Upper ankle joint | Accessory bones

Upper ankle joint

The upper ankle joint often contains an accessory bone. This is the Os trigonum, which is the second most common accessory bone in the foot after the Os tibiale externum of the foot. The Os trigonum lies behind the talus.

The Os trigonum occurs in 3-15% of the population. The Os trigonum develops between the eighth and thirteenth year of life. In girls earlier than in boys.

Often the bone core of the Os trigonum unites with the main bone of the talus. In athletes, in whom injuries to the ankle joint occur more frequently, complaints can emanate from the Os trigonum. One speaks of the Os-trigonum syndrome.

The Os trigonum is located in close proximity to three important ligaments of the ankle joint. If the ligaments are put under heavy strain, the Os trigonum can become irritated. The affected person then usually suffers from a stress-related pain in the area of the outer ankle.

Sometimes the pain is accompanied by a feeling of weakness and stiffness of the joint. As a rule, the Os-trigonum syndrome is treated conservatively. In extreme cases, however, the accessory bone must be surgically removed.


In the spine, or more precisely in the cervical spine, the Os Odontoidum occurs in some people. This bone is a bone nucleus that is not fused to the second cervical vertebra (axis). It represents the vertebral body of the first cervical vertebra.

The os odontoideum is often confused with a fracture. Less than one percent of the population has a cervical rib. It is more common in women than in men.

This cervical rib originates from the seventh cervical vertebra and is connected to the sternum via cartilage or connective tissue. In rare cases, this cervical rib can lead to a cervical rib syndrome, in which compression of nerves in the area of the plexus of the arm and impaired blood circulation in the area of the arm can occur. An additional rib can occur not only in the area of the cervical spine, but also in the lumbar spine.

The lumbar rib is much more common than the cervical rib (in about 8 percent of the population. The lumbar rib usually starts at the first lumbar vertebra, rarely also at the second lumbar vertebra. Sometimes it is only very small, but can also be a complete rib. Lumbar ribs do not cause any symptoms and therefore have no significance for the person affected.