Evaluation of intramedullary rib splints for less-invasive stabilisation of rib fractures

Background

Intramedullary fixation of rib fractures with generic Kirschner wires has been practiced for over 50 years. However, this technique has not been advanced to address reported complications of wire migration and cut-out. This biomechanical study evaluated a novel rib splint designed to replicate the less-invasive fixation approach of Kirschner wires while mitigating their associated complications.

Methods

The durability, strength, and failure mode of rib fracture fixation with intramedullary rib splints were evaluated in 27 cadaveric ribs. First, intact ribs were loaded to failure to determine their strength and to induce realistic rib fractures. Subsequently, fractures were stabilised with a novel rib splint made of titanium alloy with a rectangular cross-section that was secured with a locking screw. All fixation constructs were dynamically loaded to 360,000 cycles at five times the respiratory load magnitude to determine their durability. Finally, constructs were loaded to failure to determine their residual strength and failure modes.

Results

Native ribs had a strength of 9.7 ± 5.0 N m, with a range of 3.5-19.6 N m. Fracture fixation with rib splints was uneventful. All 27 splint constructs sustained dynamic loading without fixation failure, implant migration or implant cut-out. Dynamic loading caused no significant decrease in construct stiffness (p = 0.85) and construct subsidence remained on average below 0.5 mm. The residual strength of splint constructs after dynamic loading was 1.1 ± 0.24 N m. Constructs failed by splint bending in 44% of specimens and by developing fracture lines along the superior and inferior cortices in 56% of specimens. Regardless of the failure mode, all rib splint constructs recoiled elastically after failure and retained functional reduction and fixation. No construct exhibited implant cut-out or migration through the lateral cortex.

Conclusions

Rib splints can provide sufficient stability to support respiratory loading throughout the healing phase, but they cannot restore the full strength of native ribs. Most importantly, rib splints mitigated the complications reported for rib fracture fixation with generic Kirschner wires, namely implant cut-out and migration through the lateral cortex. Therefore, rib splints may provide an advanced alternative to the original Kirschner wire technique for less-invasive fixation of rib fractures.