Anatomic basis for a new ultrasound-guided
Mini-invasive technique for transverse metatarsal ligament release
Gabriel Camunas Nieves1,2 | Alejandro Fernández-Gibello1,2 | Simone Moroni1,3 |
Ruben Montes1 | Javier Márquez1 | Mario Suárez Ortiz4,5 | Teresa Vázquez6 |
Fabrice Duparc7 | Bernhard Moriggl8 | Marko Konschake8
Morton’s neuroma is an entrapment neuropathy of the third common plantar digital nerve, caused by the deep transverse metatarsal ligament (DTML).
Minimally invasive or percutaneous surgery is a very common procedure, but surgical effectivity of this technique remains controversial. The goal of our study was to prove the effectiveness and safety of a new ultrasound-guided technique for DTMLrelease in a cadaver model.
Materials, Methods, and Results: The DTML was visualized in 10 fresh frozen donated body to science-feet (eight male and two females, five left and five right) using an US device (GE Logic R7; 13 MHz linear probe, Madrid, Spain).
Consecutively, minimally invasive ultrasound-guided surgery was performed. Exclusion criteria of the donated bodies to science were previous history of forefoot surgery and space occupying mass lesions. The complete release of the ligament was achieved in all specimens without damage of any important anatomical structures as proven by anatomical dissection.
** Conclusions: The results of this study indicate that our novel approach of an ultrasound-guided release of the DTML is safer and more effective compared to blind techniques. The DTML could reliably be visualized and securely cut through a dorsal, minimally invasive surgical incision of only 2 mm.
** KEYWORDS: deep transverse metatarsal ligament, minimally invasive, Morton’s neuroma, ultrasound
>> INTRODUCTION
Morton’s neuroma (MN) was initially mentioned by Civinini in 1835
(Civinini, 1835).
Later—in 1845—Durlacher described the clinical Gabriel Camunas Nieves and Alejandro Fernández-Gibello contributed equally to this work. symptoms and finally in 1876, Thomas George Morton reported the Received: 21 July 2020 Revised: 28 September 2020 Accepted: 1 October 2020 DOI: 10.1002/ca.23692
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2020 The Authors. Clinical Anatomy published by Wiley Periodicals LLC on behalf of American Association of Clinical Anatomists.
Clinical Anatomy. 2020;1–7. wileyonlinelibrary.com/journal/ca 1 condition of metatarsalgia as a “peculiar and painful affliction of the fourth metatarsophalangeal articulation” (Adams, 2010; Civinini, 1835; Di Caprio, Meringolo, Shehab Eddine, & Ponziani, 2018; Durlacher, 1845; Matthews, Hurn, Harding, Henry, & Ware, 2019; Morton, 1876).
MN is not a true neoplastic or proliferative process due to its degenerative pathogenesis with histologically verified demyelination of the nerve fibers, fibrosis of the epi- and endoneurium including the so-called Renaut bodies and densely packed whorls of collagen (Adams, 2010).
Many different theories have been postulated to explain the pathogenesis of MN: repeated microtrauma, chronic traction damages, ischemia of the vasa nervorum, a secondary neurofibrosis after inflammatory intermetatarsal bursitis, increased tension in the foot fasciae and, currently widely accepted, an entrapment neuropathy of the third common plantar digital nerve due to an external compression by the deep transverse metatarsal ligament (DTML)
(Stecco et al., 2015; Valisena, Petri, & Ferrero, 2018).
The incidence of chronic entrapment of a common plantar digital nerve is highest in the third intermetatarsal space (i.e., MN), followed by the second space (i.e., Hauser’s neuroma) and least at both, the fourth (i.e., Iselin’s neuroma) and the first space (i.e, Heuter’s neuroma)
(Larson, Barrett, Battiston, Maloney, & Dellon, 2005; Matthews et al., 2019). The female-to-male ratio reported in the literature is 4:1
(Di Caprio et al., 2018). Clinically, patients complain of burning metatarsal pain, often radiating to the toes, and sharp shooting sensations of pain (Di Caprio et al., 2018). Pain is exacerbating when the patient
wears tight shoes or high heels, which leads to a narrow intermetatarsal space, augmented plantar metatarsal ground reaction forces and lastly to an extension of the metatarsophalangeal joint— resulting in compression of the common digital plantar nerve beneath the DTML (Di Caprio et al., 2018).
Apart from clinical diagnosis considered as the gold standard, imaging techniques such as ultrasonography (US) or MRI, were cited for detection of a common plantar digital nerve entrapment. Notably, both MRI and US were rated just equally or even less accurate compared to physical examination (Claassen et al., 2014; Di Caprio et al., 2018; Lee et al., 2007; Sharp, Wade,
Hennessy, & Saxby, 2003). Nevertheless, especially in skilled hands, US has its own and well documented advantages (Pastides, El-Sallakh, & Charalambides, 2012).
We are, to the best of our knowledge, not aware of studies dealing with US-visualization of the DTML as a basis for minimally invasive decompression surgery in the given context. Therefore, the goal of our study was to develop a new, landmark-based, ultrasoundguided, minimally invasive technique for a DTML-release for Morton’s neuroma.
1.1 | Normal anatomy of the DTML and its topographical relationships
The individually varying distance between the metatarsals is defined by two mostly transverse structures: the deep dorsal intermetatarsal fascia and the DTML (Figures 1 and 5). The latter in particular, helps to avoid too much splaying of the toes (Figures 1 and 5). The DTML is a mostly transverse band embedded in the plantar metatarsophalangeal joint capsule complex, which is composed of four parts connecting all heads of the metatarsal bones and heads of phalanges to form a functional unit.
Dorsally to the DTML a synovial bursa (the so-called “intermetatarso phalangeal bursa”) can be found that protects both metatarsal heads and the tendons of the interosseous muscles from fraying. Sandwiched between the ligament and the plantar fat body (also called “plantar monticuli”) (Kelikian & Sarrafian, 2011), the common plantar neurovascular bundle can be found adjacent to the third plantar plate, while the tendon of the lumbrical muscle is situated more fibularly close to the fourth plantar plate (Stecco et al., 2015) (Figures 1 and 3a).
>> MATERIALS AND METHODS
All consecutive steps described below were performed in 10 fresh frozen feet of eight male and two female cadavers (five right and five left, aged between 65 and 80 years), which belong to the Body Donation Centre.
The individuals had given their written informed consent for their use for scientific purpose prior to death. According to National Law, scientific institutions (in general Institutes, Departments or Divisions of Medical Universities) are entitled to receive the body after death mainly by means of a specific legacy, which is a special form of last
will and testament.
No bequests are accepted without the donor having registered their legacy and been given appropriate information upon which to make a decision based upon written informed consent (policy of ethics); therefore, an ethics committee approval was not necessary (Konschake & Brenner, 2014; McHanwell et al., 2020).
The exclusion criteria for this study were previous history of forefoot surgery and space occupying mass lesions.
Equipment used: high-frequency US-system with a 13 MHz linear probe (General Electric Logic R7; 8 mHz, Madrid, Spain), a scalpel for minimally invasive surgery with a beaver 64 blade, and a buttoned probe.
2.1 | “Step-by step” approach
After US-visualization of the DTML (Step I), we performed a landmark-based, minimally invasive US-guided surgical approach in all specimens (Step II), followed by anatomical dissections of the third intermetatarsal space (Step III) evaluating the effectiveness and safety of surgical release of the DTML.
2.1.1 | Step I: Anesthesia, US-identification of the DTML and skin incision
To avoid alteration of the clarity of the US image due to preprocedural local anesthesia bolus in such small probe girth we recommend a
2 NIEVES ET AL. proximal anesthesia procedure (e.g., US-guided ankle blocks) or at tarsal-metatarsal joint level.
The US probe was positioned at the sole, between the heads of the respective metatarsals and in the long axis of the third intermetatarsal space for visualization of the DTML. As a control, the US probe was turned 90 to identify the ligament spanning between the
plantar plates, and the position of the neurovascular bundle in its typical location (Figures 1 and 3a).
To ease identification of the DTML in the longitudinal view through a marked movement, a buttoned probe was simultaneously placed at the dorsum of foot between the metatarsal heads and pushed plantarly (Nieto García, 2016) (Figures 1–3b).
The dorsal longitudinal skin incision was done with a scalpel close to the surgical neck of the fourth metatarsal head (the “surgical neck” being a constriction straight proximal to the head of the metatarsal bone, which is frequently seat of fractures).
2.1.2 | Step II: Surgical procedure under US-guidance
After clear identification of DTML, we introduced the blade through the skin incision and advanced it gently toward the DTML under direct US visualization in plane. The ligament was then transected from proximal to distal. In order to verify the complete release of the DTML, the buttoned probe was introduced again, and its tip moved from proximal to distal.
In case of incomplete transection (especially its most distal fibers), the step was repeated. Prior to anatomical dissection, a retractor was inserted dorsally by enlargement of the initial incision in order to verify a widening of the intermetatarsal space under fluoroscopy (Figure 4).
2.1.3 | Step III: Anatomical dissection
An anatomical dissection of all 10 ft was finally made to verify a complete release of the DTML and to proof if no adjacent anatomical structures were injured, respectively: extensor expansion, interosseous.
>> RESULTS
In all 10 ft, the DTML was successfully identified with US in two
planes. (Figure 3a,b). With the transverse view, most important structures in the vicinity (i.e., the neurovascular bundle and plantar plates) were seen clearly (Figure 3a).
The US-appearance of the DTML was similar to the well known characteristics of a true ligament elsewhere in the locomotor apparatus: compared to sharply delineated hyperechoic borders (“white”) the substance of the rest of the ligament muscles, lumbrical muscle, the collateral ligaments, plantar plate, vessels and nerves.
For that, the widened incision for placing the first retractor as mentioned above, a further extension was done longitudinally, and another retractor inserted. Fat and connective tissue were removed carefully until we could visualize all important structures and the complete release of the DTML, respectively (Figures 1 and 5).
FIGURE 1
Frontal plane view of the intermetatarsal space at the level of third and fourth metatarsal heads (3; 4) showing topographical relationships. Red arrowheads: transection site of DTML (17),
1: extensor digitorum brevis tendon,
2: extensor digitorum longus tendon,
3: triangular adipose-fascial complex carrying superficial nerves and vessels,
4: intermetatarso-phalangeal bursa,
5: deep dorsal fascia,
6: vertical lamina of extensor aponeurosis,
7: flexor digitorum brevis tendon,
8: common digital plantar neurovascular bundle,
9: flexor digitorum longus tendon,
10: longitudinal fascicle of plantar aponeurosis,
11: plantar monticuli,
12: pretendinous fat compartment,
13: vertical extension of plantar aponeurosis forming the pretendon flexor space for adipose cushion,
14: Fibrous flexor tendon sheaths,
15: plantar plate,
16: tendon of lumbrical muscle,
17: DTML,
18: tendon of interosseous muscle.
Figure based on the work of Stecco et al. (Stecco et al., 2015) [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 2
(a) The figure shows the positioning of the instruments—buttoned probe dorsal, US transducer plantar.
> (b) Fluoroscopy of the foot before the DTML release; dotted line shows approximate area of the DTML, buttoned probe also visible.
> (c) Longitudinal scan of the DTML: The buttoned probe (BP) pushes the ligament plantarly during the surgical procedure at the third intermetatarsal space [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 3
(a) From medial to lateral,
(b) from proximal to distal: US-appearance of the deep transverse metatarsal ligament (DTML) in two
planes: the typical “white–dark–white” pattern of a ligament can be seen with hyperechoic borders (“white”), the substance of the rest of the ligament appears hypoechoic (“dark”) with just a few echogenic speckles. The mean thickness measured was 1.1 mm.
(a) transverse scan of the DTML: red arrowheads (transection zone); plantar plate (PP); flexor digitorum longus tendon (FDLT); plantar aponeurosis (PF); yellow arrowhead (neurovascular bundle)
(b) longitudinal scan of the DTML: The buttoned probe (BP) pushes the ligament plantarly during the surgical procedure [Color figure can be viewed at wileyonlinelibrary.com]
>> DISCUSSION:
In the current anatomical study, we describe a new, landmark-based minimally invasive ultrasound-guided surgical release of the DTML. The latter accounts for the majority of cases with compression of the third common digital nerve within its respective intermetatarsal space.
FIGURE 4
Confirmation of a complete release of the deep transverse metatarsal ligament (DTML) using fluoroscopy—left before, right after the ultrasound-guided surgical release with widening the third intermetatarsal space [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 5
Anatomical specimen showing the DTML and its topographical situation. From lateral to medial: *DTML: deep transverse metatarsal ligament, #common plantar digital nerve, DIM: dorsal interosseous muscle, EDBT: extensor digitorum brevis tendon, EDLT: extensor digitorum longus tendon [Color figure can be viewed at wileyonlinelibrary.com]
> CONCLUSSION:
