- Research article
- Open Access
- Open Peer Review
Knee kinematics and kinetics in former soccer players with a 16-year-old ACL injury – the effects of twelve weeks of knee-specific training
© von Porat et al; licensee BioMed Central Ltd. 2007
- Received: 24 October 2006
- Accepted: 17 April 2007
- Published: 17 April 2007
Training of neuromuscular control has become increasingly important and plays a major role in rehabilitation of subjects with an injury to the anterior cruciate ligament (ACL). Little is known, however, of the influence of this training on knee stiffness during loading. Increased knee stiffness occurs as a loading strategy of ACL-injured subjects and is associated with increased joint contact forces. Increased or altered joint loads contribute to the development of osteoarthritis.
The aim of the study was to determine if knee stiffness, defined by changes in knee kinetics and kinematics of gait, step activity and cross-over hop could be reduced through a knee-specific 12-week training programme.
A 3-dimensional motion analysis system (VICON) and a force plate (AMTI) were used to calculate knee kinetics and kinematics before and after 12 weeks of knee-specific training in 12 males recruited from a cohort with ACL injury 16 years earlier. Twelve uninjured males matched for age, sex, BMI and activity level served as a reference group. Self-reported patient-relevant data were obtained by the KOOS questionnaire.
There were no significant changes in knee stiffness during gait and step activity after training. For the cross-over hop, increased peak knee flexion during landing (from 44 to 48 degrees, p = 0.031) and increased internal knee extensor moment (1.28 to 1.55 Nm/kg, p = 0.017) were seen after training, indicating reduced knee stiffness. The KOOS sport and recreation score improved from 70 to 77 (p = 0.005) and was significantly correlated with the changes in knee flexion during landing for the cross-over hop (r = 0.6, p = 0.039).
Knee-specific training improved lower extremity kinetics and kinematics, indicating reduced knee stiffness during demanding hop activity. Self-reported sport and recreational function correlated positively with the biomechanical changes supporting a clinical importance of the findings. Further studies are needed to confirm these results in women and in other ACL injured populations.
- Anterior Cruciate Ligament
- Anterior Cruciate Ligament Injury
- Force Plate
- Vertical Ground Reaction Force
- Knee Stiffness
The anterior cruciate ligament (ACL) plays a major role in maintaining normal knee function. Injuries to the ACL are treated with training without surgery [1–3] or, more commonly, in combination with surgery [4–7]. The training usually emphasises normalisation of bilateral symmetries in joint mobility, neuromuscular control, muscle strength, and functional activity [8–12]. Neuromuscular training aims to enhance unconscious motor responses by stimulating both afferent signals and the central mechanisms responsible for dynamic joint control . Neuromuscular training has become increasingly important and now plays a major role in the rehabilitation of ACL injuries. Most neuromuscular training programmes include balance exercises, dynamic joint stability exercises, plyometric exercises, and sport-specific exercises including balance and jump movements. Each component of the neuromuscular rehabilitation programme should be closely monitored by the physiotherapist, with corrections and feedback to improve dynamic control of the knee. Rehabilitation programmes including neuromuscular training are more effective in achieving good knee function and knee stability than rehabilitation programmes without neuromuscular training [3, 12, 14].
To monitor joint biomechanics during performances such as gait, step activity or hopping, the use of kinetics and kinematics has increased. The most severely affected parameters, when analysing lower extremity kinetics and kinematics in ACL-injured subjects, are knee flexion angle and internal knee extensor moment [15–19]. Decreased knee flexion angle and decreased internal knee extensor moment contribute to increased knee stiffness during loading. Increased knee stiffness shifts the load from the knee to the hip, foot and ankle [19–23]. The knee stiffening strategy seen in ACL deficient subjects may reflect the early stages of motor skill acquisition since as the skills level improves, knee stiffening decreases . Increased knee stiffness, a load strategy frequently seen in ACL-injured subjects, is associated with excessive joint contact force . Excessive joint contact force, which is manifested by an increased vertical ground reaction force (VGRF), may, in turn, lead to the development of knee OA . This ought particularly to apply if the increased knee stiffness remains long after the injury and is present not only in the early stages of motor skill acquisition.
Dynamic stability of the knee joint depends on the ability to react quickly to sudden situation's changes. Functional joint instability may develop due to the lesion of mechanoreceptors in the joint capsule and ligaments in and surrounding the joint . Maintaining dynamic stability during different skills off movements is dependent on cortically programmed muscle activations and reflex-supplied muscle contractions . ACL-injured subjects have significantly slower reaction times and processing speeds than non-injured subjects  and thus neuromuscular training have the potential to improve muscular reaction time and joint position sense leading to improved knee kinetics and kinematics.
There is a lack of studies demonstrating the possible impact on lower extremity kinetics and kinematics due to training in subjects with an ACL injury.
We hypothesised that knee-specific training focusing on neuromuscular control would decrease the knee stiffness loading strategy commonly seen in these subjects. The aim of this study was therefore to determine if knee stiffness during loading, defined as changes in knee kinetics and kinematics of gait, step activity and cross-over hop, could be improved by a knee-specific 12-week supervised training programme.
Characteristics of the participants.
39 ± 6 (32–53)
40 ± 5 (32–53)
81 ± 5 (72–92)
80 ± 8 (70–100)
181 ± 4 (175–187)
182 ± 4 (173–187)
Leg-length injured leg (cm)
96 ± 3 (92–100)
95 ± 3 (87–101)
Leg-length non-injured leg (cm)
96 ± 3 (92–100)
95 ± 4 (88–103)
24.5 ± 2 (22.0–26.5)
24.5 ± 2 (22.1–30.3)
Tegner Activity level
5.5 ± 4 (3–8)
5.5 ± 3 (2–9)
Matched reference group
A previously described uninjured reference group , matched for age, BMI and activity level to the current study group, was used to determine whether any changes in kinetics and kinematics due to the intervention in the study group were in the direction of the reference group values or not. The mean age in the reference group was 39 years, Table 1. All participating subjects signed an informed consent form and the Ethics committee at the Medical Faculty, Lund University, approved the study.
Design and intervention
All ACL-injured subjects were evaluated before and after 12 weeks of knee-specific training by motion analysis, using the VICON system, during gait, step activity and cross-over hop. The subjects in the reference group were evaluated at baseline only. To monitor the possible clinical changes from the training program the Knee injury and Osteoarthritis Outcome Score (KOOS) questionnaire was used. Isokinetic strength was evaluated to help interpret if the possible biomechanical changes were due to improvement in strength from the neuromuscular exercise programme.
The home exercises were almost identical to the supervised programme. Instead of using a step board for knee bending or jumping exercises, the subjects were instructed to use a staircase, and instead of using a pulley machine during knee control exercises they used a rubber band. All subjects were instructed to perform the home exercises once or twice a week. After the 12-week training period, all the subjects self-reported compliance with the home exercises by a questionnaire.
Lightweight surface markers were attached directly to the skin of the subjects and placed on standardised anatomical landmarks according to the biomechanical model of Kadaba et al.  and Davis et al. . Marker position data were captured by a VICON 612 (OMG, Oxford, UK) system. This is a 3-dimensional passive marker motion capture system consisting of six cameras with a sampling frequency of 50 Hz, one data station and one PC on which the information is gathered and processed. Ground reaction force data were collected from one AMTI force plate (OR6-7, Advanced Mechanical Technologies). The size of the force plate was 505 × 465 mm and the sampling frequency 200 Hz. The marker positions were used, along with estimates of the joint centre locations and data from the force plate, to calculate the subject's 3-dimensional joint kinetics and kinematics. Calculation methods and model assumptions were as described [40–42]. The reliability of the kinetics and kinematics during gait and running is good [43, 44]. The reliability of kinetics and kinematics during step and hop activity has not been assessed.
Three trials of each of the following activities for the right and left sides, respectively, were performed with a three-minute break between activities; 1) free-speed walking, 2) ascending and descending a 25-cm high step (step activity), and 3) cross-over hop test on one leg. In all tests the right leg was tested first and the order of the tests was the same for all subjects .
The subjects walked at a self-selected, comfortable speed on a 10 m walkway. A force plate embedded in the floor was located 3.5 metres after the start. Data from at least six dynamic trials, with three clean force plate strikes from each side, were captured.
The front edge of the step was positioned approximately 60 cm from the force plate. The subject stood facing the step at a self-selected distance and was told to step up with one leg (referred to as the "supporting limb") and cross over the step with the opposite limb (referred to as the "step-over limb") . It was the "step-over limb" that landed on the force plate.
The cross-over hop test was performed on a 6 m long course where the subject hopped from side to side across a 15 cm marking strip on the floor. The subject hopped three times in succession on the same foot, crossing the centre strip on each hop . The first landing was a force plate strike.
Isokinetic strength testing
The strength of each leg was evaluated with an isokinetic dynamometer (Cybex II Dynamometer 325, Lumex Inc., Ronkonkoma, NY). The subject was secured to the apparatus with straps across the chest, pelvis, thigh and ankle, according to the Cybex manual . The subject was sitting with the thigh supported, with 90° hip flexion and the arms folded. The centre of motion of the lever arm was aligned as accurately as possible to the slightly changing flexion-extension axis of the knee joint, and the resistance pad was placed approximately 3 cm above the lateral malleolus on the tibia. The range of motion of the knee joint was set at 0–100°. The test-retest reliability of isokinetic muscle strength testing is good [46, 47]. In order to familiarise the subjects with the operation of the dynamometer before formal testing began, they were allowed several sub-maximum practise efforts, after which three consecutive maximum efforts for knee extension and flexion at angle velocities of 60°/sec were recorded. A 20 sec rest was allowed between the sets. The peak torque (Nm) of the knee extension and flexion muscle strength was recorded.
The Knee injury and Osteoarthritis Outcome Score (KOOS) was used to evaluate self-reported pain, function and quality of life [48, 49]. The KOOS consists of five subscales; Pain, Symptoms, ADL, Sport and Recreational function, and knee-related QoL, which are scored separately on a 0–100, worst-to-best, scale. The Tegner activity level scale, scored from 1–10, where 10 indicates professional soccer, was used to evaluate the current activity level . Both instruments have good validity and reliability for subjects with ACL injuries [51, 52].
Knee kinetics and kinematics data were obtained from graphs. To avoid bias, the data were read in a blinded fashion. All legs were given a number from a random number list. This list was handled by the last author and was not available to the graph reader. Kinetic and kinematic data for gait were calculated across the stance phase and swing phase and normalised to 100% of the gait cycle. A gait cycle starts at heel-strike and stops at the next heel-strike by the same foot . Kinetic and kinematic data for step and hop activity were calculated across the stance phase and normalised to 100% of stance. Calculated kinetic data were normalised for body mass in kilograms. The step activity data was normalised for leg length, as measured from the spina iliaca anterior superior (SIAS) to the medial malleolus. All modelling assumptions are based on the work by Ramakrishnan et al. . At the time of processing, all three trials were calculated and a mean of the three trials was used for analysis.
The kinematic variable studied was peak knee flexion during loading response, and the kinetic variables were internal knee extensor moment at peak knee flexion and the peak vertical ground reaction force (VGRF) during the first 25% of the gait cycle.
The kinematic variable studied was knee flexion of the supporting limb, obtained when the step-over limb landed on the force plate. The kinetic variables were internal knee extensor moment at peak knee flexion and the peak vertical ground reaction force (VGRF) of the step-over limb when landing on the force plate.
The kinematic variable studied was knee flexion during landing. The kinetic variables studied were internal knee extensor moment at peak knee flexion, and the peak vertical ground reaction force (VGRF) of the first jump when landing on the force plate.
Results are given as mean ± SD unless otherwise stated. The data were analysed using the Statistical Package for Social Sciences for Windows (SPSS Version 12.0.1). The results had a normal frequency distribution, allowing the use of parametric statistics. We found no differences in interpretation when employing parametric or non-parametric statistics. The paired samples t-test was used to determine levels of significance when comparing the groups before and after training. Pearson's correlation coefficient was used to determine the correlation between knee extensor strength and knee extensor moment, and to determine the correlation between the changes in knee kinetics/kinematics and the change in self-reported Sport and Recreational function according to the KOOS questionnaire. The level of significance for statistical measures was set a priori to p ≤ 0.05 and all tests were one-tailed.
Compliance with intervention and self-reported outcomes
Ten ACL-injured subjects took part in all twelve supervised sessions while two subjects took part in only four sessions for work-related reasons. The home exercises were performed once or twice weekly by 11 of the subjects. One subject only participated in the supervised sessions. In total, the number of completed training sessions, both supervised and non-supervised home training, averaged twice a week, and ranged from 1–3 times/week.
To the question: "Would you resume the training programme if your knee got worse?", 11 subjects replied "yes" while one replied "I don't know".
ACL-injured group before and after training
Kinetics and kinematics during gait, step activity and cross-over hop.
Reference group Corresponding side
ACL group injured side at baseline
ACL group injured side at 12 w follow-up
VGRF (BW) a
1.09 ± 0.1
1.12 ± 0.1
1.12 ± 0.1
Peak knee flexion at loading response (degrees)
17 ± 3
18 ± 4
18 ± 3
Knee extensor moment (Nm/kg), (internal moment)
0.42 ± 0.1
0.44 ± 0.2
0.49 ± 0.2
VGRF (BW) b
1.59 ± 0.2
1.66 ± 0.1
1.58 ± 0.2
Peak knee flexion of supporting limb (degrees)
52 ± 6
48 ± 9
50 ± 9
Knee extensor moment (Nm/kg), (internal moment)
0.56 ± 0.2
0.44 ± 0.3
0.54 ± 0.2
VGRF (BW) b
1.88 ± 0.1
1.86 ± 0.2
1.85 ± 0.2
Peak knee flexion during landing (degrees)
49 ± 7
44 ± 6
48 ± 5
Knee extensor moment (Nm/kg), (internal moment)
1.49 ± 0.4
1.28 ± 0.5
1.55 ± 0.6
This study indicates that neuromuscular training may introduce changes in the loading pattern of the affected leg in ACL injured subjects that are measurable by 3-dimensional motion analysis. Our study group was very homogenous with regard to some aspects; they were all mid life males who sustained an ACL injury during soccer play 16 years ago, but heterogeneous with regard to current joint status. The study group consisted of only 12 subjects and although a similar direction of change was seen for all three evaluated functions, the changes were only statistically significant during the most demanding function, the cross-over hop, indicating that the t-test comparisons may be limited by the small number of subjects. Another limitation of the study may be that there were no significant differences between the ACL-injured subjects and the controls at baseline . Thus our data should be viewed as preliminary and interpreted with caution. 3-dimensional motion analysis is a feasible method for evaluation of changes due to neuromuscular training and should be employed in future larger studies that aim to generalize these findings also to women and other ACL injured populations.
The few available studies using biomechanical outcomes to evaluate the impact of neuromuscular training have used interventions similar to those used in the present study, and similarly show improvement in joint flexion angles during gait and hop activities. Myer and co-workers studied "Drop Vertical Jump" and "Medial Drop Landing" tests to analyse the abduction angles and moment in the hip, knee and ankle. Both aspects were improved by neuromuscular training . Chmielewski et al. showed that perturbation training of ACL-deficient potential copers improved knee stiffness during gait, defined as knee flexion and co-contraction index. This change was in the direction of uninjured control subjects .
Most studies using neuromuscular training have evaluated the effect on injury prevention [35, 54–60]. Studies of neuromuscular training, in comparison to traditional strength training, in ACL injured subjects have shown better result in sensory outcomes such as proprioception, motor outcomes such as strength and functional tests, and self-reported outcomes [12, 14]. A prospective, double-blind, randomised, clinical trial in subjects with an on average one year old ACL injury compared a programme for muscle strength with a neuromuscular programme. The investigators found a significantly greater improvement in both proprioception and functional score in the neuromuscular group after 12 weeks' training . Significantly better results, evaluated by one leg hop test, strength test and self-reported questionnaires, were found after supervised neuromuscular training compared with self-monitored training in non-reconstructed ACL subjects with acute injuries . In the present study, the movement pattern was still amenable to knee-specific training, indicating that knee-specific training is feasible also for individuals 16 years past the injury. The poor correlation between quadriceps strength and knee extensor moment seen in the present study supports the theory that lower extremity kinetics and kinematics could be influenced by training focusing on neuromuscular control only without special emphasis on improving lower extremity muscle strength [12, 14].
The optimum training period or number of training sessions to improve the lower extremity loading pattern is difficult to define, largely due to differences in the subjects' body awareness and ability to respond to feedback given to improve neuromuscular control. This study showed that duration of 12 weeks and a frequency of twice a week were sufficient to decrease knee stiffness.
Despite subjects being 16 years post-injury, knee-specific training improved lower extremity kinetics and kinematics, indicating reduced knee stiffness and significantly so during the more demanding hop activity. Moreover, self-reported sport and recreational function correlated positively with the biomechanical changes indicating a clinical importance of the findings. Further studies are needed to confirm these results in women and in other ACL injured populations.
This study was supported by the Swedish National Centre for Research in Sports, the Thelma Zoéga Foundation, the Gorton Foundation, the Greta and Johan Kock Foundation, the Swedish Rheumatism Association and the Swedish Research Council.
- Buss DD, Min R, Skyhar M, Galinat B, Warren RF, Wickiewicz TL: Nonoperative treatment of acute anterior cruciate ligament injuries in a selected group of patients. Am J Sports Med. 1995, 23 (2): 160-165.View ArticlePubMedGoogle Scholar
- Daniel DM, Stone ML, Dobson BE, Fithian DC, Rossman DJ, Kaufman KR: Fate of the ACL injured patient: A prospective outcome study. The American Journal of Sports Medicine. 1994, 22: 632-644.View ArticlePubMedGoogle Scholar
- Fitzgerald KG, Axe MJ, Snyder-mackler L: The efficacy of perturbation training in nonoperative anterior cruciate ligament rehabilitation programs for physically active individuals. Physical Therapy. 2000, 80 (2): 128-151.PubMedGoogle Scholar
- Henriksson M, Rockborn P, Good L: Range of motion training in brace vs. plaster immobilization after anterior cruciate ligament reconstruction: a prospective randomized comparison with a 2-year follow-up. Scand J Med Sci Sports. 2002, 12 (2): 73-80. 10.1034/j.1600-0838.2002.120203.x.View ArticlePubMedGoogle Scholar
- Lephart SM, Henry TJ: Functional rehabilitation for the upper and lower extremity. Orthop Clin North Am. 1995, 26 (3): 579-592.PubMedGoogle Scholar
- Liu-Ambrose T, Taunton JE, MacIntyre D, McConkey P, Khan KM: The effects of proprioceptive or strength training on the neuromuscular function of the ACL reconstructed knee: a randomized clinical trial. Scand J Med Sci Sports. 2003, 13 (2): 115-123. 10.1034/j.1600-0838.2003.02113.x.View ArticlePubMedGoogle Scholar
- Mikkelsen C, Werner S, Eriksson E: Closed kinetic chain alone compared to combined open and closed kinetic chain exercises for quadriceps strengthening after anterior cruciate ligament reconstruction with respect to return to sports: a prospective matched follow-up study. Knee Surg Sports Traumatol Arthrosc. 2000, 8 (6): 337-342. 10.1007/s001670000143.View ArticlePubMedGoogle Scholar
- Mattacola CG, Perrin DH, Gansneder BM, Gieck JH, Saliba EN, McCue FC: Strength, Functional Outcome, and Postural Stability After Anterior Cruciate Ligament Reconstruction. J Athl Train. 2002, 37 (3): 262-268.PubMedPubMed CentralGoogle Scholar
- Mattacola CG, Jacobs CA, Rund MA, Johnson DL: Functional assessment using the step-up-and-over test and forward lunge following ACL reconstruction. Orthopedics. 2004, 27 (6): 602-608.PubMedGoogle Scholar
- Noyes FR, Barber SD, Mangine RE: Abnormal lower limb symmetry determined by function hop tests after anterior cruciate ligament rupture. The American Journal of Sports Medicine. 1991, 19: 513-518.View ArticlePubMedGoogle Scholar
- Wiger P, Brandsson S, Kartus J, Eriksson BI, Karlsson J: A comparison of results after arthroscopic anterior cruciate ligament reconstruction in female and male competitive athletes. A two- to five-year follow-up of 429 patients. Scandinavien Journal of Medicine and Science in Sports. 1999, 9: 290-295.View ArticleGoogle Scholar
- Zatterstrom R, Friden T, Lindstrand A, Moritz U: Rehabilitation following acute anterior cruciate ligament injuries – a 12-month follow-up of a randomized clinical trial. Scand J Med Sci Sports. 2000, 10 (3): 156-163. 10.1034/j.1600-0838.2000.010003156.x.View ArticlePubMedGoogle Scholar
- Risberg MA, Mork M, Jenssen HK, Holm I: Design and implementation of a neuromuscular training program following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther. 2001, 31 (11): 620-631.View ArticlePubMedGoogle Scholar
- Beard DJ, Dodd CA, Trundle HR, Simpson AH: Proprioception enhancement for anterior cruciate ligament deficiency. A prospective randomised trial of two physiotherapy regimes. J Bone Joint Surg Br. 1994, 76 (4): 654-659.PubMedGoogle Scholar
- Bulgheroni P, Bulgheroni MV, Andrini L, Guffanti P, Giughello A: Gait patterns after anterior cruciate ligament reconstruction. Knee surgery, Sports Traumatology, Arthroscopy. 1997, 5: 14-21. 10.1007/s001670050018.View ArticlePubMedGoogle Scholar
- Chmielewski TL, Rudolph KS, Fitzgerald GK, Axe MJ, Snyder-Mackler L: Biomechanical evidence supporting a differential response to acute ACL injury. Clin Biomech (Bristol, Avon). 2001, 16 (7): 586-591. 10.1016/S0268-0033(01)00050-X.View ArticleGoogle Scholar
- Ferber R, Osternig LR, Woollacott MH, Wasielewski NJ, Lee J-H: Gait mechanics in chronic ACL deficiency and subsequent repair. Clinical Biomechanics. 2002, 17: 274-285. 10.1016/S0268-0033(02)00016-5.View ArticlePubMedGoogle Scholar
- Lewek M, Rudolph K, Axe M, Snyder-Mackler L: The effect of insufficient quadriceps stregth on gait after anterior cruciate ligament reconstruction. Clinical Biomechanics. 2002, 17: 56-63. 10.1016/S0268-0033(01)00097-3.View ArticlePubMedGoogle Scholar
- Rudolph KS, Eastlack ME, Axe MJ, Snyder-Mackler L: 1998 Basmajian student award paper. Movement patterns after anterior cruciate ligament injury: a comparison of patients who compensate well for the injury and those who require operative stabilization. Journal of Electromyography and Kinesiology. 1998, 8: 349-362. 10.1016/S1050-6411(97)00042-4.View ArticlePubMedGoogle Scholar
- Rudolph KS, Axe MJ, Buchanan TS, Scholz JP, Snyder-Mackler L: Dynamic stability in the anterior cruciate ligament deficient knee. Knee Surg Sports Traumatol Arthrosc. 2001, 9 (2): 62-71. 10.1007/s001670000166.View ArticlePubMedGoogle Scholar
- Torry MR, Decker MJ, Viola RW, O'Connor DD, Steadman JR: Intra-articular knee joint effusion induces quadriceps avoidance gait patterns. Clin Biomech (Bristol, Avon). 2000, 15 (3): 147-159. 10.1016/S0268-0033(99)00083-2.View ArticleGoogle Scholar
- Hortobagyi T, Westerkamp L, Beam S, Moody J, Garry J, Holbert D, DeVita P: Altered hamstring-quadriceps muscle balance in patients with knee osteoarthritis. Clin Biomech (Bristol, Avon). 2005, 20 (1): 97-104. 10.1016/j.clinbiomech.2004.08.004.View ArticleGoogle Scholar
- Chmielewski TL, Hurd WJ, Rudolph KS, Axe MJ, Snyder-Mackler L: Perturbation training improves knee kinematics and reduces muscle co-contraction after complete unilateral anterior cruciate ligament rupture. Phys Ther. 2005, 85 (8): 740-749. discussion 750–744.PubMedGoogle Scholar
- Vereijken B, van Emmerik R, Whiting H, Newell K: Freezing degrees of freedom in skill acquisition. Journal of Motor Behavior. 1992, 24: 133-142.View ArticleGoogle Scholar
- Radin EL: Who gets osteoarthritis and why?. J Rheumatol Suppl. 2004, 70: 10-15.PubMedGoogle Scholar
- Konradsen L, Voigt M, Hojsgaard C: Ankle inversion injuries. The role of the dynamic defense mechanism. Am J Sports Med. 1997, 25 (1): 54-58.View ArticlePubMedGoogle Scholar
- Albright TD, Jessell TM, Kandell ER, Posner MI: Progress in the neural sciences in the the century after Cajal (and the mysteries that remain). Ann N Y Acad Sci. 2001, 929: 11-40.View ArticlePubMedGoogle Scholar
- Swanik CB, Covassin T, Stearne DJ, Schatz P: The Relationship Between Neurocognitive Function and Noncontact Anterior Cruciate Ligament Injuries. Am J Sports Med. 2007Google Scholar
- Roos H, Ornell M, Gärdsell P, Lohmander S, Lindstrand A: Soccer after anterior cruciate ligament – an incompatible combination. Acta Orthopaedica Scandinavica. 1995, 66: 107-112.View ArticlePubMedGoogle Scholar
- von Porat A, Roos EM, Roos H: High prevalence of osteoarthritis 14 years after an anterior cruciate ligament tear in male soccer players: a study of radiographic and patient relevant outcomes. Ann Rheum Dis. 2004, 63 (3): 269-273. 10.1136/ard.2003.008136.View ArticlePubMedPubMed CentralGoogle Scholar
- Jorgensen U, Bak K, Ekstrand J, Scavenius M: Reconstruction of the anterior cruciate ligament with the iliotibial band autograft in patients with chronic knee instability. Knee Surg Sports Traumatol Arthrosc. 2001, 9 (3): 137-145. 10.1007/s001670000163.View ArticlePubMedGoogle Scholar
- Roos H, Laurén M, Adalberth T, Roos EM, Jonsson K, Lohmander SL: Knee osteoarthritis after meniscectomy. Prevalence of radiographic changes after twenty-one years, compared with matched controls. Arthritis & Rheumatism. 1998, 41 (4): 687-693. 10.1002/1529-0131(199804)41:4<687::AID-ART16>3.0.CO;2-2.View ArticleGoogle Scholar
- Kellgren J, Lawrence J: Radiological assessment of osteoarthrosis. Annals of the Rheumatic Diseases. 1957, 16: 494-502.View ArticlePubMedPubMed CentralGoogle Scholar
- von Porat A, Henriksson M, Holmstrom E, Thorstensson CA, Mattsson L, Roos EM: Knee kinematics and kinetics during gait, step and hop in males with a 16 years old ACL injury compared with matched controls. Knee Surg Sports Traumatol Arthrosc. 2006, 14 (6): 546-554. 10.1007/s00167-006-0071-4.View ArticlePubMedGoogle Scholar
- Hewett TE, Lindenfeld TN, Riccobene JV, Noyes FR: The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study. Am J Sports Med. 1999, 27 (6): 699-706.PubMedGoogle Scholar
- Myer GD, Ford KR, Palumbo JP, Hewett TE: Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J Strength Cond Res. 2005, 19 (1): 51-60. 10.1519/13643.1.PubMedGoogle Scholar
- Myer GD, Brunner HI, Melson PG, Paterno MV, Ford KR, Hewett TE: Specialized neuromuscular training to improve neuromuscular function and biomechanics in a patient with quiescent juvenile rheumatoid arthritis. Phys Ther. 2005, 85 (8): 791-802.PubMedGoogle Scholar
- Petersen W, Braun C, Bock W, Schmidt K, Weimann A, Drescher W, Eiling E, Stange R, Fuchs T, Hedderich J: A controlled prospective case control study of a prevention training program in female team handball players: the German experience. Arch Orthop Trauma Surg. 2005, 125 (9): 614-621. 10.1007/s00402-005-0793-7.View ArticlePubMedGoogle Scholar
- Mandelbaum BR, Silvers HJ, Watanabe DS, Knarr JF, Thomas SD, Griffin LY, Kirkendall DT, Garrett W: Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. Am J Sports Med. 2005, 33 (7): 1003-1010. 10.1177/0363546504272261.View ArticlePubMedGoogle Scholar
- Kadaba MP, Ramakrishnan HK, Wootten ME: Measurement of lower extremity kinematics during level walking. J Orthop Res. 1990, 8 (3): 383-392. 10.1002/jor.1100080310.View ArticlePubMedGoogle Scholar
- Davis RB, Ounpuu S, Tyburski D, Gage JR: A gait analysis data collection and reduction technique. Human Movement Science. 1991, 10: 575-587. 10.1016/0167-9457(91)90046-Z.View ArticleGoogle Scholar
- Ramakrishnan H, Kadaba M, Wotten M: Lower extremity joint moments and ground reaction torque in adult gait. Biomechanics of normal and prosthetic gait. 1987, BED-Vol.4/Dsc-Vol.7: 87-92.Google Scholar
- Fransen M, Crosbie J, Edmonds J: Reliability of gait measurements in people with osteoarthritis of the knee. Phys Ther. 1997, 77 (9): 944-953.PubMedGoogle Scholar
- Diss CE: The reliability of kinetic and kinematic variables used to analyse normal running gait. Gait Posture. 2001, 14 (2): 98-103. 10.1016/S0966-6362(01)00125-4.View ArticlePubMedGoogle Scholar
- Davis G: A compendium of isokinetics in clinical usage and rehabilitation techniques. 1984, La Crosse: WI: S&S PublishersGoogle Scholar
- Frontera WR, Hughes VA, Dallal GE, Evans WJ: Reliability of isokinetic muscle strength testing in 45- to 78-year-old men and women. Arch Phys Med Rehabil. 1993, 74 (11): 1181-1185.PubMedGoogle Scholar
- Pitetti KH: A reliable isokinetic strength test for arm and leg musculature for mildly mentally retarded adults. Arch Phys Med Rehabil. 1990, 71 (9): 669-672.PubMedGoogle Scholar
- Roos EM, Roos H, Ekdahl C, Lohmander SL: Knee injury and osteoarthritis outcome score (KOOS) – validation of a Swedish version. Scandinavian Journal of Medicine & Science in Sports. 1998, 8: 439-448.View ArticleGoogle Scholar
- Roos EM, Roos H, Lohmander SL, Ekdahl C, Beynnon BD: Knee injury and Osteoarthritis Outcome Score (KOOS) – Development of a self-administered outcome measure. Journal of Orthopaedic and Sports Physical Therapy. 1998, 78 (2): 88-96.View ArticleGoogle Scholar
- Tegner Y, Lysholm J: Rating systems in the evaluation of knee ligament injuries. Clinical Orthopedics and Related Research. 1985, 198: 43-49.Google Scholar
- Roos EM, Roos HP, Lohmander LS: WOMAC Osteoarthritis index-additional dimensions for use in subjects with post-traumatic osteoarthritis of the knee. Osteoarthritis and Cartilage. 1999, 7: 216-221. 10.1053/joca.1998.0153.View ArticlePubMedGoogle Scholar
- Johnson DS, Smith RB: Outcome measurement in the ACL deficient knee – what's the score?. Knee. 2001, 8 (1): 51-57. 10.1016/S0968-0160(01)00068-0.View ArticlePubMedGoogle Scholar
- Perry J: Gait analysis, normal and pathological function. 1992, Thorofare, NJ: SLACK IncorporatedGoogle Scholar
- Caraffa A, Cerulli G, Projetti M, Aisa G, Rizzo A: Prevention of anterior cruciate ligament injuries in soccer. A prospective controlled study of proprioceptive training. Knee Surg Sports Traumatol Arthrosc. 1996, 4 (1): 19-21. 10.1007/BF01565992.View ArticlePubMedGoogle Scholar
- Myklebust G, Engebretsen L, Braekken IH, Skjolberg A, Olsen OE, Bahr R: Prevention of anterior cruciate ligament injuries in female team handball players: a prospective intervention study over three seasons. Clin J Sport Med. 2003, 13 (2): 71-78. 10.1097/00042752-200303000-00002.View ArticlePubMedGoogle Scholar
- Wedderkopp N, Kaltoft M, Holm R, Froberg K: Comparison of two intervention programmes in young female players in European handball – with and without ankle disc. Scand J Med Sci Sports. 2003, 13 (6): 371-375. 10.1046/j.1600-0838.2003.00336.x.View ArticlePubMedGoogle Scholar
- Wedderkopp N, Kaltoft M, Lundgaard B, Rosendahl M, Froberg K: Prevention of injuries in young female players in European team handball. A prospective intervention study. Scand J Med Sci Sports. 1999, 9 (1): 41-47.View ArticlePubMedGoogle Scholar
- Holm I, Fosdahl MA, Friis A, Risberg MA, Myklebust G, Steen H: Effect of neuromuscular training on proprioception, balance, muscle strength, and lower limb function in female team handball players. Clin J Sport Med. 2004, 14 (2): 88-94. 10.1097/00042752-200403000-00006.View ArticlePubMedGoogle Scholar
- Hewett TE, Ford KR, Myer GD: Anterior cruciate ligament injuries in female athletes: Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. Am J Sports Med. 2006, 34 (3): 490-498. 10.1177/0363546505282619.View ArticlePubMedGoogle Scholar
- Hewett TE, Myer GD, Ford KR: Reducing knee and anterior cruciate ligament injuries among female athletes: a systematic review of neuromuscular training interventions. J Knee Surg. 2005, 18 (1): 82-88.PubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2474/8/35/prepub
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.