Midvastus Approach to Knee

Primary Indications

Primary Total Knee Arthroplasty - Broad Use

• Most primary TKAs in normal to mildly overweight patients (BMI less than 35)
• Standard deformity correction (varus/valgus less than 20 degrees)
• Reasonable preoperative ROM (flexion at least 70-80 degrees)
• Primary osteoarthritis or inflammatory arthritis

Advantages Over Other Approaches

• Better exposure than subvastus (lower conversion rate: less than 5%)
• Faster quad recovery than medial parapatellar
• Can handle more deformity and stiffness than subvastus
• Suitable for broader patient population than subvastus

Relative Indications

Patient Requesting Muscle-Sparing Technique

• Desires faster recovery
• Midvastus balances preservation with adequate exposure

Bilateral Staged TKA

• Good balance of recovery and versatility

Younger Active Patients

• Benefit from preserved quad function
• Can tolerate some muscle split better than older patients

Contraindications

Absolute

• Revision TKA (may need extensile exposure)
• Previous open knee surgery with significant scarring

Relative

• Severe obesity (BMI greater than 35) - difficult exposure
• Severe deformity (greater than 20 degrees) - may need extensive releases
• Severe stiffness (flexion less than 60 degrees) - hard to expose
• Patella baja (low patella difficult to evert)
• Inflammatory arthritis with severe bone loss

Patient Selection

Ideal Candidate Profile

• BMI less than 35
• Flexion at least 70-80 degrees
• Standard deformity (less than 20 degrees varus/valgus)
• Primary or inflammatory OA
• No previous open knee surgery

Acceptable But Challenging

• BMI 30-35 (doable but tighter exposure)
• Flexion 60-70 degrees (need careful mobilization)
• Deformity 15-20 degrees (may need limited releases)

Poor Candidate (Consider Medial Parapatellar)

• BMI greater than 35
• Flexion less than 60 degrees
• Severe deformity (greater than 20 degrees)
• Revision TKA
• Severe bone loss

Clinical Assessment

History

• Pain location, duration, functional impact
• Previous knee procedures
• Activity level and recovery expectations
• Comorbidities

Physical Examination

• Range of motion (flexion/extension)
• Alignment (varus/valgus angle)
• Ligamentous stability
• Patellar tracking
• Skin condition

Imaging Protocol

Standard Radiographs

• AP and lateral knee
• Merchant view (patellar tracking)
• Full-length standing films (mechanical axis)

Key Measurements

• Mechanical axis alignment
• Joint space narrowing pattern
• Patella height (Insall-Salvati ratio)
• Bone quality

Standard TKA Equipment

Basic Instruments

• Standard TKA instrumentation
• Self-retaining retractors
• Periosteal elevators
• Electrocautery

TKA Components

• Femoral component (CR or PS)
• Tibial baseplate and insert
• Patellar button

Special Considerations

No Special Instruments Needed

• Standard TKA retractors adequate
• Exposure better than subvastus (standard equipment works)

Standard Supine Positioning

Positioning

• Supine on OR table
• Leg holder or side post at thigh
• Tourniquet proximal thigh
• Bump under hip (optional)

Leg Holder

• Allows 90-degree flexion
• Aids patellar eversion
• Pad carefully (peroneal nerve)

Tourniquet

• Recommended for bloodless field
• Aids VMO fiber identification
• Deflate before closure

Bony Landmarks

Palpable Anatomy

• Patella (anterior)
• Medial epicondyle femur
• Adductor tubercle
• Tibial tubercle
• Medial joint line

Neurovascular Anatomy

VMO Nerve Supply

• Descending genicular artery branches
• Nerve enters VMO from lateral/deep surface
• Distal VMO: Less dense innervation (safer to split here)
• Proximal VMO: Dense innervation (avoid splitting)

Key Anatomic Principle

• Splitting distal 3-4cm of VMO (less critical innervation zone)
• Preserves majority of VMO nerve supply
• Less denervation than medial parapatellar

Muscular Anatomy

Vastus Medialis Obliquus

• Muscle fibers run obliquely (55 degrees from vertical)
• Distal fibers insert on medial patella
• Splitting WITH fibers (longitudinally) less traumatic than cutting ACROSS

Midvastus Concept

• Split distal VMO in direction of fibers
• Minimizes muscle damage
• Preserves most of muscle mass and innervation

Step 1: Skin Incision

Incision

• Midline or slightly medial
• 5-6cm proximal to superior patella pole
• Extends to tibial tubercle or 2cm distal
• Length: 10-15cm

Subcutaneous Dissection

• Develop medial flap to patella border
• Expose VMO muscle belly
• Hemostasis with cautery

Step 2: Identify VMO Fiber Direction

Palpate VMO

• Feel VMO muscle belly medial to patella
• Identify fiber direction (oblique, 55 degrees)
• Trace fibers from proximal (thigh) to distal (patella)

Mark Split Line

• Plan oblique split THROUGH VMO
• Direction follows fibers (superior-lateral to inferior-medial)
• Start point: 3-4cm proximal to superior pole of patella
• End point: Insertion on medial patella

Step 3: VMO Split - KEY STEP

Initiate Split

• Begin 3-4cm proximal to superior patella pole
• Incise through VMO in line with fibers
• Use electrocautery for hemostasis

Extend Split

• Continue obliquely toward medial patellar insertion
• Split length: 3-4cm total
• Important: Split WITH fibers (longitudinal), not across them

Technique Tips

• Use gentle spreading with forceps to separate fibers
• Blunt dissection aids in following fiber planes
• Cauterize small bleeders as encountered

Step 4: Medial Arthrotomy

Capsular Incision

• Continue incision through medial retinaculum
• Extend from VMO split to tibial tubercle
• Standard medial arthrotomy distally

Proximal Extension

• Split extends through joint capsule
• Follows same oblique line as VMO split

Step 5: Patellar Eversion

Evert Patella

• Flex knee to 90 degrees
• Evert patella laterally
• Easier than subvastus (better exposure)
• Harder than medial parapatellar (some VMO intact)

Assess Exposure

• Should adequately visualize femoral condyles
• Access to tibial plateau
• If inadequate: extend VMO split more proximally (rare)

Step 6: Standard TKA Technique

Bone Cuts

• Tibial resection (standard guide)
• Femoral cuts (distal, anterior, posterior, chamfer)
• Sizing and rotation assessment

Balancing

• Soft tissue releases as needed
• Extension and flexion gap assessment

Component Implantation

• Trial components
• Assess tracking and stability
• Cement and implant final components

Patellar Resurfacing

• Standard technique

Step 7: Closure

VMO Repair - CRITICAL

• Re-approximate split VMO fibers
• Use #1 absorbable suture (Vicryl)
• Side-to-side repair of muscle
• 3-4 interrupted sutures through muscle belly

Capsule and Retinaculum

• Close medial capsule/retinaculum
• #1 Vicryl continuous or interrupted
• Watertight closure

Deep Fascia

• Close fascia over VMO
• 2-0 Vicryl

Subcutaneous and Skin

• 2-0 Vicryl subcutaneous
• 3-0 Monocryl or staples skin

Drain

• Consider intra-articular drain
• Remove when output less than 30mL/shift

Intraoperative Complications

Inadequate Exposure (Rare - Less than 5%)

• Much less common than subvastus (10-20%)
• If occurs: extend VMO split more proximally
• Conversion to full medial parapatellar very rare

VMO Damage

• Over-splitting (extending too far proximal)
• Splitting across fibers instead of with fibers
• Prevention:
  • Limit split to 3-4cm
  • Follow fiber direction carefully
  • Don't extend into proximal VMO (critical innervation)

Bleeding from VMO

• Muscle is vascular
• Prevention: Cauterize as you split
• Management: Direct pressure, cautery, rarely needs suture ligation

Early Postoperative Complications

Quadriceps Weakness

• Less than medial parapatellar (limited muscle cut)
• More than subvastus (some muscle damaged)
• Expected: Intermediate recovery speed

VMO Dehiscence

• Rare (less than 1%)
• If repair fails, VMO gap may persist
• Prevention: Secure repair with good tissue approximation

Wound Complications

• Similar to other approaches (2-5% hematoma, less than 1% infection)

Late Complications

Extensor Lag

• Incidence: 3-5%
• Lower than medial parapatellar (5-10%)
• Higher than subvastus (2-5%)

Patellar Maltracking

• Similar to medial parapatellar
• VMO disruption (even if limited) can affect tracking

Standard TKA Complications

• Loosening, instability, stiffness
• No difference from other approaches

Immediate Care (0-48 hours)

Mobilization

• Sit at bedside Day 1
• Ambulate Day 1-2
• Straight leg raise: Typically achieved day 4-5
  • Faster than medial parapatellar (7-10 days)
  • Slower than subvastus (2-3 days)

Pain Management

• Multimodal analgesia
• Adductor canal block (preserves quads) preferred over femoral block
• Opioids, NSAIDs, acetaminophen

Drain

• Remove when output less than 30mL/shift (24-48 hours)

Weight-Bearing and Mobilization

Weight-Bearing

• WBAT from Day 1
• Walker/crutches for 2-4 weeks
• Cane by 4-6 weeks

ROM Goals

• 90 degrees flexion by Week 1-2
• 0-110 degrees by 6 weeks

Physical Therapy

Phase 1 (0-2 weeks)

• Achieve SLR (day 4-5)
• ROM exercises
• Quadriceps sets
• Gait training

Phase 2 (2-6 weeks)

• Progressive strengthening
• Increase ROM
• Closed-chain exercises
• Wean assistive devices

Phase 3 (6-12 weeks)

• Functional restoration
• Return to ADLs
• Sport-specific training

Return to Activity

ADLs: 2-4 weeks Driving: 4-6 weeks Sedentary work: 4-6 weeks Labor: 8-12 weeks Full activities: 12-16 weeks

The midvastus approach for total knee arthroplasty has gained significant traction among Australian arthroplasty surgeons as a practical compromise between traditional medial parapatellar and the more technically demanding subvastus approach. Major Australian joint centers (Epworth Healthcare, Sydney Adventist Hospital, St Vincent's Private Hospital) report midvastus usage in approximately 20-30% of primary TKA cases, representing the most commonly employed "muscle-sparing" technique in Australian practice. Unlike subvastus, which remains confined to highly selective cases due to exposure limitations and steep learning curve, midvastus has achieved broader adoption due to its versatility across diverse patient populations and forgiving technical profile.

Australian orthopaedic training through the Australian Orthopaedic Association (AOA) increasingly includes midvastus technique during advanced arthroplasty fellowships, though medial parapatellar remains the gold standard taught during core surgical training. The Royal Australasian College of Surgeons (RACS) orthopaedic curriculum acknowledges muscle-preserving approaches as important variations but does not mandate competency given the adequacy of standard medial parapatellar for all cases. Conversion rates from midvastus to medial parapatellar in Australian practice are reported at 3-5%, significantly lower than the 10-20% conversion rates seen with subvastus, making midvastus more reliable for routine practice.

Antibiotic prophylaxis follows Therapeutic Guidelines (eTG) with cefazolin 2g IV at induction. Pain management strategies favor adductor canal blocks over femoral nerve blocks in patients undergoing midvastus approach, preserving quadriceps function while providing effective analgesia - a practice increasingly adopted across Australian public and private hospitals. Physiotherapy protocols in Australia emphasize early mobilization with straight leg raise achievement expected by postoperative day 4-5 (faster than medial parapatellar's 7-10 days but not as rapid as subvastus's 2-3 days). Hospital length of stay for midvastus TKA averages 3-4 days in Australian private hospitals and 4-5 days in public hospitals, compared to 4-5 days for medial parapatellar. Both private health insurance (Bupa, Medibank) and Medicare cover TKA regardless of surgical approach, with PBS-subsidized implants available. Workers' compensation schemes (WorkCover, icare) do not differentiate reimbursement based on surgical technique.