Tendon structure and healing Paul Baker Freeman Hospital Hand Term

Tendon structure Dense, regularly arranged tissue that attaches muscle to bone Dense, regularly arranged tissue that attaches muscle to bone Highest tensile strength of all connective tissue Highest tensile strength of all connective tissue High proportion of collagen High proportion of collagen Closely packed parallel arrangement in direction of force Closely packed parallel arrangement in direction of force Consists of 3 components Consists of 3 components Tendon, bone insertion, muscle-tendon junction Tendon, bone insertion, muscle-tendon junction

Tendon structure  Composed of fasicles derived from smaller fibrils Surrounded by epitendon Surrounded by epitendon Separated by endotendon Separated by endotendon

Tendon structure Consist of fibroblasts and collagen arranged in parallel rows Consist of fibroblasts and collagen arranged in parallel rows Contain relatively few cells and therefore has low metabolic activity Contain relatively few cells and therefore has low metabolic activity Fibroblasts produce Type I collagen Fibroblasts produce Type I collagen (85% of dry weight of tendon)

Tendon Types 2 types: 2 types: Paratenon covered tendons Paratenon covered tendons Rich vascular supply Rich vascular supply Better healing potential Better healing potential Sheathed tendons Sheathed tendons Tendon segments supplied by vinculae and osseous insertion Tendon segments supplied by vinculae and osseous insertion Avascular areas receive nutrition via diffusion from vascularised segments Avascular areas receive nutrition via diffusion from vascularised segments

Blood supply – sheathed tendon

Tendon healing Occurs through extrinsic and intrinsic processes Occurs through extrinsic and intrinsic processes Divided into 3 phases Divided into 3 phases Inflammation (Day 0-7) Inflammation (Day 0-7) Repair (Day 3-60) Repair (Day 3-60) Organisation and remodelling (Day ) Organisation and remodelling (Day ) Under action of cytokines: Under action of cytokines: PDGF (Chemotaxis) PDGF (Chemotaxis) TGFß (Collagen type) TGFß (Collagen type)

Variables that influence healing TRAUMA Cell & Matrix damage HEALING Inflammation -> Repair-> Remodelling RESULT Restoration of original tissue Scar Excessive repair Failure of healing INJURY Type Intensity Duration PATIENT Age Comorbidity Medication TREATMENT Apposition Stabilisation Loading & Motion

Inflammation (0-7 days) Inflammatory cells migrate from: Inflammatory cells migrate from: Epitendinous tissues (sheath, periosteum, soft tissues) Epitendinous tissues (sheath, periosteum, soft tissues) Epitendon and endotendon Epitendon and endotendon Defect rapidly filled with granulation tissue, haematoma and tissue debris Defect rapidly filled with granulation tissue, haematoma and tissue debris Fibronectin laid down as scaffolding for collagen synthesis Fibronectin laid down as scaffolding for collagen synthesis Extrinsic response outweighs intrinsic response Extrinsic response outweighs intrinsic response

Inflammation (0-7 days)

PDGF

Repair (3-60 days) Fibroblast migrate to zone of injury and begin to synthesise collagen by day 5 Fibroblast migrate to zone of injury and begin to synthesise collagen by day 5 Initially collagen type 3 produced which is laid down in a random orientation Initially collagen type 3 produced which is laid down in a random orientation Healing tendon Normal tendon

Repair (3-60 days) During 4th week intrinsic fibroblasts proliferate and these cells take over the healing process both synthesising and reabsorbing collagen During 4th week intrinsic fibroblasts proliferate and these cells take over the healing process both synthesising and reabsorbing collagen “Tendon Callus” “Tendon Callus” Switch to production of Type 1 Collagen which is increasingly orientated along line of force Switch to production of Type 1 Collagen which is increasingly orientated along line of force Vascular ingrowth via collagen/fibronectin scaffolding Vascular ingrowth via collagen/fibronectin scaffolding

Repair (3-60 days)

Organisation ( days) Final stability acquired during this phase by the normal physiological use of the tendon Final stability acquired during this phase by the normal physiological use of the tendon Accompanied by cross linking between fibrils further increasing tendon tensile strength Accompanied by cross linking between fibrils further increasing tendon tensile strength Complete regeneration never achieved Complete regeneration never achieved Defect remains hypercellular Defect remains hypercellular Thinner collagen fibrils Thinner collagen fibrils

Sheathed Tendons Recent work has shown intrinsic tendon cells have potential to heal sheathed flexor tendon injuries Recent work has shown intrinsic tendon cells have potential to heal sheathed flexor tendon injuries Leads to healing without a mass of repair tissue Leads to healing without a mass of repair tissue However this may compromise the recovery of tendon strength post healing However this may compromise the recovery of tendon strength post healing

Rehabilitation Early controlled mobilisation can: Early controlled mobilisation can: Reduce scar adhesions Reduce scar adhesions Facilitate healing by stimulating remodelling Facilitate healing by stimulating remodelling Excessive loading will: Excessive loading will: Disrupt the repair tissue Disrupt the repair tissue Thus optimal healing requires: Thus optimal healing requires: Surgical apposition and mechanical stabilisation Surgical apposition and mechanical stabilisation Minimal soft tissue damage Minimal soft tissue damage Optimal mechanical environment for healing Optimal mechanical environment for healing

Tendon Gap

Summary Tendon healing: Tendon healing: Weakest at 7-10 days Weakest at 7-10 days Regain most of original strength by days Regain most of original strength by days Achieve maximum strength by about 6 months Achieve maximum strength by about 6 months Early mobilisation: Early mobilisation: Increases ROM but can decrease tendon repair strength if excessive stress placed on repair Increases ROM but can decrease tendon repair strength if excessive stress placed on repair Immobilisation leads to increase tendon substance strength at expense of ROM. Immobilisation leads to increase tendon substance strength at expense of ROM.