TIS

Chapter 16
High Tibial Osteotomy / Total Knee Replacement


  1. Introduction
  2. HTO or TVO - high tibial osteotomy/tibial varus or valgus osteotomy
    Technique:

    From: Insall: Surgery of the Knee. Churchill Livingstone, 1984, p. 568


  3. Total Knee Replacement

    Indications:
    * young age is a relative contraindication in any joint replacement procedure


    Classifications/materials:
    1. Resurfacing (unconstrained) : unicondylar, unicompartmental, bicondylar or total condylar. Bicondylar and total condylar replacement can be cruciate-retaining or cruciate-existing.
      • Materials: femoral component: cobalt-chrome alloy
        tibial component: high-density polyethylene
        patellar component: polyethylene
    2. Constrained: fixed-axis metal hinge or somewhat loose (semiconstrained) with some rotation and varus/valgus. These are generally used only with severe instability


    Fixation:

    Biomechanical considerations:
    1. Compressive loads
      • like other plastics, the tibial component deforms under relatively low stresses; therefore, conformity must be maximum to avoid exceeding the elastic limit of the polyethylene
      • goal is to transmit forces to the bone over as large an area as possible to prevent focal loading
      • maintaining as much tibia as possible preserves critical cancellous bone
      • a more rigid material spreads loads out over a larger area
      • wear can be adhesive, abrasive, and fatigue

    2. AP stability
      • constrained prosthesis implies complete conformity between femoral and tibial components in the sagittal plane, or a hinged prosthesis is used; this does not provide for a normal changing center of rotation, and creates a conflict between the cruciates and the prosthesis resulting in decreased ROM, posterior tilting of the tibial component and necessary rotation is prevented

      • designs supposing the PCL to be intact tend to have less conformity, relying on the retained ligament to prevent posterior subluxation; most designs assume no ACL

      • in many cases, the cruciates are absent or are not able to be preserved; therefore partial conformity of the femoral and tibial surfaces is utilized by the design of the component creating a compressive force which "limits" undesirable motion; or by adding a guiding or stabilizing mechanism in the intercondylar area

      • nonconstrained prosthesis implies that the tibial plateaus are flat and the cruciates carry almost all of the forces; accuracy is vital; however, total reliance on the cruciates will eventually stress them excessively

    3. Varus-valgus stability
      • end result depends on gait and alignment of the prosthesis. If force is excessive, high compressive forces result under the force, and tensile stress occurs on the opposite side

      • prosthetic components which decrease varus/valgus tilting are a large surface area, a central post or two separate posts, and a rigid connection between the medial and lateral sides

      Complications of TKR:
      • loosening: bone ingrowth negatively affected by NSAIDS and surgical oopherectomy
      • infection: 0.7% incidence/1000; superficial clear with removing prosthesis, deep clear best with prosthesis removal
      • peroneal palsy: 0.2%/1000 (CPM?)
      • patellar subluxation, dislocation, fracture
      • wear and tissue reaction: ~10% develop effusion, pain or decreased ROM at average 4.5 years; polyethylene wear greatest on medial tibial plateau; many complications on the medial side: tibial component may sink into the top of the tibia
      • osteolysis
      • fractures
      • instability
      • thrombophlebitis

      Physical therapy intervention:
      • ROM: CPM through 0-30 degrees with gradual increases (expect no more than 105-115 degrees flexion)
      • Ambulation: WBAT
      • Strength: Q sets
        • SLR
        • various open & closed chain activities
        • bicycle/restorator
        • kinetron

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