**3. Clinical outcomes**

is the main goal of the developers of these devices; cruciate-retaining total knee replacement

The many reasons for retaining the posterior cruciate ligament (PCL) during total knee replacement (TKR) include improved stability, reduced shear stresses at the fixation interface, improved proprioception, and more efficient gait patterns during level walking and stair climbing; moreover, one of the most commonly cited motives for retaining the PCL is to preserve femoral rollback, which improves extensor efficiency by lengthening the moment arm and improves the range of flexion by minimizing the potential for impingement of the femur on the tibial component, reducing loosening and excessive polyethyl-

The classic indications for a PCL retaining total knee arthroplasty (TKA) are fixed flexion of less than 30°, varus less than 20°, and valgus less than 25°; joint subluxation of no more than 1

In our experience, we also use this type of implant even in the revision of a unicompartmental knee replacement caused by an aseptic loosening of the tibial component: with the use of a tibial stem, associated if necessary with an augment, we spare the PCL avoiding the

cm; structurally intact PCL (**Figures 1** and **2**); and technical ability of the surgeon [1].

**Figure 1.** Anteroposterior view of full-length lower extremity radiographs of a patient suitable for a CR-TKR.

(CR-TKR) was introduced to try to achieve these results.

ene wear.

**2. Indications**

24 Primary Total Knee Arthroplasty

Numerous retrospective studies of CR TKAs have demonstrated consistently good clinical results and excellent intermediate and long-term survival [2–5].

While first studies about old generation of CR systems showed systemically a survivorship of 90% at 10 years, new type of implant demonstrated an improved longevity to 96–100% after 10 years. National joint registries are very useful instrument to understand this phenomenon: 14th Annual report of National Joint Registry for England, Wales, Northern Ireland and the Isle of Man updated to December 31, 2016 recounts that from 2003 "More than half of all operations (56.6%) were total knee replacements which were all cemented, unconstrained and fixed, followed by 20.7% which were all cemented, posterior stabilised and fixed… Two-thirds (66.6%) of cemented implants are unconstrained (cruciate-retaining) and have a fixed bearing… The main decline in the type of primary knee surgery carried out has been in the use of all uncemented and hybrid total knee replacements over time…" (less than a third of those figures reported for the year 2003). Analyzing the risk of revisions after primary knee surgery by fixation method and constraint, it reveals how "…Cemented unconstrained, fixed bearing total knee replacement results in lower chances of revision overall compared to other combinations of constraint and bearing used in a cemented fixation of the joint with modular tibial components" and "… Uncemented/hybrid total knee replacements with posterior stabilised constraint and fixed bearings fare worse than their unconstrained bearing equivalents" [6]. Similar results were carried out by the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) 2017 Annual Report: it describes as "…the use of minimally stabilised prostheses has remained relatively constant over the last 10 years. In 2016, these accounted for 67.4% of the three prosthesis types. The use of posterior stabilised prostheses has declined from 32.9% in 2008 to 25.6% in 2016." It also reports that "…Posterior stabilised and medial pivot prostheses have a higher rate of revision compared to minimally stabilised" stating that "…Posterior stabilised prostheses have a higher cumulative incidence of infection…" and "also have a higher cumulative incidence of loosening compared to minimally stabilised prostheses" [7].

and its absence is likely to reflect anterior cruciate deficiency, alteration of the normal joint line, or other subtle changes which modify kinematics…" [11]. Similar results were obtained by Dennis et al. in 1998: they found that "…a lack of customary posterior femoral rollback in posterior cruciate-retaining designs, and conversely showing an average anterior femoral translation with knee flexion. Posterior femoral rollback, less than in normal knees, routinely was observed in posterior cruciate substituting total knee arthroplasty, attributed to engagement of the femoral component cam with the tibial post" [13]. However, the same author in a study of 2002, using a standardized technique and a specific new generation implant, found that "the subjects…experienced consistent posterior femoral rollback of the posterior cruciate-retaining total knee arthroplasty" and concluded that "having asymmetric femoral

Cruciate-Retaining Total Knee Arthroplasty http://dx.doi.org/10.5772/intechopen.74024 27

A more recent study by Banks et al. also demonstrated that "…greater axial rotations were associated with complete preservation of the PCL insertion." Definitely, in this study, it was shown a normal axial rotation and a normal condylar translation in CR group, while "cruciate-substituting or post/cam substitution of PCL… exhibited lower ranges of axial rotation

The key point is that the joint surfaces should be designed to be compatible with normal femoral rollback. Components with different curvature radius of the two condyles allow the femoral component to roll back much more laterally than medially, as on the normal knee. On the tibial side, a slightly flattened design in the sagittal plane makes the best use of the PCL preservation, allowing the femur to roll backward and rotate in a relatively normal way. At the same time, a significant congruity in the frontal plane helps to minimize stress on polyeth-

As widely explained by Sierra and Berry when performing a CR-TKR, modest posterior slope (matching patient's native slope between 3 and 7°) may help reduce tension on the PCL and facilitate knee flexion [15]. Posterior tibial slope (PTS) opens the flexion space, and this helps to obtain flexion without PCL recession. However, excessive slope may lead to compromise the insertion point of the PCL into the tibia, which can lead to flexion instability and to reduced or paradoxical femoral rollback reported more frequently in CR than in

One of the last biomechanical discoveries showed as an "increased PTS was associated with biomechanical effects leading to reductions in quadriceps force, contact stress on PF joint, and force on PCL. However, excessive PTS should be avoided to prevent progressive loosening of the TF joint gap due to the reduction of collateral ligament tension during

A reduced slope can generally lead to lift-off positive test in flexion whose treatment will be

condyles may lead to PFR with increasing knee flexion" [14].

ylene, thus reducing long-term wear [12].

extensively described in the technique paragraph.

**5. Posterior tibial slope**

PS TKR.

flexion" [16].

and condylar translation than the implant was designed to accommodate."

Focusing on the differences in clinical outcomes between TKRs with retention versus sacrifice of the PCL, a Cochrane Review published in 2013 by Verra et al. found 17 randomized controlled trials that lead to following conclusion: "… With respect to range of motion, pain, clinical, and radiological outcomes, no clinically relevant differences were found between total knee arthroplasty with retention or sacrifice of the posterior cruciate ligament. Two statistically significant differences were found; range of motion was 2.4° higher in the posterior cruciate ligament sacrificing group, however results were heterogeneous; and the mean functional Knee Society Score was 2.3 points higher in the posterior cruciate ligament sacrificing group…" but "…These differences are clinically not relevant" [8].

More recent meta-analysis obtained the same clinical conclusion [9, 10].
