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What Is Intramedullary Fixation and Its Classification and Function?

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  1. Features of intramedullary nails
  2. Classification of intramedullary nails
  3. Introduction of several commonly used intramedullary nails

Open reduction and internal fixation for the treatment of fractures include extramedullary fixation and intramedullary fixation. The internal fixation technology of plate and screw belongs to extramedullary fixation, and a biocompatible and strong method of fixing the fracture ends with built-in objects is called intramedullary fixation. Intramedullary fixation has been used in fracture internal fixation for more than 100 years, and intramedullary nailing is an essential skill for orthopedic surgeons.

Features of intramedullary nails

Advantages:

1. The intramedullary nail can control the axial line of force at the fracture site; the interlocking intramedullary nail has a better effect on preventing fracture rotation and reduces the risk of intramedullary nail fracture.

2. The closed nail penetration technique is adopted; less soft tissue stripping is required; the fracture site can’t be exposed; and the infection rate of the operation is reduced.

3. The fracture hematoma is retained by the closed nailing, which reduces the damage to the periosteal blood supply. At the same time, the debris generated during reaming is deposited on the fracture site, which has the effect of autologous bone grafting.

4. In general, the intramedullary nail does not need to be removed. Even if it needs to be removed, only a small incision should be made at the corresponding place of the locking nail and one end of the intramedullary nail.

5. The intramedullary nail and the damaged bone have a stress dispersion effect to avoid stress shielding.

Limitations:

1. The size of the bone marrow cavity limits the diameter of the intramedullary nail, thereby limiting the bending strength of the intramedullary nail. In order to achieve the purpose of increasing the bending strength of the intramedullary nail, the method of reaming is sometimes used. Still, the reaming destroys the blood supply of the endosteum.

2. Intramedullary nails (especially non-locking intramedullary nails) are not as good as plates or external fixation in controlling the rotation of the fracture.

3. Reaming can destroy the blood supply of the endosteum and affect the medial cortical bone.

4. Marrow reaming causes bone marrow components to enter the blood, which can cause fat embolism.

In order to overcome the above shortcomings, various types of intramedullary nails have been designed. Different types of intramedullary nails have different indications and contraindications. Before using them, you must have a full understanding of them in order to use intramedullary nailing correctly.

Classification of intramedullary nails

1. Elastic/rigid inner nail:

Elastic intramedullary nails have a long history of treating axially stable fractures, and several intramedullary nails usually need to be placed to obtain sufficient stability. Elastic intramedullary nails have better axial stability for axially stable fractures, but their anti-torsion effect is weak, so they are unsuitable for comminuted fractures.

Rigid intramedullary nails have higher hardness and mechanical strength than elastic intramedullary nails. The design of the intramedullary nail takes into account the anatomy of the bone and can restore normal biomechanical properties while stabilizing the fracture. For weight-bearing bone or severely comminuted fractures, thicker intramedullary nails and locking nails are required, and reaming is often required for this purpose.

2. Reamed/unreamed intramedullary nailing:

2.1 Advantages of reamed intramedullary nails:

1. Increase the cortical contact area

2. Larger diameter intramedullary nails

3. Expanded indications

4. The curvature of the medullary cavity becomes smaller, and it is easy to penetrate nails

2.2 Disadvantages of reamed intramedullary nails:

1. Destroy the blood supply

2. Possibility of fat embolism

2.3 Advantages of unreamed intramedullary nails:

1. The operation is relatively simple

2. Reduce operation time

3. Maintain endosteal blood supply

4. Generate less heat

2.4 Disadvantages of unreamed intramedullary nails:

1. The diameter of the intramedullary nail is small

2. Fixed instability

3. High chance of non-healing

3. Locking/non-locking intramedullary nails:

Since the emergence of interlocking intramedullary nails, except for Ender nails and Rush nails, which still have special indications, other non-locking intramedullary nails have basically been abandoned.

3.1 Advantage:

1. Improved stability: a) prevents shortening; b) prevents rotation

2. Expand the scope of use: a) For complex fractures; b) The fracture site is closer to the joint

3. Early Activities

3.2 Disadvantages:

1. Difficult to operate

2. Increased operation time

3. Additional motorization may be required

For some long bones (notably the femur and humerus), the screws can be inserted in a proximal-to-distal (antegrade) or distal-to-proximal (retrograde) fashion.

Introduction of several commonly used intramedullary nails

1. Gamma Nails

Gamma nails are indicated for all types of fractures from the base of the femoral neck to above the level of the lesser trochanter. Gamma nail internal fixation has no absolute contraindications except infection, and patients with severe osteoporosis need to be restricted in their early postoperative activities.

The reaming of the proximal femur is not necessary but should be determined according to the size of the medullary cavity. If reaming is required, it should be 2 mm thicker than the distal end of the intramedullary nail. The greater trochanter must be dilated to equal the proximal diameter of the main nail.

Insertion of Gamma nails must be advanced by hand; hammering is prohibited. In some patients, the anterior radian of the femur is too large, and the anterior cortex is thinned after reaming, and hammering can easily cause the anterior cortex to crack. The screw can be rotated and advanced when inserting the screw.

The correct placement of lag screws is very important. The premise is that the position of the guide pin must be placed; first, that is, the anterior position must overlap with the femoral neck axis or be slightly below it, and the lateral or oblique position guide pin should be in the center of the femoral neck.

2. Humerus Interlocking intramedullary nails

The interlocking intramedullary nail of the humerus can be inserted antegradely or retrogradely.

The antegrade nailing method is a relatively mature internal fixation technique at present. Shoulder pain and shoulder joint dysfunction are the main complications of antegrade nailing.

Retrograde nailing itself has two advantages:

①The local anatomy of the posterior approach is simple, there are no important blood vessels and nerves, and it is not easy to cause side injuries caused by surgical operations;

②All operations are performed outside the joint without affecting the rotator cuff or subacromial space and causing no damage to the elbow and shoulder joints.

However, when the nail is inserted retrogradely, the stress on the edge of the bone cortex at the entry point increases, and improper operation may cause severe complications such as splitting of the cortex at the entry point, perforation of the contralateral cortex, and supracondylar fracture.

3. Tibial intramedullary nails:

Intramedullary nailing can be used for the following injuries:

①Closed fracture of a high-energy injury

②Knee joint injury with floating knee

③Multiple injuries: Fractures of the pelvis, acetabulum, and spine

For open fractures, even if the trauma lasts for 12 hours, intramedullary nailing can also be applied on the premise of thorough debridement and reasonable application of antibiotics.

The surgical indications for Tibial intramedullary nailing can be summarized as follows:

①Closed or mild open Tibial shaft fractures with sufficient soft tissue coverage;

②Aseptic pseudoarthrosis compression fusion;

③Bone graft fusion after fracture nonunion;

④Bone lengthening, shortening, and fixation after rotational osteotomy;

⑤Fixation of the bone defect after bone tumor resection.

In closed fractures, the following conditions are suitable for intramedullary nailing:

①With femur fracture and floating knee syndrome;

②With knee ligament injury, the stability of the tibia needs to be reconstructed;

③With foot and ankle fractures;

④Unstable Tibial fractures that cannot be reduced satisfactorily;

⑤Tibial fractures in multiple trauma, for the convenience of nursing and early activities.

4. Proximal femoral nailing

The proximal femoral nail system is an intramedullary fixation material for the treatment of proximal femoral fractures developed by the AO Internal Fixation Society based on the improved design of the Gamma nail principle. PFN is suitable for fractures from the base of the femoral neck to 5 cm below the lesser trochanter, that is, all fractures of 31-A in the AO classification and fractures of the femoral shaft at the high trochanter.

4.1 Its structural features and advantages:

①The screws in the femoral head and neck consist of two pieces, the lower one is the main lag screw with a diameter of 11mm, and the upper one is an anti-rotation screw with a diameter of 6.5mm. The design of the anti-rotation screw can more effectively prevent the rotation of the broken end of the fracture.

②The groove design of the distal end of the main nail is flexible, and the distance between the distal locking nail hole and the nail tip is longer, which minimizes stress concentration and reduces the risk of femoral shaft fracture at the end of the main nail.

③The distal end of the main nail provides two locking nail holes, static and dynamic

4.2 Intramedullary Nailing Complications:

1. Infection: If the body temperature does not drop or continues to rise 2 to 3 days after the operation, antibiotics should be replaced immediately. After the infection is confirmed, local debridement should be performed, and measures such as airtight washing should be taken if necessary. Relatively conservative surgical debridement, high-dose antibiotics, and delayed closed intramedullary nailing are important factors in reducing the infection rate after intramedullary nailing for open fractures.

2. Fat embolism: General preventive measures include early and proper treatment of fractures, maintenance of water and electrolyte balance, and oxygen inhalation. Proper splinting must be done before moving the fractured patient to minimize the number of emboli that may enter the circulation. Final bone fixation should be accomplished within 24 hours of injury.

3. Deep vein thrombosis and pulmonary embolism: Due to the risk of potential complications such as severe bleeding, children and healthy young adults usually do not need drug prevention. In addition, drug prevention of DVT and PE is required. Low-molecular-weight heparins are an ideal drug of choice for patients with hip fractures or severe trauma. If anticoagulation fails or anticoagulation is contraindicated, and the patient is at risk of PE, an inferior vena cava filter can be placed.

4. Compartment syndrome: The only effective treatment is immediate decompression. All dressings are removed first, and the affected limb should be placed at the level of the heart to facilitate perfusion. If the condition worsens, the fascia must be cut immediately.

5. Delayed union and nonunion of fracture: Judging whether the fracture has healed or not should be at least 6-8 months after the fracture or operation. It is mainly related to the patient’s age, fracture type, location, and open or closed fracture. Factors related to internal fixation should be considered, such as weak fixation (broken locking nail, displacement of the intramedullary nail, dynamic locking, osteoporosis) or foreign body stimulation (cerclage wire).

6. Technology-related complications: iatrogenic fracture, fracture of internal fixation, failure of locking screws, displacement of internal fixation, etc.

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