The problem here is that there are SO many muscles in the thigh that you'd have to cut a lot of them to really incapacitate and prevent someone from being able to walk...but if you can take out a few of the muscles AND the damage the femoral artery at the same time you can do a lot more damage and debilitate them better.
Do you want this to be an injury with permanent damage...because one of the issues is going to be nerve damage depending on where we stab them, and that would be harder to recover from.
Ideally, assuming you don't want permanent nerve damage, we'll stab them in the upper thigh/groin area damaging the quadriceps muscles (I can give you actual muscle names if you need them) and the femoral artery, but (luckily) sparing the femoral nerve. This would require immediate attention in the ER to stop the bleeding from the femoral artery and a vascular consult to repair any severe damage to the artery. You're also going to need an orthopaedic surgery consult in the ER because they'll probably need to do some exploratory surgery to determine the extent of damage to the quadriceps muscles and to stitch them back together for proper healing.
Another really good injury to stop someone from walking/running would be to sever the Achilles tendon at the heel (tendons from the gastrocnemius and soleus muscles). This would really a better, less messy injury, but also probably harder to accomplish for the knife-wielding thugs. <g> It would require an orthopaedic surgery consult again...they'd need to reattach the tendon (sutures and maybe pins).
Also, the *most likely* injury, at least for someone running away from an attacker, would be a stab-wound to the back of the leg. The danger here would be damage to the sciatic nerve (very large and runs right along the back of the thigh, just deep to the muscles), very easily damaged with severe long-term consequences because it supplies most of the innervation for the lower leg and foot. The muscles at the back of the leg would be the hamstrings (again, I can supply names if you need them - there's 3). But at the back of the leg, in this type of attack, it would be more likely to be a 'stab' wound, which wouldn't cause as much damage to the muscles unless it was a very large knife. You really need more of a severing type of injury for severe damage to the muscles. Although with a big enough wound, a stab wound 'could' be bad enough to keep the person from being able to run.
Oh, and the priority when the guy comes in to the ER would be to stop the bleeding and prevent permanent damage...so preserve the nerves as much as possible. Pressure on the wound until someone can stitch up the artery (femoral, if we're going for that injury). Then once the bleeding is stopped, check the blood pressure to see if they need any kind of transfusion and/or blood pressure increasing medications. Once the guy's stopped bleeding and he's waiting for a surgery consult, check for nerve damage - feeling below the injury, two-point discrimination, etc. and you'd check for nerve damage again *after* surgery.
Hope this helps, let me know what else you need,
Jill (who wonders if it's a good idea to be giving out this kind of information <g> ).
P.S. I think I got a little carried away here, and just came back several times to add things...if you need simplification or clarification, let me know. And maybe hit me over the head with something before I answer next time so I don't go so nuts with my answer.
