general considerations in bone tumours classification,biopsy

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general considerations in bone tumours classification,biopsy

  1. 1. DEPARTMENT OF ORTHOPAEDICS, GANDHI HOSPITAL GENERAL CONSIDERATIONS IN BONE TUMORS DR . P . NAGENDRA, P.G ( M.S. ORTHO)
  2. 2. INTRODUCTION the complexity in the presentation of tumors clinically, radiologically, and histologically present an enoromous challenge to the orthopaedic surgeon, radiologist, pathologist. The complexity is also compounded by the various advancements
  3. 3. AGE and SEX DISTRIBUTION: - Most benign tumors osteosarcoma 2nd or 3rd decade ewings sarcoma - G.C.T 3rd or 4th decade - M.M, fibrosarcoma chondrosarcoma older ages metastatic bone tumors - most benign and malignant tumors except GCT : M>F
  4. 4.  ETIOLOGY: - GENETIC : ewings sarcoma --- t (11:22) translocation - increased incidence of sarcomas in pts with hereditary multiple osteocartilagenous exostosis and OI - olliers ds, maffuci s syndrome, pagets ds, FD are associated with higher incidence of sarcoma IRRADATION , VIRAL
  5. 5.  CLASSIFICATION: based on predominant matrix component and type of cell differentiation.
  6. 6. tissue of origin benign malignant bone osteoblastoma osteosarcoma cartilage Chodroblastoma exostosis chondrosarcoma fibrous FD, UBC, ABC Fibrous cortical defect MFH fibrosarcoma Blood vessels hemangioma Gorhams ds notochord chordoma unknown GCT adamantinoma
  7. 7.  PRINCIPLES OF DIAGNOSIS: - FIRST PHASE OR PREBIOPSY detailed history physical examination lab tests , plain x rays, bone scan , chest xray goal : to arrive at tentative decision whether lesion is benign or malignant or metastatic deposit first step : history – usually nonspecific - nonmechanical bone pain which is constant and often keeps the patient awake should always be investigated as it usually means that there is pathological cause , either infection or tumor
  8. 8. PHYSICAL EXAMINATION: benign – minimal findings malignant – usually tender No systemic features except in ewings sarcoma, lymphoma - fever, chills, anorexia, weight loss LAB TESTS: cbp, esr – excluding myeloma, leukemia, infection sr ca and phosphorous: metabolic ds, - hypercalcemia in secondaries, osteosarcoma, ewings, lymphoma
  9. 9. Alkaline phosphatase : currently no prognostic value no value in monitoring the course of ds LDH : doubtful prognostic value in ewings sarcoma
  10. 10. PLAIN X RAYS: - location, size, cortical integrity, margination, soft tissue mass
  11. 11. EPIPHYSEAL LESIONS : chondroblastoma giant cell tumor clear cell chondrosarcoma eosinophilic granuloma brodies abscess subchondral cysts
  12. 12. DIAPHYSEAL LESIONS : ewings sarcoma lymphoma fibrous dysplasia adamantinoma ( consider it in tibia) histiocytosis
  13. 13. LESIONS OF THE SPINE: Older than 40 years – metastases - multiple myeloma - hemangioma - chordoma ( in sacrum) younger than 30 years - vertebral body posterior elements histiocytosis osteoid osteoma hemangioma osteoblastoma ABC
  14. 14. MULTIPLE LESIONS: Histiocytosis Enchondroma Osteochondroma Fibrous dysplasia Multiple myeloma Metastases Infection hyperparathyroidism
  15. 15. TRANSVERSE LOCATION -Central - enchondroma, SBC , fibrous dysplasia - Eccentric – ABC , osteoma , GCT , fibrous cortical defect , chondromyxoid fibroma. TUMOR MARGIN OR ZONE OF TRANSITION: Most important factor in differentiation of benign from malignant lesions Benign: narrow zone or sharp Malignant: wide zone X RAYS superior to CT & MRI
  16. 16. SECOND PHASE: CT , MRI , arteriogram - CT SCAN detection of martix mineralsation, cortical involvement, periosteal reaction. - detection of tumor in flat bones and bones with complex anatomy ( scapula, ribs, pelvis)
  17. 17. MRI SCAN gives soft tissue ( muscle, neurovascular structures and fat planes) and marrow involvement - T1W image in assessing anatomy and baseline image to compare post contrast image. - T2W image in coronal or sagittal plane for staging CONTRAST images for vascular involvement - showing solid component - DYNAMIC CONTRAST images assessing response to chemotherapy
  18. 18. - also differentiate reactive edema from viable tumor - ( viable tumor enhances in early phase, - reactive edema in delayed phase) MRI also for assessing intraarticular extension intratumoral necrosis and hemorrhage skip lesions MRI IS THE SINGLE MOST USEFUL IMAGING MODALITY FOR LOCAL STAGING
  19. 19. THIRD ORDER STUDY OR BIOPSY: - final step in a systemic approach to arriving at diagnosis - Imaging studies provide more accurate information when done prior to biopsy
  20. 20. STAGING SYSTEMS - staging describes the anatomic extent, degree of aggressiveness presence or potential to develop metastasis - Two staging systems - TNM STAGING - ENNEKING STAGING
  21. 21. TNM STAGING: based on histological grade, tumor size, regional lymph node involvement, distant metastasis G- HISTOLOGICAL GRADE T -PRIMARY TUMOR G1 well differentiated Tx- cannot be assessed G2 moderately diff T1 – 8cm or less G3 poorly diff T2 – more than 8 cm G4 undifferentiated T3 – dicontinuous tumors in primary bone site
  22. 22. N – REGIONAL NODE M – DISTANT METASTASIS Nx cannot be assessed Mx – cannot be assessed N0 no involvement M0 – no distant mets N1 nodal involvement M1a – lung M1b – other sites - T1/ T2 + N0 + MO + LOW GRADE = STAGE 1 - + HIGH GRADE = STAGE 2 - T3 + N0 + M0 + LOW / HIGH GRADE = STAGE 3 - Any T + NO + any M + any G = STAGE 4 A - Any T + any N + any M = STAGE 4B
  23. 23. ENNEKING STAGING: for sarcomas arising from the musculoskeletal system - lesions derived from marrow, reticuloendothelial tissue, mesenchymal soft tissue are excluded - Based on – histological grade - - confined to anatomical compartment or not - - presence or absence of metastasis
  24. 24. Stage grade Site Metastasis 1 A LOW INTRACOMPARTEMENTAL No , Mo 1 B LOW EXTRACOMPARTEMENTAL No , Mo 2 A HIGH INTRACOMPARTEMENTAL No , Mo 2 B HIGH EXTRACOMPARTEMENTAL No , Mo 3 ANY ANY REGIONAL OR DISTANT METS
  25. 25. - Benign tumors are enclosed by true capsule - ( composed of compressed normal cells) - Sarcomas surrounded by pseudocapsule or reactive zone - High grade sarcomas have poorly defined reactive zone that may be locally infiltrated by tumor – - SATELLITE LESIONS - SKIP METASTASIS : within the same compartment
  26. 26. BONE SCAN Most sensitive means for detecting metastases even in asymptomatic WHAT IS BONE SCAN Tc label and radio pharmaceutical ( localize organ of interest) phosphate for bone is employed Phosphate incorporates into the hydroxy- apatite crystals of bone Whenever bone equilibrium is disturbed there is osteoblastic activity – shows up as increased tracer uptake
  27. 27. - It cannot determine the precise pathology that caused the disturbance - osteomyelitis, osteoid osteoma, recent fracture or granuloma – as HOT as metastatic focus - Three phase bone scanning may help - VERY LOW SPECIFICITY - NO fasting or other preparatory procedures COME- AS –YOU- ARE test - Iv inj of the RP on the morning and asked to return to scan after three hours - Typically takes half an hour to complete
  28. 28. ABNORMAL SCAN: Presence of single or multiple foci of uptake at sites that are not part of the normal scan is abnormal No characteristic appearances Solitary abnormal focus – may pose a problem rib – usually old fracture or non-specific injury vertebrae- malignancy( more if over the pedicles) flat bones- innocuous cysts or bone islands long bones- benign > malignant - Bone scan frequently false negative in M.M & some cases of R.C.C -
  29. 29. NON SKELETAL UPTAKE: Kidneys, ureters, urinary bladder – excretory channels Soft tissues- edematous tissue, lymphedema, Inflammation or injury to muscle, infarcted myocardium ( in 1st week ) , cerebral infarct & atrial myxomas ROLE IN BONE TUMORS: - Detection of multicentric or polyostotic ds - Follow up of primary bone tumors known to spread to other skeletal sites
  30. 30. PET SCAN F.D.G ( fluoro-deoxy glucose) is used For bone metastases not superior to conventional TC bone scan FDG PET may not show all the lesions identified on bone scan Uptake of FDG is within cancer cells, FDG uptake is directly proportional to tumor activity, hence it is possible to grade tumor, predict prognosis, monitor treatment response Demonstrates marrow involvement FDG upatke is gretaer in lytic lesions than in than sclerotic lesions
  31. 31. BIOPSY : -Perhaps the most imp. step in work up of bone tumors -Mankin reported a 15.9 % complication rate with 3% unnecessary amputations in analysis of 597 pts -procedure is NOT technically demanding, but it has to be planned in concordance with final procedure -poorly placed biopsy incision, badly placed drain or the complications of a biopsy are the commonest cause for an amputation instead of an otherwise possible limb salvage surgery
  32. 32. WHEN – biopsy should be regarded as the final diagnostic procedure, not as a shortcut to diagnosis - only when all the imaging studies are completed - imaging also helps the best areas to biopsy sclerotic, ossified, calcified, or necrotic areas will not yield tissue for a diagnosis WHICH – all suspected malignant and aggressive benign tumors should be biopsied prior to treatment - - osteochondromas , osteoid osteoma, enchondroma, and fibrous cortical defects donot need a biopsy - - a common error is to assume a diagnosis of chr. Osteomyelitis & proceed with debridement only to find out later that it was an ewings sarcoma
  33. 33. WHO -At several centres done by interventional radiologists and pathologists -Ideally by the SURGEON, -As the site is correctly chosen and done in a manner not to compromise the final limb salvage procedure - A surgeon who has first seen the patient should resist the temptation of doing a biopsy unless he is familiar with the limb salvage procedures -
  34. 34. WHAT IS THE CORRECT SITE: -regardless of the type, its placement is critical -the surgeon needs to know the probable diagnosis, extent of the tumor, established operative plan, -IN THE EXTREMITIES- TRANSVERSE INCISIONS CONTRAINDICATED, ONLY LONGITUDINAL INCISIONS - MAJOR NEUROVASCULAR STRUCTURES AVOIDED -BIOPSY TRACT SHOULD NOT TRANSVERSE A NORMAL ANATOMICAL COMPARTEMENT TO REACH A COMP. INVOLVED -BEST TO VIOLATE ONLY ONE COMPARTEMENT -JOINT SHOULD NOT BE VIOLATED -NO BIOPSY SHOULD BE DONE THROUGH THE JOINT OR ARTHOSCOPIC FOR ANY AGGRESSIVE TUMOR
  35. 35. -Standard orthopaedic approaches may prove inapprioate for a biopsy. -ex – biopsy of the humerus through the deltopectoral groove causes dissemination of the tumor, more appropriate is through the anterior deltoid -Anterior midline approach is not preferred for knee tumors, medial or lateral approach is preferred ( to preserve R. femoris) WHAT PART OF THE TUMOR SHOULD BE BIOPSIED -From the periphery ( centers are usually necrotic) -soft tissue component is as representative as bone -lytic areas provide the most representative tissue
  36. 36. OPENBIOPSY -material obtained is generally adequate -Less challenging to the pathologist -special tests can be done -errors in diagnosis are less -general anaesthesia usually needed -expensive -if a torniquet is used there is always a fear that oozing from tumor vessels after torniquet is removed may contaminate large area -skin removed at final procedure is more – may compromise salvage surgery
  37. 37. -large gauge percutaneous cutting needle or core needle biopsy yeilds solid specimens that are emenable to histologic analysis -Core biopsy is especially useful in difficult areas such as spine, pelvis , hip. -when needle biopsy not diagnostic, it can be repeated or an open biopsy performed -Accuracy of needle biopsy for soft tissue tumors – 96% for bone tumors – 80%
  38. 38. What needle to use -Soft mass – trucut needle biopsy -bone – jamshidi needle -Spine – coaxial needle like cook’s needle TECHNIQUE FOR BONE – jamshidi needle is advanced through stab incision until trochar touches the bone. With rotatory motion outer cortex pierced and trochar withdrawn. Cannula is further introduced into bone and rotated to core out tissue. Cannula withdrawn &core removed from cannula using stylet. Usually three cores obtained, closed with a single stitch Needle should penetrate different areas of tumor from the same point of entry by changing angle.
  39. 39. PRINCIPLES OF OPEN BIOPSY TECHNIQUE -requires careful planning and execution -Not to be regarded as a simple minor procedure 1.Skin incision – should not compromise the final definitive procedure, as small as possible, in line with the final incision. 2.No flaps should be raised, cut directly into tumor. 3.Meticulous hemostasis is necessary so that substantial post op hematoma is prevented. 4.If a hole has been created in the bone, it should be plugged with gelfoam or MMA to prevent bleeding into soft tissues 5.Be certain that adequate amount of representative tissue is obtained 6. Biopsy site closed carefully to prevent necrosis
  40. 40. 7.Suction drain should not be used if malignant ds is likely, if a drain must be used, the tract should be adjacent to and in line with biopsy incision. 8.In a needle biopsy the diagnosis is not often confident or complete, if the diagnosis is consistent with clinico- radiologic picture then traetment can be started immediately 9.If the diagnosis doesn’t match with clinico-radiologic picture the pathologist should be asked to review the diagnosis, if needed one can repeat the biopsy or do an open biopsy 10. If the orthopedist or the institution is not equipped to perform accurate diagnostic study or definitive surgery and adjunctive treatment, the pt should be referred to a treating center prior to performance of biopsy.
  41. 41. 11. All the material collected should be processed at one place. It is a bad idea to divide the material and send it todifferent laboratories. 12. The pathologist should be provided with all the clinical and imaging information.
  42. 42. FROZEN SECTION -allows the flexibility of intraoperative decision making. -report availaible in 10 – 15 min -Uses –1. any area where the surgeon is unsure about margins can be sent for frozen section and further decision can be made. - drawbacks : 1.needs decalcification an accurate diagnosis is not possible unless soft tissue component present 2. major decisions such as amputation are best taken on final paraffin section report 3.may be possible to differentiate benign from malignant , but grading is not reliable
  43. 43. ROLE OF LIMB SALVAGE -the previous inevitable sequence Diagnosis – amputation – matastasis – death has now been changed with the advances and nearly 50% with sarcomas can be cured, many retaining a useful functioning limb. - Whenever a suspected bone tumor is biopsied , it is mandatory that specimen should be sent for microbiological analysis, including tuberculosis if this is possible in DD. PRINCIPLES OF MANAGEMENT - MAIN AIM – TO CURE THE PATIENT - First step is to identify if the pt is likely to benefit from chemotherapy or other neoadjuvant treatment
  44. 44. NEO ADJUVANT CHEMOTHERAPY -initially used because of the time required to manufacture for pts undergoing salvage surgery -Now normal practice in all bone tumors requiring chemotherapy. -advantages - will allow early treatment of potential micrometastasis ( present in 80% of osteosarcoma & all pts with ewings ) - -Allow the primary tumor to shrink and thus become safer to operate - - allow an assessment of the effectiveness of this chemotherapy when recected tumor is analysed ( where there is > 90% necrosis there is significant survival advantage)
  45. 45. NEOADJUVANT RADIOTHERAPY -not usually used but occasionally in ewings sarcoma not responding well to chemotherapy. -SURGICAL DECISION MAKING - What type of surgery is depend upon diagnosis , site , extent , response to neoadjuvant chemotherapy , financial status - - KEY PRINCIPLE – any surgery must completely resect the tumor and adjacent involved soft tissues. - - aim is to achieve wide margins whenever possible - - not always possible then whether amputation or marginal excision - - main hazard of narrow margin is local recurrence which requires further surgery even amputation.
  46. 46. -If the main nerve to the limb has to be sacrificed along with bone then limb salvage is not useful. -If main blood vessels need resecting and can be replaced this is not an absolute contraindication to salvage. -presence of pathological fracture is not a contraindication ( if there is good response to neoadj chemotherapy) - The higher up the limb more likely that limb salvage is beneficial to the pt. -ASSESSING THE OUTCOME OF LIMB SALVAGE SURGERY clinician derived – MSTS score patient derived - TESS score -
  47. 47. TYPES OF LIMB SALVAGE - Autografts - Allografts - Bone lengthening - Rotationplasty - Arthrodesis
  48. 48. AUTOGRAFT -vascularized or non- vascularized -Ideal vascularized graft is one with well documented blood supply and is reasonably strong such as fibula ( extensively used to replace tumors of distal radius & parts of humerus) -In lower limb isolated allograft is not strong to allow wt bearing until it is hypertrophied. Hence combined with other form of graft. -In growing child ,proximal femoral epiphysis along with blood supply --- allows replacement of humeral head or distal radius. - Non vascularized graft can be harvested from fibula or other long bones
  49. 49. -recently , patients own tumor bone & replacing after it is sterilised -Radiotherapy best -Adv – bone fits perfectly ( esp pelvis and ankle) - - risk of recurrence in irradiated bone is very low - Extracorporeal irradiation and reimplantation is most useful
  50. 50. ALLOGRAFT -dead piece of bone harvested from donor -high risk of contamination from both donor & storage process -best results are in diaphyseal resections -Osteoarticular allografts can be used to replace end of long bones. -Complications - delayed or non union, - delayed fracture - infection - Allograft requires some form of structural support – bone cement or vascularized autograft
  51. 51. BONE LENGTHENING Time consumimg High incidence of complications Approximately 2 months for each centimetre of bone ENDOPROSTHETIC REPLACEMENT -material – titanium ( inert , light , strong ) -bearing surface – high density polyethylene -fixation of prosthesis Uncemented - time for fixation to secure and probs with bone resorption Cemented – immediate strength but loosening in long term
  52. 52. - Neat combination of the two is to use cemented fixation of the stem and hydroxyapatite at prosthesis bone junction -modern endoprosthesis are frequently modular allowing the surgeon to choose the bits he wants. -in children and unusual situations a custom made implant may be needed -main problems – infection , wear , breakage , loosening -INFECTION - MC org. to cause acute infection STAPH AUREUS & STERPTOCOCCI - Immediate drainage and iv antibiotics -Most acute turn into chronic - present with pain and increasing stiffness around a previously good functioning prosthesis. -
  53. 53. -ANY PATIENT WITH PAIN & RADIOLOGICAL LOOSENING SHOULD BE SUSPECTED OF HAVING INFECTION UNTIL PROVED OTHERWISE. -Removal of prosthesis and all infected material , filling the resulting cavity with antibiotic spacer ( often gentamycin and vancomycin) and reimplantation once all signs of infection have resolved. - this is effective in 80% cases but in some controlled only by amputation. -Risk of infection is realted to TYPE ( tibia and pelvis more risk), local radiotherapy ( more risk) , repeat operations ( increase by 2% per operation on an existing prosthesis)
  54. 54. -PROXIMAL HUMERAL PROSTHESIS – largely unsuccessful -DISTAL HUMERUS – floppy hinge type fixed to ulna -PROXIMAL FEMUR – main problem is loss of abductor lever arm ( G.medius is best attached to fascia lata ) . -muscle cant be attached to prosthesis . -PROXIMAL TIBIA - complex area to reconstruct , main problem is loss of extensor mechanism ( most surgeons routinely cover prosthesis with gastrocnemius M.) - highest risk of complications
  55. 55. ROTATIONPLASTY -To excise the diseased part of the limb and joining the remaining parts together but in doing so rotating them through 180 -frequently done tumors of distal femur. -For young children with tumors involving the entire femur is to simply resect the femur and insert lateral tibial plateau into the hip joint, producing rotated limb with false hip . ARTHRODESIS - One of the first type of limb salvage operation - Cheap and straight forward
  56. 56. SYSTEMIC THERAPY -FOR OSTEOGENIC SARCOMA - before chemotherapy 2 yr survival - 15 – 20% - with multi agent chemotherapy 5 yr survival - 60 – 70 % - neo adjuvant CT  surgical resection  adjuvant CT - cisplatin, doxorubicin, mtx ( in high dose) , ifosfamide, etoposide are most active drugs - intensification or lengthening the neoadjuvant chemotherapy has not been found to be beneficitial. - intra arterial therapy offers no advantage - outcome of pts with clinically detectable metastases at presentation is not good.
  57. 57. -FOR EWINGS FAMILY OF TUMORS -this family consist of undifferentiated at one end and PNET at the other. -prior to CT, were treated with surgery and RT - 5 yr survival <20% -Majority developed metastases despite good local control, -With multimodal therapy, survival is 60 % -current Mx is neoadjuvant CT  local therapy by either Sx or RT , and prolonged maintenance adj CT .
  58. 58. RADIOTHERAPY - MOA – critical site for radiation induced injury is DNA strands ( other sites are cell membrane and microtubules) - direct action – secondary electrons with DNA strands in 25 % cells -indirect action – secondary electrons  free radicals - with DNA strands RADIOSENSITIVITY Various factors intrinsic ( genetic) extrinsic ( epigenetic) -- clonogen fraction, histologic type , tumor cell kinetics
  59. 59. TYPES – Teletherapy brachytherapy – types are interstitial intracavitary endoluminal endovascular surface mould RT FOR SOFT TISSUE SARCOMAS RADIOTHERAPY ALONE - Inferior results - Only in pts with medical contraindication for Sx, - inoperable ds, advanced ds ,
  60. 60. SURGERY AND RADIOTHERAPY - conservative surgery plus adjuvant RT acceptable results - PREOPERATIVE RT advantages decrease the tumor cell implantation in surgical wound , borderline resectable cases rendered resectable , sensitivity to RT is maximum because of inatact vasularity. disadvantages delay in surgical resection , post op complications increased , exact dimensions and histopathological features not known to radiation oncologist .
  61. 61. POSTOPERATIVE RADIOTHERAPY - ADVANTAGES immediate surgery , no radiation induced delayed wound healing , - DISADVANTAGES post op treatment volume is larger POST OP RADIOTHERAPY PREFFERED - started as soon as operative wound completely healed - phase 1 radiation volume is tumor bed & margin of 6 – 7 cm - phase 2 tumor bed & margin of 2 – 3 cm - Total dose : 6000 – 7000 cGy over 6 – 7 weeks
  62. 62. -INTERSTITIAL BRACHYTHERAPY - imp role in STS - Minimal radiation to normal tissue Contraindications : - proximity to neurovascular bundle - tumor going across interosseous membrane - Tumors going into joint - Tumor at inaccessible sites RT IN EWINGS SARCOMA for pts who do not have a surgical option , for patients with inadequate margins
  63. 63. RT IN MULTIPLE MYELOMA - indications - palliation of pain - prevention of pathological fractures - relief of spinal cord or nerve root compression - post op residual ds EXTRACORPOREAL RT - in osteosarcoma and ewings sarcoma - adv : avoids prob with loosening of prosthesis no prob ass with allograft no cost of prosthesis
  64. 64. MEGAPROSTHESIS -Defined as special segmental bone and joint prosthesis which bridge large defects of joints and bones. -Available as modular and custom made. CUSTOM MEGAPROSTHESIS -A metallic prosthesis , tailor made for a particular patient , with specific measurements . -Design : 1st generation – stanmore fully constrained hinge type 2nd generation stanmore rotating hinge type
  65. 65. BONE BANKING - first recorded bone transplant in 1682 was xenografting by job van meekeren - bone banking in 1949 by Dr. george hyatt BONE DONATION - within 15 hrs after death or within 24 hrs if well preserved in cold within 12 hrs after death. DONOR SELECTION - EXCLUSION CRITERIA - h/o s/o hepatitis B or C - h/o or evidence or suspicion of HIV - risk factors for HIV , HBV , & HCV - Septicemia , systemic viral or mycosis or tuberculosis
  66. 66. - presence or h/o malignant ds ( exceptions include primary BCC of skin ) - h/o autoimmune ds with prolonged steroid intake - patient dying after recent major surgery or burns - significant exposure to toxic substances that may be transferred - presence or evidence of irradiation at site of donation AGE CRITERIA not for weight bearing – no max age for structural support , bone < 55 yrs tendons & fascia lata < 65 yrs cartilage , meniscus , osteochondral grafts < 45 yrs
  67. 67. TYPES OF GRAFTS 1. deep frozen graft : in liquid nitrogen or electric freezer at -20 C for 6 months & -80 C for 5 yrs 2. irradiated bone : frozen bone is irradiated by gamma rays 3. processed bone : pasteurised at 60 C for 3 hours  soaked in 0.5 % sodium hypochlorite for one hr  defatting with ethanol  demineralising with HCL 4. lyophilised, irradiated bone : to remove 95 % of moisture
  68. 68. TISSUE PROCESSING - bones are pasteurized - cut into shapes  washed free of blood and marrow - treated with 70 % ethanol ( viricidal & removes fat )  stored at – 80 C  freeze dried  double packed  TERMINAL STERILIZATION with gamma rays (25 kGy) -This dose is 40 % above the minimum required to kill the most radiorestitant bacillus pumilus E601 . - sterility assurance level is one in million failure . - main sources of contamination are four : donor , environment , equipment , personnel .
  69. 69. Reducing immunogenecity - four steps : 1. removal of all marrow 2. freezing at – 80 C 3. freeze drying 4. radiation -Hence tissue typing is not needed . BIOLOGY OF INCORPORATION - unprocessed allografts are rejected , - incorporate by revascularisation , then bone incorporates with host bone & then gets remodelled . - Two types : cortical & cancellous
  70. 70. Cancellous : incorporated more quickly more completely , slowly resorbed and new bone laid . Cortical : incorporate very slowly & partially , donot remodel , thus prone to fatigue and fracture . union occurs at junction .

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