I think it is important to understand the biomechanical changes you are making when treating your patients. So many are secondary nature that we do not even think in these terms when treating patients. We fit a heel lift, post op shoe, custom orthotic device, CAM walker so routinely, for one biomechanical purpose after another, that we forget the purpose of these devices or shoe recommendations. The reason that I think it is important is that we have to use that knowledge many times trying to create even better biomechanical forces to help our patients. Podiatrists in general as such natural biomechanical gurus. We deal with feet and our treatment affects the entire lower extremity positively and negatively. We can not escape being biomechanical experts, as all of our treatments, especially surgery, will affect the mechanics of the lower extremity and up to the top of the head. Whether you like biomechanics or not, Podiatry forces you to be the medical expert.
So, what are common biomechanical changes that we do routinely make? I will borrow the list from page 259 of my book 2 Practical Biomechanics for the Podiatrist. The list will help our future discussion. This list applies to functional foot orthoses, but also shoes changes, activity changes, taping, OTC devices, etc. Here is the list:
- Improved foot stability
- Total foot contact for improved balance and support
- Off Weighting or Off Loading
- Weight Transfer
- Limit motion somewhere (applies to all sorts of immobilization)
- Create motion
- Increase shock absorption
- Balance foot deformities
- Attempt subtalar joint neutral
- Improve first ray plantarflexion
- Elevate heel
- Support 1 or all of the 4 foot arches
- Decrease muscle activity needed to decelerate pronation
- Decrease muscle activity needed to decelerate supination
- Maximally pronate the midtarsal joint
A second similar list I have on page 261 same book:
- Slowing a motion down
- Eliminating a motion
- Reversing a motion
- Creating a motion
- Off weighting
- Stabilizing
- Strengthening
- Changing its Position for Improved Alignment
- Distributing Weight Differently
- Making the foot more flexible
- Cushioning
We will discuss examples of each one of these. It is fun to see how you are affecting the biomechanics of a patient.
Slowing a Motion Down is a huge function of custom foot orthoses (CFOs). If we have a comfortable well fitting device, and you are controlling the excessive motions of pronation, supination, lateral forefoot spread, or forward slide, the CFO should be very helpful to the patient. It is a concept that researchers are just being able to quantitate well, and predictably one of the most important functions of an athletic running orthotic device. The patient will feel a more comfortable ride, a more smooth ride, or just less problems. The most important motion may not come from the foot, but from the ankle, knee, or hip area, where a reduction of velocity of one of these proximal segments to the foot brings crucial symptom relief. I believe the common improvement in knee symptoms with custom foot orthoses is tied directly to this function change.
Eliminating a Motion happens all the time in patients who have contact phase supination. The subtalar joint must pronate for the crucial lower extremity internal rotation to complete its excursion during the contact phase. If there is contact phase supination, or external rotation of the talus, while the proximal limb is internally rotating, damage will occur somewhere along the weak spots of the chain. Yet, even for the pronators, where the foot joints are unstable and in a loose packed orientation, a stable orthotic device can eliminate motion across the many small joints of the foot leading to great pain relief. You can also build a stiff Morton's extension to eliminate motion across the first metatarso-phalangeal joint for painful Hallux Rigidus patients.
Reversing a Motion also has to do with contact phase supinators that you make into normal pronators. In the severe pronators, you will see severe internal knee rotators begin to have more normal external rotation (I think you have to encourage that with good controlling orthoses and an external hip rotator strengthening program).
Creating a Motion is most apparent across the metatarsal heads due to end of a traditional orthosis. Where the plastic ends, motion is created. This always has to be considered when making an orthotic device for metatarsal pain syndromes. Many patients are very flat footed and function maximally pronated in gait with no subtalar joint motion at all being generated. If you place that patient biomechanically in a more supinated motion with your inserts, and put some motion into the rearfoot post, you will make them move! Problems related to both poor shock absorption and a very pronated malaligned position will both be helped.
Off Weighting is a very common means of pain relief. A high arch support can both off weight the heel and forefoot while you are standing by accepting more weight. Pads (many versions exist) under say metatarsals 1, 4 and 5 can off weight 2 and 3. Varus canting can off weight the medial side of the foot, and valgus canting can off weight the lateral side of the foot. This canting or wedging can back fire if the force produced by the wedge does not cause the expected shift in weight, so monitor the symptom relief.
Stabilizing an unstable foundation may just work wonders in some patients. Even though 20 different Podiatrist may make 10 different total orthotic designs, if they all stabilize the patient, all 20 patients are going to be helped. The best example of this is myself, but I also ask patients about the good and bad of any orthotic device made or designed by someone else. When I started practice, I knew about the Root design only and this is what my patients received. I was thrilled at the 70-80% success rate I was getting for the vast majority of lower extremity compliants. Yet, since I was going to specialize in this field, I continued to make versions upon versions for various reasons. 40 years later, the orthotic device I would make for you, probably wasn't the orthotic device I would have made 40 years ago, yet both would have helped you. Golden Rule of Foot: Always Make the Patient More Stable.
Strengthening is done the normal way of progressing patients through the types of strengthening like active range of motion, isometric, progressive resistance exercises, isotonic, and functional. However, we also affect strengthening by varieties of cross training, stretching out tight muscles, avoiding over training, and progressing our return to activity very gradually.
Changing its Position for Better Mechanical Advantage By changing the mechanics of patients, we can give muscles better chance of good power. A classic example is that controlling over pronation with less heel eversion to a more vertical heel position helps a weak posterior tibial tendon get better mechanical advantages. That subtalar joint neutral position is the best to attempt to hold the patient near for ideal joint equalibrium where the inverters and everters have equal pull as one simple example.
Shifting Weight Differently can be a part of a simple arch support taking more weight than normal if ever into the arch, or in off loading padding, or in varus or valgus cants, or in heel lifts shifting weight forward. Always think with any insert you use where the weight is moving to and from where.
Making the Foot More Flexible normally requires stretching routines or soft tissue and joint mobilizations (RX or self programs). In patients that over supinate, accomplishing contact phase pronation with CFOs will restore more normal foot mobility. Adding motion to the rearfoot post in the RX can make good progress to more foot flexibility.
Cushioning is needed for injuries and for patients in general if they lack shock absorption. Cushioning works fairly well in the forefoot minus the thickness causing crowding problems for some. Cushioning works okay in the heel, but you are always sacrificing some stability. It is something that you always have to be aware of since the cushioning lifts the patients off the CFO. I try to remind the patients that I want to remove the excess cushioning at some point down the line if I do not feel they need it anymore. With patients with poor fat pads, that cushioning will be permanent.
