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Patient- and disease-specific factors associated with atrophy of the intrinsic muscles of the ulnar nerve in cubital tunnel syndrome
⁎Corresponding author: Kenichi Asano. kennichiasano1@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Patients presenting with severe neuropathy are less likely to recover after surgery for cubital tunnel syndrome. The purpose of this study was to investigate patient- and disease-specific factors associated with atrophy at presentation of the intrinsic muscles innervated by the ulnar nerve.
A retrospective data of patients with cubital tunnel syndrome were included in the study. Paralysis of the intrinsic muscles was evaluated as muscle atrophy of the first dorsal interossei, adductor pollicis, or abductor digiti minimi. The muscle atrophy group comprised 64 patients with atrophy of the intrinsic muscles. The non-atrophy group comprised 57 patients without intrinsic muscle atrophy at presentation. Univariate and multivariate regression analyses were conducted to assess patient factors including age, sex, body mass index, disease duration, comorbidities (diabetes mellitus and cervical spondylosis), and other elbow disorders (osteoarthritis of the elbow, presence of a ganglion, and cubitus varus or valgus deformity). A radiographic evaluation of elbow osteoarthritis was conducted using the Broberg and Morrey classification; osteophytes of the ulna were also assessed.
Through univariate analysis, patients in the muscle atrophy group were identified as being significantly older, with significantly longer disease duration and more osteophytes of the ulna, than those in the non-atrophy group. Cervical spondylosis and osteoarthritis of the elbow were more frequently observed in the muscle atrophy group than in the non-atrophy group. Multivariate analysis identified patient's age as an independent risk factor related to atrophy of the intrinsic muscles, while other factors were not significant association.
There was no association between the intrinsic muscle atrophy in cubital tunnel syndrome and elbow osteoarthritis. Older patients with cubital tunnel syndrome were more likely to present with atrophy of the intrinsic muscles of the ulnar nerve. Knowledge of the factors associated with severe neuropathy may allow for earlier diagnosis and therapeutic intervention.
Keywords
McGowan classification
Muscle atrophy
Cubital tunnel syndrome
Diagnosis
Severity
Patient-specific factors
1 Introduction
Cubital tunnel syndrome (CuTS) is the second most common entrapment neuropathy of the upper extremities.1 Patients presenting with severe neuropathy often progress to axonal loss and are less likely to recover sensory and motor function following surgical treatment. Prognostic factors for the postoperative outcomes of CuTS have been studied 2–4: Multivariate regression analysis of 83 patients with CuTS showed preoperative disease severity as an independent risk factor for poor prognosis.4 McGowan stage 3 is considered to reflect severe neuropathy, with paralysis of the intrinsic muscles of the ulnar nerve.5 Patient-specific factors associated with intrinsic muscle atrophy in patients with CuTS are age, male sex, body mass index, and diabetes mellitus 6–9. A high rate of osteoarthritis of the elbow, a causative factor, has also been identified in patients with CuTS.10 However, few studies have investigated the relationship between the severity of CuTS and elbow osteoarthritis. The present study hypothesis was that there is no association between the intrinsic muscle atrophy in cubital tunnel syndrome and elbow osteoarthritis. Therefore, the purpose of this study was to investigate risk factors related to atrophy of the intrinsic muscles of the ulnar nerve.
2 Material and methods
2.1 Patients
A retrospective data of patients with CuTS were collected in the study. A list of patients presenting to the hospital between 2009 and 2022 was generated from the electronic medical records database. Patients with an initial diagnosis of CuTS and older than 18 years were included. A diagnosis of CuTS required the presence of the Tinel sign at the cubital tunnel, numbness or paraesthesia in the distribution of the ulnar nerve, and motor weakness in pinching or gripping. The diagnosis was confirmed using electrical studies according to a slowing of the conduction velocities of sensory and motor ulnar nerves at the elbow. The criteria for electrodiagnosis were a slowing of conduction velocity of <50 m/s above the elbow or a decrease of conduction velocity of 15 m/s from below elbow to across elbow. Patients who had undergone previous surgery on the ipsilateral elbow or were suspected of having cervical radiculopathy or thoracic outlet syndrome were excluded. Paralysis of the intrinsic muscles was evaluated as muscle atrophy of the first dorsal interossei, adductor pollicis, or abductor digiti minimi. Intrinsic muscle atrophy was considered present if atrophy was found in at least one of these three muscles. The flexor carpi ulnaris and flexor digitorum profundus were not evaluated because they were extrinsic muscles. The severity of disease was assessed using the McGowan classification system.5
2.2 Study groups
The muscle atrophy group consisted of patients with CuTS with atrophy of an intrinsic muscle of the ulnar nerve. The non-atrophy group consisted of patients with CuTS without atrophy of any of the intrinsic muscles of the ulnar nerve.
2.3 Clinical data
Demographic data, including age, sex, body mass index, and disease duration were collected. Comorbidities (diabetes mellitus and cervical spondylosis) and other elbow disorders (osteoarthritis of the elbow, presence of a ganglion, and cubitus varus or valgus deformity) were extracted from patient charts. Osteoarthritis of the elbow was evaluated using lateral view radiographs according to the Broberg and Morrey classification (Table 1).11 Osteophytes of the ulna were assessed using cubital tunnel view radiographs and the length of each osteophyte was measured (Fig. 1). Radiographs were recaptured if the elbow was inaccurately positioned.
| Grade | Description |
| 0 | Normal joint |
| 1 | Slight joint space narrowing with minimal osteophyte formation |
| 2 | Moderate joint space narrowing with moderate osteophyte formation |
| 3 | Severe degenerative change with gross destruction of the joint |
2.4 Statistical analysis
Median and interquartile range are used to present nonparametric data. Mean and standard deviation are used to present parametric data. Univariate analysis was performed to evaluate differences between the muscle atrophy and non-atrophy groups using Student's t- and Mann–Whitney U tests for continuous variables, the chi square and Fisher's exact test for categorical variables. Statistical significance was set at p < 0.05 for all tests. Any variable showed a statistical significance was selected as an independent variable in a multivariate regression analysis. Multivariate regression analysis was performed to identify the independent risk factors associated with atrophy of the intrinsic muscles in CuTS. Odds ratios and 95% confidence intervals were determined. The cutoff value for atrophy of these muscles was determined using a receiver operating characteristic curve. Statistical analyses were performed using Ekuseru–Toukei 2010 software.
3 Results
A total of 212 patients with CuTS underwent conservative or surgical treatment. Thirteen patients who had previously undergone surgery were excluded. There were 78 patients with insufficient data and they were also excluded. Our final cohort consisted of 121 patients with CuTS, 31 of whom underwent conservative treatment and 90 of whom underwent cubital tunnel release with or without transposition within the study period. Twenty patients were classified as having McGowan grade 1 disease, thirty-seven as having grade 2, and sixty-four as having grade 3.
3.1 Age, sex, body mass index, and disease duration
The mean age of the patients was 62.7 years; 89 were male (74%) and 32 were female (26%). The mean body mass index was 23.8 kg/m2 and the median disease duration was 4 months. The muscle atrophy group comprised 47 male and 17 female participants (mean age, 67.2 years; mean body mass index, 23.2 kg/m2), whereas the non-atrophy group comprised 42 male and 15 female participants (mean age, 57.6 years; mean body mass index, 24.4 kg/m2). The median disease duration was 6 and 3 months in the muscle atrophy and non-atrophy groups, respectively.
According to the univariate analysis, age and disease duration were significantly higher in the muscle atrophy group than in the non-atrophy group. However, sex and body mass index did not significantly differ between the groups (Table 2).
| Factor | Muscle atrophy group | Non-atrophy group | p-Value |
| Age (years) | 67 (11)a | 58 (14)a | <0.001 c |
| Sex (male/female) | 47/17 | 42/15 | 0.98d |
| Body mass index (kg/m2) | 23.2 (3.3)a | 24.4 (4.8)a | 0.13c |
| Disease duration (months) | 6 (2–22)b | 3 (1–5)b | <0.001 e |
| Diabetes mellitus (+/-) | 19/45 | 15/42 | 0.68d |
| Cervical spondylosis (+/-) | 38/26 | 19/38 | <0.01 d |
| Ganglion (+/-) | 3/61 | 3/54 | 0.78d |
| Varus or valgus deformity (+/-) | 3/61 | 3/54 | 0.78d |
3.2 Comorbidities and other elbow disorders
Cervical spondylosis was more frequently observed in the muscle atrophy group than in the non-atrophy group. No significant differences in diabetes mellitus, elbow ganglion, and cubitus varus or valgus deformity were observed between the groups.
Osteoarthritis, diagnosed on radiography, was noted in 103 (85%) of the 121 elbows. Table 3 lists the number of patients in each group with the different Broberg and Morrey grades. Elbow osteoarthritis was reported at a higher rate in the muscle atrophy group than in the non-atrophy group. At 3.55 mm, the median length of the osteophytes was significantly longer in the muscle atrophy group than in the non-atrophy group (1.47 mm).
3.3 Patient- and disease-specific factors for intrinsic muscle atrophy
Univariate analysis found 5 variables as candidates for a multivariate regression analysis: patient's age, disease duration, cervical spondylosis, osteoarthritis of the elbow, and osteophytes of the ulna. Multivariate regression analysis revealed patient's age as an independent patient- and disease-specific factor associated with atrophy of the intrinsic muscles of the ulnar nerve (Table 4). There were not significant association between the intrinsic muscle atrophy in CuTS and disease duration, cervical spondylosis, osteoarthritis of the elbow, and, osteophytes of the ulna. The area under the receiver operating characteristic curve of patient's age was 71%, and the cutoff value for atrophy was 65 years (sensitivity, 63%; specificity, 70%).
| Odds ratio | 95%CI | p-Value | |
| Age | 1.08 | 1.02–1.15 | 0.013 |
| Disease duration | 1.04 | 0.99–1.09 | 0.15 |
| Cervical spondylosis | 1.66 | 0.50–5.51 | 0.40 |
| Osteoarthritis | 1.84 | 0.52–6.50 | 0.34 |
| Osteophyte | 0.95 | 0.58–1.55 | 0.84 |
4 Discussion
In this study, we retrospectively assessed the data of 121 patients with CuTS. Multivariable analysis revealed that age was an independent risk factor related to atrophy of the intrinsic muscles innervated by the ulnar nerves. The present study hypothesis was confirmed that there was no association between the intrinsic muscle atrophy in CuTS and elbow osteoarthritis. Zhang et al. reported that people with older age, higher body mass index, diabetes mellitus, and economic distress are at a higher risk for presenting with more severe disease.9 In a study that assessed a younger CuTS population (average age, 38 years), men were more likely to present with atrophy of the intrinsic muscles, whereas age was not a predictive factor associated with severe neuropathy.8 Naran et al., assessing an older CuTS population (average age, 55 years), reported that age at presentation was significantly associated with atrophy of the intrinsic muscles.7 This finding is in agreement with that of our study. The pathology of CuTS may thus differ between younger and older patients.
A mean incidence of CuTS of 24.7 cases per 100,000 people and sex-specific incidences of 32.7 for male and 17.2 for female participants has been reported.1 Richardson et al. described that men were more likely to have CuTS and identified an age effect for men.12 In the United States, the incidence rate of CuTS is 30.0 per 100,000 people and the number of incident cases increases with age,13 suggesting that aging is a factor associated with the development of CuTS. Older people may be more susceptible to degeneration of the nerve axons and neuromuscular junctions. The number and density of axons was reduced in an aged mouse model.14 A systematic review of the aging effect on peripheral nerve between young and old murine models reported that a chronic inflammatory state, delayed macrophage response, and dysfunctional Schwann cells caused a decline in the regenerative capability.15
The rate of osteoarthritis of the elbow is high in patients with CuTS.10,16 Older people are more likely to develop osteoarthritis of the elbow. Kurosawa et al. reported that the primary cause of CuTS with elbow osteoarthritis was the development of degenerative osteophytes at the humeroulnar joint.16 Iba et al. showed that the cubital tunnel pressure in osteoarthritic elbows is high.17 In a study using computed tomography, the proportion of osteophytes within the cubital tunnel were greater in osteoarthritic elbows with CuTS.18 In older patients with elbow osteoarthritis, osteophytes develop at the humeroulnar joint, increasing pressure in the cubital tunnel. Symptoms progress slowly, possibly causing a delay in patients visiting a medical institution. In 85% of our cases, radiographic images revealed elbow osteoarthritis. The occurrence of elbow osteoarthritis increases with age, with the ulnar nerve being more likely to be compressed by osteophytes around the humeroulnar joint. However, the present study showed that there was no association between the intrinsic muscle atrophy in CuTS and elbow osteoarthritis. Our findings in the current study support the theory that osteoarthritis of the elbow is related to the occurrence but not aggravation of CuTS.
5 Limitations
There are limitations to this study. First, the main limitation of this study is the retrospective design. Selection bias may be a problem because patients with severe symptoms are more likely to be followed up at the hospital. Second, preoperative severity was divided into three groups, leading to a small study population. Third, electrodiagnostic test data for diagnosing CuTS in some patients was unavailable, although most patients had such data. By excluding patients without electrodiagnostic test data, selection bias may have occurred and the study may have included a population of only those with severe disease.
6 Conclusion
In the current study, we investigated the characteristics of severe neuropathy in patients with CuTS. There was no association between the intrinsic muscle atrophy in CuTS and elbow osteoarthritis. On multivariable modelling, older individuals with CuTS were more likely to develop atrophy of the intrinsic muscles of the ulnar nerve at presentation. Knowledge of the factors associated with severe neuropathy may allow for earlier diagnosis and therapeutic intervention.
Consent to participate
Informed consent was obtained from all individual participants included in the study.
Author contributions
Data collection: Kenichi Asano, Hiroki Yokoyama, Marie Mabuchi.
Article writing, statistics: Kenichi Asano.
Re-editing: Katsuyuki Iwatsuki, Michiro Yamamoto.
Ethical approval
All study protocols were conducted according to the principles of the Declaration of Helsinki and with the formal approval of the hospital's institutional review board.
Funding statement
The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.
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