Abstract
Background
Stress from overhead throwing results in morphologic changes to the shoulder in youth baseball players. With greater valgus torque stresses, the elbow experiences injuries specifically attributed to throwing. However, no previous work that we know of has assessed throwing-related morphologic changes of the elbow without associated conditions.
Questions/purposes
(1) Do children who play competitive baseball have enlargement or overgrowth of their radial head shape and/or capitellum compared with the nondominant elbow on MRI? (2) Do children who stop playing year-round baseball have less enlargement of the lateral elbow structures than children who maintain a high level of play?
Methods
A prospective study was conducted between 2015 and 2018 on preadolescent boys who underwent voluntary MRI of their bilateral elbows before the start of the spring baseball season. Twenty-six children agreed to participate out of a four-team league that was asked to participate; their first MRI was obtained at a mean (range) age of 12 years (10 to 13). We also obtained their history related to throwing and performed a physical examination. Players had a mean of 5.6 years of playing before their first MRI, and half the children (13 of 26) were year-round baseball players. Sixty-two percent (16 of 26) reported being either or both a pitcher or catcher as their primary position. No child was excluded from participation. Three years later, these boys were asked to return for repeat MRI and physical examinations. Fifty-eight percent (15 of 26) of players were still playing at the 3-year MRI. Continued play or new onset of pain was documented. Radiographic measurements were then compared between dominant and nondominant arms, and the differences of these changes were compared between those who had continued playing during the study period and those who had quit. The measurements were made in all three planes of the radial head and capitellum, both osseous and cartilaginous. Measurement intrarater and interrater reliability were in the good-to-excellent range (intraclass correlation coefficient 0.77 to 0.98).
Results
When we compared dominant and nondominant arms, we found there was no dominant arm overgrowth (difference between baseline and 3-year measurements) in any measurement; for example, sagittal capitellum measurements in dominant arms were 2.5 ± 1.1 mm versus non-dominant arms: 2.8 ± 1.1 mm (mean difference -0.23 [95% CI -0.55 to 0.08]; p = 0.13). There was only undergrowth of the cartilaginous axial diameter of the radial head (change in dominant: 2.5 ± 1.3 mm; change in nondominant: 3.2 ± 1.7 mm; mean difference -0.64 mm [95% CI -1.2 to -0.06]; p = 0.03). There was no enlargement of the lateral elbow structures when children who continued to play were compared with children who stopped playing; for example, the difference in the bone-only growth ratio of the sagittal radial head to humerus of those still playing was 0.001 ± 0.03 and it was 0.01 ± 0.03 for those not playing (mean difference -0.01 [95% CI -0.04 to 0.01]; p = 0.29).
Conclusion
In healthy children who play baseball for multiple years between the ages of 6 to 11 years, continued torque at the elbow from throwing does not result in morphologic changes as it does in the shoulder. Despite evidence that injuries and surgery because of long-term participation in a throwing sport results in a larger radial head and capitellum, our study presents evidence that outside an injured elbow, throwing alone does not appear to change the morphology of the lateral elbow. Therefore, changes to the radial head size could presuppose other elbow pathology and future study could be performed to better evaluate the correlation.
Level of Evidence
Level I, prognostic study.
Introduction
It has been demonstrated that children who play baseball will develop morphologic changes in the bony anatomy of their throwing arms [5]. These morphologic changes are known to affect the proximal humerus and glenoid, permanently changing the physiology and function of these players’ arms. Although episodes of elbow pain were reported by 35.2% of Little League players during a single year, changes in the elbow because of throwing have not been described [9]. This is despite the fact that the force from overhead throwing may be greater at this segment of the arm than in the shoulder because of the generation of valgus torque at the elbow [3]. This valgus torque increases the contact pressure at the radiocapitellar joint, which can lead to a compressive injury of the lateral elbow [1, 7, 8, 11]. Although capitellar injuries have been extensively studied, only a small number of reports have examined the radial head side of the joint, even though the radial head is a point of major stress during pitching [12]. One such study showed that radial head lesions were common in adolescent patients with diagnosed capitellar osteochondritis dissecans [18]. In that study, the mean size of the radial head in relation to the capitellum was greater in elbows with radial head lesions than in those without radial head lesions.
Given this association, it has been postulated that the radial head may undergo hyperplasia because of repeated microtrauma from the overhead throwing motion. No previous study that we know of has attempted to evaluate this morphologic change in lateral elbow structures in children who play competitive baseball who do not have preexisting pathologic elbow conditions. Because the shoulder demonstrates morphologic changes in this uninjured cohort, we proposed that the elbow, with its increased relative torque stresses, would similarly demonstrate morphologic changes.
Therefore, we asked: (1) Do children who play competitive baseball have enlargement or overgrowth of their radial head shape and/or capitellum compared with the nondominant elbow on MRI? (2) Do children who stop playing year-round baseball have less enlargement of the lateral elbow structures than children who maintain a high level of play?
Patients and Methods
After obtaining institutional review board approval, we prospectively recruited players from a single Little League district in Southern California after the team rosters were created but before the start of any games over a week duration. A signed statement of informed consent or assent was acquired from each player per institutional review board protocol. Players of all positions were recruited from the majors division, the oldest age group in the district. Four teams existed in the majors division in 2015, each with 10 to 12 players per team. Although this league does not involve year-round play, some of the players played in multiple leagues, making them year-round players. The league commissioner presented the opportunity to all families in the division with the understanding that participation would be declined if the athlete had a contraindication to MRI.
Participation was on a first-come, first-served basis, and our budget enabled the recruitment of 26 participants. Participants ranged in age from 10 years to 13 years. Elbow pain at baseline did not preclude athletes from participation. The exclusion criteria included an injury that prevented them from completing the first season they were enrolled in, but none met this criterion. We elected to keep recruitment open to all skill positions, not knowing if the position played had an effect on the desired outcome.
At the baseline visit, each athlete underwent a bilateral elbow MRI examination. In addition, a thorough history was taken for each player. Year-round play was defined as playing a minimum of 8 months of the year, given Little League guidelines that require 4 months off from play. Each player was queried regarding their history of arm pain or of a throwing injury.
After 3 years, the original 26 players were asked to return to undergo a bilateral elbow MRI and a physical examination as well as to complete injury and athletic questionnaires to detect any changes in or correlation to continuation or cessation of baseball activities. Fifty percent (13 of 26) of the athletes met the criteria for year-round players at the time of the first MRI. All players returned at 3 years, and 58% (15 of 26) were still playing at the 3-year MRI for at least the spring season. None of the players had an injury that had caused them to stop playing. None of the boys demonstrated any lateral abnormalities on MRI over time, but two had some fragmentation of the medial epicondyle, five had edema within the medial epicondyle apophysis, four had edema of the distal humeral metaphysis, and one had a partial disruption of the ulnar collateral ligament (all findings were not present on the index MRI). Sixty-two percent of the athletes described themselves as pitchers, catchers, or both (Table 1).
Table 1.
Demographics and playing history (n = 26 players)
| Demographics | Overall (n = 26) | Still playing (n = 15) | Not playing (n = 11) | Odds ratio or mean difference (95% CI) | p value |
| Still playing at 3 years, % (n) | 58 (15) | ||||
| Mean age at baseline in years ± SD | 12 ± 1 | 11 ± 0.8 | 12 ± 0.8 | -0.4 (-1.1 to 0.2) | 0.82 |
| History of playing pitcher or catcher, % (n) | 62 (16) | 67 (10) | 55 (6) | 1.7 (0.3 to 8.3) | 0.69 |
| Private coaching, % (n) | 23 (6) | 40 (6) | 0 (0) | 1.7 (1.1 to 2.5) | 0.02 |
| Year-round players, % (n) | 50 (13) | 80 (12) | 9 (1) | 40 (3.6 to 448) | < 0.001 |
| Hand dominance, right, % (n) | 81 (21) | 80 (12) | 82 (9) | 0.9 (0.12 to 6.5) | 0.99 |
At the baseline and 3-year visits, each athlete underwent bilateral elbow MRI using a GE HdxT 1.5-T MRI machine (General Electric Healthcare, Milwaukee, WI, USA) with the following sequences: axial T1 (echo time, 12 ms to 13 ms; repetition time, 580 ms to 610 ms), axial inversion recovery (echo time, 45 ms to 50 ms; repetition time, 3475 ms to 3500 ms), sagittal T2 multiple-echo recombined gradient echo (echo time, 13.5 ms to 14 ms; repetition time, 600 ms to 650 ms), coronal inversion recovery (echo time, 45 ms to 50 ms; repetition time, 3475 ms to 3500 ms), and coronal T2 fat-saturated (echo time, 64 ms to 70 ms; repetition time, 2020 ms to 2070 ms). MRI measurements were compared between timepoints and between throwing and nonthrowing arms, then compared between those who continued playing baseball and those who stopped playing.
Primary and Secondary Study Outcomes
Our primary study outcome was the difference in radial head growth between dominant (throwing) elbows compared with nondominant elbows. We addressed this by comparing dominant to nondominant arms of all athletes in terms of change in radial head size over the study period.
Our secondary study outcome was the difference in radial head growth between athletes who had continued playing throughout the study period and those who had stopped playing at some point during the study period. We addressed this by comparing those who had stopped playing with those who had continued playing throughout the 3 years in terms of change in radial head size over the study period.
Measurement Techniques and Analyses
All measurements were made bilaterally at both timepoints by one investigator (WEH), who was blinded to any history of arm pain or the arm dominance of the player. The radial head was measured in three different planes (coronal, sagittal, and axial). For each plane, measurements were taken of both the radial head alone and the radial head with cartilage. In the coronal plane, measurements were taken parallel to the physis of the proximal end of the radius at the MRI slice with the greatest width (Fig. 1A-B. In the sagittal plane, measurements were also taken parallel to the physis of the proximal end of the radius at the MRI slice with the greatest width (Fig. 1C-D). In the axial plane, measurements were made perpendicular to the center of the radioulnar joint at the most-proximal MRI slice possible (Fig. 1E-F).
Fig. 1.
A-F (A-B) These are T2 fat saturation MR images measuring the osseous and cartilaginous portions of the radial head in the coronal plane. (A) These images show the measurement of bone and cartilage. (B) The bone-only measurement is displayed here. (C-D) These are T1 MR images measuring the osseous and cartilaginous portions of the radial head in the sagittal plane; (C) this figure shows measurements of both bone and cartilage, and (D) shows the measurement of just bone. (E-F) These are T2 fat saturation MR images measuring the osseous and cartilaginous portions of the radial head in the coronal plane. (E) This figures shows the measures of both bone and cartilage, while (F) displays the measures of just bone.
The size of the humeral capitellum and the total width of the humerus were also measured. The capitellar size was measured as the best-fit circle’s diameter at the sagittal MRI slice with the largest diameter (Fig. 2A). Measurements were taken of the capitellum alone and the capitellum with cartilage. The width of the humerus was measured perpendicular to the long axis of the humerus in the coronal plane in the MRI slice with the greatest humeral width (Fig. 2B).
Fig. 2.
A-B These MR images show measurements of the osseous and cartilaginous portions of the humerus. (A) This sagittal T1 image demonstrates the measurements of both bone and cartilage capitellum. (B) This coronal T2 image fat saturation shows the method for measuring distal humerus width.
The first 10 measurements of the first investigator (WEH) were audited by comparing the measurements with those of a second blinded investigator (EWE) to calculate interobserver agreements. The reliability of measurements was evaluated using a two-way mixed-effects model of the intraclass correlation coefficient (ICC). For the lateral elbow measurements, intrarater reliability ranged from an ICC of 0.66 to 0.99 and interrater reliability ranged from an ICC of 0.75 to 0.99, which are in the good-to-excellent range [2] (Table 2).
Table 2.
Reliability statistics and measurement error
| Measurements | ICC-intrarater | ICC- interrater | SEM |
| Coronal bone plus cartilage radial head measurements | 0.91 | 0.94 | 1.4 |
| Coronal bone radial head measurements | 0.98 | 0.97 | 1.3 |
| Sagittal bone plus cartilage radial head measurements | 0.86 | 0.93 | 1.0 |
| Sagittal bone radial head measurements | 0.96 | 0.97 | 1.0 |
| Axial (diameter) bone plus cartilage radial head measurements | 0.77 | 0.80 | 3.0 |
| Axial (diameter) bone radial head measurements | 0.96 | 0.94 | 1.8 |
| Bone plus cartilage sagittal (diameter) capitellum measurements | 0.91 | 0.90 | 1.7 |
| Bone sagittal (diameter) capitellum measurements | 0.95 | 0.96 | 1.3 |
| Bone humeral width | 0.98 | 0.95 | 3.2 |
ICC = intraclass correlation coefficient; SEM = standard error of mean.
Measurement error was calculated and is represented as the upper boundary of the 95% confidence interval of the mean absolute error. Standard deviation values from the first 10 measurements, which were used to assess the reliability of measurements, were also used to perform a power analysis for the sample size needed. The average SD across the capitellum and radial head measures was 2 mm. To detect a difference in growth between dominant and nondominant elbows of at least 2 mm, at 80% power and alpha < 0.05, a sample size of 11 pairs was needed. Thus, our sample of 26 pairs would be sufficient to detect a difference in growth of 2 mm.
We compared within-group measurements for the dominant and nondominant arms at baseline and 3 years of follow-up using repeated-measures ANOVA. We compared the calculated change between 3 years and baseline between the dominant and nondominant arm using a paired t-test. The ratio of the radial head to the width of the humerus was calculated at each timepoint and for the coronal, sagittal, and axial diameters of the radial head. We calculated the difference in that ratio between the dominant and nondominant arms to remove the issue of comparing a larger child to a smaller child (a ratio of 0 would indicate that the size of the radial head compared with that of the humerus was not different between the dominant and nondominant arms). The change in that difference in ratio was calculated as the 3-year value minus the baseline value. A negative value indicated that the discrepancy between the dominant and nondominant arms became less at the 3-year follow-up examination. A positive value indicated that the discrepancy between the arms increased at the 3-year follow-up interval. At the 3-year follow-up examination, we compared these values between athletes who were still playing and those who were no longer playing to determine whether the size of the radial head versus the humerus in the dominant and nondominant arms changed in a different manner over the timepoints in the two groups. We performed ANOVA for that comparison. Analyses were performed using SPSS version 25 (IBM Corp, Armonk, NY, USA), and alpha was set at p < 0.05 to declare significance.
Results
No Overgrowth in the Dominant Arm
When we compared the dominant and nondominant arms (Table 3), we found that there was no dominant arm overgrowth (difference between baseline and 3-year measurements) in all measurements (p > 0.05) (Table 4). There was only undergrowth of the cartilaginous axial diameter of the radial head (change in dominant: 2.5 ± 1.3 mm; change in nondominant: 3.2 ± 1.7 mm; mean difference -0.64 mm [95% CI -1.2 to -0.06]; p = 0.03). As expected in growing children, all measured values in both the nondominant and dominant arms of players grew during the study period (p < 0.001) (Table 5).
Table 3.
Measurements in both the dominant and nondominant arms at baseline, 3-year follow-up, and average change (mm)
| Measurement | Timepoint | Dominant (mm ± SD) | Nondominant (mm ± SD) |
| Coronal bone and cartilage radial head measurements | Baseline | 21.6 ± 2 | 21.9 ± 2 |
| 3 years | 24.5 ± 2 | 24.4 ± 2 | |
| Change | 2.6 ± 1 | 2.5 ± 1 | |
| Coronal bone radial head measurements | Baseline | 17.6 ± 2 | 17.6 ± 2 |
| 3 years | 21.3 ± 2 | 21.3 ± 2 | |
| Change | 3.7 ± 1 | 3.7 ± 1 | |
| Sagittal bone and cartilage radial head measurements | Baseline | 21.8 ± 2 | 21.5 ± 1 |
| 3 years | 24.0 ± 2 | 23.5 ± 2 | |
| Change | 2.2 ± 1 | 2 ± 1 | |
| Sagittal bone radial head measurements | Baseline | 16.7 ± 2 | 16.4 ± 2 |
| 3 years | 20.8 ± 2 | 20.3 ± 2 | |
| Change | 4.1 ± 1 | 3.9 ± 1 | |
| Axial (diameter) bone and cartilage radial head measurements | Baseline | 22.7 ± 2 | 22.4 ± 2 |
| 3 years | 25.2 ± 2 | 25.5 ± 2 | |
| Changea | 2.5 ± 1 | 3.2 ± 2 | |
| Axial (diameter) bone radial head measurements | Baseline | 17.4 ± 2 | 17.4 ± 2 |
| 3 years | 21.4 ± 2 | 21.5 ± 2 | |
| Change | 3.9 ± 2 | 4.1 ± 2 | |
| Bone and cartilage sagittal (diameter) capitellum measurements | Baseline | 21.6 ± 2 | 21.4 ± 2 |
| 3 years | 23.5 ± 2 | 23.7 ± 2 | |
| Change | 1.8 ± 2 | 2.3 ± 2 | |
| Bone sagittal (diameter) capitellum measurements | Baseline | 17 ± 2 | 17 ± 2 |
| 3 years | 19.6 ± 2 | 19.8 ± 2 | |
| Change | 2.5 ± 1 | 2.8 ± 1 | |
| Humeral width | Baseline | 50.1 ± 6 | 48.6 ± 5 |
| 3 years | 59.6 ± 6 | 58.3 ± 6 | |
| Change | 9.5 ± 4 | 9.7 ± 3 |
Significant differences between the dominant and non-dominant arm regarding change from baseline to 3 years; p = 0.031; data are presented as the mean ± SD; baseline and 3-year values are rounded to the nearest tenth of 1 mm; the average change values are represented at one significant digit after the decimal; all SDs are rounded to the nearest whole number; all baseline to 3-year changes in both the dominant and non-dominant arms reached significance at p < 0.001.
Table 4.
Baseline comparison of dominant and nondominant elbows
| Measurement | Dominant (mm ± SD) | Nondominant (mm ± SD) | Mean difference (95% CI) | p value |
| Coronal bone and cartilage radial head measurements | 21.6 ± 1.9 | 21.9 ± 1.8 | 0.01 (-0.32 to 0.34) | 0.94 |
| Coronal bone radial head measurements | 17.6 ± 2.1 | 17.6 ± 1.9 | -0.09 (-0.44 to 0.26) | 0.59 |
| Sagittal bone and cartilage radial head measurements | 21.8 ± 1.8 | 21.5 ± 1.4 | 0.26 (-0.17 to 0.68) | 0.23 |
| Sagittal bone radial head measurements | 16.7 ± 2.3 | 16.4 ± 1.8 | 0.21 (-0.12 to 0.53) | 0.19 |
| Axial (diameter) bone and cartilage radial head measurements | 22.7 ± 1.9 | 22.4 ± 1.8 | -0.31 (-0.11 to 0.74) | 0.14 |
| Axial (diameter) bone radial head measurements | 17.4 ± 2.0 | 17.4 ± 1.8 | -0.02 (-0.47 to 0.50) | 0.95 |
| Bone and cartilage sagittal (diameter) capitellum measurements | 21.6 ± 1.9 | 21.4 ± 1.6 | -0.18 (-0.34 to 0.71) | 0.47 |
| Bone sagittal (diameter) capitellum measurements | 17 ± 1.7 | 17 ± 1.9 | 0.00 (-0.29 to 0.29) | 0.99 |
| Humeral width | 50.1 ± 5.7 | 48.6 ± 5.2 | 1.5 (0.65 to 2.4) | 0.002 |
Significant finding = p < 0.05.
Table 5.
Change from baseline to 3 years compared between dominant and nondominant elbows
| Measurement | Dominant (mm ± SD) | Nondominant (mm ± SD) | Mean difference (95% CI) | p value |
| Coronal bone and cartilage radial head measurements | 2.6 ± 1.2 | 2.5 ± 1.3 | 0.09 (-0.34 to 0.52) | 0.68 |
| Coronal bone radial head measurements | 3.7 ± 1.4 | 3.7 ± 1.3 | 0.03 (-0.48 to 0.55) | 0.90 |
| Sagittal bone and cartilage radial head measurements | 2.2 ± 1.4 | 2 ± 1.2 | 0.14 (-0.51 to 0.79) | 0.66 |
| Sagittal bone radial head measurements | 4.1 ± 1.4 | 3.9 ± 1.1 | 0.17 (-0.30 to 0.65) | 0.46 |
| Axial (diameter) bone and cartilage radial head measurements | 2.5 ± 1.3 | 3.2 ± 1.7 | -0.64 (-1.2 to -0.06) | 0.03 |
| Axial (diameter) bone radial head measurements | 3.9 ± 1.6 | 4.1 ± 1.5 | -0.17 (-0.71 to 0.38) | 0.54 |
| Bone and cartilage sagittal (diameter) capitellum measurements | 1.8 ± 1.9 | 2.3 ± 1.5 | -0.42 (-0.99 to 0.14) | 0.14 |
| Bone sagittal (diameter) capitellum measurements | 2.5 ± 1.1 | 2.8 ± 1.1 | -0.23 (-0.55 to 0.08) | 0.13 |
| Humeral width | 9.5 ± 3.8 | 9.7 ± 3.5 | -0.20 (-1.66 to 1.3) | 0.79 |
Significant finding = p < 0.05.
No Difference After Cessation of Playing
When we compared the ratio of growth (change in the size of the radial head relative to the distal humerus in the dominant arm compared with the same ratio in the nondominant arm) in the sagittal plane in cartilage and bone measures, we found there was no difference in growth for those who were still playing at 3 years and those who were not (still playing -0.007 ± 0.05 versus not playing 0.02 ± 0.03, mean difference -0.03 [95% CI -0.07 to 0.007]; p = 0.13 (Table 6). Furthermore, there were no changes in the ratio of growth for the axial plane in cartilage and bone measures (still playing -0.01 ± 0.04 versus not playing -0.003 ± 0.04, mean difference -0.01 [95% CI -0.04 to 0.02]; p = 0.59) or coronal (still playing -0.002 ± 0.03 versus not playing 0.02 ± 0.04, mean difference -0.02 [95% CI -0.05 to 0.008]; p = 0.15) planes of the radius or for the capitellum. Similarly, when bone-only measurements were evaluated, the change in the difference in the ratio between the dominant and nondominant arms did not change between timepoints for the sagittal, axial, or coronal measures (p > 0.05).
Table 6.
Difference in growth ratio between players still playing baseball at 3 years of follow-up and those no longer playing
| Difference | Still playing | No longer playing | Mean difference (95% CI) | p value |
| Difference in growth ratio of the coronal radial head/humerus, bone and cartilage | -0.002 ± 0.03 | 0.02 ± 0.04 | -0.02 (-0.05 to 0.008) | 0.15 |
| Difference in growth ratio of the coronal radial head/humerus, bone | -0.003 ± 0.03 | 0.01 ± 0.04 | -0.01 (-0.05 to 0.02) | 0.42 |
| Difference in growth ratio of the sagittal radial head/humerus, bone, and cartilage | -0.007 ± 0.05 | 0.02 ± 0.03 | -0.03 (-0.07 to 0.007) | 0.13 |
| Difference in growth ratio of the sagittal radial head/humerus, bone | 0.001 ± 0.03 | 0.01 ± 0.03 | -0.01 (-0.04 to 0.01) | 0.29 |
| Difference in growth ratio of the axial radial head/humerus, bone and cartilage | -0.01 ± 0.04 | -0.003 ± 0.04 | -0.01 (-0.04 to 0.02) | 0.59 |
| Difference in growth ratio of the axial-radial head/humerus, bone | -0.09 ± 0.03 | 0.08 ± 0.04 | -0.01 (-0.04 to 0.02) | 0.55 |
Discussion
Valgus torque of the elbow resulting from acceleration during the overhead throwing motion increases contact pressure at the radiocapitellar joint [11]. Increases in these torque pressures cause morphologic changes in bone and joints and were described in the shoulder of throwing athletes [5]. At the elbow, these repetitive pressures cause compressive injuries of the lateral elbow that are directly related to throwing [1, 7, 8]. However, our prospective MRI evaluation of boys who play baseball demonstrated that 6 years to 9 years of throwing during peak skeletal growth (between the ages of 5 years and 14 years) does not inherently result in morphologic changes of the lateral elbow, as expected. Therefore, if changes are seen in joint morphology, then the provider should consider that pathology may be present (even if not seen on plain films), since the current evidence suggests that these enlargements can be seen with concomitant pathology, such as osteochondritis dissecans.
Limitations
There are several limitations to our study. First, it is impossible to know the exact number of throws that any child has made over their lifespan, and we could not adequately control for this throughout the study. However, 6 years of intense throwing that violated Little League guidelines for the amount of time spent playing per year seems adequate to result in any morphologic changes that could occur because of throwing, if those changes were going to occur. Second, the difference between being a pitcher or catcher versus playing first or second base is unclear, and the sample size was too small to determine whether a difference exists between the positions of most throws and least throws. Further research with a larger dataset would be required to answer this question. Third, although our sample size may have been too small to identify more-subtle changes in morphology, our post-hoc power analysis suggests that we had more than double the necessary sample size to detect differences between throwing and non-throwing arms. Future study that includes children with known lateral pathology, such as osteochondritis dissecans, may better demonstrate a correlation with disease over repetitive throwing trauma.
No Overgrowth in the Dominant Arm
In children without any pathologic conditions in their elbow or dominant arm, throwing does not inherently result in overgrowth of the lateral structures of the elbow despite repetitive stresses. This finding directly contrasts findings of the shoulder, which undergoes morphologic changes that are termed humeral retrotorsion [5]. This morphologic change develops from the repetitive stresses of throwing and correlates with injuries of the shoulder and the elbow [6, 13]. We found smaller relative axial radial head diameters in the dominant throwing arm than in the non-dominant arm. It is difficult to postulate on a potential etiology for this finding, especially when there was no noted indication in the lateral elbow. However, continuous, repetitive injury and compressive forces (not unlike that potentially seen in competitive youth baseball) inhibit the capacity of cartilage cells to multiply, thereby slowing growth of the overall structure of a skeletally immature radial head [16, 17]. The only previous study to publish on the concept that repetitive overhead throwing can result in radial head enlargement was a study that primarily evaluated capitellum osteochondritis dissecans [18]. In that study, the mean size of the radial head in relation to the capitellum was greater in elbows with radial head lesions than in those without radial head lesions. We believe that it may be the pathology that resulted in the morphologic changes rather than the throwing, and our lack of finding growth enlargement may be secondary to the children in our study having no pathology.
No Difference After Cessation of Playing
Because we found there was no difference between dominant and nondominant elbows in children after a mean of 6 years of competitive throwing in baseball, we were not surprised that our second question—whether stopping year-round baseball influenced the growth—failed to elicit any difference in the morphology of the lateral structures. No previous evidence exists on the subject of stopping sport/activity and experiencing a shift the expected change in growth morphology. This would have been the first. The next step would be in line with assessing lateral elbow pathology in children with growth morphology changes and then stopping their sport participation to determine if the changes can be reversed or slowed over time.
Conclusion
Contrary to our expected findings, there is no evidence suggesting morphology changes of the elbow are related to throwing at a young age. Therefore, families might not need to be counseled about the effect of repetitive overhead sports on their child’s elbow growth. Future study may need to focus on patients who have presented specifically for elbow pain. Perhaps a comparison of the nondominant and injured elbows will demonstrate expected changes of overgrowth in the lateral elbow structures that have been noted in previous studies on osteochondritis dissecans [4, 18], but this was not seen in our study population of uninjured children.
Acknowledgments
We thank James Bomar MPH, for preparing the figures for this manuscript.
Footnotes
One of the authors (EWE) certifies that he has received or may receive payments or benefits, during the study period, in an amount of less than USD 10,000 from Arthrex (Naples, FL, USA); in an amount of less than USD 10,000 from Orthopediatrics (Warsaw, IN, USA); in an amount of less than USD 10,000 from DePuy Synthes (Raynham, MA, USA); in an amount of less than USD 10,000 from Sportstek Inc (San Diego, CA, USA).
One of the authors (ATP) certifies that he has received or may receive payments or benefits, during the study period, in an amount of less than USD 10,000 from Orthopediatrics (Warsaw, IN, USA); in an amount of less than USD 10,000 from Smith & Nephew (Memphis, TN, USA); in an amount of less than USD 10,000 from Sportstek Inc (San Diego, CA, USA); in an amount of less than USD 10,000 from Stryker Corp (Kalamazoo, MI, USA).
Each remaining author certifies that neither he or she, nor any member of his or her immediate family, has funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.
Each author certifies that his or her institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.
This work was performed at Rady Children’s Hospital, San Diego, CA, USA.
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