURE 2. Case 4. Careful preoperative inching around the elbow failed to disclose any point of discrete conduction block. At sur- gery there was equivocal swelling of the nerve in the retrocondylar groove. On stimulation of serial 1 cm segments from the most proximal ( - ) to distal (+ ) limits of the dissection, recording from ADQ, a marked increase in latency of the CMAP onset occurred just behind and proximal to the medical epicondyle. The marked change in slope of the dotted line indicates the segments of greatest latency change. A diagnosis of retrocondylr compression was made, and the patient underwent epineurolysis and micro- scopically guided limited internal neurolysis at the point of max- imal latency change, followed by anterior subcutaneous trans- position. Pathologic examination of an epineural biopsy revealed neuroma in continuity.

segiiierital nerves and blood vessels.'."':'.:" Simple CR?'R is more innocuous and seems preferable where i t caii be expected to suffice.

Available electi-odiagnostic criteria may localize an ulnar neuropathy to the level of the elbow, but 10 precisely separ-ate cubital tunnel from retrocon-

2 m ~ I Position 2 msec msec

3.20

3.10 +I - +2 -

t3 2 00 2 0 10

A Latency (msec)

FIGURE 3. Case 10. No CMAP could be elicited from the ADO percutaneously or by intraoperative stimulation. Recording from the FCU, the preoperative study showed a marked latency change 3 cm distal to the medial epicondyle that was felt to represent CBTS. Intraoperative studies confirmed the latency change and demonstrated a major conduction block at the cubital tunnel en- trance as well. Surgery was limited to simple decompression of the cubital tunnel.

20 1.0 A Latency

(rnsec)

FIGURE 4. Normal control, percutaneous short segment incre- mental study over 1 cm segments from proximal ( - ) to distal (+ ) to the medial epicondyle (0), recording the CMAP onset latency from the ADQ. Latency changes range from 0.05 to 0.25 msec over each segment.

dylar ( K I C ) compression is c no re difficult.:',' '.'*"'.' Miller used an inching technique in search of' dis- crete areas of conduction Mock and was able to localize lesions to the CB?' i n 12 of 15 nerves by surface EMG, with intraoperative confirmation in 7 and a favorable response to simple CB?'R in most.'"'' I n contrast, Brown et al.".' ellcountered no instances of cubital tunriel conipression in 30 cases of U N E studied by short segment stimulation intraoperatively; rather, maximal conduction ab- normalities were usually situated about the tip of the medial epicondyle, and in no insraiice did the nerve appear grossly constricted or kinked at the cubital tunnel. Thus, two scholarly reviews produce diametrically conflicting observations.'!'

~ r h e limitations and technical pitfalls of per- cutaneous nerve conduction studies become mag- nified when studying short segments."- '.'' Sub- niaxinial stimulation, uncertainty over precise position of the effective cathode, and changes in excitation threshold of diseased nerve may all con- tribute t o a large percent error when stimulating very short nerve segments.".'~."'

Preoperative studies attempted to localize the pathology by inching in search of conduction block or differeritial slowing.':' Of five patients examined i n this fashion, one with CKTS was correctly di- agnosed; three percutaneous studies were nonlo- calizing: each proved to be K T C compression by IENG; and the remaining patient had acquired CBTS f'rom previous inept surgery. Serial short increment stimulation searching for both latency and amplitude changes proved a better predictor of the intraoperative findings, correctly identifving

lntraoperative Electroneurography MUSCLE & NERVE January 1988 79

six retrocondylar compressions, two cubital tunnel compressions, and suggesting abnormality at both locations in two others.

Variations in anatomy compound the electro- physiologic limitations. In 100 cadaver elbows, the anatomical relationships between the medial epi- condyle, FCU, and ulnar nerve were examined. Measurements were made from the point of dis- appearance of the nerve beneath the aponeurosis to the midpoint of a diagonal drawn from epicon- dyle to olecrenon, with the elbow flexed 30" from horizontal in an attempt to simulate survcal posi- tioning. The cubital tunnel ranged from 3 to 20 mm distal to the tip of the medial epicondyle, with a mean distance of 11.3 mm. In numerous speci- mens the cubital tunnel lay less than 1 cm distal to the epicondyle." Three specimens had dense apo- neurotic bands between the medial epicondyle and the olecrenon, and seven had an accessory anco- neus epitrochlearis, both of which have been re-

ported to cause ulnar compression. 19.1634 To dis- tinguish RTC compression from CBTS by surface EMG under such circumstances would be impos- sible.

In summary, of 17 patients undergoing pri- mary ulnar nerve explorations, 9 had RTC compression, 4 had CBTS, 3 had conduction ab- normalities at both locations, and 1 had an unusual f-ar distal compression. 'Twelve AT'S, four CBTR's, and one distal decompression resulted. There are multiple causes for UNE; the most common sites of compression are the retrocondylar groove and the cubital tunnel. Rational surgical therapy should be directed at the specific pathology. CBTR is the most benign and preferable procedure but may not be adequate for patients with retrocondylar compression. Intraoperative electroneurography can help localize the precise site of compression and aid in tailoring the surgical procedure to the needs of the individual patient.

1.

2.

3.

4.

5.

6.

7.

8.

Y.

10.

of the ulnar nerve. ] B m ] o i n t Surg (Am) 29:1087-1097, 1947.

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MUSCLE & NERVE January 1988 81