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Abstract

Introduction: Ulnar nerve enlargement is observed in ultrasound (USG) in patients with cubital tunnel syndrome (CuTS). This study aims to compare the ultrasound size of the ulnar nerve between CuTS patients and control subjects, to find the cut off size for diagnosis, and to validate the use of USG as an adjunct in CuTS diagnosis. Materials and Methods: There were 23 elbows with clinical and nerve conduction test (NCT) confirmed CuTS, and 42 elbows in the control group. Cases with elbow deformities, old ulnar nerve injuries and postoperative cases were excluded. The ulnar nerve cross sectional area (CSA) was measured at 6 different levels and positions: over the medial epicondyle (ME) in elbow flexion/extension, 2 cm and 5 cm distal to the ME, 2 cm and 5 cm proximal to the ME. A cut off CSA value for CuTS diagnosis was derived. Correlation between ulnar nerve CSAs and NCT was analysed. Results: The age and gender distribution were similar in both groups (61.2 vs 56.6; M > F, p > 0.05). The mean CSA of the CuTS group vs control group was 19.2 mm2 vs 7.0 mm2, 19.5 mm2 vs 7.1 mm2, 20.8 mm2 vs 8.1 mm2 at ME flexion, ME extension and maximal CSA respectively. The derived CSA cut off value for CuTS at ME flexion, ME extension and maximal CSA were 10.5 mm2, 11.5 mm2, and 15 mm2 respectively. The CSA difference at different levels between the 2 groups were significant except at 5 cm proximal to ME. A strong negative correlation was seen between the CSA and the across elbow nerve conduction velocity, with correlation coefficient of −0.748 at ME flexion, −0.654 at ME extension and -0.676 at maximal CSA. Conclusion: USG can be used as an adjunct for the diagnosis of CuTS with high accuracy and patient safety. It can also be used to delineate possible anatomical etiologies at the cubital tunnel.

Keywords

ultrasonic measurement cubital tunnel syndrome Hong Kong Chinese

Introduction

Cubital tunnel syndrome (CuTS) is the second commonest compressive neuropathy in the upper limb, after carpal tunnel syndrome. The prevalence ranged between 1.8% and 5.9%.¹ Common sites of compression of the ulnar nerve are between the two heads of flexor carpi ulnaris/ aponeurosis, Osborne's ligament, within the arcade of Struthers and medial epicondyle. Diagnosis of CuTS is commonly made by physical signs (McGowan grade 1-3) and symptoms. Nerve conduction test (NCT) confirms the diagnosis and quantifies the severity.² In our locality, the practice is similar. However, they have their limitations. For example, NCT may cause electromagnetic interference in patients with implantable cardiac devices.³ And in case of absent electric signal due to severe CuTS, electromyography (EMG) may be needed as an adjunct to NCT. Classical EMG finding of lower motor neuron denervation would be the presence of fibrillation potentials, positive sharp waves, and increased insertional activity.⁴ Sometimes, a spectrum of clinical findings can make the diagnosis unclear, and symptoms and signs of C8 radiculopathy may overlap with CuTS (Figure 1).

Ultrasonography is able to visualize peripheral nerves in selected areas of extremities and facilitate the diagnosis of pathological conditions. Ultrasound (USG) of the median nerve at the carpal tunnel is widely employed. Ulnar nerve enlargement is often observed in USG in patients with CuTS, especially just above and below the site of maximal compression i.e., hourglass deformity. So far, no USG data for CuTS was available for use in the Hong Kong Chinese population. Our study aims to compare the USG size of the ulnar nerve between CuTS patients and control subjects, to find the cut off size for diagnosis in our locality, and to validate the use of USG as an adjunct in CuTS diagnosis.

Materials and methods

Cases were recruited between April 2021 and October 2022. We recruited 18 patients with clinical and NCT confirmed CuTS in the orthopedic outpatient clinic of United Christian Hospital. Among them, five patients had bilateral disease. So there were a total of 23 CuTS elbows in the patient group (CuTS + ve). In the control group (CuTS-ve), there are 42 normal elbows: eight are from the asymptomatic, NCT-ve contralateral elbows of the CuTS + ve group, while 34 normal elbows from 17 subjects are recruited from the same orthopedic clinic who presented with other upper limb complaints with a normal NCT. Cases with elbow deformities, old ulnar nerve injuries, ulnar nerve subluxation and postoperative cases for cubital tunnel syndrome were excluded (Figure 1).

Figure 1.

Diagram showing the process of recruiting CuTS+ve and CuTS-ve elbows.

Clinical symptoms of CuTS consisted of weakness or clumsiness of the ulnar nerve innervated muscles, numbness and paresthesia of the fourth and fifth digits of the hand, and medial elbow pain. Patients were assessed by orthopedic surgeons at the outpatient clinic for pinprick sensation in the territory innervated by the ulnar nerve, muscle strength of the first dorsal interosseous and abductor digiti minimi using the Medical Research Council grading, presence of Tinel sign and ulnar nerve thickening.

The NCTs in the same hospital were performed with standard surface/ring electrodes, stimulation techniques, recording techniques, and filter settings as described by Kimura.⁵ Based on the American Association of Electrodiagnostic Medicine Criteria, ulnar neuropathy at the cubital tunnel was diagnosed in the presence of one of the following abnormalities: absolute nerve conduction velocity slowing above the elbow, decrease of nerve conduction velocity of more than 10 m/s across the elbow, decrease in amplitude of more than 20%, absent ulnar sensory responses, or signs of denervation in muscles innervated by the ulnar nerve on electromyography.

Demographics (gender and age) between the two groups would be compared.

General Electric Logiq P9 ultrasound machine with linear array transducer (L8-18i-RS Probe) was used to trace the ulnar nerve around the elbow (Figures 2 and 3). USG is performed or supervised by an orthopedic surgeon specialized in hand surgery to minimize interobserver variability. The subject is seated upright, with shoulder flexed to 90 degrees and his/her elbow rested on a table placed in front (Figures 4 and 5). The ulnar nerve cross-sectional area (CSA) was measured at six different levels and positions: over the medial epicondyle (ME) in 90 degree elbow flexion and full extension, 2cm and 5 cm distal to the ME in 90 degree elbow flexion, 2 cm and 5 cm proximal to the ME in 90 degree elbow flexion (Figure 6). The mean CSA values at these positions between the two groups would be compared, with p < 0.05 being statistically significant. A cut off CSA value for CuTS diagnosis was derived with receiver operating characteristic (ROC) curve. Correlation between ulnar nerve CSAs and NCT was obtained with Pearson correlation coefficient.

Figure 2.

Ulnar nerve tracing (in yellow) at the medial epicondyle in a patient with CuTS. It shows a grossly swollen nerve.

Figure 3.

Ulnar nerve tracing (in white) at the medial epicondyle in a normal subject. The nerve has a normal caliber.

Figure 4 and 5.

Subject positioning during USG: Shoulder flexed to 90 degrees and elbow rested on a table in front.

Figure 6.

Landmarks used for ulnar nerve USG tracing.

Results and discussion

There are 20 males and three females in the patient group; 27 males and 15 females in the control group (p > 0.05). The mean age of the patient group is 61.2, while the mean age of the control group is 56.6 (p > 0.05).

The ulnar nerve cross-sectional area is larger at all recorded locations and positions around the elbow for the CuTS + ve group. Most differences between the two groups are at the medial epicondyle in 90 degree elbow flexion and full elbow extension. Apart from 5cm proximal to medial epicondyle, differences in cross-sectional area in other points between the two groups are statistically significant (Table 1). A possible explanation would be: ulnar nerve is most swollen at the medial epicondyle in the CuTS + ve group, hence there will be gradual tapering of the swelling away from the pathological site. And 5cm away from the medial epicondyle is the farthest point from the compression site recorded from our study.

Comparing our study result to other similar overseas studies, our mean ulnar nerve CSA at the medial epicondyle in the CuTS + ve group, regardless of elbow position, is larger (Table 2). This can be possibly due to a delayed initial presentation to the clinic by patients in our locality. Most CuTS cases in our clinic are at McGowan grade 3.

Our cutoff value for CuTS diagnosis is 10.5 mm² at medial epicondyle at 90 degree elbow flexion (Table 3). It is similar to other studies (Table 4).

Results showed a strong negative correlation between CSA value and the above elbow motor conduction velocity, meaning the lower the velocity above elbow i.e., the more severe the CuTS, the larger the CSA of the ulnar nerve is in ultrasound (Figure 7 and Table 5). This result further shows that CSA value in USG correlates well with the severity of CuTS. We could also utilize this scatter diagram to roughly estimate the above elbow motor conduction velocity based on the ultrasonic ulnar nerve measurement at the elbow, or vice versa, during daily practice.

Figure 7.

Scatter diagram for correlating above elbow motor conduction velocity and maximal CSA in both groups.

There are several limitations in our study. The status of subjects undergoing USG (patients vs control) is not blinded to the examiner. Furthermore, we did not evaluate the USG findings in patients who only present with clinical symptoms of cubital tunnel syndrome but with a normal NCT.

Conclusion

Ultrasound of the ulnar nerve can be used as diagnosis, or adjunct to diagnosis of cubital tunnel syndrome with high accuracy and safety. In cases where NCT shows no response, or those with double crush syndrome (both cervical radiculopathy and compression at the cubital tunnel), USG would be particularly useful. It can also be used to delineate possible anatomical etiologies at the cubital tunnel such as anconeus epitrochlearis muscle, occult ganglion, ulnar nerve dislocation, etc. In future, with more similar studies performed, more standardized USG techniques and diagnostic criteria for cubital tunnel syndrome could be established.

Table 1.

Mean CSA values at different locations and elbow positions of the two groups.

Location and position of ulnar nerve	Mean CSA in CuTS + ve group (mm²)	Mean CSA in CuTS-ve group (mm²)	P value
Medial epicondyle in 90 degree elbow flexion	19.2	7.0	<0.01
Medial epicondyle in full elbow extension	19.5	7.1	<0.01
2 cm proximal to medial epicondyle	10.3	6.0	<0.01
5 cm proximal to medial epicondyle	6.4	5.6	0.143
2 cm distal to medial epicondyle	10.2	6.3	<0.01
5 cm distal to medial epicondyle	8.0	5.4	<0.01
Maximal CSA value	20.8	8.1	<0.01

Table 2.

Comparison of mean CSA of our study with a meta-analysis done by Chang et al. in 2018.

Meta-analysis, Chang et al. (2018)⁶	Country	Position of elbow at medial epicondyle	CSA of ulnar nerve of CuTS + ve group (mm²)	CSA of ulnar nerve of CuTS-ve group (mm²)
Chiou et al., 1998⁷	Taiwan	Not mentioned	10.9	5.3
Mondelli et al., 2009⁸	Italy	Full extension	9.6	5.6
Thoirs et al., 2008⁹	Australia	Averaged between full flexion/extension	12.2	8.2
Yoon et al., 2008¹⁰	Korea, USA	90 degree flexion	18.5	6.6
Kutlay et al., 2009¹¹	Turkey	Averaged between 90 degree flexion/ full extension	16	Male: 6.7 Female: 6
Bayrak et al., 2010¹²	Turkey	not mentioned	13	8.8
Ayromlou et al., 2012¹³	Iran	90 degree flexion	8	4
Zhong et al., 2012¹⁴	China	90 degree flexion	13.1	6.3
Ghanei et al., 2015¹⁵	Iran	Not mentioned	17.1	7.2
Kim et al., 2015¹⁶	Korea	90 degree flexion	12.2	7.5
Simon et al., 2015¹⁷	USA	90 degree flexion	10.6	7
Our study	Hong Kong	90 degree flexion	19.2	7
" "	" "	full extension	19.5	7.1

Table 3.

Derived cut off values for diagnosis of CuTS in our study using the ROC curve.

Elbow position and location	CSA cutoff value (mm²)	Sensitivity (%)	Specificity (%)
Medial epicondyle in 90 degree flexion	10.5	87.0	92.9
Medial epicondyle in full elbow extension	11.5	86.4	92.5
Maximal CSA	15.0	87.0	97.6

Table 4.

Comparison of cut off value for CuTS diagnosis in our study and other overseas studies.

Meta-analysis, Chang et al. (2018)⁶	Country	CSA cutoff value (mm²)	Location of ulnar nerve/ elbow position used	Sensitivity	Specificity
Wiesler et al., 2006¹⁸	USA	10	Max CSA	93%	98%
Mondelli et al., 2008⁸	Italy	10.3	cubital tunnel inlet	24.5%	45.5%
"	"	8.8	ME	"	"
Kutlay et al., 2009¹¹	Turkey	10	ME in elbow flexion	90%	100%
Volpe et al., 2009¹⁹	Italy	10	Max CSA	88%	88%
Bayrak et al., 2010¹²	Turkey	10	ME	83%	81%
"	"	11	Max CSA	95%	71%
Ayromlou et al., 2012¹³	Iran	10	Max CSA	82%	72%
Ghanei et al., 2015¹⁵	Iran	10.5	cubital fossa	92.7%	93.2%
Kim et al., 2015¹⁶	Korea	8.95	Max CSA	93.8%	88.3%
Our study	Hong Kong	10.5	ME at 90 degree elbow flexion	87%	92.9%

Table 5.

Pearson correlation coefficient between CSA and above elbow motor conduction velocity in the CuTS + ve group.

Elbow position and location	Correlation coefficient
Medial epicondyle in 90 degree flexion	−0.748
Medial epicondyle in full elbow extension	−0.564
Maximal CSA	−0.676

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Chung Pui Man

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