"He suffered a torn ACL against the Seahawks in Week 10 ...
Sean McVay announced on Friday <Nov 16, 2018> that Kupp underwent successful surgery to repair his knee injury and didn’t have any additional damage ..." [
theramswire.usatoday.com]
There is no such thing as a clean tear of an ACL. Whenever it is torn the ends of the ACL are like frayed ends of an old rope and can't be stitched back together. To fix an ACL tear the knee must be reconstructed and the ACL must be replaced with a new structure. Techniques I am aware of include using a cadaver ACL, using part of the patellar tendon, and rerouting a tendon that exists in the back of the thigh. (There may be others, and I couldn't find what one Kupp had.)
AlbaNY_Ram