Are Bone Metabolism and Bone Material Strength Evaluations Worthwhile?: Commentary on an article by Tamara D. Rozental, MD, et al.: "Longitudinal Changes in Serum Markers of Bone Metabolism and Bone Material Strength in Premenopausal Women with Distal Radial Fracture".

Abstract

Commentary The article by Dr. Tamara D. Rozental and colleagues introduces us to 2 innovative methods to improve our understanding of bone strength and fracture-healing biochemistry that maybe relevant to clinical practice. Bone mineral density (BMD) is the standard for determining bone quality and fracture risk but does not define the structural and mechanical properties of bone1. Impact microindentation provides information on the material properties of cortical bone that we as orthopaedic surgeons need in order to improve our choice of fixation strategy2. Markers of bone metabolism (MBM) have been used to assess the results of osteoporotic treatment but have not been applied to the non-osteoporotic patient to assess fracture healing or to predict potential osteoporosis3,4. Impact microindentation is a minimally invasive technique that measures the ability of the tibial cortex to resist a standardized impact force. This measures the bone’s material quality, which is the interaction of the bone’s mineral and organic elements to resist failure. This technique might allow for a better determination of the ability of bone to hold implants that are used for fracture fixation (for example, the ability to achieve screw purchase). A greater understanding of such variables would facilitate fixation decisions, including the potential need to augment fixation with use of locking screws or bone substitutes. In this study, the microindentation technique did not prove valuable in assessing bone quality, but the investigators demonstrated that the test was possible to administer in a clinical setting. MBM have demonstrated promise as markers of the healing response following the treatment of a fracture5. Sclerostin (a glycoprotein produced by osteocytes) and Dickkopf 1 (DKK1) both decrease bone formation were initially increased but then both dropped to low levels allowing the healing response to occur. Tartrate-resistant acid phosphatase (TRAP) and C-terminal telopeptide (both of which are indicators of osteoclastic activity) peaked early, indicating the need for bone removal secondary to fracture site necrosis. Bone-formation markers such as N-terminal extension propeptide of type-I collagen (P1NP) and bone-specific alkaline phosphatase (BSAP) increased throughout the healing phase. These longitudinal results are evidence that, in premenopausal women, the biochemistry of fracture healing can be evaluated. This study provides the impetus to evaluate whether MBM can determine problems in fracture healing earlier than radiographic evidence and also whether MBM can serve as an indication of early osteopenia and osteoporosis in premenopausal women6. This article had a number of strengths. Patient selection was appropriate (although it was limited to a specific group of premenopausal women with a distal radial fracture). The fractures were classified with use of an acceptable system that can be used to determine severity on the basis of the mechanism of injury (i.e., high or low energy). Finally, the study included both operatively and nonoperatively managed patients, with the former demonstrating an elevated BSAP. This article also had also several areas of concern. MBM vary depending on patient activity and the time of day when the samples are taken. The authors acknowledge this limitation, but it is important for the reader to understand that the controls were only sampled once, so any assumption regarding longitudinal MBM levels may not hold. Another issue is that there is no consensus on what constitutes a meaningful clinical difference in these results. As this study is the first to measure MBM during fracture healing, one is unsure of what these results mean. It is obvious that the results appear to coincide with our understanding of fracture healing, but this relationship has not been proven. Although this study has limitations, including a small sample size in a very specific patient population, it opens the door to a better understanding of fracture healing. Orthopaedic surgeons, particularly those specializing in fracture care, should consider this study as an impetus to further investigate the physiology and biochemistry of fracture healing.