14.5 Fractures about the elbow in children

Fractures around the elbow are a common occurrence in childhood; however, these fractures require careful assessment and treatment if complications are to be avoided.

These are the most common elbow fractures in children. Although they can occur throughout childhood there is a peak incidence between the ages of 5–8 years. A review of supracondylar humeral fractures noted that the average age was 6.7 years, 60.8% were on the left, 62.8% were in boys, and 1% were open. The usual mechanism of injury is a fall on the outstretched hand with the elbow locked in hyperextension. The natural predisposition to ligamentous laxity in this age group allows this increased hyperextension to cause the olecranon to lever in the olecranon fossa creating a stress concentration at the supracondylar area resulting in the typical extension fracture pattern.

Two per cent of these injuries have a flexion pattern and typically are caused by a direct blow to the posterior aspect of the elbow. Careful consideration of the distal humeral anatomy is needed for recognition since these fractures can be subtle. Displaced flexion fractures have a high incidence of ulnar nerve injury from where it is stretched over the posterior edge of the proximal fragment. Fracture displacement tends to be valgus, in contrast with extension supracondylar fractures which may heal in varus.

The classification described by Gartland (1959) and modified by Wilkins et al. (1996) is the most commonly used (Table 14.5.1); this is based on the degree and direction of displacement of the distal fragment on the initial x-rays. In approximately 75% of supracondylar fractures, the displacement of the distal fragment is posteromedial and the lateral spike of the proximal humeral shaft may injure the radial nerve. Whereas when the distal fragment is displaced posterolaterally, the brachial artery is at risk along with the median nerve. The direction of displacement also influences management by either pronating (posteromedial displacement) or supinating (posterolateral displacement) the forearm will help maintain fracture stability from the intact periosteal hinge prior to wiring of the fracture.

In completely displaced fractures there will be swelling, bruising, and crepitus apparent and an S-shaped deformity of the elbow may be present. The carrying angle is approximately 15 degrees of valgus but should be compared to the other side as it can vary from 0–25 degrees. Whereas with undisplaced or minimally displaced fractures, swelling and point tenderness may be the only clinical signs present. Puckering of the skin indicates penetration of the brachialis muscle by the proximal end of the humerus which increases the possibility of an open reduction being required.

Nerve injuries have been reported to occur in up to 7% of patients with supracondylar humeral fractures and all the nerves passing across the elbow should be carefully assessed. The most commonly injured is the anterior interosseous nerve since its fibres make up the part of the median nerve closest to the bone; testing for this by flexion of the index finger and thumb into an ‘O’ shape should be undertaken.

The distal circulation of the arm should also be assessed. If a radial pulse is not palpable further investigation can be performed using Doppler or pulse oximetry to assess this but this should not delay the time of operative intervention. Evaluation for compartment syndrome is needed both pre and postoperatively even when there has been no vascular compromise.

Ipsilateral forearm injuries occur in about 5–10% of patients, but the supracondylar fractures should be treated operatively and stabilized, before treatment of the other fractures.

When determining the degree of displacement of the fracture on x-ray, several features should be identified (Figure 14.5.1 and Box 14.5.1).

Treatment of supracondylar fractures is based upon their classification. Type I (undisplaced) fractures need only simple immobilization in a collar and cuff under the clothes for two to three weeks then with advice for mobilization. Swelling can be significant and application of any rigid splintage can create pressure problems and is to be avoided. Complications particularly medial collapse or impaction can occur, leading to varus malunion, and so follow-up evaluation is recommended.

The treatment of type II fractures is by reduction of the extension deformity. Due to the significant incidence of instability then it is the author’s preferred technique for stabilization of these with percutaneous pins.

In type III fractures olecranon screw traction can be undertaken, but this is now rarely used because of the lengthy hospital admission required. Traction is however useful where condition of the skin precludes the presence of wires or where fracture comminution is so severe as to prevent an acceptable reduction being maintained with percutaneous pinning.

Gentle longitudinal traction should be applied followed by closed reduction of the fracture with flexion and the appropriate forearm rotation under image intensifier control is initially performed. The adequacy of the reduction needs to be assessed using shoot through (Jones view), oblique and lateral views (the latter, particularly in unstable fractures, may demonstrate rotational malalignment but is useful for assessing displacement). Numerous variations of pinning techniques have been described in an attempt to minimize complications. The two most stable constructs consist of medial and lateral pins placed through the supracondylar ridges and into the opposite cortex or two lateral divergent pins. Stabilization using the former technique involves insertion of the lateral wire in full flexion, extending the arm and inserting the medial wire (utilizing a small incision to protect the ulnar nerve) (Figure 14.5.2). Both techniques have their advocates and the main complications of loss of reduction and iatrogenic ulnar nerve injury are technique dependent.

Once stabilized, the elbow can then be assessed for stability and reduction. Radiographic and clinical assessment, as described earlier, should be used.

After closed reduction and pinning, a wool and crepe dressing and non-removable collar-and-cuff sling are worn for 3–4 weeks. Then the pins are removed and an active range-of-motion rehabilitation programme is begun.

Open reduction is required for fractures that cannot be reduced by closed means, open fractures, and in some cases of fractures with vascular compromise. This allows the soft tissue interposition to be treated, following which stabilization can be undertaken in the same manner as for closed reduction with the benefit of direct visualization. Approaches from all directions have been described, the commonest being anteromedial or anterolateral depending upon fracture displacement. Approaching from the same side as the displacement of the proximal fragment, often allows a direct ‘cortical read’ and does not add significantly to the periosteal stripping. Where vascular compromise requires intervention an anterior approach is preferable. Delayed open reduction beyond 10 days has an increased risk of myositis ossificans.

Supracondylar humeral fracture complications can be either functional or cosmetic. Functional complications relate to nerve and vessel injury and elbow stiffness. Cosmetic complications are related to inadequate reduction creating malunion.

The majority of nerve injuries are neuropraxic from the injury itself and recover within 3 months of injury. The most common injury involves the anterior interosseous part of the median nerve.

Ulnar nerve injury most commonly occurs due to medial pin insertion but these recover in almost all cases by 3 months following pin removal.

Vascular injuries are uncommon. If the radial pulse is absent but there is good capillary refill following stabilization of the fracture then observation, especially for compartment syndrome of the forearm musculature, is the preferred management, even if the radial pulse was lost during reduction. If the arm is pulseless and capillary refill is poor the fracture should be stabilized and the situation reassessed, and if persistent, observation can still be undertaken since the vast majority of pulses return within 24h without detriment. Close observation should be undertaken with a low threshold to return the child to theatre for release of compartment syndrome and arterial exploration if necessary. The child should be transferred to a unit where facilities exist for vascular surgery.

Avascular necrosis of the trochlear has been reported from vascular injury leading to a fishtail deformity of the distal humerus, symptoms from which are delayed.

Elbow stiffness after this fracture may result in loss of terminal elbow extension. Most patients regain almost complete elbow motion, although this may require several months. Elbow stiffness also can occasionally be caused by myositis ossificans, which usually occurs after delayed open reduction or too vigorous rehabilitation.

Angular deformities result from inaccurate reduction or subsequent displacement producing a malunion. Cubitus varus (‘gunstock’) deformity is most common. The deformity remains static occurring at the fracture site rather than the joint and there are minimal functional deficits but often a considerable cosmetic deformity. Rarely this can occur in undisplaced fractures which may be a feature of vascular compromise to the lateral condyle.

Correction of cubitus varus is directed at the coronal plane deformity with various techniques having been described (Figure 14.5.3). The commonest technique of a lateral closing-wedge osteotomy may produce a lateral prominence and apparent persistence of the deformity, whereas other techniques attempt to avoid this problem using a dome osteotomy or step-cut lateral closing-wedge osteotomy.

Cubitus valgus deformity is rare. Hyperextension occurs when the lateral humeral capitellar angle is not corrected at the time of reduction and this does not improve with growth.

Fractures of the lateral humeral condyle account for approximately 15% of distal humeral fractures in children, occurring most commonly around the age of 6 years. They can be easily missed radiologically since the metaphyseal fragment appears small but the presence of point tenderness over the lateral condyle with localized swelling should alert the clinician to the possibility of this injury.

Lateral condylar fractures classically were classified by the fracture pattern; Milch (1964) described two types of fracture direction; but practically the best classification is described by Wilkins (1996) and is related to displacement.

Two mechanisms of injury have been proposed for fractures of the lateral humeral condyle fracture: a ‘push-off’ mechanism where a fall onto the hand with the elbow flexed causes the radius to push off the lateral condyle; and a ‘pull-off’ mechanism which is more common and occurs when a fall on the outstretched hand with an extended elbow creates a varus moment and the lateral condyle is pulled by the extensor muscles.

In undisplaced or minimally displaced fractures a ‘fat-pad’ sign is present. The metaphyseal fragment is difficult to visualize on the anteroposterior view and on the lateral view will appear falsely small since it is being viewed in profile. In displaced fractures the capitellar ossification centre and the radial head are not aligned, distinguishing this from a supracondylar type fracture where this is maintained. Close monitoring of these fractures is required since with displacement operative treatment is required and it is difficult to assess whether there is an intact periosteal hinge stabilizing a minimally displaced fracture.

Fractures with less than 2mm displacement can be treated conservatively by immobilization; however they need monitoring to exclude late displacement, in which case fixation will be required. Immobilization is continued until radiographic healing is present.

Fractures with less than 4mm of displacement can be treated by closed reduction and percutaneous pinning with care not to cross the fixation wires at the site of the fracture and a degree of wire divergence is preferable.

For significantly displaced or unstable fractures, open reduction and internal fixation is required. A posterolateral approach in the brachioradialis–triceps interval presents the fracture which is reduced by extension and the metaphyseal fragment is always larger than expected from radiology and can be stabilized with a cannulated small fragment screw into the metaphysis. Excellent results with no complications have been reported with screw fixation. Alternatively two K-wires can be utilized.

The commonest complications of lateral condylar fractures relate to problems of union. In undisplaced fractures treated conservatively delayed union is frequent. Possible causes are poor vascularity of the fragment, synovial fluid in the fracture preventing fracture healing, and the muscle pull of the common extensors.

Non-union is usually due to incomplete reduction of fracture fragments. Non-unions without angulation are usually asymptomatic; however, where angulation remains, a cubitus valgus deformity develops which can lead to a tardy ulnar nerve palsy. Treatment of a non-union depends on functional problems as well as progressive deformity but open reduction with bone graft and internal fixation is required (Figure 14.5.4) and ulna nerve transposition may also be indicated.

Avascular necrosis of the lateral condyle fragment can occur from open reduction; however, when union is achieved the fragment revascularizes and long-term functional deficit is rare.

Transcondylar fractures of the humerus are a physeal separation of the whole of the distal humerus and occur prior to ossification, typically under 3 years of age (Figure 14.5.5). Since this area is cartilaginous, no fracture may be apparent on x-ray and a misdiagnosis of an elbow dislocation is made. These is a rare injury infrequently reported in the literature. These fractures have also been reported as birth injuries following difficult deliveries and also in child abuse cases.

Swelling and hypermobility may be present or in the very young pseudoparalysis of the limb may be the presenting complaint. Assessment of the relationship of the medial and lateral epicondyles and the olecranon as an equilateral triangle exclude the diagnosis of dislocation and should alert the clinician to the possibility of a transcondylar fracture. Radiologically there may be loss of alignment between the radius and ulna and the humerus and the displacement is usually posteromedially. Arthrography or ultrasound may be required to confirm the diagnosis in the operating theatre prior to intervention.

Three groups are described depending on the degree of ossification present. In group A fractures (up to 12 months of age), the lateral condyle secondary ossification centre is not present and there is no visible metaphyseal fragment. In group B fractures (1–3 years) the capitellar ossification centre is present; a metaphyseal fragment, if present, is very small. Group C fractures (3–7 years) have a well-developed capitellar ossification centre and a large metaphyseal fragment.

The recognition of the fracture and its association with child abuse in children under 2 years is mandatory, up to 38% in this age group have been reported to have this mechanism of injury. The fracture is reduced by elbow flexion and pronation of the forearm should then be stabilized using two divergent lateral wires (cross K-wires are difficult to insert medially due to the cartilaginous medial epicondyle) and then immobilized but the adequacy of reduction may require arthrographic assessment. Postoperatively a supportive dressing is required with the limb held flexed by a collar and cuff worn under the clothes for 3 weeks and then mobilization following wire removal. If the fracture has been missed and is more than 5 or 6 days old it will be irreducible and is better left to heal and corrected by osteotomy at a later date if necessary.

Neurovascular complications are infrequent but cubitus varus is common although generally minor (less than 15 degrees) and is related to the difficulty of assessment of reduction in the absence of ossification of the physeal fragment. This degree of cubitus varus deformity rarely causes functional problems and rarely requires corrective osteotomy. Avascular necrosis of the trochlea can occur after this fracture and tends to occur early with a subsequent varus or fishtail deformity.

Medial humeral condylar fractures are rare, occurring around 8–14 years of age. The fracture involves the trochlea and the distal humeral metaphysis, with the attached medial epicondyle, and is inherently unstable. Up to 40% are associated with elbow dislocations.

The fracture can either enter the elbow medial to the lateral crista of the trochlea or pass directly through the medial condylar ossific nucleus. Due to the presence of the attached medial epicondyle the fracture is rotated by the common flexors so that the fracture surface presents anteromedially and the articular surface faces posterolaterally (Figure 14.5.6A).

Medial condylar fractures are caused by a direct blow on the flexed causing the olecranon to split the trochlea or where a fall is associated with a valgus stress and the forearm flexor muscles avulse the condyle.

Clinically there is medial swelling and tenderness and varus instability. Ulnar nerve function should be carefully assessed. After ossification of the trochlea and medial epicondyle the fracture is apparent on standard radiology and a fat pad sign is also present but before ossification a high index of suspicion is required and alternative techniques such as magnetic resonance imaging (MRI) may be required.

Undisplaced fractures can be treated by immobilization in a backslab but must be regularly assessed for displacement. For displaced fractures the preferred option is open reduction and internal fixation via a posteromedial approach decompressing the ulnar nerve, limiting dissection to avoid avascular necrosis. The medial condyle should be stabilized with two parallel pins or a screw (Figure 14.5.6B). Post operatively due to swelling a supportive bandage or back slab is required with immobilization in a collar and cuff for 3 weeks and then mobilization.

The common complications are non-union, avascular necrosis of the trochlea causing a ‘fishtail’ growth deformity, and stiffness. Restriction of extension is the most frequent problem. Non-union is usually secondary to delayed diagnosis and treatment or inadequate fixation. Treatment of established non-union requires bone grafting and internal fixation.

Fractures of the capitellum are a rare injury at any age, but especially in children. Anterior sleeve fractures have been reported in 8-year-old patients, but capitellar fractures are usually in older adolescents.

These fractures occur following a fall on the outstretched hand, where shear forces are transmitted through the radial head, injuring all or part of the capitellum. Recurvatum and cubitus valgus deformities may be predisposing factors.

The diagnosis of this fracture may be difficult and easily missed, particularly since they can be associated with radial head fractures. Swelling is often minimal about the elbow, with tenderness over the capitellum. A positive fat-pad sign is usually present on standard radiographs. Oblique radiographs or an MRI may necessary for diagnosis.

Two fracture patterns are described (Figure 14.5.7). Type I is a complete fracture of the capitellum, which has a portion of cancellous bone attached to the distal fragment. Type II fractures involve mainly articular cartilage with only a thin margin of subchondral bone.

Open reduction is necessary, if the metaphyseal fragment is large enough this can be reattached and secured with Herbert type screws, via a posterior approach through the lateral condyle but careful dissection is required to avoid avascular necrosis of the lateral condyle. Smaller fragments should be excised and early range of motion exercises undertaken. The complications of capitellar fractures are avascular necrosis of the fracture fragment, loss of motion about the elbow, and early degenerative arthritis.

Medial epicondylar fractures are the third most common fracture of the elbow in children, accounting for 11% of fractures about the elbow. This injury most frequently occurs between 9–14 years of age, and is four times more common in boys than in girls. Elbow dislocation occurs in approximately 30% of cases and in half of these the medial epicondylar fragment will be incarcerated in the elbow joint after reduction of the dislocation leading to a block to elbow extension.

The medial epicondyle is a traction apophysis with the forearm common flexor muscles arising from its anterior surface and the ulnar collateral ligament also being attached. Ossification of the medial epicondyle begin at 4–6 years of age, and it fuses with the distal humerus by the age of 15 years. Irregularity of ossification can give the nucleus a fragmented appearance, which can be mistaken for a fracture. In younger children some capsular attachments may remain and a positive fat-pad sign may be seen, but in older children the epicondyle is extra-articular.

Medial epicondylar fractures can be caused by a direct blow, an avulsion injury due to the pull of the common flexor muscles of the forearm, or with an elbow dislocation where under hyperextension and valgus stress the ulnar collateral ligament avulses the epicondylar. This dislocation may spontaneously reduce prior to presentation. This mechanism of injury also may produce associated injuries to the radial neck and the olecranon.

This fracture can be produced by a sudden isolated muscle contraction, such as the simple act of throwing a baseball (which can also be a chronic condition termed Little Leaguer’s elbow where elbow extension is lost and pain is reproduced by valgus stress, x-rays revealing an irregular and widened physis).

The elbow is swollen and tender medially and if the medial epicondyle is displaced, it may be palpable and freely moveable. X-rays of minimally displaced fractures may show changes to the smooth physeal edges or a widened physis. In displaced fractures, if the fragment appears at the level of the joint, an oblique radiograph should be performed to exclude incarceration of the fragment within the elbow joint.

Wilkins et al. combined several classification systems and divided medial epicondylar injuries into acute and chronic injuries. Acute injuries are further divided into (a) undisplaced or minimally displaced; (b) displaced by more than 5mm but proximal to the joint line; (c) incarcerated with no elbow dislocation; and (d) incarcerated with elbow dislocation.

Undisplaced or minimally displaced fractures should be treated with immobilization followed by early range of motion of the elbow. For displaced fractures proximal to the joint line good results with non-operative treatment are reported. Although healing in a displaced position occurs this does not lead to any functional deficit or any instability of the elbow joint. In children with high functional demands and a fracture of the dominant arm, fixation can be considered but it is debatable whether this affords any long term benefit.

The only absolute indication for operative treatment is incarceration of the fragment in the joint (Figure 14.5.8). Although successful extraction of the fragment from the joint can be achieved by manipulation in up to 40% by placing a valgus stress on the elbow while supinating the forearm and dorsiflexing the wrist, it is more likely than not that there has been a significant injury to the elbow joint to allow incarceration to occur and that this has been a dislocation that has spontaneously reduced and the fragment is better secured by open fixation affording an element of stability to the elbow joint.

Operatively the fragment is exposed via a medial approach protecting the ulnar nerve. The fragment is always larger than is apparent radiologically and can be secured with a single cannulated screw which will afford sufficient stability to allow early graduated mobilization. If ulnar nerve symptoms are present at the time of fixation, decompression of the nerve should also be performed and this is present in up to 50% of incarcerated cases.

The most serious complication of this fracture is an unrecognized incarcerated fracture fragment within the elbow joint, this becomes adherent blocking elbow motion. In patients with chronic incarceration of medial epicondylar fractures a thick fascial band binds the ulnar nerve to the underlying muscle causing ulnar nerve dysfunction. Once identified, it should be removed.

Fracture of the lateral epicondyle is rare, occurring as a traction injury from the pull of the common extensor origin. Localized swelling and tenderness are present and the only treatment required is immobilization and early mobilization; functional deficit rarely occurs. Incarceration of the fragment in the elbow joint has been reported and is the only indication for operative management to reattach the extensor origin.

T-condylar fractures occur in adolescents and have an adult fracture pattern with the fracture starting in the trochlea propagating and dividing the medial and lateral columns. This is caused by the wedge effect of the olecranon splitting the humerus following axial compression or a direct blow on the flexed elbow. Displacement of the fragments occur secondary to the pull of the forearm muscles rotating the fragments in two planes.

Gross swelling is present due to the unstable nature of the fracture and radiologically displaced fractures are readily apparent. Undisplaced fractures need careful evaluation to differentiate these from the other forms of distal humeral injury.

The classification described by Wilkins is well recognized: type I, minimally displaced; type II, displaced with no comminution; type III, displaced and comminuted.

Whilst each case should have its treatment determined by the fracture pattern the basic principles of treating this intra-articular fracture should be applied. The articular surface should be restored to congruency; the medial and lateral columns should be restored and stabilized to allow early mobilization because the attached muscles will increase displacement if adequate stability is not achieved.

Type I fractures can be treated with percutaneous pinning. Type II and III fractures require open reduction and internal fixation. The fracture needs adequate exposure by either a triceps-splitting approach, an olecranon osteotomy, or an extensile approach. Initial reduction of the articular surface is performed with stabilization using transverse fixation with subsequent reduction of the medial and lateral columns using wires is the younger adolescents or reconstruction plates at 90 degrees to each other in the older child. In Type III fractures where comminution of the columns is severe the joint surface can be reconstructed and the extra-articular fracture treated by traction to maintain alignment.

The commonest complications are elbow stiffness and loss of motion, and a degree of this is the usual outcome so the parents should be advised of this. Non-union, avascular necrosis of the trochlea, and failure of internal fixation have all been reported.

Elbow dislocations accounts for 6% of all elbow injuries in children, most commonly occurring once the physes have closed at 13–14 years of age. Up to 50% of elbow dislocations have an associated fracture, typically the medial epicondyle, the lateral condyle, and the radial head and neck.

The presence of an elbow dislocation is readily apparent as the deformity, depending on the direction of displacement and swelling, is usually significant. A detailed neurological examination should always be performed and any deficit documented prior to reduction.

The elbow has little bony stability except when fully extended. The majority of its stability is provided by the collateral ligaments and the joint capsule. The medial collateral ligament consists of anterior (taut in extension) and posterior (taut in flexion) bands. Lateral stability is provided by the radial collateral ligament and the radial head also provides stability to valgus stress. Dynamic stabilizers of the elbow are the forearm flexors and extensor muscles. The brachialis muscle protects the brachial artery and median nerve from injury during elbow dislocation.

Elbow dislocations are classified according to the direction of dislocation and the status of the proximal radioulnar joint (Table 14.5.2). When the proximal radioulnar joint is intact, the elbow can be dislocated in five directions, the commonest being posterolateral. Disruption of the proximal radioulnar joint leading to a divergent dislocation or radioulnar translocation is rare.

In uncomplicated elbow dislocations closed reduction followed by short-term (10–14 days) immobilization is the treatment of choice. Reduction is obtained by one of two methods. In the ‘push’ technique the surgeons thumb pushes on the olecranon tip causing reduction. In the alternative ‘pull’ technique the elbow is flexed 70 to 80 degrees traction applied longitudinally to the forearm reducing the dislocation. Placing the arm in supination avoids translocation of the radius and ulna during reduction.

Open reduction is indicated for (a) failed closed reduction, (b) open dislocation, (c) fractures requiring open fixation, or (d) bony fragment incarceration in the joint.

The most common complication is elbow stiffness which can be minimized by early mobilization, but there is usually a minor loss of extension. Nerve injury occurs in 10%, of which in the majority a neuropraxia and a full recovery is the norm. The ulnar nerve is the most commonly involved, particularly when the dislocation is associated with a medial epicondylar fracture, and exploration of the affected nerve should be considered at the time of fracture stabilization.

Myositis ossificans can occur typically in the brachialis muscle. Its incidence is reduced by prompt reduction, the avoidance of hyperextension, and passive mobilization.

Proximal radioulnar translocation may be unnoticed after closed reduction of a dislocated elbow. In this situation, the radius articulates with the trochlea and the olecranon articulates with the capitellum. In a posterolateral dislocation, if the forearm is hyperpronated at the same time as traction is applied, the radial head can easily pass anterior to the ulna and cause the translocation. Treatment of the translocation requires surgery open reduction.

Recurrent dislocation has either soft tissue or bony components causing the instability. Surgical stabilization using an anterior bone block or transfer of the medial epicondyle proximally to tighten the medial restraining structures can be performed for bone defects. In soft tissue instability triceps tendon transfer or lateral capsular placation are the options of choice.

With the elbow in extension and a high-energy proximally directed force being applied through the forearm a divergent dislocation can occur. The radius displaces laterally and the olecranon medially. Closed reduction usually can be easily obtained due to the degree of the soft tissue injury, by longitudinal traction releasing the humerus and then compressing the radius and ulna together before flexing the elbow where stability is maintained.

The classical history is of a sudden longitudinal pull being applied to a child’s wrist or hand (under 4 years of age) with forearm pronation and elbow extension resulting in radial head subluxation. Following this episode the child will be reluctant to use the limb, local tenderness over the radial head and annular ligament is present but swelling is rarely a feature. Supination and flexion movements of the elbow are painful but necessary to reduce the subluxation. If supination alone does not reduce the subluxation then maximal flexion followed by supination should be performed and will usually be accompanied by a characteristic snapping reduction.