OBJECTIVETo study the role of lateral collateral ligament complex on the posterolateral rotatory instability and the relationship between the radiocapitellar ratio (RCR) and the injury of lateral collateral ligament complex on X-ray images.

METHODSTwenty elbow joints from fresh-frozen adult cadavers were used to make osteo-ligamentous elbow specimens. The specimens were fixed with a self-made device to maintain posterolateral rotatory instability of the elbow joint. All the specimens were divided into two groups: group A and group B. Surgical procedures were carried out as follows in the lateral structures of group A: A1, intact specimen; A2, transection of radial ulnar collateral ligament firstly; A3, transection of annular ligament secondly; A4, final transection of the radial collateral ligament. The procedures in group B were carried out as follows: B1, intact specimen; B2, transection of the radial collateral ligament firstly; B3, transection of the annular ligament secondly; B4, final transection of the radial ulnar collateral ligament. Lateral X-ray films of elbow joint were taken, and the radiocapitellar ratio (RCR) was measured by using PACS. All analysis was performed with SPSS 17.0 software.

RESULTSGroup A: the increases in RCR had statistical differences among A1, A2, A3, and A4 groups. Group B: the increases in RCR had no statistical differences among B1, B2 and B3 groups; but the increase in RCR in group B4 was more than that in B1, B2 and B3 groups.

CONCLUSIONThe radial ulnar collateral ligament is a key structure to maintain posterolateral rotatory stability;the radial collateral ligament and the annular ligament are the secondary important structures. There are 4 grades of the posterolateral rotatory instability of the elbow, according to the X-ray imaging classification.