DISLOCATION OF TOTAL HIP PROSTHESES*

Transcription

1 VOL. 115, No. 3 DISLOCATION OF TOTAL HIP PROSTHESES* API EARANCE ON FRONTAL ROENTGENOGRAMS By RICHARI) H. DAFFNER, M.D.,f JOHN A. GEHWEILER, M.l).,f JOHN OLSON, M.D.,f JAMES W. WILSON, PH.1)., M.l)., and TERRENCE S. CARDEN, M.D4 T OTAL hip replacement for badly diseased hip joints has become a well-established mode of therapy in the past decade. Through the efforts of Charnley, McKee, Watson-Farrar, Muller, Ring and others, 8 the techniques and component materials have been refined to provide a well-functioning hip with minimal complications. DURHAM, NORTH CAROLINA The roentgen appearance of these devices has been described by Angell and Watts.2 The purpose of this communication is to describe the roentgen appearance of the dislocated prosthesis on an teroposterior roentgenograms when such dislocation may not be grossly apparent. FIG.. (A) McKee-Farrar prosthesis, normal position. Note the relationship of the lip of the cup to the femoral head-equidistant on either side. (B) McKee-F arrar prosthesis on a dried pelvis. Lines drawn along axis of each acetabular stud meet at the geometric center of the femoral head. *From the Departments of Radiolog),t and Patho1ogy, Duke University Medical center, Durham, North Carolina. 555

2 556 Daffner, Gehweiler, Olson, Wilson and Carden JULY, 1972 FiG. 2. (A and B) Dislocated McKee-Farrar prosthesis on a dried pelvis. The lines do not point to the geometric center of the femoral head. In addition, in A, too much of the femoral head is visible. DISLOCATED MCKEE-FARRAR PROSTHESIS (FLOATING MINE SIGN) The McKee-Farrar prosthesis (Fig. ul) is an all metal device which is distinguished by its studded acetabular component. In this respect it resembles the floating mines of World War II. \Vhen this prosthesis is assembled, the relationship between the acetabular studs and the femoral head is such that lines drawn along the plane of each stud meet at the geometric center of the ball (Fig. IB). In addition, the lip of the acetabulum may be seen protruding on either side of the head. When the prosthesis is dislocated, the studs are obscured by the overriding femoral head. More subtly, lines drawn along those studs which are seen will not meet at the geometric center of the head (Fig. 2, 1 and B; and 3). The lip of the acetabular cup may be obscured on either end. Also, too much of the metallic femoral head will be visible. DISLOCATED CHARNLEY-MULLER PROSTHESIS (SATURN RING SIGN) Muller s modification of Charnley s prosthesis consists of a large teflon cup with a matched modified Thompson prosthesis (Fig. 4). For roentgenographic identification, a radiopaque wire is embedded in a groove along the outer margin of the rim of this cup. This normally gives the cup the appearance of Saturn s rings equidistant from the planet, or femoral head (Fig. ). Dislocation of this prosthesis, when not

3 VOL. 115, No. 3 Dislocation of Total Hip Prostheses 557 Fic.,. Dislocated McKee-1 arrar prosthesis. A 76 year old woman caught her foot on the stairs and fell. Note that the femoral head cannot be seen below the lip of the acetabuhum; anteversion of acetabulum. (Compare with Fig. ia.) FIG.. Normal Charnley-M#{252}ller prosthesis. Note the Saturn Ring. grossly evident, resembles the McKee- Farrar dislocation with the femoral head eccentrically placed within the acetabular ring (Fig. 6, 4 and B). Either edge of the ring may be obscured by the femoral head. DISLOCATED RING PROSTHESIS (TIN WOODSMAN SIGN) The Ring prosthesis consists of a grooved acetabular cup with a stem for insertion Fic.. Charnley-M#{252}lher total hip prosthesis. The wire around the acetabular cup is for roentgenographic identification.

4 Daffner, Gehweiler, Olson, Wilson and Carden JULY, 1972 lic. 6. (A) l)islocated Charnley-M#{252}ller prosthesis. Note the relationship of the ring to the planet. (R) A more obvious dislocation of the Charnley-M#{252}ller prosthesis. This patient fell out of bed on the second day postoperatively. into the pelvis and matched to a modified Moore prosthesis (Fig. 7). It resembles the hat of the Tin \Voodsman from the li izard of Oz, with the stem pointing through the geometric center of the femoral head. In addition, there is a small space between the lips of the cup and the femoral head. When this prosthesis dislocates, the stem no longer points toward the geometric center of the femoral head (Fig. 8). There is also obliteration of the space between the cup and the ball. DISCUSSION Dislocations of total hip prostheses are uncommon. The incidence has been reported from i in 5oo4 to 4 in 58.6 The expected rate should be less than 2 per cent.7 Most of the dislocations reported in the literature were with the earlier Charnley prosthesis, which used a smaller femoral head and required osteotomv and the replacement of the greater trochanter),)7,10,14 Dislocations of the McKee-Farrar prosthesis were rare, despite the greater allowable variation in socket orientation. The majority of dislocations occur within the first 2 weeks postoperative and in many cases they are preventable. Contributing factors are nursing procedures with excessive moving of patients, improper angulation of either femoral or acetabular components, early ambulation or activity on the part of the patient, or, with the earlier Charnle\? prosthesis, technical error in replacement of the greater trochanter.1 3 #{176} One of the contributing factors to the frequent dislocation of the Charnle\- type prosthesis is the dramatic relief from pain which the patient experiences. This leads to

5 \OL. 115, No. 3 Dislocation of Total Hip Prostheses 559 their premature ambulation and exercise against the advice of their physicians and accounts for many of the immediate postoperative dislocations. Roen tgenographicallv, the dislocation may be grossly evident, with large portions of acetabular and femoral components seen separately. However, our experience has been prim arih- with patients who have dislocated in the immediate postoperative period and on whom the onl roentgenograms possible were in the anteroposterior projections, using portable units. After noting the geometry on a number of normal prostheses, we found that disturbed geometry, in an otherwise normal appearing hip prosthesis, was a reliable sign of dislocation. All of the more com- Fic. 7. The Ring prosthesis. l ic. 8. Same patient as in l igure 7, dislocated after chronic infection around the prcsthesis. Note the Tin Woodsman Sign. monly used devices have projections (studs, wire ioop, or stem) which make the geometric diagnosis possible. In addition, since replacement of the greater trochanter following osteotomv ma\? play a role in dislocation, signs of broken wires, nonunion or slippage of the greater trochanter should be checked. The Charnlev-Miiller and McKee-Farrar prostheses have eliminated the need for removal and replacement of the greater trochanter and thus the possibility of dislocation due to this factor,9 SUMMARY The roentgenographic appearance in the anteroposterior projection of dislocations of the McKee-Farrar, Charnlev-Miiller, and Ring total hip prostheses is described. Each of these devices has one or more projections on the acetabular component

6 6o Daffner, Gehweiler, Olson, Wilson and Carden JULY, 1972 which can be related geometrically to the metallic femoral head. Dislocation, when not grossly apparent, will disturb the normal geometric relationships of each component. Three signs, the Floating Mine Sign, the Saturn Ring Sign, and the Tin Woodsman Sign are described for each of the above prostheses, respectively. The more common causes of early dislocation are briefly discussed. Richard H. Daffner, M.D. Department of Diagnostic Radiology Duke University Medical Center Durham, North Carolina REFERENCES i. AMSTUTZ, H. C. Complications of total hip replacement. C/in. Orthopaed., 1970,72, ANGELL, F. L., and WATTS, F. B. Total hip replacement: roentgen appearance of current devices. AM. J. ROENTGENOL., RAD. THERAPY & NUCLEAR MED., 1970, 110, BERGFELD, J. A., EVARTS, C. M., and STEFFEE, A. D. Evaluation of Ring total hip joint prosthesis. Orthop. C/in. N. ii., 1971, 2, CHARNLEY, J. Total prosthetic replacement of hip. Reconstr. Surg. Traumat., 1969, II, CHARNLEY, J. Total hip replacement by lowfriction arthroplasty. C/in. Orthopaed., 1970, 72, GALANTE, J. Total hip replacement. Orthop. C/in. N. 1., 1971, 2, LAZANSKY, M. G. Complications in total hip replacement with Charnley technic. C/in. Orthopaed., 1970, 72, MCKEE, G. K. Development of total prosthetic replacement of hip. C/in. Orthopaed., 1970, 72, MCKEE, G. K., and WATSON-FARRAR, J. Replacement of arthritic hips by McKee-Farrar prosthesis. 7. Bone & Joint Surg., 1966, 48-B, MoRRIS, J. B., and NICHOLSON, 0. R. Total prosthetic replacement of hip joint in Auckland. C/in. Orthopaed., 1970, 72, II. MiLLER, M. E. Total hip replacement. C/in. Orthopaed., 1970, 72, RING, P. A. Complete replacement arthroplasty of hip by Ring prosthesis. 7. Bone & Joint Surg., 1968, 50-B, WATSON-FARRAR, J. McKee-Farrar artificial hip joint. Reconstr. Surg. Traumat., 1969, II, WELCH, R. B., and CHARNLEY, J. Low-friction arthroplasty of hip in rheumatoid arthritis and ankylosing spondylitis. C/in. Orthopaed., 1970, 72,