INTRODUCTION: Conventional wisdom dictates that fusion rates increase with increasing construct stiffness. Traditional pedicle screw systems generally rely upon stiff components and rigid interconnections. For ease of insertion, some "semi-rigid" systems include polyaxial connections. A favorable bio logical outcome (fusion) is only weakly related to instrumentation type and it is increasingly recognized that even semi-rigid instrumentation may be too stiff [1]. Dynesys (Dynamic Neutralization System for the Spine, Centerpulse Spine-Tech, Inc., Minneapolis, MN) has non-rigid interconnections, non-rigid polymer spacers, and pedicle screw anchorage. The biomechanics of more traditional polyaxial pedicle screw/rigid rod fixation (Silhouette ) compared to this non-rigid system are unknown. It was hypothesized that spines fixed with the non-rigid stabilization system will exhibit greater ranges of motion (ROM) than spines fixed with the all-metal semi-rigid pedicle screw system. METHODS: Twelve fresh -frozen calf lumbar spines were used. Soft tissues were removed but the discs and ligaments were left intact. Structures above L1 and below L5 were removed. Spines were kept moist and were maintained at 35-41 °C (body temperature) throughout testing. Intact spines were tested in flexion, extension, left/ right lateral bending, and left/right axial rotation. Instrumentation was applied at L3/L4 using the manufacturers’ recommended techniques and instruments. For non-rigid (Dynesys) stabilization, the facet joints were cut open. For semi-rigid (Silhouette) fixation, the facet joints were decorticated with a high speed burr and rongeurs. (This variation was necessary to accomodate geometric differences between the instrumentation types.) Spines were destabilized at the reconstructed level by creating a window in the annulus and by cutting the supraspinous, interspinous, and posterior longitudinal ligaments, and the ligamentum flavum. Six spines received non-rigid stabilization and six spines received semi-rigid fixation. Instrumented spines were retested in flexion, extension, left/right lateral bending, and left/right axial rotation. A biaxial load frame was configured with two rotary actuators with integral rotary poteniometers mounted onto glide tables. This configuration created a six degree-of-freedom spine testing machine: the rotary actuators coincided with flexion/extension and lateral bending, the glide tables coincided with anterior/posterior and medial/lateral translations, and the biaxial actuator coincided with axial rotation and axial translation of the spine. Flexion-extension, axial rotation, and lateral bending moments were applied in 1.5Nm intervals up to +/-6Nm in each direction with no axial pre-load. Position data were recorded upon a third loading cycle after two preconditioning cycles. Relative intervertebral motions were recorded by a optoelectronic position measurement system (Optotrak 3020, Northern Digital Inc., Waterloo, Ontario, Canada). Ranges of motion were derived from the momentangular displacement curves. For instrumented spines, ROM's were normalized to intact and reported. In general, groups were compared by a t -test. A significance level of p<0.05 was chosen. RESULTS SECTION: In axial rotation, flexion/extension and lateral bending, spines with non-rigid stabilization were not significantly different from spines with semi-rigid fixation. In axial rotation, neither was significantly different from intact. However, in flexion/extension and lateral bending, both were significantly different from intact. Table. Range of Motion (Percent of Intact, mean ± 1 s.d.) L/R Axial Rotation Flexion/ Extension L/R Lateral Bending Non-Rigid Fixation 125 ± 50 54 ± 12 10 ± 4 Semi-Rigid Fixation 125 ± 47 40 ± 29 13 ± 7 DISCUSSION: Both constructs substantially reduced flexion/extension and lateral bending motion but the constructs were not different from each other. Consequently, neither fixation system was superior in terms of reducing flexion/extension and lateral bending. In axial rotation, neither Dynesys nor Silhouette was different from its intact condition and the constructs were not different from each other. Neither construct substantially affected axial rotation motion. Our findings are limited to single-level, bilateral constructs; no differences between non-rigid stabilization (Dynesys) and semi-rigid fixation (Silhouette) were notable. Multi-level or unilateral constructs may likewise exhibit no differences between instrumentation types, but these variables were not included in this study. Another limitation is that calf lumbar spines were tested in this study. Wilke has found that calf and human spines are biomechanically similar and that the calf spine is an appropriate model for the human spine in vitro test s [2]. Our tests were further limited in that the spines were fresh -frozen and the spines were normal without obvious anatomic defects or disease. These limitations are accepted for all in-vitro tests. No axial preload was applied though axial preload has been shown to have an important effect when examining natural spine kinematics [3]. The best axial preload for in-vitro comparisons of posterior fixation systems remains to be demonstrated. It has been recommended by other investigators than care be taken to guarantee that any preload be consistently applied throughout testing [4]; our methodology ensured this. The constructs model fixation only immediately post-operatively and without bone graft. The effects of time of implantation may be important in several ways. First, ranges of motion and stiffness may be affected by repeated loading in -situ; in this study, a nominal number of load cycles were applied. Second, the material properties of the bone or of the implants may change with time in-situ; these changes could not be modeled. Third, successful fixation should lead to the development of a fusion mass in -situ; the biomechanical consequences of the presence of a fusion mass were not studied. Contrary to the hypothesis, non-rigid stabilization and semi-rigid fixation presented equivalent ranges of motion in axial rotation, flexion/extension, and lateral bending. Both the non-rigid stabilization system and the semi-rigid fixation system provided acute stability. REFERENCES: 1. Pfeiffer M, Deike B, Clausen JD, Wilke A, Griss P: A new semirigid implant for instrumentation of scoliosis: preliminary report. Eur Spine J 2001 Oct;10(5):427-36 2. Wilke HJ, Krischak ST, Wenger KH, Claes LE: Load-displacement properties of the thoracolumbar calf spine: experimental results and comparison to known human data. Eur Spine J 1997;6(2):129-37 3. Janevic J, Ashton-Miller JA, Schultz AB: Large compressive preloads decrease lumbar motion segment flexibility. J Orthop Res 1991 Mar;9(2):228-36 4. Cripton PA, Bruehlm ann SB, Orr TE, Oxland TR, Nolte LP: In vitro axial preload application during spine flexibility testing: towards reduced apparatus-related artefacts. J Biomech 2000 Dec;33(12):155968 Figure. Range of Motion Results 0 50 100 150 200 L/R Axial Rot Flex/Ext L/R Lat Bend P er ce nt o f I nt ac t Non-Rigid Stabilization

A controlled prospective randomized study was designed to analyze the effect of extracorporeal shock wave therapy on calcifying tendinopathy of the shoulder focused on the calcified area or the origin of the supraspinatus tendon. Fifty patients were included in the study and were treated with a Storz Minilith Sl-1 shock wave generator. The first group of patients received 4000 impulses (positive energy flux density, 0.78 mJ/mm2) in two treatment sessions after receiving local anesthesia at the origin of the supraspinatus tendon. Patients in the second group received extracorporeal shock wave therapy at the calcified area. Follow-ups were done 12 weeks and 1 year after treatment by an independent observer. An increase of function and a reduction of pain occurred in both groups. Statistical analyses showed a significant superiority of extracorporeal shock wave application at the calcified area in the primary end point (Constant and Murley score). Therefore, exact fluoroscopic focusing of extracorporeal shock wave therapy at the calcific deposit for treatment of calcifying tendinopathy of the supraspinatus muscle is recommended. Based on these results, extracorporeal shock wave application should be focused fluoroscopically with appropriate shock wave generators.

A controlled randomized study was designed to analyse the effect of extracorporeal shockwave therapy (ESWT) focussed on either the calcified region or the insertion of the supraspinatus tendon. The study included 50 patients who were treated with a Storz Minilith SI-1 prototype shockwave generator. In the treated group, 4000 impulses (ED+ 0.78 ml/mm2) were applied, under local anaesthesia to the insertion of the supraspinatus in 2 treatment sessions. Control patients received ESWT focussed on the calcified region. Follow-up examinations were carried out 12 weeks after treatment by an independent observer. We found functional improvement and pain reduction in both groups. Statistical analyses showed significant superiority of ESWT focussed on the calcified region for the parameters constant-score (primary endpoint, p < 0.001) and pain intensity (p = 0.001). For the treatment of calcific tendinitis affecting the supraspinatus, we recommend accurate fluoroscopy-controlled focussing of ESWT on the calcification. Focussing on the calcification rather than on the insertion of the supraspinatus tendon is significantly more effective. On the basis of our results, ESWT requires the use of suitable shockwave generators that permit accurate focussing.

We have performed a controlled, randomised study to analyse the effects of low-energy shock-wave therapy (ESWT) on function and pain in tendinitis of the supraspinatus without calcification. There were 20 patients in the treatment group and 20 in the control group. The former group received 6000 impulses (energy flux density, 0.11 mJ/mm2) in three sessions after local anaesthesia. The control group had 6000 impulses of sham ESWT after local anaesthesia. The patients were examined at six and 12 weeks after treatment by an independent observer who evaluated the Constant score and level of pain. We found an increase in function and a reduction of pain in both groups (p ≤ 0.001). Statistical analysis showed no difference between the groups for the Constant score and for pain. We therefore do not recommend ESWT for the treatment of tendinitis of supraspinatus.

. A new set of pedicle screws, lamina and pedicle hooks, longitudinal rods and a titanium cable was developed to overcome the increasingly obvious hazards of overly rigid spinal instrumentation. Results of the first 12 consecutive scoliosis patients with this new system are reported, with an average follow-up time of 18 months. No major complications occurred. The average correction of the deformity was well within the range of more rigid systems. The new Dorsal Dynamic Spondylodesis (DDS) system proved to be easy to use, fast, powerful, safe, versatile, and biomechanically sound. Reduction of stress-shielding effects and protection of adjacent segments can be expected, and the system warrants future application in selected prospective cases with long-term follow-up.