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. 2021 Apr 5;14(3):239–245. doi: 10.1007/s12178-021-09708-5

Narrative Review — Knee Pain in the Pediatric Athlete

Anne Kuwabara 1,✉, Emily Kraus 1, Michael Fredericson 1
PMCID: PMC8137791  PMID: 33818701

Abstract

Purpose of review

This review article seeks to highlight common youth athlete knee conditions due to overuse or trauma and elucidate differences from the adult populations.

Recent findings

Overuse conditions presented include apophysitis, osteochondritis dissecans plica syndrome, and discoid meniscus. Traumatic conditions presented include patellar instability, patellar sleeve fracture, and patellofemoral osteochondral fractures.

Summary

Knee injuries affect a significant proportion of youth athletes. These injuries place athletes at higher risk of chronic pain and potentially osteoarthritis. We have reviewed common overuse and traumatic knee injuries and differentiating factors between the adult population to improve and expedite the diagnosis, treatment, and prognosis for youth athletes with knee injuries.

Keywords: Pediatric, Sports medicine, Overuse injuries, Traumatic injuries, Knee pain

Introduction

57.7% of U.S. youth participate in organized sports according to a 2019 US Department of Health and Human Services report [1]. There are an estimated 2.5 million sport-related knee injuries in adolescents each year [2–4]. Injury types are evenly divided into overuse and traumatic injuries [5]. Children with a history of early sports specialization have a 2.25 greater odds of having an overuse injury compared with nonspecialized athletes [6]. Youth athletes who sustain knee injuries demonstrated increased pain and decreased function than uninjured controls 3–10 years after injury, which may increase risk for future osteoarthritis [7]. This demonstrates the importance for early diagnosis, treatment, and prevention. This review article seeks to highlight common youth athlete knee conditions due to overuse or trauma and elucidate differences from the adult populations.

Overuse

Apophyseal

An apophysis is a secondary ossification center where a muscle-tendon unit attaches. The tibial tubercle apophysis forms between age 11 and 14 years old and fuses with the proximal tibial epiphysis at 14 to 18 years of age [8]. The apophysis is at higher risk of injury because it is two to five times weaker than surrounding structures [9]. Apophysitis typically occurs during episodes when bone growth outpaces corresponding muscle growth [10]. Apophysitis of the knee can occur at distal pole of the patella or at the tibial tubercle. When it occurs at the inferior patella, it is called Sinding Larsen-Johansson (SLJ). At the tibial tubercle, it is referred to as Osgood-Schlatter's disease (OSD).

Osgood-Schlatter Disease

Definition

OSD typically presents during periods of rapid growth (age 10 to 15 years for males and 8 to 13 years for females) in patients who participate in sports that involve running and jumping. In adolescents 12 to 15 years old, OSD has a prevalence of 11.4% in males and 8.3% in females. Bilateral symptoms are present in 20 to 30% of patients [8].

Clinical features

History: Patients describe a history of insidious, focal pain at the tibial tuberosity that is aggravated by activity (running, jumping, kneeling, or squatting in particular). Pain subsides minutes to hours after cessation of activity.

Physical: Patients present with erythema, point tenderness and swelling or prominence of the patella tendon insertion on the tibial tubercle. Decreased flexibility of quadriceps (Ely test) or hamstrings (passive knee extension test) are also predisposing factors. Pain can be reproduced by resisted knee extension and active or passive knee flexion.

Diagnosis: OSD is diagnosed clinically. Radiographs can appear normal or may demonstrate soft tissue swelling with fragmentation of the apophysis or calcification in the distal patellar tendon in chronic cases. Clinical correlation and comparison to contralateral side is important as these findings may also be seen in normal variants. Radiographs also help rule out avulsion injury or other bony trauma. Ultrasound findings for Osgood-Schlatter reveal hypoechoic enlargement of the distal patellar tendon, non-ossified cartilage, and potential fragmentation of the tibial tuberosity [11]. On MRI, edema around the tibial tuberosity can be seen in early stages. Later stage findings may include partial tears in the apophysis or avulsion of bone or cartilage [12].

Treatment: Non-operative management is the mainstay of treatment. Initial interventions include activity modification (cross training, relative rest), ice (20 min every 2–4 h and after activity), topical or oral non-steroidal anti-inflammatories (NSAIDs), and physical therapy (quadriceps and hamstrings strengthening and range of motion). In severe cases, a short period of immobilization can be considered with bracing (knee pad, patellar tendon strap) or casting. Steroid injections are avoided due to risk of tendon weakening. However, prolotherapy has been demonstrated to improve symptoms. Topol et al. demonstrated that there was improved symptom control at 1 year in patients treated with a 12.5% dextrose solution compared to usual care [13].

Operative intervention is rare and is only indicated for refractory cases in patients that have reached skeletal maturity (~2%) or in cases of tibial avulsion fracture. Options include open or arthroscopic excision of ossicle and/or tibial tubercle.

Prognosis: Within 1–2 years, nearly half of all patients are completely recovered. Symptoms subside when the growth plate closes. A prominent bump may remain and can be tender to palpation or cause difficulty with kneeling.

Sinding-Larsen-Johansson disease

SLJ shares clinical and pathophysiologic features with OSD. It can sometimes occur simultaneously with OSD [14]. The lower pole of the patella is still cartilaginous in adolescents. On physical exam, there is focal tenderness and swelling at the inferior patella. SLJ is also a clinical diagnosis but imaging can be obtained if the diagnosis is unclear. Radiographs may be normal or show spurring at the inferior pole of the patella. At ultrasound, SLJ is characterized by swelling, thickening of the patellar tendon with possible calcifications, fragmentation of the lower pole of the patella, and infrapatellar bursitis [15]. MRI demonstrates bony spurs, fragmentation of the inferior patella associated with marrow edema, thickening and calcification of the proximal patellar tendon, and surrounding soft-tissue swelling. Treatment and prognosis are similar to OSD. Full recovery usually takes 12–24 months and should resolve when athletes reach skeletal maturity.

Osteochondritis Dissecans

Description

Osteochondritis Dissecans (OCD) describes subchondral bone separation due to a disturbance in local blood supply [16]. Incidence reported around 15 to 29/100,000 in children under 11 years old and 22/100,000 in adolescents 1–-19 years old. Boys have a four times higher incidence then girls [17]. Lesions are bilateral 25% of the time. The majority of adult OCD lesions are thought to be persistent pediatric OCD lesions. Lateral aspect of the medial femoral condyle is most common location (60%) but may also occur at the lateral femoral condyle, patellar or tibial plateau.

Clinical features

History

Symptoms can vary from insidious vague knee pain to mechanical symptoms, such as catching and locking, due to an unstable fragment. Pain with activity and recurrent effusions are common.

Physical

Patients may present with tenderness at the OCD lesion site with an antalgic gait or externally rotated leg . Pain with passive tibial internal rotation and knee flexion may indicate medial femoral condyle OCD lesion (Wilson sign). However, this is not a sensitive test as only 25% of patients with radiographically confirmed OCD lesions had a positive Wilson sign [18]. Patients with mechanical symptoms, effusions, crepitus or pain with motion more typically have unstable OCD lesions.

Diagnosis

OCD lesions can be detected on AP, Lateral, Tunnel, and Sunrise knee radiographs. Patients under age 7 may have normal variants of ossification centers that may be confused as OCD lesions. MRI is recommended for staging and treatment guidance. A higher intensity signal line behind the fragment is predictive of unstable lesions that will likely require surgery. Bone scans have also been used to assess healing potential of OCD lesions.

The Hefti Classification is used for describing MRI findings of OCD Lesions [19].

  1. Small change of signal without clear margins of fragment

  2. Osteochondral fragment with clear margins but without fluid between fragment and underlying bone

  3. Fluid is visible partially between fragment and underlying bone

  4. Fluid is completely surrounding the fragment, but the fragment is still in situ

  5. Fragment is completely detached and displaced (loose body).

Treatment/prognosis

Lesion size, location, stability and associated symptoms are important factors in determining treatment algorithms. Non-operative management includes activity and weight bearing restrictions, casting or bracing, and physical therapy to ensure safe return to sport.

Operative management is for skeletally mature patients with unstable lesions or stable lesions non-responsive to non-operative management. Operative interventions include trans-articular/retro-articular notch drilling, internal fixation, bone grafting and fixation, osteochondral autograft, and osteochondral allograft techniques. Postoperative healing time is approximately 3–6 months. Radiograph and MRI follow up imaging are generally recommended before returning to sport.

Plica syndrome

Definition

Plicae are thin folds of vascularized synovial tissue due to incomplete resorption of embryonic septa that separate the knee joint into medial, lateral, and suprapatellar compartments [20]. Anatomic studies indicate that 90% of adults have one or more plicae in their knee joints. The vast majority of plicae are incidental and asymptomatic. There are four possible plicae: suprapatellar, infrapatellar, medial, and lateral. Patients commonly have more than one plica. Medial plicae are the most common type of plicae and are most likely to be symptomatic [21]. Medial plicae are found between the infrapatellar fat pad and the medial aspect of the knee joint.

Clinical features

History

Patients with plica syndrome experience anterior knee pain associated with clicking or popping. Pain can be brought on by activities that load the patellofemoral joint such as rising from a chair, squatting, or ascending or descending stairs. Patients may have a history of a twisting injury or recent increase in activity level. Secondary causes of plica irritation include hemarthrosis, intra-articular lesions, loose foreign bodies, and rheumatoid arthritis.

Physical

On physical exam, a taut band may be palpable and tender. Other findings may include an effusion, tight hamstrings, and tight quadriceps. Two physical exam maneuvers can suggest plica syndrome: the Stutter test and the Hughston test.

Diagnosis

The gold standard for diagnosis is arthroscopy. Diagnostic studies are more important in ruling out other etiologies. Anteroposterior, lateral, and skyline radiographs should be obtained when plica syndrome is suspected but are usually normal. On MRI, plicae are usually only visualized when an effusion is present. Symptomatic plicae can appear thick with synovitis. A literature review by Stubbings demonstrated that physical exam had a 90% sensitivity and 89% specificity, ultrasound had 90% sensitivity and 83% specificity, and MRI had 77% sensitivity and 58% specificity [22].

Treatment

Medial plicae can be classified by the Sakakibara arthroscopic classification:

  • Type A: Elevation in the synovial wall

  • Type B: Appear shelf-like, but not covering the anterior surface of the medial femoral condyle

  • Type C: Large, shelf-like appearance and covering the anterior surface of the medial femoral condyle

  • Type D: Fenestrated plica with a central defect

The Sakakibara classification system helps guide treatment. Types A and B have a low likelihood to cause pain and respond to conservative therapies. Types C and D may impinge on the medial condyle due to their larger size and ultimately require surgery.

Physical therapy programs involve lower extremity stretching and knee extension exercises with the goal of strengthening the knee stabilizing musculature, hamstrings, and quadriceps. NSAIDs, ice, and intraplical corticosteroid injections are reasonable treatments at this stage to calm down inflammation [23]. Conservative management also includes avoiding activities that incite pain. At least 3 months of conservative treatment is recommended before advancing to more aggressive therapies.

If no response to conservative management or if concern for cartilage damage (Sakakibara type C/D), resection via arthroscopy is the next step.

Prognosis

Plica syndrome has a favorable prognosis. A study of 969 patients found that at a median follow-up of 27.5 months, 10% had no response, 26% improved, and 64% were symptom-free [ 24].

Discoid meniscus

Definition

A discoid meniscus is a congenital variant that is abnormal in composition and structure (decreased collagen fibers and a loss of normal fiber orientation, as well as abnormal vascularity) [25]. At birth, the entire meniscus is vascular, whereas at 9 months, only the outer two thirds are vascular. By age 10 years, the vascularity is in its adult form, involving the outer one third of the meniscus [26].

These features cause the discoid meniscus to be more unstable and prone to tearing than normal. 3 to 5% of the population have a discoid meniscus [27]. Patients with a discoid meniscus typically present at age 10 years or younger [28]. Typically, the lateral meniscus is discoid [27]. 15 to 25% have the condition in bilaterally [29]. It is prevalent in the Asian population [30].

Clinical features

History

Clinical presentation is variable, depending on shape, associated hypermobility, and concomitant meniscal tears. Patients may present with intermittent snapping and pain in the knee and a lack of full extension with or without a history of trauma [ 29].

Physical

Children aged <10 years typically present with spontaneous intermittent snapping of the knee or may be unable to achieve full knee extension [31]. A lateral joint line bulge may be present, and a clunk may be noted during a McMurray test. Older children may present with a torn meniscus, pain, swelling, as well as mechanical symptoms [26].

Diagnosis

The most commonly used classification system was proposed in 1969 by Watanabe et al. based on arthroscopy findings [32].

Type I is stable to arthroscopic probing, is block-shaped, and covers the entire tibial plateau.

Type II is stable to arthroscopic probing and covers up to 80% of the tibial plateau.

Type III demonstrates instability on arthroscopic probing because of the lack of any posterior meniscotibial attachments. The sole posterior attachment in the type III variant is the meniscofemoral ligament of Wrisberg.

All tear types can be seen with discoid meniscus. However, a horizontal cleavage tear, is a classic presentation.

Radiographs may show widening of the lateral joint space, squaring of the lateral femoral condyle, cupping of the lateral tibial plateau, and/or a hypoplastic tibial [26–28]. Magnetic resonance imaging is needed to confirm the diagnosis and to evaluate for any tears [29].

Treatment

An asymptomatic discoid meniscus requires no further intervention while patients with a tear or symptoms even without tearing may require surgery [32]. Treatment aims to re-establish normal anatomy using saucerization, tear repair, and fixation of the meniscus.

Traumatic

Patellar instability/dislocation

Definition

Patellar instability describes when the patella pathologically dislocates from the patellofemoral joint, most often laterally [33]. Patellar dislocations comprise 3% of all knee injuries, primarily in female patients age 10–16 years [34, 35]. The overall risk of recurrence after a first-time patellar dislocation in patients aged 18 years and younger is around 34 to 38% [36].

Dejour et al. described four main morphologic risk factors contributing to patellar instability including trochlear dysplasia, patella alta, patellar tilt and a lateralized tibial tubercle with resultant increased Q angle [37]. Additional risk factors include ligamentous laxity and connective tissue disorders. Marfan syndrome and Ehlers-Danlos, for instance, affect the strength of medial patellofemoral ligament (MPFL).

Patellar dislocations are also the most common cause of osteochondral fractures in the knee [38]. Pediatric patients are predisposed to developing osteochondral fractures due to incomplete ossification of the patella. After lateral dislocation, shearing of the medial patellar border during relocation typically causes the fracture.

Clinical features

History

Patients may present after direct trauma to the knee or a non-contact twisting injury of the knee [39]. It is important to assess prior dislocation events and any report of ligamentous laxity.

Physical

Physical exam findings include increased patella mobility (greater than 2 quadrants of translation with comparison to the contralateral side), apprehension to lateral translation, positive J sign, crepitus (can indicate concomitant osteochondral injury), and Bassett’s sign (focal tenderness over the MPFL femoral insertion site).

Lack of acute event would increase suspicion for chronic, congenital, or habitual patellar instability. Ligamentous laxity should also be assessed (Beighton score).

Diagnosis: Radiographs support the diagnosis of patellar instability and should include four views: anteroposterior (AP), weightbearing Rosenberg (bent knee PA), lateral, and sunrise (bent knee axial) [37]. On the sunrise view, patellar tilt (Laurin’s angle) and subluxation (Merchant’s congruence angle) can be assessed. The lateral view can be used to assess for trochlear dysplasia, which can be graded as type I (minor dysplasia), type II, or type III (major dysplasia) [40]. The Caton-Deschamps index (CDI) can also be assessed in the lateral view to evaluate patellar height [41].

MRI is usually the study of choice due to visualization of osteochondral injuries, trochlear dysplasia, growth plate status, MPFL, patellar height and ability to assess the tibial tubercle-trochlear groove (TT-TG) distance, which quantifies lateralization of the patellar tendon insertion is on the tibia.

Treatment

Non-operative management for first-time patellar dislocations is recommended in the absence of osteochondral fractures or lesion requiring excision or repair [42]. This starts with closed reduction (if not spontaneously reduced) achieved with extension of the knee combined with gentle medially directed force of the patella. This is followed by supportive bracing with a patellar stabilization brace that has a lateral buttress and immediate weight-bearing with crutch assistance for comfort, full range of motion and short-term NSAID use. Early rehabilitation should focus on closed chain and quadriceps strengthening exercises. Taping has been reported to improve coordination of quadriceps muscle activation [43].

Operative management indications include osteochondral fracture or injury with loose body, chronic instability, and failure of non-operative management. Surgical techniques include arthroscopic removal of loose bodies, medial patellofemoral ligament repair, MPFL reconstruction, Fulkerson osteotomy, lateral soft tissue release, and trochleoplasty.

Prognosis

There are no formal guidelines regarding return to play. Menetrey proposes clearance when there is no pain, no effusion, full range of motion, no objective patellofemoral instability on exam, symmetric strength and dynamic stability during sport-specific drills [44]. Development of symptomatic patellofemoral arthritis is the primary long-term concern following lateral patellar dislocation.

Patellar sleeve fracture

Definition

Due to their cartilaginous and mobile nature, pediatric patellar fractures are rare, constituting 1% of all pediatric fractures [45]. Of patellar fractures, patellar sleeve fractures constitute 57% of patellar fracture in children below 16 years of age [45]. Peak incidence occurs at 12.7 years, with a 3:1 male-to-female ratio [46]. A sleeve fracture is defined as an avulsion of cartilage or periosteum with an associated small subchondral osseous fragment from the distal or proximal pole of the patella [47]. The mechanism of injury is typically due to rapid contraction of the quadriceps muscle on a flexed knee [48]. There are four types of patellar sleeve fractures: superior (least common), inferior (most common), medial (may lead to dislocation), and lateral (related to repetitive stress from the vastus lateralis) [49]. Risk factors for adolescents include intensity sports training, rapid growth, and relative patellar mobility [46].

Clinical features

History

Patients typically present with acute anterior knee pain associated with a history of trauma [50].

Physical

Physical exam demonstrates patellar tenderness, decreased active knee extension range of motion, effusion, and a palpable gap at the inferior border of the patella [47].

Diagnosis

Before completion of secondary ossification, the patella is surrounded by a layer of protective cartilage. Therefore, most patellar sleeve fractures involving mainly cartilage lack radiographic findings of an osseous fragment. Patella alta may be present on lateral radiographs. If radiographic findings are unclear, other imaging modalities can be pursued. Sagittal MRI can characterize discontinuity between the patellar ligament and the patella and avulsed articular cartilage that may not be visible on plain radiographs [51]. This is important to distinguish from the bony avulsion at the inferior patellar insertion seen in SLJ [52].

Treatment

Treatment depends on the degree of displacement. With minimal displacement (up to 2mm), initial treatment consists of cast immobilization [53]. If greater than 2mm of displacement, surgical management with open reduction and internal fixation are pursued with to restore anatomical reduction of the articular surface with tension band wiring, trans-osseous sutures and/or intra-osseous anchor sutures. When the osteochondral fragment is small and rigid fixation cannot be attained, intra-osseous and trans-osseous anchor sutures can be considered [54].

Prognosis

Potential complications include wound infection, decreased knee flexion due to immobilization, ischemic necrosis of the patella, and muscle wasting [53, 54]. The blood supply to the patella comes from the anterior surface of the distal pole, with essentially no supply from the medial margins. Therefore, injury to the anterior and distal pole may lead to avascular necrosis of the proximal pole [53].

Conclusion

Knee injuries affect a significant proportion of youth athletes. These injuries place athletes at higher risk of chronic pain and potentially osteoarthritis. We have reviewed common overuse and traumatic knee injuries and differentiating factors between the adult population to improve and expedite the diagnosis, treatment, and prognosis for youth athletes with knee injuries.

Declarations

Conflict of Interest

Anne Kuwabara, Emily Kraus and Michael Fredericson declare that they have no conflict of interest.

Human and Animal Rights and Informed Consent

This article does not contain any studies with human or animal subjects performed by any of the authors.

Footnotes

This article is part of the Topical Collection on Non-Operative Management of Anterior Knee Pain

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Anne Kuwabara, Email: amk1@stanford.edu.

Emily Kraus, Email: ekraus@stanford.edu.

Michael Fredericson, Email: mfred2@stanford.edu.

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