What alternatives do you have if you do not want to loose the benifits of modularity ?

Perhaps we should discuss which taper is more adequate for long time function with a minimal risk of fretting or third body wear. The euro taper or the US alternative

This is very interesting: can you give further details about euro taper and the US alternative or some references? Thank you!

Maximillian,

You are right on target. All tapers are not equal in design or function.

A self-locking taper (Morse) works by producing a frictional force that holds the components together and is greater than the forces pushing the components apart.

The frictional force resists torsional and axial forces created at the modular junction, while careful tolerancing provides optimal contact along the length of the taper. The success of a self-locking taper is influenced by the design of the taper, particularly the taper angle, the roughness, and the mating materials between the “male” and “female” components.

In the last two decades, manufacturers have been altering femoral stem trunnions from various tapers such as 14/16 to 12/14. The original 12/14 Ceramtec taper was at one time referred to as a Euro taper, meaning a 12/14 off-the-shelf Ceramtec Taper.

This term was not trademarked, and some companies began altering the manufacturing tolerance as originally produce from Ceramtec. The term Euro taper still is referred to by most in Europe as an off-the-shelf 12/14 Ceramtec taper.

A 12/14 taper can have slightly different manufacturing tolerances by different manufactures and should not be used as a generic term.

All 12/14 tapers are not equal! (A Euro 12/14 taper is different than a ASTM 12/14 taper F1636)

Know what you are working with!

Recent trends in THA

Large Heads

Increased Femoral Offset

Metal on Metal

Increased physical activity by the patient

All of these increase torque moment at modular junction interface.

I have worked in modular hip designs since 1980s and Modular Junctions  can be and are a valuable tool in restoring joint mechanics but a lot can go wrong and has by not following:

MANY TAPERS DO NOT HAVE ENOUGH INTRINSIC STABILITY FOR TODAY’S HIGH DEMAND PATIENT

Not all taper junctions are designed or function equally

Know your design

Know required technique

Know design & material limits

Demand beyond compliance testing

Sound engineering principals work Incremental advancement in technology works Modularity can be designed and fabricated safely.

I have attached a paper I recently presented on this subject.

Optimizing Modular Tapers for THA

Conference Paper OPTIMIZING MODULAR TAPERS FOR TOTAL HIP ARTHROPLASTY

Thank you Thimothy for your detailed reply.

Based on your observations, mixing components from different manufacturers is quite an unsafe practice, and it is not so rare if we refer to revision arthroplasty!

Dealing specifically to couplings between the acetabular shell and its lining, there are some peculiarities:

- very often different materials are coupled

- the components are quite deformable

do you agree?

Elisabetta,

I don't have a problem mixing and matching as long as you know what you are matching. The problem comes when the surgeon assumes he knows without verification.

Example: If you are using Ceramtec off the shelf product that is supplied to two different manufactures the ceramic inserts are more than likely compatible. However you will never get the two manufactures to say that it is safe.

The industry has failed to set specific standards which has caused numerous surgical errors by not having the proper information at hand during surgery.

My recommendation is stay within the companies product line when using bearing materials.

I believe it is safe and effective to use one's acetabular components with another's stem. Example a 32 mm c.c. head  and stem with a DePuy 32mm poly liner in their metal shell. Hard on Hard bearings should not be mixed.

When in doubt do not mix but often mixing is  necessary.