Occupational lifting predicts hospital admission due to low back pain in a cohort of airport baggage handlers.

PURPOSE: To examine if occupational lifting assessed as cumulative years as a baggage handler is associated with first-time hospital diagnosis or treatment for low back disorders. METHODS: This study is based on the Copenhagen Airport Cohort consisting of male baggage handlers performing heavy lifting every day and a reference group of unskilled men from the greater Copenhagen area during the period 1990-2012. We followed the cohort in the National Patient Register and Civil Registration System to obtain information on diagnoses, surgery, mortality, and migration. The outcomes were first-time hospital diagnosis or surgery for (1) lumbar disc herniation or (2) low back pain (LBP). RESULTS: Baggage handlers (N = 3473) had a higher incidence rate of LBP, but not of lumbar disc herniation, compared to the reference group (N = 65,702). Baggage handlers with longer employment had a higher incidence of LBP compared to baggage handlers with shorter employment. The linear association of cumulative years as a baggage handler on LBP was significantly increased with an incidence rate ratio of 1.16 (95% CI 1.07-1.25) for a 5-year increase of employment as baggage handler. CONCLUSIONS: In this large cohort study, we found an increased incidence of LBP among baggage handlers compared to the reference group with indications of a dose-response relationship between years of employment and the outcome. For baggage handlers working on the apron, the incidence was particularly increased before introduction of technical lifting equipment, suggesting that preventive measures to reduce cumulative work load may have a positive effect.

Gait pattern in 9-11-year-old children with generalized joint hypermobility compared with controls; a cross-sectional study.

BACKGROUND: To study differences in gait patterns in 10-year-old children with Generalized Joint Hypermobility (GJH) and with no GJH (NGJH). METHODS: A total of 37 children participated (19 GJH, 18 NGJH, mean age 10.2 (SD 0.5) years). Inclusion criteria for GJH were a Beighton score of ≥5, with at least one hypermobile knee joint; for NGJH a Beighton score of ≤4, and no hypermobile knees and for both groups no knee pain during the previous week. All children were recorded by five video cameras, while they walked across three force platforms. Net joint moments were calculated in 3D by inverse dynamics and peak values provided input to statistical analyses. RESULTS: In the frontal plane, children with GJH had a significantly lower peak knee abductor moment and peak hip abductor moment. In the sagittal plane, the peak knee flexor moment and the peak hip extensor moment were significantly lower in the GJH group although the absolute difference was small. CONCLUSIONS: The walking pattern was the same for children with GJH and for healthy children, as there were no differences in kinematics, but it was, however, performed with different kinetics. Children with GJH walked with lower ankle, knee and hip joint moments compared to children with NGJH. However, the clinical importance of these differences during normal gait is unknown. To obtain this knowledge, children with GJH must be followed longitudinally. TRIAL REGISTRATION: The study was approved by the Committee on Biomedical Research Ethics for Copenhagen and Frederiksberg, Denmark (jnr. KF01-2006-178).

A Cohort Study on Meniscal Lesions among Airport Baggage Handlers.

Meniscal lesions are common and may contribute to the development of knee arthrosis. A few case-control and cross-sectional studies have identified knee-straining work as risk factors for meniscal lesions, but exposure-response relations and the role of specific exposures are uncertain, and previous results may be sensitive to reporting and selection bias. We examined the relation between meniscal lesions and cumulative exposure to heavy lifting in a prospective register-based study with complete follow-up and independent information on exposure and outcome. We established a cohort of unskilled men employed at Copenhagen Airport or in other companies in the metropolitan Copenhagen area from 1990 to 2012 (the Copenhagen Airport Cohort). The cohort at risk included 3,307 airport baggage handlers with heavy lifting and kneeling or squatting work tasks and 63,934 referents with a similar socioeconomic background and less knee-straining work. Baggage handlers lifted suitcases with an average weight of approximately 15 kg, in total approximately five tonnes during a 9-hour workday. The cohort was followed in the National Patient Register and Civil Registration System. The outcome was a first time hospital diagnosis or surgery of a meniscal lesion. Baggage handlers had a higher incidence of meniscal lesions than the referents. Within baggage handlers spline regression showed that the incidence rate ratio was 1.91 (95% confidence interval: 1.29-2.84) after five years as a baggage handler and then decreased slowly to reach unity after approximately 30 years, adjusted for effects of potential confounders. This relation between baggage handling and meniscal lesions was present for work on the apron which involves lifting in a kneeling or squatting position, but not in the baggage hall, which only involves lifting in standing positions. The results support that long-term heavy lifting in a kneeling or squatting position is a risk factor for the development of symptomatic meniscal lesions.

Contributions to the understanding of gait control.

This thesis is based on ten published articles. The experimental work was carried out at the Faculty of Health Sciences, University of Copenhagen. The aim was to investigate and describe a number of basic mechanical and physiological mechanisms behind human walking. The methodologies used were biomechanical movement analysis and electrophysiology. The walking experiments were carried out in a gait lab, where the subjects were video recorded while they walked across two force platforms, which measured the ground reaction forces. Net joint moments about the hip-, knee- and ankle joint were calculated by combining the movement data and the external reaction forces (inverse dynamics). Muscle activity and sensory input to the spinal cord were measured by electromyography (EMG) and electrical stimulation of peripheral nerves. The results showed that the gait pattern varies to a great degree between individuals. Some people choose to exert the highest forces about the ankle joint while others prefer to use the knee joint. By use of a cluster analysis, fifteen healthy subjects could be divided into two groups. The extensor moment about the knee joint was the main factor for separating the two gait patterns, but the group with the highest extensor moments about the knee joint also walked with more flexed knee joints, higher EMG activity in the quadriceps muscle and higher bone-on-bone forces. This may lead to development of osteoarthritis over the years. Walking on high-heeled shoes reduced the ankle joint moment significantly either because of reduced muscle fiber length and/or increased co-contraction about the joint. On the contrary, the extensor moment about the knee joint was almost doubled in the high-heeled condition compared to bare footed walking at the same velocity. Also the EMG activity increased in the leg muscles. This could be an explanation pertaining to the higher incidence of osteoarthritis in women than in men. Patients with a drop-foot cannot put the foot to the ground with the heel first. Moreover, they have to increase flexion of the hip joint during the swing phase because the foot hangs in a plantar flexed position. It was shown that the ankle joint plantar flexor moment increased in the healthy leg and that the knee joint extensor moment increased significantly in both the affected and the healthy leg. The latter is most likely due to the patients trying to avoid an asymmetrical gait pattern. It is recommended to use an orthosis with drop-foot patients in order to keep the ankle joint dorsiflexed prior to touchdown, otherwise bone-on-bone forces in both knee joints will increase and probably lead to osteoarthritis. The hip joint moment varies less between individuals. However, both during walking and running an unexplained hip joint flexor moment is present during the last half of the stance phase. The moment appears to oppose the speed of progression and it has been suggested that it serves to balance the upper body. This was investigated in a group of healthy subjects who were asked to walk with their upper body in a reclined, inclined and normal position, respectively. It was shown that the hip joint flexor moment was similar in the reclined and the normal position but lower when walking in the inclined position and it can be concluded that the upper body is not balanced by hip joint flexor muscles but rather by accelerations of the pelvis and activity in abdominal and back muscles. These experiments also showed that the trailing leg is brought forward during the swing phase without activity in the flexor muscles about the hip joint. This was verified by the absence of EMG activity in the iliacus muscle measured by intramuscular wire electrodes. Instead the strong ligaments restricting hip joint extension are stretched during the first half of the swing phase thereby storing elastic energy, which is released during the last half of the stance phase and accelerating the leg into the swing phase. This is considered an important energy conserving feature of human walking. The gating of sensory input to the spinal cord during walking and running was investigated by use of the Hoffmann (H) reflex in m. soleus and m. gastrocnemius medialis. This reflex expresses the central component of the stretch reflex, i.e. the transmission from Ia afferents to α-motoneurones in the spinal cord. The soleus H-reflex was shown to be strongly modulated during the gait cycle. In general, it was facilitated in the stance phase and suppressed in the swing phase. However, as it was the case with the biomechanical parameters, inter-individual H-reflex modulations were found and they were highly reproducible between days. One group of subjects had an almost completely suppressed H-reflex during the entire swing phase, while another group showed a gradually increasing reflex excitability during the swing phase. This group also walked with a lower extensor moment about the knee joint and higher plantar flexor moment about the ankle joint and it is speculated that this gait pattern highly relies on reflexes to deal with unexpected perturbations. The subjects with the suppressed reflex during the swing phase also showed a higher EMG activity in the anterior tibial muscle, so it is likely that the suppression of the H-reflex was at least partly due to reciprocal antagonist inhibition. All subjects showed complete suppression of the H-reflex at toeoff. This seems necessary to avoid a stretch reflex being elicited in the soleus muscle as the ankle joint undergoes a fast dorsiflexion just after toeoff. The reflex modulation is clearly an integrated part of the human gait pattern and is absolutely necessary for normal gait function with smoothe movements. Furthermore, it is anticipated that the afferent input from the muscle spindles is used to drive the motor output from the α-motoneurones together with descending activity from the motor cortex. During running the H-reflex increased in both the soleus and the gastrocnemius already before heel strike and before the onset of EMG activity in the same two muscles and with a relatively high activity in the anterior tibial muscle, but this was most pronounced in the soleus. The H-reflex was always higher in the soleus also when expressed as percentage of the maximal M-wave. This is due to the difference in muscle fiber type distribution between the two muscles. The H-reflex increased from walking to running in both muscles and further with increasing running speed. Unexpectedly, there were no signs of the faster gastrocnemius becoming more important at higher running speed. During walking it is not possible to observe a stretch reflex in the form of a synchronized activation of a large number of muscle fibers as this would disturb the movement pattern. It is rather likely that the input from Ia afferents directly contributes to activate the α-motoneurones. However, during running the stance phase is much shorter, which enables the possibility of a stretch reflex to contribute to a strong contraction during push-off. EMG peaks in the soleus with an appropriate latency were observed in the soleus during running. This was not the case with the gastrocnemius and the explanation is most likely that the gastrocnemius is biarticular and not stretched to any great extent during running.

Baggage handler seniority and musculoskeletal symptoms: is heavy lifting in awkward positions associated with the risk of pain?

OBJECTIVES: Heavy lifting is associated with musculoskeletal disorders but it is unclear whether it is related to acute reversible effects or to chronic effects from cumulated exposure. The aim of this study was to examine whether musculoskeletal symptoms in Danish airport baggage handlers were associated with their seniority as baggage handler, indicating chronic effects from cumulated workload. METHODS: We established a group of baggage handlers employed at Copenhagen Airport during the period 1983-2012 (n=3092) and a reference group of men in other unskilled occupations with less heavy work (n=2478). Data regarding work history, lifestyle and musculoskeletal symptoms were collected using a self-administered questionnaire (response rate 70.1% among baggage handlers and 68.8% among the reference group). RESULTS: The ORs of self-reported musculoskeletal symptoms during the last 12 months in the neck/upper back, lower back, shoulders, elbows, wrists, hips and knees were significantly higher in baggage handlers than in the reference group. These differences were explained by significant linear effects of baggage handler seniority for six anatomical regions. Adjustment for age, body mass index, smoking and leisure-time physical activity did not change these results. The findings were stable over age strata and among present and former baggage handlers. CONCLUSIONS: The risk of musculoskeletal symptoms in six anatomical regions increased with increasing seniority as a baggage handler. This is consistent with the assumption that cumulated heavy lifting may cause chronic or long-lasting musculoskeletal symptoms. However, we cannot exclude that other factors related to baggage handler seniority may explain some of the associations.