This is a randomized, double-blinded, standard of care-controlled clinical trial. The purpose of this study is to determine the difference in subscapularis strength and function after anatomic Total Shoulder Arthroplasty (aTSA) in patients who receive isolated subscapularis rehabilitation in addition to the standard rehabilitation after surgery at 12-month follow up. Specifically the investigators will measure subscapularis strength utilizing a dynamometer device and subscapularis function utilizing isolated subscapularis physical examination testing: belly-press, bear-hug, and lift-off tests. Additionally, investigators will document secondary outcome measures including shoulder range of motion and Patient Reported Outcome Measure Information System (PROMIS) questionnaire scores.

Study Design: This is a randomized, double-blinded, standard of care-controlled clinical trial. All adult patients undergoing anatomic total shoulder arthroplasty for glenohumeral osteoarthritis will be included and randomized after surgery into either the control group which is prescribed a standard rehabilitation protocol or the intervention group which also is prescribed the same standard rehabilitation protocol with the the addition of isolated subscapularis rehabilitation.

Purpose: To determine the subscapularis strength and function after anatomic total shoulder arthroplasty (aTSA) in patients who receive isolated subscapularis rehabilitation in addition to the standard rehabilitation protocol as compared to those who only receive the standard rehabilitation protocol at 12-month follow up. Specifically the investigators will measure subscapularis strength utilizing a dynamometer and subscapularis function utilizing isolated subscapularis physical examination testing: belly-press, bear-hug, and lift-off tests.

Hypothesis: The investigators believe that subscapularis strength can be improved using isolated subscapularis rehabilitation in addition to standard rehabilitation, leading to improved outcomes in patients receiving aTSA. This should also improve the post-operative physical examination predicting a functional subscapularis tendon.

Rationale and expectations: Anatomic total shoulder arthroplasty is often performed in patients with severe glenohumeral osteoarthritis that have an intact subscapularis. Often times it is seen that these patients return with positive isolated subscapularis tests, despite the subscapularis being intact after surgery. If these patients require revision surgery, an ultrasound is the only test that can be performed to evaluate the status of the subscapularis tendon. This study is difficult and not 100% accurate. It needs to be determined if the patient will need a reverse total shoulder arthroplasty due to the positive subscapularis test findings. Previous studies by Baumgartner et al. showed that patients that received a total shoulder arthroplasty with tenotomy improved liftoff, and bear-hug strength testing, but operative shoulder strength remained inferior to strength of the nonoperative shoulder. Patients with improvements in strength were more likely to have greater improvements in outcome scores and range of motion. It was noted that improvements in the shoulder activity level after anatomic total shoulder arthroplasty may be dependent on improvements in strength. The investigators believe that subscapularis strength can be improved using isolated subscapularis rehabilitation in addition to standard rehabilitation, leading to improved outcomes in patients receiving aTSA. This should also improve the post operative physical examination predicting a functional subscapularis tendon.

Research Plan: Patients to be included in the study will be those with glenohumeral osteoarthritis with an intact rotator cuff that are undergoing anatomic total shoulder arthroplasty. Exclusion criteris includes patients undergoing revision shouder arthroplasty, a previous subscpaularis rotator cuff repair or deficient rotator cuff, patients with inflammatory arthropathies, such as rheumatoid arthritis, and patients with a history of infection in the shoulder joint. Reverse total shoulder arthroplasty will be excluded. Non-English speaking patients will be excluded from the study in order to simplify communication with study participants. The control population will consist of patients undergoing the standard rehabilitation protocol for aTSA. Patients will be undergoing rehabilitation regardless of study participation.

Protocol and Technique:

Recruitment: Patients meeting inclusion criteria undergoing aTSA will be recruited and consented for participation in the study at their pre-operative clinic visit. Their pre-operative strength and function testing will occur at this time.

Randomization: Placement into the study group or control group will be randomized and prospectively followed. The randomization process will remain blinded to surgeon, patient, and all co-investigators except for the primary physical therapist lead in the project (lead PT). At the first post-operative visit within the first month post-operatively, the patient will receive a physical therapy prescription per standard protocol. At the time of physical therapy initiation, the lead PT in the project will contact the patient's physical therapist and provide them with instructions regarding the research study, including which group the patient has been randomized into (standard vs additional subscapularis rehab) and strict instructions to perform the physical therapy without informing the patient of their randomized assignment. Upon making contact with the physical therapist, the lead PT provides them with a manual with the exact rehabilitation protocol assigned to the patient, ensuring that regardless of which physical therapy the patient elects to undergo treatment by, they receive the same standard physical therapy, plus the same standard subscapularis rehabilitation exercises (if randomized into the study group).

Follow up testing: The post-operative strength and function of patients in both treatment groups, isolated subscapularis rehabilitation with standard rehabilitation and standard rehabilitation alone, will be measured at subsequent 3 months, 6 months and 12 month postoperative visits. Measurements taken are outlined above and include shoulder range of motion (forward flexion, abduction, abduction-erternal rotation, abduction-internal rotation, external rotation), ability to perform a belly press, lift off, and bear hug test. Strength for internal rotation and subscapularis strength will be performed, using the dynamometer.

Data: Patients will be asked to fill out questionnaires for this study at each time point (preoperative, postoperative at months 3, 6, and 12). These include PROMIS Bank v2.0 - Upper Extremity, PROMIS Bank v1.1 - Pain Interference, and ASES. Strength scores will be assessed using a Lafayette Manual Muscle Testing System Model 01165 (dynamometer) to measure peak force in lbs. The means of each group along with standard deviation will be calculated for each parameter measured. P-value of 0.05 will be utilized for statistically significant results.

Primary Endpoint: Strength (measured by dynamometer testing) of the subscapularis.

Secondary Endpoint: Function and outcomes as measured by range of motion and questionnaire scores of pain and satisfaction.

Inclusion Criteria:

• All adult patients over the age of 18
• Must have a diagnosis of glenohumeral osteoarthritis
• Must be scheduled for primary anatomic total shoulder arthroplasty.

Exclusion Criteria:

• History of prior rotator cuff surgery
• Rotator cuff deficiency
• Planned reverse total shoulder arthroplasty
• inflammatory arthropathy
• prior shoulder replacement surgery
• neurologic deficits of the affected extremity
• diagnosis of frozen shoulder
• previous infection in the shoulder.