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Biomedical subjects

I D Learmonth

Publications and source records attributed to I D Learmonth.

At least 73 records · Page 4Linked to original sources
PubMed1992

Qualitative holographic study of hemi-pelvic deformation caused by loading different hip prostheses.

The dynamic biological response of bone can materially influence the longevity of artificial implants. This paper presents a series of in vitro experiments conducted on epoxy resin models of human hemi-pelves. Different commercially available acetabular components were implanted and used for the construction of simplified three-dimensional models of the artificial hip joint. Boundary conditions included simulation of muscle groups and femoral loading. Real-time holographic interferometry, a stress analysis technique permitting whole-field simultaneous inspection of deformation patterns, was used as the experimental method. The holographic interferograms were interpreted qualitatively rather than quantitatively. High stresses were identified in the hemi-pelvis and it is postulated that these stresses may be implicated in the mechanical pathogenesis of loosening. The observed changes in the detected stress levels could influence both future design of acetabular prostheses and surgical techniques.

Biomechanical Phenomena↗
PubMed1992

The effect of polymerization of methylmethacrylate on metal-backed and non-metal-backed acetabular components.

Aseptic loosening of the acetabular component has been identified as the main cause of failure of cemented total hip arthroplasty in the long term. Wear of the high-density polyethylene has been implicated as a major contributory factor to loosening. The etiology of wear is multifactorial. The exothermic phase of polymerization of polymethylmethacrylate is associated with a 5.9% volume expansion. Using double-exposure holographic interferometry, the authors examined the influence of polymerization of cement on the internal geometry of a metal-backed cup and two non-metal-backed cups (Charnley 22 mm, Muller 32 mm). The non-metal-backed cups exhibited marked heat concentration points and disrupted fringe patterns, indicating distortion of the internal geometry of the cup. In contradistinction, the metal-backed cup showed good heat dissipation and regular fringe patterns, indicating minimal internal distortion. The differences were not quantified but were visually dramatic. The authors believe this may be an important contributory factor to cup wear in cemented total hip arthroplasty.

Acetabulum↗
PubMed1992

Survivorship of cemented total hip arthroplasty in patients 50 years of age or younger.

One hundred fifty-six Charnley low-friction arthroplasties performed in patients 50 years of age or younger are reviewed. Excluding sepsis, survivorship analysis showed a 12% probability of mechanical failure at 10 years. The detailed clinical and radiological results of 130 hips with a 3-16-year follow-up period are presented. Revision surgery was required in 14 hips (10.8%), for the following reasons: sepsis (2.3%), loose sockets (2.3%), loose stems (5.4%), and stem fracture (0.8%). Evidence of radiological loosening indicative of pending failure was present in 14 hips (12.0%). At 10 years the predicted failure rate of the surviving hips was 12%.

Adolescent↗
PubMed1991

'Pathological' fracture of the femur--a complication of failed total hip arthroplasty.

Ten patients with a major femur fracture complicating total hip arthroplasty were seen at the Princess Alice Orthopaedic Hospital between June 1986 and May 1988. Four cases were intra-operative fractures sustained at revision surgery and 6 were late postoperative fractures of the femur associated with minimal trauma. Eight patients have a pain-free and functional hip arthroplasty at a mean follow-up of 19.7 months (range 17-32 months). One patient developed deep sepsis and 1 persistent non-union: both are now well mobilised following excision arthroplasty. Predisposing factors are identified and the importance of timeous intervention to avoid this challenging complication is stressed.

Femoral Fractures↗
PubMed1990

A simple technique for varus supracondylar osteotomy in genu valgum.

Varus osteotomy of the distal femur is recommended for osteoarthritis of the knee with significant valgus deformity, but the operation is difficult to plan and perform. A simple technique involving a jig referenced to the line of the tibia is described. This allows accurate overcorrection by a few degrees, with impaction and secure fixation at the osteotomy. It has been successful, with no complications, in 12 consecutive knees.

Femur↗
PubMed1990

Core decompression for early atraumatic osteonecrosis of the femoral head.

We performed 41 core decompressions in 32 patients for stage I or stage II osteonecrosis of the femoral head. The intra-osseous pressure at the intertrochanteric level was raised in 28 (68%) and there was histological confirmation of necrosis in 36 hips (88%). After a follow-up of 10 to 84 months (mean 31) nine of the 12 stage I hips (75%) showed significant clinical or radiological deterioration; no evidence of necrosis had been found in the core specimens of the other three hips. Of the 29 hips in stage II, 25 (86%) showed significant radiological deterioration, and only five (17%) had improved clinically. We believe that once necrosis has occurred, core decompression will not significantly influence the subsequent course of the disease.

Adult↗
PubMed1989

Radiological loosening after cemented hip replacement for juvenile chronic arthritis.

We reviewed the results of 14 total hip replacements in patients with juvenile chronic arthritis. The mean age at operation was 16 years (range 12 to 22 years); follow-up was from four to 11 years (mean 8.5 years). Postoperatively pain relief was sustained in all but one hip, while movement generally remained significantly restricted. No hip has as yet required a revision operation, although eight hips (57%) show radiological changes suggestive of impending failure. All patients had severe polyarticular involvement with associated restriction of locomotor activity. Potential causes contributing to loosening such as continuing diaphyseal bone growth and increased immunocompetence in adolescence are discussed.

Adolescent↗
PubMed1989

Current status of total hip replacement. A review of biological and biomechanical factors.

Successful cemented total hip replacement represents one of the major advancements in orthopaedic surgery in recent years. However, clinical follow-up has revealed a disturbing incidence of loosening, particularly in the younger patient. Aspects of component design, materials and technique refinement considered important in improving long-term results are reviewed.

Biomechanical Phenomena↗
PubMed1989

Atlantoaxial instability and neurologic indicators in rheumatoid arthritis.

Atlantoaxial subluxation in rheumatoid arthritis is characterized by pain, disability, and occasionally death. Surgical fusion of the offending vertebrae is the appropriate surgical remedy, but it is a procedure with a high failure and complication rate. Because cord compression and myelopathy are the main complications of this condition, it would be logical to use evidence of early neurologic deficit as an indicator for surgery. A group of 250 patients with rheumatoid arthritis were investigated to evaluate the neurologic status with respect to the degree of instability in the proximal cervical spine. Neurologic isolated signs such as hyperreflexia could not be correlated with the onset of cervical myelopathy or quadraparesis or to the radiographically measured degree of atlantoaxial instability. These signs should not be used as an indication for surgery. The positive indications are intractable pain, cervical myelopathy, and severe atlantoaxial instability.

Adult↗
PubMed1988

Long-term results of Charnley low-friction arthroplasty of the hip.

The long-term results of 73 Charnley low-friction arthroplasties with follow-up of 10-14 years are presented. Eight hips required revision for socket migration resulting from excessive medialisation of the cup (2, 2.7%); breakage of the femoral stem (5, 6.8%); and loosening (1). A further 5 hips had radiological changes suggesting that they would require revision in the foreseeable future. Sixty hips (82.2%) remained clinically excellent with minimal radiological changes.

Adult↗
PubMed1988

Cervical spine instability in rheumatoid arthritis.

We present a study of 30 fusion operations in 26 rheumatoid arthritics with cervical spine instability. Atlanto-axial instability was present in 15, of whom 12 were fused; three had cord involvement and all made a partial or complete recovery following fusion. Cranial settling necessitated cranio-cervical fusion in four patients; all fused, and one with myelopathy was relieved. Subaxial instability required fusion in seven cases; two postoperative deaths followed the only two anterior interbody fusions. Posterior fusion was successful in the other five, with remission of neurological compromise in the three with myelopathy and one with radiculopathy. We conclude that neurological compromise in an unstable but mobile rheumatoid cervical spine can usually be brought to remission by immobilisation alone, so decompressive procedures are unnecessary in the first instance.

Arthritis, Rheumatoid↗
PubMed1988

Internal fixation for occipito-cervical fusion.

We describe a method of internal fixation for occipito-cervical fusion utilising a standard "small fragment" T-plate bent and fixed to the skull with three screws. The lower end of the plate is screwed and wired firmly to the spine of the axis. Of 14 patients so treated, 12 fused, one died and one failed to unite to the skull. Of eight with cord signs, seven remitted or improved and one died.

Arthritis, Rheumatoid↗
PubMed1987

Namaqualand hip dysplasia. Orthopedic implications.

Namaqualand hip dysplasia (NHD) is an inherited skeletal disorder that has been identified in 45 persons in five generations of a large family in South Africa. Involvement of the femoral capital epiphyses, which was present in all cases, led to significant orthopedic complications. Hip pain developed between three and 20 years of age and heralded the onset and gradual progression of premature degenerative arthropathy. The patients who were examined were all over 35 years of age; four had been treated by total hip arthroplasty. For appropriate and effective management of this uncommon but well-defined syndromic entity, an early and specific diagnosis is essential.

Adolescent↗