Force and Motion Analysis of the Normal, Diseased, and Prosthetic Ankle Joint

Etiology of Ankle Osteoarthritis

“…Specifically, it has been reported the ankle has a substantially smaller contact area than the hip or knee (at 500-N load: ankle, 350 mm 2 ; hip, 1100 mm 2 ; knee, 1120 mm 2 [2,13,16]). Consequently, the ankle experiences more force per square centimeter than the knee or hip [37]. Functionally, the ankle acts mainly as a rolling joint with high congruency [41].…”

Treatment of osteochondral defects of the talus

“…Th ese angles correspond to the mean sagittal ankle motion during the stance phase of gait in normal subjects. 367 Th e wedges were made of polyvinyl chloride and were covered with sand paper to prevent slipping of the specimens. Th e force was applied by gradually moving the baseplate upwards by turning two handle-actuated lead screws.…”

“…To imitate the stance phase of gait, the joint was loaded in three positions that correspond to the mean sagittal ankle motion with corresponding forces. 367 Th e loads were applied to the tibia, as was done in previous studies. 253,264,323 Th e reallife situation might have been better imitated by also loading the fi bula, which transmits 7% of the total force through the lower leg.…”

Intra-articular Contact Stress Distributions at the Ankle Throughout Stance Phase–patient-specific Finite Element Analysis as a Metric of Degeneration Propensity

“…To allow the ankle to settle into its precise anatomic apposition, guided by the tibio-talar articulation, a 200 N compressive load was then applied to the tibia in a second provisional loading step (after releasing restraints against talar rotation about the inversioneversion and internal-external rotation axes). A sequence of thirteen successive loading conditions (loads from 10 to 2800 N and rotations from 5° plantar to 9° dorsiflexion - Stauffer et al 1977) were next applied to the tibia, to simulate the entire stance phase of level walking gait ( Figure 5). As the tibia was rotated about the provisional ankle flexion/ extension axis, the talus was free to rotate as required by the tibio-talar articulation, thereby leading to effective ankle rotations which were not about a fixed axis.…”

“…where, P cumulative is the annual cumulative contact stress exposure distribution, expressed in MPa; Pî are the computed nodal contact stress values at a given increment in the gait cycle, i varying across the 13 load increments; P d is a contact stress damage threshold (2 MPa - Hadley et al 1990); and Δt i is the resident time, in seconds, associated with a given increment in the gait cycle (assuming a cadence of 58 steps/min - Stauffer et al 1977). Per-gait-cycle exposures were scaled to meaningful annual service exposures by assuming two million step cycles per year (Schmalzried et al 2000).…”