"Close to the tip, with little bone to grip": stabilizing two periprosthetic proximal femur fractures above a distal femur megaprosthesis using a combination of DHS and 3.5 mm screws

Abstract

The incidence of periprosthetic fractures is increasing, presenting significant challenges due to patient longevity and the complexity of repeated surgeries. This report details the successful treatment of a previously unreported periprosthetic fracture pattern using a modified dynamic hip screw (DHS) technique. Two cases involved patients with extracapsular fractures in short proximal femur segments above megaprostheses. The fractures were reduced and stabilized with a DHS device, complemented by 3.5 mm screws from a different manufacturer to achieve effective bicortical fixation around the thick stems. Early weight-bearing was initiated postoperatively, with both patients achieving fracture healing without mechanical complications. This approach highlights the importance of careful preoperative planning and the selection of appropriate fixation methods, particularly in complex cases where traditional solutions may not be viable.

Keywords: Dynamic hip screw (DHS); Megaprosthesis; Periprosthetic fracture; Proximal femur.

Fig. 1

Case presentations; pre-injury images and periprosthetic fractures. Case 1. X-ray telemetry showing left distal femur tumor arthroplasty with an uncemented femoral stem. Coronal CT revealing an intertrochanteric femur fracture in varus near the proximal stem tip. Axial images of the same CT. Case 2. X-ray telemetry showing right distal femur replacement with an uncemented femoral stem. Coronal CT showing an intertrochanteric femur fracture near the femoral stem. Sagittal CT revealing lateral cortex involvement at the implant tip.

Fig. 2

Surgical technique in the first case. Lateral subvastus approach and implant positioning. Intraoperative AP X-ray showing the insertion of the cephalic implant pin in relation to the distal femoral stem. Correct positioning of the pin is confirmed in the axial view. Introduction of the cephalic implant, with an additional pin preventing rotation at the fracture site. A 4.5 mm bicortical screw is inserted, and the fracture is compressed. Adequate plate-stem overlap. Bicortical fixation around the stem is achieved using 3.5 mm screws. The axial view demonstrates correct plate positioning, allowing screws to be placed both anterior and posterior to the stem. AP X-ray at 6-month follow-up showing construct stability and complete bone healing. Axial view at the same follow-up.

Fig. 3

Surgical technique in the second case. Larger subvastus approach and implant positioning, including the trochanter-stabilizing plate and additional cerclage fixation. Intraoperative X-ray AP view showing displacement of the lateral cortex. Axial view showing lateral cortex reduction using clamps and cephalic guide insertion. AP view showing adequate cephalic implant drilling and lateral cortex reduction. Final seating of the cephalic implant in the axial view, with correct plate positioning allowing for anterior and posterior bicortical screw fixation around the stem. The lateral cortex is additionally stabilized with a cerclage and a trochanteric stabilizing plate. Distal fixation with 3.5 mm bicortical screws around the stem is achieved. AP X-ray at 6-month follow-up showing complete bone healing. Axial view at the same follow-up.

Fig. 4

Preoperative assessment of implant compatibility. Lateral comparative view of the cortical screw diameters from the DHS system (top) with a head diameter of 8 mm and a thread diameter of 4.5 mm, and the Evos-Small system (bottom) with a head diameter of 5.6 mm and a thread diameter of 3.5 mm. The DHS plate has a thickness of 5.8 mm. Both screws are inserted into non-LCP holes, which have a superficial diameter of 8 mm and a deep diameter of 4.5 mm. The Evos-Small screw sits more deeply, but its head diameter exceeds the deep hole diameter by 0.9 mm, ensuring adequate fixation with enhanced polyaxiality. Lateral comparative view of both screws protruding from the opposite side of the system.