Duke Orthopaedics
Wheeless' Textbook of Orthopaedics

Screw Fixation of Acetabular Components

- See: Acetabular Component Menu 

- Discussion:
    - it is controversial as to whether screws are necessary in THR, and their are relative advantages and disadvantages;
    - cups should be designed with only 2-3 holes so as to maximize the porous coating surface and to minimize conduit for osteolysis;
    - acetabular cup insertion: 
    - advantages of screw insertion:
          - theoretically, screw fixation can close any gap created by non congrous reaming;
          - prevents the loss of compressive stresses and resultant shear stresses;
          - may be indicated in osteoporotic bone (when insertion of over-sized components may not be wise) and when additional fixation is required;
          - screw insertion is also indicated in situations in which there is insufficient bony coverage; 
     - biomechanical considerations: (design of components)
          - references:
                 - Micromotion of cementless hemispherical acetabular components. Does press-fit need adjunctive screw fixation?
                 - The relation between micromotion and screw fixation in acetabular cup.
                 - The number of screws, bone quality, and friction coefficient affect acetabular cup stability
                 - Cementless acetabular fixation with and without screws: analysis of stability and migration.

     - controversies: Do acetabular screws promote osteolysis?
          - although screws may provide excellent initial fixation, later they may be sources of fretting, which could produce wear debris, and provide a conduit
                  for migration of the polyethylene debris;
                  - inorder to reduce the chance of osteolysis some surgeons insert the least number of screws possible inorder to achieve solid fixation;
          - while screws may provide a conduit for wear debris, unfilled screw-holes may also provide access for wear debris from ultra-high
                  molecular weight polyethylene liner to area behind ingrowth cup;
                  - ultra-high molecular weight polyethylene may cold-flow (creep) into these holes, resulting in early failure of the polyethylene liner;
          - hence, it remains unclear as to whether screws strongly influence the formation of osteolysis in acetabular components which contain screw holes;
                  - Dorr et al 1998 and by Latimer 1996, there is a paucity of evidence to support notion that screw fixation leads to osteolysis;
          - certainly, if a screw does not achieve a rigid bite it should be removed - due to the risk of osteolysis; 

- Radiographic Evaluation of Screw Position:
      - Judet views;
      - references:
             - Radiographic Evaluation of Screw Position in Revision Total Hip Arthroplasty

- Screw Placement Considerations: 
     - main issue is to avoid vascular injuries
     - note that a relatively retroverted, vertically inserted cup will be at most risk for neurovascular injury;
     - hence, an optimally anteverted and positioned acetabular component will have the least risk of injury;
     - when in question, screws aimed just anterior to the sciatic notch, will find safe passage in strong bone;
     - quadrant system:
            - based on line from ASIS through center of acetabulum
            - safe quadrant is defined by two lines from the anterior-inferior iliac spine through the center of the acetabulum and posterior by a line from the sciatic notch
                    to the center of the acetabulum;
            - screws placed thru posterosuperior & posteroinferior quadrants do not emerge within the pelvis;
            - posterosuperior quadrant is the safest;
                    - in posterosuperior quad, screws > 25 mm frequently are placed thru strong bone in this area (bone around sciatic notch is especially strong); 
                    - usually do not need  screws greater than 35 mm long are placed in the posterosuperior quadrant 
                    - screws may pass into sciatic notch and endanger sciatic nerve and superior gluteal vessels;
                    - protect sciatic nerve durig placement of screws, w/ finger along sciatic notch to prevent penetration of drill or screw; 
                    - fixation of screws placed posterosuperiorly may be achieved without drilling through the second cortex, bicortical fixation is usually unnecessary;
                    - with osteoporotic bone, firm fixation of screws placed superiorly often requires that the screws reach proximally enough to contact both cortices;
                    - avoid bicortical screw placement with patients on anticoagulants;
                              - Retroperitoneal hematoma with bone resorption around the acetabular component after total hip arthroplasty: a case report and review of the literature

            - posteroinferior quadrant:
                    - in posteroinferior quad, screws are rarely longer than 20-25 mm;
                    - need to ensure that screw does not impale sciatic nerve
                    - ref: Does ischial screw fixation improve mechanical stability in revision total hip arthroplasty?
            - anterior-superior quadrant:
                    - external iliac vein is most at risk w/ anterosuperior screws, but the iliac artery may be damaged as well; 
                             - located within 7 mm of the anterior column of the pelvis at the anterior inferior iliac spine and within 4 mm at the acetabular dome;
                    -  external iliac artery: within 10 mm of the bone at the anterior inferior iliac spine and within 7 mm at the acetabular dome
                    - references:
                          - Iliopsoas Tendonitis due to the Protrusion of an Acetabular Component Fixation Screw After Total Hip Arthroplasty.
                          - Screw-augmented fixation of acetabular components. A mechanical model to determine optimal screw placement.

            - anterior-inferior quadrant::
                    - obturator artery is most at risk with anteroinferior screws;
                    - screws may injure obturator nerve, artery, and vein; 
                    - quadrilateral surface: interposition of the obturator internus muscle between the obturator vessels;

- Other Considerations:
         - if drill holes are placed eccentrically, then screw insertion may lift cup up out of the bony bed;
         - screw heads left pround wont allow liner to be fully seated 

- Complications:
      - vascular injuries:
            - most common injuries include: external iliac artery, common femoral artery, external iliac vein;
            - occurs more commonly in females and in the left hip;
            - references:
                   - Vascular injury during total hip arthroplasty: the anatomy of the acetabulum
                   - External iliac vein compression and thrombosis by a migrated acetabular screw following total hip arthroplasty
                   - Retroperitoneal hematoma with bone resorption around the acetabular component after total hip arthroplasty: a case report and review of the literature
                   - Current overview of neurovascular structures in hip arthroplasty: anatomy, preoperative evaluation, approaches, and operative techniques to avoid complications.
                   - Internal iliac artery injury and total hip arthroplasty: discovery after 10 years.
                   - Evaluation of intra-pelvic screw position prior to revision total arthroplasty--a report of 2 cases.
                   - THA With Acetabular Fixation: An Unexpected Complication
                   - An unusual cause of Grey Turner's sign.
            - visceral injuries:
                   - references:
                           - Penetrating bladder injury caused by a medially placed acetabular screw
                           - Late small intestine perforation after cementless total hip arthroplasty.

            - references:
                   - Neurovascular Injuries in Acetabular Reconstruction Cage Surgery. An Anatomical Study. 
                   - L5 Radiculopathy Secondary to Intrapelvic Placement of Acetabular Cup Fixation Screw


Structures at risk from medially placed acetabular screws

Acetabular anatomy and transacetabular screw fixation at the high hip center
Safe Zone for Transacetabular Screw Fixation in Prosthetic Acetabular Reconstruction of High Developmental Dysplasia of the Hip.

The relationship of the intrapelvic vasculature to the acetabulum. Implications in screw-fixation acetabular components.

Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty

Screw Augmentation: the gold standard for cementless cup fixation

The relation between micromotion and screw fixation in acetabular cup

[The anatomical study of safe zones of the screw fixations in acetabular revision surgery].

Anatomic Assessment of the Acetabular Fossa for Screw Fixation in Acetabular Fracture 

Current Overview of Neurovascular Structures in Hip Arthroplasty: Anatomy, Preoperative Evaluation, Approaches, and Operative Techniques to Avoid Complications.

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

Last updated by Data Trace Staff on Friday, January 30, 2015 4:28 pm

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