Esther Suter

Decrease in quadriceps inhibition after sacroiliac joint manipulation in patients with anterior knee pain

BACKGROUNDnEvidence exists that conservative rehabilitation protocols fail to achieve full recovery of muscle strength and function after joint injuries. The lack of success has been attributed to the high amount of muscle inhibition found in patients with pathologic conditions of the knee joint. Clinical evaluation shows that anterior knee pain is typically associated with sacroiliac joint dysfunction, which may contribute to the muscle inhibition observed in this patient group.nnnOBJECTIVEnTo assess whether sacroiliac joint manipulation alters muscle inhibition and strength of the knee extensor muscles in patients with anterior knee pain.nnnDESIGN AND SETTINGnThe effects of sacroiliac joint manipulation were evaluated in patients with anterior knee pain. The manipulation consisted of a high-velocity low-amplitude thrust in the side-lying position aimed at correcting sacroiliac joint dysfunction. Before and after the manipulation, torque, muscle inhibition, and muscle activation for the knee extensor muscles were measured during isometric contractions using a Cybex dynamometer, muscle stimulation, and electromyography, respectively.nnnPARTICIPANTSnEighteen patients (mean age, 30.5 +/- 13.0 years) with either unilateral (n = 14) or bilateral (n = 4) anterior knee pain.nnnRESULTSnPatients showed substantial muscle inhibition in the involved and the contralateral legs as estimated by the interpolated twitch technique. After the manipulation, a decrease in muscle inhibition and increases in knee extensor torques and muscle activation were observed, particularly in the involved leg. In patients with bilateral anterior knee pain, muscle inhibition was decreased in both legs after sacroiliac joint adjustment.nnnCONCLUSIONSnSpinal manipulation might offer an interesting alternative treatment for patients with anterior knee pain and muscle inhibition. Because this clinical outcome study was of descriptive nature rather than a controlled design, biases might have occurred. Thus the results have to be verified in a randomized, controlled, double-blinded trial before firm conclusions can be drawn or recommendations can be made.

Conservative lower back treatment reduces inhibition in knee-extensor muscles: a randomized controlled trial

BACKGROUNDnKnee-joint pathologies, such as anterior knee pain (AKP), are associated with strength deficits and reduced activation of the knee extensors, which is referred to as muscle inhibition (MI). MI is thought to prevent full functional recovery, and treatment modalities that help to reduce or eliminate MI appear necessary for successful rehabilitation. Clinical observations suggest that AKP is typically associated with sacroiliac (SI) joint dysfunction. It is unknown whether SI-joint dysfunction contributes to knee-extensor deficits and whether correction of SI-joint dysfunction alleviates MI.nnnOBJECTIVEnThe objective of this study was to assess whether conservative low back treatment reduces lower limb MI.nnnSTUDY DESIGNnIn a randomized, controlled, double-blind study the effects of conservative lower back treatment on knee-extensor strength and MI were evaluated in patients with AKP.nnnMETHODSnTwenty-eight patients with AKP were randomly assigned to either a treatment or a control group. After a lower back functional assessment, the treatment group received a conservative treatment in the form of a chiropractic spinal manipulation aimed at correcting SI-joint dysfunction. The control group underwent a lower back functional assessment but received no joint manipulation. Before and after the manipulation or the lower back functional assessment, knee-extensor moments, MI, and muscle activation during full effort, isometric knee extensions were measured.nnnRESULTSnPatients showed substantial MI in both legs. Functional assessment revealed SI-joint dysfunction in all subjects (23 symptomatic and 5 asymptomatic). After the SI-joint manipulation, a significant decrease in MI of 7.5% was observed in the involved legs of the treatment group. MI did not change in the contralateral legs of the treatment group or the involved and contralateral legs of the control group. There were no statistically significant changes in knee-extensor moments and muscle activation in either group.nnnCONCLUSIONSnThe results of this study suggest that SI-joint manipulation reduces knee-extensor MI. Spinal manipulation may possibly be an effective treatment of MI in the lower limb musculature.

Extent of Muscle Inhibition as a Function of Knee Angle

The present study was aimed at assessing muscle inhibition (MI) of the quadriceps muscles of healthy subjects as a function of knee angle. The extent of muscle activation and of twitch potentiation following maximal contractions at different knee angles were investigated. Six males and four females (mean age 29.5 +/- 6.2 yr) performed three maximal isometric knee extensions on a KinCom dynamometer with the right and left legs at 15, 30, 45, 60 and 90 degrees from full extension. MI was assessed using the interpolated twitch technique. This technique requires surface stimulation of the femoral nerve during the maximal contractions. MI was estimated by the amount of extra torque evoked by the superimposed twitch. Electromyographical (EMG) activity of the vastus lateralis muscle was measured in order to estimate muscle activation. Twitch potentiation was assessed at 5, 20, 60 and 120 s after the maximal contractions by applying a single electrical twitch to the relaxed muscle. Results revealed a strong dependency of MI on the knee angle tested; MI increased with increasing muscle lengths and was almost three times higher at 60 degrees than at 15 degrees of full extension. Muscle activation measured as the root mean square (RMS) values of the vastus lateralis EMG was the same for four out of the five muscle lengths measured; at a knee angle of 90 degrees , the RMS values were significantly higher. Twitch potentiation was observed at all knee angles following maximal contractions. Potentiation was highest immediately after contraction (i.e. 5 s after), and the amount of potentiation did not depend on the knee angle. Muscle activation and twitch potentiation only accounted for a small percentage of the differences in MI as a function of knee angle. It is suggested that increased patellofemoral pressure and increased ligament strain, which are highest between 45 and 60 degrees of full extension, might be responsible for the high MI measured at these knee angles. It is further hypothesized that the differences in MI as a function of muscle length are also associated with the shortening of the contractile elements during contractions, and the concomitant loss in force potential; a phenomenon which is probably more pronounced at short compared to long muscle lengths.

Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

The purposes of this study were to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury, and to quantify the corresponding in situ joint contact mechanics. Experiments were performed in the anterior cruciate ligament (ACL) transected knee of the cat and the corresponding, intact contralateral knee, 16 weeks following intervention. Cartilage thickness, stiffness, effective Youngs modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral joint were obtained in situ using Fuji Pressensor film, and comparisons between experimental and contralateral joint were made for corresponding loading conditions. Total joint contact area and peak pressure were increased and decreased significantly (alpha=0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stiffness were increased and decreased significantly (alpha=0.01), respectively, in the experimental compared to the contralateral joint in the four femoral and patellar test locations. Articular cartilage material properties (effective Youngs modulus and permeability) were the same in the ACL-transected and intact joints. These results demonstrate for the first time the effect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corroborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of cartilage properties and joint surface geometry from the experimental animals. We conclude that the joint contact mechanics in the ACL-transected cat change within 16 weeks of experimental intervention.

One-year changes in hind limb kinematics, ground reaction forces and knee stability in an experimental model of osteoarthritis

Long-term changes in the three-dimensional external loading, hind limb kinematics and knee stability were assessed in an anterior cruciate ligament (ACL)-transected cat model of osteoarthritis (OA). Seven skeletally mature cats (mean mass 4.6+/-1.4 kg) were studied before ACL transection (ACLT) and at 1 and 3 weeks, and at 3, 6, 9 and 12 months following ACLT. One week following ACLT, significant changes from the normal locomotion pattern were observed: peak vertical and anterior posterior ground reaction forces were decreased, particularly the peak posterior forces in the early phase of stance. Furthermore, knee angles were reduced by about 15 degrees throughout the whole gait cycle, while ankle and hip angles were reduced at paw off in the experimental compared to the contralateral hind limbs. Ground reaction forces and hind limb kinematics recovered to near pre-surgical patterns over the one year period assessed. ACLT was also associated with an increased knee instability which improved over time. X-rays suggested that there was a continued degeneration in the experimental knee over the one year period; there was osteophyte formation at the joint margins and an increase in cartilage thickness throughout the joint. It was speculated that the more flexed knee angles and the reduced anterior-posterior ground reaction forces in the ACL-transected compared to the intact hind limb represent an adaptive strategy aimed at avoiding excessive anterior displacement of the tibia in the early phase of stance. The recovery of the locomotion pattern with time might be related to the corresponding improvement of knee stability.

Decrease in elbow flexor inhibition after cervical spine manipulation in patients with chronic neck pain

OBJECTIVEnThis study measured functional capacity and subjective pain in patients with chronic neck pain before and after manipulation of the cervical spine.nnnDESIGNnOutcomes study on 16 patients with chronic neck pain.nnnBACKGROUNDnMuscle inhibition, i.e., the inability to fully activate a muscle, has been observed following joint pathologies and in low back pain conditions. Although chronic neck pain has been associated with changes in muscle recruitment and coordination in the shoulder and arms, the possibility of muscle inhibition has not been explored.nnnMETHODSnBiceps activation during a maximal voluntary elbow flexor contraction was assessed using the interpolated twitch technique and electromyography. Cervical range of motion and pressure pain thresholds were measured using a goniometer and an algometer. Manipulation of the cervical spine was applied at the level of C5/6/7, and functional assessments were repeated.nnnRESULTSnPatients showed significant inhibition in their biceps muscles. Cervical range of motion was restricted laterally, and increased pressure pain sensitivity was evident. After cervical spine manipulation, a significant reduction in biceps inhibition and an increase in biceps force occurred. Cervical range of motion and pressure pain thresholds increased significantly.nnnCONCLUSIONSnSignificant dysfunction in biceps activation was evident in patients with chronic neck pain, indicating that this muscle group cannot be used to the full extent. Spinal manipulation decreased muscle inhibition and increased elbow flexor strength at least in the short term.nnnRELEVANCEnMuscle inhibition in the biceps has not been previously documented in patients with chronic neck pain. Further research is needed to establish whether muscle inhibition is related to clinical symptoms and functional outcome. Spinal manipulation improved muscle function, cervical range of motion and pain sensitivity, and might therefore be beneficial for treating patients with chronic neck pain.

Quadriceps inhibition following arthroscopy in patients with anterior knee pain.

OBJECTIVES: This study was aimed at investigating muscle strength and quadriceps inhibition in patients with unilateral anterior knee pain syndrome. DESIGN: Functional assessments were made before an arthroscopic knee surgery and 6 weeks and 6 months following the surgical intervention. BACKGROUND: Traumatic knee injuries have been associated with severe muscle inhibition of the knee extensor muscles. Muscle inhibition is a serious hindrance in the rehabilitation process and prevents full functional recovery of the affected joint. METHODS: 30 patients participated in the study. Isometric quadriceps strength was measured using a KinCom dynamometer. Muscle inhibition was assessed using the interpolated twitch technique which requires applying a single electrical twitch to the femoral nerve during a maximal isometric knee extensor contraction. Pain was assessed with a 100 mm visual analogue pain scale. RESULTS: Pre-surgery, substantial muscle inhibition and pain was observed in the affected leg compared with the contralateral leg. Over the 6 month period there was a decrease in pain and muscle inhibition, although the decrease in muscle inhibition failed to reach statistical significance. Muscle strength showed a decrease 6 weeks post-surgery followed by an increase 6 months following surgery compared with pre-surgical values. CONCLUSIONS: The arthroscopic intervention was successful in reducing pain in patients with unilateral anterior knee pain syndrome. However, muscle inhibition was still substantial 6 months following surgery and was significantly higher in the affected and contralateral limb than in normal subjects.

Human skeletal muscle fibre types and force: velocity properties

It has been reported that there is a relationship between power output and fibre type distribution in mixed muscle. The strength of this relationship is greater in the range of 3–8 rad · s−1 during knee extension compared to slower or faster angular knee extensor speeds. A mathematical model of the force: velocity properties of muscle with various combinations of fast- and slow-twitch fibres may provide insight into why specific velocities may give better predictions of fibre type distribution. In this paper, a mathematical model of the force: velocity relationship for mixed muscle is presented. This model demonstrates that peak power and optimal velocity should be predictive of fibre distribution and that the greatest fibre type discrimination in human knee extensor muscles should occur with measurement of power output at an angular velocity just greater than 7 rad · s−1. Measurements of torque: angular velocity relationships for knee extension on an isokinetic dynamometer and fibre type distribution in biopsies of vastus lateralis muscles were made on 31 subjects. Peak power and optimal velocity were determined in three ways: (1) direct measurement, (2) linear regression, and (3) fitting to the Hill equation. Estimation of peak power and optimal velocity using the Hill equation gave the best correlation with fibre type distribution (r > 0.5 for peak power or optimal velocity and percentage of fast-twitch fibres). The results of this study confirm that prediction of fibre type distribution is facilitated by measurement of peak power at optimal velocity and that fitting of the data to the Hill equation is a suitable method for evaluation of these parameters.

Knee extensor torque and quadriceps femoris EMG during perceptually-guided isometric contractions

The aim of this study was to examine superficial quadriceps femoris (QF) EMG and torque at perceived voluntary contraction efforts. Thirty subjects (15 males, 15 females) performed 9, 5 s, sub-maximal contractions at prescribed levels of perceived voluntary effort at points 1-9 on an 11-point scale (0-10), in a random order. Surface electromyograms (EMG) of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles, as well as QF peak torque (PT), average torque (AT), and torque coefficient of variation (C.V.), were sampled. The raw EMG signals were full-wave rectified and integrated over the middle three s of each contraction. The sampled EMG signals, and PT and AT at each perceived exertion level were normalized to the average of three maximal voluntary contractions. The normalized EMG and torque values at each perceived exertion level were then compared to equivalent percent values (i.e., 10% at a perceived level of 1). The results demonstrated that at all perceived exertion levels, with the exception of the RF at a level of 2 which was equivalent to 20%, and the VL and RF muscles at a level 1 in which activation was greater than 10%, activation was significantly less than the equivalent percent value at each point on the scale. VM EMG was found to be less than the VL and RF from contraction levels 3-9. PT was shown to be less than the equivalent percent values at contraction levels 6-9. The AT was found to be lower than the expected percent value at perceived effort levels 2-9. Torque C.V. was not found to be different across the range of perceived effort. The major findings of this study suggested that humans over-estimate voluntary QF muscle torque when guided by perceptual sensations. It is also suggested that the produced EMG signals revealed a reliance on the VL muscle for knee extensor torque generation at sub-maximal levels.

Effects of speed and distance of muscle shortening on force depression during voluntary contractions

The purpose of this study was to determine the influence of speed and distance of muscle shortening on the amount of force depression for voluntary contractions. Two experimental tests were performed. In the first test, subjects performed isometric knee extensor contractions following muscle shortening produced by isokinetic knee extensions over the range 25-50 degrees. In the second test, subjects performed isometric knee extensor contractions following muscle shortening produced by isokinetic knee extensions at two speeds: 20 and 240 degrees /s. Knee extensor moments, surface electromyographical (EMG) signals of quadriceps femoris, and interpolated twitch moments were measured during all contractions and were compared with the corresponding values obtained during purely isometric contractions. Force depression following muscle shortening for the voluntary contractions tested in this study did not depend on the distance or the speed of muscle shortening. These results are in contrast to the corresponding results in the literature obtained using artificial electrical stimulation in which force depression was always found to be directly related to the distance of shortening and inversely related to the speed of shortening. The difference in force depression as a function of the distance and speed of muscle shortening between voluntary and artificial electrical stimulation may be associated with changes in activation following the voluntary shortening contractions, whereas activation is controlled and constant in all artificial stimulation protocols.