Core Stability, Knee Muscle Strength, and Anterior ...

Authors: Ozge Cinar-Medeni, PT, PhD Gul Baltaci, PT, PhD Kezban Bayramlar, PT, PhD Ibrahim Yanmis, MD

Sports Medicine

Affiliations: From the Department of Physiotherapy and Rehabilitation, Faculty of Health Sciences, Gazi University, Ankara, Turkey (OC-M); Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation, Hacettepe University, Ankara, Turkey (GB, KB); and Department of Orthopedics and Traumatology, Haydarpas$ a Hospital of Gu¨lhane Military Medical Academy, Istanbul, Turkey (IY).

Correspondence: All correspondence and requests for reprints should be addressed to Gul Baltaci, PT, PhD, Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation, Hacettepe University, S@hh@ye-Ankara, Turkey.

Disclosures: Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.

0894-9115/15/9404-0280 American Journal of Physical Medicine & Rehabilitation Copyright * 2014 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/PHM.0000000000000177

ORIGINAL RESEARCH ARTICLE

Core Stability, Knee Muscle Strength, and Anterior Translation Are Correlated with Postural Stability in Anterior Cruciate Ligament-Reconstructed Patients ABSTRACT Cinar-Medeni O, Baltaci G, Bayramlar K, Yanmis I: Core stability, knee muscle strength, and anterior translation are correlated with postural stability in anterior cruciate ligament-reconstructed patients. Am J Phys Med Rehabil 2015;94:280Y287.

Objective: The purpose of this study was to investigate the relationship of postural stability and lower extremity performance with core stability, knee laxity, and muscle strength in patients with anterior cruciate ligament reconstruction. Design: Twenty-eight anterior cruciate ligament-reconstructed subjects were included in the study. Anterior knee laxity tests, isokinetic knee muscle strength tests, and core stability tests were performed. Single-limb postural stability was assessed in both eyes-open and eyes-closed positions on a static surface and an eyes-open condition on a foam surface. A single-legged hop test was performed to assess lower extremity performance. To detect differences between the operated and healthy leg, a Mann-Whitney U test was performed, and a correlation analysis was performed using the Spearman correlation coefficient.

Results: Knee muscle strength and laxity were different between the operated and healthy legs (P G 0.05). Postural stability scores correlated with core stability tests (P G 0.05) in both the operated and healthy legs. In the operated leg, knee laxity and muscle strength correlated with the mediolateral sway index on a foam surface (P G 0.05). Knee flexor and extensor muscle strength correlated with the singlelegged hop for both legs (P G 0.05).

Conclusions: Decreased core stability, decreased knee muscle strength, and increased knee laxity correlated with single-limb postural stability. Better hop performance was demonstrated with better knee flexor and extensor muscle strength and was independent from core stability. Key Words: Knee Laxity, Postural Balance, Anterior Cruciate Ligament Reconstruction, Core Endurance

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Am. J. Phys. Med. Rehabil. & Vol. 94, No. 4, April 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.

A

nterior cruciate ligament (ACL) injury can block neural feedback mechanisms and consequently affect the motor control of the knee.1 The effects of ACL reconstruction on postural stability have been investigated by previous studies.2 The ACL has an important role in the sensory input of the knee joint,3 and deficits in proprioceptive information and postural control ensue after the injury.4 After ACL reconstruction, mildto-moderate postural control deficits might remain.2 Paterno et al.5 found that ACL-reconstructed patients with postural stability deficits in the operated limb have twice as much risk of a second injury than those who do not have postural stability deficits. Therefore, improving postural stability should be an essential topic in postoperative ACL rehabilitation. Knowledge of the factors that affect postural stability could better guide postoperative ACL rehabilitation. After ACL reconstruction, knee muscle strength and laxity can remain impaired,6Y8 and these impairments can lead to postural stability deficits. Trunk stabilization strategies were frequently used to control body sway in stance.9 Core stability greatly impacts the knee joint, and impaired core stability may lead to balance problems that occasionally result in knee and lower extremity injuries.10 In healthy subjects, higher trunk endurance was correlated with better singlelimb stance time,11 but the effect of trunk endurance and knee muscle strength on postural sway has not been investigated to date in ACL-reconstructed subjects. Hop tests are frequently used to assess lower extremity function after ACL reconstruction.12 The relationships between hop performance, knee flexor and extensor muscle strength, and knee laxity have been previously investigated.12,13 Low correlations between knee muscle strength and hop performance have been observed in a previous study, and further studies are needed to investigate the relationship between hop performance and other parameters.12 The relationship between core stability and lower extremity function has been studied.10 Electromyographic analysis indicates that the core muscles are activated before lower extremity movements.14 However, the effect of core stability on lower extremity performance has not been investigated to date in ACL-reconstructed subjects. The aims of this study were (1) to investigate the relationship between postural stability, core stability, knee laxity, and knee muscle strength and (2) to determine the relationship between lower extremity performance, core stability, knee laxity, and knee muscle strength in ACL-reconstructed patients. The hypothesis of this study was that decreased core stability, decreased knee muscle strength, and increased www.ajpmr.com

knee laxity negatively affect single-limb postural stability and lower extremity performance.

METHODS Subjects Twenty-eight ACL-reconstructed patients (age, 28.03 [7.14] yrs; body weight, 78.05 [13.33] kg; height, 177.53 [7.33] cm; body mass index, 24.63 [3.02] kg/m2) with hamstring tendon autografts were included in this study. The inclusion criteria were no rheumatologic or neurologic disease and no injuries or surgical operations during the past year. Patients with concomitant collateral ligament injuries, osteocondral defects, and meniscectomy were excluded from the study. One orthopedic surgeon performed all of the patients’ reconstructions, and all patients underwent postoperative rehabilitation for 8Y10 wks. All subjects followed a previously published rehabilitation program with three sessions per week.15 In addition, electrical stimulation to the quadriceps muscle was performed for 30 mins each session. Twenty-one patients had operations on their dominant legs, and seven patients had operations on their nondominant legs. The time between injury and surgical operation was 6.03 [7.5] mos. This study was approved by the university’s ethical committee.

Assessments Knee muscle strength, knee laxity, postural stability, and single-legged hop (SLH) tests were performed on both the operated and healthy extremities after the 16th postoperative week (mean [SD], 18.22 [2.95] wks). The healthy legs were evaluated as internal controls. Patients were evaluated during two sessions on consecutive days. In one session, knee laxity, knee muscle strength, and the SLH test were performed. In the other session, postural stability and core stability tests were performed. A 5-min rest was allowed between all tests to avoid fatigue. One examiner evaluated the patients in a randomized order. A simple randomization was performed for extremity order and test order. Anterior knee laxity was assessed with the Kneelax 3 arthrometer (Monitored Rehab System, Haarlem, Netherlands), which is a valid instrument.16 The patient’s leg was supported with thigh support just above the joint line at 30 degrees of knee flexion. The patient’s leg was drawn anteriorly with the thighheld device. Anterior tibial translation was measured with 89- and 132-N forces. The test was performed three times, and the mean score of the three measurements was recorded. Postural Stability in ACL-Reconstructed Patients

Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.

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Concentric knee flexor and extensor muscle strength was evaluated with the ISOMED 2000 (D&R Ferstl GmbH, Hemau, Germany) isokinetic dynamometer, which is a reliable device for both flexion and extension measurements.17,18 While the patient was sitting on the dynamometer chair with the hip and knee flexed 90 degrees, the center of the knee joint was aligned with the center of the dynamometer using a laser-pointing device. The patient was asked to push up the lever arm of the dynamometer as strongly as possible and return to the starting position at an angular velocity of 60 degrees/sec for five times. After a 1-min break, the same procedure was repeated at an angular velocity of 180 degrees/sec. The knee muscle strength scores were normalized by body weight.

Core Stability Tests Core stability was assessed with isometric core endurance tests because they are the most reliable for core stability-related assessments.19 A 5-min break was allowed between the core stability tests. To assess core endurance for a flexion moment, the prone-bridge test was used.20 In the prone position, the subjects propped on their elbows, placed shoulder-width apart, and their arms were set perpendicularly to the body. Their feet were set with a narrow base, and then, the subject raised their pelvis from the floor. The shoulders, hips, and ankles were required to be in a straight line, and the time that the patient could maintain this position was recorded.21 The test-retest reliability is 0.78.20 The lateral core endurance was evaluated with a side-bridge test. The test was performed on both the operated and healthy sides. In a side-lying position, the subjects propped on their elbow. The upper foot was placed in front of the lower foot on the mat for support. The subjects were instructed to raise the hips and body and to maintain a straight line over their body length. The uninvolved arm was placed across the chest. The time that the patient could maintain this position was recorded.22 The test-retest reliability is 0.99.22 The Sorenson test was used to determine back extensor endurance. The subjects were placed on the treatment table in a prone position. The upper edge of the iliac crests was aligned with the edge of the table. The lower body was fixed to the table with straps. With their arms crossed on their chest, the subjects were required to maintain their upper body in a horizontal position. The time that the patient could maintain this position was recorded.21 The test-retest reliability is 0.78Y0.98.21,22 To assess flexor endurance, the supine isometric chest raise test was used. In a supine position, the

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knees and hips were flexed 90 degrees with the hands crossed on the chest. The subjects were asked to lift the neck and upper body and stay in this position. The time that the patient could maintain this position was recorded. The test-retest reliability is 0.89.21 Single-limb postural stability was measured with the Biosway Portable System (Biodex) in eyes-open and eyes-closed conditions on a static surface and in an eyes-open condition on a foam surface. The patients were asked to stand on one leg, and their arms were placed on their contralateral shoulders for 20 secs. The patients were allowed to familiarize themselves with the test for one trial. The test was repeated three times on each limb, and the mean score was calculated by the system software. The output data from the system were overall sway index, mediolateral sway index (MLI), and anteroposterior sway index (API). Higher values indicate worse stability. The system reliability was tested with 21 healthy volunteers in a single-limb stance (two sessions on consecutive days). The intraclass correlation coefficient values were 0.89 for the overall sway index, 0.85 for the MLI, and 0.80 for the API. The SLH test for distance, which is a reliable test23,24 to assess the performance of the lower extremity, was performed. The test was performed by having the patient stand on the tested leg. The patients were asked to hop as far as possible while the hands were placed on their waist. The distance between the tip of the patient’s great toe at the starting position and the tip of the patient’s great toe at the landing position was measured. After one trial, three tests were performed, and the mean score was recorded.12 Statistical analysis was performed using Statistical Package for the Social Sciences 15.0 software. Because of small case numbers, nonparametric analyses were performed. The difference between the operated and healthy legs’ scores was assessed with a MannWhitney U test. Correlations between postural stability, SLH test, and other parameters were performed with the Spearman correlation coefficient. Significance was set at P G 0.05.

RESULTS Knee flexor and extensor muscle strength and laxity values were significantly different between the operated and healthy legs, except for the extensor peak torque (EPT) measured at 180-degree/sec angular velocity (P G 0.05) (see Table 1). In postural stability, there were no differences between the two extremities (P 9 0.05) (see Table 1). Eight patients could not stand for 20 secs on the healthy leg, and ten patients could not stand on the operated leg in the eyes-closed condition. Thus, these patients could not complete the test. On a foam


TABLE 1 Comparison of the results of operated and healthy legs N

Knee anterior translation 89 N, mm 132 N, mm Muscle strength at 60 degrees/sec FPT, Nm/kg EPT, Nm/kg H/Q strength ratio, % Muscle strength at 180 degrees/sec FPT, Nm/kg EPT, Nm/kg H/Q strength ratio, % Postural stability test results Eyes open, static surface Overall SI Anteroposterior SI Mediolateral SI Eyes closed, static surface Overall SI Anteroposterior SI Mediolateral SI Eyes open, foam surface Overall SI Anteroposterior SI Mediolateral SI SLH test

Mean (SD)

OL

HL

OL

HL

28 28

28 28

5.13 (3.02) 6.65 (3.34)

2.66 (1.55) 3.55 (1.97)

28 28 28

28 28 28

1.51 (0.57) 1.40 (0.31) 97.87 (32.87)

28 28 28

28 28 28

28 28 28

Mean Difference

P

2.46 3.10

G0.001a G0.001a

2.27 (0.62) 1.59 (0.34) 70.65 (10.49)

j0.75 j0.18 27.21

G0.001a 0.04a G0.001a

1.20 (0.42) 1.18 (0.22) 103.22 (31.93)

1.74 (0.40) 1.27 (0.25) 70.90 (8.40)

j0.54 j0.09 32.32

G0.001a 0.17 G0.001a

28 28 28

0.73 (0.20) 0.75 (0.22) 0.38 (0.11)

0.69 (0.26) 0.74 (0.19) 0.39 (0.20)

0.04 0.01 0.05

0.37 0.98 0.76

18 18 18

20 20 20

1.66 (0.57) 1.40 (0.40) 1.26 (0.64)

1.49 (0.58) 1.30 (0.39) 1.09 (0.64)

0.16 0.10 0.16

0.35 0.66 0.32

24 24 24 28

24 24 24 28

0.91 (0.23) 0.95 (0.25) 0.58 (0.23) 108.84 (34.23)

0.91 (0.27) 0.95 (0.25) 0.49 (0.18) 139.59 (22.13)

0.07 0.07 0.06 j30.74

0.86 0.95 0.07 G0.001a

a

Significant difference was found (P G 0.05). HL, healthy leg; OL, operated leg; SI, away index.

surface, four patients could not perform the test on either the operated or healthy leg. The comparisons between the operated and healthy legs’ scores are given in Table 1.

Correlation for the Operated Leg In the eyes-open condition on a static surface, the overall sway index and API correlated with the side bridge score (on the operated side) (r = j0.41, P = 0.02 and r = j0.39, P = 0.03, respectively), and the MLI correlated with trunk extensor endurance (r = j0.45, P = 0.01). In the eyes-closed position, the API correlated with the side bridge test (healthy side) (r = j0.48, P = 0.04). In the eyes-open condition on foam surface, the MLI correlated with the anterior knee laxity (89 and 132 N), EPT, and hamstring-quadriceps (H/Q) strength ratio at the velocity of 60 degrees/sec, respectively (r = 0.54, P = 0.006; r = 0.48, P = 0.01; r = 0.41, P = 0.04; and r = 0.42, P = 0.03). The SLH score correlated with the EPT, flexor peak torque (FPT), and H/Q strength ratio (P G 0.05) (see Table 2).

Correlation for the Healthy Leg In the eyes-open condition on a static surface, the MLI correlated with the H/Q strength ratio at www.ajpmr.com

60-degree/sec angular velocity (r = 0.38, P = 0.04). In the eyes-closed condition, none of the parameters correlated with postural stability scores (P 9 0.05). However, in the eyes-open condition on a foam surface, the MLI correlated with trunk extensor endurance test score (r = j0.44, P = 0.02). The SLH score correlated with the EPT, FPT, H/Q strength ratio, and prone bridge score (P G 0.05) (see Table 3).

DISCUSSION The data from this study demonstrate that decreased core stability, decreased knee muscle strength, and increased knee laxity negatively affect single-limb postural stability and that decreased knee muscle strength negatively affects lower extremity performance in ACL-reconstructed patients. In the healthy legs of patients, decreased knee muscle strength and trunk extensor endurance negatively affects the single-limb postural stability and SLH distance. Different parameters affected postural stability scores in the operated and healthy legs. In the healthy legs, the core stability scores were related to postural stability. However, in ACL-reconstructed Postural Stability in ACL-Reconstructed Patients


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TABLE 2 Relationship between SLH test and other parameters in operated leg SLH Test r Knee anterior translation 89 N j0.02 132 N j0.002 Knee muscle strength at 60 degrees/sec FPT 0.41 EPT 0.69 H/Q strength ratio j0.53 Knee muscle strength at 180 degrees/sec FPT 0.59 EPT 0.85 H/Q strength ratio j0.50 Core endurance tests Prone bridge 0.2 Sorenson test j0.07 Side bridge (OL) 0.13 Side bridge (HL) 0.16 Supine isometric chest raise j0.02

P 0.89 0.98 0.02a G0.001b 0.003b G0.001b G0.001b G0.001b 0.28 0.68 0.49 0.41 0.88

a

Correlation was significant at 0.05 level. Correlation was significant at 0.01 level. HL, healthy leg; OL, operated leg.

b

knees, core stability scores, knee laxity, and extensor strength were related to postural stability. Previous studies on ACL reconstruction considered that an approximately 2.5- to 3.0-mm difference in sagittal plane knee laxity is normal at the fourth month after the operation.25 The mean knee laxity difference is within this reference range. In this study, muscle strength deficits for both flexor and extensor muscles and SLH deficits were observed between the limbs. However, no difference in postural stability scores was observed between the operated and healthy legs. Kellis et al.26 reported that no bilateral difference in postural stability was observed 3 mos after ACL reconstruction. Other studies with longer follow-up periods confirmed this finding.25 This study’s findings are consistent with these studies. However, some studies reported contradictory results1,27 perhaps because of the use of different balance parameters, such as sway path, sway amplitude, mean speed, etc. In this study, some patients failed in the singlelimb balance test on both the operated and healthy legs in the eyes-closed position and on a foam surface. This balance failure may be caused by the loss of vision or the properties of the test surface.28 Another reason for their failure may be the strength deficits of the injured and operated legs of ACL-reconstructed subjects in comparison with uninjured, matched subjects.29 In addition, crossover neural inhibition in the healthy legs of ACL-reconstructed patients was found in a

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previous study.30 This inhibition may also cause failure in the single-limb balance tests in healthy legs. In a previous study, knee muscle strength did not correlate with stabilometric assessments performed in a darkened room.31 In this study, a darkened room was not used. Instead, stabilometric assessments were performed with eyes-open and eyes-closed conditions. In these two conditions, the knee flexor and extensor strength did not correlate with knee flexor and extensor muscle strength, and these results are consistent with the previous study. To maintain balance during stance, stability in the core region decreases the shear forces to the knee and other lower extremity joints, thereby decreasing the injury risk and improving performance.10 Trunk motion might decrease abnormal lower extremity mechanics and could decrease postural sway.10 In this study, in the eyes-open condition, lateral core endurance was related to sagittal plane postural sway, and extensor endurance was related to mediolateral sway in the operated leg. Similar to the eyes-open condition, in the eyes-closed position, decreased lateral core endurance negatively affected sagittal plane postural sway. The relation between lateral core endurance and single-limb balance can be explained by the ability of the lateral flexor muscles to control upper body movements.32 This gives the impression that balance losses in ACLreconstructed subjects were compensated for by upper-trunk strategies. In the healthy legs of ACLreconstructed patients, in the eyes-open condition TABLE 3 Relationship between SLH test and other parameters in healthy leg SLH Test r Knee anterior translation 89 N j0.1 132 N j0.21 Knee muscle strength at 60 degrees/sec FPT 0.54 EPT 0.41 H/Q strength ratio 0.18 Knee muscle strength at 180 degrees/sec FPT 0.58 EPT 0.45 H/Q strength ratio 0.17 Core endurance tests Prone bridge 0.42 Sorenson test 0.14 Side bridge (OL) 0.15 Side bridge (HL) 0.18 Supine isometric chest raise 0.17

P 0.59 0.27 0.003a 0.02b 0.34 0.001a 0.014b 0.36 0.02b 0.47 0.43 0.35 0.37

a

Correlation was significant at 0.01 level. Correlation was significant at 0.05 level. HL, healthy leg; OL, operated leg.

b


on a static surface, an increased H/Q strength ratio was related to poor stability, indicating the importance of knee extensor strength. Decreased core extensor endurance was the only unique core stability parameter that affected a postural sway parameter (MLI) on a foam surface in healthy legs. Other parameters, which were not assessed in this study, might be related to postural stability. The proprioceptive system predominantly controls balance in healthy populations.9 Poor proprioception was related to poor postural control in patients with knee osteoarthritis.33 Further studies evaluating knee joint proprioception are needed to better understand the factors affecting single-limb balance in ACLreconstructed subjects. In comparison with a static surface, a foam surface alters the sensory input of the foot base (does not absorb forces correctly) and makes balance tests more challenging.28 These properties of a foam surface enabled the authors to see the effects of knee stability on postural sway in ACL-reconstructed subjects. Increased knee laxity, extensor strength, and H/Q strength ratio deficits negatively affected postural sway on a foam surface. The effect of knee laxity and muscle strength on stabilometric assessment has been previously studied in patients with ACL injury.27 The results demonstrated that knee laxity affects the deviation of the center of pressure in women and the mean speed of the center of pressure movements in men. Knee muscle strength affects the mean speed of the center of pressure movements in women. A contrary finding was reported in chronic, ACL-deficient knees. However, in that study, only the tilt angle was used as a balance parameter.34 This study analyzed overall sway index, MLI, and API according to stabilometric evaluation and found that increased mediolateral postural sway is related to increased knee laxity (less than both 89 and 132 N) and decreased extensor strength. In ACL injuries, generally, mediolateral balance is lost,35 and increased mediolateral sway may cause a second injury. Improving knee extensor muscle strength still remains important after the fourth month to decrease mediolateral sway. The effect of knee laxity on mediolateral sway highlights the finding that approximately 2.5Y3.0 mm of bilateral laxity difference have a negative effect on single-leg stance. Because postural stability is a predictor of secondary ACL injury after ACL reconstruction, improving postural stability before sports participation is required.5 This study demonstrates that core stability, knee extensor muscle strength, and H/Q strength ratios should be improved to achieve better single-limb balance. www.ajpmr.com

Improving SLH performance is essential to be able to return to sports, and SLH testing is used as a criterion in the return-to-sports phase of postoperative ACL rehabilitation.15 Okada et al.36 showed the relation between core endurance and functional performance in healthy subjects. In a previous study, moderate correlations between core stability and athletic performance were found in football players.37 In this study, the correlation between the prone bridge test and hop distance in healthy legs was inconsistent; however, no relationship was found between core endurance and lower extremity performance in ACLreconstructed legs. This finding indicates that lower extremity performance is independent from core endurance in ACL-reconstructed legs. This study confirms previous findings12 that investigated the relationship between knee muscle strength, knee laxity, and SLH performance. According to these results, improving knee muscle strength seems to be essential for improving SLH performance, and SLH performance is independent from core stability in ACL-reconstructed legs. There were some limitations in this study. Only the deviation from the center of gravity was measured to assess single-limb stance balance. Other parameters, such as sway speed, sway area, tilt angle, and so on, were not evaluated. In this study, a real control group consisting of uninjured subjects was not evaluated. Therefore, the authors could not determine the differences between ACL-reconstructed patients and healthy controls in these relationships. Further studies comparing ACL-reconstructed patients with uninjured, matched subjects, taking into account these relationships and parameters, are warranted. The small sample size is another limitation. Further studies should include a large number of subjects. In this study, reconstruction of ACL-injured patients was performed with hamstring tendon autografts, and the results may be generalized to this population. Correlations of postural stability and hop performance with the other parameters should be investigated in patients with patellar tendon autografts or allografts in future studies, so that the effect of the reconstruction type on these relationships can be observed. In addition, these correlations may differ in patients with concomitant ligament injuries. Examining patients with multiligament injuries may be another research area.

CONCLUSIONS Postural stability scores were correlated with core stability measurements in eyes-open and eyes-closed conditions on a static surface. On a foam surface, knee Postural Stability in ACL-Reconstructed Patients


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15. van Grinsven S, van Cingel RE, Holla CJ, et al: Evidencebased rehabilitation following anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2010;18:1128Y44

REFERENCES

16. Paine R, Lowe W: Comparison of Kneelax and KT-1000 knee ligament arthrometers. J Knee Surg 2012;25:151Y4

1. Bonfim TR, Paccola CAJ, Barela JA: Proprioceptive and behavior impairments in individuals with anterior cruciate ligament reconstructed knees. Arch Phys Med Rehabil 2003;84:1217Y23 2. Howells BE, Ardern CL, Webster KE: Is postural control restored following anterior cruciate ligament reconstruction? A systematic review. Knee Surg Sports Traumatol Arthrosc 2011;19:1168Y77 3. Johansson H, Sjolander P, Sojka P: A sensory role for the cruciate ligaments. Clin Orthop Relat Res 1991;268:161Y78 4. Roberts D, Friden T, Zatterstrom R, et al: Proprioception in people with anterior cruciate ligament-deficient knees: Comparison of symptomatic and asymptomatic patients. J Orthop Sports Phys Ther 1999;29:587Y94 5. Paterno MV, Schmitt LC, Ford KR, et al: Biomechanical measures during landing and postural stability predict second anterior cruciate ligament injury after anterior cruciate ligament reconstruction and return to sport. Am J Sports Med 2010;38:1968Y78 6. Nakamura N, Horibe S, Sasaki S, et al: Evaluation of active knee flexion and hamstring strength after anterior cruciate ligament reconstruction using hamstring tendons. Arthroscopy 2002;18:598Y602 7. Keays SL, Bullock-Saxton J, Keays AC, et al: Muscle strength and function before and after anterior cruciate ligament reconstruction using semitendonosus and gracilis. Knee 2001;8:229Y34 8. Ruiz AL, Kelly M, Nutton RW: Arthroscopic ACL reconstruction: A 5Y9 year follow-up. Knee 2002;9:197Y200 9. Vaugoyeau M, Viel S, Amblard B, et al: Proprioceptive contribution of postural control as assessed from very slow oscillations of the support in healthy humans. Gait Posture 2008;27:294Y302 10. Willson JD, Dougherty CP, Ireland ML, et al: Core stability and its relationship to lower extremity function and injury. J Am Acad Orthop Surg 2005;13:316Y25 11. Barati A-h, Safarcherati A, Aghayari A, et al: Evaluation of relationship between trunk muscle endurance and static balance in male students. Asian J Sports Med 2013;4:289Y94 12. Sekiya I, Muneta T, Ogiuchi T, et al: Significance of the single-legged hop test to the anterior cruciate ligamentreconstructed knee in relation to muscle strength and anterior laxity. Am J Sports Med 1998;26:384Y8 13. Petschnig R, Baron R, Albrecht M: The relationship between isokinetic quadriceps strength test and hop tests for distance and one-legged vertical jump test

286

following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 1998;28:23Y31

extensor strength and knee laxity parameters affected postural stability. To improve single-limb postural stability after ACL reconstruction, strengthening knee extensor muscles and improving core stability are essential and knee laxity should be minimized. Enhancing knee flexor and extensor muscle strength is important to improve hop performance in ACLreconstructed subjects.

Cinar-Medeni et al.

14. Hodges PW, Richardson CA: Contraction of the abdominal muscles associated with movement of the lower limb. Phys Ther 1997;77:132Y42

17. Dirnberger J, Kosters A, Muller E: Concentric and eccentric isokinetic knee extension: A reproducibility study using the IsoMed 2000-dynamometer. Isokinet Exerc Sci 2012;20:31Y5 18. Dirnberger J, Wiesinger HP, Kosters A, et al: Reproducibility for isometric and isokinetic maximum knee flexion and extension measurements using the IsoMed 2000-dynamometer. Isokinet Exerc Sci 2012;20:149Y53 19. Waldhelm A, Li L: Endurance tests are the most reliable core stability related measurements. J Sport Health Sci 2012;1:121Y8 20. Schellenberg KL, Lang JM, Chan KM, et al: A clinical tool for office assessment of lumbar spine stabilization enduranceVProne and supine bridge maneuvers. Am J Phys Med Rehabil 2007;86:380Y6 21. Arab AM, Salavati M, Ebrahimi I, et al: Sensitivity, specificity and predictive value of the clinical trunk muscle endurance tests in low back pain. Clin Rehabil 2007;21:640Y7 22. McGill SM, Childs A, Liebenson C: Endurance times for low back stabilization exercises: Clinical targets for testing and training from a normal database. Arch Phys Med Rehabil 1999;80:941Y4 23. Kramer JF, Nusca D, Fowler P, et al: Test-retest reliability of the one-leg hop test following ACL reconstruction. Clin J Sport Med 1992;2:240Y3 24. Reid A, Birmingham TB, Stratford PW, et al: Hop testing provides a reliable and valid outcome measure during rehabilitation after anterior cruciate ligament reconstruction. Phys Ther 2007;87:337Y49 25. Henriksson M, Ledin T, Good L: Postural control after anterior cruciate ligament reconstruction and functional rehabilitation. Am J Sports Med 2001;29:359Y66 26. Kellis E, Amiridis IG, Kofotolis N: On the evaluation of postural stability after ACL reconstruction. J Sports Sci Med 2011;10:422Y3 27. Ageberg E, Roberts D, Holmstrom E, et al: Balance in single-limb stance in patients with anterior cruciate ligament injury: Relation to knee laxity, proprioception, muscle strength, and subjective function. Am J Sports Med 2005;33:1527Y35 28. Patel M, Fransson PA, Lush D, et al: The effect of foam surface properties on postural stability assessment while standing. Gait Posture 2008;28:649Y56 29. Hiemstra LA, Webber S, MacDonald PB, et al: Contralateral limb strength deficits after anterior cruciate ligament


reconstruction using a hamstring tendon graft. Clin Biomech 2007;22:543Y50

activity limitations in patients with knee osteoarthritis. J Rehabil Med 2013;45:192Y7

30. Appelberg B, Johansson H, Sojka P: Fusimotor reflexes in triceps surae muscle elicited by stretch of muscles in the contralateral hind limb of the cat. J Physiol 1986;373:419Y41

34. Lee H-M, Cheng C-K, Liau J-J: Correlation between proprioception, muscle strength, knee laxity, and dynamic standing balance in patients with chronic anterior cruciate ligament deficiency. Knee 2009;16:387Y91

31. Shiraishi M, Mizuta H, Kubota K, et al: Stabilometric assessment in the anterior cruciate ligamentreconstructed knee. Clin J Sport Med 1996;6:32Y9

35. Hewett TE, Myer GD: The mechanistic connection between the trunk, hip, knee, and anterior cruciate ligament injury. Exerc Sport Sci Rev 2011;39:161Y6

32. MacKinnon CD, Winter DA: Control of whole body balance in the frontal plane during human walking. J Biomech 1993;26:633Y44

36. Okada T, Huxel KC, Nesser TW: Relationship between core stability, functional movement, and performance. J Strength Cond Res 2011;25:252Y61

33. Sanchez-Ramirez DC, van der Leeden M, Knol DL, et al: Association of postural control with muscle strength, proprioception, self-reported knee instability and

37. Nesser TW, Huxel KC, Tincher JL, et al: The relationship between core stability and performance in division I football players. J Strength Cond Res 2008;22:1750Y4

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