Table 2.
Summary of the timing of key events observed during development of the knee joint and associated structures
| HH28 | HH30 | HH32 | HH34 | |
|---|---|---|---|---|
| Cartilage | ||||
| Knee region | Position of future knee joint discernible *indication of lateral condyle of femur at HH29 | Initial protrusion of future cranial cnemial crest | Appearance of medial condyle of femur apparent | Mature 3D shape of knee joint |
| Other joints | 1st appearance of MTP joint of 3rd digit | Appearance of IP joint in digits III & IV, MTP joint of digit II. condensation of digit I | Appearance of 1st joint in digit 1 | Bicondylar surface on MTP, joint digit 3 |
| Bone | Ossification of femur | |||
| Cavity formation | Interzone identified as region with higher cell density | Cells within interzone are orientated parallel to joint surface | 3 layers at forming interzone | Cavity formation underway |
| Capsule (α1 ColXI) | Expression localized to condensing anlagen (similar to Alcian blue at this stage) | Encapsulates knee from the cranial cnemial crest to the dorsal thigh muscle masses | α1 ColXI expression is increasingly localized,forming a thin membrane surrounding joint | |
| Muscle | Separation of thigh and shank masses. Indication of further subdivision in thigh | Separation of foot from shank. Separation of muscle blocks in thigh | Full complement of thigh muscle blocks | |
| Tendon | Broad expression in the 3 regions (knee, ankle, foot), 3 structures in digital region | Localization to presumptive tendons proximally with broader pattern in the foot | Well-defined tendons | |