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Issue 16

Table of Contents

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Association Between Physical Tests and Patients-Reported Outcomes in Athletes Performing Exercise Therapy for Patellar Tendinopathy

Dr. Cody Misuraca PT, DPT

Key takeaways:
  • In the participants from the study in last month’s research review, baseline physical tests did not predict improvements in patella tendinopathy symptoms or function
  • In the participants from the study in last month’s research review, improvements in physical tests did not correlate with improvements in patella tendinopathy symptoms or function
  • In the participants in the study from last month’s research review, double-leg vertical jump height did not significantly improve, which is in-line with previous research
  • The participants in the study from lasn’t month’s research review did demonstrate small improvements in quadriceps strength; other similar studies have mixed results for quadriceps strength improvements
  • Tests such as quadriceps isometric peak force and the double-leg vertical jump might not be the best tests for people with patella tendinopathy
  • There are other tests that make more sense for patella tendinopathy “in theory,” but have not been tested in research
  • Progression through a graded exercise program that recreates physical demands of sport might be the best test for returning people to sport

 

As a rehabilitation professional, I am a strong proponent of using objective tests and measures to aid in tracking progress and making decisions regarding readiness for people to return to sport participation after rehabbing pain and injury. That said, when we decide to use a test for these purposes, we should have some certainty that the test actually does a good job of relating to improved function and physical readiness.

We wouldn’t want to hold somebody back based on minimal or zero progress on a test that isn’t actually valid for their condition, and similarly we wouldn’t want to clear somebody to return to sport based on improvements in a test that isn’t valid. The topic of this month’s research review is an article which sought to determine the usefulness of common physical tests for people with patella tendinopathy.

This month’s review is a continuation of last month’s, now looking at a follow-up study that examined the relationship between physical tests and patient-reported outcomes following the 24-week exercise interventions for patellar tendinopathy¹. To review, the original study² utilized two different exercise programs with a goal of improving symptoms and function in athletes experiencing patella tendinopathy. One of the groups used a very simple eccentric exercise program consisting of single leg squats on a decline slant board, while the other group used a progressive exercise program that started with isometrics and then added isotonic, and then plyometric exercises based on individual progression of symptoms.

Both groups reported significant overall improvements in symptoms and function via the VISA-P questionnaire, with better outcomes in the progressive exercise group. Additionally, there were no significant differences in the number of participants in each group who returned to sport at their prior level of function. The original study performed several tests both at baseline and at follow-up, including maximum knee extensor muscle force at 60 degrees, maximum hip abductor muscle force, quadriceps, hamstring, soleus, and gastrocnemius muscle flexibility, maximum double-leg vertical jump height, and tenderness to palpation of the patella tendon.

The researchers pooled data from both groups and examined the relationship between baseline and follow-up physical tests and improvements in symptoms and function as reported by the VISA-P. Ultimately, the researchers found:

  1. No significant relationship between any of the baseline physical tests and subsequent improvements on the VISA-P
  2. No significant relationship between improvements on any of the physical tests and improvements in the VISA-P.

 

The lack of correlation between improvements in thee physical tests and improvements in the VISA-P persisted even when the participants were grouped by those who improved the least and the most on the VISA-P.

These results are somewhat unsatisfying as it would make sense to assume that certain baseline physical qualities, or changes in these physical qualities throughout the course of a rehab program, would have a relationship in symptomatic improvement. For instance, it would be reasonable to assume that individuals starting out with lower quadriceps muscle isometric peak force or vertical jump height would have “more to gain” from a rehabilitation perspective, or that improvements in symptoms and function over time would be reflected in improvements in quadriceps isometric peak for or vertical jump height (“it hurts less to engage the quadriceps or jump, so now you can engage the quadriceps harder or jump higher”).

This is not the first study to examine changes in physical tests following exercise interventions for patella tendinopathy. Regarding vertical jump height, a previous study by Sprague et al³ found that participants with patella tendinopathy did demonstrate improved jump height following a 12-week heavy-slow-resistance routine; studies by Agergaard et al⁴ utilizing 12 weeks of heavy-slow vs medium-slow loads, and Ruffino et al⁵ utilizing 12 weeks of heavy-slow vs inertial flywheel exercise found no significant changes in vertical jump height.

The authors of the current study postulate that the lack of improvement in vertical jump height could be related to the multiple variables involved in the vertical jump task, including arm swing and trunk angle. This makes sense to me – while a vertical jump task does involve a high rate of force production from the quadriceps (and thus high loads through the patella tendon), there is the potential for inter-limb compensations (getting better at putting load through the asymptomatic limb) and intra-limb compensations (getting better at using the calf and hip musculature in place of the painful quadriceps) – perhaps the participants in the study just got better at jumping “differently” over time, instead of improving their overall performance.

Regarding quadriceps muscle isometric peak force, several other studies have also reported on changes in people undergoing exercise therapy for patella tendinopathy. The study by Agergaard et al⁴ found improved quadriceps isometric peak force following their 12-week intervention, while the two studies by Sprague et al³ and Ruffino et al⁵ found no changes in quadriceps strength after their 12-week exercise programs (Sprague et al utilized an isometric peak force test, while Ruffino et al utilized 6RM tests on leg press and knee extension machines).

The present study did demonstrate a small overall improvement in quadriceps isometric peak force after 24 weeks of exercise intervention, but changes in this measure of quadriceps strength did not have a significant association with changes in VISA-P scores. While somewhat unexpected, this is also reasonable to me; the patella tendon plays a large role in transmitting forces at high speeds, and people with painful tendons tend to have more issues with high-speed loading. Since isometric peak force testing typically involves taking several seconds to build up to peak force, this test may not be specific enough to the patella tendon’s “job” to capture improvements in its function as pain improves over time.

As rehabilitation professionals, we like using various tests to track our patient’s progress over time, visualize improvement from multiple perspectives, and aid in making decisions about returning to sport. When working with people for patella tendinopathy, it may be the case that double-leg vertical jump and quadriceps isometric peak force tests are not the best tests to track progress and make decisions from. If I had to guess, I would expect some version of a jumping task that is more constrained to demand a higher contribution from the quadriceps would have a better correlation with symptomatic and functional improvements.

One possibility would be a single-leg pushback jump where the testee jumps forward onto one leg and then rapidly pushes themselves backwards again – there would still be the possibility of intra-limb compensations here, but I think this would be a more specific test for the quadriceps and patella tendon than a double-leg vertical jump.

For direct quadriceps testing, I would hypothesize that testing rate of force production (that is, how FAST can the quadriceps achieve peak force) with an isometric setup similar to what is commonly used for quadriceps isometric peak force testing would have a stronger correlation to improvements in symptoms and function.

That said, both of these tests (single leg pushback jump and quadriceps rate of force production) have yet to be validated in the research for this specific application, and the equipment required to do these tests in the clinic are typically on the pricier side (ie force plates, dynamometers with very high sampling rates, etc). My key takeaway from this study is that we can be a little more lenient with recommendations for returning to sport participation for people with patella tendinopathy when their physical tests haven’t improved significantly. And on the flip side, just because somebody has demonstrated improved isometric peak force with the quadriceps, or improved double leg vertical jump performance, that doesn’t necessarily mean they are “more ready” to return to sport than if they hadn’t demonstrated improvements there.

Similar to the approach used in Deng et al’s study that was reviewed last month, having people work through a progressive exercise program that reintroduces heavier isotonic exercises, then plyometric exercises, and then sport-specific tasks based on symptomatic improvements within the exercise program may be the best way to determine readiness for return to sport.

 

References

 

Cody Misuraca is a physical therapist and strength coach in Seattle, WA. He works as a sports physical therapist for a community hospital system and also owns Waypoint Strength and Performance LLC, which offers strength coaching services. The views and opinions expressed in this review are those of the writer and do not necessarily reflect the views or positions of any institutions he is associated with.