Femoral head fracture

A shear fracture of the femoral head, almost always produced as the head is driven out of the back of the acetabulum: the posterior rim shears off an inferomedial piece that stays behind, often still tethered by the ligamentum teres. Whether the fragment carries weight-bearing cartilage (above the fovea) and whether the neck or the acetabulum is also broken decide the treatment.

Mechanism

Posterior hip dislocation from a dashboard injury, with the hip flexed less than 90° and some abduction, so the head meets the posterior rim instead of slipping past it. Rarely an axial load or an anterior dislocation (impaction of the head on the anterior rim).

Clinical findings

• ATLS: a high-energy injury; the dislocated hip lies flexed, adducted and internally rotated.
• Sciatic nerve (mainly the peroneal division: ankle dorsiflexion and first web sensation) before and after reduction.
• Examine the ipsilateral knee (patella fracture, PCL tear) and look for a femoral shaft fracture, which can mask the dislocation.
• Exclude a femoral neck fracture on imaging before any closed reduction: forcing reduction can displace an undisplaced neck fracture (iatrogenic Pipkin III).

Imaging

• AP pelvis before reduction: exclude a femoral neck fracture before any closed reduction.
• After reduction: AP pelvis and Judet (iliac and obturator oblique) views.
• Thin-slice CT of the pelvis after reduction in every case: fragment size and position relative to the fovea, incarcerated fragments, posterior wall, impaction.

• AP pelvis: the femoral heads look unequal in size and a fragment may be seen in or below the acetabulum. Judet views for the posterior wall.
• Thin-slice CT after reduction, always: size and position of the head fragment relative to the fovea, incarcerated fragments, concentricity, marginal impaction and the posterior wall.
• Post-reduction joint widening on CT means an incarcerated fragment or interposed labrum.

Classification

31C1

Split (shear) fracture of the femoral head: the Pipkin fractures.

31C2

Depression (impaction) of the femoral head articular surface.

Pipkin I

Fragment below (caudal to) the fovea: outside the main weight-bearing zone.

Pipkin II

Fragment extends above the fovea and includes weight-bearing cartilage.

Pipkin III

Type I or II with a femoral neck fracture: worst prognosis (avascular necrosis).

Pipkin IV

Type I or II with an acetabular fracture, usually the posterior wall.

Types shown in 3D

Pipkin I

Fragment caudal to the fovea, outside the weight-bearing area. If the reduced hip is concentric and the fragment sits well, non-operative; excise or fix a displaced one.

Pipkin II

The fracture line passes above the fovea: the fragment includes weight-bearing cartilage and the insertion of the ligamentum teres. Anatomical reduction and screw fixation (anterior approach or surgical hip dislocation).

Pipkin III

Head fragment plus a femoral neck fracture. The shaft rides up and rotates out. Worst prognosis: in the young fix the neck first, in older patients replace the hip.

Pipkin IV

Head fragment plus an acetabular fracture, usually the posterior wall broken off as the head dislocated. The acetabulum dictates the approach.

31C2 depression

Impaction of the articular surface of the head, usually superior or superolateral, from the head striking the acetabular rim (typically with anterior dislocation). Easily missed on X-ray; CT shows it. Large defects may need elevation and grafting.

Treatment

Emergency

Closed reduction under deep sedation or general anaesthesia with relaxation, ideally within 6 hours, once a neck fracture has been excluded. If the hip does not reduce or a neck fracture is present: open reduction.

Pipkin I

Non-operative if the hip is concentric and the fragment sits in place with less than about 1–2 mm step: protected weight bearing. Small displaced or incarcerated fragments are excised; larger ones fixed.

Pipkin II

Anatomical reduction and fixation with countersunk or headless screws, usually through an anterior (Smith-Petersen) approach or a surgical hip dislocation (Ganz trochanteric flip), which protects the medial femoral circumflex artery.

Pipkin III

Young patient: urgent fixation of the neck first, then the head. Older patient or comminution: arthroplasty.

Pipkin IV

Fix the acetabulum by its own indications (posterior wall through a Kocher–Langenbeck approach, or surgical dislocation to address both); the head fragment is fixed or excised at the same sitting.

Aftercare

Toe-touch weight bearing for 6–10 weeks, avoid deep flexion with adduction and internal rotation early on. MRI at about 3 months if the hip hurts (avascular necrosis). Indometacin or radiotherapy is debated for heterotopic ossification prophylaxis.

Complications

• Avascular necrosis of the femoral head (highest with type III)
• Post-traumatic arthritis
• Heterotopic ossification (especially after posterior approaches)
• Sciatic nerve palsy
• Malunion of the head fragment