Tag Archive | T score

T-Scores for Diagnosing Osteoporosis: 3 Are Better Than 1

This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.

The World Health Organization (WHO) and the International Society for Clinical Densitometry (ISCD) define osteoporosis based on (DXA) measures of bone mineral density that are translated into T-scores. A T-score ≤ -2.5 at any 1 of the 3 commonly measured sites (lumbar vertebrae, femoral neck, and total hip) is considered diagnostic for osteoporosis, and a T-score between -2.5 and -1 is indicative of osteopenia. University of Pennsylvania investigators1 proposed that combining all 3 T-scores in a multivariate analysis would be “potentially more informative” than the common practice of using the single lowest T-score.

The investigators applied multivariate statistical theory to T-scores from a sample of 1,000 65-year-old white women. When both real data and simulation models were analyzed, the researchers found that more patients were diagnosed with osteoporosis using the multivariate version of the WHO/ISCD guidelines than with the current WHO/ISCD guidelines. The diagnoses of osteoporosis using this method were also associated with higher Fracture Risk Assessment Tool (FRAX) probabilities of major osteoporotic fractures (P=0.001) and hip fractures (P=2.2×10−6). The FRAX tool combines a patient’s history of fracture with age, sex, race, height, weight, and social habits such as smoking and drinking to determine the risk of a major facture in the next 10 years.

This study shows that statistically considering all 3 T-scores may reveal more cases of osteoporosis than using the single lowest T-score. The trick will be getting this insight into the hands—and minds—of those making radiologic interpretations of DXA findings.

Reference 

  1. Sebro R, Ashok S. A Statistical Approach regarding the Diagnosis of Osteoporosis and Osteopenia from DXA: Are we underdiagnosing osteoporosis? J. Bone Mineral Res Plus. In press

Owning the Bone in Spine Surgery

This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.

Approximately 20% of patients who undergo spine surgery have osteoporosis, which has a significant impact on spine-surgery complications such as failure of fixation devices and collapse fractures following fusion procedures. In a recent critical analysis review, authors focus on improving outcomes by identifying and optimizing patients with osteoporosis prior to spine surgery. The multidisciplinary team involved in that process should include primary care providers, endocrinologists, physical therapists, and orthopaedic surgeons.

The predominant tool for assessing bone mineral density (BMD) is dual x-ray absorptiometry. The diagnosis is based on a T score, which represents the number of standard deviations between the patient’s BMD and that of a healthy 30-year-old woman. Standard deviations  ≤─2.5 define osteoporosis. The Z score is similar to the T score but compares the patient to an age- and sex-matched individual.

A history of low-energy fracture, such as a wrist fracture following a fall from a standing height, is considered a sentinel event for suspicion of fragility fractures. The combination of a fragility fracture and low BMD is considered to be severe osteoporosis. The most common form of osteoporosis is associated with a postmenopausal decrease in mineralization, but there are other causes. These include advanced kidney disease, hypogonadism, Cushing disease, vitamin D deficiency, anorexia and/or bulimia, rheumatoid arthritis, hyperthyroidism, primary hyperparathyroidism, and some medications (e.g., anticonvulsants, corticosteroids, heparin, and proton pump inhibitors).

Forty-seven percent of patients undergoing spine deformity surgery and 64% of cervical spine surgery patients have low vitamin D levels. Postoperative bone health can be enhanced in women ≥51 years old with daily intake of 800 to 1,000 units of vitamin D and 1,200 mg of daily calcium. There is no solid evidence that pre- or postoperative bisphosphonates have a positive impact on bone healing. Conversely, some series have shown that teriparatide, an anabolic parathyroid hormone, may improve time-to-fusion and help reduce screw pull-out after lumbar fusion in postmenopausal women.

Calcitonin has been shown to reduce the incidence of vertebral compression fracture, but there is no concrete evidence that it supports spine-fusion healing. Similarly, there is no strong evidence for the use of estrogen or selective estrogen receptor modulators in this surgical scenario. There is evidence that when the human monoclonal antibody denosumab is combined with teriparatide, spine-fusion healing may be improved relative to the use of teriparatide alone. Finally, the review article identifies screw size, screw position, and other surgical considerations that can improve fixation strength.

Using the “Own the Bone” practices promulgated by the American Orthopaedic Association and the technical considerations described in this review, we should be able to mitigate osteoporosis-related postoperative complications in spine-surgery patients.