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Press Fit Femoral Stems

- See: Total Hip Replacement Menu:
             - Insertion of Cementless Femoral Stem:
             - Radiology of Press Fit Stems:
             - Removal of Cementless Stems

- Discussion:
    - indications:
           - younger patients (less than 65 years of age w good bone stock, and absence of hemophilia, sickle cell, or renal diseases;
    - relative contra-indications:
           - not the stem of choice for patients w/ "stove pipe" type femur, previous fracture, or previous osteotomy since these patients would 
                   not be expected to achieve a tight fit which is necessary for ingrowth;
           - poor quality bone stock is more likely to undergo plastic deformation and to allow subsidence of the femoral component;
    - design considerations: 
           - collar: 
                   - Does a collar improve the immediate stability of uncemented femoral hip stems in total hip arthroplasty? A bilateral comparative cadaver study.
                   - Subsidence of collarless uncemented femoral stems in total hips replacements performed for trauma.
                   - Comparison of collared and collarless femoral components in primary uncemented total hip arthroplasty
                   - The effect of collar on aseptic loosening and proximal femoral bone resorption in hybrid total hip arthroplasty.
                   - The biomechanical effect of the collar of a femoral stem on total hip arthroplasty.

    - coating for bone ingrowth: (see bone ingrowth
    - extent of coating:
           - proximal fixation stems:
           - distal fixation stems; 
           - references: 
                    - Porous surface replacement of the hip with chamfer cylinder design.
                    - The influence of stem size and extent of porous coating on femoral bone resorption after primary cementless hip arthroplasty.
                    - The effect of stem fit on bone hypertrophy and pain relief in cementless total hip arthroplasty
    - stiffness of femoral stem:
         - prosthesis should be minimally stiff and maximally stable;
         - prosthesis should prevent migration of particles from articular surface to stem of the prosthesis;
         - minimization of stiffness of prosthesis may result in less pain in thigh;
                - methods to minimize stiffness: creating slots (clothespin design) as well as grooves have been utilized;
                - simply increasing the flexibility of the implant w/o considering the need for additional fixation is as unwise as increasing fixation w/o 
                        thought of its effect on load transfer;
         - methods of maximizing stiffness:
                - filling of the medullary canal;
                - extensive porous coating;
                - proximal filling;
         - references:
                - Radiographic analysis of a low-modulus titanium-alloy femoral total hip component. Two to six-year follow-up.
                - Total hip arthroplasty with a low-modulus porous-coated femoral component.
    - stem motion:
         - torsional loading (rather than axial) loading is more likely to result in micromotion; 
         - less than 50 microns of motion is optimal;
         - stress levels and the quality of proximal and distal fixation must be balanced so that both proximal and distal micromotions of the 
                 stem can be reduced to an acceptable level; 
         - references: Interface Micromotion of Uncemented Femoral Components from Postmortem Retrieved Total Hip Replacements

- Complications:
    - aseptic loosening (see osteolysis):
    - stress shielding;
femoral fracture;
    - thigh pain: (see
eval of painful hip)
           - upto 20% may have mild pain, 11% will have moderate pain (which limits some activities), and about 2% will have severe pain;
           - causes:
                  - motion at bone prosthesis interface (loosening);
                  - stem position:
                        - thigh pain may be more common with varus stem position (which is revealed by distal lateral cortical hypertrophy);
                  - extent of porous coating;
                  - host bone morphology;
                  - excessive stress transfer from stem to host femur;
                  - stem material (titanium has a lower modulus of elasticity than cobalt chrome):
                  - stem size and stem size mismatch;
           - management:
                  - patients should initially be managed with time, since thigh pain may resolve over the first two years following surgery;
                  - in report by Domb B, et al (2000), the authors applied lateral cortical strut grafts w/ cerclage fixation,
                          centered over the femoral stem tip;
                          - motivation for this type of treatment is that the strut may increase the rigidity of the host bone over the region of the femoral stem tip,
                                  thereby increasing the modulus mismatch;
                          - 7 patients underwent this procedure, w/ 6 of these patients obtaining good or excellent relief of symptoms;
           - references: 
                  - Cortical strut grafting for enigmatic thigh pain following total hip arthroplasty.
                  - The effect of stem fit on bone hypertrophy and pain relief in cementless total hip arthroplasty.
                  - Pain in the thigh following total hip replacement with a porous-coated anatomic prosthesis for osteoarthritis. A five-year follow-up study

Total hip replacement with cemented, uncemented, and hybrid prostheses. A comparison of clinical and radiographic results at two to four years.
Comparison of a hybrid with an uncemented total hip replacement. A retrospective matched-pair study.
The case for porous-coated hip implants. The femoral side.
Endosteal erosion in association with stable uncemented femoral components.
Uncemented total hip arthroplasty in rheumatoid arthritis diseases. A two- to six-year follow-up study.
Cemented versus cementless total hip arthroplasty. A comparative study of equivalent patient populations.
Total hip replacement without cement for non-inflammatory osteoarthrosis in patients who are less than forty-five years old.
Mechanical consequences of bone ingrowth in a hip prosthesis inserted without cement.
Failure of intraoperatively customized non-porous femoral components inserted without cement in total hip arthroplasty.
The clinical results and basic science of total hip arthroplasty with porous-coated prostheses.
Evaluation of bone ingrowth in proximally and extensively porous-coated anatomic medullary locking prostheses retrieved at autopsy.
Clinical and roentgenographic evaluation of noncemented porous-coated anatomic medullary locking (AML) and porous-coated anatomic (PCA) total hip arthroplasties.
The porous-coated anatomic total hip prosthesis, inserted without cement. Results after five to seven years in a prospective study.
Early failure of noncemented porous coated anatomic total hip arthroplasty.
Prospective study of porous-coated anatomic total hip arthroplasty.
The uncemented porous-coated anatomic total hip prosthesis. Two-year results of a prospective consecutive series.
A prospective comparison of Butel and PCA hip arthroplasty.

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