Musculoskeletal System

Skeletal system, bony skeleton

The skeletal system (systema skeletal in Nomina Anatomica) includes bones and cartilage. The bony skeleton includes bones only. The vertebral column is part of the skeletal system, and includes the intervertebral discs (fibrocartilage). Individual vertebrae are part of the bony skeleton.

In ordinary usage, bone combines the meanings bone organ and bone tissue.

The 5 anatomical concepts related to bone are:

1. 3138006 |Bone (tissue) structure (body structure)|. Tissue type that makes up bones; a quantity of regular connective tissue consisting of osteocytes and related cells, the intercellular matrix of which is ossified; or any part thereof.
2. 90780006 |Entire bone (organ) (body structure)|. Individual bones, e.g. femur, tibia, ulna, scaphoid, lunate. An organ with cavitated parts; consists primarily of compact (cortical) and cancellous bone surrounding bone marrow cavities; also includes periosteum, endosteum (and, according to FMA, articular cartilage).
3. 118966000 |Skeletal system subdivision (body structure)|. Groups of bones, e.g. spine, skull, bony pelvis.
4. 128530007 |Entire bony skeleton (body structure)|. Pars ossea systematis skeletalis, bone part of the skeletal system.
5. 113192009 |Skeletal system structure (body structure)|. Entire skeletal system, including bones and cartilage.

Bone (tissue) is part of entire bone (organ); entire bone (organ) is part of skeletal system subdivision (system); skeletal system subdivision (system) is part of entire bony skeleton (body structure); and entire bony skeleton (body structure) is part of skeletal system structure (body structure). We can use Entire bone (system) to define aggregate concepts that involve bones.

Non-ossified bone  

Bone organs are composed primarily of bone tissue, but there are some non-ossified parts. In particular, periosteum is clearly a part of a bone organ, but is not ossified tissue.

Bone marrow, marrow cavity

Bone marrow is contained within the marrow cavity, but it is not part of the bone organ. The (empty) marrow cavity is part of the bone organ. The bone marrow structure (body structure) is not a subtype of Bone structure (body structure).

Clinically, marrow disorders are not usually considered bone disorders, nor are marrow procedures considered bone procedures.

For example,

• • Bone marrow disorders are not musculoskeletal disorders, but bone disorders are musculoskeletal disorders. Bone marrow transplants are not considered types of bone transplant.
  • 60168000 |Osteomyelitis (disorder)| is not the same as 44462005 |Osteitis (disorder)|.

Structure of (named bone), bone structure of (named bone)

To differentiate marrow, vessels, nerves, and periosteum from the actual hard tissue of bones, we differentiate structure of tibia from 12611008 |Bone structure of tibia (body structure)|. The bone marrow and other soft tissues of the tibia can then be categorized separately from the hard tissues. Bone marrow diseases are not considered musculoskeletal diseases, so bone marrow structures should not be placed in the bone (tissue) structure hierarchy.

Long bone, short bone

ICD does not use the standard anatomical definition of long bone.

For example, Benign neoplasms of long bones are distinguished from benign neoplasms of short bones; the bones of the hand are considered short bones. The anatomical definition of long bone cites the proportional relationship between length and width (length >> width). It is clear that metacarpals, metatarsals, and phalanges are included in the anatomical definition of long bone.

In order to accommodate the differences between anatomical definitions and classifications, SNOMED CT has anatomical groupings that correspond to the ICD groupings. Scapula, humerus, radius, or ulna and long bone of thigh or lower leg are used as the sites for grouper concepts that match ICD definitions and groupings.

Sternum, manubrium, body, xiphoid

The sternum is considered a bone organ. The manubrium, body, and xiphoid are parts of the sternum, classed as zones in the FMA.

Teeth, maxilla, mandible

Even though teeth are supported by the maxillary or mandibular bone, they are not part of the 70925003 |Bone structure of maxilla (body structure)| or  91609006 |Bone structure of mandible (body structure)|. Teeth are part of the  4335006 |Upper jaw region structure (body structure)| and  48077000 |Lower jaw region structure (body structure)|.

Joints, joint regions

In many diseases and procedures, reference is made to areas of the body that may ambiguously imply either a joint or a region surrounding the joint. Some common ones are:

Shoulder girdle

272691005 | Bone structure of shoulder girdle (body structure)|  This concept is used to define diseases and procedures affecting bones in the shoulder region, i.e. proximal humerus, scapula, and clavicle. It is not a bone, but a bone structure, and is part of the shoulder region. 

Intertarsal joint structure

27949001 |Intertarsal joint structure (body structure)|; SYN: Tarsal joint:  This structure is part of a group of bones forming the tarsus or tarsal joint (ankle). The  27162001 |Talocalcaneonavicular joint structure (body structure)| is the articulation between the talus (one of the seven bones of the ankle joint) and the other bones of the tarsus, and is what is meant by the rarely-used term talotarsal joint. The talocalcaneal joint is a synonym for the  127863007 |Subtalar joint structure (body structure)|. Dislocations of the subtalar joint usually involve the 127864001 |Structure of talonavicular joint (body structure)|. The subtalar and talonavicular joints constitute the talocalcaneonavicular joint.

Arm, leg, upper, lower, extremity, limb

The meaning of the words arm and leg may be misinterpreted.

• Arm may refer to the upper limb, but it may also refer to the upper part of the arm. 
• Leg may refer to the lower limb, but it may also refer to the lower part of the leg. 
• In common usage, leg is a synonym of lower extremity, and arm is a synonym of upper extremity.

In SNOMED CT, 

• 53120007 |Upper limb structure (body structure)| includes the shoulder, upper arm, forearm, wrist, and hand
• Upper arm is a synonym to 40983000 |Structure of upper extremity between shoulder and elbow (body structure)|. 
• 61685007 |Lower limb structure (body structure)| includes includes the hip, thigh, lower leg, ankle and foot. 
• Lower leg is a synonym to 30021000 |Structure of lower extremity from knee to ankle (body structure)|.  Lower leg does not include the foot.  Stedman's Medical Terminology defines lower leg as the segment of the inferior limb between the knee and the ankle.  

The word limb appears in the FSN of the body structure, while the word extremity appears as a synonym. Therefore, when constructing an FSN for a new clinical finding concept, this precedent should be followed: 

FSN:  61685007 |Lower limb structure (body structure)| 

PT: Lower limb structure

Synonym: Lower extremity

Additional descriptions of leg and arm are permitted for concepts whose FSNs refer to lower limb and upper limb respectively.  

Shoulder and hip regions, upper and lower limbs

The shoulder region is part of the upper limb, and the hip region is part of the lower limb. This follows the general pattern used in the Foundation Model of Anatomy (FMA).

The FMA defines:

• upper limb as the free upper limb and the pectoral girdle (of which the shoulder region is part).  SNOMED CT has the concept 896766000 |Structure of free upper limb (body structure)|.  
• lower limb as the free lower limb and pelvic girdle (of which the hip region is part). SNOMED CT has the concept 699617006 |Structure of free lower limb (body structure)|, i.e. the lower limb not including the pelvic girdle. 

Axilla

The axilla is bound by the upper limb laterally and the thorax medially. It may be viewed as not strictly part of the upper limb or the thorax or it may be views as part of both.  91470000 |Axillary region structure (body structure)| is defined in SNOMED CT as being both an upper limb structure and a thoracic structure.

Tendon

A muscle may be considered an entire functional unit, including attachments to the skeletal system, or merely the contractile part of this unit. In clinical use, muscle is the contractile part only. The FMA definition implies that tendons should be considered part of their corresponding muscles, rather than organs in their own right.  SNOMED CT models |Tendon structure| as a subtype of |Structure of muscle and/or tendon|. Muscle and tendon are two separate anatomical entities.

For example, the  61352006 |Structure of achilles tendon (body structure)| is not a 53451005 |Triceps surae muscle structure (body structure)| (gastrocnemius and/or soleus) muscle structure.

Muscle function

When modeling muscle categories according to their functions, assume they mean the function of the entire muscle, unless stated otherwise.