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Abstract
Objective To evaluate the presence of x ray changes in the proximal humerus growth plate of 21 young pitchers.
Design Case series.
Setting This study was conducted at the Orthopaedic and Traumatology Department of the ABC College of Medicine, Santo Andre, São Paulo, Brazil, tertiary institution.
Patients 21 male adolescent baseball pitchers, with a mean age of 14.5 years and selected from the Brazilian National Team, were studied.
Interventions The patients underwent x ray examinations of the shoulders.
Main outcome measurements The x rays of the pitchers’ shoulders were studied to determine any changes in the proximal humeral growth plate and correlate them with clinical findings.
Results Fourteen athletes (66%) had radiographic changes in the humerus growth plate but only 5 (36%) had pain complaints. Nine of these 14 cases (64%) whom the observers found radiographic changes did not complain of pain. It was also observed that there was a correlation in only 11 cases between clinical and radiographic evaluations.
Conclusion Radiographic changes in the proximal humerus growth plate were found in 66% of the cases, but 64% were asymptomatic. These changes indicate possible evolution, in the future, to a greater degree of retroversion in pitchers’ dominant shoulders.
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Pitch movement is a set of movements subdivided into six different stages. During this complex movement, the shoulder is subjected to various forces, and the outcome is the conversion of potential energy into kinetic energy. The dominant upper extremity can then reach an angular velocity of 7000°/s.1 2
Burkhart et al believe that the forces interacting with this joint during the pitch movement, especially the distraction force, lead to changes in the posteroinferior capsule; hypertrophy and consequent contracture would be the reason for a limitation of the internal rotation and an increase in the external rotation, as shown in most baseball pitchers.3
However, it is also known that these forces, acting on the proximal humerus growth plate, lead to bone changes. A number of authors have shown that throwing-motion athletes have a greater degree of humeral retroversion of the dominant shoulder compared with the non-dominant shoulder.4,–,6 This greater retroversion seems to be a beneficial adaptation of this constantly stressed region, providing greater excursion during the Late Cocking, which leads to a gain in speed. On the other hand, this greater retroversion is related to a reduction in internal rotation motion of the dominant shoulder of these athletes.5 7,–,9
The purpose of this study was to evaluate the presence of radiographic changes at the proximal humerus growth plate of 21 young pitchers of the Brazilian National Team and to correlate this with clinical measurements.
Cases and Methods
Between August and September 2005, we evaluated 21 young male baseball pitchers belonging to the Brazilian National Team. The mean age was 14.5 years (range 13 to 16 years) (table 1).
Distribution of the athletes by their age (years), dominance and presence of pain and radiographic changes
The entire study was explained to the subjects and their parents, who signed an informed consent form approved by our University Ethics Committee.
A questionnaire was given to all athletes to determine which of them had pain in the dominant shoulder. The questionnaire asked whether currently or in the past the athletes had any pain in the dominant shoulder. If the answer was yes, we tried to determine the characteristics of the pain (type, site, irradiation, improvement or worsening factors, when they have pain, intensity and its relationship to their performance).
All baseball pitchers were subjected to a radiographic evaluation of both shoulders. x Rays were taken as follows: true antero-posterior (radiograph view) (A-P) and axillary positions.
A subjective evaluation was done by comparison of the x rays of both shoulders, looking for the presence of widening, bone sclerosis and fragmentation.
In all cases, three shoulder and elbow surgery specialists did this subjective evaluation by analysing independently each x ray of both shoulders of the athletes and using a blind system and without knowledge of the dominant side of the athlete. The specialists assessed the x rays looking for the changes in the growth plate previously described (widening, bone sclerosis and fragmentation). In addition, a musculoskeletal radiologist objectively measured the physeal width with precision dial calipers at the lateral cortex of the humerus on each view.10
Statistical analysis
We used the StatXact statistical software, version 7 (CYTEL Software Corporation, Cambridge, Massachusetts) and the SAS 8.02 (SAS Institute, Cary, North Carolina). The Fisher test was used to determine whether there was (currently or in the past) any correlation between the presence of pain and the existence of radiographic changes, comparing dominant and non-dominant shoulders.
The kappa coefficient was used to evaluate whether the analyses of the x rays conducted by the three observers would match. Using the Cochran–Armitage trend test, we tried to find out whether older athletes would have higher chances of showing radiographic changes in their dominant shoulders, since we believed that such athletes would have been subjected to longer periods of exposure to factors that could promote these changes.
The Wilcoxon test was used to compare whether the physeal width of the dominant shoulders measured objectively by the musculoskeletal radiologist was greater than that in the non-dominant shoulders, even in asymptomatic athletes.
Results
Analysis of the questionnaire
Of the 21 baseball pitchers included in this study, only three complained of pain in the dominant shoulder (cases 10, 11 and 15). None of them experienced constant pain, and in all of them the pain was related with the pitch movement.
Another three athletes (cases 2, 6 and 12) had experienced pain in the past, and their pain was also related to the pitch movement. Therefore, 28.6% complained of pain (table 1).
Analysis of the x rays
In 14 cases (66%) there were changes in the proximal humerus growth plate in one of the sides, so in these cases it was possible to determine which was the dominant side. Widening was found in all of them, although bone sclerosis and/or fragmentation was found in only five cases (cases 1, 7, 12, 13 and 19) (table 1).
In the other seven cases (34%), no changes were observed; as a consequence, it was not possible to determine which was the dominant side.
Regarding the observers’ agreement about the presence or absence of radiographic changes, in 17 cases (81%) all observers agreed that there were, or were not, changes in the growth plate, and in four cases (19%) one observer did not agree with the opinion of the other two. The kappa coefficient showed that all three observers reached a substantial agreement. In those cases where one observer disagreed from the other two, we considered what the majority believed to have occurred (table 2).
Opinions of each of the observers for the presence of radiographic changes
In addition to these, the musculoskeletal radiologist found that the physeal width of the dominant shoulders was greater than that in the non-dominant shoulders. Moreover, by using the Wilcoxon test it was possible to observe that it was statistically significant (p<0.001 at the true antero-posterior radiograph and p<0.003 at the axillary positions) (tables 3, 4). In addition, the widening was confirmed even in asymptomatic athletes, and in this group it was statistically significant also (tables 5, 6).
Evaluation of the physeal width at the true axillary position view of the 21 athletes
Evaluation of the physeal width at the axillary view of the 21 athletes
Evaluation of the physeal width at the true axillary position view of the nine asymptomatic athletes with widening
Evaluation of the physeal width at the axillary view of the nine asymptomatic athletes with widening
Correlation between radiographic and clinical evaluations
Five of the six (83%) athletes who complained of pain at the questionnaire had those radiographic changes, and one athlete’s x rays showed no radiographic changes (fig 1). Nine of 14 cases (64%) in whom x rays showed radiographic changes did not complain of pain (fig 2).
True antero-posterior (neutral rotation) x ray of the left shoulder, showing a proximal humerus growth plate with no changes.
True antero-posterior (neutral rotation) x ray of the right shoulder, showing a proximal humerus growth plate with a small degree of widening and sclerosis in an asymptomatic athlete.
Thus, we observed that in only 11 cases (52%) was there any correlation between the clinical and radiographic evaluations. Using the Fisher test, we found that the number of cases with this correlation was not significant (p = 0.612).
In addition, the fact that the presence of radiographic changes cannot be correlated with the age of patients was evidenced by means of the Cochran–Armitage trend test (p = 0.832)
Discussion
Changes in the proximal humerus growth plate, associated with the presence of shoulder pain in youth baseball pitchers, have been documented in the literature.11,–,14 On the other hand, the presence of changes in the growth plate in asymptomatic athletes has not yet been well established. In the Little Leaguer’s Lesion, adolescent baseball pitchers usually complain of shoulder pain that is related to the pitch movement and often impairs their performance.11,–,14 Also, in the shoulder x rays of the dominant upper extremity of these players, a widening in the growth plate of the proximal humerus can be observed. However, some authors had observed that in some players, the proximal humerus growth plate remained widened (compared with the non-dominant shoulder) even after the symptoms had resolved.14
In addition, it is well documented in the literature that many adult baseball pitchers have a greater degree of humeral retroversion of the dominant shoulder.4,–,6 8 This retroversion is described as being responsible for the increase in the external rotation of the dominant shoulder compared with the non-dominant side, and for the reduction in internal rotation. This is probably an adaptation of the dominant shoulder subjected to pitch stress for a long period of time.4,–,6 Sabick et al performed a biomechanical study to evaluate the external rotation torque and the distraction force during fastball pitches of 14 baseball pitchers (mean age 12 years), having observed that these forces could be sufficient to cause deformations of the proximal humerus growth plate of the dominant shoulder of these baseball pitchers, and they believe that, depending on the qualitative and quantitative factors, the athlete can present an increase in the retroversion of the dominant shoulder or a lesion on the growth plate, the so-called Little League Lesion.9
The prevalence of changes in the growth plate in asymptomatic athletes, such as widening, bone sclerosis and fragmentation, has not yet been well defined. Mair et al had evaluated the x rays of 79 Little League baseball players in the 8–15-year age group and had found a prevalence of 57%. They also observed that 27% of the 79 players complained of pain and that in this group of players of the widening of the growth plate was more pronounced.10
We have observed in our study that 66% of the athletes showed changes in the growth plate, and of these 14 cases, nine (64%) were asymptomatic at the time they were evaluated by us. (The three cases of pain in the past were considered symptomatic, since we could not determine the cause of their pain and a little leaguer’s shoulder could be one of the possibilities; in addition, the widening found at their x rays could be a residual widening as described before.) These radiographic changes in the growth plate were independently observed by three orthopaedists specialised in shoulder and elbow surgery; 81% of the time, they had the same opinion, which, based on the kappa coefficient, was shown to be a substantial agreement and was sufficient for us to trust their interpretations. We also tried to be sure that there was no correlation between the radiographic findings and the clinical evaluation of these athletes, and in fact this was confirmed using the Fisher test (p = 0.612).
Similarly to Mair et al,10 we observed that in athletes with pain, the radiographic findings were more pronounced, although we were not able to confirm this quantitatively, because the number of patients in our sample was not large enough (fig 3). However, it was possible to observe that in athletes whose x rays had shown physeal widening, this was statistically more pronounced, even when we studied the asymptomatic athletes. Additionally, in this study, we did not observe whether the fact that older athletes probably were subjected for a longer period to forces that might have caused the radiographic changes in the growth plate of the proximal humerus was fundamental for the occurrence of such changes. The Cochran–Armitage trend test did not allow us to prove whether such radiographic changes were more frequent in older athletes than in younger athletes (p = 0.832).
True antero-posterior (neutral rotation) x ray of the right shoulder, showing a proximal humerus growth plate with widening and fragmentation in a young leaguer’s shoulder.
The higher percentage of radiographic changes in our study compared with that in Mair et al10 may be due to the fact that we evaluated only baseball pitchers. Among baseball players, pitchers are most subjected to external and internal rotation torque forces and to distraction force, since they perform the highest pitch counts during a game.15 16 Moreover, until last year, many of these young baseball pitchers of the Brazilian National Team did not respect the limit of pitches during the season.
As observed in our study, we believe that the radiographic changes in the growth plate as shown in nine asymptomatic athletes are due to a process of adaptation to the act of pitching, as postulated by Mair et al10 and Sabick et al,9 and perhaps these changes will evolve in the future into greater retroversion of the dominant shoulder, when compared with the non-dominant side, as observed by some authors,4,–,6 8 which can be a protective mechanism for these pitchers’ shoulders.5 8
What is already known on this topic
Forces interacting in the proximal humerus growth plate during the pitching movement lead to bone changes, and athletes who perform a throwing motion have a greater humeral retroversion of the dominant shoulder.4,–,6
What this study adds
Physeal widening in the proximal humeral growth plate is probably due to a process of adaptation to the act of pitching and may evolve in the future into a greater degree of retroversion. It is not known how much widening will lead to a Little League’s Lesion, as there was no clinical correlation.
The changes in the proximal humerus growth plate of young pitchers of the Brazilian National team was found in 66% of the cases. We conclude that there is no correlation with clinical evaluation, and 64% of these pitchers with radiographic changes were asymptomatic.
References
Footnotes
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Competing interests None.
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Ethics approval Ethics approval was provided by ABC School of Medicine Research Ethics Committee.
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Patient consent Obtained from the parents.