Introduction: Injuries to the ligamentum teres are being recognised more often with developments in imaging, such as MR arthrography, and the increasing use of hip arthroscopy. But they are difficult to diagnose, and it is not clear how best to treat them. Little is known about the mechanism of injury, nor the potential impact on hip stability of such injuries. The relationship between capsular and ligamentous contributions to stability has not been investigated.

Methods: We examined the movement of the ligamentum teres in intact, fully reduced, cadaveric hip specimens by trans osseus arthroscopy. The movement of the ligamentum teres was captured with video throughout the excursion of the hip joint. The influence of restraining capsular structures was determined by sequential transection and repeat excursion testing. Ligamentum teres injuries were generated by extreme movements, and compared with clinically observed injuries.

Results: The action of the ligamentum teres was successfully recorded in by video. The ligament was found to be the principal restraint to external rotation in extension and abduction. Injuries generated by forced rotation in this position resembled those seen in clinical practice.

Conclusion: Knowledge of the action of the ligamentum teres will improve our understanding of injury to this structure. It helps to identify described mechanisms which should raise suspicion of such an injury, and may help to design investigation and treatment protocols.