Knee Injuries in the Young Athlete

Educational Objectives

The goal of this program is to improve the management of knee injuries in children. After hearing and assimilating this program, the clinician will be better able to:

1. Choose appropriate diagnostic tests for children with knee injuries based on the mechanism and presentation of the injury.

2. Recognize common and commonly missed knee injuries.

3. Distinguish patients for whom nonoperative management of knee injuries is appropriate from those who require urgent or emergent orthopedic consultation.

Summary

Knee injuries: participation of girls in sports increasing; biomechanical alignment in girls predisposes them to greater risk for injury, compared with boys; physical examination (PE) informs about severity and urgency; large amount of swelling indicates severe injury; growth plates remain open in girls until age 14 yr and in boys until 16 yr; missing injury may have devastating consequences

Salter-Harris system: used to classify fractures, identify part of growth plate involved, and determine whether epiphysis and joint involved; higher type number indicates worse complications and greater need for rapid evaluation; growth arrest primary complication when injury not treated; type 1 — often benign; common in distal radius; tender at growth plate; deformity not always present; pain may occur with varus or valgus stress (suspicious for injury of medial collateral ligament [MCL] or lateral collateral ligament [LCL]); obtain x-ray of knee with 2 views; evaluate peroneal nerve and popliteal artery (check compartments, test pulses) as injury may result in complete transection of artery; if x-ray appears stable, splint and refer for casting in ≈2 days; emergent consultation required for any signs of displacement; injury of popliteal artery may evolve ≤24 hr (admit, monitor overnight); type 2 — usually involves fragment of metaphysis; caused by high-energy injury; fracture easily visualized; emergent orthopedics consultation required; types 3 and 4 — growth plate, joint, and cartilage involved; may cause long-term advanced arthritis if not reduced and fixed; may appear benign on x-ray (computed tomography may show more extensive displacement); obtain urgent consultation

Fracture of tibial spine: children ≥5 yr of age may tear anterior cruciate ligament (ACL) and not incur this injury; ACL attaches to tibial spine (if displaced, ACL does not function); classic history involves child falling off bicycle onto flexed, rotated knee; may also occur on trampoline or through other sports; mechanism similar to ACL injury (twisting, flexed knee); evaluate lateral x-ray (loose piece of bone in center of joint); refer quickly; some injuries reduced with casting alone, but many require prompt surgical reduction and fixation so rehabilitation may begin; if not properly reduced, may result in long-term instability with meniscal tears, chondral damage, and arthritis; previously, pediatric tibial spine fractures believed to result in tearing of ACL in adulthood (after closure of growth plates); injuries now known to exist on continuum (children with fracture of tibial spine at increased risk for subsequent ACL tear; ACL likely stretched and compromised at time of fracture); goal of surgical treatment to introduce maximal tension in ACL

ACL tear: likely if preteen or teenage athlete presents with large, swollen knee; PE difficult when swelling significant; magnetic resonance imaging (MRI) helps distinguish partial from complete tear (treatment different); start rehabilitation quickly; classic history — running athlete falls while trying to kick ball (noncontact plant-twist rotation); or, patient may describe knee buckling inward on landing from jump; dramatic swelling occurs ≤2 hr of injury (good vascularity of ACL in children results in large hemarthrosis); evaluation — diagnostic physical finding produced by Lachman test; pivot-shift test too painful unless injury chronic (perform only with patient under anesthesia); risk factors — participation in year-round sports; high intensity of sport; high number of coaches; overtraining; incidence 8-fold greater in girls than boys; Lachman test — hold knee flexed at ≈30°; keep femur stable and pull tibia forward; ACL should stretch and tighten; test positive if stretching continues; grading system not reliable; x-ray — rule out fracture; evaluate growth plates and skeletal maturity; MRI — if concerned about ligament injury or damage to cartilage

Age of patient: surgical treatment depends on skeletal maturation; assess parental height, Tanner stage, and timing of peak growth spurt (ask girls about menarche and boys about shaving); avoiding injury to growth plate during surgery important; distal femur and proximal tibia provide majority of growth of lower extremity (avoid shortening and angular deformity)

Treatment: with new technology, rate of iatrogenic physeal (growth plate) injury low; nonoperative management no longer considered efficacious, but treatment not emergent if no other injury (eg, meniscus, cartilage) present (rest may help in such cases); getting children to avoid activities difficult; bracing ineffective against problematic rotation; physical therapy helps patient to recover from initial injury and prepare for surgery; goal to reconstruct ACL before other damage occurs (ie, injury to cartilage and meniscus) and reduce risk for later arthritis; weight of patient and length of surgical delay affect rate of meniscal tears and ability to treat; young children (5-9 yr) should see pediatric sports medicine specialist

Prevention: training programs available for athletes

MCL and LCL tears: may be injured at same time as ACL or independently; MCL — usually injured by valgus force (foot going toward outside), similar to ACL (foot plants and shifts, with knee going inward); sits outside capsule of joint (large effusion indicates injury other than MCL alone); suspect MCL with small amount of swelling on medial knee or focal bruising; treat with bracing; >95% heal without surgery, even with high-grade injury; LCL — injured when, eg, athlete tackled; foot planted and knee goes toward outside (varus force); patient may have associated injury to posterior collateral ligament (isolated LCL injury less common than isolated MCL injury); no large effusion seen with isolated LCL injury; MRI — obtain if concerned about either injury with swollen knee

Patellar instability and dislocation (PD): history often similar to ligament tears (twisting, popping in and out); always rule out PD if ACL tear suspected, and vice versa (presentation similar but treatment differs); incidence higher in preteen and teenage years; incidence high in girls (valgus of knees); patella has thick articular cartilage (damage difficult to treat); not completely ossified until middle high-school years; injury may involve articular and ossifying cartilage; patella most unstable in extension (patient may not tolerate lying on bed); PD occurs when knee in slight flexion and patella collides with distal femur; rehabilitation focuses on stabilizing muscles (eg, vastus medialis obliquus); surgery focuses on static stabilizers (eg, medial patellofemoral ligament [MPFL]); MPFL attaches to proximal third of patella and medial femur, providing restraint from 0° to 30° (when trochlea not stabilizing patella); MPFL torn with every PD (MRI not needed for diagnosis but assesses other damage and reason for dislocation); PE — moving patella causes pain and fear (apprehension), unlike ACL tear; check x-ray to rule out fracture of osteochondral surface (surgery indicated within 2 wk) with initial PD; obtain MRI only if x-ray concerning for loose body; with initial PD, rehabilitation acceptable if loose body not present; cartilage lesions often seen in “gutters” on side of knee on axial images (often missed by radiologist)

Treatment: nonoperative — mainstay; brace provides comfort and enables walking; straight immobilizer used for 7 to 10 days, after which transition to patella-stabilizing brace important (encourages movement); physical therapy allows more rapid return to sports and baseline activities; recovery may take 2 to 3 mo; recurrence — incidence ≤80% in high-school athletes; discuss risk factors with initial PD; discuss surgical treatment with second PD (third PD almost inevitable); operative management — technique determined by results of MRI; goal to return athlete to sports

MRI: obtain if risk for recurrence high (eg, 3-season athlete, female, young, hypermobile)

Patellar sleeve fracture: commonly missed; difficult to assess on x-ray; before complete ossification, patella surrounded by cartilaginous ring; ossified and chondral portion may separate; if inferior pole of patella ossified, ensure patient able to perform straight-leg raise (inability raises suspicion for fracture); surgery indicated within 7 days (treatment difficult with further delay); MRI helps to visualize cartilaginous ring and confirms diagnosis

Fracture of tibial tubercle: as tibial apophysis ossifies, avulsion may occur; patient unable to perform straight-leg raise; artery runs close to fracture bed; swelling in knee may continue into anterior compartment, causing compartment syndrome; identify and treat early

Tibial sleeve fracture: avulsion of patellar tendon from tibial tubercle (bone not involved); classic history 12- to 14-yr-old boy performing squat, dive, or jump; growth plate and tendon attachment to plate become stronger at this age; patient unable to perform straight-leg raise; commonly missed (no findings on x-ray); knee swelling significant

Meniscus tears: incidence increasing dramatically, especially with ACL tear; acute injury more common in medial meniscus; if young patient has large hemarthrosis, tear of discoid lateral meniscus likely; older children more likely to tear medial side; cartilage acts as “shock absorber” (C-shaped on medial side, O-shaped on lateral side); injury commonly involves twist, pop, and swelling; unlike ACL tear and PD, blood flow not optimal and swelling occurs over 1 to 2 days (subacute hemarthrosis); PE — McMurray test main diagnostic tool; with patient flexing knee, rotate tibia internally and externally, compressing meniscus between femur and tibia; if pain present with terminal extension or flexion, obtain MRI (greater blood supply to meniscus in children increases likelihood of false-positive reading)

“Snapping knee”: hypermobile discoid lateral meniscus (“Oreo sign” may be read as complex tear by radiologists); child reports painful snapping with movement and bending of knee; congenital condition, usually present in both knees; treatment indicated only if causing problems; occasionally occurs in medial meniscus; prevalence unknown (only symptomatic cases detected); entire collagen structure of meniscus abnormal (too large; vascularity poor); distal femur catches on meniscus, resulting in tear; tear may occur with benign movement; rate of damage to cartilage high; MRI required for diagnosis; refer quickly to orthopedist

Nonossifying fibroma: common in preteens and teenagers; sometimes termed ossifying fibroma; benign condition; occurs as patient reaches skeletal maturity; part of growth plate believed to detach and be “left behind” as bone lengthens; common in distal femur and proximal tibia; orthopedic follow-up not required unless extremely large; repeat x-rays in 6 mo; resolves without intervention

Osteochondritis dissecans (OCD): commonly encountered but little understood condition; has genetic component; high-impact activities believed to be involved; in year-round athletes, bone cannot absorb load burden and piece of bone dies; damage to cartilage of greater concern than necrosis; most common location lateral aspect of medial femoral condyle; may occur on lateral side and in patellofemoral joint (order MRI in child with chronic anterior knee pain); visible on x-ray except in earliest stage; if x-ray positive, order MRI for staging and treatment determination; classification system determines urgency of referral (rapid for class 5 [loose body]); treatment — nonoperative management often possible if patient skeletally immature (better healing potential in young patients), lesion of low grade (1-3) with bone edema, and symptoms minimal; long-term complications may occur; stop all activities for ≥3 mo; use touch-down weight bearing (crutches) for symptomatic patients; acute surgery necessary if patient skeletally mature, lesion of more advanced stage (longer duration), or nonoperative management fails to relieve pain; many surgical options available (choice controversial; experts disagree)

Readings

Adams AJ et al: Tibial spine fractures in children: evaluation, management, and future directions. J Knee Surg 2018 May;31(5):374-81; Bauer KL et al: Osteochondral injuries of the knee in pediatric patients. J Knee Surg 2018 May;31(5):382-91; Cepela DJ et al: Classifications in brief: Salter-Harris classification of pediatric physeal fractures. Clin Orthop Rel Res 2016 Nov;474(11):2531-7; Cruz AI Jr et al: Pediatric knee osteochondritis dissecans lesions. Orthop Clin North Am 2016 Oct;47(4):763-75; Damrow DS et al: Patellar sleeve fracture with ossification of the patellar tendon. Orthopedics 2017 Mar 1;40(2): e357-e359. doi: 10.3928/01477447-20161026-02; Kosher MS et al: Treatment of posterior cruciate ligament injuries in pediatric and adolescent patients. J Pediatr Orthop 2012 Sep;32(6):553-60; Kramer DE et al: Collateral ligament knee injuries in pediatric and adolescent athletes. J Pediatr Orthop 2017 Dec 8. doi: 10.1097/BPO.0000000000001112; LaBella CR et al; Council on Sports Medicine and Fitness, and Section on Orthopaedics: Anterior cruciate ligament injuries: diagnosis, treatment, and prevention. Pediatrics 2014 May;133(5): e1437-50. doi: 10.1542/peds.2014-0623; Popkin CA et al: Patellar instability in the skeletally immature. Curr Rev Musculoskelet Med 2018 Jun;11(2):172-81; Pretell-Mazzini J et al: Outcomes and complications of tibial tubercle fractures in pediatric patients: a systematic review of the literature. J Pediatr Orthop 2016 Jul-Aug;36(5):440-6; Sankar WN et al: Combined anterior cruciate ligament and medial collateral ligament injuries in adolescents. J Pediatr Orthop 2006 Nov-Dec;26(6):733-6; Seitlinger G et al: What is the chance that a patella dislocation will happen a second time: update on the natural history of a first time patella dislocation in the adolescent. Curr Opin Pediatr 2018 Feb;30(1):65-70; Shieh A et al: Meniscus tear patterns in relation to skeletal immaturity: children versus adolescents. Am J Sports Med 2013 Dec;41(12):2779-83.

Disclosures

For this program, members of the faculty and the planning committee reported nothing to disclose.

Acknowledgements

Dr. Beck was recorded at the 75th Annual Brenneman Lectures, presented by the Los Angeles Pediatric Society, and held September 21-23, 2018, in Anaheim, CA. For information about upcoming CME conferences from the Los Angeles Pediatric Society, please visit www.lapedsoc.org. The Audio Digest Foundation thanks the speakers and the sponsors for their cooperation in the production of this program.

CME/CE INFO

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