Hindfoot endoscopy, also called posterior ankle arthroscopy, is keyhole (arthroscopic) surgery on the back of the ankle joint. In my practice, it is more often needed for deep pain at the back of the ankle, behind the ankle and in front of the heel, than for pain in the heel itself. See also my ankle arthroscopy page.
What it treats: pinching at the back of the ankle (posterior ankle impingement)
The classic case is someone whose foot is forced into a pointed-down position (plantar flexion). In that position the back of the ankle gets pinched, and an extra bone, loose fragments in the joint (loose bodies) or anything else caught there can cause pain; this is called posterior ankle impingement. Pain felt at the back of the ankle does not always start there; see Who it may not help. Through the keyholes, the impinging or blocking loose bodies or extra bones can be removed.
In my practice, fast bowlers are the group I see most often: the front foot can get pinched at the back of the ankle as it lands when they deliver the ball. That is an observation from my practice, not a statistic. Dancers, javelin throwers and anyone who has to work a lot with the foot pointed down can get the same pinching at the back of the ankle.
Farmers who work on uneven ground are another common group of patients I see with problems at the back of the ankle, but in them the problem can be early arthritis at the back of the ankle or in the subtalar joint, which is a different condition from impingement. The subtalar joint is the joint just below the ankle. Arthritis is covered on my foot and ankle arthritis page.
In one prospective study of 55 patients treated with hindfoot endoscopy for posterior impingement, the symptoms had started after an injury in 65% and from overuse in 35% [1]. These are the reported causes in that surgical group, not in everyone with the condition [1]. Two of the other studies described on this page concern a bone at the back of the ankle called an os trigonum [2] [3]. The authors of one study describe this extra bone as usually causing no symptoms [2].
Who it may not help
In my view, the biggest group this may not help are people whose pain at the back of the ankle does not start in the ankle at all, but comes from higher up, such as the spine or the calf muscle. The pain is felt in the same place, but its cause is elsewhere, so keyhole surgery at the back of the ankle is unlikely to help, and the original problem may need to be assessed, sometimes by another specialist such as a spine specialist.
Pinching at the back of the ankle is also a different condition from bursitis at the back of the heel (retrocalcaneal bursitis) and from Achilles tendon problems, and telling them apart is what makes the right treatment possible. Achilles tendon problems are covered on my pages on long-standing Achilles pain and Achilles tendon rupture.
In a series of 81 recreational athletes treated with keyhole surgery for impingement caused by an os trigonum, five returned to a lower level of activity [2]. The authors noted that these five had had several earlier ankle sprains and an os trigonum fracture or other problem with it, and that cartilage damage and arthritis at the back of the ankle were also seen on MRI [2]. These were descriptive observations, not proven predictors of a poorer result [2].
In the prospective study of 55 patients, the authors state that people treated for overuse did better than those treated after an injury [1]. The report available gives a score for each group, but not how many people were in each, and whether the difference was statistically significant was not established [1]. The study does not show that the cause of the problem explains the result [1].
Do I need surgery?
As my general approach to foot and ankle problems, I would normally offer non-surgical care first, with good physiotherapy and a short course of anti-inflammatory medicines, and I offer surgery if the pain or instability persists, or if there is a fracture that needs treatment.
How I do it
I work through two small keyholes, one for the camera and one for the instruments. Inside, there is some soft-tissue swelling around the space, and once I clear that space I can see the back of the ankle joint. Moving the ankle and the subtalar joint confirms which area at the back of the ankle needs work.
An important tendon runs behind the ankle: the FHL tendon, the tendon of the great toe that bends it downwards. FHL stands for flexor hallucis longus. The important nerves and blood vessels that supply the foot run on its inner side, so I stay on the outer side of the FHL tendon. Once I can see the problem, I treat it through the same two keyholes.
Keyhole or open surgery: what one trial found
In one trial in athletes, people went back to training and to their previous level of sport sooner on average after keyhole removal of an os trigonum than after open removal [3]. The trial randomly compared keyhole (endoscopic) with open removal of an os trigonum in 52 athletes with posterior ankle impingement, 26 in each group, followed for 5 years [3]. Average time to return to training was 4.58 weeks (standard deviation 1.47) after keyhole surgery and 9.58 weeks (standard deviation 3.98) after open surgery (p < 0.001) [3]. These are averages with standard deviations, not confidence intervals [3].
Average time to return to the previous level of sport was 7.12 weeks (standard deviation 2.25) after keyhole surgery and 11.54 weeks (standard deviation 3.89) after open surgery (p < 0.001) [3]. The report available does not define “previous level” further [3].
Overall complications occurred in 1 of 26 patients (3.8%) after keyhole surgery and 6 of 26 (reported as 23%) after open surgery [3]. The report available does not give the types of complication, or a test of statistical significance for this comparison [3].
A foot and ankle function score (AOFAS) after surgery was significantly better in the keyhole group (p < 0.05) [3]. The group values and the time point are not given in the report available [3]. Scores on another foot and ankle measure (VAS-FA) did not differ significantly, which does not mean the two groups were the same [3].
This is one trial, in athletes having an os trigonum removed, and its results cannot be assumed for every type of posterior impingement or every patient [3].
Risks and possible complications
Complication figures come from different studies, with different designs, follow-up and definitions, so each is given on its own and they are not combined into one range [1] [2] [4].
In the prospective study of 55 patients, there was one complication: a temporary loss of feeling at the inner side of the back of the heel [1].
In the series of 81 recreational athletes, five had complications (6.2%, as printed) [2]. Three had temporary sural nerve problems (neurapraxia), one had prolonged drainage from the inner keyhole with thinning of the fat pad and problems with skin healing, and one developed a stiff ankle from scar tissue (arthrofibrosis) [2]. That patient later had the scar tissue removed, and had nearly full ankle movement at the last follow-up [2]. The authors described the drainage case as following two earlier cortisone injections, which does not prove that the injections caused it [2].
In a group of 71 patients who had keyhole surgery at the back of the ankle for a mix of problems, 2 (2.8%) had temporary loss of feeling on the outer side of the foot [4]. This figure covers all the problems treated, not only impingement [4]. In the same group (71 of 83 eligible patients took part), 3 of 71 (4.23%) said they would not have the same procedure again if they had known what it involved [4]. This is a patient-reported answer, not a complication rate [4].
A technical report describes a different approach, through keyholes on the outer side of the ankle with the patient lying on their side [5]. It lists injury to the sural nerve and to the posterior tibial nerve and blood vessels (the posterior tibial neurovascular bundle) as potential risks [5].
The keyhole wounds are small, and it is easy to underestimate how much care they need; they can still become infected, and they need proper care. Increasing swelling in the first week is one of the warning signs set out below.
Recovery
I explain to patients that swelling is the last thing to settle, and that they need to focus on their rehabilitation, which concentrates on stretching the calf muscles to get their flexibility back; that helps them reduce the swelling. In my experience, if the result is disappointing, the commonest reason is stiffness, with a mild limp when walking, and I treat it with physiotherapy to restore the joint’s range of movement and strengthen the muscles that move it. This applies after ankle operations, such as Achilles tendon repair, broken-ankle surgery and hindfoot endoscopy, not only to hindfoot endoscopy.
Follow the recovery plan you are given for walking, wound care and exercise. See also: Recovery after ankle arthroscopy.
Getting back to sport and work: what studies report
Return times differ between studies, because each study measured something different, in a different group of patients [1] [2] [3]. They are given separately here and should not be averaged into one range [1] [2].
In the prospective study of 55 consecutive patients (median follow-up 36 months, none lost), the median time to return to work was 2 weeks, and to return to sports activities 8 weeks [1]. These are the study’s medians, not a timeline anyone can be promised [1].
In the series of 81 recreational athletes with impingement caused by an os trigonum, the average time to return to athletic activity was 9.1 weeks [2]. This was a retrospective case series, and the figure does not apply to every kind of hindfoot endoscopy or to impingement from other causes [2].
Warning signs after surgery
In the first week after keyhole surgery, where saline is used inside the joint, the warning signs are increasing swelling, increasing pain, increasing redness, or a fever that does not settle with regular medicines. Saline is sterile salt water. If you have any of these, see a doctor or see me urgently, and come to the hospital the same day. If you have sudden difficulty breathing, go to the nearest hospital emergency department straight away.
To contact us: Dr. Kini, +91 99208 61187, or the clinic, +91 98207 89797.
Questions about your own ankle
If pain at the back of your ankle has not settled with non-surgical care, see a qualified foot and ankle specialist.
Common questions
What is posterior ankle impingement?
It is pain from pinching at the back of the ankle when the foot is pointed down; an extra bone, loose bodies or anything else caught there can cause it.
Is hindfoot endoscopy the same as ankle arthroscopy?
It is a kind of ankle arthroscopy: keyhole surgery on the back of the ankle joint, also called posterior ankle arthroscopy.
Will it help if my pain comes from my back?
It is unlikely to. When the pain comes from the spine or the calf, the problem may need to be assessed where it starts.
Is keyhole surgery better than open surgery?
One trial in athletes found a quicker return to training and sport after keyhole removal of an os trigonum, but it is a single trial in a specific group, set out under Keyhole or open surgery [3].
What are the risks?
The studies report temporary changes in feeling, and in one series a case of wound drainage and a case of scar-tissue stiffness that later improved; they are set out study by study under Risks [1] [2] [4].
How soon can I play sport again?
Studies report different return times for different groups, and none of them is a promise; see Getting back to sport and work [1] [2].
Before you decide
Bring your scans, reports and questions, and we will go through your own situation and the options together.
Disclaimer: This article is for general information. It does not replace advice about your own condition from a qualified foot and ankle specialist.
About the author
Read Dr. Kini’s profileReferences
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- Nikolopoulos D, Safos G, Moustakas K, Sergides N, Safos P, Siderakis A, Kalpaxis D, Moutsios-Rentzos A. Endoscopic Treatment of Posterior Ankle Impingement Secondary to Os Trigonum in Recreational Athletes. Foot Ankle Orthop 2020;5(3):2473011420945330. doi:10.1177/2473011420945330 · PMID 35097403 · PMC8697201 doi.org/10.1177/2473011420945330
- Georgiannos D, Bisbinas I. Endoscopic Versus Open Excision of Os Trigonum for the Treatment of Posterior Ankle Impingement Syndrome in an Athletic Population: A Randomized Controlled Study With 5-Year Follow-up. Am J Sports Med 2017;45(6):1388–1394. doi:10.1177/0363546516682498 · PMID 28113040 doi.org/10.1177/0363546516682498
- Dimnjaković D, Karakaš T, Knežević I, Bojanić I. Indications for Posterior Ankle/Hindfoot Arthroscopy — Much More Than Just the Posterior Ankle Impingement Syndrome. Acta Clin Croat 2023;62(Suppl 3):50–59. doi:10.20471/acc.2023.62.s3.7 · PMID 40337655 · PMC12054458 doi.org/10.20471/acc.2023.62.s3.7
- Mak SY, Lui TH. Endoscopic Approach to Posterior Ankle via Lateral Portals. Arthrosc Tech 2020;9(4):e559–e563. doi:10.1016/j.eats.2020.01.005 · PMID 32368479 · PMC7189622 doi.org/10.1016/j.eats.2020.01.005