Soft Tissue

Menisci and intervertebral disc

Meniscal anatomy and function, and structure of the intervertebral disc

21 questions 2 source pages 1 images

Images appear with the first question taken from each source page — tap a question to open it.

Q1What are the functions of the meniscus?▸

Q2How much compressive load does the meniscus take up?▸

Q3What is the composition and macrostructure of the meniscus?▸

Cells: fibrochondrocytes (middle/inner), fibroblast-like cells (outer half), superficial zone cells
ECM: water 70%, collagen 22% (outer type I, inner type II), proteoglycans, non-collagen proteins
Superior superficial layer (random fibres); superior lamellar layer (radial fibres)
Deep layer - fibres run circumferentially to resist hoop stresses
Inferior lamellar layer (radial and random); inferior superficial layer (radial)

Q4Describe the lateral meniscus.▸

O-shaped, covers 80-85% of the lateral tibial plateau, takes 70% of compartment load
40-50% contact area reduced after meniscectomy, 200% increase in stress
Anterior horn just posterior to the ACL insertion, to which it partially blends; posterior horn anterior to the MM posterior horn
No attachment to the LCL; loose attachment to the capsule

Q5Describe the medial meniscus.▸

C-shaped, covers 60-65% of the medial plateau, takes 50% of compartment load
Larger AP diameter than width
50-70% contact area reduced after meniscectomy, 100% increase in contact stress
Anterior root 7 mm anterior to the ACL; posterior root anterior to the PCL
Attaches to the deep MCL and capsule via the coronary ligament

Q6What are the meniscal ligaments?▸

Q7What is the blood supply of the meniscus?▸

Blood supply reaches the periphery from perimeniscal plexus (lateral and medial inferior genicular arteries), supplying the peripheral 10-30%
Central 2/3 nourished by diffusion
Posterior horn supplied by the middle geniculate artery
Zones: red-red, red-white, white-white

Q8How does the meniscus bear load?▸

Compressive axial forces are converted to a radially directed force taken up as circumferential hoop stress
Radial fibres act as intrasubstance tie-rods resisting longitudinal splitting and excessive compression
The hoop must be complete - intact circumference and bony attachments
Tensile modulus: Hoop 110Mpa, Radial 10Mpa
Barrel analogy: the wedged cross-section extrudes radially, increasing circumference and generating hoop stress

Q9How does the meniscus absorb shock?▸

Intact menisci dissipate force as biphasic structures
Reduce 20% of peak force on articular cartilage and bone by increasing TFJ conformity
The collagen-GAG network resists water movement through the solid phase
Meniscal tissue is less stiff than articular cartilage because of the lower concentration of proteoglycans; Meniscal tissue is more resistant to the internal movement of water through its tissue than articular cartilage

Q10How does the meniscus provide lubrication and nutrition?▸

By increasing joint congruity it allows better fluid entrainment and hydrodynamic lubrication
The sponge phenomenon helps circulate cellular nutrients throughout the joint

Q11How does the meniscus stabilise the knee?▸

Medial meniscus posterior horn resists anterior tibial translation in an ACL-deficient knee
Meniscofemoral ligaments are secondary restraints to posterior drawer
The meniscus construct is a restraint to tibial rotation

Q12What contact area and stress changes follow partial and total meniscectomy?▸

Partial meniscectomy of the inner third: contact area -10%, peak load +65%
Total meniscectomy: contact area -75%, peak load +235%

Q13What is the association of SONK with meniscal root tears?▸

SONK (spontaneous osteonecrosis of the knee) has been suggested to relate to root tears
Female:male ratio 3:1

Q14What are the functions of the spine and intervertebral disc?📷▸

Spine: carries loads, protects neural elements, supports posture and allows locomotion
Disc resists compression - nucleus pulposus converts compression into radial force, resisted by annulus fibrosus hoop stress
Resists bending, shear and torsion (AF); restricts excessive motion
Shock absorption via viscoelastic NP (time-dependent strain behaviour)

Q15What are the components of the intervertebral disc?▸

Nucleus pulposus - derived from notochord; mucoprotein gel (water and matrix), chondrocyte -like cells, PG aggregates in a type II collagen network
Annulus fibrosus - derived from sclerotome; high type I collagen to PG ratio, fibroblast-like cells
Endplate - semipermeable membrane allowing nutrients and metabolites to diffuse through marrow cavities in the subchondral bone

Q16Describe the structure of the annulus fibrosus.▸

Anchored to the cartilaginous endplate (inner zone) and attached into osseous tissue through Sharpey fibres (peripheral zone)
Outer 1/3: concentric oblique fibres at 30 degrees, herringbone pattern, 15-25 lamellae with elastic fibres between
Inner 2/3: less dense type II collagen matrix lacking lamellar organisation
Resists hoop stress, distraction and shearing forces in different directions

Q17What is the blood and nerve supply of the disc?▸

Nutrition mainly by diffusion through the endplate, which is lined by hyaline cartilage
Only the outer annulus is innervated: sinuvertebral nerve (posterior/posterolateral), grey ramus communicans (lateral), Sympathetic ganglion of the sympathetic trunk (anterolateral disc), sympathetic branches (anterior disc)
Nerve fibres converge at the DRG

Q18What happens in disc aging?▸

Decreased vascularity of endplates -> reduced nutritional supply
Decreased synthesis and increase in proteolytic degradation(different in joint) (e.g. MMP) -> reduced PG concentration
Loss of water retention and normal biomechanical response to loading (more anisotropic stress state with a more non uniform distribution of stresses)
Increased type I:II collagen ratio and increased keratin:chondroitin sulphate ratio
Conversion to fibrocartilage, increased elastic modulus (stiffer), less distinct NP/AF demarcation
Macroscopic: loss of disc height and dehydration, annular delamination and concentric tears, endplate sclerosis

Q19How do disc aging and degeneration differ?▸

Both share similar biomechanical alterations and both start with diminished blood/nutritional supply and waste accumulation from reduced endplate porosity
degen has more distinct initiating factor: mechanical disc overload, genetic factors, immobilisation
Mechanism: increased load + decreased mechanical strength of the AF

Q20Describe the types of disc herniation.▸

Q21Why is discitis more common in children?▸

Blood vessels cross the endplate and end in the annulus up to late teens
Explained by Rudert, JBJS 1993

This site is private