Paolo Gallinaro

Oxidation in orthopaedic UHMWPE sterilized by gamma-radiation and ethylene oxide

Ten new polyethylene prosthetic components (PEs), ethylene oxide (EtO)- and gamma-sterilized, were studied by means of infrared (IR) analysis in order to evaluate oxidation. Using attenuate total reflection infrared spectroscopy the authors demonstrate that all samples show surface oxidation, formed during processing and shaping, related to mechano-degradation. By means of Fourier transform infrared (FTIR) microscopy and derivatization techniques, the EtO-sterilized PEs present different behaviour in comparison to the gamma-radiated. The former show low levels of depth oxidation that could be related to the degradation which occurred during preparation of slices for IR analysis. The gamma-sterilized PEs show higher oxidation levels, variable from sample to sample, on the surface and in the bulk. The authors demonstrate that oxidation is described both by carbonyl species distribution and by hydroperoxide concentration. The hydroperoxides could be responsible for oxidative PEs ageing in in vivo service. The different oxidation levels and distribution could depend on the conditions of gamma-sterilization, in particular on the rate of the dose absorbed, not previously reported for ready-to-implant PEs. Chain scission of gamma-radiated UHMWPE, estimated by IR analysis, results in reduction of molecular weight and consequently in less abrasive resistance. The scheme of UHMWPE oxidation due to gamma-sterilization demonstrates the inhomogeneous distribution of reactive species in PEs responsible for the unpredictable performance in vivo.

Prevention of Pin Track Infection in External Fixation with Silver Coated Pins: Clinical and Microbiological Results

Pin tract infection is a frequent complication of external fixation; according to literature its frequency ranges from 2-30%. The recent introduction of silver coating of polymeric materials was found to decrease bacterial adhesion; its clinical use with Foley catheters and central venous catheters led to significant results. To verify the ability of the same silver coating to decrease the bacterial colonization on external fixation screws, a prospective randomized study was carried out on 24 male patients; a total of 106 screws were implanted in the lower limb to fix femoral or tibial diaphyseal fractures: 50 were coated with silver and 56 were commercially available stainless steel screws. Although the coated screws resulted in a lower rate of positive cultures (30.0%) than the uncoated screws (42.9%), this difference was not statistically significant (p = 0.243). The clinical behavior of the coated screws did not differ from that of the uncoated ones. Furthermore, the implant of silver-coated screws resulted in a significant increase in the silver serum level. These results led us to consider it ethically unacceptable to continue this investigation.

In vivo UHMWPE biodegradation of retrieved prosthesis.

Sixty-two ultra high molecular weight polyethylene prosthetic components (PEs) (31 tibial plateaux and 31 cups), sterilised by gamma rays or ethylene oxide (EtO), were retrieved after 1-12 years depending on different medical reasons and were studied by FTIR spectroscopy with derivatisation of oxidised species. Esters, acids and hydroperoxides were found under the surface of the EtO sterilised PEs up to 2 mm depth. The behaviour of gamma ray sterilised PEs is more complex due to the oxidation following the sterilisation process. Ester and acid formation might arise from the diffusion of components of synovial liquid or from the oxidation process, whereas hydroperoxide formation is thought to be due to the oxidation. Abrasion and delamination process is discussed considering the topological distribution of degradation products.

Unacceptable biodegradation of polyethylene in vivo

The chemical characterization of 19 retrieved ultra-high-molecular-weight polyethylene tibial plateaux, six new ones and one raw bar was performed by means of infrared spectroscopy. The surface and bulk oxidation and biodegradation indexes were calculated. The raw bar has a measurable oxidation, which increases on the bulk and on the surfaces of the new plateaux. In the retrieved plateaux, the average oxidation index increases further both on the bulk and on the surfaces; the worse values were present on the worn area. Similar results were found for the biodegradation index. The data show that the biotic in vivo degradation is promoted by the oxidation present on the new plateaux and that it occurs through a different mechanism, abiotic thermal-, photo-, gamma-radiation oxidation, evaluated by the oxidation index.

Flexion osteotomy in the treatment of avascular necrosis of the hip.

The natural history of untreated nontraumatic avascular necrosis of the femoral head has a very poor outcome because of the high percentage of collapse of the head. Among the more conservative surgical treatments available, flexion intertrochanteric osteotomy, aimed at rotating the intact posterior portion of the femoral head into the weightbearing portion of the acetabulum, gives satisfying long-term results when planned and performed carefully on selected patients. In general, this includes young and highly motivated patients who have a diagnosis of Ficat Stage II or Stage III idiopathic avascular necrosis. According to the Merle d’Aubignè hip score, avascular necrosis with a complete or slightly reduced range of motion represents the best indication. The results of this procedure on 24 patients at a mean followup of 122 months were satisfactory in 15 patients (62.5%). Nine patients (37.5%) had a conversion to total hip arthroplasty, none of which was associated with technical difficulties related to the initial surgical procedure. Pain and walking ability improved in all patients postoperatively compared with preoperatively, although improvement in range of motion was not observed.

Experience with bipolar prosthesis in femoral neck fractures in the Elderly and debilitated

Eighty-eight bipolar Bateman hip endoprostheses for medial femoral neck fractures were implanted. The average age of the patients was 75 years. Intrahospital results proved the morbidity and mortality rates to be well within acceptable limits. Thirty patients were followed during periods of 12–74 months (median, 33 months). According to Charnley evaluation, mobility was excellent and very good in 20 patients (86%). Good function was present in 63% of patients. The majority of patients belonged to category C as defined by Charnley. Mild pain was present in 19 patients (63%); in only two cases, involving severe rheumatoid arthritis, pain was clearly related to sinkage. Radiographically, no visible protrusion or socket wear was present. Periarticular ossification occurred in 19 patients, but this did not impair function.

Eight- to ten-year results of a variable geometry stem.

This prospective study was conducted on 108 consecutive implantations straight, cementless, taper-designed stem with variable lateral flare (Pegasus; DePuy, Warsaw, Indiana) at an 8- to 10-year follow-up; DEXA scanning was performed at 3 and 12 months on a second cohort of 40 patients. The mean Harris hip score was 94.2, and no revision was performed. Measurable subsidence of the stem was found in three (2.8%) patients; the subsidence was always measured within the first year of follow-up, and did not progress at the subsequent controls. Bone mineral density decreased at 1 year, 15.1% in zone 1 and 3.4% in zone 7. Uncemented stems with a taper design, which provide a high metaphyseal fit and a low diaphyseal fit, lead to comparable and reproducible long-term results independently from other design characteristics.

Biocompatibility and osteogenetic characteristics of new biocompatible glasses

A fibre-shaped glass with qualities of biocompatibility and biodegradation could be promising for reconstructive bone surgery in orthopaedics and neurosurgery. New highly biocompatible glasses, originally made by the Italian Group of Study on Biocompatible Glass, are obtained both in cylinder and fibre shapes due to their original chemical composition (Glassfiber). This is the only glass which is also available as a continuous filament. Hydrolytic in vitro and in vivo tests demonstrate that these glasses present both good biocompatibility and adjustable biodegradation in relation to their chemical composition. The advantages of bioactive glass also being available as a continuous filament are suggested.

Biology of Primary Fracture Healing. From Experimentation with Animals to Clinical Application. A Review.

The specific radiological manifestations of primary bone healing have been known for over fifty years. In 1914, Lane (22), referred to it is as “bone healing by primary intention” and in 1949, Danis (10), described it as “soudure autogene”, or autogeneous welding. It was also known that rigid internal fixation was a “sine qua non” condition to obtain the specific pattern of healing which is characterized by the absence of callus. It has not been clear,though, whether the effect of compression is biological, or whether the callus-less healing occurs simply due to the stabilizing effect (8). Despite the uncertainty as to the cause of the beneficial effect of rigid fixation, the clinical use of compression plates gained broad recognition since their introduction by Danis in 1949 (10). Venable in 1951 (34), Boreau and Hermann in 1952 (7), Bagby and Janes in 1957 (5) described similar fixation devices. In 1955 Yamagishi and Yoshimura (37) published an experimental paper in which a moderate intermittent compression was considered to be the ideal biomechanical condition for fracture healing. According to the modern philosophy of the Russian Ilizarov, this concept is fun damental. However in 1958 Bagby and Janes (6) carried out experiments on dog femurs and concluded that a steady compression does not necessary stimulate the osteogenesis,although it is a main factor in increasing stability. In the sixties a number of histolo gical observations on primary bone healing in various species including humans were reported (2,24,26,29,32,33). Most of the work in this field came from the Work Group for the Study of Osteosyn-thesis, which was founded in Switzerland by M.E. Muller,M.Allgover and H. Willenegger in 1958. Laboratory facilities for the experimental work on the animal were provided in Davos in the “Laborato- rimn fur experimentelle Chirurgie” headed by Stephan Perren. Most of the work described in this paper in detail on the histology of primary bone healing was performed there. Further research in the same laboratory, working on sheep, showed that a pattern of secondary healing with callus was produced when internal fixation allowed for some interfragmentary motion (no compression). The amount of callus observed corresponded to the deformability of the implant and consequently to interfragmentary motion (17).