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.
Flexor tenosynovitis is an infection of the synovial sheath around the tendons of the fingers and hand. The affected finger is red, swollen, and painful due to infection occurring with deep puncture wounds, such as a splinter. Pain is located in the finger at the flexor tendon sheath. Signs of infection of the tendon sheath are called Kanavel’s Signs. There are four Kavanel’s Signs to support the presence of flexor tenosynovitis.
Flexor Tenosynovitis (Kanavel’s Signs)
- Uniform swelling of entire finger
- The finger is flexed
- Intense pain when attempting to straighten the finger
- Occurs early
- Tenderness along the tendon sheath is the most specific sign.
Treatment consists of antibiotics and surgery may be performed by incision and drainage of the infection.
A physeal injury in the distal femur in the neonate is rare. In general, traumatic neonatal physeal fracture usually occurs in the distal humerus and rarely occurs in the distal femur. The condition usually occurs due to birth trauma and usually results due to physeal separation which results in epiphyseal separation. The thigh will be swollen and there may be hypomobility of the extremity. The neonate will be fussy or irritated with significant swelling in the thigh. The condition is under diagnosed. The epiphysis is usually present at birth on x-rays. This condition can become complicated if the epiphysis is not completely ossified at birth or if the child is born prematurely. In this situation, the x-ray interpretation may be difficult. An MRI will be really helpful if the doctor is uncertain of the diagnosis. X-rays should be taken at the child at birth. The physician should look at the lateral x-ray and find the epiphysis is present and ossified at birth with varying degrees (may not be clear). Each epiphysis will line up with its corresponding bone. Epiphysis of the distal femur should line up with the femoral shaft. Epiphysis of the proximal tibia should line up with the tibial shaft. If the two epiphysis separate from each other, then this is a congenital dislocation of the knee. This can be a spectrum of injury that varies from hyperextension to subluxation, to frank dislocation. If the epiphysis is separated from its corresponding bone, for example, the epiphysis of the distal femur is separated from the shaft of the femur, then this is a physeal injury. Because the distal femur is mostly cartilaginous, you don’t see bone shifting, you see a little hint of the separation of the physis by seeing that the small ossified epiphysis is not in its normal position that corresponds with the axis of the bone. You need to know the difference between physeal injury and congenital dislocation of the knee. Accurate, gentle closed reduction with follow-up x-rays to confirm the reduction and to detect any early bony bridging.
There are three different types of osteonecrosis of the knee. There is Spontaneous Osteonecrosis of the Knee, Post Arthroscopic Osteonecrosis of the knee, and Secondary Osteonecrosis of the knee. Osteonecrosis is further classified by severity using Ficat Stages of Knee Osteonecrosis. In Stage I, the x-ray appears normal. Stage II, Sclerosis of the condyle is present. In Stage III, the crescent sign is found as well as a subchondral fracture. Stage IV, there is a collapse of subchondral bone.
Spontaneous Osteonecrosis of the Knee typically occurs in females older than 55. Usually one joint and one compartment is affected (medial femoral compartment). No etiology is known. Symptoms typically consist of a sudden onset of severe pain with decreased range of motion as well as swelling in the knee. X-rays will probably appear to be normal. An MRI is helpful, the provider may find a crescent shaped lesion. This condition can cause arthritis. If severe knee pain is present in a middle aged or elderly female patient, and the x-ray is negative, the provider should order an MRI to rule out osteonecrosis of the knee. Treatment consists of protected weightbearing as well as therapy and NSAIDs. An arthroplasty may be required when conservative treatment fails. A unicompartmental knee arthroplasty will be performed for small lesions. A total knee arthroplasty will be completed for large lesions or collapse.
Post Arthroscopy Osteonecrosis of the Knee most commonly occurs in middle aged women after a knee arthroplasty. Secondary Osteonecrosis of the knee is common in women under 55 years of age and has associated risk factors. This condition involves more than one compartment or the metaphysis of the knee. Secondary Osteonecrosis occurs bilaterally in 80% of cases and multifocal lesions may be seen. There is a cause for Secondary Osteonecrosis of the knee, which is why it can be bilateral, multiple, and everywhere. Risk factors include:
- Alcohol use
- Sickle cell disease
- Steroid use
- HIV medications
- Gaucher Disease
These patients should be screened for other joint involvement. The lesion is a subcondylar insufficiency fracture and the patient will have severe pain with weight bearing either standing or sitting. An x-ray may show a wedge-shaped lesion and MRI is the better study. A differential diagnosis is Osteochondral Dissecans, which is located in the lateral aspect of the medial femoral condyle in younger patients. Other differentials include: Occult trauma, bone bruise and overuse, as well as transient osteoporosis which is found more in middle-aged men and usually in the hip rather than the knee. Treatment consists of NSAIDs, a decrease in activity and weightbearing, and physical therapy. A scope surgery may be necessary to remove loose fragments or core decompression for lesions not extending to the joint. An Osteocondylar allograft may be performed for large, painful lesions in younger patients. A total knee replacement may be done for larger lesions, for collapse, or if multiple compartments are involved. Conservative treatment is not as successful with secondary avascular necrosis. Without surgery, secondary AVN will advance to osteoarthritis. Bisphosphonates have no effect on knee osteonecrosis.