Evaluation of the safety and efficacy of the MHP- total hip arthroplasty

The investigational device is the femoral component of a total hip arthroplasty
(THP). Total hip arthroplasty (THA) is a widely used surgical procedure with a
high success rate. The survival rate of THA with revision for any reason as end
point in national registries is in the order of 95% after 10 years. Mechanical
reasons for revision like fatigue failure, wear or aseptic loosening have
diminished. Other revision reasons like infection or component malpositioning
have become the major reason for revision. Therefore further development of
THP*s is now focusing on other aspects than just increased survival time.
Aspects like bone conservation, minimal invasive procedures, fast recovery time
and short admission time are leading factors in THP development. Also the
investigational device of this study is focusing on these aspects. In
comparison to conventional hip prostheses it has a number of different
features, like: a very high neck resection, a shallow neck resection and a
short stem in combination with cemented fixation. The goal of these features is
1) to diminish the amount of resected bone and thereby to have a better
starting point in case of revision and 2) to offer a hip stem which can be used
more easily in combination with a minimal invasive surgical approach. Because
the investigational device is only to be fixated in the methaphyseal region of
the femur it is called: Methaphyseal Hip Prosthesis (MHP). Methaphyseal hip
stems are not new. Several designs have been in the market for a prolonged
period like the Mayo Hip from Zimmer and the Cut 2000 hip from ESKA Implants.
More recently short stems like the Proxima and the Silent hip from DePuy have
been introduced in particular to address the demand for minimal invasive
surgery. All these stems are fixated to the bone without the use of bone
cement. This makes the procedure relatively easy but also makes the stability
of the implant dependent on the quality of the bone stock. In case of the MHP
it is chosen to use bone cement as fixation method. This enables immediate
weight bearing by the patient and makes the reconstruction less dependent of
the bone quality.
In order to conserve as much bone as possible it has been chosen to use a high
subcapital resection. The stem has a rather short length and the entire length
remains inside the methaphyseal trabecular bone to ensure a good
interdigitation at the cement-bone interface. The short length will increase
the interface stresses, both shear stresses in axial loading and normal
stresses due to a bending load. Therefore it is chosen to make a shallow neck
resection and to ad a collar to the stem which rests on the resection surface.
This will increase the load transfer to the femur very proximally and will
diminish the interface stresses. Proximal load transfer has the additional
advantage to protect against stress shielding induced osteopaenia.
The diminished stem-cement surface and the increased stresses at the
stem-cement interface are counteracted by longitudinal grooves on the anterior
and posterior surface of the MHP stem. Extensive laboratory testing has shown
that the stem-cement interface is able to withstand extreme high loads on the
hip joint. The whole MHP reconstruction in laboratory testing showed to have
superior strength compared to the natural femur. This protocol aims at the
first in vivo implantation.

Primary:
• To analyze the stability of the MHP using R.S.A to predict the long term
survival.
Secondary
• To analyze the short term (1 year) safety of the MHP compared to the Stanmore
hip replacement.
• To analyze the short term (1 year) efficacy of the MHP compared to the
Stanmore hip replacement.
• To analyze the long term (10 years) safety of the MHP compared to the
Stanmore hip replacement.
• To analyze the long term (10 years) efficacy of the MHP compared to the
Stanmore hip replacement using patient based questionnaires.
• To analyze the bone remodelling around the MHP (10 years) using DEXA
measurements

Single-centre prospective study with 25 patients in the study and 25 in the
control group. Open, RCT (Randomized Clinical Trial) in which the MHP is
compared with the standard Stanmore hip prosthesis.

Cemented total hip prosthesis

The MHP has not been implanted in human before. The preclinical testing gave
excellent results. Therefore risks of the MHP in vivo are unknown. All
potential risks for a hip prosthesis are reported in section A4.4.
For the study additional traditional and RSA X-rays need to be made, as well as
additional DEXA scans. Therefore the radiology exposure will increase with 6
mSv for the total study (10 years). The average annual natural dose is 2 mSv.
The questionnaires will take approximately 10 minutes at each control visit.
The RSA and DEXA scans will take approximately 15 minutes each.