The 10-year follow-up of the Delta-TT trial:
Stability of the Delta-TT cup with Polyethylene insert compared to the Delta-TT cup with Ceramic insert.

Aseptic loosening of the acetabular component of hip implants in total hip
arthroplasty (THA) remains one of the main causes of implant failure and
revision surgery. To address this issue, Trabecular Titanium (TT) has been
integrated into the Delta-TT cup, a cementless press-fit hemispheric implant,
aiming to optimize initial stability and osseointegration while reducing the
risk of long-term aseptic loosening. Studies have demonstrated that titanium
cups with a polyethylene liner facilitate a more natural load transfer to the
surrounding bone, attributing both cup and liner stiffness to the construct's
stability.

Stiffness of ceramic bearings thus might affect primary stability and migration
of implants in press-fit THA. In our initial Delta-TT Radiostereometric
Analysis (RSA) study, it was therefore hypothesized that Delta-TT cups with a
ceramic liner would exhibit more migration due to their higher stiffness
compared to Delta-TT cups with a polyethylene liner. However, the 2- and 5-year
results showed stabilization of Delta-TT cups within six months, regardless of
liner type. Although a trend towards increased migration was observed in cups
with ceramic liners, the between-group effects were small and lacked
statistical significance.

This 10-year follow-up study aims to further investigate long-term migration
patterns of the uncemented Delta-TT cup and H-MAX S stem, comparing outcomes
between ceramic and polyethylene liners. Given the predictive value of early
RSA migration patterns at the 2-year mark for identifying implants at risk of
aseptic loosening, we hypothesize that the Delta-TT cup will demonstrate good
stability at the 10-year postoperative mark. Besides, it is hypothesized that
migration of Delta TT-cups is comparable between ceramic and polyethylene
liners.

The primary objective of this study is to measure the long-term stability of
the Delta TT cup, combined with either a ceramic or cross-linked polyethylene
liner, by means of RSA at 10-years postoperatively.

Secondary objectives are to measure long-term stability of the H-MAX S stem, by
means of RSA at 10-year postoperatively. Furthermore the study aims to measure
implant survival rates and patient-reported outcomes for both the Delta-TT cup
and H-MAX S stem, comparing outcomes between the ceramic and polyethylene
group.

This study is a long-term follow-up of the Delta-TT trial, in which 52 patients
who underwent unilateral primary hip arthroplasty were randomized between a
polyethylene liner (n = 25) and a ceramic liner (n = 27). The initial study
included RSA imaging at baseline (within 3 days postoperative before
weightbearing) and at 6 weeks, 3 months, 6 months, 1 year, 2 years and 5 years
postoperatively. At these same marks PROMs were documented, including EuroQol
5D-3L (EQ5D-3L), Hip disability and Osteoarthritis Outcome Score-Physical
function Short form (HOOS-PS), Numeric (Pain) Rating Scale (NRS) and Oxford Hip
Score. In this 10-year follow-up, for the 51 patients still included in the
study at the 5-year follow-up, RSA imaging is repeated and PROMs will again be
documented. Instead of EQ5D-3 the more recent EQ5D-5L will be used, because it
shows a reduced ceiling effect compared to the EQ5D-3L version (Feng, Devlin, &
Herdman, 2015; Herdman et al., 2011). To compare these EQ5D-5L scores to the
values of the initial study they will be translated to the EQ5D-3L scores (van
Hout et al., 2012). In addition, patients will be questioned about potential
(Serious) Adverse Device Events, including re-operation related to the hip
included in the study, hip luxation, THA revision, and hip squeaking.

Patients have already been randomized in the initial study and are being
re-evaluated by means of Patient Reported Outcome Measures (PROMs) and RSA
imaging. There are, in our view, no risks associated with participation in this
study. The effective radiation dose per RSA-radiograph is 0.27 mSv. This is
negligible when compared to the natural annual exposure of 2.9 mSv. There is no
guarantee that patients will personally benefit from inclusion in this study.
Patients undergo a more thorough screening than non-study patients and may
benefit from this increased surveillance. Information gathered in this study
may benefit others undergoing THA with Delta-TT cups.