A newly described hereditary cartilage debonding syndrome

Wnts' fashion statement: from body stature to dysplasia

Bone is constantly being made and remodeled to maintain bone volume and calcium homeostasis. Even small changes in the dosage, location and duration of int/Wingless (Wnt) signaling affect skeletal development and homeostasis. Wnt/β-catenin signaling controls cell fate determination, proliferation and survival by affecting a balance between bone-forming osteoblast and bone-resorbing osteoclast cell differentiation. During early skeletal development, Wnt/β-catenin signaling is required in directing mesenchymal progenitor cells toward the osteoblast lineage. Later, Wnt/β-catenin in chondrocytes of the growth plate promotes chondrocyte survival, hypertrophic differentiation and endochondral ossification. Gain- or loss-of-function mutations in the Wnt signaling components are causally linked to high or low bone mass in mice and humans. Inactivation of Wnt/β-catenin signaling leads to imbalance between bone formation and resorption because of accelerated osteoclastogenesis due to decline in the levels of osteoprotegerin (OPG) secreted by osteoblasts or directly via Frizzled 8 (Fzd8). In this review, we provide a landscape of the Wnt pathway components in influencing progenitor cell differentiation toward osteoblasts or osteoclasts under physiological conditions as well as pathological disorders resulting in various skeletal dysplasia syndromes.

Imaging of cartilage and osteochondral injuries: a case-based review

Current high-field magnetic resonance imaging (MRI) techniques provide a sensitive and reliable diagnostic tool for the evaluation of cartilage and osteochondral injury. This article summarizes technical factors for optimal MRI evaluation of articular cartilage of the knee. There is emphasis on the important correlation of the MRI signal to the structure of the type II collagen matrix in normal cartilage, with an understanding that alterations in this signal pattern can be an important sign of cartilage injury. Finally, specific patterns of cartilage injury and application of MRI in evaluating cartilage repair are illustrated through a series of selected cases.