Prophylactic augmentation of the osteoporotic proximal femur-mission impossible?

Abstract

The high incidence of secondary hip fractures and the associated markedly increased mortality call for preventive actions that could help to avoid these injuries. By providing immediate strengthening and not relying on patient compliance, internal prophylactic augmentation of the osteoporotic proximal femur may overcome the main limitations of systemic bone drugs and wearable protective pads. However, such a method would have to provide sufficient and reliable strengthening effect with minimal risks and side effects to justify the need of an invasive treatment. The requirements for an internal reinforcement approach are thus strict and include mechanical, biological, clinical, ethical and financial criteria. Here we first attempt to describe the properties of an ideal augmentation method. Previously published methodologies and techniques developed at our research institute, including approaches using cements, metals, other materials or combined approaches, are then reviewed and evaluated according to these aspects. We conclude that none of the discussed methodologies appears to be able to deliver a sufficiently high gain-versus-risk ratio that could justify the clinical application and thus augmentation of the osteoporotic proximal femur remains a challenge. Finally, we provide suggestions for the development and evaluation of future strategies.

Figure 1

X-ray based illustration of the unpublished augmentation approaches co-developed and evaluated at our research institute. (a) Cement augmentation of the superior neck cortex using 9–10 ml PMMA (Vertecem, Synthes, Switzerland) and (b) cannulated dynamic hip screw (diameter of 7.3 mm, length of 95 mm) with 3 ml cement at the tip, augmenting the inferior neck cortex; both strategies presented by Zwicky. (c) PMMA augmentation of the inferior neck cortex using 9–10 ml bone cement by Roffler, comparing conventional (Vertecem, Synthes) and N-methyl-pyrrolidone (NMP)-modified (low modulus) cements (N=5) in a free fall test setup. (d) V-shape metal implant consisting of two, 5 mm diameter cannulated screws aligned along the superior and inferior neck cortices, respectively, connected laterally with a custom 2-hole plate and augmented at the tip with 1 ml cement (Traumacem V+, Synthes) per screw; developed by Widmer et al. (unpublished study).

Figure 2

Summary of the results of one ‘first-generation' and two ‘second-generation' femoroplasty studies. The increase in fracture load (a) and energy (b) depends on the properties of the contralateral non-augmented (control) femur, with weaker bones experiencing larger strengthening. Fracture risk of the control femora, estimated using the approximated load-to-strength ratio versus strength relationships published by Keaveny & Bouxsein (c), or by Roberts et al. (d), is shown as broken black lines. From this ratio, the magnitude of the accidental load can be estimated and used to compute the approximate load-to-strength ratio of the contralateral augmented bone (data points). A value larger than 1.0 indicates that strengthening was not sufficient and the augmented bone would probably still fracture in a low-energy sideways fall accident. Note that Heini et al. used quasi-static loading, the dynamic strength values are expected to be higher.