Despite the clinical inadequacy of stand-alone osteoplasty for consolidation of long bone pathological/impending fractures [6] and the rapid implementation of numerous alternative techniques [9,10,11,12,13,14,15,16,17,18], there has been little evaluation of the biomechanical efficacy of these procedures. In the proximal femur, a few cadaveric studies have shown that femoroplasty effectively consolidates osteoporotic bone subjected to sideways falling [20,21,22] and may reduce mechanical stress around stance-loaded simulated femoral neck tumours provided that cement filling is adequate [23]. Similarly, the novel Y-STRUT® implant (Hyprevention, Pessac, France; designed to prevent hip fracture) has undergone pre-clinical validation, demonstrating reduced fracture risk during sideways falling [24]. In contrast, there are only three prior animal studies evaluating the biomechanical effects of diaphyseal augmentation. These illustrated a lower bending strength of osteoplasty alone than when combined with bare metal stents or K-wires, in porcine and bovine models with simulated diaphyseal fractures and focal tumours [25,26,27].
The present study demonstrates that osteoplasty alone or with K-wires augmentation does not confer any consolidative advantage to diaphyseal bone undergoing 3-point bending stress. Fracture load was similar to controls for both composites, consistent with the lack of consolidative and stiffening effects. The stiffness of the tested specimens was slightly increased in composites from group 2 and group 3. Nevertheless, there was no significant difference as compared to controls.
There were four PMMA fractures, consistent with the brittle nature of PMMA and its unsuitability to resist non-compressive loads.
Multiple alternative constructs have been proposed to optimise the consolidation of oncologic long bone tumours, particularly in the proximal femur, with relatively few series treating diaphyseal tumours (only 6% of cases in a recent systematic review [6]).
In several reports, osteoplasty has been combined with dedicated spindles, modified mandrins, and multiple micro-needle mesh to optimise biomechanical resistance of PMMA to multi-directional stresses (rebar concept) [10]. Studies in the proximal femur [9, 10, 12] and long bone diaphyses [10] have illustrated good analgesia and restoration of functional status, with either no secondary fractures [9, 10] or fewer than with osteoplasty alone [12], at 6–16-month follow-up. Our study did not demonstrate any beneficial effect of osteoplasty augmented with K-wires, although this may reflect sample limitations, test protocol, or suboptimal composite material properties. Nevertheless, there remains a lack of biomechanical evidence and long-term follow-up to support these procedures.
Other studies have adapted surgical techniques to improve long bone tumour stabilisation. In the proximal femur, percutaneous screw fixation (simulating the inverted triangle configuration of orthopaedic procedures) [14, 15, 17] and placement of the Y-STRUT® device simulating a gamma nail [16] have been implemented to treat pathological/impending fractures in selected non-surgical patients. Early results are encouraging, although secondary fracture rates remain considerable (from 6 to 10%) [13, 16]. In contrast, long bone diaphyseal fixation constructs have been largely improvised using interventional radiology equipment. PMMA-filled catheters [11] have been used to simulate the load-sharing action of intramedullary nails (IMN) and augmented osteoplasty of impending fractures. In the series of Liu et al. [11], this resulted in improved analgesia, functional status, and reduced secondary fractures compared with osteoplasty alone. Unfortunately, we were unable to evaluate and replicate this procedure in vitro—possibly due to lower ambient temperature, PMMA viscosity differences, and impedance of PMMA flow by the narrow catheter tip and luminal plugging with trabecular bone rather than tumour. Currently, there is insufficient biomechanical and clinical data to support these techniques.
The most promising techniques for diaphyseal tumoural consolidation are probably flexible and bundle IMN (Fig. 5); these have been translated from orthopaedic practice to pathological/impending fractures in cancer patients [17, 18] and are already supported by substantial biomechanical and clinical evidence [28, 29]. Flexible IMN produces symmetrical bracing 3-point fixation and achieves (in combination with muscular action) dynamic multi-directional stability. Bundle IMN produces a similar effect via placement of multiple intramedullary pins until the medullary cavity is filled and there is tight compression between the nails and bone [30]. Constructs are typically augmented with PMMA to improve load-sharing and load-bearing properties. Initial clinical results have been promising. Kim et al. [18] performed osteoplasty with flexible IMN in 15 lower limb impending fractures and reported significant palliation, restoration of mobility, and local tumour control (reduction in standardised uptake value at positron emission tomography CT) at 6-month follow-up. Similarly, positive outcomes were also reported for humeral tumours [17]. Disadvantages of the technique include reduced load-sharing properties, lower resistance to torsional/bending stresses [28], and telescoping, compared with standard surgical rigid IMN with proximal/distal interlocking screw fixation [31, 32]. Further studies with long-term follow-up are required to assess these promising interventions.
Our study limitations are mainly related to unavailability of cadaveric specimens. Therefore, neither additional constructs (e.g., flexible, bundle IMN) nor other possible stresses such as torsion or axial load were evaluated. Moreover, our model did not include a bone defect simulating a diaphyseal bone tumour. However, the present study aimed at investigating the biomechanical advantage of osteoplasty or K-wires osteoplasty as compared to the native condition of the target bone. Given the results obtained, one may speculate that similar conclusions might be probably expected also in a model including the same bone defect in all the tested specimens of the three groups. Furthermore, it was not possible to assess bone mineral density and geometric measurements due to unavailability of quantitative CT or dual-energy x-ray absorptiometry or utilise intra-individual controls. However, the majority of fracture risk is accounted for by cross-sectional area of bone rather than mineralisation or morphology [33], and there may be a wide intra-individual heterogeneity even in matched cadaveric samples [34]. The test protocol could have influenced the results in terms of anisotropic effects (varus stress only) and use of hemi-tibias rather than complete bones. However, the choice of 3-point bending test rather than 4-point bending test was made to evaluate the bone strength in the direction perpendicular to the compression axis. As a matter of fact, long bones (especially in the lower limbs) subjected to axial loads can break due to buckling. Finally, 93% of fractures (mainly A2 and B0 types) were entirely consistent with a bending mechanism, and spiral A1 (torsional) pattern was seen in only two cases (7%), suggesting reasonable biomechanical reproducibility.
In conclusion, this study confirms that osteoplasty alone or in combination with K-wires does not improve the resistance of diaphyseal bone subjected to bending stress. Therefore, at the moment, long bone osteoplasty and its variants should still be considered as a suboptimal choice for the consolidation of pathological/impending diaphyseal fractures; as a result, this technique should be avoided in good-prognosis cancer patients and proposed with caution in poor-prognosis, predominantly bed-ridden cancer patients presenting with painful lytic tumours.