Anterior Interosseous Nerve- The Benedictine and O.K. Sign

A patient with a complete anterior interosseous nerve injury or a high medial nerve injury should be asked to make a fist. The first and second digits will have difficulty in flexing, while the other digits will flex. The third digit will be weak, while the fourth and fifth digits are normal. This position of the hand is similar to the position taken during a hand blessing. The Benedictine sign is different from an “ulnar claw hand”. Ulnar claw hand refers to damage to the ULNAR nerve and is seen when attempting to extend all the digits (leaving the 4^th and 5^th digits flexed). The O.K. sign is used to check for paralysis of the anterior interosseous nerve due to entrapment or compression injury. A patient with paralysis of the anterior interosseous nerve will be unable to make the O.K. sign. This is due to weakness of the flexor pollicis longus and flexor digitorum profundus muscles. A typical pinch attitude is associated with anterior interosseous nerve injury.

The anterior interosseous nerve arises from the median nerve about 4-6cm distal to the elbow, which is about 1/3 of the way down the forearm. It exits from the anterolateral aspect of the median nerve and it runs between the radius and the ulna on the interosseous membrane between and below the muscles of the flexor digitorum profundus and the flexor pollicis longus.

The anterior interosseous nerve supplies the flexor digitorum profundus muscle for the index and long fingers. It also supplies the flexor pollicis longus and the pronator quadratus muscles. The flexor digitorum profundus muscle for the index and long fingers is supplied by the anterior interosseous nerve. The medial part of the FDP is supplied by the ulnar nerve (FDP has dual innervation). The anterior interosseous nerve passes dorsal to the pronator quadratus with the anterior interosseous artery and provides innervation to the volar wrist capsule. The terminal branch of the anterior interosseous nerve innervates the carpal joint capsule.

In patients with Martin-Gruber Connection, the median nerve, or anterior interosseous nerve to the ulnar nerve in the forearm may present with intrinsic muscle weakness. It may be differentiated also from Parsonage-Turner Synrome (acute brachial plexus neuritis) and patient may have pain in the affected extremity. In anterior interosseous nerve entrapment, the median nerve conduction study result will be normal, however the needle EMG of the anterior interosseous innervated muscles will be abnormal.

Ganglion Cyst of the Shoulder

Ganglion cysts can be important when they are located around the shoulder, especially when they are located in the suprascapular notch and the spinoglenoid notch. The suprascapular nerve passes under the transverse scapular ligament at the suprascapular notch. The transverse scapular artery runs above the transverse scapular ligament. The artery and nerve joint and then pass through the spinoglenoid notch under the inferior scapular ligament. The suprascapular nerve gives branches to the supraspinatus muscle and branches to the infraspinatus muscle.

Nerve compression from a ganglion cyst at the suprascapular notch affects both the supraspinatus and infraspinatus muscles, causing a decrease in abduction and loss of external rotation of the shoulder. Nerve compression at the spinoglenoid notch affects only infraspinatus muscle, causing loss of external rotation of the shoulder with the arm to the side. Spinoglenoid notch compression is usually associated with cysts and ganglia. In addition to compression of the suprascapular nerve, these patients may also have associated posterior labral tears.

Anatomy of the Posterior Cutaneous Nerve of the Thigh

The posterior cutaneous nerve of the thigh (small sciatic nerve) arises from the sacral plexus from S1-S3. The posterior cutaneous nerve of the thigh exits from the pelvis through the greater sciatic notch below the piriformis muscle. The nerve descends below the gluteus maximus muscle along with the inferior gluteal artery. It runs into the back of the thigh beneath the fascia lata and over the long head of the biceps femoris muscle to the back of the knee. The nerve then pierces the deep fascia and accompanies the short saphenous vein to the middle of the back of the leg. The posterior cutaneous nerve of the thigh innervates the distal part of the gluteal region, the skin of the perineum and the posterior part of the thigh.

The nerve can become compressed when passing through the tunnel below the piriformis muscle and under the gluteus maximus muscle. This may result in sensitivity disturbances of the innervation area of the nerve. Causes of the syndrome may be hypertrophy or abnormality of the piriformis muscle such as entrapment below the piriformis which compresses the nerve. Compression of the nerve can also occur due to prolonged sitting. During the clinical examination, pain and sensitivity will be evident. Pain and sensitivity disturbances are characteristic of the nerve distribution site in the posterior part of the thigh down the knee. This disturbance can be from hyperesthesia to hypoesthesia or burning sensation similar to meralgia paresthetica of the lateral cutaneous nerve of the thigh.

Differential diagnosis include piriformis syndrome. The patient should avoid sitting for long periods of time, especially on a hard base. Treatment consists of physical therapy, massage, and injection. Surgery is rarely needed.

Toe Deformities

Deformities of the toes are not uncommon and can occur from muscle imbalance, or other causes such as rheumatoid arthritis, diabetes, compartment syndrome, synovitis, or neurological disorders. Hammer toe occurs as flexion of the proximal interphalangeal (PIP) joint. Hammer toe is similar to the Boutonniere deformity of the finger. Claw Toe is a hyperextension deformity of the MTP joint and flexion of the PIP and DIP, resembling a pirate hook. Claw toe is similar to an intrinsic minus deformity of the hand, or “claw hand”. Mallet toe is similar in appearance to mallet finger, and is a flexion deformity of the DIP joint.

Cauda Equina—Central Disc Herniation

Disc herniations usually occurs posterolaterally, but it may also be central. The cauda equina is composed of several nerves within the lower end of the spinal canal. The top of the spinal cord is a tubular bundle of nervous tissue extending from the brain.

The following section of the spinal cord is called the Conus Medullaris and is the lower end of the spinal cord. The Cauda Equina is made up of multiple nerve roots beginning at the level of L1.

The most common disc herniation is the Posterolateral Disc Herniation. This type of herniation is a nerve root injury, which will cause changes to both the sensory and motor skills as well as the reflexes. A posterolateral disc herniation usually affects the foot and ankle, and may cause unilateral leg pain and weakness. Observe for a positive straight leg raising test. These herniations are usually initially treated with conservative methods.  

A central disc herniation will cause cauda equina syndrome, which is a compression over the lumbosacral nerve roots. This compression will cause more back pain than leg pain, and bladder and bowel symptoms will be evident. This herniation is considered a surgical emergency.

Heel Pain & The Baxter's Nerve

Pain located at the heel can have several different causes. It is important to make the correct diagnosis for the cause of the heel pain, so that appropriate treatment can be given to the patient. Common causes of heel pain include:

1. Baxter’s Nerve Compression
2. Plantar Fasciitis
3. Fat Pad Atrophy
4. Achilles Tendonitis
5. Stress Fractures of the Calcaneus
6. Lumbar Spine Radiculopathy

The sites and locations from different causes of the pain are all very close to each other, making it difficult to determine the source of the pain and to diagnose injuries.

In plantar fasciitis, irritation and swelling will occur at the thick tissue on the bottom of the foot. This fascia can become inflamed and painful, making walking more difficult. Plantar fasciitis is most severe in the morning when patients first stand on their feet. Stretching exercises or walking, often helps in relieving the painful tightening associated with plantar fasciitis. Pain symptoms will intensify with prolonged exercise or standing.  Plantar fasciitis is usually associated with a tight heel cord.

During fat pad atrophy, the fat that cushions the calcaneus is thinned. This condition is common in elderly people and can cause significant pain while walking. It also commonly occurs in patients with a history of steroid injections.

Achilles Tendonitis is a chronic injury to the tendon that joins the heel to the muscles of the lower leg, primarily occurring from overuse. The Achilles tendon gives us the ability to rise up on our toes, allowing for the act of walking. If a patient has Achilles tendonitis, walking can be painful and difficult.

Stress fractures of the calcaneus can occur due to overuse injuries. The patient will experience weight bearing pain. Stress fracture injuries of the heel are typical in patients who engage in running sports, due to the repetitive shock being placed on the heel. Side to side compression of the calcaneus is painful.

Pain on the lateral side of the foot may be a result of L5-S1 radiculopathy.

The Baxter’s nerve is the first branch of the lateral plantar nerve. It also contributes to 20% of all heel pain causes. The Baxter’s nerve provides motor innervation to the abductor digiti minimi muscle. When the nerve is affected by compression, the symptoms are similar to planter fasciitis. Entrapment of the Baxter’s nerve may cause up to 20% of heel pain, but is still overlooked. The first branch of the lateral planter nerve is the inferior calcaneal nerve (Baxter’s Nerve).

The nerve courses vertically between the abductor hallucis and the quadratus plantae muscles, then makes a 90° horizontal turn, coursing laterally beneath the calcaneus to innervate the abductor digiti minimi muscle. The Baxter’s nerve can become entrapped within the medial heel. The entrapment will result in heel pain, paresthesia, abnormal sensations on the plantar aspect (bottom) of the heel, and medial heel tenderness. There are two sites of entrapment that are typical with Baxter’s nerve impingements. The first site is located between the fascia of the abductor hallucis and quadratus plantae muscles. The second site is where the nerve passes along the anterior aspect of the medial calcaneal tuberosity.

Treatment

Management is usually conservative and consists of heel stretching exercises, rest, NSAIDs, and Orthotics. Surgery is done as a last resort with neurolysis of the nerve after release of the deep fascia of the abductor hallucis muscle. There is a good-excellent result in about 90% of patients after decompression of the nerve. Involvement of the Baxter’s nerve may affect running athletes causing pain on the medial plantar aspect of the foot.