Medial Parapatellar Approach to the Knee

The medial parapatellar approach is the gold standard for TKA and most knee arthroplasty procedures, providing excellent visualization of all compartments. Key distinction: the skin incision is anterior midline (preserving blood supply from both medial and lateral geniculate vessels), while the arthrotomy is medial parapatellar (approximately 1cm medial to the patella border through VMO and capsule). The patella is everted laterally—never over-tension or risk avulsing the patellar tendon insertion; in stiff knees, use quadriceps snip or tibial tubercle osteotomy instead. The infrapatellar branch of the saphenous nerve (IPBSN) is always sacrificed, causing anterolateral knee numbness. The inferior geniculate artery is at risk during subperiosteal tibial elevation. The approach can be extended proximally (quadriceps snip) or distally (TTO) for difficult exposures.

The medial parapatellar approach is the most widely used surgical approach to the knee. It provides excellent exposure of the entire knee joint including medial, lateral, and patellofemoral compartments.

Primary indications:

• Total knee arthroplasty (primary and revision)
• Distal femur fractures (supracondylar, intercondylar)
• Tibial plateau fractures (bicondylar patterns)
• Removal of loose bodies
• Synovectomy for inflammatory arthritis
• Patellar fractures (if requiring extensive exposure)

Advantages:

• Excellent visualization of all compartments
• Preserves quadriceps tendon (no transection)
• Extensile - can be extended proximally or distally
• Reproducible and familiar to most surgeons
• Allows patellar eversion for resurfacing

Disadvantages:

• Sacrifices IPBSN (anterolateral numbness)
• Can be difficult in obese patients with large soft tissue envelope
• Patella eversion can be challenging in very stiff knees
• Risk of patellar maltracking if closure inadequate

Extensor mechanism:

• Quadriceps tendon - inserts on superior pole of patella
• Patella - largest sesamoid bone, bipartite variants in 2%
• Patellar tendon - inserts on tibial tubercle
• VMO - inserts on medial patella and medial retinaculum, final 15 degrees extension
• Vastus lateralis - inserts on lateral patella, stronger than VMO

Blood supply:

• Skin: Medial and lateral geniculate arteries form anastomoses
• Patella: Inferior pole blood supply from patellar tendon fat pad - do NOT strip this completely
• Danger: Medial skin incisions create lateral flap with tenuous blood supply

Nerve structures:

• Infrapatellar branch of saphenous nerve (IPBSN): Emerges from sartorius 10-12cm above joint line, crosses anterior to supply skin over anterior tibia and lateral patella. Always sacrificed in this approach - causes anterolateral numbness in distribution.
• Common peroneal nerve: Posterolateral, wraps around fibular neck. At risk during lateral retraction or correction of valgus deformity.

Key relationships:

• Capsule is continuous with periosteum anteriorly
• Medial meniscus more firmly attached to capsule than lateral
• Popliteal vessels are posterior - protect with retractors during posterior dissection

Assessment:

• Review prior surgical scars - incorporate when possible
• Assess skin quality, vascular status
• Evaluate knee ROM and contractures
• Document neurovascular status baseline
• Assess alignment (varus, valgus, flexion contracture)
• Identify challenging factors: obesity, prior surgery, stiffness

Imaging review:

• AP and lateral knee radiographs
• Mechanical axis views (long leg alignment films)
• CT if significant deformity or bone loss
• Templating for component sizes if TKA

Consent points:

• Anterolateral numbness from IPBSN sacrifice (100% expected)
• Infection risk (less than 1% primary TKA, 2-5% revision)
• Stiffness or need for manipulation
• Patellar maltracking (1-2%)
• Patellar tendon injury (rare but devastating)
• Neurovascular injury (very rare)

Key Concept: There is NO true internervous plane in the medial parapatellar approach.

Unlike hip approaches where muscles can be separated along nerve-defined boundaries, the medial parapatellar approach works by incising through the VMO muscle directly. The VMO is innervated by the femoral nerve, and the incision through it is a trans-nervous rather than inter-nervous approach.

Why no internervous plane?

• The entire quadriceps mechanism (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) is innervated by the femoral nerve
• There is no nerve boundary to exploit within the anterior knee
• The medial parapatellar incision cuts through VMO fibers that are all femoral nerve-innervated
• This is acceptable because the VMO insertion can be repaired at closure

Contrast with alternative approaches:

Standard Patient Position:

• Supine on a standard operating table
• Bump under ipsilateral hip (optional) - 10-15 degree internal rotation improves medial access
• Thigh tourniquet applied high on the thigh - avoid positioning too distally as it can limit quadriceps mobility
• Foot of bed dropped or use of leg positioning device to allow full knee flexion

Key Setup Considerations:

1. Knee Range Requirements:

   • Must achieve full extension (for component alignment verification)
   • Must achieve at least 100-110 degrees flexion (for tibial preparation)
   • If limited preoperative ROM, plan for extensile techniques

2. Draping:

   • Free drape the entire lower extremity
   • Include thigh in the sterile field (for tourniquet management)
   • Ensure groin is visible (allows assessment of leg rotation)

3. Tourniquet Considerations:

   • Standard: 250-300 mmHg above systolic pressure
   • Maximum recommended duration: 90-120 minutes
   • Consider tourniquet-free technique for patients with peripheral vascular disease

Positioning for Special Situations:

• Obese patients: May need specialized table, wider leg holders, longer instruments
• Ankylosis/stiff knee: Position to allow maximal flexion available; plan for TTO if less than 70 degrees flexion
• Bilateral TKA: Standard supine; can proceed sequentially; redrape and reprep between sides

When the patella cannot be everted safely (stiff knee, scarred knee, obese patient), use one of these extensile techniques:

Quadriceps snip technique:

• Extend arthrotomy into quadriceps tendon
• At junction of medial and middle thirds, make 45-degree oblique cut laterally
• Length: 2-4cm
• Through vastus lateralis fibers and lateral retinaculum
• Increases exposure by 20-30%
• Repair with interrupted sutures, heal reliably

V-Y turndown technique:

• Make inverted V in quadriceps tendon 8-10cm above patella
• Apex of V is midline, arms extend medially and laterally
• Turn down quadriceps with patella as unit
• At closure, advance V as Y to lengthen extensor mechanism
• Requires 6 weeks protected weight-bearing
• Risk: Extensor lag if inadequate repair or tendon quality poor

Tibial tubercle osteotomy:

• Osteotomize tibial tubercle with patellar tendon attached
• 5-6cm long, 8-10mm thick wedge of bone
• Reflect tubercle and tendon laterally with patella
• At closure, fix tubercle with 2 screws or cerclage wires
• Advantage: Preserves continuity of extensor mechanism
• Risk: Tubercle nonunion (5%), fracture propagation

Patellar tendon avulsion - catastrophic:

• Recognition: Sudden loss of resistance during eversion, palpable gap, inability to extend knee
• Immediate management: Primary repair with transosseous sutures through tibial tubercle and patella
• Augmentation: Consider augmentation with mesh or allograft
• Postoperative: Brace in extension for 6 weeks, then gradual ROM
• Prognosis: Extensor lag common even with repair

Skin necrosis:

• Risk factors: Multiple prior scars, lateral skin incision, smoking, diabetes, steroid use
• Prevention: Use most lateral prior scar, midline skin incision, atraumatic handling, ensure perfusion
• Management: Small areas - local wound care; large areas - VAC therapy, flap coverage, possible spacer removal
• Impact: Increases infection risk dramatically

Epidemiology:

• TKA is one of the most common elective orthopaedic procedures in Australia
• AOANJRR data shows over 60,000 primary TKAs performed annually
• Medial parapatellar approach used in greater than 90% of primary TKAs

Registry data (AOANJRR):

• Revision rate for primary TKA at 10 years: approximately 6%
• Most common causes of revision: infection (25%), loosening (18%), pain (14%)
• Approach-related complications not specifically tracked but patellar complications represent 3-5% of revisions

Consent considerations:

• Discuss IPBSN sacrifice and numbness (100% incidence)
• Infection risk: less than 1% primary TKA with modern prophylaxis
• Revision risk: 6% at 10 years
• Patellar complications: 3-5% (maltracking, fracture, loosening)