Bones, joints and muscles

Where you are

You have traced a skin finding from the surface into deeper tissues. Now identify the structures that support the body and produce movement. A musculoskeletal record may name a bone, a joint, a muscle, or a connecting tissue. Those names should lead to different questions.

Draw a simple chain: muscle, tendon, bone, joint, bone. Add a ligament connecting the bones near the joint. You will refine this relationship map as you read. It is a learning sketch, not a surgical diagram.

Bone is living tissue

Bone provides support and protection, works with muscles to produce movement, stores minerals, and contains marrow involved in blood-cell formation. It has a blood supply and remodels in response to changing demands. The skeleton is more than an inert frame. [anatomy-bone]

Connect each function to a location. The skull protects the brain. The vertebral column surrounds the spinal cord. The ribs help protect organs in the chest. A limb bone also acts as part of a lever system when muscles contract. [anatomy-bone]

For coding preparation, knowing the general region is only a start. A report may specify one bone and a particular portion of it. Preserve both. “Wrist region” and “distal radius” do not provide the same anatomical detail.

Build a map of the limbs

In the upper limb, learn humerus, radius, ulna, carpals, metacarpals, and phalanges. In the lower limb, learn femur, tibia, fibula, patella, tarsals, metatarsals, and phalanges. The pectoral girdle includes the clavicle and scapula; the pelvic girdle connects the lower limbs with the trunk. [anatomy-limbs]

Use two notebook routes. For the arm, move from upper arm to forearm to wrist to hand. For the leg, move from thigh to lower leg to ankle region to foot. Add the correct names after you can explain the plain-language route.

Notice the similar hand and foot terms: metacarpals and metatarsals are not the same structures. Phalanges appear in both routes, so the full documentation must tell you which digit and limb are involved. A familiar word can still be incomplete information.

A joint has several parts

An articulation is where bones meet. Joints differ in how much movement they allow. In a freely movable synovial joint, articular cartilage covers the opposing bone surfaces, a capsule encloses the joint, and the synovial membrane produces lubricating fluid in the joint cavity. [anatomy-joints]

This explains why “joint problem” is broad. The record may concern a bone surface, cartilage, a capsule, or another supporting structure. Read the specific structure named in the assessment and procedure report.

On your sketch, label the space between the bones as the joint cavity. Put cartilage on the meeting surfaces. Add the capsule around them. Explain the difference between a tissue covering a surface and a fluid occupying a space.

Tendons and ligaments have different connections

A tendon connects muscle to bone. A ligament connects bones and helps stabilize a joint. These connections explain a useful injury distinction: a sprain involves ligament injury; a strain involves muscle, its junction with a tendon, or the tendon. [injury-niams]

The terms are close in spelling but not interchangeable. A record documenting a tendon strain should not be converted into a ligament sprain because both occurred near the same joint. Identify the tissue first, then the documented injury.

Tendinitis refers to tendon inflammation. Bursitis involves inflammation of a bursa, a small fluid-filled cushioning sac near moving structures. These are additional reasons to avoid reducing every painful movement to “a muscle injury.” [injury-niams]

Muscle types fit different jobs

Skeletal muscle produces skeletal movement and is generally under voluntary control. Smooth muscle occurs in walls of hollow organs, including parts of the digestive and urinary systems. Cardiac muscle makes up the muscular wall of the heart. Smooth and cardiac contraction are involuntary. [anatomy-muscle-types]

You will meet smooth and cardiac muscle again in the organ-system lessons. Here, connect skeletal muscle to the tendon-and-bone route. A procedure on a tendon is not automatically a procedure on the muscle belly, even though the structures work together.

Fracture and dislocation describe different problems

A fracture is a broken bone. A dislocation describes complete separation of the bones forming a joint. A sprain or strain concerns different tissues. An injury mechanism may raise several possibilities, but the documented assessment must establish which applies. [injury-niams; osteoporosis-niams]

Osteoporosis weakens bone and increases fracture risk. That relationship is useful background, but an older person's fracture does not by itself document osteoporosis or settle the classification of the fracture. Read the clinical diagnosis and apply the relevant coding instructions. [osteoporosis-niams]

As you approach the injury-coding lesson, prepare a detail list: exact structure, side, location within the structure, documented injury type, and phase of care. Later instructions will show how those details determine the complete entry and required characters.

Worked example: a similar-sounding substitution

Original fictional outpatient excerpt, August 24, 2026: the assessment documents a left forearm muscle strain after lifting. The examination records painful movement. The excerpt does not establish a fracture, joint dislocation, or ligament sprain.

Underline muscle and strain together. Identify the side and region. Do not replace the assessment with “sprain” merely because that word is more familiar. Do not code a fracture because the lifting event could have caused one in a different patient.

For an outpatient diagnosis exercise, use the documented certainty and verify the candidate through the index and Tabular List. If the classification asks for a more specific muscle or region, inspect the complete record rather than supplying a guess. [icd-guidelines, I.B.1; IV.F–H]

Now change the assessment to a documented ligament sprain. The key difference is the injured connecting tissue. Your anatomy map should make that change understandable before you search for a code.

Book drill

Locate index routes for a documented muscle strain and a ligament sprain. Compare the categories and the details needed to verify complete entries. Record the tissue, region, and side separately for each route.

Then find a named limb bone in an anatomy reference. Point to its proximal and distal portions on your notebook map. Explain why a location within a bone can be more specific than the nearest familiar joint name.

Common traps

Do not exchange tendon and ligament. Do not exchange sprain and strain. Do not confuse a joint space with a bone. Do not turn a risk factor into a documented diagnosis. Keep a specific anatomical name when the record supplies it.

Practice

1. Which connecting tissue joins muscle to bone?

2. Does a ligament injury fit the sprain or strain distinction?

3. Why is “metacarpal” different from “metatarsal” in a record?

Compare your reasoning

1. A tendon. 2. Sprain concerns a ligament; strain concerns muscle or tendon structures. 3. The words identify different hand and foot bones, so substituting one changes the anatomical site.

Checkpoint

Complete the muscle-to-bone-to-joint sketch. Explain sprain, strain, fracture and dislocation as distinct concepts. For the fictional record, identify the supported diagnosis and three alternatives that the excerpt does not establish.

Sources

1. NIH/NCI SEER — Introduction to the Skeletal System. accessed 2026. Accessed 2026-09-10.
2. NIH/NCI SEER — Articulations. accessed 2026. Accessed 2026-09-10.
3. NIH/NCI SEER — Appendicular Skeleton. accessed 2026. Accessed 2026-09-10.
4. NIH/NCI SEER — Muscle Types. accessed 2026. Accessed 2026-09-10.
5. NIH/NIAMS — Sports Injuries. accessed 2026. Accessed 2026-09-10.
6. NIH/NIAMS — Osteoporosis. accessed 2026. Accessed 2026-09-10.
7. CDC/NCHS and CMS — ICD-10-CM April 1 2026 Guidelines. FY2026 April. Accessed 2026-09-10.