Both sides have worked several days on this trade, and it wasn't without a couple of hiccups. On Wednesday, ESPN's Ed Werder reported Maxwell had a shoulder injury that was concerning to the Dolphins and threatened to nix the deal. However, Maxwell passed the physical and the trade proceeded.
Maxwell has five years left on the $63 million contract he signed last year. He will make $8.5 million this season. Alonso is playing in the final year of his rookie contract and will make $991,948.
The Dolphins were ranked 25th in total defense last season and are in the process of doing a makeover. They also signed defensive end Mario Williams to a two-year contract and agreed to terms with Detroit safety Isa Abdul-Quddus, he confirmed on Twitter.
Known as a hard hitter, Abdul-Quddus, 26, has played in 74 NFL games, making 136 tackles with four forced fumbles, two interceptions, a sack and a fumble recovery.
To make room for the moves, the Dolphins also released veteran cornerback Brent Grimes, who made the Pro Bowl in his past three seasons with Miami. He was scheduled to make $8 million in 2016 and is now an unrestricted free agent.
Grimes had a successful three-year tenure in Miami. He signed with the team in 2013 and had 13 interceptions total in that span. Grimes recorded 49 tackles and four interceptions last season.
While Grimes was a Pro Bowl selection on the field, his wife, Miko, made headlines off it.
Miko Grimes, who hosts a Miami radio show, has publicly criticized Dolphins quarterback Ryan Tannehill, used Twitter to rant about things including her husband not winning MVP honors at the Pro Bowl, his alleged mistreatment by the Atlanta Falcons, what she sees as the NFL's greed and sexism, and her unhappiness with the New England Patriots for parting company with Vince Wilfork.
She was also arrested on charges of battery on a police officer, resisting arrest and disorderly conduct outside of Sun Life Stadium before a Bills-Dolphins game last season. The charges were later dropped.
ESPN Lions reporter Michael Rothstein contributed to this report.
Eagles, Dolphins trade back on after Maxwell cleared
Adam Schefter explains why the Dolphins, Eagles trade will go through now that Byron Maxwell has been cleared of injury concern.