Assessing Musculoskeletal Pain: Knee Pain at 15

Three details in two sentences do most of the diagnostic work here, and the question is built so that noticing them is the assessment. The pain is *bilateral*, which pushes hard against a traumatic or mechanical cause — a torn meniscus does not usually present symmetrically — and towards something anatomical, developmental or overuse-related affecting both limbs the same way. The patient is *fifteen*, which puts him in an open-physis age group where injuries cluster at the growth plates and apophyses rather than in the ligaments. And the catching sensation is located *under the patella*, which is anatomically specific: it points at the patellofemoral joint rather than at the tibiofemoral compartment. Say all three out loud in your reasoning, because a differential that ignores laterality and skeletal maturity will contain the wrong conditions no matter how long it is.

The question asks what *categories* you can use to differentiate knee pain, and it wants a framework rather than a longer list. Several work. Anatomical location is the most natural here — anterior, medial, lateral and posterior pain each carry their own short differential, and anterior knee pain in an adolescent is a well-defined problem. You could also organise by structure, taking bone, cartilage, ligament, tendon, bursa and synovium in turn; or by mechanism, separating acute trauma from overuse from atraumatic and systemic causes. Whichever you choose, state it explicitly and then work inside it, because the marker is assessing whether you can impose order on a symptom rather than whether you can recall conditions. A named framework applied consistently reads as clinical thinking; an unstructured list reads as recall. Say why you chose the framework you did, because the question asks what categories you can use rather than which one is correct, and a sentence justifying the choice answers it more completely than the scheme alone.

Additional history is where most of the marks sit, and the questions should be driven by the differential rather than gathered generically. Onset and mechanism: was there a single incident, or did this build up? Activity: what sport, at what volume, and did the training load change recently, since a step up in intensity is the classic precipitant for overuse presentations at this age. Aggravating and relieving factors, with particular attention to stairs, squatting and prolonged sitting, which reproduce patellofemoral pain characteristically. Mechanical symptoms: does the knee lock, give way, or swell, and does the catching correspond to a specific movement. Then growth history, prior injury, systemic features such as fever, morning stiffness or other joint involvement, and family history — because a bilateral presentation keeps inflammatory arthropathy honestly in the frame. Ask about footwear, playing surface and any recent growth spurt as well, since each is a recognised contributor to load at the knee and each suggests a management step that costs the patient nothing.

Build the differential around anterior knee pain in a skeletally immature adolescent, and say what would confirm or exclude each candidate rather than merely naming it. Patellofemoral pain syndrome fits the presentation most closely and is the commonest cause in this age group. Osgood-Schlatter disease is bilateral in a substantial proportion of cases and localises to the tibial tubercle. Sinding-Larsen-Johansson affects the inferior patellar pole. Osteochondritis dissecans deserves specific mention because it genuinely produces catching and locking and because missing it has consequences. Patellar instability or maltracking, plica syndrome, patellar tendinopathy and, at the serious end, juvenile idiopathic arthritis and neoplasm complete a defensible list. Five well-argued conditions beat ten asserted ones. Order them by likelihood and say so, because a differential presented as a ranked list demonstrates that you can weigh candidates rather than merely generate them, and it makes the subsequent examination plan follow naturally.

The examination questions are asking you to be systematic and to name the structure each manoeuvre interrogates. Inspect for effusion, alignment, quadriceps bulk and Q-angle; palpate the tibial tubercle, the patellar poles, the joint lines and the retinacula; assess active and passive range with crepitus; test quadriceps and hamstring strength and flexibility. Then the special tests, each tied to what it examines: patellar grind for the patellofemoral articular surface, patellar apprehension for instability, McMurray and Apley grind for meniscal pathology, Lachman and anterior drawer for the cruciates, varus and valgus stress for the collaterals. Examine the *unaffected* structures too and examine both knees, since a bilateral complaint means there is no normal side to compare against and asymmetry has to be found another way. Watch gait and a single-leg squat too, since both reproduce the loading that provokes patellofemoral symptoms and can reveal the dynamic malalignment that a static examination on the couch will miss entirely.

Two framing points will lift the answer. First, the question asks what anatomic structures you are assessing — that phrasing wants you to move from the name of a test to the tissue it loads, so pair each manoeuvre with its target rather than listing tests and structures in separate paragraphs. Second, be explicit about what would change your mind. Say which findings would push you towards imaging, given that radiographs are reasonable where osteochondritis dissecans or an apophyseal injury is suspected while patellofemoral pain is a clinical diagnosis needing none. Naming a red flag — night pain, systemic symptoms, an effusion out of proportion, a palpable mass — and saying what it would trigger demonstrates the safety reasoning that separates an adequate answer from a good one. Say what your working diagnosis is at the end as well, because six questions about method can produce an answer that never actually commits, and the marker is looking for a clinician rather than a checklist.