Application of cementless extension stem in revision knee replacement surgery

In total knee arthroplasty, extension stems are often used for stress transmission to reduce the stress at the bone-prosthesis interface and reduce the risk of loosening caused by implant restrictions. In addition to avoiding such risks, the guiding role of extension stems has attracted increasing attention. In knee replacement surgery, proper alignment is critical to the success of the surgery, but due to the obvious Metaphyseal bone defects and soft tissue disorders make ideal alignment difficult to achieve reproducibly.

◆Friedman et al. reported a mean tibiofemoral angle of 6.8° valgus (range 5° varus, 17° valgus) after revision surgery, and pointed out that 78% of cases were considered alignment problems.

◆Rosenberg et al. reported that 50% of tibial prostheses were in a varus position.

The patients in these surgical reports were all revised with cemented extension stems. According to the study, the least predictable and highest probability of varus misalignment outcomes usually occurred in revision surgery using cemented extension stems.

◆Nakasone et al. reported a radiological study of 52 cementless extension stems and concluded that cementless extension stems contribute to the more accurate and repeatable alignment of femoral and tibial prostheses[1].

The cementless extension stem adopts an appropriate length, bypasses the bone defect area, and forms an effective fixation through the articular surface and the diaphysis. Regarding the worrying problem of distal pain, current studies have shown that by using titanium alloy material and the distal groove[2] to simulate the elastic modulus of the human body, possible pain problems can be avoided.

RSK extension stem design concept

Reference：

[1]. Nakasone C K , Abdeen A , Khachatourians A G ,et al.Component Alignment in Revision Total Knee Arthroplasty Using Diaphyseal Engaging Modular Offset Press-Fit Stems[J].Journal of Arthroplasty,2008, 23(8):1178-1181.DOI:10.1016/j.arth.2007.10.002.

[2]. Kim Y H, Kwon O S, Kim K . Analysis of the biomechanical effect of stem-end design in revision TKA using Digital Korean model.[J].Clinical Biomechanics, 2008, 23(7):853-858.DOI:10.1016/j.clinbiomech.2008.01.010.