Injury Extra (2006) 37, 283—285

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CASE REPORT

Missed type IV AC joint dislocation: A case report

Angharad Lee, Quamar Bismil *, Richard Allom, Jeremy Pike

Department of Orthopaedics, Frimley Park Hospital, Portsmouth Road, Frimley,Surrey GU16 7UJ, United Kingdom

Accepted 5 January 2006

Introduction

Acromioclavicular (AC) joint injuries are common.Most are treated non-operatively with good results.Posterior dislocation of the AC joint is rare andrequires operative intervention. We describe a caseof AC joint injury in which the posterior dislocationwas not evident initially, and only apparent at re-evaluation 6 weeks later. The injury was successfullytreated by open reduction and internal fixation witha ‘hook’ plate.

Case report

A 25-year-old right-handed male office worker pre-sented to the Accident and Emergency Departmentafter an injury to his right shoulder girdle. He hadfallen from his mountain bike directly onto the pointof the shoulder. He complained of diffuse pain overthe shoulder girdle radiating down the arm. Clinicalexamination revealed significant swelling over theshoulder and distal clavicle. Shoulder movementwas limited by pain. There was diffuse tenderness.There was no obvious instability of the acromiocla-vicular (AC) joint. A plain AP radiograph was taken(Fig. 1). This was passed as normal. The diagnosis ofsoft-tissue injury was made. The patient was immo-

* Corresponding author. Tel.: +44 2072285161;fax: +44 1205 361568.

E-mail address: quamar.bismil@btinternet.com (Q. Bismil).

1572-3461/$ — see front matter # 2006 Elsevier Ltd. All rights resedoi:10.1016/j.injury.2006.01.016

bilised in a broad arm sling, and referred to thefracture clinic.

The patient was seen in the fracture clinic thefollowing day. The previously noted examinationfindings were confirmed. The radiograph wasreviewed. It was noted that there was partial over-lap of distal clavicle on the acromion. The radio-graph was repeated whilst suspending a 5 kg weightfrom the patient’s wrist. This did not change theappearance of the AP X-ray. The clinical impressionwas of Rockwood type III AC joint injury. The patientwas advised to use the sling for comfort; and tocommence mobilisation of the limb as pain allowed.

Figure 1 Original AP X-ray.

rved.

284 A. Lee et al.

Figure 2 Posterior dislocation evident at 6 weeks postinjury.

Figure 4 Posterior dislocation evident at 6 weeks postinjury.

Figure 5 Post-operative AP X-ray.

A fracture clinic appointment was scheduled for the6 week mark.

He was reviewed in fracture clinic 6 weeks follow-ing the injury. The patient complained of ongoing,intrusive pain. The clinical picture had evolved. Clin-ical examination now revealed that the clavicle wasdisplaced posteriorly through the trapezius muscle:i.e. Rockwood type IV injury (Figs. 2—4). The patient

Figure 3 Posterior dislocation evident at 6 weeks postinjury.

was counselled with regard to treatment options andsurgical intervention was planned.

In the operating theatre, with the patient in thebeach chair position a ‘bra strap’ incision was madeover the AC joint. The clavicle had button-holedthrough a shredded trapezius remnant. The AC jointwas reduced and held with a 15 mm 6-hole RegazoniClavicular (AO) hook plate and four screws (Fig. 5).The trapezius remnants were sutured back over theplate. The patient was seen in the outpatient clinicat 6 weeks post surgery. There were no postopera-tive complications. The hook plate will be removedat 6 months following surgery.

Discussion

Injuries to the acromioclavicular joint are common.The usual mechanism is a fall onto the point of theshoulder with a resultant downward force onto the

Missed type IV AC joint dislocation: A case report 285

acromion and clavicle. The first rib prevents furtherdownward displacement of the clavicle. If the cla-vicle is not fractured, the force is dispersed throughthe ac joint. Rockwood’s classification of theseinjuries is widely used1 and enables a logicalapproach to management.

With increasing force through the joint, there isprogressive disruption of the acromioclavicular andcoracoclavicular ligaments: in a type I injury theligaments are intact; in type II the acromioclavicularligament is disrupted; in type III both ligaments aredisrupted. Types IV through VI are rare and severe,with disruption of both ligaments along with: pos-terior displacement of the clavicle in type IV; ver-tical translation > 100% of the AC joint in type V;dislocation of the distal clavicle inferior to thecoracoid process and posterior to biceps and cor-acobrachialis tendons in type VI.

Type IV AC joint injuries are rarely described inthe literature.2 The case we describe highlights thediagnostic challenge that this injury can pose. Atinitial presentation, the posterior dislocation of theclavicle was masked by severe swelling. Further-more, the AP radiograph (including stress view) wasnot diagnostic, since the displacement was purelyposterior, i.e. in the sagittal plane. In previousreports of this injury, there has at least been ahigh-riding clavicle on the AP view.2 In the casewe present, it was only through clinical re-evalua-tion that diagnosis could be made. Thus, by the 6week mark, the swelling had subsided and the pos-terior dislocation was evident.

It has previously been noted that plain radio-graphs of AC joint injuries, with or without stressview, do not always correlate with the pathoanat-omy as seen on magnetic resonance imaging (MRI)scanning.3—5 In the case we describe, it is likely

that an oblique radiograph would have aided diag-nosis.

The six Rockwood sub-classifications are clearlyimportant in understanding AC joint injuries. How-ever, with regard to treatment it is useful to think oftwo broad groups of AC joint injury: with types Ithrough III in the first group and types IV through VIin the second. Thus, most AC joint injuries are Rock-wood types I to III and are benign. These are usuallytreated non-operatively with good results. In con-trast, types IV through VI are rare, involve severedisruption of the AC joint and surrounding structuresand require surgical intervention.1,6 At initial pre-sentation, our patient appeared to fall into the firstgroup. However, at 6 weeks it was obvious that thiswas not the case. Accurate diagnosis and classifica-tion of AC joint injuries at the initial presentation isnot always possible. Clinical reassessment at aninterval and additional radiology (oblique radio-graph, MRI scan) should be considered for such cases.

References

1. Rockwood Jr CA. Dislocations of the sternoclavicular joint.Instr Course Lect 1975;24:144.

2. Sondergard-Petersen P, Mikkelsen P. Posterior acromioclavicu-lar dislocation. J Bone Joint Surg Br 1982;64:52—3.

3. Bossart PJ, Joyce SM, Manaster BJ, Packer SM. Lack of efficacyof ‘‘weighted’’ radiographs in diagnosing acute acromioclavi-cular separation. Ann Emerg Med 1988;17:20—4.

4. Barnes CJ, Higgins LD, Major NM, Basamania CJ. Magneticresonance imaging of the coracoclavicular ligaments: its rolein defining pathoanatomy at the acromioclavicular joint. JSurg Orthop Adv 2004;13(2):69—75.

5. Antonio GE, Cho JH, Chung CB, Trudell DJ, Resnick D. Pictorialessay. MR imaging appearance and classification of acromio-clavicular joint injury. Am J Roentgenol 2003;180(4):1103—10.

6. Rowe CR. Dislocations of the shoulder. In: Rowe CR, editor.The shoulder. New York: Churchill Livingstone; 1988.