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    Degree of Spinal Deformity Affects the Success of Hip Replacement Surgery

    Patients with a spinal deformity who need a total hip replacement are at greater risk for dislocation or follow-up revision surgery, suggesting that these higher-risk patients may benefit from a more personalized approach to their surgeries to reduce the risk of poorer outcomes.

    A study led by orthopaedic surgeons at NYU Langone Medical Center provides a greater understanding of exactly how spinal deformity interacts with the pelvis and potentially increases the risk of dislocation despite positioning the acetabular cup in what surgeons have traditionally considered the ”safe zone.”

    “Surgeons should anticipate potential instability after performing a hip replacement in patients who have existing spinal deformity, and they should adjust their surgical plans accordingly,” said lead study author Aaron J. Buckland, MD, assistant professor of orthopaedic surgery in the Division of Spine Surgery and director of spine research at NYU Langone.
     
    The study was presented at the 2017 Annual Meeting of the American Academy of Orthopaedic Surgeons and was also published online on December 27, 2016, by the Journal of Arthroplasty.

    Focus on Sagittal Spinal Deformity

    Until now, no studies of the hip-spine relationship have focused on patients with sagittal spinal deformity. “Our research helps bridge any disconnect between surgeons who regularly treat spinal deformities and those who perform hip joint replacements, fostering more collaboration to improve patient outcomes,” Dr. Buckland said. 

    For this study, researchers retrospectively reviewed 107 patients who met the criteria for sagittal spinal deformity and who had 139 hip replacement procedures collectively. Using software containing detailed measurements of patients who were imaged before and after surgery, researchers analyzed the acetabular cup position, dynamic changes in cup position, and rate of instability in patients who had undergone hip replacement surgery.

    They found an 8% dislocation rate for hip replacement in patients with some degree of spinal stenosis; 5.8% of the same patient cohort required revision surgery due to recurrent dislocation. This compares with a 1% to 2% dislocation risk in the typical hip replacement population, according to Dr. Buckland.

    Positioning of the hip implant was normal in 78% of patients while supine. That number significantly decreased to 58% when patients stood due to an increase in the spinopelvic tilt. Of the patients whose hips dislocated, 80% had “safe zone” cup placement, 80% had a “safe” spinopelvic tilt, and 60% were deemed “safe” by both parameters.

    Collaborating to Improve Outcomes

    The findings of this study have led orthopaedic surgeons who perform hip replacement procedures at NYU Langone to collaborate with their spine surgeon colleagues on preoperative planning in an effort to ensure optimal outcomes in their patients.

    “The fact that high rates of dislocation occurred in patients with ‘safe zone’ placement of their artificial hips implies that our understanding of what defines acceptable acetabular positioning for these patients remains questionable,” said study co-author Jonathan Vigdorchik, MD, assistant professor of orthopaedic surgery at NYU Langone.

    “It is imperative that the degree of spinal deformity be a primary factor in preoperative planning of hip replacements”

    The research team plans future projects to examine postural analysis more closely in an effort to develop patient-specific or pathology-specific safe zones, enhance impingement-free range of motion, and study in more detail the use of a dual-mobility bearing implant in this complex patient population.

    Source

    Delsole E, Schwarzkopf R, Vigdorchik J, Errico T, Buckland A. Total hip arthroplasty in the spinal deformity population: how does deformity impact hip stability? Presented at the 2017 Annual Meeting of the American Academy of Orthopaedic Surgeons, March 14-18, 2017, in San Diego, California.