Michiel Mulier

Fatigue behavior of porous biomaterials manufactured using selective laser melting

Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4).

Bone regeneration performance of surface-treated porous titanium

The large surface area of highly porous titanium structures produced by additive manufacturing can be modified using biofunctionalizing surface treatments to improve the bone regeneration performance of these otherwise bioinert biomaterials. In this longitudinal study, we applied and compared three types of biofunctionalizing surface treatments, namely acid-alkali (AcAl), alkali-acid-heat treatment (AlAcH), and anodizing-heat treatment (AnH). The effects of treatments on apatite forming ability, cell attachment, cell proliferation, osteogenic gene expression, bone regeneration, biomechanical stability, and bone-biomaterial contact were evaluated using apatite forming ability test, cell culture assays, and animal experiments. It was found that AcAl and AnH work through completely different routes. While AcAl improved the apatite forming ability of as-manufactured (AsM) specimens, it did not have any positive effect on cell attachment, cell proliferation, and osteogenic gene expression. In contrast, AnH did not improve the apatite forming ability of AsM specimens but showed significantly better cell attachment, cell proliferation, and expression of osteogenic markers. The performance of AlAcH in terms of apatite forming ability and cell response was in between both extremes of AnH and AsM. AcAl resulted in significantly larger volumes of newly formed bone within the pores of the scaffold as compared to AnH. Interestingly, larger volumes of regenerated bone did not translate into improved biomechanical stability as AnH exhibited significantly better biomechanical stability as compared to AcAl suggesting that the beneficial effects of cell-nanotopography modulations somehow surpassed the benefits of improved apatite forming ability. In conclusion, the applied surface treatments have considerable effects on apatite forming ability, cell attachment, cell proliferation, and bone ingrowth of the studied biomaterials. The relationship between these properties and the bone-implant biomechanics is, however, not trivial.

Hyaluronic Acid in the Treatment of Knee Osteoarthritis

AbstractBackground: Although accepted as a conservative treatment option for knee osteoarthritis, the debate about the effectiveness of intra-articular treatment with hyaluronic acid (HA) is still ongoing because of contrasting outcomes in different clinical studies. Several well designed clinical studies showed a significant improvement in pain at follow-up compared with baseline but no significant improvement comparing the efficacy of HA with placebo (saline) or with other conservative treatment options. Notwithstanding the effectiveness of different types of intra-articular HA products, the question of whether one HA product is better than another is still unanswered. In this systematic review we compare the effects of intra-articularly administered HA with intra-articularly administered placebo in general and, more specifically, the effects of individual HA products with placebo. We also compare the efficacy of different HA products. Methods: A systematic review of randomized controlled trials (RCTs) was conducted using databases including MEDLINE, Cochrane Database of Systematic Reviews, Cochrane Clinical Trial Register and EMBASE. Results: Seventy-four RCTs were included in this systematic review. HA improves pain by approximately 40–50% compared with baseline levels. However, when compared with saline the difference in efficacy is not that large. Due to a large ‘placebo effect’ of saline (approximately 30% pain reduction, persisting for at least 3 months) we determined a weighted mean difference between the efficacy of HA and saline of just 10.20 using the visual analog scale for pain. It is debatable whether this difference reaches the minimum clinically important difference. Comparing the different HA products, which vary in the molecular weight, concentration, and volume of HA, we were not able to conclude that one brand has a better efficacy than another due to the heterogeneity of the studies and outcomes. Discussion: In the future it will be important to determine the exact mechanism of action of placebo as this may give us an idea of how to treat osteoarthritis more efficiently. Due to the limitations of this review (follow-up of just 3 months and large heterogeneity of the included studies), it is also important to compare the different HA products to determine which product(s), or which molecular weight range, concentration, or volume of HA is the best option to treat osteoarthritis. Our recommendation is to start large (multicenter) RCTs to give us more evidence about the efficacy of the different HA products.

Additively manufactured porous tantalum implants

The medical device industrys interest in open porous, metallic biomaterials has increased in response to additive manufacturing techniques enabling the production of complex shapes that cannot be produced with conventional techniques. Tantalum is an important metal for medical devices because of its good biocompatibility. In this study selective laser melting technology was used for the first time to manufacture highly porous pure tantalum implants with fully interconnected open pores. The architecture of the porous structure in combination with the material properties of tantalum result in mechanical properties close to those of human bone and allow for bone ingrowth. The bone regeneration performance of the porous tantalum was evaluated in vivo using an orthotopic load-bearing bone defect model in the rat femur. After 12 weeks, substantial bone ingrowth, good quality of the regenerated bone and a strong, functional implant-bone interface connection were observed. Compared to identical porous Ti-6Al-4V structures, laser-melted tantalum shows excellent osteoconductive properties, has a higher normalized fatigue strength and allows for more plastic deformation due to its high ductility. It is therefore concluded that this is a first step towards a new generation of open porous tantalum implants manufactured using selective laser melting.

What is the evidence for viscosupplementation in the treatment of patients with hip osteoarthritis? Systematic review of the literature

IntroductionOsteoarthritis (OA) is a disease of the synovial joints and is the most common cause of chronic pain in the elderly. One of the treatment modalities for OA of the hip is viscosupplementation (VS). Today there are several different formulations of viscosupplements produced by different manufactures of different molecular weights. The objective of this review is to asses the efficacy of VS treatment of hip OA osteoarthritis in the current literature.Material and methodsThe following databases were searched: Medline (period 1966 to November 2006), Cochrane Database of Systematic Reviews (1988 to November 2006), Cochrane Clinical Trial Register (1988 to November 2006), Database of Abstracts on Reviews and Effectiveness, Current Controlled Trials, National Research Register and Embase (January 1988 to November 2006). The search terms [osteoarthritis, hip (joint), viscosupplementation, hyaluronic acid, hyaluronan, sodium hyaluronate and trade names] were applied to identify all studies relating to the use of VS therapy for OA of the hip joint.ResultsSixteen articles concerning the efficacy of a total of 509 patients undergoing VS treatment for hip OA were included. Twelve European studies, three Turkish studies and one American study with Levels of Evidence ranging from I to IV evaluated the following products: Hylan G-F 20, Hyalgan®, Ostenil®, Durolane®, Fermatron® and Orthovisc®. Heterogeneity of included studies did not allow pooled analysis of data.DiscussionDespite the relatively low Level of Evidence of the included studies, VS performed under fluoroscopic or ultrasound guidance seems an effective treatment and may be an alternative treatment of hip OA. Intra-articular injection of (derivatives of) HA into the hip joint appears to be safe and well tolerated. However, VS cannot be recommended as standard therapy in hip OA for wider populations, and therefore the indications remain a highly individualised matter.

In vivo evaluation of a vibration analysis technique for the per-operative monitoring of the fixation of hip prostheses

BackgroundThe per-operative assessment of primary stem stability may help to improve the performance of total hip replacement. Vibration analysis methods have been successfully used to assess dental implant stability, to monitor fracture healing and to measure bone mechanical properties. The objective of the present study was to evaluate in vivo a vibration analysis-based endpoint criterion for the insertion of the stem by successive surgeon-controlled hammer blows.MethodsA protocol using a vibration analysis technique for the characterisation of the primary bone-prosthesis stability was tested in 83 patients receiving a custom-made, intra-operatively manufactured stem prosthesis. Two groups were studied: one (n = 30) with non cemented and one (n = 53) with partially cemented stem fixation. Frequency response functions of the stem-femur system corresponding to successive insertion stages were compared.ResultsThe correlation coefficient between the last two frequency response function curves was above 0.99 in 86.7% of the non cemented cases. Lower values of the final correlation coefficient and deviations in the frequency response pattern were associated with instability or impending bone fracture. In the cases with a partially cemented stem an important difference in frequency response function between the final stage of non cemented trial insertion and the final cemented stage was found in 84.9% of the cases. Furthermore, the frequency response function varied with the degree of cement curing.ConclusionThe frequency response function change provides reliable information regarding the stability evolution of the stem-femur system during the insertion. The protocol described in this paper can be used to accurately detect the insertion end point and to reduce the risk for intra-operative fracture.

Revival of pure titanium for dynamically loaded porous implants using additive manufacturing

Additive manufacturing techniques are getting more and more established as reliable methods for producing porous metal implants thanks to the almost full geometrical and mechanical control of the designed porous biomaterial. Today, Ti6Al4V ELI is still the most widely used material for porous implants, and none or little interest goes to pure titanium for use in orthopedic or load-bearing implants. Given the special mechanical behavior of cellular structures and the material properties inherent to the additive manufacturing of metals, the aim of this study is to investigate the properties of selective laser melted pure unalloyed titanium porous structures. Therefore, the static and dynamic compressive properties of pure titanium structures are determined and compared to previously reported results for identical structures made from Ti6Al4V ELI and tantalum. The results show that porous Ti6Al4V ELI still remains the strongest material for statically loaded applications, whereas pure titanium has a mechanical behavior similar to tantalum and is the material of choice for cyclically loaded porous implants. These findings are considered to be important for future implant developments since it announces a potential revival of the use of pure titanium for additively manufactured porous implants.

A custom-made guide-wire positioning device for Hip Surface Replacement Arthroplasty: description and first results

BackgroundHip surface replacement arthroplasty (SRA) can be an alternative for total hip arthroplasty. The short and long-term outcome of hip surface replacement arthroplasty mainly relies on the optimal size and position of the femoral component. This can be defined before surgery with pre-operative templating. Reproducing the optimal, templated femoral implant position during surgery relies on guide wire positioning devices in combination with visual inspection and experience of the surgeon. Another method of transferring the templated position into surgery is by navigation or Computer Assisted Surgery (CAS). Though CAS is documented to increase accurate placement particularly in case of normal hip anatomy, it requires bulky equipment that is not readily available in each centre.MethodsA custom made neck jig device is presented as well as the results of a pilot study.The device is produced based on data pre-operatively acquired with CT-scan. The position of the guide wire is chosen as the anatomical axis of the femoral neck. Adjustments to the design of the jig are made based on the orthopedic surgeons recommendations for the drill direction. The SRA jig is designed as a slightly more-than-hemispherical cage to fit the anterior part of the femoral head. The cage is connected to an anterior neck support. Four knifes are attached on the central arch of the cage. A drill guide cylinder is attached to the cage, thus allowing guide wire positioning as pre-operatively planned.Custom made devices were tested in 5 patients scheduled for total hip arthroplasty. The orthopedic surgeons reported the practical aspects of the use of the neck-jig device. The retrieved femoral heads were analyzed to assess the achieved drill place in mm deviation from the predefined location and orientation compared to the predefined orientation.ResultsThe orthopedic surgeons rated the passive stability, full contact with neck portion of the jig and knife contact with femoral head, positive. There were no guide failures. The jig unique position and the number of steps required to put the guide in place were rated 1, while the complexity to put the guide into place was rated 1-2. In all five cases the guide wire was accurately positioned. Maximum angular deviation was 2.9° and maximum distance between insertion points was 2.1 mm.ConclusionsPilot testing of a custom made jig for use during SRA indicated that the device was (1) successfully applied and user friendly and (2) allowed for accurate guide wire placement according to the preoperative plan.

Hyaluronic acid for the treatment of osteoarthritis in all joints except the knee: what is the current evidence?

BackgroundThe use of intra-articular hyaluronic acid (HA) is a well known treatment in patients with knee osteoarthritis (OA). In other joints, less evidence is available about the efficacy of treatment with intra-articular HA. HA is also used intra-articularly in the metatarsophalangeal-1 joint, the ankle, the hip, the sacroiliac joint, the facet joints, the carpometacarpal-1 joint, the shoulder and the temporo-mandibular joint. In this systematic review we include all prospective studies about the effects of intra-articular HA in the above-mentioned joints. Its use in the knee joint, however, will be discussed in a separate article in this journal.MethodsA systematic review was conducted using databases including MEDLINE, Cochrane Database of Systematic Reviews, Cochrane Clinical Trial Register, and EMBASE.ResultsAfter performing a solid systematic review using a rigid methodology and trying to pool the outcomes of different studies, we noticed that, compared with baseline, there is statistical evidence for a positive effect of intra-articular HA. However, there is limited evidence HA is superior to placebo and no evidence that intra-articular HA is better than corticosteroids or other conservative therapies.ConclusionOur recommendation for future research is that one should focus on adequately powered randomized trials comparing HA treatment with other types of intra-articular or conservative treatment. We think it is useless to further perform and publish (large) non-comparative prospective studies about the use of HA in the treatment of problems caused by OA. It is well perceived that HA exerts positive effects in the treatment of OA, but up to now there is no (strong) evidence available that HA is superior to other treatments of OA such as corticosteroids, physiotherapy or other conservative measures.

Two-stage revision of an infected total hip arthroplasty: a follow-up of 136 patients

Background and purpose Periprosthetic infection of a total hip arthroplasty (THA) is commonly treated with a two-stage revision procedure. After resection of the infected THA and placement of a cement spacer loaded with antibiotics, a THA is inserted at a second procedure to restore hip function and mobility. Revision surgery carries a significant risk of complications. This study focuses on hip function, rate of complications and reinfection after two-stage revision surgery for an infected THA. Patients and methods From January 1996 to April 2010, 136 patients underwent revision surgery after removal of an infected THA. Follow-up ranged from 2 years to more than 15 years. Hip function was evaluated using the modified Harris Hip Score (mHHS) and the Hip disability and Osteoarthritis Outcome Score (HOOS). Visual Analogue Scale (VAS) measured pain. Annual follow-up included radiographs of the affected hip and blood sampling for inflammatory parameters. Results After revision surgery, average mHHS was 63% and average HOOS was 54%. VAS pain averaged 26.8 on a 100-point scale and 40% of patients had no pain. Prosthesis-related complications unrelated to sepsis occurred in 32%. Most common were periprosthetic fractures, leg length discrepancy and dislocation. Reinfection occurred in 13% of these patients and Coagulase Negative Staphylococcus (CNS) was isolated in 67%. Conclusion Two-stage revision surgery is an accepted treatment for infected THAs. However, complications are common and hip function afterwards is modest. As previous studies have shown, CNS is an important microorganism in reinfection.