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Biomedical subjects

I D Learmonth

Publications and source records attributed to I D Learmonth.

At least 37 records · Page 2Linked to original sources
PubMed2003

Cementless acetabular replacement in patients with rheumatoid arthritis: a 6- to 14-year prospective study.

Sixty-three consecutive patients who had 82 Harris-Galante porous acetabular cups (HGP1) (Zimmer Inc, Warsaw, IN) implanted for the treatment of rheumatoid arthritis were prospectively assessed since 1986. At last examination, 12 patients (16 hips) had died, and 1 patient (1 hip) was lost to follow-up. A total of 65 hips in 50 patients were available for the latest review. The follow-up period was 6.8 years to 14 years (mean, 9.1 years). There had been 6 revisions: 1 for deep infection and 5 for polyethylene cup wear. Survivorship analysis for all failures estimated that 75% of hips would still be revision-free after 4558 days (12.5 years). Polyethylene wear has been identified in a further 7 cases at last examination. The average linear cup wear per year was 0.05 mm(range, 0.00-0.66 mm). There were no cases of acetabular loosening or acetabular migration. These results demonstrate the excellent durability of fixation of the HGP1 cups in patients with rheumatoid arthritis. However, a 32-mm head should probably not be used with this cup given the high associated incidence of polyethylene wear.

Acetabulum↗
PubMed2003

Development and testing of a reduced WOMAC function scale.

We used prospective data from 862 total knee and 716 total hip replacements three years after surgery in order to derive and validate a reduced Western Ontario and McMasters University Osteoarthritis Index (WOMAC) function scale. The reduced scale was derived using the advice of clinical experts as well as analysis of data. The scale was tested for validity, reliability and responsiveness. Items which were retained included: ascending stairs, rising from sitting, walking on the flat, getting in or out of a car, putting on socks, rising from bed, and sitting. The reduced and full scales had comparable, moderate correlations with other measures of function, confirming convergent validity. Cronbach's alpha was high (alpha > 0.85) with the reduced scale confirming reliability. Responsiveness was greater for the reduced scale (full = 1.4, reduced = 1.6). This reduced version of the WOMAC function scale provides a practical, valid, reliable and responsive alternative to the full function scale for use after total joint replacement. Further work is needed to demonstrate its wider applicability.

Activities of Daily Living↗
PubMed2002

Femoral impaction grafting in revision hip arthroplasty with irradiated bone.

We evaluated the results of femoral impaction grafting with the Exeter stem (Stryker Howmedica Osteonics, Newbury, UK) and irradiated bone-graft. We followed 57 hips for an average of 27 months. Endo-Klinik grading showed 8 grade 1, 22 grade 2, and 27 grade 3 hips. Radiographic analysis revealed cortical repair in 34% and graft incorporation in 39% but no evidence of trabecular remodeling. Moderate subsidence (5-10 mm) occurred in 7 patients (12.5%), and massive subsidence (>10 mm) occurred in 4 patients (7%). Complications included 6 dislocations, 3 periprosthetic fractures, and 2 stem revisions. Impaction grafting with the Exeter system produces satisfactory results for most patients, but a few hips perform poorly, and the reasons for this are unclear. We have concerns about irradiated bone-graft because the characteristic changes of graft remodeling are not seen.

Adult↗
PubMed2002

Subsidence in impaction grafting: the effect of adding a ceramic bone graft extender to bone.

The incidence of revision total hip arthroplasty is increasing dramatically and the associated demand for allograft bone is likely to exceed the available supply. In addition, allograft presents potential problems with regard to infection, antigenicity, availability, reproducibility and cost. It is therefore desirable to develop an alternative to allograft. This study investigated BoneSave, a porous tricalcium phosphate-hydroxyapatite ceramic for use in impaction grafting of the femur at revision total hip arthroplasty. The findings of an in vitro mechanical study comparing the initial stability of pure allograft, a volume mixture of 50 per cent allograft and 50 per cent BoneSave, and a volume mixture of 10 per cent allograft and 90 per cent BoneSave are reported. The BoneSave-allograft mixtures exhibit both much greater mechanical stability and reproducibility than the pure allograft (p < 0.05) at all tested loads (200-800 N). At high peak loads the high volume (90%, v/v) BoneSave mix also provided higher mechanical stability than the medium volume (50 per cent BoneSave-50 per cent allograft) mix (p < 0.05). These results demonstrate thatfrom a mechanical standpoint the tested ceramic provides adequate initial stability to be used as a bone graft extender with allograft in impaction grafting of the femur.

Animals↗
PubMed2002

Informed consent for total hip arthroplasty: does a written information sheet improve recall by patients?

OBJECTIVE: To ascertain whether a written information sheet is acceptable to patients and improves recall of the consent interview. DESIGN: Prospective randomised controlled study using questionnaires, comparing a group of patients given information in a written sheet with appropriate explanation to a group given verbal information alone. SETTING: A specialist orthopaedic surgery unit. PATIENTS: The test group was 126 patients undergoing revision or primary total hip arthroplasty; 65 patients were given information verbally, 61 patients were given written information. OUTCOME MEASURE: Patients' recall of information given, tested with a questionnaire completed on admission (mean of 18 days later). RESULTS: The patients receiving written information scored significantly higher (48% correct answers) than the patients receiving verbal information (38% correct answers). CONCLUSIONS: Written information sheets contribute to the process of informed consent. As patients' recall of information is generally poor, the sheets may also be useful medicolegally, as a permanent record of what was discussed.

Arthroplasty, Replacement, Hip↗
PubMed2001

Radiographic associations for "primary" hip osteoarthrosis: a retrospective cohort study of 47 patients.

This radiographic retrospective cohort study aims to identify relations between the prearthrotic anatomy of the hip joint and the type of subsequent osteoarthrosis (OA). Radiographs of 64 hips in 47 patients were evaluated. Several anatomical indices were measured on radiographs obtained before the onset of OA. The location, type and grade of OA were recorded on subsequent radiographs. Due to the small number of hips available, only three potential risk factors could be considered for both OA location and OA type (weight-bearing surface angle, spherical sector and neck shaft angle for both outcomes). The only variable that was found to be a significant predictor of OA location was the degree of inclination of the acetabular sourcil. Patients with craniomedial sourcils were more likely to have medial OA. No predictors of OA type could be identified. Our results suggest that the anatomy of the hip joint is a factor determining the location of developing osteoarthrosis.

Age Factors↗
PubMed2001

Harris Galante cementless acetabular replacement in avascular necrosis.

We describe the results of 76 total arthroplasties of the hip for stage-III or stage-IV avascular necrosis of the femoral head. Harris Galante Porous cups were used in 63 patients between 1986 and 1994 and followed prospectively. We reviewed 70 hips with a follow-up of more than five years (mean 7.6). At the latest review the mean Harris Hip Score had improved from a preoperative value of 29 +/- 14.7 to 94 +/- 6.8. Radiologically, there was no evidence of acetabular migration. The rate of revision for the femoral component was 8.6%, three being undertaken for loosening and three to allow downsizing of the femoral head. The rate of revision for the acetabular component was 7.1% (five cups). At the time of revision none of the cups was clinically loose, and only required the liner to be changed. The rate of complications was low with no case of deep infection or dislocation, but nine of the 76 hips (11.8%) showed grade-III heterotopic ossification. Previous studies of patients undergoing cemented total hip arthroplasty for the treatment of advanced avascular necrosis have indicated a high incidence of loosening of the acetabular component. Our findings show good medium-term results using the Harris Galante Porous cup for acetabular reconstruction, together with a variety of cemented femoral components, for the treatment of this difficult problem.

Acetabulum↗
PubMed2001

Increased chromosome translocations and aneuploidy in peripheral blood lymphocytes of patients having revision arthroplasty of the hip.

The long-term biological effects of wear debris are unknown. We have investigated whether there is any evidence of cumulative mutagenic damage in peripheral blood lymphocytes of patients undergoing revision arthroplasty of predominantly metal-on-plastic total hip replacements compared with those at primary arthroplasty. There was a threefold increase in aneuploidy and a twofold increase in chromosomal translocations which could not be explained by the confounding variables of smoking, gender, age and diagnostic radiographs. In the patients with TiVaAl prostheses there was a fivefold increase in aneuploidy but no increase in chromosomal translocations. By contrast, in patients with cobalt-chrome prostheses there was a 2.5-fold increase in aneuploidy and a 3.5-fold increase in chromosomal translocations. In six patients with stainless-steel prostheses there was no increase in either aneuploidy or chromosomal translocations. Our results suggest that future epidemiological studies of the putative long-term risks of joint replacement should take into account the type of alloy used in the prosthesis.

Aged↗
PubMed2000

Cementless acetabular replacement in the young. A 5- to 10-year prospective study.

This article presents a prospective clinical and radiologic review of 55 total hip replacements in 50 patients in which the cementless Harris-Galante porous-coated acetabular component was used. All patients were 50 years of age or younger. The cups were inserted by 15 different surgeons. The minimum followup was 5 years, with a mean of 7 years. No acetabular component has been revised for loosening, and none have migrated. Three (5.5%) cups have progressive bone-component radiolucent lines, two (3.6%) of which are complete. Six (10.9%) acetabular liners have been replaced for excessive polyethylene wear, and an additional four (7.3%) show sufficient wear to produce obvious radiographic eccentricity of the femoral head. All of the revised liners had 32-mm femoral heads and an initial polyethylene thickness of less than 6 mm. Although the results reflect excellent fixation of this component in the medium term, the incidence of exchange of the polyethylene liner for excessive wear is unacceptably high. The reduction in polyethylene thickness associated with the use of a metal-backed component and a 32-mm articulation was one of the factors contributing to the accelerated wear patterns seen in this series.

Acetabulum↗
PubMed1999

Axial preload in external fixator half-pins: a preliminary mechanical study of an experimental bone anchorage system.

OBJECTIVE: To demonstrate the effect of axial preload achieved with an experimental external fixator pin prototype on the initial stability of the pin-bone interface. DESIGN: An in vitro mechanical study comparing pin stability of an axially-preloaded experimental pin and a radially-preloaded conventional external fixation pin. BACKGROUND: The most common problem in clinical practice of external fixation is pin site failure. An experimental external fixator half-pin has been designed introducing axial preload as an alternative method of achieving a stable pin-bone interface. METHODS: Standardized measurements of pin insertion and removal torque comparing the experimental pin prototype and a conventional external fixator pin in a synthetic composite material and ovine tibial cortical bone. RESULTS: There is a positive correlation between axial preload and torque resistance of the coaxial experimental half-pin as well as significantly increased torque resistance of the axially-preloaded experimental pin over the conventional pin tested. In addition, significantly lower insertion torque of the experimental pin was observed with the applied insertion technique. CONCLUSIONS: 'Axial preload' achieved with appropriately-designed half pins might represent an effective biology-sparing method of increasing the mechanical stability of the pin-bone interface in unilateral external fixator frames. RELEVANCE: Several aspects of the current external fixator pin design and insertion technique have been implicated for the significant incidence of failure at the pin-bone interface manifested as pin loosening, pin track infection or even osteomyelitis. An axially-preloaded bone fastener system may be mechanically and biologically superior and therefore clinically advantageous.

Animals↗
PubMed1999

Digital image analysis: improving accuracy and reproducibility of radiographic measurement.

OBJECTIVE: To assess the accuracy and reproducibility of a digital image analyser and the human eye, in measuring radiographic dimensions. DESIGN: We experimentally compared radiographic measurement using either an image analyser system or the human eye with digital caliper. BACKGROUND: The assessment of total hip arthroplasty wear from radiographs relies on both the accuracy of radiographic images and the accuracy of radiographic measurement. METHODS: Radiographs were taken of a slip gauge (30+/-0.00036 mm) and slip gauge with a femoral stem. The projected dimensions of the radiographic images were calculated by trigonometry. The radiographic dimensions were then measured by blinded observers using both techniques. RESULTS: For a single radiograph, the human eye was accurate to 0.26 mm and reproducible to +/-0.1 mm. In comparison the digital image analyser system was accurate to 0.01 mm with a reproducibility of +/-0.08 mm. In an arthroplasty model, where the dimensions of an object were corrected for magnification by the known dimensions of a femoral head, the human eye was accurate to 0.19 mm, whereas the image analyser system was accurate to 0.04 mm. CONCLUSIONS: The digital image analysis system is up to 20 times more accurate than the human eye, and in an arthroplasty model the accuracy of measurement increases four-fold. We believe such image analysis may allow more accurate and reproducible measurement of wear from standard follow-up radiographs.

Hip Prosthesis↗
PubMed1998

"Biological" internal fixation of long bone fractures: a biomechanical study of a "noncontact" plate system.

Based on existing knowledge of noncontact plates, an experimental prototype of a nonperiosteal contact internal fixation implant ("noncontact internal fixator") has been designed. The construct rigidity of osteotomised synthetic composite femora, fixed with the noncontact fixator and a reamed, statically-locked intramedullary nail were compared in axial compression, two plane bending and torsion in four types of diaphyseal fractures. With the exception of axial loading in the presence of extensive comminution, the fixation stability provided by the noncontact fixator is significantly higher than that of the tested intramedullary nail. Any degree of cortical contact between the two main fragments is important for the stability of this nonperiosteal contact fixation system under axial load. Appropriately-designed "internal fixators" could provide not only a number of biological and technical advantages, but also fixation stability comparable and in certain aspects superior to that of other fixation methods.

Biomechanical Phenomena↗
PubMed1998

Tantalum ball position after total hip arthroplasty.

There are several techniques for the accurate measurement of the migration of components after arthroplasty some of which require the operative placement of tantalum balls. We have reviewed the position and migration of these markers in 64 patients after total hip arthroplasty. In 40% of cases, one or more balls was seen to be outside the proximal femur on the postoperative radiograph, although all were considered to be within the bone at operation. In two hips, one ball appeared to have migrated towards the joint, although none was seen within the joint. Misplacement was not related to the experience of the surgeon or the operative approach. Migration analysis which necessitates the insertion of tantalum balls requires careful technique to avoid a potential source of third-body wear. It should probably be used only for research in small series of patients.

Arthroplasty, Replacement, Hip↗
PubMed1997

Inadequate polyethylene thickness and osteolysis in cementless hip arthroplasty.

A matched series Porous Coated Anatomic (PCA), Howmedica, Rutherford, NJ) cementless hip arthroplasties comparing a 26-mm with a 32-mm head were reviewed. The 26-mm head was used in 63 hips of 56 patients (group 1), and the 32-mm head was inserted into 97 hips of 90 patients (group 2). The two groups were matched for age, sex, and primary diagnosis. The postoperative follow-up period ranged from 3 to 6.9 years (mean, 4.2 years) in group 1, compared with 3 to 7.9 years (mean, 4.5 years) for group 2. The mean clinical scores for pain, movement, and function were similar for the two groups. Erosive osteolytic lesions were encountered in 25.7% of the group 2 hips but in none of the group 1 cases. These lesions were not seen before 3 years after surgery and were present in Gruen zone 7 of all involved hips, although in two patients they were also noted in zone 1. Osteolysis was encountered only with the 32-mm head where the outer diameter of the metal backed cup was 52 mm or less. Therefore, inadequate polyethylene thickness, rather than head size, is implicated as the cause of plastic-particle mediated osteolysis.

Adult↗
PubMed1997

Properties of tissue from around cemented joint implants with erosive and/or linear osteolysis.

Levels of bone remodeling agents were measured in conditioned media from cultures of periprosthetic pseudosynovial membranes and related to the radiographic features of the failed joint implants. Radiographs of both cemented hip (n = 28) and cemented knee (n = 11) implants were examined and the pattern of radiolucency was classified as erosive linear, or mixed. Similar levels of interleukin-1-beta (IL-1 beta), interleukin-6, tumor necrosis factor alpha (TNF-alpha), transforming growth factor beta-1, and prostaglandin E2 (PGE2) were found in pseudosynovial membrane conditioned media from all 3 groups of hips and the knee group (all linear). Significant correlations were evident only between PGE2 and TNF-alpha levels in the linear hip group and PGE2 and IL-1 beta levels in the knee group. A close correlation was found between IL-1 beta and TNF-alpha in both linear and erosive hips. It is suggested that coregulation of these bone remodeling agents differs with the radiographic appearance of the failed joint implants. As all the implants were cemented and the results contrast with those of others obtained with pseudosynovial membrane conditioned media from cementless implants, it is considered that cement critically influences the process of implant failure.

Adult↗
PubMed1997

Massive early subsidence following femoral impaction grafting.

The incidence of massive early subsidence (subsidence greater than 10 mm) following impaction grafting of the femur in revision surgery is reported. The first 79 consecutive revision total hip arthroplasties using morselized allograft, polymethyl methacrylate cement, and a double-tapered, polished, collarless stem were reviewed. Nine (11%) of the 79 revision femoral prostheses showed massive subsidence, with another nine hips subsiding to a lesser degree. Further elucidation of the critical factors contributing to the initial stability of the biologic composite is required.

Adult↗
PubMed1997

Factors contributing to the wear of polyethylene in clinical practice.

Wear of polyethylene is a major contributor in the failure of total joint replacement. A number of different factors may predispose to increased wear of polyethylene. These can be broadly categorized as (i) material polymorphism, (ii) poor design features and (iii) three-body wear. Many of these factors contribute to the wear encountered in clinical practice. These mechanisms are reviewed and examples identified in which they have resulted in increased wear.

Biocompatible Materials↗