Reducing the failure rate of hip resurfacing in dysplasia patients: a retrospective analysis of 363 cases

Implant systems

The senior author used three separate implant systems in a consecutive fashion. Beginning in March 2001, Hybrid Corin Cormet 2000 (Corin, Cirencester, UK) devices were employed as part of a multicenter United States Food and Drug Administration trial. Beginning in 2005, Biomet (Biomet, Warsaw, Indiana) devices comprised of a cemented ReCap™ femoral component and an uncemented Magnum™ acetabular component were used. Beginning in 2007, we initiated the use of completely uncemented Biomet ReCap™ Magnum™ devices, with the Magnum™ Tri-Spike component used in higher-risk patients with the largest deformities. Currently, all devices are uncemented. Using these Biomet devices in the procedure reported here falls under the category of off-label use in the United States.

Procedure

This study spans a period of 11 years during which surgical technique evolved. A summary of surgical information from these cases is listed in Table 1. Over time, we recognized several key features in dysplasia patients: The acetabulum is always oval to a varying degree, which is present at birth and increases as the hip wears. The long axis of the oval is always from posterior inferior to anterior superior. The head rides into the superior corner of the oval and then begins to sublux. The thickest bone for placing the cup is posterior inferior. The cup is shallow, and medial wall thickness is variable (Fig. 3a). These patients exhibit hypermobility and are prone to dynamic posterior pelvic tilt on standing. The transverse acetabular ligament (TAL) is an excellent reference point for judging correct anteversion.

	Pre-2008, Group 1 (N = 121)	Post-2008, Group 2 (N = 242)	P-value
Sex (no. of hips)
MALE	35 (29 %)	64 (26 %)	0.6171
FEMALE	86 (71 %)	178 (74 %)
DECEASEDa	3 (2.5 %)	1 (0.4 %)	0.0751
Follow-up Mean Years	6.4 ± 2.31	2.6 ± 1.51	<0.0001b
Case Date Range	1/2001–7/2008	7/2008–7/2013	--
Age (yr)	48 ± 8.37	52 ± 7.05	<0.0001b
BMI	26 ± 5.04	26 ± 5.08	1.000
T-score	−0.34 ± 1.44	−0.40 ± 1.10	0.6599
Overall Failures (no. of hips)	16 (13.2 %)	2 (0.8 %)	<0.0001b
2-Year Raw Failures (no. of hips)	8 (6.6 %)	2 (0.8 %)	0.0015b
7-Year Survivorship (no. of hips)	108 (89.3 %)	240 (99.2 %)	<0.0001b
Dysplasia Grade (no. of hips)
Dysplasia I	37/51 (73 %)	188/241 (78 %)	0.4009
Dysplasia II	10/51 (20 %)	49/241 (20 %)	0.9045
Dysplasia III	0/51 (0 %)	0/241 (0 %)	1.000
Dysplasia IV	0/51 (0 %)	0/241 (0 %)	1.000
Dysplasia Osteotomy	4/51 (7.8 %)	4/241 (1.7 %)	0.0139b
Grade Unrecorded	70/121 (58 %)	1/242 (0.4 %)	<0.0001b
ASA Score	1.6 ± 0.55	1.6 ± 0.56	1.000
Femoral Component <48 mm (no. of hips)	46/121 (38 %)	79/242 (33 %)	0.3077
Femoral Component Size	48.1 ± 3.45	47.0 ± 2.91	0.0016b

^aDied with the causes unrelated to their hip arthroplasties

^bStatistically significant

DeSmet [22] demonstrated that steeper, more anteverted components were problematic especially in dysplasia patients with smaller bearing sizes (34 % patients in this study had bearing size < 48 mm). He defined the useful concept of coverage arc, which depends largely on the design features of the implant and its proper surgical positioning. We further developed this concept with the Relative Acetabular Inclination Limit (RAIL) guideline [23] (Fig. 1) for placing components based on bearing size. The RAIL dictates an acetabular inclination angle (AIA) limit on a standing AP pelvis x-ray that is different for each bearing size. We placed an arbitrary lower AIA limit of 25° on the guideline. We next developed a technique to obtain an intraoperative x-ray that was normalized to the standing position (unpublished). These techniques were fully established by mid-2008.

All operations were performed by a single surgeon (TPG). Cemented femoral components were implanted using small amounts of high-viscosity cement on both the bone and implant surfaces with an escape trough machined into the femoral head. In Group 2, stems were never cemented.

The posterior approach used in these cases was described previously [24]. A 4- to 6- in. skin incision is made; the gluteus maximus, quadratus femoris, and all 3 short rotators are released off of the bone and are subsequently repaired, the conjoined tendon is incised 1–2 cm, a neck-sparing complete capsular division and repair is performed. A pocket is created under the minimus for later placement of the head.

The head is first prepared. Typically, it is oval and foreshortened. Therefore, more is typically trimmed from the periphery than from the apex. The neck gauge is applied to measure the smallest femoral component possible. The central guidewire is placed. Although it is not critical, we attempt to place the stem neutral down the center of the neck and parallel to the calcar. There is no way to alter femoral version, and we are of the opinion that it does not matter. We have never found the need for a femoral derotation osteotomy. The head is then typically cut 6 mm (3 sizes) larger than the smallest component possible (neck gauge). If there is doubt, we cut one size larger (2 mm) and later come back and trim it down if necessary after the acetabulum is implanted. The trial head is placed and the head is then tucked into the pocket under the minimus and held with a double-angled Hohmann retractor.

The thickened labrum is excised except for a small band in the anterior inferior region against the psoas. The TAL must be preserved during this maneuver, because it is the best guide for anteversion. We find it a reliable guide even in the face of the acetabular deformity. The reamer equal to the prepared head size is used first. It is inserted at a 45° angle with the floor but pulled firmly inferiorly and posteriorly while pushing centrally (Fig. 3b). It is forced to progress into the thick posterior wall and down to the quadrilateral plate. If the surgeon is not careful and allows the reamer to seat anterior superior (AS) into the oval defect while reaming, the entire preparation is incorrect and cannot be salvaged. This cannot be overemphasized. This initial preparation serves several purposes. First, the cavity is prepared in the thicker posterior bone. Second, the anterior inferior (AI) bone adjacent to the psoas is preserved. Third, the center of rotation is corrected in high-riding cases. The medial wall is then drilled at the superior edge of the fovea and a depth gauge is used to measure the medial wall. For proper cup coverage, the cavity can be medialized until 6 mm remains medially. As soon as the optimum medial position has been achieved, larger reamers are used to expand the cavity (Fig. 3c). The reamer handle is still firmly held posteriorly and inferiorly, but the grip is slightly loosened to allow the reamer to progress slightly into the oval defect AS. A line-to-line reaming is performed if the dual energy x-ray absorptiometry (DEXA) T-score exceeds −1.0 (good bone). A 1-mm under-reaming is employed when the T-score falls below −1.0 (soft bone) (T-score is a reference to gender and race specific bone density in a healthy, young 25-year old [25]; a normal T-score is from 1 to −1). A clean reamer 1 mm larger than the head size is then used to deepen the apex of the cavity by 1–2 mm. This prevents the cup from bottoming out at the apex of the cavity and instead creates a wedge fit on the rim. The trial is placed and aligned with the TAL with an AIA dictated by the RAIL guideline. If a significant amount of the oval defect remains such that 30 % or more of the component wall is uncovered (Fig. 3d), a Tri-Spike component (Fig. 4) is chosen. If the preoperative T-score is less than −2.5, a Tri-Spike is also chosen. Otherwise, a standard Magnum™ cup is used. Approximately 5 % of these cases required a Tri-Spike component since it became available. The trial is used to determine if three criteria are met: AIA is within RAIL guidelines, anteversion is parallel to the TAL, and the cup edge is below the bone edge in the AI corner adjacent to the psoas. If these criteria are not met, the cavity typically needs to be deepened slightly to allow the trial to satisfy these conditions. After assuring the trial criteria are met, the cup, which is hemispherical with a rough titanium plasma spray coating and 4 sharp fins, is lightly impacted into the prepared cavity with a curved inserter. The position is then finely tuned with a plastic tip tamp and mallet. If the cup needs to be removed, a metal tip tamp is used on the exposed edge. When the position is correct, a secondary impactor designed to ride over the edge of the cup is used for a final impaction with a large mallet. If a Tri-Spike component is used, repositioning requires removal; technically, these are more difficult to orient perfectly according to the above criteria.

The head is trimmed if necessary to match the acetabular component. The Magnum™ cup outer diameter is 6 mm larger than the head/bearing size. All cysts are curetted and grafted. The ReCap™ component is impacted until sonic change indicates that it is fully seated. The hip is reduced and an x-ray is obtained. Closure is routine, repairing all structures anatomically in multiple layers.

Normalized to standing intraoperative x-ray

The normalized intraoperative x-ray technique (fully-developed by mid-2008) utilizes a portable, digital x-ray machine that enables immediate comparison of an image taken in the operating room (OR) with the patient’s preoperative standing x-ray. After the acetabular component is implanted according to the technique described previously [24], the OR table is rotated until the surgeon judges the pelvis to be neutral. The first film is taken. The surgeon inspects the width of the obturator foramina on the image and then asks the anesthetist to roll the table right or left to correct for any rotation. Films are repeated until the widths of the obturator foramina are symmetrical. The surgeon then compares the height of the obturator foramina to the height seen on the preoperative standing AP pelvis x-ray. The x-ray machine is tilted cephalad or caudad and films are repeated until the obturator foramina and the pelvic inlet appear as they do on the preoperative standing AP pelvis x-ray. Thus, the end result is an intraoperative image of the pelvis normalized to the patient’s preoperative standing position. This image is sent to the desktop computer in the OR and the AIA is measured. If the AIA does not meet RAIL criteria (Fig. 4), the cup is repositioned and another x-ray is obtained. With practice, this process typically takes less than 2 min, and less than 5 % of cups need repositioning.

Postoperative protocol

We previously concluded that the risk of EFF (early femoral failure: femoral neck fracture and collapse) depends largely on two factors: bone density (femoral neck T-score) and BMI [26]. Our bone management protocol establishes three groups based on these risk factors: Group A, femoral neck T-score score > 0 and BMI < 30; Group B, femoral neck T-score between 0 and −1.5 and/or BMI > 30; and Group C, femoral neck T-score < −1.5.

Group A patients are allowed to progress weight-bearing as tolerated (WBAT). They typically use crutches for 1–2 weeks and a cane for 1–2 weeks. Group B patients are also allowed WBAT but are prescribed alendronate for 6 months. Patients from Group C or any patients who require a Tri-Spike cup are placed on a slowed weight-bearing protocol and are prescribed alendronate for 1 year. They are asked to do 10 % weight-bearing for 4 weeks, WBAT with crutches for 2 weeks, and a cane for another 4 weeks. Isometric leg lifts, light aerobic activity (such as exercise bike and swimming), lower extremity weight lifting less than 50 lb, golf, and unrestricted walking is encouraged at 6 weeks for Groups A and B and at 10 weeks for Group C patients. All restrictions in all patients are lifted at 6 months, and they are encouraged to participate in full-impact sports. No formal physical therapy is requested of the patient after hospital discharge.

Deep vein thrombosis precautions include sequential compression devices started intraoperatively and discontinued at the time of hospital discharge. Ambulation and leg exercises are started within 24 h. Oral anticoagulants are started at 24 h postoperative and continued for 2–4 weeks, depending on risk analysis. Then, 81 mg aspirin is recommended for another month.

A multimodal pain management protocol and a comprehensive blood management protocol are used to eliminate transfusion and speed recovery. In the last 3 years, resurfacing has been performed as an outpatient procedure on selected patients.

Metal ion testing

Clinical and radiological analysis

Office or remote follow-up was requested at 6 weeks, 1 and 2 years, and every other year thereafter. A clinical questionnaire, radiographs, and a physical examination testing ROM and strength were performed at each visit. After 1 year, physical examinations were no longer done routinely on remote follow-ups. The OrthoTrack database (Midlands Orthopaedics, Columbia, South Carolina) supported our collection and analysis of the demographic, clinical, and radiographic data for all patients.

Patient questionnaires requested information necessary to calculate the following scores for clinical evaluation: Harris hip score (HHS) [29], University of California, Los Angeles (UCLA) activity score [30], and visual analog scale (VAS) pain score for normal and worst days [31]. HHS determines clinical outcome; UCLA activity scores measure activity level after surgery on a scale from 1 to 10, for which 10 represented the highest level of activity; VAS pain scores rate the level of pain from 0 to 10, with zero representing no pain and 10 representing maximum levels of debilitating pain.

Both supine and standing AP pelvis and lateral radiographs are taken and analyzed for component position, shifting, and radiolucencies by the senior author. The AIA is determined by measuring the angle formed between 2 straight lines: one running across the face of the acetabular component and the other across the inferior pubic rami (Fig. 2). All measurements were performed using OrthoTrack (Midlands Orthopaedics).

Statistical methods

The significance level α was defined as 0.05 for all statistical analyses in this study. A paired, 2-tailed T-test was used to calculate the significant difference between preoperative and postoperative numerical outcomes within and between dysplasia study groups; the Student’s T-test was used to compare the difference of numeric variables between groups. When comparing two population proportions, a two-sample Z-test was used. Statistical tests were performed using SAS (Cary, NC). Kaplan-Meier survivorship curves were plotted to evaluate implant survival among different groups. Log-rank and Wilcoxon tests were performed to calculate significant differences between survivorship curves. Curves and survivorship statistical tests were generated using XLSTAT (New York, NY).