Can knee arthritis cause pes planus, plantar fasciitis, and hallux valgus?

The Relationship Between Knee Arthritis and Foot Deformities

Knee osteoarthritis can contribute to the development of pes planus (flat foot), plantar fasciitis, and hallux valgus (bunion) through biomechanical alterations in the lower extremity. The most recent evidence shows a strong association between knee OA severity and foot deformities, with altered biomechanics being the primary mechanism 1.

Biomechanical Relationship Between Knee OA and Foot Deformities

Pes Planus (Flat Foot)

• Knee OA alters lower limb biomechanics, leading to compensatory changes in foot posture
• The 2024 study shows that increased severity of knee OA correlates with worsened flat foot deformity 1
• Limited ankle dorsiflexion in knee OA patients significantly increases the risk of developing flat foot (OR = 3.889) 2
• Patients with knee OA and flat feet show significantly worse functional scores compared to those without foot deformities 3

Plantar Fasciitis

• 52% of knee OA patients experience heel pain, with ultrasound confirming plantar fasciitis in 62% 2
• Risk factors for plantar fasciitis in knee OA patients include:
  • Limited ankle dorsiflexion (primary risk factor)
  • Limited plantar flexion
  • Reduced range of supination
  • Low arch (pes planus) 2

Hallux Valgus (Bunions)

• Hallux valgus is significantly correlated with increased disability in knee OA patients 3
• The hallux valgus angle shows a positive correlation with WOMAC scores (r = 0.362), indicating that more severe bunions are associated with greater knee-related disability 3

Pathophysiological Mechanisms

1. Altered Gait Mechanics

   • Knee OA causes antalgic gait patterns that redistribute weight and stress to the foot
   • Patients compensate for knee pain by altering foot strike patterns and weight distribution 4

2. Muscle Dysfunction

   • Knee OA leads to changes in muscle activation patterns in the lower leg
   • Altered timing of soleus and medial gastrocnemius muscles affects foot positioning 5
   • Increased tibialis anterior activity can contribute to foot deformities 5

3. Joint Alignment Changes

   • Knee OA often involves tibiofemoral angle changes that affect the mechanical axis of the lower limb
   • These alignment changes transfer abnormal forces to the foot 1

Clinical Implications

Assessment Recommendations

• Patients with knee OA should have regular foot examinations to detect early signs of foot deformities 4
• Assess ankle range of motion, particularly dorsiflexion, as limited mobility is a key risk factor for developing foot problems 2
• Evaluate arch height and foot posture as part of routine knee OA assessment 1

Management Considerations

• Therapeutic Footwear: Custom-made insoles can reduce plantar pressure and help prevent foot ulcers in patients with foot deformities 4
• Bracing Options: Knee braces that modify joint loading may help prevent progression of both knee OA and associated foot problems 4
• Foot-Specific Interventions: Early intervention for foot deformities may help mitigate knee symptoms 1

Special Considerations

High-Risk Populations

• Obese patients with knee OA have increased risk of developing foot deformities due to greater mechanical stress 6
• Patients with inflammatory arthritis (like psoriatic arthritis) may have both knee involvement and enthesitis affecting the plantar fascia 7

Monitoring and Follow-up

• Regular foot examinations are recommended for knee OA patients, especially those with risk factors for foot deformities 4
• Monitor for changes in gait pattern, as these may indicate developing foot problems

Common Pitfalls and Caveats

1. Overlooking Foot Symptoms: Clinicians often focus exclusively on knee symptoms while missing associated foot problems
2. Assuming Independent Pathologies: Treating foot and knee problems as separate entities rather than interconnected issues
3. Delayed Intervention: Waiting until foot deformities are severe before addressing them
4. Inappropriate Footwear: Failing to recommend appropriate footwear modifications early in treatment

The evidence clearly demonstrates that knee OA and foot deformities are interconnected through biomechanical pathways. Early detection and management of both conditions can improve overall outcomes and prevent progression of disability.