Richard A. Brand

A physiologically based criterion of muscle force prediction in locomotion.

Abstract The inversely-nonlinear relationship of muscle contraction force and the possible contraction duration (i.e., endurance) is utilized in a method to mathematically predict individual muscle forces. The method uses a nonlinear optimization scheme to solve the redundant distribution problem at the joints of interest. The method is demonstrated at the elbow during isometric contraction and in the lower extremity during locomotion. During gait, the observed muscle activity pattern in the lower extremity (as determined by EMG) shows substantial agreement with that activity pattern predicted when endurance is used as the optimization criterion. The importance of selecting muscle prediction criteria based on sound physiological bases rather than on an arbitrary or mathematically convenient basis is emphasized.

A comparison of the accuracy of several hip center location prediction methods

The purpose of this study was to estimate the accuracy with which this rotational method could estimate hip center location in a series of live subjects, and compare that to the accurary that could be obtained by the methods of Andriacchis group and Tylkowskis group in the same subjects

A biomechanical investigation of the human hip

Abstract This paper describes a biomechanical investigation of the human hip during level walking, while climbing and descending stairs, and when rising from a sitting position. Triads of flashing, light-emitting diodes attached to the pelvis, thigh, shank, and foot are photographed by a biplanar technique to generate kinematic data. Kinetic data is collected using a piezoelectric force platform. The inverse dynamics problem associated with the three lower extremity segments is solved for the time variations of the intersegmental force and moment resultants at the hip, knee, and ankle. An optimization technique is used to distribute these resultants to the load-carrying structures in the neighborhood of the hip, and to the two-joint muscles that flex and extend the knee and ankle. Typical results for a group of normal volunteers are presented and discussed.

How to write a systematic review.

Evidence-based medicine (EBM) is the combination of the best available research evidence with clinical experience and patient needs. The concept of EBM as a part of clinical decision making has become increasingly popular over the last decade. In the hierarchy of studies meta-analysis and systematic reviews occupy the highest levels. A systematic review of a clinical question can be performed by following a relatively standard form. These techniques as described here can be performed without formal training. Systematic reviews conducted in this fashion can be used as a higher form of current concepts or as review articles and replace the traditional expert opinion narrative review.

Prediction of hip joint centre location from external landmarks

Abstract The approaches to predicting the hip joint centre (HJC) location of Tylkowskis group and Andriacchis group were evaluated for accuracy and validity in children and adults of both sexes. Using Tylkowskis approach, we found that the three-dimensional (3-D) HJC location in adults (expressed as a percentage of the distance between the anterior superior iliac spines (ASIS)) was 30% distal, 14% medial, and 22% posterior to the ASIS, and predicted the HJC location to within 3.3 cm of the true location with 95% certainty. Using Andriacchis approach, we found that the HJC was located in the frontal plane distal and lateral to the midpoint of a line between the ASIS and pubic symphysis, and varied from 2.2 cm distal and 0.78 cm lateral in girls to 4.6 cm distal and 1.7 cm lateral in men. A more accurate method of estimating the 3-D HJC location combined a modification of Andriacchis approach (estimating frontal plane location of HJC) with a modification of Tylkowskis approach (estimating HJC location posterior to a frontal plane), and could predict the HJC location in adults to within 2.6 cm of the true location with 95% certainty.

Three-dimensional flexibility and stiffness properties of the human thoracic spine

Abstract Mathematical models of the human spine structure are useful in predicting biomechanical behaviour of the spine where actual experiments may never be performed. These models, to be valid, should be based upon experimentally determined mechanical properties of the spine. Three dimensional flexibility and stiffness properties, including the coupling effects, were determined for all levels of the human thoracic spine. Fresh cadaver spines were used in a 100% humid atmosphere at 22°C to preserve physiological environment. Bottom vertebra of a two vertebrae construct was fixed. Twelve forces and moments, one at a time, were applied to the top vertebra. Vertebral displacement was accurately measured in three dimensional space. Load displacement curves for the main as well as the coupled motions were plotted. Flexibility and stiffness matrices were calculated for the center of the vertebral body. Values for the matrix coefficients, the load-displacement diagrams and the variation of the mechanical properties with the spine level are presented.

Reconstruction of the hip. A mathematical approach to determine optimum geometric relationships.

The normal mechanical function of the hip is substantially altered by a variety of disorders. The surgical treatment of such conditions, particularly total hip replacement, offers the opportunity not only to replace the articular surfaces of the joint, but also to improve long-term mechanical function by reducing the loads on the joint. A mathematical model of the hip was developed to evaluate the effects of such surgically achievable mechanical alterations as acetabular placement, femoral shaft-prosthetic neck angle, neck length of the femoral prosthesis, and transfer of the greater trochanter. The loads on the hip were lowered significantly by placing the center of the acetabulum as far medially, inferiorly, and anteriorly as was anatomically feasible. Minimum joint contact forces occurred when the femoral shaft-prosthetic neck angles were small, while the minimum moments about the prosthesis stem-neck junction were found when the angles were 130 to 140 degrees. A neck length of the femoral prosthesis of thirty-five millimeters resulted in moments that were lower than those for a neck length of forty-five millimeters. Lateral transfer of the greater trochanter reduced hip-joint forces and moments but distal transfer had little mechanical effect.

Total Hip Acetabular Component Position Affects Component Loosening Rates

Loosening is the most common long-term problem following total hip arthroplasty. Many factors, including patient selection, cement technique, femoral component placement, and prosthesis design reportedly affect the incidence of loosening. Theoretically, the location of the hip center of rotation substantially affects the load on the hip, and superior and lateral hip center location will result in higher loads than medial and inferior placement. Long-term follow-up studies (average, 9.1 years after surgery) using logistical regression analysis demonstrate significantly higher rates of femoral loosening with acetabular components placed in a superior and lateral (i.e., nonanatomic) position, compared with acetabular components placed in a nearly anatomic position.

Comparison of hip force calculations and measurements in the same patient.

Many investigations report hip-contact-force estimates based either on mathematical models or on the output of instrumented implants. Data from instrumented implants have been consistently lower than mathematical predictions. The authors compared mathematical estimates derived from gait laboratory observations made in a patient with an instrumented hip implant. Appropriate modifications to past models resulted in force predictions that were reasonably similar to the output of the instrumented implant. Peak resultant forces were in the range of 2.5-3.5 body weight during level walking at a freely selected speed, while peak out-of-plane forces ranged from 0.6 to 0.9 body weight. Previous parametric hip-force predictions resulting from mathematically modeled surgical alterations may be high insofar as absolute peak values, but trends are likely correct.

Current Concepts Review - Mechanoreceptors in Joint Function*

Most surgeons and investigators consider ligaments to be passive stabilizers of the joints. However, more than 100 years ago, clinicians and investigators recognized the presence and potential roles of mechanoreceptors in the function of joints52,93,128. Perhaps because of the frequency of injuries of the anterior cruciate ligament, the functional impairment resulting from them, and the issue of whether the anterior cruciate ligament should be removed during total knee replacement, the role of mechanoreceptors in the anterior cruciate ligament recently has attracted considerable attention. It is important to ascertain the role of mechanoreceptors in the function of intra-articular ligaments in order to determine the future direction of joint reconstruction. Their importance, or lack thereof, will determine, in part, whether efforts should be directed more toward preservation of the receptors or whether the emphasis should remain on purely mechanical and kinematic aspects of joint function. Joint mechanoreceptors have been most often studied in the knee, with most recent investigations focusing on the anterior cruciate ligament. In exploring the function of mechanoreceptors in the knee, we do not intend to imply that mechanoreceptors in other joints are not important; our review is merely reflecting the literature relating to loss of function of the anterior cruciate ligament due to rupture (injury) or transection (operative treatment) rather than congenital laxity. The presence of mechanoreceptors in the anterior cruciate ligament41,66,104 has led several authors to suppose that these receptors influence motor function and, conversely, that their loss leads to dysfunction11,40,81. This notion is reinforced by the lack of a clear association between the functional outcome and the amount of passive laxity, not only after non-operative treatment23,38,118,142 of tears of the anterior cruciate …