import { OnePagerSummary, ContentSection, ExamWarning, InfoCardGrid, InfoCard, EvidenceCard, ComparisonTable, VivaScenario, MnemonicCard, ExamCheatSheet, Tab, Tabs } from '@/components/mdx' 35), stiff knees (flexion <70°), muscular patients, severe deformity (>20° varus/valgus), revision TKA - 15-20% conversion rate to medial parapatellar", "**Best indications**: Straightforward primary TKA in thin patients (BMI <30), good preoperative ROM (flexion ≥90°), minimal deformity (<15°), younger active patients prioritizing rapid recovery", "**Contraindications**: Obesity (BMI >35), knee stiffness (flexion <70°), severe deformity (>20°), revision TKA, need for extensive soft tissue releases", ]} examPearls={[ "Key technical difference: Elevate VMO subperiosteally from medial tibia (NOT through muscle) - preserves muscle architecture and nerve supply", "Preserve descending genicular artery (VMO nerve and vascular supply) - enters VMO from superomedial direction", "Advantages: Preserved extensor mechanism, fastest SLR (2-3 days), better patellar tracking, less postop pain", "Disadvantages: LIMITED exposure (15-20% conversion), steep learning curve, not suitable for obese/stiff/revision cases", ]} summary="The subvastus approach to the knee is a muscle-sparing technique for total knee arthroplasty that elevates the vastus medialis obliquus (VMO) subperiosteally from the medial tibia WITHOUT cutting through muscle fibers or quadriceps tendon, preserving VMO integrity and nerve supply from the descending genicular artery. It provides the fastest quadriceps recovery of all TKA approaches (straight leg raise 2-3 days vs 7-10 days medial parapatellar), better patellar tracking, and less postoperative pain. However, the approach has significant limitations: limited exposure leads to 15-20% conversion rate to medial parapatellar (vs <5% for midvastus), and it is contraindicated in obese patients (BMI >35), stiff knees (flexion <70°), severe deformity (>20°), and revision TKA. Best for straightforward primary TKA in thin patients (BMI <30) with good ROM and minimal deformity who prioritize rapid recovery." /> ### Primary Indications **Primary Total Knee Arthroplasty - Selected Cases** - Straightforward primary TKA in thin to normal-weight patients (BMI less than 30) - Good range of motion preoperatively (at least 90 degrees flexion) - No significant deformity (varus/valgus less than 15 degrees) - No significant flexion contracture (less than 10 degrees) - Patient desires faster recovery **Advantages Over Medial Parapatellar** - Preserves VMO muscle fibers and innervation - Faster return of quadriceps function - Earlier straight leg raise ability (2-3 days vs 7-10 days) - Better patellar tracking (preserved soft tissue balance) - Lower incidence of patellofemoral complications ### Relative Indications **Bilateral Staged TKA** - Subvastus on first knee for faster rehab - Allows better function before second knee surgery **Young Active Patients** - Higher functional demands - Benefit from preserved extensor mechanism ### Contraindications **Absolute** - Revision TKA (inadequate exposure) - Previous open knee surgery with scarring - Need for extensive ligament releases or balancing **Relative** - Obesity (BMI greater than 30) - very difficult exposure - Limited preoperative ROM (less than 90 degrees flexion) - Severe deformity (greater than 15 degrees varus/valgus) - Significant flexion contracture (greater than 10 degrees) - Muscular or athletic build (thick VMO makes dissection difficult) - Patella baja (low-lying patella difficult to evert) - Short stature (limited operative space) Subvastus approach is NOT for routine use - it's a specialized technique for straightforward primary TKA in favorable anatomy. Examiners test understanding of SPECIFIC contraindications and when to convert to medial parapatellar. ### Patient Selection - CRITICAL **Ideal Candidate Profile** - BMI less than 25-30 - Flexion at least 90 degrees - Minimal deformity (less than 10 degrees) - No previous open knee surgery - Primary osteoarthritis (not inflammatory arthritis) **Poor Candidate Profile** - Obese (BMI greater than 30) - Stiff knee (flexion less than 90 degrees) - Severe deformity requiring releases - Rheumatoid arthritis (bone fragile, difficult dissection) - Muscular build (thick VMO) ### Clinical Assessment **History** - Pain pattern and functional limitations - Previous knee surgeries or trauma - Activity level and expectations - Comorbidities (diabetes, peripheral vascular disease) **Physical Examination** - **Range of motion** - CRITICAL for approach selection - Flexion: minimum 90 degrees needed - Extension: document flexion contracture - Passive vs active ROM - Alignment (varus, valgus, neutral) - Ligamentous stability (cruciate, collateral) - Patellar tracking and mobility - BMI calculation and thigh circumference ### Imaging Protocol **Standard Radiographs** - AP and lateral knee - Merchant view (patellar alignment) - Full-length standing alignment films (mechanical axis) **Measurements** - Mechanical axis deviation - Severity of joint space narrowing - Patella height (Insall-Salvati ratio) - Less than 0.8 = patella baja (relative contraindication) - Normal: 0.8-1.2 - Bone quality assessment **CT or MRI - Selected Cases** - Complex deformity - Extra-articular deformity planning - Bone loss assessment ### Surgical Planning **Implant Selection** - Standard TKA components (CR vs PS based on PCL integrity) - Standard instrumentation (no special instruments needed) - Have thicker polyethylene options available **Anesthesia Discussion** - Spinal vs general anesthesia - Femoral nerve block consideration - Pros: Excellent pain control - Cons: Delays quadriceps function (defeats purpose of subvastus) - Recommendation: Adductor canal block instead (preserves quadriceps) ### Standard TKA Equipment **Basic Instruments** - Standard TKA instrumentation system - Self-retaining retractors (bent Hohmann, narrow) - Lamina spreaders (helpful for exposure) - Army-Navy retractors (superficial) - Electrocautery **TKA Components** - Femoral component (cruciate-retaining or posterior-stabilized) - Tibial baseplate and polyethylene insert - Patellar button (standard) **Specialized Retractors** - Narrow retractors (limited exposure) - Subperiosteal elevators - Right-angle retractors ### Fluoroscopy **Not Routinely Needed** - Standard TKA technique uses instrumentation - Consider for: - Confirming femoral/tibial cut alignment - Assessing component position if concerned ### Standard Supine Positioning **Positioning Technique** - Supine on standard operating table - Small bump under ipsilateral hip (optional - aids exposure) - Leg holder or post at thigh level - Tourniquet on proximal thigh **Leg Holder Setup** - Side post allows 90-degree flexion - Important for subvastus: flexion aids VMO visualization - Pad carefully (peroneal nerve compression risk) **Foot Position** - Foot of bed free (allow knee flexion) - OR: leg holder device (hands-free positioning) ### Tourniquet Use **Advantages** - Bloodless field for dissection - Better visualization of VMO muscle fibers - Shorter operative time **Recommendation** - Use tourniquet for subvastus approach - Deflate before closure to ensure hemostasis - Limit time to 90-120 minutes if possible ### Bony Landmarks **Palpable Surface Anatomy** - **Patella** - mobile anteriorly - **Medial epicondyle of femur** - **Adductor tubercle** (superior to medial epicondyle) - **Tibial tubercle** - anterior midline reference - **Medial joint line** - 1cm distal to medial epicondyle ### Neurovascular Anatomy - CRITICAL **Vastus Medialis Obliquus (VMO) Nerve Supply** - **Descending genicular artery** gives off muscular branches - **Nerve to VMO**: Enters muscle from lateral side (deep surface) - **Course**: Travels with descending genicular vessels - **Risk**: Transection during VMO elevation or excessive dissection - **Protection**: Blunt dissection in subperiosteal plane preserves nerve **Saphenous Nerve and Vein** - Run subcutaneously on medial aspect - Risk with skin incision - Usually not visualized if incision properly placed **Popliteal Vessels** - Posterior to joint, safe distance - Not at risk with standard subvastus approach ### Muscular Anatomy **Vastus Medialis Obliquus (VMO)** - **Origin**: Medial lip of linea aspera, adductor magnus tendon - **Insertion**: Medial patella, medial retinaculum - **Function**: Terminal 15 degrees of knee extension, patellar stabilization - **Innervation**: Femoral nerve (L3-L4) - **Key anatomic detail**: Muscle fibers run obliquely (55 degrees from vertical) **Subvastus Plane** - **Between**: VMO muscle belly and medial tibial periosteum - **Contains**: Loose areolar tissue (easy dissection plane) - **Advantage**: No muscle cut, preserves VMO innervation **Other Quadriceps Components** - Vastus lateralis (lateral) - Vastus intermedius (deep) - Rectus femoris (superficial, anterior) ### Step 1: Skin Incision **Incision Planning** - Midline or slightly medial incision - Proximal extent: 5-6cm proximal to superior pole of patella - Distal extent: Tibial tubercle or 2cm distal - Length: 10-15cm (similar to medial parapatellar) **Skin Incision** - Sharp incision through skin and subcutaneous tissue - Achieve hemostasis with electrocautery - Identify and protect saphenous vein/nerve if encountered **Subcutaneous Dissection** - Develop medial flap to expose medial border of patella - Expose VMO muscle belly medially - Identify distal VMO insertion on medial patella ### Step 2: Identify VMO and Subvastus Plane **VMO Identification** - Palpate VMO muscle belly on medial thigh - Identify muscle fibers running obliquely toward patella - Trace fibers distally to patellar insertion **Find Subvastus Plane** - **Key step**: Identify interval UNDER (deep to) VMO - Palpate medial tibial metaphysis through VMO - Plane is between VMO muscle and tibial periosteum **Initial Dissection** - Make small incision in fascia at distal VMO - Use blunt dissection to develop plane between VMO and tibia - Elevator slides easily if correct plane The subvastus plane is UNDER the VMO muscle belly - do NOT incise through VMO fibers. If you find yourself cutting muscle, you're in wrong plane. The correct plane has loose areolar tissue and minimal resistance. ### Step 3: Subperiosteal VMO Elevation **Medial Tibial Periosteal Elevation** - Begin at medial aspect of tibial tubercle - Elevate periosteum from medial tibial metaphysis - Work proximally and posteriorly under VMO **VMO Mobilization** - Blunt elevation of VMO off tibial periosteum - Sweep VMO muscle belly laterally and proximally - Preserve VMO muscle fibers (no cutting) **Extent of Dissection** - **Proximal limit**: To level of superior pole of patella - **Posterior limit**: To posteromedial capsule (MCL superficial fibers) - **Distal limit**: Tibial tubercle **Retractor Placement** - Place narrow retractor deep to VMO - Retract VMO laterally to expose joint capsule - VMO "dome" created above joint ### Step 4: Capsular Incision and Arthrotomy **Medial Arthrotomy** - Incise medial capsule and retinaculum - Start at proximal end of exposure - Extend distally to tibial tubercle - **Stay medial** - do not compromise VMO insertion on patella **Patellar Eversion** - Flex knee to 90 degrees - Gently evert patella laterally - **NOTE**: More difficult than medial parapatellar due to preserved VMO - Avoid excessive force (VMO tearing risk) **If Inadequate Exposure** - Options: 1. Extend capsular incision more proximally 2. Use lamina spreaders to widen exposure 3. Convert to medial parapatellar if truly inadequate - Do NOT force patellar eversion (VMO avulsion risk) **Limited exposure is the Achilles heel of subvastus approach** (15-20% conversion rate) **Have LOW threshold to convert** if exposure inadequate: - Unable to evert patella despite proper VMO elevation - Cannot visualize posterior femoral condyles adequately - Difficulty accessing lateral compartment for resection - Patient anatomy (obese, muscular, stiff) limits access - Severe deformity requiring extensive soft tissue releases **Conversion decision**: Better to switch approaches early than damage VMO trying to force exposure **Damage risks if forcing exposure**: - **VMO avulsion** from forced patellar eversion (disrupts muscle-sparing benefit) - **Descending genicular artery injury** (compromises VMO blood/nerve supply) - **Inadequate bone resection** (leads to component malposition, instability, early failure) **When to convert**: - Make decision EARLY (during exposure phase, before bone cuts) - Do NOT persist with inadequate exposure - Converting after bone cuts is difficult (limited access for revision cuts) ### Step 5: Standard TKA Technique **Joint Exposure Assessment** - Visualize femoral condyles - Access tibial plateau - Check for bone spurs (remove to improve exposure) **Tibial Cut** - Insert tibial cutting guide - Perform proximal tibial resection - Standard extramedullary or intramedullary guide **Femoral Preparation** - Intramedullary femoral guide (standard) - Distal femoral cut - Anterior, posterior, and chamfer cuts - Sizing and rotation assessment **Balancing and Component Implantation** - Assess extension and flexion gaps - Soft tissue balancing as needed (limited releases possible) - Trial components to assess fit and tracking - Cement and implant final components **Patellar Resurfacing** - Standard technique - Ensure adequate exposure before cutting - Check tracking after trial reduction ### Step 6: Closure **Arthrotomy Closure** - Re-approximate medial capsule and retinaculum - Use #1 absorbable suture - Ensure watertight closure **VMO Positioning** - Allow VMO to fall back into anatomic position - **No sutures through VMO muscle** (it was elevated, not cut) - VMO naturally sits over medial tibia **Deep Fascia Closure** - Close fascia over VMO with 2-0 absorbable suture - Eliminate dead space **Subcutaneous and Skin** - 2-0 Vicryl in subcutaneous layer - 3-0 Monocryl or staples for skin **Drain Placement** - Consider intra-articular drain - Remove when output less than 30mL/shift Closure advantage of subvastus: VMO wasn't cut, just elevated. No need to repair muscle - it falls back into position. Fascia closure covers the dissection plane. ### Intraoperative Complications **Inadequate Exposure (Most Common)** - **Incidence**: 10-20% in early learning curve - **Causes**: - Obesity (thick soft tissues) - Muscular build (thick VMO) - Limited preoperative ROM - Patella baja - **Management**: - Extend capsular incision - Use lamina spreaders - **Convert to medial parapatellar if needed** (don't force it) **VMO Muscle Damage** - **Tearing of VMO fibers**: From excessive retraction or forced patellar eversion - **VMO avulsion from tibia**: Poor subperiosteal technique - **Prevention**: - Gentle retraction - Correct subperiosteal plane dissection - Avoid forcing patellar eversion - **Management**: - If VMO torn: repair with sutures - If extensively damaged: consider completing as medial parapatellar **VMO Nerve Injury** - **Incidence**: Less than 1% - **Cause**: Excessive dissection into VMO substance - **Result**: Denervated VMO, loss of terminal extension strength - **Prevention**: Stay in subperiosteal plane, avoid deep VMO dissection ### Early Postoperative Complications **Quadriceps Dysfunction (Paradoxical)** - Despite muscle-sparing technique, some patients have weak quadriceps - **Causes**: VMO nerve injury, muscle trauma, pain inhibition - **Prevention**: Correct technique, early mobilization - **Management**: Aggressive physical therapy **Wound Complications (Similar to Medial Parapatellar)** - Hematoma: 2-5% - Superficial infection: Less than 1% - Deep infection: Less than 1% **Patellar Maltracking** - **Lower incidence** than medial parapatellar (VMO preserved) - If occurs: May indicate excessive VMO damage or malrotation of components ### Late Complications **Extensor Lag** - **Incidence**: 2-5% (vs 5-10% medial parapatellar) - Preserved VMO reduces risk - Management: Physical therapy **Knee Stiffness** - **Incidence**: 3-5% - Manipulation under anesthesia at 6-12 weeks if severe **Component Malposition or Loosening** - No difference from medial parapatellar - Surgeon experience critical (harder to assess landmarks with limited exposure) ### Immediate Postoperative Care (0-48 hours) **Positioning and Mobilization** - Leg elevated to reduce swelling - Knee immobilizer or brace (0-2 days) - **Early mobilization** - key advantage of subvastus - Sit at bedside Day 0 evening or Day 1 - Ambulate with walker Day 1 **Pain Management** - Multimodal analgesia - **Avoid or limit femoral nerve block** (delays quad function) - Prefer adductor canal block (preserves quads) **Drain Management** - Remove when output less than 30mL/shift - Typically 24-48 hours **Physical Therapy - Accelerated Protocol** - **Straight leg raise** (SLR): - Attempt Day 1-2 (achievable 2-3 days in most) - vs 7-10 days with medial parapatellar - Quadriceps sets, ankle pumps Day 0 - CPM machine optional (controversial benefit) ### Weight-Bearing and Mobilization **Weight-Bearing** - Weight-bearing as tolerated (WBAT) from Day 1 - Walker or crutches for safety first 2-4 weeks - Progress to cane by 4-6 weeks **Range of Motion Goals** - Passive ROM to 90 degrees by Week 1 - Active ROM to 90 degrees by Week 2 - Goal: 0-110 degrees by 6 weeks ### Radiographic Follow-up **2 Weeks** - AP and lateral knee radiographs - Assess component position and alignment **6 Weeks** - Repeat films - Assess for component shift or subsidence **6 Months and 1 Year** - Long-term implant assessment - Check for radiolucencies or loosening ### Physical Therapy **Phase 1 (0-2 weeks): Early Mobilization** - Focus on achieving SLR (faster than medial parapatellar) - Gentle ROM exercises - Quadriceps strengthening (sets, SLR) - Gait training with assistive device **Phase 2 (2-6 weeks): Progressive Strengthening** - Increase ROM (goal 0-110 degrees) - Closed-chain exercises (mini-squats, leg press) - Stationary bike when ROM adequate - Wean off assistive device **Phase 3 (6-12 weeks): Functional Restoration** - Return to normal activities of daily living - Discontinue assistive devices - Sport-specific training (low-impact) ### Return to Activity **Activities of Daily Living**: 2-4 weeks **Driving**: 4-6 weeks (off narcotics, adequate control) **Sedentary Work**: 4-6 weeks **Light Labor**: 8-12 weeks **Golf/Swimming**: 12 weeks **Full Activities**: 12-16 weeks ## Exam Day Cheat Sheet ## Evidence-Based Practice ## Australian Context The subvastus approach for total knee arthroplasty represents a specialized technique employed by select Australian arthroplasty surgeons, primarily in private practice and high-volume joint centers. While the standard medial parapatellar approach remains dominant across most Australian public hospitals (representing 80-85% of primary TKAs), the subvastus technique has gained traction among surgeons seeking to optimize early functional recovery for carefully selected patients. Major Australian arthroplasty units (St Vincent's Private Hospital Melbourne, Sydney Adventist Hospital, Epworth Healthcare) report using subvastus in approximately 15-20% of primary TKA cases, reserving it for thin patients with good preoperative range of motion and minimal deformity. Australian orthopedic training programs through the Australian Orthopaedic Association (AOA) include exposure to muscle-sparing approaches during advanced arthroplasty fellowships, though the technique is not universally taught during core surgical training. The learning curve for subvastus approach is recognized as steep, with conversion rates to medial parapatellar ranging from 10-20% during the first 50 cases. Most Australian surgeons who regularly employ subvastus approach cite patient demand for "minimally invasive" or "muscle-sparing" techniques as a factor, though evidence shows functional benefits primarily in the early postoperative period (first 6-12 weeks) rather than long-term advantages. Antibiotic prophylaxis follows Therapeutic Guidelines (eTG) with cefazolin 2g IV at induction. Pain management strategies in Australia increasingly favor regional anesthesia, but surgeons using subvastus approach specifically avoid femoral nerve blocks (which delay quadriceps recovery and negate the approach's primary advantage) in favor of adductor canal blocks that preserve quadriceps function while providing analgesia. Postoperative rehabilitation protocols are accelerated compared to medial parapatellar, with physiotherapy goals of straight leg raise by day 2-3 and discharge from hospital by day 3-4 (versus day 4-5 for standard approach). Private health insurance (via providers like Bupa, Medibank) covers TKA regardless of approach, with PBS-subsidized implants available. Workers' compensation schemes (WorkCover, icare) do not differentiate between surgical approaches for reimbursement purposes.

Subvastus Approach to Knee

Subvastus Approach to Knee