## 7 Discussion  
Varus malalignment in subtrochanteric fractures is the leading factor in nonunion, often resulting from technical errors during osteosynthesis. The fracture site endures substantial shear forces in both the medial and lateral zones, which impede the healing process [20]. In fact, residual varus is frequently observed at the nonunion site, particularly if the fixation devices fail. The approach for healing subtrochanteric nonunion has been based on static fixation. The most commonly used surgical procedure to achieve bone union is the exchange of a nail for a newly over-reamed nail [8; 9; 10]. Nailing has shown good outcomes, especially without residual varus [8; 9; 21]. A subtrochanteric nonunion in varus is challenging to manage using a nail and may even be impossible. [PERSON] et al. [12] have reported that, in some instances, an osteotomy through the fracture site was necessary to correct varus malalignment. This is a challenging surgical procedure to perform, and despite this, they report a failure rate of up to 13% when using a long intramedullary nail [12]. Open reduction using an extramedullary device and a lateral closing osteotomy appears to be the preferable surgical procedure for restoring a physiological valgus alignment of the hip in a subtrochanteric nonunion in varus [13; 14; 15]. However, [PERSON] et al. [13] recently reported an even higher rate of complications concerning this type of static fixation [13]. A total of 11 of the 40 (27.5%) patients required secondary revision surgery; one patient had a persistent nonunion, nine patients had persistent nonunions leading to hardware failure, and one patient had a peri-implant fracture due to low-energy trauma four days after the index surgery. Although static fixation using the relative stability philosophy has shown good results in other anatomical areas, the results remain suboptimal in the subtrochanteric area. Due to the difficulty of achieving primary bone healing (through rigid fixation) in a previously operated area and such a biomechanically stressed area, dynamic fixation would be desirable. However, to date, no surgical procedures have been described as able to achieve this. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Patients** & **1** & **2** & **3** & **4** & **5** & **Mean/Median** \\ \hline DHS degrees used \$ & 135\({}^{\circ}\) & 150\({}^{\circ}\) & 150\({}^{\circ}\) & 135\({}^{\circ}\) & 150\({}^{\circ}\) & 150\({}^{\circ}\) \\ \hline Duration of surgery (min) \$ & 120 & 63 & 123 & 102 & 156 & 112.8 (63–153) \\ \hline Femoral neck angle post-surgery \$ & 142\({}^{\circ}\) & 150\({}^{\circ}\) & 150\({}^{\circ}\) & 147\({}^{\circ}\) & 145\({}^{\circ}\) & 146.8 (142–150) \\ \hline Post-surgery offset (mm) \$ & 24 & 19 & 18 & 20 & 17 & 19.6 (17–24) \\ \hline Vertical distance & & & & & & \\ nonunion–head post-surgery (mm) \$ & 65 & 55 & 38 & 52 & 48 & 51.6 (38–65) \\ \hline Postoperative leg lengthening (mm) \$ & 8 & 12 & 6 & 6 & 8 & 8 (6–12) \\ \hline Time to union (months) & 4 & 6 & 6 & 5 & 4 & 5 (4–6) \\ \hline Harris Hip Score post-surgery \$ & 96 & 96 & 88 & 90 & 88 & 90 (88–96) \\ \hline \hline \end{tabular}  
*: Results are presented as a mean and range in parenthesis. \$ : Results are presented as median.  
\end{table} 
Table 2: Intraoperative parameters and postoperative radiological and clinical results. Our preliminary results show that dynamic compression can be successfully applied to treat subtrochanteric nonunion, offering several relevant advantages in comparison to static fixation in this specific area, such as the following:  
1. The stability of the nonunion site is primarily achieved through the bone, avoiding stress on the device. If the bone does not achieve union in a timely manner, there is more time before its breakage. Conventional techniques have reported up to 13% implant failures [13]. Also, using additional plates is a widespread practice and aims to increase the stability of the nonunion site [13,19].