Physical Education - Biomechanics Biomechanical

Physical Education - Biomechanics BIOMECHANICAL ISSUES of SKI BOOT-RELATED KNEE TRAUMA Knee injuries are some of the most interesting issues in orthopedics and sports medicine from the perspective of both prevention and treatment. The analysis of biomechanical causation is crucial to understanding acute traumatic knee injuries as well as long-term chronic knee problems commonly presenting in athletes at all levels of involvement. In the case of knee injuries in skiers, one testable hypothesis is the component of causation that relates to ski boots.

By design, ski boots are intended to provide external support and maintenance of advantageous ankle and knee flexion and tibial angular orientation with respect to the perpendicular as measured between the skier and the ski slope. Previous research has established a relationship between external ankle support in general and specifically, the way that altering or restricting the natural motion of the ankle joint contributes to changes in the mechanical load on anatomical structures in the knee.

Likewise, earlier studies established causal relationships between the higher incidence of acute anterior cruciate ligament ruptures among female athletes by virtue of wider female hips and the manner in which that gender-based anatomical difference accounts for increased incidence of ACL injuries in females as compared to male athletes.

Additional earlier studies also implicated rigid hinged external knee bracing intended to protect the medial collateral ligament (MCL) and lateral collateral ligament (LCL) from injuries due to direct impact in the horizontal plane encountered by American football linesmen as a contributing factor increasing acute ACL traumatic injuries by virtue of changes in biomechanical loading on knee joint structures. In light of those findings, the relationship between ski boot angles and knee injuries should be of interest to the overall study of contributing factors to knee injuries in skiers.

Article Summary: The article describes the testing of two specific hypotheses: (1) that the ski boot in its standard (neutral canting) setting causes a misalignment of two measurements of knee angles (varus valgus and internal-external rotation) as compared to the natural barefoot position; and (2) that both canting and boot rotation effect on varus valgus (VV) and internal-external rotation (IRER) angles as well.

The findings disclosed in the article implicate ski boot canting and base rotation angles are functionally related to angular changes associated with contributing to both overuse injuries such as chronic patellofemoral pain syndrome (PFPS) and also acute ACL ruptures. With respect to the chronic PFPS-related finding, the researchers discounted its functional relevance by virtue of the insignificant amount of time skiers spend in ski boots compared to the amount of time spent out of ski boots. With respect to the acute ACL rupture-related issue, the researchers considered the findings significant.

Subjective Evaluation: Skiing is a dynamic activity that involves myriad instantaneous changes in the forces acting on anatomical structures. The design of the experiment necessarily limited the analyses to comparatively simple interactions of weight distribution associated more with static force distribution than with the dynamic forces associated with skiing. Since skiing-related knee injuries most commonly occur during skiing and not during standing on the slope or walking in ski boots, there are natural limitations to the direct applicability of this study to skiing-related knee injuries.

Biomechanical Description of Technique: The experimental technique consisted of precise measurements of several knee angles known to be relevant to PFPS symptoms and to acute ACL injuries. Those measurements were ascertained through the use of skin markers distributed on the lower extremities on subjects with no known histories of knee pathology or symptomatic complaints.

After measuring VV and IRER angles in the neutral barefoot position, the researchers made similar measurements of those angles in several ski boot positions, including standing, canted, and rotated positions within the adjustable limitations of the ski boots. They also conducted measurements of simulated loading positions natural to skiing, achieved through the use of an angled platform duplicating the ski slope angle and a weighted pulley system designed to transmit downward forces between the skier and the sloped platform in the same perpendicular angle experienced during actual skiing.

Critical Analysis of Technique Selected: The technique selected provides an analysis of limited applicability to skiing because it tested only static forces rather than the many dynamic forces (both internal and external) associated with actual skiing. Less significantly, the researchers mentioned additional limitations on the accuracy obtainable through the use of skin markers, which are known to shift slightly, while pointing out that such movement is more of a concern when testing dynamic movements.

Finally, local deformation of the ski boot materials under loading complicates the precision of markers measuring forces attributable to ski boot position. This limitation is likely greatly magnified under the dynamic stresses associated with skiing compared to the static loading measurable in the study as designed. Greater precision would be possible through similar implementation of skin markers on subjects during actual skiing instead of simulated loading in the typical skiing postures.

Likewise, markers positioned on the ski boots themselves would enable researchers to minimize the imprecision due to the deformation of ski boot materials under loading. Summary: Skiing.