Article

KNEE BIOMECHANICS AND PHYSICAL PERFORMANCE; AN ACL-RECONSTRUCTED ATHLETE BEFORE AND AFTER ISOKINETIC STRENGTH TRAINING

Authors:
  • Pakistan Sports Board Islamabad
To read the full-text of this research, you can request a copy directly from the author.

Abstract

Introduction: A 29-year old male athlete (body mass: 64 kg; height: 172 cm)sustained complete ACL rupture of the right knee. He was a martial-arts player and the injurywas repetitive, overuse in nature due to cyclic unilateral loading and unloading of the rightknee during training sessions. Rupture was diagnosed through detailed patient history, clinicalphysical examination and was confirmed through magnetic resonance imaging (MRI) of theright knee. Surgical reconstruction of the ACL was planned and a patellar tendon graft wasused. His baseline isokinetic data was recorded 4 months after the surgery. Objective: Thiscase study describes the effects of isokinetic strength training on knee biomechanics andphysical function of an ACL-reconstructed martial-arts athlete. Setting: Pakistan Sports BoardIslamabad. Study period: 40 days. Materials and Methods: Biodex System 3 Pro was used totrain the athlete for 15 sessions on alternate day basis. Average peak torque, average power,total work and peak torque to body weight ratio were recorded for hamstring and quadricepsbefore and after isokinetic rehabilitation. The athlete was positioned in the dynamometer withupright back while hip and knee were flexed to 90 degrees. Unilateral isokinetic contractionswere performed according to a premeditated exercise protocol. Both hamstring and quadricepswere tested isokinetically at five different movement speeds (30deg/sec, 90deg/sec, 150deg/sec, 210deg/sec, and 270deg/sec). Five contractions were performed at each speed duringboth knee flexion and extension. At baseline, average peak torque was higher at lower speedsfor both hamstring and quadriceps. Results: As a result of rehabilitation, average peak torquefor hamstring and quadriceps significantly improved at speeds of 150deg/sec and 90deg/secrespectively. Average power, peak torque to body weight ratio, total work was also improved forboth hamstring and quadriceps. Two physical performance tests - agility run test and verticaljump test - were used to assess the effects of training and both performance tests improved 51%and 100% respectively. Conclusion: Isokinetic training improved the strength of quadricepsand hamstring after ACL reconstruction. Hamstring muscle demonstrated greater traininginducedincrements in torque production compared to quadriceps at all contraction velocities.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

Article
Full-text available
Introducción. Múltiples estudios de procesamiento de señales han reportado la aplicación de las señales de electromiografía de superficie (sEMG) en robótica y en procesos de rehabilitación motora. Objetivo. Realizar una revisión de la literatura sobre el uso de señales de sEMG como alternativa para la estimación del par de rodilla con el fin de medir objetivamente el progreso de los pacientes en las diferentes etapas de rehabilitación de lesiones de rodilla. Materiales y métodos. Se realizó una revisión de la literatura publicada entre 1986 y 2018, sin límites geográficos, en las bases de datos Engineering Village, IEEE Xplore, ScienceDirect, Web of Science, Scopus y PubMed mediante la combinación de 8 términos de búsqueda. Resultados. Al finalizar la búsqueda inicial se obtuvieron 355 registros. Luego de realizar la remoción de duplicados esta cifra descendió a 308, los cuales fueron analizados para determinar si cumplían con los criterios de inclusión. Finalmente se incluyeron 18 estudios que describen de forma comparativa cómo estimar el par a partir de señales de sEMG. Conclusión. El uso de señales de sEMG para calcular el par en una articulación es una herramienta alternativa que permite al terapeuta acceder a parámetros cuantitativos y, de esta forma, valorar el progreso de los pacientes durante el proceso de rehabilitación de rodilla.
Article
Full-text available
BACKGROUND: Kinesiotaping (KT) has become popular among athletic trainers and physical therapists. Most of KT studies investigated only the immediate responses, and only a few evaluated the long-term effects. OBJECTIVES: To evaluate the effects of 48 hours of KT on knee extensor performance of healthy subjects during isokinetic exercise at different muscle action velocities. METHODS: Twenty six healthy men were enrolled and the study presented a drop-out rate of 19%. Participants were randomly allocated to one of two intervention groups: 1. KT with the tape applied for activation of rectus femoris with 40% tension 2. Control (CO) with the tape applied on rectus femoris without tension. Measurements were collected at baseline (BL) without KT, immediately (T0) post KT application, and 24 h (T24) and 48 h (T48) after KT application. The main outcome measures were Knee extension peak torque (PT), load range (LR) and time to reach the PT (TPT). RESULTS: There were no significant differences between KT and CO for PT, LR or TPT at 60 or 240°/s, and no significant differences on time (BL, IMD, 24 h and 48 h) for both groups. CONCLUSION: Kinesiotaping did not enhance knee extensor neuromuscular performance of healthy men at different muscle action velocities. An important finding was that the continued use of the Kinesiotaping (48 h) did not influence muscle performance.
Article
Full-text available
Numerous rehab protocols have been used in rehabilitation after ACL reconstruction. Isokinetic testing is an objective way to evaluate dynamic stability of the knee joint that estimates the quality of rehabilitation outcome after ACL reconstruction. Our investigation goal was to show importance of isokinetic testing in evaluation thigh muscle strength in patients which underwent ACL reconstruction and rehabilitation protocol. In prospective study, we evaluated 40 subjects which were divided into two groups. Experimental group consisted of 20 recreational males which underwent ACL reconstruction with hamstring tendon and rehabilitation protocol 6 months before isokinetic testing. Control group (20 subjects) consisted of healthy recreational males. In all subjects knee muscle testing was performed on a Biodex System 4 Pro isokinetic dynamo-meter et velocities of 60°/s and 180°/s. We followed average peak torque to body weight (PT/BW) and classic H/Q ratio. In statistical analysis Student's T test was used. There were statistically significant differences between groups in all evaluated parameters except of the mean value of PT/BW of the quadriceps et velocity of 60°/s (p>0.05). Isokinetic testing of dynamic stabilizers of the knee is need in diagnostic and treatment thigh muscle imbalance. We believe that isokinetic testing is an objective parameter for return to sport activities after ACL reconstruction.
Article
Full-text available
The purpose of this article is to present recommendations for new muscle strength and hop performance criteria prior to a return to sports after anterior cruciate ligament (ACL) reconstruction. A search was made of relevant literature relating to muscle function, self-reported questionnaires on symptoms, function and knee-related quality of life, as well as the rate of re-injury, the rate of return to sports and the development of osteoarthritis after ACL reconstruction. The literature was reviewed and discussed by the European Board of Sports Rehabilitation in order to reach consensus on criteria for muscle strength and hop performance prior to a return to sports. The majority of athletes that sustain an (ACL) injury do not successfully return to their pre-injury sport, even though most athletes achieve what is considered to be acceptable muscle function. On self-reported questionnaires, the athletes report high ratings for fear of re-injury, low ratings for their knee function during sports and low ratings for their knee-related quality of life. The conclusion is that the muscle function tests that are commonly used are not demanding enough or not sensitive enough to identify differences between injured and non-injured sides. Recommendations for new criteria are given for the sports medicine community to consider, before allowing an athlete to return to sports after an ACL reconstruction.
Article
Full-text available
An athlete's intention to return to sport following anterior cruciate ligament (ACL) injury is a major indication for surgical intervention. The purpose of this review was to determine postoperative return-to-sport outcomes after ACL reconstruction surgery. Meta-analysis and systematic review Electronic databases including Medline, Embase, SPORTDiscus and CINAHL were searched from the earliest possible entry to April 2010. Studies were included that reported the number of patients returning to sports participation following ACL reconstruction surgery. The results were presented using the World Health Organization's International Classification of Functioning, Disability and Health as a framework and combined using proportion meta-analyses. Forty-eight studies evaluating 5770 participants at a mean follow-up of 41.5 months were included for review. Overall, 82% of participants had returned to some kind of sports participation, 63% had returned to their preinjury level of participation, and 44% had returned to competitive sport at final follow-up. Approximately 90% of participants achieved normal or nearly normal knee function when assessed postoperatively using impairment-based outcomes such as laxity and strength, and 85% when using activity-based outcomes such as the International Knee Documentation Committee knee evaluation form. Fear of reinjury was the most common reason cited for a postoperative reduction in or cessation of sports participation. The relatively low rate of return to competitive sport despite the high rates of successful outcome in terms of knee impairment-based function suggests that other factors such as psychological factors may be contributing to return-to-sport outcomes.
Article
Full-text available
The ability to maximally generate active muscle tension during resistance training has been established to be a primary determinant for strength development. The influence of intrasession rest intervals may have a profound effect on strength gains subsequent to short-term high intensity training. The purpose of this study was to examine the effects of rest interval on strength and functional performance after four weeks of isokinetic training. Fifteen healthy college aged individuals were randomly assigned to either a short rest interval group (group 1, n = 8) or a long rest interval group (group 2, n = 7). Subjects were evaluated for quadriceps and hamstring isokinetic strength at 60 (five repetitions) and 180 (30 repetitions) degrees/second and functional performance with the single leg hop for distance test. One leg of each subject was randomly assigned to a four week, three days/week isokinetic strength training programme for concentric knee extension and flexion performed at 90 degrees/second. Subjects in group 1 received a 40 second rest interval in between exercise sets, whereas subjects in group 2 received a 160 second rest period. A two factor analysis of variance for the pre-test--post-test gain scores (%) showed significantly greater improvements for isokinetic hamstring total work and average power at 180 degrees/second for the trained limb of subjects in group 2 than their contralateral non-trained limb and the subjects in group 1. Significantly greater improvements for the single leg hop for distance were also found for the trained limbs of subjects in both groups as compared with the non-trained limbs. The findings indicate that a relatively longer intrasession rest period resulted in a greater improvement in hamstring muscle strength during short term high intensity training.
Article
Full-text available
Single-group, repeated-measures prospective study. To analyze changes in impairments and disabilities among patients with anterior cruciate ligament (ACL) reconstruction and to assess the relationships between the impairment and disability outcome measures from 3 months to 2 years following ACL reconstruction. Outcomes after ACL reconstruction can be categorized as impairments or disabilities. The relationship between impairments and disabilities may be crucial to understanding physical therapy interventions and predicting long-term outcome. Sixty patients who had undergone ACL reconstruction participated in the study. Impairment measures were range of motion, pain, knee-joint laxity, and muscle performance using isokinetic muscle tests. Disability measures were the Cincinnati knee score and lower limb performance using the triple-jump and stair-hop tests. Follow-up times were 3 and 6 months and 1 and 2 years after surgery. The Cincinnati knee score results show significant improvement 1 year after surgery (84.2 +/- 13.6) compared with 6 months (76.8 +/- 13.7) and 3 months (67.4 +/- 16.3) after surgery. Quadriceps total work (percentage of normal leg) significantly improved 2 years after surgery (92.6 +/- 14.1%) compared with 1 year after surgery (81.6 +/- 16.8%). Between 37 and 75% of the variability in the Cincinnati knee score could be explained by variation in the impairment variables, and quadriceps muscle performance and pain were the most significant predictors of disability. Extension deficit and pain at 3 months were significantly related to the Cincinnati knee score at the 2-year follow-up. Up to 2 years may be needed to regain normal quadriceps muscle performance following ACL reconstruction. Pain and quadriceps muscle performance explained most of the variability in the Cincinnati knee score.
Article
Full-text available
Rehabilitation of patients with anterior cruciate ligament injury is a topic of interest among clinicians. Although numerous studies report the deficits after anterior cruciate ligament reconstruction, there are no data available on the changes in strength and functional performance before and 6 months after reconstruction surgery. This is when most patients are returning to sports activities. In the current study 31 patients with complete unilateral anterior cruciate ligament ruptures followed a controlled rehabilitation program emphasizing early range of motion after surgery and quadriceps strengthening before and after undergoing bone-patellar tendon-bone reconstruction. Strength of the hamstrings and quadriceps and five functional activities were assessed at 1 week before and 6 months after surgery. Preoperative strength assessments using a Cybex II dynamometer showed a 12% quadriceps deficit at 60 degrees per second and 9% deficit at 120 degrees per second with no hamstring deficit in the injured leg compared with the uninjured leg. Despite intensive quadriceps training, the postoperative quadriceps deficit increased to 28% at 60 degrees per second and 22% at 120 degrees per second in comparison with the uninjured leg. There was no change in hamstring strength in the injured leg. Most functional measures improved after surgery. The shuttle run improved by 10%, the side step test results improved by 17%, and the carioca test results improved by 23%. No significant difference was found in the results of the hop test. This study highlights the extent of the quadriceps deficits despite functional improvement and the difficulty in restoring quadriceps strength after bone-patellar tendon-bone reconstruction. It also questions the relationship of current functional tests to quadriceps strength and the role of maximum strength testing as a predictor of function and of safe sporting performance.
Article
Full-text available
The loss of full muscle activation contributes to weakness of the quadriceps muscle in patients with deficiency of the anterior cruciate ligament (ACL). We examined whether a deficit of voluntary activation (VA) of the quadriceps muscle can be reversed by reconstruction of the ACL and assessed its influence on muscle strength and clinical parameters. We evaluated 12 male subjects with an isolated tear of the ACL and 12 matched control subjects before operation and two years after reconstruction of the ACL. Assessment included measurements of isometric knee-extension torque at maximal voluntary contraction (MVC force), knee stability tests, the International Knee Ligament Standard Evaluation Form and the Tegner activity score. A sensitive method of twitch interpolation was used to quantify the VA and to calculate true muscle force. Before operation we found a deficit of VA on both the injured (mean +/- SEM 74.9 +/- 3.5%) and the uninjured side (74.6 +/- 3.0%) in comparison with the control group (91 +/- 0.9%). Two years after reconstruction of the ACL the VA improved significantly on both sides but remained less than that of the controls. Correlation analysis revealed an improvement of the VA in patients who returned to a higher level of activity. The deficit of true muscle force, however, persisted regardless of the clinical outcome and ligament stability.
Article
Full-text available
The present study assessed the reliability and validity of isokinetic dynamometry in the qualitative determination of the evolution of total knee arthroplasty. Cases: 20 patients whose mean age was 71.35 years, undergoing knee arthroplasty, and 25 controls whose mean age was 71.36 years. Computerized isokinetic assessment of flexor and extensor muscles using a CYBEX 6000 dynamometer. The total flexor/extensor effort ratio for the treated side of patients vs the nondominant side of controls was not significantly different. The flexion/extension ratio concerning maximum torque for the treated side of patients vs the nondominant side of controls was significantly different. By detecting deficiencies in the balance of flexor and extensor muscles (a balance that is required for uniform gait), it will be possible to select specific rehabilitation exercises according to the individual needs of each patient undergoing surgery.
Article
Full-text available
Women participated in 5 months of unilateral concentric (n = 37) or eccentric (n = 33) isokinetic resistance training of the legs and arms. Limb muscular strength increased as did total body, leg, and arm fat-free soft tissue mass, total body BMC, hip BMD, and forearm BMC and BMD. Isokinetic training benefits bone mineral acquisition. Isokinetic resistance training (IRT) is osteogenic; however, it is not known if concentric or eccentric modalities of IRT produce differential effects on bone. We tested our hypothesis that high-load eccentric versus concentric mode of IRT would produce greater increases in muscular strength, fat-free soft tissue mass (FFSTM), bone mineral density (BMD) and content (BMC) in trained legs and arms. Participants were randomized to 5 months of concentric (n = 37) or eccentric (n = 33) training. The non-dominant leg and arm were used during training; dominant limbs served as controls. Muscular strength was measured with an isokinetic dynamometer; body composition was measured by dual-energy X-ray absorptiometry. Muscular strength of the concentrically and eccentrically trained leg (18.6%; 28.9%) and arm (12.5%; 24.6%) significantly increased with training. Gains in total body (TB) BMC (p < 0.05) and, in the trained limbs, total proximal femur BMD (p < 0.05) and total forearm BMD (p < 0.05) and BMC (p < 0.05) occurred in both groups. FFSTM increased for the TB and trained leg and arm (all p < 0.001) in both modes. Regardless of the mode, high-intensity, slow-velocity IRT increases muscular strength and FFSTM of trained limbs and imparts benefits to TB BMC and site-specific BMD and BMC in young women.
Article
The aim of this systematic review was to determine which patient determinants and injury factors, before anterior cruciate ligament reconstruction by arthroscopic single-bundle techniques, affect postoperative rehabilitation. A search of PubMed, Embase, and the Cochrane Database of Clinical Trials was performed up to February 2013. After application of our inclusion criteria, a final selection was made based on studies' methodologic score assessed with the Newcastle-Ottawa Scale. Meta-analysis was planned for each prognostic factor when data were considered clinically and statistically homogeneous. Meta-analysis showed that male patients have better functional outcomes. Qualitative synthesis from 18 high-quality studies showed that patients operated on before 30 years of age reach higher activity levels. Patients with high baseline body mass index have lower activity levels after surgery. Smoking results in more symptoms and lower activity levels and subjective scores. Reconstruction before 3 months results in higher activity levels. Preoperatively, a less than 20% quadriceps strength difference, 50° of tibial external rotation or less, absence of flexion deficits, low knee influence on the patient's activity level, and less anterior knee pain result in higher functional scores. Preoperative anterior laxity difference does not predict functional scores. The prognostic value of preoperative activity and competition level for postoperative functional outcome is controversial. Patients with concomitant meniscal injuries have worse functional outcomes. The prognostic value of concomitant chondral pathology for postoperative functional outcome is controversial. Collateral ligament injury could predict functional scores or activity level. Male gender, patient age younger than 30 years, reconstruction before 3 months, and high baseline activity level contribute to better functional outcomes. Smoking, high body mass index, quadriceps strength, and range-of-motion deficits affect rehabilitation negatively. Preoperative anterior laxity does not influence rehabilitation. The role of preoperative prognostic injury factors remains unclear because of limited evidence. Level III, systematic review of Level II and III studies.
Article
Progressive strength training was performed 3 times a week for 8 weeks by 14 male students (19-31 yrs.). The training program consisted mainly of dynamic exercises for the leg extensors with maximal or close to maximal loads. The training caused significant improvements in dynamic and isometric strength. One repetition maximum in squats increased with 67%, Sargent jump with 22%, and maximal voluntary isometric contraction (MVC) with 13%, respectively. Body weight and leg muscle circumferences remained unchanged after training, whereas total body potassium, lean body mass and calculated total muscle mass increased, suggesting a change in body composition with training. Muscle biopsies were obtained from vastus lateralis for fibre analyses and determination of enzyme activities. There were no changes in muscle fibre composition or fibre area with training. The activities of Mg2+ stimulated ATPase, creatine phosphokinase and phosphofructokinase remained unchanged, whereas myokinase activity was increased after training from (1.41 to 1.52 moles x 10(-4) x g-1 x min-1, p less than 0.05). After training significant correlations (p less than 0.01) were demonstrated between Mg2+ stimulated ATPase activity and % fast twitch fibres (% FT) (r = 0.67), as well as between myokinase activity and % FT (r = 0.86).
Article
The effects of strength training of the quadriceps on peak power output during isokinetic cycling has been investigated in group of 17 young healthy volunteers. Subjects trained by lifting near-maximal loads on a leg extension machine for 12 weeks. Measurements of maximal voluntary isometric force were made at 2-3 week intervals and a continual record was kept of the weights lifted in training. Peak power output was measured at 110 rev min-1 and at either 70 or 80 rev min-1 before and after the 12 week training period. Measurements of maximum oxygen uptake (VO2max) were made on 12 subjects before and after training. The greatest change was in the weights lifted in training which increased by 160-200%. This was accompanied by a much smaller increase in maximum isometric force (3-20%). There was no significant change in peak power output at either speed. The VO2max remained unchanged with training. The role of task specificity in training is discussed in relation to training regimes for power athletes and for rehabilitation of patients with muscle weakness.
Article
The long rehabilitation period of 6 to 12 months following a major sport injury depends to a large extent on the time it takes to regain normal muscle function. In this review, rehabilitation after major joint injuries, such as knee injuries, are discussed. Rehabilitation after 'overuse injuries' will not be covered.
Article
The time course of strength gain with respect to the contributions of neural factors and hypertrophy was studied in five young men and five older men during the course of 8 weeks progressive strength training. Young and old men showed similar and significant percentage increases in strength. However, the neurophysiological adaptations in response to the training were quite different, increases in maximal muscle activation (neural factors) played a dominant role throughout the training for old subjects, while young subjects showed strength gains due to neural factors only at the initial stage, with hypertrophy becoming the dominant factor after some 4 weeks of training. Our data suggest that the effect of muscle training in the old may entirely rest on the neural factors presumably acting at various levels of the nervous system which could result in increasing the maximal muscle activation level in the absence of significant hypertrophy.
Article
We studied patients who participated in our accelerated rehabilitation program after anterior cruciate ligament reconstructive surgery to determine if they showed signs of patellar tendon graft stretching. This program initiated in 1987 emphasizes early full hyperextension, early weightbearing as tolerated, and closed-chain functional activities with rapid return to sports when the patient has attained full range of motion, approximately 65% of strength, and has accomplished the running and agility drills prescribed. A total of 209 patients met the criteria of KT-1000 arthrometer followup at the time full range of motion (5 degrees/0 degrees/135 degrees) was attained and at 2 years or more after surgery. The KT-1000 arthrometer manual maximum difference between the reconstructed and normal knees was used as the indicator of change in the graft length. All patients completed postoperative subjective questionnaires. The mean KT-1000 arthrometer value was 2.06 mm (SD, +/- 2.2) at full range of motion and 2.10 mm (SD, +/- 1.9) at more than 2 years of followup (P = 0.7961). The patients' subjective stability scores averaged 19.6 with 97% reporting no instability episodes. Based on our findings, we conclude that an accelerated rehabilitation program after this type of reconstruction does not affect long-term stability as measured by the KT-1000 arthrometer.
Article
The influence of muscle series elasticity on the relationship between torque and joint angle during dynamic contractions was studied. The torque-angle relationship during the maximal isokinetic knee extension was determined for six male subjects (25-45 years) at 0.52, 1.05, 1.57, 2.09, 2.62, 3.49 rad/s. The knee joint angle at which peak torque was observed showed a systematic shift to more extended positions, i.e., the quadriceps muscle-tendon unit length became shorter as the velocity increased [from 1.01 (0.12) rad (0.52 rad/s) to 0.75 (0.14) rad (3.49 rad/s), mean (SD)]. The corresponding difference in muscle-tendon unit length between 0.52 and 3.49 rad/s, estimated from the angle shift at peak torque and the moment arm length change of the quadriceps muscles, was 9 (4) mm. The relationship between estimated changes in muscle-tendon unit length and muscle force of the vastus lateralis and intermedius (VLI) over the seven velocities (including isometric contraction, 0 rad/s) coincided with the load-elongation properties of the series elastic component of VLI, determined separately in vivo by ultrasonography when the same subjects performed a ramp isometric knee extension. The results suggest that the torque-angle relationship is affected by the interaction between contractile and elastic components, and that peak torque angle shift is attributable to the elongation of tendinous tissues as a function of force applied to them.
Article
To investigate the therapeutic effects of different muscle-strengthening exercises on the functional status of patients with knee osteoarthritis (OA). One hundred thirty-two patients with bilateral knee OA (Altman Grade II) were sequentially divided into 4 random groups (GI to GIV). The patients in group I received isokinetic muscle-strengthening exercise, group II received isotonic muscle-strengthening exercise, group III received isometric muscle-strengthening exercise, and group IV acted as controls. The changes of muscle power of leg flexion and extension were measured with a Kinetic Communicator dynamometer, and patients' functional status was evaluated by visual analogue scale, ambulation speed, and Lequesne index before and after treatment, and at the follow-up 1 year later. The results showed that the patients with OA in each treated group had significant improvement in pain reduction, disability reduction, and in walking speed after treatment and at follow-up when compared with their initial status. Isotonic exercise had the greatest effect on pain reduction after treatment, and fewer participants discontinued the treatment because of exercise knee pain. Isokinetic exercise caused the greatest increase of walking speed and decrease of disability after treatment and at follow-up. The greatest muscle-strength gain in 60 degrees /second angular velocity peak torques was found in the isokinetic and isotonic exercise groups. A significant muscle-strength gain in 180 degrees /second angular velocity peak torques was found only in the isokinetic group after treatment. CONCLUSION AND RELEVANCE: Isotonic exercise is suggested for initial strengthening in patients with OA with exercise knee pain, and isokinetic exercise is suggested for improving joint stability or walking endurance at a later time.
The ACL Solution: Prevention and Recovery for Sports' Most Devastating Knee Injury
  • R G Marx
  • G Myklebust
Marx RG, Myklebust G. The ACL Solution: Prevention and Recovery for Sports' Most Devastating Knee Injury. Demos Medical Publishing; 2012 Jun 19.