I remember working with someone that presented with a foot type referred to as a ‘forefoot equinus’ which appears as the following…
This foot type does not allow the tibia to travel forward over the talus a.k.a the shin to travel over the ankle. It is as if the ankle is stuck in a ‘stepping on the gas’ position appearing pointed down. The ankle may travel up or ‘dorsiflex’ but will rarely enter into ‘dorsiflexion’ consequently not allowing the knee to bend forward past the toe. As a result, when the ankle cannot travel forward, it will utilize a different plane of motion to allow for functional activity such as gait. You may notice someone with this foot type walking with their foot rotated out accomplishing in the transverse plane (rotation) what cannot be accomplished in the saggital plane (forward/backward).
The foot will then pull the knee along that path introducing a lateral and rotatory force into the knee joint thus accelerating the degeneration. At the time I saw this person they looked something like this during standing.
The knee looks bad so it must be the problem? No. The knee is just doing what the foot has been telling it to do for many years. Understanding movement is critical in sleuthing the villain. Do you think after this person receives a total knee replacement that it will solve their problems? That foot is still the same, hiding in the background until addressed.