Archives of Physical Medicine and Rehabilitation
Volume 86, Issue 8 , Pages 1545-1551, August 2005

Use of Ultrasound to Increase Effectiveness of Isokinetic Exercise for Knee Osteoarthritis

  • Mao-Hsiung Huang, MD, PhD

      Affiliations

    • Departments of Physical Medicine and Rehabilitation, Kaohsiung Medical University Hospital, Kaohsiung
    • Corresponding Author InformationReprint requests to Mao-Hsiung Huang, MD, PhD, Dept of Physical Medicine and Rehabilitation, Kaohsiung Medical University Hospital, No.100 Tzyou 1st Rd, Kaohsiung 807, Taiwan
    • ,
  • Yueh-Shuang Lin, MS

      Affiliations

    • Kun-Shan University of Technology, Tainan, Taiwan.
    • ,
  • Chia-Ling Lee, MD

      Affiliations

    • Departments of Physical Medicine and Rehabilitation, Kaohsiung Medical University Hospital, Kaohsiung
    • ,
  • Rei-Cheng Yang, MD, PhD

      Affiliations

    • School of Sport Medicine, Kaohsiung Medical University Hospital, Kaohsiung

Article Outline

Abstract 

Huang M-H, Lin Y-S, Lee C-L, Yang R-C. Use of ultrasound to increase effectiveness of isokinetic exercise for knee osteoarthritis.

Objective

To investigate the effects of ultrasound (US) in isokinetic muscle strengthening exercises on functional status of patients with knee osteoarthritis (OA).

Design

Effectiveness of isokinetic muscle strengthening exercises for treatment of periarticular soft tissue disorders was compared with and without pulsed and continuous US.

Setting

Outpatient exercise program in a Taiwan medical university hospital.

Participants

One hundred twenty subjects with bilateral knee OA (Altman grade II).

Intervention

Subjects were randomized sequentially into 1 of 4 groups. Group I received isokinetic muscular strengthening exercises, group II received isokinetic exercise and continuous US, group III received isokinetic exercise and pulsed US treatment, and group IV was the control group.

Main Outcome Measures

Therapeutic effects of isokinetic exercise were evaluated by changes in ambulation speed and the Lequesne index. In addition, changes in knee range of motion (ROM), visual analog scale for pain, and muscle peak torques during knee flexion and extension were compared. Compliance in each group was recorded.

Results

Each treated group had increased muscle peak torques and significantly reduced pain and disability after treatment and at follow-up. However, only patients in groups II and III had significant improvement in ROM and ambulation speed after treatment. Fewer participants in group III discontinued treatment due to knee pain during exercise. Patients in group III also showed the greatest increase in walking speed and decrease in disability after treatment and at follow-up. Gains in muscular strength in 60°/s angular velocity peak torques were also noted in groups II and III. However, group III showed the greatest muscular strength gains with 180°/s angular velocity peak torques after treatment and follow-up.

Conclusions

US treatment could increase the effectiveness of isokinetic exercise for functional improvement of knee OA, and pulsed ultrasound has a greater effect than continuous US.

Key Words:  Exercise , Osteoarthritis , Rehabilitation , Ultrasonics

 

OSTEOARTHRITIS (OA) is a common disease associated with significant morbidity, and its prevalence increases with age.1 Radiographic abnormalities are present in more than 30% of people older than 65 years; approximately 40% are symptomatic.2 OA occurs most frequently in the knee joint, one of the most common sites of major health problems in older subjects.3 Knee pain and quadriceps weakness are reported determinants of disability in OA of the knee.4, 5 Furthermore, restricted joint range of motion (ROM) is associated with abnormal posture and may result in disability.6

OA is characterized by noninflammatory deterioration of the articular cartilage with reactive new bone formation at the joint’s surface and margins. Some studies7, 8, 9 have indicated that the primary lesion of OA is in the articular cartilage, in which the earliest change is diminution of mucopolysaccharide and chondroitin sulphate relative to the collagen in the matrix, thereby unmasking the collagen. Normally, the matrix dissipates stresses hydrostatically, but when the collagen is unmasked, its fibers are subjected to excessive flexural and torsional stresses, leading to rupture and the lesions characteristic of OA.10

The health of cartilage depends on the mechanical load it receives. Cartilage is an avascular tissue and the chondrocytes within it depend on diffusion and convection for nutrition. This process is enhanced by the cyclic loading induced by everyday activities that produce deformations, pressure gradients, and fluid flows within the tissues. Moderate to strenuous articular loading, such as that associated with regular distance running, seems to have no adverse affects on the health of normally congruent joints. However, high impact joint loading, through either a single traumatic event or repetitive events of less severity, may lead to joint degeneration.11, 12 Normal loads can also accelerate degeneration in deformed, unconstrained, or damaged joints because of instability of the arthritic joint and uneven loading force.12 Therefore, increasing the stability of an arthritic joint might theoretically prevent further deterioration.

With therapeutic exercise, OA patients may prevent accelerated degeneration resulting from disuse without causing further degeneration and pain as a consequence of joint deformity or incongruence. Several recent longitudinal studies conclude that carefully controlled exercise programs, designed primarily for OA of the knee, are indeed beneficial.13, 14 Reported benefits include increased joint mobility, increased strength, and enhanced performance in sports activities. Our previous report15 showed that isokinetic muscle strengthening exercise is more effective than isometric or isotonic exercises for diminishing disability and improving muscular strength and ambulation ability. However, patient compliance is an issue, and those studies with high compliance rates produced better results. Patient compliance depends on many elements, including consistent education, encouragement, and follow-up. Injury and complications as direct consequences of inappropriate exercise,16 such as knee pain during exercise, weakness of leg muscles, and ROM, are the major reasons for poor compliance.

Therapeutic ultrasound (US) has been used to treat many musculoskeletal diseases and is also reputed to reduce edema,17, 18 relieve pain, increase ROM,19 and accelerate tissue repair.20, 21, 22 In a review of the effectiveness of US in treating musculoskeletal conditions, Falconer et al17 found that most reports indicate that therapeutic US appears to relieve OA pain. Some investigations23 have applied US to enhance the flexibility of connective tissues. However, few reports have discussed the effect of US on therapeutic exercise for OA.

Therefore, in this study we investigated the therapeutic effect of isokinetic exercise when combined with US treatment in patients with knee OA, including effect on ROM, knee pain, muscular peak torque, and status of disability and ambulation speed immediately posttreatment and during the follow-up period.

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Methods 

Participants 

One hundred twenty patients with bilateral moderate knee OA (Altman grade II) with periarticular soft tissue pain, as identified by painful sensations during palpation or passive stretching of the arthritic knee under orthopedic examination. The locations of soft tissue pain were confirmed by the findings of musculoskeletal US images (as shown in US treatment) were selected. After radiographs were taken and patients clinically evaluated by the criteria of stages of knee OA,24 they were randomly assigned to 4 groups by a secure system of sequentially numbered I through IV opaque sealed envelopes. The physician who assigned the patients was blinded as to the treatment they would receive. Patients in each group received treatments 3 times weekly for 8 weeks. The 30 patients in group I received isokinetic muscular strengthening exercises, the 30 in group II received isokinetic exercise and continuous US, the 30 in group III received isokinetic exercise and pulsed US, and the 30 in group IV served as controls and received neither strengthening exercises nor US treatments. All groups received 20 minutes of hot packs and 5 minutes of passive ROM exercise on an electric stationary bike (20 cycles/min) of both knees before undergoing muscle-strengthening exercises. The therapeutic effects of these exercises were evaluated by changes in the arthritic knee ROM,25 visual analog scale (VAS),26 Lequesne index,27 ambulation speed, and muscle peak torques (MPT) of knee flexion and extension measured with an isokinetic dynamometer (Kin-Coma)28 before treatment, after treatment, and at follow-up 1 year later. Compliance with the prescribed exercise program in each group was also analyzed after treatment was completed. All the participants gave their informed consent for the study and the Ethical Review Committee of Kaohsiung Medical University approved the study protocol.

Measurement of Knee ROM 

Assisted active ROM was measured with a large plastic goniometer with 25-cm movable arms, marked in 1° increments. This device is reportedly reliable if the patient remains in one position for all measurements.25 Measurements of knee flexion and extension were taken with subjects lying supine on an examination couch, at maximum flexion of knee joint with the hip flexed. Concomitant hip flexion prevented premature limitation of knee motion from possible rectus femoris shortening. The fully extended knee was considered the zero position, and the degrees of maximum flexion, maximum extension, and extension deficit, when present, were recorded. A negative ROM score for extension indicated that the patient was unable to reach the zero position. The angle between maximum flexion and maximum extension was described as the excursion range.

Measurement of Pain Severity 

The severity of knee pain was evaluated by the VAS26 after patients had remained in a weight-bearing position (walking or standing) for 5 minutes in the parallel bars. The VAS instrument consisted of horizontal lines 10cm long, with anchor points of 0 (no pain) and 10 (maximum pain).

Measurement of Disability 

We evaluated each patient’s disability with the Lequesne index.27 The questionnaire included 11 questions about knee discomfort, endurance of ambulation, and difficulties in daily life. A maximum score of 26 indicated the greatest degree of dysfunction. A score of less than 7 points indicated that the patient had functional status acceptable for isokinetic exercise.15

Measurement of Ambulation Activity 

Ambulation activity was evaluated by the patient’s walking speed. The time it took to complete a predetermined distance of 50m on a treadmill as comfortably and quickly as possible was recorded. A distance was preset on the treadmill, and an alarm sounded when the 50m was completed. Walking time was recorded with a stopwatch by the same physiatrist.

Measurement of Isokinetic Peak Torque of Knee Flexion and Extension 

The maximal voluntary force capacity was evaluated by measuring the peak torque of the arthritic knee with a modified form of the method used by Snow and Blacklin28 in the following positions: (1) extension concentric (ex/con), knee extension with quadriceps contraction; (2) extension eccentric (ex/ecc), knee flexion with quadriceps contraction; (3) flexion concentric (flex/con), knee flexion with biceps femoris contraction; and (4) flexion eccentric (flex/ecc), knee extension with biceps femoris contraction. Subjects were seated and leaned against a backrest inclined at 16° from the vertical and with the seat inclined 6° from the horizontal. The axis of the knee was aligned with the axis of the Kin-Com 505 exercise arm; accuracy of alignment was checked by allowing the subject to extend the leg while pushing against the shin pad positioned over the lower third of the leg. If the pad did not move up or down the leg over the ROM to be tested, we considered the knee to be aligned with the axis of the exercise arm. Gravity-compensated torque values were corrected with the exercise arm positioned 15° from horizontal.

We use the Kin-Com’s exercise arm to set the test ROM. The angle at which knee flexor muscle shortening began (start angle) was set at 20° from horizontal, and the angle at which muscle lengthening began (return angle) was set at 85° from horizontal. To calculate torque, we measured the distance between the point of application of the generated force and the axis of rotation of the exercise arm, using the scale on the arm itself and keyed into the computer. Each subject used the same radius for all tests. Exercise-arm velocity was set to 60°/s and 180°/s, respectively, for the above isokinetic peak torque measurements.

US Treatment 

The locations of sonication (US treatment). The regions for application of US were selected according to locations of tendinopathy, enthesopathy, Baker’s cyst formation, or bursitis indicated by the real time 5 to 12MHz high-resolution linear scanner,b followed by tender point findings on orthopedic examination. The most common periarticular soft tissue lesions included anserine bursitis, medial collateral enthesitis, popliteal tendonitis, Baker’s cyst, and supra- and infrapatellar bursitis.

Continuous sonication 

The USc was set at a duty cycle of 100%, with frequency of 1MHz and a spatial and temporal peak intensity of 1.5W/cm2. The US probe was applied for 5 minutes to each treated region over the medial collateral ligament (MCL), anserine bursa, and the popliteal fossa tender points—a total treated area of approximately 25cm2. The patient was kept in a supine position with bilateral knee flexion of 90° for MCL and anserine bursa, and in a prone position with bilateral knee full extension for treatment of the popliteal fossa tender points. Sonication was performed 3 times a week for 8 weeks. The intensity of sonication was adjusted to the level at which the patient felt a warm sensation or a mild sting.

Pulsed sonication 

The same US was set at a frequency of 1MHz and a spatial and temporal peak intensity of 2.5W/cm2, and pulsed at a duty cycle of 25%. The duration of US applied to each region, and the posture of the patient being treated, were as described for continuous sonication. Sonication was performed 3 times a week for 8 weeks. The intensity of sonication was also adjusted to the level at which the patient felt a warm sensation or a mild sting.

Isokinetic Exercise 

After each arthritic joint pain and ROM were evaluated, and blood pressure and heart rate were measured, hot packs were applied and the quadriceps and hamstrings were stretched.The patient then underwent a 5-minute warm-up exercise on a stationary bicycle set without resistance. The isokinetic muscle strengthening exercise program was performed, as described in our previous study,15 for left and right knees, 3 times a week for 8 weeks (24 sessions). The isokinetic exercise program began with 60% of the average peak torque. Intensity of isokinetic exercise increased from 1 set to 5 sets during the first through fifth sessions and remained at 6 sets for the remaining 6th through 24th sessions. Each set consisted of 5 repetitions of concentric contraction in angular velocities of 30°/s and 120°/s for extensors, and 5 repetitions of eccentric and concentric contractions in angular velocities of 30°/s and 120°/s for flexors. The start and stop angles for extension exercises were 40° and 70°, and the start and stop angles for flexion exercises were 70° and 40°. Patients were allowed 5 seconds of rest between sets, 10 seconds of rest between different modes of training, and 10 minutes of rest between right and left knee training.

Compliance 

Compliance was determined by the number of participants who completed the treatment course divided by the number of initial participants. The major causes of noncompliance, and the times at which the exercise program was discontinued, were also analyzed.

Home Program Exercise Routine 

After the 3 groups completed treatment, the patients were given a home exercise program consisting of 15 minutes on a stationary bicycle or on a common bicycle with a device attached to elevate the rear wheel for subjects who did not have an exercise bike at home (18 patients).

Statistical Analysis 

We used a paired t test to study the changes in VAS, Lequesne index, ambulation speed values, and peak torques in each group immediately after treatment and at follow-up 1 year later. One-way analysis of variance with the Tukey test was used to compare those differences between 3 treated groups, and the Dunnett test was used to compare the difference between treated groups and the control group at zero time, after treatment, and 1 year later. A statistically significant difference was defined as P less than .05.

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Results 

Participants 

The 120 patients ranged in age from 42 to 72 years (mean age, 62.0±8.4y), with a female to male ratio of 4.2:1. The duration of knee pain ranged from 6 months to 11 years.

Changes in ROM 

The changes in average ROM of the arthritic knees for each group are shown in table 1. Ten subjects stopped the therapeutic exercises because of intolerable pain during exercise (5 subjects in group I, 3 in group II, 2 in group IV). Contact with 13 subjects was lost during the follow-up period (4 subjects in group I, 3 in group II, 2 in group III, 4 in the control group). The average ROM of each group was initially similar, but ROM scores later increased significantly only in groups II and III after treatment. Patients in group III showed the greatest increase in ROM, both after treatment and in the follow-up period.

Table 1. Average Knee ROM in Each Group Before and After Treatment
TimeIIIIIIIV (control)
Before105±15(60)106±13(60)105±12(60)99±15(60)
After110±17(50)115±15⁎†(54)119±15⁎†(60)95±11(56)
ΔROM5±109±14†15±14†‡4±13
Follow-up112±14(42)118±14⁎†(48)124±18⁎†‡(56)98±17(48)

NOTE. Values are mean degrees ± standard deviation (SD). Values in parentheses are the number of knees in each group at various time intervals.

⁎ Significant difference in Lequesne index in each group after treatment or follow-up (P<.05).

† Significant difference in Lequesne index in each group compared with control at various time intervals (P<.05).

‡ Significant difference compared with other treated groups (P<.05).

Changes in Knee Pain 

The changes in average scores for knee pain in each group are shown in table 2. Pain scores for groups I through IV were initially similar, but pain scores decreased significantly in all treated groups; pain scores continued to decrease significantly in groups II and III at follow-up, whereas they were increased in the controls. Patients in group III showed the greatest degree of pain reduction, both after treatment and at follow-up.

Table 2. Average VAS Score for Knee Pain in Each Group Before and After Treatment
TimeIIIIIIIV (control)
Before4.9±1.5(60)5.2±1.7(60)5.0±1.3(60)4.8±1.8(60)
After3.7±0.7(50)⁎†3.3±0.8(54)⁎†2.6±1.7(60)⁎†‡4.3±1.6(56)
ΔVAS1.2±1.41.9±1.62.4±1.8‡0.4±1.6
Follow-up3.5±1.7(42)⁎†2.6±1.4(48)⁎†2.2±1.8(56)⁎†‡6.0±1.3(48)⁎

NOTE. Values are mean score ± SD. Values in parentheses are the number of knees in each group at various time intervals.

⁎ Significant difference in VAS score in each group after treatment or follow-up (P<.05).

† Significant difference in VAS score compared with control group at various time intervals (P<.05).

‡ Significant difference compared with other treated groups (P<.05).

Changes in Lequesne Index 

Initially, the treated and control groups showed no significant Lequesne index differences. The changes in mean index values in each patient group are shown in table 3. The average scores decreased significantly in all treated groups after treatment, and at the 1-year follow-up. Patients in group I had the least reduction in Lequesne index scores after treatment, and patients in group III had the greatest reduction in disability after treatment and during the follow-up period.

Table 3. Average Lequesne Index of Patients in Each Group Before and After Treatment
TimeIIIIIIIV (control)
Before6.7±2.1(30)7.0±1.6(30)7.1±2.1(30)7.0±1.1(30)
After5.2±0.9(25)⁎†4.8±1.0(27)⁎†4.1±0.6(30)⁎†‡6.6±1.6(28)
ΔLequesne index1.6±1.42.1±1.52.9±1.8‡0.4±1.6
Follow-up5.1±1.8(21)⁎†3.9±1.5(24)⁎†3.1±1.4(28)⁎†‡7.8±1.7⁎(24)

NOTE. Values are mean score ± SD. Values in parentheses are the number of knees in each group at various time intervals.

⁎ Significant difference in Lequesne index in each group after treatment or follow-up (P<.05).

† Significant difference in Lequesne index compared with control group at various time intervals (P<.05).

‡ Significant difference compared with other treated groups (P<.05).

Changes in Ambulation Speed 

The mean changes in ambulation speed in each group are shown in table 4. Initially, the average ambulation speed did not markedly differ between treated and control groups, but the average ambulation speed increased significantly only in groups II and III after treatment. However, the average ambulation speed increased in all treated groups at follow-up when compared with the controls. Patients in group III showed the most improvement, and group I showed the least improvement both, after treatment and at the follow-up.

Table 4. Average Ambulation Speed of Patients in Each Group Before and After Treatment
TimeIIIIIIIV (control)
Before74.6±7.3(30)72.6±6.5(30)73.2±6.0(30)72.3±7.5(30)
After81.9±5.5(25)‡90.9±4.1(27)⁎†92.4±3.4(30)⁎†75.6±3.5(28)
Δambulation speed9.2±8.6‡18.6±5.519.5±7.23.4±6.8
Follow-up82.5±7.1(21)⁎†90.4±7.8(24)⁎†99.7±8.7(28)⁎†‡67.1±4.3(24)

NOTE. Values are mean m/min ± SD. Values in parentheses are the number of knees in each group at various times intervals.

⁎ Significant difference in ambulation speed in each group after treatment or follow-up (P<.05).

† Significant difference in ambulation speed compared with control group at various time intervals (P<.05).

‡ Significant difference compared with other treated groups (P<.05).

Changes in Peak Torque 

The changes in mean peak torques of knee flexion and extension in concentric and eccentric contraction in all patient groups are shown in table 5 (60°/s) and table 6 (180°/s). All the average peak torque of 60°/s in ex/con, ex/ecc, flex/ecc, and flex/con increased significantly in group II and group III, both after treatment and at the follow-up. Patients in group I showed the least improvement in peak torques, but group I showed significant improvements in muscle peak torques when compared with the control group at follow-up. Table 6 shows that patients in group III had the most improvement in peak torque at 180°/s in all contraction modes (ex/con, ex/ecc, flex/con, flex/ecc) after treatment and at follow-up, which correlates closely with joint functional improvement.

Table 5. Mean Peak Torque of Knee Flexion and Extension in Concentric and Eccentric Contraction at 60°/s in Each Group Before and After Treatment
Angular VelocityTimeIIIIIIIV (control)
60° (ex/con)Before233.1(60)236.9(60)230.3(60)237.1(60)
After255.7(50)⁎‡284.5(54)⁎†289.9(60)⁎†233.5(56)
ΔMPT21.5‡49.459.4−3.6
Follow-up273.3(42)⁎†‡321.5(48)⁎†336.1(56)⁎†221.3(48)
60°(ex/ecc)Before430.1(60)443.3(60)438.9(60)436.3(60)
After476.5(50)⁎†‡514.3(54)⁎†518.3(60)⁎†444.6(56)
ΔMPT38.5‡71.279.47.5
Follow-up485.1(42)⁎†‡587.3(48)⁎†587.4(56)⁎†410.4(48)
60°(flex/con)Before280.6(60)278.5(60)270.8(60)275.5(60)
After299.4(50)†‡319.0(54)⁎†317.9(60)⁎†267.8(56)
ΔMPT20.5‡41.347.9−8.5
Follow-up289.8(42)†‡333.2(48)⁎†348.6(56)⁎†237.3(48)⁎
60°(flex/ecc)Before337.3(60)344.5(60)341.8(60)347.1(60)
After373.4(50)†‡399.6(54)⁎†401.3(60)⁎†338.1(56)
ΔMPT33.3‡55.060.1−11.2
Follow-up379.6(42)†‡416.5(48)⁎†423.6(56)⁎†296.9(48)⁎

NOTE. Values in parentheses are the number of knees in each group at various time intervals.

⁎ Significant difference in peak torque in each group after treatment or follow-up (P<.05).

† Significant difference in peak torque compared with control group at various time intervals (P<.05).

‡ Significant difference compared with other treated groups (P<.05).

Table 6. Mean Peak Torque of Knee Flexion and Extension in Concentric and Eccentric Contraction at 180°/s in Each Group Before and After Treatment
Angular VelocityTimeIIIIIIIV (control)
180° (ex/con)Before180.5(60)178.1(60)184.1(60)185.3(60)
After203.2(50)⁎†222.3(54)⁎†265.3(60)⁎†‡181.8(56)
ΔMPT23.547.171.3‡−3.4
Follow-up212.3(42)⁎†233.1(48)⁎†279.4(56)⁎†‡163.2(48)
180°(ex/ecc)Before482.6(60)483.3(60)493.1(60)488.3(60)
After575.5(50)⁎†604.1(54)⁎†653.3(60)⁎†‡476.8(56)
ΔMPT93.5123.1163.7‡−13.2
Follow-up592.3(42)⁎†635.3(48)⁎†696.7(56)⁎†‡432.1⁎(48)
180°(flex/con)Before184.7(60)187.6(60)191.8(60)186.1(60)
After225.7(50)⁎†246.4(54)⁎†279.8(60)⁎†‡172.6(56)
ΔMPT38.461.686.3‡−14.0
Follow-up235.5(42)⁎†277.2(48)⁎†331.7(56)⁎†‡160.3(48)⁎
180°(flex/ecc)Before317.4(60)315.1(60)321.3(60)324.1(60)
After340.7(50)†359.3(54)⁎†395.5(60)⁎†‡313.4(56)
ΔMPT25.343.675.2‡−10.7
Follow-up342.1(42)†383.3(48)⁎†426.2(56)⁎†‡290.1(48)⁎

NOTE. Values in parentheses are the number of knees in each group at various time intervals.

⁎ Significant difference in peak torque in each group after treatment or follow-up (P<.05).

† Significant difference in peak torque in each group compared with control group at various time intervals (P<.05).

‡ Significant difference compared with other treated groups (P<.05).

Compliance 

Compliance was .83 (25/30) in group I, .90 (27/30) in group II, 1.0 (30/30) in group III, and .93 (28/30) in the control group. Reasons for withdrawal from the treatment included intolerable knee pain induced by the prescribed exercises in 6 of 8 patients (75%) and leg muscle weakness in 2 of 8 (25%). Treatment compliance was greater in group III, suggesting that therapeutic exercise-induced knee pain was the major reason for discontinuing treatment.

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Discussion 

Physical disability is frequently reported in patients with knee OA. However, the disability of these patients can only partly be explained by degeneration of the knee joints. Several other factors have been proposed as possible explanations for their disability, including physical factors such as reduced ROM of the knee joints. In a study of elderly Swedish subjects, Odding et al29 found correlations between knee and hip joint ROM and disability. They also found that restricted flexion of the knees was a strong risk factor for locomotor disability in activities primarily involving the lower extremities, such as walking, climbing stairs, and rising from and sitting down in a chair. Steultjens et al30 reported that restricted joint mobility, especially in flexion of the knee, appears to be an important determinant of disability in patients with OA.

The major causes of ROM limitation of the arthritic knee are joint pain and weakness of the quadriceps,30 which is one of the key muscles controlling the stability of the arthritic knee. Joint pain control and muscle strengthening exercise are therefore important in a rehabilitation program for knee OA.

Pain in the osteoarthritic knee may be caused by several conditions, including loss of articular cartilage, mechanical compression of either the medial knee compartment with varus deformity, mechanical compression of the lateral compartment with valgus deformity31; stretching of the medial or MCLs; microfractures and subchondral fracture; capsular distension by effusion; and patellar and associated syndromes such as anserine bursitis or prepatellar bursitis. Furthermore, the interaction of these factors would result in changes of intraarticular and periarticular connective tissues.

Periarticular connective tissue is composed of collagen fibers within a proteoglycan matrix. The tissue may become fibrotic, contracted, or shortened when subjected to immobilization or inactivity due to arthritic joint pain, resulting in joint capsule contractures and a limited ROM. Adaptive shortening of the muscles may also occur when a muscle immobilized in a shortened position demonstrates shortening within a week. After 3 weeks in this shortened position, the loose connective tissue in the muscle becomes dense connective tissue, and a fixed muscle contracture develops,32 resulting in the instability of the joint. However, through an appropriate physical modality such as the US we used in this study, the patients in groups II and III had more improvement in muscular peak torques and less disability, which were correlated closely with an increased ROM after periarticular soft tissue pain control.

Our previous study15 showed that although isokinetic strengthening exercise has the greatest therapeutic effect on the functional status of patients with knee OA, it also had the lowest level of compliance with treatment when compared with isotonic or isometric exercises because of exercise-induced knee pain. Patients in groups II and III had better compliance than those in group I, which may have been due to the decrease in pain in those patients who received US treatment.17

The literature appears to offer support for neither pulsed US to treat chronic inflammatory conditions, nor for thermal US to treat acute inflammatory conditions.33, 34 The high rate of compliance was related to the reduction of exercise-induced pain as in the this study, which showed that knee pain reduction in group III was greater than that in group II, implying that pulsed US is more suitable during exercise for patients with OA than continuous US.

The reduction of soft tissue pain by US could result from increased blood flow to muscles in spasm, or the rise in temperature causing relaxation of muscle guarding. Electromyographic studies show that US does not change nerve conduction velocity in small diameter nociceptive afferents.35 Consequently, it is thought that pain relief may occur as a result of the activation of A alpha- and A beta-mechanoreceptors that inhibit nociceptive transmission in A delta- and C-fiber pathways as a proposed pain-gating mechanism.

Isokinetic muscular peak torque at 60°/s and 180°/s were measured to determine the changes in MPT. Table 5 shows more MPT (at 60°/s) improvement in both groups II and III. However, groups II and III show no significant difference in degree of improvement. Furthermore, table 6 shows that improvement of MPT (at 180°/s) was significantly greater in group III than in group II. A comparison of the improvement in disability and ambulation speed implies that the improvement in MPT at 180°/s is closely correlated with functional status of arthritic knee.

In this study, we administered the sham US treatment for patients in groups I and IV, however, the absence of a warm or stinging sensation for the treated patients caused the failure of the sham US application. Consequently, the placebo effect of US in groups II and III must be considered although there were significant differences between groups II and III and groups I and IV.

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Conclusions 

US treatment, especially pulsed US, can enhance the therapeutic effects of isokinetic strengthening exercise for treating periarticular soft tissue pain in patients with knee OA.

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References 

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  • a Kin-Com; Chattecx Group, Chattanooga Corp, 4717 Adams Rd, Hixson, TN 37343.
  • b HDL 1500; ATL Ultrasound, PO Box 3003, Bothell, WA 98041.
  • c Sonopulus 590; Enraf Nonius, Röntgenweg 1, PO Box 810 2600 AV Delft, Netherlands.

 Supported by National Science Council of Taiwan (grant no. NSC-92-2314-B-037-067).No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

PII: S0003-9993(05)00223-6

doi:10.1016/j.apmr.2005.02.007

Archives of Physical Medicine and Rehabilitation
Volume 86, Issue 8 , Pages 1545-1551, August 2005

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