Working Diagnosis:
Chronic, refractory, multifactorial Achilles tendon pain

Treatment:
Given the persistence of our patient's symptoms, an ultrasound-guided peritendinous corticosteroid injection was first performed, but without benefit. The decision was then made to perform an ultrasound-guided tendon scraping with the goal of ablating neovessels and freeing the tendon from residual post-operative adhesions. At the time of the procedure, Kager's fat pad was found to be closely adherent to the ventral surface of the tendon. After the ventral tendon was scraped, Kager's fat pad was much more mobile and a greater degree of differential motion was appreciated between the two structures.

Outcome:
At the time of the procedure, the patient reported his level of function as "abnormal" with a sports-related activity function rating of 50% of normal and usual daily activity function of 70% of normal according to the Foot and Ankle Ability Measure (FAAM).

One week after tendon scraping, the patient reported a 50% reduction in pain and was cleared to progress through biking for one week and to return to higher impact activity the following week. He was instructed to continue progressive physical therapy as well.

At 7 week follow-up, the patient noted some recurrence of pain, however, it was felt appropriate to return to running as tolerated.

At 4.5 month follow-up, the patient reported his level of function as "nearly normal" with a sports-related activity function rating of 80% of normal and usual daily activity function of 80% of normal according to the FAAM.

At 5 month follow-up, the patient reported continued improvement in pain after addition of new, more supportive footwear. The current plan is to have the patient fitted for custom orthotics and to continue activity as tolerated.

Author's Comments:
This is a case of chronic Achilles tendon pain persisting after surgery and refractory to the standard of care measures. The incidence of Achilles tendinopathy in the general population is 2.85 out of 1,000 people [1] and can affect up to 9% of active runners [2]. Furthermore, about 25% of cases are recalcitrant to conservative measures and require surgery [3]. Our patient unfortunately had an unsuccessful surgery and we were able to help improve his pain and function with a much less invasive procedure that comes with a shorter recovery time and faster return to activity.

Image captions:
Sagittal T1-weighted Case Photo #1 and axial proton density Case Photo #2 MRI images of patient's left ankle that demonstrate marked thickening of the Achilles tendon, consistent with tendinosis. No discrete tear seen. Kainberger et al reported normal Achilles tendon thickness ranged from 4.0 to 5.7 mm (mean of 5.2 mm) in a group of 24 healthy adults [4].

Editor's Comments:
Kager's fat pad is formed by the flexor hallicus longus muscle/tendon anteriorly, superior calcaneal cortex inferiorly, and Achilles tendon posteriorly. The ankle joint is at the anterior/inferior corner of the fat pad, and the fat pad is continuous posterior/inferiorly with the retrocalcaneal bursa. During plantar flexion, the inferior wedge of the fat pad is separated from the Achilles tendon and moves into the bursa to allow for an improved lever arm function of the Achilles tendon. It is a critical structure in the efficient and effective plantar/dorsiflexion, and can be well visualized on xray, MRI, and ultrasound.

References:
1. Jonge, S. De, C. Van Den Berg et al. "Incidence of Midportion Achilles Tendinopathy in the General Population." British Journal of Sports Medicine 45.13 (2011): 1026-028.
2. Bedi, Harvinder S., Charlie Jowett et al. "Plantaris Excision and Ventral Paratendinous Scraping for Achilles Tendinopathy in an Athletic Population." Foot & Ankle International 37.4 (2016): 386-93.
3. Alfredson, Hakan. "Low Recurrence Rate After Mini Surgery Outside the Tendon Combined with Short Rehabilitation in Patients with Midportion Achilles Tendinopathy." Open Access Journal of Sports Medicine (2016): 51.
4. Kainberger F, Engel A, Barton P et al. "Injury of the Achilles tendon: diagnosis with sonography." American Journal of Roentgenology 155 (1990): 1031-1036.

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