Quadriceps strength to body weight ratio is a significant indicator for initiating jogging after anterior cruciate ligament reconstruction

BACKGROUND

Quadriceps strength recovery after anterior cruciate ligament (ACL) reconstruction is an important criterion for progress in rehabilitation and return to sports. The purpose of this study was to determine whether quadriceps strength to body weight ratio (QS/BW) is a significant indicator for initiating jogging after ACL reconstruction.

METHODS

Isokinetic quadriceps strength at 60°/s was measured and a jogging trial was completed 3 months after ACL reconstruction with hamstring tendon autograft in 83 patients (36 male, 47 female; mean age, 26.6 ± 12.4 years). Based on the jogging trial results, patients were assigned to either a successful jogging group (mean velocity ≥ 9 km/h) or an unsuccessful jogging group (mean velocity < 9 km/h). The association between QS/BW and successful jogging after surgery was investigated by multivariate logistic regression analysis and the cut-off value was determined by receiver operating characteristic analysis.

RESULTS

Forty-four patients (53.0%) were assigned to the successful jogging group and 39 (47.0%) to the unsuccessful jogging group. QS/BW was independently associated with initiating jogging 3 months after surgery. The cut-off value of QS/BW for successful jogging was 1.45 Nm/kg (area under the curve = 0.94; sensitivity = 88.6%, specificity = 87.2%). All of the patients who initiated jogging with QS/BW of > 1.45 Nm/kg at 3 months returned to sports without recurrence or contralateral injury by 10 months after surgery.

CONCLUSIONS

QS/BW is a significant indicator for safely initiating jogging 3 months after ACL reconstruction. The cut-off value of QS/BW for initiating jogging was 1.45 Nm/kg.

CT-based morphological assessment of the hip joint in Japanese patients: association with radiographic predictors of femoroacetabular impingement

AIMS

Femoroacetabular impingement (FAI) has been highlighted and well documented primarily in Western countries and there are few large studies focused on FAI-related morphological assessment in Asian patients. We chose to investigate this subject.

PATIENTS AND METHODS

We assessed the morphology of the hip and the prevalence of radiographic FAI in Japanese patients by measuring predictors of FAI. We reviewed a total of 1178 hips in 695 men and 483 women with a mean age of 58.2 years (20 to 89) using CT images that had been obtained for reasons unrelated to symptoms from the hip. We measured the lateral centre edge angle, acetabular index, crossover sign, alpha angle and anterior femoral head-neck offset ratio.

RESULTS

A total of 441 hips (37.4%) had pincer-type deformity (41.7% men, 31.3% women) and 534 (45.3%) had cam-type deformity (54.4% men, 32.3% women). Moreover, 773 hips (65.6%) had at least one parameter that predisposes to FAI (74.0% men, 53.6% women) and 424 hips (36.0%) had two or more parameters (43.6% men, 25.0% women).

CONCLUSION

The prevalence of radiographic FAI was common in Japanese patients who are generally considered to have dysplastic hips. Cite this article: Bone Joint J 2016;98-B:1167-74.

Fracture of a persistent olecranon physis in an adult

A persistent olecranon physis is relatively rare; a fracture through the persistent olecranon physis in an adult is particularly rare. Little is known about the pathology of this disease. We report a case of a 36-year-old man presenting with right elbow pain after he had slipped and hit his elbow, with a history of a persistent symptomatic olecranon physis when he was a junior high school baseball player. He had been diagnosed with a fracture through a persistent olecranon physis by another doctor. Ten weeks after the injury, an iliac autograft was inserted and internal fixation was achieved with Kirschner wires and a figure-of-eight tension band in our hospital. Histologically, a fracture passed through the persistent physis cartilage and degeneration of the remnant of the physis was observed. The remnant of the physis at the olecranon side had not been replaced by new bone, though the physis at the distal ulnar was nearly replaced by new bone. The patient returned to work without experiencing pain or limitation in the range of motion 6 months after the operation. Radiographic evidence of bone union was seen after removal of internal fixation at the 13-month follow-up.

Minimally invasive removal of a recurrent lumbar herniated nucleus pulposus by the small incised microendoscopic discectomy interlaminar approach

In this report, we introduce two cases of recurrent herniated nucleus pulposus (HNP) at L5-S1 that were successfully removed using the small incised microendoscopic discectomy (sMED) technique, proposed by Dezawa and Sairyo in 2011. sMED was performed via the interlaminar approach with a percutaneous endoscope. The patients had previously underdone microendoscopic discectomy for HNP. For the recurrent HNP, the sMED interlaminar approach was selected because the HNP occurred at the level of L5-S1; the percutaneous endoscopic transforaminal approach was not possible for anatomical reasons. To perform sMED via the interlaminar approach, we employed new, specially made devices to enable us to use this technique. In conclusion, sMED is the most minimally invasive approach available for HNP, and its limitations have been gradually eliminated with the introduction specially made devices. In the near future, percutaneous endoscopic surgery could be the gold standard for minimally invasive disc surgery.

New minimally invasive discectomy technique through the interlaminar space using a percutaneous endoscope

INTRODUCTION

The serial dilating technique used to access herniated discs at the L5-S1 space using percutaneous endoscopic discectomy (PED) via an 8 mm skin incision can possibly injure the S1 nerve root. In this paper, we describe in detail a new surgical procedure to safely access the disc and to avoid the nerve root damage. This small-incision endoscopic technique, small-incision microendoscopic discectomy (sMED), mimics microendoscopic discectomy and applies PED.

MATERIALS AND SURGICAL TECHNIQUE

The sMED approach is similar to the well-established microendoscopic discectomy technique. To secure the surgical field, a duckbill-type PED cannula is used. Following laminotomy of L5 using a high-speed drill, the ligamentum flavum is partially removed using the Kerrison rongeur. Using the curved nerve root retractor, the S1 nerve root is gradually and gently moved caudally. Following the compete retraction of the S1 nerve root to the caudal side of the herniated nucleus pulposus (HNP), the nerve root is retracted safely medially and caudally using the bill side of the duckbill PED cannula. Next, using the HNP rongeur for PED, the HNP is removed piece by piece until the nerve root is decompressed. A total of 30 patients with HNP at the L5-S1 level underwent sMED. In all cases, HNP was successfully removed and patients showed improvement following surgery. Only one patient complained of moderate radiculopathy at the final visit. No complications were encountered.

DISCUSSION

We introduced a minimally invasive technique to safely remove HNP at the L5-S1 level. sMED is possibly the least invasive technique for HNP removal at the L5-S1 level.

Endoscopic removal of herniated nucleus pulposus migrated dorsally to the dural sac

A herniated nucleus pulposus (HNP) migrated dorsally to the dural sac is a rare condition. Here, we present a case, in which the HNP was removed with minimally invasive spinal endoscopy. A 54-year-old man presented complaining of left leg pain and paresis. Neurologic findings and an MRI suggested an epidural tumor or a dorsally migrated HNP compressing the S1 nerve root and dural sac. With a spinal endoscope, careful laminotomy of caudal L5 and cranial S1 was made. En bloc flavectomy exposed a mass covered with a thin capsule. The mass was identified as a dorsally migrated HNP. After complete HNP fragment removal, the dural sac and S1 nerve root were decompressed. Immediately postoperative, the leg pain subsided and motor function normalized, although the patient complained of numbness at the S1 dermatome area. In summary, a large HNP that had migrated dorsally to the dural sac was successfully removed endoscopically.

Spondylolysis originates in the ventral aspect of the pars interarticularis: a clinical and biomechanical study

Lumbar spondylolysis is a stress fracture of the pars interarticularis. We have evaluated the site of origin of the fracture clinically and biomechanically. Ten adolescents with incomplete stress fractures of the pars (four bilateral) were included in our study. There were seven boys and three girls aged between 11 and 17 years. The site of the fracture was confirmed by axial and sagittal reconstructed CT. The maximum principal tensile stresses and their locations in the L5 pars during lumbar movement were calculated using a three-dimensional finite-element model of the L3-S1 segment. In all ten patients the fracture line was seen only at the caudal-ventral aspect of the pars and did not spread completely to the craniodorsal aspect. According to the finite-element analysis, the higher stresses were found at the caudal-ventral aspect in all loading modes. In extension, the stress was twofold higher in the ventral than in the dorsal aspect. Our radiological and biomechanical results were in agreement with our clinical observations.

Minimally invasive endoscopic bilateral decompression with a unilateral approach (endo-BiDUA) for elderly patients with lumbar spinal canal stenosis

OBJECTIVES

Endoscopic spinal surgery has become increasingly common year for year because it is a minimally invasive procedure. In our hospital, we introduced endoscopic bilateral decompression with a unilateral approach (endo-BiDUA) in 2006. In this paper, we review clinically and radiographically the elderly patients who underwent the endo-BiDUA.

METHODS

Fifteen patients aged over 65 years were included in this review. They had undergone endo-BiDUA between January 2006 and July 2008. Operation time, blood loss, complications, clinical outcome using the Japanese Orthopedic Association (JOA) score, and enlargement ratio of the dural tube on magnetic resonance imaging (MRI), were evaluated.

RESULTS

The mean operation time per level of endo-BiDUA was 144 min. Blood loss was about 60.2 mL. One patient had a post-surgical hematoma and required an additional laminectomy and removal of the hematoma 2 days after the surgery. No other complications such as dural tear, nerve root injury, or infection were encountered. All patients but one, who had a post-surgical hematoma, could start walking within 2 days following the surgery. Before surgery, the mean JOA score was 17.0 and it improved to about 23.3 after the surgery. The area of the dural tube increased to 408.0% after the surgery (range: 211-774%).

CONCLUSIONS

Endo-BiDUA facilitated the return of elderly patients with lumbar spinal canal stenosis to their original daily activities.

The effect of rheumatoid arthritis on the anatomy of the female cervical spine

The effect of rheumatoid arthritis on the anatomy of the cervical spine has not been clearly documented. We studied 129 female patients, 90 with rheumatoid arthritis and 39 with other pathologies (the control group). There were 21 patients in the control group with a diagnosis of cervical spondylotic myelopathy, and 18 with ossification of the posterior longitudinal ligament. All had plain lateral radiographs taken of the cervical spine as well as a reconstructed CT scan. The axial diameter of the width of the pedicle, the thickness of the lateral mass, the height of the isthmus and internal height were measured. The transverse diameter of the transverse foramen (d1) and that of the spinal canal (d2) were measured, and the ratio d1/d2 calculated.

The width of the pedicles and the thickness of the lateral masses were significantly less in patients with rheumatoid arthritis than in those with other pathologies. The area of the transverse foramina in patients with rheumatoid arthritis was significantly greater than that in the other patients. The ratio of d1 to d2 was not significantly different. A high-riding vertebral artery was noted in 33.9% of the patients with rheumatoid arthritis and in 7.7% of those with other pathologies. This difference was statistically significant. In the rheumatoid group there was a significant correlation between isthmus height and vertical subluxation and between internal height and vertical subluxation.

Conservative treatment of lumbar spondylolysis in childhood and adolescence

It has been noted that bony union of a pars defect can be achieved in children if they wear a trunk brace. Our aim was to evaluate how the stage of the defect on CT and the presence or absence of high signal change in the adjacent pedicle on T2-weighted MRI were related to bony healing. We treated 23 children conservatively for at least three months. There were 19 boys and four girls with a mean age of 13.5 years (7 to 17). They were asked to refrain from sporting activity and to wear a Damen soft thoracolumbosacral type brace. There were 41 pars defects in 23 patients. These were classified as an early, progressive or terminal stage on CT. The early-stage lesions had a hairline crack in the pars interarticularis, which became a gap in the progressive stage. A terminal-stage defect was equivalent to a pseudarthrosis. On the T2-weighted MR scan the presence or absence of high signal change in the adjacent pedicle was assessed and on this basis the defects were divided into high signal change-positive or -negative. Healing of the defect was assessed by CT.

In all, 13 (87%) of the 15 early defects healed. Of 19 progressive defects, only six (32%) healed. None of the seven terminal defects healed. Of the 26 high signal change-positive defects 20 (77%) healed after conservative treatment whereas none of the high signal change-negative defects did so. We concluded that an early-stage defect on CT and high signal change in the adjacent pedicle on a T2-weighted MR scan are useful predictors of bony healing of a pars defect in children after conservative treatment.

Callus formation during healing of the repaired tendon-bone junction. A rat experimental model

This study was undertaken to elucidate the mechanism of biological repair at the tendon-bone junction in a rat model. The stump of the toe flexor tendon was sutured to a drilled hole in the tibia (tendon suture group, n = 23) to investigate healing of the tendon-bone junction both radiologically and histologically. Radiological and histological findings were compared with those observed in a sham control group where the bone alone was drilled (n = 19). The biomechanical strength of the repaired junction was confirmed by pull-out testing six weeks after surgery in four rats in the tendon suture group. Callus formation was observed at the site of repair in the tendon suture group, whereas in the sham group callus formation was minimal. During the pull-out test, the repaired tendon-bone junction did not fail because the musculotendinous junction always disrupted first. In order to understand the factors that influenced callus formation at the site of repair, four further groups were evaluated. The nature of the sutured tendon itself was investigated by analysing healing of a tendon stump after necrosis had been induced with liquid nitrogen in 16 cases. A proximal suture group (n = 16) and a partial tenotomy group (n = 16) were prepared to investigate the effects of biomechanical loading on the site of repair. Finally, a group where the periosteum had been excised at the site of repair (n = 16) was examined to study the role of the periosteum. These four groups showed less callus formation radiologically and histologically than did the tendon suture group. In conclusion, the sutured tendon-bone junction healed and achieved mechanical strength at six weeks after suturing, showing good local callus formation. The viability of the tendon stump, mechanical loading and intact periosteum were all found to be important factors for better callus formation at a repaired tendon-bone junction.

Minimally invasive technique for direct repair of the pars defects in young adults using a spinal endoscope: a technical note

Pars defect (spondylolysis) of the lumbar spine can cause chronic low back pain, and it sometimes requires surgical intervention. Direct repair is selected for the surgery if young adult patients do not present significant disc degeneration and lumbar instability. In order to lessen damages of back muscles during surgery, we added the use of a spinal endoscope to the "Buck's screwing procedure" the direct repair. There are four steps in this procedure: 1) identification of the defect, 2) curettage (refresh) of the defect, 3) percutaneous insertion of the annulated screws and 4) cancellous bone grafting. All these steps can be done endoscopically. We treated 3 young adults--a baseball player, a professional cycle-racer and a sculptor--using this endoscopic procedure. There were no complications during or after the operation. Union was obtained in all defects within 3 months, and they returned to their previous activities within 6 months after the surgery.

Minimally invasive endoscopic removal of a herniated nucleus pulposus that had migrated to the S1 nerve root foramen

In this report, we described an adult case with a lumbar herniated nucleus pulposus that had migrated to the S1 nerve root foramen from L5-S1 disc space. Endoscopically, the migrated mass was successfully removed after laminectomy at the S1 with a small skin incision of 20 mm in length. Unlike the other levels, the intraforaminally migrated mass along the S1 root can be excised without any removal of the facet joints; therefore, additional spinal fusion is not necessary. Thus, an S1 foraminal migrated mass can be a good surgical candidate for minimally invasive endoscopic surgery.

Locking of the metacarpophalangeal joint as a result of the shape of the metacarpal head in achondroplasia

A 21 year-old woman with achondroplasia exhibited locking of the metacarpophalangeal joint of the right index finger which required surgery to release the joint. Locking was confirmed to be due to entrapment of the fan-like part of the radial collateral ligament on a metacarpal head prominence arising from epiphysial thickening.

Minimally Invasive Decompression for Lumbar Spinal Canal Stenosis in Younger Age Patients Could Lead to Higher Stresses in the Remaining Neural Arch - A Finite Element Investigation

BACKGROUND AND PURPOSE

A young patient group with the symptoms of acquired spinal stenosis has been identified recently in the literature. The patients between 25-50 years of age were found to have signs of lumbar spinal stenosis because of degenerative spinal changes. Some of them were operated on using the same limited decompression approaches as the older patients. However, this group differs from the geriatric population due to the scarcity of remodeling degenerative signs at the spine. Therefore, the possible ligamentous laxity, facet joint degeneration or only the removal of some spinal structures could lead to the increased stresses in the remaining spinal arch and could have an unfavorable course of events after the procedure. A biomechanical study has been done using an experimentally validated finite element model (FEM) of the intact L3-S1 lumbar spine to elucidate the influence of the limited decompression on range of motion (ROM) and stress distribution on the neural arch in this patient group.

METHODS

We simulated unilateral laminotomy L4 and medial facetectomy L4-5, medial facetectomy L4-5 and lateral fenestration of L5 pars interarticularis, combined transarticular lateral and medial approach with partial facetectomy L4-5, "port-hole" decompression at the L4 level, and hemilaminectomy L4 with medial facetectomy L4-5. The ROM and maximum von Mises stresses were analyzed in flexion, extension, lateral bending, and axial rotation in response to a 10.6 Nm moment with 400 N axial compression. The data were compared with the intact spine and hemilaminectomy L4 with medial facetectomy L4-5 models.

RESULTS AND CONCLUSION

The investigation revealed almost the same ROM after simulation but a considerable increase in stresses at both the pars interarticularis and the inferior facet after limited decompressions, especially in extension and rotation to the contralateral side. Stresses at the contralateral L4 pedicle were highest after L4 hemilaminectomy and medial facetectomy L4-5. Due to the observed increases in stresses, the surgeon should be aware of the possibilities of stress-fractures in this patient group.

Extruded lumbar osseous endplate causing long-term radiculopathy in an adult: an endoscopic excision

In this report, we described an adult case that had a long-term radiculopathy due to an extruded osseous endplate of the lumbar spine at the L5-S1 intervertebral disc level. The osseous material inside the extruded material was not absorbed, and it had continued compressing the nerve root for one year. Endoscopically, the bony fragment was successfully removed. After the surgery, the patient's symptom disappeared, and neurological deficits became normalized. In conclusion, we propose that surgical intervention should be taken into account for the treatment of HNP, when the extruded material contains bony fragment such as osseous endplate.

Preservation of C7 spinous process does not influence the long-term outcome after laminoplasty for cervical spondylotic myelopathy

Axial pain is one of the major complications after laminoplasty, and preservation of C7 spinous process during the procedure can reduce the axial pain. However, it has not been elucidated whether laminoplasty preserving the C7 spinous process can maintain neurological improvement for a long time. The purpose of our retrospective study was to investigate the long-term neurological outcome after open-door laminoplasty preserving the C7 spinous process for cervical spondylotic myelopathy (CSM). Clinical and radiological outcomes were analysed in 42 patients who underwent open-door laminoplasty preserving C7 spinous process and followed up for more than 5 years. Neurological function was evaluated by means of the Japanese Orthopaedic Association (JOA) scoring system for cervical myelopathy. Axial pain was assessed using a visual analog scale (VAS) at the last examination. Alignment and motion of the cervical spine were measured from radiographs, and magnetic resonance imaging (MRI) was used to evaluate postoperative compression at C7. The mean JOA score was 9.4 before surgery and 12.0 at the latest follow-up. The mean VAS score in 26 patients score was 9.7/100. No compression of the spinal cord was observed in any MRI at the latest follow-up. Preservation of the C7 spinous process does not influence the long-term outcome of CSM after laminoplasty. Although we did not have a comparative group, the procedure described here should be considered as the solution.

Adult onset tethered cord syndrome associated with intradural dermoid cyst. A case report

STUDY DESIGN

A case report and a review of literature.

OBJECTIVES

To describe a rare case of adult onset tethered cord syndrome associated with intradural dermoid cyst.

SETTING

General Orthopedics, Japan.

METHODS

A 50-year-old woman was referred to us because of right leg pain and pollakiuria. Neurological examinations and radiological assessments including myelography, computerized tomography scan and Magnetic resonance image were carried out. We diagnosed it as the adult onset tethered cord syndrome associated with an intradural cystic lesion.

RESULTS

The cystic lesion was totally removed following laminectomy from L5 through S4. Histologically, the tumor was diagnosed as a dermoid cyst.

CONCLUSIONS

Intradural dermoid could produce adult onset tethered cord syndrome, but it was not reported in the English literatures to our knowledge.

Biomechanical comparison of lumbar spine with or without spina bifida occulta. A finite element analysis

STUDY DESIGN

Biomechanical study using finite element model (FEM) of lumbar spine.

OBJECTIVES

Very high coincidence of spina bifida occulta (SBO) has been reported more than in 60% of lumbar spondylolysis. The altered biomechanics due to SBO is one considerable factor for this coincidence. Thus, in this study, the biomechanical changes in the lumbar spine due to the presence of SBO were evaluated.

SETTING

United States of America (USA).

METHODS

An experimentally validated three-dimensional nonlinear FEM of the intact ligamentous L3-S1 segment was used and modified to simulate two kinds of SBO at L5. One model had SBO with no change in the length of the spinous process and the other had a small dysplastic spinous process. Von Mises stresses at pars interarticularis were analyzed in the six degrees of lumbar motion with 400 N axial compression, which simulates the standing position. The range of motion at L4/5 and L5/S1 were also calculated.

RESULTS

It was observed that the stresses in all the models were similar, and there was no change in the highest stress value when compared to the intact model. The range of motion was also similar in all the models. The lumbar kinematics of SBO was thus shown to be similar to the intact model.

CONCLUSION

SBO does not alter lumbar biomechanics with respect to stress and range of motion. The high coincidence of spondylolysis in spines with SBO may not be due to the mechanical factors.

Biomechanical Rationale of Endoscopic Decompression for Lumbar Spondylolysis as an Effective Minimally Invasive Procedure - A Study Based on the Finite Element Analysis

We evaluated the biomechanical behavior of the endoscopic decompression for lumbar spondylolysis using the finite element technique. An experimentally validated, 3-dimensional, non-linear finite element model of the intact L3 - 5 segment was modified to create the L4 bilateral spondylolysis and left-sided endoscopic decompression. The model of Gill's laminectomy (conventional decompression surgery of the spondylolysis) was also created. The stress distributions in the disc and endplate regions were analyzed in response to 400 N compression and 10.6 Nm moment in clinically relevant modes. The results were compared among three models. During the flexion motion, the pressure in the L4/5 nucleus pulposus was 0.09, 0.09 and 0.16 (MPa) for spondylolysis, endoscopic decompression and Gill's procedure, respectively. The corresponding stresses in the annulus fibrosus were 0.65, 0.65 and 1.25 (MPa), respectively. The stress at the adjoining endplates showed an about 2-fold increase in the Gill's procedure compared to the other two models. The stress values for the endoscopic and spondylolysis models were of similar magnitudes. In the other motions, i. e., extension, lateral bending, or axial rotation, the results were similar among all of the models. These results indicate that the Gill's procedure may lead to an increase in intradiscal pressure (IDP) and other biomechanical parameters after the surgery during flexion, whereas the endoscopic decompression did not change the segment mechanics after the surgery, as compared to the spondylolysis alone case. In conclusion, endoscopic decompression of the spondylolysis, as a minimally invasive surgery, does not alert mechanical stability by itself.

Union of defects in the pars interarticularis of the lumbar spine in children and adolescents

Lumbar spondylolysis can heal with conservative treatment, but few attempts have been made to identify factors which may affect union of the defects in the pars. We have evaluated, retrospectively, the effects of prognostic variables on bony union of pars defects in 134 young patients less than 18 years of age with 239 defects of the pars who had been treated conservatively. All patients were evaluated by CT scans when first seen and more than six months later at follow-up.

The results showed that the spinal level and the stage of the defects were the predominant factors. The site of the defects in the pars, the presence or development of spondylolisthesis, the condition of the contralateral pars, the degree of lumbar lordosis and the degree of lumbar inclination all significantly affected union.

Effects of active recovery under a decreasing work load following intense muscular exercise on intramuscular energy metabolism

The effect of active recovery at a decreasing % of MVC following intense muscular exercise on intramuscular pH was investigated in vivo using 31P-MRS. Seven healthy men participated, and their right wrist flexor muscle group was examined. The subjects were asked to flex their right wrist at 60 % of the maximum voluntary contraction (MVC) every 2 s until the intracellular pH in the wrist flexor muscle decreased to 6.4. After the exercise period, the subjects underwent active or passive recovery for 10 min. For the active recovery (AR), the subject was asked to continue exercising at a decreasing % of MVC, decreasing from 25 to 5 % MVC every two min during AR. 31P-MR-spectra were obtained throughout the experiments, and from the spectra the intracellular pH (pHi) was calculated as an indicator of intracellular events. AR data were compared to data collected during passive recovery (PR). During AR, the pHi increased immediately after the exercise period; whereas in that of PR, it did not recover within 5 minutes after exercise. The results suggested that mild exercise was an effective manoeuver to promote recovery from intramuscular metabolic acidosis.

Characteristics of velocity-controlled knee movement in patients with cervical compression myelopathy: what is the optimal rehabilitation exercise for spastic gait?

STUDY DESIGN

The isokinetic strength of knee extensors and flexors was measured at various controlled velocities in patients with spastic paraparesis caused by cervical compression myelopathy.

OBJECTIVE

To evaluate leg function objectively in patients with myelopathy.

SUMMARY OF BACKGROUND DATA

Cervical compression myelopathy causes varying degrees of spastic paresis in the legs and affects the activities of patients. However, the leg function characteristics of the patients have not been fully elucidated.

METHODS

Velocity-controlled voluntary knee movements were studied in 39 patients (25 men and 14 women) with compression myelopathy. Their mean age was 60.2 years (range, 44-77 years). The patients were divided into Group A (ambulation without aid, n = 22) and Group AA (ambulation with aid, n = 17). Isometric peak torque values were measured in knee flexor and extensor muscles at 60 degrees of knee flexion, and isokinetic peak torque values were determined in maximal voluntary concentric movements of these muscles at constant angle velocities of 40 degrees, 80 degrees, 120 degrees, 160 degrees, and 180 degrees per second. The relative strength (percentage of isometric peak torque value) of the isokinetic motion was calculated at each velocity.

RESULTS

In both groups, the relative strength decreased as the velocity increased, and the degree of reduced strength in the flexors at the high velocities of 160 degrees and 180 degrees per second was significantly greater in Group AA than in Group A (P < 0.05), whereas no significant difference was found in the extensors between the groups.

CONCLUSIONS

The results indicate that isokinetic strength at a high velocity may reflect the severity of spastic paresis in the legs resulting from compression myelopathy.

Slippage mechanism of pediatric spondylolysis: biomechanical study using immature calf spines

STUDY DESIGN

This study analyzed the skeletal-age-dependent strength of the lumbar growth plate to resist anterior shearing forces using the MTS system in the immature calf spine with pars defects.

OBJECTIVE

To clarify the pathomechanism of the skeletal-age-dependent incidence of slippage in pediatric patients with pars defects by comparing the strength of the lumbar growth plate among three skeletal age groups.

SUMMARY OF BACKGROUND DATA

Isthmic spondylolisthesis occurs and progresses more frequently during the growth period, whereas it is rare afterward. However, little evidence has been demonstrated to elucidate the etiology.

METHODS

For this study, 15 lumbar functional spine units were divided into three groups according to their skeletal ages. Five were from neonates (Group 1), five from calves approximately 2 months old (Group 2), and five from calves about 24 months old (Group 3). An anterior shearing force was applied to each specimen until failure, after bilateral pars defects were created. Failure load (newtons) and displacement at failure (millimeters) were calculated from the load-displacement curve. The site of failure was confirmed by plain radiograph.

RESULTS

All 15 functional spine units failed at the growth plate. The failure load was 242.79 +/- 46.05 N in Group 1, 986.40 +/- 124.16 N in Group 2, and 2024.54 +/- 245.53 N in Group 3. Statistically significant differences were found among the three groups (P < 0.05). The displacement at failure was 7.52 +/- 1.84 mm in Group 1, 11.10 +/- 2.30 mm in Group 2, and 8.15 +/- 2.66 mm in Group 3. There were no significant differences among the groups.

CONCLUSIONS

The results indicate that the strength of the growth plate, the weakest link in this model, against anterior shearing forces depends on the skeletal maturity, and that the biomechanical weakness of the growth plate plays an important role in the slippage mechanism.

Evaluation of disuse atrophy of rat skeletal muscle based on muscle energy metabolism assessed by 31P-MRS

The purpose of this study was to evaluate disuse atrophy of skeletal muscle using a hind-limb suspension model, with special reference to energy metabolism. Twenty-four Sprague-Dawley rats were divided into four groups: control group (C), hind-limb suspended for 3 days (HS-3), for 7 days (HS-7) and for 14 days (HS-14). The gastrocnemius-plantaris-soleus (GPS) muscles in each group were subjected to the following measurements. After a 2-min rest, contraction of the GPS muscles was induced by electrical stimulation of the sciatic nerve at 0.25 Hz for 10 min, then the frequency was increased to 0.5 and 1.0 Hz every 10 min. During the stimulation, twitch forces were recorded by a strain gauge, and 31P-MRS was performed simultaneously. Maximum tension was measured at the muscle contraction induced at 0.25 Hz; the wet weight of the whole and each muscle in the GPS muscles was also measured. From the 31P-MR spectra during muscle contraction, the oxidative capacity was calculated and compared among the groups. The weights of the whole GPS muscles in C, HS-3, HS-7 and HS-14, were 2.66 +/- 0.09, 2.39 +/- 0.21, 2.34 +/- 0.21 and 2.18 +/- 0.14 (g) respectively. Thus, the muscle mass significantly decreased with time (p < 0.05). Among the GPS muscles, the decrease in weight of the soleus muscle was especially remarkable; in the HS-14 group its weight decreased to 60% of that in the C group. We evaluated maximum tension and oxidative capacity as the muscle function. The maximum tensions in C, HS-3, HS-7 and HS-14 were 519 +/- 43, 446 +/- 66, 450 +/- 23 and 465 +/- 29 (g), respectively. This was significantly greater in the C group than in any other groups, however there were no significant differences among the three HS groups. The oxidative capacity during muscle contraction in the C group was higher than in any HS group and it did not further decrease even if the suspension of the limbs was prolonged beyond 3 days. The present study showed that in disuse atrophy, muscle mass and muscle function did not change simultaneously. Thus, it is necessary to develop countermeasures to prevent muscle atrophy and muscle function deterioration independently.

Development of spondylolytic olisthesis in adolescents

BACKGROUND CONTEXT

Although it has been well documented that slippage in patients with spondylolysis is most prevalent during the growth period, the exact time when slippage initiates and halts during the growth period is still unknown. Moreover, the contribution of spinal deformities, such as wedging of the vertebral body to the slippage, remains controversial.

PURPOSE

To clarify when slippage in pediatric spondylolysis initiates and halts.

STUDY DESIGN

Retrospective study.

PATIENT SAMPLE

We radiographically examined 46 athletes under 18 years of age with spondylolysis at the fifth lumbar vertebra (L5). The mean age at the first consultation was 13.3 years. The average follow-up period was 6.0 years.

OUTCOME MEASURES

Longitudinal observation of slippage at L5 on radiogram in correlation with the maturity of the lumbar spine.

METHODS

From a lateral radiogram of each patient, percent slippage, lumbar index (LI), and skeletal age of the affected vertebra were measured. Changes in the percent slippage over time were investigated, and the correlation between the percent slippage and LI was analyzed.

RESULTS

From the cartilaginous stage to the apophyseal stage, the slippage increased in 80.0% of the patients (16 of 20). From the cartilaginous stage to the epiphyseal stage, slippage increased in 11.1% of the patients (3 of 27). None of the patients (0 of 22) showed an increase after the epiphyseal stage. In 20 patients in whom slippage increased during the follow-up period, the percent slippage at the final consultation and the LI at the first consultation showed no significant correlation; however, the percent slippage and the LI at the final consultation were significantly (p<.01) correlated.

CONCLUSION

In conclusion, slippage was more prevalent in individuals of a younger skeletal age whose lumbar spine was immature, and it halted during the epiphyseal stage when the growth period was over and the vertebra matured. Furthermore, the results suggest that wedge deformity of an affected vertebra might be the result rather than the cause of slippage.

Effects of ovariectomy on intramuscular energy metabolism in young rats: how does sports-related-amenorrhea affect muscles of young female athletes?

The purpose of this study was to evaluate the effects of ovariectomy on intramuscular energy metabolism in young rats. Twenty-four Sprague-Dawley rats (7 weeks old) were used. Twelve of them underwent ovariectomy (OVX), and the others were sham-operated on. Seven OVX rats were examined 1-week after surgery (OVX-1 group), and the other five, 4 weeks after surgery (OVX-4 group). The gastrocnemius-plantaris-soleus (GPS) muscles group was subjected to the following measurements, and the data were compared with those of the sham group (Sham-1: n = 7, or Sham-4 group: n = 5). From the 31P-MR spectra of the GPS muscles group at rest and during electric stimulation, the muscular oxidative capacity was measured. Maximum tension and wet weight of the whole GPS muscles group were also measured. Body weight in the OVX-4 group was significantly (p < 0.01) larger than that in the Sham-4 group. The weights of the whole GPS muscles group in the Sham-1, Sham-4, OVX-1 and OVX-4 groups were 1.17, 1.51, 1.25 and 1.71 (g), respectively. The muscle weight in the OVX group tended to be greater than that in the Sham group (p < 0.10). The maximum tension and oxidative capacity did not differ significantly among the groups. These data indicated that in young rats, ovariectomy induced an increase in body and muscle weight, but did not affect the maximum tension nor oxidative capacity.

The pathomechanism of spondylolytic spondylolisthesis in immature primate lumbar spines in vitro and finite element assessments

STUDY DESIGN

Immature Chacma baboon (Papio ursinus) spine specimens were used to determine load-displacement behavior as related to disc injury. This was accomplished through the application of A-P shear force until failure of FSUs with pars defects. Several finite element models (FEMs) of the FSU were developed to study the mechanism of slippage in immature baboon lumbar spines.

OBJECTIVES

The purpose was to show that spondylolisthesis (olisthesis) always occurs through the growth plate using a model similar to immature human lumbar spines. Using FEMs, the roles of facet orientation, pars interarticularis thickness, and a weak growth-plate in producing slippage were examined.

SUMMARY OF BACKGROUND DATA

Progression from spondylolysis (lysis) to olisthesis occurs, most often, during the adolescent growth spurt. The biomechanical literature dealing with the slippage mechanism in the immature lumbar spine does not provide a clear understanding and is sparse.

METHODS

Several groups of FSUs were subjected to A-P shear force until failure. The results provided displacement at failure as a function of disc injury and flexion-extension fatigue. A bilateral pars defect was created in each specimen prior to application of A-P shear force using an MTS machine. Failure sites were assessed radiographically and histologically. A nonlinear 3-D FEM of the intact L4-L5 was created from CT scans. The model was modified to predict the effects of a pars fracture, a thin pars, a weak growth plate, and facet orientation on the shear load through the growth plate and stresses in the pars.

RESULTS

Experimentally, failures always occurred through the growth-plate in the disc intact and disc-incised groups. In the intact FEM, the growth plate carried21% of the applied A-P shear force. The load increased when the facets were more sagittally oriented. The effect of thin pars and/or weaker growth plate was an increase in stresses in the pars. Changes in the load through the growth plate were minimal.

CONCLUSIONS

The weakest link in immature baboon lumbar functional spinal units (FSUs) with lysis during an A-P shear load was the growth plate, between the cartilaginous and osseous end plates. Surgeons may assess this lesion on MRI views, thereby predicting the possible development and preventing progression of olisthesis. Finite element model results predict that more sagittally orientated facets and/or a pars fracture are prerequisites for olisthesis to occur.

Effects of specific warm-up at various intensities on energy metabolism during subsequent exercise

BACKGROUND

To investigate the effects of specific warm-up at various intensities on energy metabolism during subsequent intense exercise.

METHODS

EXPERIMENTAL DESIGN

specific warm-up was consisted of 3 sets of wrist flexions for 5 min, with each set followed by a 3-min rest. The intensity of specific warm-up was set at 20%, 30% or 40% of maximal voluntary contraction (MVC). The subjects then performed a set of wrist flexions at 60% MVC for 4 min as the criterion exercise. For the control experiment, criterion exercise was done without specific warm-up.

PARTICIPANTS

Five healthy volunteers.

MEASUREMENTS

using phosphorus-31 magnetic resonance spectroscopy, spectra were obtained from the wrist flexor muscles to determine the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) and intracellular pH.

RESULTS

The Pi/PCr during the criterion exercise after specific warm-up at any intensity was not significantly different from that without specific warm-up. The intracellular pH during the criterion exercise after specific warm-up at 30% or 40% MVC was significantly higher than that without specific warm-up.

CONCLUSIONS

These results indicate that mild warm-up exercise could inhibit the development of intracellular acidosis during subsequent intense exercise.

Biomechanical studies of a dynamized anterior thoracolumbar implant

STUDY DESIGN

An in vitro investigation into the biomechanical properties of a dynamized anterolateral compression implant that allows controlled subsidence.

OBJECTIVES

To determine the extent to which both modes of the anterolateral compression implant (controlled collapsing and rigid) are able to reestablish the stability of the lumbar spine after L4 corpectomy.

SUMMARY OF BACKGROUND DATA

Over time, anterior and posterior spinal implants have been associated with progressive angulation, and occasionally implant failure and breakage. To circumvent this occurrence and provide better graft loading, dynamized or collapsing devices for clinical use have been developed.

METHODS

Eight fresh calf spines (L1-L6) were placed in a biomechanical testing frame. Pure moments of 6 Nm were loaded onto the intact spine in six directions: flexion, extension, right and left lateral bending, and right and left axial rotation. A total L4 corpectomy then was performed, and the defect grafted with a wooden dowel. Loading was repeated after the specimens were stabilized using the two modes of the anterolateral compression implant in succession.

RESULTS

The results showed that both modes of the implant (the rigid mode in particular) restore the stiffness of the unstable spine to normal levels of flexion, extension, and right and left lateral bending, even to levels exceeding normal. These devices, however, fall short of achieving normal stability in right and left axial rotation.

CONCLUSION

In the cadaveric calf spine after L4 corpectomy, restoration of stability with a dynamized anterior spinal implant is possible in flexion, extension, and right and left lateral bending, but not in axial rotation.

Stability analysis of an enhanced load sharing posterior fixation device and its equivalent conventional device in a calf spine model

STUDY DESIGN

An in vitro test of calf spine lumbar segments to compare biomechanical stabilization of a rigid versus a dynamic posterior fixation device.

OBJECTIVES

To compare flexibility of a dynamic pedicle screw fixation device with an equivalent rigid device.

SUMMARY OF BACKGROUND DATA

Dynamic pedicle screw device studies are not as prevalent in the literature as studies of rigid devices. These devices contain the potential to enhance load sharing and optimize fusion potential while maintaining stability similar to that of rigid systems.

METHODS

Load-displacement tests were performed on intact and stabilized calf spines for the dynamic and rigid devices. Stability across a destabilized L3-L4 segment was restored by insertion of either a 6 mm x 40 mm dynamic or rigid pedicle screw fixation device across the L2-L4 segment. The screws then were removed, 7 mm x 45 mm pedicle screws of the opposite type were inserted, and the construct then was re-tested. Axial pull-out tests were performed to assess the likely effects of pedicle screw replacement on the load-displacement data.

RESULTS

Results indicated a 65% reduction in motion in flexion-extension and a 90% reduction in lateral bending across the destabilized level for both devices, compared with intact spine values. Reduction in axial rotation motion was much smaller than in other modes. Axial pull-out tests showed no weakening of the bone-screw interface.

CONCLUSIONS

Both devices provided significant stability of similar magnitudes in flexion, extension, and lateral bending. In axial rotation, the devices only could restore stability to levels similar to those in an intact spine. The dynamic device offers a design that may enhance load sharing without sacrificing construct stability.

The pathomechanism of isthmic lumbar spondylolisthesis. A biomechanical study in immature calf spines

STUDY DESIGN

Anterior shearing force was applied to immature calf lumbar functional spinal units until failure.

OBJECTIVES

To clarify the mechanism of slippage in immature calf lumbar spines with pars defects as a first step to understand the mechanism of spondylolisthesis in pediatric human lumbar spines.

SUMMARY OF BACKGROUND DATA

Progression from lysis to olisthesis occurs during the adolescent growth spurt. However, the mechanism of slippage in the immature lumbar spine has not yet been understood clearly.

METHODS

Bilateral pars defects were created at the rostral vertebra. The specimens then were assigned to one of the two groups: functional spinal units with intact disc (n = 5) and with disc dissected (n = 5). In the former group, the disc was left intact, whereas in the disc dissected group, the anterior longitudinal ligament and 75% of the anterior-to-posterior depth of the disc were incised along the mid-disc plane. Using a uniaxial MTS machine (MTS System, Minneapolis, MN), anteroposterior shearing force was applied to each specimen. Failure load and displacement at failure were calculated from the load--displacement curve. Failure sites also were assessed radiographically and histologically.

RESULTS

The five functional spinal units in the intact disc group failed at 973.8 +/- 78.1 N, whereas specimens in the disc dissected group failed at 986.4 +/- 124.2 N. The data showed no significant differences between the two groups. All the specimens showed displacement through the growth plates on radiographs. Histologically, failure was observed to occur between the superior growth plate and osseous endplate of caudal vertebra, indicating that this site is the weakest link.

CONCLUSIONS

The results suggest that in the pediatric immature lumbar spine with pars defects, slippage may occur between the growth plate and osseous endplate.

Neurocentral synchondrosis fracture in immature spines associated with pedicle screw type fixation devices

The purpose of this study is to clarify the weak point in immature lumbar vertebrae associated with pedicle screw instrumentation. Ten immature thoracic and lumbar vertebrae were collected from calf spines. After installation of 6- and 7-mm-diameter pedicle screws into the pedicles of each specimen, pullout force was applied to the screw using the uniaxial MTS system until failure. Tightening torque during installation was measured. From the load-displacement curve, failure load was calculated and failure site was confirmed by radiographs. Inner pedicle diameters were measured after the pullout test, and percent fills of the pedicle screw were calculated. Mean tightening torque was 1.4 or 2.1 (Nm), mean failure load was 852.5 or 1,015.0 (N), and mean percent fill was 81.4 or 93.5% for 6- or 7-mm screws, respectively. Tightening torque and percent fill in 7-mm screws were significantly (p < 0.01) greater than that in 6-mm screws; however, failure load showed no significant difference (p = 0.10) between the two screw groups. Failure by screw pullout occurred at the screw-bone interface or through the neurocentral synchondrosis (NS). NS fractures were observed in 20% of 6-mm screws, 60% of 7-mm screws, and 40% overall, whereas interface failures occurred in 80% of 6-mm screws, 40% of 7-mm screws, and 60% overall. In NS fracture group, tightening torque (p < 0.05) and percent fill (p < 0.01) were significantly greater than in the interface failure group. The results led us to conclude that the mechanism of the NS fracture is unclear. However, NS fracture could be one of the conceivable complications associated with pedicle screw fixation in the immature spine.

A protocol to evaluate semi-rigid pedicle screw systems

The objective of the current study was to develop an in vitro testing protocol to evaluate semi-rigid pedicle screw devices. A corpectomy model protocol exists to evaluate rigid spinal implants; however, semi-rigid devices are contraindicated for this condition. This paper describes a technique that simulates more closely the conditions a semi-rigid device would see in vivo. Finally, the new testing protocol is used to evaluate the DDS pedicle screw-cable system. Benefits and shortcomings of the new protocol are discussed.

Foramen magnum schwannoma with an unusual clinical presentation: case report

This case report illustrates a patient with a unilateral localized epidural schwannoma at C1-2 level, showing contralateral spinal cord symptoms and signs. The clinical presentation was compared with the neuroradiological examinations showing an epidural cord tumor at the right C1-C2 level. However, the neurological examination revealed contralateral hemiparesis and ipsilateral hemihypoalgesia, indicating a contralateral Brown-Sequard syndrome. We presumed with this slow growing tumor, contralateral cord involvement may result from counter pressure on the spinal cord, which may be generated by cord deviation and by frequent neck rotation.

Radial nerve palsy associated with slightly angulated pediatric supracondylar humerus fracture

This report reviews a case of radial nerve palsy associated with a supracondylar fracture of the right humerus. The patient was a four-year-old boy. Radiographs of the injury showed simple extension and a slightly angulated fracture. Complete radial nerve palsy was observed at the first consultation. After three months of conservative treatment without any obvious improvement, an operative exploration of the right radial nerve was conducted. Intraoperatively, the nerve was found to be transected, with both ends of the ruptured nerve buried in scar tissue at the fracture site. Five months after the nerve suture operation, the palsy was cured completely. This case shows that even a minimal displacement fracture can be associated with severe nerve injury that requires surgical treatment.

Is the intracellular pH threshold an anaerobic threshold from the view point of intracellular events?: a brief review

Intracellular biochemical changes could be monitored noninvasivery and continuously by using nuclear magnetic resonance (NMR). In about the last decade, intracellular behavior of phosphorus compounds and pH during muscle contraction in man have been studied by 31P nuclear magnetic resonance spectroscopy (31P-MRS). During incremental load, lactic acidosis was followed by a decline in intracellular pH. 31P-MRS studies has been definitely proved that this change in intracellular pH shows the threshold behavior. Some reports discussed the intracellular pH threshold (pHT) as an anaerobic threshold (AT) from the view point of intracellular events. However, our studies revealed that pHT did not reflect the onset of lactate production. In this article, studies of intracellular pH of working muscle were reviewed in relation to an anaerobic threshold.

Effect of active recovery on intracellular pH following muscle contraction, a 31P-MRS study

The effect of active recovery after intense muscular exercise was examined by 31P-MRS. Seven healthy males participated in this study, and their right wrist flexor muscles were examined. Each subject flexed the right wrist at 60% of the maximum voluntary contraction (MVC) until the intracellular pH in the wrist flexor muscle decreased to approximately 6.4. This was followed either by active recovery (AR) which consisted of 5, 10, 20, 30 or 40% MVC exercise, and by passive recovery (PR) during a 10-min-recovery period. The intracellular pH (pHi) recovered faster during AR at each condition than during PR. Besides, from the 2nd to the 5th min of the recovery period, the pHi was significantly higher during AR than during PR. The quadratic regression curve of pHi recovery during the 10-min-recovery-period against the % MVC was obtained. The optimal contraction intensity determined from this curve was 8.7% MVC for a 10-min-recovery-period. The optimal levels were determined for another recovery duration within 10 min, and the level decreased with the prolonged recovery duration. These data suggest that mild exercise is an effective maneuver to promote the recovery from intracellular metabolic acidosis, and that the intensity of the recovery exercise should be determined according to the cooling down duration or the resting interval before the subsequent exercise performance.

Thresholds for decrease in intracellular pH and increase in blood lactate during progressive exercise: 31P-MRS study

The purpose of this study was to compare the intramuscular and the intravascular events in relation to energy metabolism during progressive arm exercise. Twelve healthy untrained Japanese males participated in this study as subjects. They performed wrist flexion in a ramp incremental load of 0.14 W/min until exhaustion. 31P-MR spectra were obtained from wrist flexor muscle before and throughout the exercise. Venous blood was also sampled from antecubital vein with one minute interval during the exercise, and a change in plasma lactate concentration (La) was observed. Intracellular pH (pH) was calculated from a chemical shift between phosphocreatine (PCr) and inorganic phosphate (Pi) of the 31P-MR spectra. Change in pH showed a threshold behavior during exercise. Threshold points at decline in pH (pHT), increase in Pi/PCr (PT), and increase in La (LT) were determined by piecewise linear regression analysis of minutes-by-minutes data. Mean values of pHT, PT and LT were 43.0, 42.5, and 24.8% of maximal work rate, respectively. LT was significantly smaller than pHT and PT. This result suggests that lactic acidosis has already existed when pH is kept at resting level, and pHT reflects the capacity of remaining intracellular biochemical homeostasis, which might be one of the physiological indices of muscle fatigue.

[Changes in intracellular pH of working muscle during constant and stepwise incremental load exercise]

In this study, subjects performed wrist flexion in isokinetic manner by using CYBEX dynamometer while their right forearm was attached in a MR magnet. 31P-MR spectra were obtained from wrist flexor muscles before and throughout the exercise. Intracellular pH of muscle was calculated from the chemical shift between phosphocreatine (PCr) and inorganic phosphate (Pi). Fifteen Japanese males volunteered as subjects. They performed two experimental protocols, i. e. constant load test (CT) and stepwise incremental load test (IT). In CT, 10 of the subjects were participated. After 2 minutes rest, wrist flexion of 10, 20, 30, 40 or 50% of maximal voluntary contraction force (MVC) was performed at 2 seconds intervals for 15 minutes. In IT, 14 including 9 of CT were participated. They performed wrist flexion in incremental contraction force of 5 steps from 10% to 50% of MVC for 3 minutes in each step. Changes in intracellular pH of muscle against contraction level show non-linear relationships both in CT and IT. From this relationship we calculated the contraction level at which pH was 6.9 (%MVC6.9). Mean values of obtained %MVC6.9 by CT and by IT were 29.3 and 30.0% of MVC, respectively. And, significant correlation was found between %MVC6.9 by CT and by IT. This result shows that %MVC6.9 was a reproducible index independent of the type of exercise test, i. e. constant or incremental load test, and might reflect the physiological characteristics of the muscle.

31P-MRS study of change in intracellular pH during sustained static contractions in human

31P-MRS spectra were obtained from human first dorsal interosseous muscle during and after the voluntary static abduction of the index finger. Endurance tasks were performed at randomly assigned contraction levels of 15, 20, 30 and 40% of maximal voluntary contraction (MVC). Muscle pH was calculated according to Taylor et al. (1983) using chemical shift between inorganic phosphate (Pi) and phosphocreatine (PCr) on the 31P-MRS spectra. Mean values of endurance times of static contractions were 7.25, 5.33 and 3.08 minutes for 20, 30 and 40% MVC, respectively. At 15% MVC, all of the four subjects maintained contraction for 30 minutes, and the contractions were terminated at 30 minutes. Muscle pH at the onset of contractions were 7.12, 6.98, 7.01 and 7.08 for 15, 20, 30 and 40% MVC, respectively. At the end of contractions when the subject could not maintain the force level, muscle pH were 6.07, 5.97 and 5.94 for 20, 30 and 40% MVC, respectively. There was no significant difference in muscle pH at the end of contractions between three conditions by one-way ANOVA. In conclusion, there was a critical muscle pH of about 6.0 where static contractions could not be maintained.