Rate of Force Development as an Adjunctive Outcome Measure for Return-to-Sport Decisions After Anterior Cruciate Ligament Reconstruction
Return to play criteria following ACL reconstruction has been a debated topic, especially as of late. Unfortunately, we do not have clear cut objective tests that will tell us when an athlete is ready to go back onto the field safely and effectively. Common tests, such as the single leg hop test, is often used as a test in the terminal phases of rehabilitation. Other objective data such as strength has been tested to determine the deficits between involved knee vs uninvolved knee. However, we are unsure whether strength translates over to field play.
In this study, rate of force development was the primary focus. The authors define RFD as the ability to produce a muscle force quickly. The study used professional soccer players over a span of 6 seasons. The athletes who suffered an ACL tear underwent surgery and all started on the same rehabilitation program. However, what was different was that at 6 months post-op the athletes underwent an additional 20 weeks of a training program focusing on RFD development. The authors decided to recommend this additional 20 weeks due to significant deficits in RFD at 6 months. Below are some of the key points of the article:
- One criterion that has been used to determine recovery and readiness to return to sport following an ACL recon- struction is achieving 85% or 90% of the maximal strength of the contralateral limb. However, it has been shown that the time required to develop muscular strength in many types of daily2 and sports activities38 is considerably shorter (0-200 milliseconds) than that required to achieve maximal contraction strength (300 milliseconds or greater).
- The RFD measured under isometric conditions has been identified as a key parameter characterizing the extent of neural drive to the muscle during explo- sive muscle actions.
- The subsequent post hoc analysis indicated no significant difference in RFD30 values between the involved and uninvolved limbs measured at baseline (preinjury) and at 12 months postreconstruction. However, there was a significant difference between limbs at 6 months post-reconstruction.
- For the involved limb, there was a significant difference in RFD30 values between baseline and 6 months, but not between baseline and 12 months
- At 6 months post-reconstruction, the average RFD30 value for the involved side was only 80% of the baseline value (TABLE 1, FIGURE 3) and only 79% of the value of the uninvolved side, which was also mea- sured at 6 months postreconstruction
- At 12 months postreconstruction, the mean RFD30 value for the involved side was 98% of the baseline value and 97% of the value of the uninvolved side.
So this asks the question: Should we be looking at RFD more closely as an indicator for return to sport? Is it more applicable/transferable to sports play?
For those of you who are part of the Sports Performance Special Interest Group in the Sports Section, this article was just brought up with a lot of good discussion!
FUNCTIONAL PERFORMANCE TESTING OF THE HIP IN ATHLETES: A SYSTEMATIC REVIEW FOR RELIABILITY AND VALIDITY
The purpose of this article that was published in IJSPT was to review the literature for reliability and validity of functional performance tests used with a young, athletic population with hip dysfunction. Four functional movement tests showed validity: deep squat, single leg squat, single leg balance, and star excursion balance test. Some very interesting points were concluded after review of the recent literature.
- The evidence for validity suggests that gluteal tendinopathy and function of the hip abductors may be assessed with the single-leg stance test, single-leg squat test and SEBT.
- Provocation of pain during 30-seconds of single leg stance had high sensitivity (100%) and specificity (97.3%) in detecting tendinopathy of the gluteus medius and minimus confirmed by magnetic resonance imaging (MRI).
- The deep squat test was performed on subjects with radiologically confirmed FAI. The maximal squat depth in subjects with FAI (41% of leg length) was significantly less when compared to healthy controls (32% of leg length). Clinicians may test maximum squat depth in patients with suspected FAI to help confirm a diagnosis of FAI.
- The FMS™ is an intriguing tool for patients with varied hip dysfunction as it tests multiple movement patterns that require different components of hip ROM, strength, and trunk control.
- Hop tests have also shown ability to discriminate injured from uninjured lower extremities, particularly in the assessment of ankle instability and post-operatively following ACL reconstruction. Researchers have established normative, gender-specific values for hop tests in young, athletic subjects. These values may serve as benchmarks that may be helpful in interpreting an “abnormal” score for a subject with hip-related dysfunction.
- The deep squat and single-leg stance test demonstrated evidence of validity in a population of patients with hip-related dysfunction.
- The SEBT and single-leg squat test provided evidence of validity through an analysis of kinematics and muscle function in healthy subjects.
What can we take away from this? Simple balance tests like single leg balance can be effective at helping determine potential hip tendinopathy. Furthermore, including deep squat and single leg stance should be part of our hip evaluations.
This review, published in the American Journal of Sports Medicine this past month (Jan. 2013), is an updated review that focuses on prevention of secondary ACL tears following ACL reconstruction. It is very well done and should be read by anyone who is currently working on an athletic patient coming off ACL reconstruction. The authors discussed some of the current concepts from a wide range of articles, as well as their own research that they performed. Predictors of future injury and evidence based practices to correct these deficiencies are discussed.
Some of the key points to the review:
- Abnormal movement patterns after an ACL rupture are not isolated to the injured knee alone. There is mounting evidence of a bilateral neuromuscular response to an ACL injury that persists and
may even be exacerbated after reconstruction
- Specifically, peak knee angles, moments, and joint powers were higher in the uninvolved limb of athletes after ACLR when compared with controls and to their own unin- jured limb. Interestingly, these behaviors are not unlike those in athletes with acute ACL deficiency
- Compensatory strategies of the uninvolved hip were the primary predictor of risk in athletes who went on to a secondary ACL injury within 1 year of returning to sports activity.
- As 1 of 4 predictive factors in a highly specific and sensitive model for secondary ACL injury risk, the transverse-plane uninvolved hip net moment impulse early during landing independently predicted the risk of a secondary injury with 77% sensitivity and 81% specific-ity.
- Much like primary ACL injuries, the majority of secondary ACL injuries are caused by noncontact mechanisms,92 under- scoring altered intrinsic neuromuscular control as an impor- tant factor in injury risk.
- Similarly, in a group of 63 athletes cleared to return to sport after ACLR, 14 of the 42 (33%) female athletes went on to a contralateral ACL rupture within 1 year. Female athletes represented 88% of the documented contra- lateral limb ACL injuries
- While deficits in hamstring strength were unrelated to functional performance tasks in athletes 6 months after ACLR,41 the ratio of hamstring-to-quadriceps torque production appears to be a key variable in the primary ACL injury risk model.63 Strength symmetry of at least 85% is now advocated for ath- letes beginning reintegration into cutting, pivoting, and jumping sports.
- Performance on the single-limb hop test for distance on ACL-deficient patients predicted their self-reported func- tion 1 year after ACLR with 71% sensitivity and specific- ity.3
- The coordinated coactivation of the hamstrings and quadriceps may play a role in mitigating primary injury risk by way of reducing ligament strain29 and promoting normal landing mechanics.26 Balanced agonist and antago- nist coactivation may also protect the reconstructed knee against second ACL injury risk via similar protective mech- anisms. Deficits in the neuromuscular coordination of the hamstrings and quadriceps on the reconstructed limb may manifest as excessive landing contact noise during both double- and single-legged landing tasks
- Progressive single-limb landing activities, like anterior and lateral jumping progressions (Figure 2), may not only accentuate post-ACLR limb deficits69 but can also provide an excellent training tool to help athletes avoid quadriceps-dominant landing techniques56 and achieve the desired level of sports performance symmetry
- The cumulative data indicate that reduced hamstring strength and recruitment is related to initial and likely secondary injury risk, which supports the use of isoki- netic testing in return-to-sport decision making and guidance of interventions to reduce the risk of a second injury.
As the list above is not all inclusive, I found those points to be very beneficial. Some things we can take away: We must look at the uninvolved side quite closely throughout the rehabilitation process, we must consider hamstring strength relative to quadricep strength for ligament stability, neuromuscular control is a huge factor in predicting secondary ACL tears, and consistently retesting biomechanics of double and single leg exercises from all 3 planes is extremely important in both identifying deficiencies and prescribing rehabilitation exercises (maybe we should consistently videotape their biomechanics as they progress?- Food for thought).