Abstract
Introduction
The interaction between the lumbosacral spine and the pelvis is complex. This interface is further complicated by preexisting pathology and by positional change. Our study examines the influence of spinal deformity on positioning of total hip arthroplasty (THA). A guideline is provided to assist in preoperative planning and improved communication between hip and spine subspecialists.
Materials and Methods
A comprehensive literature review was conducted investigating the relationship at the spinopelvic junction. Specific topics examined included methodology to measure acetabular and spinal orientation, acetabular anteversion (AA) with spinal imbalance and rigidity, hip functional range of motion with positional change, and hip functional range of motion after THA. Information and results that were consistently sourced were used to create specific recommendations for the hip and spine subspecialists. Both schematic and visual representations of the different recommendations were constructed.
Results
There is a predictable change in sagittal acetabular orientation that is influenced by lumbosacral balance and flexibility as well as by positional change. Preoperatively, patients in need of THA can be screened with sitting and standing lumbar radiographs into four categories based on flexibility and sagittal balance of the spine: flexible/balanced, flexible/unbalanced, rigid/balanced, and rigid/unbalanced. Patients in the flexible/balanced category should have AA during THA in the standard safe zone of 5 to 25 degrees. Patients with spinal rigidity will require adjustment of AA to limit impingement and dislocation. Patients with spinal imbalance, whether rigid or flexible, will be best addressed by spinal realignment or alternatively may require adjustment of AA to accommodate for compensatory pelvic retroversion.
Conclusion
Sagittal imbalance of the lumbar spine, combined with spinal fusion or ankylosis from degenerative changes, influences AA during THA. Patients can be preoperatively screened into four different categories based on lumbosacral balance and flexibility. Acetabular cup placement can be optimized based on the type and significance of coexisting spinal deformity to increase hip functional range of motion. Spinal realignment should be considered primarily for unbalanced patients before THA to ensure ideal placement of the acetabular cup.