Maurizio Crova

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.

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.

Arthroscopic Treatment of Hip Chondral Defects: Autologous Chondrocyte Transplantation Versus Simple Debridement—A Pilot Study

PURPOSE To compare the effectiveness of simple arthroscopic debridement versus arthroscopic autologous chondrocyte transplantation (ACT) for the treatment of hip chondral lesions. METHODS We carried out a controlled retrospective study of 30 patients affected by a post-traumatic hip chondropathy of the third or fourth degree, according to the Outerbridge classification, measuring 2 cm² in area or more. Of these patients, 15 underwent arthroscopic ACT, whereas the other 15 underwent arthroscopic debridement. The 2 groups were similar in age, sex, degree, and location of the pathology. All the patients were assessed before and after the procedure with the Harris Hip Score (HHS). RESULTS In both groups the mean follow-up was approximately 74 months (range, 72 to 76 months). The mean size of the defect was 2.6 cm². The patients who underwent ACT (group A) improved after the procedure compared with the group that underwent debridement alone (group B). The mean HHS preoperatively was 48.3 (95% confidence interval [CI], 45.4 to 51.2) in group A and 46 (95% CI, 42.7 to 49.3) in group B (P = .428 [no significant difference]). The final HHS was 87.4 (95% CI, 84.3 to 90.5) in group A and 56.3 (95% CI, 54.4 to 58.7) in group B (P < .001 [significant difference]). CONCLUSIONS This study indicates that an ACT procedure can be used in the hip for acetabular chondral defects. LEVEL OF EVIDENCE Level III, retrospective comparative study.

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.

Antibiotic-Loaded Cement in Orthopedic Surgery: A Review

Infections in orthopaedic surgery are a serious issue. Antibiotic-loaded bone cement was developed for the treatment of infected joint arthroplasties and for prophylaxes in total joint replacement in selected cases. Despite the widespread use of the antibiotic-loaded bone cement in orthopedics, many issues are still unclear or controversial: bacterial adhesion and antibiotic resistance, modification of mechanical properties which follows the addition of the antibiotic, factors influencing the release of the antibiotic from the cement and the role of the surface, the method for mixing the cement and the antibiotic, the choice and the effectiveness of the antibiotic, the combination of two or more antibiotics, and the toxicity. This review discusses all these topics, focusing on properties, merits, and defects of the antibiotic loaded cement. The final objective is to provide the orthopaedic surgeons clear and concise information for the correct choice of cement in their clinical practice.

Dislocation rate after hip arthroplasty within the first postoperative year: 36 mm versus 28 mm femoral heads.

Dislocation is a common and important complication of total hip arthroplasty (THA). Larger femoral heads may reduce the risk of dislocation and improve the range of movement. The aim of this study was to compare the relative risk (RR) of dislocation during the first year after THA between implants with 28mm and 36mm femoral heads. 198 consecutive hips with 28mm femoral head (Group-28) and 259 hips with 36mm femoral head (Group-36) were studied. The patients were assessed preoperatively and periodically using the Harris hip score (HHS) and radiographic analysis. The relative risk (RR) of dislocation was calculated. The average HHS significantly improved from a preoperative baseline to the last follow-up at 82.1 months (28mm) and 44.3 months (36mm). No statistically significant differences were revealed between the two groups for HHS results and complications (p>0.05), but the difference in RR of dislocation within the first year between the two groups was 7.85 (95%CI: 1.34–46.03), p=0.046. Although dislocation is multifactorial in etiology, the two groups were homogenous for all principal contributing factors except the diameter of the femoral head. Therefore, the use of 36-mm heads can reduce the risk of dislocation following THA by a factor of 8 compared to conventional 28mm heads.

Comparison of Fixed and Mobile-Bearing Total Knee Arthroplasty at a Mean Follow-up of 116 Months

BACKGROUND The superiority of mobile-bearing total knee arthroplasty implants over fixed-bearing implants, or vice versa, is still debated. METHODS A series of patients with similar clinical and radiographic characteristics were treated consecutively with 100 fixed-bearing followed by 100 rotating-platform implants. Patients underwent prospective clinical and radiographic evaluation. RESULTS The mean duration of follow-up was 116 months (range, sixty-one to 144 months). Clinical, radiographic, and implant survival outcomes were compared. No significant differences between the mobile-bearing and fixed-bearing groups were found with respect to the clinical outcome or cumulative implant survival at the time of the latest follow-up. Three of the fixed-bearing implants and one of the rotating-platform implants had required revision surgery. CONCLUSIONS No differences between mobile-bearing and fixed-bearing designs were demonstrated at a mean of 116 months of follow-up.

Rotating-hinge total knee for revision total knee arthroplasty.

Rotating-hinge knee implants are used for revision total knee arthroplasty in patients with severe ligament instability and bone loss. This study evaluated the outcomes of a series of rotating-hinge knees. Thirty-one NexGen Rotating Hinge Knees (Zimmer, Warsaw, Indiana) were implanted in 29 patients (2 bilateral), with an average age of 72.8 years. Indications for surgery were aseptic loosening (n=23), septic loosenings (n=4), tibiofemoral instability (n=3), and wear (n=1). The Hospital for Special Surgery Knee Score and the Knee Society Roentgenographic Evaluation System were used. Statistical and cumulative survival rate analyses were performed. Average follow-up was 60.3 months (range, 32-100 months). The Hospital for Special Surgery Knee Score results indicated statistically significant improvement; the total score increased from 65.5 preoperatively to 88.4 postoperatively. Average range of motion increased from 90.9° preoperatively to 114.4° postoperatively. Radiographs showed no periprosthetic bone fractures or implant ruptures. Radiolucent lines were found in 20 of 26 patients and were progressive in 2 (both revised). Complications occurred in 10 patients. The rigidity of the hinge may be associated with a risk of aseptic loosening due to the increased stress transfer to the bone from the prosthesis through the locked hinge. Rotating-hinge knee implants provided acceptable mid-term outcomes for revision knee surgery with ligamentous instability. They are not at higher risk for early loosening unless short tibial stems are used. The high percentage of failures is more related to the complex surgery and to the status of the patients than to the hinged mechanism.

In vitro comparison between commercially and manually mixed antibiotic-loaded bone cements

Purpose The purpose of this study is the evaluation of the differences and, eventually, of the advantages or disadvantages of manual formulations with respect to industrial ones. Methods Medical-grade bone cements (Palacos R® and Palacos LV®), based on poly-methyl methacrylate (PMMA) and used clinically in several cemented prosthetic devices were manually enriched with gentamicin sulphate during preparation and then compared with a commercially-available, antibiotic-loaded cement (Palacos R+G®) by means of an in vitro antibacterial test (inhibition zone evaluation). The purpose of this study was to evaluate the differences and advantages or disadvantages, if any, of manual formulations compared to commercial ones. The use of a different antibiotic (vancomycin) alone or in addition to gentamicin-containing bone cements was also considered. Results and Conclusion The commercial formulation produces an inhibition zone that is a bit larger and more regular than the manually mixed preparation. The vancomycin halo is smaller but clearer than the gentamicin halo. The addition of vancomycin to gentamicin-containing bone cements does not significantly increase the halo dimensions but could be an interesting strategy in the prevention of multiple and resistant infections.

Endo-Modell Rotating-hinge Total Knee for Revision Total Knee Arthroplasty

The goal of this study was to analyze the clinical and radiographic results and the survival rate of a series of rotating-hinge implants used for revision total knee arthroplasties in mild and severe instability. Between December 1991 and June 2004, fifty-three revision total knee arthroplasties were performed using the Endo-Modell (Waldemar LINK GmbH and Co, Hamburg, Germany) rotating-hinge prosthesis; 7 (13.2%) patients underwent partial revision of a previous Endo-Modell. All patients were evaluated preoperatively, 3 and 6 months postoperatively, and annually thereafter using the Hospital for Special Surgery (HSS) knee score and the Knee Society Roentgenographic Evaluation System (KS-RES). Mean follow-up was 155.2±40.1 months (range, 78-240 months), with 32 patients examined at the final follow-up. All HSS knee scores increased from preoperatively to last follow-up. No statistically significance differences were found in the HSS knee scores between septic and aseptic revisions and between total or partial revisions. Progressive radiolucent lines were detected in 8 (25%) patients. Implant failure occurred in 11 (20.7%) patients; the cumulative survival of the implants was 80.4% at 150 months for the final 32 patients. The authors recommend use of this implant for revision total knee arthroplasty, especially in patients with severe instability and bone loss.