Distal Femur Fractures

Distal femur fractures are difficult because of comminution, osteoporosis and intra-articular extension. The examiner will test the decision between nailing the extra-articular fracture, plating the articular one and replacing the joint in the elderly, and whether you can spot and manage the Hoffa fragment.

Who. The distribution is bimodal: young males after high-energy trauma, and elderly females after a low-energy fall, in whom osteoporosis is the major factor. Periprosthetic fractures are increasing with the volume of total knee arthroplasty.

Mechanism. The high-energy injury is an axial load with varus or valgus. The low-energy fall produces a spiral pattern. The dashboard injury is an axial load through a flexed knee.

The elderly patient. One-year mortality is 18-22%, hip-fracture territory. The "30-50%" that is often quoted is Hoellwarth's composite of death or reoperation or loss of mobility, not mortality. Fixation failure is common in osteoporotic bone, which is why the construct chosen for this patient has to carry weight from the start.

The periprosthetic fracture. A classic, examinable and modifiable risk factor for the supracondylar fracture around a knee replacement is anterior femoral cortical notching: inadvertent violation of the anterior femoral cortex when the femoral component is placed, by an oversized, flexed or anteriorly translated component, or by femoral undersizing. The notch is a stress riser at the metaphyseal-diaphyseal junction, and a notch deeper than about 3 mm is commonly cited as significantly raising the fracture risk. When you see a supracondylar periprosthetic fracture, examine the anterior cortex on the lateral film for a notch, and remember the surgical lesson of not creating one when implanting the knee in the first place.

• Other recognised risk factors: osteoporosis, rheumatoid arthritis, chronic corticosteroid use, revision surgery, female sex, and neurological disorders that increase falls

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Shape. The distal femur flares from a cylinder into the condyles and is trapezoidal in section, wider posteriorly. The lateral wall is inclined 10 degrees, sloping medially rather than standing vertical, and the anterior wall, the trochlea, is inclined 25 degrees; a plate has to match the lateral inclination or risk malalignment. The medial condyle extends further distally, which is reflected in the distal joint angle. On the lateral film, Blumensaat's line marks the slope of the intercondylar notch.

Alignment. The mechanical (weight-bearing) axis passes through the centre of the knee and the anatomic axis of the shaft lies 6 degrees in valgus to it. Restoring that axis is critical to the longevity of the joint, because malalignment overloads one compartment. The normal values are the targets of reduction:

Muscles and the deforming forces. Gastrocnemius arises from the posterior condyles and tilts the distal fragment posteriorly into extension: apex-posterior angulation, the apex pointing into the popliteal fossa. It is a knee flexor producing an extension deformity, because it acts on the fragment and not across the joint, and that contradiction is why the deformity is so often described backwards. Adductor magnus, through the adductor tubercle, pulls the shaft into varus; quadriceps, through the patella, and the hamstrings, at the proximal tibia, shorten the limb. Flex the knee to relax the gastrocnemius when reducing, because traction alone will not correct the recurvatum.

Vessels. The popliteal artery lies directly behind the femur, tethered proximally at the adductor hiatus and distally at the soleal arch and trifurcation, so a displaced fracture, above all one in hyperextension (recurvatum), stretches it like a bowstring. The superior genicular arteries wrap around the metaphysis and are the source of the fracture haematoma; the inferior geniculars run at joint level and bleed during an arthrotomy.

Implant mechanics. A nail is load-sharing and sits close to the centre of rotation. A plate is load-bearing, offset from the axis, and works as a cantilever beam, so in bridge plating the working length is what sets the stiffness of the construct; far cortical locking reduces that stiffness to promote callus.

The AO/OTA scheme (33) is the shared language, and the letter points to the implant: extra-articular fractures are nailed or plated, partial articular fractures are fixed with screws and a buttress, and complete articular fractures are plated.

The Hoffa fracture. Type B3 is the coronal-plane shear of a condyle, an intra-articular fragment that occurs with the knee in flexion and is often hidden on the plain film. It is usually one condyle, and the lateral far more often than the medial: 85% of single-condyle coronal fractures in Nork's series were lateral. Fix it with countersunk screws perpendicular to the fracture line, and fix it before the condyles are locked to the shaft.

Letenneur classification. Letenneur grades the coronal fracture by the plane and level of the fracture line on the lateral film or CT, and the grade carries prognostic weight:

• Type I: a fracture line vertical and parallel to the posterior femoral cortex, detaching the whole posterior condyle. The commonest and the most amenable to fixation, because the large fragment takes screws well
• Type II: a fragment of variable size detached at the base of the condyle in a more horizontal plane (IIa large through IIc small). The small-fragment variants are harder to fix and more prone to displacement
• Type III: an oblique fracture line, with the worst prognosis and the highest risk of avascular necrosis and fixation failure, because the fragment is small and its blood supply is compromised

Type I takes lag screws readily. Small Type II and III fragments may need a posterior buttress plate or headless compression screws. Posterior-to-anterior screws are biomechanically stronger than the technically easier anterior-to-posterior screws.

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Periprosthetic fractures (Rorabeck and Lewis). Two questions decide the treatment: is the femoral component still fixed, and is there bone to fix.

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History. What changes the plan is pre-injury function, independent or housebound, because it guides the arthroplasty decision; any previous knee replacement, with the implant type and the time since surgery; and the comorbidities that need optimising before theatre.

Examination. The limb is usually shortened and externally rotated. Check the skin posterolaterally for open spikes and anteriorly for contusion. Check the pulses and the ABI with a high index of suspicion, and examine the peroneal and tibial nerves.

Differential diagnosis. The painful, swollen distal thigh and knee has a short list, and each entry has a discriminating finding and a confirming test:

Radiographs. AP and lateral of the femur and knee, with a full-length femur film to rule out an ipsilateral hip or shaft fracture. A traction view, with traction applied manually in the emergency department, often reveals the pattern better than the initial comminuted mess and helps decide whether the articular block is reconstructable.

CT. The current standard of care for all distal femur fractures. 38% of supracondylar-intercondylar (33-C) fractures carry a coronal (Hoffa) component, and the argument for scanning is not that the plane is subtle: in Nork's series ten were found only after the skin was open, and not one of those patients had been scanned first. Scanning lifted detection from 29% to 47%. The scan also plans the trajectory of the articular reduction screws.

CTA. When the pulses are asymmetric or the ABI is below 0.9. The threshold is low because of the popliteal tethering.

The decision. Pattern and patient. An extra-articular fracture is nailed; an intra-articular one is plated after anatomic reconstruction of the joint; a Hoffa component is fixed separately; the comminuted osteoporotic fracture in an elderly patient may be better replaced than fixed; and a periprosthetic fracture over a loose component is a revision arthroplasty, because fixation over a loose implant fails. Whatever the implant, the goals run in order: restore length, restore alignment (rotation and axis), then fix it stably enough for early motion.

Algorithm

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Retrograde NailLocking PlateDistal Femoral ReplacementDual PlatingNail-Plate Combination

Who. Extra-articular (33-A) fractures, and simple intra-articular ones (C1 and C2) where the articular screws do not block the nail. The nail also earns its place in the polytrauma patient with a same-side femur and tibia, in ipsilateral hip pathology, and in bilateral fractures.

For. It is a load-sharing construct that permits immediate weight bearing, through a minimally invasive approach that strips little soft tissue, with high union rates in the A types.

Against. The entry point damages the articular surface and carries a risk of knee sepsis and anterior knee pain; distal fixation options are limited; a coronal fracture can be propagated by the nail; a complex articular fracture is not suitable; and a total knee replacement blocks the entry unless the box is open.

Who. Intra-articular (C-type) fractures, periprosthetic fractures and osteoporotic bone. The lateral locking plate (LCP or LISS) is the workhorse of the articular fracture.

The sequence. Articular first, then metaphyseal. Reduce the condyles anatomically and hold them with ex-fix clamps, fix the split with lag screws, and reconstruct the articular block; then attach that block to the shaft, restoring length and rotation, with the plate in bridging mode across the metaphysis (relative stability). The joint is exposed through a lateral parapatellar approach and the shaft is plated submuscularly (MIPO).

Working length. Leave the holes at the fracture level empty so the working length is long enough to permit micromotion and callus. Too stiff means non-union; too flexible means failure.

Who. The indications:

• Elderly (over 75) independent ambulators
• Severe comminution or bone loss
• Osteopenia prohibiting stable fixation
• Pre-existing severe osteoarthritis
• Failed fixation

What it buys. Immediate full weight bearing and one operation. In Hoellwarth's periprosthetic series the re-operation rate was numerically lower after replacement than after plating (3% versus 9%), but the difference was not statistically significant. The price is a higher initial cost and a higher infection risk.

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Why a second plate. Lateral plating alone may fail in varus when there is medial column comminution or bone loss. A medial plate, placed through a medial subvastus approach, is a strut that prevents the varus collapse.

Medial comminution

Approach

Medial subvastus

Benefit

Prevents varus collapse

Low intercondylar fracture

Approach

Dual incisions

Benefit

Captures low fragments

Non-union variants

Approach

Judet decortication

Benefit

Rigid stability

Indication	Approach	Benefit
Medial comminution	Medial subvastus	Prevents varus collapse
Low intercondylar fracture	Dual incisions	Captures low fragments
Non-union variants	Judet decortication	Rigid stability

Sanders' original nine cases name the failure mechanism precisely: with the medial buttress gone, the distal fragment rotates into varus about the junction of the distal screws and the plate. That is the axis a medial strut abolishes. Note also what that series cost - every patient was stiff (three below 90 degrees of flexion, six between 90 and 100), so a second medial approach is not free.

Neither implant alone solves the osteoporotic or comminuted metaphyseal fracture. A lateral locking plate is stiff in bending but has a long lever arm over an empty metaphysis; a retrograde nail sits on the mechanical axis and shares load but controls the short distal segment poorly and does nothing for varus.

Used together, the nail supplies an intramedullary strut on the axis while the plate holds the condyles and resists varus - the plate's screws are passed around or in front of the nail. It is the construct increasingly reached for when the alternative is a distal femoral replacement in a patient who still has a joint worth keeping.

Know its evidence status

This is a biomechanically motivated construct supported by cohort series, not by randomised data - and it is absent from both the Cochrane review and the nail-versus-plate meta-analyses cited on this page, because those compared the two implants against each other. Offer it as a reasoned option, not as a proven standard, and say why: the two failure modes are different, so combining the implants addresses both.

Weight bearing follows the construct. After a nail, weight bearing as tolerated is usually allowed; after a distal femoral replacement, weight bearing as tolerated is allowed; after a plate, touch-down or partial weight bearing (15 kg) for 6-12 weeks until callus. That restriction is why plating is less ideal for the frail elderly patient.

Prognosis. The favourable fracture is extra-articular, in good bone, anatomically reduced, moved early and in a non-smoker. The unfavourable one has complex articular involvement (C3), severe osteoporosis, a varus malreduction, delayed surgery or infection, or an open wound.

Function. Most patients achieve functional independence and return to baseline mobility. Knee stiffness is the most common functional problem, particularly after prolonged immobilisation, and arthrofibrosis may require manipulation or arthroscopic lysis of adhesions. Post-traumatic arthritis is common in the long term after intra-articular injury, and some patients come to arthroplasty.

Registry & systematic-review signals (arthroplasty for fracture):

• Distal femoral replacement (DFR) for acute fracture carries a higher revision rate than DFR for oncological reconstruction, with infection and aseptic loosening the leading failure modes.
• For periprosthetic fractures around a total knee replacement, fixation reliably fails if the femoral component is loose - revision arthroplasty is then mandatory regardless of bone stock.
• Pooled data (Senthilkumaran 2019) support acute knee arthroplasty in selected osteoporotic comminuted fractures, with 1-year mortality 18.4% and revision 3.4%.