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Revision TKR: PreOperative Considerations

                                                                                                - Assistance provided by Michael Berend MD.
- Work Up of the Painful TKR:
     - identify etiology of failure
     - determine implant type and sizing
     - recognize bone defects & bone graft
     - availability of implants required
     - expectations surgeon and patient
     - medical condition and rehab potential
     - identify reconstructive goals

- Surgical Considerations:
     - patellar component:
           - if the patellar component does not appear to be causing symptoms, and if it appears to be well fixed at surgery, consider leaving it in place;
     - femoral component:
           - determine whether the joint line has been elevated (see consequences of joint line elevation);
                 - on average the joint line is 12-16 mm above the fibula, 48-54mm below the adductor tubercle, and 25mm below the medial and lateral epicondyles;
                         - these distances vary from person to person with shorter people tending to be at the lower end of the above given ranges;
                 - this can be measured from adductor tubercle to the joint line (and compared to the opposite knee) or can be measured from the tip of the
                                   fibular head to the joint line (and compared to the opposite knee);
                         - films of the native contralateral knee or of the ipsilateral knee prior to TKA can be used to give exact measurements;
                 - in many cases, the joint line is 2 finger breadth above the tibial tubercle;
           - proximal placement of the revision femoral component moves the joint line proximally, and the kinematics of knee are significantly distorted;
                 - see: malposition of the joint line:
                 - this also results in iatrogenic patella baja w/ inefficient quad mechanism and possible impingement of patella on prosthetic tibial spine;
                 - it is therefore important that revision femoral component be seated distally enough to come close to restoring original level of knee joint line;
     - evaluation and management of bone defects
     - joint line position
     - revision for stiff total knee arthroplasty (Christensen, Vail, unpublished data 1998)
           - 13 stiff and painful TKAs (range of motion less than 70 degrees) were revised with a posterior stabilized condylar prosthesis and evaluated after
                 an average of 12.3 months  (range, 2-25 months);
           - on average, the range of motion increased from 42.1 degrees pre-operatively to 85.2 degrees post-operatively;
           - the mean flexion contracture went from 13.8 degrees to 2.9 degrees;
           - 5 of 13 revisions  required a quadriceps snip for exposure;
           - no quadriceps turndowns or tibial tubercle osteotomies were needed;
           - 4 of 13 patients required closed manipulation in the first month following revision surgery.
           - other complications included persistent stiffness, patella infera, and 2 minor wound problems.  
           - all patients had improvement in pain and were satisfied;
     - liner exchange and lysis of adhesions:

- Selection of Implants:
     - implants will be PCL sacrificing w/ medullary stems;
     - be prepared to add wedges to defects;
     - revision femoral component:
          - most stems will have a fixed distal femoral angulation (usually 7 deg);
          - most revision systems will have the femoral cuts based off of the femoral medullary stem;
     - medullary stems:
          - addition of a stem to the component generally is desirable in all techniques used for bone defects;
          - typically used if greater than 50 % of the distal femur or proximal tibia required grafting or if there is a peripheral defect requiring a block, wedge, or graft;
          - stem transfers up to 30% of force from bone subtending component to point more proximally on the femur and more distally on tibia;
          - typically a 150 mm stem is required, but in some cases a 200 mm stem is needed;
          - as noted by Haas SB, et al (1995), cement should be applied to the medullary surfaces but usually should not be applied to the medullary stems;
                 - press fit stems remove less bone than cemented stems and are easier to remove should infection occur;
                 - cementing stems causes stress shielding of the metaphysis and makes the subsequent revision more difficult;
          - cement is only used if press fit is not possible;
          - these situations may include severe osteoporosis and poor bone quality where allografting may be needed;
          - other situations where cement is used is to improve rotational stability;
          - when using cement, a distal cement plug is suggested;
          - stem lengths required for press fit are usually at least 100 mm for the tibia and 100-150mm for the femur;
          - reaming should cease once firm resistance is encountered;
                 - it is not necessary to have direct cortical contact, inorder to avoid excessive bone loss;
                 - generally, stem diameter will be the same size as the reaming diameter;
                 - once one has reached the desired stem diameter, a sleeve of that same diameter can be placed on IM rod and tibial and femoral preparation can be performed using the appropriate guides

Revision Total Knee Arthroplasty with Use of Modular Components with Stems Inserted without Cement.

Insall Award paper. Why are total knee arthroplasties failing today?

Preoperative planning for revision total knee arthroplasty:avoiding chaos.