Letter to the editor: ‘The history of the development of the regular straight stem in hip arthroplasty’

In the article titled ‘The history of the development of the regular straight stem in hip arthroplasty’, Wellauer et al. published in this journal, the history of femoral stems in total hip arthroplasty (THA) is presented very clearly (1). Of the different types of stems, the authors describe the global tissue-sparing (GTS) stem.

The authors are to be congratulated for the present significant contribution to the orthopedic literature since they brilliantly put together in a single paper the vast field of the straight femoral stems and linked one to the other by means of a genealogy tree.

However, we are concerned with the description that the authors give for the GTS stem. When reading the article, we came through two main issues that for us deserve further clarifications.

First, contrary to the CLS Brevius (2), the GTS stem should not be considered as a modification of the CLS Spotorno (where CLS stands for cementless) but as a new stem that is based upon the philosophy of its predecessor.

The triple taper design and the longitudinal fins that are sharper and developed along the entire length of the implant are a direct consequence of the influence from the CLS Spotorno.

A new elliptic octagonal cross section has been developed to fill the metaphysis, without filling the canal distally, reducing the risk of stress shielding and thigh pain. A lateral flare has been introduced to preserve bone stock in the trochanteric region and to reduce the iatrogenic damage to the soft tissue during the femoral preparation (3).

Nadorf J. et al. observed similar mechanical behaviors between the GTS and the CLS stems in terms of rotational stability and bone–implant flexibility with a lower mean bone invasiveness (metaphysis: 44.6% GTS vs 57.7% CLS; femoral shaft: 42.1% GTS vs 57% CLS) and lower implant length (93–139 mm shorter than a conventional diaphyseal stem) (3, 4).

Secondly, they state, ‘The GTS, however, performed poorly, with revision rates identified as outlier, showing again the relevance of modifications of successful designs (117)’. The reference that they mention refers to the ‘Swiss National Hip & Knee Joint Registry 2021 Report’. This register describes a 2-year revision rate of 13.8% for the GTS stem against an average of 2.6% for all the other types of stems. Therefore, the authors legitimately reported a poor performance rate of this type of stem. However, we could notice how the data about the GTS performance came from a single hospital experience of 110 patients. Moreover, the reported survival rate of 13.8% refers to the survival of the GTS + G7 bispherical combination, and no isolate data on the survival of the GTS alone are reported.

To the authors’ best knowledge, three articles in the literature investigated the performance of this specific type of femoral stem. Morales de Cano et al. published a cases series of 80 patients implanted with a GTS reporting only one complication at mean 16 months of follow-up, namely, an intraoperative periprosthetic fracture (5). Later on, the same authors published a prospective case series of 136 patients (148 GTS stems) at a mean follow-up of 26.7 months reporting again only one complication, namely an intraoperative periprosthetic fracture (6).

A retrospective cohort study was published comparing the survival rate of 374 GTS stems (0.8%) and 321 CLS (0.4%) at an average follow-up of 5 years, showing no statistically significant difference (P = 0.63) (4). A recent prospective case series of 163 patients (172 GTS stems) at a minimum follow-up of 10 years was published (7). In this study the authors observed a 99.6% survival rate for any cause of failure (96% CI: 1.06–1.97) with only six failed cases undergoing revision surgery for aseptic loosening (four cases), metallosis (one case), and periprosthetic fracture (one case). Therefore, the performance of the GTS stem would be defined as 10A*, since the revision rate at 10 years is below the benchmark 5% established by the Orthopaedic Data Evaluation Panel (ODEP) and reported by the National Institute for Health and Care Excellence (NICE) guidelines (8).

In conclusion, we feel that the statement concerning the GTS should be rewritten by the authors considering the aforementioned evidence, to provide the readers with a more complete view on the performance of this stem.