Cyclic testing of flexor tendon repairs: an in vitro biomechanical study

Forty cadaveric flexor digitorum profundus tendons were repaired using the Tajima, Halsted, Silfverskiold, or Savage techniques. The tendons were cyclically loaded in sets of 4,000 cycles beginning at 25 N and increasing by 10-N increments until failure occurred. Gap formation was continuously monitored with an extensiometer. Only the Savage repair group consistently withstood 4,000 cycles of 25-N loading, with respect to 2-mm gap formation and repair rupture. Tendon repairs subjected to cyclic loading demonstrated gap formation and repair rupture at lower loads than with static testing. Of the methods of flexor tendon repair tested, only the Savage technique could withstand simulated early active motion.     

Two reconstructive techniques for flatfoot deformity comparing contact characteristics of the hindfoot joints

The effect of two different methods of reconstruction of flatfoot deformity and the role of the posterior tibial tendon on the contact characteristics of the hindfoot joints were quantified using pressure-sensitive film. Each of 10 cadaver feet was loaded quasi-statically by an axial compressive force to simulate varying loads. First, a specimen was tested intact, then it was tested after sectioning the spring ligament and loading the specimen cyclically to create one type of flatfoot deformity. It was then tested again after reconstructing the deformity. Reconstructions used were the Dillwyn-Evans procedure (bone graft in osteotomy of the calcaneus) or the calcaneocuboid distraction arthrodesis (CCDA). We found that surgically produced flatfoot deformity altered mainly the talonavicular joint, by decreasing its contact area. The Dillwyn-Evans method had less effect on the talonavicular joint (altering 2 of 6 measured parameters) than the CCDA (3 of 6) and more effect on the anteriomedial facet (altering 3 of 6 parameters) than the CCDA (1 of 6). The Dillwyn-Evans method had more effect on the posterior facet (altering 2 of 6 measured parameters) than the CCDA (1 of 6). Function of the posterior tibial tendon had no effect on contact characteristics of the hindfoot joints after either type of reconstruction. These findings are based on measurements using a quasi-statically-loaded foot model at three selected positions, and results may be different with dynamic loading.     

The role of anteromedial foraminotomy and the uncovertebral joints in the stability of the cervical spine. A biomechanical study

STUDY DESIGN: The biomechanical role of the cervical uncovertebral joint was investigated using human cadaveric spines. Sequential resection of cervical uncovertebral joints, including clinical anteromedial foraminotomy, was conducted, followed by biomechanical testing after each stage of resection. OBJECTIVES: To clarify the biomechanical role of uncovertebral joints and clinical anteromedial foraminotomy in the cervical spine and their effects on interbody bone graft stability. SUMMARY OF BACKGROUND DATA: Although the biomechanical role of the cervical uncovertebral joints has been considered to be that of a guiding mechanism in flexion and extension and a limiting mechanism in posterior translation and lateral bending, there have been no studies quantifying this role. According to results in quantitative anatomic studies, anatomic variations exist in uncovertebral joints, depending on the vertebral level, articular angulation, and relative height of the joints. METHODS: Fourteen human functional spinal units at C3-C4 and C6-C7 underwent sequential uncovertebral joint resection, with each stage of resection followed by biomechanical testing. The uncovertebral joint was divided anatomically into three parts on each side: the posterior foraminal part, the posterior half, and the anterior half. The loading modes included torsion, flexion, extension, and lateral bending. A simulated anterior bone graft construct was also tested after each uncovertebral joint resection procedure. RESULTS: Significant changes in stability were observed after sequential uncovertebral joint resection in all loading modes (P < 0.05). The biomechanical contribution of uncovertebral joints decreased in the following order: the posterior foraminal part, the posterior half, and the anterior half. Unilateral and bilateral foraminotomy most affected the stability of the functional spinal unit during extension, causing a 30% and 36% decrease in stiffness of the functional spinal unit, respectively. The effect was less in torsion and lateral bending. After sequential resection, there was a statistically significant difference between decreases in torsional stiffness at C3-C4 and C6-C7 (P < 0.05). The stiffness of the simulated bone graft construct decreased progressively during flexion and lateral bending after each foraminotomy (P < 0.05). Increased bone graft height of 79% returned stability to the preforaminotomy level. CONCLUSIONS: This is the first study to quantitate the biomechanical role of uncovertebral joints in cervical segmental stability and the effect at each intervertebral level. The effect differs because of anatomic variations in uncovertebral joints. The major biomechanical function of uncovertebral joints includes the regulation of extension and lateral bending motion, followed by torsion, which is mainly provided by the posterior uncovertebral joints. This study highlights the clinical assessment of additional segmental instability attributed to destruction of the uncovertebral joints during surgical procedures or by neoplastic lesions.     

Preservation of the anterior urethral ligamentous attachments in maintaining post-prostatectomy urinary continence: a comparative study

PURPOSE: The impact was determined on post-prostatectomy urinary incontinence of a technique preserving the anterior attachments of the proximal urethra to the posterior pubis by comparison to the results of other surgical methods. MATERIALS AND METHODS: Urinary continence in 51 patients undergoing preservation of the anterior urethral attachments was compared to that of 70 patients undergoing an anatomical prostatectomy with resection of the bladder neck, 55 patients with preservation of the bladder neck and 14 patients undergoing a dorsal vein gathering procedure. Comparisons were made for rate of total continence, time to return of continence, incidence of extra organ disease and operative blood loss. RESULTS: Total continence at 1 year was 84.3%, 89.1%, 85.7% and 100% respectively. Immediate total continence after catheter removal was seen in 25.5% after preservation of the anterior urethral attachments, 80.4% at 3 months compared to 41.4%, 50.9% and 50% at 3 months for anatomical prostatectomy with bladder neck resection, preservation and dorsal vein gathering. Clinical staging with the incidence of specimen confined disease was similar in all groups. Mean operative blood loss was 1,031 ml. for those patients undergoing anatomical prostatectomy compared to 681 ml. for those with preservation of the anterior urethral attachments. CONCLUSIONS: Preservation of the anterior urethral attachments results in improved urinary continence and lower operative blood loss without an increase in positive surgical margins.     

Importance of the intersegmental trunk muscles for the stability of the lumbar spine. A biomechanical study in vitro

STUDY DESIGN: A biomechanical study was performed to determine the consequences of a simulation of muscle forces on the loads imposed on the functional spinal units. OBJECTIVES: No biomechanical study has investigated the effect of incorporation of agonist and antagonist muscle forces on the loading of functional spinal units. SUMMARY OF BACKGROUND DATA: Spinal disorders and low back pain are increasingly becoming a worldwide problem. Traditional conservative therapies are intended to strengthen the muscles of the trunk using a judicious regimen of physical exercises. METHODS: Eighteen whole, fresh-frozen human cadaveric lumbar spine specimens (L2-S2; average age, 53.4 years) were tested in a spine tester using pure flexion-extension, lateral bending, and axial moments. The effects of coactivation of psoas and multifidus muscles on L4-L5 mobility were simulated in vitro by applying two pairs of corresponding force vectors to L4. The segmental stability was defined by the correlation of an applied moment to the resultant deformation as shown in load-displacement curves, and the range of motion was defined as the angular deformation at maximum load. RESULTS: The coactivation of muscles was accompanied by a 20% decrease in the range of motion (i.e., a significant increase in stability) during lateral bending and axial moments. Application of flexion-extension moments and muscle coactivation resulted in a 13% increase in the sagittal range of motion. CONCLUSIONS: The action of the intersegmental agonist and antagonist muscles biomechanically increases the overall stiffness (stability) of the intervertebral joints in axial torque and lateral bending, whereas it may destabilize the segment in flexion.     

Lateral force-displacement behaviour of the human patella and its variation with knee flexion--a biomechanical study in vitro

This study measured the patellar lateral force-displacement behaviour at a range of knee flexion angles in normal human cadaver specimens. The knee extensor muscles were loaded in proportion to their physiological cross-sectional areas, the tensions being applied in physiological directions along the separate quadriceps muscles. Knee extension was blocked at a range of knee flexion angles from 0 to 90 degrees, and patellar lateral displacement versus force characteristics were measured. This experiment was repeated with three total muscle forces, 20, 175 and 350 N, which were held constant at all flexion angles. It was shown that similar stability variation was obtained with the different total muscle loads, and also the forces required to produce a range of patellar displacements (1.5, 9 mm) were examined. A 5 mm lateral patellar displacement required a constant displacing force (i.e. the patella had constant lateral stability) up to 60 degrees knee flexion, and then a significant increase at 90 degrees. The results were related to surgical and anatomical observations.     

The ankle and hindfoot of rheumatoid arthritis patients: study with computerized tomography]

According to the recommendations of the Bethesda System, the diagnosis of atypical squamous cells of undetermined significance (ASCUS) should be further qualified, when possible, as to whether a reactive or a squamous intraepithelial lesion (SIL) is favored. To determine the utility of this recently proposed terminology, we undertook this study to correlate the diagnosis of ASCUS (with or without qualifiers) with results obtained from examination of biopsy specimens. All patients were identified for the study who had a coloposcopically obtained cervical biopsy specimen or endocervical curettage specimen recorded in the surgical pathology files at Beth Israel Hospital, Boston, Massachusetts, from April 1994 through September 1994 and had either prior or concurrent Pap smear(s) reported as ASCUS, ASCUS-favor reactive, ASCUS-favor SIL, or SIL-low grade (SIL-LG). Patients with a cytologic diagnosis of SIL-LG served as a reference group. A total of 435 patients with 485 Pap smears were included. The prevalence rates of biopsy-proven SIL in patients with a cytologic diagnosis of ASCUS-favor reactive, ASCUS, ASCUS-favor SIL, and SIL-LG were 10, 28, 36, and 55%, respectively. The difference between cases diagnosed as ASCUS (with or without qualifiers) and SIL-LG, with respect to the presence of SIL at examination of the biopsy specimen, was statistically significant (P < 0.001 for all correlations). Cases diagnosed as ASCUS-favor reactive had a significantly lower rate of biopsy-proven SIL compared with those diagnosed as ASCUS and ASCUS-favor SIL (P < 0.01 for both correlations). A significant proportion of biopsy specimens with Pap smear diagnosis of ASCUS-favor SIL had SIL-high grade (15%). In contrast, an underlying SIL-high grade is much less likely in patients with ASCUS (unqualified) (3%) or when a reactive process is favored (3%). It seems justified to manage patients with ASCUS-favor SIL in a manner similar to those with SIL-LG. A conservative management seems appropriate for patients with ASCUS and ASCUS-favor reactive.     

A randomized biomechanical study of zone II human flexor tendon repairs analyzed in an in vitro model

Human telomerase, a ribonucleoprotein enzyme is known to be associated with immortalized cancer cells but is absent in most normal tissues. Thus, telomerase appears to be an attractive new target for anticancer agents and an important diagnostic marker of human cancers. Here, we describe an improved telomerase assay method based on the Dynabead biomagnetic separation theory. In this method, 5'-biotinylated (TTAGGG)3 was used as a primer for the telomerase reaction. Telomerase reaction products were then immobilized on streptavidin-coated Dynabeads and washed intensively to eliminate excess [alpha-32P]dGTP. Using this method, without the amplification of telomerase reaction products by the PCR, we were able to quantitatively detect telomerase activity in human HeLa cell extracts equivalent to between 200-500 cells. This method is anticipated to be useful for the measurement of telomerase activity in various tumor cells, for assessing potential telomerase and for understanding the biochemical aspects of the telomerase reaction.     

Support of the talus: a biomechanical investigation of the contributions of the talonavicular and talocalcaneal joints, and the superomedial calcaneonavicular ligament

The goal of this study was to determine the magnitude of force transmission to the talus by its inferior articulations to provide insight into mechanisms involving acquired deformities of the hindfoot. Cadaver feet were mounted in a loading apparatus that applied axial force through the tibia and fibula as well as tensile loading of the tendons of extrinsic musculature. This also permitted positioning of the tibia in the sagittal plane. Eighteen specimens were tested in three selected positions of the gait cycle. In one series, pressure-sensitive film was inserted into the posterior and anteromedial facets of the talocalcaneal joint as well as into the talonavicular joint. In a second series, film was inserted between the talar head and the superomedial calcaneonavicular ligament. In stance position, the specimens were also tested without posterior tibial tendon (PTT) tension. Contact areas and force transmitted across the articulations were greatest in near toe-off position, in the posterior facet of the talocalcaneal joint. The talonavicular joint, the anteromedial facet of the talocalcaneal joint, and the calcaneonavicular ligament articulation showed sequentially decreasing amounts of contact area and force transmission. Mean pressures were similar across all articulations, except in the posterior facet in near toe-off position. From heel-strike to stance, to near toe-off, a trend to increasing contact area and force was noted. No difference in contact characteristics was found in the calcaneonavicular ligament articulation after PTT release. The contact force of the calcaneonavicular ligament against the talus was found to be much smaller than those of other talar articulations; however, its medially oriented direction must contribute to stabilization of the head of the talus against medial displacement. Loss of PTT tension was not found to alter the contact forces acting at the talar head in this model, which might indicate that it shares its talar stabilizing function with other structures.     

Percutaneous pinning of proximal humerus fractures: a biomechanical study

Mechanical testing of two-part surgical neck fractures fixed with four different pin configurations was performed. Ten fresh, frozen, unembalmed humeri stripped of all soft tissues were used; the surgical neck was osteotomized perpendicular to the humerus long axis. Terminally threaded 2.5-mm AO pins were used to fix the fracture. Humeri then were tested in both torsion and bending on a custom-made jig using Instron 1331 to assess the rigidity of pinning constructs. In torsion, two lateral pin construct was significantly less rigid than all other pin configurations. The addition of an anterior pin to two lateral pins did not increase bending rigidity, but significantly increased torsional stiffness. The addition of two bicortical tuberosity pins or two bicortical tuberosity pins and one anterior pin to two lateral pins significantly increased rotational and bending rigidity. Results confirm clinical data, and the authors conclude that multiplanar pins are needed to augment torsional stiffness, and that the addition of two bicortical tuberosity pins enhances bending rigidity.     

A biomechanical study of balance recovery during the fall forward

The study deals with the biomechanics of balance recovery of human subjects in a falling forward situation. Eight subjects took part in the experiment. The subject, held in the initial leaning forward position, was released without his knowledge. The instruction was to recover the induced disequilibrium by walking. The biomechanical analysis shows two phases in the balance recovery. The first phase--preparation phase--is characterized by three events at fixed timing whatever the initial inclination. (i) Dynamic reaction time, showing no significant inter-individual variation (mean value = 90.8 ms). (ii) Braking of the forward fall, between 184 ms and 237.2 ms, depending on the subject. (iii) Beginning of the swing phase--i.e. toe-off instant--between 235.9 ms and 328.3 ms, depending on the subject. The second phase--gait execution phase--is characterized by the duration of the swing phase, the duration of the stance phase, the stride length and execution speed. The durations diminish whereas the stride length and the execution speed increase with respect to the initial inclination. For the same execution speed, the stride length is shorter than in normal walking. It has been concluded that balance recovery following an induced fall forward begins with an invariable preparation process which is followed by an adaptable recovery one.     

Physiological characteristics of identified motor units in the mouse extensor digitorum longus muscle: an in vitro approach

Difficult intubation remains one of the major risks in anaesthetic practice. Recently, as other anaesthetic societies, the French Society for Anaesthesia and Intensive Care (SFAR) has produced algorithms for the management of a difficult intubation. New laryngoscopes and blades have been marketed in recent years, however their place in these algorithms remains unclear. In this preliminary study, we compared the laryngoscopic view in 100 consecutive patients during tracheal intubation with the McCoy laryngoscope first in its normal position and after levering the distal part of the blade. All patients were included in Mallampati classes 1 and 2. Among them, 16% were classified as Cormack and Lehane grades 3 or 4 when using the blade in the normal position. These data confirm previous observations showing that the McCoy blade in normal position performs poorly as compared with the Macintosh blade. Conversely the levering of the distal part of the blade significantly decreased the incidence of Cormack and Lehane grades of 3 or 4 (2 versus 16%, P = 0.001). It is concluded that the McCoy blade is not convenient for its routine use in patients not to be at preoperatively known risk of difficult intubation. This blade significantly improves intubating conditions. Defining the exact place of this new blade in difficult intubation algorithms requires further studies.     

The role of supplemental translaminar screws in anterior lumbar interbody fixation: a biomechanical study

The immediate stabilization provided by anterior interbody cage fixation is often questioned. Therefore, the role of supplementary posterior fixation, particularly minimally invasive techniques such as translaminar screws, is relevant. The purpose of this biomechanical study was to determine the immediate three-dimensional flexibility of the lumbar spine, using six human cadaveric functional spinal units, in four different conditions: (1) intact, (2) fixed with translaminar screws (TLS), (3) instrumented with anterior interbody cage insertion with the BAK system and (4) instrumented with BAK cage with additional TLS fixation. Flexibility was determined in each testing condition by measuring the vertebral motions under applied pure moments (i.e. flexion-extension, bilateral axial rotation, bilateral lateral bending) in an unconstrained manner. Anterior fixation with the BAK alone provided significant stability in flexion and lateral bending. Additional posterior TLS significantly reduced the motion in extension and axial rotation. TLS fixation alone resulted in smaller rotations than BAK fixation in all loading directions. Based on these results, it seems that interbody cage fixation with the BAK system stabilizes the spine in some, but not all, loading directions. The problematic loading directions of extension and axial rotation can be substantially stabilized by using translaminar screw fixation. However, one should emphasize that the degree of stability needed to achieve solid fusion is not known.