FOOT ORTHOTICS AND ALPINE SKIING
by Greg Hoffmann C.PED Scott Thompson C.PED
Alpine Skiing is a fun and exhilarating sport. It is a wonderful outlet for the day to day stress of everyday life and people everywhere look forward to the freedom of carving perfect turns down the side of a quiet mountain. But even the best conditions and the finest equipment cannot deliver a good experience if the skier is in pain. According to statistics compiled by the ski industry the number of people pursuing alpine skiing as recreation today is declining. It is a commonly held theory within the industry that sore and uncomfortable feet are a primary reason why people decide to put their skis away for good. Why are so many skiers uncomfortable and what can we do about it? By first looking at the construction of a ski boot we can begin to understand the assault they can cause to the body if not adjusted properly. Think of the modern ski boot as an ankle, foot orthotic (AFO). The boot is made in two primary parts, the shoe or lower shell and the upper cuff. The job of the shoe is to envelop the foot. The job of the cuff is to firmly grasp the lower leg. The modern ski boot is made of rigid thermo-plastic and carbon impregnated materials. The molds for the boots are injection molded which means that the plastic is squirted into the mold at high temperature and pressure. The boot has several key performance areas. When the mold is injected the density and thickness of the plastic will vary over these key areas. The areas of highest stress are behind the achilles and up the spine of the boot (or calf area). The plastic will be most rigid in these parts of the boot thus restricting ankle joint dorsiflexion and plantar flexion and acting as an AFO. Most manufactures build two to four degrees of varus into the hind foot area. This can extend beyond the first MPJ depending on the model and manufacturer. They also include four to seven degrees of tibial varum into the cuff. Where did they come up with these specifications? The ski boot manufactures base their dimensions on a generic population of Average Man, Average Woman and Average Child. If everyone was built like the Average family we wouldn't be having this discussion but each of us is very different from one another and here lies the challenge. To achieve performance and comfort in a ski boot the boot must conform to the body and not vice-a-versa. Let's say Joe skier walks into a ski shop and tries on a pair of boots right out of the box. Those boots where made for Average man. As soon as Joe skier puts them on his body begins to compensate, desperately trying to turn itself into Average Man. Now the pain begins. It is the intent of the boot fitter to try to neutralize this compensation so poor Joe skier can be himself and that brings us to foot orthotics. Orthotics are the foundation of boot fitting. By first understanding the biomechanics of the skier's lower extremity, subtalar joint, mid-tarsal joint and ankle mortise we can build a foot orthotic (FO). Before anything else the foot must be flat on the floor. The alpine ski boot foot orthotic is significantly different from a full gait podiatric style foot orthotic. Alpine skiing is a mid-stance sport. The foot and lower leg are held in the mid-stance phase of the gait cycle. There is no heel strike or toe off in alpine skiing. The foot needs to be supported by a full length, full contact accommodative orthotic that matches the plantar contours of the foot closely. We try to avoid any contouring distal to the ball of the foot because this will force the plantar flexors of the foot to fire. Activating the plantar flexors will rob the gastroc and soleus of some range of motion inhibiting flexion at the ankle joint. Ankle joint dorsiflexion is critical to alpine skiing in order to stay balanced, absorb shock and navigate uneven terrain. Most full gait Podiatric style FO's are posted to put the subtalar joint in three degrees of varus and allow for up to four degrees of pronation. This adds up to a total of seven degrees of motion, too much for a rigid ski boot. The skier will not be able to safely and accurately control the ski. The calcaneous is held in two to four degrees of varus which is already built into the ski boot. If we add a FO posted at three degrees varus that is a total of six to seven degrees. This puts the skiers weight on the outside edge of the ski forcing them to internally rotate their legs in attempt to get the skis flat on the snow. The ski specific FO must be cast with the calcaneous perpendicular to the ground and extrinsically posted bringing the ground up to the foot. If a person has a forefoot valgus or varus condition and the device is intrinsically posted it will be of no benefit. The forefoot will not be able to make contact with the ground because the cuff of the boot is restricting the tibia's rotation and the wall of the boot will restrict the articulation of the mid-tarsal joint. People with forefoot varus will most commonly complain that their weight is always on the outside of their foot. The medial aspect of the knee will hurt as the joint space is pinched. Tailors bunions or skiers sixth toe are also common as the foot is constantly rocking inside of the boot. By extrinsically posting the FO and bringing the ground up to the foot we can control excessive motion and usually no further modification will be necessary. People with forefoot valgus need extrinsic posts on the lateral aspect of the FO in the forefoot area. These folks will probably complain about lateral mallaleous discomfort. The mallaleous is not the problem. The peroneal tendon is the culprit. The foot is trying to invert in attempt to find the ground. Many skiers complain of stress fractures of the tibia or tendonitis of the proneal longus tendon with prolonged rehab times. The problem is immediately solved with a simple foot bed adjustment to the lateral area. Casting Technique Of the three casting techniques the two most suitable for alpine skiing are non-weight bearing and semi-weight bearing. There are good, full-weight bearing systems available but they require a lot of experience by the person making the cast. The main difficulty with the full-weight bearing method is gravity. It is difficult to control the foot shape when a person stands on a soft, pliable casting pillow. A false, forefoot varus can appear in the cast allowing the mid-tarsal joint to unlock beyond functional control. By extrinsically posting these FOs the likely hood of creating a bunion at the First and Fifth MPJs is really high. The First will be cramped into the top of the shoe and the Fifth will be forced to the outside of the shoe as the foot slides off the device. The friction creates the bunion. The non-weight bearing systems can control the foot most accurately. But there is the possibility of getting over accurate at times if the soft tissue of the foot is pinched and not allowed to expand. Sometimes people complain that they have lost sensation on the bottoms of their feet or that they feel taller in the boot. They could actually be standing on the orthotic and not in it because once they are fully-weight bearing the soft tissue expands and will not fit the FO. A snug fitting boot can also contribute to this pinching of the soft tissue and raise the foot off of the FO. A trick in the final phase of the non-weight bearing casting process is to apply slight weight bearing pressure, not to the point where the sub-talar joint begins to compensate but just enough to let the soft tissue expand. The ideal casting technique for ski orthotics is semi-weight bearing, casting with the person seated. This technique allows you to control the foot while letting the soft tissue expand. By casting a deep heel cup the soft tissue of the calcaneous is captured and the skier will benefit from their own suspension system.. These three casting techniques are direct, using the skiers foot as a positive. The materials available today are amazing. Low temperature plastics such as Kydex, San Splint and Vivac along with rigid Plastazote or 65 durometer EVA make excellent shells. Cork, EVA and Plastazote make good posting materials. These materials are warm and they do not absorb moisture. The major drawback to the low temperature thermo plastics is the popular over-night boot dryer. These dryers get warm enough to distort and even destroy the hard work put into making a custom molded device. The best home dryers are computer fans outfitted with PVC pipe. This will provide moving but unheated air. To very briefly complete the boot fitting process the FO is adjusted to the boot board and then the boot cuff is adjusted to the skier's tibia. The boot is now conforming to the body and not the body to the boot. There is no reason for skiers to be uncomfortable in ski boots today. As more and more people are educated about skiing biomechanics we hope they will take advantage of the expertise offered by good boot fitters. Perhaps the number of people taking up the sport of skiing will begin to increase and even those who had given it up will try again and be able experience that effortless run through fresh powder that they dream of. Greg Hoffmann, C.Ped., O.S. T. Greg is the owner of Green Mountain Orthotic Lab at Stratton Mountain Ski Resort, Stratton, VT. He is the head instructor for Master Fit University a national education program for the snow sports industry teaching boot fitting, biomechanics and FO construction. He is also part of Ski Magazine's annual boot test team that critiques all makes and models of ski boots at Mount Bachelor, Oregon every spring. Scott Thompson, C.Ped., O.S.T. Scott is a partner in Green Mountain Orthotic Lab and adjunct lecturer for Master Fit University. Scott is also a member of Ski Magazine's boot test team. Table of contents blurb: Foot orthotics are the foundation of good ski boot fitting but they differ from full gait FOs because of the construction and rigid nature of the modern ski boot.