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Competitive Sports

Overuse Knee Pain in the Pediatric and Adolescent Athlete

Sweeney, Emily MD1,2; Rodenberg, Richard MD3,4; MacDonald, James MD, MPH, FACSM3,4

Author Information
Current Sports Medicine Reports: November 2020 - Volume 19 - Issue 11 - p 479-485
doi: 10.1249/JSR.0000000000000773
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Abstract

Introduction

Nearly 60 million children and adolescents participate in organized sports each year in the United States (1), and approximately half of all young athletes will have knee pain annually (2). Furthermore, there are an estimated 2.5 million sport-related knee injuries in adolescents each year, and 60% of sports-related surgeries in high school athletes involve the knee (3–5).

Approximately half of all knee injuries are because of overuse etiologies (6,7). Overuse knee injuries occur because of repetitive loading of the joint tissue with insufficient rest in between episodes of impact. In childhood and early adolescence, these injuries include apophyseal and physeal stress injuries. Overuse knee pain also is more common in children who specialize early in their sport of choice: in a large study of youth athletes, those who were highly specialized had 2.25 greater odds of having some form of overuse injury compared with nonspecialized athletes, and the most commonly injured body part in this study was the knee (8). Early specialization in basketball, volleyball, and soccer increases the risk of some overuse conditions, including patellofemoral syndrome (PFPS), Osgood-Schlatter disease (OSD), and Sinding-Larsen-Johansson (SLJ) syndrome (9). Because of the high prevalence of these overuse conditions in young athletes, it is important that providers understand the typical presentation and management. The history, examination, workup, and treatment plans for overuse knee pain in pediatric and adolescent athletes are reviewed in this article, and specific conditions are discussed in detail.

Differential Diagnosis, History, and Physical Examination

When obtaining the history for overuse knee pain, providers should ask the typical pain-related questions, including time of onset, location, severity, and quality of pain, aggravating, and alleviating factors, as well as questions regarding sudden increases in activity intensity and volume. Many patients with overuse pain also will report a recent growth spurt (often 3 in. to 4 in. in a year) (10). Patients should be questioned about systemic “red flag” symptoms, such as fevers, unintentional weight loss, and night pain, because malignancies and rheumatologic conditions, such as leukemia, osteosarcoma, Ewing sarcoma, synovial tumors, and juvenile idiopathic arthritis, can cause knee pain (10). These conditions are rare but cannot be missed. Causes of knee pain of insidious onset that are not due to a musculoskeletal condition are listed in the Table. Determining the specific location of the pain may help narrow down the etiology of overuse knee pain (11), so a good working knowledge of anatomy is necessary (Fig. 1). For example, anterior knee pain may be because of apophysitis, PFPS, or patellar or quadriceps tendinopathy. Medial knee pain is not uncommon because of an osteochondral defect or pes anserine bursitis, while lateral knee pain may be because of iliotibial (IT) band syndrome or, in children typically 10 years or younger, a discoid meniscus. Posterior knee pain typically is due to a Baker's cyst, hamstring tendinopathy, or popliteus injury.

Table - Other etiologies of insidious onset knee pain.
Diagnosis Defining Characteristics Common History and Examination Findings Diagnostic Tools Treatment
Osteoid osteoma Bone-producing tumors with a central nidus Painful, especially at night. Classically responds well to NSAIDs X-rays and CT (imaging modality of choice) show round lucency with surrounding sclerosis (25,46) NSAIDs; referral for surgical resection or radiofrequency ablation if not responsive to NSAIDs (25,46)
Osteochondroma Cartilage-capped bone spurs that are susceptible to fractures (25) May be incidental finding or may have tender, firm bump (25) X-rays show bony mass at metaphysis pointing away from physis Yearly surveillance if nonpainful; excision if painful
Bone cysts (UBC, ABC) UBC — benign tumor in the metaphysis of long bones; may cause local destruction if adjacent to the physis (17)
ABC — vascular lesion that causes bony destruction and may recur (25)
May be an incidental finding but can have a pathologic fracture due to minor trauma with pain and swelling (17) X-rays show lytic lesion that are central (UBC) or eccentrically located (ABC) with “eggshell” sclerotic rim of UBCs; CT or MRI may be helpful for differentiating cysts from other lesions (17) Observation for small asymptomatic UBCs (17); curettage and bone grafting, cryotherapy, sclerotherapy, or and radionuclide ablation for ABCs and large UBCs (17)
NOF AKA “Fibrous cortical defect” where bone is replaced with fibrous connective tissue (25) Incidental finding but may be a site of pathologic fracture (25) Well-defined lesion with sclerotic, scalloped borders on X-rays (25) No treatment necessary unless associated with fracture
Osteosarcoma Most common primary malignant bony tumor (47) Pain and swelling at distal femur or proximal tibia (most common sites) (47) “sun burst” pattern of calcified blood vessels on X-rays (11). MRI with/without contrast indicated to confirm diagnosis Chemotherapy and surgical removal (47)
Ewing sarcoma Second most common primary malignant bony tumor, typically after age 5 (48) Most are in the diaphysis or metaphysis of long bones; cause localized pain, swelling and sometimes a mass, pathologic fracture, or systemic symptoms (48) Periosteal reaction, “onion skinning” on X-rays (11) or may have Codman triangle due to periosteal reaction (48) Chemotherapy, radiation and/or surgical removal (48)
Septic arthritis Knee is second most commonly infected joint (after hip). Most commonly due to Staphylococcus aureus (49) Warm, swollen joint with decreased ROM +/− fever (49) Elevated WBC, CRP and ESR; US or MRI shows joint effusion (49) IV antibiotics and surgical drainage typically needed (49)
Osteomyelitis Staphylococcus aureus most common etiologic agent (50) Typically affects long bones in children under age 5 yr; pain, fever (50) Elevated CRP and ESR with normal or elevated WBC count; blood cultures necessary but may be normal; X-rays may be normal; MRI typically indicated (50) Appropriate IV then PO antibiotics for 3 wk with or without surgery depending on response (50)
ABC, aneurysmal bone cyst; UBC, unicameral bone cyst.

Figure 1
Figure 1:
Anatomical landmarks on a sagittal knee MRI. (A) Distal femoral physis, (B) femoral metaphysis, (C) femoral epiphysis, (D) proximal tibial physis, (E) tibial tubercle apophysis, (F) patella, (G) patellar tendon, (H) quadriceps tendon.

The physical examination for patients with knee pain should start with vital signs, including BMI, because overweight and obese children are more at risk for having knee pain (12). Fever, swelling, warmth, limited motion, and redness should clue the physician to evaluate for infections, such as septic arthritis and osteomyelitis as well as rheumatologic conditions (2,11). It is always important to assess gait in youth presenting with a complaint of knee pain. The clinician will be looking for a limp or potentially assessing for a limb length discrepancy. It is important to examine the hip as well as the knee because pathology at the hip can present as knee pain (11). At the very least, an evaluation of hip range of motion — to assess symmetry between the affected side and the unaffected contralateral side — should be done. Relevant hip pathologies to consider are slipped capital femoral epiphysis, Legg-Calve-Perthes, acute fractures of the proximal femur, and femoral neck stress fractures (10). Many athletes with PFPS and apophysitis will have poor mechanics with movements, such as squats and lunges, and may have weakness or lack of flexibility on examination (10). Measuring the popliteal angle, to assess hamstring flexibility, and checking Ely's test, to assess quadriceps flexibility, should be considered.

When assessing the knee joint proper, it is again necessary for clinicians to have a good working knowledge of anatomy, because they will be correlating points of tenderness on palpation with relevant anatomic landmarks. An assessment for an effusion is important, because this finding is unlikely to be present in more frequently encountered conditions, such as OSD, SLJ, and PFPS, but may be seen in the setting of rheumatologic or infectious problems or in osteochondritis dissecans (OCD) or synovial tumors. Range of motion and strength testing should be performed and compared with the unaffected side. Appropriate special examination maneuvers of the knee joint also should be performed as indicated. Individual examinations that pertain to specific conditions are described later in this review.

Workup

Although not always required, imaging may be helpful in determining the cause of knee pain in young athletes. X-rays should be obtained if the patient has an effusion, limited motion, bony pain to palpation, inability to bear weight, mechanical symptoms, such as “locking,” pain not improving with activity modification, or if there are “red flag” type symptoms mentioned previously (2,11). Standard two-view X-rays include anteroposterior (AP) and lateral views. Sunrise or merchant views can provide information regarding patellar alignment (13). Tunnel or notch views are helpful in evaluating for OCD or loose body and may pick up a lesion not seen on AP or lateral views; but care should be taken when evaluating X-rays in younger children to differentiate normal ossification development versus osteochondritis dissecans at the distal femur (14). If radiographs suggest OCD, a magnetic resonance imaging (MRI) should be obtained to evaluate for stability of the lesion (10,15). Nonossifying fibromas (NOF) and bone cysts may be found incidentally on X-rays. Benign and typically not causing pain, these conditions may uncommonly become weak areas of bone that are prone to acute and stress fractures (16,17). Providers who are suspicious for stress fractures with or without an NOF may need to obtain an MRI because the false-negative rate of X-rays for this condition is as high as 85% (16). If an infection or malignancy is suspected, an MRI with and without contrast is indicated (11).

Laboratory studies and synovial fluid analysis also may be necessary based on history and physical examination findings. Specific laboratories may include complete blood cell count with differential, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), antinuclear antibody with reflexive titers, Lyme titers, and gonococcal cultures (11).

Treatment

Treatments are varied and will depend on the specific diagnosis; however, many overuse injuries in children respond well to conservative measures. For many benign conditions, such as PFPS and apophysitis, stretching, activity modification, and physical therapy are appropriate. Bracing has not been found to be beneficial in PFPS (18) but patients with other conditions, such as OSD and SLJ, often improve with a patellar tendon strap (19). Lack of improvement with first line treatment suggests the need for further evaluation and treatment options, such as for unstable OCD, stress fractures, infections, or malignancies. Further workup may include advanced imaging, a discussion regarding compliance with treatment recommendations, immobilization (20), or possibly a referral to a sports medicine specialist or orthopedic surgeon.

Prevention

Prevention is vitally important when dealing with overuse injuries, as many can be avoided. Sport specialization, intensive year-round training to exclusion of other sports (21), and training load are associated with overuse injuries. A simple rule of thumb for youth and middle school athletes is to limit the number of hours in organized sport per week to less than a youth's age in years (8). For older adolescents, the authors suggest using evolving research on training loads. Recent work looking at the acute/chronic load ratio (e.g., the training load of the previous week/the 4-wk rolling average of load) has demonstrated that in many sports injury risk is low (<10%) if the acute/chronic load ratio is within the range of 0.8 to 1.3 (22). Pediatricians can guide parents and young athletes with recommendations for appropriate training load and scheduled rest periods for a month or more during the course of the year.

Specific Conditions

Apophysitis

Apophysitis of the knee occurs at distal pole of the patella or at the tibial tubercle (Fig. 2). This occurs because of repetitive traction from the patellar tendon (23). When it occurs at the inferior patella, it is called SLJ and at the tibial tubercle it is referred to as Osgood-Schlatter's disease (OSD). Sinding-Larsen-Johansson typically occurs in 10- to 13-year-old athletes, while OSD occurs in slightly older preteens and teens, usually aged 10 to 15 years (10,23). Athletes will have tenderness over the apophysis and may have slight focal swelling (24). X-rays, although not required for diagnosis, may appear normal or show fragmentation at the apophysis (10). Fortunately, apophysitis is a self-limited condition. Activity modification, stretching, ice, nonsteroidal anti-inflammatory drugs (NSAIDs), and bracing with a patellar tendon strap have all been shown to be useful in decreasing symptoms (2,10,19,25).

Figure 2
Figure 2:
Lateral knee X-rays in patients with apophysitis. (A) SLJ and (B) Osgood-Schlatter's.

Osteochondritis Dissecans

Although the exact etiology of OCD is poorly understood (15), the condition results in injury of the subchondral bone and articular cartilage (25) (Fig. 3). Some authors maintain that repetitive microtrauma plays a role in the development of this condition, noting that it is found more frequently in children who are active athletically or playing organized sports (26). In the knee, this condition most commonly occurs at the lateral aspect of the medial femoral condyle, but may occur on the lateral femoral condyle, patella, or tibial plateau as well (10) The incidence of OCD is approximately four times higher in boys than girls (27). Patients typically present with insidious onset of vague knee pain and/or catching and locking of the knee, but the examination may appear quite benign (15). Occasionally, an effusion will be present (25). Wilson's sign may be positive if the lesion is over the medial femoral condyle. This test is performed by passively placing the lower leg in internal rotation, then extending the knee from 90 degrees to 30 degrees (10). It should be noted, however, that a previous study found that only 25% of patients with radiographically confirmed OCD lesions had a positive Wilson's test (28). Radiographs, including AP, lateral, tunnel or notch views, and sunrise or merchant views will often show the lesion (24); however, an MRI without contrast is typically necessary to evaluate the stability of the lesion (10,15). Stable lesions in skeletally immature patients usually resolve with immobilization and protected weight-bearing. Progressive return to activity typically requires 12 or more weeks of bracing and activity modification (15). Skeletally mature patients with OCD and patients with unstable lesions that have loose bodies or fluid completely surrounding the fragment on MRI are less likely to heal with conservative management (15). Fixation with screws, excision of loose bodies, and various salvage procedures are often necessary for unstable lesions (15).

Figure 3
Figure 3:
OCD on the medial femoral condyle on AP (A) and tunnel (B) X-ray views.

Patellofemoral Pain Syndrome

A number of factors contribute to the development of PFPS (29). With a prevalence of 7% to 20% in adolescence (9) it is a very common condition in young athletes, especially those who have had a recent growth spurt (29). Patients present with anterior knee pain that is worse with activities such as running and squatting or with prolonged sitting (theater sign) (10). They also may report popping, catching, or a sensation of their knee giving way. On examination, the athlete may have poor quadriceps or hamstring flexibility, tenderness along the patella, a positive patellar grind test, weak hip abductors and external rotators, pain, and/or poor mechanics on a single leg squat (10). Passive range of motion of the knee may demonstrate audible or palpable crepitus. X-rays which often include sunrise or merchant views are typically normal but may show abnormalities, such as patellar tilt, patella alta, or patella baja (10). Management typically involves activity modification, ice, NSAIDs, and physical therapy (18).

Hoffa's Fat Pad Impingement

Similarly, patellar maltracking during physical activity can lead to irritation of the Hoffa's fat pad in very active young athletes. These patients have pain over the infrapatellar fat pad (14). X-rays are typically normal, but an MRI, if obtained, may show edema in Hoffa's fat pad (30). Physical therapy and activity modification are first line treatment options; however, a brief period of immobilization, corticosteroid injections, and arthroscopic resection of the fat pad also have been used in recalcitrant cases (30).

Symptomatic Bipartite Patella

A bipartite patella is typically an incidental finding due to development of two ossification centers; however, patients with this developmental variant may have insidious onset of anterior knee pain. Radiographs are diagnostic, and rarely is advanced imaging necessary (10). A brief period of immobilization with 3 wk to 4 wk of rest typically results in resolution of pain. Surgery may be necessary if patients have failed 6 months of conservative management (10).

Iliotibial Band Syndrome

Inflammation can occur in the distal IT band as it passes over the lateral femoral condyle and inserts on Gerdy's tubercle (10). This can lead to lateral knee pain, often with running or going downstairs, and athletes may report a popping or clicking sensation on the lateral side of the knee. Patients have tenderness over the lateral femoral condyle and typically have positive Ober's and Noble's tests (10). The IT band syndrome is a clinical diagnosis and rarely requires imaging. Activity modification, ice, NSAIDs, and stretching are first-line treatments (10). A steroid injection for recalcitrant cases also can be useful; however, this is done less frequently in the pediatric and adolescent population (31).

Stress Fractures

Stress fractures of the patella, distal femur, and proximal tibia are uncommon. There are only 22 case reports of patellar stress fractures in the literature (32). Despite this, providers should consider stress fracture in their differential for very active children and adolescents with focal tenderness, swelling, and limping (33), most especially if the knee pain is not localizable to the actual joint space. Stress fractures are more likely to occur near the knee if there is an NOF present (16). Because X-rays may initially be normal, an MRI should be performed if there is a high index of suspicion (16), especially in athletes with components of the female athlete triad or those with relative energy deficiency in sport (RED-S) (34–36). Young athletes with a stress fracture should be treated with immobilization, protected weight-bearing, and a cautious progression back to sport under a multidisciplinary team including physical therapy once bony healing has occurred (36). Any underlying triad or RED-S issues also should be treated and bone health evaluation (i.e., DEXA scan, laboratory tests) should be considered for assessing the possibility of low bone mineral density.

Bursitis

Although more commonly seen in adult patients, adolescent athletes may develop pes anserine or prepatellar bursitis. Bursitis is typically due to acute or repetitive microtrauma, but occasionally occurs because of infection or inflammatory conditions. Patients present with anterior knee pain, swelling, and point tenderness (25). X-rays are normal and, though rarely needed, an MRI may confirm the diagnosis by showing edema in the bursa. Activity modification, compression, NSAIDs, and physical therapy typically lead to good outcomes (37).

Tendinopathies

Although younger athletes whose growth plates are still open typically get apophysitis at the knee, older, skeletally mature adolescents in running and jumping sports tend to be prone to true tendinopathies (38). This can affect the quadriceps, patella, hamstring, and less often, the popliteus tendons. It is more common in athletes who do repetitive movements like cross-country and soccer (10). Patients will complain of activity-related pain at the site of the tendon. Radiographs are normal, but ultrasound may be helpful to confirm the diagnosis (38). Like those with apophysitis, athletes typically respond well to activity modification, physical therapy with eccentric strengthening exercises, NSAIDs, and stretching (10).

Plica Syndrome

Plica are thin, synovial folds that are typically asymptomatic (39). Patients with an inflamed medial plica may present, however, with pain, popping, and catching of the knee (2). They also may have pain when actively extending the knee from 90 degrees of flexion which indicates a positive active knee extension test (10). Imaging is often not necessary, but inflammation and thickening of the plica may be seen on ultrasound or MRI (2,40). Relative rest, NSAIDs, and physical therapy are the first line of treatment (2); however, a steroid injection and excision are occasionally necessary in those who fail conservative management (10,39).

Discoid Meniscus

Though not a true overuse injury, a discoid meniscus in a child can present with insidious onset pain and mechanical symptoms and deserves special attention in this review. A discoid meniscus is due to a congenital variant that leads to a thickened, abnormally shaped meniscus which also is abnormal in histology and ultrastructure: the discoid meniscus is notable for having decreased collagen fibers and a loss of normal fiber orientation, as well as abnormal vascularity (41). The consequence of these changes is that the discoid meniscus is more prone to tearing than a normal meniscus (42). Approximately 3% to 5% of the population have a discoid meniscus (42,43), and patients with a discoid meniscus typically present at age 10 years or younger (44). Typically, it is the lateral meniscus that is discoid (43) and 15% to 25% of patients with a discoid meniscus have the condition in both knees (45). Patients may present with intermittent snapping and pain in the knee as well as lack of full extension (45). Although some children will present with an acute injury that leads to a tear of the meniscus, others may not be able to recall an acute trauma resulting in pain. 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 spine (42,43,45). Magnetic resonance imaging is needed to confirm the diagnosis and to evaluate for any tears (43,45). An asymptomatic discoid meniscus requires no further intervention (42), but if the patient has a tear or is symptomatic, saucerization or partial meniscectomy is indicated (41,43,45).

Conclusion

Overuse knee pain is common in pediatric and adolescent athletes. This presenting complaint is especially seen in those who specialize in one sport at a young age, play sports year-round, or who exceed recommended training loads. A number of overuse syndromes discussed in this review can lead to knee pain in young athletes. Because overuse knee pain typically presents with an insidious onset and no overt trauma, it is important that treating clinicians should consider other, albeit rare, causes of knee pain — including rheumatological pathologies and malignancies — when evaluating young athletes. Sports medicine practitioners should be familiar with the common musculoskeletal etiologies of knee pain in young athletes discussed in this review. Since most conditions are self-limited and respond well to conservative measures, such as rest, physical therapy, and bracing, the vast majority of these conditions will be managed well by most practitioners without need for referral.

The authors declare no conflict of interest and do not have any financial disclosures.

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