Here is a great slide to refresh your knowledge of ACL structural anatomy.
Its important to remember that alongside the structural support it provides, the ACL also has an important sensory function. High concentrations of mechanoreceptors at the insertion of the ACL provide the CNS with vital input on knee position and movement (proprioception)
Efferent feedback has an important role in regulating muscle activity and more recent research has highlighted the neurosensory element of feeling of instability when traditionally we just thing along mechanical lines.
The media recently speculated about the discovery of a new ligament which could be the answer to curing knee injury and pain. The 'new' Anterolateral Ligament (ALL) was actually described as early as 1879 by French Surgeon Segond and prior to the advent of arthroscopic procedures, surgeons would use lateral extra articular tenodesis techniques to address rotatory knee instability.
Check out more recent research by Alan Getgood and his team on the reduction of hamstring graft failure in young high risk patients with the addition of a lateral tenodesis here https://journals.sagepub.com/doi/10.1177/0363546519896333