Total Hip Replacement (THR) is a proven and effective surgical procedure. One of the main limiting factors of the longevity of THR is the performance of the bearing surface. The optimum bearing surface choice, however, remains controversial. We wanted to understand what influenced the choice of bearing surfaces amongst South African orthopaedic surgeons. We also wanted to know if there was any consensus between surgeons and the orthopaedic trade. There is no epidemiological registry-based data available in South Africa in respect of bearing surfaces used in hip replacements. We sent out an electronic survey to all members of the South African Orthopaedic Association as well as to trade representatives. Patient parameters influencing the choice of bearing surfaces were surveyed and these included age, gender, level of activity and diagnosis. We used a regressional and tree analysis methodology to interpret the results.Introduction:
Aims, material and methods:
Antibiotic prophylaxis prior to dental and other procedures when patients have joint replacements in situ remains controversial. Recommendations seem to generally be intuitive and not based on any sound scientific evidence. Recently, the American Academy of Orthopaedic Surgeons altered their previous standpoint and suggested that orthopaedic surgeons review their current practice of routine prescription of antibiotic prophylaxis. We conducted an electronic survey of members of the South African Orthopaedic Association to determine the opinion of the average orthopaedic surgeon in South Africa in respect of this prophylaxis. 111 surgeons responded.Background:
Method:
Massive acetabular defects remain an unresolved challenge in revision arthroplasty surgery of the hip. We report on 7 patients treated with custom made acetabular components to manage these massive boney defects. After high resolution CT scans were done, custom made implants were designed in collaboration between the surgeons and the manufacturer. All implants matched the bony defects as designed.Background:
Methods:
The study was started in 2004 to determine the best bearing surface in the long term, and to measure the metal ion levels generated by each of the bearing surfaces. We present the latest updated results. A prospective randomised study was started in 2004 to compare the wear characteristics of Ceramic on X linked Polyethylene (C.O.P.), Ceramic on Ceramic (C.O.C), Ceramic on Metal (C.O.M.) and Metal on Metal (M.O.M) bearings. The level of Cobalt and Chrome ions in red blood cells have been documented at serial intervals, using the ICP – MS method. Aside from the bearing surfaces the rest of the implant is standard, using a Pinnacle Cup, Corail Stem and 28mm heads. 256 Cases were enrolled on the study. To date 71 cases have been lost due to death (26), revision (9) and lost to follow up (36), leaving us with 185 for follow-up. An even spread of cases in each bearing surface are still available for follow up, viz. 46 C.O.P, 48 C.O.C., 44 C.O.M. and 47 M.O.M. Average follow up is currently 4.8 years, ranging up to 9 years.Purpose Of Study
Material and methods
We report on a series of long-stemmed femoral components used in revision total hip replacements which fractured, and were subsequently revised. All explanted stems were analysed in respect of the reasons for failure. The patient's serial radiographs and clinical records were also analysed. All stems demonstrated some fixation distally. They all showed little proximal osteo-integration. A biomechanical analysis confirmed the vulnerability of these long stemmed modular prostheses in respect of mechanical failure. The resultant unprotected lever-arms led to local stresses in the prosthesis constructs which were above the failure threshold resulting in prosthesis fractures. These fractures all occurred at points where the prostheses were structurally most vulnerable.Methods
Results
Antibiotic loaded polymethyle methacrylate spacers are commonly used in the management of septic hip replacements. The aim of this study was to determine wear patterns on the articulating surfaces of these spacers, as well as to determine the extent of PMMA particulate debris generation.Introduction
Aim
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.
Results.
To look at the difference in metal ion levels using Ceramic on Metal (COM) and Metal on Metal (MOM) bearings in Total Hip Replacements, comparing the results between well placed and poorly placed cups. Metal ion levels using the ICP-MS method of assay have been studied as part of a prospective randomised trial between 4 different bearing combinations. The ion levels have been raised in the COM and MOM bearings. Metal ions are not raised in the Ceramic on Ceramic (COC) and Ceramic on X linked Poly(COP) bearings, showing that no other material in the study prosthesis aside from the bearing surfaces contribute to raised ion levels. Cup inclination and cup anteversion has been measured in all patients.Purpose of Study:
Methods:
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:
Results:
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.
Results.
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
The search for the ideal bearing surface in Total Hip Replacements continues. The current ‘best’ materials are felt to be combinations of metal, ceramics and cross-linked polyethylene. Laboratory studies suggest that ceramic-on-metal articulations may provide distinct advantages. This study aims to identify the best bearing surface combination with the lowest adverse side effect profile. Between February 2004 and September 2007, 164 hips were replaced in 142 patients. 39% were male and 69% were female. The average age at surgery was 53 years (17-72 years). Follow-up assessment included radiographs, the Harris Hip Score and whole blood samples for metal ion levels. Complications to date included 3 hips which needed femoral revision because of surgery related factors, and 3 cases of sepsis of which 1 settled and 2 needed revision. One hip needed revision of head and liner to a larger bearing size for recurrent dislocations, and is no longer being followed up for blood metal ions. Post-operative whole blood metal ion levels were compared to pre-operative levels to determine the increase or decrease in metal ion levels. There were no changes in those patients with ceramic-on-ceramic and ceramic-on-polyethylene articulations. Moderately raised whole blood metal ion levels were noted at 3 months in the ceramic-on-metal group, while the metal-on-metal group show the greatest increase. This study agrees with laboratory bearing surface wear studies demonstrating lower wear rates in the ceramic-on-metal group compared to the metal-on-metal group. With concerns related to high blood metal ion levels in metal-on-metal articulations, ceramic-on-metal bearing surfaces may well become a bearing surface of choice in the future, but progress needs to be monitored in the longer term.
