I have seen many references to hub and spoke hospitals/units/services.

A hub hospital is one that is more highly specialized and with better facilities to handle patients who require special procedures that cannot be provided by spoke/satellite hospitals. Spoke hospitals refer patients to hub hospitals.

See website below:
http://linkinghub.elsevier.com/retrieve/pii/S016885100200080...
We analyse the highly-regulated cardiovascular sector of the health service in the Italian region of Emilia Romagna: this sector is characterised by strict regulatory control and a great emphasis on co-ordination and co-operation between public and private producers. These features have been even more marked since 2000, due to the adoption of the ‘hub and spoke’ organisational model, whereby a close relationship of selective referral from the network of satellite cardiology units (spokes) to the six Cardiac Surgical Centres (hubs) has been developed, so as to concentrate high risk procedures in highly specialised units. We focus on coronary angioplasty procedures (PTCA) and examine relations among centres before and after the official introduction of this hierarchical system completed the regionalisation of cardiovascular services. Secondly, since earlier regional efforts to reconfigure cardiovascular care by sending referrals to a few major centres may already have produced a high level of co-ordination among units, we investigate what happens to the volume–effect advantage across hospital categories with regard to the likelihood of adverse results for PTCA. We used descriptive statistics and logistic regression models to assess the existence of selective referrals and the concentration of clinical complexity in more specialised centres. Figures were taken from a regional administrative database based on hospital discharge abstracts (SDO) for the period 1998–2000.