Osteochondritis dissecans of the humeral trochlea in two pediatric athletes: two cases and review of literature

Osteochondritis dissecans (OCD) is a focal idiopathic alteration of subchondral bone with risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis [1-2]. Originally, inflammation was implicated as the underlying etiology as reflected in the nomenclature; but currently two theories prevail: repetitive microtrauma and disruption of local vasculature with subsequent avascular necrosis [1, 3]. In either scenario, resorption at the area of injury predisposes the overlying cartilage to separation and fragmentation We herein report two unusual cases of osteochondritis dissecans (OCD) of the trochlea. The injury consisted of a focal alteration of subchondral bone secondary to repetitive micro trauma from overhead maneuvers (pitching) in two male adolescents. Only 23 other cases of OCD affecting the trochlea have been reported. We comment on this discrepancy, explore the radiographic features, and detail the non-operative management that was undertaken. We substantiate our report with a systematic review of all OCD cases of the trochlea and provide information on patient demographics, sport type, management, recuperation and finally significance of radiographic grading.


Introduction
Osteochondritis dissecans (OCD) is a focal idiopathic alteration of subchondral bone with risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis [1][2]. Originally, inflammation was implicated as the underlying etiology as reflected in the nomenclature; but currently two theories prevail: repetitive microtrauma and disruption of local vasculature with subsequent avascular necrosis [1,3]. In either scenario, resorption at the area of injury predisposes the overlying cartilage to separation and fragmentation We herein report two unusual cases of osteochondritis dissecans (OCD) of the trochlea. The injury consisted of a focal alteration of subchondral bone secondary to repetitive micro trauma from overhead maneuvers (pitching) in two male adolescents. Only 23 other cases of OCD affecting the trochlea have been reported. We comment on this discrepancy, explore the radiographic features, and detail the non-operative management that was undertaken. We substantiate our report with a systematic review of all OCD cases of the trochlea and provide information on patient demographics, sport type, management, recuperation and finally significance of radiographic grading.
involving subchondral bone. Irritation and movement of these intra-articular fragments cause joint pain and can lead to further damage [4][5][6]. The most commonly described location for OCD is the knee, typically involving the femoral condyle [7]. However, OCD has also been identified in the talar dome, tarsal navicular, femoral capital epiphysis, and elbow (5). Lesions in the elbow commonly occur in the pediatric population, and most frequently occur in the anterolateral capitellum of the humerus, but radial head, olecranon, and trochlear involvement has also been reported [1,5], [8][9][10][11][12][13][14]. The repetitive stress on the elbow associated with throwing motions seen in baseball pitchers or other overhead activities produce microtrauma that instigates the pathophysiologic processes of elbow OCD.
While OCD is most prevalent in the elbow in the radio-capitellar joint, as of 2020 only twenty-three cases of trochlear OCD have been reported; seventeen lateral and six medial as defined by Marshall et al. [1,5,[11][12]. This distribution is seen because the radio-capitellar joint is the main stabilizer of the elbow and accepts 60% of the compressive load in extension while the trochlea accepts only about 40% [1]. The pediatric population is at a higher risk due to immature bone being more susceptible to similar stressors versus mature adult bone [15].
To better document this rare condition, we report two cases of OCD at our own institution and performed a review of literature for all reported cases of OCD in the trochlea of the humerus, which has not been done since 2009 by Namba et al [13]. Consolidating these unique reports is vital to help further our understanding of this rare elbow injury. The two cases of OCD in the trochlea introduced in this manuscript include the seventh case of OCD in the medial trochlea and a large medial trochlear lesion treated non-operatively. Furthermore, based on a combination of all cases, we describe a diagnostic and treatment algorithm for this condition.
An otherwise healthy 13-yearold right-hand-dominant male baseball pitcher presented with right medial elbow pain for six months. The patient discontinued competitive sports for five months following onset and experienced a pain free interval while engaging in daily activities. Pain returned after initiating baseball, prompting the patient to seek medical care. There was no traumatic event. No numbness, tingling, weakness or other associated symptoms were reported. Physical examination demonstrated no gross deformity or asymmetry. The elbow was nontender to palpation over the entire olecranon. The patient had full range of motion with 5˚ of hyperextension which was symmetric with the contralateral elbow. Plain radiographs of the elbow demonstrated evidence of an OCD lesion along the medial border of the trochlea on the right elbow (Figure 1). Magnetic resonance imaging confirmed the diagnosis of medial trochlear OCD (Figures 2 and 3) along with minimal underlying reactive marrow edema but without detachment or evidence of fracture. Non-operative treatment was implemented, which included icing and physical therapy regimen. All throwing and/or upper extremity athletics were discontinued for a two-month period and the patient was re-evaluated after that time interval.  Upon return the patient was asymptomatic with a benign physical examination. Repeat MRI demonstrated improved osteochondral lesion of the medial trochlea with only minimal localized marrow edema and subtle chondral signal change in the remaining area ( Figure 4). No loose fragments were discerned. The patient was gradually progressed to full activities via a throwing program with appropriate restrictions. Patient has remained asymptomatic for approximately two years after his initial visit, while actively playing baseball.

Literature Review
We conducted a literature review to compare the presentation, mechanism of injury, and treatment of our two cases with those provided in literature.   The combined literature search yielded forty-one articles. In total, fifteen were deleted due to duplication.
The remaining twenty-six articles were screened by title and abstract by the authors. The following exclusion criteria was then applied to the twenty-six articles: nonrelated topics, location other than trochlea of the elbow, nonhuman subjects, non-English language papers, yielding ten manuscripts. After review, nine were included in the final analysis ( Figure  9). Additionally, we subclassified the filtered articles based on study type: we report on 7 case report and 2 case series.  operatively, and the remaining were treated in a non-operative manner.
Overall, whether the patients were treated operatively or non-operatively, the outcomes were positive with the majority of patients experiencing resolution of symptoms in five to six months post intervention.