With a series of blockbuster trades in the summer of 2007, the Boston Celtics assembled one of the best starting fives in recent NBA history: Rajon Rondo, Ray Allen, Paul Pierce, Kevin Garnett and Kendrick Perkins.

It was a perfect combination of “fit” and talent. At point, they had a 6’1 170 athletic blur with the ability to get in the lane and make every pass in the book. His lack of a jumper was off-set by three Hall of Famers who were nearly automatic from the perimeter, while the Big Three’s increasing inability to create easy looks was off-set by Rondo’s shot-creating ability.

Defensively, they had a 6’10 280 brick wall in the paint and one of the most athletic and versatile seven-footers in NBA history covering the entire floor. In three seasons, they never lost a playoff series when all five were healthy: winning a championship in 2008, losing to Orlando in 2009 when Kevin Garnett was out with a knee injury, and losing to the Lakers in 2010 when Perkins went down with a knee injury in Game 6 of the NBA Finals.

Perkins made a valiant effort to return last season, but he wasn’t the same. Boston traded him in a deadline-deal to Oklahoma City that was widely panned, but Perkins’ performance in the Western Conference Playoffs, where he was bereft of his athleticism and shot a career low 45.3% from the field, doesn’t suggest that he would have been a difference maker for the Celtics.

Yet, while Perkins should be healthier in his second year after his ACL tear, his absence leaves Boston with a gaping hole at center. Without him, they had to pick their poison in their second-round loss to Miami last year: Garnett was their only big man capable of guarding Chris Bosh 1-on-1 and defending the rim against Dwyane Wade and LeBron James. With Bosh spotting up on the perimeter, he couldn’t do both.

Most championship-caliber defenses have two athletic 6’10+ big men. Taking one out of the game, as the Bulls found out when they played Carlos Boozer instead of Taj Gibson against the Heat, can have a dramatic effect. Bosh ended Game 4, and gave Miami an insurmountable 3-1 series lead, by easily overpowering the smaller Celtic defenders for a tip-in when Garnett forced LeBron to miss a jumper up 93-90 with :30 left in overtime.

With Shaq on his way to retirement, none of the other three big men Boston had -- Glen Davis, Jermaine O’Neal and Nenad Krstic -- could serve as a defensive anchor in the paint. Jeff Green, the key player they received for Perkins, was a non-factor through most of the series. At 6’9 235, he is the stereotypical “3.5” forward -- not fast enough to defend 3’s on the perimeter or strong enough to defend 4’s in the paint.

But despite their age, Boston’s “Big Four” can still be a championship-caliber core. They just need a center who can replicate Perkins’ contribution to their 2008 championship.

It’s the same underlying dynamic the Dallas Mavericks, a talented group of veterans who needed an athletic center to cover their back defensively, faced last summer. The difference is Dallas had Erick Dampier’s expiring contract to pilfer Tyson Chandler from the Charlotte Bobcats; Danny Ainge doesn’t have any trade chips any near as valuable.

JaJuan Johnson, an athletic 6’10 big man from Purdue they found at the end of the first round, could carve out a ten-year NBA career as a “stretch 4” capable of knocking down jumpers. However, the 220-pound Johnson was only an average rebounder in college, which doesn’t bode well for his chances to win battles with Joakim Noah or LeBron in the paint, much less Dwight Howard.

With Krstic signing in Europe, Jermaine O’Neal is their only other big man. He played 24 regular season games last year and averaged 7.4 rebounds per-36 minutes of action.

Yet despite having such a thin roster, the Celtics already have $72.5 million committed for the 2011 season. Even before a new CBA which will likely make it much more difficult for high-salary teams to add talent, Boston had no real way of upgrading at the center position.

The Celtics are an aging team only one piece away from returning to title contention, but that one piece looks out of their grasp, which might explain their actions during the lockout.
 
Garnett emerged as one of the hard-liners on the player’s side in a dramatic negotiation session while Paul Pierce has been leading the push to decertify; they would have had a tougher decision if they thought the Celtics were legitimate contenders. Meanwhile, Boston’s owners, despite operating in a big market with a near-elite team, have been strong hawks.

As we have noted at RealGM, there’s a high correlation between a franchise’s place in the  standings and its owners’ position in the lockout. The course of history, as the titular character of Shakespeare’s Richard III famously complained, can be impacted by the smallest of things.

For NBA fans, Perkins’ 2010 knee injury could end up being one of them.