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Biomedical subjects

I D Learmonth

Publications and source records attributed to I D Learmonth.

At least 19 recordsLinked to original sources
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↗
PubMed1997

The pathogenesis of osteolysis in two different cementless hip replacements.

Wear of ultra-high molecular weight polyethylene has been incriminated in the osteolysis associated with aseptic loosening of hip implants. A variety of different factors can contribute to accelerated patterns of polyethylene wear and subsequent osteolysis. This paper examines the incidence of osteolysis observed in two different well-matched cohorts of cementless total hip arthroplasties. The patterns of osteolysis observed, which are ascribed to the generation of polyethylene debris, are interpreted with reference to the design of the individual prostheses.

Biocompatible Materials↗
PubMed1996

Poor reproducibility in radiographic grading of femoral cementing technique in total hip arthroplasty.

The first study of the reproducibility of a widely accepted grading system for femoral cementation in total hip arthroplasty is reported. Sixty postoperative radiographs were graded on two occasions at least 2 weeks apart by two experienced observers. The test-retest reproducibility rate was 60% for observer 1 and 70% for observer 2. The interobserver reproducibility varied between 60 and 63% for the different assessments. Between 5 and 6% of cases differed by more than one grade between tests. Kappa statistical analysis confirmed that reproducibility was poor in all cases. This cement grading system, even in the hands of experienced observers, has too high a rate of intraobserver and interobserver error to recommend its use.

Bone Cements↗
PubMed1996

Osteolytic properties of the synovial-like tissue from aseptically failed joint prostheses.

Relationships were found between the bone-resorbing ability of conditioned media (CMs) from culture of peri-prosthetic tissues and their levels of bone-remodelling agents. Bone-resorbing activity was measured by 45Ca release from pre-labelled mouse calvaria and 23 of 40 CMs exhibited bone-resorbing activity. Cytokine and prostanoid levels in the CMs were measured by immunoassay, and the levels of interleukin (IL)-1 beta, IL-6, tumour necrosis factor alpha (TNF alpha) and prostaglandin E2 (PGE2) correlated with each other, except for the latter two. Significantly higher levels of IL-6 were present in those CMs with bone-resorbing activity than in those without, and a similar pattern was observed for PGE2 and IL-1 beta. However, some CMs with high levels of IL-1 beta, IL-6, TNF alpha and PGE2 failed to induce resorption, whereas a few CMs with low levels of these agents induced resorption. Moreover, neither dialysis of CMs nor addition of neutralizing antisera to IL-1 alpha and IL-1 beta to CMs, either alone or in combination, reduced the bone-resorbing activity of the CMs. It is considered that these agents may act synergistically to mediate osteolysis around failed joint implants, but that other unidentified bone-resorbing agent(s) must be involved.

Adult↗
PubMed1996

Preliminary observations on possible premalignant changes in bone marrow adjacent to worn total hip arthroplasty implants.

Previous epidemiologic studies have suggested that there may be a risk of malignancy, especially lymphoma and leukemia, after joint replacement, but the followup has been relatively short. This is a preliminary study to see if there is any biologic basis for such a risk. Blood and bone marrow samples from 71 patients at revision arthroplasty of a loose or worn prosthesis and 30 control patients at primary arthroplasty were analyzed with cytogenetic techniques and molecular biology. There was a higher chromosomal aberration rate in cells adjacent to the prosthesis at revision surgery compared with iliac crest marrow from the same patients or with femoral bone marrow at primary arthroplasty. Clonal expansion of lymphocytes without a serum paraprotein was seen in 2 of 21 patients at revision arthroplasty performed more than 10 years after primary arthroplasty. The results of this preliminary study suggest that future epidemiologic studies should concentrate on patients with longer postoperative intervals to see if there is any risk that would be pertinent to a young patient at primary arthroplasty.

Aged↗
PubMed1996

Unpredictable progression of osteolysis following cementless hip arthroplasty. 24 femoral components followed for 6-10 years.

We reviewed 24 hips that developed femoral osteolytic lesions following cementless total hip replacement with a Porous-Coated Anatomic prosthesis after a mean of 8 (6-10) years. 15 of the hips showed hardly any radiographic deterioration in the osteolysis. 2 became much worse with dramatic loss of bone stock. Both of these hips required revision of the acetabular component as well as bone grafting of the otherwise well-fixed femoral component. The remaining 7 hips showed mild-to-moderate enlargement of the lesions. All 24 hips were asymptomatic. Blood tests and bone scintigraphy were of no predictive value in assessing the probable progression of the lesions. Serial radiography remains the cornerstone of the monitoring of osteolysis, following cementless hip replacement, the extent of bone loss being usually far greater than indicated by radiographic examination.

Adult↗
PubMed1996

The omega lateral approach to the hip.

We describe a modified lateral approach to the hip which exploits the function continuity of gluteus medius and vastus lateralis and their dense crescentic attachment to the greater trochanter. The gluteus medius is not incised or split, but is detached and mobilised with gluteus minimus as one unit. This facilitates reattachment of the glutei and helps to preserve abductor function.

Fascia Lata↗
PubMed1995

Loss of bone stock with cementless hip arthroplasty.

One hundred four porous-coated anatomic cementless hip arthroplasties followed from 2 to 6.5 years (mean, 50 months) were studied. Ninety-four percent had excellent clinical results. Thigh pain occurred in 23% of patients, but was severe in only two. "Cancelization" and rounding off of the calcar were noted in 83% of hips, whereas localized osteolysis occurred in 24 femurs and one acetabulum. Ten of these measured more than 10 mm, and all of those in the femur were located proximally. None of these patients were symptomatic and none have come to revision. Ultrahigh-molecular-weight polyethylene wear and plastic debris were implicated as the cause of osteolysis. Lytic lesions were seen only after 3 years and occurred only in patients with 32-mm femoral heads in whom the outer diameter of the acetabular component was 52 mm or less. Use of excessively thin ultrahigh-molecular-weight polyethylene in these patients may have predisposed them to accelerated wear. Section modulus mismatch resulting in stress protection is considered as an alternate mechanism of proximal bone resorption.

Adolescent↗
PubMed1995

Patch-grafting for regional femoral bone loss in cementless revision hip arthroplasty.

The authors reviewed 33 revision hip arthroplasties using the long-stemmed porous coated anatomic (PCA) prosthesis that required adjuvant patch-grafting for proximal defects of the femur. All hips were revised for aseptic loosening. The mean follow-up period was 3.7 years (2.0-5.8 years). The hips were clinically evaluated by means of the Harris Hip Score: 26 (79%) were found to be good or excellent, 3 (9%) fair and 4 (12%) poor. Graft incorporation occurred in 31/33 cases (94%). Proximal stress protection bone resorption was not seen, although cancellisation of the calcar was noted in 20/33 (60%) hips. Serial radiological review demonstrated some degree of subsidence of the femoral stem in 20/33 (60%) hips. The authors conclude that patch-grafting of the proximal femur at revision surgery incorporates and is not inhibited by the presence of a rigid long-stemmed implant.

Adult↗
PubMed1994

The A1 pulley in rheumatoid flexor tenosynovectomy. To retain or divide?

We report a detailed comparative evaluation of flexor tenosynovectomy in 55 fingers in which the A1 pulley was divided and 45 fingers in which the A1 pulley was retained. The metacarpophalangeal joint subluxed volarly in 49% when the A1 pulley was divided, compared to 11% when the pulley was preserved. Bowstringing occurred in 7% and only when the A1 pulley was divided. Ulnar deviation was 7 degrees worse when the pulley was divided. Active range of movement was limited in both groups. It was 11 degrees less when the A1 pulley was divided.

Adult↗
PubMed1994

Current thoughts on total hip replacement.

Opinion leaders in the field of total hip arthroplasty express antipodal views with bewildering frequency. New trends notwithstanding, Charnley low-friction arthroplasty has a record of outstanding success, and we should attempt to identify specific problems, and address these accordingly. Biological and biomechanical matching remain important and increased attention to meticulous cement technique should favourably improve the long-term performance of cemented implants. The concept of cementless replacement should not, however, be summarily discarded, particularly for the younger patient. The discovery of existing design limitations should lead to further development based on sound scientific research. In an era of exploding technology, cost-containment must remain a pragmatic reality in the provision of a health-care service to the community. At this stage we would recommend a cementless hip replacement for the very young, hybrid replacement (cemented stem, uncemented cup) for the middle-aged and a fully cemented replacement for the elderly.

Biocompatible Materials↗