Biomed Res Int. 2014;2014:948520.

Early results of a new rotating hinge knee implant.

Alexander Giurea1, Hans.-Joachim Neuhaus2, Rolf Miehlke3, Reinhard Schuh1, Richard Lass1, Bernd Kubista1, Reinhard Windhager1

 

1Dept. of Orthopaedics, MedicalUniversity of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria

2Dept. of Traumatology and Orthopaedics,St. Vincenz Hospital Am Stein 24, D-58706 Menden, Germany

3The Rhine-Main Center of Joint Diseases, Wilhelmstr. 30, D-65183Wiesbaden, Germany

 

Corresponding Author:

Univ. Prof. Alexander Giurea, MD

Dept. of  Orthopaedics

Vienna General Hospital

Medical University of Vienna

Email: a.giurea@gmx.at

 

Abstract

Background

Indication for rotating hinge (RH) total knee arthroplasty (TKA) include primary and revision cases, with contradictory results. Aim of this study was to report prospective early results of a new modular rotating hinge TKA (EnduRo®). For this implant several new design features and a new bearing material (carbon-fiber reinforced poly-ether-ether-ketone) have been developed. Furthermore we tried to establish a new classification of failure modes for revision TKA.

Methods

152 EnduRo® rotating-hinge prostheses were implanted in two centers. In 90 patients a primary implantation has been performed and 62 patients were revision cases. Knee Society Score (KSS), Western Ontario and McMaster Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS) and Range of motion (ROM) were assessed before surgery, 3 months postoperatively, 12 months postoperatively and anually thereafter. We defined 3 types of complications: Type 1 : Infection  Type 2: periprosthetic complications and Type 3: implant failures.

Results

KSS, WOMAC, OKS and ROM revealed significant improvements between the preoperative and the follow-up investigations. There were 14 complications (9.2%) leading to revision surgery, predominantly type 2.

Conclusion

Our study shows excellent clinical results of the EnduRo® TKA. Furthermore no premature material failure or unusual biological response to the new bearing material could be detected.

PMID: 25089279

 

Supplement

Fig1

Fig 1. EnduRo®  Knee Prosthesis

The rate of revision total knee arthroplasties (TKAs) is steadily increasing [1]. Thus there is an increasing demand for modern revision knee implants. Rotating hinge knees (RHK) have been designed in order to provide stability in knees with severe bone loss and ligamentous instability and aim at lower level of constraint if compared to fixed hinge knee implants. Fixed hinge implants resulted in high contact stresses between implant parts and the implant-bone interface, leading to early implant failure and loosening of the knee prosthesis. The EnduRo® prosthesis (Aesculap AG, Tuttlingen, Germany) represents a new modular rotating hinge design (Fig 1). It is characterized by transmission of force from the femoral component to the tibial component via the polyethylene insert with high contact area, like in primary TKA. In order to avoid high axis loads the hinge is not primarily weight bearing but provides stability of the joint in case of severe coronar or sagittal instability. In order to minimize wear and creep the axes are embedded in carbon-fiber reinforced poly-ether-ether-ketone (CRF-PEEK) flanges and bushings firstly used as a bearing material in TKA [2]. Biotribological in vitro studies showed decreased wear for this implant [2] and an in vivo murine model a biological response to the CFR-PEEK particulate debris comparable to polyethylene, which is routinely used in TKAs [3]. Furthermore the EnduRo® system offers an offset option and wedges for the tibial as well as for the femoral component in order to address certain anatomical situations in severe primary and revision cases (Fig.1).

Usually results of Knee prostheses are presented quite lately with minimum follow up of 5 years, although complications occur frequently within the first two years after implantation. Therefore early results of new implants are important to the academic community especially when new materials and design features are used.

In this prospective study we present early results of the EnduRo® rotating hinge knee in a fairly high number of patients. The outcome scores are encouraging, as we found significant improvements between the preoperative and the follow up investigations (Fig 2a). The results of our study reveal favorable results in terms of clinical improvement and range of motion (ROM) (Fig.2a, b).

 Fig2a

Fig 2a.  KSS preoperative  and postoperative at the respective follow up times for primary and revision cases

Fig2b

Fig 2b.  Shows range of motion (ROM) preoperative  and postoperative at the respective follow up times for primary and revision cases

We also introduced a new classification of complications for revision TKA in order to gain better information about implant survivorship.

The new classification for TKA complications gives us more information about prosthesis failure modes. Type 1 complications (infections) occur unrelated to the prosthesis. In type 2 complications (periprosthetic complications) surgical technique and tissue quality seem to play a certain role rather than the implant design. Type 3 complications (implant failures) give information about survivorship of the prosthesis. The most common type of complication in our study was periprosthetic complications (type 2). They occurred in 3.9% of our cases.

The overall survival rate after two years was 85.4% and the implant survivorship was 92.1 % (CI: 81.5 – 96.8)(Fig 3).  Patients, who received the implant in revision surgery experienced a six time higher risk of reoperation than patients after primary implantation. The revision group showed also inferior preoperative as well as postoperative clinical scores if compared to the primary group. Only results for ROM showed after one year no difference between the two groups, indicating the potential of the prosthesis for good postoperative range of motion (Fig 2b). These findings give us information about the impact of preoperative diagnosis on the functional outcome of revision TKA.

 

Fig3 Fig 3.  Kaplan- Meier survival curves, total and implant survival

 

Many knee surgeons recommend in case of revision surgery designs with the lowest level of constraint possible. Theoretically, we would expect that functional outcome and complication rate were superior with a less constraint design of revision TKAs (i.e. semi-constraint designs or CCK). In fact our results turned out to be superior for KSS, ROM and complication rate compared to semi-constraint designs [4].

We do think that rotating hinge implants facilitate ROM in severe primary and revision cases and are favourable for all indications of revision TKA. There was no revision due to TKA instability in our study, which often occurs within the fist two years after TKA.

Biotribologic studies have shown in vitro promising low rates of wear and debris for the EnduRo® prosthesis [2]. We were interested if these findings will correlate in clinical outcome. In our in vivo study we found no noticeable signs of biological response to the new CFR-PEEK bearing material. This macroscopic clinical view is also supported by cell culture experiments on L929 and U937 cell lines showing that CFR-PEEK PAN wear particles had no cytotoxic effects and would possible not cause adverse tissue reactions in vivo.

 

Conclusion

The preliminary results of the present study reveal that the EnduRo® rotating hinge TKA yields to good clinical, functional and radiologic results at a short-term follow-up. Functional results appear to be superior to those reported for other revision TKA implants. We do believe that this is due to improvements of implant biomechanics and biomaterials. Long-term results have to be presented in order to draw definitive conclusions regarding the survival rate.

 

References

[1] Schuh R, Dorninger G, Agreiter M, Boehler N, Labek G (2012) Validity of published outcome data concerning Anatomic Graduated Component total knee arthroplasty: a structured literature review including arthroplasty register data. International orthopaedics 36 (1):51-56. doi:10.1007/s00264-011-1255-1

[2] Grupp TM, Giurea A, Miehlke RK, Hintner M, Gaisser M, Schilling C, Schwiesau J, Kaddick C (2013) Biotribology of a new bearing material combination in a rotating hinge knee articulation. Acta biomaterialia 9 (6):7054-7063. doi:10.1016/j.actbio.2013.02.030

[3] Utzschneider S, Becker F, Grupp TM, Sievers B, Paulus A, Gottschalk O, Jansson V (2010) Inflammatoryresponseagainst different carbon-fiber-reinforced PEEK wearparticlescomparedto UHMWPE in vivo. Acta Biomaterialia 6 (11):4296-4304

[4] van Kempen RW, Schimmel JJ, van Hellemondt GG, Vandenneucker H, Wymenga AB. (2013) Reason for Revision TKA Predicts Clinical Outcome: Prospective Evaluation of 150 Consecutive Patients With 2-years Followup. Clinical Orthopaedics&Related Research 471 (7):2296-2302. doi:10.1007/s11999-0132940-8

 

Fig4 Fig 4a. Surgeons and patient (background) after worldwide first implantation of the EnduRo® rotating hinge prosthesis at the Medical University of Vienna

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