Rare case of a low energy traumatic anterior dislocation of the native hip

Background

Dislocation of the native adult hip joint is relatively uncommon and is mostly reported following high energy trauma such as road traffic collisions. They are usually reported in young patients and these are mostly men.1 Anterior dislocation of the native hip joint is rare at around 10% of all hip dislocations.2 Anterior dislocations can be further subdivided into inferior (obturator) and superior (pubic); inferior dislocation is more frequent. They are often isolated injuries, although concomitant impaction fractures of the femoral head have been reported 15%–35%3; whereas acetabular fractures are much rarer (4%).2 Due to the rarity of anterior-superior dislocations only a few small case series and case reports are available in the literature. We report a very rare case of a low energy anterior-superior hip dislocation with associated acetabular fracture.

Case presentation

We present the case of a man in his late sixties who suffered a fall while walking his dog. The patient’s dog was on a lead when the dog bolted, causing his torso to twist on his planted left leg causing him to fall. He presented to the emergency department unable to mobilise with a shortened and 160° externally rotated left leg. There was no neurovascular deficit. This was a closed isolated injury to the hip, and the patient had no other findings of note on clinical examination. The patient was fit and active working as a duck farmer, independently mobile, and had no previous problems relating to his hip. He had no significant medical history and no previous surgeries.

The initial clinical suspicion was for a fractured neck of femur. A plain radiograph of the pelvis and left hip was performed within 30 minutes of arrival, and this demonstrated an anterior-superior dislocated left hip. A bony fragment was also noted laterally (figure 1).

Figure 1

Prereduction anteroposterior and lateral radiographs showing native anterior-superior hip dislocation.

The hip was reduced under sedation in the resuscitation area of the emergency department by the on-call orthopaedic team within one hour of presentation avoiding the need for theatre. There were no immediate complications, and his hip was stable postreduction. His postreduction radiograph confirmed congruent reduction and the free bony fragment was again noted laterally, not in the joint (figure 2A). A CT scan was performed to investigate the acetabular fracture, and this showed a fracture of the anterior acetabular rim extending into the anterior-inferior iliac spine (figure 2B).

Figure 2

(A) Immediate postreduction anteroposterior pelvis radiograph. (B) Postreduction axial section from CT scan (acetabular fracture indicated).

Differential diagnosis

Given the patient’s history of a fall with a shortened externally rotated leg he was suspected to have a neck of femur fracture. Radiographs obtained after presentation provided the true diagnosis.

Treatment

Following his successful reduction, the patient was admitted to the orthopaedic ward for observation. His case was discussed with a pelvic specialist who advised that the patient could be managed non-operatively. The patient was allowed to start toe-touch weight bearing the next day. The patient tolerated this well with no ongoing instability. The patient was assessed by the physiotherapy team over the next couple of days and was deemed to manage safely with independent mobilisation. He was then discharged from hospital after a four-day stay with a six-week course of low molecular weight heparin due to the increased risk of deep vein thrombosis (DVT) with pelvic and acetabular injuries.4

The patient was counselled about the risk of avascular necrosis, post-traumatic arthritis and the possible need for early hip arthroplasty.

Outcome and follow-up

The patient was seen in clinic after six weeks. His symptoms had completely resolved and he reported only lacking confidence. On physical examination, there was no clicking sensation or apprehension to indicate a labral tear or instability. Repeat radiographs showed satisfactory positioning and congruent reduction of the hip with no features of avascular necrosis. The patient was offered physiotherapy and serial radiographic imaging to confirm that no complications developed. He was seen again at six months and at 14 months post-injury with no discomfort and radiographic confirmation of fracture healing (figure 3). Further examination revealed no evidence to indicate a labral tear or instability, and the patient felt no clicking or apprehension. His Hip Disability and Osteoarthritis Outcome Score at 14 months was 98.1%. He was therefore discharged from routine orthopaedic follow-up.

Figure 3

The 14 month follow-up anteroposterior and lateral radiographs.