Abstract
PurposeDigital templating shows reliable accuracy for straight stem systems. In recent years, the implantation of short stems through minimally invasive approaches has gained more popularity. Minimally invasive approaches (MIS) show the risk of undersizing femoral components. Therefore, we questioned the planning adherence for a curved short stem and a bi-hemispherical acetabular cup implanted through an anterolateral MIS approach.MethodsA consecutive series of 964 hips (index surgery between 2014 and 2019) with Fitmore® curved short stem and Allofit/-S® acetabular cup (both ZimmerBiomet Inc, Warsaw, IN) were included. Preoperative digital templating was conducted anterior–posterior (AP) digital radiographs of the hip using mediCAD® version 5.1 (Hectec GmbH, Altdorf, Germany). The templates of acetabular and femoral components (offset option and stem size) were retrospectively evaluated for general adherence, and according to sex, BMI and planner’s experience.ResultsPlanning adherence for the exact offset option was 70.6 and 21.6% for exact offset option and stem size. Adherence for acetabular cup ± 1 size was 74.8%. A significant difference between male and female patients for the offset option could be found (p = 0.03, z = −2983). In 22.5% of male patients, an offset option one size higher and in 12.3% of female patients an offset option one size smaller than templated was used intraoperativelyConclusionDigital templating for the Fitmore® stem in cementless THA with a minimally invasive anterolateral approach shows comparable planning adherence to the existing literature for this cementless short stem. However, a lower planning adherence was detected compared to conventional straight stem systems. In male patients, the femoral offset is frequently undersized and in female patients frequently oversized compared to the preoperative plan. Surgeons should be aware of this difficulty in digital templating for Fitmore® hip stem.
Highlights
A successful postoperative outcome after total hip arthroplasty relies on restoring the biomechanics of the hip as well as selecting the appropriate implant size [1, 2]
Cementless short stems facilitate the use of minimally invasive approaches leading to less soft-tissue damage
Digital templating for the Fitmore® stem in cementless THA with a minimally invasive anterolateral approach shows comparable planning adherence to the existing literature for this cementless short stem
Summary
A successful postoperative outcome after total hip arthroplasty relies on restoring the biomechanics of the hip as well as selecting the appropriate implant size [1, 2]. The adherence for templating ranges from 78 to 98% within one size for the femoral stem, and between 80 and 91% to within 2 mm for the acetabular component [1, 7,8,9,10]. The choice of surgical approach was shown to have an effect on component size and position [1]. Rivera et al showed an increased risk of underestimating the size of cementless short stems in total hip arthroplasty implanted through a direct anterior approach (DAA). An implantation of a femoral stem with a stem size at least two sizes smaller was six times higher in DAA without fluoroscopy compared to posterior approach (PA). Schmidutz et al [13] found a comparable effective adherence for short stem arthroplasty with an average percentage of agreement (± 1 size) of 89.0% compared to 88.5% in conventional straight stem arthroplasty
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