Last week we talked about rear foot varus and the impact it has on function. Today it’s the turn of the forefoot and a look at the varus forefoot. Again, for today we will look at the individual deformity as if it exists alone and no other deformity is present, but keep in mind that it is far more likely to be a combination in reality.
A forefoot varus is present when the forefoot is inverted relative to the rear foot. Again, I assassin prone with the feet hanging off the end of the couch. They do not need to be in sub talar neutral as you are comparing the rear foot to the forefoot. If you look down along the sole of the foot you will see the plane of the forefoot is inverted relative to the rear foot.
In the diagram you can see normal sub talar alignment and the deformity is the difference between the rear foot and the forefoot. If no forefoot varus is present then the two red lines would be parallel.
Impact of Forefoot Varus on the Foot
The main impact of a forefoot varus on the foot is that the speed and timing of the foot loading. Initially, during heel strike there is no impact from the deformity as the rear foot structure is normal and the calcaneus will begin going through eversion. However, the problems start from here, because at this point the forefoot would have begun to load by now and it can’t because of the varus position of the forefoot.
The body will want to get that forefoot down to the ground and to load the first ray as this is very important. To achieve this the sub talar joint will pronate further to achieve forefoot contact with the ground (assuming it has enough range). This has a profound effect on the foot as it has to go ‘deeper’ into pronation and will be pronating later in the gait cycle than it normally would. The speed of pronation will often be greater also, making it much harder for supination of the foot to occur at the right time.
Often the foot will lose it’s ability to re-supinate and ‘get stuck’ in pronation, forcing the person to push of from an unlocked foot. This will increase the pressure on the soft tissues (particularly the plantar fascia and tibialis posterior) due to the lack of bony stability.
Impact of Forefoot Varus on the Kinetic Chain
The most predictable effect will be on the knee. The late and rapid pronation during gait will cause the tibia to be internally rotating at a time when the femur will be driven into external rotation. This has the potential to create a torque in the knee that over time can cause symptoms with no apparent traumatic onset.
As a whole the lower limb will be less able to load as the speed and timing are disrupted. This inability to load will make it more difficult to get an effective explode from the lower limb. It’s difficult to precisely predict the exact problems this will cause because the body can choose to compensate in many different ways. However, from my experience you most commonly get opposite side knee pain and back pain.
The opposite side knee pain often looks like weak abductor muscles, however, it is (in my experience) not weak glutes in these cases, but an inability to load and explode the glutes that causes the problem. That is why in these cases strengthening the glutes will not work as the body simply cannot use the strength in function.
This is really a fairly simple overview of a very complex problem. However, it does give you a good idea of what to look for and the potential complications something like a forefoot varus can cause. As I said at the start you often see combinations of problems rather than one in isolation. Commonly, with a forefoot varus you will see a plantar flexed first ray as well. This is because as the body is trying to get the forefoot to load it makes sense that a plantar flexed first ray help reduce the impact of the forefoot varus by brining the forefoot closer to the floor. I’ll talk more about this more in the post on plantar flexed first ray.
Next time we’ll be staying with the forefoot and looking at the forefoot valgus.
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