CASE                               44                               

The patient is a 31-year-old woman who sustained a laceration to the radial side of her index finger while cutting vegetables at home. She presented to an outside emergency room where her laceration was repaired. Four days later, she presents to the office complaining of numbness along the radial side of her index finger. On examination, the patient has a 1.5 cm oblique laceration along the volar radial aspect of her index finger distal to the MP joint overlying the proximal phalanx, but is able to flex at the PIP and DIP joints without discomfort. You diagnose her with a radial digital nerve laceration and plan for operative repair.

What is a normal two-point discrimination in the tip of the index finger?

1. 0 to 1 mm

2. 2 to 6 mm

3. 6 to 10 mm

4. 10 to 15 mm

5. 15 to 20 mm

Discussion

The correct answer is (B). Two-point discrimination in the fingertips can be measured either with a static or moving examination. Normal values vary between individual patients and between the individual digits, but in general 2 to 6 mm is considered a normal two-point discrimination in the fingertips. Following trauma or reconstructive surgery, two-point discrimination is often decreased.

During surgical exploration, the radial digital nerve to the index finger is

completely lacerated. What is the relationship of the digital artery and digital nerve at the level of the proximal phalanx?

1. The relationship of the digital nerve and artery is variable

2. The digital artery is volar to the digital nerve

3. The digital nerve is volar to the digital artery

4. The digital nerve is dorsal to the digital vein

5. None of the above is true

Discussion

The correct answer is (C). Within the digits and distal to the MP joint, the digital nerves lie volar to the digital artery, a relationship which is both predictable and practical. This relationship is reversed proximal to the MP joint, where the common digital vessels lie volar to the common digital nerves.

What is the most common neural structure repaired during digital nerve coaptation?

1. Mesoneurium

2. Epineurium

3. Perineurium

4. Nerve fascicles

5. Endoneurium

Discussion

The correct answer is (B). In addition to the neural components, peripheral nerves are comprised of different layers of connective tissue surrounding the axons and fascicles. The endoneurium is the inner-most layer of connective tissue, and surrounds the myelin sheath of individual nerve fibers. The perineurium is connective tissue surrounding fascicles within the nerve, and the epineurium is the outermost layer of dense connective tissue surrounding a peripheral nerve. The most common method of digital nerve repair utilizes an epineural suture technique, which does not require intraneural neurolysis or intrafasicular dissection.

Objectives: Did you learn...?

Describe the relationship of the digital nerve and artery at the level of the proximal phalanx?

Identify the structure that is repaired during digital nerve coaptation?

CASE                               45                               

The patient is a 48-year-old, diabetic, male smoker who presents to the emergency room after sustaining a laceration to the volar aspect of his palm with a tablesaw (Fig. 4–22). In addition to injuring multiple tendons, the patient has injuries to multiple digital nerves and digital arteries. He is brought to the operating room urgently for exploration and repair; his fingers are revascularized and his digital nerves and tendons are repaired. Postoperatively, the patient inquires about his expected neural recovery.

Figure 4–22

What is the typical rate of nerve regeneration following repair?

1. 0.1 to 0.2 mm/day

2. 0.2 to 0.5 mm/day

3. 1 to 2 mm/day

4. 5 to 10 mm/day

5. 1 to 2 cm/day

Discussion

The correct answer is (C). There are many factors that contribute to the rate of regeneration of peripheral nerves, including mechanism of injury, time until repair, and individual host factors, among others. Most evidence suggests that the average rate of nerve regeneration in peripheral nerves is approximately 1 to 2 mm/day after a brief latency period.

Postoperatively, the patient has incomplete neural recovery of the radial side of his long finger and develops sharp, neuropathic pain at the site of his initial injury with a positive Tinel sign.

What is the likely cause of his neuropathic pain?

1. Tinel lesion

2. Tendon adhesions

3. Joint stiffness

4. Neuroma

5. Wallerian degeneration

Discussion

The correct answer is (D). This patient has developed a neuroma, which is manifest clinically by increased sensitivity and pain following traumatic injury to a nerve. Neuromas can be caused by scarring and incomplete nerve recovery. There are many possible interventions to ameliorate this problem, including embedding the nerve stumps in bone or muscle, injection of substances such as alcohol or phenol, and further resection or cauterization.

What are possible cause(s) of this complication?

1. Failure to resect damaged ends of the digital nerve prior to coaptation

2. Undue tension on the nerve repair

3. Too early wrist and finger extension following repair

4. Unrecognized extent of the zone of injury

5. All of the above

Discussion

The correct answer is (E). There are many possible causes of neuroma following digital nerve repair, including failure to recognize the extent of the injury and resect injured segments of the nerve, undue tension on the nerve repair, and inappropriate mobilization of the nerve coaptation site. Any of these factors, individually or in

conjunction, can lead to a painful neuroma.

Objectives: Did you learn...?

Identify the rate of nerve degeneration?

Explain the causes of nerve pain in a damaged nerve? Describe the causes of neuroma?