Human balance and posture control during standing and walking

The common denominator in the assessment of human balance and posture is the inverted pendulum model. If we focus on appropriate versions of the model we can use it to identify the gravitational and acceleration perturbations and pinpoint the motor mechanisms that can defend against any perturbation.

We saw that in quiet standing an ankle strategy applies only in the A/P direction and that a separate hip load/unload strategy by the hip abd/adductors is the totally dominant defence in the M/L direction when standing with feet side by side. In other standing positions (tandem, or intermediate) the two mechanisms still work separately, but their roles reverse. In the tandem position M/L balance is an ankle mechanism (invertors/evertors) while in the A/P direction a hip load/unloading mechanism dominates.

During initiation and termination of gait these two separate mechanisms control the trajectory of the COP to ensure the desired acceleration and deceleration of the COM. During initiation the initial acceleration of the COM forward towards the stance limb is achieved by a posterior and lateral movement of the COP towards the swing limb. After this release phase there is a sudden loading of the stance limb which shifts the COP to the stance limb. The COM is now accelerated forward and laterally towards the future position of the swinging foot. Also M/L shifts of the COP were controlled by the hip abductors/adductors and all A/P shifts were under the control of the ankle plantar/dorsiflexors. During termination the trajectory of both COM and COP reverse. As the final weight-bearing on the stance foot takes place the COM is passing forward along the medial border of that foot. Hyperactivity of that foot's plantarflexors takes the COP forward and when the final foot begins to bear weight the COP moves rapidly across and suddenly stops at a position ahead of the future position of the COM. Then the plantarflexors of both feet release and allow the COP to move posteriorly and approach the COM and meet it as quiet stance is achieved. The inverted pendulum model permitted us to understand the separate roles of the two mechanisms during these critical unbalancing and rebalancing periods.

During walking the inverted pendulum model explained the dynamics of the balance of HAT in both the A/P and M/L directions. Here the model includes the couple due to the acceleration of the weight-bearing hip as well as gravitational perturbations. The exclusive control of A/P balance and posture are the hip extensors and flexors, while in the M/L direction the dominant control is with the hip abductors with very minor adductor involvement. At the ankle the inverted pendulum model sees the COM passing forward along the medial border to the weight-bearing foot. The model predicts that during single support the body is falling forward and being accelerated medially towards the future position of the swing foot. The model predicts an insignificant role of the ankle invertors/evertors in the M/L control. Rather, the future position of the swing foot is the critical variable or more specifically the lateral displacement from the COM at the start of single support. The position is actually under the control of the hip abd/adductors during the previous early swing phase.

The critical importance of the hip abductors/adductors in balance during all phases of standing and walking is now evident. This separate mechanism is important from a neural control perspective and clinically it focuses major attention on therapy and potential problems with some surgical procedures. On the other hand the minuscule role of the ankle invertors/evertors is important to note. Except for the tandem standing position these muscles have negligible involvement in balance control.     

Shared care: a review of the literature

This review examines broad issues of concern regarding the primary/secondarycare interface. The main purpose was to identify areas of goodpractice which could be adapted for more general use. One ofthe most fundamental aspects identified was communication, whichis discussed in some detail. Also covered are shared prescribingand disease management. The data suggest that the most effectivesystem(s) of shared care has yet to be established. Furtherqualitative and economic evaluations are required, taking intoaccount patient preferences. Although the literature does describecertain practice exemplars, it is clear that inter- and intra-professionalcommunication continues to be a problem. Whilst informationtechnology may provide some of the solutions, it is concludedthat a culture change, which compels health professionals tomake sharing of patient information a much higher priority,is reauired. Keywords. Shared care, seamless care, hospital, general practice, family practice.     

Gastroduodenal ulcer. Overview of 150 papers presented before the Southern Surgical Association 1888-1986.

By the early part of this century, members of the Southern Surgical Association as well as others began to realize that gastroenterostomy alone was unacceptable for the treatment of gastric ulcer. Ulcer excision and some type of limited resection was advised. At a later date, gastric resection of varying extent, depending on ulcer size and location, became the appropriate treatment for complications of this disease. For treatment of complications of duodenal ulcer, gastroenterostomy was widely used from the latter part of the 19th century until the late 1930s. Adequate gastric resection slowly but cautiously replaced gastroenterostomy during the 1940s. Vagotomy with drainage and vagotomy with antrectomy slowly developed and replaced adequate resection by the early 1970s. Beginning in the 1970s and extending into the 1980s, fewer duodenal ulcers were seen, and many of those encountered were being adequately managed using the H2 receptor blockers. For the intractable duodenal ulcer there is currently an increasing trend to use the less invasive operation of parietal cell vagotomy. Vagotomy with antrectomy for such cases is being used less frequently. Vagotomy and drainage has lost much of its appeal. Lesser procedures have been advocated recently for treatment of marginal ulcer after incomplete vagotomy irrespective of the original operation for ulcer. Massive bleeding and acute perforation are still frequently encountered as complications but are being seen more frequently in elderly high-risk patients, some of whom will tolerate only a lesser procedure as suture ligation, vagotomy with drainage, or simple ulcer closure. It appears that we are now seeing a different duodenal ulcer pattern in the good-risk patient. The ulcers are usually small, less virulent, and less likely to be found penetrating into the pancreas and adjacent organ structures. As Claude Welch so aptly stated recently before the Association, "We are seeing a trend in ulcer surgery that is currently being seen in other areas of surgical endeavors as well." He emphasized that we must be alert to changing disease patterns and adapt our procedures to new requirements.     

Asbestos-related focal lung masses: manifestations on conventional and high-resolution CT scans

In 260 asbestos-exposed individuals evaluated by means of computed tomography (CT), 43 unsuspected pulmonary masses were found in 27 individuals. The masses included fissural pleural plaques (n = 10), dense fibrotic bands (n = 3), round atelectasis (n = 11), carcinomas (n = 3), and other presumed benign masses (n = 16). The most helpful features in the diagnosis of rounded atelectasis with CT were (a) contiguity to areas of diffuse pleural thickening, (b) a lentiform or wedge-shaped outline, (c) evidence of volume loss in the adjacent lung, and (d) a characteristic "comet tail" of vessels and bronchi sweeping into the margins of the mass. Less advanced areas of focal atelectasis had fewer classic features. Intrafissural pleural plaques were readily identified with high-resolution CT. In asbestos-related masses, the demonstration of stability over time is necessary. Careful interpretation of CT and high-resolution CT features and close surveillance can obviate the need for biopsy in the majority of instances.     

Usefulness of an enzyme-linked immunosorbent assay for detection of Giardia antigen in feces.

The usefulness of a recently developed enzyme-linked immunosorbent assay which detects Giardia lamblia antigen in feces was determined in experimentally infected humans. Giardia antigen was determined in serially collected fecal specimens from humans inoculated with two Giardia isolates, GS/M and Isr. A total of 277 stools from 18 volunteers were tested, 74 from Isr-inoculated volunteers and 203 from GS/M-inoculated volunteers. None of the five Isr-inoculated volunteers became infected, and none of their stools contained Giardia antigen. In contrast, all of the 13 GS/M-inoculated volunteers became infected, and Giardia antigen was present one or more times in the stools of each. Of 203 stools from GS/M-inoculated volunteers, 73 contained Giardia cysts, and 69 of these (94.5%) had detectable antigen. In contrast, 108 of the 203 specimens were positive for Giardia antigen and only 73 had cysts. Most antigen-positive but cyst-negative specimens occurred during treatment, but during patency 71 stools contained antigen and 65 had cysts. The enzyme-linked immunosorbent assay is infections and is easier to perform.     

Interphase cytogenetics using biotin and digoxigenin labelled probes II: Simultaneous differential detection of human and papilloma virus nucleic acids in individual nuclei.

A method was developed for the simultaneous detection of viral and human DNA in contrasting colours in routine formalin fixed, paraffin wax embedded biopsy specimens. This was achieved by non-isotopic in situ hybridisation (NISH) with a biotinylated Y chromosome probe and digoxigenin labelled probe for human papilloma virus type 6 (HPV 6). The tissues studied were peripheral lymphocytes, tonsil, and penile warts. The hybridisation signals produced by biotinylated probes were visualised in red using streptavidin peroxidase and those produced by digoxigenin labelled probes as a blue/black colour using anti-digoxigenin alkaline phosphatase. In lymphocytes and tonsil 95-100% of cells had a detectable Y chromosome; in warts only 60-70% of infected keratinocytes near the skin surface had a demonstrable Y chromosome. This suggests that this chromosome is lost or occluded in cell maturation. In simultaneous double hybridisation with both probes, HPV and Y sequences were demonstrable within the same nucleus in penile warts. This technique permits the simultaneous differential detection of two nuclei acid sequences in interphase nuclei and will have application in analysis of putative dual HPV infections and in determining the intranuclear spatial relations between nucleic acids in interphase nuclei.