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MALMÖ, Sweden, Dec. 4 -- Several years after surgery to repair a non-traumatic meniscus tear, loss of muscle strength in the quadriceps left middle-aged patients with a painful, unstable knee prone to future osteoarthritis, researchers here reported.

Strength deficits have been reported two to six months after surgery, but the resulting functional losses have not been previously described, Ylva Ericsson, PT, M.Sc., of Malmö University Hospital, and colleagues, wrote in the December issue of Arthritis Care and Research.

In a study of 45 patients (36% women, mean age 46.7) who had had an arthroscopic partial meniscectomy a mean of four years (one to six years) earlier, the patients were given performance tests (one-leg rising from a chair, one-leg hop test, and square-hop test).

They also filled out a questionnaire, the Knee Injury and Osteoarthritis Outcome Score (KOOS), which measures pain, function in daily activities (shopping, yard work), sports and recreation, and knee-related quality of life.

Lower knee extensor strength and one-leg-rising ability were worse in the operated leg compared with the unoperated leg (P≤ 0.004), but there was no difference between the two legs for the knee flexors (P>0.3).

However, the researchers found that at 60º/second and 180º /second, the mean differences in quadriceps muscle strength compared with the contralateral leg were 9% and 6%, respectively.

This translated to a loss in functional performance in the one-leg rising test compared with the contralateral leg (12 ± 10 rises versus 15 ± 11 rises, respectively, P=0.004), with a mean difference of 10%.

No differences were seen for the two other performance tests, the researchers reported. As in other studies, quadriceps muscles are usually more affected than the hamstrings after knee injury and surgery, the researchers said.

Patients with a stronger quadriceps of the operated leg compared with the nonoperated leg had less pain and better function and quality of life (ratio = 0.4-0.6, P≤0.010), the researchers found.

The thigh-muscle-strength findings correlated moderately with all the KOOS subscale categories, whereas the hamstring ratios correlated significantly with only one category, they added.

Although isokinetic tests can quantify muscle strength, the researchers said, these tests do not measure other aspects of muscle function, such as coordination and timing. Functional performance tests, such as the one-leg-rising and one-leg hop tests, they said, are an attempt to mimic the natural movements of sports or everyday life.

Different factors may influence knee-joint structure negatively following knee injuries, they said. For example, the thigh muscles play an important role in stabilizing the knee joint and in distributing the load across the joint. Insufficient muscle strength may lead to increased physical stress with more impact on cartilage as muscle fails to absorb forces during gait, leading to a risk of osteoarthritis.

The 9% quad deficit found in this study, they said, may seem small, but for osteoarthritis, which develops over 10 to 15 years, even subtle muscle impairments may prove significant.

The investigators also noted that in clinical work, patients often state that their knees are unstable. This suggests that this instability is not necessarily because of increased knee-joint laxity, but might be caused by altered lower-extremity muscle strength.

Among the study's limitations, they wrote, was its relatively small size. In addition, they said, another limitation may have been the use of the contralateral leg as the control and the lack of a healthy control group. Changes in joint-cartilage metabolism in both injured and uninjured knees have been reported after unilateral knee injury. The researchers said they were well aware of the discussion about the use of the contralateral leg in the literature, but noted that the differences would probably have been still bigger with a healthy control group.

In summary, the researchers concluded that the one-leg rising and the one-leg hop tests are suitable performance tests for these patients and emphasized the importance of providing supervised physical therapy.

They concluded that 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-age patients."

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