MCQs-Knee recon 1
– HTO – young active patients with less than 15 of varus, less than 10 degree flexion contracture, and primarily unicompartmental changes. The lack of an ACL is NOT a contraindication to HTO.
– watch out for posterior sag in patients with PCL retaining knees – their PCL may not be so good and they may develop significant AP instability
– porous ingrowth is dependent on a few things: avoidance of micromotion; approximation of the surfaces; and size of pores (150-400 microns). The optimal pore volume or volume fraction porosity is 30-40%. Obtaining intimate bone contact and avoiding micromotion are the most important factors for bone ingrowth. Titanium has not been shown to be more conducive to bone ingrowth than cobalt chrome.
– cement failure in femoral components is caused by microfracture and fragmentation of cement
– ultimate postop knee ROM is most predicted by PRE-OP knee ROM
– for medial unicompartmental knee replacement, to maximize longevity of the prosthesis it should neither rock nor tilt as the knee is put through a range of motion. The principles of uni’s are different from total knee. It is NOT recommended to put the knee in valgus, as this can lead to deterioration of the lateral side. Slight mechanical varus is acceptable, especially with implants that rest on cortical bone. Tibial loosening is the biggest problem with uni’s, so it is important that the component be well-positioned – it should not “yawn” anteriorly with knee flexion.
– comparing simultaneous bilateral vs staged total knee replacements: the only significant difference has been duration and cost of hospitalization. There is no significant difference in P.E., ROM, infection, or component loosening.
– PCL retention supposedly improves femoral rollback in flexion.
– in rheumatoids, do their hips before knees – it is easier to rehab after the total hip.
– in patients less than 55 yrs, the 10 year survivorship is actually pretty good – comparable to older patients. They are better than those in really young though.
– reducing cement porosity improves the compressive modulus of cement (increases its strength)
– The presence of a varus alignment with a high adductor moment actually predicts a poor response to HTO.
– in aspirating TKA – there is a 25% false negative result rate – need to go by clinical history and suspicion!
– the more constrained the TKA, the higher the rate of component loosening – particularly the tibia. Thus, a hinged component would be worse than a TCIII, which would be worse than a regular TKA.
– there are four independent factors that are associated with a significantly LOWER risk of failure: PRIMARY total knee arthroplasty, rheumatoid arthritis, age over 60, and the use of metal backing for the tibial component
– for osteochondral allografting of the femoral condyle lesions – tissue matched fresh osteochondral grafts produce excellent incorporation; cryogenically preserved grafts unfortunately lose most of the chondrocytes. Non-matched fresh grafts are immunogenic and are broken down.
– when looking for osteonecrosis of the femoral condyle, look on T1 MRI for loss of the high intensity signal from the marrow fat
– patients with inflammatory arthritis should not be left with their native patella in TKA. They should be resurfaced because they will have significantly less peripatellar pain than in those who do not undergo resurfacing.
– beware trying to do any reconstruction in a patient with previous sepsis, especially pseudomonas! Do arthrodesis instead.
– external rotation of the femur is a good thing for patellar tracking
– the most common cause of failure in revision TKA are patellar malalignment, component loosening, and sepsis. The most common is extensor mechanism or patellar problems.
– 10-15 year survival of TKA is about 90%
– when doing an HTO, make sure you don’t cut the medial cortex – you’ll destabilize the thing!
– successful knee arthrodesis is most dependent on the degree of bone loss.