Residency · Residency · Orthopedic Surgery
Distal Femur Fractures: Plating and Nailing Strategies
Overview
Distal femur fractures account for approximately 4 to 7% of all femoral fractures and follow a bimodal distribution: high-energy injuries in young patients and low-energy falls in elderly osteoporotic patients. These fractures are technically demanding due to the wide metaphysis, thin cortex, and proximity to the knee joint. Periprosthetic distal femur fractures above a total knee arthroplasty represent an increasingly common clinical problem.
Anatomy
The distal femoral metaphysis flares into the medial and lateral condyles, with the intercondylar notch housing the cruciate ligaments. The gastrocnemius originates from the posterior distal femur, and its pull flexes the distal fragment, producing apex posterior angulation. The supracondylar region transitions from diaphyseal cortical bone to wide metaphyseal cancellous bone, creating a mechanically vulnerable zone. The popliteal artery lies posterior to the distal femur and is at risk with posterior displacement or during posterior surgical dissection.
Classification
AO/OTA Classification
Type 33A fractures are extra-articular (A1 simple, A2 metaphyseal wedge, A3 metaphyseal comminution). Type 33B fractures are partial articular or unicondylar (B1 lateral condyle sagittal, B2 medial condyle sagittal, B3 coronal plane or Hoffa fracture). Type 33C fractures are complete articular (C1 articular simple with metaphyseal simple, C2 articular simple with metaphyseal comminuted, C3 articular comminuted).
Hoffa Fracture
A Hoffa fracture is a coronal plane fracture of the femoral condyle (33B3), more common on the lateral condyle. It is easily missed on the AP radiograph and best seen on the lateral view or CT. Treatment consists of anterior-to-posterior headless compression screws using lag technique, countersunk to avoid articular damage.
Imaging
Standard imaging includes AP and lateral radiographs of the knee, with traction views to help delineate the fracture pattern. A CT scan is essential for surgical planning of intra-articular fractures, delineating articular comminution, Hoffa fragments, and coronal plane fractures.
<image>AO/OTA classification of distal femur fractures showing extra-articular (33A), partial articular (33B), and complete articular (33C) patterns</image>
Treatment Options
Nonoperative
Nonoperative treatment is rarely indicated, reserved for nondisplaced or impacted fractures in non-ambulatory patients. Skeletal traction or cast bracing is a historical approach associated with unacceptable malunion and stiffness rates.
Retrograde Intramedullary Nailing
Retrograde nailing is indicated for extra-articular fractures (33A) and simple articular fractures (33C1) after articular reduction with lag screws. The entry point is the center of the intercondylar notch at the anterior edge of Blumensaat line on the lateral view. Advantages include load-sharing mechanics, less soft tissue dissection, minimally invasive insertion, and early weight-bearing. Disadvantages include limited ability to address articular comminution, knee joint violation, and potential inability to control wide metaphyseal fragments. Blocking screws are essential for controlling alignment in the wide metaphyseal segment, and long nails are preferred when canal diameter allows.
Lateral Locked Plating
Lateral locked plating is the most commonly used fixation method for distal femur fractures. Anatomically contoured locking plates such as the LISS and LCP distal femur plate are applied to the lateral aspect of the distal femur. They can be inserted through an open approach (lateral parapatellar or swashbuckler) or via MIPO (minimally invasive plate osteosynthesis), with submuscular plate insertion through distal and proximal incisions and indirect reduction.
MIPO Technique
The MIPO technique preserves fracture biology by avoiding direct exposure of the fracture site. Bridge plating is used without attempting anatomic reduction of metaphyseal comminution, relying instead on indirect reduction with traction and percutaneous reduction tools. The plate slides submuscularly along the lateral femur, with proximal and distal locking screws placed percutaneously. This technique is excellent for extra-articular and simple articular patterns.
Key Technical Points
The articular surface is reduced first, with lag screws from anterior to posterior for sagittal condylar splits. The mechanical axis must be restored to avoid varus or valgus malalignment. The plate is centered on the lateral condyle distally, and multiple distal locking screws (four to five) are placed for purchase in cancellous bone. Excessively long plates in the diaphysis should be avoided to prevent stress concentration. Medial plate augmentation should be considered for medial comminution, short distal segments, or osteoporotic bone.
Dual Plating
Dual plating is indicated for medial comminution with loss of the medial buttress, osteoporotic bone, and periprosthetic fractures where lateral plating alone is insufficient. A medial antiglide or locking plate is applied through a separate medial approach, providing increased stability and preventing varus collapse. The risk is additional soft tissue dissection and the need for careful handling of medial structures.
<image>Lateral locked plate fixation of a distal femur fracture using MIPO technique with minimally invasive submuscular insertion</image>
Periprosthetic Distal Femur Fractures (Above TKA)
Epidemiology
The incidence is increasing with the growing arthroplasty population. Risk factors include osteoporosis, anterior femoral notching during TKA, rheumatoid arthritis, revision TKA, and neurologic disorders.
Classification -- Rorabeck and Taylor
| Type | Displacement | Prosthesis Status | Treatment |
|---|---|---|---|
| I | Nondisplaced | Well-fixed | Hinged knee brace; protected weight-bearing |
| II | Displaced | Well-fixed | ORIF (lateral locked plate or retrograde nail) |
| III | Displaced or nondisplaced | Loose or failing | Revision TKA (distal femoral replacement or long-stemmed component) |
Type I fractures are nondisplaced with a well-fixed prosthesis. Type II fractures are displaced with a well-fixed prosthesis. Type III fractures are displaced or nondisplaced with a loose or failing prosthesis.
Su Classification
Type I fractures are proximal to the femoral component. Type II fractures originate at the proximal end of the femoral component. Type III fractures extend below the femoral component, involving the cement mantle or pegs.
Treatment
Type I fractures (nondisplaced, stable prosthesis) are managed with a hinged knee brace and protected weight-bearing with close radiographic follow-up. Type II fractures (displaced, stable prosthesis) are treated with ORIF using a lateral locked plate, which may need to overlap the prosthesis with unicortical locking screws or cables in the prosthetic zone. A retrograde nail is an option only if the prosthesis is an open-box design that allows nail passage, since most modern cruciate-retaining TKAs have a closed box. Medial augmentation should be considered in osteoporotic bone. Type III fractures (loose prosthesis) require revision TKA with a distal femoral replacement (tumor-type prosthesis) or a long-stemmed revision component. In elderly or low-demand patients with severe comminution, distal femoral replacement may be the best option even with a stable prosthesis.
Technical Tips for Periprosthetic Fracture Fixation
Locking plates provide angular stability critical in osteoporotic bone adjacent to a prosthesis. Cables or cerclage wires supplement the plate for additional fracture stability. The plate should extend sufficiently proximally to avoid stress risers, with screws staggered at the proximal end. Polyaxial locking screws improve options for screw trajectory around prosthetic components.
Nonunion and Malunion
Nonunion
The nonunion rate is 5 to 10%, higher than for femoral shaft fractures. Risk factors include open fracture, comminution, bone loss, and lateral-only fixation without medial support. Treatment involves revision fixation with medial augmentation and autologous bone grafting.
Malunion
Varus malalignment is the most common malunion pattern, resulting from insufficient medial buttress support. Rotational malunion is assessed clinically and with CT. Symptomatic malunion is treated with corrective osteotomy.
Rehabilitation
Early knee range of motion is essential to prevent stiffness, especially in intra-articular fractures. A CPM machine or therapist-assisted motion is used. Weight-bearing is typically toe-touch for 6 to 8 weeks with plate fixation and may be earlier with nailing if the pattern allows. Quadriceps strengthening and patellar mobility exercises are important, and full recovery takes 4 to 6 months.
<image>Periprosthetic distal femur fracture above TKA treated with lateral locked plate and cerclage cables</image>
Clinical Pearls
Always obtain a CT scan for intra-articular distal femur fractures because coronal plane (Hoffa) fragments are commonly missed on plain radiographs and will affect the surgical plan. The gastrocnemius flexes the distal fragment, so a bump under the distal thigh during surgery counteracts this deformity. Varus malunion is the most common complication after lateral-only plating; if medial comminution is present, dual plating or a medial strut should be seriously considered. In periprosthetic fractures, always assess prosthesis fixation to determine whether to fix the fracture around the implant or revise it. Blocking screws are as valuable for retrograde nailing of distal femur fractures as they are in the tibia and should be placed to redirect the nail and control the wide metaphysis. Short distal fragments with less than 5 cm of bone distal to the fracture are challenging for plate fixation; additional buttress fixation, cement augmentation, or distal femoral replacement in elderly patients should be considered.
References
- Zlowodzki M, et al. Operative treatment of acute distal femur fractures: systematic review of 2 comparative studies and 45 case series (1989-2005). J Orthop Trauma. 2006;20(5):366-371.
- Ricci WM, et al. Locked plates versus retrograde nailing for distal femur fractures: a multicenter randomized trial. J Orthop Trauma. 2014;28(9):515-522.
- Rorabeck CH, Taylor JW. Classification of periprosthetic fractures complicating total knee arthroplasty. Orthop Clin North Am. 1999;30(2):209-214.
- Henderson CE, et al. Locking plates for distal femur fractures: is there a problem with fracture healing? J Orthop Trauma. 2011;25(Suppl 1):S8-S14.
- Kregor PJ, et al. Distal femur fracture fixation utilizing the Less Invasive Stabilization System (LISS). Injury. 2001;32(Suppl 3):SC32-SC47.
