Does glenoid inclination affect the anterior stability of reverse total shoulder arthroplasty? A biomechanical study.

PURPOSE: The anterior stability of reverse total shoulder arthroplasty is affected by multiple factors. However, the effect of glenosphere inclination on stability has rarely been investigated, which is what this study aims to look into. METHODS: Reverse shoulder arthroplasty was performed on 15 cadaveric human shoulders. The anterior dislocation forces and range of motion in internal rotation in the glenohumeral joint (primary measured parameters) were tested in a shoulder simulator in different arm positions and implant configurations, as well as with a custom-made 10° inferiorly inclined glenosphere. The inclination and retroversion of the baseplate as well as the distance between the glenoid and coracoid tip in two planes (secondary measured parameters) were evaluated on CT scans. RESULTS: In biomechanical testing, the custom-made inclined glenosphere showed no significant influence on anterior stability other than glenoid lateralisation over all arm positions as well as the neck-shaft angle in two arm positions. The 6 mm lateralised glenosphere reduced internal rotation at 30° and 60° of glenohumeral abduction. In 30° of glenohumeral abduction, joint stability was increased using the 155° epiphysis compared with the 145° epiphysis. The mean inclination was 16.1°. The inclination was positively, and the distance between the glenoid and coracoid tip in the anterior-to-posterior direction was negatively correlated with anterior dislocation forces. CONCLUSIONS: The custom-made inferiorly inclined glenosphere did not influence anterior stability, but baseplate inclination itself had a significant effect on stability.

Experimental evaluation of precision and accuracy of RSA in the lumbar spine.

PURPOSE: Roentgen stereophotogrammetric analysis is a technique to make accurate assessments of the relative position and orientation of bone structures and implants in vivo. While the precision and accuracy of stereophotogrammetry for hip and knee arthroplasty is well documented, there is insufficient knowledge of the technique's precision and, especially accuracy when applied to rotational movements in the spinal region. METHODS: The motion of one cadaver lumbar spine segment (L3/L4) was analyzed in flexion-extension, lateral bending and internal rotation. The specific aim of this study was to examine the precision and accuracy of stereophotogrammetry in a controlled in vitro setting, taking the surrounding soft tissue into account. The second objective of this study was to investigate the effect of different focal spot values of X-ray tubes. RESULTS: Overall, the precision of flexion-extension measurements was found to be better when using a 0.6 mm focal spot value rather than 1.2 mm (± 0.056° and ± 0.153°; respectively), and accuracy was also slightly better for the 0.6 mm focal spot value compared to 1.2 mm (- 0.137° and - 0.170°; respectively). The best values for precision and accuracy were obtained in lateral bending for both 0.6 mm and 1.2 mm focal spot values (precision: ± 0.019° and ± 0.015°, respectively; accuracy: - 0.041° and - 0.035°). CONCLUSION: In summary, the results suggest stereophotogrammetry to be a highly precise method to analyze motion of the lumbar spine. Since precision and accuracy are better than 0.2° for both focal spot values, the choice between these is of minor clinical relevance.

The novel arthroscopic subscapular quadriceps tendon-bone sling procedure provides increased stability in shoulder cadavers with severe glenoid bone loss.

PURPOSE: Treatment of anterior glenoid bone loss in patients with recurrent anterior shoulder instability is a challenge. The subscapular sling method with quadriceps tendon bone (QTB) graft is a modification of the subscapular sling with a semitendinosus (ST) graft. The aim of the study was to test the biomechanical stability of the QTB sling procedure in human shoulder cadavers with severe anterior glenoid bone loss. METHODS: Fourteen cadaveric shoulders were tested with a force-moment-guided robot in three conditions: physiologically intact, anterior glenoid bone resection, and the subscapular sling procedure with a QTB graft. Joint stability was measured in anterior, anterior inferior and inferior directions in four glenohumeral joint positions: 0° and 60° of glenohumeral abduction, with each at 0° and 60° of external rotation. Maximum external rotation was measured at 0° and 60° glenohumeral abduction. Computer tomography scans were obtained preoperatively to plan the glenoid bone resection, as well as postoperatively to calculate the proportion of the glenoid bone actually resected. RESULTS: Significantly decreased translations were observed in the shoulders with the QTB sling compared to the intact joint and the glenoid bone loss model. No significant differences in maximum external rotation were observed between the three different conditions. CONCLUSION: This biomechanical study revealed a significant stabilizing effect of the arthroscopic subscapular QTB graft sling procedure in human shoulder cadavers without compromising external rotation. Clinical trials may reveal the usefulness of this experimental method.

Anatomic factors influencing the anterior stability of reverse total shoulder arthroplasty.

BACKGROUND: Several factors affect the stability of the reverse shoulder arthroplasty. The influence of bony anatomy on anterior stability remains unclear. This study aimed to identify the correlations between bony anatomy and anterior dislocation forces. METHODS: The differences in anterior dislocation force in reverse total shoulder arthroplasty reported in a previous biomechanical study were used to analyze the anatomic factors influencing anterior stability. The critical shoulder angle, glenocoracoid distance in 2 planes, and glenoid inclination were measured in the tested specimens using 3-dimensional computed tomographic scans and radiographs. Anatomic parameters were then correlated with the anterior dislocation forces. RESULTS: The critical shoulder angle had no correlation with anterior stability. The glenocoracoid distance in anteroposterior direction showed a negative correlation with the stability of a reverse shoulder arthroplasty with a 9-mm lateralized glenosphere and 155° humeral inclination in 30° and 60° glenohumeral abduction with the arm in 30° external rotation (r = -0.662, P = .004; r = -0.794, P = .011) and 30° glenohumeral abduction with neutral rotation (r = -0.614, P = .009). Using the same hardware configuration, the anterior stability had a negative correlation with the glenocoracoid distance in the mediolateral direction in 30° of glenohumeral abduction with the arm in 0° and 30° of external rotation (r = -0.542, P = .025; r = -0.497, P = .042). CONCLUSION: The distance between the coracoid tip and glenoid in 2 planes had a significant negative correlation with the anterior stability of the reverse shoulder arthroplasty with a lateralized glenosphere and 155° humeral inclination. The findings suggest that only glenoid lateralization is influenced by the bony anatomy.

Greater early migration of a short-stem total hip arthroplasty is not associated with an increased risk of osseointegration failure: 5th-year results from a prospective RSA study with 39 patients, a follow-up study.

Background and purpose - Short-stem hip arthroplasty has been a viable alternative to standard stems for the treatment of hip osteoarthritis for over 10 years. This study assessed whether a correlation existed between a greater initial increase in implant migration and inferior clinical outcomes at 5 years postoperatively. Results on these patients after 2 years have been published previously.Patients and methods - Radiostereometry and clinical scoring were undertaken after surgery and at 3, 6, 12, and 24 months, and 5 years postoperatively. The migration and the clinical outcomes data from the patients with initial migrations at 3 months above the 75th percentile (≥ 75% group) were compared with those with migrations at 3 months of less than the 75th percentile (< 75% group).Results - Between 3 months and 5 years after surgery, the mean resultant implant migrations were 0.40 mm (SD 0.32) in the ≥ 75% group and 0.39 mm (SD 0.25) in the < 75% group. The mean Harris Hip Scores and SF-36 physical scores at 5 years postoperatively were 100 (SD 0.4) and 44 (SD 12), respectively, for the ≥ 75% group and 99 (SD 2) and 50 (SD 10), respectively, for the < 75% group. The differences between the patient groups were not statistically significant.Interpretation - There was no correlation between a greater initial migration and inferior clinical outcomes at 5 years postoperatively. Despite a greater initial migration, there were no risks of early aseptic loosening and inferior midterm clinical outcomes associated with a short-stem implant with a primary metaphyseal anchorage.

Monocortical fixation of the coracoid in the Latarjet procedure is significantly weaker than bicortical fixation.

PURPOSE: A crucial step of the Latarjet procedure is the fixation of the coracoid process onto the glenoid. Multiple problems associated with the fixation have been described, including lesions of the suprascapular nerve due to prominence of the screw or bicortical drilling. The purpose of the present study was to evaluate whether monocortical fixation, without perforating the posterior glenoid cortex, would provide sufficient graft stability. METHODS: Coracoid transfer was performed in 14 scapula models (Sawbones®, Composite Scapula, 4th generation). Two groups were assigned: in one group, fixation was achieved with two screws that did not perforate the posterior cortex of the glenoid neck (monocortical fixation), in the other group, fixation was achieved with perforation of the posterior cortex (bicortical fixation). The ultimate failure load and mode of failure were evaluated biomechanically. RESULTS: Monocortical fixation was a significantly weaker construct than bicortical fixation (median failure load 221 N, interquartile range 211-297 vs. median failure load 423 N, interquartile range 273-497; p = 0.017). Failure was either due to a pullout of the screws from the socket or a fracture of the glenoid. There was no significant difference in the mode of failure between the two groups (n.s.). CONCLUSION: Monocortical fixation was significantly weaker than bicortical fixation. However, bicortical drilling and overly long screws may jeopardize the suprascapular nerve. Thus, anatomic knowledge about the safe zone at the posterior rim of the glenoid is crucial. Until further research has evaluated, if the inferior stability is clinically relevant, clinicians should be cautious to use a monocortical fixation technique for the coracoid graft.

Effect of the humeral neck-shaft angle and glenosphere lateralization on stability of reverse shoulder arthroplasty: a cadaveric study.

BACKGROUND: Lateralizing the glenosphere and decreasing the humeral neck-shaft angles are implant design parameters that reduce the risk of scapular impingement. The effects of these parameters on joint stability remain unclear. This study evaluated the effect of glenosphere lateralization and humeral neck-shaft angle on joint stability by quantifying the anterior dislocation force in different arm positions. METHODS: Reverse shoulder arthroplasty was performed on 19 human shoulder specimens. Anterior dislocation force and maximum external rotation were evaluated using a robot-based shoulder simulator. By varying the neck-shaft angle and magnitudes of glenosphere lateralization, 12 configurations were analyzed with the glenohumeral joint in 30° and 60° of abduction, in neutral, and in 30° of external rotation. RESULTS: At 30° of abduction, measurements showed significantly higher dislocation forces for the 9-mm and 6-mm lateralized glenosphere than for the 0-mm (P < .0001, P = .007) nonlateralized glenosphere. At 60° of abduction, measurements showed significantly higher dislocation forces for the 9-mm and 6-mm lateralized glenosphere than for the 0-mm (P < .0001, P = .0007) and 3-mm (P = .0003, P = .04) glenosphere. Configurations with a neck-shaft angle of 135° showed significantly higher dislocation forces than configurations with a neck-shaft angle of 145° (P = .02) or 155° (P = .02) at 30° of abduction in 30° of external rotation. Neck-shaft angle and glenosphere lateralization had no influence on maximum external rotation capability. CONCLUSION: Glenosphere lateralization significantly increased anterior stability of the glenohumeral joint without influencing the range of passive external rotation. The humeral neck-shaft angle only had a minor effect on anterior stability.

In vitro investigation of two connector types for continuous rod construct to extend lumbar spinal instrumentation.

PURPOSE: Instrumentation of the lumbar spine is a common procedure for treating pathologic conditions. Studies have revealed the risks of pathologies in the adjacent segments, with the incidence rate being up to 36.1%. Revision procedures are often required, including extension of the instrumentation by the use of connectors to adjacent levels. The aim of this study was to determine the stiffness of side-to-side and end-to-end connectors for comparison with the use of continuous rods. METHODS: Ten human lumbar spine specimens (L1-S1) were tested about the three axes under pure moment loading of ± 7.5 Nm. Nine conditions were used to investigate the functions of the extensions for different instrumentation lengths (L3-S1 and L2-S1) and different connector levels (L3/4 and L2/3). The intersegmental range of motion (iROM) and intersegmental neutral zone as well as total range of motion (tROM) and total neutral zone (tNZ) were analyzed. RESULTS: The application of the spinal system significantly decreased the tROMs (- 44 to - 83%) and iROMs in levels L2/3 (- 56 to - 94%) and L3/4 (- 68 to - 99%) in all the tested directions, and the tNZ under flexion/extension (- 63 to - 71%) and axial rotation (- 34 to - 72%). These decreases were independent of the employed configuration (p < 0.05). The only significant changes in the iROM were observed under lateral bending between the continuous rod and the side-to-side connector at level L3/4 (p = 0.006). CONCLUSION: From a biomechanical viewpoint, the tested connectors are comparable to continuous rods in terms of ROM and NZ. These slides can be retrieved under Electronic Supplementary Material.

The effect of rotator cuff malreduction on tendon tension: an evaluation of a custom-made digital tensiometer clamp.

INTRODUCTION: Rotator cuff tears are common and good-to-excellent clinical outcome is reported after subsequent repair. However, the retear rate of rotator cuff repairs has been shown to be as high as 20%. The reasons for retear seem to be multifactorial, mainly comprised by mechanical and biological aspects. Regarding mechanical causes, the role of the tendon tension and malreduction is so far unknown. First, we hypothesized that the tendon tension depends on the technique of tendon reposition and that malreduction of the tendon results in an increased tendon tension. Second, we aimed to demonstrate the inter- and intraobserver reliability of a novel custom-made digital tensiometer clamp. MATERIALS AND METHODS: A tendon defect of posterosuperior rotator cuff (reverse L-shaped) was simulated in seven cadaveric human shoulder specimens. By use of a custom-made tensiometer clamp, the supraspinatus tendon was reduced by pulling it in (1) an anterolateral direction (anatomical reduction) and (2) in a straight lateral direction (malreduction) until the footprint was completely covered. The reduction procedure was consecutively repeated to evaluate the inter- and intraobserver reliability. RESULTS: The mean traction forces for anatomical reduction and malreduction were 16.02 N (SD 8.06) and 19.52 N (SD 9.95), respectively. The difference between the two groups was statistically significant (p = 0.028). The interobserver reliability showed a correlation of r = 0.757 [95% confidence interval (CI) 0.092-0.955]. The intraobserver reliability of the three surgeons was observed to be between r = 0.905 and 0.986. CONCLUSIONS: The malreduction of the rotator cuff has a significant influence on the tendon tension and may therefore affect the healing rate of the tendon after the repair, so that a tension-balanced repair could improve the clinical results. Furthermore, the application of a novel custom-made tensiometer clamp showed good interobserver and excellent intraobserver reliabilities.

Helical Axis Data Visualization and Analysis of the Knee Joint Articulation.

We present processing methods and visualization techniques for accurately characterizing and interpreting kinematical data of flexion-extension motion of the knee joint based on helical axes. We make use of the Lie group of rigid body motions and particularly its Lie algebra for a natural representation of motion sequences. This allows to analyze and compute the finite helical axis (FHA) and instantaneous helical axis (IHA) in a unified way without redundant degrees of freedom or singularities. A polynomial fitting based on Legendre polynomials within the Lie algebra is applied to provide a smooth description of a given discrete knee motion sequence which is essential for obtaining stable instantaneous helical axes for further analysis. Moreover, this allows for an efficient overall similarity comparison across several motion sequences in order to differentiate among several cases. Our approach combines a specifically designed patient-specific three-dimensional visualization basing on the processed helical axes information and incorporating computed tomography (CT) scans for an intuitive interpretation of the axes and their geometrical relation with respect to the knee joint anatomy. In addition, in the context of the study of diseases affecting the musculoskeletal articulation, we propose to integrate the above tools into a multiscale framework for exploring related data sets distributed across multiple spatial scales. We demonstrate the utility of our methods, exemplarily processing a collection of motion sequences acquired from experimental data involving several surgery techniques. Our approach enables an accurate analysis, visualization and comparison of knee joint articulation, contributing to the evaluation and diagnosis in medical applications.

In vitro investigation of a new dynamic cervical implant: comparison to spinal fusion and total disc replacement.

PURPOSE AND METHODS: For the treatment of degenerative disc diseases of the cervical spine, anterior cervical discectomy and fusion (ACDF) still represents the standard procedure. However, long term clinical studies have shown a higher incidence of pathologies in the adjacent segments. As an alternative to spinal fusion, cervical total disc replacement (cTDR) or dynamically implants were increasingly used. This in vitro study analyzed the kinematics and intradiscal pressures in seven multi-segmental human cervical spine using hybrid multidirectional test method. The aim of our study was to compare the intact condition with a single-level dynamic stabilization with DCI(®), with cTDR (activC(®)) and with simulated ACDF (CeSPACE(®) cage and CASPAR plate). RESULTS: No significant changes in the kinematics and pressures were observed in all segments after arthroplasty. The DCI(®) significantly decreased the motion of the treated segment in flexion/extension and lateral bending with some remaining residual mobility. Thereby the motion of the upper segment was increased significantly in flexion/extension. No significant changes of the intradiscal pressures were observed. With simulated fusion the motion of the indexed level was significantly decreased in flexion/extension and axial rotation with the greatest changes in the adjacent levels and the highest pressures. CONCLUSION: Based on our biomechanical study the DCI(®) can pose an alternative to fusion, which has a lesser effect on adjacent levels. This might reduce the risk of long-term degeneration in those levels. In particular, the facet joint arthritis and kyphotic deformity, as a contraindication to the arthroplasty, could be a clinical application of the dynamic implant.

Posterior dynamic stabilization in the lumbar spine - 24 months results of a prospective clinical and radiological study with an interspinous distraction device.

BACKGROUND: Interspinous distraction devices (IDD) are due to maintain or restore intersegmental range of motion (iROM) in a controlled fashion with the aim of stabilization the affected level dynamically. The following study is the first to present clinical and radiological data with the Wallis® spacer during a follow-up of 24 months. METHODS: Ten patients underwent posterior dynamic stabilization (PDS) of the lumbar spine with an IDD (Wallis® spacer) and were controlled clinically and radiologically after 3, 6, 12, and 24 months in a prospective study design. Pain intensity, functional disability and life quality were assessed by use of subjective scores. Motion analyses were performed with the help of lateral functional x-rays to determine the iROM of the operated segments and total ROM (tROM) of the lumbar spine. In addition, roentgen stereophotogrammetric analysis (RSA) was used to measure the iROM of the treated levels. RESULTS: During the postoperative course pain and disability most clinical scores were significantly improved. After 24 months we observed statistically significant reduction in back pain intensity with a mean value of 6.0 on visual analog scale (VAS) before surgery and of 2.7 at the latest evaluation. The leg pain was also decreased without statistical significance from 4.7 preoperatively to 2.1 at final follow-up. The functional disability according to Oswestry Disability Index (ODI) and Roland-Morris Disability Questionnaire (RM) was decreased both with statistical significance at all examination dates with a mean value in ODI of 40.0 % before operation and of 17.3 % after 2 years and an initial mean value in RM of 55.2 and of 23.5 % after latest follow-up. After 24 months, the results of the health related quality of life score also showed much better values with only two exceptions. The iROM of the treated levels was reduced during each follow-up examination with preserved residual mobility. Directly postoperatively and after 3 and 12 months intersegmental mobility was statistically significantly decreased with an average iROM of 6.62° before operation and of 2.69° few days after surgery, of 3.79° and 3.16° 3 and 12 months later. At 6 (4.37°) and 24 (4.01°) months follow-up iROM was also but not statistically significantly reduced. The mean tROM did not change significantly during all postoperative controls. CONCLUSIONS: The radiological findings support the thesis of posterior dynamic stabilization by the used implant. The positive clinical findings should be interpreted with caution because of the limited number of patients and the missing control group.

Biomechanical comparison of fixation techniques for medial collateral ligament anatomical augmented repair.

PURPOSE: Although the majority of medial collateral ligament (MCL) ruptures can be treated conservatively with good results, some injuries require operative treatment. Besides MCL reconstruction, anatomical augmented repair may be considered. This study was to assess biomechanical properties of different fixation techniques regarding elongation and ultimate load to failure. METHODS: MCL anatomical augmented repair was simulated by fixation of porcine superficial digital flexor tendon grafts at porcine tibiae. Ten different fixation techniques were assessed. Fixation of the tendon graft was performed using 4.0-mm cancellous screws and either (1) 13.5-mm spiked polyether ketone (PEEK) washers; (2) 14-mm spiked washers; (3) 14-mm suture washers; (4) 14-mm customized washers; (5-8) combination of washers and No. 2 polyester sutures (FiberWire©); or using (9) single or (10) double 5.5-mm titanium suture anchors with No. 2 polyethylene sutures (Ultrabraid®). Biomechanical analysis included pretensioning of the constructs at 20 N for 30 s following cyclic loading of 250 cycles between 20 and 100 N at 1 Hz for measurement of elongation. Additionally, ultimate failure load and failure mode analysis were performed. RESULTS: Spiked PEEK washers secured with polyester sutures (5) yielded best biomechanical properties at time zero for both, elongation during cyclic loading (2.9 ± 0.7 mm) and ultimate failure load (469.8 ± 64.3 N). CONCLUSIONS: These results suggest that spiked PEEK washers secured with polyester sutures are the most appropriate fixation technique for MCL anatomical augmented repair, thus providing best requirements to allow early knee mobilization and prevent secondary knee laxity.

Analysis of migration of the Nanos® short-stem hip implant within two years after surgery.

PURPOSE: Short-stem implants provide a bone-preserving alternative in total hip arthroplasty. However, some evidence exists that the smaller implant-bone contact surface may compromise primary stability and impair osseo-integration. The purpose of this study was to analyse the migration characteristics of the Nanos® short stem over two years by means of model-based roentgen stereophotogrammetric analysis (MBRSA). METHODS: Eighteen patients aged 53.6 ± 7.2 years were included. After being treated with a Nanos implant, 14 patients were followed-up radiologically at three, six, 12 and 24 months by means of MBRSA. Early implant migration was calculated. Clinical data have been assessed in addition. RESULTS: Highest translational migration was observed with a mean value of -0.22 ± 0.39 mm along the proximo-distal axis after three months and highest rotational migration with 0.8 ± 3.2° also around the y-axis after two years. The resulting total migration was 0.46 ± 0.31 mm, with the largest proportion occurring within three months after surgery (0.40 ± 0.34 mm). CONCLUSION: The Nanos short-stem hip implant shows only a slight initial migration within three months after implantation, followed by secondary stabilisation. These results suggest both good primary stability and osseo-integration, suggesting a low risk of aseptic loosening.

Patella tracking and patella contact pressure in modular patellofemoral arthroplasty: a biomechanical in vitro analysis.

INTRODUCTION: In the recent years modular partial knee prosthesis with the opportunity to combine unicompartmental tibiofemoral (UKA) and patellofemoral prosthesis (PFJ) were introduced to the clinics. To date, little is known about the biomechanics of these bi-cruciate retaining prosthetic designs. Aim of this study was to evaluate the influence of a PFJ in bicompartmental arthroplasty (UKA + PFJ) on patella tracking and retropatella pressure distribution. METHODS: A dynamic in vitro knee kinemator simulating an isokinetic extension cycle of the knee was used on eight knee specimen. Patella tracking and patellofemoral contact pressure were evaluated using pressure sensitive films after implantation of a medial UNI and after subsequent implantation of a PFJ. RESULTS: Whereas the area contact pressure remained the same after PFJ implantation, the contact area was reduced significantly and significantly elevated peak pressures were determined in deep flexion and close to extension. The patella tracking was not significantly altered, however, effects of edge loading could be shown. CONCLUSION: When using PFJ prosthesis, one must be aware of altered pressure introduction on the retropatella surface compared to the physiological situation. The elevated peak pressures and reduced contact area may be an argument for patella resurfacing and the problems of edge loading indicate that care must be taken on the correct implantation of the device with no implant overhang.

Anterior stability of the reverse shoulder arthroplasty depending on implant configuration and rotator cuff condition.

INTRODUCTION: The aim of this study was to investigate the stabilizing influence of the rotator cuff as well as the importance of glenosphere and onlay configuration on the anterior stability of the reverse total shoulder replacement (RTSR). MATERIALS AND METHODS: A reverse total shoulder replacement was implanted into eight human cadaveric shoulders, and biomechanical testing was performed under three conditions: after implantation of the RTSR, after additional dissection of the subscapularis tendon, and after additional dissection of the infraspinatus and teres minor tendon. Testing was performed in 30° of abduction and three rotational positions: 30° internal rotation, neutral rotation, and 30° external rotation. Furthermore, the 38-mm and 42-mm glenospheres were tested in combination with a standard and a high-mobility humeral onlay. A gradually increased force was applied to the glenohumeral joint in anterior direction until the RTSR dislocated. RESULTS: The 42-mm glenosphere showed superior stability compared with the 38-mm glenosphere. The standard humeral onlay required significantly higher anterior dislocation forces than the more shallow high-mobility onlay. External rotation was the most stable position. Furthermore, isolated detachment of the subscapularis and combined dissection of the infraspinatus, teres minor, and subscapularis tendon increased anterior instability. CONCLUSIONS: This study showed superior stability with the 42-mm glenosphere and the more conforming standard onlay. External rotation was the most stable position. Detachment of the subscapularis as well as dissection of the complete rotator cuff decreased anterior stability.

The lasso-loop, lasso-mattress and simple-cinch stitch for arthroscopic rotator cuff repair: are there biomechanical differences?

PURPOSE: Various stitching techniques have been described to facilitate arthroscopic repair of rotator cuff tears. The aim of the present study was to compare the biomechanical properties of the lasso-loop, lasso-mattress and simple-cinch stitch for rotator cuff repair. METHODS: Twelve infraspinatus tendons were harvested from sheep and split in half. The tendons were randomized into three different stitch configuration groups for biomechanical testing: lasso-loop, lasso-mattress and simple-cinch stitch. Each specimen was first cyclically loaded on a universal materials testing machine under force control from 5 to 30 N at 0.25 Hz for twenty cycles. Then, each specimen was loaded to failure under displacement control at a rate of 1 mm/s. Cyclic elongation, peak-to-peak displacement and ultimate tensile load were reported as mean ± standard error and compared using one way analysis of variance. The type of failure was recorded. RESULTS: No differences in cyclic elongation (1.31 ± 0.09 mm for the simple-cinch vs. 1.49 ± 0.07 mm for the lasso-mattress vs. 1.61 ± 0.09 mm for the lasso-loop stitch, p = 0.063) or peak-to-peak displacement (0.58 ± 0.04 mm for the simple-cinch, 0.50 ± 0.03 mm for the lasso-mattress and 0.62 ± 0.06 mm for the lasso-loop stitch, p = 0.141) were seen between all tested stitch configurations. In the load-to-failure test, the simple cinch stitch (149.38 ± 11.89 N) and the lasso-mattress (149.38 ± 10.33 N) stitch demonstrated significantly higher ultimate load than the lasso-loop stitch (65.88 ± 4.75 N, p < 0.001). All stitch configurations failed with suture pull out. CONCLUSIONS: The lasso-mattress and the simple-cinch stitch showed similar biomechanical properties with significant higher tensile loads needed for failure than the lasso-loop stitch.

In vitro-analysis of kinematics and intradiscal pressures in cervical arthroplasty versus fusion--A biomechanical study in a sheep model with two semi-constrained prosthesis.

BACKGROUND: As an alternative technique to arthrodesis of the cervical spine, total disc replacement (TDR) has increasingly been used with the aim of restoration of the physiological function of the treated and adjacent motions segments. The purpose of this experimental study was to analyze the kinematics of the target level as well as of the adjacent segments, and to measure the pressures in the proximal and distal disc after arthrodesis as well as after arthroplasty with two different semi-constrained types of prosthesis. METHODS: Twelve cadaveric ovine cervical spines underwent polysegmental (C2-5) multidirectional flexibility testing with a sensor-guided industrial serial robot. Additionally, pressures were recorded in the proximal and distal disc. The following three conditions were tested: (1) intact specimen, (2) single-level arthrodesis C3/4, (3) single-level TDR C3/4 using the Discover® in the first six specimens and the activ® C in the other six cadavers. Statistical analysis was performed for the total range of motion (ROM), the intervertebral ROM (iROM) and the intradiscal pressures (IDP) to compare both the three different conditions as well as the two disc prosthesis among each other. RESULTS: The relative iROM in the target level was always lowered after fusion in the three directions of motion. In almost all cases, the relative iROM of the adjacent segments was almost always higher compared to the physiologic condition. After arthroplasty, we found increased relative iROM in the treated level in comparison to intact state in almost all cases, with relative iROM in the adjacent segments observed to be lower in almost all situations. The IDP in both adjacent discs always increased in flexion and extension after arthrodesis. In all but five cases, the IDP in each of the adjacent level was decreased below the values of the intact specimens after TDR. Overall, in none of the analyzed parameters were statistically significantly differences between both types of prostheses investigated. CONCLUSION: The results of this biomechanical study indicate that single-level implantation of semi-constrained TDR lead to a certain hypermobility in the treated segments with lowering the ROM in the adjacent levels in almost all situations.

Biomechanical comparison of two surgical techniques for press-fit reconstruction of the posterolateral complex of the knee.

BACKGROUND: To date, various surgical techniques to treat posterolateral knee instability have been described. Recent studies recommended an anatomical and isometric reconstruction of the posterolateral corner addressing the key structures, such as lateral collateral ligament (LCL), popliteus tendon (POP) and popliteofibular ligament (PFL). Two clinical established autologous respective local reconstruction methods of the posterolateral complex were tested for knot-bone cylinder press-fit fixation to assess efficacy of each reconstruction technique in comparison to the intact knee. NULL HYPOTHESIS: The knot-bone cylinder press-fit fixation for both anatomic and isometric reconstruction techniques of the posterolateral complex shows equal biomechanical stability as the intact posterolateral knee structures. STUDY DESIGN: This was a controlled laboratory study. METHODS: Two surgical techniques (Larson: fibula-based semitendinosus autograft for LCL and PFL reconstruction/Kawano: biceps femoris and iliotibial tract autograft for LCL, PFL and POP reconstruction) with press-fit fixation were used for restoration of posterolateral knee stability. Seven cadaveric knees (66 ± 3.4 years) were tested under three conditions: intact knee, sectioned state and reconstructed knee for each surgical technique. Biomechanical stress tests were performed for every state at 30° and 90° knee flexion for anterior-posterior translation (60 N), internal-external and varus-valgus rotation (5 Nm) at 0°, 30° and 90° using a kinemator (Kuka robot). RESULTS: At 30° and 90° knee flexion, no significant differences between the four knee states were registered for anterior-posterior translation loading. Internal-external and varus-valgus rotational loading showed significantly higher instability for the sectioned state than for the intact or reconstructed posterolateral structures (p < 0.05). There were no significant differences between the intact and reconstructed knee states for internal-external rotation, varus-valgus rotation and anterior-posterior translation at any flexion angles (p > 0.05). Comparing both reconstruction techniques, significant higher varus-/valgus stability was registered for the fibula-based Larson technique at 90° knee flexion (p < 0.05). CONCLUSIONS: Both PLC reconstructions showed equal biomechanical stability as the intact posterolateral knee structures when using knot-bone cylinder press-fit fixation. We registered restoration of the rotational and varus-valgus stability with both surgical techniques. The anterior-posterior translational stability was not influenced significantly. The Larson technique showed significant higher varus/valgus stability in 90° flexion. The latter is easier to perform and takes half the preparation time, but needs grafting of the semitendinosus tendon. The Kawano reconstruction technique is an interesting alternative in cases of missing autografts.

A novel implant-free tibial pull-press-fixation for ACL reconstruction.

INTRODUCTION: Extracortical fixation techniques in anterior cruciate ligament reconstruction bear the risk of tunnel enlargement, while close-to-aperture fixations often show lower failure loads. The purpose for this study was to investigate the biomechanical benefits of a novel implant-free combination of an extra-cortical and close-to-aperture fixation. MATERIALS AND METHODS: Quadrupled human cadaveric semitendinosus tendons were fixed to 30 porcine tibiae with either a cannulated interference screw (I), an implant-free post-fixation (S), or a novel pull-press fixation (P). Specimens were cyclically loaded 20 times between 20 and 60 N followed by 500 cycles with 60-200 N, followed by a load-to-failure test with 1 mm/s. RESULTS: The mean elongation of the tendons in the P-group during the 500 cycles between 60 and 200 N was significantly lower (5.69 ± 2.16 mm) compared to 9.20 ± 3.21 mm in S-group and 9.37 ± 3.1 mm in the I-group (p < 0.05). The mean maximum load-to-failure was significantly higher in the P-group (728.2 ± 76.4 N) compared to 476.4 ± 68.8 N in the S-group and 625.9 ± 82.5 N in the I-group (p < 0.05). Stiffness of the constructs in the P-group was significantly higher (121.7 ± 44.9 N/mm) compared to 46.2 ± 17.7 N/mm in the S- and 72.8 ± 29.8 N/mm in the I-group (p < 0.03). CONCLUSIONS: This study indicates superior biomechanical properties of a novel implant-free tibial pull-press fixation to conventional implant-free and close-to-aperture interference screw fixations in terms of cyclic elongation and maximum load-to-failure. LEVEL OF EVIDENCE: Not applicable, basic science study.