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Biomedical subjects

M L Porter

Publications and source records attributed to M L Porter.

At least 19 recordsLinked to original sources
PubMed2000

Charnley low-friction arthroplasty for Paget's disease of the hip.

This study investigated the perceived risks and complications associated with total hip arthroplasty for Paget's disease. A total of 98 Charnley low-friction arthroplasties were performed on 76 patients, 27 men (37 hips) and 49 women (61 hips), whose average age was 67.4 years (range, 51-79 years). Intraoperative blood loss averaged 388 mL (range, 110-1,730 mL), and minor heterotopic ossification occurred in 24 hips (25%), with significant changes in 4 hips (4%). After average follow-up of 10.4 years (range, 5.5-20 years), 10 acetabular (10%) and 8 femoral (8%) implants had loosened aseptically, but there was no evidence of progressive protrusio acetabuli or femoral deformity after operation. Survivorship to revision was 98% at 10 years (95% confidence interval [CI], 95%-100%) and 91% at 15 years (95% CI, 80%-100%) for the acetabular component and 93% (95% CI, 87%-99%) and 89% (95% CI, 80%-99%) for the femur. The only increased risk identified was nonunion of the trochanteric osteotomy (13%).

Aged↗
PubMed1998

Long-term results of cemented Charnley low-friction arthroplasty in patients aged less than 30 years.

The results of cemented Charnley low-friction arthroplasty in patients aged less than 30 years are presented. Eighty-three arthroplasties were performed on 55 patients with an average age of 24.9 years (range, 17-29 years) and an average follow-up period of 240 months (20 years; range, 62-360 months). There were 2 nonfatal pulmonary emboli, 2 cases of deep sepsis, and 3 fractured femoral implants. Twenty-eight acetabular components migrated (34%), 25 have been revised (30%), and the average annual acetabular wear rate was 0.12 mm. Sixteen femoral implants subsided (19%), and fracture of the tip of the cement mantle occurred in 8 hips (10%). Nineteen femoral components (23%) were revised; femoral osteolysis was seen in 15 hips (18%) and changes in the calcar in 33 (38%). Acetabular component survivorship was 92% (95% confidence interval, 85-98%) at 10 years, 70% (60-81%) at 20 years, and 68% (57-79%) at 25 years, with the figures for the femoral implant being 93% (87-98%), 76% (66-86%), and 73% (62-85%), respectively.

Adolescent↗
PubMed1998

Tarsal tunnel syndrome: a study of the clinical and neurophysiological results of decompression.

The neurophysiological and clinical outcomes of surgical decompression of 22 cases of tarsal tunnel syndrome are analysed. Recent work by Pfeiffer & Cracchiolo has suggested a successful outcome in only 44% of cases. We have reviewed the outcome of surgery both clinically and with the use of nerve conduction studies. Pre- and post-operative motor conduction delays in the plantar nerves are compared with clinical results found both in the clinic and later by a postal questionnaire. Despite careful clinical and neurophysiological assessment prior to a full surgical release, only 42% of patients had a satisfactory outcome. A larger reduction in plantar nerve conduction delay post-operatively corresponded well to an improvement in symptoms. However, we were unable to predict which cases would respond to decompression using clinical or electrophysiological methods. We question the use of nerve conduction studies in the diagnosis of tarsal tunnel syndrome, and also the role of surgery in the management of this condition.

Decompression, Surgical↗
PubMed1997

An automated method for assessing routine radiographs of patients with total hip replacements.

This paper describes a new, fully automated method of locating objects on radiographs of patients with total joint replacements (TJRs). A statistical computer model, known as an active shape model, was trained to identify the position of the femur, pelvis, stem and cup marker wire on radiographs of patients with Charnley total hip prostheses. Once trained, the model was able to locate these objects through a process of automatic image searching, despite their appearance depending on the orientation and anatomy of the patient. Experiments were carried out to test the accuracy with which the model was able to fit to previously unseen data and with which reference points could be calculated from the model points. The model was able to locate the femur and stem with a mean error of approximately 0.8 mm and a 95 per cent confidence limit of 1.7 mm. Once the model had successfully located these objects, the midpoint of the stem head could be calculated with a mean error of approximately 0.2 mm. Although the model has been trained on Charnley total hip replacements, the method is generic and so can be applied to radiographs of patients with any TJR. This paper shows that computer models can form the basis of a quick, automatic method of taking measurements from standard clinical radiographs.

Computer Simulation↗
PubMed1997

Long-term results of total hip replacement in young patients who had ankylosing spondylitis. Eighteen to thirty-year results with survivorship analysis.

We determined the long-term results of total hip replacement in a series of young patients who had ankylosing spondylitis. Between 1966 and 1978, forty-three Charnley low-friction arthroplasties were performed in twenty-four patients who had an average age of 28.8 years (range, nineteen to thirty-nine years) at the time of the operation. There were seventeen men and seven women. The average duration of follow-up for the series was 22.7 years (range, one month [a perioperative death] to 30.3 years). Four patients (seven hips) had died an average of 12.6 years (range, one month to 18.7 years) after the operation. The twenty surviving patients had clinical and radiographic follow-up until the time of writing or until both of the original components had been revised. All patients had substantial relief of pain and improvement of function and the range of motion of the joint. Twenty-one patients (88 per cent; thirty-nine hips) were completely free of pain (6 points, according to the scale of Merle d'Aubigne and Postel), and the remainder had only slight discomfort (5 points). Ten acetabular components and one femoral component were revised because of aseptic loosening, and one patient had a revision of both components because of late deep infection. Three additional femoral components were revised during a revision operation for a loose acetabular component. Although the femoral components were not loose, they had been in place for more than ten years and it was thought likely that the bearing surface was damaged. The average time to revision was 13.3 years (range, 4.0 to 20.3 years). At an average of 22.7 years, thirty-eight (88 per cent) of the original femoral components and thirty-two (74 per cent) of the original acetabular components remained in situ. The average annual rate of acetabular wear was 0.12 millimeter for the entire series. Only six hips (14 per cent) had minor heterotopic ossification, and none of the hips had clinically important ossification (class III or IV according to the system of Brooker et al.). To our knowledge, the present report describes the largest series of total hip arthroplasties, with the longest duration of follow-up, in young patients who had ankylosing spondylitis. Survivorship analysis with use of the Kaplan-Meier method revealed that the probability of survival of the femoral component (with 95 per cent confidence intervals) was 91 per cent (83 to 99 per cent) at twenty years and 83 per cent (72 to 94 per cent) at thirty years. The probability of survival of the acetabular components was 73 per cent (61 to 84 per cent) at twenty years and 70 per cent (57 to 83 per cent) at thirty years. The probability that both components would survive was 91 per cent (82 to 100 per cent) at ten years, 73 per cent (61 to 84 per cent) at twenty years, and 70 per cent (57 to 83 per cent) at thirty years. The Charnley low-friction arthroplasty provided consistently good long-term results, with a low rate of complications and revisions, in this group of young patients.

Adult↗
PubMed1997

Total hip arthroplasty for congenital dysplasia or dislocation of the hip. Survivorship analysis and long-term results.

Two hundred and thirty-two total hip replacements with cement were performed between 1965 and 1987 in 190 patients who had osteoarthrosis secondary to acetabular dysplasia resulting from congenital dysplasia or dislocation of the hip. Forty-nine patients (fifty hips) who died or who did not have at least three years of clinical and radiographic follow-up were excluded; therefore, the study comprised 141 patients (182 hips), 125 of whom were women and sixteen of whom were men. The mean age at the time of the operation was 42.5 years (range, 19.5 to 76.5 years), and the mean duration of follow-up was 9.9 years (range, 3.1 to 22.8 years). A Charnley low-friction prosthesis with a 22.25-millimeter femoral head was used in all hips. A trochanteric osteotomy was performed in 164 hips. A direct lateral approach was used only when there was a limb-length discrepancy of less than two centimeters. Bulk autogenous graft was not used to augment the fixation of the acetabular component. The hips were divided into two groups on the basis of the degree of subluxation or dislocation according to the classification of Crowe et al. One hundred and thirty-six hips were grade I, II, or III (indicating subluxation) (Group S), and forty-six hips were grade IV (indicating dislocation) (Group D). At the most recent follow-up evaluation, 128 (94 per cent) of the 136 hips in Group S and forty-four (96 per cent) of the forty-six hips in Group D caused no or only slight pain (a score of 6 or 5 points, respectively, according to the system of Merle d'Aubigné and Postel). Nineteen cups (10 per cent) and five stems (3 per cent) failed and were revised. The rate of revision for loosening of the femoral component in Group D (2 per cent [one stem]) was similar to that in Group S (3 per cent [four stems]). In comparison, the rate of revision of the acetabular component in Group D (15 per cent [seven cups]) was almost twice that in Group S (9 per cent [twelve cups]). This study demonstrated satisfactory clinical results at a mean of nearly ten years. The fixation of the femoral components appeared to be satisfactory; however, the failure of the fixation of the acetabular components in Group D (the dislocated hips) is a cause for concern.

Adult↗
PubMed1997

The long-term results of Charnley low-friction arthroplasty in young patients who have congenital dislocation, degenerative osteoarthrosis, or rheumatoid arthritis.

We present the long-term results of 226 Charnley low-friction arthroplasties that were performed with use of cement in 161 patients between 1966 and 1978. Forty-four patients (sixty hips) had congenital dislocation of the hip, fifty-four patients (sixty-six hips) had degenerative osteoarthrosis, and sixty-three patients (100 hips) had rheumatoid arthritis. There were 114 female patients and forty-seven male patients. The average age of the patients at the time of the operation was 31.7 years (range, seventeen to thirty-nine years). Sixty-five patients (40 per cent) had a bilateral hip replacement. Thirty-eight patients (24 per cent; fifty-five hips), twenty-seven of whom had juvenile-onset chronic rheumatoid arthritis, died during the follow-up period. The average duration of follow-up for the entire series until the time of death, revision of both components, or the latest evaluation was 236 months (19.7 years; range, twenty-four to 361 months). Survivorship analysis was performed with the Kaplan-Meier method. At twenty-five years, the survival of the femoral component (with 95 per cent confidence intervals) was 89 per cent (80 to 98 per cent) in the patients who had congenital dislocation of the hip, 85 per cent (77 to 93 per cent) in the patients who had rheumatoid arthritis, and 74 per cent (61 to 87 per cent) in the patients who had degenerative osteoarthrosis. The rate of survival of the acetabular component was lower: at twenty-five years, it was 58 per cent (42 to 74 per cent) in the patients who had congenital dislocation, 79 per cent (70 to 88 per cent) in the patients who had rheumatoid arthritis, and 59 per cent (41 to 77 per cent) in the patients who had degenerative osteoarthrosis. The forty-four patients (sixty hips) who had congenital dislocation had the highest rates of aseptic loosening (twenty-two hips; 37 per cent), migration (seventeen hips; 28 per cent), and revision (twenty-two hips; 37 per cent) of the acetabular component. The fifty-four patients (sixty-six hips) who had degenerative osteoarthrosis had the highest rates of aseptic loosening (seventeen hips; 26 per cent) and revision (eighteen hips; 27 per cent) of the femoral component as well as the highest rate of femoral endosteal lysis (thirteen hips; 20 per cent). The sixty-three patients (100 hips) who had rheumatoid arthritis had the lowest prevalences of loosening and revision of the acetabular component but the highest rates of trochanteric non-union (fifteen hips; 15 per cent) and mortality (twenty-seven patients; 43 per cent). The average rate of wear of the acetabular component for the entire series was 0.11 millimeter per year; the average rate for the revised components (0.19 millimeter per year) was higher than that for the surviving components (0.09 millimeter per year). This was a consistent finding in each of the three diagnostic groups, and an increased annual rate of wear was found to be significantly associated with increased rates of migration and revision of the acetabular component (p < 0.01 for both). The femoral component proved to be durable: the twenty-five-year rate of survival for the entire series was 81 per cent (95 per cent confidence interval, 76 to 87 per cent). The major factors that limited the longevity of the cemented total hip implants in the present study were wear, loosening, and revision of the acetabular component, for which the twenty-five-year probability of survival was 68 per cent (95 per cent confidence interval, 61 to 75 per cent).

Acetabulum↗
PubMed1996

Quantifying the kinematics of natural and prosthetic knee flexion.

A new method has been developed for quantifying knee kinematics during flexion. This method was used to measure knee kinematics from lateral radiographs taken at different angles of flexion with the two femoral condyles superimposed in each image, thus standardizing the plane of flexion-extension. When applied to the radiogaphs of five healthy male volunteers (age range 21-26 years), it showed that flexion was accompanied by translation between the articular surfaces. Knee kinematics were also measured in five patients after total knee replacement (TKR) surgery with a Kinemax Modular Total Knee prosthesis (Howmedica, Warsaw, Indiana). In the TKR patients, a translation was detected in three out of the five patients. This indicates that the prosthesis is capable of restoring normal kinematics, but does not always do so.

Adult↗
PubMed1996

Long-term survival analysis of total hip replacement.

The results of 1555 primary total hip replacements in 1375 patients performed over an 11-year period were reviewed. When analysed by standard life tables, our findings show encouraging results with survival rates of 96% at 10 years, and are similar to those already published from specialist units. In all, 35 patients had undergone revision surgery. The most common reason for revision was deep postoperative infection. The perioperative mortality was 2% with 0.25% of patients having fatal pulmonary emboli. We believe the cemented Charnley total hip replacement continues to give excellent long-term results in the hands of general orthopaedic surgeons and its continued widespread use can be recommended.

Adult↗
PubMed1995

The huckstep nail. Stable fixation of mechanically deficient femoral bone.

A Huckstep intramedullary nail was used to treat 23 fractures in which the femur was mechanically deficient due to pathologic fracture, nonunion, or complex fracture in osteoporotic bone. All nailings were performed by open surgery, and in some cases this was augmented by corticocancellous bone grafting. The Huckstep nail allows the use of multiple cross screws at 15-mm intervals, providing immediate and adequate stability with successful early postoperative weightbearing. The results at followup were good in functional and radiologic terms, with no cases of fixation failure or infection. The quality of instrumentation allowed the nail and screws to be inserted without difficulty; however, the straight profile of the nail may cause problems in the distal femur, as seen in 1 patient. The authors conclude that this device offers significant mechanical and practical advantages over most other forms of fixation, where early weightbearing is desired in the presence of deficient bone. It is not ideal for distal femoral fractures, particularly in the presence of excessive femoral bowing.

Aged↗
PubMed1993

Muscle strength following total hip arthroplasty. A comparison of trochanteric osteotomy and the direct lateral approach.

Twenty-seven patients who had hip arthroplasty operated on with trochanteric osteotomy were compared with 54 patients when the direct lateral approach was used. The strength of the hip abductors, adductors, extensors, and flexors were measured at least 2 years following surgery. The strength of these muscle groups recovered to the same level as those on the nonoperated side, and there was no significant difference between the two groups of patients. Functionally, the direct lateral approach is a safe alternative to trochanteric osteotomy.

Aged↗
PubMed1993

A method for the kinematic evaluation of the knee following anterior cruciate ligament injury and reconstruction.

A quantitative method for assessing the kinematics of the knee in the sagittal plane has been developed in order to evaluate the role of the anterior cruciate ligament following injury and reconstruction. Measurements were made on a series of lateral radiographs obtained at different angles of flexion with the limb weight-bearing and the foot and ankle rotated so that the condyles of the femur overlapped. The kinematics of the joint were then defined by recording the path of the tip of the medial tibial spine as flexion proceeded, using a coordinate system based on the femur. This method overcomes the problems inherent in quantifying knee kinematics by using the pathway of the centre of rotation. In an amputated knee, tibial positions could be specified to within approximately 1.2 mm. There were no significant differences between results obtained at the beginning and end of a six month period for the normal knees of two patients; the standard deviation of the measured tibial positions was approximately 1.6 mm.

Anterior Cruciate Ligament↗
PubMed1993

Long-term results of Charnley low-friction arthroplasty in young patients.

We report the long-term outcome of 218 Charnley low-friction arthroplasties in 141 patients who were 40 years old or younger at the time of surgery. The minimum follow-up was ten years with a mean of 16 years. The probability of the femoral component surviving 20 years was 86% and of the acetabular component, 84%. The chance that both components would survive for this period was 75%. The pathological diagnosis significantly influenced implant survival. In rheumatoid patients the probability of both components surviving at 20 years was 96% compared with 51% in patients with osteoarthritis. Clinical assessment of 103 patients (166 hips) in whom the arthroplasty was still functioning showed that 94% of hips had minimal pain or none. We conclude that in young patients cemented total hip replacement is a good procedure for those with rheumatoid arthritis but that the results are much less reliable in those with osteoarthritis.

Adolescent↗
PubMed1992

Bending and fracture of the femoral component in cemented total hip replacement.

A computer method was used to make 41 measurements on the geometry of insertion of the femoral component in 200 Charnley total hip replacements. Surgery had been performed at least 12 years before, giving results which were classified as: success (90); fracture (56); or loose (54), according to rigid selection criteria. Fracture was associated with heavier patients in which there was poor proximal fixation of the femoral component but adequate distal fixation. Stems with a medial disposition proximally were more common in the fracture group than in the successful or loose groups. Sequential measurements of bending and subsequent fracture were made on the follow-up radiographs of 24 of the 200 cases (6 fracture and 18 successful). These measurements allowed bending to be detected at an earlier stage than by simple inspection of the radiographs.

Aged↗
PubMed1992

Aseptic loosening of the femoral component in cemented total hip replacement.

The purpose of this study was to identify factors which predispose to aseptic loosening of the femoral component in cemented total hip replacement. Its design was based on rigid selection criteria, so that successful and loose replacements which employed the same surgical technique were compared. Measurements of patient anatomy and of the insertion of the femoral component were made, by an accurate computer technique, on initial post-operative radiographs. Loosening was associated with heavier patients with a wider medullary canal which was flared proximally. This difference in anatomy led to differing distributions of cement in the successful and loose replacements. Medial cement-bone demarcation, at the mid-stem level, was also associated with loosening. These findings indicate the importance of optimizing the size of the prosthesis with respect to the femoral morphology.

Bone Cements↗