HEX-Based Femur Lengthening over the Nail

Femur lengthening over the nail (LON) has a specific problem – the risk of jamming the mobile fragment with the nail. To exclude collision with a nail, tangential insertion of bone components (wires and threaded pins) (Paley et al., J Bone Joint Surg Am (79-A): 1464–1480 (1997)) or extracortical clamp device, SUV clamp (Solomin et al., Orthop Res Traumatol 3: 20–25 (2018)), is used. The second reason for jamming is the collision of the nail with the bone cortex. This is due to the fact that the distraction vector in the Ilizarov apparatus is straight, but the nail and femur in the sagittal plane have a bend (curvature). Forced distraction does not always solve this problem, as a result of which there can be a premature consolidation of the distraction regenerate (Kocaoglu et al., J Bone Joint Surg 86-A: 2406–2411 (2004)). With the simultaneous elimination of the concomitant torsional deformity and subsequent lengthening, the occurrence of jamming of the bone fragment is likely. The lengthening of the femur over the nail using an orthopedic hexapod (Solomin et al., Method for femoral lengthening over the nail. Patent RF, no. 2638279, 2017; Shchepkina et al., Depart Traumatol Orthop 45: 26–35 (2021)) excludes nail jamming, since a distraction not rectilinear can be chosen, but in accordance with the curvature of the femur and the intramedullary nail. To do this, the “multi-total residual” option of orthopedic hexapod Ortho-SUV Frame (OSF) software is used (Solomin, Hexapod external fixator systems. Springer Nature Switzerlend AG, pp. 198–238, 2021). A Hex-based LON with an OSF was used in a patient with a 4 cm femur shortening and accompanying 46° torsional deformity. Simultaneously with the elongation over the nail, torsional deformity was corrected without the nail jamming. The period of correction and external fixation was 47 days. The restructuring of the distraction regenerate was ascertained 4 months after the frame was dismantled. An excellent anatomical and functional result was obtained.