import { OnePagerSummary, ContentSection, ExamWarning, InfoCardGrid, InfoCard, EvidenceCard, ComparisonTable, VivaScenario, MnemonicCard, ExamCheatSheet, Tab, Tabs } from '@/components/mdx' 35), severe deformity (>20° varus/valgus), stiff knee (flexion <70°), revision TKA - use medial parapatellar for these", ]} examPearls={[ "\"Goldilocks approach\" - not too much muscle damage (medial parapatellar), not too little exposure (subvastus) - just right for routine TKA", "Key technical point: Split THROUGH VMO fibers obliquely at 55° (WITH fiber direction), NOT across them (would cause more damage)", "Advantages: Faster SLR than medial parapatellar (4-5 vs 7-10 days), better exposure than subvastus (<5% vs 15-20% conversion), minimal VMO denervation", "Disadvantages: Still cuts some VMO (not truly muscle-sparing like subvastus), requires steeper learning curve than standard medial parapatellar", ]} summary="The midvastus approach to the knee is a limited muscle-splitting technique for total knee arthroplasty that splits the distal 3-4cm of vastus medialis obliquus (VMO) longitudinally in line with muscle fibers at a 55° oblique angle. It represents a compromise between the subvastus approach (muscle-sparing but limited exposure with 15-20% conversion rate) and the standard medial parapatellar approach (excellent exposure but slower quadriceps recovery). The midvastus approach provides better exposure than subvastus (<5% conversion rate), faster quadriceps recovery than medial parapatellar (straight leg raise 4-5 days vs 7-10 days), and is ideal for most primary TKAs in normal to mildly overweight patients (BMI <35) with standard deformity correction needs." /> ### 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 Midvastus is the most VERSATILE muscle-preserving approach - it can handle a broader range of cases than subvastus while still providing faster recovery than medial parapatellar. Examiners test understanding of this "middle ground" positioning. ### 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 The midvastus split MUST follow VMO fiber direction (55° oblique) - cutting transversely across fibers causes more damage and defeats the muscle-preserving benefit. Think "split with the grain" like splitting wood. ### 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 VMO repair at closure is IMPORTANT - although split was limited to 3-4cm and followed fibers, proper repair optimizes muscle healing and function. Don't just close capsule and ignore the split muscle. ### 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 ## Exam Day Cheat Sheet ## Evidence-Based Practice 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.

Midvastus Approach to Knee

Midvastus Approach to Knee