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The Diabetic Foot

The diabetic foot is a very significant problem, it leads to amputation, and in many cases over time, it leads to the patient’s mortality from their manifestation and their diabetic foot ulcers. This is the person that comes into your office with that stinking, smelling, nasty ulcer on the plantar aspect of the foot that has been there for a while, and they haven’t noticed it, but now the foot is starting to get red hot and swollen.

If you look at the x-rays and look at the foot, that ulcer is happening because there is an underlying deformity, neither the bone or the joint is putting increased pressure, increased forces on the skin and it’s broken down, so they man come to the office not because they have the bony joint deformity, but because they have cellulitis, they have a draining foot with osteomyelitis.

On examination, they’re not going to feel the monofilament, the monofilament is basically a pressure sensitive test. That is the most subtle finding in diabetic peripheral neuropathy. They are going to lose their protective sensation, the pressure sensation in the plantar aspect of the foot. Monofilaments are available through the American Diabetic Association.

He may want to treat the open injury and make sure they don’t get an infection, more likely than that, they probably will not repair that, but if someone has a laceration up around the ankle where you are now concerned that the anterior tibial tendon has been lacerated and the EHL tendon has been lacerated, those are probably two of the more important ones in terms of function for gait. That is something that is probably going to need to be repaired, and it could also be associated with a traumatic arthrotomy of the ankle joint, so the orthopaedic surgeon needs to know about that sooner.

When I look at someone who presents to me with a foot complaint, I try to break it up into what the primary pathology is, and what are the secondary manifestations that they are coming to me to complain about? The foot is a complex weight bearing surface. There re 28 bones and nearly 60 articulating surfaces, so there are a lot of inter-relationships going on between the different segments of the foot, the hind foot, mid foot and forefoot, and problems in one region can have manifestations elsewhere. So it is very important to recognize what the root cause of the problem is.

So when I think of the problems, I start to look at the structural malalignments that might be present in the patient’s foot, is the arch too high, is it too low? Is there some imbalance of the muscle forces that is causing that problem; or imbalance of those muscle balance forces driving the secondary manifestations. Also, as I talked about before, compensatory deformities. There could be a problem in the hindfoot, but the patient comes in to see you because there is a forefoot problem. That is where it hurts them, that is where it’s difficult for them to wear their shoes. So by way of the anatomy, the osteology of the foot.

There are the seven tarsal bones in the hindfoot region, we have that defined as the calcaneus, and the talus, that separates the hindfoot from the midfoot through the transverse tarsal joint. The remaining five tarsal bones are the middle, medial and lateral cuneiform, the cuboid bone, and the navicular. Then you enter into the forefoot which has the five metatarsal bones and the 14 phalanges. As you know, in the hallux, there are only two phalanges, whereas in the lesser toes, there are three, and then the two sesamoids that are under the first metatarsal head. Ligaments are important for static stabilization of the arch of the foot, both it’s longitudinal arch and the transverse arch. The spring ligament, if you look on the slide here, again we are looking up under the foot, here is the calcaneus, here are the metatarsals down here, the spring ligament is sort of a sling that runs from the calcaneus to the navicular, a sling for the arch and the medial aspect of the foot. The long plantar ligament is an important ligament for stabilizing the lateral border of the foot and then Lisfranc ligament, you may have heard about those in terms of people having foot dislocations, when the common location is through the Lisfranc joint, that is the joint that separates the midfoot bones, those five bones, the cuneiforms and the cuboid from the metatarsals, and there are strong ligaments.

Another concept that I use frequently when I am looking at foot problems, is that the foot should have an axis of balance. That axis of balance runs along the sagittal plane. It goes from the center of the calcaneus, to the center of the midfoot, and runs between the second and third metatarsals in the forefoot. Weight bearing forces are balanced across that access medially and laterally, in fact, minimal muscle activity is required for quiet standing. The muscle forces, or the dynamic forces during the phases of gait are also balanced across this access for dorsiflexion, plantar flexion, but mostly for inversion and eversion of the foot to stabilize and square the foot up to the ground surface. Now that axis of balance is dynamic, you can lock and unlock the arch of your foot during gait when the primary movers of that is the posterior tibial tendon which attaches to the navicular and into the midfoot, and it maintains the arch. Then there are the everters of the foot, the peroneal tendons.

It needs to be rigid when you’re standing on it, and it needs to be flexible as it strikes to the ground, so it can absorb the shock forces and the weight bearing forces as it strikes the ground. These static restraints such as the ligaments, as they start to weaken and the foot starts to collapse, you start to overwork or atrophy some of the dynamic restraints, the tendons that are trying to stabilize the foot along that axis of balance, and the axis of balance becomes disrupted. I put this slide up here to show you a relatively well aligned foot in this patient. Her left foot is widened out here, but essentially there is the center of her calcaneus and that weight bearing axis runs between the second and third metatarsal. On this side where she has a very severe flat foot, here is her hindfoot, we sort of estimate that here is about the center of the calcaneus, and you see if you draw that straight line, the axis of balance is shifted. Pretty much now all her metatarsals now shifted out laterally, as she is adducting through this talar navicular joint. You can imagine structures over here become lax, both the tendons and the ligaments, structures over here become contracted. So now, you have the axis of balance disrupted and now you have further forces that are acting to contribute to worsening of the deformity. Foot posture - it is very important to get weight bearing x-rays, nonweight bearing x-rays of the foot, and even later when we get to the ankle, x-rays can look very normal of the foot when you are not standing on it, and a lot of pathology and malalignments come out when you get those weight bearing views. Again, I tend to think of foot posture into three different situations, pes planus valgus of the flat foot as demonstrated in the slide here, essentially, this person had no arch, or their mid foot bones are essentially touching the ground instead of being a good 2 cm up and off the ground, versus a high arch foot, a cavus foot, and then the standard neutral or balance foot, which we call plantar grade.

Hallux valgus. So as we go through this section of the talk, we are going to try and think of these problems as their primary pathology and their secondary manifestations and that is going to drive how we treat these problems. This is going to be a situation where someone is going to present to you with a painful bunion. The medial eminence of their foot rubs in a shoe, it gets sore, it gets red, it hurts them. In very severe cases, they are also going to complain bitterly of the fact that the second toe just doesn’t behave, cocks up and rubs in the top of the shoe, and they may have even more painful callous.