Tibial varum is a biomechanical abnormality that can have a great deal of negative effect upon the skier’s ability to ski normally [4]. Tibial varum is a result of an uncompensated varus deformity of the tibia which transmits instantaneously to the ski–snow interface and causes the skier to ride excessively on the outside edge of the ski. When a skier has more than 8–10° of tibial varum deformity, he or she will have a great deal of difficulty initiating the parallel turn without “catching” the outside edge of the ski. Skiers who chronically ski on the outside edges of their skis when attempted to “set-up” the next turn will have difficulty getting on to their inside edges, and when they do will often cross tips, which can eventually lead to sudden falls and possible injury [1]. High-performance boots of this day and age provide a boot cuff adjustment to accommodate varying degrees of tibial varum in order to create a flat ski surface. One of the simplest and most reliable means of treating tibial varum is to use a full-length, canted, in-boot foot orthosis. The advantage of this method is that the orthosis provides for total foot contact within the boot, affording the skier greater correction of lower extremity imbalances within the foot and leg. Another typical problem that can be eliminated with a balanced footbed or orthosis is the reduction of friction on bony areas of the foot against the boot, while simultaneously affording a comfortable, dependable, balanced footbed that helps to provide effectual edge control [4].

Skiers who have tibial valgum or genu valgum of the knees will be constantly on the inside edges of their skis. The inward position of the knee sets the skier up for potential crossing the ski tips, as well as decreased control of the uphill ski. These skiers will relate that they “caught an edge” even on the flat terrain as a result of this lower leg position. In addition the skier will also complain of medial collateral ligament strain from excessive internal femoral rotation, leading to patellar tracking and patellofemoral joint syndrome pain. Tibial valgum is associated with coxa vara– genu valgum as well excessive pronation of the feet. Orthosis control will typically correct the improper knee position and allow for a more neutral position of the foot on the ski. However, when this is not sufficient the use of a cant may be necessary to provide for lower extremity alignment. The knee position can be visualized to be more frontal when the skier stands on a bench with both the orthosis and the cant in place.

Forefoot varus imbalance can also lead to a forefoot that “rides” on the outside edge of ski, similar to a subtalar varus. When the skier stands on a platform and a vertical plumb line is dropped from the midpoint of the patella, it should drop directly down to the vicinity of the second metatarsal. However, if the line drops more laterally, forefoot varus imbalance may continue to be present. Additional forefoot posting on a full-length orthosis may be required to correct this imbalance. The skier will be able to feel the difference and relate much more stability in the forefoot. It is important not to overcorrect the rearfoot with extrinsic posting which can elevate the heel causing a potential rearfoot boot fit problem, and/or irritation at the posterior aspect of the heel. Skiers have often complained about boot fit and comfort. They often state that their feet hurt, and that they are cold, tight and irritating. Compared to years when first skiing with laced leather boots, technological advances in design and performance have made boot comfort a standard in the industry. Designs have changed over the years, having gone from the traditional overlap design, then through a rear-entry revolution and now having come full circle back to a forward entry and hybrid designed performance boot. From a biomechanical standpoint ski boots have become extremely sophisticated biomechanically. There are a number of adjustable features now on boots which include internal versus external canting systems, adjustable spoilers or shaft-angle adjustments, boot flex, forward lean, internal/external heaters, as well as custom heat-moldable liners made of ethyl vinyl acetate (EVA). To facilitate the use of custom foot orthoses, most ski boots have footbeds that easily can be removed. Most ski shops offer custom insoles that can be made readily by using computer technology or with an apparatus which places the foot in a semi-weight-bearing neutral position, with knee stabilizer apparatus built into the platform to accurately align the knee over the foot, for complete lower leg correction. The traditional prescription can either be made with computer technology and plaster casting in neutral position outside the boot or from an in-boot cast while the skier assumes a neutral ski stance position, quite often functioning which much greater control than the custom insole, due to increased correction and stability in the rearfoot, subtalar joint, midtarsal joint, and forefoot. By locking the midtarsal joint, and controlling excessive pronation/supination, we can achieve greater stability and balance which will afford the skier greater edge control and better performance. When looking at the ski boot, there are five areas of concern: