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Astros' Stassi Hook'd by the Hamate

Subber10 breaks down the biomechanics of the wrist in relation to Max Stassi's hamate injury and how that affects him within the game of baseball.

Jonathan Dyer-USA TODAY Sports

Hamate injuries have been around for awhile but grew in popularity several years ago when some coach decided to go all pitcher mom and recommended surgery for it before there was a problem. Yeah, remember those crazy parents wanting to put their middle school pitchers under the knife for Tommy John Surgery before they tore a UCL because they thought it would increase their velocity? If I remember correctly, it was a college coach who thought it was a good idea to have the hook of the hamate removed before it caused his players to miss time if it broke. Stick to coaching...

Well, Max Stassi is the latest to fall victim of this bone to fracture and have to have it surgically fixed. But what is it about the hamate that breaks and why?

For those who care a little about anatomy, there are two rows of carpal bones at the base of the hand. The first row work with the two bones in the forearm to create the wrist. The second row work with longer bones in the hand (metacarpals) to form the hand. The hamate is in this second row and is on the side of pinkie finger. It's an irregular shaped bone due to it forming a hook on the palm side of the bone.

The hook is the part that is relevant. This is where fractures for baseball players (and golfers) usually happen. This hook and pisiform bone together create the Guyon Canal which is where the ulnar nerve sits. You make one side of this canal unstable with the fracture and you create pressure on this nerve resulting in the potential for pain, numbness, tingling, and grip weakness. The ulnar nerve controls four different muscles that are involved in gripping after this are of potential entrapment.

But, that's not all. That hook is also where the flexor carpi ulnas (FCU) attaches. Whenever this muscle is activated or stretched, it pulls on that fracture site. This particular muscle is active in wrist flexion (think of the motion of the wrist while shooting a basketball) and during ulnar deviation (think of waving your wrist to the side of the pinky). This muscle is very active in a lot of baseball specific activities.

Since Stassi bats right-handed and the fracture was in his left hand, think about the left wrist during his swing. We talk about quick wrists in swings. That quick wrist flick right before contact is partly ulnar deviation (not strictly) and has a lot of FCU activation. Yeah, that's going to painful.

Stassi's left hand is his glove hand and has to have a lot of control of his glove. Think about catching. The wrist is usually in a little bit of extension and radial deviation. The two motions opposite of what the FCU does. However, as the ball hits the glove, the ball forces the wrist to go further into those motions. But, the FCU is directly responsible for slowing that motion down, so it contracts to slow the wrist down and counter act  the force of the ball hitting the glove. Again, that muscle will be pulling this fracture site.

So, we now see why it's painful and has to be fixed. Fixing for the average person is usually casting to allow it heel. Not the best option for an athlete as the repetitive impact from swinging and catching will likely cause it to happen again. So, you either remove the hook or you fixate it. Removal is an easier recovery but is not always the most desirable as other than the FCU, there are two other small muscles (flexor digiti minimi brevis and opponens digiti minimi) also attach there and are important for grip. Also ligaments attach there that help stabilize the wrist and hand. By removing the hook, you reduce stability and reduce strength for grip. Fixating is a longer recover (6-8 weeks) but has the best overall outcome.

Once fixated, therapy consists of restoring ROM and strength. Once that is restored, progression with impact and force through allows for return to activities. The wrist and hand are often difficult rehabs because there are way more nerve endings in the area making it more sensitive and because of how fragile the structures are in the area. We're talking about very small muscles, tendon, ligaments, and bones compared to rest of the body which is a problem because strength of soft tissue structures (tendons, ligaments, and muscle) are usually directly related to cross sectional area (how thick it is). So, being aggressive is not an option.

Being as Stassi has been said to be out for a significant amount of time, it's safe to assume he had it fixated since removal usually has a rehab time frame of a couple of weeks. That is reason to believe that he'll have a return to normal strength with grip and general wrist strength, or at least close to it. It's common for players to have significant reduction in power following the surgery. That has a lot to do with that ulnar deviation right before contact in the swing. People who are naturally strong tend to not have as much of an issue with this. While smaller quick twitch guys tend to have more issues. Stassi is a bit of both. He's short but he's naturally stocky and strong. It's tough to really predict how much his power will be affected. But, the most important aspect of a catchers game to the Astros is his defense, that will not be affected in the long run.