Proximal humeral fractures in Sweden-a registry-based study.

Proximal humeral fracture is the third most common osteoporotic fracture. To our knowledge, this is the first nationwide population-based registry study in adults that includes both inpatient and outpatient visits. Thus, we were able to report the true incidence rates and trends in the treatment of proximal humeral fractures. INTRODUCTION: Proximal humeral fractures are among the most common osteoporotic fractures. Valid epidemiologic population-based data, including both inpatient and outpatient visits, however, are lacking. METHODS: To investigate the Swedish national incidence rates and treatment trends of proximal humeral fractures, we obtained data from the Swedish Hospital Discharge Register between 2001 and 2012. All adult patients (≥18 years of age) in the Swedish Hospital Discharge Register were included. Outpatient visits have been included in the register since 2001. RESULTS: We identified 98,770 patients (women n = 72,063; 73 %) with proximal humeral fractures between 2001 and 2012. In 2001, the sex-specific incidence of proximal humeral fractures was 134.5 per 100,000 person-years for women and 49.2 for men. In 2012, the corresponding values were 174.6 for women and 68.1 for men, increasing 30 % in women and 39 % in men. A total of 17,013 surgical procedures were conducted between 2001 and 2012. Open reduction and internal fixation with a plate was the most common procedure (n = 5050, 30 %), followed by endoprosthetic implantation (n = 3962, 23 %) and intramedullary nailing (n = 3376, 20 %). The proportion of surgically treated patients increased from 12.1 % in 2001 to 16.8 % in 2012 for women and from 15.1 % in 2001 to 17.1 % in 2012 for men. CONCLUSION: The Swedish national incidence of proximal humeral fractures has been increasing, although it seems to have peaked in the elderly population during 2008-2010. The rate of surgical treatment has increased substantially, particularly open reduction and internal fixation with a plate. To our knowledge, this is the first nationwide epidemiologic study for Sweden reporting the incidence of proximal humeral fractures and including all inpatient and outpatient visits.

Treatment of full thickness focal cartilage lesions with a metallic resurfacing implant in a sheep animal model, 1 year evaluation.

BACKGROUND: Full depth focal cartilage lesions do not heal spontaneously and while some of these lesions are asymptomatic they might progress to osteoarthritis. Treatment for these lesions is warranted and the gold standard treatment at younger age remains biological healing by cell stimulation. In the middle-age patient the success rate of biologic treatment varies, hence the surge of non-biological alternatives. Our objective was to evaluate the efficacy and safety of a metallic implant for treatment of these lesions with respect to the long-term panarticular cartilage homeostasis. METHODS: The medial femoral condyle of 16 sheep was operated unilaterally. A metallic implant was inserted in the weight-bearing surface at an aimed height of 0.5 mm recessed. Euthanasia was performed at 6 or 12 months. Implant height and tilt was analyzed using a laser-scanning device. Damage to cartilage surfaces was evaluated macroscopically and microscopically according to the Osteoarthritis Research Society International (OARSI) recommendations. RESULTS: Thirteen sheep were available for evaluation and showed a varying degree of cartilage damage linearly increasing with age. Cartilage damage of the medial tibial plateau opposing the implant was increased compared to the non-operated knee by 1.77 units (p = 0.041; 95% CI: 0.08, 3.45) on a 0-27 unit scale. Remaining joint compartments were unaffected. Implant position averaged 0.54 recessed (95% CI: 0.41, 0.67). CONCLUSIONS: Our results showed a consistent and accurate placement of these implants at a defined zone. At this position cartilage wear of opposing and surrounding joint cartilage is limited. Thus expanded animal and human studies are motivated.

Fixation of a double-coated titanium-hydroxyapatite focal knee resurfacing implant: a 12-month study in sheep.

OBJECTIVE: Focal cartilage lesions according to International Cartilage Repair Society (ICRS) grade 3-4 in the medial femoral condyle may progress to osteoarthritis. When treating such focal lesions with metallic implants a sound fixation to the underlying bone is mandatory. We developed a monobloc unipolar cobalt-chrome (Co-Cr) implant with a double coating; first a layer of commercially pure titanium (c.p.Ti) on top of which a layer of hydroxyapatite (HA) was applied. We hypothesised that such a double coating would provide long-lasting and adequate osseointegration. DESIGN (MATERIALS AND METHODS): Unilateral medial femoral condyles of 10 sheep were operated. The implants were inserted in the weight-bearing surface and immediate weight-bearing was allowed. Euthanasia was performed at 6 (three animals) or 12 months (six animals). Osseointegration was analysed with micro-computer tomography (CT), light microscopy and histomorphometric analyses using backscatter scanning electron microscopy (B-SEM) technique. RESULTS: At 6 months one specimen out of three showed small osteolytic areas at the hat and at 12 months two specimens out of six showed small osteolytic areas at the hat, no osteolytical areas were seen around the peg at any time point. At both time points, a high total bone-to-implant contact was measured with a mean (95% confidence interval - CI) of 90.6 (79-102) at 6 months and 92.3 (89-95) at 12 months, respectively. CONCLUSIONS: A double coating (Ti + HA) of a focal knee resurfacing Co-Cr implant was presented in a sheep animal model. A firm and consistent bond to bone under weight-bearing conditions was shown up to 1 year.

Focal knee resurfacing and effects of surgical precision on opposing cartilage. A pilot study on 12 sheep.

BACKGROUND: Full thickness cartilage lesions (ICRS grade 3-4) and focal lesions of degenerative origin may progress to osteoarthritis (OA). Such focal lesions can be treated by metallic implants. We hypothesized that such treatment results in opposing surface cartilage damage that correlates with implant position (height) relative to the adjacent cartilage surface. This relationship was investigated using a sheep animal model. METHODS: Both medial femoral condyles of 12 sheep were operated. The implants, were inserted in the weight-bearing surface at different heights relative to the surrounding cartilage. Euthanasia was performed at 6 or 12 weeks. After retrieval, implant height was analyzed using laser scanning. Damage to the opposing tibial cartilage was evaluated macroscopically and microscopically according to the modified Mankin score. RESULTS: Twenty-two knees were available for evaluation and showed cartilage lesions ranging from severe damage (Mankin stage 11) to almost pristine conditions (Mankin stage 1). There was a strong correlation between implant height and cartilage damage. Standard deviation from the aimed implant height was 0.47 mm. CONCLUSIONS: Our results showed significant surgical imprecision and protruding implants imposed severe cartilage damage. We therefore suggest implants should be placed recessed (approx. 0.5 mm) below the surrounding cartilage in this animal model. These results encourage further studies of metallic implants yet the utmost precision regarding position is required.

Lower limb skeletal muscle function after 6 wk of bed rest.

Force, electromyographic (EMG) activity, muscle mass, and fiber characteristics were studied in seven healthy men before and after 6 wk of bed rest. Maximum voluntary isometric and concentric knee extensor torque decreased (P < 0.05) uniformly across angular velocities by 25-30% after bed rest. Maximum quadricep rectified EMG decreased by 19 +/- 23%, whereas submaximum (100-Nm isometric action) EMG increased by 44 +/- 28%. Knee extensor muscle cross-sectional area (CSA), assessed by using magnetic resonance imaging, decreased by 14 +/- 4%. Maximum torque per knee extensor CSA decreased by 13 +/- 9%. Vastus lateralis fiber CSA decreased 18 +/- 14%. Neither type I, IIA, and IIB fiber percentages nor their relative proportions of myosin heavy chain (MHC) isoforms were altered after bed rest. Because the decline in strength could not be entirely accounted for by using decreased muscle CSA, it is suggested that the strength loss is also due to factors resulting in decreased neural input to muscle and/or reduced specific tension of muscle, as evidenced by decreased torque/EMG ratio. Additionally, it is concluded that muscle unloading in humans does not induce important changes in fiber type or MHC composition or in vivo muscle contractile properties.

Effects of lower limb unloading on skeletal muscle mass and function in humans.

A model to simulate effects of microgravity on skeletal muscle mass and function in humans has been developed. Unilateral lower limb unloading that allowed ankle, knee, and hip joint mobility was conducted in six healthy men by suspending one lower limb and having the subjects walk on crutches. They performed maximal unilateral concentric or eccentric quadriceps actions at different angular velocities before and after 4 wk of suspension and after 4 days and after 7 wk of uncontrolled recovery. Peak torque (PT) and angle-specific torque (AST) were measured. Muscle cross-sectional area (CSA) and radiological density (RD) of the thigh were assessed by means of computerized tomography. Concentric and eccentric PT and AST across speeds decreased (P less than 0.05) by 22 and 16%, respectively, in response to unloading. At 4 days of recovery PT (-11%) and AST (-7%) were still lower (P less than 0.05) than before. Muscle CSA and RD decreased (P less than 0.05) by 7 and 6%, respectively. After 7 wk of recovery PT, AST, CSA, and RD had returned to normal. The control limb showed no changes over the experimental period except for a 6% decrease (P less than 0.05) in RD. It is suggested that this human model of unloading could serve to simulate effects of microgravity on skeletal muscle mass and function because reductions in muscle mass and strength were of similar magnitude to those produced by bed rest.

Maximal instantaneous muscular power after prolonged bed rest in humans.

A reduction in lower limb cross-sectional area (CSA) occurs after bed rest (BR). This should lead to an equivalent reduction in maximal instantaneous muscular power (W(p)) if the body segments' lengths remain unchanged. W(p) was determined during maximal jumps off both feet on a force platform before and on days 2, 6, 10, 32, and 48 after a 42-day duration BR. CSA of thigh muscles was measured by magnetic resonance imaging before and on day 5 after BR. Before BR, W(p) was 3.63 +/- 0.43 kW or 48.6 +/- 3.3 W/kg. On days 2 and 6 after BR, W(p) was reduced by 23.7 +/- 6.9 and 22.7 +/- 5.4% (P < 0.01), respectively. Thigh extensors CSA (CSAEXT) was 16.7 +/- 4.7% (P < 0.01) lower than before. When normalized per CSAEXT, W(p) was reduced by only 4.8 +/- 4.5% (P < 0.05). By day 48 of recovery, W(p) had returned to baseline values. Therefore, if W(p) is appropriately normalized for CSA of the extensor muscles, the reduction in CSAEXT explains most of the decrease in W(p) decrease after BR. Other factors such as a deficit in neural activation or a decrease in fiber-specific tension may account for only 5% of the W(p) loss after BR.

Muscle control in elite alpine skiing.

PURPOSE: The purpose of this study was to determine whether muscle control may be influenced by accelerative forces brought about by the downhill displacement of body mass in combination with the sharp turns during alpine skiing. METHODS: Sixteen elite skiers performed either super G (SG), giant slalom (GS), slalom (SL), or freestyle mogul (FM) skiing. Knee and hip joint angles and electromyographic (EMG) activity of the knee extensors were recorded. RESULTS: During the course of a turn, the minimum (deepest stance position) knee angle of the outside (main load-bearing) leg ranged from 60 degrees to 100 degrees, where the smallest angle was obtained in the FM event. Among the traditional alpine disciplines, smaller knee angles were obtained in the high-speed events (i.e., knee angle: SG

Involvement of eccentric muscle actions in giant slalom racing.

Joint angular movements and muscle activation (EMG), were determined in male elite racers while performing the giant slalom. Movement cycles averaged 3.5 +/- 0.6 s (left plus right turn), and knee angle ranged 66-114 degrees (180 degrees = straight leg). Knee extensor muscle use was dominated (rectified EMG; P < 0.05) by the leg controlling the outside (downhill) ski during the turn. Time spent while decreasing knee angle (eccentric muscle action) of outside leg averaged 1.0 +/- 0.2 s. This phase was longer (P < 0.05) than the average push-off (concentric muscle action) phase of 0.5 +/- 0.1 s. Moreover, EMG activity of the outside leg during eccentric muscle actions exceeded (P < 0.05) that of concentric actions and was similar to that attained during maximum isometric knee extension in laboratory tests. Knee and hip angular movement ranged 20-50 degrees. Average joint velocities equalled 20-40 degrees.s(-1) during the turning phase. Thus, competitive giant slalom skiing is dominated by slow eccentric muscle actions performed at near maximum voluntary force. Because of their greater ability to generate force, eccentric muscle actions may be warranted or even required to resist the G-forces induced during the turn phase.

Quadriceps EMG/force relationship in knee extension and leg press.

PURPOSE: This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. METHODS: Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). RESULTS: There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. CONCLUSIONS: The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.

A gravity-independent ergometer to be used for resistance training in space.

An ergometer, to be used for resistance training in space, has been developed and validated. It is designed to activate the extensor muscles of the knee and ankle joints while performing the leg press exercise. Resistance is provided independent of gravity by using the inertial focus of a flywheel. Eleven men performed two series of consecutive maximal voluntary concentric and eccentric muscle actions. Force, power, work and electromyographic (EMG) activity, measured during exercise on this ergometer and a traditional leg press resistive apparatus were similar. This mechanical ergometer seems to meet the operational and technical requirements of equipment that can be flown and used in space. Also, the physiological responses to acute exercise suggest that adaptations similar to those achieved by traditional weight training can be produced. Exercise using the inertia ergometer would, therefore, probably also be effective in combating the muscle atrophy and loss of strength that occur in microgravity.

Force and power characteristics of a resistive exercise device for use in space.

We have developed a non-gravity dependent mechanical device, which provides resistance during coupled concentric and eccentric muscle actions, through the inertia of a spinning fly-wheel (Fly-Wheel Ergometry; FWE). Our research shows that lower-limb FWE exercise can produce forces and thus muscular stress comparable to what is typical of advanced resistance training using free weights. FWE also offers greater training stimuli during eccentric relative to concentric muscle actions, as evidenced by force and electromyographic (EMG) measurements. Muscle use of specific muscle groups, as assessed by the exercise-induced contrast shift of magnetic resonance images, is similar during lower-limb FWE and the barbell squat. Unlike free-weight exercise, FWE allows for maximal voluntary effort in each repetition of an exercise bout. Likewise, FWE exercise, not unassisted free-weight exercise, produces eccentric "overload". Collectively, the inherent features of this resistive exercise device and the results of the physiological evaluations we have performed, suggest that resistance exercise using FWE could be used as an effective exercise counter-measure in space. The flywheel principle can be employed to any exercise configuration and designed into a compact device allowing for exercises stressing those muscles and bone structures, which are thought to be most affected by long-duration spaceflight.

Designing methods for musculoskeletal conditioning in weightlessness.

There is an immediate need to find methods to combat the skeletal muscle deconditioning that occurs in microgravity. Important features to be considered for any ergometer or exercise method to be used as a countermeasure against musculoskeletal deconditioning in space include heavy muscular loading of the postural muscles of the lower limbs and that eccentric and concentric muscle activations can be performed. Those are major requirements to produce optimal gains in strength and muscle mass at 1-g and probably to counteract muscle atrophy and strength loss in microgravity. Resistance exercise with a strength-ergometer, using the fly-wheel principle was carried out at a low oxygen cost and required no external power supply. We have developed a resistance training system employing this ergometer so that force and power production easily can be monitored and calibrated. It is suggested that the features of this ergometer meet the presented requirements for use during long-term space missions.

Persisting muscle atrophy two years after replacement of the hip.

Muscle atrophy has been demonstrated in patients suffering from osteoarthritis of the hip, but little is known about muscular recovery after total hip replacement (THR). A total of 20 patients with unilateral osteoarthritis of the hip were assessed before, six months and two years after THR. The cross-sectional area and radiological density of the muscles of the hip, thigh, calf and back were measured using CT. We hypothesised that the muscles would not recover fully after operation. After two years comparison of the limb with the THR with the healthy limb showed that there was such a reduction in the cross-sectional area in iliopsoas (7.0%; p = 0.006) and the hip adductors (8.4%, p = 0.003) and in the radiological density in gluteus maximus (10.1 Hounsfield units; p < 0.001), gluteus medius/minimus (5.6 Hounsfield units; p = 0.011), iliopsoas (3.9 Hounsfield units; p < 0.001) and the adductors (2.4 Hounsfield units; p = 0.022). Thus, there was persistent muscle atrophy in muscles acting about the hip two years after THR. We suggest that an earlier operation or a more intensive rehabilitation may reverse these changes.

Signal intensity of MR-images of thigh muscles following acute open- and closed chain kinetic knee extensor exercise - index of muscle use.

Exercise-induced shifts in signal intensity (SI) of magnetic resonance (MR) images were examined to assess indirectly muscle use in closed- and open-chain knee extensor exercises. Eight men performed five sets of 8-12 repetitions in the leg press (LP) and the seated knee extension (KE) exercises at 50, 75 and 100%, respectively of the 5 x 10 repetition maximum (RM) load. Prior to exercise and after each load setting, images of the thigh were obtained. The increase in SI (Delta SI) of the quadriceps at 100% load was greater (P < 0.05) after KE (32.1 +/- 9.0%) than after LP (21.9 +/- 9.2%). Regardless of load, the four individual muscles of the quadriceps showed similar changes in SI after LP. The three vastii muscles showed comparable increases in SI after KE. M. rectus femoris showed greater (P < 0.05) Delta SI than the vastii muscles at 100%. Neither exercise produced increase in SI of mm. semimembranosus, semitendinosus, gracilis or biceps femoris. Mm. adductor magnus and longus showed increased (13.3 +/- 6.5%; P < 0.05) SI after LP, but not after KE, at 100% load. The present data also infer greater involvement of the quadriceps muscle in the open-chain knee extension than in the closed-chain leg press exercise. The results of the current investigation also indicate similar over-all use among the three vastii muscles in LP and KE, but differential m. rectus femoris use between the two exercises. This report extends the merits of the MR imaging technique as an aid to study individual muscle involvement in a particular exercise task.

Changes in muscle function in response to 10 days of lower limb unloading in humans.

Force-generating capacity and electromyographic (EMG) activity of the knee extensor muscles were studied before and after short-term (10 d) unilateral lower limb unloading and during 4 days of recovery. Ten healthy males used crutches to prevent one of their lower limbs from weight-bearing while maintaining joint mobility as well as daily ambulatory activities. Knee extensor torque and quadriceps rectified EMG during maximal voluntary isometric contraction (MVC) was measured repeatedly before and after the intervention. Also, EMG at a fixed submaximal level (100 Nm; 30-45% MVC) and maximal angular velocity (AVmax), during unresisted knee extension, were assessed. Maximum torque decreased (P < 0.05) by 13 +/- 8% in response to unloading while maximum EMG activity did not change after unloading or during recovery (P = 0.35). Submaximum EMG increased (P < 0.05) by 25 +/- 16% after unloading. Maximum and submaximum torque/EMG ratio decreased (P < 0.05) after unloading. AVmax decreased (P < 0.05) by 9 +/- 8% after unloading. The post value, however, was not different from that of the weight-bearing limb. Torque, EMG and AVmax were recovered (P > 0.05) after 4 days of resumed weight-bearing. The pronounced decrease and the rapid recovery in maximum torque appears not to be attributed to a change in muscle mass alone. Because the findings of unchanged maximum EMG and increased EMG at a submaximal force level suggest no change in neural drive, we propose that unspecific tissue factors in part impair muscle function in response to short-term loss of weight-bearing activity. Results also indicate that recovery in muscle function after short-term unloading seems to be completed in a time span shorter than the period of preceding inactivity.

Effects of spaceflight on muscle.

NASA: Studies using healthy humans in experimental models of weightlessness are reported. A unilateral lower limb unloading model is explained. Effects of unloading on muscle strength, work capacity, muscle atrophy, force-velocity characteristics of muscle, and recovery after unloading using the model are discussed. Mechanisms that explain impaired muscle function following unloading in space flight are examined. Results using hindlimb-suspended rats are compared with the human model.^ieng

Dynamic neck strength training effect on pain and function.

This study examined whether neck resistance training could increase strength and reduce pain in workers with a high prevalence of neck disorders. Middle-aged women workers (n = 17) exercised twice weekly for 8 weeks. Each session (12min) consisted of three sets of 12 repetitions of resisted rotation, flexion, and extension muscles using hydraulic dampers. Resistance was set individually and progressively increased every second week. Angle-specific maximal isometric rotator, extensor, and flexor torque was measured before and after training. Torque during rotation, flexion and extension increased (p < .05) on average 35%, 27%, and 19%, respectively, after training. Perceived pain, assessed using a four-graded scale, was reduced (p < .05) after training. It is suggested that 12 minutes of specific neck strength training twice weekly for 8 weeks increases strength of rotator, extensor, and flexor muscles of the neck. Also all individuals who had pain reported reduced perceived neck pain after training.

Changes in lower limb muscle cross-sectional area and tissue fluid volume after transition from standing to supine.

Lower limbs show acute fluid shift in response to transition from upright to supine body position. It is hypothesized that this would affect tomographic estimations of muscle mass and composition. Seven healthy subjects were investigated during the initial 120 min of bed rest, using repeated computerized tomography (CT) and continuous bioelectrical impedance analysis (BIA). Thigh and calf muscle cross-sectional area (CSA) decreased (P < 0.05) by 1.9 and 5.5% whereas fat CSA decreased (P < 0.05) by 4.1 and 4.4%, respectively. Radiological density (RD) of muscle showed a simultaneous increase (P < 0.05) by 4.8% in calf but not (P > 0.05) in thigh. No changes occurred (P > 0.05) in muscle or fat CSA or muscle RD in either thigh or calf between the first and second hour of bed rest. Fluid shift, as estimated by BIA, showed an exponential decay in thigh (tau th = 30 min) and calf (tau c2 = 37 min) by 2.5 and 8.7%, respectively, from first to 120 min of bed rest. Moreover, the calf showed an initial rapid (tau c1 = 8 s) 2.2% decrease. The demonstrated short-term changes in leg CSA were more pronounced in the calf than in the thigh. They were similar in muscle and subcutaneous fat. These fluid shifts merit consideration when tomographic imaging techniques are used to estimate muscle mass and composition.