CASE 1. A twenty-year-old man sustained a type-IIIA5 open Monteggia fracture-dislocation of the left elbow in a motor-vehicle accident. Initially, he was noted to have intact motor and sensory function. Emergency treatment consisted of irrigation and débridement of the open wound, plating of the ulnar fracture through a dorsal approach, and closed reduction of the anterior subluxation of the radial head. Two days later, the patient was returned to the operating room for repeat irrigation and débridement of the wound. Five days after the injury, iliac-crest bone-grafting and delayed primary closure of the wound was performed. A posterior plaster splint was applied after the entire upper extremity had been wrapped with cotton padding (Webril; Kendall Health Care Products, Mansfield, Massachusetts). The splint was held in place with use of a wrap of non-elastic bias-cut stockinette. In the recovery room, physical examination showed that motor and sensory function of the upper extremity were intact. The next day, however, repeat examination revealed the absence of flexion of the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. The splint was removed, and blood-impregnated cotton padding was found to be stretched tightly across the antecubital fossa. The padding was removed, and a new splint was applied. When the patient was discharged from the hospital four days later, the physical findings were unchanged. The nerve deficit was still evident two weeks postoperatively when the sutures were removed. However, physical examination one month postoperatively revealed a complete return of motor function.
CASE 2. A twenty-two-year-old man sustained displaced midshaft fractures of both bones of the right forearm in a motorcycle accident. When he was admitted to the hospital, motor and sensory function were noted to be intact. Open reduction and internal fixation with iliac-crest bone-grafting was performed for both fractures. The limb was placed in a posterior plaster splint after it had been wrapped with cotton padding. In the recovery room, physical examination confirmed normal motor and sensory function. Later that day, however, the patient was noted to be unable to flex the interphalangeal joint of the thumb or the distal interphalangeal joint of the index finger. Sensation in the hand remained intact. The splint was removed, and blood-impregnated cotton padding was found to be wrapped tightly across the antecubital fossa. The padding was removed, and a new splint was applied. Two days later, the motor deficit was noted to be resolving. By the time of the first postoperative visit to the clinic ten days later, motor function had returned to normal.
CASE 3. A fifty-year-old woman fell on the outstretched left hand and sustained fractures of both bones of the left forearm. The initial evaluation in the emergency room revealed that motor and sensory function were intact throughout the extremity. Two days later, the patient was managed with open reduction and internal fixation of the fractures; the limb was then wrapped with cotton padding and was placed in a posterior plaster splint. Motor and sensory function initially remained intact; on the morning after the operation, however, the patient was noted to be unable to flex the interphalangeal joint of the thumb or the distal interphalangeal joint of the index finger. The splint was removed, and the cotton padding was found to be compressing the antecubital fossa. The padding was removed, and a new splint was applied. Four days later, before the patient was discharged from the hospital, motor function was found to have returned to normal.
CASE 4. A twenty-one-year-old man sustained a minimally displaced fracture at the junction of the middle and distal thirds of the left ulna secondary to a gunshot wound. He was admitted for observation, and neurovascular examination revealed that motor and sensory function were intact. The limb was wrapped with cotton padding and was placed in an above-the-elbow fiberglass cast. Less than twenty-four hours later, the patient reported tingling in the thumb and the index finger and was noted to be unable to flex the interphalangeal joint of the former and the distal interphalangeal joint of the latter. The cast was removed, and blood-tinged cotton padding was found to be tightly wrapped at the level of the antecubital fossa. Compartment pressure was measured and was found to be less than ten millimeters of mercury (1.33 kilopascals) in both compartments of the forearm. During the next two days, the flexion of the distal interphalangeal joint of the index finger returned, but the patient continued to have decreased sensation in the distribution of the median nerve and no function of the flexor pollicis longus. One week later, at the time of he first outpatient visit, motor and sensory function had returned to normal.
The anterior interosseous nerve arises from the posterior aspect of the median nerve five centimeters distal to the medial humeral epicondyle and passes with the main trunk of the median nerve between the two heads of the pronator teres7,18. It continues along the volar aspect of the flexor digitorum profundus and then passes between the flexor digitorum profundus and the flexor pollicis longus, running in close apposition to the interosseous membrane to enter the pronator quadratus7,8,18. It also send sensory fibers to the distal radio-ulnar, radiocarpal, intercarpal, and carpometacarpal joints13. Variations in the distribution of the nerve have been noted; it may supply all or none of the flexor digitorum profundus and part of the flexor digitorum superficialis8,14.
A Martin-Gruber anastomosis, a communication between the median and ulnar nerves, was found by Hirasawa in 10.5 per cent of forearms and by Thomson in 15 per cent. It has been reported9 that one-half of these communications arise from the anterior interosseous nerve. It is possible that a plasty of the anterior interosseous nerve can lead to weakness or paralysis of the muscles of the hand normally supplied by the ulnar nerve9.
Palsy of the anterior interosseous nerve has occurred in association with internal fixation of fractures of the forearm1,8, supracondylar fractures of the humerus12, fibrous bands11, the use of forearm straps in the treatment of lateral epicondylitis2, and the treatment of closed fractures of the forearm without internal fixation17. To our knowledge, there has been one instance of anterior interosseous nerve palsy after use of a Robert-Jones-type bandage for the treatment of a fracture of the lateral end of the clavicle15, two instances after use of a Kenny-Howard splint for the treatment of a dislocation of the acromioclavicular joint10, and one instance after use of a Velpeau dressing following a modified Bristow procedure3. With the exception of direct laceration of the never, the etiology of the palsy has been damage caused by stretching or direct compression4.
In our four patients, the common finding was a tight strip of cotton padding stretched across the antecubital fossa. The padding had become bloody. After the blood had dried, the padding formed a rigid compressive band. No patient had a hematoma. On examination, it appeared that the padding had been wrapped around the limb with the elbow in less than 90 degrees of flexion and that the elbow had then been flexed to 90 degrees for application of the cast or the splint. The padding was wedged into the antecubital fossa, causing compression of the anterior interosseous nerve and, in one patient (Case 4), of the median nerve as well. In all four patients, the anterior interosseous nerve syndrome developed within twenty-four hours after application of the splint or the cast and resolved within twenty-four hours after application of the splint or the cast and resolved within four weeks without operative exploration and decompression.
No similar complications involving the radial or ulnar nerve have been noted at our institution. Susceptibility of the anterior interosseous nerve to volar compression by a constrictive dressing in the region of the antecubital fossa may parallel the situation created by a band of fibrous tissue11. The anatomical location of the anterior interosseous nerve also may predispose it to damage caused by extended compression. It is plausible that the nerve could become trapped between the constrictive volar dressing and the potentially unyielding interosseous membrane. Since the cases of these four patients were identified, it has become our practice to ensure that the elbow is positioned at the desired angle (usually 90 degrees) before application of the cotton padding. The limb is then maintained in this position (with care being taken to avoid any additional flexion of the elbow) until the splint or the cast has hardened. No other instances of this complication were identified during the two years after these four patients were managed.
Iatrogenic injury to the anterior interosseous nerve is uncommon; however, its true frequency may be underestimated. The diagnosis is often missed, with the patient being the first to notice the deficit as a weakness in pinch strength1,3,8. This nerve palsy is usually, but certainly not always, transient3. The cases of these four patients illustrate the need for conscientious physical examination and careful postoperative application of the splint or the cast. Early diagnosis and prompt release of the offending constrictive dressing resulted in a rapid, complete return of function of the nerve in all of our patients. The much too common practice of flexing the elbow after application of the cotton padding may have been the etiology of many palsies of the anterior interosseous nerve that were previously attributed to traction, direct compression by bone-holding forceps, or formation of a postoperative hematoma1,8. We believe that this cause of anterior interosseous nerve syndrome is presently unrecognized and, consequently, overlooked.