Purpose: The preoperative prevalence of osteoporosis and/or osteopenia and overall bone quality in prospective total knee arthroplasty (TKA) patients may affect the postoperative outcome after prosthetic insertion into the bone. The purpose of this study is to determine the baseline bone mineral density (BMD) and bone turnover in preoperative, female, primary TKA patients.
Methods: We prospectively measured the lumbar spine and hip BMDs using dual-energy X-ray absorptiometry (DEXA) scans in a cohort of 119 knees (107 patients) one day before surgery. We also assessed bone turnover using urinary levels of N-telopeptide (NTX), a type I collagen crosslinker, normalized to creatinine.
Results: The prevalence of osteoporosis by DEXA scan (T-score ≤ -2.5) among the TKAs was 12% in the spine and 10% in the hip. Eighty-three knees (70%) had osteopenia or osteoporosis of either the spine or hip. The mean T-score of the spine was -0.7 (SD 1.6), which is within normal limits, and of the hip was -1.2 (SD 1.0), which is defined as osteopenia. The mean Z-scores of 0.9 (SD 1.4) in the spine and 0.6 (SD 0.9) in the hip were positive. The median urinary NTX/creatinine ratio was elevated at 58.1 (interquartile range: 13.7 to 188.4).
Conclusion: Based on Z-scores, the TKA patients had higher spine and hip BMDs than the age-matched general population. Elevated NTX levels may suggest a systemic or local abnormal bone turnover. Further study is needed to determine whether such turnover, as a type of patient-related medical systemic disorder, affects postoperative clinical outcomes.
Keywords: Bone turnover; Dual energy x-ray absorptiometry; Osteoarthritis; Preoperative bone mineral density; Urinary N-telopeptide, Total knee arthroplasty.