To examine thigh muscle strength, functional performance, and self-reported outcome in patients with nontraumatic meniscus tears 4 years after operation, and to study the impact of a strength deficit on self-reported outcome and evaluate the feasibility of 3 performance tests in this patient group.
The study group comprised 45 patients (36% women, mean age 46.7) who had an arthroscopic partial meniscectomy a mean of 4 years (range 1–6 years) previously. Main outcome measures included isokinetic strength of knee extensors and flexors, functional performance (1-leg hop, 1-leg rising, and square-hop tests), and a self-reported questionnaire (Knee Injury and Osteoarthritis Outcome Score).
We found lower knee extensor strength and worse 1-leg rising capacity in the operated leg, but no difference between operated and nonoperated leg for knee flexors (P ≤ 0.004 and P > 0.3, respectively). Patients with a stronger quadriceps of the operated leg compared with the nonoperated leg had less pain and better function and quality of life (r = 0.4–0.6, P ≤ 0.010). We found the 1-leg rising and 1-leg hop tests to be suitable performance tests in middle-aged meniscectomy patients.
Quadriceps strength is reduced in the meniscectomized leg compared with the nonoperated leg 4 years after surgery. This relative quadriceps weakness significantly affects objective and self-reported knee function, pain, and quality of life, indicating the importance of restoring muscle function after meniscectomy in middle-aged patients.
Meniscectomy has generally been accepted as a treatment with favorable results, i.e., effective symptom relief and fast improvement of knee function (1, 2). However, functional limitations after meniscectomy have been reported in both short-term (3, 4) and long-term followup studies (5, 6). Furthermore, radiographic signs of osteoarthritis (OA) have been reported in approximately half of the individuals 10–15 years after meniscectomy (7–9). Meniscus tears, often referred to as degenerative tears, may be associated with incipient OA and represent an early sign of disease in the middle-aged population (5). The reason for the functional limitations experienced by patients who have undergone meniscectomy is not clear. Strength deficits have been reported 2–6 months after surgery (10, 11), although the functional implications of a strength deficit have not been elucidated. Accordingly, there is no consensus regarding the importance of restoring muscle function after meniscectomy (12–14). Meniscectomy patients are usually prescribed a home exercise program, but supervised physical therapy is not considered necessary (15).
In the present study, muscle strength, functional performance, and self-reported outcome were examined in patients with nontraumatic meniscus tears 4 years after meniscectomy. Furthermore, the impact of a strength deficit on self-reported outcome and the feasibility of 3 performance tests were evaluated.
PATIENTS AND METHODS
Patients who had an arthroscopic meniscectomy at age 35–45 years were identified through the surgical code system. To be eligible, patients had to have been operated on between 1 and 6 years prior to the study start. An invitation letter with a questionnaire comprising comorbid conditions, current work and leisure activity level, current walking ability, and knee-related problems was sent to 166 patients. Patients had to be able and willing to participate in an exercise intervention during 4 months with physical tests before and after the intervention (16). Exclusion criteria were as follows: a cruciate ligament injury of either knee, severe cartilage changes at the arthroscopy, steroid medication, physical limitations due to comorbid condition, depression, sick leave/sick pension caused by knee dysfunction, lack of outdoor walking ability, or were competitive athletes. A total of 81 patients accepted the invitation and 56 who fulfilled the inclusion criteria were invited to participate in the study. This report describes patients at baseline. The study was approved by our institutional review board.
The evaluation included isokinetic tests of muscle strength, functional performance tests, and a self-reported disease-specific questionnaire. The strength and functional performance of the operated leg was compared with the results of the nonoperated leg. Body mass index (BMI) was calculated after obtaining height and weight by a wall-mounted ruler and a calibrated scale. The standardized formula for BMI (kg/m2) was used.
Isokinetic muscle strength testing.
Isokinetic muscle strength was tested with a computerized dynamometer (Biodex System III Pro with Biodex Advantage Software; Biodex Medical Systems, Shirley, NY). Before the test, patients warmed up on a stationary bicycle for ∼10 minutes. The patient sat with the thigh supported with 90° hip flexion and the arms folded over the chest. The body and thigh were fastened to the chair with straps. The verbal instructions were standardized. Patients were allowed to practice the isokinetic movements before the test. To minimize the risk of bias, the nonoperated leg was tested before the operated leg. We measured concentric peak torque of knee extensors and knee flexors at angular velocities of 60°/second and 180°/second in the range of 15–95° flexion. Peak torque (in Nm) refers to the highest registered muscle contraction, evaluated as force times length of the moment arm over a certain joint. In correlations with functional performance tests, peak torque values were calculated as percentages of body weight. Biodex System III has been tested for reliability and validity (17).
Functional performance tests.
The 1-leg hop test, described by Tegner et al (18), has been shown to be reliable in healthy volunteers and athletes (19, 20). The patient, standing on 1 foot with the hands on the back, was asked to jump as long as possible and land steadily on the same foot. The patient had to be able to land and stand on 1 leg long enough for the examiner to measure the hop distance. The test was repeated at least 3 times, or as long as the patient made further progress. The best attempt was recorded.
The 1-leg rising test was designed to evaluate knee and hip extensor strength in a functional position in middle-aged patients (21). The patient sat on a 48-cm high chair and was asked to rise on 1 leg as many times as possible in succession, without swinging the body or arms. The number of rises was recorded. The test was terminated when the patient failed to rise or if the patient either made compensatory arm movements or fell back to the chair during the test. The test was terminated with the last correct rise.
The square-hop test, developed and used in clinical practice by physical therapists, is a measure of dynamic postural balance, coordination, and strength in the thigh and calf muscles. It has been tested for intertest and intratest reliability (r = 0.94 and 0.74, respectively) in 41 individuals (19 knee-injured individuals and 22 controls) (22, 23). In brief, the patient stood outside a 30 × 35–cm square marked on the floor with tape and was instructed to jump clockwise in and out of the square on the nonoperated leg, all the time facing the same direction. In this way, patients had to jump first forward into the square, then sideways to the left out of the square, then sideways to the right into the square again, then forward out of the square, backward into the square again, thereafter sideways to the right out of the square, then sideways to the left into the square, and finally backward out of the square to the starting position (Figure 1). Patients were instructed to continue to jump in this pattern as long as they could. The number of times the foot touched inside the square without touching the tape was recorded. Patients were allowed to stand still on 1 leg to regain their balance, but not to make a double hop or to jump in the wrong direction. The number of correct hops into the square was recorded. The procedure was repeated on the operated leg. After the test, the patient was allowed to start over again and have a second try, and finally the best series of each leg was recorded.
For assessment of knee-related symptoms, function, and quality of life, the Knee Injury and Osteoarthritis Outcome Score (KOOS) was used (24). The KOOS is a patient-administered questionnaire, which consists of 5 subscales: pain, other symptoms, function in activities of daily living (ADL), function in sport and recreation, and knee-related quality of life. The previous week is taken into consideration when answering the questions. Standardized answer options are given (5 Likert boxes) and each question receives a score from 0 to 4. A normalized score (100 indicating no symptoms and 0 indicating extreme symptoms) is calculated for each subscale. The KOOS has high test–retest reproducibility (intraclass correlation coefficient >0.75) (24, 25). The KOOS has been validated for meniscectomy (24) and the sport and recreation and quality of life subscales have been shown to be more discriminative than the pain, other symptoms, and ADL subscales in patients with posttraumatic OA after meniscectomy (26).
The same examiner (YBE) tested all patients. After informed consent was provided, height and weight were obtained. A 10-minute warm-up on a stationary bicycle was followed by the 1-leg hop, 1-leg rising, and square-hop functional performance tests. The nonoperated leg was consistently tested before the operated leg. Between tests, patients recovered as they answered the self-administered questionnaires. Isokinetic strength of the lower extremities was measured on a separate occasion during the same week.
Results are presented as the mean ± SD. Difference between the operated and the nonoperated leg was expressed as a percentage to facilitate comparison with previous studies. A strength and functional performance ratio was calculated by dividing the result of the operated leg by the result of the nonoperated leg. These ratios were used in correlation analyses. In tests where a zero value could occur, 1.0 was first added to all results to avoid division error.
Paired-samples t-test was used to determine differences in outcome between the operated and the nonoperated leg, and the 1-sample t-test was used to compare self-reported outcome between the study group and 2 reference groups (26). Correlation analyses were performed according to Spearman. All statistical analyses were performed with SPSS, version 11.5 (SPSS, Chicago, IL).
Eleven of the 56 patients who had agreed to participate in the study did not attend due to work or other commitments. Characteristics of the 45 patients examined are shown in Table 1. There were no differences between men and women in age (P = 0.21), followup time (P = 0.39), or BMI (P = 0.69). The mean BMI for the group was 26.5 kg/m2 (Table 1).
Higher activity level = recreational sports such as golf, hiking, biking; lower activity level = yard work, shopping, etc.; BMI = body mass index.
Age, mean ± SD years
45.7 ± 3.2
46.1 ± 2.9
44.8 ± 3.5
Time since surgery, mean ± SD years
4 ± 1.3
Higher/lower activity level, no.
BMI, mean ± SD kg/m2
26.5 ± 3.3
Knee pain, no. yes/no
Operated knee, no. right/left
Isokinetic knee extensor strength, at angular velocities 60°/second and 180°/second, was lower for the operated leg than for the nonoperated leg (P ≤ 0.002) (Table 2). At 60°/second and 180°/second, the mean difference of the quadriceps muscle strength compared with the contralateral leg was 9% and 6%, respectively. With respect to knee flexors, there was no difference between the operated and nonoperated leg (P > 0.3) (Table 2).
Values are the mean ± SD unless otherwise indicated. The paired t-test was used to compare the operated and nonoperated limb. PT = peak torque; ext = extension; flex = flexion; max reps = maximum number of repetitions.
Isokinetic strength, Nm
PT ext 60°/second
161 ± 49
179 ± 47
16.5 ± 25
9 ± 14
PT ext 180°/second
113 ± 31
122 ± 30
7 ± 14
6 ± 11
PT flex 60°/second
86 ± 28
89 ± 27
2 ± 15
1 ± 18
PT flex 180°/second
84 ± 25
87 ± 24
1.7 ± 11
1 ± 17
Square-hop (max reps)
6 ± 4
6 ± 6
0.2 ± 5
−19 ± 88
1-leg hop (cm)
108 ± 33
111 ± 32
3.6 ± 15.5
2 ± 18
1-leg rising (max reps)
11.5 ± 10
15 ± 11
3.8 ± 8.5
10 ± 87
For the 1-leg rising test, the result of the operated leg was worse than that of the nonoperated leg (mean ± SD rises 12 ± 10 and 15 ± 11, respectively; P = 0.004) (Table 2). The mean difference was 10%. For the other 2 functional performance tests, square-hop and 1-leg hop for distance, no differences were seen between the operated leg and nonoperated leg (Table 2).
Self-reported symptoms, knee-related function, and quality of life.
Patients reported symptoms and functional limitations on the KOOS, with mean scores for different dimensions varying between 63 and 89. The mean ± SD subscale scores were 83 ± 14 for pain, 83 ± 14 for other symptoms, 89 ± 13 for ADL, 63 ± 26 for sport and recreation function, and 64 ± 20 for knee-related quality of life. The KOOS results compared with 2 reference groups from a previous study (26) are shown in Figure 2. Patients with radiographic OA who underwent meniscectomy 17 years ago (n = 41, mean age 57) and age- and sex-matched controls without OA or known knee injury (n =50, mean age 53) were used for comparison. The 1-sample t-test was used to determine differences between groups. Our study group scored worse than the age-matched healthy control group in all 5 scales (P < 0.001). In comparison with the postmeniscectomy group with OA, our group scored better in the symptoms, ADL, and sport and recreation scales (P = 0.002, P < 0.001, and P = 0.006, respectively), but scored at the same level as the OA group in the pain scale (P > 0.5) and quality of life scale (P = 0.1).
Relationship between muscle strength and self-reported outcomes.
The quadriceps ratio between the operated leg and nonoperated leg at 60°/second and 180°/second angular velocities correlated moderately with all 5 KOOS subscale scores (r = 0.38–0.60, P ≤ 0.010), whereas the hamstrings ratio only correlated significantly with 1 subscale, KOOS symptoms (r = 0.39, P = 0.009) (Table 3).
Table 3. Spearman's correlation between ratio of strength and the 5 subscales of the Knee Injury and Osteoarthritis Outcome Score (KOOS)*
ADL = activities of daily living; Sport/rec = sport and recreation; QOL = quality of life; see Table 2 for additional definitions.
Result of the operated leg divided by the result of the nonoperated leg.
PT ext 60°/second
PT ext 180°/second
PT flex 60°/second
PT flex 180°/second
Relationship between muscle strength and performance-based function.
The quadriceps ratio at 60°/second and at 180°/second showed a moderate correlation to the 1-leg rising ratio (r = 0.4 and 0.5, respectively; P ≤ 0.004). The hamstring strength ratio at 180°/second showed a low correlation to the 1-leg rising ratio (r = 0.3, P = 0.029). There was no significant correlation between the quadriceps strength ratio and the 1-leg hop ratio or the square-hop ratio (r ≤ 0.2, P > 0.1).
Feasibility of performance tests.
Most patients could perform the 1-leg rising test, although 7 patients failed to rise on 1 leg. The test identified differences between the operated leg and nonoperated leg, and correlated moderately with quadriceps strength adjusted for body weight and with hamstring strength adjusted for body weight in the operated leg at 60°/second (r = 0.4, P = 0.010). All patients performed the 1-leg hop test, which correlated strongly with isokinetic quadriceps strength adjusted for body weight at 60°/second in the operated leg and nonoperated leg (r = 0.7–0.8, P < 0.001), and with hamstring strength adjusted for body weight in the operated leg and the nonoperated leg (r = 0.7, P < 0.001). The square-hop test was performed by all but 1 patient and results ranged from 0 to 17 hops for the operated leg. Some patients found it difficult to follow the instructions. The square-hop test demonstrated a moderate correlation to isokinetic quadriceps strength adjusted for body weight on the operated leg and nonoperated leg (r = 0.5 and 0.4, respectively; P < 0.001).
The finding that isokinetic and performance-based knee extensor strength is lower in the operated leg than the contralateral leg 4 years after meniscectomy due to a nontraumatic tear has not been reported previously. The postoperative rehabilitation period aims to decrease the strength difference between the limbs to that found in healthy individuals (18). After testing strength in healthy controls, Petschnig et al (27) found ≤5% difference between the right and left leg, whereas Borges (28) did not find any significant differences. In persons who have undergone meniscectomy, quadriceps strength deficits of 12–18% have been found 2–6 months after surgery (10, 11, 29), but reports of muscle strength deficits in the long term are scarce. Holder-Powell et al (30), who examined young subjects with various knee injuries, found deficits of 20% 5 years postinjury. They concluded that after knee injuries, the strength of the quadriceps muscle does rarely return to the preinjured state (30). In the present study, we found a deficit of 9% in isokinetic quadriceps strength and a functional deficit of 10% in the 1-leg rising test. As in our study, other studies have demonstrated that the quadriceps muscles are usually more affected than the hamstrings after knee injury and surgery (12, 31).
Few studies have examined the relationship between strength deficits and function. With isokinetic tests it is possible to quantify muscle strength, but the significance of other aspects of muscle function such as coordination and timing is not measured. Functional performance tests are designed as attempts to mimic natural movements of sports or everyday life. They are complex because they challenge strength and endurance as well as coordination and involve multiple joints and muscle groups. Accordingly, functional tests cannot separately measure the different components that constitute performance. In a previous study, the complexity of this issue has been examined. Approximately one-third of the variation of functional capacity can be explained by the variation of isokinetic strength (32). Moffet et al (29) found that patients with strength deficits >25% had locomotor abnormalities in movements and muscle activations that affected stair-climbing performance. In patients with anterior cruciate ligament–reconstructed knees, Wilk et al (33) found a positive correlation between quadriceps strength and subjective knee scores and functional hop tests. In the present study, the association between the quadriceps strength deficits and self-reported symptoms and function suggests a close relationship between muscle strength and functional limitations in middle-aged patients who have undergone meniscectomy. Furthermore, the relationship between the quadriceps strength ratio and the 1-leg rising test ratio may indicate that decreased quadriceps strength is a contributing factor to these patients' limited knee function.
Different factors may influence knee joint structures negatively following knee injuries. The thigh muscles play an important role in stabilizing the knee joint and distributing the loads evenly across the joint (34, 35). Insufficient muscle strength likely leads to increased physical stress with more cartilage impact loading as the muscles fail to absorb forces during gait (36). Decreased proprioceptive acuity may affect the maintenance of joint stability because coordination of limb position and muscle activity is dependent on adequate sensory input from the knee joint structures (37, 38). Becker et al (39), who investigated quadriceps strength and maximal voluntary activation in patients 4 years after meniscectomy, found decreased quadriceps activation and muscle strength in both legs of their patients compared with a healthy control group. Regarding the relationship between limb muscle impairment and future joint disease, Hurley (40) hypothesized that muscle dysfunction is an important factor in the pathogenesis of OA. Results of 2 longitudinal studies suggest that quadriceps weakness may predict radiographic OA development (41, 42). A 9% quadriceps deficit 4 years after meniscectomy as in the present study may seem small, but in the perspective of a disease that develops over 10–15 years, even subtle muscle impairments may prove significant. Meniscectomy that decreases the joint weight-bearing area and increases femorotibial loading (43) is associated with OA (5, 8, 9). Muscle impairment with poor joint stabilization and decreased muscular shock absorption may make the knee cartilage in a meniscectomized joint even more vulnerable. It is noteworthy that patients in the present study displayed low self-reported outcome scores, with respect to pain and quality of life, similar to meniscectomy patients with radiographic OA (26).
In the present study, 3 performance tests were included as a complement to the strength tests. The 1-leg rising test, which has been suggested to predict the development of radiographic knee OA (42), detected differences between the operated leg and the nonoperated leg. Seven patients failed to rise 1 time on the operated leg, and an association between the test and quadriceps and hamstring strength was seen. The other 2 performance tests, square-hop and 1-leg hop for distance, were originally designed and validated for young athletes with an anterior cruciate ligament injury (22). The older and less fit patients in the present study had problems coordinating their movements in the square-hop test. Results demonstrated a moderate correlation to quadriceps strength, implying that the square-hop test is related to thigh muscle strength. The 1-leg hop test was easier to perform because everyone could hop in a forward direction. The 1-leg hop test gives an indication of the amount of confidence the patient has in his or her knee. This test has recently been tested and recommended for use in middle-aged patients who have undergone meniscectomy (44).
In clinical work, meniscectomy patients often state that their knees are unstable. This is not necessarily due to increased knee joint laxity, but might be caused by altered lower-extremity muscle strength and neuromuscular control (45). Interestingly, patients with meniscus injury or anterior cruciate ligament deficiency show similar self-reported scores for instability (24). In the present study, the 1-leg hop test in the operated leg and the nonoperated leg correlated strongly with thigh muscle strength, indicating that strength is an important factor for achieving a good hop length. The functional performance test results had a wide range. Some patients performed better on the operated leg than on the nonoperated leg. Leg dominance may have played a role, but because only one-third of the patients could state which leg was the dominant leg, separate analyses with respect to leg dominance were not possible. Based on our results, the 1-leg rising and 1-leg hop tests seem suitable to assess functional performance in middle-aged meniscectomy patients. Both tests are feasible, as they require minimal equipment.
A limitation of our study is the lack of a healthy control group. We chose to use the contralateral leg as a reference leg, well aware of the discussion about this procedure in the literature (5, 22, 27). Changes in joint cartilage metabolism in both injured and uninjured knees have also been demonstrated after unilateral knee injury (46). However, the difference between a healthy control group and our study group would probably have been bigger than that between the operated leg and contralateral leg in the same individual. Another limitation is the relatively small study group. However, this is compensated for by a rather homogeneous study group (middle age, isolated meniscal injury, degenerative tear, partial resection) and the combination of objective and patient-relevant outcome measures. The patients were not familiar with isokinetic testing before the study, but they were allowed to practice before measurements were obtained and they consistently started the test with the nonoperated leg. If a training effect did occur, this would have been to the advantage of the operated leg and would have resulted in a smaller deficit. Pain may affect the results in isokinetic testing by reflexive inhibition of muscles (37). In the study group, 4 patients experienced pain in the operated knee during this test. Subgroup analyses, comparing groups with or without pain during tests, did not show any differences between patients with or without pain regarding knee extensor deficits.
In summary, the present study demonstrated that 4 years after meniscectomy, patients had reduced quadriceps strength in the operated leg compared with the nonoperated leg. We conclude that this relative quadriceps weakness significantly affects objective and self-reported knee function, pain, and quality of life, indicating the importance of restoring muscle function after meniscectomy in middle-aged patients.