Periosteum, which covers most bones except for the articular surfaces, tendon insertions, and sesamoid bones, is divided into two layers. The outer fibrous layer contains fibroblasts.
The inner cellular layer, also referred to as the cambium (Latin for a change) layer, contains progenitor cells that develop into osteoblasts and chondroblasts. This is the layer that is responsible for forming lamellar bone to increase bone width, and forming woven bone in response to injury.
The periosteum is attached to bone by Sharpey’s fibers, collagen fibers that penetrate the full width of the cortex at sites exposed to high tension forces.
A recent quantitative study Allen and Burr showed that the periosteum of the human femoral neck is predominantly fibrous, with significantly less cellular periosteum than diaphyseal bone. They found mineralizing tissue in the expected location of this cellular layer. This replacement of the cellular layer by mineralization is also found along the diaphyses of long bones as people age.
All of this means that there may be little if any callus formation with femoral neck fractures. This comes into play in assessing post-fixation healing in adults. Contrary to intertrochanteric fractures, which show increasing callus formation and sclerosis with progression of healing, femoral neck fractures show no such association, making radiographic assessment of healing difficult
- Allen MR, Burr DB. Human femoral neck has less cellular periosteum, and more mineralized periosteum, than femoral diaphyseal bone. Bone. 2005 Feb;36(2):311-6.
- Szechinski JW, Grigorian MA, Grainger AJ, Elliott JM, Wischer TK, Peterfy CG, Genant HK. Femoral neck and intertrochanteric fractures: radiographic indicators of fracture healing. Orthopedics. 2002 Dec;25(12):1365-8; discussion 1368.