Today I saw a new client for an evaluation of their knee pain. Both of their knees are symptomatic, but the L one is what made them come in to see me as it was recently swollen and painful after an awkward move when sitting/squatting down to rest when they were skiing.
There were some findings for the L knee, but it was nothing major. Everything checked out okay in terms of ligament stability, and I recommended some exercises according to what deficits were found. What stood out more was the overall performance of their R leg.
In the process of assessing the function of the L knee I compared to the R side to determine their relative baseline. In our discussion they mentioned about 15 years ago they tore the R ACL, had it surgically repaired, and of course rehabbed it. This side was also still causing some pain if they weren't careful with how they moved or squatted.
When I asked them to demonstrate a squat and a lunge these are what I saw, as I have recreated for you below. Lunge (view lead leg as "surgical side"):
And their squat:
This is what is called a hip strategy. The majority of motion, and loading is occurring at the hips to relatively offload the knee. This is a bad sign if you are in the interest of not re-tearing your ACL (hip strategy for landing from jumping is a risk factor for re-injury).
Another risk factor is having roughly 85% or less quadriceps strength (Quad Index) compared to non-surgical side. Even with their L knee hurting, being the reason they came in to see me, their L quad averaged 71 lbs of extension force over 4 attempts while their R quad average 56 lbs. Sure enough that's only about 80% relative strength. Again another risk factor for re-injury.
I measured their quad strength like so:
It's not exactly a state-of-the-art isokinetic machine, but I think this is one of those situations where good enough will do just fine. While not the gold standard, it was sensitive enough to pick up a vital performance deficit. This person came to me for their L knee pain, but their goal is to continue skiing so you better believe I sent them on their way with homework for their R knee as well. Downhill skiing imposes significant forces to the lower extremities and especially at the knees. This is not inherently a bad thing, it's a question of if the person is ready to handle that specific demand. In this case, with their history and ongoing risk factors it is in their best interest to address the deficits on the R side if they want to decrease their risk of ACL re-injury when skiing.