Total Knee Arthroplasty via Small-Incision Midvastus Approach
Introduction
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Total knee arthroplasty (TKA) is highly successful in managing symptomatic end-stage knee arthritis
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Traditionally performed through standard medial parapatellar arthrotomy with eversion of patella
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Benefits—Earlier return of quadriceps function and motion, improved flexion, less postoperative narcotic use, and improved cosmesis
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Safe and accurate use of small-incision midvastus approach depends on understanding of anatomy, gentle soft-tissue handling, use of mobile window through accurate retractor placement, and minimally invasive surgery instrument use
Patient Selection
Indications
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Same as those for standard TKA—Disability from knee arthritis, refractory to nonsurgical measures
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Should first try course of activity modification, anti-inflammatory medication, physical therapy, and weight reduction
Contraindications
TABLE 1
Relative Contraindications to the Small-Incision Midvastus Approach
Substantial quadriceps muscle mass in men |
Significant obesity (body mass index >40 kg/m2) |
Severe coronal plane deformity |
Flexion contracture >25° |
Passive flexion <80° |
Severe patella baja |
Significant scarring of the quadriceps mechanism |
Revision surgery |
Preoperative Imaging
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Standing AP, lateral, 45° flexed PA, Merchant view radiographs
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Interpret radiographs for deformity, bone loss, presence of patella baja, and bone quality
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For deformity, useful to anticipate appropriate distal femoral cut angle and height of tibial resection
Procedure
Patient Positioning
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Same as for standard TKA
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Use lateral support so leg sits without being held by assistant
Special Instruments
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Specialized instrumentation is critical
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Smaller cutting blocks and guides with rounded edges for smaller incisions
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Side-specific instruments and cutting guides
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Rigid saw blade with narrow body that fans out at distal tip
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Some systems have implants specifically for use with minimally invasive technique, such as short keel or modular stem tibial components and asymmetric tibial trays
Surgical Technique
Video 63.1 Mini-Midvastus Approach. Steven B. Haas, MD, MPH; Stephen Kim, MD (16 min) |
Anesthesia
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Authors prefer combined spinal/epidural anesthetic with indwelling epidural patient-controlled anesthesia for 48 hours
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Bupivacaine femoral nerve block
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Intravenous cefazolin; vancomycin for penicillin allergy
Exposure
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Exsanguinate leg with Esmarch bandage; inflate tourniquet to 250 to 300 mm Hg
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Perform medial arthrotomy from superior pole of patella to level of tibial tubercle; leave 5-mm cuff of tissue adjacent to tubercle
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Split vastus medialis obliquus (VMO) in line with its fibers at level of superior pole of patella (Figure 3)
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Initiate first centimeter of VMO muscle split sharply and finish with blunt finger dissection; prevents injury to distal innervation of vastus musculature; split is 2 to 4 cm long
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Preserve suprapatellar pouch except in severe inflammatory disease
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Extend knee and carry subperiosteal dissection around medial pretibial border, releasing meniscotibial attachments
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Retract and subluxate patella laterally, do not evert; partially excise infrapatellar fat pad
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Release tibial attachment of anterior cruciate ligament and anterior horn of lateral meniscus
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Place thin bent Hohmann retractor laterally to retract patella
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Create small synovial window over anterolateral femoral cortex to aid initial anterior femoral resection
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