Force displacement characteristics of the posterior cruciate ligament.

The percent force changes in the posterior cruciate ligament were calculated using a previously validated computerized knee model after the femoral insertion sites were varied 2.5 and 5.0 mm in an anterior, posterior distal, anterior distal, and posterior distal direction. The tibial insertion sites were also varied 2.5 and 5.0 mm in the medial, lateral, proximal, and distal directions. Percent force changes were measured over a range of 0 degree to 90 degrees. These insertion sites simulated potential surgical placement errors. Results of this study demonstrated that the greatest percent force changes in the posterior cruciate ligament were at full extension. The greatest absolute percent force change between 0 degree and 90 degrees of flexion was with a femoral insertion of the posterior cruciate ligament placed 5 mm anterior to its normal attachment site, which resulted in a 39% change in the posterior cruciate ligament force. Distal femoral site attachment had the least effect (10% at 5.0 mm). Alterations at the tibial attachment site were less sensitive than on the femur; the greatest absolute percent force changes occurred with medial and lateral attachment sites (14% and 15%, respectively, at 5.0 mm). A minimal amount of percent force changes were seen between 45 degrees and 75 degrees of knee flexion in all positions tested for both tibial and femoral attachment sites. This model suggests that, like the anterior cruciate ligament, the force in the posterior cruciate ligament is also sensitive to attachment site position. As in anterior cruciate ligament studies, the femoral attachment site was found to be more sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gait biomechanics and the evolution of total joint replacement

The history and evolution of total knee and total hip replacement has been influenced substantially by the knowledge obtained from gait analysis studies. Many of the mechanical problems associated with these devices have been analyzed and evaluated in terms of the mechanics of walking. The magnitude and pattern of the forces at the hip and knee joints derived from gait analysis studies have provided valuable input into the design criteria of both total hip and total knee replacements. Information generated from the gait analysis of patients with total joint replacements has provided objective criteria for assessing functional recovery following this procedure. In addition to providing a basis for design evaluation, the key to the analysis of function following joint replacement is the ability to identify functional adaptations specific to design features. Gait analysis provides a unique opportunity to obtain objective information that cannot be obtained through other clinical means and provides a means for evaluating current designs and future design modifications.     

The anterior cruciate ligament-deficient knee with varus alignment. An analysis of gait adaptations and dynamic joint loadings.

Thirty-two patients with an ACL-deficient knee and lower limb varus alignment and 16 healthy controls were analyzed during level walking using a force-plate and optoelectronic system. The forces and moments of the lower limb and knee joint were measured and knee joint loads and ligament tensile forces were calculated using a mathematical model. The majority of patients (20 of 32) had an abnormally high adduction moment at the affected knee. The adduction moment showed a statistically significant correlation to high medial tibiofemoral compartment loads and high lateral soft tissue forces, but not to the degree of varus alignment on standing roentgenograms. Fifteen of 32 knees had abnormally high lateral soft tissue forces. We interpreted these gait findings as indicative of a medial shift in the center of maximal joint pressure and an increase in lateral soft tissue forces to achieve coronal plane stability. Further, there is the likelihood of separation of the lateral tibiofemoral joint and "condylar lift-off" during periods of the stance phase. If this occurs, all of the load-bearing forces would shift to the medial tibiofemoral joint and relatively large tensile forces would occur in the lateral soft tissue restraints. The flexion moment, as related to the quadriceps muscle force, was significantly lower than the control knees in 40% of the involved knees, and the extension moment, as related to the hamstring muscle force, was significantly higher in 50% of the involved knees. We interpret this finding as a gait adaptation tending to diminish quadriceps muscle activity and enhance hamstring muscle activity to provide dynamic anteroposterior stability of the knee joint. The fundamental assumption of this paper is that any combination of conditions leading to higher medial joint forces is associated with factors leading to more rapid degeneration of the medial compartment in patients with ACL deficiency, varus deformity, and lax lateral ligaments.     

Characterization of gait parameters in patients with Charcot-Marie-Tooth disease

The gait of five patients with Charcot-Marie-Tooth(CMT) disease was analyzed using light-emitting diodes and a force plate. The flexion-extension motions of the hips, knees, and ankles, as well as their moments (vector sums of forces acting at the joints) in the flexion-extension and abduction-adduction planes, were quantified. The gait of the CMT patients showed abnormalities consistent with both distal weakness (ankle dorsi- and plantar-flexors) and weakness of the hip abductor muscles. The latter weakness appeared to produce asymmetric hip moments and truncal instability in the mediolateral plane during ambulation. However, the extent to which the gait was abnormal appeared not to be exclusively related to the severity of the sensorimotor conduction deficits in the peripheral nerves. In the four patients for whom nerve conduction velocity studies were available, decrease in the lower-extremity distal conduction velocities and evoked motor amplitude potentials did not correlate with the severity and extent of the gait abnormalities.     

Methodology for long-term wear testing of total knee replacements

This article begins to address the validation requirements of wear testing on total knee replacements in a knee simulator. The knee simulator has four stations. The axial force is variable but reaches a maximum of 2.3 kN. Physiologic anteroposterior shear force and rotational torques are supplied to the knee. The forces and displacements are timed to coincide with those of a typical gait cycle. Kinematics of the simulator are dependent on the type of knee being tested. Tests of designs with well known clinical histories were done to 10 million cycles. The relative amounts and types of wear shown by the designs were similar to that found in their clinical histories. Wear tracks on more conforming designs were larger, and the penetration into the plastic appeared to be less. This did not necessarily mean that wear, as measured by loss of material, was reduced on conforming designs. Delamination of the plastic was achieved only after aging the tibial components. Wear particles isolated from the lubricating fluid were similar in size and shape to those isolated from in vivo specimens. However, the relative amounts of wear particle shapes were different depending on the design. At the start of the tests, all of the flexibly mounted tibial components showed more motion than after 5 million cycles, indicating that the surface of the plastic became more conforming. This study showed that knee wear similar to wear observed in vivo can be reproduced in the laboratory. The parameters and methods elucidated in this introductory study should form the basis for use in preclinical wear tests of total knee replacements.     

Risk factors for progressive cartilage loss in the knee: a longitudinal magnetic resonance imaging study in forty-three patients

OBJECTIVE: To evaluate the rate of progression of cartilage loss in the knee joint using magnetic resonance imaging (MRI) and to evaluate potential risk factors for more rapid cartilage loss. METHODS: We evaluated baseline and followup MRIs of the knees in 43 patients (minimum time interval of 1 year, mean 1.8 years, range 52-285 weeks). Cartilage loss was graded in the anterior, central, and posterior regions of the medial and lateral knee compartments. Knee joints were also evaluated for other pathology. Data were analyzed using analysis of variance models. RESULTS: Patients who had sustained meniscal tears showed a higher average rate of progression of cartilage loss (22%) than that seen in those who had intact menisci (14.9%) (P 相似文献   

Coventry Award paper. Backsurface wear and deformation in polyethylene tibial inserts retrieved postmortem

Wear and deformation were characterized at the backsurface of 25 posterior cruciate-retaining total knee arthroplasty polyethylene inserts retrieved postmortem from 20 subjects. The mean implantation time was 64.1 months (range, 4-156 months). The backsurface of the inserts was inspected using a stereomicroscope with a digital optical system. Coronal histologic sections of 13 proximal tibias were inspected for the presence and extent of penetration of granuloma. Damage to the backsurface was limited. Polishing was recorded on 21 (84%) of the inserts and abrasive wear on five (20%) inserts. Pitting was present in 21 (84%) components, but involved less than 1% of the area in all but one of these components. Delamination and cracking were not observed. Extrusions were seen in all 10 of the components that had screw holes in the tibial tray. A correlation was found between the depth of penetration of the granuloma along the posteromedial screw and the height of the corresponding extrusion. The anteroposterior profiles showed a concave deformation of the backsurface in 24 (96 %) of the cases. The concave deformation of tibial inserts may facilitate accumulation and transportation of wear debris to the tibial bone-implant interface through the screw holes in implants designed for cementless fixation.     

Stem curvature and load angle influence the initial relative bone-implant motion of cementless femoral stems

A 6 df measurement system was used to investigate the initial relative bone-implant motion of two types of cementless total hip replacement femoral components—a straight stem and a curved stem. Five pairs of fresh frozen femurs from human cadavers were tested with loads applied to the femoral head at angles characteristic of level walking, stair-climbing, and rising from a chair. The most important findings were that (a) the resultant proximal translations were twice as high with the straight stem as with the curved stem at load angles encountered in stair-climbing and rising from a chair, (b) both stem types had more motion at load angles encountered in stair-climbing and rising from a chair than in level walking, with the increases ranging from 3 to 14-fold, (c) there was as much as 66-fold more motion distally than proximally, and (d) the amount of interface motion varied by 5-fold between the medial and lateral surfaces of the distal part of the implant because of the combined effects of translation and rotation. The amount of initial bone-implant motion of the femoral component was found to be particularly sensitive to off-axis loading; this suggests that stair-climbing and rising from a chair should be avoided in the early postoperative period when a cementless porous-coated femoral stem has been used.     

Quantitative analysis of the relative effectiveness of 3 iliotibial band stretches

OBJECTIVE: To compare the relative effectiveness of 3 common standing stretches for the iliotibial band (ITB): arms at side (stretch A), arms extending overhead (stretch B), and arms reaching diagonally downward (stretch C). DESIGN: Each subject's biomechanics was captured as a 3-dimensional image by using a 4-camera gait acquisition system with a forceplate. SETTING: University biomotion laboratory. PARTICIPANTS: Five male elite-level distance runners. INTERVENTIONS: All participants performed each of the 3 standing stretches for the ITB. MAIN OUTCOME MEASURES: For each stretch, change in ITB tissue length and the force generated within the stretched complex was measured. Data were then combined and analyzed by using kinetic values assessment. RESULTS: All 3 stretches created statistically significant changes in ITB length (P<.05), but stretch B, incorporating overhead arm extension, was consistently most effective both for average ITB length change and average adduction moments at the hip and knee. CONCLUSIONS: Adding an overhead arm extension to the most common standing ITB stretch may increase average ITB length change and average external adduction moments in elite-level distance runners.     

Comparison of clinical and dynamic knee function in patients with anterior cruciate ligament deficiency

BACKGROUND: Whether passive measures of isokinetic muscle strength deficits and knee laxity are related to the dynamic function of the anterior cruciate ligament-deficient knee remains unclear. HYPOTHESES: Arthrometer measurements are not predictive of peak external knee flexion moment (net quadriceps muscle moment), isokinetic quadriceps muscle strength correlates with peak external knee flexion moment (net quadriceps muscle moment), and isokinetic hamstring muscle strength correlates with peak external knee extension moment (net flexor muscle moment). STUDY DESIGN: Cross-sectional study. METHODS: Gait analysis was used to assess dynamic function during walking, jogging, and stair climbing in 44 subjects with unilateral anterior cruciate ligament deficiency and 44 control subjects. Passive knee laxity and isokinetic quadriceps and hamstring muscle strength were also measured. RESULTS: Arthrometer measurements did not correlate with peak external flexion or extension moments in any of the activities tested or with isokinetic quadriceps or hamstring muscle strength. Test subjects also had a significantly reduced peak external flexion moment during all three jogging activities and stair climbing compared with the control subjects and this was correlated with significantly reduced quadriceps muscle strength. CONCLUSIONS: Absolute knee laxity difference did not correlate with dynamic knee function as assessed by gait analysis and should not be used as a sole predictor for the outcome of treatment. Patients with greater than normal strength in the anterior cruciate ligament-deficient limb performed low- and high-stress activities in a more normal fashion than those with normal or less-than-normal strength.