Knee Pain on Sitting-to-Standing with History of Trauma

Clinical Interpretation

Differential Diagnosis

1. Patellofemoral Pain Syndrome (PFPS) / Chondromalacia Patellae (Most Likely)

• Pain is anterior, worse with prolonged knee flexion (sitting), stair climbing, kneeling, and squatting
• Sit-to-stand is a classic aggravating movement
• Chondromalacia patellae = softening of the articular cartilage on the posterior patellar surface; trauma is a recognized precipitant
• Risk factors: quadriceps weakness, gluteal weakness, patellar subluxation/dislocation, prepatellar bursitis, Q-angle > 20 degrees (more common in females)

• Tenderness on medial/lateral patellar borders (especially post-subluxation/dislocation)
• Patellar grind test - direct anterior-to-posterior pressure on the patella while patient contracts quadriceps; positive if it evokes sudden pain
• Pain reproduced on single-leg squat on the affected side
• Crepitus at the patellofemoral joint suggests degenerative change
• "Theatre sign" - pain with prolonged sitting

2. Patellar Subluxation / Dislocation (Post-Traumatic)

• Mechanism: direct blow to medial patella, twisting injury, or forceful quadriceps contraction with knee flexed
• Post-reduction: knee immobilizer in full extension, orthopedic follow-up within 1-2 weeks
• High rate of recurrent dislocation despite physical therapy; persistent pain and laxity may need surgery
• On examination: medial and lateral patellar border tenderness, apprehension sign with lateral patellar displacement

3. Meniscal Tear

• Cardinal sign: joint line tenderness (medial or lateral)
• Symptoms: intermittent locking, effusion (typically delayed 12-24 hrs), "giving way," clicking/catching
• The posterior horn is more commonly injured (increased forces in flexion)
• Medial meniscus is most frequently torn but has poor blood supply - healing is impaired
• Sit-to-stand loads the posterior horn and can reproduce pain
• Tests: McMurray test, Thessaly test, joint line palpation
• MRI is preferred imaging (arthroscopy is gold standard); plain X-ray will miss it

4. ACL / PCL / Collateral Ligament Injury

• ACL: pop + immediate hemarthrosis, instability/"giving out," positive Lachman test; pain with weight-bearing transitions
• PCL: posterior force on flexed knee (dashboard injury, fall); sensation of femur "falling off" tibia; posterior drawer test
• MCL/LCL: tenderness along respective joint line, pain with valgus/varus stress
• Sit-to-stand loads the knee in mid-flexion where cruciate and collateral integrity is important

5. Osteochondritis Dissecans (OCD)

• Subchondral bone necrosis with overlying cartilage disruption
• Pain, swelling, giving-way episodes
• Most common at the lateral aspect of the medial femoral condyle
• Diagnosed on X-ray (subcortical lucency); CT/MRI for full extent
• Non-weight bearing until orthopedic review

6. Anterior Fat Pad Syndrome (Hoffa's Disease)

• Trauma to the anterior fat pad leads to fibrous changes and pinching, especially with genu recurvatum
• Pain at the anterior knee, worse with extension
• Treatment: activity modification, ice, padding, injection; rarely arthroscopic excision

7. Post-Traumatic Arthrofibrosis / CRPS

• Inflammatory pain lasting months following surgery or trauma
• CRPS (formerly RSD): pain out of proportion to findings, swelling, warmth, hyperhidrosis progressing to trophic skin changes, stiffness, patellar osteopenia
• Sit-to-stand aggravates any stiff, fibrotic knee

Key Differentiating Features

Investigations

1. Plain X-rays (AP, lateral, sunrise/skyline view) - assess patellofemoral joint space, fractures, OCD, osteoarthritis
2. MRI - gold standard for soft tissue (menisci, ligaments, cartilage, bone edema)
3. Ultrasound - useful for tendon integrity, bursitis

Management Approach

• Rest, activity modification, ice
• NSAIDs for pain and inflammation
• Physical therapy - quadriceps strengthening, hip abductor strengthening (improves PFPS outcomes), VMO rehabilitation
• Patellar taping/bracing
• Weight management

• Meniscal repair/debridement (especially locked knee or failed conservative therapy)
• ACL reconstruction (younger, active patients)
• Lateral release, tibial tubercle realignment (recurrent patellar instability)
• Arthroscopy for loose bodies (OCD), arthrofibrosis