Zac Gallen Forearm Fracture: MLB Injury Watch & Return Timetable for Diamondbacks Pitcher

Kyle Trimble is a licensed physical therapist here to provide MLB injury analysis on Zac Gallen forearm fracture.

Arizona Diamondbacks starting pitcher Zac Gallen has been sidelined recently following forearm soreness in his right arm. A thorough evaluation revealed that he has a hairline stress fracture on the radial head within the forearm. A timeline has not yet been established for Gallen to return from the team, but there are clues to identify when a realistic return occurs.

Zac Gallen Forearm Fracture

The radial head is on the proximal portion of the radius, one of two bones in the forearm. The radial head is held in place by the annular ligament and articulates with the ulna in order to allow in turning the hand, or pronation/supination. 

Elbow anatomy. (Credit:

Gallen noted that he injured the forearm when he got jammed by a pitch during batting practice. He then had difficulty throwing his curveball which led to further examination. It’s very likely that Gallen forcefully contracted the supinator muscle in his forearm when he got jammed trying to swing at the pitch. This muscle connects over the radial head and the contraction may have been so great that it injured the bone. Add in the throwing mechanics of a curveball, requiring the hand to supinate, further stressing the already injured area.

Example of curveball rotation. (Credit: Sharp Magazine)

He has been cleared to lightly throw and play catch, indicating that they likely caught the injury early. There isn’t much literature on this type of stress fracture, but a case study indicated that this could be a 12-week recovery based on shutting Gallen down to heal, then progressing him through a throwing program. 

Considering he is doing light toss, I’d consider his recovery timeline to be 8-to-12 weeks. The fracture needs time to fully heal and then re-establish the demands of high-level throwing. The best-case scenario is that he comes back mid-May, but a return of June may be more appropriate to ensure that he doesn’t have any setbacks and his performance not affected.

MLB Betting & Fantasy Baseball Outlook

Draft Gallen, but don’t use a high pick on him, address other needs first. Stash him if you can and watch the news reports in early May to see when he might begin to return. If the Diamondbacks struggle, Gallen’s return to the lineup could spark a turnaround.

Kyle Trimble is a licensed physical therapist who also works as an injury spotter for Dr. David Chao. Kyle has extensive experience in outpatient orthopedics, skilled nursing, acute care hospital, and home care. He’s also a member of Bills Mafia and runs the website Banged Up Bills.

Disclaimer from Kyle: My opinions are my own. Any thoughts I have on the injuries are based on media reports, my knowledge of the injury, and speculation based on the information currently available including video and print media. This information is subject to change based on the information released by the team.

After reading Kyle’s update on Zac Gallen right forearm stress fracture, get more MLB betting and fantasy baseball tips:

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