To date the principal focus of the mechanism of cervical spine fracture has been directed towards head/neck circumference and vertebral geometric dimensions. However the role of other measurements, including chest circumference and neck length, in a standard cervical fracture population has not yet been studied in detail. Cervical fractures often involve flexion/extension type mechanisms of injury, with the head and cervical spine flexing/extending, using the thorax as an end point of contact. Thus, the thorax may play an important role in neck injuries.
Polyethylene wear in total hip arthroplasty Is associated with generation of particulate wear debris and component failure. Wear has both mechanical and biological consequences with one of the most important of these being the stimulation of immune medicated periprosthetic osteolysis in response to polyethylene particles. It has been shown that the amouont of wear debris generated correlates with the degree of osteolysis encountered. Unfortunately, the assessment of wear of components remains difficult and we wished to apply a new digitised technique of measuring wear using engineering computer softwear on a population of uncemented total hip replacement (THR) patients. Forty patients having primary uncemented THR (ABG 1 prosthesis) for osteoarthritis were enrolled in the study. Seventeen had a 28mm femoral head implanted and 23 had a 32mm head. There were 28 females and 12 males concerned, all having standardised (120 cm hip to x-ray tube) ;weight bearing antero-posterior plain radiographs of the hip performed in the immediate post-operative period and again at a mean of 6 years post-operatively (range 54 – 96 months). The x-rays were then scanned to computer and analysed using Autocad software. The analysis essentially involved 4 steps, namely assessing sphericity of the cup, sphericity of the head, superimposition of the post-operative and 6 year radiographs an.d obtaining computer generated analysis of both the amount and direction of wear. The results of our analysis demonstrated that there was an overall mean wear of 0.157mm per year (range 0.08 – 0.27mm). Of the 17 patients with a 28mm head the mean wear was 0.143mm per year, whereas the 32mm heads were associated with a mean wear rate of 0.188mm per year, with the difference reaching statistical significance (p=0.004). Analysis of the direction of wear demonstrated that as expected wear typically occurred in a superolateral direction with a mean vector of 9° lateral to the vertical axis of the hip. These results primarily demonstrate the usefulness of appropriate computer software in determining wear of components in THR. This allows for assessment of rate and degree of wear which may be important in identifying patients at particular risk of developing significant osteolysis, loosening and ultimately component failure. The results are also consistent with previous reports of increased volumetric wear with large diameter heads and direction of wear in retrieval studies. It is therefore promising as an investigative tool for the in vivo assessment of inovations in THR design in the future.
High complication rates and technical difficulties of intra-medullary fixation in children with osteogenesis imperfecta has prompted the modification of existing rod systems. The Sheffield telescoping intramedullary rod has T-piece which is permanently fixed and is expanded to reduce metaphyseal migration. This study analyses the outcome of this rod system over an 11-year period. 32 rods were inserted in the lower limbs of 11 children with osteogenesis imperfecta. All children had multiple fractures of the bones before rod insertion.24 rods were inserted into femur, of which 3 were exchange procedures for complications. 8 rods were inserted into tibia. 4 children had intramedullary rodding of all the 4 lower limb bones. The outcome was measured in terms of mobility status, incidence of refractures and rod related complications. Complications encountered include 2-rod migrations, one instance each of broken rod, bent rod and valgus drift in the tibia.There was no instance of epiphyseal damage or growth arrest. Our series demonstrates that there is significant reduction in refractures and improvement in the mobility status in children with osteogenesis imperfecta following intramedullary fixation. The frequent complication of T-piece separation and the need for reoperation has been overcome with Sheffield modification of rod design. Though the incidence of rod related complications remain high, our study concludes that Sheffield rod system compares favourably with the existing intramedullary devices for osteogenesis imperfecta in the literature.
The longevity of total joint arthroplasty relies on articulating surfaces that are durable and produce little polyethylene debris and consequent osteolysis and loosening. In an effort to improve wear characteristics of the acetabular line, Hylamer (Du Pont Depuy Orthopaedics, Warsaw, Indiana) was produced as an alternative to ultra high molecular weight polyethylene. To date however reports using Hylamer with Cobalt chrome, stainless steel and alumina ceramic femoral heads have yielded results that have not reached the potential of initial in vitro trials. No study has examined the outcome following a Zirconia femoral head and a Hylamer acetabular shell. The tribological properties of Zirconia make it an ideal countersurface with low friction and long term durability. This study examines the outcome when these components were used in combination with a select cohort of patients and evaluates the benefit of their continued use. From 1994 to 1997 fifty one patients had Hylamer cup with zirconia femoral head elite total joint arthroplasty performed. Forty-seven patients with fifty-eight arthroplasties were included in this study. All patients were less that fifty years with a male preponderance. There were eleven bilateral arthroplasties all of which had the second procedure at least two months from the index procedure. The principle diagnosis was osteoarthritis in forty-three hips with rheumatoid disease in twelve hips. The remaining two patients were operated on for end stage osteonecrosis. The Elite total joint arthroplasty (DePuy, Warsaw in.) was used in all cases. The 22.225mm zirconia head was used exclusive in this study. The Hylamer shell used was a solid polyethylene block with a minimum depth of 6mm. Both the acetabular and femoral component were cemented with Palacos polymethylmethacrelate (Howmedica, Rutherford NJ) using third generation cementing techniques. Patients were evaluated both clinically and radiographically three months and six months following surgery and thereafter at yearly intervals. Both the SF36 questionnaire and Mayo score were used to evaluate subjectively and objectively patient outcome. Regression analysis was used to determine if the age, sex and weight of the patient as well as the angle of inclination of the acetabular cup correlated with polyethylene wear and outcome. Kaplan Meir survival analysis was used to calculate the probability of survival of the original prosthesis. There was no correlation between age, weight nor sex of the patient and outcome. The angle of inclination was correlated with a poorer ourcome but this did not reach statistical significance. The mean linear wear rate was 0.021mm year (range 0.011–0.055). Ten year survivalship analysis was calculated at 97%. SF 36 scores were standardised and the mean post operative score was 89 (range 62–97). The results presented are significantly better than previously described in clinical trials using Hylamer liners. The reasons for this are multifactorial. This study used 22.225 mm heads in association with a solid cemented polyethylene acetabular block. Both have been associated with lower volumetric wear but neither have been used on previous studies of Hylamer. In addition the tribological properties of Hylamer may have been undermined in previous studies by poorly conforming countersurfaces using a different manufacturer for femoral and acetabular components. Finally the use of a second generation ceramic, zirconia with a Hylamer liner has produced medium term outcomes that confound previous reports and that exceed many published reports on traditional polyethylene liners.
