Biomechanical Investigations

Reports indicate that height restoration has the potential benefit of reducing postfracture kyphosis and its associated sequelae.7-9,18,19 The magnitude of height restoration mentioned in the preliminary clinical reports discussed earlier is similar to that measured ex vivo.14 In the ex vivo study by Belkoff et al.,14 average actual height restoration (average of six height measurements made circumferentially about the vertebral body) was 2.5 ± 0.7 mm.7-9,18 It is important to note that this ex-vivo study of osteoporotic vertebral bodies that were compressed to create simulated fractures and repaired with PV suggested that half of the compressed height recovers elastically,14 a phenomenon similar to that reported in vivo.20 In addition, PV restored 30% of the height that was not elastically recovered in ex vivo specimens, whereas kyphoplasty restored 97%.14 The actual height restoration seems to range from 2.5 to 3.5 mm, values similar to those reported clinically.13

One of the theoretical advantages of kyphoplasty over standard PV is that the former may permit the injection of cement under lower pressures, a factor that could be important for the use of calcium phosphate and hydroxyapatite cements, which are bioresorbable but difficult to inject.21-25 A recent ex vivo study comparing a hydroxyapatite-forming cement and a poly(methyl methacrylate) cement found that height restorations were similar and that they were qualitatively as easy to inject, but the former produced a weaker and less stiff repair.15 It was found that osteoporotic vertebral bodies are similarly easy to inject when the same hydroxyapatite cement is directly injected into them.15 Thus, it appears that the ease of injection of the hydroxyapatite cement may have more to do with its composition than with the environment into which it is injected. Injection pressure was not measured in either study, but it seemed to be similarly low in both situations.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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