“I twisted my knee playing football — it swelled up, it clicks and catches, and sometimes it locks so I can’t straighten it”

A MENISCAL TEAR is suggested by a TWISTING injury on a planted/loaded knee, an EFFUSION developing over hours (rather than immediately), JOINT-LINE tenderness, and MECHANICAL symptoms — clicking, catching, giving way and LOCKING — with McMurray’s test able to support but not reliably exclude the diagnosis. Apply the OTTAWA KNEE RULES (Stiell 1996–1997, international) to decide on X-ray (to exclude fracture): image if age ≥55, isolated patellar tenderness, fibular-head tenderness, inability to flex to 90°, or inability to weight-bear for 4 steps (immediately and in clinic). Recognise the more urgent presentations: a TRUE LOCKED KNEE or true locking episodes in a young person (unable to fully extend, often a displaced bucket-handle meniscal tear blocking the joint) need urgent MRI and orthopaedic review because early repair may be possible (BASK 2019), with same-day assessment if locked now, and an acute ACL injury — immediate haemarthrosis (rapid swelling), an audible "pop" and instability/giving way — warrants orthopaedic/MRI assessment; distinguish a genuinely locked knee from pain-limited pseudo-locking. Screen for septic arthritis (fever, hot joint). Manage stable, non-locking meniscal injuries initially conservatively (RICE, analgesia, physiotherapy with quadriceps strengthening and range of motion, activity modification), as many small/degenerate tears settle (NICE NG226 for degenerative knees), and arrange MRI and orthopaedic referral for a true locked knee (urgent), persistent significant mechanical symptoms, suspected ACL/ligament injury, or failure of conservative management — with arthroscopy in selected cases. Safety-net for locking that won’t unlock, inability to weight-bear, or instability, or a hot very swollen knee.