The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 89, Issue 2

Scientific Articles | February 01, 2007

Results of Metal-on-Metal Hybrid Hip Resurfacing for Crowe Type-I and II Developmental Dysplasia

Harlan C. Amstutz, MD¹; John T. Antoniades, MD¹; Michel J. Le Duff, MA¹

¹ Joint Replacement Institute, Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, CA 90007. E-mail address for H.C. Amstutz: hamstutz@laoh.ucla.edu

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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from The Los Angeles Orthopaedic Hospital Foundation and the William McGowan Charitable Fund, Inc. In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Wright Medical Technology). Also, a commercial entity (Wright Medical Technology) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

Investigation performed at the Joint Replacement Institute at Orthopaedic Hospital, Los Angeles, California

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2007 Feb 01;89(2):339-346. doi: 10.2106/JBJS.F.00576

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Abstract

Background: Modern hip resurfacing implants may increase stability and preserve more bone than conventional total hip arthroplasty. The purpose of this retrospective study was to analyze the mid-term results in a consecutive series of middle-aged patients with developmental dysplasia of the hip treated with hybrid resurfacing joint arthroplasty.

Methods: Metal-on-metal hip resurfacing was performed in fifty-one patients (fifty-nine hips), forty-two of whom were female and nine of whom were male. The average age at the time of surgery was 43.7 years. Radiographic and clinical data were collected at six weeks, at three months, and at yearly follow-up visits. Seven hips had Crowe type-II developmental dysplasia of the hip and fifty-two had type-I.

Results: The follow-up period ranged from 4.2 to 9.5 years (average, 6.0 years). Initial stability was achieved in all but three hips. The clinical outcomes, as rated with the University of California at Los Angeles (UCLA) hip score, improved significantly compared with the preoperative ratings. On the average, the pain rating improved from 3.2 to 9.3 points; the score for walking, from 6.0 to 9.7 points; the score for function, from 5.7 to 9.6 points; and the score for activity, from 4.6 to 7.3 points (all p = 0.0001). The mean Short Form-12 (SF-12) mental score increased from 46.6 to 53.5 points, and the mean SF-12 physical score increased from 31.7 to 51.4 points (both p < 0.0001). The mean postoperative Harris hip score was 92.5 points. On the average, the range of flexion improved from 106° to 129.6°; the abduction-adduction arc, from 41.9° to 76.9°; and the rotation arc in extension, from 32.1° to 84.8° (all p = 0.0001). Four patients delivered a total of six healthy babies since the time of implantation of the prosthesis. Radiographic analysis showed a decrease in the mean body weight lever arm from 118.5 mm preoperatively to 103.9 mm postoperatively (p = 0.007). There were five femoral failures requiring conversion to a total hip arthroplasty. One hip showed a radiolucency around the metaphyseal femoral stem. There were no complete acetabular radiolucencies, and all sockets remained well fixed.

Conclusions: The mid-term results of metal-on-metal resurfacing in patients with Crowe type-I or II developmental dysplasia of the hip were disappointing with respect to the durability of the femoral component. However, the fixation of the porous-coated acetabular components without adjuvant fixation was excellent despite incomplete lateral acetabular coverage of the socket. More rigorous patient selection and especially meticulous bone preparation are essential to minimize femoral neck fractures and loosening after this procedure.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

Figures in this Article

Total hip arthroplasty in patients with developmental dysplasia of the hip offers unique reconstructive challenges secondary to deficient acetabular bone stock, abnormal femoral anatomy, limb-length discrepancy, abductor insufficiency, and muscle contractures, all occurring in a younger patient population^1-4. The long-term results with cemented acetabular designs were mostly limited by the survival rate of the acetabular component, with high rates of aseptic loosening noted radiographically^5-7.

Resurfacing arthroplasty presents the advantage of preserving femoral bone stock at the initial operation, which facilitates conversion to a total hip arthroplasty if one is necessary. However, initial surface arthroplasties with polyethylene featuring cemented one-piece acetabular components required more extensive reaming of the acetabulum than was necessary for total hip arthroplasty. Consequently, the results in patients with developmental dysplasia of the hip were inferior to the results in patients with other conditions, and acetabular failures were more prevalent than failures on the femoral side⁸. Also, survivorship analysis comparing cemented total hip prostheses with cemented resurfacing implants in young patients with developmental dysplasia of the hip showed similarly poor results in association with both prosthetic designs⁹. Ultimately, the early failure of these surface replacements was attributed to polyethylene wear debris-induced periprosthetic osteolysis^10,11.

More recently, the use of uncemented acetabular components for total hip arthroplasty in patients with developmental dysplasia of the hip has yielded favorable results^12,13. The stability of these components is related to the adequacy of the bone coverage of the socket, the preoperative deformity, and the location of the hip center³. Anderson and Harris suggested that at least 70% host bone coverage is necessary to obtain stability of uncemented sockets with adjunctive screw fixation¹⁴. Reconstructive techniques used to compensate for the lack of acetabular coverage include bone-grafting^4,14,15 and placement of reinforcement rings^16,17.

There is currently a paucity of information on the performance of cementless acetabular components used for resurfacing in patients with developmental dysplasia of the hip, and we found no data on resurfacing with a cementless acetabular component without adjunctive fixation. Only a short-term report by Knecht et al.¹⁸ highlights the good functional results of the new generation of metal-on-metal hybrid resurfacing of the hip.

Our initial report on the short-term results of the implantation of the first 400 Conserve Plus resurfacing prostheses (Wright Medical Technology, Arlington, Tennessee) included forty-three hips with developmental dysplasia of the hip¹⁹. Three hips were revised, one because of subluxation, one because of a femoral neck fracture, and one because of loosening of the femoral component. These patients were considered to have been at risk for early failure after the risk factors for loosening²⁰ and neck fracture²¹ were identified.

The purpose of the present study was to provide a midterm analysis of the clinical and radiographic results of metal-on-metal hybrid resurfacing in patients with Crowe type-I or II²² developmental dysplasia of the hip.

Materials and Methods

Materials and Methods | Results | Discussion | References

Fifty-nine hips (fifty-one patients) with a diagnosis of osteoarthritis secondary to developmental dysplasia of the hip were treated between November 1996 and February 2002 with the Conserve Plus hip resurfacing system. During the study period, the senior author (H.C.A.) also performed 449 hip resurfacing procedures for disorders other than developmental dysplasia of the hip. All of the hips were reconstructed with the original standard 5-mm-thick socket. In addition to the eight patients with bilateral Conserve Plus resurfacing, four had a contralateral total hip arthroplasty. The average age (and standard deviation) at the time of the surgery was 43.7 ± 8.9 years (range, fifteen to 63.8 years). Nine patients (18%) were male and forty-two were female (82%); nineteen of the female patients were of childbearing age (forty years old or less). Fifty-two hips were classified as Crowe type I and seven, as Crowe type II²². In Crowe type-I developmental dysplasia of the hip, the vertical subluxation of the hip (measured from the inferior margin of the teardrop to the head-neck junction) is <50% of the diameter of the normal femoral head (or <10% of the height of the pelvis on an anteroposterior pelvic radiograph). Crowe type-II hips show vertical subluxation of 50% to 75%. The selection criterion for this study was a center-edge angle of =20° or a history of developmental dysplasia of the hip treated previously with an osteotomy. Nine previous osteotomies (three acetabular and six femoral) had been done in eight hips (one hip had both types of osteotomy). Two of these hips had had multiple (as many as seven) operations before the resurfacing. In addition to acetabular dysplasia, a severe deformity of the femoral head was seen in eighteen hips.

The study was approved by our institutional review board and was conducted as a Food and Drug Administration investigational device exemption trial with continued access. The indications for hip resurfacing were a young age and/or high activity level for patients with end-stage joint degeneration.

All resurfacings were performed by the senior author. A posterior approach was used in all hips but one, for which a transtrochanteric approach was employed. The acetabular shell is hemispherical (170°) with a sintered porous coating for cementless fixation, which was a 1-mm press-fit in all cases. All of the shells used in the series were 5 mm thick. The details of the initial surgical technique have been described elsewhere^23,24. All acetabular components were placed with at least 60% bone coverage in the frontal plane, with the component medialized to increase coverage and placed at the an-atomic hip center. Sixteen femoral metaphyseal stems were cemented.

The patients stayed in the hospital for an average of four days. Low-dose Coumadin (warfarin) was used for prophylaxis against deep venous thrombosis. Partial weight-bearing was maintained for six weeks. Radiographic and clinical follow-up evaluations were performed at six weeks, at three months, and then yearly. One patient did not provide any postoperative radiographs, but her clinical data were recorded. All follow-up examinations were performed by the senior author at our center or in one of twenty nationwide, annually held, satellite clinics.

Clinical follow-up included calculation of Harris hip scores²⁵, University of California at Los Angeles (UCLA) hip scores²⁶, and Short Form-12 (SF-12) scores²⁷; measurement of the range of motion; and evaluation of limb length by block testing. Abductor and body weight lever arms^28,29 were measured on radiographs preoperatively and postoperatively, and femoral stem-shaft angles were recorded as an assessment of component positioning in the frontal plane³⁰. Radiolucent lines of >1 mm in thickness around the acetabular shell were recorded on the basis of the zones described by DeLee and Charnley³¹. For the femoral side, a radiographic rating system was devised in which a score of 0 to 9 points was assigned on the basis of radiolucency in three zones around the femoral stem¹⁹. We considered a score of =7 points to be an indication of a risk of loosening.

Failures included conversion to total hip arthroplasty for any reason. Postoperative complications such as dislocations, infections, fractures, nerve injuries, and reoperations were noted.

Two-tailed paired Student t tests were used to compare preoperative and postoperative data. Comparisons between subgroups of the cohort were carried out with use of two-tailed, two-sample equal variance Student t tests. A p value of <0.05 was deemed to be significant.

Results

Materials and Methods | Results | Discussion | References

Clinical Results

The average follow-up period was 6.0 years (range, 4.2 to 9.5 years). Preoperative and postoperative UCLA hip scores, SF-12 mental and physical scores, and postoperative Harris hip scores are summarized in Table I. The activity scores of the patients in whom the hip had been resurfaced despite poor bone quality (femoral cysts of >1 cm) were significantly lower than those of patients with good bone quality (mean, 7.18 compared with 7.50 points, p = 0.0001). Of the twenty-one Charnley class-B patients (with involvement of the contralateral hip), thirteen (62%) had bilateral implants at the time of the last follow-up. (One had the second hip resurfaced, but the duration of follow-up was too short for that hip to be included in this series.) With the numbers studied, there was no significant difference (p = 0.269) between the Harris hip scores of the Charnley class-A patients (unilateral involvement) and those of the Charnley class-B patients. The preoperative and postoperative ranges of motion are reported in Table II.

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TABLE I Preoperative and Postoperative Clinical Scores

	Average Score (Range) (points)
	Preop.	Postop.	P Value
UCLA
Pain	3.2 (1 to 5)	9.3 (2 to 10)	0.0001
Walking	6.0 (3 to 9)	9.7 (6 to 10)	0.0001
Function	5.7 (3 to 10)	9.6 (4 to 10)	0.0001
Activity	4.6 (2 to 8)	7.3 (2 to 10)	0.0001
SF-12
Physical	31.7 (17 to 57)	51.4 (19 to 61)	0.0001
Mental	46.6 (20 to 67)	53.5 (26 to 62)	0.0001
Harris hip score^*	Not available	92.5 (41 to 100)	Not available

The data specific to the computation of the Harris hip score were collected after January 2000 only, in anticipation of the beginning of the Conserve Plus clinical trials, and are missing for the first twenty cases in this series.

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TABLE I Preoperative and Postoperative Clinical Scores

	Average Score (Range) (points)
	Preop.	Postop.	P Value
UCLA
Pain	3.2 (1 to 5)	9.3 (2 to 10)	0.0001
Walking	6.0 (3 to 9)	9.7 (6 to 10)	0.0001
Function	5.7 (3 to 10)	9.6 (4 to 10)	0.0001
Activity	4.6 (2 to 8)	7.3 (2 to 10)	0.0001
SF-12
Physical	31.7 (17 to 57)	51.4 (19 to 61)	0.0001
Mental	46.6 (20 to 67)	53.5 (26 to 62)	0.0001
Harris hip score^*	Not available	92.5 (41 to 100)	Not available

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TABLE II Preoperative and Postoperative Range of Motion

	Average Range of Motion (Range) (deg)
	Preop.	Postop.	P Value
Flexion	106 (70 to 150)	129.6 (90 to 170)	0.0001
Flexion contracture	15.9 (0 to 45)	0.9 (0 to 10)	0.0001
Abduction^*	26.4 (-10 to 55)	48.1 (25 to 65)	0.0001
Adduction^*	15.5 (-10 to 45)	28.8 (20 to 40)	0.0001
Rotation arc^*	32.1 (0 to 85)	84.8 (40 to 130)	0.0001

Measurements performed in extension.

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TABLE II Preoperative and Postoperative Range of Motion

	Average Range of Motion (Range) (deg)
	Preop.	Postop.	P Value
Flexion	106 (70 to 150)	129.6 (90 to 170)	0.0001
Flexion contracture	15.9 (0 to 45)	0.9 (0 to 10)	0.0001
Abduction^*	26.4 (-10 to 55)	48.1 (25 to 65)	0.0001
Adduction^*	15.5 (-10 to 45)	28.8 (20 to 40)	0.0001
Rotation arc^*	32.1 (0 to 85)	84.8 (40 to 130)	0.0001

Measurements performed in extension.

Preoperatively, twenty-two patients (43%), one of whom had bilateral disease, had a limb-length discrepancy. The amount of discrepancy was determined by placing blocks under the short limb to level the pelvis and then asking the patient to bend forward to make certain the sacrum was level. All of the patients who had equal limb lengths preoperatively had equal lengths postoperatively. Of the twenty-three patients with a preoperative limb-length discrepancy, sixteen had equal lengths postoperatively and seven had a residual discrepancy. Table III summarizes the preoperative and postoperative data on the severity of the discrepancies.

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TABLE III Limb-Length Discrepancy

	No. of Patients
	Equal Lengths	Short <1 cm	Short 1-<2 cm	Short 2-3 cm
Preop.	29	10	10	2
Postop.	44	3	2	2

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TABLE III Limb-Length Discrepancy

	No. of Patients
	Equal Lengths	Short <1 cm	Short 1-<2 cm	Short 2-3 cm
Preop.	29	10	10	2
Postop.	44	3	2	2

Four patients (average age, thirty-three years; range, twenty-three to thirty-nine years) in this series had normal pregnancies and gave birth to a total of six healthy children since the time of the resurfacing.

Radiographic Results

The average abductor lever arm was 53.9 mm (range, 35 to 95 mm) preoperatively and 55.9 mm (range, 40 to 72 mm) postoperatively (p = 0.63). The average body weight lever arm was 118.5 mm (range, 90 to 145 mm) preoperatively and 103.9 mm (range, 80 to 121 mm) postoperatively (p < 0.007). No patient had an abductor limp, and a positive Trendelenburg sign was reversed in fourteen patients. The average stem-shaft angle was 140.1° ± 7.9° (range, 120° to 160°). The outer diameter of the cup averaged 52 mm (range, 46 to 62 mm), with an average abduction angle of 42.9° (range, 24° to 56°). The average center-edge angle was 14.6° ± 10.7° (range, 0° to 55°), with eight hips having had a prior acetabular osteotomy.

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Fig. 1-A and Fig. 1-B: Fig. 1-A Preoperative radiograph of a thirty-two-year-old woman. Note the extreme deformity of the femoral head. There was 2 cm of limb shortening compared with the contralateral side. The inset shows the femoral head after preparation. No bone was removed from the dome, and multiple drill holes were made in this sclerotic bone. Fig. 1-B The femoral component loosened at seventy-four months, and the hip was revised to a stem-type total hip arthroplasty with use of a large (44-mm) femoral head corresponding to the inside diameter of the Conserve Plus socket left in situ. The inset shows a microradiograph of the sectioned retrieved head. The black area around the bone is fibrous tissue. Note the excessive amount of cement that was applied in the dome area in an attempt to compensate for the limb-length discrepancy, with the component left proud, which we believe was a contributing factor in the ultimate loosening of the component.

One femoral stem was associated with radiographic lucency, but the patient was symptom-free at the time of the last follow-up. There were no cases of acetabular loosening or changes in the position of the acetabular component. One patient exhibited two radiographic lesions of <1 cm on the femoral neck. These lesions were consistent with bone resorption, but they did not seem to be progressing at the time of the most recent examination.

Conversion to Total Hip Arthroplasty

Six hips required conversion to a total hip arthroplasty. One was converted at four years, after multiple subluxations secondary to impingement. The patient had had prior valgus femoral and acetabular osteotomies resulting in poor femoral offset, which was responsible for trochanteric-ischial impingement. The other five hips were revised because of a femoral failure (two femoral neck fractures, at two and five months²¹, and three cases of femoral component loosening, at three, 6.2, and 8.4 years; Figs. 1-A and 1-B, and 1-C). All six hips were successfully converted to a total hip arthroplasty. All of the episodes of loosening occurred in the first fourteen hips to be treated in this series.

Complications

There were two cases of instability in addition to the case described above. A sixty-three-year-old woman required acetabular reorientation three days after the surgery, when it was recognized that there was excessive anteversion of the cup, and another patient had a postoperative dislocation secondary to extensive soft-tissue release to locate a broken scalpel blade. The postoperative dislocation required closed reduction only, and the hip was stable for the next 7.5 years³². There were also a femoral nerve palsy and a postoperative femoral vein clot followed by bleeding associated with the use of heparin, all in the same patient. These complications resolved without sequelae.

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Fig. 1-C: Anteroposterior radiograph showing the hip four months after conversion to a total hip arthroplasty. A 44-mm unipolar femoral head matching the well-fixed acetabular cup was used with a double-wedge tapered grit-blasted stem.

Discussion

Materials and Methods | Results | Discussion | References

Hip resurfacing with polyethylene bearings in patients with developmental dysplasia of the hip resulted in high failure rates. In one study⁹, 65% of THARIES surface arthroplasties (Zimmer, Warsaw, Indiana) failed at an average of five years. The dominant mode of failure was acetabular loosening (71%), often with considerable bone loss. The remainder of the failures were associated with femoral neck fracture (16%) or aseptic loosening (13%). New surface arthroplasty implants with metal-on-metal bearing surfaces and a thinner non-cemented acetabular cup have alleviated the problems of osteolysis secondary to polyethylene debris and have been associated with markedly improved prosthetic survival.

The main limitations of the present retrospective review are related to the relatively short follow-up, as more definite answers would be provided with a minimum of ten years of follow-up. The clinical results (pain, walking, function, and Harris hip scores) of the patients in this series were similar to those reported for other patients treated with this resurfacing arthroplasty¹⁹, regardless of the etiology of the disease (Figs. 2-A and 2-B). There were no socket failures and no radiographic signs of loosening of the acetabular component in this series, despite the absence of adjunctive fixation and the incomplete bone coverage laterally. In this study, the hip center was routinely medialized, possibly enhancing cup fixation. The rough porous beaded surface locks the socket into the bone with impaction and provides rigid initial stability when the cavity is reamed correctly to 1 mm less than the outside dimension of the component. The initial stability is obtained primarily from an interference fit between the anterior and posterior columns^23,24. Because of this very secure stability, it is possible to leave the component uncovered laterally by as much as 20%, as was done in seventeen cases.

The two femoral neck fractures in this series were previously reported²¹ and were analyzed in retrieval studies performed in a group of more than 600 implants. The risk factors for femoral neck fracture included poor bone quality with large cysts and inadequate component seating²¹. Because of poor bone quality, both patients would have been better served by an initial total hip arthroplasty, but both have done well after uncomplicated conversions to a total hip arthroplasty.

Three of the femoral components that loosened or were associated with radiolucency were implanted in hips with severe cystic disease³³. In another hip with femoral loosening, as illustrated in Figures 1-A and 1-B, and 1-C, the bone was sclerotic as a result of reconstruction without removal of any dome bone and the femoral component was left proud with a thick cement mantle. We previously reported that femoral cysts and small component size (<48 mm) were known to be the most important risk factors for aseptic loosening of femoral components inserted with the bone-preparation and cementation techniques utilized at that time^19,20. However, we do not believe that the procedure is contraindicated in hips with these risk factors, especially in young patients (less than fifty-five years of age) because we have improved the initial stability with changes in our surgical technique. It is now our practice to cement the metaphyseal stem in hips that both require a small femoral component (<48 mm) and have large cysts (>1 cm). Other changes in technique include much more meticulous bone preparation with removal of cystic material, the addition of 0.125-in (3.2-mm) drill holes into the dome and chamfered areas, jet lavage, and drying with use of suction of both the dome and subsequently the lesser trochanter when the component is placed on the head^24,33. Since we made these modifications in our technique, there have been no cases of loosening and the components have remained stable despite high activity levels (a UCLA activity score of >7 points) of twenty-two patients (43%), including a professional tennis instructor who had good bone quality. It is also now our practice to recommend nonimpact recreational sports when there are large cystic defects, and, reflecting this advice, the activity scores of the patients with such defects were lower than the scores for those with good bone quality.

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Fig. 2-A and Fig. 2-B: Fig. 2-A Preoperative radiograph of a thirty-five-year-old woman, an ideal candidate for resurfacing because of a high head-neck ratio and absence of femoral bone cysts. Note the lateral subluxation of the femoral head. The inset shows the femoral head after bone preparation; the bone quality is excellent. Fig. 2-B At 5.8 years following resurfacing, the patient had excellent clinical scores (UCLA scores of 10 points for pain, walking, and function and 7 points for activity) and an excellent range of motion.

The five conversions to total hip arthroplasty done at our hospital were performed without complications. Two of them were done with a unipolar ball with the well-fixed socket left in situ. In the other three cases, the socket was exchanged because the unipolar balls were not then available. These sockets were removed, with some loss of bone, with use of standard curved gouges, and the replacement socket was an average of 4 mm (range, 2 to 6 mm) larger than the initial shell.

Dislocation rates after total hip arthroplasty in patients with developmental dysplasia of the hip have ranged from 0% to 11% in the literature^5-7. Gerber and Harris reported a dislocation rate of 10% in forty-seven hips at six to eight years following treatment with head sizes in the 22 to 26-mm range³⁴. However, Silber and Engh reported no postoperative dislocations or problems with instability in nineteen hips followed for an average of three years after treatment with a 22, 28, or 32-mm head¹². We had hoped that the inherent stability of the larger head size (average, 42 mm) used in our patients would eliminate dislocation as a complication, and the dislocation rate of 5% is disappointing. However, the dislocations in our series were related to patient selection and technique issues, and the review of these cases and subsequent experience indicate that this prevalence can be effectively reduced by optimizing the technique. Because hips with developmental dysplasia are flexible and are likely to achieve extraordinary mobility, it is now our practice to increase the anteversion of the socket to 20° to 30°, especially in women, to favor internal rotation. Our checks of stability after component insertion have also been modified to include a better assessment of anterior stability²⁴. Forty degrees of external rotation in extension is desirable, and any sources of impingement should be corrected. We recommend that the socket be inserted below the rim of the anterior wall to reduce the possibility of iliopsoas irritation. In cases of severe anteversion of the femoral head (>20°), the anteversion of the socket should be lessened.

Limb-length equalization was achieved in the majority of our patients. Forty-four of our fifty-one patients had equal limb lengths postoperatively. In general, full normalization of limb lengths and hip biomechanics is more challenging with resurfacing than with total hip arthroplasty. When the anatomy is severely abnormal, it is unusual to be able to safely gain >1 cm of length, and this can be accomplished only by reaming and implanting the socket distal to the location of the dysplastic acetabulum, at the location of the true acetabulum, and most certainly not by leaving the femoral component proud on the reamed femoral head²¹.

There has been some concern regarding the advisability of implanting metal-on-metal implants in women of child-bearing age because of a concern that the ion levels may cause birth defects. Brodner et al.³⁵ reported on three women who had elevated serum ion levels following metal-on-metal total hip arthroplasty but found no cobalt or chromium ions in the cord blood at the level of detection of the testing facility utilized. At present, there is insufficient data to determine the level of risk, and ongoing studies to establish baseline levels in women of child-bearing age and to monitor levels in their children are recommended.

In conclusion, the medium-term clinical results of the Conserve Plus metal-on-metal surface arthroplasty in patients with Crowe type-I or II developmental dysplasia of the hip did not meet our initial expectations, although the porous-coated socket fixation has been excellent. While the prevalences of femoral neck fracture and femoral component loosening have been higher than desired, we have been able to lessen the risk of femoral loosening and neck fracture by improving patient selection as well as with femoral bone preparation and fixation including cementing of the stem in patients at risk for loosening. ?

References

Materials and Methods | Results | Discussion | References

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Gill TJ, Sledge JB, Muller ME. Total hip arthroplasty with use of an acetabular reinforcement ring in patients who have congenital dysplasia of the hip. Results at five to fifteen years. J Bone Joint Surg Am.1998;80: 969-79.80969 1998

Nunn D. The Ring uncemented polyethylene cup in the abnormal acetabulum. J Bone Joint Surg Br.1987;69: 756-60.69756 1987 [PubMed]

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Topics

femoral neck fractures ; femur ; hip region ; hip dislocation, congenital ; hip joint ; metals ; arthroplasty ; hip replacement arthroplasty ; dysplasia

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Harlan C. Amstutz, John T. Antoniades, Michel J. Le Duff; Results of Metal-on-Metal Hybrid Hip Resurfacing for Crowe Type-I and II Developmental Dysplasia. The Journal of Bone & Joint Surgery. 2007 Feb;89(2):339-346.

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