BIOMECHANICS Winter Sports Medicine and the Podiatrist 99 Alpine and Cross Country Skiing and Snowboarding are all sports with which DPM’s should be familiar. BY JEFFREY A. ROSS, DPM, MD or DPM’s, alpine skiing, nique, or performance problems relat- Whatever the reason, you may be the cross-country skiing, and ed to foot or boot-fit discomfort. One skier’s last hope after attempting to snowboarding have become must understand the concepts of lower correct the situation first at the ski another area where podiat- extremity biomechanics related to ski- shop or with the boot fitter. ric lower extremity expertise Fcan be focused. The sports podiatrist can become involved at a variety of The skier can be a very challenging patient. levels. Understanding the individual sports, knowing their biomechanics, as well as the patient’s special needs, can enhance your overall sports prac- ing, boot design, boot fitting, as well as Alpine Skiing Biomechanics tice. Many skiers and boarders who the relation between a ski orthotic and Alpine or downhill skiing is a might not find the answers at the ski the boot in which it sits. complex skill that requires controlled shop will look to you for the right Unlike the average runner who pronation, setting the foot, ankle, and solutions. Whether it’s for canting has a small bag of running shoes, lower extremity on the inside edge. boots and skis or prescribing and fab- the skier who makes the trip to your Pronation sets the inside edge of the ricating footbeds and orthoses, you office has a big bag filled with ski downhill (control) ski and allows for can help to prevent injuries and pro- boots, as well as foot beds and or- the skier to lean inward against the ski, vide more comfort for your patients thotics. The skier’s visit to your office which holds a skid-less arc throughout during their winter exercise season. may be because of chronic foot pain the turn. While balanced on a beam of The skier can be a very challenging due to the boots, or his/her perfor- flexible composite (6.3 cm wide), the patient. Be aware of his/her numerous mance being affected by the inability skier drives the shin forward against concerns, whether due to biomechani- to be totally comfortable in the boot the stiff boot cuff and swings the hips cal imbalances leading to poor ski tech- while initiating and completing turns. PhotoDisc Continued on page 100 www.podiatrym.com SEPTEMBER 2018 | PODIATRY MANAGEMENT BIOMECHANICS Winter Sports (from page 99) pinated subtalar joint) by prescribing a Ski Fitters and DPM’s variety of orthotics for control in their The foot specialist or sports med- to the opposite direction. The ski rolls ski boots. icine specialist should have a basic onto its sharp steel edge and bites the For many years custom insoles understanding of the ski boot de- snow, creating an arc across the hill (molded to the foot in the ski shop) sign (just like an understanding of (Ross & Subotnick, 1999). Skiing is have been effective for mild foot and the running shoe), as well as skiing analogous to ballet on snow, where the lower leg imbalances, particularly biomechanics and performance. You skier encounters many centrifugal as well as g-forces during the turns, while simultaneously attempting to keep the center of gravity in line over the center You should know the sport before you of the ski. Any change in the normal treat the athlete. biomechanical balance can alter the skier’s ability to develop a controlled turn, thus predisposing the skier to injury if the abnormality is signifi- cant enough. Variable factors, such as structural bio- mechanical deformity, functional deformity or dynamic imbalance of 100 muscle groups can also have an influence on a skier’s performance, and help predict poten- tial injury. Skiers who have biomechanical Figure 1: Ski boot that is reversible: after removing the shell, it can become a Figure 2: Solomon ski boot overlapping abnormalities will com- snowboard boot with upper buckle posterior pensate by obtaining pronatory forces from other joints, for exam- ple, the hips and knees, in order to ski effec- tively. Using the Elec- tro-Dynogram (EDG), Ross (1985) showed that forces are transmit- ted from both the fore- foot and the rearfoot, which the skier utilizes in up-and down-weight- ing, as well as in the completion of turns. Figure 3: Technica traditional ski boot Figure 4: Snowboard boots (harder shell and softer shell) on Abnormalities which with upper buckles anterior snowboard were observed includ- ed: excessive foot pronation, shortened for the overpronator skier (Figure 6). should know the sport before you heel contact with excessive propulsive However, for the more severe rearfoot treat the athlete. It is essential for the phase on the toes, extreme forward and forefoot abnormalities, prescrip- foot specialist to establish a work- lean of the boot, as well as asymme- tion orthoses can be a valuable way ing relationship with the boot shop, try between the two feet. These com- to provide proper foot bed balance, as well as the ski boot fitter (Figure bined affected the skier’s effectiveness and to improve ski performance and 9). These individuals have a working and overall performance. The sports efficiency (Ross & Cohn, 1984). Boots understanding of basic biomechanics medicine podiatrist can assist skiers to today typically will have easy-to-cus- in relation to boot performance, fit, overcome some of these lower extrem- tomize liners and removable full- and comfort; but they also understand ity abnormalities, including poor skiing length soft support systems within their own limitations in addressing the style, poor edge control, as well as foot the inner boot. The pre-existing insole more challenging foot and lower leg imbalances (e.g., rearfoot varus/valgus, may be substituted with a custom in- problems and they generally prefer to forefoot varus/valgus, pronated or su- sole or prescription orthotic. Continued on page 102 SEPTEMBER 2018 | PODIATRY MANAGEMENT www.podiatrym.com BIOMECHANICS Winter Sports (from page 100) have experts assist them in diagnosis and treatment. This relationship can prove to be extremely satisfying and rewarding. The foot specialist can aid in the selection process for the “right boot” (similar to helping to choose the right running shoe) (Figures 2, 3). Podiatrists help to determine the foot type, biomechanical weakness and areas of weakness and stress. DPM’s diagnose bony deformities, biomechanical imbalances, areas of the foot where the boot might cause friction and irritation, as well as those skiers who may suffer from circula- tory impairment, nerve entrapment, and metabolic disorders. With this information, a ski boot fitter can then determine if the skier needs a boot de- signed for a flat or high arched foot, a narrow or wide foot, a boot with high 102 volume, a pure forward entry boot, or possibly a hybrid (with both overlap and rear entry design), or a boot with a narrow heel pocket. Tibial Varum Figure 5: (Left) Uncompensated Tibia Vara in the Ski Boot: The boot cuff does not compensate ade- Tibial varum is one of the more quately for the tibia vara, predisposing the skier to ride on the outside ski edge. common lower extremity biomechan- ical abnormalities that can have a (Right) Tibia Vara—Measurement: The skier is standing on the baseboard of the boot with the liner negative impact on a skier’s perfor- removed, and has assumed the functional skiing position. The cuff can then be aligned to the longi- mance. Tibial varum is a result of tudinal axis of the lower leg. Note that if the skier uses a footbed or corrective orthotic, the device an uncompensated varus deformity must be placed on the baseboard of the boot before correction of the tibia, which transmits instan- taneously to the ski-snow interface, and causes the skier to ride exces- By keeping the orthotic as thin as possible, there will be sively on the outside edge of the ski. Those skiers who have greater than more volume for the foot and toes to function. 8 to 10 degrees of tibial varum will have a great deal of difficulty initiat- ing a parallel turn without “catching” other foot and lower leg abnormal- to the front-entry and hybrid-designed the outside edge of the ski (Figure 5). ities that can contribute to a skier’s performance boots. Ski boots have difficulty in both edge control and evolved biomechanically, as well, of- Boot Technology performance. These include genu fering adjustable features, such as: Boot technology has improved so valgum, subtalar varus, forefoot val- internal or external canting systems, that high performance boots provide gum, transverse plane asymmetry, as adjustable “spoilers” or shaft angle a boot cuff adjustment to accom- well as leg length discrepancies. adjustments, boot flex, forward lean, modate for varying degrees of tibial The common complaint that boot internal/external heaters and custom varum and help to create a flat ski fitters and foot specialists hear is, “my heat-moldable liners made of ethyl-vi- surface. One of the simplest ways of feet hurt in my boots!” In addition, nyl acetate (EVA). treating high degrees of tibial varum skiers often complain that their feet DPM’s should be aware that the in the skier is to use a full-length, are tight, that they are cold, and that ski boot removable foot bed may be canted orthotic within the boot. The they experience friction, irritation, and replaced with custom-made orthoses. reason for its success is that you are blisters. As we have seen, techno- Many of these devices are made in providing total foot contact within logical development of the ski boot the ski shop with a computer imprint the boot, correcting biomechanical has gone from a traditional overlap of the skier, or by placing the foot foot imbalances within the foot and design to a skier-friendly rear-entry in a semi-weight-bearing neutral po- lower leg.