FSHP Academy
Human Anatomy — all lessons

Foundations of Anatomy

Anatomical terminology, planes, axes and movement directions

The Skeletal System

Skeletal system: structure and functionsBone structure, remodelling and adaptation to loading

Joints and the Muscular System

Joint types and classificationJoint mechanics: arthrokinematics and stabilityThe muscular system: organisation and major muscle groupsMuscle architecture: pennation, length and cross-sectional areaMuscle fibre types

Regional Functional Anatomy

Spine and postureThe shoulder complexThe hip complexThe knee complexThe ankle and foot complexCore and pelvic stabilityElbow and wrist functional anatomyCervical and thoracic spine functional anatomy

Joint mechanics: arthrokinematics and stability

How joint surfaces roll, glide and spin, what holds joints together, and how this informs exercise selection and progression.

Intermediate Evidence: Strong evidence 3 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Distinguish osteokinematics from arthrokinematics
  • Describe roll, glide and spin and the convex–concave principle, including its limits
  • Explain passive, active and neural contributions to joint stability
  • Use close-packed and open-packed positions and degrees of freedom in exercise decisions

Before this lesson

Why this matters

Two people can perform the same squat with very different joint mechanics. Understanding what happens inside the joint and what keeps it stable underpins injury prevention, rehabilitation and coaching cues.

Fundamental concepts

  • Osteokinematics — movement of bones through planes (flexion, abduction, rotation) — covered in planes and axes.
  • Arthrokinematics — movement between joint surfaces [neumann2017]:
    • Roll — new points on one surface contact new points on the other (a tyre rolling).
    • Glide (slide) — one point slides across new points (a braked tyre skidding).
    • Spin — one point rotates on a single point (a spinning top).

The convex–concave principle

  • Convex surface moving on a fixed concave surface → roll and glide in opposite directions (e.g., humeral head on glenoid during abduction: rolls up, glides down, staying centred).
  • Concave surface moving on a fixed convex surface → roll and glide in the same direction (e.g., tibia on femur in open-chain knee extension).

This is a useful mental model, but imaging studies show joints do not always behave as the rule predicts — translations depend on muscle activity, capsule tightness and load. Treat it as a guide rather than a law [neumann2017].

Joint stability

Stability = the ability to maintain or return to a controlled position under load. It comes from four overlapping sources:

SourceExamples
Bony congruenceDeep hip socket; shallow glenoid
Passive tissuesLigaments, capsule, labrum, menisci
Active (muscular)Rotator cuff compressing the humeral head; hamstrings resisting anterior tibial translation
Neural controlProprioception, reflexes and planned muscle activation timing

Close-packed positions (maximal congruence, ligaments taut — e.g., full knee extension, ankle dorsiflexion) are stable but poor at absorbing force. Open (loose)-packed positions allow more accessory motion.

Practical application

Common mistakes and misconceptions

  • “Mobility joints vs stability joints.” The popular “joint-by-joint” model can be a useful teaching heuristic, but every joint needs both mobility and control for the task.
  • “Clicking means instability.” Painless noises are common and usually benign.

Case study

Athlete: a 24-year-old basketball player with two right ankle sprains this season. Strength testing is normal, but single-leg balance with eyes closed is poor on the right. The coach adds progressive balance, hop-and-stick and reactive drills alongside strength — targeting the neural component of stability — and liaises with the physiotherapist on return to sport testing.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Technical needs verification — opens a YouTube search

Arthrokinematics: roll, glide and spin

Physiotutors

You will understand: joint surface motion and the convex–concave principle

Why: Physiotherapy-focused, clinically relevant.
Introductory needs verification — opens a YouTube search

Joint stability: static vs dynamic stabilisers

Kenhub

You will understand: how bones, ligaments and muscles share stabilising roles

Why: Clear anatomical visuals.

Knowledge check

Knowledge check · 0/5

1. When a convex surface moves on a fixed concave surface (e.g., humeral head in glenoid), the classic rule says roll and glide occur…

Answer B. Convex-on-concave — roll and glide in opposite directions, keeping the head centred.

2. The close-packed position of a joint is when…

Answer B. Close-packed = maximal congruence and ligament tension, e.g., full knee extension.

3. Which is an active (muscular) contributor to stability?

Answer C. Rotator cuff muscles compress the humeral head into the glenoid.

4. Proprioceptive deficits after an ankle sprain mainly affect which stability system?

Answer C. Damaged ligaments carry mechanoreceptors; impaired feedback affects neuromuscular control.

5. Which statement about the convex–concave rule is most accurate?

Answer B. Studies of the glenohumeral and other joints show translations that do not always follow the rule.

Short-answer & application questions

  1. Describe the stabilisers of the knee in each category (bony, passive, active, neural).
  2. Why is full knee extension (close-packed) a less suitable position to absorb landing forces?
  3. Explain to a client why “joint stability” training includes balance and reaction drills, not just strength.

Key takeaways

  • Osteokinematics describes bone movement in planes; arthrokinematics describes surface motion (roll, glide, spin) inside the joint.
  • The convex–concave principle is a useful guide, but imaging shows real joints do not always follow it.
  • Stability comes from bone shape, passive tissues (ligaments, capsule, labrum, menisci), muscles and neuromuscular control.
  • Mobility and stability are not opposites to be traded globally; each task needs controlled motion at each joint.

Connected topics

anatomy

The knee complex

anatomy

The shoulder complex

biomechanics

Levers, torque and moment arms

prehab rehab

Principles of injury prevention and recovery

corrective exercise

Corrective strategies: inhibitory, lengthening, activation and mobility

References

  1. Neumann DA (2017). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation (3rd ed.). Elsevier. Textbook check pending
  2. Betts JG, Young KA, Wise JA, et al. (2022). Anatomy and Physiology 2e — Chapter 9: Joints. OpenStax, Rice University. · Link Textbook check pending
  3. Doherty C, Delahunt E, Caulfield B, et al. (2014). The incidence and prevalence of ankle sprain injury: a systematic review and meta-analysis of prospective epidemiological studies. Sports Medicine, 44(1):123–140. doi:10.1007/s40279-013-0102-5 Meta-analysis check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.