Histological study of the developing human femur ORIGINAL ARTICLE Eur. J. Anat. 18 (4): 273-282 (2014) Vidhu Dhawan 1 , Kanchan Kapoor 2 , Mahesh Sharma 2 , Balbir Singh 3 , Alka Sehgal 4 and Suman Kochhar 5 1 Dept. of Anatomy, All India Institute of Medical Sciences, New Delhi, India, 2 Dept. of Anatomy, Govt. Medical College & Hospital, Chandigarh, India, 3 Chattisgarh Ayush & Health Sciences University, Raipur, India, 4 Dept. of Obstetrics & Gynecology, Govt. Medical College & Hospital, Chandigarh, India, 5 Dept. Of Radiodiagnosis, Govt. Medical College & Hospital, Chandigarh, India SUMMARY The development of the long bones at various gestational ages in the fetus has always been a subject of interest for many clinicians. Some mor- phometric parameters such as length, etc., are considered standard parameters for evaluation of the gestational age of the fetus. However, not much emphasis is laid upon morphometric param- eters to assess the histological changes in these age groups. Therefore, the present study was undertaken to determine the histological changes occurring in a developing bone. 30 fetuses sent to the Dept. of Anatomy for routine fetal autopsy by the Dept. of Obstetrics and Gynaecology were selected for the microscopic study of the femur. Left femora were extracted, and transverse and longitudinal sections were taken and stained with hematoxylin and eosin. The epiphysis of the growing bone exhibited the formation and prolifer- ation of different zones in different age groups. The formation and distribution of distinct cartilage canals has been evidenced as early as 13 +2 weeks of gestation in the growing epiphysis. The appearance of a secondary centre of ossification in the distal femoral epiphysis was observed as early as 28 +4 weeks. The diaphysis showed the formation of a cancellous bone with increasing trabeculae proliferating more on one side of the shaft. The above observations are discussed in the light of available literature. Key words: Femur – Developing bone – Cartilage canals – Secondary ossification centre INTRODUCTION Endochondral ossification is the process by which the embryonic cartilaginous model of most bones contributes to longitudinal growth and is gradually replaced by bone (Mackie et al., 2008). During normal endochondral ossification, the entire femur initially forms an avascular cartilaginous an- lage at about the seventh week of gestation. At this stage no osteoblasts are produced by the cells in the chondrogenic layer of the developing peri- chondrium surrounding the cartilage model, be- cause differentiation is taking place in an avascular environment (Hamilton et al., 1972; Burkus et al., 1993). The endochondral bone development de- pends upon neovascularization, and an early gen- eration of vascularized cartilage canals is an initial event which precedes the formation of a second- ary centre of ossification (Blumer et al., 2008). Cartilage canals are described as tubes of vascu- larized mesenchyme containing proliferating blood vessels and perivascular cells invading the epiphy- sis from the perichondrium (Blumer et al., 2005, 2006). The literature stated previously contains several hypotheses regarding the mode of formation of cartilage canals. These perichondral invaginations of blood vessels and connective tissue have been found within the epiphysis prior to the appearance of a secondary centre of ossification in avian (Lutfi, 1970; Blumer et al., 2004a,b, 2005, 2006, 2007; Eslaminejad et al., 2006) and most mammalian 273 Submitted: 12 December, 2013. Accepted: 24 March, 2014. Corresponding author: Dr. Vidhu Dhawan, Senior Resident, Room No. 1026, Dept. of Anatomy, All India Institute of Medi- cal Sciences, Ansari Nagar, New Delhi-110029 , India. Tel: 917838257119. E-mail: vidhu.dr@gmail.com