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    Why Do Some Patients Develop a Sacral Insufficiency Fracture after THA?

    Total hip arthroplasty (THA) may be a risk factor for sacral insufficiency fracture (SIF), particularly on the non-operative side, according to a study from Germany recently published online ahead of print by The Journal of Bone & Joint Surgery.

    The study, from the University of Jena in Eisenberg, Germany, also provides evidence that loss of bone density leading to SIF begins within the first postoperative year following THA.

    What Is the Role of THA?

    Sacral insufficiency fracture occurs as a result of decreased bone mineral density in the sacrum. These fractures most commonly occur in older women, causing low back pain that worsens with activity. These fractures are becoming increasingly common as the population ages and lives longer, leading to more people with osteoporosis.

    Although several risk factors for SIF have been identified, the role of THA has been unclear. The researchers from Germany designed a 2-part study to assess the influence of THA on the development and localization of SIF.

    In the first part, they reviewed the records of 171 patients diagnosed with SIF, from which they identified 50 patients who had previously undergone THA in 1 or both hips. The patients’ average age was 79 years, and 40 of the patients were women. On average, SIF developed about 8 years after THA.

    Among the 31 SIF patients who had undergone THA in just 1 hip, the SIF was located on the non-operative side twice as often as on the operative side, 42% vs. 19%, respectively. The remaining 39% of patients developed SIF on both sides of the pelvis.

    In the second part of the study, the researchers investigated 39 patients with initially healthy bone mineral density who underwent THA. Changes in bone density were assessed in computed tomography scans performed at 1 year after THA. The results showed a small but significant reduction of bone mineral density in the sacrum, but only on the non-operative side. No significant change in bone mineral density in the sacrum were observed on the operative side.

    “Spatially Different Bone Remodeling”

    Over time, THA may lead to “spatially different bone remodeling,” as a result of changes in load transmission through the pelvis, the study authors said. They noted that a key question remains unresolved: Does THA cause decreased bone loss on the non-operative side of the sacrum, or does it prevent bone loss on the operative side of the sacrum?

    Additional research is needed, they said, to address the identified remodeling process, as well as to investigate the effects of different implants and a longer time period on the development of SIF.

    Source

    Graul I, Strube P, Vogt S, Matziolis G, Brodt S, Hölzl A. Does total hip arthroplasty influence the development and localization of sacral insufficiency fractures? J Bone Joint Surg Am. 2021 Nov 22. doi: 10.2106/JBJS.21.00218. Online ahead of print.