Stem design affects templating adherence in total hip arthroplasty - a retrospective cohort study comparing two types of cementless short stems

BACKGROUND: Preoperative templating is crucial when performing total hip arthroplasty (THA) as it facilitates the correct restoration of the joint biomechanics and reduces the risk of adverse events associated with component under- or over-sizing. Templating and execution of stem placement is highly dependent on the actual stem design. Therefore, we aimed to compare the templating adherence between a neck-resecting and a partially neck-sparing cementless short stem and to evaluate the influence of patient-specific factors like sex and Dorr type on the templating adherence.

METHODS: This retrospective cohort study evaluated the preoperative templates of 345 consecutive THAs performed by a single surgeon. A neck-resecting short stem (Fitmore, ZimmerBiomet) combined with a bi-hemispherical cup (Allofit, ZimmerBiomet; Group A) was used in 160 cases and a partially neck-sparing short stem (ANA NOVA alpha proxy, ImplanTec GmbH) combined with a bi-hemispherical cup (ANA NOVA alpha cup, ImplanTec GmbH; Group B) in 185 cases. The templating adherence was evaluated for stem size and offset option as well as cup size.

RESULTS: Group A showed a lower overall templating adherence with regard to stem size compared to Group B (26.9% vs. 36.2% exact match, p = 0.063; 57.5% vs. 71.4% ± 1 size, p = 0.007). In female patients templating adherence with regard to stem size was significantly lower in Group A (26.5% vs. 44.4% exact match, p = 0.012). For Dorr type B femora, significantly lower templating adherence was observed within Group A with regard to stem size (26.4% vs. 39.6% exact match, p = 0.013). No significant differences between both study groups were found with regard to adherence to the templated offset option (60.6% vs. 60.5% exact match, p = 0.987) and cup size (43.1% vs. 40.0% exact match, p = 0.557).

CONCLUSIONS: For both stem types, the overall rate of exactly matching the templated stem sizes was relatively low. However, templating adherence was significantly higher in female patients and in Dorr type B femora with a partially neck-sparing stem, which should be considered by surgeons performing THA using cementless short stems.

TRIAL REGISTRATION: This trial was registered at the local ethics committee (Registration Number: 1094/2023).