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The Paediatric Knee

Introduction

Childhood sports participation is increasing and in turn the incidence of paediatric sporting injuries seen in a sports medicine practice is increasing. The knee joint in the child athlete, like the adult, is a source of high morbidity. The aim of this synopsis is to discuss the common paediatric knee problems and to highlight the differences where they exist to the adult patient.

The assessment of a child’s knee can be rewarding and straightforward if a systematic approach is followed. Fortunately many of the conditions occurring in this age group are self-limiting and full recovery is the usual outcome. However more serious conditions may occur and if these are missed especially if during the rapid growth phase the consequences of a missed diagnosis are significant. To regard all knee pain in a child as "growing pains" is folly. If an informed systematic approach is followed the child with for example hip pathology or a tumour will hopefully not be missed.

The History and Examination

The clinical approach to the child, in particular the young child, will require a greater emphasis on initially establishing rapport with the patient so that an adequate history and examination may be performed. Never miss the opportunity to observe the young child in the waiting room and walking into your office, as this may be your last chance!

For the young child a detailed history from the parents in particular focusing on developmental milestones and family history where indicated is important. If the problem is an acute injury a detailed mechanism of the injury should be sought. If the older child is accompanied by a parent ask the child first.

SPECIAL CONSIDERATIONS IN THE CHILD

  1. Referred pain from the Hip
  2. The hip joint should always be examined first before the clinician assesses the knee. Pain from the hip, like in the adult, is referred usually to the medial joint line of the knee.

    Restricted abduction in flexion indicates hip pathology until proven otherwise.

    Two common hip pathologies to consider are Perthes disease (age 6-10) and Slipped femoral epiphysis (age 10-14).

  3. High index of suspicion for growth plate fractures
  4. It should always be remembered trauma resulting in ligament injuries in adults might in children result in bone or growth plate fractures. Isolated knee ligament injury is rare in children younger than 14 years as the ligaments are stronger than the physes.

    Also remember even if the initial X ray is normal and the child either limps or is unable to weight bear and the physis is tender a fracture should be suspected and the child treated as such.

  5. Tumour
  6. Benign and malignant (primary and metastatic) tumours do occur about the knee. Local trauma often focuses attention on an area in which a tumour is subsequently diagnosed.

    Tumours can present with pain, swelling or pathological fracture and one should always like in the adult bear this diagnosis in mind when assessing knee pain especially if the symptoms and signs are atypical.

  7. Infection
  8. The most common organisms responsible for osteomyelitis are Staphylococcus aureus, Streptococci, E Coli, Proteus and Pseudomonas. Often no primary infective site is found. The most common presentation is pain, warmth and tenderness over the affected part and an unwillingness to move the adjacent joint. It is possible to get an effusion in the neighbouring knee joint however the growth plate usually prevents infective spread into the joint.

    All patients should be checked for diabetes or impaired immune function.

  9. Inflammatory Arthritis
  10. Still’s disease (juvenile RA) should also be part of one differential diagnosis.

Patellofemoral Conditions

Recent studies suggest that one in two children will suffer significant patellofemoral pain. Girls are more likely than boys as are children with certain lower limb morphologies and to a lessor degree more active children.

The aetiology, classification and treatment of this very common clinical problem remains contentious and a simplified approach is presented below realizing there is often a spectrum of symptoms and signs that cross the indistinct classification boundaries.

  1. Habitual Patellar Dislocation
  2. This condition is congenital and is usually apparent in the infant/toddler. Every time the knee is flexed the patella dislocated laterally. The usual cause is a shortened extensor mechanism and the treatment is a lengthening soft tissue procedure (e.g. Z plasty lengthening of rectus femoris).

  3. Acute Patellar Dislocation
  4. Is usually secondary to a twisting fall, the quads contract and pull the patella over the LFC. Pain is poorly localized. The patella is laterally displaced and there is a prominent MFC.

    To reduce the patella apply medial pressure to the patella and extend the knee. If the patella has spontaneously reduced it is important to differentiate this injury from in particular an ACL rupture or a fracture.

    An X ray is important as often there is an associated osteochondral fracture either from the retropatellar surface, the lateral femoral trochlear of the medial aspect of the patella.

    An arthroscopy may be indicated to remove or reimplant a loose body or otherwise the injury is treated conservatively.

  5. Recurrent Patellar Dislocation/Subluxing Patellae
  6. 50% of acute dislocations recur. The condition is often bilateral and affects girls more than boys in a ration 2:1. There is often a family history.

    Numerous aetiological factors are associated

    1. Increased Quadriceps ("Q") angle. Q angle>20 degrees. Clinical examination may show one or more of genu valgum, internal femoral torsion, external tibial torsion. Pronated feet may exacerbate the problem.
    2. Generalised Ligamentous laxity (hypermobile patella).
    3. Quadriceps muscle abnormality. Examination may demonstrate a weak and/or dysplastic VMO, a short vastus lateralis, a tight ITB or tight bands in the lateral retinaculum.
    4. Abnormal Patellofemoral Articulation including patella alta, a shallow femoral trochlear/deficient LFC or a flat retropatellar surface.

    In addition to the above clinical signs the patellar apprehension test is usually positive.

    X ray may show patella alta and define any malalignment of the patellofemoral joint on the skyline view.

    The conservative management of this condition is well documented.

    It is important to realize recurrent dislocators run the risk of osteochondral damage and later arthritis.

    Surgery should be delayed until skeletal maturity if possible as disruption of the tibial tubercle may result in physeal arrest. If surgery is indicated it will involve a soft tissue procedure (VMO advancement/lateral release). Also surgery may be indicated to treat chondral lesions or remove loose bodies.

  7. Anterior Knee Pain
  8. Also known as PFPS/Chondromalacia patellae/patellar migraine/excess lateral patellar pressure syndrome.

    The history is one of anterior knee pain during or after exercise and is often exacerbated by stairs. There may be a positive movie goer’s sign.

    The examination is often normal. There may be any of the signs seen in the subluxing patellae given above and there may be an effusion, tenderness of the patellar/retropatellar surface and in particular tight hamstrings.

    Aetiological factors include

    1. Pathologic patellofemoral alignment secondary to an increased Q angle, patella alta, VMO insufficiency, muscle tightness (hamstrings, ITB, vastus lateralis and lateral retinaculum or rectus femoris) and excessive pronation.
    2. Trauma. A single traumatic episode to the Patellofemoral joint may initiate the condition.

    As with the clinical signs the pathological changes of the articular cartilage is variable from no abnormality to extensive chondral lesions.

    Management is largely conservative involving VMO retraining, patellar taping, stretching tight structures and relative avoidance of aggravating activities. Surgery is reserved for certain chondral lesions and where significant malalignment of the PF joint exists and patellar subluxation/dislocation coexists.

  9. Osgood-Schlatter’s disease
  10. Is very common

    Is an apophysitis.

    Diagnosis is not difficult as the history and examination are classical. The child (10-13 years) will present with gradual onset of localized pain at the tibial tubercle. The pain will be exacerbated by exercise (especially distance running and jumping), squatting, stair climbing and stretching the quadriceps.

    On examination there is marked tenderness at the tibial tubercle with often a bony prominence with overlying soft tissue swelling. The Quadriceps and hamstrings are invariably tight and there may be intercurrent PF malalignment and anterior knee pain.

    Treatment includes:

    • Relative rest
    • Ice
    • Stretching Hamstrings and calves (avoid stretching Quads as may aggravate)
    • Reassurance the condition will abate

    Surgery is rarely necessary except where X rays show a separated fragment of bone, which is acutely tender in a skeletally mature knee. Simple excision of the fragment often gives a very good result.

  11. Sinding-Larson Johansson Disease
  12. Is a similar condition to OS disease but affects the distal patellar apophysis and the associated proximal patellar tendon. Localised tenderness occurs at this point.

    Management of SLJ disease is similar to OS however it may cause more disruption to sporting activities and be less amenable to treatment.

Angular Deformities

The standing femoral tibial angle varies through childhood.

At birth there typically is a varus angle of approximately 10 degrees.

At 18-24 months there typically is a neutral relationship.

At 3.5 years there typically is a valgus angle of approximately 15 degrees.

By 6-7 years most children will have an alignment in the adult range of up to 7 degrees of varus or valgus.

When to be concerned?

  1. When the deformity is severe.
  2. When alignment is asymmetric.
  3. When alignment is inappropriate for the childs age.

Causes include

  1. Infantile tibia vara ( Blount’s disease)
  2. Epiphyseal dysplasia’s
  3. Physeal fracture
  4. Epiphyseal dysplasias
  5. Adolescent Tibia vara.

In most cases the concerned parent or older child can be reassured and followed up if necessary. However if any of the above are suspected an X ray and Specialist referral is indicated.

OCD

Osteochondritis Dissecans (OCD) (defined as a small area of avascular bone on an articular surface e.g. knee, elbow, ankle, hip) in the knee occur on

  1. The lateral aspect of the MFC (most commonly)
  2. The LFC
  3. The PF joint (rarely)

It is more common in boys (3:1) and is bilateral in approximately 25%. OCD usually presents between ages 10 – 20 years.

The aetiology is unknown but most believe it is secondary to trauma, or to aseptic necrosis or a failure of ossification.

The patients presents with pain, swelling, catching and/or locking and on examination there is usually an effusion and quadriceps wasting.

Plain radiography defines the lesion. A tunnel view of the intercondylar notch is required to define the lesion on the MFC. Some clinicians obtain a bone scan to demonstrate whether the lesion is healing. A relatively "cold " scan suggesting there is unlikely to be any further healing.

Most clinicians are routinely using MRI to now to aid in their management of these patients. In most cases (except the frankly separated fragments and loose bodies) the articular cartilage remains intact and there is a variable degree of separation of a fragment of subchondral bone.

The management of OCD for most surgeons depends on clinical, radiological and if necessary arthroscopic findings. However some are more conservative and others when they operate either choose to remove the fragment and perform an osteoplasty/chondroplasty while other surgeons make every attempt to salvage the fragment and internally fix it usually with a Herbert screw. The arthroscopic grading system of Guhl and the details of various surgical decisions are beyond the scope of this summary.

The prognosis is relatively good with most returning to their normal activity level in 4-6 months and there is a low incidence of subsequent premature osteoarthritis.

Meniscal Injuries

Traumatic meniscal injuries in children are rare. In general they may not demonstrate the same clinical picture as an adult with a meniscal tear. The pain may not be well localized and there may not be an effusion. Therefore the clinician should have a high index of suspicion. Many now use MRI to define a suspected meniscal injury.

The majority of meniscal tears in children are associated with a discoid lateral meniscus. The discoid or "D" shaped lateral meniscus affects 1-2 per 100 children and is often bilateral. Most cause problems, which implies the meniscus has an inherent propensity to tear. The child usually describes a traumatic event, which may be minor and is thereafter troubled by lateral joint line pain and often catching or locking.

Plain radiographs may suggest a discoid meniscus with a flattened LFC, however MRI demonstrates the abnormality.

Management involves partial lateral meniscectomy.

Ligamentous Injuries

Knee ligament injuries are rare in young children. The most significant ligamentous injury is ACL disruption. The ligament rarely ruptures in its midsubstance and more commonly avulses a bony fragment more often at the tibial insertion. Management for this is prompt fixation of the bony avulsion.

The child with ACL injury usually has similar historical and examination findings to the adult.

Anterolateral instability is a cause of premature degenerative joint disease in young athletes. These children should be strongly advised to have their joints stabilized before they return to active sports.

The surgical reconstruction of an ACL deficient knee has be achieved in Australia in a child as young as 7 years. The hamstrings function as the graft and meticulous care is taken to avoid the growth plates. If the athlete is close to skeletal maturity they may decide to wait and restrict their activities and have an "adult" style reconstruction once their growth plates have fused.

The Paediatric Knee>

 

 

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