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Knee function and knee muscle strength in middle-aged patients with degenerative meniscal tears eligible for arthroscopic partial meniscectomy
  1. Silje Stensrud1,
  2. May Arna Risberg2,3,
  3. Ewa M Roos1
  1. 1Research Unit for Musculoskeletal Function and Physiotherapy, Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark
  2. 2Department of Sport Medicine, Norwegian Research Center for Active Rehabilitation, Norwegian School of Sport Sciences, Oslo, Norway
  3. 3Department of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway
  1. Correspondence to Silje Stensrud, NIMI, pb. 3843 Ullevål Stadion, Oslo 0855, Norway; silje.stensrud{at}nimi.no

Abstract

Background Functional limitations exist postmeniscectomy, but preoperative data are scarce.

Purpose To examine knee function, knee muscle strength and performance in middle-aged patients with degenerative meniscal tears, eligible for arthroscopic partial meniscectomy.

Study design Cross-sectional study.

Methods Eighty-two participants with MRI verified degenerative meniscal tear (35% women, mean age 49 years) answered the Knee injury and Osteoarthritis Outcome Score (KOOS) and were tested for isokinetic knee muscle strength and lower extremity performance (one-leg hop for distance, 6 m timed hop and maximum number of knee-bends in 30 s). Limb Symmetry Index (LSI) was used to express side-to-side differences in per cent using the non-injured leg as the control. An LSI ≥90% was considered normal.

Results Mean scores of the five subscales of the KOOS were from 13 to 36 points lower compared with a population-based reference group and similar to patients prior to anterior cruciate ligament reconstruction. Quadriceps strength and lower-extremity performance were impaired for the injured leg compared with the non-injured leg (p<0.001), with a mean difference of 13% in quadriceps strength and between 8% and 13% in lower-extremity performance. Between 41% and 52% of the participants had abnormal LSI values in quadriceps muscle strength and lower-extremity performance.

Conclusion Middle-aged patients with a symptomatic degenerative meniscal tear experience functional knee problems when eligible for meniscectomy. Included participants reported difficulty with knee pain, symptoms, function and quality of life and quadriceps strength and lower-extremity performance were impaired. Approximately 50% of the study group had clinically relevant impairments in quadriceps strength and lower-extremity performance, defined as >10% differences between the injured and the non-injured leg.

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Introduction

Middle-aged persons commonly suffer from degenerative meniscal tears, which are different from traumatic lesions in that they often occur without significant trauma. Degenerative meniscal tears can be associated with knee joint symptoms, but most tears are actually asymptomatic.1 The treatment of non-traumatic degenerative meniscal tears in middle-aged patients represents a great challenge since there is only weak evidence for many of the treatments currently used.1 Arthroscopic partial meniscectomy is the most frequent orthopaedic surgery in the USA, with more than 50% of the procedures performed in patients 45 years of age or older.2 Still, arthroscopic surgery in this age group is not found to provide any additional benefit compared with sham surgery,3 optimised non-operative treatment4 or supervised exercise.5 ,6

After meniscectomy, short-term and long-term reductions in self-reported functional limitations, muscle strength and lower-extremity performance are reported.7–10 Less is, however, known prior to surgery in patients with an MRI-verified non-traumatic medial meniscal tear, self-reported mean scores of the Knee injury and Osteoarthritis Outcome Score (KOOS) are reported to range from 20 to 79 on a 0–100 worst to best scale.5 The lowest mean scores were reported on the subscales of ‘knee related quality of life’ and ‘function in sports and recreation’, indicating severe self-reported functional limitations prior to meniscectomy. It is however virtually unknown as to whether patients eligible for arthroscopic partial meniscectomy have reduced objectively measured knee function. No studies have looked at lower extremity performance prior to surgery, and only two studies with small sample sizes have reported preoperative findings of knee muscle strength.11 ,12 A pilot study of 10 participants (mean age of 38 years) reported decreased preoperative isokinetic knee extension strength at 30° per second compared with a control group.11 Another study of 22 participants (mean age of 35 years) reported significantly lower preoperative peak torque isokinetic knee extension at 60° per second in the injured leg compared with the non-injured leg, while no differences were found at other velocities or in knee flexion strength.12 The small sample sizes and lack of strict inclusion and exclusion criteria make results difficult to interpret. It is believed that knee muscle weakness is one of the earliest and most frequent findings in patients with knee osteoarthritis (OA),13 ,14 and thus it is plausible that strength deficits, particularly in the quadriceps, may also occur in cohorts with a degenerative meniscal tear, a group known to be of increased risk of OA development.

Studies on the comparatively younger anterior cruciate ligament (ACL) injured population indicate that greater preoperative quadriceps muscle strength predicts a better postoperative outcome;15 ,16 however, there is a gap in knowledge regarding middle-aged patients eligible for meniscectomy. Such knowledge could have important implications for preoperative and postoperative management, prompting us to study muscle function in a well-defined group of middle-aged patients with an MRI-verified degenerative meniscal tear.

The aim of the present study was to examine self-reported knee function, bilateral muscle strength and lower-extremity performance in middle-aged patients with symptomatic degenerative meniscal tears eligible for arthroscopic partial meniscectomy.

Materials and methods

Participants

The first 82 participants included in an ongoing randomised controlled trial (Clin.Gov ID: NCT01002794) were included in the present study. Participants were recruited from two Norwegian hospitals; Oslo University Hospital and Martina Hansens Hospital, from October 2009 to December 2011. Participants were referred from primary care for consideration of arthroscopic surgery based on a history of pain and functional limitations. Eligibility for surgery was defined as a clinical diagnosis of symptomatic meniscal tear, which consisted of the clinical impression of the treating orthopaedic surgeon based on physical examination, history and MRI.17 Men and women aged 35–60 years with a unilateral knee pain for more than 2 months without significant trauma, eligible for arthroscopic surgery and able to take part in an exercise programme were considered eligible for inclusion. A degenerative tear of the meniscus was confirmed by MRI. Standing posterior–anterior radiographs of the injured knee in a fixed flexion position were obtained using a plexiglass frame (SynaFlexer, Synarc Inc, San Francisco, California, USA).18 The Kellgren and Lawrence (KL) OA grading system was used,19 and participants with a KL grade 2 or less were included. Cases with acute locked knee, ligament injuries or knee surgery within the previous 2 years were excluded. At inclusion, the participants were clinically examined by either a physical therapist and an orthopaedic surgeon, or only an orthopaedic surgeon, depending on the recruiting hospital. The surgeons examined the MRIs to decide participant eligibility, and one of the surgeons graded the radiographs. The physiotherapist and the two surgeons had a consensus meeting prior to the start of the study in order to optimise consistency in the recruitment.

Included participants were tested by one single physical therapist. All participants filled out the KOOS questionnaire at the clinic prior to testing. Thereafter, they completed a standardised 10 min warm-up on a stationary bike followed by bilateral testing of isokinetic muscle strength and finally three tests of lower-extremity performance. Randomisation was performed in order to decide which leg was tested first.

The study was approved by The Regional Ethical Committee, Health Region South-East Oslo, Norway, and all participants signed a written informed consent form prior to inclusion. The rights of the participants were protected by the Declaration of Helsinki.

Outcome measures

Knee injury and Osteoarthritis Outcome Score

The KOOS is a patient-reported outcome measure consisting of five subscales scored separately: pain, other symptoms, function in daily living (ADL), function in sport and recreation and knee-related quality of life (QOL). The scores are transformed to a 0–100 scale, where 100 represent no knee-related problems.20 A clinically important difference has not formally been assessed; however, the currently recommended cut-off is 10 points.20 The KOOS is validated in patients with different knee injuries undergoing different procedures, including meniscectomy.21

Knee muscle strength

Isokinetic knee muscle strength was assessed using an isokinetic dynamometer (Biodex 6000 System, Biodex Medical Systems Inc, Shirley, New York, USA). Testing at 60° per second consisted of four practice repetitions, followed by five maximum effort repetitions. The participants were placed in an upright seated position on the Biodex dynamometer chair and secured with straps to minimise body movements. Arms were crossed over the chest. The tested range of motion was from 90° of knee flexion to full extension. Isokinetic torque values were measured in Newton metres (Nm) for peak torque, and in joules (J) for total work. Peak torque was defined as the highest value among all five repetitions. Knee pain during testing was self-reported by the participants immediately after completing the test, using a 0–10 numeric rating scale ranging from no pain to worst imaginable pain.

Lower-extremity performance

Three reliable and valid tests 22–24 were used to evaluate lower-extremity function: the maximum number of knee-bends in 30 s,24 ,25 the one-leg hop for distance (OLH) and the 6 m timed hop (6MTH).26 ,27

The maximum number of knee-bends in 30 s tests the ability to perform fast changes between eccentric and concentric muscle force over the knee joint in a range between 15° and 30° of knee flexion.28 This is a skill that has shown to be impaired in long-term follow-ups of individuals following meniscectomy.8 Participants stood aligned with the long axis of the foot to a straight line, and toes were placed on a perpendicular line. The examiner gave fingertip support to prevent rotation at the pelvis and to provide some balance control. The participant was asked to bend the knee until the line along the toes was no longer visible (approximately 30° of knee flexion). A stopwatch was used, and the number of knee-bends performed in 30 s was recorded. Prior to the test, the participant performed a practice trial with any number of knee-bends to get familiarised with the test, including the desired degree of knee flexion.

The OLH test requires muscle power, strength, balance and confidence in the knee.24 Participants stood shod on one foot, with hands behind their back, and were asked to hop as far as possible, landing and balancing on the same foot long enough for the examiner to determine the distance of the jump using a tape measure fixed to the floor. Participants were not allowed to move the foot after landing. Distance was measured (in centimetres) from the toe in the starting position to the heel in the landing position. Participants performed two practice trials to familiarise themselves with the test, and then two test trials on each leg. The best trial of the two was recorded.

The 6MTH test requires participants to perform one-legged hops in series as fast as possible over a distance of 6 m. Time (in seconds) from start to reaching the 6-metre line was recorded using a stopwatch. Arms could be used freely, but the other foot was not allowed to touch the ground during the test. One practice trial was performed, followed by two test trials on each leg. The best trial of the two trials was recorded.

Statistical analysis

Descriptive data were given as percentages, mean values with SD or median with range depending on the test variable. Mean values and 95% CI of the five subscales of the KOOS were plotted for the studied group and for a population-based reference group.29 No overlap between the 95% CIs was interpreted as the groups were significantly different. To determine differences in outcomes between the injured and non-injured leg we used paired samples t tests; if the data were not normally distributed, non-parametric statistics were used. Normality was assumed if there was no or minimal difference between the mean and the median value, if the SD multiplied by two was less than the mean value, and if there was a normal-looking histogram. In order to correct for multiple testing a post hoc Bonferroni adjustment was applied. Because of the seven tests performed, the p value for significance was set to <0.007 (ie, 0.05/7). The Limb Symmetry Index (LSI) was used to express the side-to-side difference in per cent using the non-injured leg as control (injured leg/non-injured leg×100). An LSI ≥90% for an individual in a single test was considered normal.30 ,31 Statistical analyses were performed with PASW Statistics, V.18 (IBM, New York, USA).

Results

Eighty-two participants (35% women) on average 49 (±6.4) years of age and with an average body mass index of 27 (±3.8) were included. Most participants (77%) had no radiographic features of OA, 22% had osteophytes equivalent to KL grade 1 and only 5% had definite radiographic OA defined as KL grade 2. Characteristics of the participants are presented in table 1.

Table 1

Characteristics of the participants

Self-reported knee function

Mean scores for the five different KOOS subscales ranged from 44 (subscale QOL) to 77 (subscale ADL). Mean scores with 95% CI for the different subscales, age-matched population-based reference group 29 and pre-ACL reconstruction scores from the Norwegian National Knee Ligament registry (NKLR)32 appear in figure 1. The mean scores of the five subscales for the pre-meniscectomy group were 13 (subscale other symptoms) to 36 (subscale QOL) points worse than for the population-based controls, and there were no overlaps between CIs, indicating that the differences were statistically significant. The premeniscectomy group reported similar mean scores to the pre-ACL reconstruction group.

Figure 1

Mean scores (with 95% CI) of the five subscales of the KOOS for the pre-meniscectomy study group (n=82), mean scores (with 95% CI) for an age-matched population-based reference group (n=79)29 and preoperative mean scores from the Norwegian Knee Ligament Registry (n=8897).32 A score of 100 represents no knee-related problems and a score of 0 represents extreme problems.  ADL, function in daily living; OQL, knee-related quality of life; Sport/Rec, function in sport and recreation.

Knee muscle strength

Median (range) self-reported pain during strength testing was 0 (0–7) assessed on a 0–10 numeric rating scale ranging from no pain to worst imaginable pain. Since pain during testing was uncommon, no adjustments for pain during testing were made. Isokinetic knee extension strength was significantly lower for the injured leg than for the non-injured leg, with a mean difference in peak torque of 13% (p<0.001; table 2). Isokinetic knee flexion strength was lower for the injured leg compared with the non-injured leg; however, the difference was not statistically significant (p≤0.015). The proportion of participants with normal LSI values ranged from 48% to 59% for knee extension variables, and from 62% to 71% for knee flexion variables (figure 2).

Table 2

Isokinetic knee muscle strength and lower-extremity performance tests for the injured leg, the non-injured leg and the difference (n=82)

Figure 2

Percentage of participants with normal and abnormal Limb Symmetry Index (LSI) in isokinetic knee muscle strength and three lower-extremity performance tests. A test score for an individual was considered normal if the LSI was ≥90%. 6MTH, 6 m timed hop test; Kneebends/30s, maximum number of knee-bends in 30 s; OLH, one-leg hop for distance test; PT, peak torque; TW, total work. *n=81.

Lower-extremity performance

For all three tests the results of the injured leg was significantly worse than for the non-injured leg, with mean differences ranging from 8% to 13% (p<0.001; table 2). The proportion of participants with normal LSI values ranged from 53% to 57% for the lower-extremity performance tests (figure 2).

Discussion

The purposes of this study were to examine self-reported knee function, symptoms and QOL, in addition to knee muscle strength and lower extremity performance in middle-aged patients with degenerative meniscal tears eligible for arthroscopic partial meniscectomy. This is the first study to present preoperative data from a well-described sample of this common patient group, and with a sample size much greater than what previously has been reported in the literature. Overall findings were that middle-aged patients with degenerative meniscal tears reported increased pain and symptoms, and reduced knee function and knee-related QOL compared with population-based controls, and have impairments in quadriceps muscle strength and lower-extremity performance of the symptomatic leg.

The mean KOOS scores show that the participants on average have important self-reported symptom and functional limitations. Compared to an age-matched population-based reference group29 (figure 1), the mean KOOS scores were 13–36 units worse for the five different subscales, indicating significant and clinically important differences in all measured constructs.20 It seems plausible that this group of middle-aged patients would be less physically active, and thus experience less knee pain and better knee function than comparatively younger and more physically active individuals with a traumatic knee injury. However, when comparing the mean scores of the middle-aged premeniscectomy group to data from younger and more physically active patients prior to ACL reconstruction from the NKLR, 32 mean scores were similar (figure 1). This similarity in self-reported status confirms the serious problems that middle-aged patients with a degenerative meniscal experience when eligible for meniscectomy.

Quadriceps strength and lower-extremity performance were significantly impaired for the injured leg compared to the non-injured leg. Mean differences between legs were greatest in peak torque isokinetic knee extension (13%) and the OLH test (13%). Our pre-operative results are in line with short-term33–35 and long-term10 reports of quadriceps strength deficits, ranging from 9% to 20% between injured and non-injured leg after arthroscopic meniscectomy, indicating factors other than surgery being responsible for the impaired muscle function. It may be plausible that the differences found between legs in this present study (8–13%) represent a clinically important difference. In support of clinical importance, a deficit in quadriceps muscle strength between legs smaller than the one found in this study was previously reported to be associated with worse self-reported pain after meniscectomy.10

LSI is commonly used in reports of isokinetic muscle strength and single-leg hop performance.36–38 An LSI ≥90% is often considered to indicate normal limb symmetry in young athletes,30 ,37 ,38 and is also used as a criterion for successful rehabilitation and return to sport after injury.39 By this definition, approximately half of the participants in our study had abnormal LSI values in quadriceps muscle strength and the two hop tests (figure 2). Whether ≥90% is the optimal cut-off for normal LSI in this group of middle-aged patients is not known. Typically, the 90% cut-off is applied in younger and more physically active patients but an LSI<90% was associated with impaired walking ability and standing balance in healthy elderly women,40 confirming the clinical validity of this cut-off also in populations other than young athletes.

Findings in younger and older populations with knee injury and knee OA, respectively, suggest muscular deficits to be clinically important and modifiable. In ACL injured populations greater preoperative quadriceps muscle strength was able to predict a better postoperative outcome15 ,16 and in patients with knee OA muscle strength is more closely related to pain than radiographic features.41 ,42 It is thus plausible that preoperative functional deficits, as found in this study, have an impact on the postoperative outcome also in this patient group. Furthermore, strategies designed to optimise muscle strength and muscle function may have the potential to reduce the amount of disability and pain in middle-aged individuals with a degenerative meniscal tear. Therefore, future exercise studies are warranted in this patient group. Our findings suggest that exercise programmes should include both strength training and neuromuscular training, which have some principle differences. Traditional quadriceps strength training aims to increase muscle force output, while neuromuscular exercises aim to improve the position of the trunk and lower limb joints relative to one another, as well as optimising the quality of the movement.43 We found impairments in both muscle strength and functional performance; hence, both these aspects should be targeted in exercise programmes for middle-aged patients with degenerative meniscal tears. We recently found such a programme to be feasible and efficacious in 20 cases.44

In conclusion, middle-aged patients with a symptomatic degenerative meniscal tear reported difficulty with knee-related pain, symptoms, function and QOL on a level similar to younger subjects eligible for ACL reconstruction. Quadriceps knee muscle strength and lower-extremity performance of the symptomatic leg were impaired, and approximately 50% of the participants had clinically relevant impairments, defined as >10% differences between the injured and the non-injured leg, in quadriceps strength and two of the three performance tests. Findings confirm that functional knee problems are present prior to surgery in middle-aged patients with a degenerative meniscal tear.

What are the new findings

  • Middle-aged patients with a symptomatic degenerative meniscal tear report mean scores of 13–36 points lower than a population-based reference group for the five subscales of the KOOS, indicating clinically relevant difficulty with knee related pain, symptoms, function and quality of life premeniscectomy.

  • Fifty per cent of the study-group had more than 10% difference between legs in quadriceps strength as well as a number of functional tests.

  • Functional limitations previously seen in postmeniscectomy are also present in presurgery.

How might it impact on clinical practice in the near future

  • Findings suggest that preoperative or postoperative training may have the potential to limit functional impairments which could, in turn, improve outcome. However, this will need to be tested using a randomised controlled design.

Acknowledgments

We would like to acknowledge the orthopaedic surgeons Dr Lars Engebretsen and Dr Nina Kise for assistance in the data collection. We would also acknowledge Robin Christensen for statistical advices.

References

View Abstract

Footnotes

  • Contributors All authors planned the study. SS did the data collection, the data analysis and manuscript writing. EMR and MAR contributed to the analysis and the manuscript writing.

  • Funding This study was supported with funding from Sophies Minde Ortopedi AS, Health Region South-East Oslo, Norway, The Swedish Rheumatism Association, The Swedish Scientific Council, Region of Southern Denmark and The Danish Rheumatism Association.

  • Competing interests None.

  • Ethics approval The Regional Ethical Committee, Health Region South-East Oslo, Norway.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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