Tefillin for someone missing an arm
1 What is the halacha when someone is missing their left (weaker arm) from the kibores? 2 What is the halacha when someone has a full arm cast which covers even the kibores? It appears that in the first case the person is completely exempt from placing tefillin shel yad 27:1 Rema; Shulchan Aruch HaRav 27:3, in the second case they should put on tefillin, to satisfy the opinion of the Rashba, (that does not hold there is a problem of chatzitzah with Tefillin), however without a bracha (based on S A HaRav ibid:7. There is the opinion of the Magen Avraham 27:3 (also quoted in the S A HaRav 27:3, which is inserted in special parenthesis), that in the first case the tefillin shel yad should be placed on the right arm, without a bracha. Does the Magen Avraham hold the same for the second case? Is it correct to say that Lehalacha Lemassah one does not follow the Magen Avraham in this case(s)?