Alpha Defensin- Tests Orthopedic Surgeons Should Think About

The alpha-defensin test is a relatively new test that could help patients to diagnose periprosthetic joint infection. Alpha-defensin is a biomarker-based test for prosthetic joint infection, and it is measured in the synovial fluid. Alpha-defensins are antimicrobial peptides released by the neutrophils in response to infection. Alpha-defensins act like natural antibiotics which work to rapidly destroy the infection. Studies indicate that alpha-defensins are not significantly elevated by other causes of inflammation which can cause false positives by increasing the sedimentation rate (ESR) and the C – reactive protein (CRP). In patients with negative cultures, the alpha-defensin test can diagnose infection even if the patient is on antibiotics. So you aspirate the hip and the cell count will be marginally elevated and the culture will be negative. The physician does not know if the patient has infection or not, so the physician will order the alpha-defensin test which will not be affected if the patient is on antibiotics. The alpha-defensin test may also be helpful when there is a question of contamination of the culture. The scenario is: the patient will have hip pain, so you will get blood work. You find the sedimentation rate and CRP is elevated, so you decide to aspirate the hip. Clinically it does not seem that the patient has infection, but when you culture the fluid, the culture comes back positive and you don’t know then if this is a true infection or a contaminant, so then you get the alpha-defensin test. Diagnosing prosthetic infection can be challenging in patients with adverse local soft tissue reaction secondary to failed metal on metal corrosion of the femoral head and neck junction. The patients may have pain, difficulty in walking, and fluid collection around the joint. The presentation can mimic infection or can be the result of concomitant infection, making the diagnosis very difficult, especially if there is elevation of the sedimentation rate and the CRP. The synovial white count (WBC count) may be elevated, especially if the manual cell count is not obtained. Automated cell count may count the debris and give you a false positive, elevated number. Cultures of the synovial fluid will be negative, so in these scenarios, everything points towards infection but the culture is negative. In some cases, purulence may be present intraoperatively without infection. Also, if you take these patients to surgery, an intraoperative frozen section with the number of cells less than 5 may exclude infection despite the fact that purulence may be present intraoperatively in the hip region. This is a situation where the alpha-defensin test could be helpful preoperatively because the physician should try aggressively to find out preoperatively if there is an infection or not in the joint. There is some concern that the alpha-defensin test may give a false positive result in patients with adverse, local soft tissue reaction. Although the alpha-defensin test appears helpful, more studies are necessary to assert the validity of this test.

Flexor Tenosynovitis of the Hand—Kanavel’s Signs

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)

1. Uniform swelling of entire finger
2. The finger is flexed
3. Intense pain when attempting to straighten the finger
   1. Occurs early
4. 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.

Distal Clavicle Osteolysis

Osteolysis is bone erosion, the bone is dissolving or lost. There is a localized area of inflammation, hyperemia, microfracture, bone resorption, and eventually arthritis of the AC joint. The condition affects the distal end of the clavicle due to micro stress fractures. It typically affects younger male patients. It occurs from activities that require overhead heavy lifting, repetitive motion, and the use of a jack hammer. The condition is also common in weight lifters.

During the examination, you will find localized pain, swelling, and tenderness over the AC joint area. Additionally, the provider will find a positive cross body adduction test. An x-ray will show erosion of the outer end of the clavicle. The acromion is okay. There may be osteopenia, osteolysis, tapering and cystic changes of the clavicle. An MRI may be obtained to rule out additional shoulder pathology. An MRI will show a high signal in the distal clavicle.

Imaging

Acromioclavicular Joint Radiography- Zanca View

Direction of the x-ray beam: The beam is directed with the cephalad angle of 10 degrees. Clavicular osteolysis can be assessed using the Zanca view. The acromion will be normal with the abnormality isolated to the distal clavicle. The Zanca view is also used for diagnosis of arthritis of the AC joint. It will show osteophytes and joint space narrowing. The findings of the x-rays may not represent the patient’s real symptoms.

Differential Diagnosis

Erosion or absence of the distal ends of the clavicle may be seen in a wide range of conditions.

Bilateral Erosions

• Hyperparathyroidism
• Rheumatoid arthritis
• Scleroderma

Unilateral Erosion

• Post-traumatic Osteolysis
• Myeloma
• Metastases
• Osteomyelitis

 

Treatment consists of rest, NSAIDs, ice, and activity modification. Injections may be given blindly or with ultrasound guidance. If pain persists despite conservative methods, surgery may be considered. An arthroscopic or open resection of the distal clavicle may be performed. An arthroscopy allows for evaluation of the shoulder joint. In open surgery, repair the trapezius and deltoid fascia adequately. Surgery is successful in about 90% of cases. The surgeon will resect 5-10mm of bone and keep the posterior-superior ligament intact because it maintains horizontal stability of the clavicle.

 

Supracondylar Fractures of the Humerus in Children

Supracondylar fractures constitute approximately 50% of all elbow fractures. The supracondylar region is thin and weak and thus can fracture easily. These fractures are classified into two different types: extension and flexion.

Extension type fractures are the most common type, occurring approximately 95% of the time. Extension fractures typically occur due to falling onto an outstretched hand. With extension fractures, the distal fragment of the humerus displaces posteriorly. Anterior interosseous neurapraxia is the most common nerve palsy occurring with supracondylar fractures. Injury to the anterior interosseous nerve will lead to weakness of the flexor digitorum profundus muscle to the index finger and the flexor pollicis longus muscle. The patient will not be able to make an “OK” sign or bend the tip of his index finger. Radial nerve neurapraxia is the second most common palsy and is evident by weakness in wrist and finger extension.

The second type of fractures, flexion type fractures are rare and occurs due to falling directly on a flexed elbow. In flexion type fractures, the distal fragment is displaced anteriorly. This type of fracture may be accompanied with ulnar nerve neurapraxia. Injury to the ulnar nerve will lead to a loss of sensation along the little finger. Later on, the patient may also have weakness of the intrinsic hand muscles and clawing.

 

Gartland Classification System

The Gartland Classification System provides physicians with a way to categorize supracondylar humerus fractures. There are four classifications and are as follows: Type I fractures are nondisplaced fractures; Type II are angulated with an intact posterior cortex; Type III are completely displaced; and Type IV has complete periosteal disruption with instability in both flexion and extension.

Radiology

Plain AP and lateral x-rays should be obtained. A posterior fat pad sign seen on a lateral view x-ray should increase your suspicion of an occult fracture around the elbow. On a lateral view x-ray, the anterior humeral line is drawn along the anterior border of the distal humerus. Normally, the anterior humeral line should run through the middle third of the capitellum. In extension type fractures, the capitellum will be displaced posteriorly, relative to the anterior humeral line.

The Baumann’s Angle is formed by a line perpendicular to the axis of the humerus and a line going through the physis of the capitellum. Normally, the Baumann’s angle should measure at least 11° (variable).

 

Physical Examination

It is important to assess the neurovascular structures. The anterior interosseous nerve is assessed by asking the patient to do the “OK” sign with their hand. The radial nerve is assessed by asking the patient to extend their wrist and fingers. Ulnar nerve damage is usually indicated by the loss of sensation along the little finger; however, later on the patient may have weakness of the intrinsic hand muscles and clawing.

Treatment

Nonoperative treatment is usually indicated for type I fractures. This treatment usually consists of splinting or casting the elbow for a duration of 3-4 weeks. It is very important to remember not to flex the elbow in the splint or cast beyond 90° in order to avoid vascular compromise and compartment syndrome.

Operative treatment is usually indicated for Types II and III, and are usually treated by a closed reduction and percutaneous pinning. During reduction, pronation of the forearm during elbow flexion helps to correct a varus deformity. After reduction, the surgeon will want to check for a gap in the fracture, as the neurovascular bundle may be trapped there. The surgeon will need to free the brachialis muscle from the fracture site if it is interpositioned there. Fixation is usually achieved with 2-3 divergent lateral pins, depending on stability. Medial pins may also be added depending on stability; however, the surgeon will need to be aware of the ulnar nerve when placing the medial pin.

Open reductions are only performed when closed techniques are unable to achieve the appropriate reduction of the fracture. The surgeon will want to avoid posterior dissection in order to preserve the vascularity of the fractured segment. Fracture reduction and fixation should be done emergently in cases of vascular compromise.

Complications

Neurapraxia is a common complication of supracondylar fractures and usually resolves on its own—thus, treatment is observation only. A cubitus varus deformity may occur due to a malunion of the fracture. This only presents as a cosmetic problem since it does not affect the function of the arm or elbow. Additionally, this deformity can be corrected later on by a supracondylar valgus osteotomy. Vascular problems, such as compartment syndrome, may also occur. Volkmann’s ischemic contracture may occur due to a compression of the brachial artery with then patient is placed in a cast with the arm in hyperflexion (more than 90°).

Important Scenerios

A patient may present with a Displaced Type III fracture and a pulseless hand. He may have adequate circulation—which is evident by the normal temperature and color of the hand—or he may have inadequate circulation—indicated by a cold blue hand. In both cases, an urgent closed reduction and percutaneous pinning is required. Once this has been performed and the circulation is adequate, the surgeon can observe the patient and place them in a splint that is at a 45° angle. However, if the patient continues to have inadequate circulation after the closed reduction, then the patient will require a vascular exploration and repair.