1.1. Background: Decreased quadriceps and hamstring strength is common even one year after a total knee arthroplasty. Hence, patients with persistent functional complaints treated at the Maastricht University Medical Centre (MUMC+) received a progressive strength training program.
1.2. Objectives: The aim of this study was to investigate the impact of the progressive strength training program on quadriceps and hamstring strength.
1.3. Methods: Patients were referred to the outpatient physical therapy department of MUMC+ and received a 6-week progressive strength training program. Their isokinetic quadriceps and hamstring strength and functional ability were assessed before and after the program.
1.4. Results: Men significantly improved in terms of all strength parameters assessed at an angular velocity of 60°/sec and 180°/sec. Women only improved their quadriceps strength at 180°/sec. No significant improvement at functional level was seen.
1.5. Conclusion: A 6-week progressive strength training program has a positive impact on the isokinetic quadriceps and hamstring strength in both men and women, but not on functional ability.
1.6. Level of Evidence: Level 3.
2. Keywords: Arthroplasty; Knee; Physical Therapy; Rehabilitation; Total
A Total Knee Arthroplasty (TKA) generally
reduces pain and restores range of motion in patients with end-stage Osteoarthritis
(OA) of the knee. This is important as an increase in the incidence of knee OA
is expected in the next years due to an ageing population and a trend toward obesity
[1,2]. Notwithstanding these generally positive
results, however, quadriceps and hamstring strengths remain lower than those of
healthy controls, even one year after TKA [3-8].
Decreased quadriceps and hamstring
strength negatively influences knee stability, increasing the risk of falls and
generating a feeling of uncertainty in patients .
Additionally, activities like rising from a chair, standing, walking and
climbing stairs become more difficult, which leads to a loss of independency [9-15].
A number of explanations can
be given for this decreased strength. Firstly, pain-induced disuse in the
pre-surgical phase changes activity patterns and reduces strength . Secondly, the bio-kinematics change due to the surgical procedure, the possible
resurfacing of the patella and the removal of the cruciate ligaments [6,7,11]. Thirdly, proprioception is changed as a result of the surgery as such (removal
of the tibia and femur ends, removal of the cruciate ligament, cleaving of the
joint capsule, and the ingrowth of scar tissue) [6,7,11] And finally, it can result from possibly inadequate post-surgical therapy. Comparison and investigation of
the therapeutic validity of the post-surgical therapy after TKA is difficult
because of the considerable diversity in the amount and intensity of therapy applied
worldwide, as well as because of the lack of accurate descriptions of the therapy
provided [17,18]. Two
systematic reviews, by Pozzi, et al. (2013)  and Skoffer, et al. (2015),  were unable to draw unambiguous conclusions on
the effect of progressive strength training on the muscle strength of patients
after TKA, based on the results of three (methodologically low-rated) Randomized
Clinical Rials (RCTs). However, the studies by Petterson, et al. (2009) , Petterson, et al (2011)  and Johnson
et al. (2010)  all showed a significant
improvement in isometric quadriceps strength.
to the two reviews based on RCTs, there have been three pilot studies in recent
years. A pilot study by Jakobsen, et al. in 2012
found an improvement in isometric quadriceps strength after a two-week, thrice
a week, progressive strength training program in 14 patients. They started
within 2 days after surgery with leg press and knee-extension exercises at a
training intensity of around 80% of one Repetition Maximum (1RM) and performed 2×10
repetitions. Combined with gait training, range of motion exercises, functional
activities, balance training and stretching, one session lasted 60 minutes. However,
an RCT by Jakobsen, et al.  in 2014 did
not find a significant difference in quadriceps strength 8 weeks after TKA,
compared with pre-surgical values after a 7-week, twice a week, progressive
strength training program, and compared with a therapy without strength
training. They started between days 6 and 8 after surgery and performed 2×12
repetitions; the exact intensity was not reported, although the authors stated that
they had adjusted the load in accordance with the repetitions at each session. Each
session lasted 60 minutes, but the strengthening part was only 15 minutes. Husby,
et al.  performed an RCT in which they compared
a maximal strength training program with standard rehabilitation. Their program
had a higher intensity (80-90% of 1RM) and fewer repetitions (4-5 repetitions).
They were able to find a significant improvement in quadriceps strength after an
8-week, thrice a week program, starting on day 8 after surgery. The total
duration of a session was 30 minutes. Both Petterson, et al.  and Johnson,
et al.  found an improvement in functional
ability after a strength training program, after 12 months and 4 weeks,
respectively. This is in contrast with Husby, et al. 
who found no improvement in functional ability after their strength training
differences with the program offered in our study is that we started between 3 and
18 months after surgery, in those patients who had remained significantly
hampered by a strength deficit. Therapy was initiated when they expressed
complaints at a follow-up visit to their orthopaedic surgeon. A second
difference is the strength measurement, as we tested isokinetic strength.
According to Lauermann, et al.  isokinetic and isometric strength improvements should
not be mixed, as percentages of muscle weakness based on these measurements
differ between the two methods, when compared with controls. Presenting baseline and change values in isokinetic strength after TKA
and after a progressive strength training program is therefore useful to
understand isokinetic strength development and to enable comparison of
therapies. In addition, greater insight into the impact of a progressive
strength training program on the quadriceps and hamstring strength is useful in
the investigation of the therapeutic validity of post-TKA therapy [2,16,26] This was also noted by Bandholm, et al,  who stated
that the ‘pill’ of physical therapy may not contain the right stimulus or may not
be given at the right moment. Hence, the main aim of our study was to examine
the impact of 6-week progressive strength training program, described in detail
and starting at least 3 months after TKA surgery as part of usual care in the
MUMC+, on quadriceps
and hamstring muscle strength and functional ability of patients after a TKA.
Patients with complaints after receiving a TKA at MUMC+, who were not
receiving physical therapy at that moment, were referred to the hospital’s outpatient
department for physical therapy. They were offered a 6-week progressive
strength training program.
Patients were enrolled during regular follow-up
appointments with their orthopaedic surgeon at the knee outpatient clinic at
the MUMC+ Department of Orthopaedic Surgery. Patients were eligible to
participate if they met the following inclusion criteria: having undergone primary
TKA at the MUMC+ at least 3 months ago, age <80 years, subjectively reported
complaints regarding physical functioning, and no simultaneous outpatient
physical therapy. Patients with a limited cognitive function or with limited command
of Dutch which interfered with filling out questionnaires, or who were unable
to follow instructions, were excluded. Patients
eligible for training were referred to the MUMC+ outpatient physical therapy
department by their attending surgeon. The baseline maximal isokinetic quadriceps and
hamstring strengths of their affected leg were measured with a Biodex System
Pro 3 dynamometer (Biodex Medical Systems, Shirley, NY, USA), by an experienced
physical therapist. Values were compared with normative values from healthy controls
(n=295). The normative values were calculated using equations obtained in a previous study . The normative values are
given in (Table 1). Patients with inadequate strength were informed about the
MUMC+ physical therapy program, a 6-week progressive strength training program.
This retrospective study investigated the data of
twelve patients who attended the therapy at MUMC+ after a TKA, and was approved
by the regional ethics committee (METC 2018-0519). It was performed in accordance with the Declaration
of Helsinki. Since patients were treated with usual care, no written informed
consent was obtained, but all patients were able to object to the use of their
data in scientific publications. None of these twelve patients did. All
patients agreed with physical therapy at MUMC+ and were able to withdraw from physical
therapy treatment at any moment.
Surgeries were performed by two orthopedic surgeons, both with extensive
experience with the prosthesis. All patients received a cemented Scorpio NRG® prosthesis (Stryker, Kalamazoo, Michigan, USA) or an Attune® Knee System (DePuy Synthes, Raynham, Massachusetts, USA). After a medial parapatellar approach, the surgeons used a bony
referenced, tibia first technique. A cemented patella component was used in all
patients, and a tourniquet was only used during the cementation period of the
demographic characteristics, including age (years), sex (M/F), height (m),
weight (kg), Body Mass Index (BMI) in kg/m2,
side of TKA (R/L) and time since TKA surgery (months) were obtained during the
strength and functional ability were both assessed before and after the 6-week
progressive strength training program, by an experienced physical therapist.
isokinetic quadriceps and hamstrings strength, in Newton Meter (Nm), was
measured with the Biodex System Pro 3 dynamometer (Biodex Medical Systems,
Shirley, NY, USA) at angular velocities of 60°/sec
(5 repetitions) and 180°/sec (10
repetitions). The Biodex is a reliable and valid measurement instrument and is
the gold standard for measuring maximal isokinetic strength up to angular
velocities of 300°/sec  Measuring isokinetic strength was preferred to isometric
strength measurements: Lauermann, et al.  reported that since the percentage of patients diagnosed with muscle
weakness was higher when calculated on the basis of isometric muscle strength
measurements than with isokinetic strength measurements, the isometric strength
difference could be an overestimation of the muscle weakness and could
underestimate the effect of an intervention .
ability was assessed with the Western Ontario and McMaster Universities
Osteoarthritis Index (WOMAC). This self-administered disease-specific health questionnaire has been designed
to measure the functional ability of the osteoarthritic knee before and after TKA
surgery [30,31] The WOMAC
provides aggregate scores for each of 3 subscales: joint pain, joint stiffness
and functional ability. Together, they yield the WOMAC sum score. The 5-point
Likert version of the WOMAC was used in our study, with a scale ranging from 0
to 96 points (0 indicating no pain or dysfunction). Afterwards the scores were
standardized to a 0-100 scale, with 100 indicating no pain or dysfunction. The
WOMAC is a responsive instrument that yields reliable and valid measurements in
a population of patients with knee OA and after a TKA, and has been used
extensively to evaluate this patient population [30-34]
6-week strength training program, patients had two sessions a week (total of 12
session), with at least 48 hours between two individual training sessions. Each
session lasted 45 minutes and started with a warm-up cycle ergometer session (5
minutes, at a self-chosen comfortable wattage) and cool-down walking on a
minutes, at a self-chosen comfortable speed). Before the
start of the strength training program, an X-Repetition Maximum (XRM) assessment
of all individual exercises was performed to test individual strength. Thereafter,
the Oddvar Holten diagram  was used to
calculate the 1RM from the XRM  The XRM is a
frequently used alternative to calculate the 1RM, because the 1RM is often not feasible
 The resulting 1RM was used to design an
individual progressive strength training program, according to the American
College of Sports Medicine guidelines, starting at 60% of the 1RM [16,38]. All patients received an individual training
protocol, with prescriptions for resistance, as well as the number of
repetitions (8-15) and sets (3-4). The patients were instructed to take a pause
of 60 seconds between sets. The total workload was adjusted at each session, by
raising the resistance and the number of repetitions or sets according to the
personal rating on the Borg Rating of Perceived Exertion Score (Scale 0-10) . If patients rated their exertion as ‘tolerable’
(Borg 0-4), weight was increased (one step being 10 kg for the leg press, 2.5
kg for the leg extension and 2 kg for the leg curl), and the number of repetitions
was reduced to the starting value of 8. If patients rated their exertions as
‘heavy’ (Borg 5-10), the number of repetitions was first increased (from 8 to
10 or in a subsequent session from 10 to 12 repetitions). When patients had reached
3 sets of 12 repetitions, the weight was increased by one step in the next
session, and the repetitions were reduced to the starting point of 8. If at
that moment an increase in weight was not possible, an extra set was added (4
sets instead of 3). The original weight and repetitions were retained, and in
the subsequent session the weight was once again increased, and the number of
repetitions again reduced (as described above). Patients were tested and
trained on three different stationary resistance training stations (Leg Press,
Leg Curl and Leg Extension). To prevent a dominant role of the non-surgical leg
in the training, we decided to test and train both legs unilaterally, to achieve
sufficient training stimulus for each leg .
Data were analyzed
with SPSS, version 22.0 for Windows (IBM®
SPSS ® Statistics version 22.0).
Descriptive statistics were used for sex, age, height, weight, TKA side and
time since TKA surgery. The data for the two sexes are presented separately
below. Normality was tested with the Shapiro-Wilk test. In case data were normally
distributed, data is presented as means ± Standard
Deviation (SD) and, where appropriate, in absolute numbers and percentages. Otherwise,
medians and percentiles are used. Paired sample t-tests were used to test mean differences
in continuous data between baseline and follow-up measurements. A cut-off value
for significance of 0.05 was used. Values were also compared with normative
values calculated using formulas for normative values of healthy controls which
we have published earlier  (Table 1).
patients were referred to the physical therapy department. One patients had
strength values comparable with the normative values for healthy persons and
was therefore excluded from this progressive strength training program. The
other twelve were included between March 2016 and January 2018. They were seven
men (age 66.0 [6.3] years, BMI 28.9 [4.9] kg/m2)
and five women (age 67.4 [7.3] years, BMI 32.5 [9.4] kg/m2) (Table 2). Patients were referred
between 3 and 18 months after TKA surgery. Adherence to therapy was good;
all patients completed the program and attended 12 sessions. No adverse events
were seen during this period. One patient had a delay of 10 days between
the 11th and 12th sessions, due to illness (influenza). Five patients
received a Scorpio NRG ® knee system
(Stryker, Michigan, USA) and seven patients an Attune® knee system (Depuy Synthesis Companies,
improved in terms of quadriceps (Figure 1) and
hamstring strength. One woman’s hamstring strength decreased, as did another
woman’s quadriceps strength. Overall, a favorable change of 45-81% was seen: the
men had a significant improvement on all isokinetic strength parameters (p=
0.00-0.01). (Figure 2) The overall change
for the women was 12-37%, and only the isokinetic quadriceps 180°/sec strength showed significant improvement (p
= 0.02). (Figure 3) Comparison with normative
values showed that the men scored 35-46% of these values at baseline. After the
6-week progressive strength training program, this was 59-71% (Figure 2). As regards the percentage of the normative
value for women, this was 55-79% before the start of the program and 73-94%
afterwards (Figure 3).
in the change in functional ability was high, with five patients improving
their WOMAC function score, four patients deteriorating and three not showing
any change (change < 5 standardized points). The individual change is shown
in (Figure 4).
This study examined the impact of a 6-week
progressive strength training program, started at least 3 months after TKA surgery,
on the change in isokinetic quadriceps and hamstring strength and the
functional ability of patients who had undergone a TKA. The results show a
significant improvement in all strength parameters for men and for one
quadriceps strength measurement in women. No significant improvement in
functional ability was seen, since the change in functional ability was highly
variable. Our results are in agreement with those of several previous studies [9,20-23]. Although all of these studies started the
training program earlier after surgery than ours, it is useful to know that
progressive strength training which starts at a later moment after surgery
still has a positive impact on muscle strength. It is important to notice that
direct comparison with our results is impossible, since these other studies
used isometric instead of isokinetic strength measurements, and did not present
their results for men and women separately, or failed to describe their
interventions in detail. Although the sample size in our study was small, the
fact that two women showed a decrease in one of the two hamstrings or quadriceps
strength measures suggests that women only improved significantly regarding quadriceps
strength at an angular speed of 180°/sec.
It is important to note that the two women whose hamstrings or quadriceps
strength deteriorated both reported mild influenza complaints.
No adverse events were reported during the
therapy sessions in our study. In general, patient compliance was high and most
of the patients continued their exercise training after our program, since the
training and the strength measurement results encouraged them to maintain
training. In addition, they experienced a positive change in their daily life
and became enthusiastic about the training sessions. Our findings confirm that progressive
resistance training is possible and safe in patients after a TKA. Although our patients
improved their muscle strength, there was high variance in the change on the
WOMAC function score. Due to this high variance and the small sample, no conclusions
can be drawn regarding functional change. This corresponds to what has been reported
in the literature , although Johnson, et al.  found an improvement on the Timed Up and Go test after their
4-week program. An explanation for this difference may lie in the fact that
performance-based tests are driven by muscle strength while self-reported
questionnaires are driven by pain, as mentioned by Pozzi, et al.  Possible reasons for the high variance we found could
be the short duration of our program, as 6 weeks may have been too short to see
an improvement in functional ability, since patients were adjusting their daily
life routine to this therapy. In addition, the statistical power of our study may
have been too low to detect a significant change in functional ability. Finally,
the patients expanded their activities, which might mean they experienced their
limitations more clearly, giving them a better insight into their individual
functional abilities and problems, which could result in greater acceptance of their
position in the rehabilitation process.
Our study had some limitations. Firstly, given
the small sample size, the power was too small to draw conclusions regarding
the change in functional ability. Secondly, the fact that we did not find a
significant difference in functional ability might have been influenced by the
fact that we chose a patient-reported outcome measure; a performance test might
be more directly related to muscle strength. Thirdly, our pre-post study design
had some limitations as regards studying the effectiveness of a progressive
strength training. Therefore, the results have to be interpreted with caution.
Nevertheless, this study has yielded important evidence and starting points for
future studies to evaluate the addition of progressive strength training to the
standard physical therapy program after TKA .
Although the results of this study are promising
in terms of improving the quadriceps and hamstring strengths of patients after
a TKA, further studies are required to compare our progressive strength
training with the functional training often given in outpatient physical
therapy departments and to investigate the effect of progressive strength
training on the change in functional ability in a larger population.
Additionally, the long-term effects of a progressive strength training program
on strength remain unknown, as do the optimal and ultimate moments for starting
strength training. Finally, the optimal duration of the program should also be
In conclusion, a 6-week progressive strength
training program starting at least 3 months after TKA surgery had a positive
impact on isokinetic quadriceps and hamstring strengths in men and women, though
no significant improvement in functional ability was detectable.
A 6-week strength training program, starting at least 3
months after TKA surgery, has a favorable effect on quadriceps and hamstring
strength, though not on functional ability. Caution is necessary in
interpreting our findings, since we only included a small population and we did
not compare with other therapies. Therefore, further research to investigate
the long-term impact of a strength training program, comparing our program with
other therapies, would be useful, and impact on functional ability should also
be investigated in a larger population.
We would like to thank R. van Marm, B. Nijst, R. Ridder, K. Steeghs, M.
Wawer and A. Weemaes for their contribution.
10. Conflict of Interest
The regional ethics committee (METC of the azM/UM) approved this study
under number METC 2018-0519. The authors certify that there is no conflict of
interest and that this study did not have any financial support.
Figure 1: Shows the change in quadriceps strength of all individual patients before
and after training, in Nm. Each
line represents an individual patient. Their sex is given to the right of the
diagram (F[Female] and M[male]).
Figure 2: Shows the mean quadriceps and
hamstrings strengths in men, at baseline and after the training program, in Nm
with standard deviations Q60:
isokinetic quadriceps strength 60°/sec.
Q180: isokinetic quadriceps strength
180°/sec. H60: isokinetic hamstring strength 60°/sec.
H180: isokinetic hamstring strength
180°/sec. Normative values are the
means of the individual normative values based on sex and age. * Significant
improvement between baseline and post-training assessments (p < 0.05)
Figure 3: Shows the mean quadriceps and
hamstrings strengths in women, at baseline and after the training program, in
Nm with standard deviations Q60:
isokinetic quadriceps strength 60°/sec.
Q180: isokinetic quadriceps strength
180°/sec. H60: isokinetic hamstring strength 60°/sec.
H180: isokinetic hamstring strength
180°/sec. Normative values are the
means of the individual norm values based on sex and age. * Significant
improvement between baseline and post-training assessments (p < 0.05).
4: Shows the change in WOMAC Function score of each individual patient
before and after training. Each line represents an
individual patient. The sex is given to the right of the diagram (F[Female] and
TABLE 1 Normative values
Table 1: Shows the normative values calculated using equations including age and sex . Nm: Newton meter. SD: standard deviation. Q60: isokinetic quadriceps strength 60°/sec. Q180: isokinetic quadriceps strength 180°/sec. H60: isokinetic hamstring strength 60°/sec. H180: isokinetic hamstring strength 180°/sec.
TABLE 2 Patient Characteristics
Table 2: Shows the patients characteristics. BMI: Body Mass Index, SD: Standard Deviation.
Citation: Berghmans DDP, Lenssen AF, Emans PJ, de Bie RA (2018) A Progressive Strength Training Program Starting 3 Months Post Total Knee Arthroplasty Surgery Improves Strength but Not Functional Outcome. J Orthop Ther: JORT-1118. DOI: 10.29011/2575-8241. 001118