The cemented custom femoral stem--a 10 year review.

We report a series of 706 patients (759 hip implants) with an average follow up of 10.5 years (range, 10-11 years) following total hip replacement (THR) using a cemented custom-made femoral stem and a cemented HDP acetabular component. The fate of every implant is known. One hundred and seventy-four patients (23%) were deceased at the time of their 10-year review all died with a functioning THR in situ. Four hundred and sixty-two patients (61%) were subsequently reviewed. One hundred and twenty three patients (16%) were assessed by telephone review, as they were too ill or unwilling to attend. Kaplan-Meier survival analysis (all components) demonstrated a median survival at 10 years of 96.05% or 95% Confidence Intervals (CI) for median survival of (94.41% to 97.22%). Revision surgery occurred in 30 cases (3.9%). Seventeen had full revisions (2.2%) and 13 (1.7%) socket revisions only. Twenty-one out of 30 revisions were for infection or dislocation. There were 2 cases (0.3%) of revision for aseptic loosening of the stem. The 10-year results of the custom femoral titanium stem are encouraging and compare well with other cemented systems.

The impact of curricular change on medical students' knowledge of anatomy.

BACKGROUND: In recent years, following the publication of Tomorrow's Doctors, the undergraduate medical curriculum in most UK medical schools has undergone major revision. This has resulted in a significant reduction in the time allocated to the teaching of the basic medical sciences, including anatomy. However, it is not clear what impact these changes have had on medical students' knowledge of surface anatomy. AIM: This study aimed to assess the impact of these curricular changes on medical students' knowledge of surface anatomy. SETTING: Medical student intakes for 1995-98 at the Queen's University of Belfast, UK. METHODS: The students were invited to complete a simple examination paper testing their knowledge of surface anatomy. Results from the student intake of 1995, which undertook a traditional, 'old' curriculum, were compared with those from the student intakes of 1996-98, which undertook a new, 'systems-based' curriculum. To enhance linear response and enable the use of linear models for analysis, all data were adjusted using probit transformations of the proportion (percentage) of correct answers for each item and each year group. RESULTS: The student intake of 1995 (old curriculum) were more likely to score higher than the students who undertook the new, systems-based curriculum. CONCLUSION: The introduction of the new, systems-based course has had a negative impact on medical students' knowledge of surface anatomy.

Uncemented custom-made femoral components.

We present our experience of total hip replacement (THR) in younger patients using a custom-made smooth titanium alloy femoral prosthesis. Measurements made from pre-operative marker radiographs allowed creation of templates and subsequent computer analysis to mill the stem prior to surgery. Fifty-one such cementless implants were carried out in 43 patients between January 1993 and June 1996 with follow-up to an average of 47 months. Sixteen hips have required revision to date; 13 of these operations were for aseptic loosening. Two more were awaiting revision, giving an overall failure rate of 35.3 %. The average duration from primary operation to revision was 47 months. Thus, even though the concept of an uncemented custom-made femoral component is attractive, the failure rate was found to be unacceptably high. This device may achieve "fit and fill", but adequate bone on- or in-growth was not achieved. On the basis of these data we have discontinued the use of this implant since 1996. (Hip International 2002; 4: 365-70).

Detection of prosthetic hip infection at revision arthroplasty by immunofluorescence microscopy and PCR amplification of the bacterial 16S rRNA gene.

In this study the detection rates of bacterial infection of hip prostheses by culture and nonculture methods were compared for 120 patients with total hip revision surgery. By use of strict anaerobic bacteriological practice during the processing of samples and without enrichment, the incidence of infection by culture of material dislodged from retrieved prostheses after ultrasonication (sonicate) was 22%. Bacteria were observed by immunofluorescence microscopy in 63% of sonicate samples with a monoclonal antibody specific for Propionibacterium acnes and polyclonal antiserum specific for Staphylococcus spp. The bacteria were present either as single cells or in aggregates of up to 300 bacterial cells. These aggregates were not observed without sonication to dislodge the biofilm. Bacteria were observed in all of the culture-positive samples, and in some cases in which only one type of bacterium was identified by culture, both coccoid and coryneform bacteria were observed by immunofluorescence microscopy. Bacteria from skin-flake contamination were readily distinguishable from infecting bacteria by immunofluorescence microscopy. Examination of skin scrapings did not reveal large aggregates of bacteria but did reveal skin cells. These were not observed in the sonicates. Bacterial DNA was detected in 72% of sonicate samples by PCR amplification of a region of the bacterial 16S rRNA gene with universal primers. All of the culture-positive samples were also positive for bacterial DNA. Evidence of high-level infiltration either of neutrophils or of lymphocytes or macrophages into associated tissue was observed in 73% of patients. Our results indicate that the incidence of prosthetic joint infection is grossly underestimated by current culture detection methods. It is therefore imperative that current clinical practice with regard to the detection and subsequent treatment of prosthetic joint infection be reassessed in the light of these results.

Antimicrobial susceptibility of bacteria isolated from orthopedic implants following revision hip surgery.

The susceptibilities of 49 isolates recovered from orthopedic implants to seven antimicrobial agents were evaluated by the broth microdilution method. Ciprofloxacin and vancomycin were more active than gentamicin, representing aminoglycosides which are routinely incorporated into bone cement, and also more active than the peroperative antimicrobial agents cefamandole and erythromycin. The use of ciprofloxacin and vancomycin in vivo, therefore, warrants further evaluation.

Improved detection of infection in hip replacements. A currently underestimated problem.

Our aim was to determine if the detection rate of infection of total hip replacements could be improved by examining the removed prostheses. Immediate transfer of prostheses to an anaerobic atmosphere, followed by mild ultrasonication to dislodge adherent bacteria, resulted in the culture of quantifiable numbers of bacteria, from 26 of the 120 implants examined. The same bacterial species were cultured by routine microbiological techniques from only five corresponding tissue samples. Tissue removed from 18 of the culture-positive implants was suitable for quantitative tissue pathology and inflammatory cells were present in all samples. Furthermore, inflammatory cells were present in 87% of tissue samples taken from patients whose implants were culture-negative. This suggests that these implants may have been infected by bacteria which were not isolated by the techniques of culture used. The increased detection of bacteria from prostheses by culture has improved postoperative antibiotic therapy and should reduce the need for further revision.

A statistical analysis of hip scores.

Thirteen methods of hip scoring were applied in the postoperative assessment of 47 hip arthroplasties. Their results were found to be inconsistent, often giving contrary measures of success in the same patient. Ten variables were measured during the postoperative review of 256 hip arthroplasties and the data were submitted to multivariate factor analysis. This revealed that the ten variables could be reduced to three factors: pain, which correlated poorly with any other variable (Spearman correlation, r < 0.02); functional activity (distance walked, use of walking aids, stair climbing, use of public transport, limp, sitting and tying shoelaces); and deformity and range of movement. The range of hip flexion correlated closely with the sum of the arcs of movement and with Gade's index (Spearman correlation, r > 0.9). We suggest that, for outcome assessment, only three variables need to be recorded: pain, walking distance and range of hip flexion. The combination of these three measures into a single hip score is misleading.

Pressurization of bone cement under standard, flanged and custom acetabular components for total hip replacement.

Custom acetabular components are proposed to achieve uniform cement mantles, even in irregular acetabula presented at revision, in order to enhance fixation. One aim of developing custom components was to permit pressurization of bone cement by the components at insertion and maintain the pressure during polymerization. A model acetabulum was set up for the insertion of standard, flanged and custom components under constant force. Cement pressure was measured at the floor of the acetabulum by means of a piezoelectric diaphragm transducer. Polythene tubes were inserted in the model acetabular walls to estimate penetration of cement into cancellous bone. Insertion of the standard and flanged components caused cement pressures up to 106 kPa which decayed to less than 21 kPa as cement escaped at the rim and the components came into contact with the acetabulum. The custom component maintained a pressure of over 60 kPa during polymerization from an initial pressure of 105 kPa and examination of cement mantles on removal showed no evidence of contact. The custom component also showed enhanced penetration of cement, especially around the rim of the acetabulum. It is concluded that the custom component design achieves higher cement pressures and that better fixation will result.

A review of 100 consecutive Richard's total knee replacements.

One hundred consecutive Richard's Maximum Contact (RMC) knee replacements were performed in Belfast between 1978 and 1982. Most of the 100 knees (86 patients) involved had been in severe pain, had marked stiffness or gross knee deformity, or were chairbound because of the knee. They were reviewed between five and eight and a half years (mean five years and eleven months) after operation. Thirteen patients (13 knees) died before review leaving eighty seven knees in 73 patients available for study. Using a modification of the British Orthopaedic Association knee function assessment chart, 26 knees (30%) were graded as excellent, 22 (25%) as good, 19 (22%) as fair and nine (10%) as poor. There were five implant failures, four the result of deep infection, one due to loosening. Six patients were chairbound at review and were also graded as failures. These results support the view that total knee replacement approaches the predictability and success of arthroplasty of the hip.

A prosthesis augmentation device for the prevention of recurrent hip dislocation. A preliminary report.

At present, revision is the only standard option for cases of recurrent hip prosthesis dislocation. A device is described that contains the head of the femoral component, preventing dislocation, while only slightly restricting external rotation of the affected leg. The device can be inserted through a small incision, minimizing operation time. This device differs from others, e.g., the reversed acetabular cup, by being predrilled (with drill guide supplied), modular in design, and tailored to the dimensions of the cup site.

Survivorship analysis of the Ring hip arthroplasty.

Two hundred fifty-three Ring mark 2 metal-on-metal hip arthroplasties performed between 1968 and 1974 were evaluated using survivorship analysis. Using revision as the criterion for failure, the authors found a cumulative survival rate of 60.4% after 21 years. The results are compared with data from previous studies that used survivorship analysis for metal-on-metal hip arthroplasties, and it is shown that the Ring hip arthroplasty performed as well as the McKee-Farrar prosthesis and better than the Stanmore prosthesis.

Synovial sarcoma: a clinicopathological review.

We have reviewed 20 cases of synovial sarcoma. The main clinical and pathological features of these cases are outlined. Typically these tumours arise in the leg in young adults with a long history before presentation and diagnosis. Clinical and radiological findings are unhelpful in making an early diagnosis. The five year survival rate in this series was 43%. The best guide to prognosis was assessment of mitotic activity. A high index of suspicion is required if the diagnosis is not to be missed. Adequate wide excision of the tumour is the mainstay of treatment.

Microencapsulation using poly(DL-lactic acid). IV: Effect of storage on the microcapsule characteristics.

Poly (DL-lactic acid) [DL-PLA] microcapsules containing phenobarbitone were prepared using a W/O emulsion method. Microcapsules of nominal C : P ratio, 1 : 2 and 1 : 3 using three different molecular weight polymers, 20,500, 13,300 and 5,200 were investigated to study the effect of storage conditions on the microcapsule properties. All microcapsules were stored under desiccated condition at temperatures of 4 degrees, 20 degrees and 37 degrees C for six months. Storage temperatures of 4 degrees and 20 degrees C did not cause appreciable changes in the release rate after storage. Microcapsules stored at 37 degrees C showed an annealing effect, causing shrinkage of microcapsules, and lowering of the release rate after storage for six months. The microcapsules prepared from low molecular weight DL-PLA fused completely whilst stored at 37 degrees C and the other two high molecular DL-PLA also showed some aggregation. There were insignificant variations in the mean microcapsule diameter during storage. The phenobarbitone content of the microcapsules was also unchanged.

Microencapsulation using poly(DL-lactic acid). III: Effect of polymer molecular weight on the release kinetics.

Poly(DL-lactic acid) [DL-PLA] microcapsules containing phenobarbitone (PB) were prepared using a w/o emulsion-evaporation method. DL-PLA of three different molecular weights, 20,200, 13,300 and 5,200 were used to prepare microcapsules of nominal core: polymer (C:P) ratios of 1 : 2, 1 : 2.5, 1 : 3 and 1 : 4. The release of PB was investigated in aqueous buffer of pH 2, pH 7 and pH 9 at 37 degrees C and found to follow a square root of time dependent release mechanism. The first order and zero order release mechanisms were disproved by the lower correlation coefficient of the release data as compared to that of the t1/2 mechanism. These microcapsules showed an initial burst phase release followed by a lag phase, during which time little PB was released. This lag time was affected by the polymer molecular weight and pH of the buffer. The polymer matrix was hydrated during the lag phase and a steady state release occurred. The steady state release rate per unit specific surface area (Kh2/SSA) was found to increase exponentially with the increase in core loading of the microcapsules. However the extent of normalized release rate reduced linearly with the increase in polymer molecular weight at any particular core loading (e.g. 20 per cent or 30 per cent). Increases in the normalized steady state release rate with an increase in buffer pH could be correlated to PB solubility in the dissolution medium. PB release from these microcapsules was diffusion controlled. However, swelling and erosion also contributed to the release process.

Biodegradable poly(lactic acid) and poly(lactide-co-glycolide) microcapsules: problems associated with preparative techniques and release properties.

Poly(lactic acid) [PLA] and its co-polymers with glycolic acid [PLCG] have been known to be biodegradable and histocompatible for the past 20 years. Their physico-chemical and biological properties have been found suitable, in many instances, for sustaining drug release in vivo for days or months. Several dosage forms for parenteral administration have been investigated using these polymers and a microencapsulation technique is chosen frequently for its unique properties. There are a limited number of published papers concerning preparation and characterization of PLA or PLCG microcapsules, possibly because of commercial unavailability and difficulties in the synthesis of reproducible batches of these polymers. However, microcapsules can be made using different traditional and non-traditional techniques containing core materials ranging from biological proteins to synthetic drugs. An attempt is made here to review problems associated with the different microencapsulation techniques using PLA or PLCG. In vivo and in vitro drug release from these microcapsules is also reviewed.

Dislocation of total hip replacements. A comparative study of standard, long posterior wall and augmented acetabular components.

Augmentation of the acetabular component of total hip replacements is a method of increasing stability and preventing recurrent dislocation. We report a series of mechanical experiments designed to evaluate the turning moments and angles required to dislocate standard, long posterior wall and two different augmented prostheses.

Microencapsulation using poly(DL-lactic acid). I: Effect of preparative variables on the microcapsule characteristics and release kinetics.

Poly(DL-lactic acid) (DL-PLA, molecular weight 20,500) microcapsules containing phenobarbitone (PB) as a reference core were prepared using a water/oil (W/O) emulsion system. Surface morphology, particle size and 'encapsulation efficiency' of the microcapsules prepared using different preparative variables have been investigated. Buffer pH 9 was used as a dissolution medium to determine the affect of preparative variables on the release rate from these microcapsules. With an increase in temperature of evaporation the microcapsule surface became increasingly irregular and porous, due to deposition of phenobarbitone crystals near the vicinity of the microcapsule surface leading to rapid release of the core. The normalized release rate was found to increase exponentially with an increase in the temperature of evaporation. Microcapsule morphology was also severely affected due to differences in polymer concentration in the disperse phase solvent. With the increase in polymer concentration, the microcapsule surface was found to be increasingly irregular and non-continuous, due to rapid precipitation of the polymer. Increased polymer concentrations also increased mean microcapsule diameter. The release rate increased with the increase in polymer concentration due to surface defects and did not exhibit a straight line correlation. When core loading was very high (e.g. C:P, 2:1 and 1:1), crystals of phenobarbitone appeared at the surface and these caused a very rapid burst effect. However, microcapsules containing a lower phenobarbitone content were found to follow t1/2 dependent release. The encapsulation efficiency was not seriously affected due to variations in temperature of preparation and polymer concentration. However, with the decrease in initial core loading the encapsulation efficiency of microcapsules was found to be reduced.

Microencapsulation using poly(DL-lactic acid). II: Effect of polymer molecular weight on the microcapsule properties.

Poly(DL-lactic acid) (DL-DPA) of three different molecular weights, 20,500; 13,300 and 5200, was used to prepare microcapsules containing differing contents of phenobarbitone (PB), as a reference core. A water/oil (W/O) emulsion evaporation method was used. The effect of polymer molecular weight on the particle size, 'encapsulation efficiency', morphology, density, thermal behaviour and swelling property has been reported. A general trend towards lowering the mean microcapsule size, both by volume and population, was observed with respect to lower polymer molecular weight. The gross morphology of the microsapsule surface, encapsulation efficiency and density were unaffected by variations in polymer molecular weight. Differential scanning calorimetric analysis of the microcapsules showed a lowering of glass transition temperature after microencapsulation. The melting endotherm for phenobarbitone also indicated the presence of crystalline drug in the microcapsule matrix. These microcapsules were found to swell in the aqueous environment and the mean size increased linearly with time. However, the rate of swelling was higher with low molecular weight polymer and also depended on core loading.