Gruen's Zones - Domonic Simon 6/11/2003

Thomas A. Gruen, M.S.Gregory M. McNeice, Ph.D. and Harlan C. Amstutz, MD

Clinical Orthopaedics &Related Research. (141):17-27, 1979 Jun.

Retrospective sequential radiographic evaluation of 350 consecutive patients with 454 cemented femoral stems designed for the identification and classification of their modes offailure.

Eventually analysed 301 patients with 389 THRs with 6 month to 6 year follow up.

(65 excluded due to; sepsis,loss to FU and radio lucent cement).

7 Zones were used from lateral to medial calcar via the tip.

Looseness was defined as; fractured acrylic cement and an interface gap between prosthesis-cement or cement-bone.

Sequential radiographic evaluation;

a. width and length of radiolucent zones

b. appearance of sclerotic bone reaction

c. widening of the acrylic cement fracture gap

d. additional fragmentation of cement

e. gross movement of femoral component

f. stem fracture

Failure defined as deviation from stable femoral component

4 modes of failure identified:

Ia. Pistoning;radiolucent zone between stem and acrylic. Often resulting in an acrylic fracture

Ib. Pistoning;interuption of the mechanical bond at the cement bone interface with subsequent slip. Inadequate interdigitation of cement. Produces radiolucent zone around the interface with a sclerotic reaction. Most common mode.

II. Medial midstem pivot; combined week medial calcar support and lack of distal cement support.

III Calcar pivot; hang up of proximal-medial stem and medial-lateral toggle due to lack of distal cement support.

IV Bending cantilever fatigue; loss of proximal support. Medial migration of the proximal stem and rigid fixation of the distal stem.

Results

76 out of 389 showed Radiographic evidence of looseness (19.5%) zonal distribution as shown:

            Fractured acrylic (n=17)        radiolucency at stem- cement interface (n=40)         Radiolucency at bone- cement interface (n=43)