LISS and MIPO in Orthopedic Plating

Understanding the Relationship First

• MIPO is a surgical technique/approach - a philosophy of how you insert and apply a plate
• LISS is a specific implant system - the first widely adopted device designed to be used with MIPO principles

PART 1: MIPO - Minimally Invasive Plate Osteosynthesis

Principle

1. Preserve the fracture biology - the fracture zone is left undisturbed ("zone of injury untouched")
2. Indirect reduction - length, alignment, and rotation are restored without directly visualizing the fracture
3. Bridge the fracture - the plate spans the comminuted zone, providing relative stability (not absolute rigidity)
4. Submuscular tunnel insertion - the plate is slid under muscles through small proximal and distal incisions only
5. Secondary bone healing - the relative-stability construct allows micromotion, promoting callus formation

"The principles of fixation with the application of a bridging construct while preserving the fracture biology are similar to those for open plating. MIPO technique allows preservation of the blood supply to the fracture fragments, in turn improving secondary bone healing."

• Rockwood and Green's Fractures in Adults, 10th ed.

How MIPO is Performed (General Steps)

• Two or three small incisions (3-5 cm each) are made proximal and distal to the fracture
• An extraperiosteal submuscular tunnel is created manually along the bone surface
• The plate is slid through the tunnel without exposing the fracture site
• Fracture reduction is achieved indirectly using traction, distractor frames, or external fixators
• Screws are placed percutaneously through stab incisions guided by the targeting arm or fluoroscopy

Figure: MIPO anterior approach for humeral shaft fractures - showing the proximal and distal windows (A) and plate insertion via a tunneling instrument (B). (Rockwood and Green's, 10th ed.)

Where MIPO is Used

Advantages of MIPO

• Preserves periosteal vascularity - lower nonunion and infection rates
• Less blood loss intraoperatively
• Smaller incisions - better cosmesis, less wound complications
• Shorter operative time in experienced hands
• Reduced need for bone grafting in comminuted fractures
• Early mobilization possible due to construct stability

PART 2: LISS - Less Invasive Stabilization System

What is LISS?

"An internal-external fixator made of titanium and, therefore, has a different modulus of elasticity than other plating systems."

Distinguishing Design Principles of LISS

1. Fixed-angle locking screws - screw threads engage the plate holes (threaded screw holes), creating a fixed-angle construct. The screw cannot toggle in the plate, so it behaves like an internal fixator - not unlike an external fixator placed under the skin.
2. Unicortical self-drilling, self-tapping locking screws - because the locking mechanism provides angular stability, bicortical purchase is not mandatory (though bicortical is preferred in osteoporotic bone for better pullout resistance).
3. No plate-to-bone compression required - unlike conventional plating where friction between plate and bone provides stability, LISS relies entirely on the locked screw-plate construct. The plate does not need to be contoured exactly to the bone surface and is not pressed against periosteum, preserving blood supply.
4. Radiolucent targeting/insertion arm - the plate is attached to a radiolucent guide arm ("handle") that allows insertion through a submuscular tunnel and guides percutaneous screw placement without direct visualization.
5. Titanium material - lower modulus of elasticity than stainless steel, allowing slight elastic deformation and stress-sharing with bone.
6. Pre-contoured anatomic design - designed specifically for distal femur (femoral LISS) or proximal tibia (tibial LISS), with fixed hole geometry matching the condylar anatomy.

Figure: The LISS system with its radiolucent guide arm, showing the plate applied to the distal femur with locking screws spanning a comminuted fracture zone. (Campbell's Operative Orthopaedics, 15th ed.)

LISS Insertion Technique (Distal Femur Example)

Figure: LISS technique for distal femur. A: Plate inserted via lateral submuscular tunnel using the radiolucent guide arm. B: Plate stabilized to the distal femur at both ends with provisional pins. C: Fracture reduction fine-tuned; self-drilling unicortical locking screws placed. D: Definitive fixation. (Rockwood and Green's, 10th ed.)

Clinical Application and X-Ray Appearance

Figure: Distal femur fracture before and after LISS fixation. Note the characteristic parallel locking screws in the condylar segment and spaced diaphyseal fixation - the hallmark of bridge plating. (Rockwood and Green's, 10th ed.)

PART 3: Key Differences - LISS vs MIPO

Evolution of Condylar Fixation Designs

Figure: Evolution of distal femoral condylar fixation. Left to right: 95-degree blade plate, DCS (Dynamic Condylar Screw), modern fixed-angle locking plate (LISS-type), variable-angle locking plate. (Rockwood and Green's, 10th ed.)

PART 4: Bridge Plating - The Mechanical Foundation

"Bridge plating is most commonly utilized to span comminuted metaphyseal and diaphyseal fractures. Rather than striving for anatomic reduction and compression of individual fracture fragments, the comminuted region is simply bridged. The resultant construct provides relative rather than absolute stability."

• Rockwood and Green's, 10th ed.

• Long working length (distance between the most proximal and distal screws) - reduces construct stiffness, allows micromotion, stimulates callus
• Spaced screws - screws clustered near the fracture increase stiffness; spreading them out reduces stiffness appropriately
• Far cortical locking (FCL) screws (newer concept) - near cortex overdrilled so screw engages only far cortex, creating elastic cantilever bending and balanced callus formation

PART 5: Complications

Complications of MIPO Technique

Complications of LISS Specifically

Risk Factors for Nonunion (LISS/Locking Plate)

• Open fractures (OR 2.42 for nonunion; OR 3.47 for infection)
• Diabetes mellitus
• Obesity
• Stainless steel implant (vs titanium)
• Overly rigid construct (short plate, clustered screws)
• Excessive construct stiffness impairing callus

PART 6: Indications for MIPO/LISS

• Comminuted metaphyseal and diaphyseal fractures (AO A1-A3)
• Complex intra-articular fractures (AO C1-C3) - articular surface reduced openly, metaphysis bridged with MIPO
• Periprosthetic fractures above stable TKA or below well-fixed THA
• Osteoporotic fractures (poor bone quality)
• Open fractures (reduced infection vs conventional open plating)
• Fractures in patients requiring early mobilization

• Simple transverse fractures amenable to compression plating
• Fractures requiring absolute stability (articular step-offs requiring lag screws)
• Severely contaminated open fractures (external fixator preferred first)

Summary: Conceptual Framework

Historical progression:
Open plating (high infection/nonunion)
     ↓
Biological principles introduced (Mast et al.) - indirect reduction, biology preservation
     ↓
Fixed-angle implants (blade plate, DCS) - better stability
     ↓
LISS (1990s) - first "internal external fixator"; combined locking screws + MIPO approach
     ↓
Modern MIPO with LCP/variable-angle systems - greater flexibility, better anatomic contouring

• LISS proved that minimally invasive insertion of a fixed-angle locking plate dramatically reduces infection and nonunion compared to conventional open plating
• MIPO is the umbrella technique now applied with all modern locking plate systems
• The two are inseparable in history but distinct in definition: one is a method, the other was a pioneering device