Although most fresh navicular fractures without displacement can be healed by means of cast braking, prolonged braking can lead to joint stiffness and affect the functional rehabilitation of the hand and wrist. Moreover, prolonged cast braking is often difficult to accept for patients who cannot wear casts for work or for some young patients who love sports. Therefore, in recent years, orthopedic surgeons in Europe and the United States have begun to try to treat fresh undisplaced or mildly displaced navicular fractures surgically, with the minimally invasive surgical method of percutaneous compression screw internal fixation being the most advantageous.
There are two access options for percutaneous internal fixation of the navicular bone. The traditional approach is the palmar approach, in which screws are placed from the distal pole of the navicular bone to the proximal pole. The dorsal approach was first reported by Slade and colleagues in 2002 and involves placement of screws from the proximal to the distal aspect of the navicular articular surface. Although there are no clinical studies showing better outcomes with this approach, there are experimental studies showing that the dorsal approach allows for more accurate placement of the screws in the central axis of the navicular bone. Furthermore, for proximal third or proximal pole fractures of the navicular bone, the dorsal approach is more biomechanically advantageous for screw placement from the proximal pole.
We were the first in China to use the dorsal approach with percutaneous compression screw internal fixation for specific types of navicular fractures from 2008 to 2009, with satisfactory results at recent follow-up. However, compared with the palmar approach, the dorsal approach with percutaneous placement of screws is a relatively new treatment technique with some technical difficulties, and there is no clinical experience in China on the application of this treatment method in the country. Moreover, we found that the size and length of the navicular screws available in China are not designed for the three-dimensional morphology of the navicular bone in Chinese, and complications may occur and affect the surgical efficacy if there is insufficient experience. Therefore, this paper provides a detailed introduction of this treatment technique and discusses and analyzes the problems that need to be noted in clinical application.
Devices and internal fixation
Pressurized internal fixation between fracture blocks is an inherent requirement for the treatment of navicular fractures, and since the navicular screw without a cap can be completely buried under the cartilage to avoid joint wear, the use of a pressurized hollow screw without a cap is the standard for internal fixation of navicular fractures. During percutaneous minimally invasive surgery, the position of the placement guide pin and screw must be monitored using a mini-imaging fluoroscope. Intraoperative wrist arthroscopy may be used simultaneously to further define the fracture and morphology and to assess ligamentous injury and repositioning.
Surgical steps
(1) Position and anesthesia The patient is placed in the supine position with the affected upper extremity abducted on the surgical table and operated under brachial plexus anesthesia.
(2) Guide needle placement
Prior to surgery, fluoroscopy is used to confirm the shape of the navicular fracture line and whether the fracture is displaced from all angles. Most mildly displaced navicular fractures can be repositioned by pushing the navicular tuberosity from the palmar side to the dorsal side. After fluoroscopy confirms that the fracture is not displaced or is repositioned, the patient’s wrist is placed in a flexed position at approximately 45 degrees and the proximal pole of the navicular can be palpated slightly distal to the Lister’s tuberosity on the dorsal surface of the wrist. The needle is inserted through the skin slightly ulnar to the proximal pole of the navicular bone, and the tip of the needle is placed against the proximal pole of the navicular bone, pointing slightly distal to the palmar navicular tuberosity, and the direction of the needle is confirmed to be in the central axis of the navicular bone by fluoroscopy in the frontal position. A small 0.5-cm-long incision can also be made at the site where the needle enters the skin to confirm that the needle does not cross the extensor tendon.
The guidewire is advanced to the palmar side and penetrated through the skin slightly distal to the navicular tuberosity or through the mostly angular bone, and the guidewire is pulled back distally to the palmar side with an electric drill until the tail of the guidewire is buried under the proximal cartilage of the navicular bone and the radial wrist joint movement is not restricted.
The wrist joint was placed in the flexion-extension 0 degree position, and fluoroscopy was performed in the orthogonal, lateral, navicular, pre-rotation and post-rotation oblique positions, with each position confirming that the guide pin was located in the central axis of the navicular bone. If the guide pin is not in the central navicular axis, another guide pin is placed until a satisfactory position is obtained. Avoid repeatedly threading the needle, as this can lead to loosening of the needle tract and make it difficult to maintain the correct needle position.
After confirming the position of the guide needle in the central axis of the navicular bone, flex the wrist at approximately 45 degrees and use the electric drill to advance the guide needle retrogradely in a palmar, distal to proximal, dorsal direction to penetrate the skin from the dorsal side. Under fluoroscopic surveillance, the needle is then pulled back from the dorsal side with an electric drill until the tip of the needle is just buried under the distal cortex of the navicular bone.
(3) Measuring the depth of the screw
Put the depth gauge into the guide needle to measure the depth, and if necessary, confirm that the gauge has reached the proximal cartilage surface of the navicular bone by fluoroscopy. Keep the wrist joint flexed to prevent the guide pin from bending. The length of the screw chosen is the bathymetric length minus 4 mm so that the screw is placed 2 mm below the articular surface at both the proximal and distal poles. (The most common complication of percutaneous screw fixation is the protrusion of the tip or tail of the screw into the bone surface due to the excessive length of the screw placement.)
(4) Before screw placement for marrow expansion, the guide pin is advanced distally and palmarly for a period of time to penetrate the skin in order to prevent the guide pin from being carried out by the hollow drill after marrow expansion. A small dorsal incision is made to bluntly separate the bone to the proximal pole of the navicular bone before reaming, or a sleeve can be used to avoid damaging the surrounding tendons or soft tissues during reaming. If self-tapping screws are used, they should also be expanded to the fracture line to ensure that the screws can function as compression screws after placement. Dilation must be performed under fluoroscopic surveillance to prevent excessive dilation from penetrating the contralateral cortex and interfering with compression between the fracture blocks.
Screws of appropriate length are inserted along the guide pin and placed 2 mm below the distal cortex under fluoroscopic surveillance. If the screw is over-torqued into the contralateral cortex beyond this position, the sustained propulsive force may instead be converted into a force that causes separation of the fracture fragment.
For unstable or mildly displaced fractures, an additional anti-rotation guide pin or fine kerf pin can be placed before reaming and screwing in the screw, and the anti-rotation pin can be removed after the screw is placed. If the fracture is very unstable, especially for proximal pole fractures, the distal fracture block has a larger force arm relative to the proximal bone block, which can create a larger moment on the fracture end during wrist movement and can lead to screw loosening and pressure dissipation and fixation failure. In this case, it is sometimes necessary to place a 1.5-mm kerf pin or a screw without a cap from the distal navicular bone to the cephalic bone to temporarily control the movement of the midcarpal joint and thus reduce the stress on the fracture end. The trans-medial carpal joint fixation is removed after postoperative CT confirms fracture healing.
Postoperative rehabilitation
All patients began finger joint, shoulder and elbow joint exercises immediately after surgery. For patients with lumbar fractures, guided active wrist exercises and gradual finger pinching exercises can be started after surgery. After review of radiographs and, if necessary, CT examinations every 4-6 weeks and the appearance of definite evidence of imaging healing, the resumption of more intense physical activities and physical labor can be gradually started. For proximal fractures, guided active wrist exercises should be started after 4 weeks of postoperative cast restraint, and gradual resumption of physical activity and physical work should be started after CT examination shows evidence of fracture end healing.
Results
The average operative time was 30 minutes. On imaging evaluation, the screws were located in the long axis of the navicular bone in all cases. Intraoperative fluoroscopy and postoperative CT confirmed that the screws were of appropriate length and were located below the subchondral bone on both the proximal and distal sides.
Follow-up ranged from 4 to 6 months, with a mean of 5 months. All patients had one-stage healing of the small dorsal carpal incision; fractures were healed with a mean healing time of 8 weeks for lumbar fractures and 12 weeks for proximal pole fractures. The lumbar fractures did not require external fixation after surgery, and the patients resumed their original work 2 weeks after surgery, and gradually started to resume physical activities of the wrist after the fractures healed. None of the patients had wrist pain during functional activities, and the wrist mobility reached more than 90% of the contralateral side.
DISCUSSION
I. Selection of surgical indications
Percutaneous internal fixation is mainly indicated for fresh navicular fractures, and it can also be used for non-displaced fractures that are seen later than 3 weeks, without evidence of bone discontinuity such as sclerosis of the fracture end. Absolute surgical indications include proximal pole fractures of the navicular bone; unstable proximal third navicular fractures that are mildly displaced but can be closed and repositioned. Relative indications include stable fresh navicular fractures without displacement, patients who cannot receive cast braking and have a strong need for early activity or sports. It should be noted that contraindications to surgery include those who cannot be closed and repositioned; patients with significant evidence of bone discontinuity or ischemic necrosis of the proximal fracture mass on imaging.
II. Characteristics of percutaneous internal fixation surgery
The advantage of percutaneous internal fixation over incisional surgery is that it avoids further interference with navicular blood flow and damage to the ligamentous structures that play an important role in the stability of the wrist joint. It also makes it possible to perform functional activities early after surgery because of the compression fixation between the fracture fragments. Recent evidence-based studies have shown that the use of percutaneous internal fixation can shorten the healing time of stable fresh navicular fractures and reduce the incidence of osseointegration; moreover, patients can return to work and sports activities earlier than with plaster braking, and patient satisfaction is higher; this treatment is more cost-effective for patients who cannot wear plaster for work or young patients who like sports.
Third, the clinical application needs to pay attention to the problem
The size and length specifications of the currently available domestic navicular screws are not specifically designed for the three-dimensional morphology of the national navicular bone (Figure 3). Our previous anatomical study showed that the size and shape of the navicular bone is relatively small, and the diameter of the proximal pole of the navicular bone is narrower than that of the distal pole, which is especially prominent in female patients. The caudal diameter of some domestic navicular screws is larger than the average width of the proximal pole of the navicular bone in the Chinese population, therefore, not all of the currently available screw products are suitable for the Chinese population when screws are placed from the proximal pole. Clinically, we have seen cases where the caudal end protruded from the articular surface due to improper screw selection, resulting in wear of the articular surface. Therefore, preoperative care should be taken to select a screw with a suitable caudal diameter to reduce the incidence of complications.
Accurate placement of screws is the key to the quality of surgery. Because of the high incidence of osseous nonunion in navicular fractures, the position and length of the placed screws are required. The requirement for mechanical stability requires that the screws be placed in the central long axis of the navicular bone, and biomechanical studies have shown that placement of relatively long screws is mechanically more stable than short screws. However, if the screws are too long beyond the articular surface, serious consequences in terms of cartilage wear will result. Therefore, the optimal position and length of screw placement is currently accepted to be along the central long axis of the navicular bone and 2 mm below the articular surface at both the proximal and distal poles[7,8] . However, the length of the long axis of the navicular bone is relatively short in the Chinese population, and in practice, screw manufacturers often do not have all lengths available, so cases can sometimes be seen in which the surgical outcome is affected by choosing screws of unsuitable length. Therefore, the surgeon should know the average length range of the navicular long axis in the Chinese population and confirm that all the screws that may be needed are available before surgery.
Compared with the palmar approach, the dorsal approach to screw placement is a relatively new treatment technique, especially if a minimally invasive method of percutaneous or small incision is used to place the screws, which is surgically demanding, difficult to perform, and has a long learning curve. According to the literature and our experience, intraoperative placement of hollow screw guides often requires several attempts and repeated x-ray fluoroscopy to obtain a relatively satisfactory guide pin placement, even for more experienced specialists. Poor placement and length of the screw can lead to complications or treatment failure. Therefore, this technique should be performed by a physician who has some experience in incisional surgery.