What are the differential diagnoses (DDXs) for a patient presenting with knee pain and tibial eversion?

Differential Diagnoses for Knee Pain with Tibial Eversion

The primary differential diagnoses for knee pain with tibial eversion (external tibial torsion) include miserable malalignment syndrome, patellofemoral pain syndrome with rotational malalignment, early patellofemoral osteoarthritis, and component malrotation if the patient has undergone total knee arthroplasty. 1, 2

Primary Pathological Considerations

Miserable Malalignment Syndrome

• This represents the most specific diagnosis when external tibial torsion exceeds 37-70° and is associated with anterior knee pain. 2
• The syndrome consists of femoral anteversion (typically >30°) combined with excessive external tibial torsion (>37°), creating a complex torsional deformity that mechanically overloads the patellofemoral joint. 2
• Patients characteristically present with anterior knee pain during weight-bearing activities, particularly stair climbing and squatting. 2
• The external tibial rotation causes the foot to point outward while the patella faces forward, creating abnormal tracking forces. 2

Patellofemoral Pain Syndrome with Rotational Deformity

• PFPS is the most common cause of anterior knee pain in patients under 40 years, and rotational malalignment significantly contributes to its development. 1, 3
• External tibial torsion increases lateral patellar tracking forces, predisposing to retropatellar pain that worsens with knee flexion under load. 1, 4
• The condition presents with pain during stair climbing (91% sensitive), squatting, and prolonged sitting with flexed knees. 3, 5
• Lower extremity rotational deformities act as predisposing factors rather than direct causes—patients with unilateral symptoms often have similar morphology in their asymptomatic contralateral limb. 4

Early Patellofemoral Osteoarthritis

• Patients aged 45-55 years with knee pain and normal radiographs can have elevated T2 mapping values on MRI indicating early cartilage changes that present clinically identical to PFPS. 1
• The medial compartment bears 70-80% of joint load during mid-stance gait, but rotational malalignment can alter this distribution and accelerate cartilage degeneration. 6
• Bone marrow lesions and synovitis/effusion are significantly related to frequent knee pain in osteoarthritis patients. 1

Post-Arthroplasty Component Malrotation (If Applicable)

• Internal malrotation of femoral and/or tibial components is the most common cause of patellofemoral instability after total knee arthroplasty (1-12% incidence). 6
• Excessive combined internal rotation of tibial and femoral components is directly proportional to the severity of patellofemoral complications. 6
• The tibial component should be positioned in approximately 18° of internal rotation relative to anatomic landmarks. 6
• Even 180° rotation of a mobile-bearing tibial insert can occur with minimal trauma, causing persistent pain and stiffness. 7

Critical Diagnostic Distinctions

Why External Tibial Torsion Causes Anterior Knee Pain

• The external rotation of the tibia creates a mechanical mismatch between foot progression angle and patellar orientation, forcing abnormal lateral tracking of the patella during gait. 2, 4
• This malalignment increases the Q-angle functionally (even if static Q-angle appears normal), elevating lateral retinacular tension and subchondral stress. 4
• Patients with symptomatic knees demonstrate significantly greater femoral anteversion and lateral tibial torsion compared to healthy controls, though their asymptomatic contralateral knees may show similar morphology. 4

Referred Pain Sources to Exclude

• Hip pathology must be evaluated if knee imaging is normal, as hip disorders commonly refer pain to the knee. 1, 8, 9
• Lumbar spine pathology should be considered when knee radiographs are unremarkable and clinical evidence suggests spinal origin. 1, 8, 9

Diagnostic Algorithm

Initial Clinical Assessment

• Document the foot progression angle during gait—external rotation >20° suggests significant tibial torsion. 2
• Assess for anterior knee pain during squatting (91% sensitive for patellofemoral pathology). 3
• Measure Q-angle, though recognize that patients with unilateral symptoms may have bilateral rotational deformities. 4
• Examine for knee effusion, which indicates underlying pathology requiring further investigation. 1, 8

Imaging Sequence

• Obtain anteroposterior and lateral knee radiographs first to exclude fractures, osteoarthritis, and loose bodies. 1, 8, 9
• If radiographs are normal or show only effusion and pain persists, proceed to MRI without contrast to evaluate soft tissue pathology, bone marrow lesions, and early cartilage damage. 8
• CT scan with rotational profile is indicated when rotational malalignment is suspected, measuring femoral version, tibial torsion, and tibial tubercle-trochlear groove distance. 2
• For post-arthroplasty patients, CT is the modality most commonly used for measuring component rotation. 6

Common Pitfalls to Avoid

• Do not order MRI without recent radiographs (within the past year)—approximately 20% of patients inappropriately receive MRI without prior radiographs. 8, 9
• In patients over 45 years, meniscal tears are equally common in painful and asymptomatic knees, making MRI findings potentially misleading. 8
• The presence of rotational deformity in the asymptomatic contralateral limb does not exclude it as the cause of unilateral symptoms—threshold effects likely exist. 4
• Recognize that stair climbing shows strong evidence for NO increased risk of developing knee OA, distinguishing it as a pain-provoking activity in existing pathology rather than a causative factor. 1