Introduction

Cementless modular revision stems are widely used in revision hip arthroplasty with promising results in medium- and long-term follow-up [1]. In complex revision surgery the advantages of stem modularity are the greater variability for restoration of the leg length, femoral offset, femoral anteversion and soft tissue tension [2, 3]. The proper reconstruction of the anatomic centre of rotation and press-fit bone fixation of the revision stem are essential for long-term outcome [4]. The individual intra-operative anatomical situation can be addressed by modular-designed prosthesis and allows nearly physiological joint reconstruction [4]. In difficult anatomical findings the use of a distal diaphyseal press-fit stem provides more options than non-modular revision stems [2]. The cementless distal diaphyseal fixating modular MRP-TITAN revision stem (Fig. 1) has excellent short- and long-term results in a number of studies, with low mechanical failure rates and high overall survival rates. Most of the reports with higher patient numbers are multicentre-designed, have different exclusion criteria and use different stem lengths with or without additional distal fixation [3, 5, 6]. Because of these shortcomings, we investigated the clinical and radiological outcomes, of femoral revision arthroplasty with the 200-mm curved MRP-TITAN stem in a retrospective, monocentric and consecutive study.

Fig. 1
figure 1

The 200-mm curved MRP-TITAN stem (MRP-TITAN®; PETER BREHM, Weisendorf, Germany)

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Patients and methods

From our own database, we identified 136 patients who underwent a femoral revision arthroplasty using a 200-mm curved MRP-TITAN stem in our institution during the years 2005–2011. Twenty-three patients were lost to follow-up (16.9 %) and 24 patients died from non-implant-related reasons with the femoral stem not revised (17.6 %). Of the 89 patients analysed, 43 were women and 46 men, with a mean age of 72.3 (min. 52, max. 95) years. The major diagnosis leading to indicate total hip arthroplasty (THA) was primary osteoarthritis in 78 % of the cases, post-traumatic osteoarthritis in 4 %, and others in 18 % of the cases. Stem revision was performed on average 109 (min. one, max. 420) months after primary THA. When necessary, cup revision, liner exchange or synovectomy was performed additionally. In all cases we used a lateral approach with lateral skin incision and excision of the old scar. Mean follow-up time was 55 (min. 24, max. 117) months.

Clinical assessments included determination of the Harris Hip Score and the Merle d’Aubigné and Postel Score. The health-related quality of life was determined with the visual analogue pain scale (VAS). Pre-operative and postoperative standard radiographs were available for all patients. The radiographs were analysed for signs of implant loosening regarding the criteria by Kavanagh and Fitzgerald [7] and periprosthetic radiolucencies according to Gruen in zones 1–7. Pre-operative femoral defects were classified according to the paper of Pak et al. [8]. We defined revision of an MRP-TITAN stem as a failure when patients underwent re-revision surgery for any reason.

Statistical analysis

The main end point of this study was the overall survival after revision hip arthroplasty implanting the MRP-TITAN stem, and univariate analysis was performed using the Kaplan-Meier test and the log-rank test, respectively.

We compared the global range of motion preoperative to postoperative by using t-test for paired data. A p value of <0.05 was considered to be statistically significant. For statistical analysis the SPSS 15.0 program (SPSS, Chicago, IL, USA) was used.

Results

The main indications for revision of the primary femoral implant were aseptic loosening (48 %), periprosthetic joint infection with two-stage treatment using an articulating antibiotics-impregnated cement spacer (38 %), periprosthetic fracture (10 %) (Fig. 2), and fracture of the primary THA stem (2 %). Preoperative femoral defect classification revealed a Paprosky I defect in 9.1 % of the cases, Paprosky II A in 38.6 %, Paprosky II B in 18.1 %, and Paprosky II C in 10.3 %. Larger femoral bone defects were found in 15.8 % of the patients according to Paprosky III A and 8.1 % with a Paprosky III B defect. The type of failure and the pre-operative defined bone defect revealed no significant difference in all parameters investigated.

Fig. 2
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Periprosthetic femur fracture in a 71-year-old woman treated by revision using a 200-mm curved MRP-TITAN stem and osteosynthesis with cerclages around the femur

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In the clinical outcome patients achieved 75.1 points (min. 18, max. 100) in the Harris Hip Score and 14.4 points (min. 5, max. 18) in the Merle d’Aubigné and Postel Score. Mean level of persisting pain was 0.7 (VAS). The rate of patients without any pain revealed 89.7 %. Patients were satisfied in 88.4 % with their results, 10.1 % were partly satisfied and only 1.5 % were not satisfied according to the patients’ subjective satisfaction consideration.

In the radiographic evaluation, 96 % of the cases had stable stem ingrowth without any radiolucencies or stem migration. In Gruen zone 1 only 4 % showed a radiolucency of less than 1 mm without any hints for aseptic loosening. According to Brookers’ classification, 61.4 % of the patients revealed no periarticular ossifications, 26.1 % had Brooker type I, 5.7 % Brooker type II and 6.8 % Brooker type III ossifications [9].

The global range of motion was significantly increased in the postoperative clinical follow-up compared to the preoperative status (Fig. 3).

Fig. 3
figure 3

Preoperative and postoperative range of motion at latest follow-up (*p < 0.05)

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The calculated overall survival for using the MRP-TITAN stem in revision hip arthroplasty revealed 85.6 % survival at 9.75 years’ follow-up (Fig. 4). Six out of 89 (6.8 %) patients were considered failures of revision with the MRP-TITAN due to re-revision. Reasons for repeated revision were early postoperative superficial infection (3), treated with head and inlay exchange, meticulous debridement and antibiotic medication for four weeks postoperatively. Two patients were revised because of recurrent dislocation with head and inlay exchange and one patient with fascia defect was treated with secondary suture. None of all the patients had an exchange of the MRP-TITAN stem.

Fig. 4
figure 4

Survival during follow-up after implantation of an MRT-TITAN stem with revision for any reason as end point

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Discussion

Revision hip arthroplasty using a diaphyseal cementless fixating stem is a frequently performed revision procedure with very different outcome reports. Recent papers revealed rates of aseptic loosening between 4 and 16 % using the modular Revitan stem, Wagner stem and other porous-coated stems [1, 10–13]. In contrast, our revision rate using the MRP-TITAN stem is 6.8 %, with a Kaplan-Meier survival rate of 85.6 % after 9.75 years. These promising results were supported by findings of Wirtz et al. [5], showing a 15-year survival of 85 %, with a revision rate of 6 %. Many authors reported up to 10 % axial migration with subsidence as the main reason for revision stem failure [1]. The subsidence rate for the MRP stem is lower with a mean of ca. 4 % migrations [5, 14, 15]. Nevertheless, we could not find any stem subsidence or axial migration after a mean follow-up of 55 months. The main surgical factor to prevent any migration or subsidence is a perfect diaphyseal contact area of the implant to the bone over a distance of 70 mm [6] for the MRP stem and 30 mm for the Revitan stem. Compared with the clinical results of the MRP-TITAN stem, an increased failure was reported for the Revitan stem [1]. The specific geometry of the MRP-TITAN with longitudinal rips, a rough surface and a taper-shape bowed design seem to be the major key for the very encouraging outcome results. A study from Gravius et al. [16] reported no corrosion or fretting at all modular interfaces using the MRP stem because of a specific manufacturing process of the Morse taper junctions [17]. These data were supported by the findings of Wirtz et al. [5]. Also, we could not detect any osteolysis around the modular connections of the stem.

In the clinical outcome, our patients revealed very promising results with a Harris Hip score of 75.1 points and a Merle d’Aubigné and Postel score of 14.4 points. Different single and multicentre studies reported slightly lower results for the Harris Hip score in a larger patient cohort with 70–71.4 points, respectively, using the MRP stem [6, 15]. In contrast, Wirtz et al. [5] showed a Harris Hip score of 79 points in a large multicentre study with different designs of the MRP-TITAN stem. Our findings regarding the Merle d’Aubigné and Postel score are supported by 15.2 points in this score published by Schuh et al. [14]. Recurrent dislocation is one of the common problems after revision THA. In our study, we found a rate of 2.3 %. Wirtz et al. [18] reported in their multicentre study a rate of 4–12 % for the MRP stem equivalent to dislocations rates to other femoral stems [10, 19]. The persisting pain level after revision to an MRP-TITAN stem was 0.7 in our series. Van Diemen et al. [20] reported a level of 2.68 in the VAS using a modular femoral revision stem. The excellent outcome concerning pain supports the potential advantage of the MRP stem to properly reconstruct the hip [5].

We acknowledge the shortcomings of our study, including the design as a retrospective and descriptive study without a control group. Nonetheless, this is a large and monocentric study elucidating important issues related to revision hip surgery, and emphasises outcome and treatment in a demanding operative situation.

Conclusions

To the best of our knowledge, we are presenting a consecutive, monocentric and retrospective study with the largest sample sizes presently published using the 200-mm curved MRP-TITAN revision stem for using the advantages of a modular design with diaphyseal fixation. The MRP-TITAN stem is a promising option for patients with failed THA and Paprosky type I-III femoral defects.