X-ray dissection of normal joints
Joint cavity
The joint space shown on X-ray is actually composed of three parts: joint cartilage, inter-articular fibrochondrite, and true joint cavity, so the x-ray shows that the joint space is wider than the actual one. In general, articular cartilage and inter-articular fibrochondrite are not visualized, and can only be shown after MRI or calcification of cartilage.
The joint space varies with age and generally narrows with age. The joint space in childhood is wider than in adults due to the presence of epiphyseal cartilage.
Articular surfaces
Because the articular cartilage is not visualized, the joint surface on the x-ray is the bony cortex at the end of the bone. The bony cortex is thin and dense, with smooth edges.
Synovial membrane
The inner tissues of the joint capsule. There is also a synovial sac attached to the knee and shoulder joints that are susceptible to friction, and they are not shown on X-rays. May be shown when the synovial membrane is swollen and the joint effusion is present.
ligament
The outer layer of the joint capsule is made up of dense fibrous tissue. Ligaments near the knee, hip and ankle are developed.
Anatomically the joint can be divided into:
(1) movable joints (such as knee joints);
(2) Oligomotic joints (such as intervertebral joints);
(3) Immovable joints (such as the cranial suture of the skull).
The anatomical classification of the joints is shown in the figure below.
An example of a normal joint is shown in the picture below.
Sequence of routine imaging analyses of joint lesions
(1) Whether there are abnormalities in the alignment of the bones that make up the joint, and the joints on both sides are compared with each other.
(2) Whether there are abnormalities in the epiphyseal and bone ends that make up the joint.
(3) Whether the joint space is widened or narrowed, and whether there is a free body inside it.
(4) Whether the joint surface is complete, whether there is hyperplasia, hardening, bone sparring or destruction.
(5) Whether the joint capsule and the surrounding soft tissues are swollen or not, and the ligaments are not calcified.
(6) If necessary, MRI examination may be performed to diagnose whether the meniscal is torn or congenital malformations.
The normal width of each joint in adults seen on x-rays is shown in the table below.
The values in the above table are for reference only, and to find that the joint space is narrowed, a comparative method can generally be taken:
(1) Comparison with the same age or the joint space of the same name.
(2) Comparison of the joint space of the same name on both sides.
(3) Before and after comparison during the tracing process.
(4) Comparison with adjacent joint space.
If a patient has taken several joint x-rays, reference may also be made to adjacent joint spaces.
The joint space of the upper extremities from the shoulder joint to the interphalangeal joint gradually narrows. The elbow is 1 mm narrower than the shoulder joint, and the elbow joint, wrist joint, metacarpophalangeal joint and interphalangeal joint are gradually reduced by 0.5 mm.
The lower limbs are the widest, sometimes 0.5 to 1.0 times wider than the hip joint, the hip joint is 1 mm wider than the ankle joint, the ankle joint is 1 mm wider than the metatarsal, metatarsophalangeal joint and proximal interphalangeal joint, and the distal inter-toe joint is slightly wider than the proximal interphalangeal joint.
Source: Panda Radiation