Bone Injury, Regeneration, and Repair

Bone (Fracture) HealingBONETwo forms of bone tissue Cortical or compact bone Cancellous or trabecular boneTwo types of bone (mechanical & biological properties) Woven or immature bone Lamellar or mature boneWOVEN BONE More rapid rate of deposition & resorption Irregular woven pattern of matrix collagen fibril Four times the number of osteocyte per unit volume Irregular pattern of matrix mineralization Less stiff & more easily deformedBone Healing Direct Primary bone healing Cutting cones Seen with absolute stability Indirect Secondary bone healing Callus formation; resorption at fx site; Seen with relative stability

Direct Bone HealingAbsolute Stability Compression of two anatomically reduced fracture fragments. No displacement of the fracture under functional load. Examples: Lag screw Plate => compression, buttress, Tension band

Indirect Bone HealingRelative Stability Motion between fracture fragments that is compatible with fracture healing. Motion is below the critical strain level of tissue repair. Examples: IM nails Bridge plate External Fixator

Direct Bone Healing Gap healing Haversian remodelingOsteoclast resorb fracture line deposition osteoblastBlood vessels formationThe new bone matrix + osteocytes

New Haversian Systems or primary osteons

Primary bone healing after rigid fracture fixation. Contact healing occurs in the cortex underlying the plate, by direct Haversian remodeling. Layers of bone are first laid down perpendicular to the long axis of the bone, and are then replaced by longitudinally oriented osteons by cutting cones progressing across the gap.Indirect stages Indirect Bone HealingIndirect Stages:1. Inflammation 1-7 days2. Soft callus 3 weeks Repair 3. Hard callus 3 4 months4. Remodeling months => years

Indirect bone healing1. InflammationBegins w/ fx and ends w/ fibrous tissue or cartilage formation. Hematoma is formed, becomes organized, granulation tissue formation. . Indirect Bone Healing1. InflammationFracture damages the bone, blood vessels, bone matrix and surrounding soft tissue Haematoma Inflammatory mediators Dilatation blood vessel Plasma exudat inflammatory cells PMN lecocytes Macrophages LymphocytesRelease byplatelets inj.cellsIndirect Bone Healing 1. InflammationMacrophageDegranulating platelets release Cytokines (PDGF, TGF ) Interleukin 1 & 6 Prostaglandin E2 (PGE2)Invitiation of the repair processIndirect Bone Healing1. INFLAMMATIONInflammatory Necrosis Tissue and Exudate ResorbedFibroplasty & Chondrocytes AppearsProduce new matrix(The fracture callus)

Indirect bone healing2. Soft callus Begins in 3 to 4 days with the appearance of granulation tissue, matures into fibrous tissue and firbrocartilage, stabilizes site w/ internal and externalcallus, pain and inflammation end. Indirect bone healing3. Hard callus Mineralization and conversion to bone. Endochondral ossification of fibrocartilage forming cancellous bone. Indirect Bone Healing:Callus

Indirect Bone Healing4. RemodelingBegins in middle of repair phase, continues until fx clinically healed Osteoclastic tunneling (cutting cones) in concert with osteoblast deposition Can continue up to 7 yearsRemodeling based on stresses (Wolffs law)19-cutting cone= ostoclast at point, followed by capillaries, followed by osteoblasts laying down osteoid. Once callus is calcified (woven bone)become target for ingrowth of cutting cones and remodeling into haversian system. The new blood vessels bring the perivascular cells from inner cambian layer which become osteoblastsRemodelingHueter-Volkmann lawin the skeletally immature, bone growth is relatively inhibited in areas of increase pressure and relatively stimulated in areas of decreased pressure or tensionWolffs lawthe remodeling of bone or soft tissue is influenced and modulated by mechanical stress

20The classic example given is a childs skull; the remodeling occurs by which new bone is placed on the outside, while on the inside the increasing pressure pushes away the old bone which atrophies with pressure.

22Rough estimation fracture healing timeBone Healing TimeClavicle 3-8 weeksScapula 6 weeksRib 4 to 5 weeksHumerus 4-10 weeksRadius & ulna 6 weeksMetacarpal 3 to 4 weeksFingers 2-3 weeksPelvis 4 - 6 weeksRough estimation fracture healing timeBone Broken Healing TimeFemur 12 weeksPatella 4-6 weeksTibia,fibula 10-24 weeks Metatarsal 5 to 6 weeksToe 2 to 4 weeks

FACTORS IN BONE HEALINGPatient Variables* Age* NutritionHealing process needs Energy Proteins & carbohydrates Corticosteroid ( ) Growth hormone Thyroid hormone Calcitonin Insulin Anabolic steroids DM Rickets* Systemic hormones* Nicotine- Inhibit fracture healing ( Vascularization?) Rate fracture healingFrame healingFACTORS IN BONE HEALINGPatient variablesFACTORS IN BONE HEALINGTissue Variables* Cancellous or cortical bones* Bone necrosis* Bone diseasePathologic fracture Osteoprosis Osteomalacia Primary malignant bone tumors Metastatic bone tumors Benign bone tumors Bone cysts Osteogenesis imperfecta Pagets disease Fibrous dysplacia Hyperparathyroidism * InfectionFACTORS IN BONE HEALINGTreatment Variables Apposition of fracture fragments Loading & micromotion Loading a fracture site stimulates bone formation Micromotion promotes fracture healing Fracture stabilizationTraction Cast Imm Ext.Fixation Int.FixationFacilitate fracture healing byPreventing repeated disruption ofRepair tissuePotential disadvantage of int.fixation : Surgical exposure disrupted hematoma, blood supply Risk of infection Rigid fixation alter fracture remodeling, bone densityFACTORS BONE HEALINGTreatment VariablesFACTORS IN BONE HEALINGTreatment VariabelBone GraftsCancellous graftQuick to revascularizeCreeping substitutionCortical graftSlow remodelling process which weakens then re-strengthens Synthetic graftCalcium phosphate, silicon, aluminumMainly osteoconductive31Similar to regeneration of osteonecrosis of cancellous bone. Complications Delayed healing.Non healing.Joint involvement - ankylosisAbnormal position arthritis.Bone necrosis nutrient arteryInvolucrum formation.Pseudoarthrosis

THE END