Former U.S. President George H.W. Bush was released Sunday from a hospital in the state of Maine after four-day treatment for a fractured vertebrae caused by a fall at his summer home.

Bush's spokesman Jim McGrath said in a tweet that the 91-year-old was "very grateful" as he returned to his vacation home in Kennebunkport from the Maine Medical Center in Portland where he received the treatment.

"President and Mrs @GeorgeHWBush extend their great gratitude to the doctors, nurses and staff @Maine Med 4 their kind and professional care," said another tweet by McGrath.

Bush, the oldest living former U.S. president, broke a bone in his neck after he fell at the home last Wednesday. His family and doctor did not disclose the cause of his fall, except for saying that he had a cracked C2 vertebrae but his spine was not damaged.

The former president is suffering from a lower-body Parkinson's disease which has forced him to use a wheelchair since 2011. He was hospitalized in Houston, Texas in December for a week of treatment of breath shortness.

Bush, who served two terms as vice president under President Ronald Reagan before winning the presidential race in 1988, is the 41st U.S. President and father of George W. Bush, the 43rd U.S. President, and Jeb Bush, who is running for president in 2016 as a Republican candidate.