Summary Medial Ulnar Collateral Ligament Injuries are characterized by attenuation or rupture of the ulnar collateral ligament of the elbow leading to valgus instability in overhead throwing athletes. Diagnosis is usually made by a combination of physical exam and MRI studies. Treatment for most individuals is rest and physical therapy. Surgery is reserved for high level overhead athletes such as pitchers. Epidemiology Incidence literature shows increasing occurrence of UCL injuries and reconstructions becoming more common among high school and amateur pitchers Demographics overhead athletes who place significant valgus stress on their elbows originally described among javelin throwers, now much more common in baseball pitchers relatively uncommon in skeletally immature throwing athletes login to view 2 more bullets Risk factors exceeding youth baseball pitch count and inning restrictions higher pitch velocity deficits along kinetic chain (shoulder and core weakness, loss of shoulder motion, etc.) Etiology Pathophysiology mechanism of injury login to view 10 more bullets Associated conditions traction-related ulnar neuritis olecranon (posteromedial) impingement elbow arthritis Anatomy Osseous elbow is complex hinge composed of ulnohumeral, radiocapitellar, and radioulnar joints valgus carrying angle ranging from 6 to 11 degrees Ligaments medial ulnar collateral ligament (UCL) divided into three components login to view 12 more bullets Biomechanics elbow stability evenly split between osseous and soft tissue structures UCL primary restraint to valgus stress from 30 to 120 degrees of flexion login to view 1 more bullet Presentation History acute injuries may present with a "pop" associated with pain and difficulty throwing Symptoms decreased throwing performance login to view 2 more bullets pain login to view 2 more bullets ulnar nerve symptoms login to view 1 more bullet Physical examination inspection login to view 4 more bullets range of motion login to view 2 more bullets neurovascular login to view 1 more bullet provocative tests login to view 11 more bullets Imaging Radiographs recommended views login to view 3 more bullets optional views login to view 3 more bullets findings login to view 1 more bullet MRI indications login to view 1 more bullet MR-arthrogram - diagnostic login to view 2 more bullets findings login to view 4 more bullets Dynamic ultrasound can evaluate laxity with valgus stress dynamically sensitivity and specificity operator dependent Differential Medial epicondylitis Flexor-pronator strain Ulnar neuropathy Valgus extension overload Treatment Nonoperative rest and physical therapy login to view 5 more bullets Operative UCL anterior band ligament reconstruction (Tommy John Surgery) login to view 9 more bullets UCL repair login to view 6 more bullets Techniques Rest and physical therapy technique login to view 3 more bullets UCL anterior band ligament reconstruction overview login to view 3 more bullets approach login to view 7 more bullets soft tissue login to view 5 more bullets bony work and reconstruction login to view 19 more bullets postoperative care login to view 8 more bullets UCL repair approach login to view 1 more bullet soft tissue login to view 2 more bullets bony work login to view 2 more bullets postoperative care login to view 1 more bullet Complications Ulnar neurapraxia most common, 3-26% incidence treatment login to view 1 more bullet Medial antebrachial cutaneous (MABC) nerve injury crosses at distal aspect of the incision Fracture of ulna or medial epicondyle risk factors login to view 1 more bullet treatment login to view 1 more bullet Elbow stiffness risk factors login to view 1 more bullet treatment login to view 2 more bullets Inability to regain preinjury level throwing ability more common following revision reconstructions Prognosis Formerly a career-ending injury UCL reconstruction provides high rates of return to throwing and sport worse outcomes following revision reconstructions Outcomes and return to sport following surgical MUCL reconstruction (Tommy John surgery) depend on precise recreation of the MUCL and diligent rehabilitation.