Long-Term Patient-Reported Outcomes After Release of the Ulnar Nerve in Guyon’s Canal

Abstract

Background:

There are no large studies describing patient-reported outcomes after ulnar tunnel release (UTR). The aims of this study are to describe the causes of ulnar tunnel syndrome (UTS), the incidence of UTR, and identify factors associated with long-term patient-reported outcomes after UTR.

Methods:

We reviewed the medical charts of 76 adult patients who had an UTR for UTS at 1 of 5 academic medical centers between January 1, 2003 and January 1, 2017. Of these patients, 30 completed a follow-up questionnaire including the PROMIS Upper Extremity (PROMIS-UE), Numerical Rating Scale for Pain Intensity (NRS Pain), the Global Rating Scale of Change, and a custom questionnaire about satisfaction and current UTS-specific symptoms.

Results:

Approximately 3% of the patients who underwent a decompression surgery of the ulnar nerve at one of our centers between 2003 and 2017 had a UTR. The most frequent described cause of compression was ganglion cyst (16%). The 30 patients who completed the follow-up survey had a mean ± SD PROMIS-UE score of 46.0 ± 12 and a median (interquartile range) NRS Pain score of 0.5 (0-4). Twenty-five patients (83%) described themselves improved compared to before UTR. Bivariate analysis showed that patients who had a preoperative electromyography and nerve conduction velocity study (EMG/NCV) positive for UTS had a higher mean ± SD PROMIS-UE score compared to patients who had a negative EMG/NCV for UTS, respectively 48 ± 12 versus 37 ± 7.6, P = .04.

Conclusion:

Diagnosis of UTS is challenging and made with substantial variation among surgeons. We observed that most patients improve after UTR, but patients with a negative EMG/NCV have a lower PROMIS Upper Extremity score at long-term follow-up.

Introduction

Ulnar tunnel syndrome (UTS), also known as Guyon’s canal syndrome, is a compression neuropathy of the ulnar nerve in or around Guyon’s canal.^1-3 There is a wide range of causes for UTS, and clinical presentation can include both motor and sensory symptoms depending on the anatomic zone of compression.^1,4 There are various proposed causes for UTS, but the incidence and prevalence of UTS remains unknown.^1-5

Owing to the variety of causes and symptoms of UTS, diagnosis can be challenging.^1-7 Symptoms can be nonspecific and related to coexisting pathologies such as carpal tunnel syndrome (CTS), ulnar neuropathy at the elbow (UNE), thoracic outlet syndrome, or cervical radiculopathy.^1,3-11 Electrodiagnostic testing, magnetic resonance imaging (MRI), radiography, and ultrasound can be used to locate the zone of compression and identify the cause of compression.^1,3,12,13 However, these diagnostic modalities are imperfect, and there is wide variation in practice in establishing a diagnosis.

The treatment for UTS can be either conservative or surgical depending on the cause and severity of the symptoms. Prior reports aimed to describe the outcome of surgical treatment, but did not all describe patient-reported outcomes on function, satisfaction, or improvement. These studies also consisted of small cohorts limiting the inclusion of different causes for UTS.^4,5,10 The primary aim of this study is to identify factors associated with the long-term patient-reported outcomes after ulnar tunnel release (UTR). Secondary aims are to describe the causes of UTS and the incidence of UTR among all patients in our institutional system who had any decompression surgery of the ulnar nerve.

Methods

Study Design

After approval of our Institutional Review Board, we identified 225 patients using Current Procedural Terminology code 64719: Neuroplasty and/or transposition of the ulnar nerve at the wrist. We included adult patients who had an UTR for UTS at 1 of 5 academic medical centers between January 1, 2003 and December 31, 2016.

After manual chart review, we excluded patients with a laceration of the ulnar nerve, who had an acute UTR after a wrist trauma or compartment syndrome, who had their index surgery before 2003, who had a procedure for hypothenar hammer syndrome, who had an UTR because of an infection, or who had an incomplete medical chart (Supplemental Material 1). This resulted in a cohort of 76 patients who underwent UTR for UTS. Ulnar tunnel syndrome was diagnosed by the treating surgeon based on clinical symptoms and/or electrodiagnostic studies.

The medical charts of 76 patients were reviewed to collect data on variables such as patient characteristics, comorbidities, preoperative symptoms, surgical and traumatic history of the wrist, forearm, or elbow, concomitant decompression surgeries and/or pisiformectomy, and electromyography and nerve conduction velocity study (EMG/NCV) results. Preoperative symptoms were gathered from the clinical notes and defined based on the outcome of physical examination. Sensory symptoms consisted of tingling and/or numbness in the ulnar side of the hand (ring and small finger). Motor symptoms included weakness or visible atrophy of the intrinsic muscles. Information on the cause of UTS was gathered from the operative notes. Residual symptoms were retrospectively assessed based on the last clinical note. We also assessed if patients had multifocal neuropathy of the ulnar nerve (UTS with cubital tunnel syndrome and/or C8/Th1 radiculopathy).

Long-Term Follow-Up Data

Patients were contacted by letter and invited to complete a REDCap survey by e-mail or phone. The following instruments were included in the REDCap survey: PROMIS Upper Extremity Physical function CAT v2.0 (PROMIS-UE), 11-item Numerical Rating Scale for Pain Intensity (NRS Pain), 7-item Global Rating Scale of Change (GRSoC), and a custom questionnaire containing questions about satisfaction, current UTS specific symptoms, additional treatments received, and medication use (Supplemental Material 2).

The PROMIS-UE measures self-reported upper extremity function from 0 to 100; a higher score indicates better function. The mean ± SD PROMIS-UE score of the general U.S. population is 50 ± 10. The NRS Pain is scaled from 0 to 10; a higher score indicates more pain. The GRSoC evaluates the patient’s current health with respect to their UTS compared to before their surgery on a 7-point scale from significantly worse (−3) to significantly better (+3) (Supplemental Material 3).

Demographics

The mean ± SD age of our main cohort was 54 ± 15 years. Patients presented with solely ulnar sensory symptoms in 23 cases (30%), solely ulnar motor symptoms in 12 cases (16%), and both ulnar sensory and motor symptoms in 41 cases (54%). Forty-three patients (57%) had pain in the ulnar side of the hand or wrist at presentation. Forty-nine patients (64%) had ulnar neuropathy at the wrist combined with a diagnosis of CTS, UNE, and/or carpal arthritis at the same wrist (Table 1). There was only one patient diagnosed with C8 radiculopathy, but this patient did not participate in the follow-up survey. None of the patients included had a diagnosis of brachial plexopathy.

Table 1.

Descriptive Characteristics.

Characteristic	All patients (n = 76)	Follow-up participants Patients (n = 30)
Age at surgery, mean (SD), y	54 (15)	54 (15)
Male sex, n (%)	34 (45)	11 (37)
Diabetes, n (%)	4 (5.3)	0 (0)
Rheumatoid arthritis, n (%)	6 (7.9)	3 (10)
Dominant hand affected a , n (%)	28 (42)	12 (44)
Smoker at time of surgery, n (%)	13 (17)	5 (17)
Bilateral UTS, n (%)	2 (2.6)	0 (0)
History of wrist/forearm/elbow trauma, n (%)	20 (26)	8 (27)
History of wrist/forearm/elbow surgery, n (%)	25 (33)	9 (30)
Prior carpal tunnel release	9 (12)	0 (0)
Prior cubital tunnel release	1 (1.3)	0 (0)
Prior ulnar tunnel release	1 (1.3)	1 (3.3)
Pisiformectomy	1 (1.3)	1 (3.3)
Ulnar shortening	2 (2.6)	1 (3.3)
Trauma surgery	11 (14)	6 (20)
EMG/NCV positive for UTS (excl. patients without EMG/NCV results) b , n (%)	49 (73)	22 (79)
Multifocal neuropathy of the ulnar nerve, n (%)	17 (22)	10 (33)
EMG/NCV group, n (%)
EMG/NCV positive at wrist	43 (57)	19 (63)
EMG/NCV positive at wrist and elbow	6 (7.9)	3 (10)
EMG/NCV non-localizable, ulnar neuropathy present	7 (9.2)	2 (6.7)
EMG/NCV negative at wrist, positive at elbow	1 (1.3)	1 (3.3)
EMG/NCV negative (normal)	7 (9.2)	3 (10)
No EMG/NCV results available	3 (3.9)	0 (0)
No EMG/NCV study performed	9 (12)	2 (6.7)
Concomitant surgeries, n (%)
UTR	27 (36)	14 (47)
UTR & CTR	25 (33)	4 (13)
UTR & CuTR	14 (18)	7 (23)
UTR & Carpectomy	6 (7.9)	2 (6.7)
UTR & CTR & CuTR	3 (3.9)	3 (10)
UTR & CTR & Carpectomy	1 (1.3)	0 (0)
Symptoms at presentation, n (%)
Sensory	23 (30)	10 (33)
Motor	12 (16)	6 (20)
Combined	41 (54)	14 (47)
Pain wrist/hand at presentation, n(%)	43 (57)	15 (50)
Time to clinical follow-up, median (IQR), years	4.4 (1.9-12.0)
Time to survey, median (IQR), years	6.2 (4.4-10.7)

Note. SD = standard deviation; UTS = ulnar tunnel syndrome; EMG/NCV = electromyography/nerve conduction velocity; CTR = carpal tunnel release; CuTR = cubital tunnel release; IQR = interquartile range; UTR = ulnar tunnel release.

^aData regarding dominant hand unknown, n = 6.

^bPatients who had an EMG/NCV study, n = 67.

Twelve patients were excluded from follow-up because they were deceased (n = 9) or non-English speaking (n = 3). Fifteen patients declined participation. Nineteen patients could not be reached by phone or mail. Thirty patients completed the study survey. The median (interquartile range [IQR]) time to follow-up of patients who participated in the research questionnaire was 6.2 years (4.4-10.7).

Electrodiagnostic Testing

Results of the EMG/NCV were available in 64 patients (84%) from their medical chart. In 37 patients, we found detailed EMG/NCV results, and for 27 patients, we only found the conclusion of the EMG/NCV report. In 9 patients (12%), an EMG/NCV was not performed, and in 3 patients (3.9%), a conclusion of the EMG/NCV was unavailable. For analysis, patients were divided into 7 groups based on the EMG/NCV findings: (1) ulnar neuropathy at the wrist only; (2) ulnar neuropathy at the wrist and elbow; (3) non-localizable ulnar neuropathy; (4) EMG/NCV negative at the wrist and positive at the elbow; (5) normal ulnar nerve study; (6) EMG/NCV results not available; and (7) EMG/NCV not performed (Table 1). In addition, we included a dichotomous explanatory variable dividing patients in 2 groups: patients who had a “positive EMG/NCV for UTS” (including patients with an EMG/NCV positive for ulnar neuropathy at the wrist or ulnar neuropathy at the wrist and elbow) and patients who had a “negative EMG/NCV for UTS” (including patients with nonlocalizable ulnar neuropathy, an EMG/NCV negative at the wrist and positive at the elbow, and a normal ulnar nerve study).

Surgical Treatment

Twenty-seven patients (36%) underwent solely UTR, and 49 patients (64%) had a combination of UTR, cubital tunnel release, and/or carpal tunnel release (CTR; Supplemental Material 4).

In 17 patients (22%), both the cubital tunnel and Guyon’s canal were released: in 6 patients (7.9%) because the EMG/NCV was positive for ulnar neuropathy at both the elbow and wrist, in 8 patients (11%) because the EMG/NCV was positive for ulnar neuropathy at the wrist and clinical exam signs were positive for UNE, in 2 patients (2.6%), both the wrist and the elbow were explored for compression because the EMG/NCV was positive for ulnar neuropathy but non-localizable, and in one patient (1.3%) because the EMG/NCV was positive for UNE and a positive Tinel sign at Guyon’s canal.

All patients who underwent a CTR in combination with an UTR and/or cubital tunnel release, had an EMG/NCV positive for CTS.

Seven patients (9.2%) had ulnar neuropathy with piso-triquetral tenderness and/or radiologic evidence for pisiform arthritis. These 7 patients underwent UTR combined with pisiformectomy of which 1 patient had a concomitant resection of a prominent edge on the hook of hamate causing ulnar neuropathy.

In 15 patients (20%), a mass in Guyon’s canal was found and excised in combination with UTR: 12 ganglions (16%), 2 lipomas (2.6%), and 1 mass of the median artery (1.3%).

Statistical Analysis

The association of normally distributed continuous outcomes (PROMIS-UE) with continuous, dichotomous, and categorical variables was calculated using Pearson correlation, student’s t-test and the analysis of variance (ANOVA). For nonnormal-distributed continuous outcomes (NRS Pain and GRSoC), we used Spearman’s rank correlation, Wilcoxon rank-sum test, and Kruskal-Wallis test. The association between dichotomous outcomes (sensory symptoms) with continuous, dichotomous, and categorical variables was calculated using Student’s t-test and Fisher’s Exact test. To mitigate confounding, variables with a P value < .10 in bivariate analysis were entered into a multivariable model to identify factors independently associated with patient-reported outcomes. A P value of less than .05 was considered statistically significant.

Results

Incidence

Within our study timeframe, approximately 3% of the patients (76 of 2619) who underwent a decompression surgery of the ulnar nerve (UTR and/or cubital tunnel release) at one of our centers had a Guyon’s canal release. Of these patients, 0.6% (17 of 2619) had a release of both Guyon’s canal and the cubital tunnel.

Cause of Compression

The cause of compression was described in or around Guyon’s canal in 47 patients (62%; Table 2). In 27 patients (36%), a clear cause of compression was not described, and in 2 patients (2.6%), only a compression at the elbow was described. The most frequent described cause of compression was ganglion cyst (16%).

Table 2.

Intra-Operative Findings.

Intra-operatively found causes	All patients (n = 76)
Cause of compression in or around Guyon’s canal, n (%)	47 (62)
Ganglion cyst	12 (16)
Muscular constriction at the arc of the hypothenar muscles from the hook of hamate	9 (12)
Posttraumatic scarring	6 (7.9)
Fascial bands and/or fibrous tissue in Guyon’s canal	5 (6.6)
Pisohamate ligament	3 (4.0)
Synovitis/fascial thickening	3 (4.0)
Lipoma	2 (2.6)
Post-surgical scarring	2 (2.6)
Volar carpal ligament	2 (2.6)
Mixed: fibrous band and median artery mass	1 (1.3)
Muscle anomaly	1 (1.3)
Bony impingement	1 (1.3)
Cause of compression in Guyon’s canal unclear: not described/idiopatic, n (%)	27 (36)
Cause of compression found at the elbow, n (%)	2 (2.6)

Outcome at Last Clinical Visit

Improvement and residual symptoms at the time of last clinical visit are described in Table 3.

Table 3.

Outcome at Last Clinical Visit.

Characteristic	All patients (n = 76)
Clinical improvement, n (%)
Improved	62 (82)
Persistent	9 (12)
Recurrent	3 (4.0)
Worse	2 (2.6)
Residual pain n (%)
Residual pain	16 (21)
No residual pain	60 (79)
Residual symptoms n (%)
No residual symptoms	23 (30)
Residual sensory symptoms	18 (24)
Residual motor symptoms	15 (20)
Residual combined symptoms	20 (26)
Time to last clinical visit up, median (IQR), months	4.4 (1.9-12.0)

Note. IQR = interquartile range.

Patient-Reported Outcomes at Time of the Survey

The 30 patients who completed the follow-up survey had a mean ± SD PROMIS-UE score of 46.0 ± 12, a median (IQR) NRS Pain score of 0.5 (0-4), and a median (IQR) GRSoC score of 3 (1-3). Twenty-five patients (83%) described themselves improved than before UTR (Table 4). Twenty-six patients (87%) reported they would have the same surgery again if given the choice.

Table 4.

Improvement at Time of Follow-Up Based on the Global Rating Scale of Change.

Improvement compared to before surgery, n = 30		n (%)
(+3)	Significantly improved	16 (53)
(+2)	Improved	4 (13)
(+1)	Minimally improved	5 (17)
(0)	Unchanged	1 (3.3)
(−1)	Minimally worse	0 (0)
(−2)	Worse	1 (3.3)
(−3)	Significantly worse	3 (10)

At long-term follow-up, 19 patients (63%) experienced symptoms of ulnar neuropathy in the last month (weakness, numbness, tingling and or ulnar-sided hand or wrist pain) of which 12 (63%) had persistent symptoms and 7 (37%) had recurrent symptoms. Eleven patients (37%) reported residual sensory symptoms such as numbness and/or tingling in the ring and small finger (Table 5).

Table 5.

Results Ulnar Tunnel Syndrome Questionnaire.

Characteristic	Patients (n = 30)
Additional surgery for ulnar tunnel syndrome, n (%)	0 (0)
Experienced symptoms in the last month, n (%)
Yes	19 (63)
No	11 (37)
Recurrent or persistent symptoms, n (%)
Persistent	12 (63)
Recurrent	7 (37)
Specific symptoms, n (%)
Numbness and/or tingling in fourth and fifth finger	11 (37)
Ulnar sided pain	9 (30)
Weakness in hand with pinch or grip	19 (63)
Lack of coordination when using hand	9 (30)
Clawing of small and ring fingers	5 (17)
Inability to cross fingers	9 (30)
Atrophy or shrinking of the muscles in the hand	7 (23)
No symptoms or complaints in the hand	5 (17)
Other symptoms or complaints in the hand	17 (57)
Difference in strength after surgery, n (%)
Decrease in strength	9 (30)
No change in strength	9 (30)
Increase in strength	11 (37)
I don’t know	1 (3.3)

Bivariate analysis showed that patients who had a preoperative EMG/NCV positive for ulnar neuropathy at the wrist had a higher mean ± SD PROMIS-UE score compared to patients who had a negative EMG/NCV for ulnar neuropathy at the wrist, respectively 48 ± 12 versus 37 ± 7.6, P = .04 (Table 6).

Table 6.

Characteristics of the Patients Who Completed the Long-Term Follow-Up Questionnaire; Bivariate Analysis of the PROMIS Upper Extremity.

Characteristic (continuous variables)	Correlation coefficient		P value
Age at surgery, correlation coefficient	−0.20		.30
Characteristic (dichotomous variables)	Mean (SD)		P value
	Yes	No
Male sex	46 (12)	46 (12)	.97
Rheumatoid arthritis	41 (14)	47 (12)	.44
Dominant hand affected a	47 (14)	46 (11)	.87
Smoker at time of surgery	45 (10)	46 (12)	.90
History of wrist/forearm/elbow trauma	45 (14)	46 (11)	.86
History of wrist/forearm/elbow surgery	42 (13)	48 (11)	.24
Pain wrist/hand at presentation	46 (10)	46 (13)	.90
Mass in or near Guyon’s canal (ganglion/lipoma)	48 (12)	45 (12)	.56
EMG/NCV positive for UTS (excl. patients without EMG/NCV results) b	48 (12)	37 (7.6)	.04
Multifocal neuropathy of the ulnar nerve	47 (10)	45 (13)	.70
Characteristic (categorial variables)	Mean (SD)		P value
EMG/NCV group			.28
EMG/NCV positive at wrist	49 (12)
EMG/NCV positive at wrist and elbow	42 (5.7)
EMG/NCV non-localizable, ulnar neuropathy present	34 (4.9)
EMG/NCV negative at wrist, positive at elbow	48 (–)
EMG/NCV negative (normal)	35 (7.5)
No EMG/NCV study performed	48 (11)
History of wrist/forearm/elbow surgery (categorized)			.63
No history of wrist/forearm/elbow surgery	48 (11)
Prior ulnar tunnel release	51 (–)
Pisiformectomy	33 (–)
Ulnar shortening	38 (–)
Trauma surgery	43 (16)
Concomitant surgeries			.31
UTR	47 (14)
UTR & CTR	45 (10)
UTR & CuTR	51 (9.4)
UTR & Carpectomy	34 (6.1)
UTR & CTR & CuTR	39 (4.8)
Symptoms at presentation			.15
Sensory	41 (11)
Motor	53 (10)
Combined	46 (12)

Note. Values in bold indicate statistical significance at P < .05. SD = standard deviation; EMG/NCV = electromyography/nerve conduction velocity; UTS = ulnar tunnel syndrome; UTR = ulnar tunnel release; CTR = carpal tunnel release; CuTR = cubital tunnel release; PROMIS = patient-reported outcome measurement information system.

^aData regarding dominant hand unknown, n = 3.

^bPatients who had an EMG/NCV study, n = 28.

Similar bivariate analyses were used for the GRSoC, NRS Pain, and sensory symptoms at time of follow-up (Supplemental Material 5, 6, and 7).

Although not significant, there is a trend that patients with preoperative pain at the wrist have a higher median (IQR) NRS Pain score after UTR than patients without preoperative pain, respectively 3 (0-4) versus 0 (0-3), P = .07. Patients with an EMG/NCV negative for UTS had more frequently a higher NRS Pain score after UTR than patients with a positive EMG/NCV for UTS, respectively 4 (3-7) versus 0 (0-3), P = .03 (Supplemental Material 6). Multivariable logistic regression did not show that 1 of these 2 variables were independently associated with a higher NRS Pain score after UTR (Table 7).

Table 7.

Factors Independently Associated With Pain Intensity at Time of Follow-Up; Multivariable Linear Regression.

Characteristics	Coefficient (95% CI)	Standard error	P value
Preoperative pain at the ulnar side of the hand/wrist	0.75 (−1.33 to 2.83)	1.01	0.47
EMG/NCV negative for UTS	2.38 (−0.15 to 4.91)	1.23	0.065

Note. CI = confidence interval; EMG/NCV = electromyography/nerve conduction velocity; UTS = ulnar tunnel syndrome.

Bivariate analysis showed that at time of follow-up, smokers (n = 4, 80%) had sensory symptoms more frequently than patients who did not smoke (n = 7, 28%, P = .047) and those patients with normal preoperative EMG/NCV (n = 3, 100%) had sensory symptoms more frequently than patients who did not have an normal EMG/NCV (n = 8, 30%, P = .03) (Supplemental Material 7).

Discussion

This study described attributed causes for surgically treated UTS and which factors are associated with long-term patient-reported outcomes after UTR. The mean PROMIS-UE score after UTR (46 ± 12) is just below the average score of the general U.S. population (50 ± 10). In addition, 83% of the patients described themselves improved after surgery and 37% had residual sensory symptoms at time of follow-up. Patients with a negative preoperative EMG/NCV for UTS had a lower PROMIS-UE score after surgery than patients with an EMG/NCV positive for UTS. In addition, patients with preoperative pain or a negative EMG/NCV tended to have more pain after UTR. Smokers and patients with a normal EMG/NCV reported to have sensory symptoms more frequently than non-smokers or patients who did not have a normal EMG/NCV.

In most of our cases, a clear cause of compression was classified as idiopathic (27 of 76, 36%). Although it is unlikely that a clear cause of compression such as ganglion cyst was missed and not described, other pathologies might be overlooked. Ganglion cyst was most frequently described as cause for UTS (12 of 76, 16%). Prior studies are consistent with our findings in that idiopathic UTS (45%-82%) is the most common followed by UTS secondary to ganglion cyst (3.2%-62%).^1,4-6,9,14

Bivariate analyses found that patients who had a negative EMG/NCV for UTS had an inferior upper extremity function score than patients with a positive EMG/NCV for UTS. This analysis excluded patients who had no EMG/NCV. Although some consider EMG/NCV the gold standard, the sensitivity of a standard EMG/NCV is respectively 66% for UTS and 37% to 86% for UNE.^9,15-21 It is commonly argued that if an EMG/ NCV test is negative but clinical signs suggest ulnar neuropathy, release is reasonable. However, we found that long-term outcomes appear to be superior if EMG/NCV test is diagnostic for UTS.

Our interpretation is that a patient with a negative EMG/NCV study for UTS is unlikely to have moderate or severe nerve compression at the wrist. It is more likely that patients with a negative EMG/NCV at the wrist have either a nerve compression at another site (cubital tunnel or cervical spine) or have a borderline or mild nerve compression that is not detectable by EMG/NCV. Patients with mild or borderline cases who opt for surgery may have more difficulty with adapting, illness perception, or coping with these symptoms to start.^11,22 In addition, the magnitude of physiologic change after a surgical release in a borderline or mild case is smaller than in a moderate or severe case. Prior studies report that patients with nonlocalizable ulnar neuropathy have more severe clinical disability and electrophysiological findings than patients with EMG/NCV proven UNE, and patients with multifocal neuropathy have a lower postoperative function score than patients with only one focal compression.^23,24 In addition, provocative tests such as the Tinel sign may be less reliable in patients with symptoms of ulnar neuropathy and a normal EMG/NCV. ²⁵

Some reports in the literature argue that sensitivity and specificity of a EMG/NCV for UTS can be increased to respectively 90-95% and 100% when measurements such as conduction block and conduction velocity at the wrist are included.^9,15 Conduction block at the wrist is defined as a ≥50% decrease in compound muscle action potential amplitude without temporal dispersion.^9,15 These measurements are not standard in most EMG/NCV tests and could be helpful when the diagnosis of Guyon’s canal compression is under consideration. More recent modes of diagnosis including MRI and ultrasound may be useful in diagnosing nerve compression and improve success of decompression surgery, but this requires further study.^1,12,19,26

Bivariate analyses showed that at time of follow-up, patients who smoke and patients who had a normal preoperative EMG/NCV had sensory symptoms more frequently compared to patients who did not have a normal EMG/NCV or did not smoke. Owing to the small sample size and the fact that none of the patients with a normal EMG/NCV smoked, we were not able to assess the independent relationship of these factors and sensory symptoms. Prior studies do suggest that smoking may be related to adverse healing after surgery, impaired vascularization of the nerve, and worse pain and sensory outcomes after nerve decompression surgery.^27-33 In addition, smoking may be associated with poor coping and adaptation.^34-36 Although not significant, patients who smoke tend to have a higher median NRS pain after UTR (Table 7).

In our study, 33% of the patients had a UTR and CTR of which 80% were classified as idiopathic UTS. Prior studies report that 18% to 71% of the EMG/NCV proven UTS cases have coexisting CTS and suggested that CTR can decrease pressure in Guyon’s canal and improve the electrophysiologic values and symptoms of ulnar neuropathy.^{4,6,8,9,15,37} Overall, there is a wide variation in the threshold for diagnosis of UTS among clinicians in our institution: Some rely on clinical diagnosis, while others rely on diagnostic studies. Diagnosis of Guyon canal syndrome based on electrophysiologic studies is challenging, especially in studies that cannot localize the site of compression. Our study showed that patients with a negative EMG/NCV for UTS more frequently have worse PROMIS and pain scores after an UTR than patients with a positive EMG/NCV for UTS. In those cases, the results of these study can help with patient counseling, making the choice to operate in 2 different sessions, or choosing for conservative treatment first.

Our results must be considered in light of the study’s limitations. First, the results of these study are limited to patients who had surgical treatment for UTS at an academic medical center with expertise in management of trauma and peripheral nerve surgery. There is no ICD code for UTS which makes it very difficult to identify patients who were solely treated conservatively. It may be possible that there are differences in symptom improvement or coping style between patients who elect surgery versus conservative treatment. Second, 53% of the subjects (34 of 64) did not participate in long-term follow-up and the outcomes of those who did not participate may be different than those who did. However, of the patients that did not participate 56% (19 of 34) could not be reached, which may be due to the fact that contact information gets outdated over time. ³⁸ Baseline data were comparable for both participants and nonparticipants except for number of concomitant CTR’s and history of previous CTR (Supplemental Material 8). Future research, ideally prospective with a larger sample size, may be needed to understand if there are differences in patient-reported outcomes between those with or without a concomitant CTR and those with or without a history of previous CTR. The response rate of our study is similar to other studies using this methodology.^38-40

Third, the GRoC is subject to recall bias as we ask patients to retrospectively evaluate their improvement years after treatment. Fourth, although our study is one of the largest series evaluating the outcome of UTR, our sample size is still relatively small. We were therefore underpowered to detect small differences between patient groups and assess the independent association between smoking and our outcome variables. Fifth, our study was not able to compare preoperative patient-reported outcome scores with the long-term follow-up scores. In addition, these patient-reported outcome scores can be negatively impacted by other upper extremity pathology. However, with the help of the GRoC, which specifically asked patients how much there UTS symptoms improved due to the surgery, we were able to let the patient quantify how much he/she improved or deteriorated compared to before surgery.

Conclusion

We found that most of the patients improved after UTR (83%) with only a mild functional deficit and low NRS pain scores; however, the range of outcomes was wide. The diagnosis of UTS is made with substantial variation among surgeons. We observed that patients with a negative preoperative EMG/NCV for UTS had a lower PROMIS-UE scores after surgery than patients with an EMG/NCV positive for UTS. Our findings suggest that establishing diagnosis with electrodiagnostic studies may help optimize indicating which patients are likely to benefit from UTR.