2.2.1 Total knee arthroplasty (TKA)
OA of the knee can severely impact on a patient’s functional status and quality of life.
Total knee arthroplasty (TKA) is a reliable and one of the most cost-effective methods for the treatment of knee osteoarthritis. TKA is primarily indicated in severe degenerative arthritis and inflammatory arthritis as well in post-traumatic arthritis when conservative methods are no longer effective. The aims of this well-characterized surgical procedure are not only to achieve pain relief but also to improve knee function and the total quality of life (Arokoski et al. 2007, Ethgen et al. 2004, Gill and Joshi. 2001, Koskinen et al. 2008).
In the primary TKA operation, the damaged articular cartilage and subchondral bone are removed and replaced by metallic (chromium-cobalt and titanium) and plastic (polyethylene) prosthetic components which are designed to mimic the normal anatomical joint shape and function. Successful total knee arthroplasty has often been assessed on whether it achieves the restoration of the knee to neutral alignment postoperatively. Due to the continuous development of surgical techniques and prosthesis designs occurring over last decades, the TKA procedures have become increasingly reliable treatment protocols (Cherian et al. 2014, Koskinen et al. 2008, Luo 2004).
The annual number of the knee arthroplasty surgical operations has been increased dramatically during the last 20 years and the demand is expected to grow also in the future. The most substantial change has occurred in the numbers of elderly patients but in addition, there has been a substantial growth in the numbers of TKA operations performed on patients aged 50 − 60 years (Derman et al. 2014, Dixon et al. 2004, Robertsson al. 2000, Robertsson et al. 2001).
Since the 1980s, the annual volume of TKAs has increased significantly in Finland (Leskinen et al. 2012), for example in 2013, a total of 11433 knee arthroplasty operation were performed in the nation’s hospitals (National Institute of Health and Welfare 2013).
The survival of the knee prostheses has improved during the most recent decades; in several register studies the 5 to 15 years’ survival rates of prostheses have been reported to be between 88 and 98 % when using the need for some kind of revision as an endpoint ( Argenson et al. 2013, Koskinen et. al 2008, Niinimäki et al. 2014, Victor et al. 2014).
2.2.2 Unicompartmental knee arthroplasty (UKA)
Since the early 1970s, UKA has also become a more popular method for treating unicompartmental medial condylar knee osteoarthritis. However, there is still no consensus about its benefits as a surgical procedure (Insall and Walker. 1976, Koskinen et al. 2007, Koskinen et al. 2008).
At the present time, UKAs are widely used to treat isolated unicompartmental knee osteoarthritis although it is important to ensure careful patient selection and correct surgery-related indications such as stable knee joint, no high-grade deformity and one
compartment disease. It seems that the advantages of UKA include lower postoperative morbidity, a quicker return to routine activities, and more normal feelings in the knee (Berger et al. 2005, Lim et al. 2012, Niinimäki et al. 2014). In their systematic review, Griffin et al. (2005) found that the range of motion was better in UKA compared with TKA.
Complication rates after UKA and TKA were similar but deep vein thrombosis was reported more often after TKA. The functional outcome after UKA appears to be at least as effective as TKA.
It is believed that UKA has better bone sparing properties and relies more on an intact ligament-based stability compared to TKA. However, there are similarities between the procedures i.e. both implants replace the articular surfaces of either the medial or the lateral femoral condyle and the adjacent tibial plateau surface (Canale and Terry 2013).
It has been reported that there is a greater risk of revision following UKA compared with primary TKA (Niinimäki et al. 2011). This is estimated via a term called survivorship;
this is the most important end point after knee replacement surgery. According to a large register study based data from Finnish Arthroplasty Register, it seems that UKAs had an inferior long-term survivorship compared with cemented TKAs, even after adjusting for the age and sex of the patients. Kaplan-Meier survivorship of UKAs was 89.4% at 5 years, 80.6% at 10 years, and 69.6% at 15 years; the corresponding rates for TKAs were 96.3%, 93.3%, and 88.7% (Niinimäki et al. 2014).
UKA and TKA are both recommended for the treatment of medial compartment osteoarthritis in the varus knee. Traditionally, studies have reported favorable functional results and patient satisfaction from TKA i.e. this knee arthroplastic procedure seems to be offer long-term success (McAllister 2008). There are also studies reporting that UKA may confer promising advantages over TKA if one takes into consideration cost-effectiveness, speed of recovery, postoperative range of motion and the retention of the cruciate ligaments (Arirachakaran et al. 2015, Padgett et al. 1991, Soohoo et al. 2006,).
2.2.3 UKA revision
Some surgeons have reported that outcomes after UKA revision can be comparable to TKA (Chakrabarty et al. 1998, Foong and Lo 2014). Nevertheless, it has also been generally observed in long term follow-up studies that the revision UKA to TKA is technically more difficult and functionally less satisfactory in terms of the final follow-up when compared to situation after a primary TKA (Craik et al. 2015, Rancourt et al. 2012).
When a UKA failure occurs, a revision procedure will usually be needed i.e. UKA needs to be converted to TKA. Despite concerns regarding a higher risk of revision, UKA continues still to be used as an alternative to TKA. When choosing between the UKA and TKA, patients should be informed of advantages of both procedures; in particular, they also should be advised about the generally higher revision risk after UKA (Koskinen et al.
2008, Niinimäki et al. 2011, Niinimäki et al. 2014).
2.2.4 Measuring outcome after knee replacement surgery
As is the case with many medical procedures, the evaluation of parameters like value and effectiveness of TKA depend on our definition of a ‘successful’ treatment. These include relief of the patient’s symptoms, restoration of their physical function, and improvement of their post-operative condition from the pre-operative situation. Previous studies have shown that somewhere from 10% to 25% of patients are dissatisfied with the outcome of knee replacement at one to three years after surgery. The main reason is the presence of residual symptoms and the failure of the procedure to meet the patient’s pre-operative expectations (Gandhi et al. 2009, Lingard et al. 2006, Noble et al. 2005, Noble et al. 2006). The presence of preoperative psychologic distress has been also associated with poorer 1-year outcomes for function and quality of life in patients undergoing TKA (Utrillas-Compaired et al. 2014).
Although the patients’ subjective opinions are the most valuable after operation, other parameter measuring protocols including both clinical and radiological definitions of outcome have been used to estimate the results after knee replacement surgery. In general, a deviation from the normal mechanical axis of less than ± 3 degrees from neutral has been considered to be an acceptable outcome measured from postoperative anterior-posterior radiographs (Fig. 2) (Ewald 1989, Ramkumar et al. 2015, Sampath et al. 2009).
Patients’ reported outcome measures are widely used in the assessment of outcomes after TKA in joint registries and large studies. The approach of the different measurements protocols can vary but all need to be valid, reliable and responsive (Kreibich et al. 1996).
There are four commonly used objective and subjective protocols for evaluating the quality of life and ability to function after knee replacement surgery: Knee Society Score rating system (KSS) (Insall et al. 1989), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) (Bellamy et al. 1988, Ramkumar et al. 2015), Oxford Knee Score (OKS) (Maempel et al. 2016) and Knee Injury and Osteoarthritis Outcome Score (KOOS) (Collins et al. 2016).
The WOMAC include 24 questions in three classes (Pain, Stiffness and Physical function). The patient is given a VAS (visual analogue scale)-assessment of the WOMAC on a scale from 0 mm (no pain, stiffness or disability in physical function) to 100 mm (severe pain, stiffness or disability on physical function), and the sum of scores is calculated within all classes. The aggregate scores for each dimension are calculated as an average within all three classes.
The postoperative walking ability and balance can be measured in a timed Get- Up- and- Go test. In this test, the patient is initially sitting on a chair and stands up after receiving a sign, walks 3 meters and then turns around, returns to the chair and sits down.
The time from leaving the chair until returning back and being seated again is measured.
This test assesses the patient’s postoperative walking ability and balance (Mathias et al.
1986).
Patients’ preoperative and postoperative pain can be assessed reliably by levels from 1 to 10 on a Visual Analog Scale (VAS) (Hawker et al. 2011).
Matsuda et al. (2013) concluded in their retrospective questionnaire that patient satisfaction is difficult to measure. The avoidance of varus alignment and the achievement of better ROM appear to be important for increasing patient satisfaction.
Figure 1. The mechanical axis of the lower limb is defined by combining the mechanical axis of the femur defined by the line from the centre of the femoral head to the centre of the knee joint and the mechanical axis of the tibia defined by the line from the centre of the knee to the centre of the ankle. A deviation of within ± 3 degrees from neutral is considered to be an acceptable outcome.
2.3 KNEE ARTHROPLASTY AND OBESITY