Instability in the knee after an anterior cruciate ligament (ACL) rupture is measured by the means of the Lachman test (displacement) and by the Pivot Shift test (rotation). Both tests are graded from 0 to III, being 0 completely stable and III completely unstable.

We used those tests to evaluate the pre and postoperative stability of patients who underwent ACL reconstruction surgery using two different surgical techniques.

So we have paired data (pre and postoperative), an ordinal evaluation scale and a factor that separates our sample in two groups (technique). What statistical test should we use?

And if the factor had more than two groups (imagine that we also wanted to compare results in patients with different race, for instance)?

And what if the preoperative stability was considered irrelevant? Meaning that we would only be comparing the postoperative results.

Thank you for your kind help.