Higher than expected revision rates have been observed in large bearing metal-on-metal total hip replacements. We have introduced a metal on metal hip screening clinic at our unit and report the results. All patients who had a metal-on-metal total hip replacement implanted at our unit were recalled to clinic. Screening consisted of clinical examination, Oxford hip score, radiographs, MARS MRI and serum cobalt/chromium ion levels. MRI scans were graded (Norwich Classification) by a single consultant radiologist who was blinded to the history, examination, and metal levels. Patients were sub-classified into 6 groups, which determined further follow up and were either entered into a regular screening programme or referred to a revision arthroplasty surgeon for a decision on whether revision was requiredBackground:
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Urinary catheterisation may be associated with a risk of infection in hip and knee arthroplasty, however post-operative urinary retention can be distressing for the patient. This study investigates the factors that might predict the need for post-operative catheterisation. A prospective blinded study of 128 consecutive patients undergoing lower limb arthroplasty was carried out. Data obtained included sex, age, joint (hip or knee), prostate score (IPSS), previous urinary retention, co-morbidities and residual bladder volume after attempted complete voiding measured using an ultrasound bladder scanner. Anaesthetic type and requirement for urinary catheterisation postoperatively were recorded. Predictive risk factors were identified using binary logistic regression, and expressed as odds ratios (OR) and 95% confidence intervals (CI). The mean age was 69.5 years. There were 56 males and 72 females. 38 patients (30%) required post-operative catheterisation. Logistic regression identified the following predictive risk factors: bladder scan volume per ml increase (OR 1.006; CI 1.000–1.012); male sex (OR 5.51; CI 2.01–15.16); previous catheter (OR 4.26; CI 1.53–11.82); spinal/epidural/combined spinal epidural anaesthesia (OR 6.78; CI 1.75–26.32); moderate IPSS score (OR 5.15; CI 1.73–15.37); severe IPSS score (OR 3.53; CI 0.605–20.54). Our model specificity is 91%, positive predictor value 71% and negative predictor value 82%.
Urinary catheterisation can cause bacteraemia and therefore may be associated with a risk of infection in hip and knee arthroplasty. However postoperative urinary retention can be distressing for the patient. This study investigates the factors that might predict the need for postoperative catheterisation in order to help develop a protocol to decide who should be electively catheterised. A prospective blinded study of 128 consecutive patients undergoing lower limb arthroplasty was carried out. No patient underwent perioperative catheterisation. Data obtained included sex, age, joint (hip or knee replacement), prostate score (IPSS), previous urinary retention, comorbidities and residual bladder volume after attempted complete voiding measured using an ultrasound bladder scanner. The type of anaesthesia and the requirement for urinary catheterisation postoperatively were recorded. Predictive risk factors were identified using binary logistic regression, and expressed as odds ratios (OR) and 95% confidence intervals (CI).Introduction
Methods
ARMD (Adverse Reaction to Metal Debris) is an increasingly recognised complication of metal on metal hip replacements. The MHRA (Medical and Healthcare Related Devices Agency) have advised a blood cobalt or chromium level above 7 mg/L is a threshold for further investigation, stating that “low levels are reassuring and strongly predict not having an adverse outcome”. Cross-sectional imaging should be performed when levels are above 7 mg/L. We have performed a study investigating the specificity and sensitivity of chromium and cobalt metal ion levels as a screening measure for ARMD. 79 ASR hip replacements were performed at our hospital and 75 (95%) of these underwent a Metal Artefact Reduction Sequence (MARS) MRI scan. All patients (64 hips) who had not undergone revision were invited to take part in this study. 57 patients with 62 hip replacements completed hip and activity scores, had blood cobalt and chromium ion level measurements and 3D-CT to measure acetabular component position. Acetabular component inclination (>50 degrees), small head size (< 51mm) and female gender were significantly correlated with raised chromium (Cr) and cobalt (Co) ion levels. An ARMD was detected using MRI in 18 (29%) of the hips in this study. The incidence of ARMD was significantly higher when chromium concentration was above 7 mg/l (p = 0.02). Chromium ion levels >7 mg/L had a sensitivity of 56% and specificity of 83% for ARMD, and cobalt ion levels >7 mg/L 56% and 76% respectively. 40 patients had cobalt levels <7 mg/L and 33 had chromium levels <7 mg/L, but 8 of these had an ARMD on MRI. All 8 patients had minimal symptoms (Oxford Hip Score ≥ 44 out of 48). The Medicines and Healthcare Products Regulatory Agency (MHRA) has recommended that cobalt and chromium levels be measured in patients with a metal-on-metal hip replacement and cross-sectional imaging performed when these levels are above 7 μg/L. This study has shown that by using this threshold, in patients with this implant combination, the sensitivity and specificity for the detection of ARMD is low and patients with soft tissue disease may be missed. Furthermore the presence of MRI detected ARMD, in the absence of significant clinical symptoms and with metal ion levels <7 μg/L is of concern. MoM implants at risk of failure are associated with raised cobalt and chromium levels. However metal ion analysis alone is not reliable as a screening tool for ARMD, which is often clinically “silent”. We recommend the routine use of MARS MRI as the safest method of ARMD diagnosis in patients with MoM implants.
Of the 76 hips that were MRI scanned, 27 (36%) had typical features of a MOM reaction. These were classified as mild in 10 (13%), moderate in 13 (17%) and severe in 4 (5%). 78 patients completed an OHS and the mean score was 21. The mean OHS was 29 pre-operatively in those that had been revised, 25 in patients with abnormal MRI findings and 20 in those with a normal MRI. 10 patients with abnormal MRIs had a near perfect OHS (15 or less)
