Article: Hemispheric Titanium Porous Coated Acetabular Component without Screw Fixation

Click here to read article in Adobe Acrobat format.


Hemispheric Titanium Porous Coated Acetabular Component Without Screw Fixation

Lawrence D. Dorr, MD*, Zhinian Wan, MD*, and Jondy Cohen, MD*

One hundred fifteen hips in 108 patients with primary total hip arthroplasty using the anatomic porous replacement hemispheric acetabular component implanted without adjunctive screw fixation had a mean postoperative follow-up time of 6 years (range 5-7.4 years). Clinical evaluation was performed using the Harris hip score and patient self assessment using a modified Short Form-36 questionnaire. Radiographs were measured for radiolucent lines, polyethylene wear, osteolysis, migration, and fractures. No acetabular metal shell had been revised for loosening or was radiographically loose with or without migration (more than 3 mm) at final follow up. Reoperation was done in nine (8%) hips because of polyethylene insert wear or disassembly. No fracture of the acetabular bone occurred at the time of surgery or was observed on radiograph. Fixation of the metal shell was stable, with progressive radiolucent lines observed at final follow up in 2% of the hips. Osteolysis was recorded in one patient with two acetabular components. The fixation of noncemented hemispheric porous coated acetabular components is more related to the technique of acetabular bone preparation and press fit implantation than to whether additional screws or peg fixation are used. Fixation of this acetabular component without screws at an average of 6 years after surgery is reproducible and predictable in primary hip arthroplasty. The design of modular polyethylene inserts has been improved and should reduce the wear rate of reoperations of the polyethylene insert.

Revision and reoperation of the acetabulum is the most common reason for repeated surgery in total hip arthroplasty. 7,12, 23, 43, 44 Radiographic evidence of loosening or migration has been reported in as many as 11% to 50% of acetabular components in cemented total hip arthroplasty at 10 to 21 years after surgery. 7,21,35, 43 With noncemented acetabular components, fixation failure has occurred less frequently, but reoperation for wear and disassembly of the polyethylene insert has been common. 11, 13, 34, 36, 43

Additional concerns with noncemented modular acetabular components include the increased wear measured of the polyethylene and the incidence of expansile osteolytic defects in the first 5 to 10 years. 20, 25, 34, 40, 43, 46 The use of screws as adjunctive fixation for the metal acetabular component has been implicated as causing impingement on the polyethylene inert, fretting wear, corrosion between the screws and the shell, screw fracture, and the vascular injury. 21-23, 41 Acetabular components with adjunctive peg fixation have been reported to have an increased incidence of osteolysis that ranges from 9% to 205 in 5 to 10 years. 19, 25, 46

In 1988 the anatomic porous replacement hemispheric porous coated acetabular component (APR, Sulzer Medica, Austin, THERAPY) first was implanted without adjunctive screw fixation. Morsher et al 31, 32 and Gordon Hill (as reported by Schmalzried et al) 36 were using a similar technique with different components. Morscher et al31, 32 subsequently published their experience that fixation with bone screws made no difference as compared with that without the use of screws. Schmalzried et al36 reported that none of these implants were loose or revised at 5 years after surgery. In addition, laboratory studies subsequently suggested that components with press fit fixation were stable. Won et al42 and Kwong et al26 observed in the laboratory that if the acetabular component was inherently stable by press fit techniques supplemental screw fixation did not significantly enhance the stability of the implant. The current study assesses the results seen with a press fit porous coated hemisphere with a minimum of 5 years or postoperative follow-up.

From a computer database of 207 primary total hip arthroplasties performed from June 1988 to November 1990, 132 primary total hip arthroplasties with press fit acetabular components were performed by the senior author (LDD). All hips during this period that were reconstructed by this technique were reviewed. An additional 75 hips were implanted with the same component using additional screw fixation. The first acetabular components implanted without screws were done so selectively to be able to observe the early results of this technique and confirm that early migration would not occur. Hips were selected by intraoperative confidence that the components was secure without screw fixation. From June 1988 to December 1988, 30% of noncemented cups were press fit; in 1989, 68% and in 1990, 93%. All of these hips were included in this study. Seventeen hips were excluded from statistical analysis because 10 patients with 11 treated hips died before 5 years of follow-up, and five patients with six treated hips were lost to follow-up. These 15 patients (17 hips) had no radiographic loosening or revision of acetabular components, and had satisfactory clinical results before death or at last follow-up. One hundred fifteen hips in 108 patients with a minimum 5-year follow-up were included in this study.

The APR hemispheric porous coated acetabular component was used in all hips. The acetabular component is a hemisphere and is manufactured from titanium +6% aluminum, +4% vanadium alloy with a pure titanium porous coating named cancellous structured titanium. The porous coating is heat sintered to the alloy with a pore size of 490 um and 55 volume % ingrowth available. The metal shell has 3-mm thick walls. Thus, a 49-mm shell with a 28-mm femoral head would have a 7.5-mm thick polyethylene insert. The modular polyethylene inserts used in these hips were circumferentially incongruent with the metal shell (a gap) by 0.5 to 0.75 mm and had rotatory motion of 0.5 mm (fig 1) The femoral head was cobalt chrome.

The femoral components used were the APR 1 stem in 54 hips, with 32 noncemented and 22 cemented; the APR II in 21 hips, with 17 noncemented and four cemented; and the APR II stem with a sleeve that was noncemented in 40 hips. In these hips the choice of the stem and fixation was based on the age of the patient , the quality of bone of the femur, and the stage of development of the femoral stem prosthesis. The design of the acetabular component did not change.

A posterior surgical approach was used in all hips. 8 The goal of the acetabular preparation technique was to optimize contact between the metal shell and the bone and to provide a press fit between metal and bone. The acetabulum was reamed progressively with hemispheric reamers to obtain circumferential bone contact with bleeding cancellous or subchondral bone. The initial reamer size used was 4 mm smaller than the size expected to be needed from templating the radiograph. Reaming was done with a to and fro motion, rather than a rotatory motion, from a transverse to a horizontal inclination of the reamer. The final reamer was inclined firmly under the superior acetabular rim to ream this bone to a hemisphere from its normal sloped anatomy. The final reamer size was determined by complete rim contact of the reamer, even if this meant thinning of the medial bone. A trial shell the same size as the final reamer was inserted. If this trial shell showed loosening in either the superoinferior or anteroposterior (AP) plane, the next size trial shell was inserted. If this second trial shell fit satisfactorily, the implant for that trial shell was selected. If the second trial shell could not be seated fully, the rim of the acetabulum was reamed by that size reamer. The reamer was not seated fully. This technique resulted in a flaring of the acetabulum because it had been reamed deeply to a size 2 mm smaller than the rim. The second trial shell now would have a secure fit. The actual porous coated acetabular component was 1 mm larger than the final trial shell used. For example, if a 52-mm trial shell was used, a 53-mm acetabular component was implanted. This technique meant that in many patients the acetabulum was underreamed by 1 to 3 mm. The position of the acetabular component was preferred to be 40 mm abduction (theta angle) and 20° anteversion.

Clinical follow-up information was obtained by interview and physical examination by one of the authors (LDD) or the clinical fellows for each patient. Harris hip scores 17 were determined preoperatively, 6 and 12 months after the operation, and annually thereafter. For this study, the preoperative, 2-year, and final follow-up scores were compared. Patient self-assessment was available at final follow-up for 78 hips. The self assessment used was a modified Short Form-36 using 23 questions (Form HBK21, Orthographics, Salt Lake City, UT.) The questions from this form that were evaluated and compared with the physician?s score were (1) the patient?s grade of operation, (2) pain, and (3) limp.

Radiographic examination included an AP radiograph of the pelvis centered over the pubic symphysis, which included the proximal femur so that the femoral stem could be visualized, and a 17-inch Lowenstein lateral of the hip. These radiographs were obtained preoperatively; 3, 6, and 12 months after surgery; and annually thereafter. No jig was used for these radiographs, but two radiographic technicians obtained all of the postoperative radiographs, and emphasis was placed on patient position and radiographic exposure. T he magnification of radiographs was corrected by the k known diameter of the metal femoral head. Radiographic measurements were performed on the preoperative, 3-month, 2-yeare, and final follow up postoperative films. The preoperative radiographs were measured for Type A, B, and C femoral bone10 to be able to evaluate the influence of osteoporotic bone on fixation. The diagnosis of the etiology of the arthritis also was classified from the preoperative film. From postoperative radiographs the angle of inclination of the acetabular component was measured with the method first described by Yoder et al 45 and modified by Callaghan et al.6 The coverage of the acetabular component by host bone on the AP radiograph was measured as a percent of the acetabular circumference. Migration of the acetabular component was defined as linear in the direction of medial, superior (or both), or rotational, which is a change in the angle of inclination of the component. The method modified by Callaghan et al16 was used for determining a fixed reference on the pelvis. A horizontal line connected the inferior points of the bony teardrops, and vertical lines were drawn through the medial edge of the teardrops; the position of the metal shell was measured from these reference points.

The acetabulum was divided into three zones as described by DeLee and Charnley9 for assessment of the radiolucent lines in the AP and lateral radiographs. The contact of the surface of the acetabular component with acetabular bone was measured by zones. Regions in which the surface of the acetabular component was not in contact with bone appeared as radiolucent lines on the immediate postoperative radiographs and were classified as gaps to distinguish them from radiolucent lines that appeared on subsequent radiographs in zones where no gaps initially had existed. The radiographic measurements were made by one observer (ZW), who performed the measurements without clinical knowledge of the patient. The width of the radiolucent line in each zone was measured visually using a micrometer. Radiolucent lines were recorded as increased if in serial radiographs the number of radiolucent lines increased; decreased if fewer radiolucent lines were observed; and stable if there was no change in the occurrence of radiolucent lines. If there was a complete radiolucent line around the acetabular component and the width of the radiolucent line was greater than or equal to 2 mm with or without acetabular migration, the component was classified as loose. Migration of more than 3 mm was considered loosening.

Acetabular fracture was identified by visual assessment during surgery and by radiographic assessment immediately after operation.

Polyethylene wear was measured by modification40 of the technique of Livermore et al.28 Femoral head displacement that was measured on the 3-month radiograph was considered creep of the polyethylene,2,4,11 and subsequent displacement was considered wear. Three head sizes were used (26 mm, 28 mm, and 32 mm). The head size was selected randomly by surgeon choice with no firm criteria for selection.

Fixation of the stem was measured by zonal analysis or radiolucent lines as described by Gruen et al.16 Cemented fixation was grade by the ABCD grading scale of Barrack et al.3 Noncemented fixation was graded by a modification of the system of Engh et al.14 The modification is used for smooth diaphyseal femoral stems with metaphyseal bone ingrowth fixation because the radiographic pattern of remodeling differs. Almost no proximal osteopenia occurs, and the radiographic classification of stable fibrous fixation is not applicable.11 Type IA fixation has radiolucency only in Zone 4, Type IB has three to five radiolucent zones around the smooth stem, Type II has radiolucent zones in all smooth zones; and Type III has divergent radiolucency or migration of the stem.30

All data were analyzed statistically using SPSS software (SPSS Inc. Chicago, IL). The Wilcoxon test was used to compare the Harris hip score and the pain score, limp score, and rating of clinical results between the physician grade and patient self assessment. The chi squared test was used to analyze radiolucent lines between hips with Types A and B compared with bone Type C.

Forty-two patients with 45 treated hips were woman, and 66 patients with 70 treated hips were men. The average follow up was 6 years (range, 5-7.4 years). T he average age was 60 years (range, 24-86 years). Fifteen patients were younger than 45 years of age, 36 were older than 60 years of age. The average weight was 177 pounds (range, 106-325 pounds). Twenty-five patients weighed less than 150 pounds, 61 weighed 150 to 200 pounds, and 29 weighed more than 200 pounds. The reason for the operation was osteoarthritis in 97 hips, osteonecrosis in eight hips, rheumatoid arthritis in four hips, developmental dysplasia in four hips, and traumatic arthritis in two hips.

The preoperative mean Harris hip score was 48.1, the postoperative score at 2 years was 94.3, and a final follow-up was 91.2. Before surgery, the mean pain score was 17.9. At 2 years and final follow-up, the scores were 42.5 and 43.2 respectively. The preoperative mean limp score was 5, the limp score at 2 years after surgery was 10.3, and at final follow-up was 9.7. According to the Harris hip score, 67.8% of hips were rated as excellent. 20.1% of hips as good, 8.6% as fair, and 2.6% as poor. Thirteen hips were rated as fair and poor with the reason in five patients being spine disease; four had stem Type II or III fixation; two had a weak gluteal medius with rapid onset of buttock pain; one had rheumatoid arthritis; and one had cancer. Patient self assessment evaluation at final follow showed 71.8% of patients rated their hip as excellent, 15.8% as very good, 7.7% as good, 2.6% as fair, and 1.3% as poor. The average pain score was 38.9 and the average limp score was 9.6. Comparison of the physician?s clinical evaluation with he patient?s self assessment gave no statistical difference for limp score (p = 0.38) and rating of clinical results (p>0.05). The pain score was statistically different (p=0.006), with the patient listing more pain than did the physician. Patient evaluation showed that 20 hips had more pain than physicians reported. Six patients had back pain; two had psychiatric difficulties; two had rheumatoid arthritis; one had fracture o the femur; one had Reiter?s syndrome; and in nine patients, no reason was identified for the difference.

All hips had at least 90% coverage of the acetabular component on radiograph, with 100% coverage in 84 hips, 95% in 28 hips, and 90% in three hips. The coverage of acetabular components was not related to radiolucent lines. No acetabular fractures were identified, either during surgery or on radiographs. The average acetabular angle of abduction inclination (theta angle) was 46.4° (range, 35° -60° ). Anteversion could not be measured accurately on the postoperative radiographs because of the metal acetabular shell.

The average polyethylene insert thickness for the 115 hips was 10.5 mm+ 1.9 mm. For 49 hips with 26-mm femoral heads, the average polyethylene thickness was 10.7 mm+ 1.8 mm; for 28-mm heads, the polyethylene thickness was 10.7 mm+ 1.6 mm; and for 22 hips with 32-mm heads, polyethylene insert thickness was 9.8 mm+ 2.3 mm. The average linear polyethylene wear for 115 hips was 0.168 mm per year. In 104 hips that did not require operation, polyethylene wear was 0.128 mm per year, compared with 0.336 mm per year in 11 hips with reoperation. Between the hips with and without reoperation there was no statistical difference for patient age, gender, weight, and diagnosis (all p > 0.05). One of the 11 hips had polyethylene thickness less than 8 mm. In this hip, a 49 mm metal shell was used with a 3-mm thick polyethylene insert, and the polyethylene insert disassociated (Table 1).

Overall, measurement of fixation showed that all postoperative periods no acetabular component had migration more than 3 mm (from the 3-month postoperative film). Radiolucent gaps appeared in 39 hips on the initial postoperative radiographs. Twenty hips had a radiolucent gap in two zones. Zone 2 most frequently had a postoperative radiolucent gap, and these gaps were the ones that most often persisted at final follow-up. All 20 hips with two zones had a radiolucent line in Zone 2, with an accompanying Zone 1 or Zone 3 line (Table 2). None of these gaps were greater than 1 mm. The incidence or radiolucent gaps was higher on AP radiographs than on lateral radiographs. As was the incidence of final radiolucent lines. In 26 of 39 hips, these radiolucent gaps were not present on final radiographs, and in 13, the radiolucent gap on the initial radiograph was measured as a constant radiolucent line on final radiographs (Fig 2). Three hips that did not have a radiolucent gap on the postoperative radiograph did have a radiolucent line on the final follow-up radiograph. Thus, 16 hips had radiolucent lines on final radiographs, with three of these being progressive (Table 2) All three of these radiolucent lines appeared in the first two years after surgery. On the radiographs obtained 2 years after surgery, as compared with those obtained immediately after surgery, no change in the incidence of radiolucent lines was present in 85 (73.9%) hips. At 2 years after surgery, radiolucent lines decreased in 27 (23.5%) hips and appeared in three (4.3%) hips.

At the final postoperative follow-up, 99 hips had radiolucent lines around the acetabular component. Eleven hips had a radiolucent lines in one zone and five hips in two zones. All five hips with the radiolucent line in two zones had a radiolucent line in Zone 2 with a second line in either Zone 1 o 3 (Fig 2). In a comparison of the occurrence of radiolucent lines measured at 2 years after surgery with that at final follow-up, there was no change in 109 (94.9%) hips, and radiolucent lines had decreased in six hips (5.2%). No new radiolucent lines occurred after 2 years of postoperative follow-up.

Twenty-seven hips had bone Type A, 73 had bone Type B, and 15 had Bone Type C. On radiographs obtained immediately after surgery, 30% of hips with Type A bone had radiolucent gaps, compared with 33% of hips with Type B bone, and 46% of hips with Type C bone. There was no statistical difference among the bones types (p = 0.51). At final follow-up, 7.4% of hips with Type A bone had a radiolucent line, compared with 17.8% of hips with Type B bone, and 6.7% of hips with Type C bone (p =0.28).

Focal osteolysis40 was present in one patient with bilateral total hip arthroplasty. By 4 years after surgery, the linear wear in this patient was 3.5 mm in the left hip and 3 mm in the right hip. The metal shell size was 49 mm, femoral head size was 26 mm, and polyethylene insert thickness was 8.5 mm, and polyethylene insert thickness was 8.5 mm. Osteolysis was present in the femur and acetabulum of the left hip and the acetabulum of the right hip. Reoperation was performed for exchange of the polyethylene and femoral head. Four years after reoperation the patient has a Harris hip score of 93 in the left hip and 100 in the right hip.

Of 115 hips, 25 had cementless stems, and 90 had noncemented stems. In 25 cemented stems after surgery, cement technique was Grade A in 17 hips, Grade B in two, and Grade C2 in six. At final follow-up, there were no loose cemented stems. At final follow-up in noncemented stems, 21 hips had fixation Type 1A; 63 hips had Type IB; four hips had Type II; and two hips had Type III.

Eleven hips had reoperations or revisions (see Table 1). In all 11 hips the polyethylene insert and the femoral head were changed. In each of these 11 hips the acetabular component was examined for fixation and no acetabular shell was found to be loose, and none was revised. The polyethylene insert and femoral head were replaced in seven hips because of severe polyethylene wear and the presence of osteolysis in the femur. Disassembly of the polyethylene occurred in two hips, and in one hip the polyethylene insert was worn severely and fractured. One hip was surgically treated again for chronic dislocation, and a new hooded polyethylene insert and a longer modular femoral head were placed. This patient had no additional dislocation and at final follow-up had a Harris hip score of 100. One hip was revised for a loose noncemented femoral stem. In all reoperations, the replacement polyethylene insert and femoral head size permitted the use of at least 8 mm of polyethylene, and the insert had better congruency than did the initial insert used (Fig1).

In these hips the acetabular components implanted without adjunctive screw fixation functioned well. None of the metal shells required revision for loosening, none were loose, and only 2.6% had progressive radiolucent lines at final follow-up. The mechanical failure rate (revised & Loose0 for fixation of these sockets was 0%. The clinical results in this study were influenced more by the function of the femoral stem and the acetabular polyethylene insert than by the fixation of the acetabular component. The mechanical failure rate for all of the arthroplasties (loose or revised femoral and acetabular components) was 2.6%. Reoperation for worn or loose polyethylene inserts was 7.8%. Clearly, the fit of the polyethylene insert is the weakness of this noncemented modular acetabular component. Wear and disassembly also have been reported with other noncemented acetabular components.20,25,34,43 Changes have been made by most manufacturers to correct this weakness (Fig1).

Fixation of the metal shells was stable and predictive of durability of the acetabular component. As measured by revisions, at a similar postoperative time, fixation with this hemispheric porous coated socket, press fit without adjunctive screws or pegs, was not better than that with cemented fixation or fixation with the use of screws or pegs. At a similar follow-up time of 5 to 7 years, Hozack et all22 and Schulte et al37 had a 1% revision of the Charnley cup. With the Harris design II (Howmedica, Rutherford, NJ) all polyethylene component, Harris et al18 had 2% revision at 6 years. Zicat et al46 reported 1% revision at 7 years using the anatomic medullary locking (AML, DePuy, Warsaw, IN) acetabular components with pegs. Schmalzried and Harris34 had no revisions at 5 years with the Harris-Galante prosthesis 1(HGPI, Zimmer, Warsaw IN) with adjunctive screw fixation.

However, using the criteria of radiographic loosening or progressive radiolucent lines, fixation was better with this noncemented implant and technique. Radiographic loosening rates are related to the technique of measurement used and the person who does the measurement.5 In this study, there were no loose components, there was an overall 2.6% incidence of progressive radiolucent lines, and no case had progressive radiolucent lines after the second postoperative year. Cemented sockets have shown a high rate of progression of loosening and radiolucent lines between 5 and 10 years after surgery. Stauffer,38 using the Charnley cup, had 6.5% loose at 5 years of follow-up and 11.3% loose at 10 years of follow-up. Harris et al18 and Mulroy and Harris33 reported 2% loosening at 6 years of follow-up, with an increase of 42% at 11 years of follow-up. Hozack et al22 had 25% with either loose or migrated cups at 10 years using the Charnley cup. Ziegler and Lachiewicz47 reported on the trial all polyethylene acetabulum (Johnson and Johnson, Braintree, MA) and had 15% loose at 5 years of follow-up; at 10 years, 30% were loose. These results show some differences associated with the design of the polyethylene acetabular component used. Femoral head size also has been implicated in the data of Kelley and Johnston24 with the Iowa all polyethylene cup (Zimmer, Warsaw, IN). At 6 years after surgery, Kelley and Johnston24 had 21.4% loose cups when using a 28-mm femoral head and 4.3% loose when using a 22-mm femoral head.

The importance of surgical technique to fixation is shown by the difference in results with noncemented components. As observed in this study, the absence of progression of radiolucent lines after the second postoperative year to the seventh postoperative year has been reported by two other studies. Zicat et al46 using the AML porous coated component with pegs and Latimer and Lachiewicz27 using the HGPI acetabulum with an adjunctive screw fixation had no progressive radiolucent lines. Although Latimer and Lachiewicz27 used screw fixation and Zicat et all used pegs, all used the technique of underreaming and required a stable fit of the acetabular component, just as was done in the hips in this study. This intraoperative stability of fixation before adjunctive pegs or screws seems to be important for the absence of progressive radiolucent lines. Schmalzried and Harris,34 using a line to line fit of the acetabular component and primary screw fixation, reported 27% with progressive radiolucent lines. The PCA (porous coated anatomic Howmedica, Rutherford, NJ) acetabular component had adjunctive peg fixation but was fitted with line to line reaming. Heeking et al19 reported 9% with migration and progressive radiolucent lines at 5 to 7 years after surgery.

Wear in these acetabular components was not less than in the sockets with adjunctive fixation. The most common reason for reoperation in these hips was wear of the acetabular inset. The current authors? overall linear wear rate was 0.168 mm per year. With 28-mm femoral heads, the wear rate was 0.14 mm per year, which was the same as that reported by Woolson and Murphy43 using the HGP 1 acetabulum. The linear wear in these sockets is lighter than that of 0.08 mm per year reported for the all polyethylene Charnley socket used by Schulte et al.37 The highest wear in this study occurred with 26-mm heads and was 0.29 mm per year. This accelerated wear with 26-mm heads was attributed to rapid creep of the polyethylene. 11,29,39 Because of the gap caused by the creep, the polyethylene insert became out of round with the femoral head and permitted accelerated linear wear.29

Clearly, the weakness of noncemented modular acetabular components is the wear that occurs and particularly the possibility of severe accelerated wear in some hips. In the hips in this study, , there often was 0.5 mm eccentricity of the femoral head on the 3-month radiograph. This eccentricity was caused by creep that occurred because there was a 0.5-0.75-mm gap between the polyethylene insert and the metal shell.11 Loading of the femoral head after surgery closed the gap in the axial direction of load and created an immediate eccentricity in the polyethylene. This out of round articulation allowed sliding of the femoral head, and this sliding promotes accelerated wear.11

In this study the incidence of identified acetabular osteolysis is 2%, which is comparable with the 1.2% reported by Schmalzried and Harris 34 to have occurred with screw fixation. Latimer and Lachiewicz27 using screw fixation observed no osteolysis and Schmalzried et al36 observed no osteolysis without screw fixation. There is no evidence that the use of screws increases the incidence of osteolysis. An increased incidence of osteolysis is reported in sockets with pegs. Using the porous coated anatomic socket, Kim and Kim25 reported 9% osteolysis at 5 years, and Astion et al1 reported 20% for the same period. Engh et al15 reported 18% with the AML cup at an average of 9 years follow-up. Both of these hip systems have femoral components that had circumferential coating and a low incidence of femoral osteolysis. The APR and HGP femoral components did not have circumferential coating, and this resulted in a greater incidence of femoral osteolysis. Perhaps this was the reason the APR and HGP acetabular components had lesser acetabular osteolysis. Debris will seek the path of least resistance.35 This path of least resistance differs for these hip systems, with the femoral component being the pathway for the APR and the HGP systems, whereas the acetabulum is the pathway for the PCA and AML hip systems.

The assessment of clinical outcome of these hips provide a significant finding regarding grading of pain. Patients graded pain greater than did physicians, although the patients graded their overall result the same as the physician (and even somewhat better). With patient self assessment, 3.9% of patients rated their results as far and poor, whereas by the Harris hip score, physicians rated 11.2% as fair and poor. The average Harris pain score at final follow-up by the patient was 38.9, compared with 42.2 by the physician. Patients did not discriminate hip pain from leg pain because of the wording of the question on the self assessment form. Future outcome instruments need to help the patient better distinguish these pains for a more accurate measure of hip pain.

The conclusions of this study regarding fixation emphasize the importance of the technique of preparation of the acetabular bone to provide an intrinsically stable press fit of the acetabular component. The technique of an underreamed press fit acetabular component has provided the most stable fixation interface. The use of adjunctive screw fixation is not necessary but can be used safely at the discretion of the surgeon. The advantages of not using adjunctive screw fixation are the time saved at the initial surgery for insertion of the screws and, more importantly, the time saved for removal of the screws at any future necessary revision surgery. The use of additional screw fixation is most needed when performing total hip replacement in hips with osteoporotic (Type C) bone.




Return to Dr. Cohen's Main Page

Return to Top

hipaa compliance | site map | website design by spotlite design ..