Sports Medicine Research: In the Lab & In the Field: Predictors of Self-Reported Knee Function in Nonoperatively Treated Individuals with ACL Injury (Sports Med Res)
Tuesday, November 22, 2011

Predictors of Self-Reported Knee Function in Nonoperatively Treated Individuals with ACL Injury

Single-Legged Hop Tests as Predictors of Self-Reported Knee Function in Nonoperatively Treated Individuals with Anterior Cruciate Ligament Injury

Grindem H, Logerstedt D, Eitzen I, Moksnes H, Axe M, Snyder-Mackler L, Engebretsen L, Risberg M. Am J Sports Med. Epub 2011 Aug 9  

The decision to advise operative versus nonoperative treatment in the anterior cruciate ligament (ACL) deficient patient is becoming more challenging. The standard of care across the world varies; in America immediate reconstruction is typical, while in many European countries an attempt at nonoperative care is the norm. The decision to recommend nonoperative care involves objective screening information, subjective reported function, and desired activity level post intervention. The goal of this investigation was to determine if any of the 4 typically utilized hop tests (single hop for distance, crossover hop for distance, triple hop for distance, or 6-m timed hop), which are used to provide objective measures of functional status, could predict knee reported function one-year post injury in 91 patients that elected nonoperative treatment (link to hop test descriptions). The average time between injury and hop testing was 74 ± 30 days because the clinic required patients to undergo five weeks of rehabilitation to ensure adequate hop performance, no knee effusion, and as a precursor for possible reconstruction. Only patients with no other intra-articular injuries (asymptomatic meniscal tears were permissible) and not returning to high-level cutting sports were considered for non-operative treatment limiting those that pursue nonoperative care to 44% of all ACL ruptures treated. Among the participants that elected nonoperative treatment the use of the single-limb hop for distance was the only significant predictor of future reported knee function (IKDC 2000). A cut off of 88% symmetry index on the single-limb hop test (jumping at least 88% of the distance with the injured limb as compared to the uninjured) predicted return to approximately normal knee function with 71.4% sensitivity and 71.7% specificity. Stacking the other hop tests with the single-limb hop for distance did not improve predictive value.

Nonoperative treatment for ACL rupture while growing in popularity does require proper assessment to determine if the outcome will be successful. This study demonstrates that the symmetry index for the single-limb hop for distance test can help predict knee function one year later. Furthermore, this study further validates this test as a screening tool for ACL operative decision making. However, this study was completed in an observational manner to their normal clinic guidelines thus it must be emphasized that while other authors (Hurd et al. Part 1, Part 2) have returned athletes to high level pivoting sports those in this study were recommended operative treatment. This may lead many patients to report relatively high function secondary to not returning to previous activities. Also they did not report their raw hop distances so it is unknown if their hop scores were approximately normal for age or gender and if the symmetry index was influenced by the patient hopping high or low distances.This may explain some of their false negative and positive results of the testing. Does anyone work in a clinic setting that does ACL screening or considers nonoperative care? If so any insights into situations where this has been a challenge? Any tools or ideas you like to employ in this decision making process?

Written by: Dustin Grooms
Structural Changes Occur in Knees After ACL Tears

Grindem H, Logerstedt D, Eitzen I, Moksnes H, Axe MJ, Snyder-Mackler L, Engebretsen L, & Risberg MA (2011). Single-legged hop tests as predictors of self-reported knee function in nonoperatively treated individuals with anterior cruciate ligament injury. The American Journal of Sports Medicine, 39 (11), 2347-54 PMID: 21828364


Jeffrey B. Driban, PhD, ATC, CSCS said...

Dustin: Interesting post. In the second paragraph you state that it was unknown if "the symmetry index was influenced by the patient hopping high or low distance? How does the hopping distance play into interpreting the symmetry index? How do you account for hop distance?

Dustin Grooms said...

Excellent question Jeff! Essentially interpreting the symmetry index should also consider the distance hopped. Since this study did not report any raw hop data we are unable to frame their index scores. This is because some patients may simply not give full effort and have symmetrical hop scores, this maybe a reason for their false positive and negative results, those patients with symmetrical hops may have had poorer outcomes because they did not give full effort and if they had given full effort their symmetry index would be lower and not indicative of nonoperative treatment. We notice this in our practice and one simply has to have an idea of normative data for a population and\or experience in the test to determine if the patient is giving full effort and continually encourage them to try to jump as far as possible. Another way around it is to take the peak of the trials instead of averaging the trials. However, as this study did not report such data we don’t know if this is the case… maybe those that turned out to be non-copers also had low hop scores??

Kristal N said...

Remember this only looks at knee function at one year. Check the guidelines for long-term implications for the meniscus as the 3 year risk of meniscal tear is quite high but I do not remember if those folks went back to sport.

Link to guidelines:

Jeffrey B. Driban, PhD, ATC, CSCS said...

Dustin: Are there any articles you could recommend for normative data on the symmetry index? If not, are there any rules of thumb that a clinician could use to determine if the person is not providing full effort (and therefore, making their symmetry look better)?

Kristal: Thanks for the link. It's a very interesting set of guidelines. I think function and structure are two different, but both very important, things to look at among surgical versus nonsurgical care. One of the challenges with assessing surgical or nonsurgical management beyond 1 to 3 years is how rapid our management of ACL injuries has changes. I think we also need to get a better idea of how to identify copers that can function at high levels without ACLs. I think that's where this study is interesting. It showed a clinical protocol for filtering out potential noncopers (perhaps a little to conservatively since they excluded people that wanted to return to high-level loading sports) and then conducted the screening. Unfortunately, they would still have a lot of people that screened as potential copers but actually fail. It's interesting to note that ACL reconstruction doesn't tend to reduce the risk of OA down the road but again we need to keep in mind that surgical and nonsurgical management have changed considerable over the past 10 to 30 yeas and that the older studies may not have tried to identify copers and noncopers. I think this is a very interesting area of research and may lead to another major change in our management of ACL injuries.

Dustin Grooms said...

Kristal: I know the Delaware group has returned folks to high level activity and NCAA division 1 sports, but their current follow up did not hit the 3 year mark. I am told we should see the long-term follow ups coming out soon if not recently.

Jeff: De Carlo Journal of sports rehab 1997 Normative data for ROm and SLhop in high school is a decent starting point
Van der Harst Clinical biomech Leg kinematics and kinetics in landing from a single-leg hop for distance.

Both of those are good places to start, really just looking at the means and standard deviations from any study that reports them is helpful. There are multiple ACL specific investigations that report hop lengths for the ACL vs. healthy side that can be helpful as well to give you a ball park.

Jake Marshall ATC said...

Can some one explain to me what a symmetry index is? I assume it is a a way to statistically say how symmetric the hops were. But I try not to assume.


Dustin Grooms said...

Hey Jake,

The symmetry index is the involved leg distance hopped divided by the uninvolved leg distance hoped. So if you jump 90 cm on your ACL leg and 100 cm on your non-injuried leg you would have a symmetry index of 0.90 or be 90% symmetric. Good question to interpret the results :)

Mark Feger said...

This article is very interesting and the findings are initially surprising as the least athletic task resulted in the greatest predictive ability. However the single leg jump for distance is the one task out of the four that gives the purest estimation of quadriceps function without regards to other hip and thigh musculature. With the understanding that the quadriceps are shown to be inhibited in many ACL deficient patients could that be why the single leg hop gave the best indication? Therefore individuals having a greater than 88% symmetry index could theoretically have less inhibited quadriceps initially and consequently report greater function at the 1 year follow up.

Dustin Grooms said...

That is a very cool point Mark! While some of the other hop tests may be considered more intensive, a key issue with them is that momentum is a factor with them all but not the very basic single leg hop for distance. If you bring up the article and view the 4 tests it is clear that controlling forward momentum is a key component of especially the other three; as such the need to generate maximum force is less so as this is partially washed out by the repeated nature of the tests and not coming back to a full stop. Thus by removing it and making the test boil down to a single power output measure perhaps this removes some of the ability to compensate with momentum or other strategies over the longer distances. The inhibition point is very interesting… As the super imposed burst technique to quantify inhibition is done so by measuring force production, it makes sense that a test that boils down to a one time max force production would correlate the most with possible quadriceps muscle inhibition… A very cool study would be correlating those two tests (quad inhibition level with single leg hop), as that would give a great easy clinical measure of inhibition.

David Logerstedt said...

Dustin and Jeff,
I am pleased that you reviewed this article. This is a timely article looking at the predictability of hop tests on knee function in ACL deficient patients. To boil it down, patients with knee function within normal ranges were 2.5 times more likely to hop greater than 88% hop LSI on the single hop than those with knee function below normal ranges.

First, the patients choose nonoperative treatment, not operative treatment. Second, the IKDC 2000 subjective knee form was used to measure knee function. As intent to return to previous level of ac¬tivity is not a predictor of actual return, measuring success after injury should not be based on return to sports but how the knee functions and the patient’s satisfaction of that function.

In regards to the raw hop distances, first there is very little research on normative data for all 4 hop tests. (DeCarlo 1997, Ross 2002) However, these are data for high school and collegiate athletes. This study included ages from 13 to 60. Secondly, we have found that the uninvolved limb is relatively stable in regards to hop distance over several testing periods. Lastly, we can assume that the researchers have some quality control in place to ensure patients gave maximal effort. We must consider that patients may be apprehensive or fearful to hop maximally on either limb.

Jeff, the study did not exclude those that wanted to return to high level sports, they only recommend that they don’t. Two, this did not filter out potential non-copers. No ACL screening was used in this study to classify potential copers and noncopers. Level III-IV athletes were excluded, much different from being a noncoper. Level is based on the type of sports the patient participates in.

From this study, we have no way of knowing if quadriceps inhibition was a factor. The Norway group uses isokinetic testing, not isometric testing with burst superimposition. Remember, the correlation with quadriceps strength and hop testing is moderate at best. We use burst superimposition testing with isometric MVIC. We do not let people hop if there is profound quadriceps weakness or substantial inhibition, as we think it is unsafe and exposes the patient to too much risk for reinjury.

Great blog. Glad to see it.

David Logerstedt, PT, PhD
Post-doctoral Research Fellow
University of Delaware

Dustin Grooms said...

Thanks for responding Dr. Logerstedt! Excellent response and addressing of the concerns brought up. Great to see the author and expert in the area join the discussion!

Hege Grindem said...

I will only add some points to David's response.

The Delaware and Norway collaborative research group has what is likely the most extensive scientific database on hop tests in ACL-injured patients. In our data, there simply is no association between raw hop scores on the unaffected leg and the symmetry index. Thus, in our results, the symmetry index was fully independent of whether the patient has high or low hop distances. Furthermore, in this paper we did not average the trials, we used the peak. The two methods yield similar results in terms of symmetry indexes - at least when following our protocol for hop testing.

Whether quadriceps strength, inhibition, neuromuscular control or the patient's confidence in knee function are the most important factors is an interesting discussion. The purpose of this paper was however to utilize easily accessible tests that clinicians can use to identify, rather than explain, differences in self-reported 1 year outcome.

Thank you again for reviewing the paper, we truly appreciate it.

Hege Grindem, PT, MSc
Norwegian Research Center for Active Rehabilitation, Department of Sport Medicine, Norwegian School of Sport Sciences, Department of Orthopaedics, Oslo University Hospital, and the Norwegian Sports Medicine Clinic

Jeffrey B. Driban, PhD, ATC, CSCS said...

Hege & David: Thank you for the comments. This is exciting research and I look forward to seeing how this progresses.

Could you clarify your guidelines for selecting patients for surgical or nonsurgical management? The paper suggested that "the main reason for choosing nonoperative treatment is that the patient does not aim at returning to level I pivoting sports and experiences acceptable or no functional limitations". Does this infer that if a patient has adequate function after the 5-week rehab period that they would be recommended for nonoperative treatment while an individual with episodes of giving way during that period would be recommended for reconstruction? If this is the case, could this be a quasi-screening (granted not validated yet) for copers (managing to regain some form of functional ability sans ACL) and noncopers (episodes of giving way or insufficient stability)? This strategy along with suggesting patients trying to return to high level sports undergo reconstruction seems to increase the likelihood of nonoperative success by reducing the number of potential noncopers; correct? In your experience (clinical or research) do you find that even though you recommend a reconstruction to an individual trying to return to high level sports that the patient still wants to try nonoperative management? For example, you had 54% of the cohort participating in level I sports at baseline. In your practice are many of those patients returning to level I sports or deciding to change their level of sport participation?

Thanks for the comments and I look forward to more research in this area.

Hege Grindem said...

Hi Jeff,
You are absolutely right. Nonoperative candidates at our institution are essentially patients who do not play/want to return to soccer, football, basketball, etc, and who have adequate function.

All patients at our institution undergo 5 weeks of rehab before the decision of surgery or nonop treatment is made. For the operatively treated patients, this improves preop knee function-which correlates to better postop knee function. We also find that patients need time to properly understand the differences between a nonop and op treatment plan, and they get a feeling of how their knee would function with rehab alone. Some patients also adjust to their life without level I sports participation, and decide not to go back to sport during this period.

I think I understand and agree with your statements regarding copers and noncopers, however it is confusing because a coper is defined as a nonoperatively treated patient who returns to sport without episodes of giving way. We do not aim for these patients to return to sport e.g. to finish the remainder of the season, as the intent behind the University of Delaware classification into potential copers and noncopers did. Our patient selection is for long term nonoperative treatment.

Regarding your last questions, I encourage you to follow our coming papers.

Hege Grindem, PT, MSc
Norwegian Research Center for Active Rehabilitation, Department of Sport Medicine, Norwegian School of Sport Sciences, Department of Orthopaedics, Oslo University Hospital, and the Norwegian Sports Medicine Clinic

Jeffrey B. Driban, PhD, ATC, CSCS said...

Thanks Hege for the additional information. I look forward to seeing your upcoming papers. Best of luck!

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