Predicting postoperative urinary retention after lower limb arthroplasty.

A simple scoring system that enables surgeons to make an estimation of the likelihood of postoperative urinary retention (POUR) in patients undergoing lower limb total joint replacement would be a useful one. This would enable selection of high risk patients who merit pre-operative catheterisation in a clean theatre environment rather than risking urinary retention and its associated complications late at night on the ward by junior, inexperienced staff. The International Prostate Symptom Score (IPSS) is such a scoring system and we assessed its reliability in predicting those male patients likely to go into POUR. We selected all male patients undergoing lower limb total joint arthroplasty under spinal anaesthesia and calculated their IPSS. We found a statistically significant increase in the likelihood of POUR as IPSS rises (p = 0.0002). We concluded that the IPSS is a quick and easy method of predicting those at risk of POUR, allowing them to be catheterised prophylactically, preventing possible complications.

Condyloma acuminatum-like lesion of the urinary bladder progressing to invasive spindle cell carcinoma.

Condyloma acuminata of the urinary bladder is a rare finding, particularly in the absence of similar lesions of the external genitalia. We present a case in which an isolated condyloma acuminatum-like lesion rapidly progressed to a poorly differentiated spindle cell carcinoma, underlying the need for careful endoscopic follow-up of patients with such lesions.

Failure of detection of pneumothorax on initial chest radiograph.

Failure to detect a pneumothorax may have serious complications. A case of a pneumothorax, which may have been overlooked if thoracic computed tomography had not been performed, is discussed.

Experimental investigation of the distribution of residual strains in the artery wall.

Arterial wall stresses are thought to be a major determinant of vascular remodeling both during normal growth and throughout the development of occlusive vascular disease. A completely physiologic mechanical model of the arterial wall should account not only for its residual strains but also for its structural nonhomogeneity. It is known that each layer of the artery wall possesses different mechanical properties, but the distribution of residual strain among the different mechanical components, and thus the true zero stress state, remain unknown. In this study, two different sets of experiments were carried out in order to determine the distribution of residual strains in artery walls, and thus the true zero stress state. In the first, collagen and elastin were selectively eliminated by chemical methods and smooth muscle cells were destroyed by freezing. Dissolving elastin provoked a decrease in the opening angle, while dissolving collagen and destroying smooth muscle cells had no effect. In the second, different wall layers of bovine carotid arteries were removed from the exterior or luminal surfaces by lathing or drilling frozen specimens, and then allowing the frozen material to thaw before measuring residual strain. Lathing material away from the outer surface caused the opening angle of the remaining inner layers to increase. Drilling material from the inside caused the opening angle of the remaining outer layers to decrease. Mechanical nonhomogeneity, including the distribution of residual strains, should thus be considered as an important factor in determining the distribution of stress in the artery wall and the configuration of the true zero stress state.

The effect of age on residual strain in the rat aorta.

Residual stress is observed in many parts of the cardiovascular system and is thought to reduce transmural stress gradients due to intravascular pressure. Its development is closely associated with normal growth and pathological remodeling, although there appear to be few previous reports of the relationship between aging and residual stress. We have estimated residual strain (an indicator of the magnitude of residual stress) at ten sites along the aorta of rats aged 2.5 to 56 weeks by measuring the degree to which rings of vessel spring open when cut (opening angle). At all ages the opening angle decreased along the aorta, reaching a minimum near the renal arteries and increasing toward the aorto-iliac bifurcation, a result that confirms previous studies. During growth, although the unloaded circumference of the aorta increased steadily, the wall thickness and medial surface area fell to a minimum at the age of 6 weeks before continuing a steady increase. Similarly, the opening angle decreased between the ages of 2.5 and 6 weeks, thereafter increasing with age. In the abdominal aorta, a strong correlation between opening angle and wall thickness relative to midwall radius (h/R) was seen; whereas in the thoracic segment, in which no increase in h/R with age occurred, no such relationship was found. These observations are in keeping with a recently proposed hypothesis that residual stress will change in response to growth-related changes in vessel geometry driven by a tendency to minimize the nonuniform stress distribution inevitably found in pressurized thick-walled cylinders.

Toddler's fracture.

"Toddler's fracture" can be difficult to diagnose but should be suspected whenever a child presents to the accident and emergency department with a limp or fails to bear weight on the leg. Irritable hip and subacute osteomyelitis must feature in the differential diagnosis. The history may or may not include an obvious traumatic episode. Rather than fracture, elastic bowing of the bone and consequent periosteal stripping may explain symptoms in some cases.

Analysis of the strain and stress distribution in the wall of the developing and mature rat aorta.

The variation of wall stress distribution with age in the thoracic and abdominal aortas of normotensive rats was studied. Dimensions of the zero-stress configurations were measured at the ages of 4, 8, 12, 20, and 52 weeks. Using data from previously published inflation tests, the circumferential stress-strain relationship was obtained in each age group. The calculated stress distribution showed that the average circumferential stress remained practically constant after the age of 20 weeks. The circumferential stress at the innermost part of the arterial wall was greater than the stress at the outermost part, but the difference was maintained at a moderate level with adjustments in the zero-stress configuration. It is speculated that, after the age of 20 weeks, changes in arterial geometry and rheological properties tend to maintain a constant stress distribution under varying conditions of loading. This distribution was achieved by enhanced growth at the inner part of the media in comparison with the growth at its outer margins and suggests that during development and maturity, the growth of the aorta is modulated by circumferential stress.