Joel Embiid, the University of Kansas seven-footer who was expected to be the first pick in tonight's NBA draft, just had two screws inserted into the navicular bone in his right foot.1 Embiid is expected to miss 4-6 months and the stress fracture—his second in three months—may cost him millions of dollars.2 Many teams are understandably wary of drafting an injury-prone big man, especially one who just suffered the same fracture that ultimately derailed the careers of two other notable giants: Yao Ming and Bill Walton.3 So what's the deal? Why are these big men so fragile?
It's a complex issue, and the answer begins with biological processes that take place long before a seven-footer ever steps onto a basketball court. To understand why they break down, it helps to understand why these guys are so tall in the first place. Height, it turns out, is determined by the interaction of genetics, nutrition, and socioeconomic factors like standard of living and access to health care. (The tallest men are from the Netherlands, with an average height of six feet; the shortest are from Indonesia, with an average height of 5-foot-2). Size at birth is determined more by maternal nutrition and placental growth factors than by genetics because the proteins that influence growth are not fully expressed while a child is in the womb. As a result, there's a poor correlation between birth length and adult height; a tall infant is not necessarily destined for a career in the NBA.
Although tall stature is as common in childhood as short stature, few families seek medical attention if their kid is tall, presumably because it is socially acceptable and largely considered to be advantageous. But it's important to identify a young athlete in whom tall stature or an accelerated growth rate is a symptom of an underlying disorder because it may later predispose him (or her) to injury. Pediatricians do this by asking three initial screening questions:
- Is the child's height abnormal for the population?
- Is the child's growth abnormally rapid?
- Is the child's growth within the range for the family?
If I'm an NBA scout, I'd want to know if Joel Embiid—or any other prospect—was flagged by one of these screening questions when he was a kid. If so, the player may be at risk for one of a host of dangerous medical conditions that cause someone to grow to seven feet tall. The first that comes to mind, possibly because of its in-your-face name, is gigantism, which is caused by excess growth hormone. (The adult version of this disease is called acromegaly.) Growth hormone increases muscle mass and protein synthesis, stimulates growth of internal organs (excluding the brain) and helps break down fat in a process called lipolysis. Unfortunately, growth hormone also reduces liver uptake of glucose, which can cause dangerous swings in blood sugar, and can lead to diabetes. Jorge González, the 7-foot-7 former NBA player whom the Atlanta Hawks drafted in 1988—and later became WWF star Giant Gonzalez—died from complications related to gigantism and diabetes at the age of 44.
The other life-threatening disease to consider is Marfan syndrome. It's an abnormality of connective tissue characterized by tall stature, long, thin fingers (arachnodactyly), disproportionately long arms compared with the trunk (dolichostenomelia), and hyperextension of joints.4 It can also cause aortic enlargement and sudden death. Just last week NBA prospect Isaiah Austin, a 7-foot-1 center who played last season for Baylor, discovered through genetic testing that he suffers from Marfan syndrome. The diagnosis was devastating, because it immediately ended his career, despite the fact that it can be a painless condition. But the risk of sudden death while playing basketball with Marfan's is simply too great; a quick, jarring movement—or any movement during vigorous exercise—could induce a potentially lethal ventricular arrhythmia. (His agent just revealed that Austin has an elite insurance policy worth at least one million dollars.)
"His health is the most important thing," Baylor coach Scott Drew recently said, "and while it's extremely sad that he won't be able to play in the NBA, our hope is that he'll return to Baylor to complete his degree and serve as a coach in our program."
On the other hand, Embiid might just be a tall guy, one who doesn't have some obscure syndrome or life-threatening condition that might predispose him to injury. When it comes to height, someone has to be at the end of the bell curve, and it might be him.5 If that's the case—if he's just the dude who won the genetic lottery—we still need to consider why he keeps getting hurt. Most players don't suffer two stress fractures—he had a spinal stress fracture in March—in the span of a few months. So what's going on?
It makes sense that tall athletes would be at greater risk for injury because their bones are longer and they tend to weigh more, which puts added stress on the body every time they jog up and down the court, dive for a loose ball, or lunge for a rebound. But surprisingly, the data doesn't back that up. A 17-year review of injuries in the NBA—which looked at more than a thousand players and over three thousand injuries—found no correlation between injury rate and player demographics, including age, weight, NBA experience, and most importantly, height.6 (Injuries and player demographic information were reported by each team's athletic trainer. Criteria for reportable injuries were those that resulted in a practice or game being missed, or those requiring emergency care). So while it seems like big men break down far more often than other players, it doesn't appear to be true. We just take notice when they do.
The takeaway here is that you can't simply look at a tall basketball player and know if he's going to spend his career in the limelight or on the sideline. Some seven-footers play injury free for decades while others seemingly get hurt just trying to get out of bed in the morning. (I'm looking at you, Greg Oden.) We also know big men respond differently to the same injury. A navicular fracture hobbled Yao Ming and Bill Walton, but Zydrunas Ilgauskas, a 7-foot-3 center who played for Miami and Cleveland, suffered a navicular fracture early in his career, and went on to finish with nine generally healthy seasons. Why was he different?
The answer isn't obvious, and relates to a complex set of variables, including the tensile strength of his tendons and ligaments, the musculoskeletal system's ability to dissipate damaging forces that that can accelerate fracture, as well as the regenerative properties of his osteoblasts, the cells that synthesize bone. It's possible Ilgauskas was just as fragile as every other big man, but he was better at healing.
It's impossible to say exactly how Joel Embiid's career will turn out, but to make an educated guess, we'd need to have a look at his medical records. Going into the draft, his doctors undoubtedly know far more about his risk for injury—and his ability to recover—than the executives running the NBA franchise that ultimately decides to take a chance on him.
1 The tiny bone's name derives from its resemblance to a small boat – the Latin word for boat is navicula – and it was his second stress fracture in three months.
2If Embiid slides from the first overall pick to number six, he stands to lose approximately $10,018,983 in the next four years, including $4,554,960 of guaranteed salary.
3Ming suffered the injury in 2008 and 2009 and retired in 2011; Walton was limited to just 14 games between 1978 and 1982 because of foot fractures.
4 The basic defect in Marfan syndrome has been traced to an altered fibrillin gene (FBN1) on chromosome 15q21.1
5 Those people, the ones without a pathologic explanation to account for their excessive height, tend to have what's called familial tall stature.
6Lateral ankle sprains were the most frequent orthopaedic injury (13.2%), followed by patellofemoral inflammation (11.9%), lumbar strains (7.9%), and hamstring strains (3.3%). Navicular stress fractures were quite rare.
Matt McCarthy is board-certified in internal medicine. You can follow him on Twitter here.