What Are the Consequences of Mechanical Knee Alignment?
Stephen Howell, MD, and his colleagues from the University of California at Davis in Irvine have demonstrated that using mechanical alignment techniques to achieve a neutral hip-knee-ankle angle in total knee arthroplasty often results in:
- Tight collateral ligament in 0° of extension
- Instability in a compartment between 0° of extension and 90° of flexion that is uncorrectable by collateral ligament release
- Changes in limb and knee alignment from normal
In a study Dr. Howell presented at the 2nd Annual Pan Pacific Orthopaedic Congress, they sought to calculate the frequency and range of these undesirable consequences when the knee is aligned in 5° or 7° valgus.
To simulate TKA, they used a 3D bone model of a normal lower extremity from 50 white subjects. The knee was aligned in 5° or 7° valgus in the coronal plane. In the axial plane, the internal-external rotation of the femoral component was set:
- Perpendicular to the anteroposterior axis of the trochlear groove (Method 1)
- Parallel to the transepicondylar axis (Method 2)
- 3° externally rotated to the posterior condylar axis (Method 3)
- Gap-balanced to the tibial resection at 90° of flexion (Method 4)
Dr. Howell and his colleagues reported the following findings:
- The proportion of TKAs requiring a 2-mm or more release of a tight collateral ligament was 60% and 64% in the 5° and 7° valgus knees, respectively.
- The proportion of TKAs with 2 mm or more of instability between 0° of extension and 90° of flexion was 60% and 64% for Method 1, 58% and 74% for Method 2, and 54% and 48% for Method 3 in the 5° and 7° valgus knees, respectively.
- The proportion of TKAs with 2° or more change in limb and knee alignment from normal was 54% and 62% in the 5° and 7° valgus knees, respectively.
We asked Dr. Howell to comment on the implications of this study. Click the image above to hear his comments.
Producer: Michael Szuch; Director: Michael Bugera; Post Production: Charles J. Maynard
Gu S, Howell S, Hull M. Does a TKA in 5° Or 7° valgus frequently have collateral ligament imbalance and abnormal alignment? Presented at the 2nd Annual Pan Pacific Orthopaedic Congress, July 22-25, 2015, Kona, Hawaii.