24.1 Orthopaedics and rheumatology

Introduction

The child who has pathology of the bones and joints may present in a variety of ways. Acute paediatric musculoskeletal conditions range from the many infective, inflammatory and other causes of limp and limb pains, to the isolated acute limb fracture as a result of moderate trauma, which is among the top ten paediatric emergency department (ED) presentations in Australia.¹ An awareness of the range of possible conditions and their clinical appearance, and skilled physical examination and clinical reasoning, are essential for optimal outcomes.

The child with acute musculoskeletal pain or dysfunction

General approach

The spectrum of musculoskeletal pathology occurring in the paediatric population, with the exception of some fractures and adolescent injury, is very different from that seen in the adult population.

Infant and child development have extensive influence on the musculoskeletal pathology seen and its manifestations, as well as the techniques used in assessment. These differences are outlined in Table 24.1.1.

Table 24.1.1 How children differ: impact of development on musculoskeletal pathology
Body proportions
• Large, heavy head: higher fulcrum for spinal disruption • Low centre of gravity • Relatively short legs
Physiology of developing bone
• Zone of calcification: weakest point of muscle/tendon/ligamentous/bony continuum • Increased plasticity means increased susceptibility to plastic deformation, e.g. torus, bowing fractures • Physeal vulnerability predisposes to specific pathological responses to subacute or chronic microtrauma, e.g. avascular necrosis of ossification centres, slipped upper femoral epiphysis • Physeal damage from fracture or ischaemia produces long-term complications • High blood flow to physeal zones increases risk of vascular dissemination of bacterial disease, e.g. osteomyelitis
Joints and ligaments
• Increased flexibility means less brittleness and fewer fractures in response to arcuate deformation, e.g. carpal, tarsal, rib, vertebral fractures less common • Ligaments generally stronger than bones: sprains uncommon and complete ligamentous tears rare
Exposure to mechanisms
• Infant-abuse mechanisms especially shearing/shaking forces • Pre-school children fall on average four times a day (same-level falls) • Highly active pre- and school-age children have frequent, relatively low-force impactions from falls (monkeybars, trees) • Pedestrian vs. car causes classical femoral or tibial/fibula injuries from fender, plus head injury from secondary impact • High-force MVA/MBA/high energy sports injuries increase from adolescence
Immunology
• Increased incidence of bacterial and viral infection • More rapid dissemination of, and destruction from, bacterial infection
Psychology
• Fear and pain make young children difficult to examine and increase importance of observation and gentle handling • Immature intellectual development means poor verbalisation of symptoms, incomplete self-other differentiation, and other blocks to symptom communication • Medical management of traumatic experiences, such as injuries, may influence future psychological responses to trauma • Altered body perception increases susceptibility of adolescents (particularly females) to unconsciously exaggerated dysfunction in response to minor injuries
Healing
• Rapid healing of most fractures (e.g. femoral fractures: infants 3 weeks!) • Enormous remodelling potential of deformation within arc of use • Great ability to compensate, physically and psychologically, for loss of function • Minimal stiffness after immobilisation

MBA, motorbike accident; MVA, motor vehicle accident.

The limping child

The wide spectrum of causes of limp in children is illustrated in Table 24.1.2. In terms of frequency, common causes in different age groups are outlined in Table 24.1.3.

Table 24.1.2 Causes of acute limp in children
Trauma
• Fractures – accidental and non-accidental
Infection (point focus)
• Septic arthritis • Osteomyelitis • Inguinal lymphadenitis • Muscle abscess, e.g. psoas
Post-infective
• Rheumatic fever/post-streptococcal arthritis • Post-infectious arthritis, e.g. Salmonella, Shigella, or Campylobacter enteritis • Serum sickness • Post-immunisation inflammation
Inflammatory
• Transient synovitis • Vasculitis, e.g. Henoch–Schönlein purpura or Kawasaki disease • Inflammatory arthritis in lower limbs or axial skeleton, e.g. oligoarthritis • Enthesitis in pelvis or lower limbs, e.g. enthesitis related arthritis • Associated with, e.g. systemic lupus erythematosus, dermatomyositis, or inflammatory bowel disease
Primary bone disorders
• Slipped upper femoral epiphysis (SUFE) • Avascular necrosis, e.g. Perthes’ disease (hip), Freiberg’s disease (metatarsal heads) • Osteochondroses, e.g. Osgood–Schlatter disease (patellar tendon insertion), Sever’s disease (Achilles tendon insertion) • Unicameral bone cyst/aneurysmal bone cyst/fibrocystic disease/eosinophilic granuloma • Blount disease (asymmetrical tibial physis closure) • Tarsal coalitions
Neoplastic
• Leukaemia • Neuroblastoma • Bony tumours, e.g. Ewing’s sarcoma, osteosarcoma • Non-malignant tumours, e.g. osteoid osteoma, enchondroma
Haematological
• Haemarthrosis, e.g. Haemophilia A • Sickle cell disease arthropathy
Physical
• Splinter/foreign body • Compensatory, e.g. footwear • Soft-tissue and overuse injury • Joint hypermobility syndrome • Plantar warts/calcaneal spurs • Bites and envenomation
Psychological and idiopathic pain syndromes
• Pain amplification syndromes, conversion disorders • Complex regional pain syndrome (CRPS, previously known as reflex sympathetic dystrophy)
Abdominal
• Appendix • Infective and inflammatory bowel disease
Spine
• Scoliosis • Discitis • Transverse myelitis • Spondylolisthesis • Scheurman’s disease • Guillain–Barré syndrome

Table 24.1.3 Common causes of acute limp/single-limb dysfunction in children of various ages presenting to the ED with no specific history of trauma

Diagnoses that require specific treatment to avoid further damage or danger are primarily displaced or unstable fractures (including slipped upper femoral epiphysis), abusive injury (as a presenting feature or incidental finding), bone or joint infection, and neoplastic processes, principally bone tumours and leukaemia.

Table 24.1.4 Tips for assessing young children
• The foundation of acute musculoskeletal diagnosis is precise localisation of pain and dysfunction • The foundation of a productive paediatric examination is a relaxed, non-fearful child • Personality and parental factors aside, a gentle, slow-moving, highly observant examiner whom the child senses has the trust of the parent, will be most successful in gaining meaningful information
1. Be friendly and establish rapport with the parent 2. Ask parents for clues about site of pain, e.g. is it worse during nappy changes or being picked up under arm, crying associated with going over bumps in car ride, etc. If the child is old enough, ask them to tell or show you exactly where it hurts 3. Where possible, observe child at free play before attempting palpation 4. Visually scan child for alterations of posture, symmetry, or function 5. Record any other clues, such as temperature, dysmorphic features, bruising, psychological state 6. Examine the infant or child in parent’s arms (under 6 months and over 5 years they may often be assessed on the couch without concern) 7. Introduce a washable or disposable toy, such as light, name-badge, or ‘funny face’ 8. Make your first touch very gentle and at a site distant from the target limb! Keep some touch continuous so the rhythm is reassuring. Verbal soothing, such as a hum, may settle anxiety 9. Palpate the limb in question from one end to the other, watching the child’s face continuously 10. The first sign of discomfort may be an eyebrow flicker (i.e. a pre-frown) or a flinch 11. If discomfort is sensed, move touch to another area immediately and slowly move back in even more gently for confirmation and further information 12. Put all joints through their full range of movement unless discomfort is noted 13. Examine the spine, groin, and abdomen of all lower limb or gait-disturbed children 14. Areas of focal tenderness or limited range of motion can be further assessed by radiology or ultrasound

Other useful features in assessment include:

Observation and examination

• Gait if ambulant.

• Posture and symmetry.

• Activity level.

• Well-being – fever, heart rate.

• Bones, joints, soft tissues.

• Skin integrity.

• Abdomen and spine.

• Lymphadenopathy and lymphadenitis.

• Focal pathology, e.g. warts, bites, and callosities.

Lower limb joint examination should occur with the patient lying supine on the couch. Take note of the resting position of the joints and any asymmetry, redness, swelling, or wasting. Joints should be compared in symmetrical posture as position influences external appearance. Isolate joints (e.g. knee) when assessing range of motion so that incidental movement of another joint (e.g. hip) does not cause misleading results.

When assessing hip range of motion, the ‘flexion adduction’ test ² may be helpful: with buttocks flat on the bed, flex the hip (first the unaffected and then the affected) to 90 degrees while supporting the lower leg. Then gently attempt to fold the knee over the contralateral leg without child lifting the buttock off the couch. In the normal hip this adduction should allow the ipsilateral knee to be positioned over the opposite leg whereas an inability to adduct past the midline is common in the irritable hip or other causes of hip joint pathology.

At the conclusion of the history and examination the emergency physician should have established the overall well-being of the child, the site and severity of musculoskeletal pain, practical precipitants, and the likelihood of traumatic, infective, or other processes. In patients with minimal physical findings, or findings out of keeping with other aspects of history and examination, the environmental and psychological context of the limp should be explored further. Clues to possible neoplastic illness are discussed later in this chapter.

The child whose examination findings suggest an isolated irritable hip is likely to have one of the pathologies outlined in Table 24.1.5. A suggested pathway for investigation is shown in the algorithm in Fig. 24.1.1. This algorithm incorporates the findings of a number of studies of the prognostic significance of various features of the limping child with respect to septic arthritis, which are further discussed below.

Table 24.1.5 Comparative features of paediatric hip-joint pathology

Fig. 24.1.1 Algorithm for management of children >2 years presenting with acute irritable hip.

Investigations

A number of recent research findings have allowed for more selective and meaningful investigation of the limping child.

Inflammatory markers

Traditional blood investigations for inflammatory markers include full blood count (FBC), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).

FBC is useful primarily to flag bone marrow dysfunction. Each cell line (haemoglobin, white cells and platelets) should be individually assessed. The sensitivity of a raised white cell count (WCC) (>12 × 10⁹ L^–1) for the identification of septic arthritis is variable (20–75%).^3,⁴ The absence of an elevated white cell response should never be used to rule out septic arthritis. ESR has shown higher sensitivity (90–95%) in identifying the subgroup with septic arthritis; however, this may miss early infection.³ CRP has shown superior sensitivity (up to 80%)⁴ and specificity in the early identification of invasive bacterial infection in general and of septic arthritis in particular. CRP rises within 24 hours of acute illness, and also falls rapidly and can be used to monitor effectiveness of treatment.⁵

Radiology

X-ray

X-rays are usually non-contributory in children under 10 years of age with acute onset limp (<1 week) without a specific trauma history. Radiological findings in osteomyelitis are usually not present for up to 10 days from the onset of illness, at which time there may be periosteal elevation outlined by new bone formation and/or lucent areas.⁶ Due to the higher burden of pelvic or gonadal irradiation, non-selective or routine pelvic/lower limb radiology should not be encouraged. An effusion is better diagnosed by ultrasound, and deep soft tissue infection such as osteomyelitis, by magnetic resonance imaging (MRI). X-rays are required in trauma with focal tenderness or non-weight-bearing, to rule out SUFE (see below) in the adolescent child with hip pain/dysfunction with or without a trauma history, and in cases of persistent unexplained pain or limb dysfunction.

Ultrasound

Ultrasound is a sensitive, non-invasive assessment tool for evaluation of the irritable hip. It will detect even small hip effusions, may show a subperiosteal pus collection in some cases of osteomyelitis, and may be diagnostic for Perthes’ disease and SUFE,⁷ although it is not usually the first-line investigation for these pathologies. Disadvantages of ultrasound include variations in quality from different operators, and difficulty in after-hours access. An ultrasound cannot distinguish between reactive and infective effusions; however, the presence of an effusion confirms organic pathology and its absence in a clinically abnormal presentation should prompt a search for an extrasynovial focus. There is controversy over the place of ultrasound-guided hip aspiration in the evaluation of the irritable hip with an effusion.⁸ The majority of Australian paediatric orthapaedic units favour orthopaedic evaluation of irritable hips with selective aspiration and arthrotomy/washout under general anaesthesia. However, ultrasound-guided diagnostic hip aspiration has a role in some units.⁹^–¹¹

Bone scan

Isotope bone scans with three-phase technetium-99m MDP are sensitive early, and well tolerated by children, but lack specificity. Confusion may arise particularly in relation to physeal sites, where uptake is already above base-line. ‘Hot’ scans indicate increased osteoblastic uptake and generally relate to a response to infection or injury. A ‘cold’ scan suggests infarction, which in severe cases may be a consequence of osteomyelitis. Bone scan is of particular value in children in whom multifocal disease is suspected e.g. neonatal osteomyelitis or chronic recurrent multifocal osteomyelitis (CRMO).⁶

MRI

MRI is excellent for detailed delineation of soft-tissue and bony pathology, particularly when surgery is planned.¹² It is the investigative modality of choice to delineate the site of possible bacterial infection in a child with localised musculoskeletal pain and a septic picture in whom septic arthritis has been ruled out by clinical assessment, ultrasound or arthrocentesis.¹³ Limitations include cost, access limitations, and the need to remain still for a longer time period, necessitating general anaesthetic in most small children.

Clinical decision making in a child with a limp

Relative weightings of various symptoms and signs in the various acute paediatric hip pathologies are expressed in Table 24.1.5 and Fig. 24.1.1. However, spinal, abdominal, and pelvic pathology can present as a limp, and must be considered prior to this narrowed focus. The infant or toddler, because of their increased risk for invasive bacterial illness, also represents a special circumstance and the ill child under 2 with an abnormal acute musculoskeletal assessment is best admitted for combined paediatric and orthopaedic assessment and investigation.

The child over 2 with acute atraumatic localised knee or hip pain and an abnormal hip examination is most likely to have an irritable hip (transient synovitis), and the main issue is to exclude septic arthritis. An ultrasound assessment should confirm the suspicion of a hip effusion as suggested by examination, but does not differentiate between transudate and exudate. Table 24.1.6 lists conditions at higher risk of septic arthritis which must be flagged; however, the majority of infections occur in children without underlying pathology. Various attempts have been made to create a valid decision rule with a high sensitivity and specificity for bacterial infection,^4,¹⁴^–¹⁶ however none have demonstrated sustained power prospectively. The four most important variables to give a predicted probability of septic arthritis in a given child with an acutely irritable hip are shown in Table 24.1.7. Degree of pain and range of motion of the joint are auxiliary clinically important variables in the differentiation.

Table 24.1.6 Risk factors for septic arthritis
Relative immune deficit
• Neonates • Malnourished • HIV infection • Immunosuppressive therapy • Corticosteroid therapy
Injury mechanism
• Penetrating trauma
Joint disease
• Chronic arthritis • Sickle cell disease

Table 24.1.7 Features suggestive of deep bacterial infection in a child with an acutely irritable hip
Non-weight-bearing Febrile >38.5°C WCC > 12×10⁹ L^–1 ESR > 40 mm hr^–1 CRP > 20 mg L⁻¹

Specific syndromes

Transient synovitis

Transient synovitis is a self-limited inflammatory disorder of uncertain aetiology, occurring particularly in boys (70%) in the age group 3–10 years. The onset of lower limb pain is generally gradual and initially may be localised to hip, knee, groin or thigh. The child may be mildly unwell or have had a recent non-specific upper respiratory tract illness, although this is not uniformly present. Range of movement at the hip joint is usually mildly diminished, with discomfort at the end-points of the range. A hip effusion is present. Transient synovitis is a diagnosis of exclusion, the major differential being septic arthritis. Children with localised hip pain should be managed according to the algorithm in Fig. 24.1.1, and non-weight-bearing children with a hip effusion who do not have needle aspiration to rule out septic arthritis should be admitted under the close observation of the orthopaedic team. Weight-bearing children without unusual or high risk features can be managed with parental instruction, ibuprofen, and ED follow up in 2 days.^17,¹⁸

Prognosis

Taylor et al showed a 15% recurrence rate in transient synovitis,¹⁹ and there is some concern about occult Perthes’ being an underlying diagnosis, especially in those with delayed bone age at the first imaging.²⁰ All children discharged with this presumptive diagnosis should have orthopaedic follow up if pain or limp persists or recurs.