How to Evaluate Varus and Valgus Deformity of the Knee
Instability accounts for 25% of revision total knee arthroplasty (TKA), making it one of the most common reasons for early and late revision procedures. [1-3]
That’s why it’s so important for surgeons to address varus or valgus deformity during the index surgery, Matthew P. Abdel, MD, told attendees at ICJR’s inaugural course for senior residents and fellows, Advanced Techniques in Total Hip & Knee Arthroplasty, whether they use cruciate retaining or posterior stabilized implants. [4,5] Otherwise, the patient has a strong chance of requiring revision TKA.
During his presentation, Dr. Abdel, from Mayo Clinic in Rochester, Minnesota, reviewed how he categorizes the amount of varus or valgus deformity and described how he alters his surgical technique to accommodate the deformity.
It all starts with standing long leg radiographs, which provide a good view of the overall alignment of the of the hip/knee/ankle complex, the contribution of the femur and tibia to the deformity, and the mechanical and anatomic axes. These radiographs are then used to determine the amount of varus or valgus deformity, which Dr. Abdel categorizes as mild, moderate, and severe:
- Mild deformity: 0° to 5°; use standard technique
- Moderate deformity: 5° to 10°; use a modified technique
- Severe deformity: More than 10°; use advanced techniques
Dr. Abdel admitted, though, that he does not measure these angles. He takes a more pragmatic approach to evaluating the deformity: He determines mild, moderate, or severe deformity by dropping a plumb line from the center of the hip to the center of the ankle on the long leg radiograph:
- The patient has mild varus deformity if the plumb line is within the medial tibial plateau.
- The patient has moderate varus deformity if the plumb line touches only the very medial aspect of the medial tibial plateau.
- The patient has severe varus deformity if the plumb line does not touch any part of the medial tibial plateau.
- The patient has mild valgus deformity if the plumb line is within the lateral tibial plateau.
- The patient has moderate valgus deformity if the plumb line touches only the very lateral aspect of the lateral tibial plateau.
- The patient has severe valgus deformity if the plumb line does not touch any part of the lateral tibial plateau.
The surgical technique for a severe deformity, whether varus or valgus, builds on the techniques used for managing mild and moderate deformities, Dr. Abdel said. Click the image above to watch his presentation and learn more about the progression of his surgical technique from mild to moderate to severe deformity.
In summary, he noted that:
- Most moderate varus and valgus deformities can be addressed with a posterior stabilized TKA.
- Valgus or varus constraint should only be used as a last-ditch effort after the knee has been fully balanced.
- Some patients with severe valgus deformities may need a rotating-hinge TKA.
Disclosures: Dr. Abdel has disclosed that he receives royalties from Stryker.
- Callaghan JJ, O’rourke MR, Saleh KJ. Why knees fail: lessons learned. J Arthroplasty. 2004 Jun;19(4 Suppl 1):31-4.
- Fehring TK, Valadie AL. Knee instability after total knee arthroplasty. Clin Orthop Relat Res. 1994 Feb;(299):157-62.
- Parratte S, Pagnano MW. Instability after total knee arthroplasty. J Bone Joint Surg Am. 2008 Jan;90(1):184-94.
- Pagnano MW, Hanssen AD, Lewallen DG, Stuart MJ. Flexion instability after primary posterior cruciate retaining total knee arthroplasty. Clin Orthop Relat Res. 1998 Nov;(356):39-46.
- Schwab JH, Haidukewych GJ, Hanssen AD, Jacofsky DJ, Pagnano MW. Flexion instability without dislocation after posterior stabilized total knees. Clin Orthop Relat Res. 2005 Nov;440:96-100.