A childhood-limp question may contain a familiar age, a recent viral illness and a plausible benign explanation. The task is to decide whether the whole presentation supports that explanation. Weight-bearing, systemic illness, the duration of symptoms and the hip examination can change the answer more than a memorable diagnostic phrase.
These original practice cases show how to compare possibilities without turning an age range into a diagnostic rule. They also separate the most likely diagnosis from the safest next action. In an acutely unwell child, arranging appropriate assessment can be the priority before a definitive cause has been established.
Start with the decision, then build the differential
Before reading the options, identify what the stem asks. A diagnosis question requires the best explanation of the information provided. A management question may require urgent referral, further examination or an investigation. Naming a possible condition is not enough when the patient needs an immediate action.
Four questions organise the first pass: is the child systemically well, can they bear weight, how did the problem develop, and where does examination localise the pain? The NHS overview of limping in children highlights the importance of assessment and urgent features. The examples below develop those observations into examination reasoning.
Case one: the recent viral illness is not the decisive detail
A four-year-old has a recent upper respiratory illness, but now has a temperature of 39 C, severe hip pain and refuses to bear weight. Passive movement is markedly painful. The options include transient synovitis, reassurance with review, urgent hospital assessment and routine physiotherapy.
Urgent assessment is the appropriate next action. A preceding viral illness can make transient synovitis attractive, but it does not account safely for this combination of fever, severe pain and inability to bear weight. Septic arthritis and other serious causes need prompt consideration.
NICE guidance on fever in under-fives identifies non-weight-bearing, limb swelling and non-use of an extremity as features that can indicate bone or joint infection. The practice point is not that every febrile limp has one diagnosis. It is that a benign label should not postpone assessment of a concerning presentation.
When reviewing this item, ask which part of the stem you gave most weight to. If the words "recent viral illness" determined the answer before you processed the examination, the error was premature closure rather than failure to remember the differential.
Case two: a well child still needs a complete assessment
A five-year-old develops a mild limp after a viral illness. They are afebrile, appear well and can bear weight with discomfort. There is a short history, no significant trauma and no concerning systemic or neurological feature after examination. Transient synovitis may be a reasonable working diagnosis once important alternatives have been considered.
The difference from case one is the whole clinical picture. A reassuring assessment supports a less urgent plan, but it should include an appropriate review and instructions to return if pain increases, fever develops or weight-bearing deteriorates. Improvement is part of the subsequent assessment; it should not be assumed in advance.
An examination question may ask what additional information is most useful before management is decided. In that situation, assessing weight-bearing, temperature and the hip can be more valuable than immediately ordering a broad panel of blood tests. The answer depends on what the stem has already established.
For revision, write a two-column comparison of these first two cases. Keep the viral history in both columns. Move the fever, severity, movement restriction and ability to walk between them. This makes the discriminatory information more visible than a list of isolated condition summaries.
Case three: a persistent limp changes the differential
A seven-year-old has a gradually developing limp over six weeks. They are otherwise well and sometimes complain of knee pain. Examination finds restricted hip movement, particularly abduction and internal rotation. A continuing diagnosis of a brief post-viral problem no longer explains the course adequately.
Perthes disease becomes an important consideration in this pattern. East Lancashire Hospitals' information on Perthes disease describes a gradually developing limp, variable pain and hip stiffness. The knee complaint should not stop the examination at the knee.
The duration is doing useful work in the question. It turns a single episode into a persistent process and makes reassessment necessary. Repeating advice intended for a short, improving illness would ignore the new evidence.
The next revision task is to compare a persistent well-child limp with an acute painful limp. Identify which findings support investigation and specialist assessment even when the child is not febrile. Systemic wellness is helpful information, but it does not establish that every musculoskeletal problem is self-limiting.
Case four: the knee may be reporting a hip problem
A 13-year-old presents with knee pain and a limp. The knee examination does not explain the symptoms. Hip internal rotation is restricted, and the leg tends to rotate externally when the hip is flexed. Slipped upper femoral epiphysis should be considered urgently.
NHS Inform's SUFE guidance describes the hip disorder and its possible referred symptoms. A suspicious presentation requires urgent orthopaedic assessment, with weight-bearing avoided while that is arranged. The NHS Tayside pathway reinforces the need for urgent management.
An answer limited to knee exercises misses the anatomical source. The useful habit is to examine the joint above and below when symptoms and local findings do not fit. In an SBA, an otherwise normal knee can be a deliberate clue that the site of pain and the site of disease differ.
Avoid turning useful patterns into absolute rules
Age helps organise a differential but does not make a diagnosis. A child outside a commonly taught age range still needs an explanation for concerning symptoms. Similarly, fever may be absent in serious disease, and the ability to walk does not exclude every important disorder.
Persistent night pain, systemic symptoms, bruising, unexplained swelling or a presentation inconsistent with the stated mechanism should broaden the assessment. NICE suspected-cancer guidance provides relevant pathways for concerning bone and systemic presentations in children. Safeguarding concerns also require attention to the full history and examination.
A short method for reviewing these questions
After each item, record the detail that changed the decision: systemic illness, inability to bear weight, persistence, hip restriction or discordance between symptoms and examination. Then attempt another example that changes only one of those features. This makes it possible to see whether your reasoning changes appropriately.
The iatroX AKT bank and Socratic Tutor can support that comparison by helping you explain why an alternative was tempting and what it failed to account for. Spaced review is most useful when it revisits the clinical distinction, rather than only the original diagnostic label.
Frequently asked questions
Does a recent viral illness establish transient synovitis?
No. It is one contextual feature. Systemic illness, severe pain, restricted movement and inability to bear weight can require urgent assessment despite that history.
Why should the hip be examined when a child reports knee pain?
Hip pathology can produce referred knee pain. A knee examination that does not explain the complaint should prompt assessment beyond the painful site, especially when a limp or restricted hip movement is present.
Should these four diagnoses cover all my childhood-limp revision?
No. They teach useful contrasts, but the differential also includes trauma, inflammatory disease, other infection, neurological conditions, malignancy and safeguarding concerns. The task is to use the complete presentation to decide what needs consideration.
Practise interpreting the decisive details with iatroX's MRCGP AKT question bank.