# Patellar Dislocation > Patellar dislocation for NEET-PG Orthopaedics: lateral dislocation, MPFL tear, apprehension test, TT-TG distance, first-episode care and MPFL reconstruction. - Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/patellar-dislocation - Exam / course: NEET-PG · Subject: Orthopaedics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Patellar Dislocation", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/patellar-dislocation ## Direct answer A pivoting teenager feels the kneecap escape laterally, the knee buckles into a strange flexed pseudo-locked posture, and by the time imaging happens the patella has usually flipped back on its own — first-time lateral patellar dislocation, the commonest acute patellar problem. The medial patellofemoral ligament, avulsed from the femur or patella, is the restraint lost; risk factors gather around trochlear dysplasia, patella alta, an increased tuberosity-trochlear groove distance and generalised laxity, clustering in adolescent girls. A first episode is managed conservatively — brief immobilisation followed by quadriceps, especially vastus medialis, rehabilitation — while recurrent instability or an osteochondral fragment loose in the joint moves management toward arthroscopy and medial patellofemoral ligament reconstruction, with tubercle realignment for marked malalignment. ## What you must remember - **Direction and structure:** virtually always lateral; the medial patellofemoral ligament (MPFL) is the primary medial restraint in early knee flexion and is torn in nearly every acute dislocation. - **Who:** adolescent and young adult females, ligamentously lax, often with a family history; occasionally habitual (displacing with every flexion cycle) in children, a different mechanical problem. - **The risk-factor quartet:** trochlear dysplasia (the dominant anatomical factor), patella alta, tuberosity-trochlear groove distance above about 20 millimetres, and an increased Q angle with weak vastus medialis. - **The named test:** the patellar apprehension test — laterally directed pressure on the patella at 20 to 30 degrees of flexion makes the patient seize the thigh in anticipation of dislocation; positive in instability, pathognomonic enough for exams. - **Imaging:** skyline or Merchant views for congruence and fragments; magnetic resonance imaging confirms the MPFL tear and the osteochondral shearing injury off the medial patellar facet and lateral trochlea. - **First-episode management:** conservative — a short period of bracing in extension, then structured physiotherapy emphasising vastus medialis, hip abductors and core; the exceptions are an osteochondral loose body and extensor-mechanism disruption, which are operated. - **Recurrent dislocation:** MPFL reconstruction, typically with a gracilis tendon graft, adding tibial tubercle medialisation or distalisation when the TT-TG distance is markedly increased. ## The kneecap that won't stay A 16-year-old netballer plants her foot, twists, and feels the kneecap shift out; the knee swells within hours with a haemarthrosis, and the story of it "going back with a clunk" as she straightened the leg completes the classical history. She is tender along the medial retinaculum, apprehensive under lateral patellar pressure — the examination's decisive moment — and the skyline view shows a small osteochondral fragment lying in the lateral gutter, sheared from the medial patellar facet. This first episode breaches the conservative rule at one point: the loose body. Arthroscopy removes or fixes the fragment, the haemarthrosis is decompressed, and she still completes the standard rehabilitation, because her first dislocation earns her ligament a chance to heal. Eight months later she dislocates stepping off a bus — the natural history of neglected risk factors. The pathway now measures the anatomy: magnetic resonance imaging shows trochlear dysplasia and an MPFL scarred in laxity, and the TT-TG measures 21 millimetres. Surgery addresses both — MPFL reconstruction with a gracilis graft to rebuild the checkrein, and a medialising tubercle osteotomy to realign the extensor corridor — after which rehabilitation is slower and squatting returns late. Indian counselling has one extra paragraph: deep squatting and cross-legged sitting load the patellofemoral joint heavily and are cultural daily functions, so return-to-activity guidance is negotiated with the family, not merely prescribed. ## How the exam frames it Four stems carry the marks. The direction — lateral, always. The structure — MPFL, whose name examiners now expect rather than the old vague "medial retinaculum". The test — apprehension, described with the patient's protective grasp as the positive endpoint. The management fork — first episode conservative, recurrent or fragment-bearing episodes surgical, with TT-TG above 20 millimetres as the number that adds a tubercle procedure. Trochlear dysplasia earns its own question as the strongest anatomical predictor. The habitual dislocation of childhood — the patella tracking out with every flexion — appears as a contrast stem: a different entity, often with tight lateral retinaculum or quadriceps contracture, treated by addressing that pathology rather than reconstruction. ## Frequently asked questions ### Which ligament is torn in acute patellar dislocation? The medial patellofemoral ligament, the primary medial stabiliser of the patella in early flexion, avulsed from its femoral or patellar attachment. ### What is the patellar apprehension test? Laterally directed pressure on the patella with the knee at 20-30 degrees of flexion; the patient's reflex seizing of the thigh from fear of dislocation constitutes a positive result. ### How is a first-time dislocation managed? Conservatively — brief bracing, then structured quadriceps and vastus medialis rehabilitation — unless an osteochondral loose body or extensor-mechanism injury mandates surgery. ### What TT-TG distance is considered abnormal? Above about 20 millimetres (with 15-20 borderline), indicating lateralisation of the tibial tuberosity that may warrant realignment alongside ligament reconstruction. ### When is MPFL reconstruction performed? For recurrent dislocation or persistent instability after adequate rehabilitation, typically with a gracilis tendon graft, combined with tubercle transfer when malalignment is severe.