Is the degree of carrying angle associated with ulnar nerve instability? A cross-sectional study of high school baseball pitchers

Abstract

Background

An increased carrying angle (CA) on the throwing side has been observed in professional pitchers. Elbow alignment is known to be a factor in the strain stress on the ulnar nerve. Ulnar nerve instability (UNI), in which the nerve snaps forward over the medial epicondyle during elbow flexion, is reportedly more common in pitchers than in other players. However, no studies have examined the association between elbow alignment and UNI severity in baseball players. This study assessed the correlation between the CA and UNI severity in high school baseball pitchers.

Methods

A total of 106 high school baseball pitchers who underwent medical checkups during the off-season in 2023 were examined. Ultrasound examinations were conducted to assess the presence or absence of UNI and medial joint space under rest and gravity stress on both sides of the elbow. The participants were divided into the following 3 groups based on the ultrasonographic findings of UNI: no instability (type N), subluxation (type S), and dislocation (type D). Clinical and physical examinations were performed, which included measurement of CA, grip strength, key pinch strength, and a check for ulnar nerve symptoms bilaterally.

Results

The distribution of UNI types on the throwing side was 37%, 31%, and 32% for types N, S, and D, respectively. A similar distribution was found on the nonthrowing side: 36% for Type N, 32% for Type S, and 32% for Type D. Overall, there was no statistically significant difference in the prevalence of these types between the 2 sides. The CA of the throwing arm did not differ significantly between the 3 UNI groups: Type N (13.6° ± 0.4°), Type S (12.7° ± 0.3°), and Type D (12.0° ± 0.3°) (P = .25). On the throwing side, the different UNI types did not show significant differences in the degree of ulnar collateral ligament laxity or in other clinical and physical findings.

Conclusion

This study found no significant difference in bony alignment, as indicated by the CA, between the degrees of UNI among high school baseball pitchers. When categorized by UNI type, no significant differences were observed in the throwing side with respect to ulnar collateral ligament laxity or other clinical and physical findings.

Ulnar nerve instability (UNI) is characterized by the anterior displacement of the ulnar nerve from the cubital tunnel upon elbow flexion, a mechanism that can induce neuritis and neuropathy.^2,5 Nevertheless, UNI has a high prevalence in the general population,^{7,10,12,13,19,22,}28, 29, 30^,42 and prior research indicates that this mechanical instability is not always correlated with clinical neurological symptoms.^{7,10,12,29,42} Previous studies have investigated UNI in overhead athletes, particularly baseball players.^{18,20,23,35,40} UNI is recognized as a contributing factor to medial elbow pathology in overhead athletes. As the throwing motion subjects the ulnar nerve to repetitive tensile and transverse forces, proactive screening for its early identification is advised.¹ Although studies have documented a high prevalence of ulnar nerve subluxation in overhead athletes (particularly throwers), it is often noted that the condition does not necessarily lead to additional pathology.^23,35,40 Whether or not UNI is a direct cause of pathological conditions remains unclear.

The carrying angle (CA), formed by the long axes of the humerus and ulna, serves as a primary indicator of elbow alignment.⁴ Throughout childhood and adolescence, the elbow joint undergoes a normal developmental process characterized by a gradual increase in both the CA and range of motion (ROM), which stabilizes once skeletal maturity is achieved.^3,4,17,31,41 A recent investigation involving professional pitchers demonstrated an increased CA on the dominant throwing side, due to adaptive changes at the elbow during development, highlighting a key relationship between this anatomical measure and baseball.¹⁴ Nevertheless, malalignment of the elbow joint has been identified as a contributing factor to ulnar nerve strain and instability.^{8,27,33,34,39} With a cubitus varus deformity, flexion of the elbow causes anteromedial displacement of the triceps, which can result in dynamic compression and traction of the ulnar nerve, ultimately causing neuropathy.^27,34,39 Cubitus valgus elongates the path of the ulnar nerve across the elbow, leading to traction neuropathy from the increased tension.^8,33

No reports have investigated the association between the degree of elbow alignment and UNI severity in baseball players. This study assessed the correlation between the CA and UNI severity, as well as clinical and physical findings, among high school baseball pitchers.

Materials and methods

Participants

A total of 110 high school baseball pitchers who underwent medical checkups during the off-season in 2023 were examined. A comprehensive evaluation process is implemented annually for regional high school baseball pitchers, encompassing the screening of throwing-related disorders and assessment of overall physical status. Following these evaluations, personalized conditioning protocols were developed and shared with each pitcher to optimize their physical health. The exclusion criteria were a history of surgery on the elbow joint and a history of trauma, such as elbow joint fracture or dislocation.

All participants and their parents provided informed consent to participate in this study, which was approved by the Gunma University Hospital Clinical Research Review Board (no. 1003).

Questionnaire assessments

Information was gathered via a questionnaire that examined participant demographics and relevant history (throwing side, baseball experience, and incidence of elbow pain in the previous year). For this investigation, an operational definition of elbow pain was established as a condition that was a direct result of the throwing motion and led to cessation of participation for a minimum of seven days.

Height and weight measurements

Height measurements were performed using a digital height meter (A&D Co., Ltd., Tokyo, Japan). A multifrequency segmental body composition analyzer (MC780U; Tanita Corp., Tokyo, Japan) was used to record body weight.

Elbow range of motion measurements

Elbow ROM was assessed with the participants seated. Measurements were performed with the shoulder at 90° elevation and the wrist fully supinated. A goniometer was centered on the lateral epicondyle with its arms aligned along the longitudinal axes of the humerus and radius. The measurements were performed by a single experienced orthopedic surgeon to ensure consistency. Each parameter was measured simultaneously. The intrarater validity and reliability of this protocol were assessed in our previous study by the same examiner.³⁶

CA measurements

The bilateral CA were measured with a digital goniometer, positioning the elbow in maximum extension, and forearm in full supination (Fig. 1).³⁸ For all measurements, the participants wore short sleeves to ensure that landmarks were visible. All measurements were performed by the same examiner to minimize variability. Our previous study confirmed the reliability of the method; a single examiner, blinded to limb dominance, measured 10 participants twice (1 week apart) to establish intratester reliability (ICC = 0.99). A second examiner's measurements confirmed high intertester reliability (ICC = 0.96).⁴³ The intrarater and inter-rater reliability tests in our previous study were conducted by the same examiner as in this study.

Figure 1.

With the patient supine and the elbow fully extended, one goniometer was aligned with the arm’s axis and the other with the forearm’s axis.

Ultrasonographic technique

Assessment of the elbow medial joint space

To assess the medial joint space (MJS), participants were positioned supine with their shoulders at 90° of abduction/maximal external rotation, elbow at 30° of flexion, and forearm in a neutral position. An experienced orthopedic surgeon captured ultrasound images of the ulnohumeral joint bilaterally, first at rest with the arm supported to prevent stress (Fig. 2A) and then under gravity-induced valgus stress with the support removed (Fig. 2B). We defined MJS as the distance from the trochlea to the coronoid process (Fig. 2C) and calculated the "gap" as the change between the 2 conditions. The reliability of this measurement technique has been confirmed in a previous study.³⁷

Figure 2.

(A) The assessment of UN instability: normal type. Transverse US of the UN revealed no abnormal findings. (B) The assessment of UN instability: subluxation type. Transverse US of the UN subluxation. (C) The assessment of UN instability: dislocation type. Transverse US of the UN revealed dislocation. ME, medial epicondyle; UN; ulnar nerve; US, ultrasonography.

UNI evaluation

An orthopedic surgeon with 10 years of experience performed the ultrasonography to assess UNI. After measuring the MJS of the elbow, the examiner stabilized the participant's shoulder and passively flexed the elbow from full extension to its end range. The ulnar nerve's position was then classified according to the Okamoto et al²⁸ system as Type N (nerve does not reach the apex of the epicondyle) (Fig. 3A), Type S (nerve reaches the apex) (Fig. 3B), or Type D (nerve crosses the apex) (Fig. 3C). The final diagnosis was made by consensus with a second surgeon.

Figure 3.

Ultrasound measurement of the ulnohumeral joint width. (A) At rest position. (B) Gravity stress position. (C) US image. The ulnohumeral joint space was defined as the distance from the edge of the humeral trochlea to the ulnar coronoid process. This width was measured bilaterally at the anterior band level both with and without the application of valgus gravity stress. MEH, medial epicondyle of the humerus; TH, trochlea of the humerus; CU, coronoid process of the ulna; CFT, common flexor tendon; UCL, ulnar collateral ligament; US, ultrasonography.

The evaluation of neurological symptoms and motor function

We gathered subjective data by asking participants about any dysesthesia in their fourth and fifth fingers during the 2023 pitching season. Objective data included an assessment of Tinel sign in the cubital tunnel and measurements of bilateral grip and key-pinch strength. We performed the elbow flexion test⁶ and the shoulder internal rotation elbow flexion test²⁶ to provoke symptoms of cubital tunnel syndrome. All strength tests were performed by a single orthopedic surgeon using a digital dynamometer (Takei Scientific Instruments Co., Ltd., Tokyo, Japan) and pinch gauge (MG-4320NC pinch gauge, B&L Engineering, Santa Ana, CA, USA). For all measurements, participants were seated in the standardized position recommended by the American Society of Hand Therapists: shoulder adducted and neutrally rotated, elbow flexed to approximately 90°, with the forearm and wrist in a neutral position.¹⁵ The final value used for analysis was the average of 2 trials for each measurement on both the throwing and nonthrowing sides.

Statistical analysis

Categorical variables were described as counts (percentages), and their associations were analyzed using the chi-square test or Fisher exact test. Continuous variables were assessed for normality using the Shapiro-Wilk test. Continuous variables were expressed as the mean ± standard deviation. For three-group comparisons, we used a 1-way analysis of variance (with Bonferroni post hoc) for normal data and Kruskal-Wallis test (with Steel-Dwass post hoc) for nonparametric data. For two-group comparisons, continuous variables were compared using the t-test or Mann-Whitney U test. The correlation between GAP distance, which refers to the difference in the ulnohumeral joint space measured with and without gravity-induced valgus stress, and CA on the bilateral side was assessed using Spearman rank correlation coefficient. As the sample size was determined by the total number of eligible participants available during the regional screening period, an a priori power analysis was not conducted. Instead, a post hoc power analysis was performed using G∗Power (version 3.1) to evaluate the achieved power for each comparison. The threshold for statistical significance was set at P < .05.

Results

Of the 110 initial candidates, 106 met the inclusion criteria. A total of 106 participants were included in the study. Four participants were excluded from the final analysis: 1 due to incomplete data and 3 who met the predefined exclusion criteria (a history of surgery on the elbow joint and a history of trauma). Consequently, the data from 106 pitchers were included in the final statistical analysis. All participants were male, with a mean age of 16.5 (±0.7) years old. The mean baseball playing history was 8.5 (±2.0) years. The results revealed 31 cases without UNI, 15 with unilateral UNI, and 60 with bilateral UNI. The prevalence of UNI was 71% among the 106 participants. The results revealed 31 cases without instability and 75 cases with instability in both the elbows. The prevalence of UNI was 71% in the 106 participants (Table I).

Table I.

Prevalence by type of ulnar nerve instability in the throwing and the nonthrowing side.

Throwing side UNI type	Nonthrowing side UNI type	Number	Prevalence
Type N	Type N	31	29%
Type N	Type S	6	6%
Type N	Type D	2	2%
Type S	Type N	7	7%
Type S	Type S	17	16%
Type S	Type D	9	8%
Type D	Type N	0	0%
Type D	Type S	11	10%
Type D	Type D	23	22%

UNI, ulnar nerve instability.

Table II compares the throwing and nonthrowing sides. Relative to the nonthrowing side, the throwing elbow exhibited significantly decreased flexion ROM (138.7° ± 12.8° vs. 142.1° ± 4.3°, P < .001) and extension ROM (2.3° ± 4.9° vs. 5.9° ± 4.4°, P = .006). The CA was significantly greater on the throwing side (12.7° [±4.1°] vs. 12.0° [±4.3°], P = .007). The prevalence of each UNI type on the throwing and nonthrowing sides, respective, was as follows: Type N, 37% and 36%; Type S, 31% and 32%; and Type D, 32% and 32%. There was no significant difference between the pitching and nonpitching sides in the rates of 3 types of UNI (P = .99; Table II). Regarding the experience of numbness in the ring and little fingers during pitching, there was a considerable difference between the throwing and nonthrowing sides (P = .006; Table II). However, the pitching and nonpitching sides did not differ significantly in the prevalence of positive provocative tests for cubital tunnel syndrome, including Tinel sign (P = .28; Table II), elbow flexion test (P = .12; Table II), and shoulder internal elbow flexion test (P = 1.00; Table II). The MJS of the elbow was significantly greater on the throwing side than on the nonthrowing side for the gravity-stressed (4.1 [±0.7] mm vs. 3.8 [±0.6] mm, P < .001) and gap (0.5 [±0.4] mm vs. 0.2 [±0.3] mm, P < .001) measurements (Table II). There was no significant correlation between the GAP distance and CA on the bilateral side (throwing side: r = 0.01, P = .89; nonthrowing side: r = −0.01, P = .94).

Table II.

A comparison of clinical and physical findings between the throwing and nonthrowing side.

Evaluation criteria	Throwing side	Nonthrowing side	P value
Elbow ROM (°)
Extension	2.3 (4.9)	5.9 (4.4)	<.001
Flexion	138.7 (12.8)	142.1 (4.3)	.006
Carrying angle (°)	12.7 (4.1)	12.0 (4.3)	.007
Type of ulnar nerve instability (n)			.99
Normal	39	38
Subluxiation	33	34
Dislocation	34	34
Grip (kg)	35.6 (6.4)	36.0 (6.9)	.38
Key pinch (kg)	8.7 (1.3)	8.7 (1.4)	1.00
Ulnar nerve symptoms
Dysesthesia during pitching			.006
Positive (n)	9	0
Negative (n)	97	106
Cubital tunnel syndrome provocative test
Tinel sign			.28
Positive (n)	15	9
Negative (n)	91	97
Elbow flexion test			.12
Positive (n)	4	0
Negative (n)	102	106
Shoulder internal elbow flexion test			1.00
Positive (n)	1	0
Negative (n)	105	106
Medial gap of the elbow joint
Without gravity stress (mm)	3.6 (0.7)	3.6 (0.6)	.98
With gravity stress (mm)	4.1 (0.7)	3.8 (0.6)	<.001
Gap distance∗ (mm)	0.5 (0.4)	0.2 (0.3)	<.001

ROM, range of motion.

Mean values are shown with the standard deviation in parentheses.

Statistically significant: P < .05.

^∗Medial gap with gravity stress minus medial gap without stress.

A comparison of the data for the throwing arm categorized by UNI type is shown in Table III. There were no significant differences in height, weight, body mass index, physical metrics (elbow ROM, CA, grip power, and key pinch power), or neurological findings (eg, numbness during pitching or the rate of positive cubital tunnel syndrome provocation tests (Table III). The medial elbow joint gap in the Type D group was significantly larger than those in the Type N and Type S groups, both at rest and under gravity stress to evaluate medial collateral ligament laxity (Type N, 3.5 [0.7] mm; Type S, 3.4 [0.5] mm; Type D, 3.9 [0.7] mm; P < .05; Table III). Table IV presents a comparison of data from the nonthrowing side stratified by UNI type. All UNI types were comparable in terms of measured outcomes. There were no statistically significant differences in height, weight, body mass index, elbow ROM, CA, grip or key-pinch strength, frequency of numbness in the ring and little fingers during pitching, or rate of positive provocative tests for cubital tunnel syndrome. Significant differences were observed in the medial elbow joint gaps. Under nonstressed and stress conditions, the medial gap on the throwing side in Type D was significantly larger than that in Type S and Type N. Under nonstressed conditions, the medial gaps on the nonthrowing side in Type D were significantly larger than those in Type N, and under stress conditions, the medial gaps on the nonthrowing side in Type D and Type S were significantly larger than those in Type N. However, no significant difference was observed in the gap distance between each type of UNI in both elbows.

Table III.

Characteristics of the throwing side by type of ulnar nerve instability.

Evaluation criteria	Type N (n = 39)	Type S (n = 33)	Type D (n = 34)	P value
Height (cm)	172.0 (7.5)	172.8 (7.5)	172.7 (5.7)	.86
Weight (kg)	70.3 (13.4)	69.8 (11.4)	67.2 (8.2)	.56
BMI (kg/m2)	23.6 (3.1)	23.4 (2.9)	21.9 (4.0)	.22
Distribution of pitching laterality
Right	35	28	22	.02
Left	4	5	12
Elbow ROM (°)
Extension	2.5 (4.5)	2.5 (5.4)	1.9 (4.8)	.68
Flexion	137.3 (20.6)	139.7 (3.3)	139.5 (4.5)	.77
Carrying angle (°)	13.5 (4.6)	12.6 (3.6)	12.0 (4.0)	.60
Grip (kg)	34.3 (7.4)	36.0 (6.3)	36.7 (5.1)	.26
Key pinch (kg)	8.7 (1.3)	8.6 (1.3)	8.8 (1.2)	.77
Ulnar nerve symptoms
Dysesthesia during pitching				.72
Positive (n)	4	2	2
Negative (n)	35	31	32
Cubital tunnel syndrome provocative test
Tinel sign				.33
Positive (n)	8	4	3
Negative (n)	31	29	31
Elbow flexion test				.37
Positive (n)	2	2	0
Negative (n)	37	31	34
Shoulder internal elbow flexion test				.33
Positive (n)	0	1	0
Negative (n)	39	32	34
Medial gap of elbow joint
Without gravity stress (mm)	3.5 (0.7)	3.4 (0.5)	3.9 (0.7)†‡	.001
With gravity stress (mm)	4.0 (0.7)	3.9 (0.6)	4.4 (0.5)†‡	.008
Gap distance∗ (mm)	0.5 (0.4)	0.5 (0.4)	0.5 (0.4)	.92

BMI, body mass index; ROM, range of motion.

Mean values are shown with the standard deviation in parentheses.

Statistically significant: P < .05.

^∗Medial gap with gravity stress minus medial gap without stress.

^†Significantly different (P < .05) from Type N values.

^‡Significantly different (P < .05) from Type S values.

Table IV.

Characteristics of the nonthrowing side by type of ulnar nerve instability.

Evaluation criteria	Type N (n = 38)	Type S (n = 34)	Type D (n = 34)	P value
Hight (cm)	171.8 (6.4)	173.2 (7.2)	172.4 (7.3)	.70
Weight (kg)	69.6 (12.0)	70.3 (12.0)	67.5 (9.7)	.62
BMI (kg/m2)	23.5 (3.0)	23.4 (2.9)	22.0 (4.2)	.39
Distribution of nonpitching laterality				.36
Right	5	7	9
Left	33	27	25
Elbow ROM (°)
Extension	5.3 (4.6)	5.7 (4.4)	6.8 (4.2)	.32
Flexion	142.2 (4.4)	142.0 (4.5)	142.2 (4.1)	.98
Carrying angle (°)	12.1 (4.9)	12.5 (4.0)	11.3 (4.0)	.39
Grip (kg)	35.3 (6.9)	36.6 (6.3)	36.1 (7.4)	.74
Key pinch (kg)	8.5 (1.5)	8.9 (1.4)	8.7 (1.3)	.48
Ulnar nerve symptoms
Dysesthesia during pitching				1.00
Positive (n)	0	0	0
Negative (n)	38	34	34
Cubital tunnel syndrome provocative test
Tinel sign				.36
Positive (n)	4	1	4
Negative (n)	34	33	30
Elbow flexion test				1.00
Positive (n)	0	0	0
Negative (n)	38	34	34
Shoulder internal elbow flexion test				1.00
Positive (n)	0	0	0
Negative (n)	38	34	34
Medial gap of the elbow joint
Without gravity stress (mm)	3.4 (0.6)	3.7 (0.6)	3.8 (0.6)†	.009
With gravity stress (mm)	3.6 (0.5)	3.9 (0.7)†	4.0 (0.6)†	.003
Gap distance∗ (mm)	0.2 (0.2)	0.3 (0.4)	0.2 (0.2)	.38

BMI, body mass index; ROM, range of motion.

Mean values are shown with the standard deviation in parentheses.

Statistically significant: P < .05.

^∗Medial gap with gravity stress minus medial gap without stress.

^†Significantly different (P < .05) from Type N values.

Discussion

One distinguishing characteristic of our results is that no significant differences in CA were observed across the 3 groups on either side (throwing side, P = .60; nonthrowing side, P = .39; Tables III and IV). Static bony morphology, specifically the CA, does not appear to be a direct cause of UNI, suggesting that the overall limb alignment does not inherently predispose a pitcher to ulnar nerve subluxation or dislocation. In healthy children, the CA and elbow ROM generally increase throughout skeletal growth.^3,4,17,31,41 Specifically, several studies have reported that the clinical CA increases progressively until approximately 15 years of age, followed by a slight stabilization or decrease as skeletal maturity is reached.^3,17,31,41 Our study identified a significant side-to-side difference in the valgus CA between the dominant and nondominant elbows of high school pitchers, similar to other research findings.^14,43 This asymmetry is likely an adaptive response to the immense repetitive valgus stress placed on the elbow during pitching, which can reach approximately 64 Nm per pitch.¹⁶ The traditional and potential mechanisms underlying this adaptation include lateral physis growth arrest, chronic tension on the medial collateral ligament, and compressive wear of the radiocapitellar articular cartilage, among other factors.¹⁴ A progressive increase in the CA during the developmental years can lead to significant clinical sequelae. These may include cubital tunnel syndrome, elbow instability, pain with exercise, a flexion deficit, and an elevated risk of both dislocation and fracture of the distal humeral epiphysis.³² Furthermore, previous cadaveric investigations have shown that ulnar nerve strain at the cubital tunnel peaks during the early acceleration phase of throwing, which corresponds to the point of maximum elbow flexion.¹ We hypothesized that an increased throwing-side CA and the peak ulnar nerve stretch during the early acceleration phase of throwing act synergistically to cause UNI. However, our findings suggest that, at least for the CA in high school baseball pitchers without a history of elbow trauma injury, there is no association with UNI.

Our study demonstrates that UNI in high school baseball pitchers is not primarily driven by underlying elbow joint instability or pathological bone alignment. Previous studies suggest that medial laxity or malalignment may increase nerve stress.^24,25 Our results showed no significant differences in GAP distance across UNI types, and no pathological deformities were observed in all subjects. These findings indicate that UNI in this cohort occurred independently of clinical instability. This conclusion is supported by Nagashima et al,²⁵ who found that although ulnar nerve strain increases significantly with elbow flexion, it is not further elevated by cubitus valgus alignment. However, some studies associate ulnar collateral ligament (UCL) dysfunction with nerve elongation²⁴ or suggest that bony malalignments such as cubitus varus can shift the triceps and increase mechanical stress.^{8,27,33,34,39} Our data suggest that these structural factors were not the primary drivers of UNI in our cohort.

Our data revealed that the increased CA on the throwing side was not accompanied by enlargement of the medial joint gap at rest. This suggests that valgus deformity on the throwing side does not stem from joint instability but rather reflects bony adaptation resulting from repetitive throwing stress. To evaluate the laxity of the UCL, we calculated the GAP distance and the difference in joint gap between gravity-stressed and nonstressed conditions, and examined its correlation with CA. The results showed no significant correlation between the GAP distance and CA. This fact further supports the hypothesis that the increased CA on the throwing side in this study population is primarily driven by bony structural changes caused by repetitive stress rather than soft tissue factors such as UCL laxity. The Type D group exhibited significantly wider joint gaps, both with and without gravity stress on both sides; however, no significant difference in GAP distance was observed among the 3 groups. These findings suggest that UNI is associated with static joint morphology (baseline gap width) rather than with dynamic joint instability induced by stress.

In the present study, no significant difference was found between the types of UNI in terms of the presence of subjective clinical ulnar nerve symptoms during pitching, grip strength, key-pinch power, and positive or negative rates for cubital tunnel syndrome provocation tests during the medical check on bilateral sides. The elbow joint on the nonthrowing side acts as a lever to optimize rotational energy and undergoes rapid kinematic shifts from mild flexion during the stride phase to acute flexion during the acceleration phase. In this study, we investigated ulnar nerve symptoms to clarify the impact of these dynamic movements on the nonthrowing side. Previous studies have reported conflicting results regarding the association between UNI and ulnar nerve symptoms.^{7,10,12,18,29,42} In our earlier studies involving general residents across multiple age groups, no significant association was found between UNI and symptoms of the ulnar nerve.¹² Although UNI is mechanically capable of inducing neuritis due to anterior nerve displacement, clinical evidence suggests that it often exists as a nonpathological phenomenon. Consistent with previous reports,²³ the present results highlight a notable clinical discrepancy in that UNI is prevalent among overhead athletes and serves as a potential risk factor for medial elbow pathology; however, it may not consistently manifest as clinical neuropathy.

Several limitations of the present study warrant mention. First, causality between the degree of CA and the onset of UNI could not be determined because of the cross-sectional nature of the study. A prospective longitudinal study in a younger cohort is necessary to clarify the pathophysiology of UNI and establish its role as a potential risk factor for pitching injuries. Second, one limitation of this study had a relatively small sample size for the subgroup analysis. A post hoc power analysis for the CA values yielded a power of 0.16, suggesting that our study was underpowered to detect subtle differences in this specific parameter. Future studies with larger cohorts are required to confirm these findings.

Third, because this study was restricted to a cohort of high school pitchers, caution is warranted when applying these results to other age groups. Fourth, the unblinded nature of the ultrasound examinations is a methodological limitation. The measurements were performed by a single experienced physician who was aware of limb dominance (throwing vs. nonthrowing), and the potential for observer bias could not be excluded. Fifth, our assessment was based solely on physical examination, as electrophysiological tests were not performed. The inclusion of these procedures would have provided an objective measure of the nerve function, allowing for the detection of subclinical neuropathy. However, it is clinically common to encounter pitchers who present with symptomatic ulnar neuropathy at the elbow during throwing motion, despite having NCS results within normal limits.¹¹ Sixth, this study did not assess the degree of triceps brachii development, a factor previously reported to be associated with UNI.⁴⁰ Finally, a limitation of this study is its reliance on goniometry for CA measurement, which can be influenced by elbow ROM, muscle bulk, and adiposity. The CA was measured at maximum extension to minimize error. Although extension ROM deficits can affect CA, the restrictions in this cohort were mild (mean, 2.3° throwing vs. 5.9° nonthrowing). Given these modest values and the absence of severe contractures, the impact of decreased extension ROM on CA measurements was likely minimal. Furthermore, radiographic methods lack standardized anatomical axes.^9,21 While we used a validated protocol,³² the absence of a universal gold standard for either method complicates definitive accuracy assessments, highlighting the need for future research.

Conclusion

This study found no significant differences in elbow alignment (CA) among high school pitchers based on UNI type. The distribution of UNI classifications (Types N, S, and D) was similar between the pitching and nonpitching arms. Furthermore, UNI type did not significantly correlate with UCL laxity or other clinical findings on the throwing side.