Introduction : Rupture of the Radial Collateral Ligament (RCL) of the index metacarpophalangeal (MCP) joint is mostly related to acute local mechanical causes, which severely affect the stability of the MCP joint. Radial collateral ligament (RCL) injuries account for 10-40% of collateral ligament injuries of the thumb metacarpophalangeal joint.ere, we present an extremely rare case of chronic RCL injury. Patient Concern : Pain in the thumb of the right hand accompanied by weakness when trying to grasp something. Complaints are not accompanied by swelling. Patient said 2 years ago had an accident. Thumb at right hand is said to be swollen and shifting. Diagnosis : Based on the combination of physical examination, X-ray, and ultrasonic and magnetic resonance imaging, the patient was diagnosed with Radial Collateral Ligament rupture. Eventually, intra-operative findings confirmed the diagnosis. Intervention : Patient was underwent ligament reconstruction using a Palmaris Longus tendon graft. Conclusion : Favorable results suggest that the free tendon graft using Palmaris Longus is a suitable, safe, and technically feasible procedure for the operative treatment of chronic instability of the thumb metacarpophalangeal joint after radial hyperadduction trauma and complete rupture or deinsertion of the radial collateral ligament.