Arthritis and osteoarthritis - Patterns of joint involvement
Do you know the characteristic patterns of joint involvement in different arthritic diseases?
We’ll be showing you just that in part 3 of our Chalk Talk series on arthritis and
osteoarthritis. Knowing the patterns is quite helpful in pinpointing the type of arthritis.
To first illustrate the patterns of joint involvement, we’ve marked the most important
joints in this image:
The shoulder girdle consists of the sternoclavicular joint, the acromioclavicular joint, and the
glenohumeral joint. The arm comprises the elbow, wrist, as well
as the finger joints. Let’s take a detailed look at the fingers as knowledge of the anatomy
of the joints is important for the differential diagnosis.
Each finger consists of metacarpophalangeal joints, which are separated from the proximal
interphalangeal joints and the distal interphalangeal joints. These are easy to remember as an acronym:
The distal interphalangeal joint as DIP, the proximal interphalangeal joint as PIP, and
the metacarpophalangeal joint as MCP. The MCP joint of the thumb is also termed the
1st metacarpophalangeal joint and needs to be clearly differentiated from the carpometacarpal
joint, which connects the thumb to the carpal bones. In contrast to the fingers, the thumb
has one interphalangeal joint.
The individual vertebrae of the spine are connected by small facet joints. On each side
of the lower spine are the sacroiliac joints, in short, SIJ.
The lower limb consists of the hip joint, knee joint, as well as the upper ankle joint.
We can also see the joints of the foot: The metatarsophalangeal joints, or in short MTP,
the PIP joints, which are located between the proximal and intermediate phalanges, and
the DIP joints, which are located between the intermediate and distal phalanges. Let’s
not forget the two joints of the big toe. The first MTP joint is located between the
metatarsal bone and the proximal phalanx, whereas the interphalangeal joint of the big
toe is located between the distal and proximal phalanges.
Well, this may seem somewhat overwhelming at first; but we’ll be taking a gradual
approach in explaining their significance in arthritic disorders.
Now let’s move on to the most important guiding principles used in classifying the
distribution patterns and the number of joints affected.
Let’s first look at the differences between large and small joints. Large joints include
the glenohumeral joint, elbow, hip joint, knee, and ankle. These large joints can be
differentiated from small joints, namely the joints of the fingers and toes. The wrist
is also made up of several small component joints and is considered a small joint.
In addition to differentiating joints into small and large joints, another means is to
look at whether the joints of the body axis or the extremities are affected, that is if
there is axial or peripheral joint involvement. Axial joint involvement affects the spine
or sacroiliac joints, whereas peripheral joint involvement affects the joints of the arms
and legs.
An important aspect to consider when determining the pattern of joint involvement is whether
it is symmetric or asymmetric, or, in more specific terms, whether there’s bilateral
involvement of the same or different joints. For example, bilateral small joint involvement
of the hand is considered symmetric. By the way, the MCP and PIP joints of the same digits
on both hands aren’t necessarily in an identical distribution, resulting in a mirror-image
effect. Symmetric involvement is also found in bilateral involvement of the MCP and PIP
joints, which affects different digits. Let’s take a detailed look using this example: Here
we can see that the MCP joints of digits 2 to 4 are affected and represents symmetric
involvement. The PIP joint of digit 2 on the left and the PIP joint of digit 3 on the right
are also affected. Despite this pattern of joint involvement, it’s still considered
symmetric.
In contrast, the pattern of joint involvement in different digits is asymmetric, as shown
here. The second and fourth digits are affected in the left image, whereas only the fifth
digit is affected in the image on the right. Each pattern of joint involvement indicates
a different condition.
As well as determining the distribution pattern, another aspect to consider is whether the
upper or lower extremities are involved.
Finally, let’s look at the number of joints involved. Single joint involvement is termed
monoarthritis. If two to four joints are involved, it’s defined as oligoarthritis, which is
derived from the Greek word ‘oligos’ meaning few. The involvement of at least five joints
is termed polyarthritis.
However, the number of joints involved should also be considered in the disease course,
as the number of affected joints can increase gradually. So, it’s important to remember
that oligoarthritis can begin as monoarthritis, and polyarthritis can develop from monoarthritis
or oligoarthritis. Though, it has proven to be useful to classify the conditions according
to whether they occur as monoarthritis, polyarthritis, or oligoarthritis. We’ll be taking a detailed
look at this classification in the next episode. But for now, it’s time for the quiz.