Articular geometry of the tibia has been studied in relation to the functional axis and extra-articular bone landmarks, using a Cartesian coordinate system. Thirty-one cadaver limbs were used, 26 of them paired. The donor age range was 61 to 89 years (17 females, 14 males), none of whom showed evidence of significant arthritic deterioration. Most linear parameters were greater in males than females (p less than 0.005), and correlations between these parameters were noted, e.g., tibial length versus plateau width (r = 0.7, p less than 0.01) with both genders combined. Gender differences occurred in only two of the angular parameters--tibial torsion (p less than 0.025) and foot rotation (p less than 0.005). For the latter, mean rotation was internal (-5 degrees) for males, and external (11 degrees) for females. No correlations between angular parameters were found. In the paired limbs, there was asymmetrical distribution of just two parameters--varus tilt of the tibial plateau margins (p less than 0.005) and lateral deviation of the tuberosity (p less than 0.025). The data complement a previous report on the femur. These studies are relevant to the kinematics of the lower limb, design and sizing of resurfacing components, and possibly to the pathogenesis of osteoarthritis.

A method is described which provides standardised reproducible radiographic images of the lower limb. Anteroposterior and lateral radiographs are digitised and processed by computer to provide graphic/numeric displays of angles and linear measurements, relating the centre points of the hip, knee, and ankle. Two cases illustrate how surgical planning is facilitated when standardised data are available. These data confirm the close relationship between postoperative limb alignment and positioning of prosthetic elements.

Some arthritic knees with varus deformity show excessive valgus angulation of the femoraijoint surface with proximal tibia vara. This causes a downward and medial inclination of the articular surfaces in the coronal plane. The patients we studied had a medial shift of the standing load-bearing axis, and arthritic changes mainly in the medial compartment. Some also had lateral tibial subluxation with twisting of the distal femur and proximal tibia in opposite directions. We assessed the articular geometry by precise radiographic analysis, and compared the results with those in normal volunteers and a group of osteoarthritic patients. The prevalence of this type of deformity in our osteoarthritic patients was 1 1.5%; its recognition allows the use of specific operative correction that may include double osteotomy or the precise orientation of prosthetic components. Stability of the knee depends upon long-bone alignment, articular surface geometry and the resistance to subluxation provided by ligamentous and capsular structures. Instability may predispose to osteoarthritis (Cooke and Pichora 1985).

A new technique has been devised to investigate the penetration of antibiotics through the gram-negative outer membrane; the application here was to study intrinsic resistance of Escherichia coli K-12. Exponential cells in broth were briefly treated with 2.5 mM ethylenediaminetetraacetic acid at 5°C to disrupt the outer membrane penetration barrier, and the response of treated and untreated cells to antibiotics was compared by turbidimetry. A barrier index was derived to describe the ability of 7 beta-lactam and 10 other antibiotics to penetrate the outer membrane of strain Y10. There was correlation between the molecular weight and logio barrier index (r = 0.59, P = 0.01). The envelope mutant D22 (envA) had low barrier indexes for erythromycin, rifampin, ampicillin, and cloxacillin. For the beta-lactams, outer membrane penetration and affinity for inner membrane target site(s) triggering cell lysis were measured as independent components of the overall activity; although penetration and overall activity varied greatly, the affinities of most were within a narrow range.The limiting layers of the gram-negative cell envelope are the cytoplasmic or inner membrane (IM) and the outer membrane (OM) (29). Between the IM and OM is a murein sacculus within a tenuous space known as the periplasm, which contains a number of wall-associated enzymes (28).The OM is a barrier to molecules above a critical size; in Escherichia coli and Salmonella typhimurium, the penetration of oligopeptides (25) and oligosaccharides (8) declines sharply as the molecular weight exceeds 600, and they are essentially excluded at 1,000. Similarly, there is at least partial exclusion of some antibiotics by the OM contributing to "intrinsic" resistance (12), although in most cases the effect has not been well quantified. According to a popular model, solutes may penetrate the OM through narrow aqueous pores which restrict entry nonspecifically by size, and so provide a molecular sieving function (8). This function involves certain OM proteins which have been called "porins" (14,17,18,19,22).In this paper, we describe a technique which was used to measure the penetration of 17 antibiotics through the OM of E. coli K-12. A preliminary report has been made (30). The OM penetrability barrier was disrupted by brief treatment with ethylenediaminetetraacetic acid (EDTA), and the turbidimetric response of treated and normal cells to antibiotics was then compared over a short period of growth. (There was no adjustment of the external osmotic pressure). In support of the pore model, we found that antibiotic penetration through the OM was limited by molecular weight, and that the limits agreed well with those for oligosaccharides (8). However, it was clear that in some cases other variables must also control penetration.Beta-lactam antibiotics were differentiated with respect to penetration ofthe OM and affinity for the IM target site(s) promoting cell lysis. This gave an insight into the basis for the wide range of activities against E. coli which are encount...

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