Differential Diagnosis of Knee Pain: A Physiotherapy Guide

Anterior knee pain is the most frequent knee complaint in young and active patients. The key conditions to differentiate include:

Patellofemoral Pain Syndrome (PFPS) — Diffuse anterior knee pain aggravated by stairs, squatting, prolonged sitting (cinema sign), and running. No specific structural pathology on imaging. Often associated with poor hip and quadriceps control.

Patellar Tendinopathy — Localised pain at the inferior pole of the patella. Worse with loading activities (jumping, landing). Point tenderness on palpation of the tendon. Common in jumping athletes.

Osgood-Schlatter Disease — Adolescents with pain and swelling at the tibial tuberosity. Aggravated by activity. Often bilateral. Self-limiting.

Fat Pad Impingement (Hoffa's Syndrome) — Pain in the infrapatellar region, worse with knee hyperextension. Positive Hoffa's test.

Prepatellar Bursitis — Swelling directly over the patella. History of kneeling (carpet layers, plumbers). Tender on direct palpation.

Medial Collateral Ligament (MCL) Sprain — History of valgus stress injury. Pain and tenderness along the medial joint line. Positive valgus stress test. Graded I–III by severity.

Medial Meniscus Tear — Joint line tenderness, pain with twisting movements, possible locking or giving way. Positive McMurray's test (medial). More common in older patients with degenerative tears; traumatic tears occur in younger patients.

Pes Anserine Bursitis — Pain and tenderness 2–3 cm below the medial joint line. Common in overweight, middle-aged women and patients with osteoarthritis.

Medial Plica Syndrome — Medial knee pain with a palpable, tender band. Snapping or clicking sensation. Often misdiagnosed as meniscal pathology.

Iliotibial Band Syndrome (ITBS) — The most common cause of lateral knee pain in runners. Pain at the lateral femoral epicondyle, typically at 30° of knee flexion. Positive Ober's test and Noble compression test. Aggravated by running downhill.

Lateral Collateral Ligament (LCL) Sprain — History of varus stress injury. Less common than MCL injury. Positive varus stress test.

Lateral Meniscus Tear — Lateral joint line tenderness. Positive McMurray's test (lateral). Less common than medial meniscus tears.

Proximal Tibiofibular Joint Dysfunction — Often overlooked. Pain at the proximal fibular head. Aggravated by ankle dorsiflexion and knee flexion.

Baker's Cyst (Popliteal Cyst) — Posterior knee swelling and tightness. Often secondary to intra-articular pathology (meniscal tear, OA). Confirmed by ultrasound.

Posterior Cruciate Ligament (PCL) Injury — Less common than ACL injury. Mechanism: direct blow to anterior tibia (dashboard injury). Positive posterior drawer test and posterior sag sign.

Hamstring Tendinopathy — Proximal or distal hamstring pain. Proximal: pain at the ischial tuberosity, worse with sitting. Distal: pain at the medial or lateral hamstring insertions.

Osteoarthritis — Diffuse knee pain, crepitus, reduced range of movement, bony enlargement. Worse with activity and after rest. More common in older patients.

When assessing knee pain, use this systematic approach:

1. Location of pain — Anterior, medial, lateral, or posterior? This immediately narrows your differential.
2. Mechanism of onset — Traumatic or insidious? Traumatic onset raises suspicion of ligament, meniscal, or bony injury.
3. Aggravating factors — Stairs and squatting → PFPS. Running → ITBS. Twisting → meniscal. Loading → patellar tendinopathy.
4. Special tests — Use tests to confirm or refute your working hypothesis. No single test is definitive — use clusters of findings.
5. Red flags — Unexplained swelling, locking, giving way, or night pain require further investigation. Refer if in doubt.

Documenting your reasoning clearly — including what you ruled out and why — is as important as reaching the correct diagnosis.