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BioMed CentralPediatric Rheumatology

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Open AcceReviewReview for the generalist: evaluation of anterior knee painKristin M Houghton*
Address: Division of Rheumatology, British Columbia's Children's Hospital, K4-119 Ambulatory CareBuilding, 4480 Oak Street, Vancouver British Columbia, Canada V6H 3V4 and Allan McGavin Sports Medicine Centre, University of British Columbia, 3055 Wesbrook Mall, Vancouver British Columbia, V6T 1Z3, Canada

Email: Kristin M Houghton* - [email protected]

* Corresponding author

AbstractAnterior knee pain is common in children and adolescents. Evaluation and management ischallenging and requires a thorough history and physical exam, and understanding of the pediatricskeleton. This article will review common causes of chronic anterior knee pain in the pediatricpopulation with a focus on patellofemoral pain.

BackgroundAnterior knee pain (see Figure 1) is one of the most com-mon musculoskeletal complaints seen in the pediatricpopulation. A fairly extensive differential diagnosis existsas anterior knee pain is a fairly nonspecific phenomenon.A thorough history and physical examination with atten-tion to anatomic location of the pain, inciting factors,relationship of associated symptoms as well as a generalassessment of growth and development will aid in theevaluation and treatment of this disorder. An awareness oftypical injury patterns can aid the physician in narrowingthe differential diagnosis. Identification of worrisomesigns and symptoms will also help in defining which casesmay require further evaluation. All pediatric patients pre-senting with knee pain require evaluation for ipsilateralhip and lumbar spine disorders. This article will reviewcommon causes of chronic anterior knee pain in the pedi-atric population with a focus on patellofemoral pain. It isnot meant to be an exhaustive review and will not reviewacute traumatic knee injuries. Lateral, medial or posteriorknee pain will be covered in a subsequent article.

Clinical historyThe clinical history should include a thorough descriptionof the pain characteristics (location, character, onset,duration, change with activity or rest, aggravating andalleviating factors, night pain); trauma (acute macro-trauma, repetitive microtrauma, recent/remote); mechan-ical symptoms (locking or extension block, instability,worse during or after activity); inflammatory symptoms(morning stiffness, swelling); effects of previous treat-ments and the current level of function of the child.Patients with overuse anterior knee pain may report a sen-sation of giving way or instability. This sensation is usu-ally a pseudo-giving way due to what is coined the"quadriceps inhibitory reflex" or a neuromuscular inhibi-tion that occurs secondary to pain, muscle weakness,patellar instability or joint instability. It is important tonote that true instability is suggestive of internal derange-ment of the knee most commonly associated with ante-rior cruciate ligament (ACL) tears or meniscal injury [1].

A history of previous injury or knee surgery, chronicinflammatory joint disease or bleeding diathesis, is signif-icant, especially if knee swelling is present.

Published: 4 May 2007

Pediatric Rheumatology 2007, 5:8 doi:10.1186/1546-0096-5-8

Received: 28 December 2006Accepted: 4 May 2007

This article is available from: http://www.ped-rheum.com/content/5/1/8

© 2007 Houghton; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Physical examinationThe basic anatomy of the knee is shown in Figure 2. Theknee is the largest joint in the body and is comprised ofthe patellofemoral joint, medial tibiofemoral joint, lateraltibiofemoral joint and superior tibiofibular joint. It is amodified hinge joint with primary motion in the sagittalplane (flexion – extension). During the clinical assess-ment the physician should try and reproduce the patient'sknee pain through palpation as well as biomechanicalevaluation. Biomechanical examination is important indetermining any potential predisposing or contributingfactors. This should include an assessment for genetic pre-disposing factors such as excessive stiffness, loose-jointed-ness, and/or poor muscle tone. Functional biomechanicsshould be assessed by evaluation of gait, and maneuverssuch as jumping, hopping (single and double-leg) andsquatting. Knee swelling is unusual in anterior knee painand generally implies intra-articular pathology, synovitisor loose body. The contralateral knee and ipsilateral hipshould always be examined [2,3].

Physical examination in patients with anterior knee pain1. ObservationStanding [pelvis heights, lower limb alignment, "Q"quadriceps angle (formed by the intersection of the linedrawn from the anterior superior iliac spine to the centreof the patella and the line drawn from the centre of thepatella to the tibial tuberosity. Normal Q angles are 8 to12° for males and 15 to 18° for females) [4,5], patellaralignment, muscle asymmetry or wasting]. (See Figure 3)[6].

Supine [lower limb lengths and alignment, patellar posi-tion, patellar tilting or rotation]

Squat [patellar tracking and "J" sign: medial shift of thepatella as it enters the trochlea in early flexion, suggestiveof vastus medialis obliqus (VMO) weakness or tight lat-eral retinaculum]

Gait [lower limb alignment, hip abduction weakness, sub-talar pronation]

2. Range of motionActive movements [knee flexion (135°), knee extension(0°), internal and external rotation (10°), isometricquadriceps contraction]

Passive movements [patellar tilt, lateral tracking of patellaor increased Q angle]

3. PalpationSurface anatomy is best appreciated with the knee flexedto 90 degrees. The point of maximal tenderness should becorrelated with the underlying bone or soft tissue anat-omy. Palpate and note tenderness over the patellofemoraljoint, bones, menisci and along the course and attach-ments of ligaments and tendons. Patients with patel-lofemoral pain typically have tenderness over the medicaland/or lateral patellar facets, superior and inferior poles of

A) Anterior anatomy of the kneeFigure 2A) Anterior anatomy of the knee. (Picture courtesy of Allan McGavin Sports Medicine Centre, Vancouver, Canada).

Patients with anterior knee pain localize the pain to the ante-rior knee and will point to the entire extensor mechanism, rather than to specific anatomic regions [1]Figure 1Patients with anterior knee pain localize the pain to the ante-rior knee and will point to the entire extensor mechanism, rather than to specific anatomic regions [1].



the patella or patellar tendon. Pain over the physes orjoint line is not part of patellofemoral pain.

Effusion [may be visible or palpable. In situations wherethere is minimal fluid, compression of the suprapatellarpouch may decrease the joint volume and aid detecting aneffusion].

4. Special tests1) Patellar tilt test [patient supine and knee extended –apply downward pressure to the medial edge of the patellato assess lateral patellar restraints. Test is positive if thepatellar tilt angle is more than 5 degrees.]

2) Medial and lateral patellar glide [push patella mediallyand laterally noting degree of movement relative to widthof patella, > 75% translation is hypermobile]

3) Quadriceps setting/grind test, patellar inhibition[suprapatellar resistance while patient performs isometricquadriceps contraction with knee in full extension. Painindicates a positive test.]

4) Patellar compression test [direct compression of thepatella into the trochlea, pain indicative of articular carti-lage degeneration or acute chondral injury]

5) Patellar apprehension test [apply lateral pressure topatella at 30° knee flexion, positive if patient feels insta-bility or pain]

6) Lachman test [positive for anterior cruciate insuffi-ciency if there is anterior translation of tibia on femurwith knee in 30° flexion]

7) Posterior drawer test [positive for posterior cruciate lig-ament insufficiency if there is posterior translation of tibiaon femur with knee in 90° flexion]

8) McMurray's test [positive for meniscal tear if palpableor audible click. Patient supine, flex hip to 90°, maximallyflex knee followed by passive knee extension, first withexternal tibial rotation while applying a varus stress at theknee (lateral meniscus) and then with internal tibial rota-tion while applying a valgus stress (medial meniscus) atthe knee]

9) Trendelenberg test [positive when patient stands onone leg and contralateral hip drops, indicative of gluteal/hip abductor weakness]

5. FlexibilityThe knee should be moved thru active range of flexionand extension and then placed thru full passive range ofmotion. Active range of knee motion includes flexion(135°), extension (0°), internal and external rotation(10°). Muscles that span two joints are important forfunctional range of motion and should be tested inde-pendently (hamstrings, rectus femoris, gracilis, tensor fas-cia lata and iliotibial band, and gastrocnemius muscles).

6. StrengthKnee extension and flexion

Hip extension, flexion, abduction, adduction.

7. Hip joint and lumbar spine examRange of motion. Further detailed exam as appropriate.

The quadriceps "Q" angle is formed between the line joining the anterior superior iliac spine (ASIS) and the centre of the patella and the line joining the centre of the patella and the tibial tuberosity [6]Figure 3The quadriceps "Q" angle is formed between the line joining the anterior superior iliac spine (ASIS) and the centre of the patella and the line joining the centre of the patella and the tibial tuberosity [6].



8. Neurovascular examPatellar reflex [L2, L3, L4]

Sensation of lower leg in major dermatomes

Popliteal and dorsalis pedis artery pulsations

InvestigationsLaboratory tests are almost never necessary in evaluating apatient with anterior knee pain. CBC, ESR or CRP, bloodand joint cultures should be done if infection is suspected.Arthritis is a clinical diagnosis; ANA, rheumatoid factorand HLA-B27 are helpful in classification and treatmentbut not diagnosis.

ImagingRadiographs and magnetic resonance imaging (MRI) arethe most common imaging tools used to assess the pedi-atric knee. As with all tests, false positive and false nega-tive results may occur and clinical correlation is necessary.

RadiographsRoutine radiographs of the knee include weight-bearinganteroposterior (AP) and lateral views. The AP viewallows evaluation of the distal femoral physis, proximaltibial physis, tibial intercondylar eminence, and patella.The lateral view allows evaluation of the position of thepatella and tibial tubercle. Axial (skyline patellar profile)and tunnel (notch) views are part of the traditional ortho-pedic evaluation. The axial view is tangential to the ante-rior aspect of the flexed knee (usually 30 to 45 degrees ofknee flexion) allowing evaluation of the congruity of thepatellofemoral articulation and a measure of patellar tilt.The tunnel (notch) view, most commonly used in pediat-rics to diagnose osteochondritis dissecans, is an AP radio-graph with the knee flexed to 20 degrees to allowevaluation of the articular surfaces of the distal femoralcondyles [7].

Magnetic Resonance Imaging (MRI)MRI is a powerful tool in diagnosing knee disorders. Inthe absence of established guidelines, it is commonly mis-used as a screening examination. MRI images are obtainedin axial, coronal and sagittal planes. MRI allows evalua-tion of the soft tissues including the muscles, tendons,menisci, cruciate and collateral ligaments, retinaculum,neurovascular bundle, bursa and synovium. MRI alsoallows a more detailed evaluation of osseous structuresincluding articular and physeal cartilage, subchondralbone, periosteum, and bone marrow elements. Intrave-nous injection of gadolinium is not routine but is usefulto delineate synovial enhancement [8].

MRI should be done only after a thorough clinical exami-nation and standard radiographs are unable to provide a

specific diagnosis. Ideally it should be ordered by a physi-cian capable of interpreting the images and providingdefinitive treatment.

Common causes of chronic anterior knee painPain receptors are present within several knee structures,including the patella, synovium, fat pad, tendon,subchondral bone, and quadriceps retinaculum [9-11]].Any of these structures, individually or in combination,can cause anterior knee pain. Most causes of anterior kneepain involve the patellofemoral joint and the extensormechanism of the knee. The term anterior knee pain isoften used interchangeably with patellofemoral pain. Pre-vious literature has also interchanged the term "chondro-malacia patella" with anterior knee pain but this is nowout of favor; chondromalacia patella is a surgical findingnot a diagnosis. Patients with anterior knee pain do notnecessarily have chondromalacia patella and patientswith chondromalacia do not uniformly have pain. Ante-rior knee pain may be caused by conditions unique to thegrowing pediatric skeleton including hip disease (slippedcapital femoral epiphyses and Perthe's disease) or osteo-chondroses (Osgood-Schlatter disease or Sinding-Larsen-Johansen disease). Anterior knee pain is occasionallycaused by serious underlying systemic disease includinginflammatory conditions and malignancies.

Patellofemoral Pain SyndromePatellofemoral pain (PFP) is the most common kneeproblem presenting to primary care physicians. Patel-lofemoral syndrome is a non-specific descriptive termused to describe pain in and around the patella.

EpidemiologyPFP affects active and non-active children, is more com-mon in girls and is most common during the adolescentgrowth spurt. Up to 30% of all visits to sports medicinepractitioners are for anterior knee pain. Incidence rates of7% and 10% have been reported in young male andfemale athletes respectively [12]. Symptoms usually affectboth knees with one side more symptomatic than theother.

EtiologyThe etiology of PFP is unclear. There are currently twomain theories: malalignment of the patella relative to thefemoral trochlea with resultant articular cartilage abnor-malities, and excessive mechanical loading and chemicalirritation of local nerve endings with resultant peripatellarsynovitis [13,14]. Soft tissue tightness is common duringthe adolescent growth spurt with resultant inflexibilitiesaltering the stress through the patellofemoral joint. Acutetrauma, repetitive microtrauma/overuse and malalign-ment all can lead to increased strain on the peripatellarsoft tissues or increased patellofemoral joint stress.



Anatomy and biomechanicsThe patella functions to facilitate knee extension andincreases the force of extension by up to 50% [15]. It cen-tralizes the forces of the quadriceps, helps transmit theforce to the patellar tendon and tibial tuberosity, and alsoprotects the patellar tendon from contact with the femur.The patellofemoral joint reaction force (PFJR) acts per-pendicular to the articular surface and increases withincreasing knee flexion. PFJR is calculated to be 0.5 timesbody weight while walking, 3 to 4 times when climbingstairs, 7 to 8 times when squatting and 20 times bodyweight when jumping [16]. The patella changes its orien-tation during movement. Patellar tracking is determinedby both static (medial and lateral retinaculum, bonyarchitecture of the trochlea) and dynamic forces (quadri-ceps) acting on the patella, the congruity of the patel-lofemoral articular surfaces and the alignment andbiomechanics of the lower extremity.

Risk factorsIncreased patellofemoral joint stress and altered patellartracking may increase the risk for PFP. Direct trauma to aflexed knee may disrupt the articular cartilage and repeti-tive microtrauma from chronic overloading (weight bear-ing exercise) may increase patellofemoral stress.

Malalignment of the lower extremity influences patellartracking and may include genu valgum, genu varum, genurecurvatum, leg length discrepancy, femoral anteversion,external tibial torsion, lateral displacement of the tibialtubercle, and excessive pronation of the subtalar joint[14]. Larger Q angles (genu valgum, femoral anteversion,external tibial torsion and subtalar joint pronation) areassociated with increased static patellofemoral joint stressbut clinical studies fail to demonstrate a consistent corre-lation between larger Q angles and PFP [14]. Lateral dis-placement of the tibial tubercle greater than 10° from themidpoint of the patella may cause lateral tracking of thepatella and PFP [14].

Quadriceps muscle weakness or imbalance with relativevastus medialis (VMO) weakness or imbalance in neu-romuscular control of the VMO and vastus lateralis (VL)may cause PFP. The VMO is the weakest portion of thequadriceps, the first to atrophy with disuse and the last torehabilitate. VMO weakness results in lateral shifting andtracking of the patella during the last 30° of extensionwith resultant reduction in patellofemoral contact areaand increased patellofemoral stress. Weakness of the glu-teal muscles can also influence patellar tracking as theyassist in extension of the knee by virtue of their insertioninto the iliotibial tract, in addition to their primary func-tion to extend, abduct and externally rotate the hip.

Muscle inflexibilities can contribute to PFP. Tight quadri-ceps are less able to absorb eccentric loads and offloadstress to the quadriceps, patellar tendons and hamstrings,thus increasing the PFJR. Inflexibility of the gastrocnemiusleads to increased subtalar pronation which may influ-ence patellar tracking. Hamstring tightness also increasesthe PFJR; an associated knee flexion contracture is com-mon in adolescents during rapid growth. Hip flexion con-tractures cause a functional knee flexion contracturewhich also increases the PFJR. Tightness of the lateral ret-inaculum, iliotibial band and lateral structures can causeincreased lateral tracking of the patella and excessive stresson the lateral patellofemoral joint.

Patients with PFP may have decreased proprioceptionalthough it is unclear whether decreased proprioception iscausative of or a result of patellar maltracking [17,18].

Congenital anomalies of the patella or trochlea associatedwith PFP include hypoplasia of the medial patellar facet,hypoplasia of the medial trochlea and flattening of thetrochlear groove, hypoplasia of the lateral femoral con-dyle, patella alta, and patella inferna [14].

Clinical historyThe most common presenting complaint is dull and achyknee pain during and after activity, pain after prolongedsitting with the knee in flexion ("theatre sign") and stiff-ness. Pain may be peripatellar or retropatellar. Aggravat-ing activities include weight bearing sport, stairs(descending worse than ascending) and squatting. Swell-ing is unusual. True instability does not occur but patientsoften report "giving way" due to reflex inhibition of thequadriceps muscle secondary to pain, effusion or decon-ditioning. Historical clues to differentiate instability from"giving way" include the occurrence of instability (menis-cal or ligament injury) with pivoting or twisting versus theoccurrence of "giving way" with increased PFJR such asascending or descending stairs or walking on an incline.

Physical examLower extremity alignment should be noted. There maybe pain with squatting. VMO wasting may be marked.There may be variable superolateral or inferomedial reti-nacular or patellar facet tenderness. The lateral soft tissuepatellar restraints are often tight with decreased passivemedial patellar glide. The quadriceps setting/grind test isthe most specific test with 96% specificity and 40% sensi-tivity [19].

ManagementReassurance and education are the most important com-ponents of multimodal therapy. Gradual improvementand resolution of symptoms is the rule. Other therapiesinclude: activity modification (decrease forces across



patellofemoral joint), flexibility exercises (hamstrings,quadriceps, iliotibial band, lateral retinaculum, gastrocne-mius), strengthening of the vastus medialis, patellar track-ing exercises, cryotherapy, short term NSAID therapy,patellofemoral orthoses or patellar taping, and shoeorthoses (subtalar pronation). Any training errors shouldalso be addressed. General return to play guidelines canbe followed for PFP and most causes of anterior knee pain(see Table 1).

Patellofemoral instability and patellar subluxationPatellofemoral dysplasia, whether congenital or acquired,represents a spectrum of disorders characterized by staticand dynamic malalignment of the patella relative to thedistal femur. Malalignment results in maltracking of thepatella with resultant instability and potential osteochon-dral injury. Four clinical subtypes are recognized based onthe degree of malalignment: mild dynamic imbalance ofthe patella with excessive loading of the lateral patellarand femoral facets (lateral patellar compression syn-drome); chronic subluxing patella; recurrent patellar dis-location; and chronic (or obligatory) dislocation of thepatella. Patients with patellofemoral instability may com-plain of anterior knee pain, episodic giving way, lockingand catching sensations associated with recurrent effu-sions. On examination, findings are similar to PFP. Patellaalta, tenderness over the medial patella femoral ligament,positive patellar apprehension test or frank lateral disloca-tion may be elicited. Treatment includes stretching tightlateral structures (vastus lateralis, iliotibial band),strengthening medial structures (VMO), knee orthoses forpatellar stabilization, and foot orthoses to correct exces-sive subtalar pronation. Orthopedic referral and possiblesurgical management is recommended for recurrent andchronic obligatory patellar dislocation.

Patellar tendinopathy"Jumper's knee" or patellar tendinopathy is a commoncause of infrapatellar pain. Pain is usually maximal at thepatellar attachment and proximal tendon and is aggra-vated by jumping or hopping. In children and adolescentsthe osteochondroses/traction apophysitis Osgood-Schlat-ter (OSD) and Sinding-Larsen-Johansson (SLJD) diseasecommonly present with pain at the attachments of thepatellar tendon. (See osteochondroses section below) PFP

is commonly associated with patellar tendinopathy. Onexamination there is local tenderness over the patellar ten-don; thickening or nodules may be palpable. There maybe abnormalities of the PF joint. Treatment requires loadreduction (activity modification, biomechanical correc-tion), cryotherapy and progressive eccentric strengthen-ing.

OsteochondrosesOsgood-Schlatter (OSD) and Sinding-Larsen-Johansson(SLJD) disease are osteochondroses and traction apo-physitis affecting the extensor mechanism of the knee.OSD occurs at the growth plate of the tibial tuberosity atthe inferior attachment of the patellar ligament and ismore common than SLJD, which occurs at the inferiorpole of the patella at the superior attachment of the patel-lar ligament. Both conditions present in adolescence dur-ing the growth spurt and are characterized by welllocalized pain aggravated by exercise. On examinationthere is well localized tenderness and soft tissue swelling.There is often tightness of surrounding muscles, especiallythe quadriceps, hamstrings and gastrocnemius. Both OSDand SLJD are clinical diagnoses and radiographs are notusually required. If pain is severe or there is marked swell-ing radiographs should be obtained to exclude bonytumors or infection. Typical radiographs of OSD showenlargement and fragmentation of the tubercle (Figure 4).Management is conservative; these are self-limited condi-tions that resolve with skeletal maturity but symptomsmay persist for up to 24 months. Treatment includes activ-ity modification, local cryotherapy, local muscle stretch-ing and strengthening, and correction of any predisposingbiomechanical factors, such as subtalar pronation withphysical therapy, bracing and/or orthotics. Occasionallyin OSD, symptoms may persist with skeletal maturity dueto non-union of the tibial tuberosity. The separate frag-ment should be excised.

Fat pad irritation/impingementThe infrapatellar fat pad is richly innervated and injurymay cause anterior knee pain. Impingement of the infrap-atellar fat pad between the patella and the femoral con-dyle may be secondary to direct trauma or acutehyperextension injury. Chronic irritation may be associ-ated with patellar tendinopathy, patellofemoral syn-

Table 1: Return to play guidelines

1. Control pain and inflammation PRICE (protect, rest, ice, compression, elevation)

2. Optimize range of motion Active and passive exercises3. Optimize strength Isometric, isotonic exercises4. Optimize proprioception Balance, patellar tracking exercises5. Functional and sport specific skills Running, jumping, pivoting etc.6. Return to usual activities or sport Practice before competitive play



drome or exposure to recurrent synovitis. Pain is oftenworsened by knee extension, prolonged standing andkneeling. On examination there is localized tendernessand swelling in the fat pad with posterior displacement ofthe inferior pole of the patella. Associated predisposingbiomechanical factors include genu recurvatum and ante-rior tilting of the pelvis. Treatment includes local cryother-apy, taping the patella to reduce the amount of tilt andimpingement, local muscle flexibility and strengthening,and correcting lower limb biomechanics as in patellofem-oral syndrome.

Referred pain from the hip or lumbar spineAll patients with knee pain require evaluation of their hipsand lumbar spine. Children with Perthe's disease orslipped capital femoral epiphysis (SCFE) may presentwith knee pain. Perthe's disease, an idiopathic avascularnecrosis/osteonecrosis of the femoral epiphysis usuallyaffects 4 to 10 year olds, is more common in boys and isbilateral in 10%. Children usually present with a limp or

pain in the hip, thigh or knee. Examination of the knee isnormal but there is limited internal rotation and abduc-tion of the ipsilateral hip. Trendelenberg may be positive.Radiographs vary with the stage of the disease but mayshow evidence of bone necrosis, fragmentation, reossifi-cation or remodeling and healing. Treatment consists ofrest from aggravating activities and range of motion exer-cises. Occasionally orthoses or surgery may be required.Generally, the condition resolves and children return totheir activities. The main long-term concern is early oste-oarthritis.

SCFE, displacement of the proximal femoral epiphysis onthe femoral neck, usually affects 10 to 15 year olds and ismore common in boys. Adolescents usually present witha limp and may have hip, groin or knee pain. The kneeexam is normal, the hip is often preferentially held inabduction and external rotation with decreased active andpassive internal rotation and adduction. Trendelenbergmay be positive. Radiographs (anterior-posterior and frogleg lateral) of the hip may show widening and irregularityof the physis with posterior inferior displacement of fem-oral head. SCFE may compromise the vascular supply tothe femoral head and lead to avascular necrosis; all caseswarrant orthopedic referral. Treatment includes nonweight bearing, traction and surgery with epiphyseal fixa-tion and osteotomy. Most patients do well after surgicalfixation. Complications include avascular necrosis andchondrolysis. Patients require long term follow up asSCFE may develop within 12 to 18 months in the contral-ateral hip, if prophylactic pinning is not performed [20].

Osteochondritis DissecansOsteochondritis dissecans (OCD) may affect the knee;most commonly the lateral aspect of the medial femoralcondyle but also the lateral femoral condyle or patella.OCD is an idiopathic lesion of bone and cartilage result-ing in bone necrosis and loss of continuity with subchon-dral bone. There may be partial or complete separation ofarticular cartilage with or without involvement ofsubchondral bone. It occurs in adolescence and lesionsare bilateral in 20%. Proposed etiologies include acutetrauma, repetitive microtrauma, vascular insufficiency ornormal growth variant [1]. Adolescents may present withactivity related pain and swelling. Locking and catchingdue to fragment instability is uncommon.

On examination, there may be focal bony tenderness,knee effusion and evidence of a loose fragment withextension block or palpable loose body. Wilson's sign isseen in medial femoral condyle lesions. (Wilson's sign ispositive if pain is reproduced by flexing the knee to 90°and rotating the tibia medially while extending the knee.Pain occurs at approximately 30° and is relieved by lateralrotation of the patella.) Radiographs may show a radiolu-

Osgood-Schlatter diseaseFigure 4Osgood-Schlatter disease. Lateral radiograph of the knee demonstrating fragmentation of the tibial tubercle with over-lying soft tissue swelling. (Radiograph courtesy of BC Chil-dren's Hospital)



cent lesion, subchondral fracture, potential separationwith subchondral bone and a loose body. OCD lesionscan be missed on routine non weight bearing anterior/posterior and lateral radiographs; tunnel (notch) andaxial (skyline patellar profile) views are required to viewthe articular surfaces of the distal femoral condyles andpatella (See Figures 5 and 6) [21]. MRI may show cartilagechanges earlier with contrast enhancement of intact carti-lage lesions [21].

Treatment depends on the stage of the lesion and the skel-etal maturity of the patient with early lesions in skeletallyimmature patients having the best prognosis. Skeletallymature patients or patients presenting with a locked kneeor symptomatic loose body require urgent orthopedicevaluation. Treatment options include modified activitywith or without weight-bearing; immobilization; cryo-therapy; anti-inflammatories; drilling of subchondralbone to improve vascularity; reattachment and or removalof loose bodies and OATS procedure (osteochondral allo-graft transplant) [22].

Synovial plicaThe knee has normal synovial folds that are residualembryonic remnants persisting from when the knee cavitywas a septated structure. Occasionally, pathological con-ditions occur within the plica(e) due to local synovitiscaused by acute, direct or repetitive microtrauma. Theinflamed plica can become trapped between the patellaand the femoral condyle. Impingement can cause furtherinflammation and fibrosis with abrasion of the femoralcondyle, changes in the articular surface and reactivechanges in the subchondral bone. Diagnosis is clinical;

common complaints are of medial knee pain worsenedwith running, stair climbing or squatting accompanied bysnapping and catching during flexion (usually flexion arc30–70 degrees). On examination the medial patellar reti-naculum from the patella to the medial femoral condyleor anteromedial joint line may be tender. The plica maybe palpable as a thickened band that is tender whenpressed against the edge of the condyle. Managementincludes patellar mobilization and massage, flexibilityexercises for the hamstrings, quadriceps and gastrocne-mius, and anti-inflammatory medications with surgicalremoval of the plica reserved for recalcitrant symptoms.

Quadriceps tendinopathyPain arising at the quadriceps tendon attachment to thepatella is uncommon in the pediatric population. Onexamination there is tenderness at the superior margin ofthe patella and pain is exacerbated by resisted quadricepscontraction. Treatment includes local massage at the siteof pain in addition to the general principles used for patel-lar tendinopathy.

Bipartite patellaThe patella ossifies between 3 and 5 years of age with grad-ual coalescence of multiple ossification centers. Accessoryossification centres often occur; the most common loca-tion is the superolateral patella. A bipartite patella is usu-ally an asymptomatic, incidental radiographic finding.Radiographs show regular smooth fragment margins withno evidence of soft tissue swelling, differentiating thelesion from acute fracture. Occasionally bipartite patellamay cause anterior knee pain. Clinically there is soft tissuetenderness at the superolateral pole of the patella. Initialtreatment is conservative with modified activity and local

Osteochondritis dissecansFigure 6Osteochondritis dissecans. Tunnel or notch views show the cystic changes more clearly [21].

Osteochondritis dissecansFigure 5Osteochondritis dissecans. Anterior posterior radiograph shows minimal cystic changes affecting the lateral aspect of the medial femoral condyle [21].



flexibility and strengthening exercises. Surgical optionsinclude excision or fixation of the bipartite patella orrelease of the vastus lateralis insertion [2].

Stress fracture of the patellaStress fractures of the patella are rare causes of anteriorknee pain. In the pediatric population, it is reported injumping athletes who present with intense localized painwith possible overlying soft tissue swelling. Radiographswill detect chronic stress reaction; early lesions are bestdetected by radionucleotide bone scan.

BursitisThere are multiple bursas around the knee. Bursa are syn-ovial lined structures that provide a low-friction interfacebetween tissues to provide smooth motion. Bursitis,inflammation of the bursa, can be secondary to repetitivemicrotrauma from overuse, direct trauma, autoimmunedisease including juvenile idiopathic arthritis (JIA) andsystemic lupus erythematosus (SLE), or infection. Prepa-tellar bursitis is the most common bursitis of the knee,presenting with anterior knee pain and swelling. Infrapa-tellar bursitis may also cause anterior knee pain mimick-ing patellar tendinopathy but can be diagnosed by carefulpalpation for localized tenderness. In both conditions it isimportant to differentiate fluid in the bursa from intraar-ticular effusion. Treatment includes local cryotherapy,nonsteroidal anti-inflammatory medications (NSAID's)and avoidance of further direct trauma to the bursa. Ifthere are any signs of septic bursitis the bursa should beaspirated and appropriate antibiotics prescribed.

Inflammatory disordersOligoarticular JIA often presents with monoarticular kneearthritis. Children may present with anterior knee painbut the typical history of morning stiffness, gradual reso-lution of pain with activity and clinical exam findings usu-ally allow the practitioner to make the correct diagnosis. Acomplete joint and systemic examination to exclude otherjoint involvement is important as is screening for asymp-tomatic uveitis associated with JIA.

The JIA subtype, Enthesitis Related Arthritis, is unique inthat it is more common in school-age boys, is frequentlyassociated with the genetic marker HLA-B27 and inflam-mation of the entheses may be a prominent finding.Enthesitis (inflammation at the attachment of tendons,ligaments and fascia to bone with characteristic pain onpalpation) around the knee may be confused withOsgood's Schlatter or Sinding-Larsen Johannsen disease.Enthesitis is usually associated with arthritis and symp-toms are more prominent in the morning, which helps todifferentiate it from the osteochondroses and tractionapophysitis group.

Treatment of arthritis includes physiotherapy for improv-ing range of motion and strength, NSAID's and poten-tially local intra-articular corticosteroid injection ordisease modifying anti-rheumatic therapy. All childrenand adolescents suspected of having JIA or other chronicinflammatory arthritis should be referred to a pediatricrheumatologist.

Pain amplification syndromesMany pediatric patients with severe chronic musculoskel-etal pain do not have an identified cause. The cause ofamplified musculoskeletal pain is unknown, but minortrauma, underlying chronic illnesses and psychologicaldistress have been associated. This condition has beencalled many terms including reflex sympathetic dystrophy(RSD), reflex neurovascular dystrophy (RND), complexregional pain syndrome, and chronic musculoskeletalpain syndrome with or without autonomic dysfunction.Typically, an affected child sustains minor trauma to thelower extremity which results in pain out of proportion tothe injury.

On physical examination, patients may be unwilling toweight bear, manifest allodynia (pain generated by nor-mally non-painful stimuli), and autonomic changes suchas excessive perspiration, edema, cyanosis, mottling, andcoolness of the skin. General and neurovascular exam arenormal.

Diagnostic studies are typically not helpful. X-rays mayshow osteopenia but only in chronic cases with significantdisability. MRI can show regional bone marrow edema,and a technetium bone scan may show decreased uptake[23].

TumorsBenign and malignant tumors are rare causes of knee pain.Symptomatic benign bone lesions include osteochon-droma, nonossifying fibroma with stress fracture, osteoidosteoma and chondroblastoma. Malignant bone tumors,include local osteosarcoma or Ewing's sarcoma, leukemiaor metastases from neuroblastoma. Benign synovialtumors include pigmented villonodular synovitis (PVNS)and hemangioma. Malignant synovial tumors include sar-comas.

ConclusionAnterior knee pain is common in children and adoles-cents. Evaluation and management is challenging andrequires a thorough history and physical exam, andunderstanding of the pediatric skeleton. Most causes ofanterior knee pain involve the patellofemoral joint andthe extensor mechanism of the knee. It is important forthe clinician to consider conditions unique to the growingpediatric skeleton including hip disease (slipped capital



femoral epiphyses and Perthe's disease) or osteochon-droses (Osgood-Schlatter disease or Sinding-Larsen-Johansen disease). Anterior knee pain is occasionallycaused by serious underlying systemic disease includinginflammatory conditions and malignancies. The clinicalhistory and physical exam often lead to correct diagnosisand identify cases requiring further evaluation, imaging orreferral. General return to play guidelines can be followedfor PFP and most causes of anterior knee pain

AbbreviationsACL = anterior collateral ligament

AP = anteroposterior

JIA = juvenile idiopathic arthritis

MRI = magnetic resonance imaging

NSAID('s) = non-steroidal antinflammatory drugs

OATS = osteochondral allograft transplant

OCD = osteochondritis dissecans disease

OSD = Osgood-Schlatter's disease

PFJR = Patellofemoral joint reaction force

PFP = Patellofemoral pain

PVNS = pigmented villonodular synovitis

RND = Reflex neurovascular dystrophy

RSD = Reflex sympathetic dystrophy

SCFE = Slipped capital femoral epiphysis

SLE = systemic lupus erythematosus

SLJD = Sinding-Larsen-Johansson

VL = vastus lateralis

VMO = vastus medialis obliqus

AcknowledgementsI thank our patient who consented to have his radiograph included in this manuscript and the Allan McGavin Sports Medicine Centre for contributing anatomy pictures from patient care handouts.

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