Shoulder Instability: An Athlete’s Guide Explaining Why Your Performance is Suffering – Part I Epidemiology

            It was the fourth inning and our starting pitcher was starting to give up multiple hits and already at a high pitch count due to the other team’s patience at the plate. I was standing at short stop wondering how we were going to stop the bleeding and feeling helpless because nothing was coming my way. Our coach recognizing the scenario, decided it was time for a pitching change.

Baseball Field

He decided to bring in our strong closer, Greg, as he had the fastest two seamer on the team, which would shake things up from our curve ball throwing starter. Greg started warming up on the mound and you could tell immediately something was wrong. Usually able to paint the corners, he was all over the place, and a couple wild throws even found the backstop.

            Deciding he better start before things got to ridiculous, Greg signaled to the umpire he was ready and the game resumed. But things didn’t get any better. Soon Greg was walking batters, hitting batters, and letting runners advance as he couldn’t control his fastball. Needless to say, the game did not turn around and go our way. After the game, Greg said his arm felt heavy, he felt like he couldn’t control his throw, and also, he wasn’t throwing his normal speed. He continued to struggle for the rest of the season and just wasn’t the same after that outing.

            I was frustrated because nothing aggravated me more than walking in runs, I’d rather make the other team earn those runs. But it wasn’t until years later when I was in Physical Therapy school that I understood what Greg was going through. He had experienced shoulder instability, an injury experience by many overhead throwing athletes.


            Shoulder instability is frustrating for athletes because they start having pain in the shoulder, feel the shoulder is unstable, and notice their performance is decreasing without understanding what is happening. Shoulder instability is excessive shoulder movement that leads to pain, functional deficits, or apprehension, and should not be confused with joint laxity. Laxity is excessive translation between the head of the humerus and the glenoid fossa on the shoulder blade, but it is asymptomatic and very natural in some athletes who need good shoulder mobility.

            Due to the wide range in symptoms that athletes will report, varied clinical findings, and multiple causes, true shoulder instability can be difficult to diagnose. It is due to compromise in the shoulders passive (bone, ligaments, labrum) and/or active (muscles) stabilizers. The shoulder can become unstable in many different directions: anteriorly (forward), posteriorly (backwards), inferiorly (down), or it can be multi-directional (2 or more of the above). Causes can be traumatic, an event that pushes the shoulder past it’s anatomical limit (no ambiguity in what happened with this situation), or atraumatic, a gradually change overtime due to overuse causing joint laxity and weakening of the muscles.

            The severity is often classified into subluxation, the humeral head returns to the joint without intervention, dislocation, assistance is needed to return the humeral head back onto the glenoid fossa, or micro-instability, the joint stays in place but there is excessive translation of the humeral head on the glenoid fossa.

            So, who are most at risk for getting shoulder instability? It tends to affect younger, active individuals; especially if they play a repetitive overhead throwing sport like baseball, tennis, swimming, volleyball, or badminton.  The one-year incidence rate for young athletes is 2.8%. If we look at College level athletes, about 10% of injuries occur at the shoulder, and 23% of those are due to shoulder instability.

            In order to avoid surgery and regaining previous function through a rehab program, it is important to properly diagnose shoulder instability and get treatment early on. A successful rehabilitation program will be based on the type and degree of instability, frequency of instability, direction of instability, and level of play of the athlete. In the next blog, we will dive deeper into the anatomy of shoulder instability and where rehabilitation treatments can go wrong to prevent the ideal outcome!

            Here at Competitive Edge Physical Therapy, we enjoy treating athletes of all levels and have had great success with our protocol for treating shoulder instability.  The reason we have been so successful is our use of technology and hour-long appointment times allows us to properly diagnose the direction and cause of instability, as well as ensure proper training to ensure every exercise is helping the client improve in controlling their shoulder. We love seeing our clients get back to playing pain free and at higher performing levels!

            If you want to hear more about what we do here at Competitive Edge Physical Therapy, feel free to stop by our clinic in San Jose, CA, give us a call, or check out our website at!


  1. Lynch, B., Ridge-Hankins, T., Vyas, D. “Shoulder Instability: A Review of Anatomical and Biomechanical Considerations, Prevalence, and Diagnosis as well as Nonoperative and Operative Management”. Alternative Special Topics: Innovations in Practice. Independent study Course 25.3.1.

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