Acoustic, mechanical and near-infrared profiling of osteoarthritic progression in bovine joints.

Early-stage treatments for osteoarthritis are attracting considerable interest as a means to delay, or avoid altogether, the pain and lack of mobility associated with late-stage disease, and the considerable burden that it places on the community. With the development of these treatments comes a need to assess the tissue to which they are applied, both in trialling of new treatments and as an aid to clinical decision making. Here, we measure a range of mechanical indentation, ultrasound and near-infrared spectroscopy parameters in normal and osteoarthritic bovine joints in vitro to describe the role of different physical phenomena in disease progression, using this as a basis to investigate the potential value of the techniques as clinical tools. Based on 72 samples we found that mechanical and ultrasound parameters showed differences between fibrillated tissue, macroscopically normal tissue in osteoarthritic joints, and normal tissue, yet did were unable to differentiate degradation beyond that which was visible to the naked eye. Near-infrared spectroscopy showed a clear progression of degradation across the visibly normal osteoarthritic joint surface and as such, was the only technique considered useful for clinical application.

The effect of the Rim Cutter on cement pressurization and penetration on cemented acetabular fixation in total hip arthroplasty: an in vitro study.

The Rim Cutter (Stryker Orthopedics, Mahwah, New Jersey) is a tool designed to cut a ledge inside the rim of the acetabulum, onto which a precisely trimmed, cemented, flanged cup can be fitted. The aim was to investigate the effect of the Rim Cutter on the intra-acetabular cement mantle pressure and the depth of cement penetration during cup insertion. The study had two parts. In the first part, hemi-pelvis models were fitted with pressure sensors. Pressure in the acetabulum was measured on insertion of a conventional cemented flanged cup with and without the use of a Rim Cutter to prepare the rim of the acetabulum. The second part assessed cement penetration when the same cups were inserted into a foam shell model. The shell was mounted in a jig and had holes drilled in it; the distance that cement penetrated into the holes was measured. A significant increase in cement pressure at the apex (p = 0.04) and the rim (p = 0.004) is seen when the Rim Cutter is used. Cement penetration in the Rim Cutter group was significantly increased at the rim of the acetabulum (p = 0.003). Insertion of a flanged cup after the acetabulum is prepared with the Rim Cutter leads to a significant increase in cement pressure and penetration during cup insertion in vitro when compared with conventional flanged cups.

Assessment of common hyperelastic constitutive equations for describing normal and osteoarthritic articular cartilage.

With the aim of providing information for modelling joint and limb systems, widely available constitutive hyperelastic laws are evaluated in this paper for their ability to predict the mechanical responses of normal and osteoarthritic articular cartilage. Load-displacement data from mechanical indentation were obtained for normal and osteoarthritic cartilage at 0.1 s(-1) and 0.025 s(-1) and converted to the stress-stretch ratio. The data were then fitted to the Arruda-Boyce, Mooney-Rivlin, neo-Hookean, Ogden, polynomial, and Yeoh hyperelastic laws in the MATLAB environment. Although each of the hyperelastic laws performed satisfactorily at the higher rate of loading, their ability to fit experimental data at the lower loading rate varied considerably. For the preferred models, coefficients were provided for stiff, soft, and average tissues to represent normal and degraded tissue at high and low loading rates. The present authors recommend the use of the Mooney-Rivlin or the Yeoh models for describing both normal and degraded articular cartilage, with the Mooney-Rivlin model providing the best compromise between accuracy and required computational power.

Diffuse reflectance near infrared spectroscopy can distinguish normal from enzymatically digested cartilage.

A non-destructive, diffuse reflectance near infrared spectroscopy (DR-NIRS) approach is considered as a potential tool for determining the component-level structural properties of articular cartilage. To this end, DR-NIRS was applied in vitro to detect structural changes, using principal component analysis as the statistical basis for characterization. The results show that this technique, particularly with first-derivative pretreatment, can distinguish normal, intact cartilage from enzymatically digested cartilage. Further, this paper establishes that the use of DR-NIRS enables the probing of the full depth of the uncalcified cartilage matrix, potentially allowing the assessment of degenerative changes in joint tissue, independent of the site of initiation of the osteoarthritic process.

Fresh-frozen vs. irradiated allograft bone in orthopaedic reconstructive surgery.

The use of allograft bone is increasingly common in orthopaedic reconstruction procedures. The optimal method of preparation of allograft bone is subject of great debate. Proponents of fresh-frozen graft cite improved biological and biomechanical characteristics relative to irradiated material, whereas fear of bacterial or viral transmission warrants some to favour irradiated graft. Careful review of the literature is necessary to appreciate the influence of processing techniques on bone quality. Whereas limited clinical trials are available to govern the selection of appropriate bone graft, this review presents the argument favouring the use of fresh-frozen bone allograft as compared to irradiated bone.

An alternative mechanical parameter for assessing the viability of articular cartilage.

This paper is a sequel to previously published findings showing that mechanical indentation alone cannot clearly discriminate between normal and degraded articular cartilage. Consequently, the structural elasticity potential Rc = epsilon r/sigma i, which combines indentation stress sigma i with near-instantaneous rebound epsilon r following unloading, is hypothesized as a potential cartilage assessment parameter, which arguably measures the integrity of the collagen fibre-proteoglycan entrapment system. To establish the validity of our hypothesis, samples of normal intact, artificially degraded, and osteoarthritic bovine cartilage were subjected to quasi-static compression at 0.1 s(-1) and 0.025 s(-1) to 30 per cent strain and then unloaded. A significant reduction in recovery was observed for artificially and naturally degraded samples in the first 5s following unloading (p < 0.01). The structural elasticity potential provided a considerable improvement over the results obtained using the individual indentation and rebound parameters to distinguish between paired normal and artificially degraded samples and indicated a high statistical significance of p < 0.005 when applied to the differentiation of normal and osteoarthritic samples.

Low cost polymer intramedullary nails for fracture fixation: a biomechanical study in a porcine femur model.

INTRODUCTION: Whilst intramedullary nailing is a commonly accepted technique for lower limb fracture fixation, the cost of nails can be prohibitive in hospitals in developing nations. In these institutions bone cement has found many off label applications, that whilst are effective do not meet manufacturers guidelines. The aim of this study was to examine the biomechanics of one such application, fracture fixation using a bone cement intramedullary nail. MATERIALS AND METHODS: Five porcine femurs underwent a mid-shaft osteotomy and were fixed using a nail made from antibiotic simplex bone cement. The torsional and flexural stiffness and shear modulus of these constructs were compared to five intact porcine femurs. RESULTS: The bone cement intramedullary nail was able to achieve relative stability in both torsion, with a mean shear modulus of 0.17 GPa and in flexion with a mean flexural stiffness of 358 N/mm. This corresponds to 47 and 22% of the respective measurements in the intact femurs. The mean ultimate flexural strength of fracture/nail constructs was 936 +/- 350 N, which is 20% of the ultimate flexural strength of an intact porcine femur (4,820 +/- 698 N). CONCLUSION: Intramedullary nails made from bone cement were able to provide sufficient promise in this situation to warrant further investigation for their applicability as a low cost alternative for use in developing countries.

Cell response in mixtures of surfactant-culture medium--towards a systemic approach to cell-based treatments for focal osteoarthritis.

Osteoarthritis (OA), the most common form of arthritis is a degenerative joint disease, which causes severe long-term pain and physical disability. It is becoming more important to improve diagnosis and understanding of the disease process and subsequently develop new intervention to delay or even reverse the disease progress. Our study was designed to combine two relatively novel treatment techniques, autologous chondrocyte transplantation (ACT) and proposed application of medical remedies based on surface-active phospholipids. To this end we exposed chondrocyte to culture environments with mixtures of culture medium and phospholipid solutions. Following various culture periods, cell survival and well-being were determined by measuring proliferation and assessing morphological features, and comparing these with the behaviour of cells grown in classical which were not mixed with surfactant, i.e., control culture medium. Scanning electron microscopy and light microscopy demonstrate that the cells exposed to mixtures with surfactant were as healthy as those in the control environment with polygonal morphology, while proliferation assay indicated a noticeably higher level of proliferation over similar periods, for cells cultured in media that was mixed with surfactants. Also, the cells in media with unsaturated surfactants responded better than those cultured in mixtures containing saturated surfactant.

Joint laminate degradation assessed by reflected ultrasound from the cartilage surface and osteochondral junction.

The ability to quantify and qualify the progression of joint degeneration is becoming increasingly important in surgery. This paper examines the patterns of relative ultrasound reflection from normal, artificially and naturally degraded cartilage-on-bone, particularly investigating the potential of the ratio of reflection coefficients from the surface and osteochondral junction in distinguishing normal from osteoarthritic tissue. To this end, the reflection coefficients from the articular surface and osteochondral junction of normal cartilage-on-bone samples were calculated and compared to samples after the removal of proteoglycans, disruption of the collagen meshwork, delipidization of the articular surface and mechanical abrasion. Our results show that the large variation across normal and degraded joint samples negates the use of an isolated bone reflection measurement and to a lesser extent, an isolated surface reflection. The relative surface to bone reflections, calculated as a ratio of reflection coefficients, provided a more consistent and statistically significant (p < 0.001) method for distinguishing each type of degradation, especially osteoarthritic degradation, and due to the complementary relationship between surface and bone reflections was found to be an effective method for distinguishing degraded from normal tissue in the osteoarthritic joint, independent of the site of initiation of the osteoarthritic process.

Validation for the reduced Western Ontario and McMaster Universities Osteoarthritis Index function scale.

PURPOSE: To assess the criterion validity, repeatability, and the missing value protocol of the reduced Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function scale ('reduced scale'). METHODS: Three separate studies were performed: a cross-over study to compare the full- and reduced-scale scores in 66 UK patients for validity, a test-retest study for repeatability in 103 Australian patients, and a study for the missing value protocol of the reduced-scale questionnaire. RESULTS: There was no significant difference between scores for the full- and reduced-scale questionnaires in both cross-over and test-retest studies. For the missing value protocol of the reduced-scale questionnaire, when 3 or more of the 7 items were missing, the patient's response was regarded as invalid and the sub-scale score was eliminated from further analysis; when 2 or fewer items were missing, the mean value of the sub-scale was substituted for the missing values. CONCLUSIONS: The reduced-scale questionnaire retains excellent validity and repeatability. Its use is recommended along with the original pain dimension in studies of total joint replacement.

Structural adaptations in compressed articular cartilage measured by diffusion tensor imaging.

OBJECTIVE: To demonstrate the use of diffusion tensor magnetic resonance micro-imaging to observe adaptations of collagen fibres to mechanical compression in articular cartilage. METHODS: Spin-echo and diffusion tensor images (156x156microm in-plane resolution, 2mm slice thickness) of bovine cartilage were obtained at a magnetic field of 7.0T in relaxed and compressed states. The parameters determined were: T2, maximum and mean diffusivity, direction of the maximum diffusion eigenvector and fractional anisotropy of diffusion. RESULTS: A correlation was found between the compressive strain applied to the cartilage and the change in both magnitude and direction of the maximum diffusivity. Compression resulted in a decrease in both the maximum and mean eigenvalues, particularly in the surface and transitional zones, while the change in orientation of the eigenvectors corresponding to maximum diffusion was greatest in the transitional region. In this region, the average orientation of the principal eigenvectors with respect to the normal to the articular surface increased by up to 40 degrees, indicating that the collagen fibre bundles were oriented more parallel to the surface when compressed. CONCLUSIONS: Diffusion tensor imaging can be used to monitor the changes in the direction of the collagen fibres due to compression. It may form the basis of a new non-invasive approach to functional evaluation of cartilage, with potential applications in the diagnosis and treatment of osteoarthritis.

Re-design of the Exeter V40 long-stem femoral component for ease of removal.

Clinical experience shows that removal of the Exeter long-stem femoral component (220 mm, 240 mm, 260 mm) of total hip arthroplasty is extremely difficult, often requiring splitting of the femur. To identify the reason for this, measurements of stem geometry and force required to pull the stems out of the cement mantle were conducted on three original Exeter long-stem and one standard femoral components. All implants required an initial force of approximately 4 kN for release from the cement. The long-stem components then required much larger forces and hence much higher expenditure of energy to pull them clear of the cement. This was attributed to the reverse taper seen on the nominally cylindrical distal section of the long-stem components. Following re-design of the manufacturing process to ensure the taper continued to the implant's distal tip, four further implants were tested. These demonstrated the requirement for initial cement release but then required no further energy expenditure similar to the standard stem. This study clearly demonstrated that the original difficulty in removing these long stems was owing to the manufacturing process resulting in a reverse taper on the distal stem. The adoption of recommended manufacturing changes to ensure the taper continues to the distal tip removed this difficulty.

Platelet and leukocyte activation in salvaged blood and the effect of its reinfusion on the circulating blood.

Postoperative wound drainage reinfusion reduces the frequency of homologous blood transfusion. The salvaged blood is depleted of coagulation factors but may contain platelets and leukocytes which are activated, and therefore potentially procoagulant. We ascertained the degree of activation of platelets and leukocytes in salvaged blood and asked whether their infusion produced any measurable effect on patients' coagulation system. We prospectively randomized 24 patients who had total knee arthroplasties to reinfusion of salvaged autologous blood (n = 12) or a standard drain with no reinfusion (n = 12). Analysis of the salvaged blood showed marked activation of platelets as shown by their expression of P-selectin, CD40 ligand, and Factor V/Va, and as increased numbers of platelet-derived microparticles. After reinfusion there was no measurable effect on activation markers of circulating platelets or leukocytes but there was a decrease in platelet count in the reinfused group compared with the control group. Levels of prothrombin fragment F1 + 2 (suggesting thrombin formation) increased in the reinfused group compared with control group, possibly indicating activation of coagulation systemically. The platelets and leukocytes in salvaged blood are markedly activated and their reinfusion causes a decrease in platelet count in the recipient and a possible increase in thrombin generation potentially favoring thrombosis.

In vitro degradation of articular cartilage: does trypsin treatment produce consistent results?

It is common practice in laboratories to create models of degraded articular cartilage in vitro and use these to study the effects of degeneration on cartilage responses to external stimuli such as mechanical loading. However, there are inconsistencies in the reported action of trypsin, and there is no guide on the concentration of trypsin or the time to which a given sample can be treated so that a specific level of proteoglycan depletion is achieved. This paper argues that before any level of confidence can be established in comparative analysis it is necessary to first obtain samples with similar properties. Consequently, we examine the consistency of the outcome of the artificial modification of cartilage relative to the effects of the common enzyme, trypsin, used in the process of in vitro proteoglycan depletion. The results demonstrate that for a given time and enzyme concentration, the action of trypsin on proteoglycans is highly variable and is dependent on the initial distribution and concentration of proteoglycans at different depths, the intrinsic sample depth, the location in the joint space and the medium type, thereby sounding a note of caution to researchers attempting to model a proteoglycan-based degeneration of articular cartilage in their experimental studies.

A review of prosthodontic management of fibrous ridges.

'Fibrous' or 'flabby' alveolar ridges pose significant problems for the provision of stable and retentive dental prostheses for affected patients. In particular, problems arise during the act of impression taking, when forces cause the mobile denture bearing tissues to become distorted. The purpose of this paper is to review the impression techniques that can be used to optimise the treatment of edentulous patients with 'flabby' alveolar ridges.

An algorithm for locating the center of the ankle joint in knee navigation surgery.

The primary aim of computer-assisted knee arthroplasty is to improve the alignment of the implanted prostheses. Accurate component alignment is dependent on the establishment of accurate anatomical reference points. Current techniques for establishing the center of the ankle joint, especially in the coronal plane, rely solely on clinical judgment in relation to the position of the center of the ankle joint. The aim of this study was to determine if an algorithm could be developed, based on establishing the most prominent points on the medial and lateral malleoli on 3D CT scans, to accurately and reproducibly establish the position of the center of the ankle joint. To determine this, images of 20 ankles were obtained and axial, coronal, and sagittal 2D reconstructions were manipulated on a workstation. Two observers independently performed relevant measurements and calculations. The calculated data was found to be reproducible with a very small standard deviation in each plane. This algorithm is able to provide accurate measurements of the ankle joint in knee navigation surgery. Caution must be exercised in anatomically abnormal ankles, as the calculations of the ankle center were found to be significantly different.

Safe femoral pin placement in knee navigation surgery: a cadaver study.

A number of navigation systems used for total knee replacement surgery currently require the insertion of a distal femoral reference sensor pin, which is placed anterior to posterior just superior to the level of the knee joint. There is potential for the posterior neurovascular bundle to be damaged during the insertion of this sensor device. The aim of this cadaveric study was to identify the structures at risk during insertion of the distal femoral sensor, and determine whether a safe zone for insertion could be identified. Sixteen cadaveric lower limbs (8 pairs) were studied. In each knee Steinman pins were passed from anterior to posterior, 5 cm proximal to the level of the femoral articular cartilage, directly AP and angled at 30 degrees passing medially or laterally. All pins that were passed directly from anterior to posterior and from lateral to medial passed within 5 mm of a major neurovascular structure, while 62.5% of pins passing from medial to lateral passed within 5 mm of a major neurovascular structure. The popliteal vessels and the sciatic nerve are at risk of injury from a navigation pin or drill placed in the distal femur during knee navigation. Caution should be exercised in passing these pins and alternate methods of fixing femoral sensors should be considered.

Characterization of ARC, apoptosis repressor interacting with CARD, in normal and dystrophin-deficient skeletal muscle.

Duchenne muscular dystrophy is an X-linked recessive disorder, primarily characterized by progressive muscle weakness and wasting. The disease results from the absence of dystrophin, however the precise molecular mechanisms leading to muscle pathology are poorly understood. Dystrophic muscles undergo increased oxidative stress and altered calcium homeostasis, which may contribute to myofiber loss by triggering both necrosis and apoptosis. Recent studies have identified ARC (apoptosis repressor with caspase recruitment domain) as an abundant protein in human muscle that can inhibit both hypoxia and caspase-8-induced apoptosis as well as protect cells from oxidative stress. To explore a potential role for ARC in protecting muscle fibers from dystrophic breakdown, we have cloned and characterized murine ARC and studied its expression in normal and dystrophic mouse muscle. ARC is expressed at high levels in striated muscle and displays fiber-type restricted expression patterns. ARC expression levels are normal in dystrophic mdx mice, although the intracellular localization pattern of ARC is slightly altered compared with normal muscles. Overexpression of ARC in transgenic mdx mice failed to alleviate the dystrophic pathology in skeletal muscles, suggesting that misregulation of the molecular pathways regulated by ARC does not significantly contribute to myofiber death.

Normal and prosthetic synovial joints are lubricated by surface-active phospholipid: a hypothesis.

Much evidence supports the hypothesis that surface-active phospholipid (SAPL), which imparts the thin hydrophobic outermost lining to the normal articular surface, is the boundary lubricant reducing friction to remarkably low levels. We review this evidence and further hypothesize that SAPL produced in type B synoviocytes will also lubricate prostheses after implantation. This could explain why implanted hips display far less wear than hips in simulated wear trials do, even using protein as the lubricant whereas rougher surfaces can be tolerated in vivo. We introduce the concept that a deficiency of SAPL might explain the selective failure of prostheses just as osteoarthritic articular surfaces are deficient. This, in turn, leads to the replenishment of SAPL, as tested in OA, and the concept of prelubricating prostheses before implantation.