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- PATIENTS AND METHODS
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.
- Top of page
- PATIENTS AND METHODS
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.