Metal ion levels are used to track the performance of metal containing bearings in hip replacement patients. Changes in whole blood metal ion levels are indicators of wear rates in these bearings. Normal metal ion levels are variable, and range widely. Changes in these “non-bearing” levels over a period of time may influence the monitoring of these bearings. As part of a prospective randomised trial of different bearing surfaces, whole blood metal ion levels were monitored. This included four cohorts of patients, namely ceramic-on-ceramic (CoC), ceramic-on-polyethylene (CoP), ceramic-on-ceramic (CoC) and ceramic-on-metal (CoM). Serial whole blood metal ion levels in the non-metal bearings, namely CoC and CoP, were analyzed. There was no consistency in these whole blood metal ion levels. Intra-patient variations in these levels over a period of time could not be due to bearing-produced metal ions as these were all metal free, and thus not the source of any endogenous ions. These intra-patient variations may reflect changes in exogenous exposure to these metal ions, fluctuations in these patient's metabolic functions or production of metal ions from non-bearing prosthetic sources.Methods.
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The advantages of computer navigated total knee replacement are well documented in the literature, however, increased surgical time and cost issues remain the major deterrent for the wide use of this technology. Placement of cutting jigs under computer guidance forms a major aspect of computer assisted knee replacement surgery. The use of a motorized mini-robotic cutting jig allows for a more precise and time efficient execution of the femoral cuts under computer guidance. We present a preliminary report on our experience using standard computer assisted surgery (CAS) jigs and mini robotic motorized jigs in computer navigated knee replacement We compared our experience using standard jigs and mini-robotic jigs in knee replacement. A cohort of patients involved in a study comparing navigated and standard total knee replacements received TKA using a Bi-Cruciate Stabilised Knee System. A pilot cohort of patients received total knee replacement using standard computer navigation by the pi galileo system without the mini-robots while awaiting acquisition of the mini robot system. We compared our experience using the same pi galileo system with mini robotic cutting jigs to the cohort without the mini-robotic cutting guides. Reduction in surgical time was statistically significant when using the motorized mini robotic jigs. Blood loss was identical in both cohorts, and cut precision was better in the cohort with the motorized mini robotic jigs.Methods:
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Monitoring the performance of hip replacements post-operatively is tedious and costly, necessitating radiological examinations as well as other specialized examinations such as whole blood metal ion levels. In an effort to control escalating costs, we conducted an ethically approved clinical trial to assess the efficacy of basic acoustic monitoring equipment to asses these implants. An electronic stethoscope was successfully used to record sounds from the hips of participants with different bearing surfaces. The sounds were recorded while conducting a standardized movement sequence. A 5th order Savitzky-Golay filter with a window width of 21 points was used to remove background noise. The recordings were also listened to by ear and three primary classes of sounds were identified. Frequency components contained in the classes were identified using spectrograms and Welch power density spectra. The sounds were correlated with different patient factors including component positioning, BMI and length of time that the implant was in situ. The skewness and kurtosis of the power spectra were calculated and found to be different for each class. Further frequency analysis was conducted with the aid of the discrete wavelet transform. This met with some success as different frequency levels were found in each sound class. All bearing surfaces produced some noise. The most sounds were produced by the ceramic-on-metal group, even though not in the audible range, and those participants with a body mass index in the obese range. Sounds were also detected in the ceramic-on-polyethylene implants. However, no consistent links between these factors and the sounds produced could be identified. Specifically, the lack of correlation between sound occurrence and length of implantation indicates that this technique is not useful in predicting possible failures or future complications in real time.Method.
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There has been much controversy around metal on metal hip replacements of late due to adverse metal reactions. There is evidence implicating lymphocyte mediated response (type IV delayed-hypersensitivity) to metal debris generated by the implants as one of the main factors responsible for the reactions. Our understanding of these adverse reactions continues to improve but we also recognize that the majority of patients with MOM implants are asymptomatic with well functioning implants. Studies have shown up to 16% allergy to metal ions on pre-operative allergy patch testing. We set out to determine the incidence of hypersensitivity to Cobalt, Chromium and Molybdenum in a arthroplasty population. We assayed whole blood using a validated optimized lymphocyte transformation test, MELISA as part of a prospective randomized study on large diameter bearing surfaces. We recruited 47 subjects, 19 males, 28 females (35–75 yrs). Specific exclusions included presence of metal implants in the body and industrial exposure to metals.Introduction
Method
Maximizing efficiency in total knee replacement surgery is desirable and one of the key aspects is optimum utilization of available theatre time allocation. The level of complexity of the pathology is often one of the determinants of the length of operative time. Body mass index (BMI) has also been positively correlated with operative time. However, two patients with the same BMI but different body habitus (central obesity vs generalized obesity) may present different challenges during surgery. An index focusing on the anthropometry of the lower limb (supra-patella index SPI) has been proposed and we hypothesize that it correlates more closely with operative time than BMI. BMI and SPI were determined in all patients recruited into a prospective trial of a specific knee implant. All patients were operated on by one of two surgeons in a standardized manner. Data including operative time and tourniquet time were determined.Introduction
Method
