Per Renström

Strain within the anterior cruciate ligament during hamstring and quadriceps activity

The objectives of this study were to measure strain in the ACL during simulated: (1) hamstring activity alone, (2) quadriceps activity alone, and (3) simultaneous quadriceps and hamstring activity. Seven knee speci mens removed from cadavers were studied. Heavy sutures applied to load cells were attached to the hamstring and quadriceps tendons. Loads were then applied manually (hamstrings) and/or with an Instron testing machine (quadriceps) to simulate isometric con tractions of the various muscle groups. Strain was measured using a Hall effect transducer. Acting alone, the isometric hamstring activity decreased ACL strain relative to the passive normal strain at all positions tested. Thus, hamstring exercises are not detrimental to ACL repairs or reconstruction and can be included early in the rehabilitation program after ACL surgery. Acting alone, at flexion angles of 0° to 45°, the quad riceps significantly increased the strain within the ACL relative to the passive normal strain. Strain in the ACL during simultaneous hamstring and quadriceps activity was significantly higher than that during passive normal motion from full extension to 30° of flexion. The ham strings are not capable of masking the potentially harm ful effects of simultaneous quadriceps contraction on freshly repaired or reconstructed ACLs unless the knee flexion angle exceeds 30°.

Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement

The incidence of anterior cruciate ligament (ACL) injury remains high in young athletes. Because female athletes have a much higher incidence of ACL injuries in sports such as basketball and team handball than male athletes, the IOC Medical Commission invited a multidisciplinary group of ACL expert clinicians and scientists to (1) review current evidence including data from the new Scandinavian ACL registries; (2) critically evaluate high-quality studies of injury mechanics; (3) consider the key elements of successful prevention programmes; (4) summarise clinical management including surgery and conservative management; and (5) identify areas for further research. Risk factors for female athletes suffering ACL injury include: (1) being in the preovulatory phase of the menstrual cycle compared with the postovulatory phase; (2) having decreased intercondylar notch width on plain radiography; and (3) developing increased knee abduction moment (a valgus intersegmental torque) during impact on landing. Well-designed injury prevention programmes reduce the risk of ACL for athletes, particularly women. These programmes attempt to alter dynamic loading of the tibiofemoral joint through neuromuscular and proprioceptive training. They emphasise proper landing and cutting techniques. This includes landing softly on the forefoot and rolling back to the rearfoot, engaging knee and hip flexion and, where possible, landing on two feet. Players are trained to avoid excessive dynamic valgus of the knee and to focus on the “knee over toe position” when cutting.

Anterior Cruciate Ligament Strain Behavior During Rehabilitation Exercises In Vivo

Before studying the biomechanical effects of rehabili tation exercises on the reconstructed knee, it is impor tant to understand their effects on the normal anterior cruciate ligament. The objective of this investigation was to measure the strain behavior of this ligament dur ing rehabilitation activities in vivo. Participants were pa tient volunteers with normal anterior cruciate ligaments instrumented with the Hall effect transducer. At 10° and 20° of flexion, ligament strain values for active exten sion of the knee with a weight of 45 N applied to a sub jects lower leg were significantly greater than active motion without the weight. Isometric quadriceps muscle contraction at 15° and 30° also produced a significant increase in ligament strain, while at 60° and 90° of knee flexion there was no change in ligament strain relative to relaxed muscle condition. Simultaneous quadriceps and hamstrings muscles contraction at 15° produced a significant increase in ligament strain compared with the relaxed state but did not strain the ligament at 30°, 60°, and 90° of flexion. Isometric contraction of hamstrings muscles did not produce change in ligament strain at any flexion angle. Exercises that produce low or un strained ligament values, and would not endanger a properly implanted graft, are either dominated by the hamstrings muscle (isometric hamstring), involve quad riceps muscle activity with the knee flexed at 60° or greater (isometric quadriceps, simultaneous quadri ceps and hamstrings contraction), or involve active knee motion between 35° and 90° of flexion.

A Prospective Study of Ankle Injury Risk Factors

Many factors are thought to cause ankle ligament in juries. The purpose of this study was to examine injury risk factors prospectively and determine if an abnor mality in any one or a combination of factors identifies an individual, or an ankle, at risk for subsequent inver sion ankle injury. We examined 145 college-aged ath letes before the athletic season and measured gener alized joint laxity, anatomic foot and ankle alignment, ankle ligament stability, and isokinetic strength. These athletes were monitored throughout the season. Fifteen athletes incurred inversion ankle injuries. Statistical analyses were performed using both within-group (un injured versus injured groups) data and within-subject (injured versus uninjured ankles) data. No significant differences were found between the injured (N = 15) and uninjured (N = 130) groups in any of the param eters measured. However, the eversion-to-inversion strength ratio was significantly greater for the injured group compared with the uninjured group. Analysis of the within-subject data demonstrated that plantar flex ion strength and the ratio of dorsiflexion to plantar flex ion strength was significantly different for the injured ankle compared with the contralateral uninjured ankle. Individuals with a muscle strength imbalance as meas ured by an elevated eversion-to-inversion ratio exhib ited a higher incidence of inversion ankle sprains. Ankles with greater plantar flexion strength and a smaller dorsiflexion-to-plantar flexion ratio also had a higher incidence of inversion ankle sprains.

Anterior cruciate ligament replacement: comparison of bone-patellar tendon-bone grafts with two-strand hamstring grafts. A prospective, randomized study.

Background: The purpose of this investigation was to evaluate replacement of a torn anterior cruciate ligament with either a bone-patellar tendon-bone autograft or a two-strand semitendinosus-gracilis autograft to compare the results of clinical testing, patient satisfaction, activity level, functional status, and muscle strength.Methods: Fifty-six patients with a torn anterior cruciate ligament were enrolled in a prospective, randomized, controlled study. Twenty-eight underwent reconstruction with a bone-patellar tendon-bone autograft, and twenty-eight were treated with a two-strand semitendinosus-gracilis autograft. Patients were followed for an average of thirty-nine months (range, thirty-six to fifty-seven months). At the time of final follow-up, twenty-two patients in each group were evaluated in terms of clinical test findings, patient satisfaction, activity level, functional status, and isokinetic muscle strength.Results: The objective outcome of replacement of the torn anterior cruciate ligament with a bone-patellar tendon-bone graft was superior to that obtained with a two-strand semitendinosus-gracilis graft. At the three-year follow-up interval, the patients in whom a hamstring graft had been used had an average of 4.4 mm of increased anterior knee laxity compared with the laxity of the contralateral, normal knee, whereas the patients in whom a bone-patellar tendon-bone graft had been used had an average of 1.1 mm of increased knee laxity. Fourteen percent (three) of the twenty-two patients with a hamstring graft had a mild pivot shift, and 27% (six) had a moderate pivot shift. Only 14% (three) of the twenty-two patients with a bone-patellar tendon-bone graft had a mild pivot shift, and none had a moderate pivot shift. At the same follow-up interval, the patients in whom a hamstring graft had been used had significantly lower peak knee-flexion strength than those who had a bone-patellar tendon-bone graft (p = 0.039). In contrast, the two treatments produced similar outcomes in terms of patient satisfaction, activity level, and knee function (ability to perform a one-legged hop, bear weight, squat, climb stairs, run in place, and duckwalk).Conclusions: After three years of follow-up, the objective results of anterior cruciate ligament replacement with a bone-patellar tendon-bone autograft were superior to those of replacement with a two-strand semitendinosus-gracilis graft with regard to knee laxity, pivot-shift grade, and strength of the knee flexor muscles. However, the two groups had comparable results in terms of patient satisfaction, activity level, and knee function.

The treatment of injuries of the anterior cruciate ligament.

The treatment of injuries of the anterior cruciate ligament. R Johnson;B Beynnon;C Nichols;P Renstrom; The Journal of Bone & Joint Surgery

Sports injuries during the Summer Olympic Games 2008.

Background Standardized assessment of sports injuries provides important epidemiological information and also directions for injury prevention. Purpose To analyze the frequency, characteristics, and causes of injuries incurred during the Summer Olympic Games 2008. Study Design Descriptive epidemiology study. Methods The chief physicians and/or chief medical officers of the national teams were asked to report daily all injuries newly incurred during the Olympic Games on a standardized injury report form. In addition, injuries were reported daily by the physicians at the medical stations at the different Olympic venues and at the polyclinic in the Olympic Village. Results Physicians and/or therapists of 92 national teams covering 88% of the 10 977 registered athletes took part in the study. In total, 1055 injuries were reported, resulting in an incidence of 96.1 injuries per 1000 registered athletes. Half of the injuries (49.6%) were expected to prevent the athlete from participating in competition or training. The most prevalent diagnoses were ankle sprains and thigh strains. The majority (72.5%) of injuries were incurred in competition. One third of the injuries were caused by contact with another athlete, followed by overuse (22%) and noncontact incidences (20%). Injuries were reported from all sports, but their incidence and characteristics varied substantially. In relation to the number of registered athletes, the risk of incurring an injury was highest in soccer, taekwondo, hockey, handball, weightlifting, and boxing (all ≥15% of the athletes) and lowest for sailing, canoeing/kayaking, rowing, synchronized swimming, diving, fencing, and swimming. Conclusion The data indicate that the injury surveillance system covered almost all of the participating athletes, and the results highlight areas of high risk for sport injury such as the in-competition period, the ankle and thigh, and specific sports. The identification of these factors should stimulate future research and subsequent policy change to prevent injury in elite athletes.

The effect of weightbearing and external loading on anterior cruciate ligament strain

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anterior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing conditions. Our objective was to compare the ACL strain response under weightbearing and non-weightbearing conditions and in combination with three externally applied loadings: (1) anterior-posterior shear forces, (2) internal-external torques, and (3) varus-valgus moments. A strain transducer was implanted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20 degrees of flexion. A significant increase in ACL strain was observed as the knee made the transition from non-weightbearing to weightbearing. During anterior shear loading, the strain values produced during weightbearing were greater than those of the non-weightbearing knee (shear loads <40N). At higher shear loads, the strain values became equal. During axial torsion, an internal torque of 10Nm strained the ACL when the knee was non-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbearing with the application of external torques and low internal torques (<3Nm). The strains became equal for higher internal torques. For V-V loading, the ACL was not strained in the non-weightbearing knee. However, weightbearing increased the ACL strain values over the range of moments tested. These data have important clinical ramifications in the development of rehabilitation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft.

Ankle ligament injury risk factors: a prospective study of college athletes

Over two million individuals suffer ankle ligament trauma each year in the United States, more than half of these injuries are severe ligament sprains; however, very little is known about the factors that predispose individuals to these injuries. The purpose of this study was to determine the risk factors associated with ankle injury. We performed a prospective study of 118 Division I collegiate athletes who participated in soccer, lacrosse, or field hockey. Prior to the start of the athletic season, potential ankle injury risk factors were measured, subjects were monitored during the athletic season, and injuries documented. The number of ankle injuries per 1000 person‐days of exposure to sports was 1.6 for the men and 2.2 for the women. There were 13 injuries among the 68 women (19%) and seven injuries among the 50 men (13%), but these proportions were not significantly different. Women who played soccer had a higher incidence of ankle injury than those who played field hockey or lacrosse. Among men, there was no relationship between type of sport and incidence of injury. Factors associated with ankle ligament injury differ for men relative to women. Women with increased tibial varum and calcaneal eversion range of motion are at greater risk of suffering ankle ligament trauma, while men with increased talar tilt are at greater risk. Generalized joint laxity, strength, postural stability, and muscle reaction time were unrelated to injury.

The Strain Behavior of the Anterior Cruciate Ligament During Squatting and Active Flexion-Extension A Comparison of an Open and a Closed Kinetic Chain Exercise

The effects of weightbearing (closed kinetic chain) and nonweightbearing (open kinetic chain) exercises on the biomechanical behavior of an injured anterior cru ciate ligament or a healing anterior cruciate ligament graft are unknown. To understand the effects of these exercises on the healing graft, we measured the strain behavior of the normal anterior cruciate ligament in human subjects while they performed squatting, a closed kinetic chain exercise, and active flexion-exten sion of the leg, an open kinetic chain exercise. The maximum anterior cruciate ligament strain values ob tained during squatting did not differ from those ob tained during active flexion-extension. Also, anterior cruciate ligament strain values obtained during squat ting were unaffected by the application of elastic resis tance intended to increase muscle activity. These find ings indicate that squatting, which produces a substantial compressive joint force, does not necessar ily protect the anterior cruciate ligament more than active flexion-extension of the leg, which is character ized primarily by contraction of the dominant quadri ceps muscle. These findings also demonstrate that increasing resistance during the squat exercise does not produce a significant increase in anterior cruciate ligament strain values, unlike increased resistance dur ing active flexion-extension exercise.