What could be causing my knee pain that occurs when I stand up but not when I'm walking?

Knee Pain When Standing Up But Not While Walking

Your knee pain that occurs specifically when standing up but not during walking most likely represents patellofemoral pathology, particularly involving the patellofemoral joint under loaded flexion positions, or early osteoarthritis with bone marrow lesions that are mechanically stressed during the sit-to-stand transition.

Most Likely Diagnoses Based on Your Symptom Pattern

Patellofemoral Disorders

• Patellofemoral cartilage loss and friction syndrome are strongly associated with anterior knee pain during loaded activities like standing from a seated position 1, 2.
• The patellofemoral joint experiences maximum compressive forces during knee flexion under load (such as rising from a chair), which explains pain during standing but not during the lower-stress activity of walking 1.
• Patellar tendinopathy commonly causes anterior knee pain during activities requiring knee extension against resistance 2.
• Fat pad impingement syndromes and Hoffa's disease (characterized by synovitis >2mm in Hoffa's fat) correlate specifically with peripatellar pain during mechanical stress 1, 2.

Early Osteoarthritis with Bone Marrow Lesions

• Bone marrow lesions (BMLs) are strongly associated with increased knee pain, particularly during weight-bearing transitions 1.
• BMLs represent areas of increased edema-like signal in subchondral bone that are mechanically sensitive during loading 1.
• Synovitis and joint effusion may indicate the origin of pain in early osteoarthritis, causing pain during specific mechanical stresses like standing 1.

Subchondral Insufficiency Fractures

• These fractures most commonly involve the medial femoral condyle in middle-aged to elderly females and cause pain during weight-bearing transitions 1.
• Radiographs are often initially normal, with MRI identifying these fractures earlier 1, 2.
• This condition can progress to articular surface fragmentation and collapse if not identified 1, 2.

Critical Differential: Rule Out Referred Pain First

Lumbar Spine Pathology

• Referred pain from the lower back must be considered when knee symptoms occur during specific movements, especially if knee radiographs are unremarkable 1, 3.
• Radicular symptoms or nerve compression can manifest as knee pain during position changes without back pain 3.
• A thorough lumbar spine examination including straight leg raise should be performed before attributing all symptoms to knee pathology 3.

Hip Pathology

• Hip pathology commonly refers pain to the knee and should be evaluated if knee imaging is normal 1, 2.
• Hip range of motion and provocation tests should be examined, as hip disorders can cause knee pain during standing transitions 3.

Diagnostic Algorithm

Initial Clinical Evaluation

• Assess for anterior knee pain during squatting, which is 91% sensitive and 50% specific for patellofemoral pain 4.
• Examine for joint line tenderness (83% sensitive and 83% specific for meniscal pathology) 4.
• Perform McMurray test with concurrent knee rotation and extension (61% sensitive, 84% specific for meniscal tears) 4, 5.
• Check for crepitus in the patellofemoral compartment and limited range of motion suggesting osteoarthritis 5.

Imaging Strategy

• Begin with weight-bearing radiographs including frontal projection, tangential patellar view, and lateral view 1, 6.
• Approximately 20% of patients with chronic knee pain undergo MRI without recent radiographs, which should be avoided 1, 2, 6.
• If radiographs are normal or show only joint effusion but pain persists, proceed to MRI without IV contrast 1.
• MRI accurately depicts BMLs, synovitis, effusion, cartilage abnormalities, and subchondral insufficiency fractures 1.
• If knee imaging is unremarkable and clinical evidence suggests spinal or hip origin, image those areas 1, 3, 6.

Treatment Approach

Conservative Management (First-Line)

• Exercise therapy focusing on hip and knee strengthening is first-line treatment for patellofemoral pain 4.
• Weight loss if overweight, education, and self-management programs are recommended for osteoarthritis 4.
• Exercise therapy for 4-6 weeks is appropriate for most meniscal pathology 4.
• Foot orthoses or patellar taping in combination with strengthening exercises for patellofemoral disorders 4.

When Conservative Treatment Fails

• Intra-articular corticosteroid injections and radiofrequency ablation of genicular nerves have shown effectiveness 7.
• Hyaluronic acid infiltrations are conditionally recommended 7.
• Surgical referral should be considered only for end-stage disease after exhausting conservative options 4, 7.

Critical Pitfalls to Avoid

• Not all structural abnormalities seen on imaging are symptomatic, particularly in patients over 45 years 1, 3.
• The majority of people over 70 years have asymptomatic meniscal tears 1.
• Bilateral structural abnormalities can exist with primarily unilateral symptoms in patients over 70 years 2, 6.
• Radiographs may be initially normal in subchondral insufficiency fractures, which later show articular surface fragmentation 2, 3.
• Do not overlook referred pain from hip or lumbar spine before attributing all symptoms to knee pathology 2, 6.
• Surgery is not indicated for degenerative meniscal tears even in the presence of mechanical symptoms like locking or catching 4.