Hallucal interphalangeal ossicle: anatomy and basis of ultrasound-guided surgical shaving

Hallucal OI is a common cause of painful lesions on the IPJ complex^{1,2,3,4,5,7,8}. This ossicle can attach to several adjacent structures, including the tendons, metatarsal base, and plantar fascia, together forming an IPJ-capsulo-ligamentous-sesamoid complex.⁸.

In the first part of our study, we tested our hypothesis that ultrasound is a more sensitive diagnostic tool for hallucal OI than fluoroscopy, which is in agreement with the literature.^16,17,18. The prevalence revealed by ultrasound and dissection in our study was 41.6%, while fluoroscopy detected OI in only 16.6% (39.9% accuracy in fluoroscopy while ultrasound 100 %). Other groups such as Davies and Dalal and Suwannahoy et al. showed a prevalence of up to 88% over 100 IPJ dissections^1.19. A meta-analysis and systematic review by Yammine in 2014 showed quite similar results, reporting a prevalence of 71.6% in dissections but only 22.8% in plain radiographs.⁹. Due to the sample size, the author’s objective was not to describe the prevalence of OI in the general population, which would inevitably have been biased, but to establish the accuracy of the diagnosis. comparing the prevalence between ultrasound, plain x-rays and dissection. .

In three of our samples examined with US, the OIs appeared only partially ossified. They could not be visualized by subsequent fluoroscopy. Dissection of these three cases also revealed partial ossification. These results confirm that ultrasound is a much more sensitive tool for IO diagnosis than fluoroscopy. In cases where the OI did not appear ossified, it could still be diagnosed by ultrasound due to its typical appearance: a well-demarcated nodular fibrocartilaginous structure with regular echogenicity. This was also reported in a previous study by Burman and Lapidus²⁰.

In dissections, IO showed typical intractable plantar keratosis at IPJ with or without associated biomechanical (fascial) alterations; these have also been described as cofactors for hyperpronation, functional hallux limitus or hallux rigidus, associated with hallux extensus interphalangeus^21,22,23. Despite conservative treatment, intractable plantar keratosis can be very disabling and require surgery for rapid recovery.^21.23. Given its sensitivity and non-invasive nature, ultrasound could be recommended as a first option diagnostic tool rather than radiography to confirm the diagnosis of OI.

Since the 1970s, different approaches to IO excision have been described.²⁴. Few of them have performed the so-called minimal incision (mini-open) procedure, published in 1982 and 1989^25.26. Compared to techniques reported in the literature, our “ultra” minimally invasive medial surgical approach, chosen because of its safety and the convenience of ultrasound guidance, protects all important anatomical structures.²⁷. Over the past decade, some US-guided surgeries for other foot and ankle problems have been shown to be safe and effective in both anatomical cadaver dissections and clinical trials.^28.29. To our knowledge, the present study describes the first ultra-minimally invasive ultrasound-guided technique with a medial approach for the evaluation of an IO plasty. This technique, from our point of view, has a great advantage over open surgery. First, it is performed without ischemia, which potentially reduces post-surgical pain and is particularly useful for patients with higher morbidities (eg, diabetics). Second, the incision is minimal (1.5 mm), classifying this surgical technique as “ultra-minimally invasive”. This results in minimal side effects in terms of fibrosis (which can entrap adjacent nerves), better cosmetic outcome, less infection, less postoperative pain and faster recovery. Therefore, there is no need for surgical cast or surgical shoe, and patients could be supported after the first post-operative day. This US-guided technique is an excellent way to perform surgery with minimal damage to healthy tissue such as skin, fat, and fascia. Our post-surgical recommendations are limited to wearing running shoes for the first week with a light bandage, often combined with an orthosis.

Compared to open surgery and MIS (fluoride-guided) surgeries, an ultrasound-guided approach has the advantage of directly controlling the soft tissues throughout the procedure, which helped us protect adjacent anatomical structures, especially the medial plantar nerve. Nerve damage can lead to severe neuropathies as described by Mann and Wapner²¹. In a preclinical anatomical study, Le Corroller et al. also showed that the proper medial plantar digital nerve is visible next to the first metatarsal-phalangeal joint when ultrasound is used³⁰. The authors of this study reported the ability to visualize similar small nerves, showing monofascicular features for the medial plantar nerve at the foot and ankle revealed by US³¹. They also verified by dissections that the medial plantar nerve can be properly visualized medial to the IPJ and that injury to anatomical structures can be avoided during ultrasound-guided surgical procedures.^28.31.

A limitation of our study is the small sample size of 18 fresh frozen feet; other clinical studies, already in progress, are necessary to validate our results.