Knee Pain during Strength Training Shortly following Fast-Track Total Knee Arthroplasty: A Cross-Sectional Study

Background Loading and contraction failure (muscular exhaustion) are strength training variables known to influence neural activation of the exercising muscle in healthy subjects, which may help reduce neural inhibition of the quadriceps muscle following total knee arthroplasty (TKA). It is unknown how these exercise variables influence knee pain after TKA. Objective To investigate the effect of loading and contraction failure on knee pain during strength training, shortly following TKA. Design Cross-sectional study. Setting Consecutive sample of patients from the Copenhagen area, Denmark, receiving a TKA, between November 2012 and April 2013. Participants Seventeen patients, no more than 3 weeks after their TKA. Main outcome measures: In a randomized order, the patients performed 1 set of 4 standardized knee extensions, using relative loads of 8, 14, and 20 repetition maximum (RM), and ended with 1 single set to contraction failure (14 RM load). The individual loadings (kilograms) were determined during a familiarization session >72 hours prior. The patients rated their knee pain during each repetition, using a numerical rating scale (0–10). Results Two patients were lost to follow up. Knee pain increased with increasing load (20 RM: 3.1±2.0 points, 14 RM: 3.5±1.8 points, 8 RM: 4.3±2.5 points, P = 0.006), and repetitions to contraction failure (10% failure: 3.2±1.9 points, 100% failure: 5.4±1.6 points, P<0.001). Resting knee pain 60 seconds after the final repetition (2.7±2.4 points) was not different from that recorded before strength training (2.7±1.8 points, P = 0.88). Conclusion Both loading and repetitions performed to contraction failure during knee- extension strength-training, increased post-operative knee pain during strength training implemented shortly following TKA. However, only the increase in pain during repetitions to contraction failure exceeded that defined as clinically relevant, and was very short-lived. Trial Registration ClinicalTrials.gov NCT01729520


(B) Registration of knee pain during rehabilitation exercises after total knee arthroplasty
Thomas Linding Jakobsen and Thomas Bandholm, Clinical Research Centre, Copenhagen University Hospital, Hvidovre, Denmark.

Introduction
Total knee arthroplasty (TKA) is offered to patients with severe knee osteoarthritis to reduce knee pain and improve functional performance (Leopold, 2009). Shortly following surgery, patients experience a substantial loss of knee-extension strength and functional performance (Mizner et al., 2005;Stevens et al., 2003), making them more dependent postoperatively, as compared to presurgery.
The average loss of knee-extension strength after TKA is around 80% at discharge after 2.4 postoperative nights (Holm et al., 2010), and 60% 1 month postoperatively (Mizner et al., 2005;Stevens et al., 2003). As the loss of knee-extension strength is related to the loss of functional performance after TKA (Holm et al 2010), it is desirable to reach the strength level observed preoperatively, or further than that. This is likely achievable through rehabilitation that includes progressive strength training as a rehabilitation modality (Holm & Kehlet, 2009) It requires, however, that such exercise implemented shortly after TKA is tolerable with respect to knee pain, even though the exercise intensity increases progressively. This has recently been indicated (Jakobsen et al., 2011). However, we lack a more detailed description of knee pain while patients perform progressive strength training at different training loads and repetitions after TKA.

Purpose
The project aims to describe patients' self-perceived knee pain during the 2 most commonly used strength training exercises for the operated leg in the first weeks after TKA.

Material and methods
Twenty-four patients, having received a recent primary TKA and with no loading or movement restrictions, are referred to outpatient rehabilitation in their home county approximately 1 week after surgery. During their rehabilitation, they will be asked to rate their knee pain on a numerical ranking scale ranging from 0 to 10, while they perform the strength training exercises: kneeextension and leg press, at different loads and repetitions (see Figure 1). Before and after each strength training set, knee swelling (knee joint circumference) and range of motion of the operated knee joint, will be assessed, using a tape measure and a goniometer, respectively (Jakobsen et al., 2009).

Practical matters
The project is conducted as an integrated part of the outpatient rehabilitation for patients with TKA, as it takes place in patients' home counties. The local rehabilitation sites already use strength training as part of their rehabilitation of these patients. During this, the physiotherapists routinely measure knee pain and knee joint range of motion of the operated leg in patients with TKA. It means that for the present project, the physiotherapists will only have to register knee pain and range of motion slightly more systematically than is already part of routine practise.

Ethical considerations
The project does not appear to be associated with ethical problems. All the included patients will follow routine outpatient practise after TKA, as it is commonly offered at their home county.

What are the clinical perspectives?
The knowledge gathered from this project will have the potential to be implemented in the rehabilitation of patients after TKA, shortly following surgery. As progressive strength training is likely imperative for the regain of knee-extension strength following surgery, it is important to know which exercises, loads and repetitions that are tolerated the best by these patients shortly following surgery.