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Radiology of Press Fit Femoral Stems

- See:
       - Post Op X-rays for THR:
       - Press Femoral Stems:

- Normal Adaptive Changes:
    - proximally coated femoral stems should show fusiform cortical hypertrophy along the coated portions of the stem and absence of radiolucent lines;
    - distally radiolucent lines will surround the uncoated portion of the stem;
    - densification & bidging of bone:
          - densification & bidging of bone between cortex & porous ingrowth surfaces suggests bone ingrowth fixation (esp at border between 
                 the coated and the uncoated portions);
          - bone proximal to these areas may atrophy, presumably because it is stress shielded;
    - spot welds:
          - cancellous hypertrophy which arises from trabeculae from the cortex to the porous coated surface or to the distal aspect of the 
                 porous coating;

- Stress Shielding:

- Radiolucent Interval:
    - development of radiolucent interval around prosthesis suggests a fibrous interface between metal and bone;
    - if this lucent interval is seen of ingrowth portion of prosthesis it suggests lack of ingrowth;
    - divergent radiolucent lines in area of ingrowth indicate loosening;
    - a press fit stem surrounded by fibrous ingrowth may be considered stable, if there is no evidence of subsidence;

- Reactive Sclerotic Line:
    - if reactive sclerotic line is seen parallel to metal surface, fixation is probably fibrous rather than bony ingrowth;
    - sclerotic pedicle of bone distal to stem tip is = lack of ingrowth;
    - radiographic confirmation of lack of bone ingrowth exists when prosthesis either has subsided measurably or is noted to have divergent 
          sclerotic lines surrounding the stem;

- Pedistal Formation (Hypertrophy of Distal Tip):
    - hypertrophy of bone near distal tip of component, although not directly indicative of loose component, certainly suggests an abnormal stress
          concentration and may represent a stress shielding of proximal portion of femur;
    - postoperative x-rays that demonstrates subsidence, endosteal pedestal formation (bridging bone) at tip of prosthesis, & lucent interval along medial
          border of stem, are all signs of non cemented component that has not achieved bony ingrowth stabilization;

- Settling of Stem:
    - settling of stem in canal & cortical hypertrophy occur distally on the medial aspect of the tip of the stem.
    - technetium 99m bone scan shows increased uptake around stem on right side consistent with loosening of femoral component;
    - radionuclide scanning is quite helpful in evaluation of painful THR because it is sensitive but nonspecific;
           - although bone scans may help, many noncemented THR, esp long stems, may show some increase in activity;
           - w/ lack of ingrowth, bone scan would show modest uptake around loose femoral component, however, mild uptake can be expected 
                   at the tip of stable components;

- Bone Scan for THR:
    - although bone scans may help, many noncemented THR, esp long stems, may show some increase in activity

Roentgenographic assessment of the biologic fixation of porous-surfaced femoral components