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The Response of Articular Cartilage to Mechanical Injury.

Mankin·J Bone Joint Surg Am·1982·1,229 citations·Basic Science
PubMed
SummaryAbstract on PubMed →

This 1982 Current Concepts Review by Mankin synthesizes experimental evidence on how articular cartilage responds to three types of mechanical injury. It explains why the avascular nature of cartilage fundamentally limits healing compared with other musculoskeletal tissues. The injury-type framework — superficial laceration, deep penetrating, and blunt impact — remains the organizing taxonomy for cartilage pathology and surgical decision-making.

Key Findings

  • Superficial lacerations confined to cartilage provoke only a brief metabolic burst that subsides by 1–2 weeks, leaving the defect permanently unhealed — yet stable for at least 2 years with no progression to osteoarthritis.
    –→ Isolated chondral injuries without bone penetration carry a relatively benign natural history; incidental findings at arthroscopy rarely require aggressive intervention.
  • Deep injuries violating subchondral bone recruit marrow-derived cells via a vascular fibrin scaffold, but repair tissue retains up to 20% type-I collagen — a fibrocartilage-hyaline mixture, not true hyaline cartilage.
    –→ This phenotypic inferiority explains why marrow-stimulation techniques produce functional but impermanent repair.
  • Osteochondral defect size is the critical variable determining repair success (equine model, 3-month follow-up):
    –< 3 mm* — complete repair achieved at 3 months; lesion undetectable at 9 months
    –≥ 9 mm* — no complete repair achieved in any specimen
  • Chondrocyte death occurs at impact strains of 40% or more; strains of 10% or less cause no apparent chondrocyte injury.
    –Repetitive subthreshold loading (40 min/day for 1 week) still produces ~20% hexosamine loss and ~20% increase in bone stiffness — early osteoarthritis markers.
  • Continuous passive motion after full-thickness defects produced repair tissue more closely resembling hyaline cartilage than fibrocartilage at 4 weeks, compared with immobilization or limited ambulation.
    –→ Foundational mechanobiological evidence behind CPM use after cartilage surgery.
Board PearlCartilage cannot heal superficial injuries due to avascularity — only subchondral violation recruits repair cells, explaining why microfracture works.

Clinical Relevance

William Hunter wrote in 1743 that ulcerated cartilage, once destroyed, is not repaired. Mankin's 1982 review gave that observation its mechanistic explanation and clinical framework.

When a patient has an isolated chondral lesion that does not reach bone — found incidentally at arthroscopy. The evidence says: leave it alone or debride it, but do not expect repair. These lesions are stable and rarely progress.

When you make the decision to perform microfracture or subchondral drilling, you are deliberately crossing the tidemark to recruit marrow-derived cells. The resulting fibrocartilage is functional but imperfect, which is why defect size matters: stay below 3 mm for reliable healing, and counsel patients that tissue above 9 mm will not fully fill.

The CPM data reported here, drawn from Salter's concurrent rabbit work, is why we mobilize cartilage repair patients early rather than immobilize them. Motion drives differentiation toward hyaline-like tissue.

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The Response of Articular Cartilage to Mechanical Injury.

Mankin·J Bone Joint Surg Am·1982·1,229 citations·Basic Science
PubMed
SummaryAbstract on PubMed →

This 1982 Current Concepts Review by Mankin synthesizes experimental evidence on how articular cartilage responds to three types of mechanical injury. It explains why the avascular nature of cartilage fundamentally limits healing compared with other musculoskeletal tissues. The injury-type framework — superficial laceration, deep penetrating, and blunt impact — remains the organizing taxonomy for cartilage pathology and surgical decision-making.

Key Findings

  • Superficial lacerations confined to cartilage provoke only a brief metabolic burst that subsides by 1–2 weeks, leaving the defect permanently unhealed — yet stable for at least 2 years with no progression to osteoarthritis.
    –→ Isolated chondral injuries without bone penetration carry a relatively benign natural history; incidental findings at arthroscopy rarely require aggressive intervention.
  • Deep injuries violating subchondral bone recruit marrow-derived cells via a vascular fibrin scaffold, but repair tissue retains up to 20% type-I collagen — a fibrocartilage-hyaline mixture, not true hyaline cartilage.
    –→ This phenotypic inferiority explains why marrow-stimulation techniques produce functional but impermanent repair.
  • Osteochondral defect size is the critical variable determining repair success (equine model, 3-month follow-up):
    –< 3 mm* — complete repair achieved at 3 months; lesion undetectable at 9 months
    –≥ 9 mm* — no complete repair achieved in any specimen
  • Chondrocyte death occurs at impact strains of 40% or more; strains of 10% or less cause no apparent chondrocyte injury.
    –Repetitive subthreshold loading (40 min/day for 1 week) still produces ~20% hexosamine loss and ~20% increase in bone stiffness — early osteoarthritis markers.
  • Continuous passive motion after full-thickness defects produced repair tissue more closely resembling hyaline cartilage than fibrocartilage at 4 weeks, compared with immobilization or limited ambulation.
    –→ Foundational mechanobiological evidence behind CPM use after cartilage surgery.
Board PearlCartilage cannot heal superficial injuries due to avascularity — only subchondral violation recruits repair cells, explaining why microfracture works.

Clinical Relevance

William Hunter wrote in 1743 that ulcerated cartilage, once destroyed, is not repaired. Mankin's 1982 review gave that observation its mechanistic explanation and clinical framework.

When a patient has an isolated chondral lesion that does not reach bone — found incidentally at arthroscopy. The evidence says: leave it alone or debride it, but do not expect repair. These lesions are stable and rarely progress.

When you make the decision to perform microfracture or subchondral drilling, you are deliberately crossing the tidemark to recruit marrow-derived cells. The resulting fibrocartilage is functional but imperfect, which is why defect size matters: stay below 3 mm for reliable healing, and counsel patients that tissue above 9 mm will not fully fill.

The CPM data reported here, drawn from Salter's concurrent rabbit work, is why we mobilize cartilage repair patients early rather than immobilize them. Motion drives differentiation toward hyaline-like tissue.

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