This research examined developmental continuity between "cruising" (moving sideways holding onto furniture for support) and walking. Because cruising and walking involve locomotion in an upright posture, researchers have assumed that cruising is functionally related to walking. Study 1 showed that most infants crawl and cruise concurrently prior to walking, amassing several weeks of experience with both skills. Study 2 showed that cruising infants perceive affordances for locomotion over an adjustable gap in a handrail used for manual support, but despite weeks of cruising experience, cruisers are largely oblivious to the dangers of gaps in the floor beneath their feet. Study 3 replicated the floor-gap findings for infants taking their first independent walking steps, and showed that new walkers also misperceive affordances for locomoting between gaps in a handrail. The findings suggest that weeks of cruising do not teach infants a basic fact about walking: the necessity of a floor to support their body. Moreover, this research demonstrated that developmental milestones that are temporally contiguous and structurally similar might have important functional discontinuities. Keywords crawling; cruising; walking; locomotion; developmental continuity Developmental ContinuityThe question of developmental continuity-"Where do new skills come from?"-is a central and long-standing issue in developmental psychology. Proponents of developmental continuity claim that new skills grow from the seeds of prior accomplishments. One line of evidence that old and new skills are related is adjacent temporal ordering, where a new skill appears in the footsteps of its predecessor or as one skill disappears another quickly appears on the scene. A second line of evidence is physical similarity, where old and new skills are similar in form or map onto each other structurally. The most important line of evidence is shared psychological function, where the earlier and later appearing skills rely on the same underlying psychological mechanisms to accomplish the same goals. In this case, experience

The repair of diseased or damaged cartilage remains one of the most challenging problems of musculoskeletal medicine. Tissue engineering advances in cartilage repair have utilized autologous and allogenic chondrocyte and cartilage grafts, biomaterial scaffolds, growth factors, stem cells, and genetic engineering. The mesenchymal stem cell has specifically attracted much attention because of its accessibility, potential for differentiation, and manipulability to modern molecular, tissue and genetic engineering techniques. Mesenchymal stem cells provide invaluable tools for the study of tissue repair when combined with a carrier vehicle/matrix scaffold, and/or bioactive growth factors. However, an underappreciated source of knowledge lies in the relationship between fetal development and adult tissue repair. The multitude of events that take place during fetal development which lead from stem cell to functional tissue are poorly understood. A more thorough understanding of the events of development as they pertain to cartilage organogenesis may help elucidate some of the unknowns of adult tissue repair.

Symptomatic articular cartilage lesions have gained attention and clinical interest in recent years and can be difficult to treat. Historically, various biologic surgical treatment options have yielded inconsistent results because of the inferior biomechanical properties associated with a variable healing response. Improving technology and surgical advances has generated considerable research in cartilage resurfacing and optimizing hyaline tissue restoration. Biologic innovation and tissue engineering in cartilage repair have used matrix scaffolds, autologous and allogenic chondrocytes, cartilage grafts, growth factors, stem cells, and genetic engineering. Numerous evolving technologies and surgical approaches have been introduced into the clinical setting. This review will discuss the basic science, surgical techniques, and clinical outcomes of novel synthetic materials and scaffolds for articular cartilage repair.

Background The importance of the radial head to elbow function and stability is increasingly apparent. Although preservation of the native radial head is preferred, severely comminuted fractures may necessitate resection or arthroplasty. Silastic radial head arthroplasty has been condemned on the basis of several sporadic reports of silicone synovitis. However, problems of ''overstuffing,'' cartilage wear, and motion loss are becoming apparent with metal prostheses, indicating this also is not an ideal solution. Thus, the choices remain controversial. Questions/purposes We asked whether intact or reconstructed primary elbow stabilizers permit use of silastic radial head implants without fragmentation, failure, and silicone synovitis. Methods We retrospectively reviewed 23 patients with unreconstructable radial head fractures who were treated with silastic radial head arthroplasty and concomitant repair and/or reconstruction of the medial ulnar collateral ligament and/or lateral ulnar collateral ligament. Analysis included range of motion, pain, stability, and radiographic assessments; Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire; and Mayo Elbow Performance Score (MEPS). The minimum followup was 16 months (average, 69.6 months; range, 16-165 months). Results At last followup, the mean elbow flexion was 145°, extension 11°, supination 80°, and pronation 83°. The mean MEPS score was 88.9. The mean DASH score was 11.8. There were eight reoperations, none resulting from failure of the radial head implants. Conclusions These results demonstrate silastic radial heads can be used with low complication rates and without evidence of synovitis when concomitant elbow ligament repair or reconstruction is performed.

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