Hoffa Fractures

A Hoffa fracture is a coronal-plane fracture of the posterior aspect of a femoral condyle, first described by Albert Hoffa in 1904. It is relatively rare and it is frequently missed.

Mechanism. A direct blow to the flexed knee, the dashboard injury, or an axial load with the knee in flexion, and usually high-energy trauma. With the knee flexed the load produces combined shear and compression that splits the posterior condyle off in the coronal plane. That coronal orientation is why the fracture is so easily missed on AP and lateral radiographs: the line is often invisible on the AP view and tangential on the lateral.

Who. Coronal-plane condylar fractures are rarer than sagittal-plane condylar fractures. There is a male predominance, the patient is typically a young adult, and the mechanism is usually high-energy: motor vehicle and motorcycle collisions, and falls.

Why lateral. The lateral condyle is involved about twice as often as the medial, a 2:1 ratio. It is the more prominent condyle, and the typical blow lands on the lateral side of a flexed knee. An external rotation moment is a common loading pattern, and tension from the iliotibial band may contribute to the lateral forces.

Associated injuries. The fracture may be isolated or one part of a larger injury:

• Supracondylar or intercondylar femoral fracture, in 30-40%
• ACL or PCL injury
• Tibial plateau fracture
• Patellar fracture
• LCL and posterolateral corner (may be injured)
• Neurovascular injury (rare)

The condyles. The distal femur has two condyles articulating with the tibia, and they are not symmetrical:

The blood supply. A complete Hoffa fragment is essentially avascular. It has no anterior soft-tissue attachments and no ligamentous attachments; what remains is the posterior periosteum and capsule, and the gastrocnemius origin, which may provide some blood supply, especially on the lateral side. The vessels at stake are the lateral superior and inferior geniculate arteries and their medial counterparts, which reach the posterior condyle through the capsule. The fracture line, the surgical dissection and posterior countersinking all threaten that same narrow pedicle.

Why it matters. In many fractures the periosteal supply helps the bone heal; a Hoffa fragment relies entirely on healing from the intact condyle once it is fixed. That is the argument for anatomic reduction and stable fixation, and for technique that spares the pedicle: preserve every millimetre of posterior capsular attachment you can, and clear the cartilage rather than stripping bone when seating screws.

Biomechanics. The posterior condyle is the weight-bearing surface in flexion, and the fragment may rotate or displace with knee motion. Malreduction alters knee mechanics, and any articular step-off accelerates arthritis.

Posterior structures at risk during surgery. Each has an approach that endangers it:

• Popliteal vessels: central, protected by fascia
• Common peroneal nerve: the lateral approach
• Saphenous nerve: the medial approach
• Gastrocnemius muscle: retracted, not cut

Letenneur. The most widely used system, defined by the orientation of the fracture line relative to the posterior femoral cortex:

What drives difficulty is fragment size and comminution rather than the type number: the smaller the posterior fragment, the less subchondral bone there is for screw purchase, and the more a buttress or antiglide plate earns its place.

By condyle. The condyle involved sets the approach:

History. The answers that matter:

• Mechanism: dashboard, direct blow, fall
• High-energy or low-energy
• Associated injuries
• Pre-injury function and activity level

Examination. The findings and what each one means are tabulated below. Assess ligamentous stability, accepting that pain may limit the examination. Three things the table does not say: check the skin for open wounds, abrasions and fracture blisters; check the compartments after a high-energy mechanism; and the neurovascular examination is pulses, motor function and sensation.

Radiographs. AP, lateral and oblique views of the knee. The fracture may be subtle or invisible. What there is to see: a coronal fracture line through the posterior condyle; on the lateral view, the fragment overlapping the intact condyle, the double density sign of superimposed condyle and fragment; and any associated supracondylar fracture. Measure fragment size and displacement where the films allow it.

CT. Thin-slice CT with sagittal and coronal reconstructions is mandatory for every suspected Hoffa fracture; plain radiographs alone are insufficient. It shows the orientation of the fracture line, the fragment size as a percentage of the condyle, displacement and comminution, and it is where the screw trajectory is planned.

MRI. Not routine. It may help where a ligament injury is suspected and it can assess cartilage damage; in practice it is usually obtained after the fracture has healed if symptoms persist.

Differential. The acutely painful, swollen knee after distal femoral trauma:

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Algorithm

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The decision. Nearly every displaced Hoffa fracture is fixed, and most surgeons fix the undisplaced ones as well. The anatomy explains why: the posterior condyle bears load during knee flexion and the fragment has few soft-tissue attachments to hold it in position, so even an undisplaced fracture may displace with knee motion, and non-operative management carries a high risk of secondary displacement.

Nonunion. The major concern, because the fragment is avascular. The risk factors are inadequate fixation, smoking and displacement; prevention is stable fixation with good compression, anatomic reduction and smoking cessation. An established nonunion needs revision fixation with bone graft, and plate fixation if the screws have failed.

Malunion. It alters knee mechanics, and even a small step-off wears cartilage. Prevention is the treatment: confirm the reduction intraoperatively, because correction afterwards requires an osteotomy, which is difficult.

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Post-traumatic arthritis. The table's 20-30% occurs despite good treatment; it is related to the cartilage damage sustained at injury, and malreduction increases the risk. The one-page summary's 54% is a different measurement: Onay's series, 7 of 13 patients at a mean follow-up of 93 months. Read the two figures together. Arthrosis after an intra-articular fracture takes years to appear, so the longer a series looks, the more it finds. Severe cases may require arthroplasty.

The principles. Early motion prevents stiffness. Delayed weight bearing protects the fixation, because the posterior condyle bears load in knee flexion and premature loading may lose the reduction or lead to nonunion; full weight bearing waits for radiographic evidence of healing. Monitor for loss of reduction, individualise the programme to the stability of the fixation, and follow up long term for arthritis.

What decides the result. Anatomic reduction and stable fixation. Any articular step-off leads to accelerated arthritis, and stable fixation allows the early motion that prevents stiffness while protecting healing.

Long-term concerns. The problems that surface late:

• Post-traumatic arthritis, which may develop years later
• Stiffness, usually manageable with physiotherapy
• Hardware prominence, which may need removal
• Functional limitations in high-demand activities

Global epidemiology:

Guideline and consensus position (there is no dedicated single-society Hoffa guideline):

The recommendations converge: there is broad international agreement on CT diagnosis, anatomic reduction, lag-screw fixation and fixing the Hoffa fragment first in combined injuries.

Registry evidence:

• There is no joint or fracture registry that tracks Hoffa fractures specifically; major registries (NJR, AJRR, AOANJRR, SHAR, Norwegian, NZJR) capture arthroplasty, not coronal condylar fixation. Evidence therefore rests on systematic reviews and single-centre series.

Practice variation: