Minimally Invasive Surgery (MIS) in Orthopedics

Definition

Historical Background

• Arthroscopy pioneered the concept of MIS in orthopedics in the 1970s-80s, beginning with knee arthroscopy.
• Minimally invasive hip arthroplasty has been performed through small incisions since the 1980s.
• Progress in endoscopy, fluoroscopy, intramedullary nailing, and implant design (locking plates, tubular retractors) expanded MIS to the spine, trauma, and foot/ankle surgery.

Principles of MIS

1. Minimal soft-tissue disruption - incisions are planned to avoid or split (rather than detach) muscles along their fiber lines.
2. Preservation of blood supply - especially important at fracture sites to promote bone healing.
3. Indirect reduction - fractures are reduced by ligamentotaxis or closed manipulation rather than direct exposure of the fracture site.
4. Use of specialized instruments - longer retractors with narrow blades, angled reamers, fiberoptic lighting, outrigger guides for percutaneous screw placement, tubular dilators for the spine.
5. Fluoroscopic guidance - intraoperative image intensification compensates for reduced direct visualization.

Applications in Orthopedics

1. Arthroscopy

• Knee: Meniscectomy, ACL/PCL reconstruction, chondral procedures, synovectomy, loose body removal.
• Shoulder: Rotator cuff repair, Bankart repair for instability, subacromial decompression, biceps tenodesis.
• Hip: Labral repair, femoroacetabular impingement (FAI) correction, loose body removal, osteochondral procedures.
• Elbow: Loose body removal, lateral epicondyle release, olecranon fossa debridement.
• Ankle: Impingement syndrome, osteochondral defects, synovectomy.

2. Minimally Invasive Hip Arthroplasty

• Performed through an incision of 10 cm or less (typically 8-10 cm).
• Common approaches: single posterior incision (most common), direct anterior approach (DAA).
• The DAA is a modification of the Smith-Petersen approach; provides superior acetabular exposure but femoral preparation is technically demanding.
• Advantages: reduced blood loss, less postoperative pain, shorter hospital stay, faster rehabilitation, better cosmetic result.
• Contraindications/limitations: obese patients (BMI >30), muscular males, revision surgery, hip dysplasia, prior reconstructive procedures - these require larger incisions.
• Golden rule: Never hesitate to lengthen the incision if exposure is inadequate. A well-performed operation through a larger incision is preferable to an unsatisfactory result through a small one.

3. Minimally Invasive Plate Osteosynthesis (MIPO)

• Fracture is reduced primarily by ligamentotaxis.
• The plate is slid in a submuscular plane through small proximal and distal incisions, avoiding direct exposure of the fracture site.
• Proximal screws placed percutaneously using outrigger guides or fluoroscopy.
• Commonly combined with precontoured locking plates, which act as internal fixators.

• Preserves fracture haematoma and periosteal blood supply, promoting secondary (callus) bone healing
• Less soft-tissue damage and wound complications
• Lower infection rates compared to open reduction and internal fixation (ORIF)
• Reduced risk of iatrogenic nerve injury (e.g., radial nerve in humeral shaft fractures)
• Better functional recovery

• Thorough knowledge of anatomy and at-risk structures
• Proficiency in indirect reduction techniques
• Understanding of functional reduction (length, alignment, rotation)

4. Intramedullary Nailing

• Advantages: preserves fracture biology, early weight-bearing, lower infection rate.

5. Minimally Invasive Spine Surgery (MISS)

• Microdecompression (tubular/microscopic laminotomy): Unilateral approach with bilateral decompression for lumbar stenosis; preserves paraspinal muscles, spinous processes, supraspinous and interspinous ligaments.
• Minimally invasive posterior cervical foraminotomy: Via tubular distractors; results equivalent to open foraminotomy; avoids need for fusion.
• Percutaneous pedicle screw fixation: Screws placed through separate stab incisions using fluoroscopic guidance; less muscle denervation.
• Lateral interbody fusion (XLIF/DLIF): Through a minimally invasive direct lateral approach (L1-L4/L5).
• Endoscopic discectomy: Full-endoscopic technique for lumbar disc herniation; results equal to conventional microdiscectomy.

6. Foot and Ankle MIS

• Minimally invasive chevron-Akin osteotomy for hallux valgus - fourth-generation technique using fluoroscopy guidance.
• Minimally invasive cheilectomy for hallux rigidus.
• Minimally invasive arthrodesis for small joint fusions.
• Advantages over open: fewer wound complications, lower sural nerve injury risk, faster recovery.

Advantages of MIS in Orthopedics (Summary)

Disadvantages and Pitfalls

1. Steep learning curve - most MIS techniques require special training before results match open surgery.
2. Reduced visualization - risk of malpositioned implants, unrecognized fractures, neurovascular injury.
3. Implant malpositioning - in hip arthroplasty: cup malposition leading to dislocation, leg-length inequality, stem malalignment causing loosening.
4. Wound complications - excessive skin traction to compensate for small incision can cause skin necrosis and wound dehiscence.
5. Limited indications - obese patients, severe deformity, revision surgery, or complex fracture patterns may not be suitable.
6. Radiation exposure - increased intraoperative fluoroscopy use for surgeon and patient.
7. Cost - specialized instruments and implants increase costs.

Complications Specific to MIS

• Implant loosening from suboptimal bone preparation
• Dislocation from malpositioned components (hip arthroplasty)
• Neurovascular compromise from inadequate exposure
• Delayed union/nonunion from suboptimal reduction
• Skin necrosis from excessive wound retraction

Conclusion

Minimally Invasive Surgery (MIS) in Orthopedics

Definition

Principles

1. Minimal soft-tissue disruption - muscles split along fiber lines rather than detached
2. Preservation of blood supply - especially at fracture sites
3. Indirect reduction - by ligamentotaxis rather than direct fracture exposure
4. Specialized instruments - narrow retractors, angled reamers, tubular dilators, outrigger guides
5. Fluoroscopic guidance - compensates for reduced direct visualization

Applications

1. Arthroscopy

• Knee: Meniscectomy, ACL reconstruction, chondral procedures
• Shoulder: Rotator cuff repair, Bankart repair, subacromial decompression
• Hip: FAI correction, labral repair
• Ankle: Impingement, osteochondral defects

2. Minimally Invasive Hip Arthroplasty

• Incision ≤10 cm (typically 8-10 cm); single posterior or direct anterior approach (DAA)
• Benefits: less blood loss, less pain, shorter hospital stay, faster rehabilitation
• Golden rule: Never hesitate to lengthen the incision if exposure is inadequate

3. Minimally Invasive Plate Osteosynthesis (MIPO)

• Plate slid in a submuscular plane through small proximal and distal incisions
• Fracture reduced by ligamentotaxis; screws placed percutaneously with locking plates
• Preserves fracture haematoma and periosteal blood supply, promoting secondary bone healing

4. Intramedullary Nailing

• Closed nailing of femur, tibia, humerus - fracture not opened
• Preserves fracture biology; allows early weight-bearing

5. Minimally Invasive Spine Surgery (MISS)

• Microdecompression: Unilateral approach with bilateral decompression; preserves paraspinal muscles
• Percutaneous pedicle screw fixation: Via stab incisions under fluoroscopy
• Endoscopic discectomy: Results equivalent to open microdiscectomy
• Lateral interbody fusion (XLIF): Through direct lateral approach

6. Foot and Ankle

• MIS chevron-Akin osteotomy (hallux valgus), MIS cheilectomy (hallux rigidus)
• Fewer wound complications, lower nerve injury risk

Advantages vs Disadvantages

Complications

• Implant loosening/malposition (hip arthroplasty)
• Neurovascular compromise from inadequate exposure
• Delayed union/nonunion
• Wound dehiscence from excessive skin retraction

Key Points for Exam

• MIS does not mean a rushed or compromised operation - patient safety takes priority over incision size
• The learning curve is the most cited disadvantage across all MIS techniques
• MIPO preserves fracture biology by avoiding direct exposure - promotes secondary (callus) healing
• Contraindications include obesity (BMI >30), revision surgery, severe deformity, and complex fracture patterns