Functions, disabilities and perceived health in the first year after total knee arthroplasty; a prospective cohort study

Osteoarthritis (OA) is one of the ten most disabling diseases in developed countries: 9.6% of all men and 18.0% of all women over 60 years of age have symptomatic osteoarthritis [1]. While pain is the most prominent symptom, 80% of these patients have limitations in movement, and 25% cannot perform daily activities [1]. An increase in prevalence is expected due to ageing and obesity [1‐5].

In end-stage osteoarthritis, joint replacement is an effective intervention to reduce pain and improve functioning in the majority of patients [3, 6‐9]. However, it has been reported that 15–30% of patients still experience pain and loss of function after total knee arthroplasty (TKA) [7, 9‐12].

Several studies have investigated recovery after TKA. Although most describe a 10–20% improvement in quadriceps strength and gait parameters in comparison to the pre-operative status, values remained lower than in healthy peers or the uninvolved leg [11‐19]. A correlation between quadriceps strength and functional performance after TKA [18, 19] seems logical, for functional performance can be assumed to improve with quadriceps strength. Several studies found improvements in patient-reported outcome measures (PROMs), functional status and quality of life. [12‐14, 20, 21]. However, patients often did not regain optimal health [22]. No relation with strength is investigated in these studies.

Although several studies investigated aspects of recovery after TKA, no study yet has incorporated all domains of the International Classification of Functioning, Disability and Health (ICF) in their assessment. Interesting findings in the ICF domains may be missed by the limited follow-up, population size and incompleteness of ICF domains of other studies. We therefore performed a prospective cohort study in which 150 patients scheduled for TKA were followed till 1 year after surgery, and in which we systematically assessed all domains of the ICF. Our first objective was to provide a more complete overview of current physical recovery rates of patients with TKA in the first year after surgery in the Netherlands. We hypothesize that the patients in our study will improve on all parameters in the first year after surgery. Our second objective is to generate normative quadriceps and hamstrings strength values for patients receiving a TKA in the Netherlands.

Between March 1, 2011 and March 1, 2013, we included 150 patients, 71 men and 79 women, with a mean age of 64.7 ± 8.0 years. The majority of patients had surgery of the right knee (right 89, left 61) and mean BMI was 31.2 kg/m² for men and 30.7 kg/m² for women (Table 2). We lost 4 patients at 3-months follow-up and an additional 3 at the 12-month measurement. Not all patients were able to come to the hospital for the follow-up measurements, so data on physical tests (strength, temporospatial gait parameters and ROM) were unavailable for 7 patients at 3-months and for 9 patients at the 12-month measurement (4 of whom were the same as those at the three-month measurement).

With the exception of the SF12, patients improved significantly on all questionnaires over 3 and 12 months. The largest improvement occurred within the first 3 months. The largest and significant improvement of the SF12 Physical component was only between baseline and 3 months (Table 3).

The GPE is shown in Fig. 1. After 3 months, 5.3% of all patients reported to have fully recovered from surgery, and after 1 year 25.3% did so. After 3 months, 2.7% of all patients were totally dissatisfied with the result and the treatment, against 1.3% after 1 year. Overall, the majority of patients were satisfied with the result, but had some residual complaints.

Figure 2 and 3 show respectively the 60°/s isokinetic quadriceps and hamstrings muscle strength in the peri-operative phase of men and women. After 3 months the quadriceps isokinetic strength measured at 60°/s speed is back on pre-surgical level for women (baseline 43.4 Nm [27.8]; 3 months 46.1 Nm [17.1]; significance 1.000) and for men (baseline 67.9 Nm [35.5]; 3 months 73.3 Nm [26.2]; significance 0.521). The quadriceps 180°/s only improved significantly in men in 3 3 months (baseline 43.3 Nm [23.0]; 3 months 50.5 Nm [17.4]; significance 0.005), women were back on pre-surgical level (baseline 29.2 Nm [16.4]; 3 months 30.0 Nm [11.7]; significance 1.000). Over 12 months a significant improvement was demonstrated, at both angular speeds and for both sexes (women 60°/s: 64.5 Nm [18.9] 180°/s: 38.2 [11.8]; men 60°/s: 95.2 Nm [30.5] 180°/s: 61.8 [19.1]). 60 °/s Isokinetic Hamstrings strength in men and women improved significantly in the first year after surgery, compared to pre-surgical values (women; baseline 33.3 Nm [18.9]; 3 months 39.8 Nm [16.7]; significance 0.009; 12 months 50.7 Nm [16.2]; significance 0.000; men; baseline 48.0 Nm [23.4]; 3 months 65.6 Nm [22.8]; significance 0.000; 12 months 77.2 Nm [26.1]; significance 0.000). 180°/s Isokinetic Hamstrings strength only improved significant in in men in both time periods (baseline 37.8 Nm [18.6]; 3 months 47.1 Nm [17.8]; significance 0.000; 12 months 54.4 Nm [20.9]; significance 0.002. and in women only between 3 and 12 months (baseline 24.4 Nm [12.6]; 3 months 27.1 Nm [11.3]; significance 0.263; 12 months 33.3 Nm [11.6]; significance 0.000.)

We also compared muscle strength of our patients with that of healthy individuals. At baseline, our patients had 51.6 to 63.3% of the quadriceps strength of healthy persons, and 56.8–69.5% of the hamstrings strength. At 3 months, values were 55.7 to 64.4% of the quadriceps and 76.1–79.5% of the hamstrings, respectively, and at 12 months 72.0 to 81.7% and 88.4 to 100.7%, respectively.

Table 4 lists the ROM values. The mean baseline flexion was 120°. Flexion was limited immediately after surgery, but increased again during the first weeks. After three months, flexion had returned almost to baseline value, although there was still a significant difference. At 12 months, the flexion had returned to baseline level. Overall, extension ROM did not change significantly after a TKA.

Table 5 shows walking speed and step length. The step length of the healthy and surgical leg increased significantly over time. With increasing step length, walking speed also increased significantly over time after TKA (98.9 cm/s at baseline, 108.4 cm/s at 3 months and 117.0 cm/s at 12 months). Improvement of walking speed between baseline and the 3-month measurement was comparable to that between the 3- and 12-month measurements. The largest improvement in step length was between baseline and 3-month measurements.

This study reports on the first year of physical recovery of patients undergoing a TKA in the Netherlands and could therefore be useful in informing patients about prognostic consequences of a TKA.

The most remarkable finding in this study is the persistent limited muscle strength. Whilst other outcome measures improved to nearly normal values compared to the healthy population, quadriceps strength lagged behind. Before surgery, strength was half of that of matched healthy persons, a higher deficit than reported in the literature [12, 15]. Three months after surgery, mean strength was comparable to pre-surgical values. Although strength increased from 3 till 12 months after TKA, it never reached ‘healthy’ values. We do not expect that pain has a role in the muscle strength deficit since a large amount of patient did not experienced pain during strength measurement after the surgery, in contrast with the measurement pre-surgically. One reason could be the changed kinematics of the knee (altered patellofemoral kinematics) and/or muscle loss due to surgery. A change in strength was seen in an in vitro study by Ostermeier et al., who compared hinged and non-hinged TKAs [39]. Further, during therapy focus is on functional training and isokinetic strength measurement is not performed standardly. Our large study population underlined the muscle deficit already reported in other studies with a smaller sample size [12, 15‐19]. In these studies even a higher deficit was described 3 months after surgery [12, 18]. Further, the total gain in muscle strength in the first year was higher in our study compared to the literature [15]. This could be due to the larger improvement in the first months compared with the literature. A reason could be the health care system in the Netherlands. The main part of all patients receive routinely a prescription for physical therapy after the TKA surgery for 1 year physical therapy. Generally, they have therapy twice a week. This could result in a faster and larger improvement of muscle strength which focuses on activity level, like walking with and without crutches and walking stairs. This is in contrast with the amount of physical therapy patients receive in other countries worldwide. Bade et al. described only that 26% of all patients receive outpatient physical therapy [12]. This could also possibly explain the smaller deficit of walking speed in our study. Walking speed in our pre-surgical [12, 13] and post-surgical patients is higher than reported in the literature in which patients with a TKA walked 20% more slowly than healthy individuals 1 year after surgery [8, 13, 17]. Before surgery, the walking speed of patients in our study (98,9 cm/s) was 20.0–26.1% lower than in a healthy population (healthy walking speed for women [60–69 years] 1.24 m/s and for men [60–69 years] 1.34 m/s) [40]. After surgery, walking speed (108.4 cm/s) increased but remained lower than in healthy persons (between 81.0–87.3% of the healthy walking speed) [40]. After 12 months, walking speed (117.0 cm/s) still increased, but did not reach the healthy level (attaining between 87.3 and 94.2% of the walking speed of healthy individuals). However, in terms of managing pedestrian street crossings with lights (which are designed for 1.2 m/s), 81% of our population were unable to cross the street safely before their surgery. After 3 months, this percentage had decreased to 65%, but after 12 months it was still 49%.

Pua et al. [41] investigated the relationship between walking speed and physical parameters in the first 16 weeks after TKA. They found ipsilateral quadriceps strength as strongest predictor for walking speed. No linear relationship existed till 111 N, a steep rise in gait speed was observed with every gain in muscle strength. After 111 Newton the speed increased more gradually [41]. However, according to Alnahdi et al. [42], the influence of quadriceps strength on gait patterns is only moderate till 6 months and in the period till 1 year it even decreases.

All questionnaires regarding level of functioning, quality of life and patient-specific complaints yielded lower scores compared to healthy controls, both pre- and postsurgical. (For healthy peers, we assumed highest possible score on the WOMAC, KSS and PSFS [related to knee problems] may be expected. For the SF12 we used reference data from the United states of America in which the healthy population had a score on the mental part of 51.6 and 43.9 on the physical part [43]). However, a large and significant increase was reported on all questionnaires over the 12 months following surgery. This is in agreement with previous studies [4, 9, 12‐15, 18, 20‐22]. Only, our population seemed to recover faster; they performed on pre-surgical level at 3months, while in other studies this took about 6 months [12]. Again, this could be due to the amount of physical therapy in the Netherlands, focused on activities like walking, walking stairs and making transfers.

Possible due to the faster increase in strength, walking speed and questionnaires, our patients were more satisfied compared to those in other studies, as seen on the GPE (8.7% dissatisfied at 3 months, 7.9% dissatisfied at 12 months, whereas in other studies 15–30% of the patients were dissatisfied) [7, 9‐12]. However, a relation between satisfaction and improvement in pain, function and handicap is difficult, and therefore, according to Genet et al. satisfaction should be investigated as an independent parameter [14].

Nonetheless, patients’ physical capability can be satisfying, their spare capacity could be less, giving a higher risk for frailty in case of a trauma or hospitalization. Therefore, despite of the importance of their satisfaction as success indicator for surgery, measuring their functional activity level is an important indicator.

Quality of life, activities, muscle strength and gait parameters improve significantly after a TKA. However, complaints on activities and walking speed remain. Most striking was the limited quadriceps strength, which we believe may restrict patients in daily life. Therefore, future studies should address the impact of strength training after a TKA on the improvement in muscle strength and daily activities.