Biomechanical comparison of a new expandable intramedullary nail and conventional intramedullary nails for femoral osteosynthesis in dogs

Abstract

Intramedullary nailing of diaphyseal femoral fractures is a commonly used treatment method in dogs because of its biological and biomechanical advantages compared to bone plating. To achieve adequate resistance of the intramedullary nail against torsional and axial compressive forces, additional application of transcortical screws is needed. As these interlocking screws represent a frequent cause of post-operative complications, a new expandable intramedullary nail (EXPN) was developed, which was designed to provide adequate fracture stabilisation without the need for transcortical fixation. The evaluation of the biomechanical properties of the new EXPN with regard to torsional, compressive and bending stability as well as direct comparison to the biomechanical properties of conventional Steinmann (STMN)-and interlocking (ILN) nails was carried out with different biomechanical test arrangements. No significant statistical differences regarding the torsional and bending resistance between the EXPN and ILN group were seen, which indicates that rotatory as well as bending stability of the innovative EXPN is similar to the conventional ILN. Nevertheless, the percentage deviation between the attempted and successfully reached physiological compressive forces was significantly higher (p = 0.045) in the EXPN group compared to the ILN group, which indicates that the compressive stability of the innovative EXPN might be weaker compared to the ILN. In summary, the new EXPN represents an interesting alternative to conventional intramedullary nails. However, in direct comparison to conventional interlocking nails, the EXPN has shown weaknesses in the neutralization of axial compressive forces, which indicates that at least biomechanically the interlocking nail seems advantageous. Further in-vitro and in-vivo investigations are required before clinical use can be recommended.

Which of the three different intramedullary nail designs is superior in the treatment of femoral shaft fractures?

“…In previous biomechanical studies conducted with some expandable nail designs (41,42), these were found to be insufficient in respect of rotational loading compared to locking nails. In contrast, there are also studies showing that resistance to rotational loading is similar to that of classic nails and resistance to compressive loading is weak (43). Bekmezci et al (8) recommended that therefore, non-locking nails should not be used in multi-fragmented fractures and metaphyseal region fractures.…”

“…Most authors advocate that static locking is appropriate for the prevention of rotation and shortening (44). By limiting micro-movement, static locking provides length of the fracture line and rotation is prevented (43). Static locking controls loading, shortening and rotation, but as stress is reduced in the fracture line, bone union is slowed down and osteolysis develops (44).…”

Biomechanical evaluation of a novel orthogonal angle-stable interlocking nail in a canine femur model Novel orthogonal angle-stable interlocking nail

“…The differences between the internal diameters of the screws/bolts used in Groups 2 and 3 (3.2 mm) compared to Group 1 (2.4 mm) infer a marked increase in the area moment of inertia (AMI) of the screws, justifying such an event [28]. Plenert [29] demonstrated greater resistance of the sets formed by nails interlocked with screws of increased diameter in compression and torsion tests. Despite the methodological differences, both studies used supraphysiological loads, which does not invalidate the sets’ ability to be resistant enough in a hypothetical clinical scenario.…”

Intramedullary nail: the past, present and the future – a review exploring where the future may lead us

“…Intramedullary nail: the past, present and the future -a review exploring where the future may lead us Orthopedic Reviews 5) was tested in an animal study in Germany. 27 This IMN featured expandable segments and bridging elements but proved to be weaker in neutralizing axial compressive forces when compared to traditional solid IMNs. 27 However, common to all expandable IMN designs, the challenge faced is removing the nail when complications do arise.…”

“…27 This IMN featured expandable segments and bridging elements but proved to be weaker in neutralizing axial compressive forces when compared to traditional solid IMNs. 27 However, common to all expandable IMN designs, the challenge faced is removing the nail when complications do arise. However, no studies have been conducted or reported on the ease of removing these novel expandable IMNs if required at a later stage.…”