Short stems have been developed to conserve bone stock, especially in younger populations undergoing a total hip arthroplasty (THA), and showed similar functional outcomes compared to conventional stems. Recent literature suggested that stem length might be an independent risk factor for acute periprosthetic femoral fracture in direct anterior THA (1) or with different short stem designs (2). The purpose of the present study was to compare the incidence of acute periprosthetic femoral fractures, between stems of the same manufacture (Taperloc microplasty vs Taperloc complete), which have the same stem characteristics, except for the stem length which is 35 mm shorter in Taperloc microplasty during posterior and lateral THA.

Our institution's arthroplasty database was searched for all primary total hip arthroplasties utilizing short femoral stems performed between August 2016 and August 2023. Pre-operative X-rays for each case were analysed to characterize the proximal femoral geometry, specifically the canal bone ratio (CBR) and canal flare index (CFI). Data analysis was performed to identify risk factors for periprosthetic fractures.

For the time period assessed, 2107 femoral stems (Taperloc Microplasty:1727, Taperloc complete: 380) were implanted. Females constituted 53% of the cohort. The average patient age was 70±11 years. The periprosthetic fracture rate was 0.94%, with 20 periprosthetic fractures (Taperloc Microplasty:17, Taperloc complete: 3) excluding 2 greater trochanteric fractures (1 at each group), identified at follow-up of three months. There was no significant difference between the periprosthetic fracture rates between the two stems (0.98% vs 0.79%, p>0.72) The multivariate regression analysis demonstrated that the stem length, CBR, CFI, age, and gender were not risk factors for periprosthetic fracture.

The present study demonstrated that both Taperloc Microplasty and Taperloc complete stems had similar rates of periprosthetic fractures, and the stem length was not a risk factor for a periprosthetic fracture during uncemented THA.

1. Tamaki T, Cementless Tapered-Wedge Stem Length Affects the Risk of Periprosthetic Femoral Fractures in Direct Anterior Total Hip Arthroplasty. J Arthroplasty. 2018 Mar;33(3):805-809. 2. Staunton P. Acute Periprosthetic Hip Fracture with Short Uncemented Femoral Stems. J Arthroplasty 2024 accepted.

Introduction

Gluteus medius is disrupted during lateral approach total hip arthroplasty (THA) which may impact its function and ability to control the pelvis. The objective was to compare gluteus medius activation and joint mechanics associated with a Trendelenburg sign (pelvic drop, trunk lean) during gait and hip abductor strength between patients that underwent lateral or posterior THA approaches one year post-surgery and healthy adults.

Utilising the (ACS-NSQIP) database, we aimed to evaluate the impact of resident level of training on surgical outcome following (TKA) and to compare the US and Canadian health care training system in regards to 30 days postoperative complications and readmission rates.

Using the (CPT) codes we selected from the 2011 and 2012 NSQIP database elective primary TKA with the resident surgeon involved. Of these, all cases with a primary diagnosis code of infection, fracture, mechanical complication, or malignancy and all cases with incomplete or incongruous demographic information were excluded. We also eliminated all the cases with the Attending not present. A total of 2513 cases were included in the study. The cases were stratified into three groups according to the postgraduate level of training {PGY 1 to 3 (junior resident), PGY 4 to 5 (senior resident), and fellow}. Univariate analysis of all patient demographics, comorbidities, intra and postoperative variables, length of surgery, hospital stay and 30 days readmission rates were conducted in order to identify differences between the groups. A standard student's t test was used for continuous variables while the ChiSquared was used for categorical variables. Multivariable logistic regression models were created to assess the independent effect of the resident level of training on the 30 days major complication and re-admission rates while controlling for all other variables.

We identified, 854 (34%) TKAs with junior residents, 1013 (40%) TKAs with senior residents and 646 (26%) TKAs with fellows' participation. Junior residents had a significant (p<0.0001) longer operative time (107±36 minutes) compared with senior residents and fellows. Length of hospital stay was longer in the fellow group probably because of their involvement in more complicated cases. Additionally, an increased number of blood transfusion was observed for the cases performed with involvement of senior residents when compared with the other two groups. However, no significant difference in complications was observed across training levels. When comparing US (2074 TKAs) versus Canada (423 TKAs) cases, we found that fellow contribution to TKA surgeries is higher in Canada. The occurrence of pulmonary embolism and pneumonia was three times higher in Canada cases, while blood transfusion was more frequent in US. Increased operative time, ASA class, age, diabetes, percutaneous cardiac intervention, and steroid use were all independent risk factors for complications following primary TKA. However, no significant difference was observed between the two groups with regards to major complications suggesting no difference between Canadian and American training system in regards to post operative complication.

Our results support previous study study indicating that involvement of residents did not affect the surgical outcome within 30 days when compared to cases with no resident involvement. Our study suggests that resident level does not independently increase the risk of short term complications and support continuing involvement of junior trainees in TKA.

Hip resurfacing offers an attractive alternative to conventional total hip arthroplasty in young active patients. It is particularly advantageous for bone preservation for future revisions. Articular Surface Replacement (ASR) is a hip resurfacing prosthesis manufactured by DePuy Orthopaedics Inc. (Warsaw, IN). The manufacturer voluntarily recalled the ASR system in 2010 after an increasing number of product failures. The present study aimed to determine the long-term results in a large cohort of patients who received the ASR prosthesis.

Between February 2004 and August 2010, 592 consecutive hip resurfacings using the ASR (DePuy Orthopaedics Inc., Warsaw, IN) resurfacing implant were performed in 496 patients (391 males and 105 females). The mean age of the patients at the time of the surgery was 54 (range: 25 to 74) years. Osteoarthritis was the most common diagnosis in 575 hips (97.1%). The remaining patients (2.9%) developed secondary degenerative disease from ankylosing spondylitis, avascular necrosis, developmental hip dysplasia, and rheumatoid arthritis. Clinical and radiographic information was available for all patients at the last follow up. Cobalt (Co) and chromium (Cr) levels were measured in 265 patients (298 hips) by inductively coupled plasma-mass spectrometry (ICP-MS).

The average follow up of the study was 8.6 years (range: 5.2 to 11.6 years). The mean Harris hip and UCLA scores significantly improved from 44 and 2 pre-operatively to 85.3 and 7.1 respectively. The median Co and Cr ion level was 3.81 microgram per liter and 2.15 microgram per liter respectively. Twenty-seven patients (5.4%) were found to have blood levels of both Co and Cr ions that were greater than 7 microgram per liter. Fifty-four patients (9.1%) were revised to a total hip arthroplasty. Kaplan-Meier survival analysis showed a survival rate of 87.1% at 8.6 years with revision for any cause and 87.9% if infection is removed. A significantly higher survival rate was observed for the male patients (90.2%, p <0.0001) and for the patients with ASRs with femoral heads diameters larger than 52 mm (90.1%, p=0.0003).

This study confirms that patient selection criteria are of great importance to the overall survivorship of hip resurfacing arthroplasty. Improved clinical results have been reconfirmed with the use of larger diameter femoral heads.

Hip fractures are among the most common orthopaedic injuries and represent a growing burden on healthcare as our population ages. Despite improvements in preoperative optimisation, surgical technique and postoperative care, complication rates remain high. Time to surgery is one of the few variables that may be influenced by the medical team. The aim of the present study was to evaluate the impact of time to surgery on mortality and major complications following surgical fixation of hip fractures.

Utilising the American College of Surgeons' National Quality Improvement Program (NSQIP) database, we analysed all hip fractures (femoral neck, inter-trochanteric, and sub-trochanteric) treated from 2011 to 2013 inclusively. We divided patients into three groups based on time to surgery: less than one day (<24h), one to two days (24–48h), and two to five days (48–120h). Baseline characteristics were compared between groups and a multivariate analysis performed to compare 30-day mortality and major complications (return to surgery, deep wound infection, pneumonia, pulmonary embolus, acute renal failure, cerebrovascular accident, cardiac arrest, myocardial infarction, or coma) between groups.

A total of 14,730 patients underwent surgical fixation of a hip fracture and were included in our analysis. There were 3,475 (24%) treated <24h, 9,960 (67%) treated 24–48h, and 1,295 (9%) treated 48–120h. Thirty-day mortality and major complication rates were 5.0% and 6.2% for the <24h group, 5.3% and 7.0% for the 24–48h group, 7.9% and 9.7% for the 48–120h group respectively. After controlling for baseline demographic differences between groups (age, sex, race) as well as pertinent comorbidities (diabetes, dyspnea, chronic obstructive pulmonary disease, chronic steroid use, hypertension, cancer, bleeding disorders, and renal failure), time to surgery beyond 48h resulted in greater odds of both mortality (1.45, 95%CI 1.10–1.91) and major complications (1.45, 95%CI 1.12–1.84).

Time to surgery is one of the few variables that can be influenced by timely medical assessment and access to the operation room. Expediting surgery within 48h of hip fracture is of paramount importance as it may significantly reduce the risk of mortality as well as major complications.

Osteoarthritis (OA) is a multifactorial disease that affects millions of Canadians. Although, there is not one specific mechanism that causes OA, the biological outcome is cartilage degradation. The articular cartilage in joints is composed primarily of the proteoglycan aggrecan and type II collagen (Col II) which together provide cartilage with functional properties. In OA, the imbalance of the anabolic and catabolic activities of chondrocytes favors cartilage catalysis. The main inflammatory cytokine involved in cartilage degradation is interleukin (IL) 1β. It has previously been demonstrated that Link N, a 16 residue peptide derived from proteolytic cleavage of link protein, can stimulate matrix proteins in normal cartilage and intervertebral discs (IVDs). Recently, we showed that a shorter sequence of Link N (sLink N), consisting of the first 8 residues of the peptide, has the potential to increase synthesis of matrix proteins in IVD cells in vitro and stimulate repair in ex vivo IVD organ culture. There are currently no treatments that actively repair cartilage in OA joints. In the present study, we aimed to evaluate the potential of sLink N as a therapeutic agent in the repair of OA cartilage.

OA cartilage was isolated from four donors undergoing total knee replacement (50–70 y). Cells were recovered from the cartilage of each knee by sequential digestion with Pronase followed by Collagenase, and expanded in PrimeGrowth culture medium (Wisent Bioproducts, Canada; Cat# 319–510-CL, −S1, and −S2). After 7 days in culture, cells were treated for 24h with sLink N (0.5, 5, 50, 500 or 5000 ng/ml) or sLink N in combination with IL-1β (1 ng/ml) to mimic an inflammatory milieu. Conditioned media was collected and measured for proteoglycan (GAG) release using the safranin O and for Col II synthesis by Western blotting. Human articular cartilage explants including cartilage with subchondral bone were prepared from the same donors using the PrimeGrowth Isolation kit (Wisent, Canada) and cultured for 21 days in presence of IL-1β (1ng/ml) and sLink N (0.5, 5, 50, 500 or 5000 ng/ml). Aggrecan and Col II were extracted with guanidine buffer and measured by Western blotting.

Treatment of OA chondrocytes significantly increased the GAG and Col II synthesis. The EC50 dose-response of sLink N on GAG synthesis was 67 ± 41 nM [65 ± 40 ng/ml] and the GAG synthesis reached a maximum of 194 ± 30% with the highest dose above control. When chondrocytes were cultured in the presence of IL-1β, GAG synthesis was also elevated by sLink N above control. Treatment of OA cartilage explants with sLink N increased the content of aggrecan and Col II even in the presence of IL-1β.

Our results suggest that sLink N is a growth factor supplement that can increase cartilage matrix protein synthesis, and a chondroprotective agent, by modulating the catabolic effects of IL-1β. sLink N is the first small-peptide to demonstrate potential in cartilage repair of OA joints.

Introduction

Metal-on-metal (MoM) articulations in total hip replacement (THR) have become an attractive option for young, active patients. Short-term reports have demonstrated elevated systemic metal ion levels in the blood and urine. Disseminated concentrations of cobalt and chromium have raised concern regarding cellular toxicity, chromosomal damage and adverse local soft tissue reactions.

Long-term studies are required to support the increased use of MoM bearings in younger patients given their potential deleterious effects. The purpose of the current study was to report the 7–13 year clinical, radiographic, and metal ion results in patients following MoM THR.

Introduction: Several studies have shown the presence of cobalt (Co) and chromium (Cr) ions in blood, urine, and organs of patients after THA using Co-Cr alloy-based implants. Even though it is well known that exposure to heavy metals may lead to significant alterations in human sperm morphology and motility, less is known on the effect of Co and Cr on semen parameters after metal on metal (MOM) hip replacement.

Methods: Semen was collected form 10 patients between 41 and 49 years old (mean=45.9±3.0 years) by masturbation after 2–3 days of abstinence. The time of implantation varied from 1 to 9 years (mean=5.1±3.9 years). Samples were collected in a sterile container and examined within 1h after ejaculation for morphology, motility, and number of sperm cells following standard criteria. All patients were doing well at their follow-up visits (Harris Hip Score=94±4; UCLA activity a score=7±1) and no sign of osteolysis was observed on X-rays.

Co and Cr concentrations were measured in both the seminal plasma and in the blood of patients by inductively coupled plasma-mass spectroscopy (ICP-MS).

Results: results showed that the levels of Co in the seminal plasma and the blood of the patients were not statistically different. However, the level of Cr was significantly lower in the seminal plasma than in the blood of the patients. The ejaculate volume (2.1 ±0.6 ml), the sperm density (66±53 x 106), the total sperm count (151±75 x 106/ml), the pH (8), and the percentage of normal morphology (46±18%) were in the range of the WHO criteria for fertile population and also in the range of reference patients in the city of measurements. However, the viability was lower than that observed in a fertile population without prosthesis (41±19%).

Conclusions: results of the present study strongly suggest that both Co and Cr ions crossover to the semen but that their concentrations were too low to significantly affect sperm parameters of young patients with MM prosthesis. Further longitudinal studies are however necessary to conclusively determine the effect of metal ions from MM prosthesis on sperm parameters.

Introduction: Metal on metal hip implants continue to be successful alternatives to conventional bearings in younger patients with osteoarthritis. Levels of metal ions such as cobalt (Co) and chromium (Cr) increase in patients with metal bearing hip replacements and resurfacings. These particles are cytotoxic, induce bone loss, and lead to malignant tumors in rats. A subset of these patients are considered outliers as they have unusually high levels of Co and Cr ions. Given the increasing prevalence of metal bearings and the potential for cellular toxicity, we attempted to determine whether patient or surgical factors could account for abnormally elevated ion levels.

Methods: We analyzed the Co and Cr levels from whole blood in 661 patients with metal on metal hip bearings. Patient outliers were defined as those who had ion levels ≥ three-fold the mean value. Twenty-four patients (3.6%) had abnormally high metal ion levels, which included 15 patients that underwent total hip replacements and 9 patients following hip resurfacings. These patients were followed prospectively with the Harris Hip Score (HHS) and the University of California Los Angeles (UCLA) activity score. Serial radiographs and ion levels were analyzed at regular intervals. Oxidative stress markers (total anti-oxidants, peroxide, and nitro-tyrosine) were also measured from whole blood to determine if these correlated with an increase ion levels in outlier patients.

Results: Post-operative HHS and UCLA activity scores improved significantly compared to pre-operative values. There was no statistical correlation between outlier ion levels, patient demographics, HHS and UCLA activity scores. Radiologic parameters such as cup inclination and femoral component neck-shaft angle could not account for higher ion levels in these outliers. Oxidative stress markers were similar to the levels observed in the control patients with normal ion values following with metal on metal hip implants.

Conclusion: We could not identify any patient or surgical factors that could explain the abnormally high metal ion levels in the outlier patients. This suggests that the cause of ion level increase is multifactorial. The clinical relevance of such high levels of ions remains unknown given that there was no increase in serum oxidative stress markers. Further studies are necessary to better understand the effect of abnormal elevations in metal ions given the recent concerns of pseudotumours following metal on metal hip implants.

Aim: To determine the MRI findings in patients with persistent painful metal on metal (MOM) hip arthroplasty and compare the results with a control group of patients with MOM or metal on polyethylene THA without symptoms.

Methods: 20 patients with normal inflammatory markers and normal plain radiographic imaging that had undergone primary THA were enrolled to this study. Patients were chosen to be included in 4 groups;

Patients having metal-on-polyethylene THA or resurfacing without pain (Control group),

Operated hips were evaluated with MRI by one musculoskeletal radiologist who was blinded to the radiographic findings and clinical symptoms. All images were assessed for the presence of a juxtaarticular or periprosthetic abnormalities, including fluid collections, soft tissue masses, osseous abnormalities, and patterns of contrast enhancement of lesions.

Results: 5 patients were included in each group. All patients had undergone their THA at least 1 year prior to the MRI examination (mean 18 months). MRI findings including muscle atrophies, joint effusions, stress fractures, bone marrow oedema and muscle avulsions were equally distributed in all groups.

Conclusions: MOM THA or high metal ion levels had no specific MRI findings to explain the hip pain in these groups of patients.

Hip surface replacement is an alternative for young patients considered for hip replacement. The in vivo release of ions from these surfaces has yet to be well evaluated. In the present study, we compared the concentrations of metal ions in blood of patients with hip surface replacement and metal-on-metal (MM) total hip arthroplasty (THA).

Blood was collected six months and one year after implantation time into Sarstedt Monovette® tubes for trace metal analysis from patients having Articular Surface Replacement (ASR®, DePuy Orthopaedics; n=61), 28 mm-head MM THA (n=18), and 36 mm-head MM THA (n=25). The concentrations of cobalt (Co), chromium (Cr), and molybdenum (Mo) were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS). Since metal ions are potent inducers of oxidative stress, total antioxidant, peroxide, and nitrotyrosine levels (oxidative stress markers) were also measured in plasma of the patients.

The median Co and Cr levels progressively and significantly increased in the three groups during the first year post-operation (compared to patients without hip bearings (n=25)). After six months, the levels of Co and Cr were significantly higher in patients with ASR and 28 mm MM THA than in patients with 36 mm MM THA. There was no difference after one year. The level of activity, as measured by the UCLA activity score, was higher in ASR patients than in 28 and 36 mm MM THA after one year. No differences were observed for Mo levels in these patients when compared to our control group. There was no increase of oxidative stress marker levels in patients with ASR and 36 mm MM THA and no correlation between the concentrations of Co and Cr ions and the levels of oxidative stress markers.

Our results show that, at one year post-operation, the concentration of ions in patients with ASRs is similar than those in patients with MM THAs. Moreover, results suggest that metal ions liberated from MM bearings do not induce damage to macromolecules by oxidative stress in plasma of patients. Longer follow-ups are still required to characterise the concentration of ions in ASR and to determine conclusively the effects of elevated circulating ions.

Although the etiology of low back pain is unclear, it is believed that intervertebral disc (IVD) degeneration plays a major role. In the present study, we sought to determine if bovine IVD cells maintain their phenotype in a mouse subcutaneous injection model, while embedded or not in biocompatible matrices.

Nucleus pulposus (NP) cells were isolated from adult bovine tails. Ten million cells were resuspended either in 500 ƒÝl of DMEM or in a negatively (alginate) or positively (chitosan) charged matrix. The mixtures were then injected subcutaneously in Balc/c nude mice. After two weeks, the mice were sacrificed and the implants harvested. The implants were examined histologically with a hematoxylin and eosin stain. The implant size was measured and the cells were counted. Proteoglycan was assessed by the GAG assay. The expression of type I and II collagens, aggrecan, and CD24 genes was analyzed by reverse transcription ¡V polymerase chain reaction (RT-PCR).

Histologic evaluation confirms the presence of cells in all NP implants. The presence of alginate increased the implant size, the number of cells in the implants, and to a lesser extent, the proteoglycan content, compared to implants formed with cells injected alone. However, chitosan had no effect on the implant size, the number of cells and the aggrecan content. NP implants expressed the same pattern of genes as the native NP tissue (i.e. type I and II collagens, aggrecan, and CD24). The presence of alginate did not affect this expression pattern whereas chitosan decreased slightly their expression.

After injection in mice, bovine NP cells appeared to retain their native phenotype. The RT-PCR analysis revealed that NP cells expressed aggrecan, type I and type II collagens as well as CD24, a specific marker for the NP phenotype. Also, NP cells can be embedded in matrices to produce NP-like features in vivo. In conclusion, we have developed a simple mouse subcutaneous injection model that recreates the features of the native IVD and avoids the need to use a disc degeneration model.

The aim of this study was to analyze in human macrophages the effects of Co²⁺ and Cr³⁺ ions on the activity of caspase-8 and caspase-3, initiator and executioner of apoptosis, respectively. Caspase-3 and -8 activities were measured by colorimetric assays. Results show that Co²⁺ ions induced caspase-3 activity in a time-dependent manner. Co²⁺ had no effect on caspase-8 activity. The activation of caspase-3 by Cr³⁺ was time-dependent while caspase-8 activity reached a maximum after eight hours and decreased thereafter. Since caspase-8 is primarily activated by membrane-associated events, our results suggest that Cr³⁺ interacts with cell membrane components to induce macrophage apoptosis, whereas Co²⁺ seems to stimulate apoptosis most likely through intracellularly located mechanisms.

Because of their potential for improved wear performance, there has been a revived interest in metal-metal bearings, made of cobalt-chromium-molybdenum alloys, as an alternative to the use of conventional metal-polyethylene bearings. However, metal ion toxicity remains a major cause for concern. Previous studies suggested that both cobalt (Co²⁺) and chromium (Cr³⁺) ions induce macrophage apoptosis. The interest in apoptosis lies in the fact that it offers specific targets for therapeutic intervention.

The aim of this study was to analyze the effects in human macrophages of Co²⁺ and Cr³⁺ ions on the activity of caspase-8 and caspase-3, initiator and executioner of apoptosis, respectively.

U937 human macrophages were exposed to 0–10 ppm Co²⁺ (CoCl₂) and 0–500 ppm Cr³⁺ (CrCl₃). Caspase-3 and caspase-8 activities were measured by colorimetric assays based on the recognition of specific amino acid sequences (DEVD and IETD, respectively).

Results show that Co²⁺ ions induced caspase-3 activity with a significant increase after four hour incubation and a maximal 2.65-fold increase reached after twenty-four hour with 10 ppm. Co²⁺ had no effect on caspase-8 activity.

Cr³⁺ ions significantly stimulated caspase-3 activity after four hours with a maximal 1.75-fold stimulation reached after twenty-four hours, reaching only 50% of that observed with Co²⁺. Caspase-8 activity was significantly increased after two hours incubation, peaking at eight hours with a 2.2-fold increase, and decreasing thereafter.

Since caspase-8 is primarily activated by membrane-associated events, our results suggest that Cr³⁺ interacts with cell membrane components to induce macrophage apoptosis. On the other hand, Co²⁺ seems to stimulate caspase-3 activity and apoptosis most likely through intracellularly located mechanisms.

Purpose: To investigate the effect of amifostine and dexrazoxane on bone mass of the vertebrae and femurs of doxorubicin treated male rats.

Methods: Amifostine, Doxorubicin and Dexrazoxane were purchased from SMBD-Jewish General Hospital Pharmacy. Lactating Sprague Dawley dams with 14 male pups were purchased from Charles River Canada. At neonate day 10, rat pups were randomly divided into 4 groups of n=5. Pups were injected once intraperitoneally with either Phosphate Saline Buffer 1X (saline), or drugs, AMF (50 mg/kg), AMF + DOX (50 mg/kg +3 mg/ kg), or with AMF + DXR + DOX (50 mg/kg + 60 mg + 3 mg/kg, 20:1 DXR to DOX ratio). AMF and DXR were injected 30 minutes prior to the DOX injection. After injection, rat pups were returned to their mothers until weaning on neonate day 22. Rats were then sacrificed at day 38 (28 Post-Injection, PI). Bone mineral density (BMD) and micro computed tomography were analyzed.

Results: Dissection of male pups days 1, 5 or 9 post-injection did not reveal any intestinal or organ damage. AMF treatment alone led to a slight but not significant increase in the right femoral, left femoral and lumbar vertebral BMDs. Similarly, AMF + DOX or AMF + DXR + DOX treated rats had no significant change in either femoral and vertebrae BMD.

Conclusions: We recently showed that a single injection of DOX in young female rats is associated with low bone turnover resulting in vertebrae and femur bone growth deficits. However, no such a difference was detected when similarly treated males were examined. The role of sex steroid hormone at this age is unclear as sex hormones level are very low in neonates at the time of injection and the rats, male and female, were sacrificed prior to puberty. To define the role of sex hormone in the observed gender-specific drug susceptibility we plan on comparing the response of intact to ovariectomized female rats to the drug regimen.

Funding : Other Education Grant

Funding Parties : CIHR

Metal particles and ions are liberated from the articular interface of metal-metal (MM) total hip arthroplasties. To better understand their cellular effect, we analyzed the internalization of these metal particles and ions by macrophages in vitro. Macrophages were exposed to metal particles isolated from MM prostheses cycled in a hip simulator and to metal ions. Cells were processed for transmission electron microscopy analysis. Results reveal the internalization of metal particles and Cr³⁺ ions in specifically localized cytoplasmic areas. This study is the first to reveal that metal particles of clinically relevant size and Cr³⁺ ions are internalized by an apparently active process.

In order to minimize articular interface wear, metal-metal (MM) hip implants have been considered as an alternative to conventional metal-polyethylene bearings. While the local histological effects of the metallic particles and ions appear to be similar to that seen with metal-polyethylene hip replacements (i.e., a foreign-body macrophage response), little is known about the cellular effects of these metal particles and ions.

The purpose of this study was to better understand the cellular effect of metal particles and ions, we analyzed their internalization by macrophages in vitro.

J774 mouse macrophages were exposed to metal particles isolated from serum of MM prostheses cycled in a hip simulator and to Cr³⁺ (CrCl₃) and Co²⁺ (CoCl₂) ions. Cells were then processed for transmission electron microscopy analysis.

Micrographs revealed the internalization of metal particles and Cr³⁺ ions in specifically localized cytoplasmic areas, suggesting that they are phagocytosed via an active pathway. Energy disperse X-ray analysis spectra of macrophages incubated with Cr³⁺ revealed a chromium phosphate composition. The same structure and composition were also observed when Cr³⁺ ions were incubated in culture medium without cells, suggesting that they were formed outside the cells. Co²⁺ ions did not form visibly agglomerated structures.

This study is the first to reveal that metal particles of clinically relevant size are internalized by an apparently active process and that Cr³⁺ ions can be internalized by macrophages after binding to phosphorus or phosphoproteins. Kinetic studies are now necessary to better understand the mechanism of phagocytosis and the ultimate outcome of these particles and ions in macrophages.

Purpose: To develop an improved understanding of the in vivo behavior of intervertebral disc (IVD) cells for determining the phenotype of a differentiated stem cell in tissue engineering applications.

Methods: Nucleus pulposus (NP) and annulus fibrosus (AF) cells were isolated from adult bovine tails while notochordal cells were extracted from fetal bovine intervertebral disc. Ten million cells (of each cell type) in 500 & #61549;l of DMEM were then injected subcutaneously in C57Bl/6 mice. After 2 weeks, the mice were sacrificed and the specimens harvested. They were examined grossly, histologically and by scanning electronic microscopy (SEM) for the evidence of IVD-like structure formation. Proteoglycan was assessed by the GAG assay and PCR for analysis of gene expression. Control tissue (from bovine NP and AF) were directly fixed in glutaraldehyde, without any isolation technique and examined in SEM.

Results: After 2 weeks, SEM examination of specimens from AF and NP closely resembled normal bovine AF and NP. Of special interest here was the finding that some mice injected with cells from the AF developed an organized arrangement of parallel collagen fibres while NP cells injected mice had an amorphous structure with few collagen fibers. The GAG assay showed pro-teoglycan content for each samples, ranging from 3.8 microg to 26 microg. The morphology of the specimens retrieved from notochordal cells injected mice were also amorphous punctuated with thin collagen fibrils.

Conclusions: This study demonstrates that subcutaneous injection of bovine disc cells in mice can result in formation of disc structures similar to those of the bovine IVD. We believe that the cellular communication of the bovine disc cells is maintained in the mouse leading to architectural organization of the collagen fibers with the mouse as a source of nutrients. This technology may be useful in determining the phenotype of a differentiated stem cell for tissue engineering of IVD.

The in situ increased production of matrix metalloproteinases (MMPs) has been associated with the development of periprosthetic osteolysis. The aim of the study was to compare the effect of Co²⁺ and Cr³⁺ ions on macrophages matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of MMP (TIMP-1) expression. Using reverse transcription-polymerase chain reaction (RT-PCR), we showed that both Co²⁺ and Cr³⁺ ions induce the expression of MMP-1 and TIMP-1 in a dose-dependent manner. Since MMP-1 and TIMP-1 participate in the extracellular matrix degradation and tissue remodeling, our results suggest that the modulation of MMP-1 and TIMP-1 may contribute to the development of periprosthetic osteolysis.

The in situ increased production of matrix metalloproteinases (MMPs) has been associated with the development of periprosthetic osteolysis. Aseptic loosening due to periprosthetic osteolysis is the major cause of total hip arthroplasty failure. Because of their potential for improved wear performance, there has been a revived interest in metal-metal bearings, made of cobalt-chromium-molybdenum alloys. However, metal particle and ion toxicity remains a major cause for concern.

The aim of the study was to determine the effects of Co²⁺ and Cr³⁺ ions on the expression of matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinase-1 (TIMP-1), two proteins participating in the extracellular matrix degradation and tissue remodeling.

Human U937 macrophages were incubated with Co²⁺ and Cr³⁺ ions. The expression of MMP-1 and TIMP-1 mRNAs was measured by reverse transcription-polymerase chain reaction (RT-PCR) and calculated as the ratio of the house keeping gene GAPDH expression.

Results show that both Co²⁺ and Cr³⁺ ions induced in a dose-dependent manner the expression of PCR products (mRNAs) of MMP-1 (135 bp) and TIMP-1 (328 bp). Co²⁺ ions were more effective in inducing MMP-1 and TIMP-1 expression than Cr³⁺ ions. The induction of MMP-1 and TIMP-1 paralleled the induction of TNF-α mRNA expression.

Our results demonstrate that the expression of MMP-1 and TIMP-1 were up regulated by incubating macrophages with Co²⁺ and Cr³⁺ ions, suggesting that metal ions contribute to tissue damage in the periprosthetic environment and that variations in MMP-1 and TIMP-1 expression may contribute to periprosthetic osteolysis.

Purpose: Knowledge of factors regulating the turnover, repair, and degeneration of the intervertebral disc (IVD) is lacking. Although type II collagen (CII) fragments accumulate in the degenerative IVD, little is known of how they affect the degenerative process. In this study, the effect of a CII fragment, CII-(245–270), known to be critical in arthritis was investigated on gene expression of proteinases, collagen, and proteoglycan by bovine disc cells to determine its role in matrix turnover.

Methods: Cells isolated from the nucleus pulposus (NP) and annulus fibrosus (AF) of adult bovine tails were cultured in the absence (control) or presence of the fragment. The fragment CII-(245–270) (US Biological, Massachusetts) was dissolved in culture medium to a final concentration of 1& #956;g/ml. PCR was performed and products were visualized by ethidium bromide staining.

Results: Addition of the CII-(245–270) peptide at 1& #956;g/ml to NP and AF cells enhanced expression of genes for MMP-1, cathepsin K, and aggrecan after 48 hours compared with the control. MMP-13 was also upregulated in the NP. In contrast, the effect in the AF was time dependent. Type II collagen was upregulated throughout the culture time in the NP as opposed to the AF where its expression was enhanced only on day 2.

Conclusions: We have shown that the CII-(245–270) peptide can alter gene expression of proteinases, collagen, and proteoglycan in bovine disc cells. The present study reveals the complex interrelationships of gene expression in the disc that accompany fragmentation of type II collagen. This new information suggests that increased levels of these fragments, in degenerated discs, may stimulate disc breakdown but may also attempt to protect the disc, by unknown mechanisms Funding: Other Education Grant Funding Parties: AO foundation, Switzerland

Recent evidence indicates that link N can stimulate synthesis of proteoglycans and collagen by adult (2–4 years old) bovine disc tails. Here we sought to determine the effect of link N on the accumulation of disc matrix proteins from young (eight to twenty month old) bovine tails. We show that degradation products of link protein generated by matrix metalloproteinases cannot “feed-back” and stimulate matrix assembly of the disc matrix from young bovine tails but may have a regulatory role in cell proliferation. Link N may have value only in stimulating the growth and regeneration of the old damaged intervertebral disc.

To date, there have been no reports on the effect of the amino terminal peptide of link protein (DHLSD-NYTLDHDRAIH) (link N) on disc cells from young (eight to twenty month old) bovine coccygeal discs. Link N is produced when removed by proteolysis from the N-terminus of the link protein of cartilage proteoglycan aggregates. We recently showed that link N can act directly on disc cells from adult (two to four years old) bovine discs to stimulate matrix production (J Cell Biochem, 2003; 88:1202–13).

To examine whether link N can play a role in maintaining the matrix integrity of young bovine disc cells.

Nucleus pulposus (NP) and annulus fibrosus (AF) cells were isolated from fresh grade I discs from young steers, and cultured in pellets at 1 million cell per tube in 1 ml of DMEM-high glucose supplemented with 1% 100X Pen-Strep, 1% ITS, 1 mg/ml BSA, and 50 μg/ml ascorbic acid. Cell pellets were digested and then analysed for sulfated glycosaminoglycan, type II collagen, percent denatured type II collagen, type IX collagen, and DNA content, using specific assays.

A concentration of 100 ng/ml link N significantly increased the DNA content of AF cells. However, link N had no significant effect on proteoglycan, type II and type IX collagen accumulation.

This study demonstrates that link N at a concentration of 10 ng/ml and 100 ng/ml cannot stimulate matrix production but may increase cell division in young bovine disc tails.

Purpose: Articular surface replacement (ASR) is an alternative for young patients considered for hip replacement. The in vivo release of ions from these surfaces has yet to be well evaluated. The purpose of the present study was to compare the concentrations of metal ions in blood of patients with ASR and metal-on-metal (MM) total hip arthroplasty (THA).

Methods: Blood was collected 6 months after implantation time into Sarstedt Monovette® tubes for trace metal analysis from patients having ASR (n=61), 28 mm-head MM THA (n=18), and 36 mm-head MM THA (n=25). The concentrations of cobalt (Co), chromium (Cr), and molybdenum (Mo) were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS).

Results: The median Co level was not significantly different between the 3 groups (2.35 ppb, 2.00 ppb, and 2.50 ppb for the 28 mm MM THA, 36 mm MM THA, and the ASR patients, respectively). The median Cr level was significantly lower in the 36 mm MM THA patients (0.10 ppb) compared to the 28 mm MM THA (0.15 ppb) and the ASR (0.40 ppb) patients. The median Mo level was significantly lower in the 36 mm MM THA patients (1.30 ppb) compared to the 28 mm MM THA (2.00 ppb) and the ASR (1.50 ppb) patients.

Conclusions: Our results show that the level of ions in 36 mm MM THA patients was lower than in 28 mm MM THA patients. This can be explained by the fact that 28 mm MM bearings are resistant to microseparation during the normal gait cycle, which is theoretically accompanied by a reduction of fluid film lubrication and increased potential for the production of wear debris. Our results also show that the ion levels in patients having ASRs is similar to that observed in 28 mm MM THA patients but higher than in 36 mm MM THA patients. The diametric clearance of ASRs is typically much greater and the potential for a ‘suction fit’ may be less, leading to higher ion production. The concentration of ions in long-term follow-up remains however to be elucidated. Funding: Educational Grant from the Canadian Orthopaedic Foundation