SPECIAL CONSIDERATIONS IN IMAGING THE EPIPHYSEAL PRIMARY PHYSIS

– Written by Julián Forero-Millán, Samuel Sisay Hailu, Dennis Caine, and Jie C. Nguyen, USA

INTRODUCTION

Participation in youth sport has important and wide-ranging health benefits. However, year-round participation that involves highly repetitive movements fosters an environment where overuse injuries are likely to occur. Overuse injuries occur due to repetitive submaximal loading of the musculoskeletal system when rest is not adequate to allow for structural adaptation¹. For example, overhand pitching in baseball can be associated with overuse injuries involving the dominant shoulder and elbow. 

Overuse injuries may involve the ligaments, tendons, muscles, joint cartilage and growth plates. The precise site of injury depends on regional skeletal maturity and severity of the insult. Among the skeletally immature, the strongest structures are the ligaments, tendons, and muscles, whereas the growth cartilage of the physis, underlying either an apophysis or an epiphysis, is the weakest and thus, more likely to sustain injury.

Physeal stress injuries (PSIs) are unique to skeletally immature athletes, which can involve both the epiphyseal growth plate (a.k.a., pressure epiphysis) and apophyseal growth plate (a.k.a., traction apophysis). Pressure epiphyses are situated at the ends of long bones and are subjected to compressive and rotational forces whereas traction apophyses are located at the site of attachment of muscle tendons to bone and are subjected primarily to tensile forces (Figure 1). PSIs involving the epiphyseal primary physis can lead to deformity and growth disturbance with severity dependent on the insult and anatomic location.

Because overuse injuries of the epiphyseal growth plate may involve one or more components of the epiphyseal-physeal-metaphyseal (EPM) complex, these injuries are collectively referred to as epiphyseal PSIs. The EPM complex is located at ends of long bones and consists of the epiphysis, physis, and metaphysis (Figure 2). The epiphyseal growth plate is located between the epiphysis and metaphysis and contributes to lengthening of the underlying bone. Bone growth and response to injury are dependent on differential blood flow to the EPM complex. Protecting these growth plates is essential, as impairment or dysfunction can result in lifelong morbidity and the risk for premature osteoarthritis².

Epiphyseal PSIs are of particular interest clinically due to the potential for future growth disruption and angulation deformity, with injuries often clustering near periods of rapid growth².  This article provides an overview of epiphyseal PSIs in youth sport with particular emphasis on the importance of imaging in the early diagnosis and treatment of these injuries. Case examples of epiphyseal PSIs are provided, including those associated with growth disturbance. Precise and timely imaging is essential for the generation of preventive measures that can reduce delayed diagnosis and long-term morbidity².

EPIPHYSEAL GROWTH PLATE STRESS INJURIES

Vulnerability of the epiphyseal growth plate

The vulnerability of the epiphyseal growth plate is summarized by Caine et al.³ Briefly, the epiphyseal growth plate is made of cartilage but is less resistant to stress than adult articular cartilage.  During the adolescent growth spurt, structural changes in growth plate cartilage occur that result in a thicker and more fragile epiphyseal growth plate. This is because bone mineralization follows linear growth, leaving the bone temporarily more porous and prone to stress injury and mechanical failure. Recent evidence involving youth athletes indicates that physeal injuries are particularly elevated around peak height velocity, which fits well with the proposed underlying mechanisms for this growth-injury relationship³.

Overuse injury involving the epiphyseal growth plate

In contrast to fractures, often the result of a single traumatic event, PSIs develop gradually from repetitive loading, which occurs when a child overtrains in a particular sports activity. As described by Caine et al.² epiphyseal PSIs develop following repetitive submaximal stress, causing microtrauma to one or more components of the growth plate complex. The resulting pattern of injury depends not only on the anatomical location, sport(s) played, and offending action, but also on the compressive, rotational tension, and/or shearing forces involved.

A framework representing our emerging understanding of the pathophysiologic mechanisms and outcomes of epiphyseal PSIs was recently proposed by Caine et al.⁴. Briefly, physeal widening, the most common manifestation of epiphyseal PSI (Figure 3), is postulated to be the result of altered metaphyseal perfusion, which allows hypertrophic chondrocytes to persist^5-7. The apparent extension of chondrocytes into the metaphysis is due to ongoing growth within the adjacent unaffected normal physis. These injuries are usually reversible, if diagnosed and treated with conservative treatment, allowing restoration of metaphyseal perfusion ^4,6,7. However, if undiagnosed or sub-optimally treated, progressive insults can lead to damage to the epiphysis and epiphyseal-sided blood supply, increasing the risk for irreversible growth deformity⁷.

Youth at risk for epiphyseal PSIs

Children and adolescents participating in a variety of high impact repetitive sports activities – including baseball, badminton, climbing, cricket, dance, gymnastics, rugby, soccer, swimming, tennis, and volleyball – may sustain epiphyseal PSIs². While early sport specialization and over-training likely contribute to the increased risk and frequency of this injury, non-elite young athletes can also be at risk, particularly following an intense exposure to sports².

Body regions where epiphyseal PSIs are most likely to occur?

Best studied sites of injury in the published literature include the proximal humerus, medial epicondyle, distal radius, and phalanges of the fingers². The epiphyseal growth plates most at risk for a stress-related injury are the ones most loaded during repetitive activity. For example, a gymnast may repetitively bear weight on the distal radial physis while performing floor routines whereas a climber may repetitively stress the long and ring fingers while rock climbing².

CASE EXAMPLES

Shoulder

Background

Proximal humerus PSIs are postulated to stem from chronic repetitive micro-traumatic shear, torque, and/or traction forces on the proximal humerus⁸. This condition was first reported involving the throwing arm of skeletally immature youth baseball pitchers. However, youth athletes who practice repetitive overhand action and specialize in other sports – including gymnastics, tennis, swimming, volleyball, badminton, and cricket – have also been diagnosed with proximal humerus PSIs². 

Although one study reports a growing frequency of proximal humerus PSIs among youth baseball players⁸, little is known on the overall prevalence or incidence of these injuries. In a recent study of 2022 male baseball players between the ages of 9 and 12, 41 (14.9%) agreed to undergo radiographic examination of the shoulder, with 15 (36.6%) of these young throwers reporting pain in the dominant shoulder demonstrating classic findings of proximal humerus epiphyseal PSI⁹.   

Clinical presentation

Patients present with pain involving the dominant shoulder, triggered by overhead activities and exacerbated during throwing motions¹⁰. Some reports show weakness, fatigue, or a “clicking” sensation, although neurological symptoms are rare⁸. On clinical examination, focal tenderness is typically present along the lateral proximal humerus, and some can experience ipsilateral glenohumeral internal rotation deficit^8,10.

Diagnostic imaging

Imaging workup starts with shoulder radiographs, but early finding can be subtle.  If proximal humeral physeal widening is suspected, contralateral comparison views can be obtained. Physeal widening may be focal, centered along the anterolateral physis, or diffuse, involving the entire physis.  Other radiographic findings can include metaphyseal sclerosis, indistinctness or loss of the zone of provisional calcification (ZPC)¹⁰(Figure 4). 

In children with diffuse or atypical shoulder pain, MRI can be considered, which allows direct visualization of the growth plate, detection of marrow edema, and exclude alternative sources of pain (e.g.: glenohumeral joint internal derangement).  On MRI, physeal widening, loss of ZPC, physeal, and subjacent marrow edema are more readily apparent ¹⁰ (Figure 5).

Knee

Background

In the knee, epiphyseal PSIs preferentially affect the distal femur and proximal tibia². These injuries are postulated to be the result of repeated compression, rotational, shearing, valgus and/or varus forces during sports activities, including baseball, basketball, football, gymnastics, rugby, softball, running, soccer and tennis².  Unfortunately, there is limited epidemiological data on the precise prevalence of these injuries² as physeal stress injuries are often grouped with other categories of injury such as fractures or overuse injuries.

A concern associated with physeal stress injury of the knee is the risk of premature closure of the growth plate. Although incompletely understood, there is emerging evidence of a possible link between increased incidence and severity of genu varum alignment among male soccer players and asymmetric physeal stress that may have occurred during childhood and adolescence¹¹. It is postulated that this altered alignment is the result of repetitive rotation and compression forces asymmetrically affecting the growth plates of knee joints¹². However, longitudinal studies are needed to better clarify this association and determine causality.

Clinical presentation

In contrast to the shoulder, the knee has been less extensively studied. Symptoms tend to be vague and are associated with activities that progressively worsen over time. On physical examination, tenderness over the physis can be elicited².  While early findings may be subtle or absent, prolonged untreated or inadequately managed cases carry an increased risk of not only epiphyseal deformities, but also permanent longitudinal growth disturbance and limb length discrepancy¹¹.

Diagnostic imaging

Again, radiographs are the first-line screening imaging modality, which also helps to exclude alterative diagnoses.  MRI allows direct visualization and characterization of the hyaline cartilage of the growth plate, highly sensitive for detection of subtle and asymmetric findings, including physeal widening, increased signal intensity, integrity of the ZPC, and subjacent marrow edema (Figure 6)¹². The morphology of physeal widening correlates with the nature of the insult, with a broader area of widening observed in cases of ongoing or repeated injuries⁶.

GROWTH DISTURBANCE

If epiphyseal PSIs are undiagnosed or suboptimally treated, progressive and cumulative insults can lead to damage of the epiphysis and epiphyseal blood supply, increasing the risk for irreversible growth deformity⁷.  In a recently published systematic review that included 101 case reports and case series on patients with epiphyseal PSIs from various sports and included various anatomic locations, growth-related complications occurred in 12.7% (57/448)².

Growth disturbance is best studied among gymnasts.  Specifically, the higher prevalence of ulnar positive variance is postulated to be associated with excessive and repetitive loading of the distal radius ¹³.  Wrist pain is common among gymnasts.  Radiographs may show stress-related changes of the distal radial physis, development of positive ulnar variance, and/or partial or complete closure of the distal radial growth plate when compared to the distal ulna¹³ (Figure 7). 

Clinical presentation

Patients report activity-related pain centered in the dorsal distal forearm and wrist, which worsens during axial-loaded dorsiflexion and can be bilateral in about one-third ¹⁴. Symptoms worsen with increased training intensity¹⁵. On examination, tenderness is present along the distal radial physis and pain is elicited by extreme dorsiflexion and axial loading¹⁴. Side-to-side differences in ulnar variance can occur but has not been found to correlate with hand dominance¹⁶.

Diagnostic imaging

On imaging, radiographic findings vary dependent on severity and chronicity. Early findings are limited to the physis whereas late findings can include ulnar positive variance¹⁴ and premature physeal closure, focal clefting, or sclerosis of the radial metaphysis¹⁷ (Figure 8).  While ulnar variance can be estimated on MRI, cost-effectiveness and potential variability in the measured values dependent on wrist position and image selection make MRI less ideal for determining ulnar variance when compared to radiographs^18,19.

CONCLUSION

Year-round participation in youth sport that involves high levels of repetitive movement fosters an environment where overuse injuries are likely to occur. Stress injuries involving the epiphyseal-physeal-metaphyseal (EPM) complex, or epiphyseal physeal stress injuries (PSIs), are a particular concern given their potential for future growth disturbance and potential risk for premature osteoarthritis. This article provides an overview of epiphyseal PSIs, including case examples of epiphyseal PSIs affecting the shoulder, wrist, and knee of young athletes. The importance of diagnostic imaging in the early diagnosis and treatment planning of these injuries is highlighted. Precise and timely imaging is essential for the early identification of epiphyseal PSIs and the generation of preventive measures that can reduce delayed diagnosis and long-term morbidity.

Julián Forero-Millán, MD¹

Samuel Sisay Hailu, MD¹

Dennis Caine, PhD²

Professor Emeritus

Jie C. Nguyen, MD, MS^1,3

1               Department of Radiology, Children’s Hospital of Philadelphia, Philadelphia, PA, USA

2              Department of Education, Health and Behavior Studies, University of North Dakota, Grand Forks, ND, USA

3              University of Pennsylvania, School of Medicine, Philadelphia, PA, USA

Contact: nguyenj6@chop.edu

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