Femoral head fractures are very rare injuries, almost always caused by hip dislocations.
The femoral head is fed by three arteries, the main one of which is the medial femoral circumflex. If this is disrupted, there is a high risk of avascular necrosis.
The standard classification of femoral head fractures is that of Pipkin
The key criterion in the Pipkin classification is whether the femoral head is fractured above or below the fovea.
- Type 1 - femoral head fracture below the fovea
- Type 2 - femoral head fracture above the fovea
- Type 3 - femoral head fracture (regardless of location) associated with a femoral neck fracture
- Type 4 - femoral head fracture associated with an acetabular fracture.
(Author's note: as argued elsewhere a better classification system would correlate with treatment requirements. A BMSD modification of Pipkin would be: Type 1 - head fracture with concentric reduction and no fragments; Type 2 - head fracture with either fragments or lack of reduction; Type 3 - head fracture with femoral neck or acetabular fractures, the presence of which demands priority treatment.)
Most patients with a femoral head fracture have had a dislocation after high energy trauma. A typical case would be a car accident in which the patient was an unrestrained passenger. In such an accident, the knee strikes the dashboard, and the force is propagated up the leg. The hip, when flexed approximately 90 degrees and slightly adducted, is at particular risk for dislocation. The head fracture occurs from impact or shearing by the acetabulum.
Because femoral head fractures result from a high energy mechanism of injury, apply The First Rule of Veterinary Medicine: a full trauma evaluation has to be carried out.
The key to diagnosis is to document the fracture on standard x-rays. If there is any concern of an acetabular fracture, a CT scan is necessary. Also, a good lower extremity examination to rule out knee injuries especially is needed. When doing a diagnostic work-up, time is of the essence, as the risk of avascular necrosis is proportional to the amount of time that the head is out and the blood supply compromised.
The first phase of treatment is to reduce the femoral head, if dislocated. A closed reduction should be attempted, in the interest of time. The one exception to this is if there is a femoral neck fracture, at which point open reduction is almost certainly necessary.
Head fractures classified as Pipkin 1 and Pipkin 2 with concentric reduction and no loose fragments in the joint can be treated non-operatively. These criteria can be determined with CT scans.
Operative indications include loose intraarticular fragments, irreducible dislocation or residual subluxation of the femoral head, comminuted Pipkin 2s involving the superior weight bearing portion of the femoral head, Pipkin 3 and Pipkin 4 in which the acetabular fracture requires operative fixation. Surgical approaches include the modified Smith-Peterson approach for more anterior fractures or a posterolateral approach with trochanteric osteotomy and surgical dislocation of the hip.
Owing to the paucity of series reported in the literature, treatment recommendations appear to be based on common sense and experience rather than evidence. These include:
- excision of small fragments and open reduction and internal fixation of large ones;
- performance of a primary hemi-arthroplasty if there is a neck fracture in an "older" patient; and
- ORIF of the acetabular fracture if present.
What is not defined is how small is "small" and how old is "older".
With femoral head fracture and dislocation there can be injury to the blood vessels supplying the head, namely the medial femoral circumflex, leading to AVN or nonunion of the femoral head fragment. This same vascular supply is also at risk if a posterior surgical dislocation is chosen as part of treatment. It is also possible to damage the articular cartilage, leading to a post traumatic DJD. Also, stretch injuries to the nerves can lead to palsies, and stretch injuries to the blood vessels can lead to thrombosis. Post injury heterotopic ossification is not uncommon after surgery.
Red Flags and Controversies
Does resection of fragments lead to instability?