An Introduction to Hip Problems in Children

An Introduction to Hip Problems in Children
Marlis Sabo, Meds 2005
Children are susceptible to a variety of hip problems throughout the period of skeletal maturation. Some are
emergencies, while others are self-limited and relatively benign. Some are also linked to the developmental
stage of the child. It is important to recognize those conditions requiring timely treatment and referral. The
following is a brief discussion of some of the conditions that must be considered in approaching a child with
a lower limb complaint.
INTRODUCTION
The hip in childhood is a highly dynamic and developing
structure. For optimal hip growth and function into adulthood, the
head of the femur and the cup of the acetabulum must be maintained in correct contact. Furthermore, unique properties of the
hip during early development make it susceptible to certain conditions present only in childhood. Assessing the hip in children
can be difficult. In addition to poor symptom description on the
part of the child, the symptoms may be misleading (such as knee
pain in hip pathology) or confusing (such as recent trauma that
may be irrelevant to the diagnosis). Important information
includes a correct characterization of any pain present (location,
day vs night pain, duration, severity, ability to weight bear), duration of any limp, the child’s past medical and developmental history, other symptoms (fever, rashes, weight loss, decreased movement of the leg in infants), and family history.1 The physical
examination is of great importance, and should include an examination of gait, inspection, palpation of the hip and pelvis, and
assessment of range of motion.1 Both hips should be examined, as
should the knee and lumbar spine. Attention should also be given
to vital signs such as temperature, body habitus, and skin rashes.
Appropriate investigations depend on the clinical presentation,
but in nearly every case, plain film radiography forms the starting
point. The differential for limp and hip/leg pain is long and varied, and can be imposing. This paper discusses some of the more
common and important disease entities of the paediatric hip.
SEPTIC ARTHRITIS OF THE HIP
Hips are the second most common joint to be infected, with
the incidence of infection decreasing with the age of the child.2
The child’s presentation depends somewhat on age, but includes
anterior hip and thigh pain, pseudoparalysis (unwillingness to
move the limb), fever, recent infection (such as pharyngitis), and
possibly a history of trauma.2 On examination, the child would
hold the hip in external rotation, abduction and slight flexion as
this maximizes the space inside the capsule, which would be full
of purulent material.2 Pain would be elicited with internal rotation, extension, and flexion more than 60º.2 Muscle guarding may
be evident, and one should palpate both hip and pelvis for tenderness.2 An abdominal exam is indicated as a psoas abscess
(although rare) could present similarly.2
Appropriate investigations include a CBC and differential,
ESR, CRP, blood cultures, and serum glucose. The white cell
count may be misleadingly low depending on the age of the
child.2 The joint itself should also be aspirated emergently for
material that can be cultured (positive in 50-80%), Gram stained,
and assessed for white cell count and glucose. Compared with
plasma, the aspirate glucose is reduced.2 A white cell count
greater than 50,000/mL (>90% polymorphonuclear cells)2,3 is
also highly suggestive. Plain films show soft tissue edema, loss of
tissue planes, widening of the joint space, capsular distension,
UWOMJ 74(2) 2006 43
Table 1: Considerations on the differential of pain and limp
in children1, 2, 10
Condition
Pain
Septic Hip
+
Acute Hematogenous Osteomyelitis +
Slipped Capital Femoral Epiphysis
+
Legg-Calvé-Perthes Disease
+/–
Developmental Dysplasia
Irritable Hip
+
Post-Infectious Arthritis
+
Juvenile Chronic Arthritis
+
Collagen Vascular Diseases
+
Henoch-Schonlein Purpura
+
Leukemia
+
Bone Tumors
+/–
Psoas Abscess
+
Pyomyositis
+
Sickle Cell Disease
+
Fracture
+
Dislocation
+
Low back disorders
+
Knee disorders
+
Foot and Ankle disorders
+
Neuromuscular disorders
-
Limp
+/Pseudoparalysis
+
+
+
+
+
+
+
+
+/–
+/–
+/–
+/No WB
+/No WB
+
+
+
+
subluxation, and possibly an osteomyelitis.2 Ultrasound can be
used to differentiate a septic hip from an irritable hip.2 Bone
scintigraphy with gallium can also help sort out difficult cases.2
A septic hip is an urgent issue in a child, and requires surgical drainage and IV antibiotics.2 The common pathogens are
somewhat age-dependent, but overall, Staph. aureus and streptococcus species are implicated in most cases.2 Complications
include premature physeal closure, growth abnormalities,
pseudoarthrosis, subluxation or dislocation of the femoral head,
and acetabular dysplasia.2 Risk factors for a poor outcome
include age under 6 months, delay of more than 4 days to treatment, associated osteomyelitis, and Staph. aureus infection.2
ACUTE HEMATOGENOUS OSTEOMYELITIS
Acute hematogenous osteomyelitis affects roughly 1:5,000
children under age 13, with 50% of these occurring in children
under 5 years old.4 The femur is the site of infection in 27% of
cases. Like septic arthritis, the common pathogens are Staph.
aureus and streptococcus species.4 It is important to note that
because of the unique blood supply and capsular structure of the
developing hip, a femoral osteomyelitis can erode into the hip and
cause a comorbid septic arthritis. The most common historical
features are fever, pain, and limited use of the extremity.4
Lethargy and anorexia are less common. On examination, there
may be point tenderness. Swelling is age-dependent such that a
very small child with a thinner periosteum may have a great deal
more swelling than an older child. Range of motion is reduced,
and there may be cellulitis overlying an abscess.
As with septic arthritis, a CBC and differential, ESR, CRP,
blood culture, and direct aspiration for culture are indicated. Plain
44
UWOMJ 74(2) 2006
film radiographs begin to show changes at 48 hours with soft tissue swelling.4 Periosteal new bone formation becomes visible at
5-7 days, while osteolytic changes don’t appear until 10-14 days
after onset. On bone scintigraphy, cold spots (ischemia) are more
predictive than hot spots. MRI is most useful for defining the
marrow of long bones and for planning surgical debridement.
Management is mainly medical, with surgery reserved for
cases requiring decompression, debridement, and facilitation of
antibiotic delivery. Current opinion on antibiotics suggests that at
least three weeks of IV and PO antibiotics are required, with
neonates receiving the entire course by IV. Complications include
recurrent or chronic infection, pathological fracture, growth disturbances, and side effects of the antibiotics including rash, GI
upset, and neutropenia. Given delays in diagnosis or inadequate
treatment, adverse outcomes are as common as 6% of cases.4
IRRITABLE HIP (TRANSIENT SYNOVITIS)
Transient synovitis of the hip is the most common cause of a
childhood limp aside from traumatic events.3 Its incidence is 14/1000, peaking between 3 and 8 years of age. There is also a seasonal variation in cases. Boys and Caucasian children are more
commonly affected, with neither side affected more. In 5% of
cases, the synovitis is bilateral. The child presents with hip pain,
limp, and may have had a preceding illness. The presentation can
mimic that of septic hip, but the symptoms and findings are less
severe. As a result, labs such as CBC, ESR and CRP are done
more to rule out other serious conditions.3 Plain AP and frog-leg
views of the hip are taken, also to rule out more serious problems.
Ultrasound of both hips can help to distinguish between irritable
hip and septic hip. The key findings are echo-free joint effusion2
and widening of the medial joint space more than 1 mm compared with the other hip.3 Since this is a self-limiting condition,
once other conditions requiring therapy have been ruled out,
observation is adequate.
LEGG-CALVÉ-PERTHES DISEASE
Perthes disease is a condition of femoral head necrosis, collapse, and regeneration most commonly found in boys between
the ages of 4 and 10 years (although girls are also affected).5 The
etiology is unknown, although a variety of theories have been
postulated. Children present with mild pain, often referred to
thigh or knee, and a limp. The patient may also present with a history of trauma. On physical exam, the child may appear small for
their age, have an antalgic gait, a positive Trendelenburg sign,
limited internal rotation, quadriceps atrophy, and adduction contracture leading to the appearance of a short leg.5 The hallmark
diagnostic test are AP and frog-leg radigraphs of the hip and
pelvis showing such signs as widened cartilage, sclerosis, collapse of the femoral head, and the cresecent sign of subchondral
fracture. A variety of classification systems exist, based on the
severity of involvement of the femoral head. In the very young
with limited involvement, observation may be adequate therapy.
In others with more severe disease, the basic principle of therapy
is maintaining containment of the femoral head within the acetabulum, achieved with casting, bracing, or surgical intervention.5
Sequelae include degenerative arthritis, coxa magna, and growth
disturbance.
SLIPPED CAPITAL FEMORAL EPIPHYSIS
Slipped capital femoral epiphysis (SCFE) is a condition in
which the femoral head slides posteromedially off the femoral
neck through the growth plate.6 The prevalence is 2/100,000, and
is more common in boys than girls. Because it occurs in the gap
between the onset of rapid growth and the onset of sex hormone
production, this is a disease of early adolescence (averaging 13
years old in girls, 15 years old in boys). Children with SCFE are
often obese (>95th percentile for weight), or, less commonly, have
some endocrinopathy such as hypothyroidism, hypogonadism,
hypopituitarism, or renal osteodystrophy. Two types of slips
occur: stable and unstable. In stable slips, the pain is located in the
hip and groin, and is much worse with walking. On exam, an
antalgic gait with the leg in external rotation is observed, and loss
of internal rotation, flexion and abduction can be demonstrated.6
In acute slips, a history of trauma is sometimes present, and the
child will not be able to bear weight on the affected side. The hallmark investigation for SCFE is a set of AP and frog-leg lateral
radiographs.6 The femoral head will be posteromedial to its correct location, demonstrated by drawing a line along the femoral
neck (Klein’s line). In SCFE, the line will no longer intersect the
femoral epiphysis. In unstable slips, reduction is attempted while
in stable slips, fixation of the slip in its existing position are the
goals of treatment. Complications include involvement of the
contralateral side (in 20-40%, not necessarily simultaneously),
avascular necrosis (up to 50% in unstable slips), chondrolysis,
and osteoarthritis.6, 7 Because of this, careful follow-up after fixation is required until the child is out of the danger window.
INFLAMMATORY ARTHRITIS
This is a heterogenous group of disorders including Juvenile
Chronic Arthritis (JCA), Ankylosing Spondylitis (AS), Lyme disease, and other inflammatory conditions.2 Juvenile Chronic
Arthritis presents in one of three ways: Still’s disease, polyarticular,
or pauciarticular joint involvement. The pauciarticular form is most
likely to present with single hip involvement. The presentation is
not as florid as a septic joint, and may include pain, other joint
involvement, fever, weight loss, morning stiffness, or rash.2 Of
importance is the high risk of iridocyclitis in the pauciarticular
form that could lead to blindness if not treated by steroids. Lyme
arthritis can be suspected if the child lives in or has traveled to an
endemic area. An attempt to elicit a history of the characteristic
erythema migrans occurring 3-21 days after the tick bite is also
useful in diagnosing Lyme disease.2 The seronegative arthropathies
such as AS present with leg joint involvement in slightly older children. Appropriate investigations include CBC and differential,
ESR, CRP, RF, ANA, and Lyme serology.2 In JCA, Rheumatoid
Factor (RF) may be positive only in a minority of patients, and
these children are usually more severely affected. Complications
include differential growth of the affected limb (often larger than
the normal side), and destruction of the articular structures.8
DEVELOPMENTAL DYSPLASIA OF THE HIP
The incidence of developmental dysplasia (DDH) is 11.5/1,000 live births, with risk factors including female gender,
firstborn children, breech presentation, family history, oligohydramnios, and comorbid limb problems such as metatarsus
adductus. Patients usually do not present with a history as the disease is usually uncovered on screening physical examination at
birth.9 Key physical findings include positive Ortolani (an audible clunk as the hip reduces while being abducted) and Barlow (a
posterior dislocation of the hip when posterior pressure is applied
on a flexed hip) tests, leg length discrepancy, asymmetric skin
folds, and if the child remains undiagnosed at time of walking, a
waddling gait and hyperlordosis.9 Ultrasound is an important
component of diagnostic testing as the hip is mostly cartilage at
this point in life. Plain x-rays, however, can also offer important
information. The acetabular index is the angle between a line
drawn through the triradiate cartilage of the acetabula and a line
connecting the brims of the acetabulum on each side.9 A normal
acetabular index is up to 25º degrees. Increased values suggest
that the femoral head is not located correctly and corresponding
changes are causing a shallowing of the acetabulum. If caught
early, a Pavlik harness worn constantly for 6 weeks results in a
cure in 95% of cases. From 6 months to 2 years of age, skin traction, closed reduction and casting in a hip spica can keep the head
correctly located as well. After two years of age, open reduction
is the only effective treatment option. If untreated, pain, degenerative osteoarthritis, and differential limb growth can result.9
SUMMARY
The potential causes of hip pain or limp in a child are many
and varied, ranging from local disease such as septic hip or DDH
to systemic disease such as inflammatory arthritis. Some are true
emergencies, while others simply require reassurance and observation. In any event, important diagnoses ought not to be missed,
and one should not be fooled by lack of pain in the hip area. An
index of suspicion is necessary for timely diagnosis and referral,
and to avoid potentially disastrous sequelae.
AUTHOR’S NOTE
Although several important hip diseases were briefly discussed in this paper, this is by no means a comprehensive discussion of the subject. For more information, please consult the references listed below.
REFERENCES
1. Flynn JM, Widmann RF. 2001. The Limping Child: Evaluation and
Diagnosis. JAAOS 9(2):89-98.
2. Sucato DJ, Schewnd RM, Gillespie R. 1997. Septic Arthritis of the Hip
in Children. JAAOS 5(5):249-60.
3. Benson MKD, Fixsen JA, Macnicol MF, Bleck EE. 1994. Children’s
Orthopaedics and Fractures. Churchill Livingstone. Edinburgh.
4. Song KM, Sloboda JF. 2001. Acute Hematogenous Osteomyelitis in
Children. JAAOS 9(3):166-75.
5. Skaggs DL, Tolo VT. 1996. Legg-Calvé-Perthes Disease. JAAOS 4(1):916.
6. Aronsson DD, Karol, LA. 1996. Stable Slipped Capital Femoral
Epiphysis: Evaluation and Management. JAAOS 4(4):173-81
7. Reynolds RAK. 1999. Diagnosis and treatment of slipped capital
femoral epiphysis. Current Opinion in Pediatrics 11(1):80
8. Swann M. 1987. Juvenile Chronic Arthritis. Clinical Orthopedics and
Related Research. (219):38-49.
9. Morrissy RT, Weinstein SL. 1996. Lovell and Winter’s Pediatric
Orthopedics (4th ed). Lippincott-Raven. Philadelphia.
10. Hollister JR. 2003. Rheumatic Diseases. In Current Pediatric Diagnosis
and Treatment (16th ed). Hay WH, Hayward AR, Levin MJ, Sondheimer
JM. McGraw Hill. New York.
UWOMJ 74(2) 2006 45