Rationale of Cruciate Retaining Design in Rheumatoid Arthritis: A Review of Clinical Analysis and its Role in Rheumatoid Arthritis

3.1. Long Term Survivorship

Patients with Rheumatoid arthritis usually present for TKA at a younger age when compared with primary osteoarthritis, approximately ten years younger [2]. Hence the survival of the implant plays a major role in these patients. The data accumulated from heterogenous centres have determined the survivorship analysis using Kaplan Meier, Cutler Ederer and Armitage actuarial methods. In this review, survivorship of the implant was based on the need for re operation for any reason.

From the studies listed in Table 1, it is evident that the ten-year survival of CR in RA is comparable to that of the CR in OA knees which is 90% as evidenced by Abdel et el in 5389 cruciate retaining TKA [3]. Furthermore, it was summarised that the most durable result is following a cruciate retaining prosthesis in an elderly woman with inflammatory arthritis by Rand et al. in a large cohort of 11,606 knee arthroplasties [4].

3.2. Functional Outcome

A long-term assessment functional outcome assessment in patients with RA is essentially required considering the relatively younger population present for TKA. Among the studies included in this article, the functional outcome assessment had been made using the knee society functional outcome score and hospital for special surgery score. One of the earliest studies by Gill and Joshi demonstrated excellent functional outcome scores only in 15% of knees at final follow up [5]. With time, the design of cruciate retaining had evolved and the functional outcomes have improved ever since.

This change is noted in several studies across the globe, a 25 year follow up study from Mayo clinic demonstrated a good functional outcome score (mean score 79) at the end of 25 years [6, 7]; a minimum 15 year follow up study from Korea noted an excellent post-operative functional score of 80 at final follow up [8]; a 12 year follow up study from Japan shows a good mean functional outcome score of 70 at final follow up [9]. These findings further reiterate the favourable long term functional status of cruciate retaining prosthesis.

3.3. Proprioception

A posterior cruciate ligament (PCL) with intact neural structures aids in proprioception, whereas a PCL deficient knee leads to instability and early degenerative changes in the knee [10]. The structural integrity of posterior cruciate ligaments was assessed by a histopathological study which demonstrated the intactness of PCL in RA patients with grade 3 or grade 4 of the disease [11]. The findings suggest that a careful intra-op assessment of PCL integrity is required and sacrificing the PCL without proper patient selection is not ideal.

3.4. Range of Motion

Cruciate retaining design is a less constrained prosthesis which allows better controlled femoral roll back than posterior stabilised design. Among the available literature Table 1, the maximum average range of motion of 115^o was noted in a 22 year follow up study by Lee et al. and correlates with the average knee ROM after TKA in OA patients [8]. The longest follow up study till date from Mayo clinic demonstrates an average knee ROM of 100^o [6, 7]. Considering the reduced ambulatory status in RA, an average ROM of 100⁰ would improve the mobility and quality of life substantially.

4.1. Failure Due to Instability

It is a popular belief to use a more constrained design such as a PS implant in patients with RA, this was largely based on a 6-year follow up study from the Hospital for special surgery, New York which reported a 50% incidence of posterior instability in cruciate retaining design leading to revision [12]. However, apart from this isolated study which indicates such a high rate of instability using CR design; there are numerous long term outcome studies from multiple centres which disapproves of this fallacy.

The role of CR design with regards to posterior instability in RA patients is evidenced in the following studies, Miller et al. [7] in a 25 year follow up study reported that only two patients required re-operation due to instability; Gill and Joshi [5] evidenced that one patient (1\66) required re-operation for posterior instability; Belleman et al. [13] had documented that there is no statistically significant difference between CR and PS with regards to posterior instability in his long term study. Additionally, biomechanical studies have demonstrated the role of PCL in varying degrees of flexion and its importance as a primary restraint against posterior translation in varying angles of flexion [14, 15].

4.2. Aseptic Loosening

Component loosening after total knee arthroplasty is a cause for revision and occurs usually due to an increased polyethylene wear debris generated, which triggers an immune response leading to resorption of the bone-implant interface. In rheumatoid arthritis, there is a theoretical risk of accelerated resorption of bone-implant interface due to a reactivation of synovitis [16]. An isolated study has reported the incidence of revision due to aseptic loosening to be in 3 (4.5%) out of 66 knees in which cruciate retaining prosthesis was used [5]. Apart from this study, long term studies with a follow up period of up to 25 years have clearly evidenced that the survival rate of implant at the end of ten years, fifteen years and twenty five years was 100% with component loosing due to aseptic causes as the end point [6-9, 17].

4.3. Periprosthetic Fracture

Rheumatoid arthritis is a progressive disease leading to symmetrical joint space reduction and secondary arthritis. In addition, chronic steroid use leads to osteopenia which subsequently leads to a poor bone quality. Archibeck had reported one case of peri prosthetic fracture using a CR design out of 72 knees [6]. The use of PS design demands an obligatory box cut which further weakens the intercondylar notch in a patient with a small sized femur and leads to a theoretical risk of peri prosthetic fracture [18]. Hence it is imperative that bone resection is minimal during knee arthroplasty.