COMparison of Posterolateral and direct Anterior approach in uncemented total hip arthroplasty with a Short Stem prosthesis

Short-stems total hip prostheses, such as the NANOS prosthesis, pose possible
advantages for active patients. Because a large part of the column femoris
remains intact it is possible to create a more anatomical reconstruction of the
hip joint. This leads to better off-set restoration which may improve hip
abductor function1,2. A reduced capacity of the abductor muscles might result
in aberrant hip abduction/adduction pattern during walking, which might be
problematic in for example the regulation of medio-lateral balance during
walking. Another advantage in active patients is that the NANOS stem fixates
proximally in the femur leaving more bone stock for a possible subsequent
revision. Because of the proximal fixation it is suspected that the NANOS
causes less stress shielding of the trochanter region3 and flexibility of the
femur shaft is left intact leaving a natural capacity to bending forces on the
femur shaft
The NANOS prosthesis was developed in 2002. Since its release positive results
have been presented (table 1 and table 2) for complication rates and revision
rates. Also, an ODEP 3A* rating was assigned in 2016.

The use of short stems corresponds with the trend of direct anterior and
minimal invasive hip surgery we have seen last years. With these techniques
more muscles are left intact and might therefore result in a better functional
outcome, leading to shorter operation time, less perioperative complications
and less muscle damage4. Thus, both the short stem total hip prostheses as well
as the direct anterior and minimal invasive approaches in hip surgery can be
considered relatively recent innovations in THA and both are aimed at improving
functional and clinical outcome, mainly in the short term. However, the
clinical and functional effectiveness of the combination, i.e. whether the use
of short stem prostheses is even more effective when used during the direct
anterior approach compared to when used during the regular posterolateral
approach in THA, is as far as we know not yet investigated. Important
parameters in THA which may be related to clinical and functional outcome are
the level of fixation and positioning of the (short) stem, which are thought to
be affected by surgical approach. In literature, it is well established that
early migration (migration within two years after THA) of the stem is
predictive for late aseptic loosening of the stem5,6. The computer-assisted
Einzel-Bild-Roentgen-Analyse (EBRA) system was evaluated to detect stem
migration of 1 mm with a specificity of 100% and a sensitivity of 78%7. This
method is less invasive and easier to use in a clinical setting then the gold
standard RSA method. A migration threshold of 1.5 mm after two years was found
to be highly predictive for later aseptic loosening and significantly increased
risk of revision 5. Comparing the level of migration of the short stem of the
hip prosthesis for the direct anterior approach and the posterolateral approach
in THA might add to the knowledge base of the effectiveness of the direct
anterior approach and may help in evidence based clinical decision making when
deciding for the best treatment option when a patient*s hip needs to be
replaced.

Primary Objective:
The primary objective of this study is to investigate whether the NANOS femoral
stem placed by means of the direct anterior approach (DAA) results in a better
rigid fixation, stem position and off-set restoration at two years follow-up in
comparison with the NANOS stem placed using the posterolateral approach (PLA)
in patients with hip osteoarthritis who need a total hip arthroplasty (THA).

Secondary Objectives:
The secondary objective is to compare THA with the short stem NANOS prosthesis
using the DAA with the PLA for perceived pain, functioning of the hip, quality
of life, isometric hip abduction force and quality of walking during the first
two years after surgery.

This study will be a single center, randomized controlled clinical trial (RCT).
This study contains two arms, one with patients treated by means of the DAA and
one with patients treated by means of the PLA.
Two surgeons will be participating in this study. Both are senior hip
orthopedic surgeons for the NANOS prosthesis and both orthopedic surgeons can
and will perform the DAA and the PLA. If the indication for primary hip
arthroplasty is established, patients were asked if they wanted to participate.
Patients who were interested in participating got an appointment with the
research nurse after one week. Then informed consent was signed. Registry of
data and block randomization will be executed via Castor.

As primary outcome we use the migration of the NANOS prosthesis in mm as
measured with EBRA-FCA software. In addition, we will investigate functional
outcome and quality of life with the HOOS and EQ-5D questionnaires.
Basic balance and gait performance will be tested using the timed *up &
go* (TUG) test, instrumented with inertial sensors to measure body segment
accelerations and angles, and a two times 50 meter walk at their preferred
walking speed, also instrumented with inertial sensors8*12. For the TUG test13,
in short, participants will be asked to stand up from a chair, walk for 3
meters, walk back to the chair and sit down on the chair. The time needed to
perform the TUG test as instructed will be registered. In addition, the
participants will wear validated inertial sensors (McRoberts Dynaport Hybrid,
Dimensions 87 x 45 x 14 mm, Weight 74 grams)14, which will be attached to the
lower back with Velcro fixation.
The study will take place between 2017 and 2020 in the Noordwest
Ziekenhuisgroep location Alkmaar.

Two surgeons will be placing the NANOS stems. Both surgeons will use the direct
anterior approach (DAA) and the posterolateral approach (PLA). Both surgeons
have extensive experience with both these approaches and previous experience
with the NANOS stem.

We will use a follow-up protocol that is similar to the NOV (Dutch orthopedic
society) THA guidelines18. This protocol contains postoperative clinical and
radiological visits at 6 weeks and one year. In addition, we will send patients
functional evaluation questionnaire (HOOS, VAS) at 3 and 6 months. At 24 months
we will schedule an additional clinical and radiological follow-up visit.

Considering the fact that both intervention and control treatment are currently
being performed as part of normal treatment
procedures without any known increased risks for patients, we expect that the
risk of participating in this study will be minimal.
The burden of participating will consist of filling in questionnaires and
undergoing walking tests, and a single extra outpatient appointment and two
x-rays two years after surgery.