Osteochondritis dissecans of the humeral capitellum in identical twin baseball players

Osteochondritis dissecans (OCD) is a focal idiopathic alteration of subchondral bone; it has an inherent risk of instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis.⁷ Occurrence of OCD is common in the elbow and knee joints. OCD of the humeral capitellum generally affects adolescent athletes (eg, baseball players and gymnasts) who engage in repetitive overhead or upper extremity weight-bearing activities.^3,5 The prevalence of capitellar OCD in baseball players ranging from 10 to 12 years of age has been reported to be 2.1/1,000.¹² The injury can progress to the separation of a segment of cartilage and subchondral bone, forming a loose body.¹

Many etiological theories have been proposed for the onset and progression of OCD, including trauma, diet, rapid growth, anatomic characteristics, lack of blood supply, necrosis of subchondral bone, and heredity.^2,6,16,20 The exact etiology of OCD of the humeral capitellum is still unclear, but the primary cause is believed to be repetitive trauma to the poorly vascularized capitellum.⁹ Genetic factors are also thought to play a role in the pathogenesis; however, the genetic basis of OCD remains unknown.² To our knowledge, the unique presentation of OCD affecting male identical twin baseball players, in the absence of syndromic features, has not been reported before. Here, we present 11-year-old identical twin baseball players with almost identical radiographic, computerized tomography, magnetic resonance imaging, ultrasound, and macroscopic findings and clinical course of OCD of the humeral capitellum.

Case report

The patients were 11-year-old male identical twins who had been actively engaged in baseball for 4 years. The patients practiced baseball four times per week and were right-handed. The clinical history was unremarkable with no medical records or history of previous major trauma to the elbow. They were of similar physique, 147 cm tall, weighing 35 kg, and developmentally normal for their age. Twin A played mainly in the short-stop position. Twin B played mainly in the catcher position. Informed consent was received to report this case.

The twins participated in a baseball elbow medical examination held at the beginning of the off-season and were diagnosed with OCD of the humeral capitellum by ultrasonography. Three months before the examination, both twins had experienced elbow pain on throwing during baseball but had no pain on throwing at the time of the examination. During the examination, the range of motion, valgus stress test, and tenderness of the medial epicondyle or humeral capitellum were assessed physically. Twin A had a slight limitation in the range of motion in elbow extension and flexion. Twin B did not indicate any abnormalities in the physical findings. Thereafter, ultrasonography of the medial epicondyle and humeral capitellum revealed similar OCD findings (Fig. 1) and medial epicondyle abnormalities in both twins, who were advised to visit an orthopedic hospital.

Figure 1.

Ultrasound images at the time of baseball elbow medical examination. Images in the top row are a sagittal section, and those in the bottom are a coronal section. Almost the same subchondral bone irregularity can be seen at almost the same location at the humeral capitellum (white arrows).

One month later at the orthopedic hospital, X-ray examination revealed almost the same OCD findings (Fig. 2). The twins were instructed to cease throwing and to visit a doctor every other month.

Figure 2.

Radiographs at the first hospital visit. Top images are of the right elbow; the bottom images are of the left elbow. Forty-five-degree tangential view imaging shows OCD lesions in the lucent stage at almost the same location (white arrows). No lesions were found on the healthy side.

Two months later, the patients were gradually allowed to recommence throwing. After undergoing an X-ray examination 6 months after the first visit (Fig. 3), the patients stopped visiting the hospital.

Figure 3.

Radiographs after 6 months from first hospital visit. Lucent area extends to the center of the capitellum.

After the last hospital visit, the twins completed the entire baseball season (lasting for six months) without pain in their elbows. Twin A played mainly in the pitcher position, and twin B in the catcher position during the last season. However, when they returned to the orthopedic hospital after the season, they indicated that the OCD had worsened (Fig. 4). They hoped to continue playing baseball and decided to undergo surgery after discussion with their parents.

Figure 4.

Image findings after the season (1 year after the first visit). (a) The lesion is enlarged, and a fragmentation can be seen on radiographs. (b) Short tau inversion recovery (STIR) magnetic resonance imaging of the humeral capitellum showed signal changes around the OCD lesion. (c) A large area of bone-lucent images can be seen on the sagittal CT images. (d) Large lesions of almost same shape can be seen on 3DCT images.

They underwent surgery to transplant the auto osteochondral graft from the unloaded part of the knee joint into the OCD lesion. Twin A had a 9 × 10-mm osteochondral fragment removed, and φ4.5-mm and φ3.5-mm osteochondral grafts were transplanted. Twin B had a 9 × 13-mm osteochondral fragment removed, and two φ4.5-mm osteochondral grafts were transplanted (Fig. 5).

Figure 5.

Intraoperative photographs. In both patients, free cartilage fragments were removed, and osteochondral grafts were transplanted.

A splint was fixed for 2 days after the surgery, and then the range of motion for training was initiated. Two and a half months after the surgery, throwing exercises were gradually started. Four months after the surgery, they were allowed to throw at maximal effort and returned to playing competitively. The twins were able to play baseball without any pain when throwing; there were no abnormal physical findings when they visited the hospital six months after the surgery (Fig. 6).

Figure 6.

Radiographs at the six months post-surgery. The lucent area remained in twin A, but the repair was good in both patients.

Discussion

We have documented our experience with 11-year-old identical twin baseball players with almost identical radiographic, computerized tomography, magnetic resonance imaging, ultrasound, and macroscopic findings and clinical course of OCD of the humeral capitellum. OCD of the humeral capitellum has been well described in the dominant arm of Little League baseball pitchers and is thought to be caused by repetitive increased loading of the radiocapitellar joint.⁴ This experience with OCD cases of identical twin baseball players suggests that heredity is also an important factor for OCD.

The exact etiology of OCD of the capitellum is presently unknown, but repetitive trauma to the poorly vascularized capitellum is believed to be the primary cause.⁹ It is postulated that the mechanics during pitching places increased valgus stress and compression on the elbow, particularly during late cocking and early acceleration.⁵ Differences in biochemical properties of the radial head and capitellum are also believed to contribute to microtrauma, with the stiffer radial head articulating with the softer lateral capitellar surface causing increased strain.¹⁸ McManama et al reported repetitive trauma from throwing sports as the etiology in half of 14 patients who underwent surgical management for capitellar OCD lesions; however, it remains unclear as to why the other half had OCD lesions.¹⁴ Therefore, it seems that repetitive microtrauma is not the only cause of OCD.

Ischemia has also been implicated as a potential contributor to the progression of OCD because of its vascular anatomy. Haraldsson et al noted that the predominant blood supply was from end-arteries entering posteriorly and passing through compressible epiphyseal cartilage, with no connection to adjacent metaphyseal vessels.⁹ This tenuous blood supply is at risk of repetitive elbow injury.

It is generally accepted that repetitive microtrauma and ischemia are the leading causes of OCD lesions in the capitellum; however, there have been sporadic reports of a genetic link. To date, this predisposition for OCD in certain families has not been linked to any specific gene. Familial OCD is a disease in which articular cartilage on the surface of the knee, ankle, and elbow joints separates from the subchondral bone tissue. Stattin et al reported that this disease is caused by a missense mutation in the agrecan gene, which is a typical cartilage component.¹⁹ The identical twin baseball player OCD cases suggest that heredity is one of the most important factors. Although genetic testing was not performed in this case, genetic factors are expected to be elucidated with the development of genetic testing in the future.

Several cases of OCD of the humeral capitellum in twins have been reported previously. OCD of the nondominant elbow in fraternal twins was reported by Kenniston et al.¹⁰ Matsuura et al reported cases of fraternal twins who had been actively engaged in competitive rhythmic gymnastics with similar bilateral OCD of the capitellum.¹³ Pudas et al reported cases of identical twin ice hockey players.¹⁷ The twin cases in this study showed very similar image findings and clinical courses compared to those of the twin OCD cases reported in the literature.^10,13,17 Genetic factors may account for a large proportion of several potential factors for OCD.

Screening using ultrasonography enables early detection and provides an opportunity for successful conservative treatment.¹¹ Harada et al reported that ultrasonography was useful and reliable (as confirmed by radiographic findings) for detecting elbow injuries.⁸ Ultrasonography is very useful for routine examination of OCD because it is noninvasive and cost-effective.¹⁵ Ultrasonographic imaging has been used to diagnose early OCD without elbow pain in baseball elbow medical examinations.¹¹ Our cases also showed asymptomatic OCD on ultrasonography and were treated conservatively. Unfortunately, continuing baseball after conservative treatment exacerbated the condition of OCD, and surgical treatment was required. However, the period of pitching restrictions was off-season, and it was possible to return to competitive sport four months after the surgery. Early detection of OCD by ultrasonography may have had a positive effect on minimizing the withdrawal period in these cases.

Conclusion

We have described the OCD of the capitellum in identical twin baseball players. As these were identical lesions in identical twins, this supports the theory that OCD has a genetic background. For OCD, screening by ultrasonography is considered effective for early detection and provides an opportunity for early treatment.

Disclaimers

Funding: This work was not funded by any private, industrial, or governmental organization.

Conflicts of interest: The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

Consent: The patients provided informed consent.