Avascular necrosis (AVN), or osteonecrosis, is death of a segment of bone due to disruption of the blood supply. Extraosseous or intraosseous interruption of the venous or arterial blood flow. AVN may be caused due to fractures of the femoral neck or dislocations of the hip, or due to mechanical disruption of blood vessels. Trauma to the deep branch of the Medial Femoral Circumflex Artery may occur with antegrade rod placement during piriformis entry in children. Posterior dislocation of the femoral head should be reduced in an expedited way to decrease the risk of thrombosis of the vessels which supply the femoral head. Osteonecrosis develops in about 2-20% of hips that are reduced within 6 hours. The risk of osteonecrosis will increase with delay in reduction of the hip. Osteonecrosis appears within two years after the injury. It is evident within one year in most patients.
With a Pipken fracture, the patient should be informed about the complications of AVN preoperatively. Fixation failure is associated with osteonecrosis or nonunion. The effect of the anterior approach on osteonecrosis is not known. Stress fractures should be pinned before displacement occurs. Displacement will have a bad result. Osteonecrosis can be clinically significant when followed by lateral segmental collapse. The more vertical the fracture line, the greater the chance of AVN occurring. In acetabular fracture fixation, during intraoperative dissection for acetabular fracture reduction and fixation, avoid injury to the ascending branch of the Medial Femoral Circumflex Artery (MFCA). Fractures of the hip in children are associated with a high rate of osteonecrosis.
The pilon fracture has two classifications that are commonly used. The first classification is the Ruedi-Allgower Classification, which is an old classification, and the second is known as the AO/OTA Classification.
The Ruedi-Allgower Classification is separated into three types. Type I fractures are cleavage fractures with no significant joint incongruity and no displacement of the fractured fragments. Type II fractures have a significant articular incongruity with minimal metaphyseal comminution or impaction. Type III fractures have significant articular comminution and a metaphyseal impaction; this is a very bad injury.
You will find three types of AO/OTA classifications and they are as follows: Extra-articular, partial articular, and complete articular. The extra-articular fractures are further broken down into simple (A1), metaphyseal wedge (A2), and metaphyseal complex fractures (A3). All of these extra-articular fractures are named “A”, followed by a number based on the complexity of the fracture. Partial-articular fractures are classified further with the letter “B” and are identified as Pure Split (B1), Split Depression (B2), and Multi-fragmentary depression (B3).
Split Depression fractures are a supination/adduction fracture of the ankle which is identified as a vertical fracture of the medial malleolus. The anteromedial portion of the plafond may also be impacted. The impaction or depression unique to this fracture is commonly missed, making this fracture a classic question on orthopaedic examinations. If the surgeon misses the impaction fracture after fracture fixation, they will need to revise the fixation and be sure to elevate the impaction or depression; additionally, they will need to restore the joint congruity before fixing the fracture. The surgeon will need to fix the fracture with a plate or screws. If screws are used, they have to be parallel to the joint in order to compress the fracture. If a plate is used, it should be an anti-glide plate.
The “C” fractures are Complete Articular fractures and have complete joint involvement. The Complete Articular fractures are broken down into Articular Simple/Metaphysis Simple (C1), Articular Simple Metaphysis Multi-fragmentary (C2), and Articular Multi-fragmentary/Metaphysis Multi-fragmentary (C3). C3 fractures are a very difficult fracture and probably has the worst prognosis.
Classically, there is a typical pilon fracture fragment. Usually there are three main joint fragments. The Three fragments are the:
- Medial Malleolus
- Attached to the deltoid ligament
- Anterolateral Fragment
- Chaput Fragment- attached to the anterior inferior tibiofibular ligament
- Volkmann Fragment
- Posterolateral fragment attached to the posterior inferior tibiofibular ligament
When the fibula is intact, the lateral collateral ligament of the ankle may rupture (fibula is intact in 20% of the cases).
The hamate is one of the many carpal bones of the hand and wrist. The Hamate bone is a triangular bone located in the distal carpal row situated on the ulnar side of the hand. The Hamate is composed of a body and a hook. The ulnar nerve passes through the Guyon’s canal between the Hamate and Pisiform bones. The ulnar nerve can become injured by a fracture of the body (rare) or by a fracture of the hook (common) which may cause neuropathy of the ulnar nerve within the Guyon’s canal. Missing the fracture can lead to persistent pain from nonunion. Hamate hook fractures are most often seen in racquet, bat, or club sports such as hockey and golf. Fractures of the Hamate bone are difficult to diagnose and routine x-rays may not show the fracture. Hook fractures of the Hamate are best seen by carpal tunnel x-ray views; however, a CT scan is the best study. The physician should rule out the ossification center (os hamuli proprium).
During the clinical evaluation, the physician should observe for hypothenar pain, as well as pain and paresthesia of the ring and small finger due to ulnar nerve compression in the Guyon’s canal. There may be weakness of intrinsics and a decrease in grip strength. The most common findings are pain and tenderness on the ulnar side of the wrists, distal to the wrist joint. The pull test is recently described. During the pull test, the palm of the hand is placed into supination. The wrist is in full ulnar deviation. Fingers of the patient should be flexed. The examiner pulls on the ulnar two digits with the patient resisting the pull. A positive test with pain in the area of the hook indicates a fractured hook of Hamate injury. Differential diagnosis include a pisiform fracture. When the physician is checking the Hamate hook for a fracture, if the ulnar side hook is normal, they should then check the pisiform bone. A CT scan may be necessary.
Treatment for acute fractures include early immobilization for 4-6 weeks to avoid nonunion. For a symptomatic nonunion of the hook of Hamate, there will need to be an excision of the fracture fragment. An ORIF is rare.