Patients who tackle the slopes have specific requirements for orthotics. In addition to reviewing the pedal mechanics and biomechanics of skiing, our expert panelists take a closer look at the design of ski boots and what impact the skier’s skill level will have on prescribing an appropriate orthotic. Without further delay, here is what they had to say.
Q: What pedal mechanics are unique to skiing?
A: During alpine skiing, the patient’s lower extremities never go through a complete gait cycle, notes Nicholas Sol, DPM, CPed. He says skiers should ideally have knee flexion during the entire contact cycle, asynchronous single and double limb support, and limited pedal mechanics between midstance and early propulsion.
In order to make efficient turns and maintain their balance, skiers must tip both skis onto the corresponding inside and outside edges, according to Brian T. Maurer, DPM, and Michael J. Schneider, DPM. They say the key is maintaining weight and pressure along the inside edge of the downhill ski. When initiating a turn, skiers maintain control by directing the downhill knee medially and transferring the load into the foot over the inside edge. As Drs. Maurer and Schneider note, rotating the tibia internally causes a closed kinetic chain pronation of the foot that transfers the pressure through the boot onto the ski edge.
“The higher the level of skier, the more subtle the dynamic,” say Drs. Maurer and Schneider.
If the skier has an unstable or overpronated foot, he or she may have difficulty turning as the “medial arch of the foot may collapse within the boot before the edging force can be transferred to the ski edge,” according to Drs. Maurer and Schneider.
Q: How is a ski boot different from a walking shoe?
A: Unlike most footwear, ski boots do not allow normal gait, according to Drs. Maurer and Schneider. Dr. Sol concurs, noting that alpine ski boots are designed to resist flexion at the MTPJs and limit flexion at the ankle. All of the panelists agree that ski boots are intended to lock the foot in a stable position in order to ensure that direction from the hips, knees and lower legs will be transferred directly onto the edge of the ski.
The more rigid the ski boot, the better the ability of the skier to efficiently transfer these forces, point out Drs. Maurer and Schneider.
Q: How does a ski boot affect pedal mechanics?
A: While rigid ski boots lock the foot and prevent normal gait, Drs. Maurer and Schneider point out that these boots do allow rotational motion of the tibia as the knee is adducted to put pressure over the inside ski edge.
Dr. Sol adds that turning the pelvis and torso clockwise causes external rotation of the right leg and outside edging of the right ski while simultaneously causing internal rotation of the left leg and inside edging of the left ski.
Ensuring a proper boot fit is essential. Drs. Maurer and Schneider note that skiers with excessive tibial varum will often have significant problems with a boot that is improperly fit. When there is a good fit, the cuff of the boot should align with the position of the tibia.
However, if there is not a snug fit of the boot cuff and too much room medially, Drs. Maurer and Schneider point out “there will be an inefficient transfer of force to the ski edge as the tibia and knee move medially.” As a result, they explain that skiers with bowed legs will ride their outside edges and have difficulty turning whereas skiers with knocked knees will ride the inside edges and often have to exaggerate knee movements in order to begin turning.
Q: How does one’s skiing level affect pedal mechanics?
A: Beginning skiers tend to lean backward and emphasize heel weighting, according to Dr. Sol. He adds that heel weighted skis allow less stability and the least amount of directional control.
Drs. Schneider and Maurer concur. They say this tendency in novice skiers can lead to difficulty turning and boot-related injuries such as subungual hematoma, dorsal nerve compression and irritation of bony prominences across the metatarsal-cuneiform joints.
More advanced skiers tend to evenly weight and/or forward weight their skis, points out Dr. Sol. He explains that evenly weighted skis provide the most stable support and control over direction.
Drs. Maurer and Schneider say advanced skiers maintain forward pressure of the tibia on the boot cuff. They emphasize that leaning forward and flexing into the boot cuff allows movements from the hips and knees to transfer more quickly into the edge of the ski.
Q: What considerations are unique to the placement and function of an orthotic in a ski boot?
A: When patients are wearing shoes, Dr. Sol says STJ pronation and supination are primarily influenced by the shape of the supporting surface, pedal function and shoe structure. When patients wear ski boots, STJ pronation and supination are “more of a passenger responding to the forces generated by knee function,” according to Dr. Sol.
The usual biomechanical goal with shoes is controlling pedal mechanics. With ski boots, the goal is to control knee function by accommodating pedal function, notes Dr. Sol.
Drs. Maurer and Schneider have developed the semi-rigid Snowthotic, an on-snow device fashioned from a neutral off-weightbearing cast. The doctors say the device is extrinsically posted forefoot (full width) and rearfoot. The Snowthotic incorporates a medial flange and a lateral clip that lock the foot into the boot. Drs. Maurer and Schneider say the device offers an “integrated system,” which responds to direction from above with greater precision and less effort.
They also point out that one can modify the Snowthotic to accommodate specific pathologies, including sesamoiditis and neuroma.
Q: What general guidelines do you recommend when translating a successful walking or jogging orthotic prescription into a skiing orthotic prescription?
A: As a general principle, Dr. Sol increases the flexibility of the orthotic shell when translating an orthotic prescription from shoes to alpine ski boots. He notes you should always evaluate the ski boot before prescribing, fitting and dispensing ski orthotics. To that end, he will remove the liner from its shell to assess fit and examine the shell’s interior.
Dr. Sol says most boot manufacturers include one or more rigid interior soles for width adjustment. He notes that alpine ski boots become more narrow when the skier raises the foot higher in the shell and become wider as the foot lowers in the shell. Therefore, if a boot fits tight without any interior soles, Dr. Sol says adding an orthotic will raise the foot in the shell and make the boot more narrow.
“Controlling orthotic bulk is vital in these cases or, conversely, new ski boots may become necessary,” says Dr. Sol.
Since loose-fitting boots become more narrow with the orthotic, placing rigid interior soles between the bottom of the boot shell and the liner will provide a more snug fit, according to Dr. Sol.
Orthotic impression techniques vary and include in-boot casting, partially weighted foam boxes and standing techniques to align the knee. In the experience of Drs. Maurer and Schneider, the standard neutral position negative cast is effective. They say the goal is to lock the foot into a neutral position within the boot and permit the efficient transfer of hip and knee movements into the ski edges.
With the aforementioned Snowthotic, they note that using an extrinsic, sulcus-length, forefoot post balances any forefoot varus or valgus, and evenly distributes weightbearing pressure across the metatarsal arch. Drs. Schneider and Maurer also point out that you can accommodate the forefoot post with cutouts or balance pads for plantarflexed metatarsals, capsulitis, bursitis and sesamoid pathology.
Dr. Sol founded the Walking Clinic, PC and practices in Colorado Springs, Col. He is a consultant to Tekscan.
Dr. Schneider is certified in podiatric surgery by the American Board of Medical Specialties in Podiatry and is a Fellow of the Academy of Ambulatory Foot Surgery. He practices at Schneider-Maurer Foot and Ankle Associates in the Colorado Rockies.
Dr. Maurer is certified in foot surgery by the American Board of Podiatric Surgery and is a Fellow of the American College of Foot and Ankle Surgeons. He is an Associate of the American Academy of Podiatric Sports Medicine and practices at Schneider-Maurer Foot and Ankle Associates in the Colorado Rockies.