remember that with a resurfacing or a THR – one is not aiming to
give supra normal movement. One is merely trying to restore
normal movement present before the onset of hip arthritis.
The head- neck offset is an important determinant of ROM. This
is restored by a properly done resurfacing even in patients who
have a poor head neck offset as in FAI ( femoro – acetabular
impingement. Hence full restoration of ROM is consistently
possible in a resurfacing.
A big ball THR has an abnormally high head neck offset due to
the thin neck. Thus in theory a big ball THR can produce supra
normal movement . However this is neither desirable or feasible
in clinical practise as the head neck offset is only one of the
factors influencing ROM. Other factors like soft tissue tension
come into play. If one goes on making the neck thinner
progressively and the head progressively larger — it is wrong
to imagine that this will translate progressively into continued
increase in Range of Movement.
In a badly done resurfacing, impingement can occur and this will
lead to abnormal wear pattern and in extreme cases can be seen
on x-rays. A properly done Resurfacing will definitely match any
type of THR for the ROM.
It is moot point that a Big ball THR will be more forgiving for
surgical errors than a resurfacing in respect to ROM.
With best regards
Information obtained by
Vicky Marlow Freelance Patient Advocate Volunteer 2008