Beyond the Cubital Tunnel: Use of Adjunctive Procedures in the Management of Cubital Tunnel Syndrome

Abstract

Background:

Our management of cubital tunnel syndrome has expanded to involve multiple adjunctive procedures, including supercharged end-to-side anterior interosseous to ulnar nerve transfer, cross-palm nerve grafts from the median to ulnar nerve, and profundus tenodesis. We also perform intraoperative brief electrical stimulation in patients with severe disease. The aims of this study were to evaluate the impact of adjunctive procedures and electrical stimulation on patient outcomes.

Methods:

We performed a retrospective review of 136 patients with cubital tunnel syndrome who underwent operative management from 2013 to 2018. A total of 38 patients underwent adjunctive procedure(s), and 33 received electrical stimulation. A historical cohort of patients who underwent cubital tunnel surgery from 2009 to 2011 (n = 87) was used to evaluate the impact of adjunctive procedures. Study outcomes were postoperative improvements in Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire scores, pinch strength, and patient-reported pain and quality of life.

Results:

In propensity score–matched samples, patients who underwent adjunctive procedures had an 11.3-point greater improvement in DASH scores than their matched controls (P = .0342). In addition, patients who received electrical stimulation had significantly improved DASH scores relative to baseline (11.7-point improvement, P < .0001), whereas their control group did not. However, when compared between treatment arms, there were no significant differences for any study outcome.

Conclusions:

Patients who underwent adjunctive procedures experienced greater improvement in postoperative DASH scores than their matched pairs. Additional studies are needed to evaluate the effects of brief electrical stimulation in compression neuropathy.

Keywords

cubital tunnel syndrome nerve diagnosis supercharged end-to-side nerve transfer electrical stimulation nerve compression propensity score

Introduction

Surgical management of cubital tunnel syndrome is a moving target. Originally described by Panas in 1878,¹ nearly a century passed until Feindel and Stratford ascribed the disease to the structure of the cubital tunnel in 1958.² In their foundational work, Feindel and Stratford also hypothesized that simple decompression of the cubital tunnel would produce equivalent outcomes as anterior transposition of the ulnar nerve. Since then, the debate between these procedures, and others, persists.³ Despite multiple systematic reviews and meta-analyses, no surgical technique has been shown to conclusively produce superior outcomes, and not all patients achieve satisfactory recovery.^4,5

A survey of the American Association for Hand Surgery found that although 88% of hand surgeons were very satisfied with their carpal tunnel surgery outcomes, only 44% were very satisfied with their cubital tunnel surgery outcomes.⁶ Part of the difficulty in managing cubital tunnel syndrome is that the condition is a broad spectrum. Patient presentations are polymorphic, and a patient’s symptomatology typically evolves over months to years. Moreover, current clinical classification systems aimed at grading preoperative severity do not correlate well with patient outcomes.^7,8

Advances in our understanding of nerve pathophysiology and regeneration over the past decades have led us to consider treatments beyond surgery at the cubital tunnel. These include adjunctive surgical procedures, such as side-to-side profundus tenodesis, supercharged end-to-side anterior interosseous to ulnar motor nerve transfer (SETS nerve transfer), and cross-palm nerve grafts from the median to sensory component of the ulnar nerve (cross-palm grafts), as well as intraoperative brief electrical stimulation.^9-14 The effects of these treatments on patient outcomes in routine clinical practice remain unclear.

The primary aim of this retrospective study was to evaluate the impact of adjunctive surgical procedures on clinical outcomes. An additional aim was to evaluate the effects of brief electrical stimulation in these patients.

Materials and Methods

Medical records were obtained for consecutive adults with clinical evidence of cubital tunnel syndrome who underwent operative management by the senior author (S.E.M.) from 2013 to 2018. Exclusion criteria were history of ulnar nerve transection, brachial plexopathy, cervical radiculopathy, or other concomitant neurologic disorders. Extracted historical information included patient demographics, handedness, and previous cubital tunnel surgery. Preoperative assessment involved electrodiagnostic studies, measurement of key pinch strength (pinch gauge; B&L Engineering, Santa Ana, California), and assessment of disease impact. Electrodiagnostic studies, consisting of nerve conduction studies and needle electromyography (EMG), were recorded from the first dorsal interosseous and/or abductor digiti minimi (ADM).¹⁵ Important electrodiagnostic parameters for our patient management included compound motor action potential (CMAP) amplitude at wrist, sensory nerve action potential (SNAP) amplitude, conduction velocity across the elbow segment, the presence of spontaneous activity (fibrillations and positive sharp waves), and configuration of motor unit potentials. Assessment of disease impact involved the Disabilities of Arm, Shoulder, and Hand (DASH) questionnaire¹⁶ and a pain evaluation questionnaire,¹⁷ which included 10-cm Visual Analogue Scale (VAS) for average pain level experienced over the previous month and impact of pain on quality of life. Pinch strength, DASH, and VAS measures were also collected at each postoperative visit. Study outcomes were postoperative improvements in these 4 parameters.

Surgical Management

Management was guided by a previously published treatment algorithm (Figure 1).^18,19 Patients received 1 of 3 treatment options: transmuscular ulnar nerve transposition (UNT) alone,²⁰ UNT and Guyon’s canal release (GCR), or UNT and GCR plus one or more adjunctive procedures. Patients with entrapment at the arcade of Struthers specifically underwent release of this band.^21,22 Adjunctive procedures included side-to-side profundus tenodesis, SETS nerve transfer, and cross-palm grafts. The choice of treatment was determined by the degree of nerve injury and clinical complexity, which were informed by the following objective factors: intrinsic muscle strength, nerve conduction studies, EMG findings (fibrillations, positive sharp waves suggestive of denervation, and/or motor unit potential morphology), and/or history of cubital tunnel surgery. In addition, intraoperative brief electrical stimulation (Checkpoint Nerve Stimulator & Locator; Checkpoint Surgical, Cleveland, Ohio) was used for select patients with more severe cubital syndrome beginning in 2016. Following decompression of the cubital tunnel, with the tourniquet removed and without local anesthetic, electrical stimulation was performed for approximately 10 minutes using a 2-mA current and 100-µs pulse width proximally on the ulnar nerve.

Comparison Cohort (2009-2011)

To assess the impact of adjunctive procedures on outcomes, patients were compared with those in a previously published cohort²³ who underwent cubital tunnel surgery by the senior author (S.E.M.) between 2009 and 2011. This cohort was selected for comparison because patients received surgery before development of the management strategy used in the 2013-2018 cohort. Adjunctive procedures were not part of routine practice between 2009 and 2011, and all patients in this cohort received either UNT or UNT with GCR. Release of entrapment at the arcade of Struthers was also not part of routine practice during this time. No patient received electrical stimulation.

Statistical Analyses

Differences in baseline characteristic and postoperative outcomes between the 2009-2011 and 2013-2018 cohorts were evaluated by χ² and Wilcoxon rank sum tests, when appropriate. Multivariable linear regression models for improvement in DASH score, pinch strength, pain, and quality of life were developed to further assess overall differences between cohorts. Each model initially included age, sex, body mass index (BMI), dominant hand involvement, receipt of prior cubital tunnel surgery, conduction velocity (across the elbow segment), reduced CMAP amplitude at the wrist (below 6 mV), and abnormal EMG, as well as preoperative DASH score, pinch strength, pain, and quality of life. Compound motor action potential amplitude was dichotomized due to the known nonlinear relationship between axonal loss and motor function; the function remains relatively constant until loss of 70% to 80% axons, after which it drops precipitously.^19,24 Final models were achieved through backward elimination, in which variables with P values greater than .10 were sequentially removed.²⁵

Patients in both cohorts may be divided into 3 severity categories corresponding to the 3 treatment options used in the 2013-2018 cohort. Differences in preoperative characteristics for patients receiving each treatment option were examined by χ² test or one-way analysis of variance, when appropriate. In addition, propensity score matching was used to evaluate the impact of treatment options on outcomes. Patients who received each treatment option in the 2013-2018 cohort were matched to those with similar preoperative characteristics in the 2009-2011 cohort, who likely would have received the same treatment had the 2013-2018 management strategy been used.

Propensity scores were calculated using a nonparsimonious multivariable logistic regression model with receipt of adjunctive procedures as the dependent variable. The independent variables were selected a priori based on their relevance in determining the treatment and known impact on clinical outcomes, and included preoperative pinch strength, abnormal EMG, reduced CMAP, and history of cubital tunnel surgery.^7,18-20 Patients who received adjunctive procedures in the 2013-2018 cohort were matched 1:1 to patients in the 2009-2011 cohort through greedy nearest neighbor matching with a caliper width of 0.2 times the standard deviation of the logit of the propensity score.²⁶ Patients in the 2013-2018 cohort without suitable matches were excluded. Postoperative improvements in DASH score, pinch strength, pain, and quality of life within matched pairs were assessed by Wilcoxon signed rank test. A similar process was used to generate matched pairs for patients who received UNT alone and UNT with GCR.

Propensity scores were also used to match patients who received electrical stimulation to those in the 2013-2018 cohort who did not. Matching and outcome assessment were performed as described above. For the purpose of comparison with prior studies, improvements in DASH score, pinch strength, pain, and quality of life relative to baseline for each treatment arm were evaluated by Wilcoxon signed rank test. In addition, differences in the rate of improvements between treatment arms were evaluated by multivariable linear regression models. For each model, predictor variables were days of follow-up, receipt of electrical stimulation, and the interaction between follow-up and electrical stimulation to examine slope change. Only the 2013-2018 cohort was used for the above analyses to better ascribe differences in outcomes to electrical stimulation. All analyses in this study were performed using SAS version 9.4 (SAS Institute Inc., Cary, North Carolina), and P values less than .05 were considered statistically significant.

Results

Overall Cohort Comparisons

The 2013-2018 cohort consisted of 136 patients, and the 2009-2011 cohort consisted of 87 patients. Preoperative information, treatments, follow-up time, and patient outcomes for each cohort are compared in Table 1. Of the 38 (28%) patients in the 2013-2018 cohort who underwent at least 1 adjunctive procedure, 24 (63%) had side-to-side profundus tenodesis, 31 (82%) had SETS nerve transfer, and 25 (69%) had cross-palm grafts. In addition, 33 (24%) patients received brief electrical stimulation. Preoperative characteristics for patients undergoing each treatment option are compared in Table 2. Patients who received adjunctive procedures tended to have lower conduction velocity and weaker pinch strength, and they were also more likely to have reduced wrist CMAP amplitude and abnormal EMG. There was no significant difference in the proportion of patients with entrapment at the arcade of Struthers.

Table 1.

Comparison of Patient Characteristics Between the 2009-2011 and 2013-2018 Cohorts.

Characteristic	Cohort
	2009-2011 (n = 87)	2013-2018 (n = 136)	P value
	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value
Age, y	49 (38 to 60)	59 (46 to 68)	.0002
Gender (female)	49 (56.3)	33 (24.3)	<.0001
BMI, kg/m²	28.1 (24.7 to 32.7)	28.9 (25.6 to 33.3)	.4196
Dominant hand affected	40 (54.1)	68 (50.0)	.5744
Previous cubital tunnel surgery	13 (14.9)	43 (31.6)	.0051
Arcade of Struthers release	—	44 (32.3)	—
Electrodiagnostic testing
Conduction velocity, across elbow, m/s	46 (38 to 56)	38 (27 to 52)	.0005
Reduced CMAP amplitude, wrist^a	15 (19.2)	70 (51.5)	<.0001
Abnormal electromyography	31 (45.6)	91 (71.1)	.0005
Preoperative
DASH score	39.4 (27.5 to 51.7)	31.7 (21.7 to 53.3)	.1924
Pinch strength, lbs	12.5 (10 to 17)	11 (7 to 16)	.0149
VAS pain score	6 (4 to 7.5)	6 (3.5 to 8.5)	.2797
VAS quality of life score	7.5 (4.5 to 8)	6.5 (3 to 8.5)	.4625
Follow-up, d	90 (48 to 239)	174 (86 to 327)	.0020
Outcomes (improvements)
DASH score (pre-post)	6.4 (−2.5 to 16.3)	9.6 (0.9 to 19.7)	.1071
Pinch strength (post-pre)	1 (−2 to 4)	2 (−2 to 4)	.7728
VAS pain score (pre-post)	1 (−0.5 to 3.5)	2.5 (0.5 to 5.5)	.0110
VAS quality of life score (pre-post)	1.5 (0.5 to 4.5)	2.5 (0 to 5)	.5229

Note. p values <0.05 are bolded. IQR = interquartile range; BMI = body mass index; CMAP = compound muscle action potential; DASH = Disabilities of the Arm, Shoulder, and Hand; VAS = Visual Analogue Scale.

CMAP amplitude was dichotomized with a cutoff of 6 mV.

Table 2.

Characteristics of Patients in the 2013-2018 Cohort Who Received Different Treatment Options.

Characteristic	Treatment option
	Cubital tunnel only (n = 18)	Cubital tunnel + GCR (n = 80)	Cubital tunnel + GCR + adjunctive procedures (n = 38)	P value
	Median (IQR) or No. (%)	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value
Age, y	48 (38 to 60)	57 (46 to 67)	63 (46 to 70)	.2841
Gender (female)	5 (27.8)	21 (26.3)	7 (18.4)	.6070
BMI, kg/m²	28.0 (23.6 to 32.9)	29.0 (25.3 to 33.9)	29.0 (25.7 to 31.8)	.4728
Dominant hand affected	8 (44.4)	47 (58.8)	13 (34.2)	.0395
Previous cubital tunnel surgery	2 (11.1)	27 (33.8)	14 (36.9)	.1256
Arcade of Struthers release	8 (44.4)	27 (33.8)	9 (23.7)	.2755
Electrodiagnostic testing
Conduction velocity, across elbow, m/s	46 (37 to 44)	40 (31 to 55)	29 (0 to 40)	<.0001
Reduced CMAP amplitude, wrist^a	1 (5.6)	35 (43.8)	34 (89.5)	<.0001
Abnormal electromyography	10 (58.8)	45 (60.8)	36 (97.3)	.0002
DASH score	24.2 (16.6 to 29.2)	33.3 (21.7 to 53.3)	35.8 (28.3 to 58.3)	.1120
Pinch strength, lbs	17 (10 to 22)	12 (10 to 16)	8 (5 to 11)	< .0001
VAS pain score	6 (3 to 8)	7 (4 to 9)	6 (3.5 to 8)	.6424
VAS quality of life score	3 (2.5 to 7)	6.5 (3 to 8.5)	7 (4 to 9)	.2559
Follow-up, d	133 (43 to 267)	166 (93 to 325)	216 (117 to 413)	.2403
Outcomes (improvements)
DASH score (pre-post)	5.0 (−2.6 to 15.5)	8.0 (−1.0 to 17.8)	17 (5 to 23)	.0202
Pinch strength (post-pre)	0 (−9 to 3)	2 (−2 to 4)	2 (0 to 4.5)	.0314
VAS pain score (pre-post)	1.5 (0 to 2.5)	2 (0 to 5.5)	3 (1 to 6)	.0820
VAS quality of life score (pre-post)	0.5 (−0.5 to 2.5)	2 (0 to 4)	4 (1.5 to 6)	.0204

Note. p values <0.05 are bolded. GCR = Guyon’s canal release; IQR = interquartile range; BMI = body mass index; CMAP = compound muscle action potential; DASH = Disabilities of the Arm, Shoulder, and Hand; VAS = Visual Analogue Scale.

CMAP amplitude was dichotomized with a cutoff of 6 mV.

When compared with the 2009-201l cohort, patients in the 2013-2018 cohort tended to be older (P = .0002), women (P < .0001), and more likely to have previous cubital tunnel surgery (P = .0051), abnormal EMG (P = .0005), reduced wrist CMAP amplitude (P < .0001), and lower preoperative pinch strength (P = .0149) (Table 1). They also had longer follow-up (median 174 vs 90 days, P = .0020) than those in the 2009-2011 cohort because patients receiving nerve transfers required longer follow-up than those receiving cubital tunnel surgery alone. The final multivariable linear regression models for DASH score, pinch strength, pain, and quality of life improvement are described in Supplemental Table S1. The cohort a patient belonged to only had a significant impact on quality of life improvement, with the 2013-2018 cohort experiencing a 1-point greater improvement in VAS score (95% confidence interval [CI], 0.20-1.78; P = .0149).

Assessment of Treatment Groups

The propensity score analyses resulted in 3 matched subgroups: the UNT-only subgroup had 28 patients, the UNT with GCR subgroup had 84 patients, and the adjunctive procedures subgroup had 30 patients. The preoperative characteristics for patients in each of these subgroups are compared in Table 3. Among those who received adjunctive procedures (n = 38), there were no significant differences in the types of adjunctive procedures performed or in treatment outcomes for those included in the propensity score analysis (n = 15) compared with the total group of 38 patients (Supplemental Table S2). As expected, patients within each matched subgroup were substantially more similar than in the overall cohort comparisons shown in Table 1. Patients who received adjunctive procedures had an 11.3-point greater improvement in DASH scores than their matched pairs (P = .0342). In contrast, there were no significant differences in outcomes for the other subgroups.

Table 3.

Propensity Score–Matched Subgroups for Different Treatment Options.

Characteristic	Propensity score–matched subgroups
	Cubital tunnel only			Cubital tunnel + GCR			Cubital tunnel + GCR + adjunctive procedures
	2009-2011 (n = 14)	2013-2018 (n = 14)	P value	2009-2011 (n = 42)	2013-2018 (n = 42)	P value	2009-2011 (n = 15)	2013-2018 (n = 15)	P value
	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value
Age, y	48 (46 to 58)	48 (38 to 60)	.8077	51 (43 to 62)	51 (41 to 63)	.5261	53 (45 to 62)	60 (46 to 68)	.3028
Gender (female)	8 (57.1)	5 (35.7)	.1797	22 (52.4)	15 (35.7)	.4798	7 (46.7)	1 (6.7)	.0339
BMI, kg/m²	27.8 (25.1 to 28.7)	29.0 (23.6 to 32.9)	.3258	28.1 (25.1 to 32.2)	28.2 (25.0 to 33.4)	.5640	28.5 (27.4 to 34.2)	30.1 (25.8 to 31.6)	.6698
Dominant hand affected	8 (66.7)	6 (42.9)	.3173	27 (71.1)	27 (64.3)	.4054	11 (78.6)	3 (20.0)	.0114
Previous cubital tunnel surgery	1 (7.1)	1 (7.1)	>.9999	8 (19.1)	11 (26.2)	.2568	2 (13.3)	3 (20.0)	.5637
Electrodiagnostic testing
Conduction velocity, across elbow, m/s	40 (34 to 58)	46 (34 to 53)	.9393	42 (37 to 51)	44 (35 to 57)	.5672	39 (33 to 46)	25 (0 to 40)	.0034
Reduced CMAP amplitude, wrist^a	2 (14.3)	1 (7.1)	.3173	13 (31.0)	10 (23.8)	.2568	12 (80.0)	11 (73.3)	.3173
Abnormal electromyography	10 (71.4)	7 (50.0)	.2568	24 (57.1)	21 (50.0)	.4386	13 (86.7)	14 (93.3)	.3173
Preoperative
DASH score	34.7 (21.7 to 45.8)	23.8 (16.6 to 55.8)	.4631	38.3 (26.7 to 48.3)	32.5 (23.3 to 54.2)	.7218	25.8 (19.2 to 50.9)	30.5 (21.1 to 40.9)	.6772
Pinch strength, lbs	11.5 (10 to 17)	17 (10 to 22)	.7109	12 (10 to 16)	11 (8 to 15)	.1227	12 (10 to 17)	12 (7 to 14)	.1648
VAS pain score	6.5 (3 to 7)	6 (2.5 to 8)	.7354	6 (3.5 to 7.5)	6.5 (4 to 9)	.4915	6 (4.5 to 7)	5 (3 to 8.5)	.9341
VAS quality of life score	6 (4.5 to 7.5)	3.5 (2.5 to 7)	.0640	7.5 (4.5 to 8)	6.5 (3.5 to 8.5)	.8021	7.5 (1 to 8)	7 (4 to 8.5)	.3998
Outcomes (improvements)
DASH score (pre-post)	7.8 (−0.8 to 12.1)	7.9 (0 to 15.8)	.6698	3.5 (−3.4 to 13.1)	6.6 (−5.0 to 18.1)	.4719	0.42 (−8.51 to 22.41)	18.4 (9.7 to 21.6)	.0342
Pinch strength (post-pre)	1.5 (−2 to 3)	1 (−9 to 3)	.3835	2 (−2 to 4)	2.5 (0 to 6)	.5183	1 (−1 to 6)	1 (−5 to 4)	.6390
VAS pain score (pre-post)	1 (0 to 2.5)	2 (0 to 3)	.6250	1.5 (0 to 4)	3 (0.5 to 5)	.1671	2 (0.5 to 3.5)	2.5 (1 to 7)	.1937
VAS quality of life score (pre-post)	1.5 (0 to 4.5)	1 (0 to 2.5)	.7422	1.5 (0.5 to 4.5)	1.5 (−1 to 3.5)	.7071	1.5 (0.5 to 4.5)	5 (2 to 7)	.0522

CMAP amplitude was dichotomized with a cutoff of 6 mV.

As described in Table 4, patients receiving electrical stimulation tended to have lower conduction velocity across the elbow and were more likely to have a history of previous cubital tunnel surgery, reduced CMAP amplitude, and abnormal EMG. The propensity score analysis resulted in a matched subgroup that consisted of 28 patients who received electrical stimulation and 28 controls who did not; preoperative characteristics were similar between cases and controls (Table 4). As shown in Table 5, patients who received electrical stimulation had significantly improved DASH scores relative to baseline (11.7-point improvement, P < .0001), whereas the controls did not. However, there were no significant differences between treatment arms for any study outcome (Table 4). In addition, there were no significant differences in the rates of improvement over time between treatment arms.

Table 4.

Evaluation of Patients Who Received Electrical Stimulation in the 2013-2018 Cohort, Overall and in a Propensity Score–Matched Subgroup.

Characteristic	Entire 2013-2018 cohort			Propensity score–matched subgroup
	No electrical stimulation (n = 103)	Electrical stimulation (n = 33)	P value	No electrical stimulation (n = 28)	Electrical stimulation (n = 28)	P value
	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value	Median (IQR) or No. (%)	Median (IQR) or No. (%)	P value
Age, y	57 (45 to 69)	62 (46 to 67)	.5714	59 (51 to 72)	63 (46 to 67)	.3033
Gender (female)	27 (26.2)	6 (18.2)	.3489	6 (21.4)	4 (14.3)	.4142
BMI, kg/m²	28.6 (25.7 to 33.8)	29.7 (25.5 to 32.1)	.4540	28.3 (26.5 to 32.5)	29.6 (25.6 to 31.4)	.5484
Dominant hand affected	55 (53.4)	13 (39.4)	.1615	14 (50.0)	12 (42.9)	.6171
Previous cubital tunnel surgery	28 (27.2)	15 (45.5)	.0495	13 (46.4)	11 (39.3)	.4142
Electrodiagnostic testing
Conduction velocity, across elbow, m/s	40 (31 to 53)	32 (7 to 42)	.0064	37.5 (24 to 43)	29 (0 to 40)	.2270
Reduced CMAP amplitude, wrist^a	45 (43.7)	25 (75.8)	.0013	20 (71.4)	20 (71.4)	>.9999
Abnormal electromyography	62 (63.9)	29 (93.6)	.0015	25 (89.3)	26 (92.9)	.3173
Preoperative
DASH score	29.8 (19.6 to 51.3)	35.8 (27.5 to 58.3)	.1527	29.4 (15.8 to 49.2)	33.3 (25.0 to 58.3)	.3683
Pinch strength, lbs	11.5 (8 to 16)	10 (7 to 14)	.2856	10.5 (8 to 15)	10.5 (7 to 15)	.4652
VAS pain score	7 (4 to 8)	6 (3 to 8.5)	.7412	6 (3 to 8.5)	5 (2.5 to 8.5)	.6993
VAS quality of life score	6.5 (3 to 8)	7.5 (4 to 9)	.2014	7 (3 to 9)	7.5 (4 to 10)	.6572
Outcomes (improvements)
DASH score (pre-post)	8.4 (0 to 18.1)	16.6 (5 to 23.3)	.0823	5.0 (−6.8 to 15.0)	11.7 (4.6 to 20.8)	.6525
Pinch strength (post-pre)	2 (−1 to 5)	0 (−5 to 4)	.1298	2 (−2 to 4)	−1 (−5 to 3)	.1474
VAS pain score (pre-post)	2.5 (0.5 to 5.5)	3 (0 to 5)	.9296	2 (0.5 to 4)	2.5 (0 to 5)	.9451
VAS quality of life score (pre-post)	2 (0 to 4)	4 (1.5 to 6.5)	.0179	2.5 (0 to 4)	4 (1.5 to 6)	.1901

CMAP amplitude was dichotomized with a cutoff of 6 mV.

Table 5.

Changes in Disabilities of the Arm, Shoulder, and Hand Score, Pinch Strength, Pain, and Quality of Life for Each Treatment Arm (Electrical Stimulation vs No Electrical Stimulation) of the Propensity Score–Matched Subgroup for Electrical Stimulation.

Characteristic	Control (n = 28)		Electrical stimulation (n = 28)
Characteristic	Median (IQR) or No. (%)	P value	Median (IQR) or No. (%)	P value
DASH score (pre-post)	5.0 (−6.8 to 15.0)	.2253	11.7 (4.6 to 20.8)	.0001
Pinch strength (post-pre)	2 (−2 to 4)	.2304	−1 (−5 to 3)	.3992
VAS pain score (pre-post)	2 (0.5 to 4)	.0001	2.5 (0 to 5)	<.0001
VAS quality of life score (pre-post)	2.5 (0 to 4)	.0011	4 (1.5 to 6)	<.0001

Note. p values <0.05 are bolded. IQR = interquartile range; DASH = Disabilities of the Arm, Shoulder, and Hand; VAS = Visual Analogue Scale.

Discussion

Patients who underwent adjunctive procedures outside the cubital tunnel had significantly greater improvements in DASH scores than their matched controls from a historical cohort. This 11.3-point increase corresponds to the minimally clinically important difference in DASH score suggested by previous studies.^27,28 Pinch strength, pain, and quality of life tended to improve irrespective of the adjunctive procedures. Nonetheless, patients in both cohorts often had residual elevations in DASH scores, weakness, persistent pain, and reduced quality of life postoperatively.

From Bench to Beside and Back Again

Ideal management of the full spectrum of this disease, and thus ideal recovery, remains a humbling challenge. In pursuit of this goal, our management of cubital tunnel surgery has continued to evolve. Early successes after the introduction of a new procedure, such as the first SETS nerve transfer in 2011,²⁹ gave rise to larger practice change as familiarity with the procedure and evidence of its benefits grew. Moreover, we recently modified the SETS to also transfer the nerve to the ADM to the deep motor branch of the ulnar nerve in a “double SETS” procedure. New practices may also advance our understanding of disease pathophysiology, which may in turn lead to the introduction of additional practices. Indeed, even minor advances in clinical management are often the culmination of years of anatomical, basic, and translational research.

For example, years of animal studies demonstrated that brief electrical stimulation enhances axonal outgrowth, reinnervation, and functional recovery in acute nerve injury models, potentially through increased expression of neurotrophins, cyclic adenosine monophosphate, and proregenerative macrophages.^30,31 Electrical stimulation was also recently shown to promote axonal regeneration in chronically denervated motor and sensory nerves, which suggested its potential utility in compression neuropathy.³² Additional steps toward clinical translation were discoveries that electrical stimulation is as effective as FK506 in promoting recovery³¹ and that 10 minutes of stimulation promotes axon growth and produces similar benefits in functional recovery as 60 minutes of stimulation,³³ reducing necessary anesthesia and operating time. Moreover, electrical stimulation is increasingly used for intraoperative neural monitoring, such as during thyroid and parathyroid surgery,³⁴ and nerve identification/protection during dissection. Our stimulation protocol (10 minutes with a 2-mA current and 100-µs pulse width) was based on these prior works.

The indications for intraoperative electrical stimulation, its effects on functional recovery in chronic neuropathy, and ideal stimulation protocols are all active areas of study. In this study, electrical stimulation was generally offered to patients with symptomatic weakness and reduced functional axons, as evidenced by reduced CMAP amplitude and/or EMG changes consistent with denervation. Key to patient selection is the concept that motor function is relatively preserved until a rapid drop at approximately 70% to 80% axonal loss.^19,24 This implies the following: (1) that a patient with significant muscle weakness has already lost most of the healthy axons to that muscle; and (2) that dramatic improvement in motor function is possible through recovery of only a small number of axons. Patients near this tipping point of 70% to 80% loss would likely experience the most benefit from electrical stimulation. Similarly, it is probable that patients with neither minor disease nor very severe chronic neuropathy would substantively benefit from electrical stimulation. Several patients in this study had profound ulnar neuropathy that persisted despite prior cubital tunnel surgery, and this high disease severity may partly explain why electrical stimulation did not have a significant impact between treatment arms.

Measuring Treatment Effects in Clinical Practice

Although translational studies are paramount for clinical advances, effects in animal models are not easily measured in humans. Chief among several potential explanations is the enormous complexity of clinical presentation. Comorbidities, variations in disease severity, modifications in behavior due to the disease or its treatment, and a patient’s subjective experience of his or her illness may all influence whether and to what degree that patient demonstrates benefits from treatment. For example, consistent with several animal studies, a pilot randomized controlled trial (RCT) of patients undergoing carpal tunnel release found that electrical stimulation resulted in earlier and more complete muscle innervation, when compared with baseline.¹² Yet, these patients experienced little improvement in functional outcomes relative to controls. An additional RCT by Power et al¹³ found, as in our study, that electrical stimulation had a positive impact on cubital tunnel surgery outcomes relative to baseline, but its effects relative to controls were nonsignificant. Therefore, conclusions regarding the efficacy of electrical stimulation for clinical practice are limited at present, given the benchmark of therapeutic efficacy (ie, the new treatment is superior to control) has not been achieved. Taken together, these studies suggest that additional and larger studies may be needed to evaluate the impact of electrical stimulation.

Ethical Innovation and Clinical Implications

There is no generally accepted or reliable way to classify disease severity for cubital tunnel syndrome.¹⁹ Several variables that are commonly assumed to portent worse prognosis (eg, reduced conduction velocity) have not actually been shown to predict treatment outcomes.^7,19 Consequently, nerve surgeons largely rely on their clinical judgment and technical expertise to determine their management of this complex disease. The decision to offer or adopt a new procedure with relatively limited clinical evidence is not uncommon in nerve surgery.³⁵ The core principles of beneficence and nonmaleficence maintain that a procedure should be offered only if it may produce a credible benefit to the patient over existing alternatives and if this benefit justifies potential harms. Although we demonstrated that adjunctive procedures improved postoperative DASH scores, we emphasize that this does not imply that they should be offered in all cases or in all practice settings. Similarly, our finding that electrical stimulation did not affect patient outcomes does not necessarily mean that it should not be offered as part of cubital tunnel surgery.

Propensity Score Analysis

Propensity scores are a relatively new and underused tool that may help bridge the gap between observation studies and RCTs. In a well-designed RCT, treatment arms may differ significantly in some baseline characteristics, but these differences are due to chance. In contrast, patient selection in routine practice is not assigned at random but by several clinical factors. Propensity score analysis helps account for this treatment-selection bias so that observational studies may more closely match RCTs. The propensity score represents how likely a patient is to receive a treatment based on his or her baseline characteristics. Matching treated to untreated patients by their propensity score, in theory, produces pairs that only meaningfully differ in treatment allocation. By comparing the effect of treatment within matched pairs, its overall impact can be determined.

Conclusions in this study were drawn from the propensity score analysis. Multivariable linear regression was reported in part to highlight advantages of propensity score matching. For example, these regression models did not account for differences in treatments or in the management strategies used to select these treatments. Treatment was not included as a variable because procedures were not assigned independently of other variables; indeed, they were selected based on these clinical characteristics. This situation, termed multicollinearity, is an underrecognized problem in epidemiological and clinical research that produces unstable and biased estimates in statistical models.³⁶ In the setting of multicollinearity, it may be impossible to determine the contributions of a given variable while holding other covariates constant. For example, the impact of a procedure that is only offered to patients with reduced wrist CMAP amplitude (eg, SETS nerve transfer) cannot be evaluated independently of CMAP amplitude. An additional complicating factor is that some patients with severe disease in the 2013-2018 cohort were considered operative candidates partly because adjunctive procedures were available. Indeed, the 2013-2018 cohort tended to have more severe disease, in terms of pinch strength and electrodiagnostic studies, than the 2009-2011 cohort. Propensity scores have clear applications in such complex situations, which are particularly common in nerve surgery research.

Limitations

As a retrospective study, patient cohorts may have varied in unmeasured characteristics that may have influenced treatment assignment and/or study outcomes. This study also included a broad spectrum of disease severity, and heterogeneity in disease severity within treatment groups may have influenced study outcomes in complex and unpredictable ways. Similarly, patients in this study may have had more severe disease than the average patient with cubital tunnel syndrome, as the senior author’s practice includes a relatively large proportion of redo cubital tunnel surgeries and patient referrals from other hand surgeons. Consequently, the results of this study may not be generalizable to all practice settings. The sample size was modest, particularly for the propensity score–matched subgroups, which resulted in relatively wide CIs for effect estimates and reduced power to detect true differences between treatment groups. It also prohibited assessment of the individual impact of each adjunctive procedure in this study, although the impact of SETS nerve transfer and cross-palm grafts in cubital tunnel syndrome has been evaluated previously.^11,14 Although the DASH has been extensively validated,^16,23 it is an imperfect measure of disease impairment. There may have also been salient differences in specific DASH items, which were not evaluated in this study. Ultimately, additional and preferably prospective or randomized studies are needed to corroborate our findings before advocating for widespread practice change.

Conclusions

Our management of cubital tunnel syndrome has expanded to include multiple adjunctive procedures as well as electrical stimulation in patients with severe disease. Those who underwent profundus tenodesis, SETS nerve transfer, and/or cross-palm nerve grafts experienced greater improvement in postoperative DASH scores than their propensity score–matched pairs who did not receive adjunctive procedures.

Supplemental Material

sj-pdf-1-han-10.1177_1558944721998022 – Supplemental material for Beyond the Cubital Tunnel: Use of Adjunctive Procedures in the Management of Cubital Tunnel Syndrome

Supplemental material, sj-pdf-1-han-10.1177_1558944721998022 for Beyond the Cubital Tunnel: Use of Adjunctive Procedures in the Management of Cubital Tunnel Syndrome by Adam Evans, William M. Padovano, J. Megan M. Patterson, Matthew D. Wood, Warangkana Fongsri, Carie R. Kennedy and Susan E. Mackinnon in HAND

Footnotes

Authors’ Note

This work was performed at Washington University in St. Louis, St. Louis, MO.

Ethical Approval

The study design was approved by our institutional review board (#201207085). Criteria for approval were met per 45 CFR 46.111 and/or 21 CFR 56.111, as applicable.

Statement of Human and Animal Rights

This article does not contain any studies with human or animal subjects.

Statement of Informed Consent

Informed consent was obtained when necessary.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: S.E.M. and M.D.W. have been the recipients of research support from Checkpoint Surgical, Inc. Specifically, they were principal investigators for an industry-sponsored research agreement from Checkpoint Surgical, Inc. to Washington University receiving $250 000 in 2019-2020. No personal compensation was provided. Checkpoint Surgical, Inc. did not influence or affect the experimental design or outcome of the studies.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Adam Evans

William M. Padovano

J. Megan M. Patterson

Matthew D. Wood

Carie R. Kennedy

Susan E. Mackinnon

Supplemental material is available in the online version of the article.

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Supplementary Material

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