Ranawat Classification for Valgus Knee Deformity
The Ranawat classification for valgus knee deformity consists of three types based on the severity of deformity and the integrity of the medial soft tissue structures. This classification system helps guide surgical approach and treatment strategy for patients with valgus knee deformities 1.
Classification Types
Type I
- Mild valgus deformity secondary to bone loss in the lateral compartment 2
- Soft tissue contracture on the lateral side 2
- Medial soft tissues and capsular ligament complex remain intact 2, 1
- Typically requires lateral soft tissue release during surgical correction 2
Type II
- Moderate valgus deformity with obvious attenuation of the medial capsular ligament complex 2, 1
- Medial structures are compromised but still functional 1
- Less than 10 mm of medial opening during valgus stress test at 10° of knee flexion 3
- Requires both lateral release and medial ligament reconstruction/tightening procedures 2
Type III
- Severe valgus deformity with significant compromise of medial structures 1
- Often associated with valgus malpositioning of the proximal tibial joint line after overcorrected proximal tibial osteotomy 2
- May require more constrained implants or specialized surgical approaches 1, 4
Clinical Implications
Surgical Approach
- Type I deformities can typically be managed with lateral soft tissue release alone 2
- Type II deformities require both lateral release and medial capsular ligament tightening 2, 1
- Type III deformities may require constrained implants and specialized surgical techniques 1
Correction Potential
- Recent research suggests that the maximum theoretical correction value of knee valgus deformity can reach up to 25° using appropriate techniques 5
- Lateral unicompartmental knee arthroplasty (LUKA) through lateral approach has shown good results for treating various types of valgus deformities 5
Assessment Methods
- Radiographic evaluation using weight-bearing AP and lateral radiographs is essential 6
- Standing long-leg (hip-to-ankle) views provide optimal assessment of alignment 6
- AP views obtained in 10 degrees of internal rotation improve interpretation of varus and valgus alignment compared to neutral AP views 6
Considerations for Treatment
- Mechanical axis deviation Zone 2 or greater despite optimized medical treatment may require surgical intervention 6
- Guided growth techniques depend on remaining growth potential and must be carried out at least 2-3 years before skeletal maturity 6
- Computer-assisted surgery (CAS) has shown benefits in achieving proper alignment and joint-line restoration in patients with Ranawat type-II valgus arthritic knees 4
Understanding the Ranawat classification is crucial for proper preoperative planning and selection of appropriate surgical techniques to address valgus knee deformities, ultimately improving patient outcomes and reducing complications.