Reproducible radiographs of acetabular prostheses. A method assessed in 35 patients

Radiology's Achilles' heel: error and variation in the interpretation of the Röntgen image

The performance of the human eye and brain has failed to keep pace with the enormous technical progress in the first full century of radiology. Errors and variations in interpretation now represent the weakest aspect of clinical imaging. Those interpretations which differ from the consensus view of a panel of "experts" may be regarded as errors; where experts fail to achieve consensus, differing reports are regarded as "observer variation". Errors arise from poor technique, failures of perception, lack of knowledge and misjudgments. Observer variation is substantial and should be taken into account when different diagnostic methods are compared; in many cases the difference between observers outweighs the difference between techniques. Strategies for reducing error include attention to viewing conditions, training of the observers, availability of previous films and relevant clinical data, dual or multiple reporting, standardization of terminology and report format, and assistance from computers. Digital acquisition and display will probably not affect observer variation but the performance of radiologists, as measured by receiver operating characteristic (ROC) analysis, may be improved by computer-directed search for specific image features. Other current developments show that where image features can be comprehensively described, computer analysis can replace the perception function of the observer, whilst the function of interpretation can in some cases be performed better by artificial neural networks. However, computer-assisted diagnosis is still in its infancy and complete replacement of the human observer is as yet a remote possibility.

Different effects of phagocytosable particles during bone formation versus remodeling

Previously, small phagocytosable particles of high density polyethylene (HDPE) but not Ti6-Al4-V alloy, at a concentration of 10(8) particles/mL inhibited net bone formation in vivo after 3 weeks in the bone harvest chamber (BHC). These findings reflected the effects of particles during the phase of bone ingrowth. In this study, we tested whether these effects persisted or were different during the phase of bone maturation and remodeling. BHCs were bilaterally implanted in mature male NZW rabbits. After a 6-week period for osseointegration, the contents of the chamber were harvested and discarded. One percent sodium hyaluronate, the carrier, was then placed within the canal of the chambers bilaterally and the tissue within the chambers was harvested 3 weeks later. HDPE particles were then inserted unilaterally for a 3-week period, followed by Ti6-Al4-V for 3 weeks, HDPE for 6 weeks, and Ti6-Al4-V for 6 weeks. The side chosen for each treatment was switched consecutively; the nonimplanted, contralateral chamber served as a control. At 3 weeks the control treatments yielded trabeculae of woven bone in a fibrovascular stroma. By 6 weeks, the peripheral trabeculae were thicker, and a central marrow cavity was developing. Bone ingrowth was less with HDPE particles at 3 and 6 weeks compared to controls. Ti6-Al4-V particles did not inhibit bone ingrowth at 3 weeks but showed a trend at 6 weeks. The characteristics of particles affect the differentiation, maturation, and remodeling of mesenchymal tissue differently.

Intermittent micromotion and polyethylene particles inhibit bone ingrowth into titanium chambers in rabbits

We performed a histomorphological and morphometric analysis of the effects of short daily periods of micromotion and phagocytosable particles of high density polyethylene (PE) on bone ingrowth into a 1 x 1 x 5 mm canal within a titanium chamber in rabbits. The micromotion chamber (MC) was implanted in the tibia of nine mature New Zealand white rabbits. After osseointegration and first harvest of tissue, 40 micromotions (amplitude = 0.5 mm) were applied daily at a rate of 1 Hz for a 3-week period. The tissue within the chamber was then harvested. For the second treatment, PE particles (10(8)/mL) were placed within the canal. The tissue in the chamber was harvested 3 weeks later. The next treatment was a 3-week rest period, in which neither micromotion nor particles were utilized; a harvest followed. The final treatment combined PE particles and micromotion, followed by a harvest 3 weeks later. Sections from control harvests contained extensive trabecular bone arranged longitudinally throughout the canal in a fibrovascular stroma. Micromotion produced longitudinally oriented fibrous tissue within the chamber. PE particles were associated with macrophages, surrounding and engulfing the birefringent particles. The combination of particles and micromotion produced a fibrous stroma laden with macrophages. PE particles and micromotion, alone or together, produced a similar effect in inhibiting bone ingrowth, compared to nonmoved chambers without particles. In this short-term experiment, no additive or potentiating effect of these two stimuli could be demonstrated.