I found this explanation which appears to describe it and the therapy required pretty well:
The First Rib and Shoulder Pain Does raising your arm overhead cause pain or discomfort? What about turning your head and trunk? Do your hands ever go numb? Did you have unsuccessful treatment for shoulder pain? You may be experiencing effects from rib dysfunctions, more specifically, the 1st rib. Ribs can become displaced with minor force, yet cause major dysfunction. First rib dysfunction can be due to muscular imbalance or a true subluxation (rib moves in/out of place) of the rib itself. Put another way, the first rib is like the “baby in the family” – never gets blamed, but is often the cause of a lot of problems. Rib dysfunction is implicated in neck, shoulder, arm, and back pain. Causes of First Rib Dysfunction Most of the time, first rib dysfunction is from either tight muscles in the neck (overuse or posture), or from breathing improperly. If you are a “chest breather” (incorrect), the rib moves up and down with inhalation and exhalation. As a result, it can become elevated due to muscle tightness. Symptoms of First Rib Dysfunction If you have a rib dysfunction, you may be experiencing persistent symptoms such as trapezius spasms, neck/shoulder pain, headaches, jaw pain, mid-back pain or even numbness down the arm, which just does not resolve with treatment. First rib dysfunction pain can refer to the neck, shoulder, neck/upper trapezius, or even cause thoracic outlet syndrome. Raising your arms up to perform overhead activities such as throwing an object or combing your hair can have direct impact on the position of your ribs, more specifically your 1st rib. The position as to what you sleep in could directly affect your ribs (stomach sleepers more probe to 1st rib elevation). As a result, the arm can become numb, have tingling in it, feel weak, feel “heavy,” or have a bluish/purple (“cyanotic”) appearance. Treatment of First Rib Dysfunction First rib dysfunction can be treated in a number of ways. Mobilization techniques by a physical therapist can reduce and sometimes eliminate the pain. Stretching of the chest, neck, and shoulders can help as well. Posture re-training, thoracic spine mobility training, and instruction in proper breathing techniques are all effective ways to treat this.
If so, I would find a different therapist.
https://www.ptwoburn.com/post/my-first-what
The First Rib and Shoulder Pain
Does raising your arm overhead cause pain or discomfort? What about turning your head and trunk? Do your hands ever go numb? Did you have unsuccessful treatment for shoulder pain? You may be experiencing effects from rib dysfunctions, more specifically, the 1st rib. Ribs can become displaced with minor force, yet cause major dysfunction. First rib dysfunction can be due to muscular imbalance or a true subluxation (rib moves in/out of place) of the rib itself. Put another way, the first rib is like the “baby in the family” – never gets blamed, but is often the cause of a lot of problems. Rib dysfunction is implicated in neck, shoulder, arm, and back pain.
Causes of First Rib Dysfunction
Most of the time, first rib dysfunction is from either tight muscles in the neck (overuse or posture), or from breathing improperly. If you are a “chest breather” (incorrect), the rib moves up and down with inhalation and exhalation. As a result, it can become elevated due to muscle tightness.
Symptoms of First Rib Dysfunction
If you have a rib dysfunction, you may be experiencing persistent symptoms such as trapezius spasms, neck/shoulder pain, headaches, jaw pain, mid-back pain or even numbness down the arm, which just does not resolve with treatment. First rib dysfunction pain can refer to the neck, shoulder, neck/upper trapezius, or even cause thoracic outlet syndrome. Raising your arms up to perform overhead activities such as throwing an object or combing your hair can have direct impact on the position of your ribs, more specifically your 1st rib. The position as to what you sleep in could directly affect your ribs (stomach sleepers more probe to 1st rib elevation). As a result, the arm can become numb, have tingling in it, feel weak, feel “heavy,” or have a bluish/purple (“cyanotic”) appearance.
Treatment of First Rib Dysfunction
First rib dysfunction can be treated in a number of ways. Mobilization techniques by a physical therapist can reduce and sometimes eliminate the pain. Stretching of the chest, neck, and shoulders can help as well. Posture re-training, thoracic spine mobility training, and instruction in proper breathing techniques are all effective ways to treat this.