import { ComparisonTable, ContentSection, EvidenceCard, ExamCheatSheet, ExamPearl, ExamWarning, InfoCard, InfoCardGrid, MedicalImage, MnemonicCard, OnePagerSummary, SafetyAlert, Tab, Tabs, Timeline, TimelineItem, VivaScenario, VivaScenarioSection } from '@/components/mdx' {/* SECTION 1: ONE-PAGER SUMMARY */} {/* SECTION 2: EXAM WARNING */} **The skin incision is anterior midline**, not medial. This preserves blood supply to skin flaps from both medial and lateral geniculate vessels. Medial skin incisions risk lateral flap necrosis. **The arthrotomy is medial parapatellar** - approximately 1cm medial to the patellar border. This goes through capsule and VMO insertion. Too lateral risks patellar maltracking; too medial makes closure difficult. **Never over-evert the patella**. Excessive lateral eversion can avulse the patellar tendon insertion. In stiff knees, perform quadriceps snip or tibial tubercle osteotomy rather than force eversion. The **infrapatellar branch of saphenous nerve (IPBSN)** crosses the incision and is always sacrificed. Counsel patients about anterolateral knee numbness postoperatively. {/* SECTION 3: MNEMONICS */} 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. {/* SECTION 4: OVERVIEW */} 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) The medial parapatellar approach is preferred over lateral approaches because: (1) the VMO insertion is weaker than the vastus lateralis, making medial elevation easier; (2) most patients have valgus alignment, making medial release advantageous; (3) the patella naturally everts laterally when the knee is flexed. **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 {/* SECTION 5: ANATOMY */} **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 The patella receives most of its blood supply through the **inferior pole** via the fat pad. Aggressive fat pad debridement during TKA can compromise patellar blood supply and lead to patellar necrosis or fracture. Preserve fat pad attachments when possible. **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 {/* SECTION 6: PREOPERATIVE PLANNING */} {/* REMOVED: 4-flow-chart.png */} **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) **Multiple longitudinal scars**: Use the most lateral scar to preserve medial blood supply. Minimum 6cm distance between parallel incisions. **Transverse scars**: Can cross perpendicular scars but risk skin necrosis at intersection. **Flexion less than 70 degrees**: Plan for extensile techniques (quadriceps snip, V-Y turndown, or tibial tubercle osteotomy). Do NOT force patellar eversion in a stiff knee. {/* SECTION 7: INTERNERVOUS PLANE */} **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. **Definition**: A surgical plane between two muscles that are supplied by different nerves. This allows separation without denervating either muscle. **Example**: Posterior hip approach (between gluteus medius/maximus [superior gluteal] and short external rotators [L5/S1 plexus]) **No internervous plane**: The VMO is incised directly through its substance. This is necessary because the extensor mechanism is a continuous structure. **Repair required**: The VMO must be repaired during closure to restore extensor mechanism function. **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 When asked about internervous planes in the medial parapatellar approach, state clearly: "The medial parapatellar approach does NOT utilize a true internervous plane. The entire quadriceps mechanism is femoral nerve-innervated. The approach works by incising through the VMO insertion on the medial patella, which must be carefully repaired at closure to prevent extensor lag and patellar maltracking." **Contrast with alternative approaches:** | Approach | Internervous Plane Status | Nerve Considerations | |----------|---------------------------|---------------------| | Medial parapatellar | NO internervous plane | Transects VMO (femoral nerve) | | Subvastus | NO true plane | Works deep to VMO without transecting | | Midvastus | NO true plane | Splits VM fibers (still femoral nerve) | | Lateral parapatellar | NO true plane | Transects VL (femoral nerve) | {/* SECTION 8: POSITIONING AND PATIENT SETUP */} **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 **Supine, hip bump, thigh tourniquet, free drape.** Foot of bed drops for flexion. Surgeon stands laterally, assistant medially. C-arm accessible from contralateral side. **Alternatives to assistant**: Leg holder maintains knee position during bone cuts. Allows surgeon to work with both hands. Position can be changed during procedure. **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 {/* SECTION 9: SURGICAL TECHNIQUE */} {/* REMOVED: 1-mouse-surgical-proceduresa-an-incision-was-made-in.png */} ### Patient Positioning and Preparation **Position:** - Supine on standard operating table - Bump under ipsilateral hip (optional, improves access) - Thigh tourniquet applied high and snug - Foot of bed dropped or leg holder used **Setup:** - Ensure full ROM possible - hip flexion, knee flexion to 130 degrees - Lateral post at distal thigh for valgus stress - Adequate padding at thigh tourniquet - Both arms tucked or on arm boards Patient supine, bump under hip if needed. Apply thigh tourniquet. Ensure full knee ROM available with foot of bed down or leg holder. Prepare entire leg from mid-thigh to ankle. Include foot in field for alignment checks. Impervious stockinette over foot, adhesive drapes to isolate leg. Ensure free mobility of knee. Elevate leg 60 seconds OR apply Esmarch bandage. Inflate tourniquet to 300mmHg (or 100mmHg over systolic). Mark incision, confirm full ROM, check tourniquet pressure, time-out complete. Tourniquet use in TKA is controversial. **Benefits**: Better visualization, cement pressurization. **Risks**: Increased pain, quadriceps dysfunction. Most surgeons use tourniquet for cementing only. Inflate after exsanguination, deflate after cement cured and closure begun. ### Skin Incision **Landmarks:** - Superior: 5cm above superior pole of patella - Course: Anterior midline over patella and patellar tendon - Inferior: End at level of tibial tubercle (or 1cm medial to tubercle) - Length: 15-20cm (shorter for minimally invasive TKA) **Technique:** 1. Mark incision with knee extended - anterior midline 2. Incise skin and subcutaneous tissue with knife 3. Achieve hemostasis of skin edges with cautery 4. Identify patellar margins by palpation 5. Deepen through prepatellar bursa to expose anterior capsule If prior scars exist, use the most **lateral** incision to preserve medial blood supply. If scars are more than 6cm apart, you may use a more optimal line. If scars are transverse, cross at 90 degrees to minimize skin flap compromise. **Skin flap management:** - Create full-thickness flaps (skin and subcutaneous fat together) - Minimize undermining - only as needed for exposure - Handle with atraumatic technique - Keep flaps moist with saline-soaked gauze during procedure The anterior midline skin incision preserves blood supply from both medial and lateral geniculate vessels, ensuring skin flap viability. ### Medial Parapatellar Arthrotomy **Key principle:** The arthrotomy is **medial parapatellar** - approximately 1cm medial to the patellar border. **Step-by-step technique:** Start **1cm medial to patella** at midpoint of patella height. Extend superiorly through VMO fibers, staying 1cm medial to patella edge. Continue into quadriceps tendon (medial 1/3 to 1/2 of tendon). Extend incision inferiorly, curving slightly medially to end 1cm medial to tibial tubercle at level of joint line. This protects patellar tendon insertion. Complete arthrotomy through joint capsule - full thickness. Enter joint, noting any synovial fluid, loose bodies, or pathology. With knee extended, elevate medial soft tissues subperiosteally off proximal tibia. Use Cobb elevator. Take 5-10mm sleeve of periosteum, capsule, and MCL as one layer. Preserve PCL insertion posteriorly. Partially excise infrapatellar fat pad for visualization. **Preserve fat pad attachments to inferior pole of patella** to maintain patellar blood supply. The VMO fibers run at 50-55 degrees to the long axis of the femur, inserting on the superomedial patella. Your arthrotomy cuts across these fibers. During closure, repair VMO with sutures in a pants-over-vest fashion to recreate this oblique pull, critical for patellar tracking. **Subperiosteal elevation landmarks:** - Medially: Elevate 2-3cm medial to medial femoral and tibial joint lines - Anteriorly: Elevate tibial periosteum to allow tibial subluxation - Posteriorly: Preserve PCL insertion on tibia (if retaining PCL for CR TKA) During elevation, the **inferior geniculate artery** branches will be encountered and should be cauterized. ### Patellar Eversion and Exposure **Technique:** 1. Flex knee to 90 degrees 2. Retract patella laterally with hand or retractor 3. Apply gentle traction to evert patella 4. Hook retractor under lateral patella to maintain eversion 5. Subluxate tibia anteriorly for full exposure If the patella will not evert easily, **DO NOT FORCE IT**. Excessive force can avulse the patellar tendon insertion, a catastrophic complication. Instead, perform one of the following extensile techniques: - **Quadriceps snip** (45-degree oblique cut in VL) - **V-Y quadriceps turndown** (for severe stiffness) - **Tibial tubercle osteotomy** (preserves extensor continuity) **Exposure optimization:** - Place blunt Hohmann retractors medially and laterally at joint level - Use narrow retractors posteriorly for femoral cuts (protect popliteal vessels) - Lamina spreaders or bone levers to hold tibia anteriorly - Sequential flexion and extension for different bone cuts **Signs of adequate exposure:** - Can see medial and lateral gutters clearly - Can deliver posterior femoral condyles anteriorly - Can subluxate tibia anteriorly with knee flexed - Can externally rotate tibia to access medial compartment The goal is a "box" view - rectangular exposure of joint with clear sight lines to anterior, posterior, medial, and lateral aspects. ### Closure Technique **Crucial principle:** The extensor mechanism must be repaired with appropriate tension to prevent extensor lag. Ensure trial components or final implants provide stable, balanced knee. Patella tracked centrally. No tilt or subluxation. Full ROM achieved. Deflate tourniquet (if used) after cement cured or implants stable. Achieve hemostasis with cautery. Avoid excessive cautery near nerves. Close medial capsule and retinaculum with interrupted or running absorbable suture (0 or 1 Vicryl). Start inferiorly at tibial level, work superiorly. Overlap medial structures to advance VMO distally (imbrication). Repair VMO insertion to patella in **pants-over-vest** fashion - overlap medial VMO edge over lateral capsule by 5-10mm. Use interrupted figure-of-8 sutures. This recreates oblique VMO pull and prevents patellar maltracking. Close proximal quadriceps tendon medial split with running or interrupted suture. Ensure tension recreates extensor lag-free extension. Close subcutaneous fat with 2-0 Vicryl in layers to eliminate dead space. Irrigate thoroughly before final closure. Close skin with subcuticular 3-0 Monocryl or staples. Apply sterile dressing and compressive wrap. The **pants-over-vest closure** advances the medial VMO and retinaculum distally over the lateral capsule by 5-10mm. This recreates the normal VMO oblique vector (50-55 degrees) and prevents lateral patellar maltracking. Essential for preventing anterior knee pain and patellofemoral problems postoperatively. **Final checks before closure:** - Patella tracks centrally through full ROM (no tilt or J-sign) - Full passive extension achieved (no extensor lag) - Flexion to at least 110-120 degrees - Knee stable in extension and flexion These checks ensure proper closure tension and implant position, critical for successful outcome. {/* SECTION 8: EXTENSILE TECHNIQUES */} 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 {/* SECTION 9: COMPLICATIONS */} **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 The most important principle to prevent patellar tendon avulsion: **If the patella will not evert easily with knee flexed and gentle traction, perform an extensile technique.** Never apply excessive force. A quadriceps snip takes 2 minutes and heals reliably; a patellar tendon avulsion is a career-threatening complication for the patient. {/* SECTION 10: EVIDENCE BASE */} {/* SECTION 11: VIVA SCENARIOS */} {/* SECTION 12: MCQ PRACTICE POINTS */} **Q: Why is the skin incision for medial parapatellar approach placed in the anterior midline rather than medially?** A: **To preserve blood supply to skin flaps from both medial and lateral geniculate vessels.** A medial skin incision creates a lateral skin flap with tenuous blood supply, risking skin necrosis. **Q: What nerve is invariably sacrificed during the medial parapatellar approach, and what is the clinical consequence?** A: The **infrapatellar branch of the saphenous nerve (IPBSN)** is sacrificed as it crosses the anterior incision. This causes **anterolateral knee numbness** in 100% of patients, which is usually well-tolerated but must be discussed during consent. **Q: How far medial to the patellar border should the arthrotomy be made in the medial parapatellar approach?** A: Approximately **1cm medial to the patellar border**. Too lateral makes closure difficult and risks patellar maltracking; too medial makes the flap creation and exposure difficult. **Q: What is the first-line extensile technique when the patella cannot be everted safely during TKA?** A: **Quadriceps snip** - a 2-4cm oblique cut at 45 degrees laterally through the vastus lateralis at the junction of medial and middle thirds of the quadriceps tendon. It is simple, provides 20-30% additional exposure, and heals reliably. **Q: What is the pants-over-vest closure technique and why is it important?** A: The **pants-over-vest technique** advances the medial VMO and capsular edge distally and overlaps it over the lateral capsule by 5-10mm. This recreates the normal VMO oblique vector (50-55 degrees) and prevents lateral patellar maltracking. **Q: What is the primary blood supply to the patella and why is this clinically important?** A: The patella receives most of its blood supply from the **inferior pole via the infrapatellar fat pad**. This is why aggressive fat pad debridement during TKA can compromise patellar blood supply, leading to patellar necrosis or fracture. Preserve fat pad attachments to the inferior pole. {/* SECTION 13: AUSTRALIAN CONTEXT */} **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) For Orthopaedic Operative Surgery station, you must be able to describe the medial parapatellar approach in detail: patient positioning, skin incision (anterior midline), arthrotomy location (1cm medial to patella), structures at risk (IPBSN, patellar tendon, inferior geniculate vessels), and closure technique (pants-over-vest). Know the extensile techniques (quadriceps snip, V-Y turndown, TTO) and when to use each. {/* SECTION 14: EXAM CHEAT SHEET */}

Medial Parapatellar Approach to the Knee

Medial Parapatellar Approach to the Knee