Mechanical Instability After an Acute Lateral Ankle Sprain

Article Outline

• Abstract
• Methods
  • Subjects
  • Instrumentation
  • Testing Procedures
  • Statistical Analysis
• Results
• Discussion
• Conclusions
• References
• Copyright

Abstract 

Hubbard TJ, Cordova M. Mechanical instability after an acute lateral ankle sprain.

Objective

To examine the natural recovery of mechanical laxity after an ankle sprain over an 8-week period.

Design

Prospective cohort study.

Setting

Biodynamics research laboratory.

Participants

Subjects with an acute lateral ankle sprain (n=16; 7 men, 9 women; age, 19.5±0.7y; mass, 64.6±8.1kg; height, 171.9±9.6cm) and healthy controls (n=16; 7 men, 9 women; age, 20.4±1.7y; mass, 76.9±11.1kg; height, 176.5±11.1cm) participated.

Interventions

Not applicable.

Main Outcome Measures

Subjects with acute ankle sprains were tested 3 days after injury and again 8 weeks later. Anterior and posterior displacement (mm) and inversion and eversion rotation (°) were measured with an instrumented arthrometer. For each dependent variable, a 2 × 2 × 2 repeated-measures multivariate analysis of variance was performed.

Results

A significant interaction was found between group, time, and side for anterior translation (F=4.24, P=.05). There were also significant main effects for group. There was significantly more anterior displacement at day 3 (F=19.52, P=.001) and at week 8 (F=8.45, P=.010) in the injured group compared with the healthy group. There was also significantly more inversion rotation at day 3 (F=2.70, P=.002) and at week 8 (F=5.4, P=.033) in the injured group compared with the healthy group.

Conclusions

The lack of significant differences in mechanical laxity over an 8-week period suggests that natural recovery of laxity takes longer than 8 weeks. Further research needs to be conducted to examine how long this laxity persists and the role ankle rehabilitation plays in mechanical stability restoration.

Key Words: Arthrometry, articular, Rehabilitation

List of Abbreviations: AP, anteroposterior, ATFL, anterior talofibular ligament, CAI, chronic ankle instability, CFL, calcaneofibular ligament, FADI, Foot and Ankle Disability Index, MANOVA, multivariate analysis of variance

ANKLE SPRAINS are the most common injury in sports-related activity.¹ A negative consequence of approximately 40% of lateral ankle sprains is the development of CAI.² CAI is the development of repetitive ankle sprains and persistent symptoms after injury.³ Research over the past 40 years has unsuccessfully tried to elucidate the causes of CAI. Recent evidence has suggested mechanical instability of the ankle may lead to the development of CAI,⁴, ⁵, ⁶, ⁷, ⁸ which may be present as a result of incomplete healing of the ligaments of the ankle.

Previous research has reported mechanical instability at the ankle after damage to the lateral ligaments of the ankle. Compared with an intact condition, Kovaleski et al⁹ reported a significant increase in anterior displacement and inversion/eversion rotation with sectioning of the ATFL and CFL. Sectioning of the ATFL alone also significantly increases anterior displacement compared with an intact condition.⁹ Bahr et al¹⁰ also reported observable mechanical instability with sectioning of the ATFL alone, but significant changes in mechanical instability with sectioning of both the ATFL and CFL. Similar studies¹¹, ¹² have also reported mechanical instability after sectioning of the ATFL alone, and the ATFL combined with the CFL. These studies demonstrate damage to the lateral ligaments similar to the damage experienced after a lateral ankle sprain lead to mechanical instability of the ankle. If the ligaments do not heal appropriately, this mechanical instability could remain and lead to the development of CAI.

Numerous investigations have assessed mechanical instability after an acute lateral ankle sprain.¹³, ¹⁴, ¹⁵, ¹⁶, ¹⁷ These studies reported that despite rehabilitation and treatment, it appears that a moderate percentage (≈30%) of subjects have mechanical ankle instability up to a year after an initial ankle sprain. The lack of stability restoration may be due to improper ligament healing or the ligaments healing in an elongated state. Current management of ankle sprains may not allow for proper mechanical stability restoration. Although the aforementioned¹⁸, ¹⁹, ²⁰, ²¹, ²² studies reported mechanical instability after an acute sprain, the methods to assess mechanical instability (manual stress test and stress radiography) have been questioned in the literature. Mechanical instability was assessed with methods that have poor reliability and validity, which may have led to improper determination of mechanical stability status.¹⁸, ¹⁹, ²⁰, ²¹, ²²

The recent development of an instrumented arthrometer has led to a more reliable assessment of mechanical stability at the ankle.²³, ²⁴ The ankle arthrometer gives researchers the ability to assess ligament status by assessing mechanical instability at the ankle. This device has allowed researchers and clinicians to determine the mechanical status of the ligaments after injury so that proper immobilization, exercise progression, and return to activity decisions can be made. In spite of its strengths, the arthrometer has not been used to measure instability immediately after an acute injury. Therefore, the purpose of this project was to examine the natural recovery of mechanical instability by measuring instability immediately after an acute lateral ankle sprain and again 8 weeks later.

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Methods 

Subjects 

Sixteen subjects with a first-time acute unilateral ankle sprain (7 men and 9 women; age, 19.5±0.7y; mass, 64.6±8.1kg; height, 171.9±9.6cm) and 16 healthy controls with no history of ankle injury (7 men and 9 women; age, 20.4±1.7y; mass, 76.9±11.1kg; height, 176.5±11.1cm) participated in the study. There were no significant differences in age (P=.282), height (P=.137), or weight (P=.941) between the 2 groups. The involved ankle of the injured group was matched with the same side (right or left) of the healthy group. All subjects in the injured group were diagnosed with a grade 1 or 2 lateral ankle sprain by the same certified athletic trainer. Subjects in both groups could have no previous history of lower leg or ankle injury to either ankle. Classification of ankle injury was based on the classification described by Bergfeld et al.²⁵ A grade 1 ankle sprain was defined as a partial tear of the lateral ligament complex, and a grade 2 was defined as decreased motion, some loss of function, torn ATFL, intact CFL, some ligamentous instability (positive anterior drawer), swelling, hemorrhage, and point tenderness. Of the 16 subjects with acute ankle sprains, 3 had grade 1 sprains, and 13 had grade 2 sprains. These subjects were tested 3 days after injury and again 8 weeks later, while control subjects were tested at their convenience and again 8 weeks after their first test. No subjects participated in a formal rehabilitation program, as we wanted to assess the natural recovery of mechanical stability after an acute ankle sprain. All subjects were advised to use ice and elevation to help with pain and swelling, and they were given an Ace bandage to help with swelling. An Ace bandage was worn by all subjects for an average of 2.3±1.2 days after the initial test session. All subjects signed the university's approved informed consent form.

Instrumentation 

Measurement of ankle-subtalar joint stability was performed with a portable instrumented ankle arthrometer.²³, ²⁴ The ankle arthrometer has been reported to have high reliability and validity.⁹, ²³, ²⁴ The arthrometer consists of an adjustable plate that is fixed to the foot, a load-measuring handle that is attached to the footplate through which the load is applied, and a tibial pad attached to the tibia. A 6 degrees of freedom spatial kinematic linkage connects the tibial pad to the footplate that measures all components of motion (3 rotations and 3 translations) of the footplate relative to the tibial pad.²³, ²⁴ Measurements quantify the AP load-displacement and inversion-eversion rotational laxity characteristics of the ankle-subtalar joint complex (talocrural and subtalar joints). The spatial kinematic linkage of the arthrometer measures the relative motion between the arthrometer footplate and the reference pad attached onto the tibia. A computer with an analog to digital converter was used to simultaneously calculate and record data. The resulting AP displacement (mm) and inversion-eversion rotation (degree of range of motion) were recorded. A custom software program written in LabView 7^a was used for data collection.

The FADI is a subjective self-report of function that has 2 components to gauge the amount of self reported disability. The main FADI assesses activities of daily living, and the Sports Scale assesses more difficult tasks that are essential to sport. Reliability and sensitivity of both components have been previously reported in subjects with and without ankle instability.²⁶ A self-report of function was given to all subjects so we could determine how function changes 8 weeks after an acute lateral ankle sprain.

Testing Procedures 

At both testing sessions (3d and 8wk after injury), all subjects filled out an injury history form as well as the main FADI and FADI Sport. Additionally, at both testing sessions, mechanical joint stability was measured with an instrumented ankle arthrometer. The ankle arthrometer assessed ankle laxity by previously described testing procedures.²³, ²⁴ Subjects were positioned lying supine on the treatment table. The foot was positioned so that it extended over the edge of the table. A restraining strap was wrapped around the distal lower leg 1cm above the malleoli to prevent lower-leg movement during testing. The examiner secured the arthrometer to the foot by placing the bottom of the foot onto the footplate and adjusting the heel and dorsal clamps. The heel clamp prevented the device from rotating on the calcaneus, while the dorsal clamp secured the foot to the footplate. The tibial pad was then positioned 5cm above the ankle malleoli and secured to the lower leg. To minimize variation, the arthrometer was oriented and positioned in a similar manner for all tests. The order of testing was randomly assigned between ankles, and 1 examiner (T.J.H.) obtained all measurements.

The ankles were positioned at neutral (0° of flexion) during testing.²³, ²⁴ To record total AP displacement, the ankle was loaded with 125N of anterior and posterior force. Starting at the neutral position, an anterior load was applied initially, followed by a posterior load. For inversion-eversion rotation, the ankles were loaded to 4N·m of inversion and eversion torque. Starting at the neutral position, inversion loading was applied first, followed by eversion loading. The computer monitor was visualized to control the amount of force required to obtain the maximum load of 125N for AP displacement and 4N·m for inversion-eversion rotation.

Statistical Analysis 

All results were analyzed with SPSS statistical software, version 13.^b For each dependent variable (anterior displacement, inversion rotation, main FADI score, FADI Sport score), a 2×2×2 repeated measure MANOVA was run with the between factor being group (injured, control), time (3 days, 8 weeks), and the within factor with repeated measures being side (involved, uninvolved). Follow-up univariate F tests were used to assess the effect of group, time, and side on each dependent variable. Effect sizes were also calculated for all dependent variables. To calculate effect sizes, we used the involved ankle of injured group vs the matched ankle of the control group. The level of the significance was set a priori at P value of .05 or less for all analyses.

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Results 

Means and standard deviations (SDs) for all dependent variables are presented in Table 1, Table 2. A 2×2×2 repeated-measure MANOVA revealed a significant interaction for group, time, and side for anterior translation (F=4.24, P=.05). Follow-up univariate F tests revealed significant main effects for group and side. There was significantly more anterior displacement at day 3 (F=19.52, P=.001) and at week 8 (F=8.45, P=.010) in the injured group compared with the healthy group (fig 1). Additionally, there was significantly more anterior displacement for the involved ankle of the injured group compared with the uninvolved ankle of the injured group at day 3 (F=10.87, P=.001) and at week 8 (F=9.516, P=.001). There were no significant differences in the amount of anterior displacement between day 3 and week 8 for the injured group (P=.08).

Table 1. Dependent Variables 3 Days After Injury

NOTE. Values are means ± standard deviations.

Abbreviation: FADI, Foot and Ankle Disability Index.

Table 2. Dependent Variables 8 Weeks After Injury

NOTE. Values are means ± standard deviations.

Abbreviation: FADI, Foot and Ankle Disability Index.

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• Fig 1. 

  Means ± SDs for anterior displacement (mm) after an acute ankle sprain. *Significant difference between groups (P=.001). ^†Significant difference between groups (P=.010).

There was no significant interaction found between group, time, and side for inversion angular displacement (F=1.658, df=1.0, P=.215). However, follow-up univariate F tests revealed significantly more inversion rotation at day 3 (F=12.70, P=.002) and at week 8 (F=5.4, P=.033) in the injured group compared with the healthy group (fig 2). Additionally, there was significantly more inversion rotation for the involved ankle of the injured group compared with the uninvolved ankle of the injured group at day 3 (F=4.73, P=.002) and at week 8 (F=2.40, P=.047). The amount of inversion rotation significantly decreased (F=17.00, P=.033) between day 3 and at week 8 for the injured group. Effect sizes were high for anterior displacement at day 3 and at week 8 (1.92 and 1.5, respectively) and for inversion rotation (1.63 and 1.45, respectively), which indicates the clinical importance of our laxity results.

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• Fig 2. 

  Means ± SDs for inversion rotation (°) after an acute ankle sprain. *Significant difference between groups (P=.002). ^†Significant difference between groups (P=.033).

There was a significant interaction for group, time, and side for the FADI (F=25.66, P=.001) and FADI Sport (F=33.22, P=.001). Follow-up univariate F tests revealed significant main effects for group, time, and side. For the main FADI scale, the scores for the involved ankles of the injured group were significantly less (F=21.8, P=.001) than the control group, and the uninvolved ankles of the injured group (F=4.496, P=.003) at day 3. Similarly, for the FADI Sport scale, the scores for the involved ankles of the injured group were significantly less (F=26.06, P=.001) than the control group and the uninvolved ankles of the injured group (F=5.115, P=.001) at day 3. At week 8 for the main FADI scale, the scores for the involved ankles of the injured group were significantly less (F=4.336, P=.001) than the control group, and the uninvolved ankles of the injured group (F=6.123, P=.001). Similarly, for the FADI Sport scale, the scores for the involved ankles of the injured group were significantly less (F=3.847, P=.006) than the control group and the uninvolved ankles of the injured group (F=3.856, P=.006) at week 8. Additionally, the injured group score on the FADI (F=17.14, P=.001) and the FADI Sport (F=25.78, P=.001) significantly improved between day 3 and 8 weeks after the injury.

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Discussion 

We found that 8 weeks after natural recovery from a grade 1 or 2 lateral ankle sprain, mechanical laxity is still significantly present in the ankle. Specifically, there was significantly more anterior displacement and inversion rotation compared with a healthy group 3 days after injury. Eight weeks after the initial injury, anterior displacement did not significantly decrease, indicating that ligament stability may not be restored. Interestingly, we did report an increase in inversion rotation even though all subjects had a negative-inversion talar tilt. All subjects were diagnosed with a grade 1 or 2 lateral ankle sprain, with no damage to the CFL (as detected by a talar tilt test). The increased inversion laxity on the arthrometer may mean the subjects had a more severe ankle sprain then originally diagnosed. This may be because the arthrometer is more reliable than standard manual stress tests. Solely relying on manual stress tests to assess ligament injury may lead to injuries being classified as less severe, and this may also lead to improper management and the development of mechanical instability.

All subjects enrolled onto the study did not participate in formal rehabilitation; however, at the initial visit, subjects were instructed to treat their sprain with rest, ice, compression, and elevation. One of the reasons mechanical laxity did not change over the first 2 months after the ankle sprain may be because of the lack of direct treatment and management of the ankle sprains. However, lack of treatment of acute ankle sprains is actually quite common: it has been reported that approximately 55% of people experiencing ankle sprains do not seek treatment from a health care professional.²⁷ Lack of initial proper management and rehabilitation and the view that “it's just an ankle sprain” may lead to a lack of recovery of mechanical stability 8 weeks after the initial injury. Protection of the joint and directed rehabilitation may be able to improve the mechanical status of the ankle joint after initial sprain and then prevent further joint injury.

To our knowledge, no other studies have examined acute mechanical laxity at the ankle with an instrumented ankle arthrometer. However, an instrumented ankle arthrometer has been used to measure mechanical laxity in patients with CAI.⁶ Anterior displacement in patients with CAI has been reported to be on average 12 to 14mm, with inversion rotation averaging 34° to 35°.⁶ The injured subjects in the current study averaged 15mm of anterior displacement and 36° of inversion rotation 3 days after injury. Those averages improved slightly to 14mm and 34°, which compare favorably to patients with CAI. The lack of mechanical stability after the acute injury may lead to the development of CAI.

In addition to the observed mechanical instability, subjective level of function was also impaired in subjects with acute ankle sprains. Scores on the FADI and FADI Sport were significantly less than the healthy group. Although scores on both scales significantly increased over the 8-week period, they were still significantly different from the healthy group 8 weeks after the initial injury. On the main FADI, the involved ankle of the injured group averaged 88% and on the FADI Sport 72%. On these questionnaires, subjects consistently reported difficulties with activities that involved running, cutting, and jumping. They also reported issues with activities of daily living, including going up and down stairs, walking long distances, and general pain. All 16 injured subjects had returned to their normal physical activity (exercise) or sport (intramurals) before the 8-week testing session, despite their significant impairment in function. All 16 subjects stated that they were not able to do certain activities that involved running or cutting, or able to compete at the same level as before their ankle sprain, but they all stated they wanted to be active. It may be this early return to activity, despite subjectively not feeling ready, that may also lead to chronic joint pathology.

Several previous studies have examined mechanical stability after an acute ankle sprain.¹³, ¹⁴, ¹⁵, ¹⁶, ¹⁷, ²⁸ Although these studies did not use an ankle arthrometer to assess laxity, it is important to note that previous research has also shown increased mechanical laxity several weeks to months after an acute sprain. These studies also reported that despite rehabilitation and treatment, there was still a moderate percentage (≈30%) of subjects with objective mechanical laxity and subjective instability up to a year after an initial ankle sprain. Given that all of the studies included a period of immobilization as part of their treatment, initial management may not allow for proper ligament healing, which would result in increased mechanical laxity. One of the original studies examining mechanical laxity at the ankle after an acute ankle sprain was performed by Freeman.¹⁵ Although mechanical stability did improve over 3 months, 42% and 33% of subjects from each treatment group had an increased talar tilt compared with their uninvolved healthy ankle at 3 months. Konradsen et al¹⁶ also took stress radiographs of the ankle immediately after injury and 3 months postinjury. Five percent of subjects manifested pathologic stress values at 3 months. Munk et al¹⁷ also used stress radiographs in addition to a manual stress examination to measure mechanical stability 9 to 13 years after an ankle sprain. They reported that over half the subjects had mechanical laxity 1 year after injury.

Manual stress tests have also been used to assess mechanical laxity after an ankle sprain. Avci and Sayh²⁸ reported 30% of subjects had a positive anterior drawer test 2 weeks after injury, and 11% had a positive anterior drawer test 6 weeks after injury. Cetti et al¹⁴ reported approximately 12% of subjects had a positive anterior drawer at 8 weeks after injury. The last study to measure mechanical stability subjectively was by Brostrom,¹³ in which it was reported that 28% of subjects in one treatment group and 31% of subjects in another group had a positive anterior drawer over 1 year after the initial ankle sprain. Although most subjects were free of symptoms at follow-up, 20% reported that the ankle felt unstable. The results from these studies have been questioned as a result of the lack of reliability and validity of the measures used to assess mechanical laxity.¹⁸, ¹⁹, ²⁰, ²¹, ²² However, the methods used in the current study have been reported as both reliable and valid assessments of mechanical laxity at the ankle, suggesting that our reported lack of significant decrease in mechanical laxity 8 weeks after injury are a reflection of the true pathology of ankle injury.

On the bases of previous research and the results of the current study, it is imperative that initial treatment and rehabilitation of ankle sprains be examined. With the high percentage of recurrence and chronic symptoms, it appears that treatment and rehabilitation of ankle sprains is needed to manage ankle sprains. Further research should examine mechanical stability over a period longer than 8 weeks and should also examine what sensory changes are present after an ankle sprain. Initial management and rehabilitation plans should be examined to determine how to best help restore mechanical stability and overall function after an acute lateral ankle sprain.

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Conclusions 

After an acute grade 1 or 2 lateral ankle sprain, there is significantly more anterior displacement and inversion rotation compared with a healthy group. Additionally, anterior displacement did not significantly decrease 8 weeks after the initial injury, indicating that ligament stability may not be restored. This lack of mechanical stability 8 weeks after injury may lead to further ankle joint pathology. Further research needs to be conducted to examine how long this laxity persists and the role ankle immobilization and rehabilitation play in mechanical stability.

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• b SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.