November 2015

Shear-wave elastography could help optimize Achilles rehab

Karin Silbernagel, PT, PhD, ATC, and Daniel Cortes, PhD, use ultrasound to examine a patient’s Achilles tendon. (Photo courtesy of Karin Silbernagel, PT, PhD, ATC.)

Karin Silbernagel, PT, PhD, ATC, and Daniel Cortes, PhD, use ultrasound to examine a patient’s Achilles tendon. (Photo courtesy of Karin Silbernagel, PT, PhD, ATC.)

By Cary Groner

Researchers at the University of Delaware in Newark are using a new ultrasound-based technique to better understand the effects of rehabilitation on the Achilles tendon, which could help optimize rehab protocols to improve long-term function.

A variety of problems complicate recovery from Achilles tendon ruptures, and patients often retain deficits in the damaged limb long after initial healing has occurred. One study reported that most patients still had symptoms, a reduced quality of life, and functional deficits 12 months after injury regardless of whether they received surgical or nonsurgical interventions.1 Another found significant functional deficits on the injured side even after two years.2

One issue is that healed tendons often end up longer than they were originally, regardless of treatment. Tendon elongation deprives the gastrocnemius muscles of leverage and diminishes plantar flexion capabilities. Early mobilization after surgery slightly reduces elongation, and this correlates with better clinical outcomes.3 But, even though such rehabilitation protocols are becoming more popular, it remains to be seen how much they’ll actually improve patients’ long-term function.

Few people know more about the interface between tendon evaluation and rehabilitation than Karin Silbernagel, PT, PhD, ATC. Silbernagel, a Swedish researcher and coauthor of many of the relevant papers, is now an assistant professor in the Department of Physical Therapy at the University of Delaware.

“There may be less extreme elongations in surgically treated patients, but there’s still a difference between the injured and uninjured leg,” Silbernagel said. “In our research, we’re trying to determine whether early mechanical loading will make things better; if so, it probably has to happen within the first two or three months. But you can’t just do more; you have to do the right things.”

Silbernagel acknowledged that no one yet knows how to gauge when early loading is too early—when help becomes harm.

“Our lab is working on biomarkers that help us understand how mechanical properties change during healing, because when we know that, we can start implementing early exercises,” she said. “The specifics of dosage will be important; many repetitions may stretch the tendon too much.”

Like many clinicians, Silbernagel uses ultrasound to assess tendon length, thickness, and so forth. But it has its limitations.

“It doesn’t tell me anything about the mechanical properties of the tendon—how strong it is or how it changes over time,” she explained.

When tendons heal, compositional and structural changes lead to localized differences in the viscoelastic properties of the tissue. Existing attempts to measure these things tend to be invasive, such as the perioperative implantation of tantalum beads that allow roentgen stereophotogrammetric analysis.4 Despite its drawbacks, the technique has shown significantly larger strain variations in patients treated nonsurgically than surgically.5

Ideally, however, such variables could be measured without implanting radioactive substances into the tendon stumps. Silbernagel and her colleagues believe they’re on the track of such a technique; it’s called continuous shear-wave elastography (cSWE) and it’s so new the papers about it are hot off the press.6,7

The technique calculates viscoelastic properties by applying continuous shear waves with an external actuator, then measuring the wave speed at different excitation frequencies. For the first time, it allows researchers and clinicians to measure the viscoelastic properties of tendons in vivo.

“This may help evaluate tendon recovery, compare the effectiveness of different therapies, and devise patient-specific therapy programs,” Silbernagel said. “Ideally, when we work with patients to build their strength, the body might be able to adapt to longer tendons. I think early physical therapy—mechanical loading of the tendon within the first three months—is crucial. So if we can use this new technique to track and adapt the effect we’re having, there may be significant benefits.”

REFERENCES
  1. Olsson N, Silbernagel KG, Eriksson BI, et al. Stable surgical repair with accelerated rehabilitation versus nonsurgical treatment for acute Achilles tendon ruptures: a randomized controlled study. Am J Sports Med 2013;41(12):2867-2876.
  2. Olsson N, Nilsson-Helander K, Karlsson J, et al. Major functional deficits persist two years after acute Achilles tendon rupture. Knee Surg Sports Traumatol Arthrosc 2011;19(8):1385-1393.
  3. Kangas J, Pajala A, Ohtonen P, Leppilahti J. Achilles tendon elongation after rupture repair: a randomized comparison of two postoperative regimens. Am J Sports Med 2007;35(1):59-64.
  4. Schepull T, Kvist J, Andersoon, C, Aspenberg P. Mechanical properties of during healing of Achilles tendon ruptures to predict final outcome: a pilot Roentgen stereophotogrammetric analysis in 10 patients. BMC Musculoskelet Disord 2007;8:116.
  5. Schepull T, Kvist J, Asperberg P. Early e-modulus of healing Achilles tendons correlates with late function: similar results with or without surgery. Scand J Med Sci Sports 2012;22(1):18-23.
  6. Cortes DH, Suydam SM, Silbernagel KG, et al. Continuous shear-wave elastography: a new method to measure viscoelastic properties of tendons in vivo. Ultrasound Med Biol 2015;41(6):1518-1529.
  7. Suydam SM, Soulas EM, Elliott DM, et al. Viscoelastic properties of healthy Achilles tendon are independent of isometric plantarflexion strength and cross-sectional area. J Orthop Res 2015;33(6):926-931.

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