This document discusses diarthrodial joints and joint motion. It identifies important connective tissue structures in diarthrodial joints like synovial fluid, articular cartilage, meniscus, ligaments, tendons, and muscles. These structures provide lubrication, load distribution, joint stability, and transmission of forces. Joints allow six degrees of freedom consisting of three translations and three rotations. Applying statics to joint biomechanics problems requires assumptions like known axes of rotation and muscle attachments, negligible friction, and consideration of only two-dimensional forces. Anthropometric data provides average human body measures used in the analysis.

1. Diarthrodial Joints and
Joint Motion
BioE 3200 Fall 2015

2. Learning Objectives
 Identify important structures and
anatomical features of diarthrodial
joints
 Apply statics to solve 2D joint
biomechanics problems
 Summarize important assumptions needed to
apply statics to joint biomechanics problems
 Create accurate free body diagram of joints

3. Important connective tissue
structures in diarthrodial joints:

4. Functions of connective tissues
in diarthrodial joints:
◦ Synovial fluid – lubrication, load distribution
◦ Articular cartilage – bearing surface; load
distribution
◦ Meniscus – joint stability, load distribution
◦ Ligaments and tendons – joint
stability/transmission of muscle forces to
bone
◦ Muscle – creates forces for motion; joint
stability
◦ Bone – load transmission at the joint; creates

5. Joint Motion
 Six possible
degrees of
freedom
◦ 3 translations
◦ 3 rotations
 Defined relative
to 3 orthogonal
directions
http://www.highlands.edu/academi
cs/divisions/scipe/biology/faculty/h
arnden/2121/images/synovialtypes
.jpg

6. Assumptions when applying
statics to biomechanics
problems: Axes of rotation are known
 Only one muscle group is controlling
movement of a joint
 Locations of muscle attachments are
known
 Line of action of muscle tendon is known
 Segmental weights and centers of
gravity are known
 Frictional factors at joint are negligible
 Dynamic aspects of joint are ignored
 Only forces in 2D considered
 Deformations of connective tissues
ignored

7. Anthropomorphic measures used
in applying statics to
biomechanics Anthropometry:
Study of human
body dimensions
and masses by
segment and area
 Data on average
anthropomorphic
measures allows us
to determine limb
lengths, weights and
locations of centers
of gravity.