The elbow is hinge joint,with rotaion in a single constrainedplane.It is composed of three joints:the ulno -humeral joint which isthe primary determinant of the bony elbow stability;theradiocapitellar joint which affords secondary v algus stress resistanceto compressive loads across the joint;and the radioulnar joint.Theelbow has two major ligaments,medial and lateral collateralligaments,which are of great imasxsportance to the stability of thejoint.The medial collateral ligament consists of three basiccomponents and anterior oblique, a posterior oblique and a smalltransverse non-functioning band.The anterior band is the primaryconstraint to valgus instability.The lateral collateral ligament'scomponents are : the lateral ulnar collateral ligament ,which is thesignificantly important component,the radial collateral ligament ,theaccessory ligament and the quadrate ligament.The three prerequisitefor the stability of the ulnohumeral articulation are an intact jointsurface,the anterior medial collateral ligament and the ulnar part ofthe lateral collateral ligament.Although chronic valgus instability israrely a debilitating complication of elbow dislocatior, recent studiesof the anatomy and citology of injury have fostered an aw areness ofits role in high-performance athletes. The overuse of the upperextremity may result in micro-rupture of the soft tissues such as themedial collateral ligament and tendons.Micro -tears within theligaments and tendons can lead to frank disruptio n of thesestructures if the offending activity is continued. The diagnosis of MCL insufficiency is based on detailed historyand physical examination.Posterolateral rotatory instability of theelbow is a clinical entity that can be distinguished from dislocation ofthe elbow.it can be diagnosed by the test of posterolateral rotatoryinstability .the cause appears to be insufficiency (laxity ordetachment of the origin)of the ulnar part of the lateral collateralligament.Recurrent instability is usually due to insufficiency of theLUCL,with attenuation of the other secondary soft tissue constrainton the lateral side.A rational approach to the management ofcomplex instability recognizes both the articular and the soft tissuecontributions.it should be simplified by stating that the prese nce ofnormal articular architecture,the anterior band of the MCL and theulnar part of the LCL are all that is required for a stable elbow.Theprinciple of reconstruction is to restore the functional integrity ofthese two bands,which are analogous to eac h other .this is currentlydone using palmaris longus tendon reconstructions in treating valgusinstability in throwing athletes and posterolateral rotatoryinstability.The anatomic placement of the origins is critical to thesuccess of each surgery.Also external and internal fixation ofassociated fractures and rdial head arthroplasty has an importantrole in elbow instability.