VERTEBROPLASTY:

SUBSEQUENT FRACTURES
(author: Thammo Weise)

The effective pain reduction that can be achieved by both vertebroplasty and kyphoplasty procedures is beyond doubt. Numerous publications prove this achievement. However, the issue of fractures that can potentially occur after cement augmentation continues to be debated controversially. Recently there have been – mostly retrospective – studies that investigated new aspects of the techniques and in particular their long-term effects.

Essentially, the literature lists three main reasons for subsequent fractures. As becomes apparent by the authors named in parentheses, the three reasons are by no means mutually exclusive.

Fractures in adjacent vertebral bodies occur:

1. As a natural effect of progressive osteoporosis. There is never involvement of an isolated bone, but always of the entire skeletal apparatus. Even without cement augmentation, the risk of suffering another fracture after an initial one increases by a factor of four (Heini, Lindsay, Fribourg).
2. As a result of increased movement. The patients return to a more physically active lifestyle due to the pain reduction. Vertebrae that were not augmented are therefore subjected to increased stress (Uppin, Heini).
3. Due to the changed biomechanics of the spinal column. The injected bone cement increases the bone’s rigidity to a factor of up to 36. The occurring forces are distributed to the adjacent vertebrae and thus cause a new fracture (Baroud, Polikeit).

All three reasons listed must be regarded as hypotheses that are still awaiting final proof. The first two arguments are without doubt plausible, but cannot be influenced within the framework of therapy. The third hypothesis, which has been approached numerically using the Finite Elements Method (FEM), confirms the so-called “supporting pillar effect“. It states that, as the rigidity of the treated vertebral bodies increases, the joint flexibility of the affected spinal column region decreases significantly. Upon movement, the muscular system applies a contrary force, which in turn increases the pressure on the adjacent spinal disk. This is assumed to result in a directly increased fracture risk. This situation could perhaps be improved by reducing the E module (measure of flexibility) of the bone replacement material to human equivalent values. Another possibility for improvement is “minimal filling“, i.e. injection of only a few milliliters of cement per vertebral body. There are numerous studies that address the issue of subsequent fractures. However, so far no study group was able to show generally applicable results. For example, one can find studies that contradict an increased fracture risk, while other publications could not detect a direct association between therapy and fractures. With the focus of the investigations mainly on pain reduction, various correlated factors, such as applied volume, types of leakages occurring, unipedicular or bipedicular access or the patients’ gender, have often been given insufficient attention.

However, all opinion makers agree on one point: In the question of subsequent fractures, no difference can be detected between kyphoplasty and vertebroplasty.

Warmest regards,

Thammo Weise