Local anesthetic injection resolves movement pain

Local anesthetic injection resolves movement pain, motor dysfunction, and pain catastrophizing in individuals with chronic Achilles tendinopathy, a non-randomized clinical trial

Key Points
Local anaesthetic injection of the Achilles appears to immediately increase calf function and reduce pain and catastrophizing in subjects with Achilles tendinopathy, suggesting peripheral nociceptive input may be a key factor.
Kinesiophobia (which is thought to influence long term outcomes) was not affected by the injection.
There were no differences between subjects with Achilles tendinopathy and the control group in indicators of nociplastic pain.

BACKGROUND AND OBJECTIVE
People with Achilles tendinopathy (AT) demonstrate motor dysfunction, especially
of the calf complex. This motor dysfunction may be linked to psychological factors such as fear of movement. For example, research has found subjects with kinesiophobia regained less calf muscle endurance (measured by heel raises) following a tendon loading programme (1). The presence of pain appears to reduce muscle activation (2), suggesting peripheral nociceptive input may cause motor dysfunction. There is conflicting evidence regarding whether nociplastic pain (driven by sensitization of the central nervous system) is a factor in persistent Achilles tendinopathy.

This study sought to identify indicators of altered central processing (which may suggest nociplastic pain) and determine which of these indicators remain after a local anaesthetic injection into the Achilles tendon in patients with Achilles tendinopathy.

METHODS
The study design was a mechanistic, non- randomized controlled trial. 23 patients with Achilles tendinopathy were recruited alongside 23 controls matched for age, sex, and BMI. Laboratory-based testing of movement-evoked pain ratings, motor performance, pain psychology questionnaires and sensor testing was carried out. All tests were repeated twice with the Achilles tendinopathy group receiving an anaesthetic injection after the first round of testing.

Measurements included calf raise endurance, numeric pain score over last week, movement- evoked pain during the study, VISA-A and the Brief Pain Inventory. Subjects completed 3D motion analysis of stair ascent and ‘waltz box step’, as well as the Tampa Scale of Kinesiophobia (TSK) and Pain Catastrophizing Scale (PCS). Pressure pain threshold (PPT), conditioned pain modulation and temporal summation were also assessed.

People with Achilles tendinopathy demonstrate motor dysfunction of the calf complex.

Peripheral, nociceptive input can be an important piece of the pain puzzle in Achilles tendinopathy.

RESULTS
At baseline the AT group had signs of motor dysfunction in that they were able to complete fewer heel raises compared to the control group. They also had high levels of pain catastrophizing and kinesiophobia and lower pressure pain thresholds. There were no differences between groups for any of the indicators of nociplastic pain.

Following the injection, the AT group had reduced movement-evoked pain and improved calf function – they were able to complete a similar amount of calf raises to the control group. PCS scores (indicating catastrophization) reduced immediately after the injection but returned to near baseline levels when assessed a week later. The injection appeared to have no effect on levels of kinesiophobia.

Furthermore, in the AT group there were correlations between improved heel raise performance and reduced kinesiophobia, but a reduction in pain was not significantly correlated with a reduction in this measure of fear of movement.

LIMITATIONS
The inclusion/exclusion criteria may present a limitation as patients with localized pain on palpation were included and subjects with a ‘systemic condition contributing to pain with activity’ (such as fibromyalgia) were excluded. This may have led to a selective group of patients with only localized symptoms and without many of the features of nociplastic pain.

In addition, the PCS scores were well below clinical cut-off of 30 which would question the clinical significance of changes in this measure.

Finally, the injection was used as a way to reduce or remove peripheral nociceptive input, but it may have had ‘central effects’ too such as expectation of pain relief.

CLINICAL IMPLICATIONS
When we’re putting together the pain puzzle for a patient it’s challenging to know what the key pieces are. We’ve theorized that central factors may be driving pain and so, in some cases, focused more on addressing these factors through education and understanding. However, it appears in this study that peripheral nociceptive input may be key in Achilles tendinopathy. Once that input was reduced by the injection there was an immediate improvement in pain and calf function. Nociplastic pain was not detected. So perhaps we can conclude that peripheral, nociceptive input can be an important piece of the pain puzzle in AT. This would make sense as symptoms are typically well localized and load- related.

This study also hints at another important piece of this puzzle – kinesiophobia (fear of movement). It is associated with longer term outcomes following rehab in AT (1) and heel raise performance, and it didn’t seem to change when peripheral nociceptive input was reduced in this trial.

These findings support an approach to Achilles tendinopathy management that seeks to reduce nociceptive input through load management and increase tissue load capacity through progressive loading, while also reducing fear of movement using education and graded exposure. A short- term reduction in pain alone (as achieved through an injection in this study) appears unlikely to be enough to reduce kinesiophobia and improve long term outcomes.

Chimenti R, Hall M, Dilger C, Merriwether E, Wilken J and Sluka K (2020) Local Anesthetic Injection Resolves Movement Pain, Motor Dysfunction, and Pain Catastrophizing in Individuals With Chronic Achilles Tendinopathy, a Non-Randomized Clinical Trial. Journal of Orthopaedic & Sports Physical Therapy, pp.1-3

SUPPORTING REFERENCES
1. Silbernagel KG, Brorsson A, Lundberg M. The majority of patients with Achilles tendinopathy recover fully when treated with exercise alone: a 5-year follow-up. Am. J. Sports Med. 2011;39:607-613.
2. Henriksen M, Aaboe J, Graven-Nielsen T, Bliddal H, Langberg H. Motor responses to experimental Achilles tendon pain. Br. J. Sports Med. 2011;45:393-398.