SROM Hip System


- See:

- PreOperative Planning:
    - preoperative leg length:
    - acetabulum:
         - evaluation of cup position:
         - acetablar component loosening
         - use a wax pen to mark the tear drop and the superior aspect of the acetabulum, and overlie the acetabular templates to determine 
                the proper sizes;
         - cup selection:
                - deep profile cups (often used for revisions);
                - SP+6 are required for greater lateral offset;
         - center of rotation:
                - will determine the center of rotation of the femoral head;
    - femoral component:
         - draw the "lateral endosteal line" to help determine the starting point for straight entry down the medullary canal;
                - this line will help determine need for trochanteric osteotomy;
                - when a cemented femoral component has been placed in significant varus, then consider the need for an extended trochanteric 
                        osteotomy in order have adequate access to the lateral cortex (and avoid perforation);
         - restoration of neck length (and calcar):
                - neck lengths come in 36 and 42 mm;
         - trochanteric osteotomy
                - if osteotomy is required, determine where the lateral osteotomy cut will lie in relation to the proximal sleeve;

- Stem Diameters:
    - proximal stem diameter is always 5 mm wider than the distal diameter;
    - available from (9/14) to (19/24);
    - reamers:
           - straight reamers are inserted (beginning at 8 mm) and are sequentially reamed until cortical contact is achieved;
                  - reamers must be of same size or 0.5 mm larger than minor diameter size;
           - flexible reamers are used for curved femoral stems and are over-sized by 1-2 mm;

- Stem Lengths:
    - strainght stems:
           - available as standard, long, X-long, and XX-long;
           - stems are interchangable for both left and right femurs;
           - allow variable anteversion;
    - curved stems: (anterior bow);
           - available in long, X-long, and XX-long;
           - must have specific right or left stem;
           - version is pre-determined;

- Femoral Necks:
    - all neck are set at 135 deg;
    - standard necks: 30, 36 and 42 mm;
    - standard neck w/ lateral offset: 30 mm + 4 mm, 36 mm + 4 mm, and 42 mm + 8 mm;
    - calcar replacements: (21 mm)
         - CR: 36 mm
         - CR + 4 mm;
         - CR + 8 mm;

- Proximal Sleeve:
    - inner diameter refers to the proximal stem diameter;
    - outer diameter (cone size):
           - B: adds 3 mm to stem diameter;
           - D: adds 5 mm to stem diameter;
           - F: adds 7 mm to stem diamet;
           - F-oversize: adds 9 mm;
    - conical reamers:
           - conical reamers are inserted down to the marking for the neck length desired (30, 36, 42 mm) as referenced off the top of the greater 
                  trochanter;
           - hand reaming is continued until cortical contact is achieved;
           - if the top of the conical reamer is below the lesser trochanter, then use the calcar replacement neck (36 / 21 mm);
           - note that counter-clockwise reaming will disassemble the reamer;
    - conical reamer sizes:
           - 14 mm / B reamer (14 + 3 = 17 mm diameter)
           - 14 mm / D reamer (14 + 5 = 19 mm diameter)
           - 14 mm / F reamer (14 + 7 = 21 mm diameter)
           - 16 mm / B reamer (16 + 3 = 19 mm diameter)
           - 16 mm / D reamer (16 + 5 = 21 mm diameter)
           - 16 mm / F reamer (16 + 7 = 23 mm diameter)
           - 18 mm / B reamer (18 + 3 = 21 mm diameter)
           - 18 mm / D reamer (18 + 5 = 23 mm diameter)
           - 18 mm / F reamer (18 + 7 = 25 mm diameter)
           - 20 mm / B                  23 mm
           - 20 mm / D                  25 mm
           - 20 mm / F                  27 mm
           - 22 mm / B                  25 mm
           - 22 mm / D                  27 mm
           - 22 mm / F                  29 mm
           - 24 mm / B                  27 mm
           - 24 mm / D                  29 mm
           - 24 mm / F                  31 mm

- Femoral Head / Lateral Offset:
    - available in +0, +6, +12 mm;

- Calcar Miller:
    - determine the most optimal direction for the calcar miller (usually miller);
    - miller jig sizes range from 2 to 9 and are based upon the conical reamer size;
    - insert the miller frame down the canal to the level of the desired femoral neck cut, as referenced off the tip of the greater trochanter;
    - position the miller ring over the region with the best bone (usual medial);
    - miller cutter diameter is the same size as the original proximal stem size (14 to 24 mm);
    - partially withdraw the miller frame, insert the miller cutter down to the pilot hole;
    - lower the miller frame and begin cutting unitl cortical bone is reached;
    - the appropriate triangle size is read from markings at the top of the sleeve;
     - triangle size: (medial extension of the triangle)
           - small: adds 9.5 mm from the cone outer diameter;
           - large: adds 13.5 mm from the cone OD;
           - XX-large: adds 17.5 mm from the cone OD;

- Considerations for Trial Stem Insertion:
    - straight stems:
         - appropriately sized trial sleeve is pressed into place;
         - appropriately sized sleeve introducer (14 to 24 mm) is attached to sleeve introducer handle;
                - subsequently screw on the distal pilot shaft (5 mm less than sleeve introducer);
         - the smooth portion of the introducer should face the greater trochanter, so that the slots in the sleeve fit into the stem;
         - once stem is seated, the version can be set (each click is 10 deg);
                - this version can be marked on the femoral neck using cautery;
    - bowed stems: the trial sleeve and stem are inserted at the same time;
         - version is pre-determined with bowed stems;

- Considerations for Prosthetic Stem Insertion:
    - straight stems:
         - seat the proximal sleeve:
                - appropriately sized prosthetic sleeve is pressed into place;
                - appropriately sized sleeve introducer (14 to 24 mm) is attached to sleeve introducer handle;
                       - screw on the distal pilot shaft (5 mm less than sleeve introducer);
                - insert the assembly into the sleeve (smooth portion facing greater trochanter) and tap the assembly until the sleeve is fully seated;
         - straight stem insertion:
                - the appropriately sized stem (and neck length) are carefully inserted through the proximal sleeve w/ care to maintain the same 
                       version that was achieved w/ the trial reduction;
                       - the "medial midline" of the prosthesis is aligned with the previously made mark on the femoral stem;
                - use the stem driver to impact the stem down into the proximal sleeve;
    - bowed stems: the trial sleeve and stem are inserted at the same time;
         - version is pre-determined with bowed stems

- Case Examples:
   



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, May 17, 2012 10:51 am