MINNEAPOLIS — Minnesota’s program for keeping sex offenders confined after they complete their prison sentences is constitutional, a federal appeals court ruled Tuesday, reversing a lower-court judge who said it violates offenders’ rights because hardly anyone is ever released.

A three-judge panel of the 8th U.S. Circuit Court of Appeals sided with the state, which argued that the program is both constitutional and necessary to protect citizens from dangerous sexual predators who would otherwise go free. The appeals court sent the case back to the lower court.

Seven offenders are currently free on provisional releases from the Minnesota Sex Offender Program, and only one has been permanently discharged, even though the program is more than 20 years old. That led U.S. District Judge Donovan Frank in 2015 to declare the program unconstitutional and order changes to make it easier for people to get on a pathway for release. As of Tuesday, 721 people were being held under the program.

The appeals court ruled that Frank erred in finding the program unconstitutional, saying he held the state to an overly high standard when he declared the program shocked the conscience. The panel concluded that the plaintiffs failed to demonstrate that any of the state’s actions or shortcomings in the program “were egregious, malicious, or sadistic as is necessary to meet the conscience-shocking standard.”

Dan Gustafson, lead attorney for the plaintiffs in the class-action lawsuit, said they’re “really disappointed” and are considering an appeal to either the full 8th Circuit or to the U.S. Supreme Court. He said Frank’s ruling had given them some hope that they weren’t just being “warehoused.”

The Minnesota case has been closely watched by lawyers, government officials and activists in the 20 states with similar programs. While civilly committed offenders in California, Wisconsin, New Jersey and other states are allowed to re-enter society after completing treatment, Minnesota has the highest per capita lockup rate, and its courts didn’t order the unconditional release of anyone from its program until August.

Eric Janus, a professor at Mitchell Hamline School of Law in St. Paul and an expert on the program, said it appears the 8th Circuit used the lower “rational basis” standard, which gives the state more leeway in designing and implementing the program, when it decided that the program is constitutional. He said he doesn’t think that leaves Frank any room to still find the program unconstitutional.

“I would say it’s not a complete death-knell” for the critics of the program, Janus said, noting the possibility of further appeals. “But this is a very serious setback.”

Gov. Mark Dayton welcomed the decision while insisting it wouldn’t stop his efforts to improve the program, including seeking funding for less-restrictive facilities.

“That means we can continue to make the reforms that we have started and at affordable costs to our state budget,” Dayton said.

The program is run by the Minnesota Department of Human Services. The agency’s commissioner, Emily Piper, also welcomed the court’s decision that the program was constitutional, but she said the Legislature needs to provide more money to keep it that way.

She said the program faces “significant challenges” in complying with other court orders to move people in advanced treatment stages into less-restrictive settings. Among other things, Piper said, the courts have ordered provisional discharges for six people but there’s no place to send them.

Minnesota’s offenders are confined by court order for treatment at secure facilities in Moose Lake and St. Peter that are ringed by razor wire, though there’s a section outside the wire at St. Peter for people in the later stages of treatment who have limited freedoms. They’re officially considered patients or residents, not prisoners. But the lawsuit argued that the program amounts to a life sentence.

Frank stopped short of shutting the program down in 2015, instead ordering changes including risk assessments for all patients to determine which could be put on a faster path toward release into less restrictive settings. The 8th Circuit stayed his rulings while it considered the appeal.

Minnesota has struggled for years with the rising costs of the program. It costs more than $120,000 a year to house just one resident, triple the cost of prison.

But lawmakers — many fearful of appearing soft on crime — have resisted major changes. The constitutionality has been in dispute from the start, but state and federal courts consistently affirmed it until Frank ruled in 2015.