November 2011

Chronic ankle instability affects postural control

Figure 2. Measuring dynamic postural control.

Research suggests that individuals with chronic ankle instability use different movement strategies to maintain postural control than individuals with healthy ankles. These changes may be related to alterations in movement variability associated with ankle instability.

By Lisa Chinn, MS, ATC, and C. Collin Herb, MEd, ATC

Chronic ankle instability (CAI) is a phenomenon that has been reported to occur in 30% to 70% of individuals who suffer an initial lateral ankle sprain.1,2 CAI has been defined as the occurrence of repetitive bouts of lateral ankle instability and feelings of “giving way,” often resulting in numerous subsequent ankle sprains.3

Repeated ankle sprains represent a serious healthcare issue in the U.S. CAI has been connected to degenerative changes,4 reduced physical activity,5,6 activity limitations,7,8 withdrawing from professional activities,9 and, potentially, increased body mass index.10 Although the underlying etiology of CAI is not fully understood, it is believed that an initial ankle sprain can lead to sensorimotor function alterations. One aspect of the sensorimotor system that has received much research attention is postural control.

Postural control research

Postural control has been defined as the ability to maintain stability above a narrow base of support.11,12 Although the general definition of postural control is well understood, the methods used for measuring postural control are diverse. Researchers and clinicians have used single- and double-limb stance, static and dynamic tasks, different constraints on subjects, as well as instrumented and noninstrumented measures. Each method has advantages and disadvantages; however, with all the various methods and measurements of postural control, the published literature is not consistent regarding quantification of altered postural control.

Figure 1. Modified Romberg position on a force plate.

Riemann13 published a 2002 review of literature on CAI and postural control. In his report, Riemann references Freeman and colleagues,11,14 the first researchers to propose a link between CAI and altered postural control. Since the early work of Freeman et al, however, researchers have presented mixed results from studies comparing individuals with CAI and healthy controls.12,15-19 Riemann points out that research has also produced conflicting results with regard to alterations in balance in injured versus noninjured limbs of individuals with CAI.16,20

While Riemann did not perform any statistical analysis, he concluded that the current literature could not establish a clear link between CAI and altered postural control. He believed the lack of universal inclusion and exclusion criteria for CAI and variations in research procedures are the cause of disparities in published results. Studies re­ported using a wide range of populations, including profes­sional basketball players, amateur soccer players, gymnasts, college students, and others.

Researchers also looked noninstrumented outcomes, such as time to stabilization following a jump, or counting “errors” during single-limb stance of unstable surfaces, as well as instrumented outcomes such as center of pressure force plate measures. The many variations in methods meant no strong conclusions could be drawn.

In 2008, McKeon and Hertel21 performed a systematic review to evaluate whether postural control is affected ad­versely in CAI. Their paper included only studies in which participants balanced in a modified Romberg position and that presented center of pressure measurements from a force plate. They identified eight articles16,18-20,22-25 that fit their inclusion criteria. After calculating effect sizes, the authors stated that postural control appears to be adversely affected in those with CAI compared with healthy controls, but also noted the results were not conclusive. The effect sizes indicated that postural control was worse in individuals with CAI, however, the effect size point measures were generally weak and several of the confidence intervals were large, crossed zero, or both. Even when limiting the included studies to those with single-limb balance on a force plate, similar to Riemann,13 McKeon and Hertel cited inconsistent criteria for CAI, as well as the variation in participants, methods, and outcome measures, as potential reasons for conflicting results. The included studies also reported varying length in trial times, sampling rates, and participant demographics.

A relatively new force plate measure that can be assessed during static balance is the time-to-boundary (TTB) method of assessing spatiotemporal characteristics.26 Whereas center of pressure measures assess only the location of center of pressure in relation to the base of support, TTB incorporates both the location and the velocity of each center of pressure point. TTB estimates the time it would take for the center of pressure to reach the boundary of the base of support if the center of pressure was to continue on its trajectory at its instantaneous velocity.22 A lower TTB indicates the individual in question has less time to make a postural correction before losing control, or, more simply, a lower TTB means greater postural instability.

Hertel and Olmstead-Kramer22 reported that the five of six TTB measures showed significant differences between persons with CAI and healthy controls, whereas only one of eight traditional center of pressure measures found similar results. Other studies have also found that persons with CAI display lower TTB measures while maintaining single-limb balance.27-29 The differences in TTB measures indicate that, while preserving postural control, CAI patients function closer to their boundary of support or have faster velocities compared with healthy controls.

Researchers have attempted to evaluate force plate measures to determine if there is one specific measurement to distinguish between the ankles of controls and those with CAI.30,31 Ross et al30 recorded 15 different center of pressure force plate measures while participants performed single-limb, eyes-open static balance for 20-second trials. They report that standard deviation of the ground reaction force in the medial-lateral direction had “fair” accuracy for discriminating between unstable and stable ankles. This measure accurately classified 68.2% of the measured ankles.

Knapp et al31 also evaluated force plate measures, including TTB, to determine if a single force plate measure could discriminate between CAI and healthy ankles. In their study, participants performed single-limb balance for 10 seconds, however, they reported both eyes-open and eyes-closed results. Overall, of the 30 different force plate outcomes evaluated, three measures were predictors of CAI status: eyes-closed standard deviation of center of pressure in the medial-lateral direction; eyes-closed percentage of center of pressure range used in the medial-lateral direction; and eyes-closed absolute minimum of TTB in the medial-lateral direction. However, none of the significant measurements had strong likelihood ratios associated with them, indicating that a single force plate measure cannot completely predict CAI status.

Pope et al32 further evaluated postural control by assessing the location, on the plantar aspect of the foot, of the center of pressure and the most unstable (TTB minima) data points.  Overall, they found the CAI group positioned their center of pressure more anteriorly and laterally on their base of support compared with healthy controls. Other researchers have reported lateral plantar pressure distributions while walking in CAI,33,34  but this was the first study to evaluate the location of the center of pressure.

Many authors13,21,32,35-38 point out that published studies look only at successful trials of postural control. In order to complete the required task, CAI subjects may utilize different postural control strategies com­pared with healthy indivi­duals. In healthy volun­t­eers, measurements of postural control in single-leg stance reveal that the head, trunk, and leg func­tion as one unit, with rotations and corrections occurring at the ankle. Horak and Nashner de­scribe this mechanism as an “ankle strategy” where muscular contractions in the leg will reposition the body over the supportive foot to maintain balance.39 In contrast, Riemann13 believes that CAI patients are specifically using a “hip strategy” to facilitate “normal” postural control, leading investigators to conflicting results. McKeon and Hertel21 and Pope et al32 include the potential use of a knee strategy as well as a hip strategy to maintain postural control. Although it is difficult to accurately document and quantify the use of a hip or knee strategy, studies have shown that those with CAI have altered proximal kinematics35,40-43 and neuromuscular stimulation43-47 during a variety of tasks, indicating that CAI has altered movement patterns. Pope at al32 refer to various variability theories as an explanation for these alterations.

Variability theories

The belief that movement variability is essential for the stability and function of the sensorimotor system is a concept that has developed only recently.48 Movement variability has been viewed as both detrimental and beneficial to skilled coordinated movement. The generalized motor program theory identifies variability as error in movement, planning, and execution. This theory states that, with practice, variability will be reduced or potentially eliminated, whereas the uncontrolled manifold hypothesis states that variability is associated with motor redundancy. In addition, generalized motor program theory maintains that a controller allows some elements to have high variability as long as they remain in a selected subspace. In contrast, dynamical systems theory states that inherent movement variability is essential for enabling individuals to maintain postural control under changing conditions.48,49 This theory has been used in neuromuscular dysfunction and Parkinson disease research along with sports medicine injury research.49,50

Variability in systems depends on constraints of the systems, the task being accomplished, degrees of freedom of the system, and the difficulty of the task. Stergiou et al51 augmented this theory by stating that desired variability should be nonlinear. They believe there is an optimal zone of variability, and that a decrease in this optimal zone creates a rigid system while an increase results in a noisy and unstable system.

The human body has many joints and degrees of freedom between these joints, giving the sensorimotor system numerous pathways to accomplish tasks.48-50 This affords the body many ways to accomplish goals and, if one part of the system falters, the body can go to another option to accomplish its goal.52 Spontaneous pattern formation between component parts has been found to emerge through self-organization.50 This process of self-organization depends on constraints that are placed on the body by the task, the environment, and the organism itself.50 Davids et al50 defines constraints as boundaries or features that interact to limit the form of biological systems searching for optimal states of organization. When tasks are required by the body, the ability to accomplish a goal in multiple ways places less stress on specific tissues and allows flexibility to perturbations or constraints. This system flexibility allows the body to disperse stresses among different tissues, providing a longer adaptation time between loading events.

Organized movement patterns are known as coordinative structures and are believed to be the body’s way of organizing and controlling complex movements.50 These coordinative structures allow the human body to exploit the interconnectedness of the system. However, in some parts of the system variability can reflect individuals’ compensatory action. In sports variability can be observed in athletes who are skillful at highly dimensional tasks and exploiting available degrees of freedom.50 Less skilled athletes fix their degrees of freedom and demonstrate more variability that is not functional or necessary.

The variability, or “noise,” produced during postural control studies in the past was not explained, but this variability has now been identified as unavoidable and functional.50 Cognitive scientists have been unable to reveal, even in elite athletes, reproducible invariant movement patterns. Therefore, the goal of treatment in sports medicine should not be to achieve an ideal movement pattern but to encourage patients to overcome the constraints that affect them in order to improve functional capacity and, subsequently, performance.50 Evidence has indicated that variability in joint coordination is an essential component of functional movement, providing necessary flexibility for successful task execution.53

Figure 3. Sample center of pressure output.

Studies of movement variability during jump-landing tasks suggest that athletes with CAI appear to have less movement variability than healthy athletes.54 Interestingly, athletes with CAI also have less movement  variability than “copers,” who have a history of ankle sprain but no lingering instability. Additional research suggests that movement variability may be influenced by whether the ankle instability is functional or mechanical in nature.55 Athletes with functionally unstable ankles demonstrate greater frontal-plane movement variability, while those with mechanically unstable ankles demonstrate greater anterior-posterior ground reaction force variability. The implications of these variability patterns for postural control in patients with CAI, however, are unclear.


Researchers are interested in determining the underlying causes of postural instability in individuals with CAI. Clinicians and athletes, hoverer, ultimately want to know if rehabilitation can change the alterations. McKeon et al28 found that, after four weeks of balance training, force plate measures improved in those with CAI compared with a group with CAI who did not complete the training. Similarly, Sefton et al56 had a group of persons with CAI perform six weeks of balance training and reported that participants improved significantly compared with a group of healthy controls who did not perform any rehabilitation. Further research should be done to determine the most effective rehabilitation protocol in altering postural control to help clinicians treat CAI patients.

Overall, people who suffer ankle sprains do not completely comprehend the potential long-term effects of not fully treating and rehabilitating the injury. Individuals who develop CAI most likely suffer from postural control changes, however, they often believe that little can be done for their pathology and choose to alter their lifestyle to accommodate their instability. Research confirms the potential of rehabilitation protocols for improving postural control in those with CAI. Clinicians should be aware of these rehabilitation protocols, educate patients, and implement balance training rehabilitation protocols to help those with CAI.

Lisa Chinn, MS, ATC, and C. Collin Herb, MEd, ATC, are doctoral students studying chronic ankle instability in the Kinesiology Program at the University of Virginia in Charlottesville.


1. Garrick JG. The frequency of injury, mechanism of injury, and epidemiology of ankle sprains. Am J Sports Med 1977;5(6):241-242.

2. Waterman BR, Owens BD, Davey S, et al. The epidemiology of ankle sprains in the United States. J Bone Joint Surg Am 2010;92(13):2279-2284.

3. Hertel J. Functional anatomy, pathomechanics, and pathophysiology of lateral ankle instability. J Athl Train 2002;37(4):364-375.

4. Harrington KD. Degenerative arthritis of the ankle secondary to long-standing lateral ligament instability. J Bone Joint Surg Am 1979;61(3):354-361.

5. Konradsen L, Bech L, Ehrenbjerg M, Nickelsen T. Seven years follow-up after ankle inversion trauma. Scand J Med Sci Sports 2002;12(3):129-135.

6. Anandacoomarasamy A, Barnsley L. Long term outcomes of inversion ankle injuries. Br J Sports Med 2005;39(3):e14.

7. Gerber JP, Williams GN, Scoville CR, et al. Persistent disability associated with ankle sprains: a prospective examination of an athletic population. Foot Ankle Int 1998;19(10):653-660.

8. Birmingham TB, Chesworth BM, Hartsell HD, et al. Peak passive resistive torque at maximum inversion range of motion in subjects with recurrent ankle inversion sprains. J Orthop Sports Phys Ther 1997;25(5):342-348.

9. Verhagen RA, de Keizer G, van Dijk CN. Long-term follow-up of inversion trauma of the ankle. Arch Orthop Trauma Surg 1995;114(2):92-96.

10. Morrison KE, Hudson DJ, Davis IS, et al. Plantar pressure during running in subjects with chronic ankle instability. Foot Ankle Int 2009;31(11):994-1000.

11. Freeman MA, Dean MR, Hanham IW. The etiology and prevention of functional instability of the foot. J Bone Joint Surg Br 1965;47(4):678-685.

12. Tropp H, Odenrick P. Postural control in single-limb stance. J Orthop Res 1988;6(6):833-839.

13. Riemann BL. Is there a link between chronic ankle instability and postural instability? J Athl Train 2002;37(4):386-393.

14. Freeman MA. Instability of the foot after injuries to the lateral ligament of the ankle. J Bone Joint Surg Br 1965;47(4):669-677.

15. Tropp H, Odenrick P, Gillquist J. Stabilometry recordings in functional and mechanical instability of the ankle joint. Int J Sports Med 1985;6(3):180-182.

16. Tropp H. Pronator muscle weakness in functional instability of the ankle joint. Int J Sports Med 1986;7(5):291-294.

17. Konradsen L, Ravn JB. Prolonged peroneal reaction time in ankle instability. Int J Sports Med 1991;12(3):290-292.

18. Perrin PP, Bene MC, Perrin CA, Durupt D. Ankle trauma significantly impairs posture control–a study in basketball players and controls. Int J Sports Med 1997;18(5):387-392.

19. Bernier JN, Perrin DH, Rijke A. Effect of unilateral functional instability of the ankle on postural sway and inversion and eversion strength. J Athl Train 1997;32(3):226-232.

20. Isakov E, Mizrahi J. Is balance impaired by recurrent sprained ankle? Br J Sports Med 1997;31(1):65-67.

21. McKeon PO, Hertel J. Systematic review of postural control and lateral ankle instability, part I: can deficits be detected with instrumented testing. J Athl Train 2008;43(3):293-304.

22. Hertel J, Olmsted-Kramer LC. Deficits in time-to-boundary measures of postural control with chronic ankle instability. Gait Posture 2007;25(1):33-39.

23. Rozzi SL. Balance training for persons with functionally unstable ankles. J Orthop Sports Phys Ther 1999;29(8):478-486.

24. Baier M, Hopf T. Ankle orthoses effect on single-limb standing balance in athletes with functional ankle instability. Arch Phys Med Rehabil 1998;79(8):939-944.

25. Cornwall MW, Murrell P. Postural sway following inversion sprain of the ankle. J Am Podiatr Med Assoc 1991;81(5):243-247.

26. Hertel J, Olmsted-Kramer LC, Challis JH. Time-to-boundary measures of postural control during single leg quiet standing. J Appl Biomech 2006;22(1):67-73.

27. McKeon PO, Hertel J. Spatiotemporal postural control deficits are present in those with chronic ankle instability. BMC Musculoskelet Disord 2008;9:76.

28. McKeon PO, Ingersoll CD, Kerrigan DC, et al. Balance training improves function and postural control in those with chronic ankle instability. Med Sci Sports Exerc 2008;40(10):1810-1819.

29. Wikstrom EA, Fournier KA, McKeon PO. Postural control differs between those with and without chronic ankle instability. Gait Posture 2010;32(1):82-86.

30. Ross SE, Guskiewicz KM, Gross MT, Yu B. Balance measures for discriminating between functionally unstable and stable ankles. Med Sci Sports Exerc 2009;41(2):399-407.

31. Knapp D, Lee SY, Chinn L, et al. Differential ability of selected postural-control measures in the prediction of chronic ankle instability status. J Athl Train 2011;46(3):257-262.

32. Pope M, Chinn L, Mullineaux D, et al. Spatial postural control alterations with chronic ankle instability. Gait Posture 2011;34(2):154-158.

33. Nawata K, Nishihara S, Hayashi I, Teshima R. Plantar pressure distribution during gait in athletes with functional instability of the ankle joint: preliminary report. J Orthop Sci 2005;10(3):298-301.

34. Nyska M, Shabat S, Simkin A, et al. Dynamic force distribution during level walking under the feet of patients with chronic ankle instability. Br J Sports Med 2003;37(6):495-497.

35. Gribble PA, Robinson RH. Alterations in knee kinematics and dynamic stability associated with chronic ankle instability. J Athl Train 2009;44(4):350-355.

36. Gribble PA, Robinson RH. An examination of ankle, knee, and hip torque production in individuals with chronic ankle instability. J Strength Cond Res 2009;23(2):395-400.

37. Brown C, Padua D, Marshall SW, Guskiewicz K. Individuals with mechanical ankle instability exhibit different motion patterns than those with functional ankle instability and ankle sprain copers. Clin Biomech 2008;23(6):822-831.

38. Brown CN, Mynark R. Balance deficits in recreational athletes with chronic ankle instability. J Athl Train 2007;42(3):367-373.

39. Horak FB, Nasher LM. Central programming of postural movements: adaptation to altered support surface configurations. J Neurophysiol 1986;55(6):1369-1381.

40. Gribble PA, Hertel J, Denegar CR. Chronic ankle instability and fatigue create proximal joint alterations during performance of the Star Excursion Balance Test. Int J Sports Med 2007;28(3):236-242.

41. Gribble PA, Hertel J, Denegar CR, Buckley WE. The effects of fatigue and chronic ankle instability on dynamic postural control. J Athl Train 2004;39(4):321-329.

42. Caulfield B, Garrett M. Changes in ground reaction force during jump landing in subjects with functional instability of the ankle joint. Clin Biomech 2004;19(6):617-621.

43. Caulfield BM, Garrett M. Functional instability of the ankle: differences in patterns of ankle and knee movement prior to and post landing in a single leg jump. Int J Sports Med 2002;23(1):64-68.

44. Beckman SM, Buchanan TS. Ankle inversion injury and hypermobility: effect on hip and ankle muscle electromyography onset latency. Arch Phys Med Rehabil 1995;76(12):1138-1143.

45. Bullock-Saxton JE. Local sensation changes and altered hip muscle function following severe ankle sprain. Phys Ther 1994;74(1):17-28.

46. Bullock-Saxton JE, Janda V, Bullock MI. The influence of ankle sprain injury on muscle activation during hip extension. Int J Sports Med 1994;15(6):330-334.

47. Van Deun S, Staes FF, Stappaerts KH, et al. Relationship of chronic ankle instability to muscle activation patterns during the transition from double-leg to single-leg stance. Am J Sports Med 2007;35(2):274-281.

48. van Emmerik RE, van Wegen E. On the functional aspects of variability in postural control. Exerc Sport Sci Rev 2002;30(4):177-183.

49. Davids K, Glazier P. Deconstructing neurobiological coordination: The role of the biomechanics-motor control nexus. Exerc Sport Sci Rev 2010;38(2):86-90.

50. Davids K, Glazier P, Araujo D, Bartlett R. Movement systems as dynamical systems: The functional role of variability and its implications for sports medicine. Sports Med 2003;33(4):245-260.

51. Stergiou N, Harbourne R, Cavanaugh J. Optimal movement variability: a new theoretical perspective for neurologic physical therapy. J Neurol Phys Ther 2006;30(3):120-129.

52. McKeon PO, Hertel J. The dynamical-systems approach to studying athletic injury. Athl Ther Today 2006;11(1):31-33.

53. Clark JE, Phillips SJ. A longitudinal study of intralimb coordination in the first year of independent walking: a dynamical systems analysis. Child Dev 1993;64(4):1143-1157.

54. Brown C, Bowser B, Simpson KJ. Movement variability during single leg jump landings in individuals with and without chronic ankle instability. Clin Biomech 2011 Aug 20. [Epub ahead of print.]

55. Brown CN, Padua DA, Marshall SW, Guskiewicz KM. Variability of motion in individuals with mechanical or functional ankle instability during a stop jump maneuver. Clin Biomech 2009;24(9):762-768.

56. Sefton JM, Yarar C, Hicks-Little CA, et al. Six weeks of balance training improves sensorimotor function in individuals with chronic ankle instability. J Orthop Sports Phys Ther 2011;41(2):81-89.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.