Minimally invasive surgical (MIS) procedures rely on anatomical references to localize structures not directly visible to the surgeon. This manuscript describes a combined method of plane-by-plane dissection and sectional anatomy of fresh-frozen specimens to locate the structures at risk during MIS procedures.
The growing popularity of minimally invasive surgical (MIS) procedures makes it necessary that new anatomical references arise, to aid in tridimensional orientation and localization of structures that are not directly visible to the surgeon. This is especially critical for structures at risk like nerves or blood vessels. Optimization of the handling of cadaveric material and the combination of multiple techniques compensate for the limited availability of adequate specimens. The described protocol combines anatomical plane-by-plane dissection and sectional anatomy of fresh-frozen specimens to help localize relevant structures, such as nerves, arteries, veins and to correctly position the portals during MIS procedures. Depiction of these structures in anatomy textbooks can differ from what is encountered in the surgical field; and for this reason, new anatomical studies with a surgical orientation are needed. However, this is a complex, time-consuming technique requiring specific training. The anatomical references described with the so-called ‘clock method’ provide the surgeon with an easy and reproducible system to locate the path of the nerves at risk in Hallux Valgus MIS procedures. This model can be extrapolated to many other minimally invasive surgical procedures.
Hallux valgus is a common pathology affecting the first toe, in which the proximal phalanx is deviated laterally while the first metatarsal is deviated medially1. Percutaneous or minimally-invasive surgical (MIS) techniques for hallux valgus were amongst the first described in this discipline, and numerous studies report their benefits but also their risks2. Hallux Valgus MIS correction involves osteotomies performed through small incisions using specific surgical instruments. Given that open dissections are not performed, the risk of damage to neurovascular structures is higher than when these are identified during open surgery. Also, as in any surgical procedure, the positioning of the patient and the surgeon around the operating table are far from the anatomical position depicted in classic anatomical books or papers.
The neurological structures at risk during Hallux Valgus surgery are the dorsomedial nerve of the big toe, the branch of the superficial peroneal nerve, and the dorsolateral nerve of the big toe, branch of the deep peroneal nerve. The purpose of this study is to describe the position of these nerves with regards to incisions used in hallux surgery and to illustrate it with a new method easily reproducible in surgical conditions. Moreover, a safe portal for the use of percutaneous instruments is described.
A thorough anatomical knowledge is essential in any surgical field, especially during minimally invasive procedures. The development of new surgical and imaging techniques requires a new understanding of both the bi-dimensional and the tri-dimensional location of anatomical landmarks. Previously reported anatomical dissection techniques were developed by our team to overcome the limitations of the classic dissection techniques3,4,5,6 and here are applied to reproduce the skin incisions and instrument entry portals corresponding to the MIS procedures used to treat hallux valgus (HV) and rigidus (HR) pathology. The method is thus applicable to those surgical techniques that evolved from traditional open surgery to MIS3,4,5,6.
This study was approved by the institutional Ethical Committee (Comissió de Bioètica, UB). The dissection procedures were carried out by an experienced anatomist, specifically trained in plane-by-plane dissection technique. This is an essential prerequisite to ensure a successful outcome of the experiment.
1. Preparation
2. Dissection
3. Freezing
4. Sawing
5. Measurements
Using the clock method, the dorsomedial and dorsolateral nerves were consistently found between 10 and 2 o'clock (Figure 1). The dorsomedial nerve was found at an average of 26.2° medial to the medial border of the EHL, which corresponds to a zone between 12 and 2 o'clock in a right foot, and between 10 and 12 o'clock in a left foot. The dorsolateral nerve was 32.3° lateral to the medial border of the EHL in average, which corresponds to a zone between 12 and 2 o'clock in a left foot, and between 10 and 12 o'clock in a right foot.
Figure 2 shows the typical distribution of dorsomedial and dorsolateral nerves as revealed by the anatomical plane-by-plane dissection.
Figure 1: Frontal cross section of a right foot showing the position of the dorsomedial nerve (1) and dorsolateral nerve (2). A clock sphere has been superimposed onto the first metatarsal head. Double-headed arrows show the area where nerves have been found to be in this study. Please click here to view a larger version of this figure.
Figure 2: Anatomical plane-per-plane dissection (dorsal view of a foot) showing the typical distribution of dorsomedial and dorsolateral nerves as has been found in this study. 1. Dorsomedial nerve of the first toe. 2. Dorsolateral nerve of the first toe. 3. Dorsomedial nerve of the second toe. Please click here to view a larger version of this figure.
The basis of the method used in this study is a combination of sectional anatomy and anatomical plane-by-plane dissection, as it has been practiced historically7. This requires not only anatomical knowledge but also specific training for what is a time-demanding technique that greatly relies on the skills of the dissector. Consequently, some anatomical images provided in anatomical textbooks or scientific papers, especially in the field of orthopedic surgery, lack accuracy and are not instructive enough to be useful for the surgeon performing cutting edge techniques, like minimally invasive procedures. For this reason, it has been suggested in the literature that anatomical studies should be carried out with a close collaboration between the experts, surgeons and anatomists8.
The use of fresh-frozen specimens is essential to obtain reliable anatomic results, especially when studying superficial structures as nerves. The use of fixated specimens frequently produces changes in the volume and position of the anatomical structures. Likewise, nervous and vascular structures are susceptible to displacement during its handling at the time of the dissection. For this reason, we have included three critical steps in our technique to ensure that nerves will not be displaced: the dissection performed in the study does not affect the subcutaneous tissue, nerves are fixed with intra-articular needles at the first metatarsophalangeal joint, and specimens are frozen before the sawing process.
Thawing of the samples could lead to the displacement of relevant anatomical structures, thus the need for careful preparation and freezing of the samples. The previous preparation and mounting of the cutting material are important to achieve reliable measures.
One of the possible limitations of this technique arise when the nerve to be studied is not near a joint, which will preclude fixation of the nerve with a needle. The use of a vascular labeling technique could overcome this issue, as vascular structures are in most cases parallel to nerves9.
An increasing number of surgical procedures are nowadays performed by minimally invasive methods, where neurological structures are not directly visualized2,3. In these cases, three-dimensional orientation is paramount for the surgeon. Anatomical references with the clock method provide the surgeon with an easy and reproducible system to locate the nerve position in relation with surgical incisions for Hallux Valgus Minimally Invasive procedures.
This technique, which combines plane-by-plane dissection and sectional anatomy in fresh-frozen specimens has been successfully used to provide anatomical guidance for the newest minimally invasive surgical procedures3,4,10,11.
The authors have nothing to disclose.
We thank the technical staff of the Dissecting Room of the Bellvitge Campus of the University of Barcelona for their skillful assistance. We thank the Audiovisuals department for their work with the video included as part of this publication. We thank the body donors of the Faculty of Medicine of the University of Barcelona.
Adson Non-Toothed dissection forceps | Bontempi | BD-31 | |
Adson Toothed dissection forceps | Bontempi | BD-30 | |
Surgical scalpel handle nº 4 | Swann-Morton | 4 | |
Surgical scalpel blades nº 24 | Swann-Morton | 24 | Ad libitum |
Iris scissors- curved | Bontempi | FG-2 | |
Periostotome P-24 | Bontempi | 718-24G | |
Intramuscular 23G sterile needles | Totclinic | 23 | Ad libitum |
Goniometer | |||
Latex gloves | Ad libitum | ||
Gauze pads | Ad libitum | ||
Non-Sterile surgical drape | |||
Saw | EXAKT Advanced Technologies GmbH | EXAKT 312 Pathology Saw |