ACFT NOSE GEAR STRUT DAMAGED AND TOW BAR BROKE DURING PUSHBACK OF B737-800.

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THE ACFT WAS READY FOR PUSHBACK FROM GATE. ALL PAX WERE SEATED AND CABIN SECURE FOR GATE DEP. THE CAPT CALLED FOR THE 'BEFORE START' CHKLIST AND ALL 5 ITEMS WERE COMPLETED PER THE COMPANY'S B737 AOM NORMAL PROCS SECTION. THE CAPT TOLD ME TO GIVE GND CTL AN ADVISORY CALL ABOUT THE PUSHBACK AND SUBSEQUENT PLANNED DEICING THAT WAS TO BE DONE JUST OFF THE GATE. JUST AS I HAD FINISHED TELLING GND CTL OF THE PUSHBACK; THE CAPT TOLD THE PUSHBACK CREW VIA INTERPHONE 'BRAKES RELEASED; CLRED TO PUSH.' JUST AS THE CAPT WAS SAYING THIS; I HEARD THE PARKING BRAKE HANDLE RELEASE. JUST AS HE FINISHED THE STATEMENT; THE PUSH CREW STARTED THE PUSHBACK. I SUDDENLY NOTICED THE PARKING BRAKE LIGHT WAS STILL ILLUMINATED AND I HOLLERED 'BRAKES!' SIMULTANEOUSLY THE ACFT LURCHED AND WE HEARD A LOUD BANG. WHEN QUERIED; THE PUSH CREWS ADVISED THAT THE TOW BAR HAD INDEED BROKEN (SHEAR PIN SHEARED). THE CAPT WAS THEN TOLD HE BETTER COME DOWN TO THE RAMP TO LOOK AT THE NOSE GEAR. ON INITIAL INSPECTION; THE NOSE GEAR WAS TURNED ALMOST 90 DEGS L (PAST THE TOW LIMIT MARKING) AND THE 'LUG' WHERE THE TOW BAR ATTACHES TO THE NOSE GEAR HAD BROKEN OFF. SOME FACTORS THAT HELP ATTRIBUTE TO THIS WERE THE VERY FAST RESPONSE BY THE PUSH CREW WHEN ADVISED THEY WERE CLRED TO PUSH; AND MORE IMPORTANTLY; THE ICY; SNOW COVERED RAMP CONDITIONS. THIS ALLOWED THE NOSE GEAR TO FREELY SPIN WHEN THE TOW BAR BROKE. WHEN THE TOW BAR BROKE THERE WAS A LOSS OF 160000 LBS OF RESISTANCE ON IT AND WITH THE EASE OF A NOSE GEAR TO SPIN DID JUST THAT -- ALLOWED IT TO SPIN RIGHT ON AROUND. MANY TIMES I SEE CREWS ATTEMPTING TO PUSH BACK IN AN EXPEDITIOUS MANNER. WE ALL NEED TO REMEMBER THAT WITH ADVERSE WX AND RAMP CONDITIONS EXTRA CAUTION NEEDS TO BE EXERCISED. IT APPEARS THAT POSSIBLY A STUCK PARKING BRAKE VALVE MIGHT BE TO BLAME AND NOT A HVY ACFT ON A CONTAMINATED RAMP. COMPANY INVESTIGATION IS CONTINUING. SUPPLEMENTAL INFO FROM ACN 456517: AS I CALLED 'BRAKES RELEASED CLR TO PUSH;' I RELEASED THE PARKING BRAKE. I FELT THE BRAKES RELEASE THROUGH THE PEDALS. I BELIEVE I SAW THE BRAKE LIGHT GO OUT. I AM EXPERIENCED ENOUGH TO RECOGNIZE THE HAZARDS OF COMPLACENCY. NEVERTHELESS; WE ARE CREATURES OF HABIT. IT IS PROBABLE THAT I THOUGHT I DID; BUT IN FACT DID NOT. HAD THE RAMP NOT BEEN SLIPPERY; HAD THE PUSHBACK CREW NOT BEEN SO PROFICIENT AND READY TO GO; AND HAD I MADE EXTRA SURE (AS I DO NOW) THE BRAKE LIGHT WAS OUT; MAYBE I WOULDN'T HAVE DAMAGED THE ACFT.