The joint between the attachment of the 8th and 9th rib with the 7th rib is a synovial joint.
Most of the joints in the thoracic cavity- interchondral , sternocostal , costovertebral and costotransverse joints , are plain synovial joints because the thoracic cavity needs to expand during inspiration.
The exception are :-
• 1st sternocostal joint - Synarthrosis ( fibrous)
• Interchondral joint between the 9th and 10th cartilages is never synovial and sometimes absent .
• Costochondral joints are primary cartilagenous joints ( synchondrosis)
• Midline joints like manubriosternal and xiphisternal joints are secondary cartilagenous joints of symphysis type.