Factors Predicting Change in Pelvic Posterior Tilt After THA

Abstract

In total hip arthroplasty, steep cup inclination should be avoided because it increases the risk of edge loading. Pelvic posterior tilt should be carefully monitored because it increases cup inclination and anteversion, leading to edge loading or impingement. The authors evaluated how much the pelvic tilt angle changes from the supine position referenced in planning for cup orientation preoperatively to the standing position 1 year after total hip arthroplasty (Δref). The pelvic tilt angle was measured in 124 patients who underwent total hip arthroplasty due to osteoarthritis, and the mean Δref was -9.5°±5.3° (range, -23° to 5°). Preoperative compression fractures, spondylolisthesis, and disk-space narrowing were predictive of increased pelvic posterior tilt after total hip arthroplasty. The authors mathematically calculated how much change in pelvic posterior tilt was clinically possible with the original cup alignment, which ranged from 40° to 45° of radiographic inclination and 0° to 30° radiographic anteversion to more than 50° of inclination. Even if the maximum posterior tilt (23°) occurred, no edge loading would occur in almost half of those original cups. Surgeons should aim for 40° of inclination. When the original cup inclination was 40°, edge loading was prevented. Edge loading caused by steep cup inclination can be prevented by adjusting the cup orientation to account for predicted pelvic tilting, but spinal alignment must also be considered because lumbar kyphosis can increase postoperative pelvic posterior tilt.

The Association of Tibia Femur Ratio and Degenerative Disease of the Spine, Hips, and Knees

“…15,25,26 In addition, a more proximal knee joint would cause the pelvis to increase forward tilt during the heelstrike phase of gait, 27 an established cause of hip osteoarthritis. [28][29][30][31][32][33] Song et al 15 showed increased mechanical work during gait for patients with limb-length discrepancies >3 cm, perhaps by a similar mechanism, decreasing the distance between the knee and hip joint relative to the distance between the knee and ankle joint.…”

Pelvic Tilt in Patients Undergoing Total Hip Arthroplasty: When Does it Matter?

“…We could not predict the relatively rare occurrence of a large change in pelvic tilt, which would confound tilt-adjusted component position. The pelvis is a dynamic link between the axial and appendicular skeleton, and studies have demonstrated the importance of taking into account the condition of the spine for preoperative planning of acetabular component position throughout a range of functional positions [18,19]. …”

In reply

“…Thirdly and lastly, no lumbosacral comorbidities are mentioned, except the absence of instrumented lumbosacral fusions that were considered an exclusion criterion. However Kyo et al demonstrated that disc space narrowing, spondylolisthesis and pre-existing compression fractures are predictive factors for posterior pelvic tilt after THA [7]. What about the distribution of these spine diseases in the reported series?…”