Shares of the Scottsdale, Ariz., company at last check were 20% higher at $69.50. Bloomberg noted the company was trading on record volume.
Joint Corp. President and CEO Peter D. Holt said in a statement that the company's inclusion in the index recognizes the company's staff and system members for their dedication to patients.
Joint Corp. recently opened its 600th location, in Bowling Green, Ky.
The company, which has about 225 employees, has centers in 34 states and is working on a goal of 1,000 units by the end of 2023.
Earlier this month, Joint Corp. said first-quarter revenue increased 29% from a year ago to $17.5 million.
In March Cubic agreed to be acquired by private-equity firm Veritas Capital and hedge fund Elliott Investment Management at a raised buyout offer of $75 cash a share.
The deal marked an end to a bidding war, which also involved a revised takeover bid from Singapore Technologies Engineering.
The Cubic-Veritas-Elliott deal is valued at around $3 billion, including the assumption of debt.