Multivariable models in orthopaedic research: a methodological review of covariate selection and causal relationships.

OBJECTIVES: The aim of this study was to evaluate the methods used for including or excluding covariates in a multivariable model and to find out how common is the Table 2 Fallacy in studies recently published in high-quality orthopaedic journals. METHODS: A systematic review was conducted in the MEDLINE database. We included all studies that presented the results of a multivariable model in a table and published in seven orthopaedic journals with the highest ranked impact factors in 2019. RESULTS: Table 2 Fallacy was found in 67% (129/193) of the evaluated studies in which a multivariable model was used. Only 16% (31/193) of all studies had included the variables based on causal inference. Furthermore, only three of these studies used causal diagrams to illustrate the causal inference. Altogether, 35% (67/193) of the studies included variables based on statistical methods. CONCLUSIONS: Confounder selection and the interpretation of the results of the multivariable model showed notable challenges in orthopaedic studies recently published in the top orthopaedic journals. Based on the results of our review, it seems that more education in statistics and increased knowledge is required to decrease the occurrence of these statistical issues in orthopaedic research.

Scheduled Emergency Trauma Operation: The Green Line Orthopedic Trauma Surgery Process Of Care.

BACKGROUND AND AIMS: Traditionally, patients requiring an orthopedic emergency operation were admitted to an inpatient ward to await surgery. This often led to congestion of wards and operation rooms while, for less urgent traumas, the time spent waiting for the operation often became unacceptably long. The purpose of this study was to evaluate the flow of patients coded green in a traffic light-based coding process aimed at decreasing the burden on wards and enabling a scheduled emergency operation in Central Finland Hospital. MATERIALS AND METHODS: Operation urgency was divided into three categories: green (>48 h), yellow (8-48 h), and red (<8 h). Patients, who had sustained an orthopedic trauma requiring surgery, but not inpatient care (green), were assigned an operation via green line process. They were discharged until the operation, which was scheduled to take place during office hours. RESULTS: Between January 2010 and April 2015, 1830 green line process operations and 5838 inpatient emergency operations were performed. The most common green line process diagnoses were distal radial fracture (15.4% of green line process), (postoperative) complications (7.7%), and finger fractures (4.9%). The most common inpatient emergency operation diagnosis was hip fracture (24.3%). Green line process and inpatient emergency operation patients differed in age, physical status, diagnoses, and surgical procedures. CONCLUSION: The system was found to be a safe and effective method of implementing orthopedic trauma care. It has the potential to release operation room time for more urgent surgery, shorten the time spent in hospital, and reduce the need to operate outside normal office hours.

Complications following 250 cemented modular hip hemiarthroplasties.

BACKGROUND AND AIMS: Hemiarthroplasty is a common method of treating displaced femoral neck fractures, especially among elderly non-active patients with frailty syndrome. Complications arising from the use of a modern, modular hemiendoprosthesis via a posterior approach have been poorly reported in this population. The aim of this study was to evaluate complications and mortality associated with the use of Lubinus sp II cemented, unipolar hemiarthroplasty prosthesis and posterior approach during a 9-year follow-up. MATERIAL AND METHODS: All patients (244) who received hemiarthroplasty due to an acute fracture of the femoral neck in Central Finland Hospital, Jyvaskyla, Finland, during 2007 and 2008 were included. Patient records were retrospectively reviewed for intraoperative and postoperative complications. RESULTS AND CONCLUSION: Women composed 70% (n = 171) of the study population. Mean age was 83 years for women and 80 years for men. A total of 31 (12%) complications were found in 30 patients. These were 12 dislocations (5% of all patients), 5 (2%) periprosthetic fractures, 2 (0.8%) superficial and 5 (2%) deep infections, 1 (0.4%) protrusion of the prosthesis, 2 (0.8%) intraoperative fractures, and 2 (0.8%) partial sciatic nerve palsies. Conversion to total hip replacement was performed in 9 cases (4%) and a reoperation was required in 15 (6%) cases. Mortality rate at 9 years was 78% (95% confidence interval = 72%-83%). The overall rate of complications was acceptable although mortality was high in this comorbid patient population. The need for conversion to total hip arthroplasty and reoperation is low.

Mild or moderate renal insufficiency does not increase circulating levels of cobalt and chromium in patients with metal-on-metal hip arthroplasty.

AIMS: To determine whether there is any association between glomerular filtration rate (GFR) and blood cobalt (Co) and chromium (Cr) levels in patients with metal-on-metal (MoM) hip arthroplasty. PATIENTS AND METHODS: We identified 179 patients with a unilateral 36 mm diameter head as part of a stemmed Summit-Pinnacle MoM hip arthroplasty. GFR was calculated using the Modification of Diet in Renal Disease formula. RESULTS: Normal renal function (GFR ≥ 90 ml/min/1.73 m2) was seen in 74 patients. Mild renal insufficiency (GFR 60 to 89 ml/min/1.73 m2) was seen in 90 patients and moderate renal insufficiency (GFR 30 to 59 ml/min/1.73 m2) in 15. There was no statistical difference in Co and Cr levels between patients with normal renal function and those with mild or moderate renal insufficiency. No correlation was seen between creatinine and blood metal ion levels or between GFR and blood metal ion levels. Linear regression analysis did not show any association between Co and Cr levels and GFR. CONCLUSION: We did not find any association between GFR and blood metal ion levels. Consequently, the accumulation of Co and Cr in blood due to renal insufficiency does not seem to be a major risk in patients with mild or moderate renal insufficiency. Cite this article Bone Joint J 2017;99-B:1147-52.

High prevalence of noise following Delta ceramic-on-ceramic total hip arthroplasty.

AIMS: We evaluated the short-term functional outcome and prevalence of bearing-specific generation of audible noise in 301 patients (336 hips) operated on with fourth generation (Delta) medium diameter head, ceramic-on-ceramic (CoC) total hip arthroplasties (THAs). PATIENTS AND METHODS: There were 191 female (63%) and 110 male patients (37%) with a mean age of 61 years (29 to 78) and mean follow-up of 2.1 years (1.3 to 3.4). Patients completed three questionnaires: Oxford Hip Score (OHS), Research and Development 36-item health survey (RAND-36) and a noise-specific symptom questionnaire. Plain radiographs were also analysed. A total of three hips (0.9%) were revised. RESULTS: There were 52 patients (54 hips, 17%) who reported noise, and in 25 (48%) of them the noise was frequently heard. In the multiple regression analysis, the only independent risk factor for noise was a specific THA brand, with a threefold increased risk (95% confidence intervals 1.39 to 6.45, p = 0.005) of noise compared with the reference THA brand. Patients with noisy hips had lower median OHS (43 versus 46.5, p = 0.002) and their physical functioning (p = 0.021) subscale in RAND-36 was reduced. CONCLUSION: Noise was surprisingly common in this population. Cite this article: Bone Joint J 2017;99-B:44-50.

Repeated metal ion measurement in patients with bilateral metal on metal (ASR™) hip replacements.

BACKGROUND: Blood metal ion measurements have become a cornerstone in the surveillance of metal-on-metal (MoM) hip replacements. Interpretation of these levels in patients with bilateral MoM hip replacements, however, is challenging. We therefore asked (1) if there is a clinically significant change in whole blood (WB) Co or Cr levels in repeated WB assessment in patients operated on with bilateral ASR hip replacements, and (2) what proportion of patients has WB Co or Cr level below the previously established safe upper limits (SUL) (Co<5.0µg/L, Cr<7.4µg/L) in the repeated WB metal ion assessment. HYPOTHESIS: We hypothesized that there is a significant difference between repeated Co and Cr level measurement performed within one year±4 months interval in patients with bilateral ASR hip replacements. MATERIALS AND METHODS: We identified all patients (n=139) who had received bilateral ASR hip replacements (278 hips). Patients (n=76, 152 hips) who had undergone two blood metal ion measurements within eight to sixteen months' time interval were included in the study analysis. Study cohort included 38 patients with bilateral ASR hip resurfacings (mean age 53 years, median follow-up 4.6 years, median femoral diameter 51mm) and 38 patients with bilateral ASR XL total hip replacements (mean age 60 years, median follow-up 3.6 years, median femoral diameter 49mm). RESULTS: There was no significant change in Co and Cr levels between the repeated measurements in the HR cohort. Both Co and Cr were significantly higher in the THR cohort in the repeated measurement (Co: 8.3µg/L vs. 12.6µg/L, Cr: 3.15µg/L vs. 3.4µg/L, both P<0.001). WB Co and Cr levels remained below SUL and within their initial values during a mean one-year measurement interval in the majority of patients with bilateral high risk HR device. In contrast to this, 21.1% of patients with THRs had WB Co ion levels exceeding the SUL in the first measurement. WB Co values significantly increased over the measurement interval in the THR group. DISCUSSION: Annual blood metal ion measurement is not useful in patients with bilateral hip resurfacings who have undergone at least one preliminary screening including both metal ion measurement and cross-sectional imaging. It seems, however, to be beneficial in patients with bilateral high risk MoM THR. LEVEL OF EVIDENCE: Level III (retrospective comparative study).

Surveillance of Patients with Metal-on-Metal Hip Resurfacing and Total Hip Prostheses: A Prospective Cohort Study to Investigate the Relationship Between Blood Metal Ion Levels and Implant Failure.

BACKGROUND: We designed a prospective, single-center study to assess whether blood metal ion levels could predict implant failure in patients managed with unilateral metal-on-metal hip resurfacing or total hip arthroplasty. METHODS: Five hundred and ninety-seven patients who had received unilateral Articular Surface Replacement prostheses at least twelve months earlier were recruited. Blood metal ion levels were compared between the group of patients with failed implants and the group with non-failed implants. Implant failure was defined as prostheses associated with revision, an intention to revise, or poor patient-reported hip function (Oxford Hip Score, <31 of 48). Specificity, sensitivity, area under the curve, positive and negative predictive values, and odds ratios were calculated. Logistic regression analysis was used to identify other risk factors for implant failure. RESULTS: Patients with failed arthroplasty had significantly higher blood cobalt and chromium ion levels than did patients with non-failed arthroplasty (p < 0.01). Blood cobalt ion levels were disproportionately raised in patients with failed total hip arthroplasty (8.2 µg/L) compared with patients with failed hip resurfacing (2.5 µg/L) (p = 0.018). Blood chromium ion levels were not significantly different in patients with failed total hip arthroplasty and failed hip resurfacing (p = 0.058). The maximum value of either metal ion had good discriminant ability to predict implant failure (area under the curve, 0.76). A 7-µg/L cutoff had a positive predictive value of 0.75 (95% confidence interval, 0.66 to 0.82) and a negative predictive value of 0.82 (95% confidence interval, 0.78 to 0.86). In patients managed with total hip arthroplasty, for each increase of 1 µg/L there was a 23% (p < 0.001) increase in the odds of them being in the failed group. For patients managed with hip resurfacing, the increase in odds was 5% (p < 0.001). CONCLUSIONS: Raised levels of blood metal ions were associated with failed metal-on-metal hip resurfacings and total hip arthroplasties. A threshold level of 7 µg/L had inadequate sensitivity to be used in isolation as a screening test for implant failure, but it provided nearly optimal misclassification rates. No level had a perfect positive predictive value, and so we discourage surgeons from performing revision surgery based on blood metal ion levels alone. Levels of cobalt ions were raised out of proportion to levels of chromium ions in failed total hip arthroplasty and may reflect a different mechanism for metal ion generation. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.