2.1. Case Description

A 68-year-old deaf male patient (60 kg, 175 cm, BMI 19.6 kg/m²) with clinically manifest osteoporosis suffered a femoral neck fracture following a low-energy fall on his right hip. The initial treatment with uncemented THA was performed elsewhere (Versafit CC Trio cup with highly-crosslinked polyethylene liner, 32 mm CoCr head, Quadra-H stem; Medacta, Castel San Pietro, Switzerland), through a direct anterior approach on a traction hemi-table (Figure 1). The stem was undersized by two sizes compared to preoperative templating and implanted in varus position in relation to the axis of the femoral diaphysis (Figure 1A). The patient recovered from the operation without complications and was able to return to his partially institutionalised everyday life. A postoperative leg-length discrepancy, however, hampered ambulation, with recurrent tripping.

Zone of interest of the anteroposterior radiographies of the pelvis after total hip replacement (A) and after the patient had suffered the periprosthetic fracture of the proximal femur (B). Dashed lines at the tip of the greater trochanter help identify posttraumatic sintering of the stem. Note that the stem was undersized, with more than 1 mm between the stem and the inner cortex. Scale-up of (B), marked by a white rectangle, is provided in (C) to better illustrate the dense line, most likely the hydroxyapatite (HA) coating, separated from the stem, marked by white arrowheads. These tissues could be sampled for further analysis. (D) shows the condition after revision. The osteotomy, which was necessary to retrieve the stem, is visible, as are the cerclage cables used for fixation of the fracture and the osteotomy. Additionally, note the thinner liner in the cup, to accommodate the larger head.

Approximately 14 months postoperatively, following another low-energy fall on his right hip, the patient suffered a multifragmentary periprosthetic fracture of the proximal femur with loosening of the stem (Figure 1B). Corresponding to a periprosthetic fracture unified classification system (UCS) type B2 [18], stem revision was indicated. Surgery was performed through a transfemoral approach to the hip, formally completing exposure through the fracture fragments [19,20]. This approach ensures good distal purchase of the uncemented, tapered, fluted, modular revision stem (Revitan straight, Zimmer Biomet, Winterthur, Switzerland) used [21]. The stem in situ was loose and could be retrieved without any instrumentation. Delamination of the HA coating from the stem had already been suspected on the preoperative conventional radiographies (Figure 1C). Fragments from the bone at the implant interface could be chiselled off easily from the endostal surface of the medial cortex of the femur for further analysis before reaming for the new stem. The tissue samples were fixated and sent for further examination in a buffered formaldehyde solution (4%) (Formafix, Hittnau, Switzerland). Good osteointegration of the cup was confirmed, and it was therefore left in place, despite excessive anteversion of 28°, and measured in the plane of the lateral inclination [22,23]. However, to reduce the risk of dislocation, the liner was exchanged to accommodate a 36 mm head [22]. Internal fixation of the proximal femur was achieved with cerclage cables (Dall-Miles 2.0 mm; Stryker, Kalamazoo, MI, USA). As the femoral offset could not be reconstructed anatomically with the new stem, a certain degree of leg-lengthening had to be accepted, to avoid instability of the hip.

Microbiological samples and routine histopathological analysis showed no signs of infection. Postoperative recovery was uneventful. Follow-up more than two years postoperatively was uneventful, except that the leg length discrepancy had to be compensated with shoe sole raise on the contralateral side.