Carl Zetterberg

The activity of individual trunk muscles during heavy physical loading.

The myoelectric activity of ten trunk muscles were recorded, using intramuscular electrodes, when ten subjects made maximal and 50% of maximal static exertions in standing postures. Exertions were made in flexion, extension, and left and right lateral bending. Three heavy-lifting tasks also were studied. A biomechanical model was used to predict the forces in the trunk muscles, and the predictions then were compared to the measurements. The abdominal muscles were all active in attempted flexion, while the erector spinae muscles were inactive. In attempted extension, the erectors were maximally active, but considerable activity was present in the abdominal muscles as well. The highest activity levels recorded in the oblique abdominal muscles were in lateral bending. There were high degrees of correlation between the measured muscle activities and predicted muscle tensions for the erector spinae and rectus abdominus muscles, while the correlation coefficients for the oblique abdominal muscles were lower (0.4-0.7). The study indicates that inclusion of antagonistic activity is an important consideration to improve model predictions. The oblique abdominal muscles appear to be more active, in general, than predicted. For the longitudinal trunk muscles, the predictions are excellent throughout.

FRACTURES OF THE PROXIMAL END OF THE FEMUR IN GOTEBORG, SWEDEN, 1940-1979

A total of 3475 fractures of the proximal femur occurring in Göteborg. Sweden, in 1965, 1969, 1970, 1975, 1978 and 1979 were reviewed, and the information obtained was compared with earlier published epidemiologic data from Göteborg presented by Mårtensson (1962) for the years 1940-1959. A highly statistically significant age specific increase in fracture incidence was found for trochanteric as well as cervical fractures, and for both women and men. The fracture incidence increased from about 3 per 1000 in 1965 to 5 per 1000 in 1979, and the yearly number of fractures in this city from 104 in 1940 to 788 in 1979. With the present trend the fracture incidence will double over the next 20 years.

Incidence of hip fracture in Western Sweden 1974-1982: Comparison of rural and urban populations

Several epidemiological studies in northern Europe have shown that fractures in the elderly exceed the expected increase in the aging populations. We have compared the incidence of hip fracture in the rural county of Skaraborg and the city of Göteborg in Sweden. After adjustment for age changes in the population, the incidence of hip fracture in Skaraborg County was lower than in Göteborg during the period 1974-1984. The non-age-related increase in the incidence of fractures found in the city was not confirmed in the rural area.

Ten-year survival after fractures of the proximal end of the femur.

Two hundred and eighty-eight patients who sustained a fracture of the proximal end of the femur in 1975 were followed up for 10 years. The mean age of the patients was 75 years. Seventy-two percent were women. Age was the single most important factor determining long-term survival. Other important factors were category of accommodation, sex and place of injury. After 10 years only 1.4% of the patients discharged to an institution were alive compared to 40% of the patients discharged to their own homes.

FEMORAL NECK FRACTURES IN YOUNG ADULTS

A total of 110 fractures of the neck of femur were studied in 108 patients 17 to 50 years old. The aims were to analyze why these fractures occur in young adults, and what results can be expected after internal fixation. Severe trauma caused about half of the fractures. In the remaining group chronic and disabling disorders were usually present at the time of injury. Seventeen patients were known to abuse alcohol. Aseptic necrosis with late segmental collapse occurred in 41 per cent of the hips (45/110), comparatively more often in patients who were 45 years or younger. Only 16 of the 73 patients who were seen at follow-up (22 per cent) had a perfect result. It is concluded that femoral neck fractures in patients younger than 45 years occur because of significant trauma in a healthy subject, or minor trauma in subject with predisposing disease. The incidence of late segmental collapse is greater than in elderly patients with femoral neck fractures. A less satisfactory result can therefore be expected.

Electromyography of the paravertebral muscles in idiopathic scoliosis Measurements of amplitude and spectral changes under load

The myoelectric activity of the paraspinal muscles was recorded in girls with idiopathic scoliosis and in healthy controls. The muscles of the back were loaded isometrically and the signals recorded at the T8 and L3 levels were analysed as regards amplitude and frequency. A comparatively higher signal amplitude was found on the convex side of the scoliosis curve. This was found to be due to a lower amplitude on the concave side when the scoliosis group was compared to the controls. The amplitude difference was correlated to the degree of scoliosis. A shift in the myoelectric spectrum toward lower frequencies occurred during the loading period. There were no differences in this respect between the sides of the scoliosis, nor were there differences between the scoliosis patients and the controls. Secondary adaptation to the higher load demand by the muscles on the convex side in scoliosis is the most probable explanation for our observations.

Bone mineral content and fixation strength of femoral neck fractures A cadaver study

We measured the bone mineral content (BMC) of 21 human femoral autopsy specimens using Radiographic Attenuation Technique (RAT). The specimens were then tested for stiffness in a material-testing machine. Osteosynthesis was performed after medial femoral neck osteotomy, using 1 of 3 different pinning methods: 2 hook pins (LIH), 2 cannulated screws (Uppsala), and 3 cannulated screws (CHP). The specimens were allocated to each method by grouping them in triplets with similar BMC. Cyclic loading at 500-1000 N and 1 Hz was performed during 50 minutes. The amount of axial compression during loading was measured. Finally, loading to failure was done and post-fixation stiffness and ultimate compression strength recorded. With one exception, all cases failed where the BMC was less than 0.4 g/cm2. No differences between the methods of osteosynthesis were found. The fixation strength was mostly dependent on the strength of the bone, i.e., the degree of osteoporosis.

The role of prerotation of the trunk in axial twisting efforts.

The myoelectric activity of selected trunk muscles was recorded during the development of controlled isometric axial torques. Muscle activity was measured bilaterally over the erector spinae, the rectus abdominus, the oblique external and the oblique internal abdominal muscles at the L3 level. Subjects first applied graded isometric torque efforts over a 10 second ramp up to maximum voluntary contraction with the trunk in neutral rotation. They then repeated the effort with the trunk twisted to the left and right. The largest electromyographic activities were found in the agonistic oblique muscles, but considerable antagonistic activity was present also. While the activity of the internal oblique and rectus were bilaterally similar in symmetric standing a difference occurred between the two sides when the trunk was twisted to the right or left. Axial prerotation of the trunk by 30° in the direction of torque development marginally decreased the maximal developed torque, whereas prerotation in the opposite direction increased the developed torque.

Fixation of femoral neck fracture: A randomized 2-year follow-up study of hook pins and sliding screw plate in 222 patients

We compared fixation with hook pins or sliding screw plate in a prospective randomized study of 222 patients with a cervical hip fracture. Radiographic evidence of early redisplacement, nonunion, or late segmental collapse was found in 43 of 122 patients operated on with two hook pins and in 40 of 100 patients operated on with the sliding screw plate. According to the actuarial method, the failure rate after 2 years was 38% with hook pins and 46% with screw plates, which not is a significant difference. Due to early redisplacement, reoperation with an endoprosthesis was performed within 0.5 (2) years in 11 (22) patients in the hook-pin group and in 4 (17) patients in the sliding-screw plate group.

Workload and musculoskeletal problems: a comparison between welders and office clerks (with reference also to fishermen)

Previous studies have shown that subjective as well as clinical shoulder signs and symptoms are more common among welders than among office clerks. In the present study we wished to further evaluate the influence of different jobs on musculoskeletal problems, as well as the relationship between objective signs and subjective symptoms. This study confirmed that symptoms and signs from the shoulder were more common among the welders, who also had more subjective symptoms and clinical signs from other parts of the musculoskeletal system. Range of motion in different joint systems was, however, similar in the two groups except in external rotation of the shoulder, where welders had a more limited range. The degree of co-existence of subjective symptoms and clinical signs differed between different parts of the musculoskeletal system and was low particularly in the low back, hips, and ankles. This indicates low validity of many common clinical methods for determining musculoskeletal dysfunction. General health was good in both vocational groups and isometric strength for the welders was intermediate between that of office clerks (who had lower strength) and that of fishermen (who had higher strength, as disclosed in a previous investigation). To a similar degree welders and fishermen also had objective signs from most parts of the musculoskeletal system, whereas subjective symptoms from some parts of the body and medical consultations due to these problems were more common among welders. Atrophied shoulder muscles were more common among welders than among fishermen, whereas crepitations in the shoulder tended to be more common among the fishermen. This indicates that heavy dynamic work and prolonged static work may both induce shoulder injuries, but of different types.