Article Index

Guido Grappiolo, Mattia Loppini, Umile Giuseppe Longo, Francesco Traverso, Giuseppe Mazziotta, Vincenzo Denaro

Abstract

Fifty-five hips undergoing acetabular reconstruction with trabecular metal (TM)-coated cup and TM augments were reviewed at an average follow up of 53.7 months (36–91). Bony defects were Paprosky type IIIA in 42 and type IIIB without pelvic discontinuity in 13 hips. The average HHS increased from 40 (27–52) preoperatively to 90.5 (61–100) postoperatively (P < 0.0001). Four (7.3%) of 55 hips underwent acetabular components revision: three cases of loosening (5.4%), and one of recurrent instability (1.8%) were reported. Survival rate at 2 and 5 years was 96.4% and 92.8%. In conclusion, the use of TM-coated cups and augments could be considered an effective management of Paprosky type III defects without pelvic discontinuity providing good clinical and radiographic outcomes in the mid term.


Keywords 

total hip arthroplasty; acetabular reconstruction; bone defect; trabecular metal; augment

The management of severe acetabular bone defects in hip revision surgery is challenging. The goals of revision surgery include to correct the cranial migration of the hip center of rotation (COR) restoring the biomechanics of the hip with an effective function of the abductors [1], and to preserve the acetabular bone stock.

The use of trabecular metal (TM) cups has widely increased during the past decade 2., 3., 4. and 5.. TM is a biomaterial made out of tantalum characterized by high 3D porosity (70–80%), high friction and low modulus of elasticity. It provides primary stability at the time of the procedure, and allows a deep bony in-growth leading to a secondary biologic fixation 6. and 7.. Because the type of bone defect is variable, the TM augments have been also introduced for the management of severe bone defects in the acetabular reconstruction. Indeed, the variability of augments in terms of size and shape allows to perform a customized reconstruction maximizing the contact with the host bone restoring the hip COR.

Given its biomechanical properties and biocompatibility, the association of TM cups and augments could represent an effective management of bone defects in acetabular reconstructions. Although some authors investigated the use of TM cups and augments in this setting 3., 8., 9., 10., 11., 12., 13., 14., 15., 16. and 17., they performed studies including patients with different types of bone defects, ranging from Paprosky grade IIA to grade IIIB with pelvic discontinuity, who underwent revision surgery using TM acetabular cups with or without TM augments. Therefore, data arising from these studies refer to non-homogenous populations managed with different surgical techniques. To our knowledge, only two previous studies assessed a small case series including patients affected by Paprosky type IIIA defect managed with the association of TM acetabular components and augments 10. and 11.. In our opinion, further evidence is required to confirm the effectiveness of TM-coated cup and augment association in Paprosky type III defects.

The aim of this retrospective case series was to assess the clinical and radiographic outcomes of TM augments associated with cementless TM acetabular components for the management of Paprosky type IIIA and IIIB defects without pelvic discontinuity. The null hypothesis was that the acetabular reconstruction with TM-coated cups and augments provides a statistically significant improvement of range of motions (ROMs) of the hip and Harris Hip Score (HHS) values, and reduction of limb-length discrepancy (LLD) and cranial migration of the hip COR.


Patients and methods

In the present study were included only patients who underwent acetabular reconstruction with the use of TM cup associated with TM augments because of aseptic loosening of the acetabular component. Moreover, only patients with a minimum follow-up of two years were included.

Clinical and radiographic evaluations were performed before and immediately after surgery, and one, three, six, and twelve months from surgery. Subsequently, all patients were examined once per year.

The clinical evaluation was performed by an independent physiatrist which was blinded for type of surgery, and included the physical examination with the measurement of ROMs of the hip and the HHS. The assessment of ROMs was performed with a universal goniometer according to standard measurement guidelines [18]. The HHS score ranged from 0 to 100 points and it was classified as follows: excellent (between 90 and 100), good (80–89), fair (70–79), and poor (< 70) [19]. At the last follow-up, the satisfaction of patients after surgery was evaluated with a self-reported scoring system including 4 stages: very satisfactory, satisfactory, moderately satisfactory, or unsatisfactory.

All patients had conventional radiographs in anteroposterior (AP) view of the pelvis and Lowenstein lateral view of the hip in both preoperative and follow-up evaluations. Two independent testers, one radiologist expert in musculoskeletal radiology and one senior orthopedic surgeon which was not involved in the surgery of these patients, were enrolled to grade the acetabular bone defects. Disagreements between the two testers were resolved by using the intraoperative description of the defect.

According to the classification of Paprosky et al [20], the acetabular defects were graded in the preoperative AP radiographs by using four bony landmarks: teardrop defect, ischial lysis, Kohler's line integrity, and superior defect with superior migration of the hip COR 20. and 21..

Radiographic assessments were performed by the radiologist expert in musculoskeletal radiology. The digital preoperative and postoperative radiographs in AP view were used to assess the LLD with the software Hip Arthroplasty Templating 2.4.3 running with OsiriX v.5.8.1 64-bit. The measurements were performed using the ischium and less trochanter as landmarks (Fig. 1 and Fig. 2). The preoperative and postoperative COR positions in the vertical axis from the interteardrop line and in the horizontal axis from the teardrop were also measured [17].

Fig. 1
Fig. 1.

Preoperative radiograph (AP view) showing aseptic loosening of the acetabular cup with a Paprosky type IIIA acetabular defect in a 47 year-old woman. The radiograph demonstrates superior lateral migration of the hip COR (37 mm above the superior obturator line), preserved Kohler's line, ischial, and lateral wall of the teardrop osteolysis. The line tangent to both ischium bones is used as landmark of pelvis position. The two lines crossing the tip of the lesser trochanter of each femur respectively are used to measure the limb-length discrepancy. In the present case, the preoperative limb-length discrepancy is 23.3 mm. A 10-cm reference line is reported.

Fig. 2
Fig. 2.

Postoperative radiograph (AP view) showing TM-coated cup and TM augment at one month in the same patient. The new hip COR is 15 mm above the superior obturator line. The preoperative limb-length discrepancy is 1.4 mm. A 10-cm reference line is reported.

The postoperative radiographs were assessed to detect radiolucent lines adjacent to the acetabular implant and/or augments according to DeLee and Charnley [22], or component loosening. The prosthetic construct was considered unstable if a radiolucent line with at least 1 mm of width crossed all three acetabular zones or if any component migration could be found. The fibrous stability of the construct was characterized by a radiolucent line with less than 1 mm of width crossing two of the three acetabular zones, while the construct was considered stable with presence of bone ingrowth if the prosthetic components were in close contact with pelvic bone and no radiolucent lines could be found in at least two of the three acetabular zones [3]. Loosening was defined by a change greater than 10° in the component abduction angle or if the whole cup moves 6 mm up or below, on vertical plane, or 6 mm medial or lateral, on horizontal plane, from his postoperative position [10]. The presence of heterotopic ossification was evaluated according to Brooker's classification [23].

Written informed consent was obtained from each patient before the surgical procedure. All procedures were performed through the posterolateral approach. The acetabular reconstruction was performed after the removal of failed components, debridement of the remaining acetabular cavity, and assessment of the acetabular bone loss. The location of the bony defect was reported by using a clock-face description where 12 o'clock indicated the side toward the head of patient, and 6 o'clock was the side toward the obturator foramen [24]. To clarify the data presentation, the site of defect was standardized to the right hip (Table 1).

Table 1.

Location of the Bony Acetabular Defect.

LocationNo. of Hips (n = 55)
From 8 o'clock to 1 o'clock 3
From 8 o'clock to 2 o'clock 5
From 9 o'clock to 1 o'clock 3
From 9 o'clock to 2 o'clock 4
From 9 o'clock to 3 o'clock 8
From 9 o'clock to 4 o'clock 2
From 9 o'clock to 5 o'clock 3
From 10 o'clock to 2 o'clock 7
From 10 o'clock to 3 o'clock 10
From 10 o'clock to 4 o'clock 3
From 10 o'clock to 5 o'clock 2
From 11 o'clock to 3 o'clock 2
From 11 o'clock to 4 o'clock 3

Because of the severe bone loss, in all patients no adequate primary stability of the acetabular trial could be obtained, and the acetabular tantalum augment (Zimmer, Warsaw, Indiana) was used to fill the defect and stabilize the cup. The number and position of the augments were determined by the bone loss pattern. The most common position was in the posterior-superior position. If necessary, the shape of the augments was modified with a metal cutting burr to provide an appropriate filling of the defect and increase the contact surface with the acetabular cup [10]. The median number of used augments was 1 (range, 1–3) (Table 2). The augments were fixed to the pelvic bone with a median number of 2 (range, 1–3) screws, maintaining the trial in place. The fenestrations within the augments and the remaining bony defects were filled with homologous morcellized cancellous bone in 26 hips and allograft cancellous bone chips in 29. No patient received a structural bone graft. The modular multi-hole shell (Zimmer, Warsaw, Indiana) was used in all patients, with a median diameter of 54 (range, 44–70) (Table 2). The cup was placed with a press-fit technique. Before impacting, polymethylmethacrylate cement was placed in the external surface of the definitive cup only in the areas facing the augments [8]. Finally, a median number of 3 (range, 2–7) screws was used to secure the acetabular component to the pelvic bone and increase the primary stability of the construct. Highly cross-linked polyethylene liner was used in all hips (Table 2). The bearing surfaces were metal on polyethylene in 35 hips, ceramic on polyethylene in 20.

Table 2.

Details on Implanted Acetabular Components and Liners.

Acetabular ComponentNo. of Hips (n = 55)
Cups  
 Modular multi-hole shell: 55
 44 mm-diameter 1
 48 mm-diameter 2
 50 mm-diameter 10
 52 mm-diameter 8
 54 mm-diameter 18
 56 mm-diameter 1
 58 mm-diameter 8
 62 mm-diameter 4
 64 mm-diameter 2
 70 mm-diameter 1
Augments  
 52 × 20 mm 2
 54 × 20 mm 18
 54 × 15 mm 13
 54 × 10 mm 11
 58 × 20 mm 5
 58 × 15 mm 1
 58 × 10 mm 4
 62 × 20 mm 2
 62 × 10 mm 2
 66 × 20 mm 2
 66 × 15 mm 2
 66 × 10 mm 3
Liner  
 Highly cross-linked polyethylene liner 55
 Standard 4
 10° elevated rim 41
 20° elevated rim 10
Femoral head  
 28 mm-diameter 1
 32 mm-diameter 52
 36 mm-diameter 1
 40 mm-diameter 1

The patients were allowed to stand on the second postoperative day, and to walk with crutches and a 50% of weight-bearing. During the eight weeks following the surgery, they underwent a physical therapist-assisted rehabilitation program to progressively increase abductor resistance and weight-bearing. After two months, patients were allowed to walk without crutches and full weight-bearing.

All the analyses were performed using SPSS for Mac (version 16.0, SPSS Inc, Chicago, Illinois). The categorical data collected for the study were gender, preoperative diagnosis, type of acetabular bone defect, satisfaction of the patient after surgery, radiological loosening of the acetabular components, radiolucent lines adjacent to the acetabular implant and/or augments, and heterotopic ossification. The numerical data collected for the study were age, BMI, HHS values, ROMs of the hip, LLD, and cranial migration of the hip COR. Descriptive statistics was calculated. The statistical significance of improvement of HHS values, ROMs of the hip, and LLD was assessed using the two tails Wilcoxon signed ranks test for paired sample because the data were non-normally distributed. A P value less than 0.05 was considered significant.

The kappa coefficient was used to assess the intratester and intertester agreement. The morning and afternoon evaluations were used to estimate kappa for the intratester agreement. To estimate the intertester agreement, the morning and afternoon assessments were pooled. The strength of agreement from kappa values was interpreted as follows: less than 0.20, poor; 0.21–0.40, fair; 0.41–0.60, moderate; 0.61–0.80, good; and 0.81–1.00, very good.

Implant survival was defined as the time from first revision surgery with TM cup and augment to revision of acetabular prosthetic components for any reason and was estimated with Kaplan–Meier method. Ninety-five percent confidence intervals were calculated.


Results

Between February 2005 and January 2011, 65 hips (64 patients) underwent acetabular reconstruction with the use of TM cup associated with augments. Of these, 9 were excluded because of the preoperative diagnosis: “one-stage” and “two-stage” THA reimplantation for infection in 2 and 3 hips respectively, Girdlestone in 3, and chronic hip displacement in 1. One hip with a preoperative diagnosis of aseptic loosening was excluded because the patient died of pneumonitis 18 months after surgery.

Finally, 55 hips (54 patients) were included in the study. According to the classification of Paprosky et al [20], a Paprosky type IIIA defect was found in 42 hips, whereas a Paprosky type IIIB defect was present in 13 hips. No patients had pelvic discontinuity. Of those, 30 underwent revision of the acetabular component alone, 25 received a total revision surgery. Patients included 18 men and 36 women, with an average age of 63.5 years (range, 35–86) at the time of surgery. The average body mass index was 26.1 kg/cm2 (range, 19.5–40). The mean follow-up was 53.7 months (range, 36–91). No patients were lost to follow-up, but one 73 year-old woman died 44 months after surgery because of encephalitis.

The average HHS increased from 40 (range, 27–52) preoperatively to 90.5 (range, 61–100) at the last follow-up (P < 0.0001). The final scores were excellent in 37 hips, good in 12, modest in 5, and poor in 1. The average value of flexion changed from 83° (range, 45°–100°) before surgery to 117° (range, 80°–130°) at the last follow-up (P < 0.0001); abduction changed from 27° (range, 10°–45°) to 40° (range, 20°–50°) (P < 0.0001); adduction changed from 17° (range, 0°–30°) to 31° (range, 15°–45°) (P < 0.0001); internal rotation changed from 12° (range, 0°–20°) to 23° (range, 10°–35°) (P < 0.0001); and external rotation changed from 21° (range, 5°–30°) to 35° (range, 20°–45°) (P < 0.0001). Clinical picture after surgery was rated as very satisfactory by 33 patients, satisfactory by 18 patients, moderately satisfactory by 3 patients, and unsatisfactory by 1 patient.

Preoperative assessment of the acetabular bone defect according to the classification of Paprosky et al [20] showed a very good intratester (tester 1: weighted K = 0.89, P < 0.0001; tester 2: weighted K = 0.93, P < 0.0001) and intertester agreement (weighted K = 0.86, P < 0.0001).

The mean preoperative LLD was 16.6 mm of shortening (43 mm to 6 mm short) on the affected side, while the postoperative mean LLD was 1 mm of shortening (8 mm short to 6 mm long) (P < 0.0001). The mean vertical position of COR from the interteardrop line changed from 42.3 mm (range, 22–63 mm) preoperatively to 25.7 mm (range, 17–44 mm) postoperatively (P < 0.0001). The mean horizontal position of COR from the teardrop changed from 37.8 mm (range, 15–61 mm) preoperatively to 39.2 mm (24–53 mm) postoperatively (P > 0.05).

Radiological loosening of the acetabular components was found in 3 (5.4%) out of the 55 hips. Radiolucent lines were noted in 3 (5.4%) out of the 55 hips. Of these, two patients showed a 1 mm line in zone 1 and 2 at 6 and 24 months from surgery respectively, whereas one had a 1 mm line crossing three acetabular zones at 12 months after surgery. In all patients, radiolucencies were not progressive at the latest follow-up. Heterotopic ossification was found in 11 (20%) out of the 55 hips. Of these, 7 patients showed a grade I of ossification according to Brooker, 2 a grade II, and 2 a grade III. No patients required further surgery for ossification's removal.

Follow-up data were available for all the patients included. With a mean follow-up of 53.7 months, 4 (7.3%) out of 55 hips underwent acetabular components revision surgery. The survival rate at 2 and 5 years was 96.4% and 92.8%, respectively. The mean implant survival was 85.8 months (95% CI: 80.9–90.8), whereas the median implant survival was unreached in our population (Fig. 3).

Fig. 3
Fig. 3.

Kaplan–Meier analysis: cumulative prosthesis survival calculated with 95% confidence intervals. The vertical hatches on the curve represent the censored patients: participants who dropped out of the study or who did not develop the event by the end of the study.

Among the four patients who underwent acetabular components revision surgery, one 51 year-old woman developed aseptic loosening of the cup with hip dislocation after 30 months from surgery (Fig. 4). Since the augment was still fixed to the bone at the time of revision surgery, she received a revision shell with a cemented liner without removal of the augment. One 61 year-old woman showed aseptic loosening of the cup and augment at 17 months from surgery (Fig. 5), and underwent second revision to change both shell and augment. Subsequently, she developed aseptic loosening of the cup with dislocation of the prosthesis after 16 months, and underwent third revision with Ganz's cage and tantalum-coated cup used as augmentation. One 52 year-old man showed aseptic loosening of the cup and augment after 38 months from surgery (Fig. 6), and underwent revision of both shell and augment. Finally, one 53 year-old woman developed recurrent instability after 2 months from surgery, and underwent total revision associated with shortening of the femur.

Fig. 4
Fig. 4.

Aseptic loosening of the cup with hip dislocation at 30 months after surgery in a 51 year-old woman. The radiograph (AP view) shows superior lateral migration of the hip COR, retroacetabular and ischial osteolysis, and screw breakage. A 10-cm reference line is reported.

Fig. 5
Fig. 5.

Aseptic loosening of the cup and augment at 17 months after surgery in a 61 year-old woman. The radiograph (AP view) shows superior medial migration of the hip COR, interruption of Kohler's line, ischial osteolysis, and screw breakage. A 10-cm reference line is reported.

Fig. 5
Fig. 6.

Aseptic loosening of the cup and augment at 38 months after surgery in a 52 year-old man. The radiograph (AP view) shows superior medial migration of the hip COR, interruption of Kohler's line with the cup moving into the pelvis, and severe ischial osteolysis. A 10-cm reference line is reported.

Of note, a 62 year-old woman had further surgery without revision of acetabular implants, because of a periprosthetic fracture managed with revision of femoral component alone and additional fixation with cable.

No cases of deep venous thrombosis, pulmonary embolism or death were reported as a result of the surgical procedure.


Discussion

The present study accepted the null hypothesis showing that the acetabular reconstruction with TM-coated cups and augments provides a statistically significant improvement of hip ROMs and HHS values, and reduction of LLD and cranial migration of the hip COR in patients affected by Paprosky type III defects without pelvic discontinuity.

Over the next twenty years, the number of primary and revision total hip arthroplasties (THAs) in the United States has been estimated to increase by 174% and 137% respectively [25]. Since aseptic loosening, bearing surface wear, and osteolysis are the most common causes of THA failure in both Europe 26. and 27. and United States [28], revision surgery can be technically demanding whether severe acetabular bone defects need to be addressed at the time of the reconstruction. The management of Paprosky type III defects should include the anatomical reconstruction of the lesion with the restoration of the hip COR and host bone stock. Although the structural bone grafting may address such issues, some authors reported high rate of failure, ranging from 22% to 45%, in the long term 29. and 30.. During the revascularization and remodeling, the allograft is weak and unable to transfer the load bearing from the implant to the host bone leading to the collapse of the graft and the loosening of the prosthesis [31].

In literature, reconstruction cages associated with structural allograft reported controversial results. Although the technique provides a good primary stability, high rates of mechanical failure (from 9% to 64%) have been reported in type III acetabular defects 32., 33. and 34.. Although structural allograft can be remodeled and gradually transformed into normal living bone [35], the lack of porous surface of the cage determines the inability to promote a secondary biologic fixation at the implant-graft interface [32]. Moreover, when the liner is cemented into the cage, a reduced amount of cement penetrates through the screw holes and bonds the pelvic bone. For these reasons, a fatigue failure of the screws or flanges of the cages can occur in the long term.

Bilobed oblong components have been also proposed for the management of superior acetabular bone defects. Although they may fill the lesion maximizing the contact between host bone and implant and restore the hip COR, they reduce the bone stock and could not fit the defect [31]. Moreover, some authors reported a failure rate greater than 20% with a follow-up of 41 months [36].

The use of TM cups and augments has recently increased for the management of severe bony defects 3., 8., 9., 10., 11., 12., 13., 14., 15., 16. and 17.. However, previous studies are affected by some biases. First of all, the sample included patients with different preoperative diagnosis, from loosening to wear and infection, and different types of bone defects, from Paprosky grade IIA to grade IIIB with pelvic discontinuity. Second, the revision surgery was performed using TM acetabular cups with or without TM augments.

To our knowledge, only two previous studies assessed a small case series including patients affected by Paprosky type IIIA defect managed with the association of TM acetabular components and augments 10. and 11.. Sporer et al [10] reviewed 28 acetabular revisions at an average follow-up of 36 months (from 12 to 48) and reported only one case of revision for recurrent instability (3.5%). On the other hand, Del Gaizo et al [11] reviewed 37 acetabular revisions at an average follow-up of 60 months (from 26 to 106), reporting an overall revision rate of 21.6%. Because both studies included patients with Paprosky type IIIA defect with loosening as more frequent preoperative diagnosis, we could hypothesize that the length of follow-up plays a role in determining such difference in the overall revision rate. However, despite the higher overall revision rate, Del Gaizo et al reported only one case of aseptic loosening (2.7%) and two cases of recurrent instability (5.4%).

In our series, we included only patients with aseptic loosening to minimize bias related with different preoperative diagnoses. We also excluded patients who underwent primary hip arthroplasty, because of the better quality of the host bone that has not been previously aggressed. Compared with two previous studies 10. and 11., we included only patients with Paprosky type IIIA and IIIB defects without pelvic discontinuity. At an average follow-up of 53.7 months (from 36 to 91), we reported three cases of loosening (5.4%), and only one case of recurrent instability (1.8%). These findings confirm the results of previous studies also in patients with Paprosky type IIIB defect without pelvic discontinuity. Moreover, we reported a lower overall revision rate (9.1% versus 21.6%).

In literature, the survival rate of TM cup and augment constructs has been estimated from 92% to 99% in the mid-long term 12. and 15.. However, these findings are referred to a sample including patients with mild to severe bone acetabular defects. In this study, we reported a survival rate at 2 and 5 years of 96.4% and 92.8% respectively in a population affected only by severe bony lesions. Moreover, these results are better than those reported for structural bone grafting, reconstruction cages and oblong cups.

The augments represent a modular system allowing the surgeon to perform a customized acetabular reconstruction. Regardless of the size and shape of the bony lesion, the combination of TM-coated cups and augments provides a modular construct filling the defect and maximizing the contact with the host bone. In this series, we were able to manage severe bony lesions, such as Paprosky type IIIA and IIIB defects without pelvic discontinuity. Moreover, we found that this system allows the surgeon to achieve a significant reduction of the cranial migration of hip COR.

In our practice, we aim to restore the anatomical position of the COR to achieve an effective function of the abductors [1]. During the surgical procedure, we try to achieve the best acetabular trial position in terms of COR height, cup anteversion and abduction even though there is partial stability of the construct. Then, we use the TM augments to fill the defect and stabilize the cup. Finally, despite the quite large size of bone defects, we were usually able to use medium-size cups. In our opinion, the use of non-large cups could allow to prevent impingement between the acetabular construct and soft tissues around the hip.

Major limitations of the study are the retrospective design and the lack of a control group. The uncontrolled design prevents us to prove that the reconstruction with augments is superior to other techniques described to manage these patients, including reconstruction cages, structural allografts, and bilobed or oblong components. However, according to our results, we believe that the use of TM augments associated with TM cups approach could be considered an effective management of Paprosky type III defects without pelvic discontinuity.

Another limitation is that we did not perform an a priori power analysis and sample size calculation; we planned to include in the study all the eligible patients who underwent acetabular reconstruction with TM cups and augments during the index period. However, we performed a post hoc power analysis on our results showing that the study had a power of 0.90 to detect a significant difference between preoperative and postoperative values of HHS, ROMs of the hip, and LLD by using the two tails Wilcoxon signed ranks test for paired sample, with an alfa error (the probability of yielding a type I error) equal to 0.05 and an effect size equal to 0.4.


Conclusion

The use of TM-coated cups and augments could be considered an effective management of Paprosky type III defects without pelvic discontinuity providing an anatomical reconstruction of the lesion with the restoration of the hip COR with good clinical and radiographic outcomes in the mid term.


Acknowledgment

We would like to thank the Livio Sciutto Foundation for Medical Research. This is a non-profit social organization that recorded in its database the data of the patients included in the study, with the previous consent of the patients and respecting the current law on privacy.


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GAP II

GAP II è un sistema per l’archiviazione di dati clinici e chirurgici di pazienti sottoposti ad interventi di chirurgia protesica di anca, ginocchio e spalla.