Saunders, Inman, and Eberhart define six anatomic determinants that minimize center-of-gravity displacement during normal walking. They then use force-plate analysis and biomechanical modeling to show how disease or surgical fixation disrupts these determinants and forces compensatory motion at intact joints. The central question: what makes bipedal gait energetically efficient, and how does pathology break that efficiency?
Every gait abnormality you observe in clinic is a compensation, not just a deficit. This paper is the reason we think that way. When you see a patient with a stiff knee walking with exaggerated pelvic hike and contralateral heel rise, recognize that the center-of-gravity path is being preserved at metabolic cost. The knee determinant alone, when lost, nearly triples swing-phase energy demand.
When planning a knee arthrodesis, fix the joint at 15-20 degrees of flexion — the paper explicitly shows this preserves a more normal center-of-gravity path than full extension.
The 300% energy cost threshold is the clinical ceiling: once two major determinants are gone simultaneously (e.g., above-knee amputation without a functional prosthetic knee), compensation fails entirely. In elderly patients, that cardiovascular burden shortens life.
This framework also explains why ankle arthrodesis is relatively well tolerated (knee and hip compensate fully) while combined foot-and-knee loss is devastating. A principle directly applicable when counseling patients before limb-salvage versus amputation decisions.
Saunders, Inman, and Eberhart define six anatomic determinants that minimize center-of-gravity displacement during normal walking. They then use force-plate analysis and biomechanical modeling to show how disease or surgical fixation disrupts these determinants and forces compensatory motion at intact joints. The central question: what makes bipedal gait energetically efficient, and how does pathology break that efficiency?
Every gait abnormality you observe in clinic is a compensation, not just a deficit. This paper is the reason we think that way. When you see a patient with a stiff knee walking with exaggerated pelvic hike and contralateral heel rise, recognize that the center-of-gravity path is being preserved at metabolic cost. The knee determinant alone, when lost, nearly triples swing-phase energy demand.
When planning a knee arthrodesis, fix the joint at 15-20 degrees of flexion — the paper explicitly shows this preserves a more normal center-of-gravity path than full extension.
The 300% energy cost threshold is the clinical ceiling: once two major determinants are gone simultaneously (e.g., above-knee amputation without a functional prosthetic knee), compensation fails entirely. In elderly patients, that cardiovascular burden shortens life.
This framework also explains why ankle arthrodesis is relatively well tolerated (knee and hip compensate fully) while combined foot-and-knee loss is devastating. A principle directly applicable when counseling patients before limb-salvage versus amputation decisions.