Ti-6Al-4V is the most common alloy used for orthopaedic implants. Its popularity is due to low density, superior corrosion resistance, good osseointegration and lower elastic modulus when compared to other commonly used alloys such as CoCrMo and stainless steel. In fact, the use of Ti64 has even further increased lately since recent controversy around adverse local tissue reactions and implant failure related to taper corrosion of CoCrMo alloy. However, implants made from Ti64 can fail in some cases due to fatigue fracture, sometimes related to oxide induced stress corrosion cracking or hydrogen embrittlement, or preferential corrosion of the beta phase. Studies performed with Ti-6Al-4V do often not consider that the alloy itself may have a range of characteristics that can vary and could significantly impact the implant properties. These variations are related to the material microstructure which depends not only on chemical composition, but also the manufacturing process and subsequent heat treatments. Different microstructures can occur in implants made form wrought alloys, cast alloys, and more recently, additive manufactured (AM) alloys. Implant alloy microstructure drives mechanical and electrochemical properties. Therefore, this study aims to analyse the microstructure of Ti-6Al-4V alloy of additive manufactured and conventional retrieved orthopaedic implants such as acetabular cups, tibial trays, femoral stem and modular neck by means of electron backscatter diffraction (EBSD). Microstructural features of interest include grains shape and size, phase content and distribution, preferred grain orientation (texture), alloying elements distribution (homogenization) and presence of impurities. Additionally, we demonstrate the direct impact of different microstructural features on hardness. We analysed 17 conventional devices from 6 different manufacturers, 3 additive manufactured devices from 2 different manufactures and 1 control alloy (bar stock). The preliminary results showed that even though all implants have the same chemical composition, their microstructural characteristics vary broadly. Ti64 microstructure of conventional alloys could be categorized in 3 groups: equiaxed grains alloys (Fine and Coarse), bimodal alloys and dendritic alloys. The additive manufactured implants were classified in an additional group on its own which consists of a needle-like microstructures - similar to Widmanstätten patterns, Fig. 1, with a network of β phase along α phase grains. Furthermore, AM alloys exhibited residual grain boundaries from the original β grains from the early stage of the solidification process, Fig. 2. These characteristics may have implication on the fatigue and corrosion behaviour. In addition, it we observed inhomogeneous alloying element distribution in some cases, Fig. 3, especially for the additive manufactured alloys, which also may have consequences on corrosion behaviour. Finally, the hardness testing revealed that the implants with large grain size, such as AM alloys, exhibit low hardness values, as expected, but also the amount of beta phase correlated positively with lower hardness. Grain aspect ratio and beta phase grain size correlated positively with higher hardness. In summary, we found that common Ti64 implants can exhibit a broad variety of different alloy microstructures and the advent of AM alloys introduces an entirely new category. It is imperative to determine the ideal microstructure for specific applications.

Little is known about the relationship between head-neck corrosion and its effect on the periprosthetic tissues and distant organs of patients hosting well-functioning devices. The purpose of this study was to investigate in postmortem retrieved specimens the degree and type of taper damage, and the corresponding histologic responses in periprosthetic tissues and distant organs.

Fifty postmortem THRs (34 primaries, 16 revisions) retrieved after 0.5 to 26 years were analyzed. Forty-three implants had a CoCrMo stem and seven had a Ti6Al4V stem. All heads were CoCrMo and articulated against polyethylene cups (19 XLPE, 31 UHMWPE). H&E sections of joint pseudocapsules, liver, spleen, kidneys and lymph nodes were graded 1–4 for the intensity of various inflammatory cell infiltrates and tissue characteristics. Corrosion damage of the taper surfaces was assessed using visual scoring and quantitated with an optical coordinate measuring machine. SEM analysis was used to determine the acting corrosion mode. Polyethylene wear was assessed optically. The majority of tapers had minimal to mild damage characterized by local plastic deformation of machining line peaks. Imprinting of the stem topography onto the head taper surface was observed in 18 cases. Column damage on the head taper surface occurred in three cases. All taper surfaces scored moderate or severe exhibited local damage features of fretting and/or pitting corrosion.

Moderate or severe corrosion of the head and/or trunnion was present in nine hips. In one asymptomatic patient with bilateral hips, lymphocyte-dominated tissue reactions involving perivascular infiltrates of lymphocytes and plasmacytes were observed. In this patient, mild, focal lymphocytic infiltrates were also present in the liver and kidneys, and there was focal histiocytosis and necrosis of the para-aortic lymph nodes. These two implants, which had been in place for 58.6 and 60.1 months, had severe intergranular corrosion of the CoCrMo trunnion, and column damage and imprinting on the head taper. In the other 41 hips, macrophage responses in the joint pseudocapsule to metallic and/or polyethylene wear particles ranged widely from minimal to marked. Focal necrosis in the pseudocapsules of 12 arthroplasties was related to high concentrations of CoCrMo, TiAl4V, TiO, BaSO4 and polyethylene wear particles. High concentrations of these particles were also detected in para-aortic lymph nodes. Rare to mild macrophages were observed in liver and spleen.

This is a comprehensive study of wear and corrosion within well-functioning postmortem retrieved THRs, and the resulting local and distant tissue reactions. One of eight patients with moderate or severe corrosion did have a subclinical inflammatory response dominated by lymphocytes after five years. To what extent such an inflammatory process might progress to become symptomatic is not known. Ionic and particulate products generated by corrosion disseminated systemically. The minor lymphocytic infiltrate in the liver and kidneys of one subject with bilateral severely corroded head-neck junctions might suggest possible metal toxicity. The diagnosis of adverse tissue reactions to corrosion of modular junctions can be challenging. Postmortem retrieval studies add to our understanding of the nature and progression of lymphocyte-dominated adverse local and potentially systemic tissue reactions to corrosion of modular junctions.

Introduction

Ideally, standardized wear testing protocols replicate the in vivo motions and forces of TKR patients. In a previous study with 30 TKR patients, two distinct in vivo gait patterns emerged, one characterized as having low anteroposterior (AP-L) motion and the other high anteroposterior (AP-H) motion. The aim of this study was to determine the effect of the two in vivo-determined gait patterns on total and backside insert wear in comparison with the ISO standard 14243-3. In order to differentiate and accurately quantify topside and backside wear, a novel technique was employed where different lanthanide tracers are incorporated into the polyethylene during manufacture.

Wear and corrosion debris generated from total hip replacements (THR) can cause adverse local tissue reactions (ALTR) or osteolysis, often leading to premature implant failure. The tissue response can be best characterized by histopathological analysis, which accurately determines the presence of cell types, but is limited in the characterization of biochemical changes (e.g. protein conformation alteration). Fourier transform infrared micro-spectroscopy imaging (FTIRI) enables rapid analysis of the chemical structure of biological tissue with a high spatial resolution, and minimal additional sample preparation. The data provides the most information through multivariate method carried out by hierarchical clustering analysis (HCA).

It is the goal of this study to demonstrate the beneficial use of this multivariate approach in providing pathologist with biochemical information from cellular and subcellular organization within joint capsule tissue retrieved from THR patients.

Joint capsule tissue from 2 retrieved THRs was studied. Case 1: a metal-on-polyethylene THR, and Case 2: a dual modular metal-on-metal THR. Prior to FTIRI analysis, tissue samples were formalin-fixed paraffin-embedded and 5μm thick microtome sectioned samples were prepared and mounted on BaF₂ discs and deparaffinized. FTIRI data were collected using high-definition transmission mode (pixel size: ∼1.1 μm²). Hyperspectral images were exported to CytoSpec V2.0.06 for processing and reconstruction into pseudo-color maps based on cluster assignments.

Case 1 exhibited a strong presence of lymphocytes and macrophages (Fig. 1a). Since the process of taking second derivatives reduces the half width of the spectral peaks, it increases the sensitivity toward detecting shoulders or second peaks that may not be apparent in the raw spectra (Fig. 1b). Thus, areas occupied by lymphocytes and macrophages can be easily distinguished providing a fast tissue screening method. Here, HCA was able to distinguish macrophages and lymphocytes based on the infrared response, even in areas where both occurred intermixed. (Fig. 1c) The tissue in direct proximity to cells had a slightly altered collagenous structure. Case 1 also exhibited multiple glassy, green particles which can typically observed around THRs that underwent taper corrosion (Fig. 2a). HCA image was able to visualize and distinguish large CrPO₄ particles, embedded within fibrin exudate rich areas, collagenous tissue without inflammatory cells, and a nearby area with a strong macrophage presence and some finer CrPO₄ particles (Fig. 2d). Moreover, this method can not only locate macrophages, but distinguish particle-laden macrophages depending the type of particles within the cells. In Case 2 (Fig. 3a), clustering results (Fig. 3 b&c) are consistent with the fact that different particle types are associated with MoM bearing surface wear (Co rich particles), corrosion of the CoCrMo taper junctions (Cr-oxides and –phosphate), fretting of Ti-alloy dual modular tapers (Ti-oxides, Ti alloy particles), and even suture debris, which all occurred in this case. Although details of debris types are not available, specifications are possible by coupling other techniques.

The results demonstrate that multivariate FTIRI based spectral histopathology is a powerful tool to characterize the chemical structure and foreign body response within periprosthetic tissue, thus providing insights into the biological impact of different types of implant debris.

For any figures or tables, please contact the authors directly.

Total Knee Arthroplasty (TKA) necessitates disruption of well-vascularised tissue during exposure and soft tissue release as well as from the cutting of bone, and thus bleeding into the joint space routinely occurs to some degree following TKA. Defining a complication from bleeding is not necessarily straightforward, but includes 3 different conditions: hemarthrosis, hematoma, and bloody wound drainage. All of these conditions can be seen in the normal postoperative setting, and when mild, may be simply observed. However, persistent swelling resulting in clinical symptoms should be appropriately treated.

A hemarthrosis is defined as blood being contained in the knee capsule. Although some bleeding is expected, “excessive” hemarthrosis results in increased pain limiting or difficulty regaining motion. If high levels of fluid pressure are present, rupture of the arthrotomy may occur. A hematoma occurs when intra-articular blood escapes the arthrotomy and drains into the overlying soft tissues. This may occur following performance of a large lateral release or an insufficient arthrotomy closure or simply secondary to a large hemarthrosis under tension. Symptoms include ecchymosis, soft tissue swelling, and potential skin complications. Increased pain and limited range of motion frequently accompany these symptoms. Wound drainage may present as a knee that continues to have bloody or serous drainage that continues long after the first or second dressing change. It is this continued wound drainage that is most worrisome, with increased wound infection rates when prolonged drainage is allowed to persist.

While excessive bleeding during the early postoperative period is most common, isolated or recurrent hemarthrosis may occur long after recovery from surgery. The incidence of postoperative hemarthrosis is not well studied, but the need for surgical treatment is uncommon. Recurrent hemarthrosis is also relatively rare after TKA and has been reported at rates between 0.3% and 1.6%. The etiology of this complication can be systemic or local, and initial workup should include coagulation studies to rule out any underlying systemic coagulopathy. Conservative therapy including rest, cooling, and elevation is the preferred treatment for mild cases. If conservative treatment is not successful, or the acute hemarthrosis is clinically tense, interfering with recovery, or threatening wound healing, drainage may be the preferable option. This can be done by opening the arthrotomy in the operating room or through large bore arthroscopy cannulae. Careful attention to debridement of clotted blood must be followed by a meticulous search for potential sources of bleeding which should be managed appropriately.

Recurrent hemarthrosis may occur at any time but is not commonly diagnosed until the patient has left the early recovery period. Repeated bleeding episodes may lead to an inflammatory cascade that propagates bleeding events more readily. If coagulation studies are normal, the most common source is the impingement of proliferative synovium or other retained soft tissue between the articulating components of the knee prosthesis. Other causes may be multifactorial and synergistic but are not well understood, making diagnosis and treatment more difficult. If symptoms persist, classical treatment has consisted of open or arthroscopic synovectomy. Over the past decade angiography and angiographic embolization of the source of bleeding has been successful. In a recent meta-analysis including 99 patients, technical success rates of 99% were noted, though 2 cases became infected and 10 cases suffered recurrent bleeding episodes. Radio-active synovectomy has also been successful.

INTRODUCTION

The lifetime of total hip replacements (THR) is often limited by adverse local tissue reactions to corrosion products generated from modular junctions. Two prominent damage modes are the imprinting of the rougher stem topography into the smoother head taper topography (imprinting) and the occurrence of column-like troughs running parallel to the taper axis (column damage). It was the purpose of this study to identify mechanisms that lead to imprinting and column damage based on a thorough analysis of retrieved implants.

Introduction

Little is known about the relationship between head-neck corrosion and its effect on periprosthetic tissues and distant organs in the majority of patients hosting apparently well-functioning devices. We studied the degree and type of taper damage and the histopathologic response in periprosthetic tissue and distant organs.

Introduction

There are several potential biological mechanisms that may influence aseptic implant failure including excessive innate and adaptive immune responses to implant debris. We investigated the hypothesis that patients with painful total joint replacements will exhibit elevated levels of metal reactivity and inflammatory markers compared to patients with well-performing TJA. We evaluated this hypothesis by testing for metal hypersensitivity using in vitro LTT assay and analyzing serum levels of selected inflammatory markers.

Thromboembolic disease (TED) remains as a major concern for orthopaedic surgeons and is a well-known complication of lower extremity joint replacement procedures. While there is voluminous literature on the topic, it is difficult for the average orthopaedic surgeon to keep up with all the advancements in this area as well as the newer pharmacological options for prophylaxis. To address this, the American Academy of Orthopaedic Surgeons (AAOS) has developed a clinical practice guideline (CPG) in this area to provide treatment recommendations based on the best available evidence. Historically, guidelines for TED prophylaxis have been based largely on randomised controlled trials whose outcome measure was venographically documented deep vein thrombosis (DVT). However, many venographically documented DVTs, particularly those distal to the popliteal vein, are of no clinical consequence. Therefore, in the AAOS CPG the systematic review of the literature was focused on those outcomes that have the most clinical relevance: all-cause mortality, symptomatic or fatal pulmonary embolism (PE), proximal DVT, major bleeding and symptomatic DVT rates.

Using these as the clinically important endpoints, it is evident that the extant literature is insufficient to provide definitive guidance in this area and to make specific recommendations about optimal pharmacological prophylaxis. Nonetheless, one strong recommendation has emerged from this systematic review: the guideline recommended against routine post-operative duplex ultrasonography screening of patients who undergo elective hip or knee arthroplasty. Only one risk factor – previous history of TED – had evidence demonstrating a higher risk beyond the risk from elective hip or knee arthroplasty itself (weak recommendation). There was not sufficient evidence that other potential risk factors increase the risk of TED, likely because of the relatively high background risk of elective hip or knee arthroplasty. In addition, there is very little evidence defining populations at increased risk for bleeding and bleeding-associated complications associated with pharmacological prophylaxis. However, the panel did come to a consensus that patients with known bleeding disorders or active liver disease are at an increased risk for post-operative bleeding. In these circumstances, it is recommended that mechanical compressive devices be the primary modality of prophylaxis as pharmacologic prophylaxis may increase the risk of bleeding.

There was a moderate strength recommendation for the superiority of neuraxial anesthesia to limit blood loss even though there is no demonstrable effect on the incidence of TED. Finally, there was a moderate grade recommendation that pharmacologic agents (including aspirin) and/or mechanical compression devices be utilised for the prevention of VTE in patients that are undergoing elective hip or knee arthroplasty who are not at elevated risk beyond that of the surgery itself for VTE or bleeding. Clearly there is great need for better evidence with appropriately powered studies that examine the most clinically relevant outcomes in TED prophylaxis.

General Principles: All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex Mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue.

Acute tibial tuberosity avulsion: Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex can provide additional support.

Acute Patella Tendon Rupture: End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed.

Acute Quadriceps Tendon Rupture: These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct.

Patella Fracture: Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision.

Chronic Disruptions: While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects.

Recently, corrosion at the head-neck junction in metal-on-polyethylene bearing total hip arthroplasty (THA) has been recognized as a cause of adverse local tissue reactions (ALTR). Serum metal levels have been advocated as a tool for the diagnosis of ALTR, however no prior studies have specifically examined their utility. The purpose of this study was to determine the optimal cut-off values for serum cobalt and chromium in diagnosing ALTR after metal-on-polyethylene bearing THA.

We reviewed 447 consecutive patients with serum metal levels tested at our institution and identified 62 with a metal-on-polyethylene bearing who had axial imaging or underwent reoperation to confirm the presence or absence of ALTR. Receiver operating characteristic curves were produced to identify cut-off thresholds to optimize sensitivity and diagnostic test performance was characterized.

42 Of the 62 patients (66%) were positive for an ALTR. The best test for the diagnosis of ALTR was the serum cobalt level (area under the curve [AUC]=99%). A threshold cut-off of ≥ 1.0 ng/ml had a sensitivity of 100%, specificity of 90%, positive predictive value (PPV) of 96%, and negative predictive value (NPV) of 100%. Serum chromium levels were also diagnostic (AUC=87%). A threshold cut-off of ≥ 0.15 ng/ml had a sensitivity of 100%, specificity of 50%, PPV of 81%, and NPV of 100%. Finally, serum cobalt to chromium ratio was also helpful for diagnosis (AUC=90%). A threshold cut-off of 1.4 for the cobalt to chromium ratio offered a sensitivity of 93%, specificity of 70%, PPV of 87%, and NPV of 82%.

Measurement of serum cobalt with a threshold value of 1.0 ng/ml in our experience is the best test for identifying the presence of ALTR in patients with a metal-on-polyethylene THA. Measurement of chromium and the ratio of cobalt to chromium are also of value.

Metal-on-metal bearing surfaces were reintroduced to take advantage of the reduction in volumetric wear afforded by these bearings and reduce the complications of osteolysis and aseptic loosening. In addition, metal-on-metal hip resurfacing and many metal-on-metal total hip replacement systems employed large diameter femoral heads, thereby reducing the risk of dislocations. Unfortunately, many metal-on-metal systems demonstrated poor survivorship and were associated with adverse local tissue reactions (ALTRs) related to metal debris generated from the bearings and/or modular connections.

Careful clinical surveillance of patients with metal-on-metal bearings is warranted to identify patients with ALTR at an early stage in order to intervene prior to the development of extensive peri-articular soft tissue damage. Monitoring may include serum or whole blood metal levels and metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) depending on the patient's signs and symptoms and the track record of the implanted device. While there currently is a lack of high quality evidence-based guidelines on the management of patients with either symptomatic or asymptomatic metal-on-metal total hip replacements, professional organizations have issued consensus-based algorithms to guide the practitioner in management. Ultimately, the decision for revision surgery should not be based on a single diagnostic test but on the entire clinical scenario.

Bone is a dynamic organ with remarkable regenerative properties seen only otherwise in the liver. However, bone healing requires vascularity, stability, growth factors, a matrix for growth, and viable cells to obtain effective osteosynthesis. We rely on these principles not only to heal fractures, but also achieve healing of benign bone defects. Unfortunately, we are regularly confronted with situations where the local environment and tissue is insufficient and we must rely on our “biologic tool box.” When the process of bone repair requires additional assistance, we often look to bone grafting to provide an osteoconductive, osteoinductive, and/or osteogenic environment to promote bone healing and repair.

The primary workhorses of bone grafting includes autogenous bone, cadaver allograft, and bone graft substitutes. Among the first types of bone graft used and still used in large quantities today include autogenous and cadaver allograft bone. Allografts are useful because it is present in multiple forms that conform to the desired situation. But autogenous bone graft is considered the gold standard because it possesses all the fundamental properties to heal bone. However, it has been associated with high rates of donor site morbidity and typically requires an inpatient hospitalization following the procedure only adding to the associated costs.

The first bone graft substitute use was calcium sulfate in 1892, and over the past 122 years advancements have achieved improved material properties of calcium sulfate and helped usher in additional bioceramics for bone grafting. Today there are predominantly 4 types of bioceramics available, which include calcium sulfate, calcium phosphate, tricalcium phosphate, and coralline hydroxyapatite. They come in multiple forms ranging from pellets and solid blocks to injectable and moldable putty. In comparison to autogenous bone graft, the primary limitation of bioceramics are the lack of osteogenic and osteoinductive properties. Bioceramics work by creating an osteoconductive scaffold to promote osteosynthesis. The options of bone graft substitutes don't end with these four types of bioceramics. Composite bioceramics take advantage of the differing biomechanical properties of these four basis types of bioceramics to develop improved materials. To overcome the lack of osteoinductive and osteogenic properties growth factors or bone marrow aspirate can be added to the bioceramic. As a result, the list of combinations available in our “biologic tool box” continues to expand. More than 20 BMPs have been identified, but only BMP-2 and BMP-7 have FDA approval.

As we look forward to areas of future research and need within orthobiologics, some will likely come in the near future while others are much further in the future. We will continue to strive for the ideal bone graft substitute, which will have similar osteoinductive properties as autograft. The ultimate bone graft substitute will likely involve stem cells because it will allow an alternative to autogenous bone with the same osteogenic potential.

Introduction

Wear debris from polyethylene tibial inserts has been associated with limited longevity of total knee replacements (TKRs). While material factors were studied extensively and considerable progress has been made, there is little knowledge about surgical factors, particularly on how the wear rate is related to implant positioning.

It was the purpose of this study to determine the combined effect of patient and implant positioning factors on the volumetric wear rate of TKRs. Our hypothesis was that implant alignment has a significant impact on the wear rate when controlled for other patient factors.

Modern hip implants feature a modular design, whereby the individual components of the implant are assembled during the surgery. Increased reported failure rates associated with the utilization of modular junctions have raised many clinical concerns about the increased release of metal ions/debris leading to adverse local tissue reactions. Implant materials are subject to a myriad of mechanical motion and forces, and varying electrochemical conditions and pH changes from the surrounding environment. To date, no studies have attempted to model the collected data in order to predict the performance of the materials so that precautions can be taken before the problem reaches the critical stage. This study reports the effects of pH variation, displacement variation, and load variation on the mechanical and corrosion behavior of the hip implant modular junction system, tested with a custom-built fretting-corrosion apparatus. The main objective of this study is to combine the complete data set of the in-vitro experiments to create fretting-corrosion wear maps that can predict the dangerous domains of the hip implant modular system.

For each test, the flat portions of two CoCrMo pins were loaded perpendicularly against a Ti6Al4V Rod (Ti alloy) in a Flat-on-flat configuration in a simulated synovial fluid in order to simulate the modular hip implant system. A schematic diagram of contact conditions is presented in Figure 1. A sinusoidal displacement was applied onto the rod, which articulated against the CoCrMo alloy pins, at a frequency of 1Hz. The experiential data from the fretting-corrosion tests has been used to create fretting-corrosion maps. The variables incorporated into the maps include: total mass loss, electrochemical destabilization, pH variation, load variation, displacement variation, and visual examination of the wear features of the contact zone. Total mass loss has been estimated via measurement of the simulator fluid by ICP-MS technique. Electrochemical destabilization was evaluated by a single parameter (V_Drop). The electrochemical destabilization of the tribosystem was evaluated by measuring the drop in potential, V_Drop (V vs. SCE), resultant from the initiation of the fretting phase. The V_Drop refers to the initial cathodic drop in potential in response to the initial onset of fretting motion.

The data from the in vitro fretting-corrosion experiments has been combined to create four fretting-corrosion maps (Figures 2A–3D). Partial slip wear features and mechanical behavior was observed at 25µm displacement. 25–150µm displacement amplitudes showed gross slip behavior. Anything larger than 150µm displayed wear features that were indistinguishable from sliding wear. In general, total mass loss and V_Drop increased with increasing displacement. Samples that were tested at pH 6.0 or higher showed signs of material transfer and higher V_Drop. Finally, there was a general decrease in V_Dropwith increased applied load and pH.

In general, the wears maps were able to offer some predictive validity, however, there were some discrepancies between visual observations and the observed damage parameters. It is possible that other parameters could offer better correlation. Future studies will be conducted to measure other parameters.

For figures/tables, please contact authors directly.

Introduction

There are increasing reports of total hip replacement (THR) failure due to corrosion within modular taper junctions, and subsequent adverse local tissue reactions (ALTRs) to corrosion products. Modular junction corrosion is a multifactorial problem that depends on material, design, patient and surgical factors. However, the influence of alloy microstructure on corrosion has not been studied sufficiently. Especially for cast CoCrMo, there are concerns regarding microstructure variability with respect to grain size and hard-phase volume fraction. Therefore, it was the goal of this study to (1) identify different types of microstructures in contemporary implants, and (2) determine implications of alloy microstructure on the occurring corrosion modes.

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990s, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure.

We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction (ALTR). Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to ALTRs secondary to metal on metal bearing surfaces. While modularity in total hip replacement has demonstrable clinical benefits, modular junctions increase the risk of tribocorrosion and the types of ALTRs seen in patients with accelerated metal release from metal-on-metal bearing total hip replacements. The use of modular connections should be minimised in routine primary total hip replacement to avoid tribocorrosion-induced ALTRs.

Bone is a dynamic organ with remarkable regenerative properties seen only otherwise in the liver. However, bone healing requires vascularity, stability, growth factors, a matrix for growth, and viable cells to obtain effective osteosynthesis. We rely on these principles not only to heal fractures, but also achieve healing of benign bone defects. Unfortunately we are regularly confronted with situations where the local environment and tissue is insufficient and we must rely on our “biologic tool box.” When the process of bone repair requires additional assistance, we often look to bone grafting to provide an osteoconductive, osteoinductive, and/or osteogenic environment to promote bone healing and repair.

The primary workhorses of bone grafting include autogenous bone, cadaver allograft, and bone graft substitutes. Among the first types of bone graft used and still used in large quantities today include autogenous and cadaver allograft bone. Allografts are useful because it is present in multiple forms that conform to the desired situation. But autogenous bone graft is considered the gold standard because it possesses all the fundamental properties to heal bone. However, it has been associated with high rates of donor site morbidity and typically requires an inpatient hospitalization following the procedure only adding to the associated costs.

The first bone graft substitute use was calcium sulfate in 1892, and over the past 122 years advancements have achieved improved material properties of calcium sulfate and helped usher in additional bioceramics for bone grafting. Today there are predominantly 4 types of bioceramics available, which include calcium sulfate, calcium phosphate, tricalcium phosphate, and coralline hydroxyapatite. They come in multiple forms ranging from pellets and solid blocks to injectable and moldable putty. In comparison to autogenous bone graft, the primary limitation of bioceramics are the lack of osteogenic and osteoinductive properties. Bioceramics work by creating an osteoconductive scaffold to promote osteosynthesis. The options of bone graft substitutes don't end with these four types of bioceramics. Composite bioceramics take advantage of the differing biomechanical properties of these four basis types of bioceramics to develop improved materials. To overcome the lack of osteoinductive and osteogenic properties growth factors or bone marrow aspirate can be added to the bioceramic. As a result, the list of combinations available in our “biologic tool box” continues to expand. More than 20 BMPs have been identified, but only BMP-2 and BMP-7 have FDA approval.

As we look forward to areas of future research and need within orthobiologics, some will likely come in the near future while others are much further in the future. We will continue to strive for the ideal bone graft substitute, which will have similar osteoinductive properties as autograft. The ultimate bone graft substitute will likely involve stem cells because it will allow an alternative to autogenous bone with the same osteogenic potential.

Currently, there is considerable interest in the role that metal allergy may play in the clinical performance of orthopaedic devices. The extant literature suggests that metal allergy is a real clinical phenomenon, albeit the prevalence and clinical impact are not defined. Degradation products in the form of ionic or particulate debris can complex with local proteins and alter their conformation so that they may not be recognised as self-proteins. This can result in an adaptive immune response. The typical paradigm proposed for such an allergy is that of a delayed type hypersensitivity response (Type 4) whereby the antigenic stimulus interacts with antigen presenting cells and T lymphocytes to elicit a cell mediated immune response. There is some evidence that patients with metal-on-metal bearings and/or high serum metal levels elicit more response to metal antigen challenge measured as either patch test sensitivity or lymphocyte proliferation. Thus, while there is an idiosyncratic aspect of the allergic response, there is also a dose response component.

The diagnosis of metal allergy remains a challenge as patch testing has not been shown to correlate well with clinical symptoms. In-vitro assays, such as lymphocyte transformation testing, have promise but await robust clinical validation before they can be considered reliable diagnostic testing modalities. Allergy to implanted metal orthopaedic devices is a rare clinical event, and is a diagnosis of exclusion. Revision surgery should be considered a last resort with the understanding that the outcomes are unpredictable. Given the limitations of current diagnostic modalities, widespread screening of patients for metal allergies prior to TKA is not recommended.

Controversy remains regarding the optimal treatment for iatrogenic injury to the medial collateral ligament (MCL) during primary total knee arthroplasty (TKA). Some authors have recommended converting to a prosthesis that provides varus/valgus constraint while others have recommended primary repair. In this study, we report the results of 45 patients who sustained intra-operative MCL injuries during primary TKA that were treated with primary repair.

Of 3922 consecutive primary TKA there were 48 (1.2%) intra-operative MCL lacerations or avulsions. One patient was lost and one died before 24 months follow up. All but one patient underwent primary repair with placement of components without varus/valgus constraint. This left 45 knees with a mean follow up of 89 months (range, 24 to 214 months). The mean HSS knee scores increased from 47 to 85 points (p<0.001). No patients had subjective complaints of instability. No patients had excessive varus/valgus laxity when tested in full extension and 30 degrees of flexion. The range of motion at the time of final follow-up averaged 110 degrees (range, 85 to 130 degrees). Five knees required treatment for stiffness with 4 knees undergoing manipulation under anaesthesia and 1 knee undergoing open lysis of adhesions with polyethylene articular surface exchange. Two knees underwent revision for aseptic loosening of the tibial component. In the three knees that underwent open revision, the MCL was noted to be in continuity and without laxity.

Primary repair with 6 weeks of post-operative hinged bracing after iatrogenic injury to the MCL during primary TKA was successful at preventing instability although stiffness was seen in approximately 10% of patients. The increased morbidity associated with implantation of a semi-constrained or constrained implant may be unwarranted in this situation.