Thomas P. Andriacchi

A framework for the in vivo pathomechanics of osteoarthritis at the knee

The in vivo pathomechanics of osteoarthritis (OA) at the knee is described in a framework that is based on an analysis of studies describing assays of biomarkers, cartilage morphology, and human function (gait analysis). The framework is divided into an Initiation Phase and a Progression Phase. The Initiation Phase is associated with kinematic changes that shift load bearing to infrequently loaded regions of the cartilage that cannot accommodate the loads. The Progression Phase is defined following cartilage breakdown. During the Progression Phase, the disease progresses more rapidly with increased load. While this framework was developed from an analysis of in vivopathomechanics, it also explains how the convergence of biological, morphological, and neuromuscular changes to the musculoskeletal system during aging or during menopause lead to the increased rate of idiopathic OA with aging. Understanding the in vivo response of articular cartilage to its physical environment requires an integrated view of the problem that considers functional, anatomical, and biological interactions. The integrated in vivoframework presented here will be helpful for the interpretation of laboratory experiments as well as for the development of new methods for the evaluation of OA at the knee.

A study of lower-limb mechanics during stair-climbing

The motions, forces, and moments at the major joints of the lower limbs of ten men ascending and descending stairs were analyzed using an optoelectronic system, a force-plate, and electromyography. The mean values for the maximum sagittalplane motions of the hip, knee, and ankle were 42, 88, and 27 degrees, respectively. The mean maximum net flexion-extension moments were: at the hip, 123.9 newton-meters going up and 112.5 newton-meters going down stairs; at the knee, 57.1 newton-meters going up and 146.6 newton-meters going down stairs; and at the ankle, 137.2 newton-meters going up and 107.5 newton-meters going down stairs. When going up and down stairs large moments are present about weight-bearing joints, but descending movements produce the largest moments. The magnitudes of these moments are considerably higher than those produced during level walking.

Knee adduction moment, serum hyaluronan level, and disease severity in medial tibiofemoral osteoarthritis

OBJECTIVE The adduction moment at the knee during gait is the primary determinant of medial-to-lateral load distribution. If the adduction moment contributes to progression of osteoarthritis (OA), then patients with advanced medial tibiofemoral OA should have higher adduction moments. The present study was undertaken to investigate the hypothesis that the adduction moment normalized for weight and height is associated with medial tibiofemoral OA disease severity after controlling for age, sex, and pain level, and to examine the correlation of serum hyaluronan (HA) level with disease severity and with the adduction moment in a subset of patients. METHODS Fifty-four patients with medial tibiofemoral OA underwent gait analysis and radiographic evaluation. Disease severity was assessed using the Kellgren-Lawrence (K-L) grade and medial joint space width. In a subset of 23 patients with available sera, HA was quantified by sandwich enzyme-linked immunosorbent assay. Pearson correlations, a random effects model, and multivariate regression models were used. RESULTS The adduction moment correlated with the K-L grade in the left and right knees (r = 0.68 and r = 0.60, respectively), and with joint space width in the left and right knees (r = -0.45 and r = -0.47, respectively). The relationship persisted after controlling for age, sex, and severity of pain. The partial correlation between K-L grade and adduction moment was 0.71 in the left knees and 0.61 in the right knees. For every 1.0-unit increase in adduction moment, there was a 0.63-mm decrease in joint space width. In the subset of patients in whom serum HA levels were measured, HA levels correlated with medial joint space width (r = -0.55), but not with the adduction moment. CONCLUSION There is a significant relationship between the adduction moment and OA disease severity. Serum HA levels correlate with joint space width but not with the adduction moment. Longitudinal studies will be necessary to determine the contribution of the adduction moment, and its contribution in conjunction with metabolic markers, to progression of medial tibiofemoral OA.

The influence of total knee-replacement design on walking and stair-climbing.

The relationship between gait and prosthetic design was studied during level walking and stair-climbing for twenty-six asymptomatic patients after total knee replacement. An age-matched group of fourteen control subjects was also studied. Five designs of total knee replacement Geomedic, Gunston, total condylar, duopatellar, and Cloutier were used. Differences in gait could be identified on the basis of prosthetic design. The more stressful stair-climbing test produced more clearly differentiated function among the different designs. Patients who were treated with the least-constrained cruciate-retaining (Cloutier) design of prosthesis were the only group that had a normal range of motion during climbing up and down stairs. Two groups of patients with semiconstrained (total condylar and Geomedic) designs had a lower than normal range of knee fiexion while descending stairs. Patients with the other designs of prosthesis had a normal range of knee motion on stair-climbing. Kinematic and anatomical differences among the five designs did not have as great an influence on function during level walking as they did during stair-climbing. The results of this study indicate that after total knee replacement even asymptomatic patients with excellent clinical results have an abnormality of gait. The features of the abnormality were common to most of the patients in the series, and consisted of a shorter than normal stride length, reduced mid-stance knee flexion, and abnormal patterns of external flexion-extension moment of the knee. Although an explanation of these abnormalities of gait is not completely possible at this time, they appear to be related to the interaction of the kinematics of the knee and surrounding soft tissues. CLINICAL RELEVANCE: It appears that patients with less constrained cruciate-retaining designs of total knee replacement have a more normal gait during stairclimbing than patients with more constrained cruciate-sacrificing designs. During level walking, patients with five quite different designs all had abnormalities of gait in spite of a successful clinical result. There is currently a great deal of controversy regarding which type of total knee prosthesis provides better Funded in part by National Institutes of Health Grants KO4AMO()493 and ROIAM2O7O2 and by the Arthritis Foundation. 1 Department of Orthopedic Surgery . Rush-Presbyterian-St. Luke’s N’lcdical Center. 753 Wcst Congress Parkway, Chicago. Illinois 60612. gait. An improved understanding of gait and the variables associated with total knee designs is essential in addressing this controversy. Quantitative studies of gait during activities of daily living are needed to generate this information, and will be useful for the evaluation of total kneereplacement devices and for providing understanding of the loading patterns that may occur during normal activity. Several studies have evaluated gait in patients with knee disease. These investigations included kinematic analyses I .6.7.9.I i.2I , time-distance measurements, and force-plate measurements. There have also been several kinetic and force-analysis studies of function in normal subjects and in patients after treatment for knee disabilitiesaIa14l7ao. The common finding of these studies was that patients who appear to be clinically asymptomatic after joint replacement have abnormal gait patterns. Currently, little is known about the nature of the gait abnormality in patients after total knee replacement or its relationship to total knee-replacement design. The purpose of this study was to evaluate the relationship between gait and total knee-replacement design. The prosthetic knees that were selected for this study were considered to be representative of cruciate-sacrificing and sparing designs with varying amounts of constraint. The parameters ofgait that we observed included time-distance patterns and motion and moments of the knee joint. The gait of patients who had received one of five different designs of total knee replacement was evaluated and cornpared with that of control subjects. Materials and Methods Twenty-six patients. in five experimental groups. were studied during level walking and stair-climbing. Patients were grouped according to which of five total knee designs they had received. The five implants selected for this study were the Geomedic, Gunston, total condylar. duopatellar, and Cloutier designs. The five designs of prosthesis were selected to represent varying shapes of the articular surfaces and the retention of one, both, or neither cruciate ligament. The Geomedic prosthesis has fairly congruous articular surfaces. requires removal of the anterior cruciate ligament, permits retention of the ps)sterior cruciate ligament. and does not include a patellar flange or resurfacing. The Gunston prosthesis consists of two separate semicircular runners that articulate with two independent tibial components, permits retention of both cruciate ligaments. and does not include patellar resurfacing or a patellar flange. The total condylar design requires the sacrifice of both cruciate ligaments. with anterior-posterior stability provided by the conformity of the tibial articulating surfaces; all patients with this design had patellar resurfacing. The duopatellar prosthesis permits retention of the posterior cruciate ligament. includes a patellar flange. and allows patellar resurfacing, which was performed in all of the patients whom we examined. The Cloutier prosthesis allows retention of both cruciate ligaments and the femoral condyles are asymmetneal, diverge. and have varying radii of curvature. The tibial component of the Cloutier device consists of flat articular surfaces supported on a metal retainer, and the design has a patellar flange. but patellar resurfacing was not performed in our patients. The patients selected for this study were matched according to postoperative pain. function, passive range of motion, and joint stability. A point system based on The Hospital for Special Surgery knee.rating system was used to quantitate

Walking speed as a basis for normal and abnormal gait measurements

Abstract Gait observations of normal subjects and patients with knee disabilities are presented. Time-distance measurements and ground reaction force parameters are reported in relation to walking speed. Regression analysis is used to establish simple functional relations between ground reaction force amplitudes and walking speed. It is shown that basic time distance measurements observed over a range of walking speeds can be useful indicators of gait abnormalities associated with knee disabilities. For example, clinical improvement after treatment is found to be consistent with changes in these gait parameters. These results indicate the usefulness and importance of considering gait measurements in relation to walking speed when attempting to classify gait abnormalities.

The knee adduction moment during gait in subjects with knee osteoarthritis is more closely correlated with static alignment than radiographic disease severity, toe out angle and pain

This study tested whether the peak external knee adduction moments during walking in subjects with knee osteoarthritis (OA) were correlated with the mechanical axis of the leg, radiographic measures of OA severity, toe out angle or clinical assessments of pain, stiffness or function. Gait analysis was performed on 62 subjects with knee OA and 49 asymptomatic control subjects (normal subjects). The subjects with OA walked with a greater than normal peak adduction moment during early stance (p = 0.027). In the OA group, the mechanical axis was the best single predictor of the peak adduction moment during both early and late stance (R = 0.74, p < 0.001). The radiographic measures of OA severity in the medial compartment were also predictive of both peak adduction moments (R = 0.43 to 0.48, p < 0.001) along with the sum of the WOMAC subscales (R = −0.33 to −0.31, p < 0.017). The toe out angle was predictive of the peak adduction moment only during late stance (R = −0.45, p < 0.001). Once mechanical axis was accounted for, other factors only increased the ability to predict the peak knee adduction moments by 10–18%. While the mechanical axis was indicative of the peak adduction moments, it only accounted for about 50% of its variation, emphasizing the need for a dynamic evaluation of the knee joint loading environment. Understanding which clinical measures of OA are most closely associated with the dynamic knee joint loads may ultimately result in a better understanding of the disease process and the development of therapeutic interventions.

Gait adaptations by patients who have a deficient anterior cruciate ligament.

Sixteen patients who had unilateral deficiency of the anterior cruciate ligament and ten healthy control subjects were analyzed during level walking, jogging, and ascending and descending stairs. Kinematic and kinetic findings for the right and left hips, knees, and ankles of all of the patients and control subjects were recorded during each activity. Substantial differences from normal function were observed for both limbs of the patients during level walking and during jogging. The magnitude of the maximum moment that tended to flex the knee was reduced the most (140 per cent) during level walking. It was reduced less (30 per cent) during jogging, it was not changed while the patient descended stairs, and it was slightly increased while he or she ascended stairs. The reduction in the magnitude of the flexion moment about the knee was interpreted as the patients effort to reduce or avoid contraction of the quadriceps. Reduction of the flexion moment reduces any contraction of the quadriceps because there must be a mechanical balance between the external moment (due to body weight and the weight and inertia of the segment of the limb) that tends to flex the knee and an internal moment (generated by contraction of the quadriceps) that tends to extend the knee. This so-called quadriceps-avoidance gait was related to the angle of flexion of the knee when the maximum flexion moment occurred during each activity. This angle of flexion was 20 degrees during walking, 40 degrees during jogging, and approximately 60 degrees during stair-climbing.(ABSTRACT TRUNCATED AT 250 WORDS)

A Point Cluster Method for In Vivo Motion Analysis: Applied to a Study of Knee Kinematics

A new method for deriving limb segment motion from markers placed on the skin is described. The method provides a basis for determining the artifact associated with nonrigid body movement of points placed on the skin. The method is based on a cluster of points uniformly distributed on the limb segment. Each point is assigned an arbitrary mass. The center of mass and the inertia tensor of this cluster of points are calculated. The eigenvalues and eigenvectors of the inertia tensor are used to define a coordinate system in the cluster as well as to provide a basis for evaluating non-rigid body movement. The eigenvalues of the inertia tensor remain invariant if the segment is behaving as a rigid body, thereby providing a basis for determining variations for nonrigid body movement. The method was tested in a simulation model where systematic and random errors were introduced into a fixed cluster of points. The simulation demonstrated that the error due to nonrigid body movement could be substantially reduced. The method was also evaluated in a group of ten normal subjects during walking. The results for knee rotation and translation obtained from the point cluster method compared favorably to results previously obtained from normal subjects with intra-cortical pins placed into the femur and tibia. The resulting methodology described in this paper provides a unique approach to the measurement of in vivo motion using skin-based marker systems.

The role of ambulatory mechanics in the initiation and progression of knee osteoarthritis.

Purpose of ReviewThis review examines recent in-vivo studies of ambulation and discusses the fundamental role of mechanics of ambulation in the initiation and progression of osteoarthritis at the knee. Recent FindingsRecent studies have supported earlier findings that a high adduction moment at the knee during ambulation was most frequently reported to influence the progression of medial compartment osteoarthritis. In contrast to previous findings in patients with osteoarthritis, recent work on healthy subjects reports that cartilage thickness increases with high ambulatory loads. Kinematic changes were associated with the initiation of osteoarthritis. Recent studies of subjects with high risk factors for knee osteoarthritis (obesity and anterior cruciate ligament injury) reported a relationship between kinematic changes during ambulation and the initiation of osteoarthritis at the knee. This review also contrasts the relative influence on osteoarthritis of knee mechanics measured during ambulatory and nonambulatory activities. SummaryThe initiation of osteoarthritis occurs when healthy cartilage experiences some condition (traumatic or chronic) that causes kinematic changes during ambulation at the knee to shift the load-bearing contact location of the joint to a region not conditioned to the new loading. The rate of progression of osteoarthritis is associated with increased load during ambulation.

A relationship between gait and clinical changes following high tibial osteotomy.

We studied the cases of twenty-one patients with high tibial osteotomy in order to determine the relationship between knee-joint loading during gait and clinical outcome. The patients were tested before surgery, one year after surgery, and again at an average of 3.2 years after surgery. An age-matched group of fifteen control subjects was also studied. The results of this study indicate that certain characteristics of preoperative walking are associated with postoperative clinical results. In particular, the moment tending to adduct the knee joint during walking preoperatively was predictive of postoperative clinical results. The patients were classified into a high adduction-moment group and a low adduction-moment group according to the magnitude of the knee-adduction moment. The adduction moment was reduced in both groups after high tibial osteotomy. However, the average postoperative adduction moments in the low adduction-moment group were still significantly lower than those in the high adduction-moment group. The two groups were indistinguishable on the basis of preoperative knee score, initial varus deformity, immediate postoperative correction, age, and weight. However, at an average 3.2-year follow-up, patients with low preoperative adduction moments had substantially better clinical results than did patients with high adduction moments. The low adduction-moment group had 100 per cent excellent or good clinical results, while only 50 per cent of the patients in the high adduction-moment group had an excellent or good result. Furthermore, there was a significant recurrence of varus deformity in the patients in the high adduction-moment group.(ABSTRACT TRUNCATED AT 250 WORDS)