The BOX TAR was developed from a collaborative effort of the Rizzoli Orthopaedic Institute (Drs. Giannini, Catani, Leardini) in Italy and Oxford University (Dr. O'Connor) in England in the late 1990s. This non-constrained, mobile-bearing prosthesis is a three-component implant with metal components fixed to the proximal talus and the distal tibia and interposed UHMWPE meniscal bearing. The upper UHMWPE surface is concave, not flat is in previous designs. The biomechanical development of this prosthesis type has been well documented in the literature by its designers.1-3 Original research studies by the designers of this prosthesis focused on movement and stability of the ankle and sought to provide detailed understanding of the role of the ligaments in controlling and limiting joint movement.
In 2001 Leardini developed a geometrical model of the intact human ankle complex that established the basic principles for design of a new total ankle prostheses.1 Seven lower leg specimens were prepared for passive flexion analysis using a stereophotogrammetric system. It was shown that the geometry of the articular surface of the ankle is strictly related to that of the ligaments. Therefore, the author stated that the ideal TAR design should be based on ligament compatibility and the careful reconstruction of ligaments should be performed in any foot and ankle surgery to recreate the normal kinematics and mechanics of the ankle.1 A four-bar linkage model was developed from this initial study that also showed that both rolling and sliding motions take place at the talocrural joint.
In 2004 Leardini et al described the BOX TAR design and rationale, including compatibility to the physiological function of surrounding ligaments.2 The designers aimed to reproduce physiological ankle mobility with the following design features:
- Spherical convex tibial component
- Talar component with radius of curvature in the sagittal plane longer than that of the natural talus
- Fully conforming meniscal bearing.
Preliminary results from their study of two female patients demonstrated the feasibility of their surgical technique.2 Reggiani et al developed a finite element model to address the BOX TAR analysis during the stance phase of gait.3 Overall kinematics, contact pressures, and ligament forces were analyzed during both, passive (eg, virtually unloaded) and active (eg,stance phase of gait) conditions. The authors showed that this prosthesis design could allow the necessary ROM and constrain the motion of the prosthetic components, especially the mobile bearing.3
Affatato et al have used a four-station knee joint simulator to address meniscal wear of the BOX TAR mobile bearing.4 The knee wear simulator was able to reproduce load-motion patterns comparable to those of a replaced ankle. Tests of three specimens showed a linear penetration of 0.0178, 0.0081, and 0.0339 mm per million-cycle. The linear penetration observed in this study was comparable to that found in ceramic-to-polyethylene or metal-to-polyethylene couplings.4
Two years later, Affatato et al performed a comparative study of wear behavior in the BOX TAR between an in vitro simulation and retrieved prostheses.5 Three retrieved mobile bearings were available from revision surgeries performed 24, 24, and 9 months after the initial TAR surgery. Visual and microscopic observations, analyses, and Raman crystallinity-based measurements showed similarity between the patterns generated experimentally using a four-station knee joint simulator and those seen in retrievals with similar wear duration.5
Ingrosso et al performed gait analysis in BOX TAR patients by a stereophotogrammetric system with eight M2-cameras.6 The study included 10 patients with a follow-up of 6 and 12 months after the surgery. Normal patterns and ROMs were observed in all 10 patients at both follow-ups.6
Giannini et al presented short-term results in 51 patients who were treated with a BOX TAR.7 The minimum follow-up in this study was 24 months. All patients showed significant functional improvement as assessed by the AOFAS score. A revision arthroplasty had to be performed In one patient because of lateral impingement, resulting in a 3-year cumulative survivorship of 97%.7 The main indication for this procedure was stage III ankle OA (with subtotal or total disappearance or deformation of joint space) with preserved or restored ankle anatomy.8
In summary, the design process and biomechanical properties of the BOX TAR have been documented in detail.1-3 The designers claim that it maintains complete congruency during the entire arc of motion and closely resembles normal ankle biomechanics. Studies addressing the wear behavior in this prosthesis design have significantly contributed to the understanding of modern three-part prostheses.4,5 The short-term results are promising, with high satisfaction among treated patients, good functional results, and a low revision rate.7 However, all aforementioned studies were performed by one of designers of this prosthesis; therefore, further study by independent groups should be performed. Long-term results have to provide evidence on their clinical success.
- Leardini,A.: Geometry and mechanics of the human ankle complex and ankle prosthesis design. Clin Biomech (Bristol , Avon ), 16:706-709, 2001.
- Leardini,A., O'Connor,J.J., Catani,F., and Giannini,S.: Mobility of the human ankle and the design of total ankle replacement. Clin Orthop Relat Res, 424:39-46, 2004.
- Reggiani,B., Leardini,A., Corazza,F., and Taylor,M.: Finite element analysis of a total ankle replacement during the stance phase of gait. J Biomech, 39:1435-1443, 2006.
- Affatato,S., Leardini,A., Leardini,W., Giannini,S., and Viceconti,M.: Meniscal wear at a three-component total ankle prosthesis by a knee joint simulator. J Biomech, 40:1871-1876, 2007.
- Affatato,S., Taddei,P., Leardini,A., Giannini,S., Spinelli,M., and Viceconti,M.: Wear behaviour in total ankle replacement: a comparison between an in vitro simulation and retrieved prostheses. Clin Biomech (Bristol , Avon ), 24:661-669, 2009.
- Ingrosso,S., Benedetti,M.G., Leardini,A., Casanelli,S., Sforza,T., and Giannini,S.: GAIT analysis in patients operated with a novel total ankle prosthesis. Gait Posture, 30:132-137, 2009.
- Giannini,S., Romagnoli,M., O'Connor,J.J., Malerba,F., and Leardini,A.: Total ankle replacement compatible with ligament function produces mobility, good clinical scores, and low complication rates: an early clinical assessment. Clin Orthop Relat Res, 468:2746-2753, 2010.
- Giannini,S., Buda,R., Faldini,C., Vannini,F., Romagnoli,M., Grandi,G., and Bevoni,R.: The treatment of severe posttraumatic arthritis of the ankle joint. J Bone Joint Surg Am, 89 Suppl 3:15-28, 2007.