Submuscular Minimally Invasive Locking Plate Fixation of Distal Femoral Fractures

Overview

Distal femoral fractures make up about 6% of all femoral fractures. They typically result from high-energy trauma in young patients and from low-energy falls in osteoporotic elderly patients; a third of young patients have multiple injuries, and almost half of high-energy intraarticular fractures are open (AO). Periprosthetic fractures are increasing with the number of knee arthroplasties (AO).

The goals of surgery are anatomic reduction of the articular surface, restoration of limb alignment and length, stable internal fixation, rapid mobilization and early knee rehabilitation (Rockwood). Traditional wide open reduction of the comminuted metaphysis has fallen out of favor because of high nonunion and failure rates; biological plating with less traumatic soft tissue handling is now the gold standard (AO).

Current locking condylar plates combine the stability of a fixed-angle device with the option of submuscular insertion. Campbell uses them for most AO/OTA type A and C fractures that need plate osteosynthesis; outriggers allow proximal screws to be targeted percutaneously with minimal further damage to the comminuted metaphysis.

Relevant Anatomy (AO)

• Viewed end-on, the distal femur is trapezoidal: the posterior part is wider than the anterior, the medial surface is inclined about 25° and the lateral surface about 10°. The plate must sit on this lateral surface. The patellofemoral inclination slopes about 10° posteriorly.

• Normal anatomic lateral distal femoral angle (aLDFA) is 80–84°; the contralateral side is a reference for coronal alignment.

• Variation in femoral bow (e.g., in Asian patients) can cause mismatch of precontoured plates; proximal mismatch of an 11-hole DF-LCP often produces valgus.

• Deforming forces: Quadriceps, hamstrings and adductors shorten the limb and pull it into varus; the gastrocnemius flexes the distal fragment. The typical deformity is anterior displacement of the proximal fragment (which may pierce the quadriceps or skin) with the distal fragment flexed, in varus and rotated posteriorly.

• Vascular injury occurs in about 3% and nerve injury in about 1%; the superficial femoral artery is at risk in the adductor canal. Associated patella fractures occur in about 15% and meniscal or cartilage injuries in 8–12%.

Classification (AO/OTA 33)

Evaluation

• Careful neurovascular examination; Doppler or angiography may be needed to confirm the superficial femoral artery is intact (AO).

• Ligament examination is painful and unreliable before fixation; examine after fixation (AO).

• Traction radiographs help if there is major shortening (AO).

• CT (2D/3D) is recommended for intraarticular fractures, particularly to detect coronal posterior condylar (Hoffa) fractures that are often missed on plain films and can change the surgical plan (AO; Rockwood).

Indications

• Operative treatment should be considered for nearly all displaced distal femoral fractures in physiologically stable adults (Rockwood). Indications include all displaced fractures, articular displacement, and malalignment (AO).

• Nonoperative treatment (knee immobilizer) is reserved for impacted, undisplaced extraarticular (type A) fractures or nonambulatory patients unfit for surgery (AO).

Implant Choice

• Extraarticular fractures: Retrograde nail or plate; in osteoporotic bone or with limited distal bone stock (periprosthetic), locking plates give more secure fixation (AO).

• Intraarticular fractures: Anatomic open reduction of the articular block under direct vision, lag screw compression (position screws if there is bone loss), then fixation of the block to the shaft with a plate or nail depending on the pattern (AO).

• 95° fixed-angle devices (condylar blade plate, dynamic condylar screw) maintain alignment and resist secondary varus, but they are technically demanding (AO). Locking periarticular plates have replaced them for most fractures; Rockwood's authors now use the blade plate mainly for nonunions, malunions and corrective osteotomies.

• Rockwood authors' preference: Retrograde nailing when possible, because the mechanics are better than plating and reaming may add a biological stimulus; plating is now used relatively less, and implant combinations are used for the most complex fractures.

Timing and Damage Control

• Isolated closed fractures: Internal fixation within the first 24–48 hours; if surgery must be delayed more than 24–36 hours, use a temporary external fixator or tibial pin traction (Rockwood).

• Damage control (polytrauma, open fractures with severe soft tissue injury, vascular injury, or an inexperienced team): a knee-spanning external fixator (AO). Place two Schanz screws anteromedially in the tibia and two anteriorly in the femur, well away from the later surgical field and the lateral femur; restore length before pins are driven through the quadriceps (AO). The articular block can be reconstructed first with minimal lag screw fixation (AO).

• Open fractures: Most wounds are anterior with quadriceps injury. Early antibiotics and meticulous debridement (AO). Rockwood supports early internal fixation after debridement for type I, II and IIIA wounds that can be made clean, and external fixation with delayed fixation for IIIB/IIIC or heavily contaminated wounds.

Factors Contributing to Nonunion and Failure (Campbell)

• Locking plates remove the need for routine bone grafting in some open fractures despite metaphyseal bone loss (Campbell).

• Posterior cortical contact is strongly associated with primary union (Campbell).

• Callus through comminuted metaphyseal zones is inconsistent; dynamic locking or far cortical locking has been advocated to increase micromotion at the lateral cortex (Campbell). Far cortical locking screws, which fix only in the far cortex, reduce construct stiffness and produce more balanced callus (Rockwood).

Preoperative Planning (Rockwood)

• A written preoperative plan for every case (few are "simple"): implant, direct vs indirect reduction, and whether a percutaneous technique is feasible; order long plates in advance if inventory is limited.

• Radiolucent flat table; C-arm from the opposite side; confirm unobstructed AP and lateral images before draping.

• General anesthesia with full muscle paralysis is preferred to overcome the strong deforming forces.

• Equipment: universal distractor (or external fixator), fixed-angle plates, radiolucent targeting guides for MIPO, large clamps; a sterile tourniquet helps the articular part.

• Image the uninjured limb as a template; consider draping it into the field as a clinical and radiographic control.

Surgical Technique

Positioning

1. Supine on a radiolucent table, with a well-padded bump under the ipsilateral hip so the limb lies in normal rotation (Campbell; Rockwood).

2. Flex the knee 30–45° over a bump or triangle to relax the gastrocnemius; full extension produces recurvatum and shortening (AO). Flexing the knee to about 60° helps prevent recurvatum and hyperextension (AO).

3. Contralateral radiographs help judge rotation and act as a reference (Campbell).

4. A proximal tibial traction pin and bow give better control of axial length and rotation (Campbell). Shortening can be corrected with manual traction or a distractor (AO).

5. In osteopenic bone with complex fractures, a little shortening from impaction may be preferable to instability (AO; Rockwood).

Approaches

Open wounds may dictate the approach; plan debridement so that the definitive approach is not compromised (AO).

Articular Reduction

1. Expose the distal femur through the lateral parapatellar (swashbuckler) approach; usually only its distal part is needed for articular reduction. Extraarticular fractures and simple articular components can be approached directly laterally (Campbell).

2. Reduce the condylar fragments with K-wires and reduction forceps (Campbell). Percutaneous Schanz screws in the medial condyle help reduce and clamp simple articular fractures (AO).

3. Fix with 3.5 mm cortical or cannulated lag screws; in comminuted articular fractures use position screws instead of lag screws to avoid narrowing the articular block (AO). Screws must not interfere with the planned plate position or locking screws (AO; Rockwood).

4. Place the condylar plate guide on the lateral cortex to plan the interfragmentary lag screws so that they do not block the plate (Campbell).

5. Hoffa fragments: Fix with two or more 2.7 or 3.5 mm countersunk lag screws or headless compression screws placed anterior to posterior; occasionally a small antiglide plate (Rockwood). They require anatomic reduction (AO).

6. In some complex fractures, first reduce the simpler condyle to the shaft, then reduce the complex condyle to this construct (AO).

Metaphyseal (Indirect) Reduction (Rockwood; AO)

1. Length: A universal distractor (proximal pin anterior in the femoral shaft, distal pin in the proximal tibia or distal femur) restores length and gross alignment; Rockwood's authors use it whenever there is shortening.

2. Sagittal plane: A towel roll or bump under the supracondylar region corrects flexion of the condyles; moving it a few centimeters makes a large difference. An anterior-to-posterior Schanz screw in the articular block acts as a joystick for sagittal control; a second AP Schanz screw in the shaft helps rotation (AO).

3. A posterior cortical "key" fragment above the condyles, well seen on the lateral view, is very useful to judge flexion–extension and can be held with large pointed forceps (Rockwood).

4. Simple spiral or oblique fractures can be reduced with minimally invasive cerclage wires before plating (AO). Provisionally fix with K-wires or connect the Schanz screws to the spanning fixator (AO).

Distal Plate Positioning

1. Using anatomic landmarks and fluoroscopy, slide the plate submuscularly onto the reconstructed condyles, with or without first reducing the proximal fragments (Campbell). Center the plate on the lateral surface and align it with the lateral condyle (Rockwood).

2. Insert a 2.5 mm guidewire through the central hole of the wire guide, parallel to the femorotibial joint line, and confirm on an image (Campbell).

   • This wire is critical: It sets the distal plate position in the coronal plane; if it is not parallel to the joint, varus or valgus malalignment results (Campbell; AO; Rockwood). Anatomic plates are designed to sit at 95–98° to the shaft, building in 5–8° of valgus (Rockwood).

   • Anatomic variants such as a hypoplastic lateral condyle can make plate positioning very difficult; study contralateral knee radiographs during templating (Campbell).

3. On the lateral view, confirm that the distal part of the plate is parallel to the posterior cortex, so that sagittal alignment is correct (Campbell; AO). Pins and screws in the distal femur should stay within Blumensaat's line and the subchondral line of the patellofemoral joint (Rockwood).

4. Insert additional guidewires through the locking guides to secure the plate to the distal fragment (Campbell).

Restoring Length, Rotation and Sagittal Alignment

1. Apply longitudinal traction and use the targeting device to insert a provisional guidewire in the most proximal hole. Length and rotation must be confirmed before this step. In very comminuted fractures, one proximal wire may not hold length on its own (Campbell).

2. Once length and rotation are set, place a small bolster under the metaphysis to adjust flexion and extension (Campbell).

3. Make sure the plate is centered on the shaft proximally on both views, using a mini-open incision if needed (Rockwood). Small coronal corrections can be made with a conventional screw through the plate (AO).

Plate Offset: Internal–External Fixator

1. Many periarticular plates do not fit every femur. If offset is not recognized, pulling the plate to bone with threaded reduction tools or nonlocking screws produces varus or valgus malalignment (Campbell).

   • When offset is present, apply the plate as an internal–external fixator with locking screws to preserve anatomic coronal alignment.

   • Reduction matters more than plate–bone contact (Campbell).

2. When the plate does fit, a nonlocking screw or a "push–pull" device can draw the shaft to the anatomic plate to fine-tune varus–valgus alignment (Rockwood). In complex fractures, reducing the fracture to the plate is often easier than the reverse (Rockwood).

Screw Insertion

1. Lag before lock: Insert all nonlocking screws in a segment before any locking screws in that segment (Rockwood).

2. Locking screws can go in any order; Campbell's preference is the central distal screw first, then the surrounding distal screws. The condylar segment is fixed mainly with locking screws (Rockwood).

3. Posterior distal screw: If the most distal posterior hole lies behind Blumensaat's line, use a short screw (e.g., 28 mm) to avoid entering the notch; a notch view helps (Rockwood). Imaging in about 25° of internal rotation reveals prominent medial screw tips (AO).

4. Fix proximally with 4.5 mm cortical or 5 mm locking screws through the targeting device, with at least eight cortices proximally (Campbell; Rockwood). Bicortical locking screws are recommended; unicortical-only shaft fixation (LISS) has a high failure rate (AO). Three or four bicortical proximal screws are preferred (AO).

5. To reduce the stress riser at the plate end, consider a unicortical locking screw or bicortical nonlocking screw in the most proximal hole (Campbell).

6. Construct (Campbell; Rockwood): Use a long plate with well-spaced screws, with eight or more holes above the most proximal extent of the fracture if possible, and fill no more than about 50% of the holes. Avoid locking screws close to metaphyseal comminution, because an overly rigid construct may impair callus.

7. Simple, well-reduced A1 fractures: Compress the fracture (eccentric drilling, articulated tensioner, or push–pull screw with a Verbrugge clamp) for absolute stability; the plate can only be loaded effectively if the medial cortex is restored (Rockwood).

8. Severe medial comminution: A lateral plate alone may be insufficient; add a short 3.5 mm anteromedial plate (AO), dual plating or a nail–plate construct (Rockwood).

9. Retighten all screws before closure; close fascia and skin in standard fashion (Campbell).

Less Invasive Stabilization System (LISS)

• The LISS is a titanium internal–external fixator, so its modulus of elasticity differs from other plating systems; its application is very similar to the minimally invasive locking condylar plate technique (Campbell).

• It depends on the reduction being achieved before the implant is positioned (Campbell).

• It was designed for locking screws only, inserted percutaneously through a guide. Unicortical and bicortical screws exist, but fixation should not rely on unicortical screws because of high failure rates (AO). Titanium LISS failures occurred by loss of shaft fixation through loosening of unicortical screws (Rockwood).

• Early series: union in 37 of 40 (93%; Schütz) and 58 of 61 (95%; Kregor) patients, with malalignment recognized as a potential problem (Rockwood).

Postoperative Care

• Start early passive motion, with some active motion as tolerated; emphasize passive extension to prevent contracture (Campbell). Assisted active hip, knee and ankle motion can start as early as 48 hours if soft tissues allow; CPM may help (AO; Rockwood).

• Weight bearing:

  • Campbell: no weight bearing for 10–12 weeks, with active and passive motion during this period.

  • Rockwood: in stable type A fixation, partial weight bearing (about 20 lb) at 3–6 weeks; for intraarticular (B/C) injuries, delay weight bearing for about 10–12 weeks. Immediate full weight bearing has been considered for carefully selected elderly patients with type A fractures, without significant difference in outcomes.

  • AO: good bone and simple fractures allow partial (10–15 kg) loading after surgery; bridge-plated comminuted fractures need more protection, with gradual loading once callus appears at 6–12 weeks.

Complications

• Malalignment: Axial and rotational malalignment are typical problems (AO). Malalignment of more than 5–10° is likely to affect knee mechanics and gait (Rockwood). A high rate of rotational malalignment (38.5%) has been reported after MIPO (AO). External rotation is common because the weight of the leg or targeting device rotates the distal segment (Rockwood).

• Plate malposition (AO; Rockwood):

  • Too distal → soft tissue irritation and medialization of the articular block ("golf club deformity").

  • Too posterior on the condyles → screw penetration of the intercondylar notch.

  • Plate rotation → screw malposition (external rotation causes trochlear penetration or poor purchase).

• Nonunion: Historically 29–38% delayed or nonunion with conventional plates; 4.7% in a systematic review of modern fixation, and one in eight distal femoral fractures needed reoperation, most often for nonunion (Rockwood). Nonunion was 10.7% with submuscular plating vs 32% with open reduction (AO). Risk factors include open fractures, diabetes, smoking, obesity, short plates, stainless steel plates and infection (AO; Rockwood). Treatment: revision or augmented fixation, exchange to a nail, or both; graft atrophic nonunions (Rockwood).

• Infection: Should not exceed 3–5% in closed fractures at experienced centers; treat with debridement and culture-specific antibiotics, retaining stable implants (Rockwood).

• Knee stiffness and posttraumatic arthritis (Rockwood).

• Previous knee arthroplasty increases the risk of implant failure (AO).

• Distal femoral replacement is an alternative in selected elderly patients with C-type fractures; reoperation rates were similar to ORIF in retrospective comparisons (Rockwood).

References

1. Rudloff MI. Fractures of the lower extremity. In: Azar FM, Sawyer JR, Throckmorton TW, eds. Campbell's Operative Orthopaedics. 15th ed. Philadelphia: Elsevier; 2026. Chapter 59, Technique 59.24.

2. Oh JK. Femur, distal. In: Buckley RE, Moran CG, Apivatthakakul T, eds. AO Principles of Fracture Management. 3rd ed. Stuttgart: Thieme; 2017. Chapter 6.6.3. (Turkish edition: AO Kırık Tedavisinin Prensipleri.)

3. Collinge CA, Roward LG. Distal femur fractures. In: Tornetta P III, Ricci WM, Ostrum RF, McKee MD, Ollivere BJ, de Ridder VA, eds. Rockwood and Green's Fractures in Adults. 10th ed. Philadelphia: Wolters Kluwer; 2024. Chapter 58. (Turkish edition: Erişkin Kırıkları.)