Abstract
Background
The region where the ulnar nerve (UN) is swollen in baseball players with ulnar neuropathy is not apparent. This study investigated the UN's cross-sectional area (CSA) at each entrapment point in baseball players. We also aimed to clarify the relationship between valgus instability and the CSA of the UN.
Methods
Forty baseball players were separated into healthy and ulnar neuropathy groups. The CSA and valgus instability were measured using ultrasonography (US). Relative to the medial epicondyle (MEC), the arcade of Struthers (SA) was 5 cm proximal, the cubital tunnel was the posterior part, and Osborne's ligament was defined as 3 cm distal. The ulnohumeral joint space was imaged as a low-echo space between the distal-medial corner of the trochlea and the proximal edge of the sublime tubercle.
Results
The UN in the ulnar neuropathy group had significant swelling in the cubital tunnel and Osborne's ligament. We found a weak positive correlation between the CSA and ulnohumeral joint space, and the ulnohumeral joint space at rest and valgus stress.
Conclusion
Evaluation and treatment of UN, especially cubital tunnel and Osborne's ligament, are necessary for the rehabilitation of baseball players presenting with ulnar neuropathy and valgus instability.
Keywords: Ulnar neuropathy, ulnar nerve, valgus instability, throwing elbow
Introduction
Medial elbow injuries are caused by excessive valgus stress at the medial elbow during throwing.1–3 Ulnar nerve (UN) entrapment neuropathy is present in approximately 25% of throwing athletes with medial elbow pain. 4 It has been reported that an increase in valgus instability, which frequently occurs in baseball players, increases UN tension. 5 Thus, the UN is important in evaluating medial elbow injuries caused by throwing.
Ulnar neuropathy is primarily evaluated with nerve conduction studies. However, this assessment is challenging to perform in a clinical setting. Recently, nerve evaluation has been performed using ultrasonography (US).6,7 Chang et al. reported that cross-sectional area (CSA) is the most commonly used measurement for diagnosing entrapment neuropathies. 6 The involved nerve tends to flatten at the entrapment site and becomes swollen proximal to the level of entrapment. 6 However, no study has clarified the region where the UN is swollen in baseball players with ulnar neuropathy.
Ulnar neuropathy is thought to be over 10 mm2 of the CSA in the UN. 6 The three main entrapment points of the UN are the arcade of Struthers (SA), cubital tunnel, and Osborne's ligament. 8 However, there have been no previous studies on the measurement of CSA by entrapment point of UN in baseball players with ulnar neuropathy.
Valgus instability is a risk factor for ulnar neuropathy. Increased valgus instability in baseball players increases the strain load on the UN. Therefore, it is necessary to clarify the relationship between the CSA of the UN and valgus instability in baseball players.
The primary purpose of this study was to investigate the CSA of the UN at each entrapment point in baseball players. The second purpose of this study was to clarify the relationship between valgus instability and the CSA of the UN.
Methods
We recruited 40 baseball players between June 2019 and March 2021 to have ultrasound measurements on both elbows. We verbally explained the purpose of the study and obtained a signed consent. This study was approved by the ethics committee of our institution (authorization number: 2019-019). The study subjects were separated into the healthy and ulnar neuropathy groups (Table 1). The healthy group consisted of 20 athletes who, in both elbows, were without medial elbow pain while throwing or abnormalities in the ulnar collateral ligament on the US. In the healthy group, 4 players were pitchers and 16 were fielders. The ulnar neuropathy group consisted of 20 athletes with unilateral medial elbow pain on maximal external rotation (MER), a positive UN stretch test, and motor or sensory ulnar neuropathy. In the ulnar neuropathy group, 12 players were pitchers and 8 were fielders (Table 1). The UN stretch test was defined as medial elbow pain or ulnar numbness at 90° shoulder abduction, maximum elbow flexion, forearm supination, and wrist dorsiflexion. Motor ulnar neuropathy was defined as weakness of the abductor and opponens digiti minimi muscles. 9 Sensory ulnar neuropathy was defined as numbness or paresthesia in the fifth digit and ulnar halves of the fourth digit. 9 Exclusion criteria were trauma or surgery to the throwing elbow, concomitant osteitis dissecans or olecranon disorders, and accompanying symptoms of thoracic outlet syndrome.
Table 1.
Baseball player demographics.
| Ulnar neuropathy group (n = 20) | Healthy group (n = 20) | |
|---|---|---|
| Age (years) | 16.9 ± 1.4 | 20.1 ± 1.1 |
| Height (㎝) | 173.4 ± 5.9 | 170.9 ± 5.8 |
| Weight (kg) | 66.9 ± 8.1 | 65.8 ± 9.3 |
| Position | Pitcher 12 Fielder 8 | Pitcher 4 Fielder 16 |
The CSA of the UN was measured using an US (SNiBLE yb, KONICA MINOLTA, Tokyo, Japan) with an 11 MHz linear transducer in B mode. The imaging position was 90° abduction, 90° external rotation of the shoulder, and 90° flexion of the elbow. SA was defined as 5 cm proximal to the medial epicondyle (MEC) (Figures 1[a] and 2[a]), cubital tunnel was defined as the posterior part of the MEC (Figures 1[b] and 2[b]), and Osborne's ligament was defined as 3 cm distal to the MEC (Figures 1[c] and 2[c]). These imaging positions were performed based on previous studies and were visualized at the US examination. 10 In the image evaluation, the CSA of the UN on the throwing and non-throwing sides was measured using the tracing function in the US software (Figure 2). One examiner performed the procedure from imaging to measurement. The ultrasonographer has 7 years of clinical experience. Using this method, one examiner measured ten healthy adults before our study.
Figure 1.
Imaging points of each ulnar nerve (UN). (a) Arcade of Struthers (SA): 5 cm proximal part from the medial epicondyle (MEC). (b) Cubital tunnel: posterior part of the MEC. (c) Osborne's ligament: 3 cm distal part from the MEC.
Figure 2.
Ultrasonography (US) image of ulnar nerve (UN) cross-sectional area (CSA). (a) Arcade of Struthers. (b) Cubital tunnel. (c) Osborne's ligament.
The measurement of elbow valgus instability was performed in the same method as in previous studies.11,12 All players were positioned supine on the bed with MER of the shoulder, the shoulder at 90° of abduction, the elbow flexed to 90°, and the forearm in the neutral position. The examiner applied valgus gravity stress to the players’ arms in this position. The medial side of the elbow was imaged from the top of the MEC and sublime tubercle (ST). The ulnohumeral joint space was imaged as a low-echo space between the distal-medial corner of the trochlea and the proximal edge of the ST (Figure 3). The horizontal distances were measured as the ulnohumeral joint space between the distal-medial corner of the trochlea and the proximal edge of the ST. The horizontal distances at rest and valgus stress were measured.
Figure 3.
Ultrasound images of the ulnohumeral joint space at rest and gravity valgus stress. The MEC, the UCL, and the ST are obtained.
MEC: medial epicondyle; ST: sublime tubercle; UCL: ulnar collateral ligament.
The intra-rater reliability of UN's CSA measurements was examined in advance. The intra-rater reliability was defined as poor (<0.5), moderate (0.5–0.75), good (0.75–0.9), and excellent (>0.9), and as absolute reliability, the standard error of measurement (SEM) was calculated. We used the Mann–Whitney U test to evaluate the CSA for each structure comparing the throwing and non-throwing sides as well as the healthy and ulnar neuropathy groups. For statistical analysis, the CSA of the UN at each point on the throwing side was compared among the three groups using a one-way analysis of variance. Subsequently, the Tukey–Kramer test was performed as a multiple comparison test after a one-way analysis of variance. In addition, the relationship between the CSA of the UN and the ulnohumeral joint space was determined using a single correlation analysis. Statistical significance was set at p < 0.05. Statistical analyses were performed by the same examiner using SPSS Statistics version 25.
Results
Intra-rater reliability was highly reproducible (Table 2).
Table 2.
Intra-rater reliability (ICC1.2).
| ICC | 95％CI | SEM | ||
|---|---|---|---|---|
| Arcade of Struthers | Good | 0.84 | 0.34-0.96 | 0.004 |
| Cubital tunnel | Excellent | 0.90 | 0.57-0.98 | 0.005 |
| Osborne’s ligament | Excellent | 0.97 | 0.89-0.99 | 0.003 |
The CSA of the UN on the throwing side of the healthy group was 0.08 cm2 for SA, 0.08 cm2 for cubital tunnel, 0.08 cm2 for Osborne's ligament, and 0.07 cm2 for all three points on the non-throwing side. The CSA of the UN on the throwing side of the ulnar neuropathy group was 0.08 cm2 for SA, 0.11 cm2 for cubital tunnel, 0.11 cm2 for Osborne's ligament, and 0.07 cm2 for all three points on the non-throwing side (Table 3).
Table 3.
Comparison of ulnar nerve (UN) cross-sectional area (CSA) between the two groups.
| Unit: CSA (㎝2) | Ulnar neuropathy group | Healthy group | ||||
|---|---|---|---|---|---|---|
| Arcade of Struthers (SA) | Cubital tunnel | Osborne's ligament | Arcade of Struthers | Cubital tunnel | Osborne's ligament | |
| Throwing side | 0.09 ± 0.01 | 0.11 ± 0.02 | 0.11 ± 0.02 | 0.07 ± 0.01 | 0.08 ± 0.01 | 0.08 ± 0.01 |
| Non-throwing side | 0.07 ± 0.001 | 0.07 ± 0.001 | 0.07 ± 0.01 | 0.07 ± 0.001 | 0.07 ± 0.001 | 0.07 ± 0.001 |
The UN on the throwing side was compared between the healthy and ulnar neuropathy groups, and the UN in the ulnar neuropathy group was significantly swollen at cubital tunnel, Osborne's ligament, and SA (Figure 4). The UN of the ulnar neuropathy group was compared between the throwing and non-throwing sides, and the UN of the throwing side was significantly swollen at all points (Figure 5). A comparison of UN in the ulnar neuropathy group between the three points showed significant swelling in the cubital tunnel and Osborne's ligament groups compared to the SA (Figure 5).
Figure 4.
Comparison of ulnar nerve (UN) cross-sectional area (CSA).
Figure 5.
Comparison of ulnar nerve (UN) cross-sectional area (CSA).
The healthy group's ulnohumeral joint space at rest and valgus stress was 4.21 ± 1.01 cm, 5.08 ± 1.13 cm. The ulnohumeral joint space at rest and valgus stress in the ulnar neuropathy group was 4.76 ± 0.74 cm, 5.83 ± 0.81 cm (Table 4). A positive correlation between the CSA of the UN and the ulnohumeral joint space was found between the CSA of the cubital tunnel and the ulnohumeral joint space at rest and valgus stress (p = 0.0002, p = 0.00007). A positive correlation was found between the CSA of Osborne's ligament and the ulnohumeral joint space at rest and valgus stress (p = 0.001, p = 0.0003). A weak positive correlation was found between the CSA of the SA and the ulnohumeral joint space at valgus stress (p = 0.006) (Table 5).
Table 4.
Comparison of ulnohumeral joint space between the two groups.
| Unit: ㎜ | Ulnar neuropathy group | Healthy group | ||
|---|---|---|---|---|
| Rest | Valgus stress | Rest | Valgus stress | |
| Throwing side | 4.76 ± 0.74 | 5.83 ± 0.81 | 4.21 ± 1.01 | 5.09 ± 1.14 |
Table 5.
Correlation between two groups of ulnar nerve (UN) cross-sectional area (CSA) and ulnohumeral joint space.
| Rest | Valgus stress | |
|---|---|---|
| Arcade of Struthers (SA) | 0.24 | 0.35** |
| Cubital tunnel | 0.45** | 0.49** |
| Osborne's ligament | 0.40** | 0.45** |
**p < 0.01; *p < 0.05.
Discussion
Many studies measuring CSA are reported on the US evaluation for ulnar neuropathy. It has been suggested that ulnar neuropathy occurs in > 0.1㎝2 of the CSA of the UN. 6 However, no previous studies have been performed on the measurement of CSA by the entrapment point of UN in baseball players with ulnar neuropathy. In this study, we compared the CSA of the UN in the healthy and ulnar neuropathy groups at three entrapment points. The UN on the throwing side in the ulnar neuropathy group was also compared across the three points. The UN in the ulnar neuropathy group showed structural changes from swelling in cubital tunnel and Osborne's ligament. A weak positive correlation between the CSA of the UN and the ulnohumeral joint space was found between the CSA of the cubital tunnel and the ulnohumeral joint space at rest and valgus stress. Therefore, baseball players with ulnar neuropathy and valgus instability may have nerve entrapment at the cubital tunnel and Osborne's ligament and swelled UN. We clarified that the CSA of the UN in the deep region of Osborne's ligament was swollen in baseball players with medial elbow pain during MER during throwing.
Swelling of the nerve proximal to the entrapment point is most commonly diagnosed using US to diagnose entrapment neuropathies. 6 It is frequently accepted that increased pressure on the peripheral nerve affects its microcirculation and, therefore, blood supply. Chronic compression may predispose to capillary leakage and neural edema.13–15 The area within the cubital tunnel decreases beyond 90 °of elbow flexion. 16 There are three layers of connective tissue (fascia) on the surface of the cubital tunnel. 17 The fascia is thought to cause inflammation and degeneration of connective tissue, restrict nerve gliding, and lead to nerve entrapment. These changes may have resulted in ulnar neuropathy due to nerve entrapment, resulting in nerve swelling in the cubital tunnel and Osborne's ligament. There is a negative correlation between CSA of the UN and nerve conduction studies. 18 The presence of ulnar neuropathy can be easily determined using US by measuring the CSA of the UN.
Tai et al. found that athletes with elbow injuries had increased forward movement and flattening of UN. 19 Ulnar neuropathy in baseball players is a common elbow injury in pitchers and is reportedly caused by entrapment of the UN at the elbow.19,20 Excessive valgus stress continues to be applied to the medial elbow, and repetitive mechanical stress of the UN increases.2–3,21 During maximum external rotation (MER) of the throwing motion, the elbow flexes between 90 and 120°.22,23 It has been reported that the strain on the UN increases as the elbow flexion increases, suggesting that the strain on the UN may increase during MER of pitching.5,24 Valgus instability of the elbow is also a risk factor for ulnar neuropathy. Mihata et al. reported that UN length and tension increased with increasing elbow valgus instability. 5 When a peripheral nerve is inflamed due to repeated stresses, even 3% of nerve strain can provoke pain and other nerve symptoms. 25 These factors suggest that excessive valgus stress of the elbow, excessive elbow flexion, and valgus instability of the elbow cause ulnar neuropathy. Patients with preoperative ulnar neuropathy demonstrated improvement after UCL reconstruction without specific nerve-related surgical intervention. 26 Preoperative ulnar neuropathy may be the result of excessive traction on the nerve during athletic activity and that stabilization of valgus instability may relieve this traction phenomenon. There are no studies suggesting the effect of conservative treatment on ulnar neuropathy caused by pitching. It is necessary to clarify the effect of conservative treatment on ulnar neuropathy in the future.
This study had several limitations. First, because this was a cross-sectional study, it is unknown when ulnar neuropathy occurs. Since the effect of the change in the UN on pain has not yet been examined, a prospective study is necessary. Although the relationship between valgus instability and the CSA of the UN was clarified in this study, the cause of the swelling of the UN is not clear. In the future, it is necessary to conduct longitudinal studies to further investigate the factors contributing to ulnar neuropathy. Second, nerve conduction tests for ulnar neuropathy and electromyography of the UN's innervated muscles were unavailable.
Conclusion
In conclusion, we found that the CSA of the UN in baseball players with ulnar neuropathy was significantly swollen on the cubital tunnel and Osborne's ligament on the throwing side. Measurement of CSA at the entrapment point is necessary to evaluate baseball players with ulnar neuropathy. Evaluation and treatment of UN, especially cubital tunnel and Osborne's ligament are necessary to rehabilitate baseball players presenting with ulnar neuropathy.
Acknowledgments
The authors acknowledge Ashiya Orthopedics Sports Clinic for assistance with this project. We would like to thank Editage (www.editage.com) for English language editing.
Footnotes
Contributorship: Shintarou Kudo and Issei Noda researched literature and conceived the study. Shintarou Kudo, Issei Noda, Msashi Kitano, and Yusuke Fukumoto were involved in protocol development, gaining ethical approval, patient recruitment, and data analysis. Issei Noda wrote the first draft of the manuscript. All authors reviewed and edited the manuscript and approved the final version of the manuscript.
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.
Ethical approval: This study was approved by the Ethics Review Committee of Morinomiya University of medical sciences (approval number 2019-019).
Informed consent: Written informed consent was obtained from the patient(s) for their anonymized information to be published in this article.
Guarantor: Shintarou Kudo.
ORCID iD: Issei Noda https://orcid.org/0000-0002-5569-5570
References
- 1.Cain EL, Dugas JR, Wolf RS, et al. Elbow injuries in throwing athletes: a current concepts review. Am J Sports Med 2003; 31: 621–635. [DOI] [PubMed] [Google Scholar]
- 2.Fleisig GS, Andrews JR, Dillman CJ, et al. Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med 1995; 23: 233–239. [DOI] [PubMed] [Google Scholar]
- 3.Regan WD, Korinek SL, Morrey BF, et al. Biomechanical study of ligaments around the elbow joint. Clin Orthop Relat Res 1991; 271: 170–179. [PubMed] [Google Scholar]
- 4.Roedl JB, Gonzalez FM, Zoga AC, et al. Potential utility of a combined approach with US and MR arthrography to image medial elbow pain in baseball players. Radiology 2016; 279: 827–837. [DOI] [PubMed] [Google Scholar]
- 5.Mihata T, Akeda M, Künzler M, et al. Ulnar collateral ligament insufficiency affects cubital tunnel syndrome during throwing motion: a cadaveric biomechanical study. J Shoulder Elbow Surg 2019; 28: 1758–1763. [DOI] [PubMed] [Google Scholar]
- 6.Chang KV, Wu WT, Han DS, et al. Ulnar nerve cross-sectional area for the diagnosis of cubital tunnel syndrome: a meta-analysis of ultrasonographic measurements. Arch Phys Med Rehabil 2018; 99: 743–757. [DOI] [PubMed] [Google Scholar]
- 7.Lauretti L, D'Alessandris QG, De Simone C, et al. Ulnar nerve entrapment at the elbow. A surgical series and a systematic review of the literature. J Clin Neurosci 2017; 46: 99–108. [DOI] [PubMed] [Google Scholar]
- 8.Prasetyo M, Rahardja RR, Yanuar A, et al. Ultrasonography evaluation of the normal ulnar nerve in adult: comparison of the cross-sectional area at elbow extension and flexion. Eur J Radiol Open 2021; 8: 100331. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Maruyama M, Satake H, Takahara M, et al. Treatment for ulnar neuritis around the elbow in adolescent baseball players: factors associated with poor outcome. Am J Sports Med 2017; 45: 803–809. [DOI] [PubMed] [Google Scholar]
- 10.Simon NG, Ralph JW, Poncelet AN, et al. A comparison of ultrasonographic and electrophysiologic ‘inching’ in ulnar neuropathy at the elbow. Clin Neurophysiol 2015; 126: 391–398. [DOI] [PubMed] [Google Scholar]
- 11.Noda I, Kudo S. Relationship between pain, elbow valgus instability, and the function of flexor pronator muscles in baseball players. JSES Int 2021; 5: 31–34. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Otoshi K, Kikuchi S, Shishido H, et al. Ultrasonographic assessment of the flexor pronator muscles as a dynamic stabilizer of the elbow against valgus force. Fukushima J Med Sci 2014; 60: 123–128. [DOI] [PubMed] [Google Scholar]
- 13.Lundborg G, Dahlin LB. Anatomy, function, and pathophysiology of peripheral nerves and nerve compression. Hand Clin 1996; 12: 185–193. [PubMed] [Google Scholar]
- 14.Mackinnon SE. Pathophysiology of nerve compression. Hand Clin 2002; 18: 231–241. [DOI] [PubMed] [Google Scholar]
- 15.Tapadia M, Mozaffar T, Gupta R. Compressive neuropathies of the upper extremity: update on pathophysiology, classification, and electrodiagnostic findings. J Hand Surg Am 2010; 35: 668–677. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.James J, Sutton LG, Werner FW, et al. Morphology of the cubital tunnel: an anatomical and biomechanical study with implications for treatment of ulnar nerve compression. J Hand Surg Am 2011; 36: 1988–1995. [DOI] [PubMed] [Google Scholar]
- 17.Macchi V, Tiengo C, Porzionato A, et al. The cubital tunnel: a radiologic and histotopographic study. J Anat 2014; 225: 262–269. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Terlemez R, Yilmaz F, Dogu B, et al. Comparison of ultrasonography and short-segment nerve conduction study in ulnar neuropathy at the elbow. Arch Phys Med Rehabil 2018; 99: 116–120. [DOI] [PubMed] [Google Scholar]
- 19.Tai TW, Kuo LC, Chen WC, et al. Anterior translation and morphologic changes of the ulnar nerve at the elbow in adolescent baseball players. Ultrasound Med Biol 2014; 40: 45–52. [DOI] [PubMed] [Google Scholar]
- 20.Wiesler ER, Chloros GD, Cartwright MS, et al. Ultrasound in the diagnosis of ulnar neuropathy at the cubital tunnel. J Hand Surg Am 2006; 31: 1088–1093. [DOI] [PubMed] [Google Scholar]
- 21.Vinitpairot C, Jianmongkol S, Thammaroj T, et al. Ulnar nerve strain in functional elbow and shoulder motions. J Hand Surg Asian Pac 2019; 24: 323–328. [DOI] [PubMed] [Google Scholar]
- 22.Fleisig GS, Kingsley DS, Loftice JW, et al. Kinetic comparison among the fastball, curveball, change-up, and slider in collegiate baseball pitchers. Am J Sports Med 2006; 34: 423–430. [DOI] [PubMed] [Google Scholar]
- 23.Nissen CW, Westwell M, Ounpuu S, et al. Adolescent baseball pitching technique: a detailed three-dimensional biomechanical analysis. Med Sci Sports Exerc 2007; 39: 1347–1357. [DOI] [PubMed] [Google Scholar]
- 24.Aoki M, Takasaki H, Muraki T, et al. Strain on the ulnar nerve at the elbow and wrist during throwing motion. J Bone Joint Surg Am 2005; 87: 2508–2514. [DOI] [PubMed] [Google Scholar]
- 25.Dilley A, Lynn B, Pang SJ. Pressure and stretch mechanosensitivity of peripheral nerve fibres following local inflammation of the nerve trunk. Pain 2005; 117: 462–472. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Jones KJ, Dines JS, Rebolledo BJ, et al. Operative management of ulnar collateral ligament insufficiency in adolescent athletes. Am J Sports Med 2014; 42: 117–121. [DOI] [PubMed] [Google Scholar]