Authors: Jefferson Brand, MD, Richard Hardy, Ed.D., LAT, CSCS, Christopher Butler, Ph.D., Emily Monroe, MD
Richard Hardy Ed.D., LAT, CSCS
111 17th Ave E #101, Alexandria, MN 56308
Office number: 320-589-6443
Cell number: 320-760-2031
Richard Hardy is a certified athletic trainer and coordinator of research at Heartland Orthopedic Specialists in Alexandria, MN. He is also contracted to the University of Minnesota Morris where he serves as an instructor and provides athletic training services.
Kinetic chain injuries and their relationship to subsequent ACL tears
Purpose: The relationship between previous kinetic chain injuries and the likelihood of anterior cruciate ligament (ACL) injuries remains under-explored. We compared the number of ankle injuries between subjects that had a surgically treated ACL tear to subjects that had a surgically treated shoulder injury (e.g., labral tear). We evaluated if a previous disruption of the lower kinetic chain (e.g., ankle injury) is a predisposing factor for ACL injuries. Our hypothesis was that ACL reconstruction patients will have a higher rate of previous ankle injuries than the control group (surgically treated labral tear).
Methods: Overall, 108 patients have undergone either ACL reconstruction or labral repair surgery. To insure similarity, we assessed Tegner activity level, knee alignment, and Beighton scale. Patients completed a questionnaire about demographics, ankle injury history, and the AOFAS Ankle-Hindfoot scale. ANOVA statistically tested demographic data. Fisher’s exact test was used to determine if differences in previous ankle injury rates existed between groups.
Results: Overall, 63 patients (34 males/29 females) had ACL reconstruction and 45 patients (36 males/9 females) in the control group had surgery for labral lesions. No statistical differences occurred (P>0.05) for demographic data (age, BMI), Tegner activity scale, knee alignment, Beighton scale, or AOFAS Ankle-Hindfoot scores for each ankle. This suggests that the groups were comparable. Previous ankle injuries were common in both groups but not statistically significant.
Conclusions: Comparing surgically ACL injured knees to surgically treated labral tears, there was no significant difference in the rate of previous ankle injury. Therefore, previous ankle injuries may not predispose nor protect against future anterior cruciate ligament injuries.
Applications in sport: The knee is a link in the kinetic chain between the hip and ankle joints. Due to this, dysfunction of the ankle or hip joints could negatively affect the function of the knee joint. Therefore, we set out to see if ankle injury history is a predisposing factor for tears of the ACL of the knee. Through our research, we found that this was not the case; ACL tears occur independently to the kinetic chain.Keywords: Kinetic chain, anterior cruciate ligament, ankle injuries
In 1955, Art Steindler (17) described a kinetic chain as “a combination of several successively arranged joints constituting a motor complex”. In the lower extremity, the kinetic chain consists of the hip, knee, and ankle joints (14). In the lower kinetic chain, ankle sprains are the most common injury in sports (3,4,11). An ankle sprain may represent a weak link that protects the chain against a knee injury (i.e., an ankle sprain buffers the leg against a more serious knee injury). Or, an ankle sprain may represent a proprioceptive and kinesthetic change in the lower kinetic chain and may make the risk of anterior cruciate ligament (ACL) injury more likely. However, we cannot answer either of these conjectures with confidence, as there is little published evidence about ankle sprains or ankle injuries and their relationship to subsequent kinetic chain injuries (10, 13).
However, a few studies have explored the topic of kinetic chain injuries and future predisposition to later injuries. Injuries to the hips may increase the risk for knee injuries, as the knee is part of the same kinetic chain (1,5). After analyzing football athletes, Bedi et al. (1) reported that femoroacetabular impingement may significantly increase the risk of ACL injury due to the increased resistance to femoral internal axial rotation during a dynamic maneuver such as a pivot landing. Furthermore, Gomes et al. (5) reported a strong association between decreased hip range of motion and ACL ruptures in soccer players. Therefore, since the ankle joint acts as the kinetic link between the lower leg and foot, it is reasonable to assume that injuries to the ankle are predisposing factors for knee injuries.
To address the shortcomings in these previous studies, we propose comparing patients with surgically proven labral injuries without a previous ACL injury. These patients may represent a suitable and comparable group with respect to age, BMI, affected side, activity level, knee alignment and level of ligamentous laxity. Therefore, our investigation compared those patients with a surgically proven ACL tear to those with a surgically proven labral tear (control group) for prevalence of previous ankle injuries.
By comparing patients with surgically treated ACL tears to a control group with injuries outside the lower kinetic chain (i.e., shoulder labral tears), we sought to evaluate if a previous disruption of the lower kinetic chain (e.g., ankle injury) is a predisposing factor for ACL injuries. We hypothesized that patients with an ACL reconstruction will have a higher rate of previous ankle injury (due to their location on the lower kinetic chain) when compared to a matched series of patients within our control group. Our null hypothesis was that there would be no difference in previous ankle sprains between the ACL reconstruction group and the control group (labral tears).
The University of Minnesota Institutional Review Board approved this investigation. The sample consisted of patients treated by the senior author between September 2011 and June 2014. Patients were divided into either an ACL reconstruction group or the control group. Inclusion criteria required patients to have had either an ACL or a labral tear that was verified arthroscopically and treated surgically. Patients that were excluded from the study included those who had a knee dislocation, a history of both an ACL injury and a labral injury, a revision to their ACL reconstruction or labral repair, or did not agree to participate.
Informed consent was obtained from either the patient or from a parent or legal guardian if the patient was less than 18 years of age. Demographic data was then collected from each patient (gender, weight, height, BMI). To ensure the group similarity, the patients completed the Tegner activity scale and the senior author examined both knees, evaluating knee alignment (measured by goniometer) and Beighton score for ligamentous laxity (scores greater than 4 were considered ligamentously lax). The patients then completed a questionnaire and the AOFAS Ankle-Hindfoot score. The questionnaire identified previous ankle injuries and characterized the side, timing, and frequency of the ankle injury as well as treatment, time missed, and use of an ankle brace. The type of injury and sport of participation at the time of injury were also collected with this questionnaire. The AOFAS Ankle-Hindfoot score was used to assess the impact that the ankle sprains had on the patient. Although the AOFAS Ankle-Hindfoot scale may not be a valid patient reported outcome measure, we used it as it was not a primary outcome measure of this investigation (7,12,15,16).
Comparisons between groups with categorical variables (type of injury, gender, knee alignment, history of ankle sprain, brace usage) were analyzed using Fisher’s exact test. Continuous variables (age, weight, height, BMI, Tegner score, Beighton score, number of ankle injuries, missed time from activities) were analyzed using ANOVA. Statvue (SAS, Wilmington, NC) was used for analysis.
Our primary variable was the difference in the number of ankle injuries between the patients with ACL reconstruction and the control group and the number of previous ankle injuries. As there is no pilot or investigational data as to what would represent a clinically meaningful difference between groups, we were unable to conduct an a priori power analysis for our primary variable.
Of the 123 patients recruited for our study, 15 did not meet our inclusion criteria (1 had a knee dislocation, 3 had both an ACL injury and a labral injury, 5 presented for revision to their labral repair and 6 presented for revision to their ACL reconstruction). Thus, our final sample consisted of 108 consecutive patients in which 63 patients ((F/M) 29/34, (R/L) 34/29) had ACL reconstruction and 45 patients ((F/M) 9/36, (R/L) 29/16) were in the control group. Analysis of demographic data revealed that more males (36) than females (9) were in the control group (P=0.0075) (Table 1). Outside of this finding, demographic data was comparable between both groups. More patients in the control group did suffer an ankle injury than in the ACL reconstruction group (75.6% vs. 64.1% respectively), however, this was not a significant finding (P=0.5749).
From our sample, there were 57 total ankle injuries (Table 2). There was not a statistically significant difference for ipsilateral or contralateral sided ankle injuries when compared to patients that had a right-side ACL group to the control group that had a right-side labral repair. The same was also true for the left side with ipsilateral and/or contralateral ankle injuries (Figures 1 and 2).
There was no significant difference in location and types of ankle injuries between both groups (P=0.5749) and there was no significant difference between the two groups whether the injury was contact or non-contact (P=0.1182). Ten percent (3 right side and 3 left side) of patients from the ACL group reported the use of ankle braces while nine percent (2 right side and 2 left side; 1 of the 2 indicated that they had their ankle taped) of the control group reported the use of ankle braces. There was no difference in the frequency of ankle sprains between the ACL group and the control group for those not wearing ankle braces (P=0.33) and those wearing ankle braces (P=1.0).
To test the relationship of kinetic chain injuries, we compared patients with ankle injuries who later suffered an ACL tear (experimental group) or a labral tear (control group). We sought to learn if a previous ankle injury is a predisposing factor for ACL injuries of the knee, which is part of the ankle’s kinetic chain. We found no difference between the two groups.
This finding is supported by Liu and Stubblefield (10) who reported that it is unlikely that mechanical ankle instability affects injuries at more proximal joints. They came to this conclusion after analyzing 72 NCAA Division I athletes. However, only the most elite collegiate athletes participate at this level of athletics, therefore, making inferences about the general public is unreliable. For this reason, we sampled the general public and our results showed that the kinetic chain was not affected by previous ankle sprains.
Although, our study lends support to Liu and Stubblefield’s (10) investigation that knee injuries occur independently to the kinetic chain, there is some literature that refutes our findings. Kramer et al. (8) compared 33 adult females with a history of ACL injury to 33 adult females with no history of knee injury and reported that those with a history of ACL injury were more likely to have had an ipsilateral ankle injury. Our groups were larger than Kramer et al. (8) and consisted of both genders. Our study also compared other confounding variables (e.g., Beighton scale).
The strength of our investigation is that we have not identified a positive relationship between a previous ankle sprain and an ACL tear after controlling for confounding variables in both genders. This is comforting evidence to the multitude of young athletes that have had a previous ankle sprain. However, once injured, the risk for another injury increases (2,6,9). It is our recommendation that athletes participate in an injury prevention training program and consider ankle bracing to decrease the likelihood of suffering an initial injury or reinjuring the previously injured joint.
There are several limitations to this investigation. First, the ankle sprain data was collected at a distant time from the injury, thus is subject to recall bias. Second, the female to male ratio was different between the two groups suggesting that they may not be comparable. Third, despite the larger number of patients enrolled, this investigation may be underpowered. Fourth, although the data was not analyzed, we used the AOFAS Ankle-Hindfoot score, which may not be a validated measure.
Comparing surgically treated ACL injured knees to surgically treated labral tears, there was no significant difference in the rate of previous ankle injury. Therefore, previous ankle injuries may not predispose nor protect against future ACL injuries.
APPLICATIONS IN SPORT
The knee is a link in the kinetic chain between the hip and ankle joints. Due to this, dysfunction of the ankle or hip joints could negatively affect the function of the knee joint. Therefore, we set out to see if ankle injury history is a predisposing factor for tears of the anterior cruciate (ACL) ligament of the knee. Through our research, we found that this was not the case; ACL tears occur independently to the kinetic chain.
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Figure 1. A bar graph comparing the contralateral ankle injuries by the side of the ACL injury and labral injury. For example, the right sided ACL injury are compared to the labral injured patients for previous left sided ankle injuries. None represents no previous ankle injury. Sprain indicates a previous ankle sprain by patient history. Fracture is patient reported history of a previous ankle fracture.
Figure 2. A bar graph comparing the ipsilateral ankle injuries by the side of the ACL injury and labral injury. For example, the right sided ACL injury are compared to the labral injured patients for previous right sided ankle injuries. None represents no previous ankle injury. Sprain indicates a previous ankle sprain by patient history. Fracture is patient reported history of a previous ankle fracture.