Allan J. Aho

Clinical use of bone allografts.

Modern techniques of bone allograft surgery provide a treatment modality for management of difficult skeletal defects. In oncological limb-salvage surgery, allograft reconstructions permit re-establishment of skeletal continuity and function after a wide resection of bone tumour. Bone allografts are increasingly used in salvage of difficult bone stock deficiencies following failed total joint replacements. Union between the allograft and the host bone takes place slowly and the use of autogenous bone graft at the graft-host junction is recommended for induction of repair. Internal repair (revascularization and substitution of the original graft bone with new host bone) also progresses slowly and seems to be confined only to the superficial surface and the ends of the graft. Biomechanically, a massive allograft may serve a structural function in the absence of advanced revascularization and creeping substitution processes. Infection of an allograft is a disastrous complication, whereas non-union of the graft-host junction and fracture of the graft are amenable to surgical treatment. Osteochondral allografts tend to show gradual deterioration of the articular cartilage with time, necessitating occasionally late resurfacing arthroplasty. It is evident that there is more active immune response to osteochondral grafts than was thought previously. Bone allografts induce cell-mediated and antibody-mediated cytotoxicity specific for donor antigens similar to that seen after organ transplantations. Not only the basic mechanisms of bone allograft rejection but also the clinical features of bone allograft rejection are poorly characterized. Clinically, new non-invasive imaging techniques should be applied in determining the metabolic activity of bone in order to find the optimal loading of healing allografts. Although the clinical results of massive bone allografts are still not completely predictable, the method has proved to be a technically and biologically feasible alternative for non-biological skeletal reconstructions.

Polymethylmethacrylate composites: disturbed bone formation at the surface of bioactive glass and hydroxyapatite.

The effects of polymethylmethacrylate on bone formation were studied alone and as composites in combination with hydroxyapatite and bioactive glass in the rabbit subchondral femur. Radiographs, histology, computer assisted histomorphometry, scanning electron microscopy and energy dispersive X-ray analysis were used for evaluation. A total of 60 cones were implanted for 3, 6 and 12 weeks. The composite cones consisted of granules of bioactive glass (S56.5P4) or hydroxyapatite embedded in polymethylmethacrylate. Pure polymethylmethacrylate cones served as controls. At the interface of the cones, bone contact was observed only when bioactive glass or hydroxyapatite was present at the cone surface. Fibrous tissue was always found at the polymethylmethacrylate-tissue interface. The osteoconductive bone formation at the surface of bioactive glass and hydroxyapatite was disturbed by polymethylmethacrylate. It seemed to resist bone formation at the interface of both bioactive glass and hydroxyapatite. However, bioactive glass was better able to withstand the detrimental effect of polymethylmethacrylate than hydroxyapatite.

Human acute pancreatitis: a light and electron microscopic study.

The histology and ultrastructure of resected pancreas from seven patients suffering from acute haemorrhagic pancreatitis were studied. Special attention was paid to necrotic acini and zymogen granules. Acinar cells in the border of necrotic and non-necrotic parenchyma contained lipid droplets, autophagic vacuoles, bundles of intermediate filaments and degenerated cell organelles, including zymogen granules, PAS-positive material derived from secretory proteins was situated in dilated acinar lumina and in the interstitium, and proved to be fibrillar in fine structure. There were thrombosed vessels and extravasated erythrocytes at the border of the parenchymal necrosis. Bundles of intermediate filaments were often the only identifiable structures in the severely necrotic acinar cells. The amount of lipid was decreased in damaged fat cells. Older fat necroses were surrounded by myofibroblasts. It was concluded that acinar and fat cells undergo concomitant necrosis in the inflamed pancreas, zymogen granules degenerate in the acinar cells at the border of necrotic and non-necrotic areas, and secretory proteins may be displaced in the interstitium outside acinar lumina. Myofibroblasts participate in the healing of autodigestive injuries.

Experimental pancreatitis in the rat. Development of pancreatic necrosis, ischemia and edema after intraductal sodium taurocholate injection.

Acute hemorrhagic pancreatitis was induced in rats by injecting sodium taurocholate into the common biliopancreatic duct. The extent of pancreatic necrosis was quantified in histological sections during the course of the disease. The proportion of necrotic acini was low, although the amount of necrosis increased from 3.3% of pancreatic parenchyma at 15 min to 10.5% at 12 h. The degree of ischemia in the inflamed pancreas was estimated by extracting intravenously injected toluidine blue from the gland. The amount of the dye in the gland decreased progressively during 12 h to 58.8% of the amount in normal pancreas. The development of pancreatic edema was studied by recording the water content of the gland. The edema was maximal at 3 h and resolved partly in 12 h after the induction of the disease. Necrosis and ischemia become progressively more pronounced in the edematous pancreas during sodium taurocholate-induced acute hemorrhagic pancreatitis. This kind of pathophysiologic course is also thought to characterize human pancreatitis. The present simple model of acute hemorrhagic pancreatitis in the rat is suitable for quantitative observations on the development of pancreatic damage under various experimental conditions.

Bone bank service in Finland: Experience of bacteriologic, serologic and clinical results of the Turku Bone Bank 1972–1995

560 bones were harvested by The Turku Bone Bank between 1972-1995. It was started with massive allografts for bone tumor surgery, but today most are femoral heads for hip revision surgery. The increase in harvested bones nearly trebled from 1984-1989 to 1990-1995. Only 1 positive hepatitis C test was found. There were no hepatitis B or HIV positive donors. The incidence of discarding after screening was 24%, with positive bacterial growth (8%, usually Staphylococcus epidermidis) as the commonest reason. 2 massive grafts with negative cultures when harvesting were positive after thawing and resulted in deep infection. 369 allografts were transplanted. The infection rate of massive allografts for bone tumor surgery was 5/63 in 1973-1995, and 2/52 in 1985-1995. The infection rate for hip revision surgery was 3.4%. The clinical functional results correspond to those reported in larger international series.

Subchondral bone and cartilage repair with bioactive glasses, hydroxyapatite, and hydroxyapatite-glass composite.

The repair of an osteochondral defect in rabbit femur was studied with three kinds of bioactive glasses (BG), hydroxyapatite (HA), and hydroxyapatite-glass (HAG) composite. Seventy-two osteochondral defects were created in 18 rabbits. Sixty-four cylinders were implanted and eight defects were left empty as controls. Histomorphometry, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) were used for evaluation. Small osteochondral defects in rabbit femur found to heal themselves by regeneration. The three BGs, HA, and HAG led to direct lamellar bone repair of subchondral bone and restoration of articular surfaces mostly with hyalinelike cartilage in 12 weeks. However, the composition of the materials affects their behavior. Chondrogenesis took place earlier with the BGs than with HA. HAG degraded too much, glass 14 was too reactive and brittle, and the high alumina content in glass 11 disturbed its bone-bonding ability. Glass 7 and HA were the most balanced in the repair process. A special preparation method was used to retain soft tissues fairly unchanged and enable them to the observed together with hard tissues in SEM analysis.

Experimental Pancreatitis in the Rat: The Role of Phospholipase A in Sodium Taurocholate-induced Acute Haemorrhagic Pancreatitis

Acute haemorrhagic pancreatitis was induced in rats by injecting 0.2 ml of 5% (92.9 mmol/l) aqueous solution of sodium taurocholate into the common biliopancreatic duct. Lysolecithin was separated from the pancreatic homogenate by thin-layer chromatography and quantified by phosphorus determination. The lysolecithin content increased rapidly, remained elevated for 12 h, and returned to the control level 24 h after the injection. Treatment with a trypsin inhibitor, aprotinin (Trasylol), given intraperitoneally and intravenously during 2 h postoperatively (800,000 units/kg of body weight) had no beneficial effects compared with physiological saline treatment. When the animals were treated similarly with a phospholipase A inhibitor, procaine hydrochloride (40 mg/kg of body weight), 45% of them survived 72 h (p less than 0.01). It was concluded that phospholipase A, which converts lecithin into lysolecithin, plays a significant role in the pathogenesis of acute pancreatitis.

Immune responses and clinical outcome of massive human osteoarticular allografts

Cell mediated immune responses as measured by lymphocyte proliferation induced by the mitogens phytohemagglutinin and concanavalin A and antigen extracts of donor derived bone were studied within 2 years after wide resection of bone tumors in 18 patients receiving fresh frozen massive osteoarticular allografts. No uniform changes were seen in mitogen induced responses in 18 patients. However, five of nine patients tested with antigen extracts of donor derived bone showed elevated immune responses, one moderate and four weak. The incorporation of the allograft (evaluated by repeated radiographs; specific isotope techniques; clinical outcome assessed by the functional rating scores of Mankin-Waber and the Musculoskeletal Tumor Society; and histologic biopsy findings on new bone formation) did not differ in these patients from those in patients without any response to donor derived tissue. During a long term followup (mean, 11 years; range, 2–20 years), degenerative joint and sclerotic density bone changes developed after 2 to 4 years without correlation to immune responses. Histologic specimens showed no signs of immunologic reaction, and no clinical rejection episodes were recorded. A slightly variable immune response to allograft bone seems to occur, but its clinical significance for outcome of the grafts remains to be determined. The low immune responses might reflect a low antigen release rate through an indirect pathway or immunologic tolerance to antigens or proteins shed from massive allografts that are nonliving scaffold implants during the creeping substitution process, corresponding to the low immune response and the slow histologic repair.

Ultrasonic Device in Bone Cutting: A Histological and Scanning Electron Microscopical Study

The immediate and the long-term effects on bone produced by an ultrasonic cutting device and an oscillating saw were compared histologically and by scanning electron microscopy. The long bones and scapulas of rabbits were used as experimental material. By scanning electron microscopy the osteotomy surface produced by the ultrasonic saw was observed to be rougher than that produced by oscillating saw, but there were no microfractures. Histologically the early regeneration of the bone tissue was delayed to some degree after ultrasonic cutting, but the regeneration process as a whole was found to be the same after cutting with either of the saws.

Bioactive glass versus hydroxylapatite in reconstruction of osteochondral defects in the rabbit

We studied osseointegration of a bioactive glass (BG) and hydroxylapatite (HA) in rabbit femur epiphyseal and metaphyseal regions. 17 BG and 24 HA cones implanted in defects through arthrotomy were analyzed. The holes for implants were drilled through distal femur joint surfaces. The cartilage wound repaired generally by fibrous tissue. Histomorphometry showed that 61, 78, and 79 percent of BG surface was covered by bone at 3, 6, and 12 weeks, respectively. The corresponding figures for HA were 47, 67, and 78 percent. Chemical bonding between bone and implants of both types was confirmed by scanning electron microscopy (SEM) and energy-dispersive x-ray analysis (EDXA). Formation of a calcium phosphate-rich layer on the surface BG implant was demonstrated by EDXA. Our results indicate that the osseointegration rate of bioactive glass does not differ from that of hydroxylapatite.