Malcolm H. Pope

Mechanical changes in the knee after meniscectomy

A compression testing machine was used to transmit increasing loads at various strain rates across twelve canine and twelve human cadaver knees. The specimens were originally evaluated with both menisci intact and the same tests were repeated with one meniscus removed and then with both menisci removed. This investigation showed that the menisci perform a load-transmitting and energy-absorbing function in the knee joint. The stress acting across the joint increased significantly after meniscectomy. The intact meniscus was deformed during compressive loading rather than being passively pushed away, thus demonstrating the presence of hoop stresses within the meniscus.

Risk factors in low-back pain. An epidemiological survey.

ABSTRACTA survey was done on 1221 men between the ages of eighteen and fifty-five years who had been seen in a family-practice facility between 1975 and 1978 Each patient completed a questionnaire concerning any history of low-back pain, associated symptoms in the lower limbs, resultant disability, types of health care utilized, certain occupational characteristics, exposure to vehicular vibration, and sports activities. We found that 368 patients (30. 1 per cent) had never experienced low-back pain, 565 (46.3 per cent) had or were having moderate low-back pain, and 288 (23.6 percent) had or were having severe low-back pain. Patients with severe low-back pain had significantly more complaints in the lower limbs, sought more medical care and treatment for the low-back pain, and had lost more time from work for this reason. Risk factors associated with severe low-back pain included jobs requiring repetitive heavy lifting, the use of jackhammers or machine tools, and the operation of motor vehicles. Patients with severe pain were more likely to be cigarette-smokers and had a greater tobacco consumption as measured by both the number of cigarettes smoked per day and the number of years of exposure. Patients with moderate low-back pain were more often joggers and cross-country skiers when compared with the asymptomatic men and the men with severe low back pain. Otherwise, there were no identifiable differences related to sports activity.

Strain within the anterior cruciate ligament during hamstring and quadriceps activity

The objectives of this study were to measure strain in the ACL during simulated: (1) hamstring activity alone, (2) quadriceps activity alone, and (3) simultaneous quadriceps and hamstring activity. Seven knee speci mens removed from cadavers were studied. Heavy sutures applied to load cells were attached to the hamstring and quadriceps tendons. Loads were then applied manually (hamstrings) and/or with an Instron testing machine (quadriceps) to simulate isometric con tractions of the various muscle groups. Strain was measured using a Hall effect transducer. Acting alone, the isometric hamstring activity decreased ACL strain relative to the passive normal strain at all positions tested. Thus, hamstring exercises are not detrimental to ACL repairs or reconstruction and can be included early in the rehabilitation program after ACL surgery. Acting alone, at flexion angles of 0° to 45°, the quad riceps significantly increased the strain within the ACL relative to the passive normal strain. Strain in the ACL during simultaneous hamstring and quadriceps activity was significantly higher than that during passive normal motion from full extension to 30° of flexion. The ham strings are not capable of masking the potentially harm ful effects of simultaneous quadriceps contraction on freshly repaired or reconstructed ACLs unless the knee flexion angle exceeds 30°.

The biomechanics of anterior cruciate ligament rehabilitation and reconstruction

The rehabilitation of knee injuries involving the anterior cruciate ligament (ACL) is controversial. This paper describes strain in the normal and reconstructed ACL during a series of passive and active tests of knee flexion with and without varus, valgus, and axial rotation torques on the tibia. Strain in the human knee ACL was significantly different depending on whether the knee flexion angle was changed passively or via simulated quadriceps contraction. The knee joint capsule was found to be important for strain protection of the ACL. Quadriceps activity did not strain the normal or recon structed ACL when the knee was flexed beyond 60°, but significantly strained the tissue from 0 to 45° of knee flexion. Immobilization may not protect the ACL if isometric quadriceps contractions are allowed to occur. Properly placed reconstructions exhibited strain behav ior which closely followed the anteromedial band of the ACL.

Epidemiologic Studies of Low-back Pain

The records of 3920 patients (2068 females, 1852 males) entering a model family practice unit between 1975 and 1978 have been analyzed. Eleven percent of males and 9.5% of females reported an episode of low-back pain during that 3-year interval. The complaint of medically reported low-back pain was significantly related to occupational factors such as truck driving (P<0.001), lifting, carrying, pulling, pushing, and twisting (P<0.001 for all variables) as well as nondriving vibrational exposure (P<0.001). Patients reporting low-back pain also reported more episodes of anxiety (P<0.001) and depression (P<0.001) and had more emotionally stressful occupations (P<0.001). The mean number of pregnancies was greater in women with low-back pain (2.6) than in those without (1.6) (P<0.001). The low-back pain sufferers were more likely to be cigarette smokers (P<0.001), particularly when smoking was accompanied by a chronic cough (P<0.001). This population is currently under prospective study to define the relevance of each of these risk factors to the complaint of low-back pain.

Anterior Cruciate Ligament Strain Behavior During Rehabilitation Exercises In Vivo

Before studying the biomechanical effects of rehabili tation exercises on the reconstructed knee, it is impor tant to understand their effects on the normal anterior cruciate ligament. The objective of this investigation was to measure the strain behavior of this ligament dur ing rehabilitation activities in vivo. Participants were pa tient volunteers with normal anterior cruciate ligaments instrumented with the Hall effect transducer. At 10° and 20° of flexion, ligament strain values for active exten sion of the knee with a weight of 45 N applied to a sub jects lower leg were significantly greater than active motion without the weight. Isometric quadriceps muscle contraction at 15° and 30° also produced a significant increase in ligament strain, while at 60° and 90° of knee flexion there was no change in ligament strain relative to relaxed muscle condition. Simultaneous quadriceps and hamstrings muscles contraction at 15° produced a significant increase in ligament strain compared with the relaxed state but did not strain the ligament at 30°, 60°, and 90° of flexion. Isometric contraction of hamstrings muscles did not produce change in ligament strain at any flexion angle. Exercises that produce low or un strained ligament values, and would not endanger a properly implanted graft, are either dominated by the hamstrings muscle (isometric hamstring), involve quad riceps muscle activity with the knee flexed at 60° or greater (isometric quadriceps, simultaneous quadri ceps and hamstrings contraction), or involve active knee motion between 35° and 90° of flexion.

Muscular Response to Sudden Load: A Tool to Evaluate Fatigue and Rehabilitation

Study Design Subjects were exposed to fatiguing and restorative interventions to assess their response to sudden loads. Objectives To investigate the erector spinae and rectus abdominis response characteristics to “sudden load” and the effect of fatigue and rehabilitation. Summary of Background Data Unexpected loads, which people often experience, can lead to high forces in the spine and may be a cause of low back injury. Methods Muscle responses to sudden load were mediated by fatigue, walking, expectation, method of load application, exposure to vibration, and cognitive‐behavioral rehabilitation in patients with chronic low back pain. A novel technique, perfected in this work, called wavelet analysis, was used to analyze these data. Results Reaction time was affected by fatigue and expectation. Vibration exposure significantly increased the muscle response time. Walking was able to ameliorate that effect. Back muscles responded differently, depending on whether loads were applied to the back through the hands or through the trunk. Electromyographic reaction time and magnitude decreased in patients after a 2‐week rehabilitation program. Conclusions Sudden loads can exacerbate fatigue effects. Walking after driving reduces the risk to the back caused by handling unpredictable loads. Vibration exposure guidelines should be more conservative. Patients have longer response times than healthy subjects, but patients can improve their response to sudden loads via rehabilitation. Patients exhibit a flexion‐extension oscillation at 5 Hz in response to a sudden load, suggesting that the 5‐Hz, seated, natural frequency observed during whole‐body vibration may result from neurophysiologic control limits.

Are occupational drivers at an increased risk for developing musculoskeletal disorders

Study Design This study analyzed the role of exposure to driving and other covariates in reports of back, neck, and shoulder pain and resultant disability. Cohorts in Sweden and the United States were compared. Objectives To establish the effect of mechanical and psychosocial factors in reporting back, neck, and shoulder pain and work loss. Summary of Background Data There are numerous reports of a positive relationship between back pain and driving. However, exposure data are minimal. The influence of job satisfaction has not been assessed. Methods The physical factors affecting reports of back, neck, and shoulder pain were investigated in a two‐country cohort study of bus and truck drivers and sedentary workers. Vibration exposure was obtained by directly measuring the vibration imposed on the driver during a typical work day. Lifting exposure was attained by questionnaire. Cumulative exposure was computed based on work history. Musculoskeletal health information was based on a modified nordic questionnaire, and other questionnaires recorded the physical and psychosocial aspects of the work environment. Results Of the sample, 50% reported low back pain, with no difference between countries. The highest risk factors (odds ratios) for back and neck pain were long‐term vibration exposure, heavy lifting, and frequent lifting. A combination of long‐term vibration exposure and frequent lifting carried the highest risk of low back pain. Work loss from low back pain was influenced by perceived job stress. Conclusions Vibration (resulting from driving) and lifting cause back, neck, and shoulder pain, whereas inability to work seems affected by stress at work.

Etiology of Spondylolisthesis: Assessment of the Role Played by Lumbar Facet Joint Morphology

This study examined the role of facet joint morphology in the etiology of both degenerative spondylolisthesis and isthmic spondylolysis. To this end, the axial facet joint morphology of the lower lumbar spine in a normal population and in populations of patients with spinal stenosis or degenerative spondylolisthesis at L4-5 and in patients with isthmic spondylolysis at the L5 level were characterized. Computed tomographic scans were digitized, defining the axial morphology of the normal facet joint at five stations from proximal to distal within the joint. Assessments were made of facet joint orientation, transverse articular dimension, depth of the articular surface, and shape of the articular surface at levels L3-4, L4-5, and L5-S1. There was a gradually more coronal orientation from proximal to distal among the stations at each level, and a maximal transverse articular dimension at the level of the superior endplate of the caudad vertebra. Minimal error in the recording process at this level, in addition to the maximal joint dimension, made this level the most representative of the overall morphology and most useful for further studies. At the L4-5 level, a significantly more sagittal facet orientation was found in the degenerative spondyiolisthesis group when compared to both the normal population and spinal stenosis groups (P< 0.01). At L5-S1, the only significant morphologic difference between the normal population and the patients with isthmic spondylolysis was reduced transverse articular dimension. These results support the hypothesis that patients developing degenerative spondylolisthesis are predisposed to this by a developmental sagittal orientation of the L4-5 facet joints

Transmissibility of 15-Hertz to 35-Hertz Vibrations to the Human Hip and Lumbar Spine: Determining the Physiologic Feasibility of Delivering Low-Level Anabolic Mechanical Stimuli to Skeletal Regions at Greatest Risk of Fracture Because of Osteoporosis

Study Design. Experiments were undertaken to determine the degree to which high-frequency (15–35 Hz) ground-based, whole-body vibration are transmitted to the proximal femur and lumbar vertebrae of the standing human. Objectives. To establish if extremely low-level (<1 g, where 1 g = earth’s gravitational field, or 9.8 ms−2) mechanical stimuli can be efficiently delivered to the axial skeleton of a human. Summary of Background Data. Vibration is most often considered an etiologic factor in low back pain as well as several other musculoskeletal and neurovestibular complications, but recent in vivo experiments in animals indicates that extremely low-level mechanical signals delivered to bone in the frequency range of 15 to 60 Hz can be strongly anabolic. If these mechanical signals can be effectively and noninvasively transmitted in the standing human to reach those sites of the skeleton at greatest risk of osteoporosis, such as the hip and lumbar spine, then vibration could be used as a unique, nonpharmacologic intervention to prevent or reverse bone loss. Materials and Methods. Under sterile conditions and local anesthesia, transcutaneous pins were placed in the spinous process of L4 and the greater trochanter of the femur of six volunteers. Each subject stood on an oscillating platform and data were collected from accelerometers fixed to the pins while a vibration platform provided sinusoidal loading at discrete frequencies from 15 to 35 Hz, with accelerations ranging up to 1 gpeak-peak. Results. With the subjects standing erect, transmissibility at the hip exceeded 100% for loading frequencies less than 20 Hz, indicating a resonance. However, at frequencies more than 25 Hz, transmissibility decreased to approximately 80% at the hip and spine. In relaxed stance, transmissibility decreased to 60%. With 20-degree knee flexion, transmissibility was reduced even further to approximately 30%. A phase-lag reached as high as 70 degrees in the hip and spine signals. Conclusions. These data indicate that extremely low-level, high-frequency mechanical accelerations are readily transmitted into the lower appendicular and axial skeleton of the standing individual. Considering the anabolic potential of exceedingly low-level mechanical signals in this frequency range, this study represents a key step in the development of a biomechanically based treatment for osteoporosis.