Week 29: Trauma Week 3/4: Bones

A knee dislocation is a very serious injury which involves dislocation of the tibiofemoral joint and disruption of all the ligamentous structures. Posterior dislocations occur when with high velocity direct trauma to a flexed knee, such as a dashboard impact in a motor vehicle crash. The most serious consequence of knee dislocation is a popliteal artery injury. The popliteal artery runs in the popliteal fossa and its relative immobility makes it susceptible to disruption when dislocation occurs. A popliteal artery injury is a true emergency. When repair is delayed for more than 8 hours, the amputation rate is greater than 90%. Hard signs of vascular injury include absent pulses, limb ischemia (e.g. a cool, mottled foot), rapidly expanding hematoma, palpable thrill or audible bruit, or history of pulsatile bleeding (in the case of penetrating trauma or open injury). Though not considered a hard sign, paresthesias also raise concern for injury to popliteal structures. The workup-up for ruling out popliteal injury includes serial physical exams, ankle-brachial indices (ABI), CT angiography, conventional angiography, and duplex ultrasonography. Patients with vascular injury require emergent surgical repair.

Carpal tunnel syndrome is a median mononeuropathy and the most common mononeuropathy in the body. Classic symptoms include pain and paresthesias on the volar side of the first, second, and third fingers and radial half of the fourth finger with symptoms most notable at night. Fourth finger sensory dysfunction on the radial aspect of the finger only is very specific for the diagnosis of carpal tunnel syndrome. Extension and flexion at the wrist commonly exacerbate the condition and can aid in diagnosis. Using the Phalen test, by holding the wrists in maximum flexion for at least 1 minute, reproduction of the symptoms helps to point toward this diagnosis. A positive Tinel sign yields tingling after tapping on the wrist where the median nerve passes through the carpal tunnel between the carpal bones and the flexor retinaculum. Both of these tests have poor sensitivity, and if negative, do not effectively rule out the diagnosis. A more specific finding is divided sensation of the fourth finger, with dysfunction on the radial aspect only. Treatment for carpal tunnel syndrome includes a splint on the wrist and NSAIDs. Recurrent symptoms sometimes warrant steroid injections by a hand surgeon and possibly surgical decompression.

WHY THE OTHER ANSWERS ARE WRONG

Some patients have weakness in the muscles of the hand, a condition known as Guyon canal syndrome or handlebar palsy. It is an ulnar mononeuropathy rather than a median neuropathy as with carpal tunnel syndrome. In this rare syndrome, there is compression of the ulnar nerve at the wrist that causes weakness of the intrinsic muscles of the hand. What often happens is that the sensory function of the ulnar nerve is spared or involves only the palmar aspect of the fifth finger and half of the fourth. Carpal tunnel can cause weakness in the thenar eminence, but not the traditional intrinsic muscles of the hand.

Carpal tunnel syndrome is caused by compression of the medal nerve in the inflamed carpal tunnel between the flexor retinaculum and carpal bones, not at the medial epicondyle. Compression here causes cubital tunnel syndrome, and patients have numbness and tingling in the fifth and lateral fourth digits.

Carpal tunnel syndrome is the most common mononeuropathy in the body and involves the median nerve, not the ulnar nerve. The most common ulnar nerve mononeuropathy is cubital tunnel syndrome. Patients typically have paresthesias of the fifth and lateral fourth fingers. Ultimately, weakness of the intrinsic muscles can ensue.

The correct answer is inability to fully extend the knee. The remaining answer choices are all components of the Ottawa Knee Rules, which include: Age over 55 years old, isolated patella tenderness, tenderness at head of fibula, inability to flex knee 90 degrees, and inability to bear weight (4 steps) immediately after injury or in the ED.

Compartment syndrome is diagnosed by a compartment pressure greater than 30 or a ∆ measurement (diastolic BP – compartment pressure) <30. This patient's pressure difference is 25 which is strongly suggestive of compartment syndrome. The femur is in a large compartment and it is typically difficult to sustain compartment syndrome. More concerning areas are the anterior tibial compartment and the forearm.

A. Anterior talofibular ligament
The correct answer is anterior talofibular ligament (ATFL) injury. The anterior-posterior and oblique x-ray views of the right ankle demonstrate a normal mortise and no fractures. There is, however, right lateral ankle soft tissue swelling. Typically, the mechanism of injury helps determine the location of ligamentous injury. The most common mechanism is inversion of the plantar-flexed foot, leading to lateral ankle sprains due to injury of the anterior talofibular ligament (ATFL), the calcaneofibular ligament, and posterior talofibular ligament. Of the three ligaments, the ATFL is the most commonly injured.

B. Calcaneofibular ligament
This patient is presenting with an ankle sprain and with lateral ankle sprains, the most common ligament injured is the anterior talofibular ligament. The calcaneofibular ligament may also be injured, but isolated calcaneofibular ligament injury is uncommon.

C. Deltoid ligament
This patient is presenting with a lateral ankle sprain and the deltoid ligament is on the medial side of the ankle, is much stronger, and is much less prone to injury.

D. Tibiofibular syndesmosis
Injury to the tibiofibular syndesmosis is an uncommon, but significant, injury. Injury to this structure characterizes a “high” ankle sprain. However, the squeeze test of the tibia-fibula is reported negative, making this diagnosis less likely. The squeeze test involves compression of the fibula against the tibia at the mid-calf level, trying to reproduce pain while attempting to widen the syndesmosis between the distal tibiofibular space.

The X-ray demonstrates an anterior knee dislocation. It is important to differentiate between a knee dislocation (tibiofemoral) and patellar dislocation. The patellar dislocation is less severe and typically without other associated injuries. A knee dislocation may not always be present on arrival to the ED as spontaneous reduction can occur prior to arrival. However, even with spontaneous reduction, significant pain and soft tissue swelling remains. In an anterior knee dislocation surrounding vascular and nerve structures are at risk. The dislocation results in significant ligamentous injury. The neurovascular bundle running behind the knee is at risk. The life threatening injury is laceration of the popliteal artery within this bundle. In addition to lacerations of the vascular structure, dissection is also possible from the shear injury occurring during the trauma. The popliteal vein is the other vascular structure within the bundle. The common peroneal nerve is located within the bundle and the neurologic injury associated with an anterior dislocation. This dislocation is associated with an injury to the common peroneal nerve in 20 to 40% of patients. The common peroneal nerve arises from the L4-S2 nerve roots and branches into the deep and superficial peroneal nerves. These nerves supply sensation to most of the dorsum of the foot sparing the lateral most portion of the foot. The motor function of the common peroneal is dorsiflexion of the ankle.

Metatarsal fractures are responsible for one third of foot fractures. Fractures at the base of the metatarsal are uncommon in the first through fourth metatarsals. The isolated fracture at the base of the fifth metatarsal is common and management depends on which form of the two fractures occurs. The Jones fracture is a transverse fracture occurring in the diaphysis of the bone at least 1.5 cm distal to the end of the bone. The Jones fracture tends to displace with further weight bearing. With improper immobilization there is a higher percentage of nonunion of the fracture fragments. Therefore, patients should be immobilized in a posterior splint and given crutches for non-weight bearing ambulation. The pseudo-Jones fracture is an avulsion fracture of the tuberosity at the base of the fifth metatarsal. The injury often occurs as a result of a lateral ankle strain with tension at the attachment of the peroneus brevis tendon. These patients are treated with a compression dressing and weight bearing as tolerated. Providers may elect to give the patients a hard sole shoe.

The lateral radiograph shows a perilunate dislocation in which the lunate remains aligned with the distal radius, however the remaining carpal bones are dorsally displaced. There is significant ligamentous injury. The mechanism of injury is generally a fall on an outstretched hand (FOOSH). Patients complain of wrist pain and swelling, and tenderness is noted over the carpal bones on exam. If untreated, the patient is at risk for developing median nerve compression, avascular necrosis, compartment syndrome and long-term disability. A hand surgeon should promptly evaluate the patient with a plan for urgent open dislocation reduction.

Anterior shoulder dislocations are the most common type of shoulder dislocation. The axillary nerve is the neurologic structure most at risk for injury during a shoulder dislocation. Sensation over the deltoid muscle is the way in which axillary nerve function is tested on physical examination. Additionally, distal nerve function of the median, radial and ulnar nerves should be evaluated as part of the complete evaluation of the shoulder joint. It is important to document all findings of the neurovascular examination prior to any attempts as a baseline. Posterior dislocations are associated with significant injury 30% of the time to intrathoracic and mediastinal structures. These complications include: injury to the great vessels, tracheoesophageal fistula, pneumothorax and brachial plexus injuries.

This case describes a patient with an ankle syndesmosis injury which if not properly treated leads to chronic ankle instability and pain. The image shows widening of the tibio-fibular joint as well as a widened ankle mortise. This ankle requires non-weight bearing an urgent othopedic consultation for possible operative fixation.