Wierd P. Zijlstra

Cobalt and chromium ions reduce human osteoblast-like cell activity in vitro, reduce the OPG to RANKL ratio, and induce oxidative stress.

Metal‐on‐metal hip arthroplasty is associated with elevated levels of cobalt and chromium ions. The effects of cobalt and chromium ions on cell number, activity, expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) and oxidative stress on human osteoblast‐like cells were addressed. Saos‐2 cells were supplemented with Co2+, Cr3+, or Co2+ + Cr3+ (1:2) at 0, 1, 10, and 100 µg/L and incubated for 24, 48, 72, and 96 h. Cell activity was assessed by MTT‐assay and cell number by Crystal Violet staining. RNA levels of OPG and RANKL were evaluated using real‐time quantitative polymerase chain reaction (qPCR). Compared to controls Co2+ reduced cell numbers: at 10 µg/L by 17 ± 8% after 48 h and at 100 µg/L after 24 h by 35 ± 8%. Cr3+ decreased cell numbers at 10 µg/L after 48 and 72 h. Co2+ + Cr3+ combined at 1 µg/L lowered cell numbers after 24 and 96 h (17 ± 13, resp. 13 ± 4%). The 10 and 100 µg/L concentrations reduced cell numbers significantly after 24, 48, and 96 h. Cr3+ reduced osteoblast activity at 1, 10, and 100 µg/L at all incubation times. The strongest reduction (11 ± 1%) was seen at 100 µg/L after 96 h. The OPG/RANKL ratio was reduced after 72 h with almost all Co2+ and Cr3+ concentrations. After 96 h, glutathione, superoxide dismutase, and catalase levels were indicative for an oxidative stress response in all samples. In conclusion, cobalt and chromium ions reduce human osteoblast activity, reduce OPG/RANKL ratio and lead to oxidative stress.

No superiority of cemented metal-on-metal vs metal-on-polyethylene THA at 5-year follow-up.

A randomized controlled trial was performed to compare the cemented Stanmore metal-on-metal (Biomet, Warsaw, Indiana) total hip arthroplasty (THA; 102 hips) to the cemented Stanmore metal-on-polyethylene (Biomet) THA (98 hips). The primary outcome was clinical performance. Radiological performance, serum cobalt analysis, and prosthetic survival were secondary outcome measures. At a mean follow-up of 5.6 years, 5 patients were lost to follow-up, 18 died, and 4 were revised (3 metal-on- metal, 1 metal-on-polyethylene). Harris Hip Scores improved from 48 to 90 in the metal-on-metal patients (P<.001) and from 46 to 87 in the metal-on-polyethylene patients (P<.001). Oxford Hip Scores changed from 40 to 19 in the metal-on-metal group (P<.001) and from 40 to 18 in the metal-on-polyethylene group (P<.001). For both Harris and Oxford Hip Scores, there was no significant difference between the 2 groups. Five-year survival with revision for any reason was 97% (95% CI 93%-100%) in the metal-on-metal group and 99% (95% CI 97%-100%) in the metal-on-polyethylene group. All revisions were indicated for aseptic loosening (metal-on-metal: 3 cup revisions; metal-on-polyethylene: 1 total revision). At 5-year follow-up, cemented metal-on-metal THA showed no clinical superiority over metal-on-polyethylene THA.

No Superiority of Cemented Metal-on-Metal Over Metal-on-Polyethylene THA in a Randomized Controlled Trial at 10-Year Follow-up

In a randomized controlled trial, 102 cemented Stanmore 28-mm metal-on-metal total hip arthroplasties (THAs) were compared to 98 metal-on-polyethylene THAs in 195 patients. At a mean follow-up of 10 years, 11 patients (11 hips) were lost to follow-up, 53 patients (55 hips) died, and 6 patients (6 hips) underwent revision. Average age of the surviving patients was 79 years. Harris Hip Scores and Oxford Hip Scores had increased significantly in both groups (P=.000). Ten years postoperatively, mean Harris Hip Score was 86 in the metal-on-metal patients and 87 in the metal-on-polyethylene patients (P=.441); Oxford Hip Scores were 27 and 24, respectively (P=.494). Wear was present in 30 of 52 polyethylene cups. Periprosthetic radiolucencies were seen in 57% of the metal-on-metal patients and in 52% of the metal-on-polyethylene patients (P=.680); they were mainly seen in DeLee & Charnleys zones 1 and 2. Serum cobalt and chromium concentration were higher in the metal-on-metal group (cobalt 1.1, chromium 1.0 vs 0.5 and 0.5 mug/L, respectively; P<.001). Patients with high ion levels (maximum 9.5 and 11 mug/L, respectively) all showed high Harris Hip Scores and few or no periprosthetic radiolucencies, and none were revised. Ten-year survival was 95.5% in the metal-on-metal group (4 revisions) and 96.8% in the metal-on-polyethylene group (2 revisions; P=.402). All revisions were indicated for aseptic loosening. One case of aseptic lymphocytic vasculitis-associated lesions and no pseudotumors were observed. The absence of clinical superiority of the cemented metal-on-metal bearing and the concerns over their biological effects have led us to favor the cemented metal-on-polyethylene THA.

Effect of femoral head size and surgical approach on risk of revision for dislocation after total hip arthroplasty An analysis of 166,231 procedures in the Dutch Arthroplasty Register (LROI)

Background and purpose — Recurrent dislocation is the commonest cause of early revision of a total hip arthropasty (THA). We examined the effect of femoral head size and surgical approach on revision rate for dislocation, and for other reasons, after total hip arthroplasty (THA). Patients and methods — We analyzed data on 166,231 primary THAs and 3,754 subsequent revision THAs performed between 2007 and 2015, registered in the Dutch Arthroplasty Register (LROI). Revision rate for dislocation, and for all other causes, were calculated by competing-risk analysis at 6-year follow-up. Multivariable Cox proportional hazard regression ratios (HRs) were used for comparisons. Results — Posterolateral approach was associated with higher dislocation revision risk (HR =1) than straight lateral, anterolateral, and anterior approaches (HR =0.5–0.6). However, the risk of revision for all other reasons (especially stem loosening) was higher with anterior and anterolateral approaches (HR =1.2) and lowest with posterolateral approach (HR =1). For all approaches, 32-mm heads reduced the risk of revision for dislocation compared to 22- to 28-mm heads (HR =1 and 1.6, respectively), while the risk of revision for other causes remained unchanged. 36-mm heads increasingly reduced the risk of revision for dislocation but only with the posterolateral approach (HR =0.6), while the risk of revision for other reasons was unchanged. With the anterior approach, 36-mm heads increased the risk of revision for other reasons (HR =1.5). Interpretation — Compared to the posterolateral approach, direct anterior and anterolateral approaches reduce the risk of revision for dislocation, but at the cost of more stem revisions and other revisions. For all approaches, there is benefit in using 32-mm heads instead of 22- to 28-mm heads. For the posterolateral approach, 36-mm heads can safely further reduce the risk of revision for dislocation.

Pseudotumour incidence, cobalt levels and clinical outcome after large head metal-on-metal and conventional metal-on-polyethylene total hip arthroplasty: mid-term results of a randomised controlled trial

We compared the incidence of pseudotumours after large head metal-on-metal (MoM) total hip arthroplasty (THA) with that after conventional metal-on-polyethylene (MoP) THA and assessed the predisposing factors to pseudotumour formation. From a previous randomised controlled trial which compared large head (38 mm to 60 mm) cementless MoM THA with conventional head (28 mm) cementless MoP THA, 93 patients (96 THAs: 41 MoM (21 males, 20 females, mean age of 64 years, standard deviation (sd) 4) and 55 MoP (25 males, 30 females, mean age of 65 years, sd 5) were recruited after a mean follow-up of 50 months (36 to 64). The incidence of pseudotumours, measured using a standardised CT protocol was 22 (53.7%) after MoM THA and 12 (21.8%) after MoP THA. Women with a MoM THA were more likely to develop a pseudotumour than those with a MoP THA (15 vs 7, odds ratio (OR) = 13.4, p < 0.001). There was a similar incidence of pseudotumours in men with MoM THAs and those with MoP THAs (7 vs 5, OR = 2.1, p = 0.30). Elevated cobalt levels (≥ 5 microgram/L) were only associated with pseudotumours in women with a MoM THA. There was no difference in mean Oxford and Harris hip scores between patients with a pseudotumour and those without. Contrary to popular belief, pseudotumours occur frequently around MoP THAs. Women with a MoM THA and an elevated cobalt level are at greatest risk. In this study, pseudotumours had no effect on the functional outcome after either large head MoM or conventional MoP THA.

Acetabular bone density and metal ions after metal-on-metal versus metal-on-polyethylene total hip arthroplasty; short-term results

Information on periprosthetic acetabular bone density is lacking for metal-on-metal total hip arthroplasties. These bearings use cobalt-chromium instead of titanium acetabular components, which could lead to stress shielding and hence periprosthetic bone loss. Cobalt and chromium ions have detrimental effects on bone. It is unknown whether serum metal ion levels affect bone density clinically. We compared cementless large femoral head (mean 48 mm) metal-on-metal total hip arthroplasties (M2a-Magnum, Biomet) to cementless 28 mm metal-on-polyethylene total hip arthroplasties (Mallory-Head, Biomet) in a randomised clinical trial. We evaluated periprosthetic acetabular bone density and serum metal ion levels at 1 year postoperatively. Acetabular bone density was analyzed with dual energy x-ray absorptiometry in four horizontal regions of interest in 70 patients. After one year, acetabular bone density decreased (-3.5% to −7.8%) in three of four regions of interest in metal-on-polyethylene patients, but was retained in metal-on-metal patients. Bone density preservation was most pronounced superior to the metal-on-metal cup (+1% versus −3.7%). Serum cobalt, chromium and titanium ion levels were not related to bone density, nor to acetabular inclination or femoral head size. Oxford and Harris hip scores were similar in both groups. Contrary to our hypothesis, acetabular bone density was retained with metal-on-metal total hip arthroplasty, compared to metal-on-polyethylene arthroplasty. Bone preservation was most pronounced in the area superior to the cup. This could be a benefit during future revision surgery.

The effect of bearing type on the outcome of total hip arthroplasty: Analysis of 209,912 primary total hip arthroplasties registered in the Dutch Arthroplasty Register

Background and purpose — Alternative bearing surfaces such as ceramics and highly crosslinked polyethylene (HXLPE) were developed in order to further improve implant performance of total hip arthroplasties (THAs). Whether these alternative bearing surfaces result in increased longevity is subject to debate. Patients and methods — Using the Dutch Arthroplasty Register (LROI), we identified all patients with a primary, non-metal-on-metal THA implanted in the Netherlands in the period 2007–2016 (n = 209,912). Cumulative incidence of revision was calculated to determine differences in survivorship of THAs according to bearing type: metal-on-polyethylene (MoPE), metal-on-HXLPE (MoHXLPE), ceramic-on-polyethylene (CoPE), ceramic-on-HXLPE (CoHXLPE), ceramic-on-ceramic (CoC), and oxidized-zirconium-on-(HXL)polyethylene (Ox(HXL)PE). Multivariable Cox proportional hazard regression ratios (HRs) were used for comparisons. Results — After adjustment for confounders, CoHXLPE, CoC, and Ox(HXL)PE resulted in a statistically significantly lower risk of revision compared with MoPE after 9 years follow-up (HR =0.8–0.9 respectively, compared with HR =1.0). For small (22–28 mm) femoral head THAs, lower revision rates were found for CoPE and CoHXLPE (HR =0.9). In the 36 mm femoral head subgroup, CoC-bearing THAs had a lower HR compared with MoHXLPE (HR =0.7 versus 1.0). Crude revision rates in young patients (< 60 years) for CoHXLPE, CoC, and Ox(HXL)PE (HR =0.7) were lower than MoPE (HR =1.0). However, after adjustment for case mix and confounders these differences were not statistically significant. Interpretation — We found a mid-term lower risk of revision for CoHXLPE, CoC, and Ox(HXL)PE bearings compared with traditional MoPE-bearing surfaces.

Medication Use is a Better Predictor of Length of Hospital Stay in Total Hip Arthroplasty Than the American Society of Anesthetists (ASA) Score

BACKGROUND Length of hospital stay (LOS) greatly influences costs of total hip arthroplasty (THA). LOS is, among others, dependent on patient comorbidity. American Society of Anesthetists (ASA) scores are traditionally used as comorbidity measure, but simple medication-based measures may suffice. Therefore, the objective of the study is to determine if medication-based measures (count of medication and the medication-based index Chronic Disease Score [CDS]) have a surplus value compared to a diagnosis-based measure for comorbidity (ASA score) to predict LOS in THA. METHODS A retrospective cohort study. THA patients from 3 hospitals were included for 2009-2013, and demographic data, comorbidity (ASA score), and medication use (count of medication and CDS) were collected. A binomial regression model was used to compare the predictive ability of the medication-based and diagnosis-based measures. RESULTS A total of 2,282 THA patients were included. Number of medications proved a statistical significant predictor of LOS. LOS increased 6% (incidence rate ratios: 10.06 [confidence interval: 1.03-1.09]) with each medication. Neither the CDS nor the ASA score had a statistically significant relation to LOS. CONCLUSION The medication-based measure count of medication is a better predictor for LOS in THA than the CDS and ASA score. This simple measure also appears to have more clinical relevance, as it has a higher range in scores than diagnosis-based indexes and is easily applicable.

Predicting Failure in Early Acute Prosthetic Joint Infection Treated With Debridement, Antibiotics, and Implant Retention: External Validation of the KLIC Score

BACKGROUND Debridement, antibiotics, and implant retention (DAIR) is a widely used treatment modality for early acute prosthetic joint infection (PJI). A preoperative risk score was previously designed for predicting DAIR failure, consisting of chronic renal failure (K), liver cirrhosis (L), index surgery (I), cemented prosthesis (C), and C-reactive protein >115 mg/L (KLIC). The aim of this study was to validate the KLIC score in an external cohort. METHODS We retrospectively evaluated patients with early acute PJI treated with DAIR between 2006 and 2016 in 3 Dutch hospitals. Early acute PJI was defined as <21 days of symptoms and DAIR performed within 90 days after index surgery. Failure was defined as the need for (1) second DAIR, (2) implant removal, (3) suppressive antimicrobial treatment, or (4) infection-related death within 60 days after debridement. RESULTS A total of 386 patients were included. Failure occurred in 148 patients (38.3%). Patients with KLIC scores of ≤2, 2.5-3.5, 4-5, 5.5-6.5, and ≥7 had failure rates of 27.9%, 37.1%, 49.3%, 54.5%, and 85.7%, respectively (P < .001). The receiver-operating characteristic curve showed an area under the curve of 0.64 (95% confidence interval 0.59-0.69). A KLIC score higher than 6 points showed a specificity of 97.9%. CONCLUSION The KLIC score is a relatively good preoperative risk score for DAIR failure in patients with early acute PJI and appears to be most useful in clinical practice for patients with low or high KLIC scores.

Fatal Cobalt Toxicity after a Non-Metal-on-Metal Total Hip Arthroplasty

This case illustrates the potential for systemic cobalt toxicity in non-metal-on-metal bearings and its potentially devastating consequences. We present a 71-year-old male with grinding sensations in his right hip following ceramic-on-ceramic total hip arthroplasty (THA). After diagnosing a fractured ceramic liner, the hip prosthesis was revised into a metal-on-polyethylene bearing. At one year postoperatively, X-rays and MARS-MRI showed a fixed reversed hybrid THA, with periarticular densities, flattening of the femoral head component, and a pattern of periarticular metal wear debris and pseudotumor formation. Before revision could take place, the patient was admitted with the clinical picture of systemic cobalt toxicity, supported by excessively high serum cobalt and chromium levels, and ultimately died. At autopsy dilated cardiomyopathy as cause of death was hypothesized. A third body wear reaction between ceramic remnants and the metal femoral head very likely led to excessive metal wear, which contributed systemic cobalt toxicity leading to neurotoxicity and heart failure. This case emphasizes that fractured ceramic-on-ceramic bearings should be revised to ceramic-on-ceramic or ceramic-on-polyethylene bearings, but not to metal-on-polyethylene bearings. We aim to increase awareness among orthopedic surgeons for clinical clues for systemic cobalt intoxication, even when there is no metal-on-metal bearing surface.