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.

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal.

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1,500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3 degrees , cage with 2.8 degrees , block without 3.4 degrees , and physiologic 6.6 degrees , all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.

Comparative biomechanical testing of anterior and posterior stabilization procedures.

STUDY DESIGN: This is a comparative in vitro biomechanical study in a calf lumbar spine model. OBJECTIVES: The objective was to compare the primary stability of an anterior instrumentation, an intercorporal cage in combination with an anterior instrumentation, and a posterior instrumentation for monosegmental spondylodesis. SUMMARY OF BACKGROUND DATA: Spondylodesis can be achieved through a posterior lumbar fusion, posterior lumbar intercorporal fusion, or an anterior lumbar intercorporal fusion. The posterior lumbar fusion is the gold standard, although the anterior approach offers some potential advantages to the transpedicular posterior techniques. METHODS: Stability testing was performed on 30 calf lumbar spine motion segments in a physiologic state (n = 30), with either an isolated anterior (MACS) or posterior instrumentation (SOCON), and with an anterior instrumentation augmented with an intercorporal cage (MACS-Cage, n = 10, respectively). Range of motion, neutral zone, and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1500 N. RESULTS: The isolated posterior instrumentation was found to be more stable than the isolated or augmented anterior instrumentation in flexion/extension, although no significant differences were observed in lateral bending or axial rotation. The results of this biomechanical study suggest that an augmented anterior instrumentation provides similar stability for bony fusion as does the golden standard posterior instrumentation, with the exception of flexion/extension. CONCLUSION: An augmented anterior instrumentation may provide similar stability for bony fusion as does the posterior instrumentation.

Shoulder arthrodesis: indications, technique, results, and complications.

Complications after shoulder arthrodesis are frequent. Through results and comparisons with the literature, the presented article analyzes the correlation of complications with the specific operative techniques, indications, and postoperative treatment. Between 1964 and 2001, a total of 43 cases of shoulder arthrodesis (13 screw and 30 plate arthrodeses) were performed and then analyzed after a mean of 6.7 years (range, 0.5-36 years). Surgery was carried out on 10 female patients (23%) and 33 male patients (77%) with a mean age of 35 years (range, 11-82 years). These patients had the following indications: paralysis (32 [74%]), osteoarthritis or humeral head necrosis (15 [35%]), infection (7 [16%]), and persistent shoulder instability (6 [14%]). The extent of active movement after arthrodesis was 56 degrees abduction (range, 20 degrees - 90 degrees) and 60 degrees forward flexion (range, 20 degrees - 105 degrees), with an increase in the Constant score in all cases, from a mean of 27 points preoperatively to 57 points postoperatively (difference, 30 points). The patients rated the outcome of surgery as excellent, good, or satisfactory in 91% of cases. Complications after shoulder arthrodesis were noted in 12 of 43 patients (28%). The most frequent complications after screw/plate arthrodesis included pseudarthrosis, 2 (15%)/3 (10%); infection, 1 (8%)/4 (13%); and fracture of the humerus, 0/4 (13%). No specific judgment can be attributed to the different osteosynthesis techniques used in shoulder arthrodesis, either in the cases presented at our clinic or in the literature. Pseudarthrosis appeared to be less frequent in cases of plate arthrodesis compared with screw arthrodesis. However, the application of plates resulted more often in infection, postoperative fractures of the humerus, and the necessity for removal of material. Particularly in patients with paralysis, a shoulder arthrodesis resulted in an improvement in postoperative active function and presented a suitable operative option.

Reconstructive operations for the upper limb after brachial plexus palsy.

Limited function due to paralysis following brachial plexus lesions can be improved by secondary operations of the bony and soft tissue. Between April 1994 and December 2000, 109 patients suffering from arm-plexus lesions underwent a total of 144 reconstructive operations guided by our concept of integrated therapy. The average age at the time of surgery was 32 years (range: 15-59). The following operations were performed: shoulder arthrodesis (23), trapezius transfer (74), rotation osteotomy of humerus (9), triceps to biceps transposition (9), transposition of forearm flexors or extensors (8), latissimus transfer (7), pectoralis transfer (1), teres major transfer (1), transposition of flexor carpi ulnaris to the tendons of extensor digitorum (10), and wrist arthrodesis (2). Prospectively, in all patients, the grade of muscle power of the affected upper extremity was evaluated prior to surgery. The follow-up period for all 144 operations was, on average, 22 months (range: 6-74). By means of operative measures, almost all patients obtained an improvement of shoulder function (100%) and stability (>90%), elbow flexion (85%), and hand, finger, and thumb (100%). When muscles malfunction after brachial plexus lesions, one should take into account the individual neuromuscular defect, passive joint function, and bony deformities; different procedures such as muscle transpositions, arthrodeses, and corrective osteotomies can then be performed to improve function of the upper extremity. Each form of operative treatment presents patients with certain benefits and all are integrated into a total treatment plan for the affected extremity.

Risk evaluation of thermal injury to the cervical spine during intradiscal laser application in vitro.

OBJECTIVE: We aimed to investigate temperature distribution during laser and its possible thermal damage to the neurovascular structures. BACKGROUND DATA: Percutaneous laser disc decompression (PLDD) is now being performed as a minimally invasive intradiscal technique for the operative therapy of non-sequestered herniated cervical discs. As yet, no experimental basic research has been reported with regard to temperature rise and distribution in the cervical region during laser radiation. MATERIALS AND METHODS: An in vitro laser procedure was performed on human cervical intervertebral discs under standardized conditions. A thermo-camera was used to monitor in real-time the zones sensitive to temperature increase. RESULTS: Average intervertebral disc volume was 2000 mm3. With a total energy conduction of 600 Joules, a temperature increase of around 30 degrees C was shown with an initial temperature of 28 degrees C at the posterior longitudinal ligament lying immediately in front of the myelon. The defect volume was less than 1% of the total intervertebral disc volume. CONCLUSION: If, during laser application, the total amount of conducted energy is too high, with an unfavorable position of the fibers in the intervertebral space, there is a risk of thermal damage to the spinal cord and nerve roots.

Long-term outcome following high tibial osteotomy with tension bend principle.

BACKGROUND: High tibial osteotomy has been successfully performed on patients with varus gonarthrosis for many years now. The prospective study presented here serves to verify the long-term outcome of this procedure. METHODS: A supratuberous high tibial osteotomy was carried out on 100 patients with varus gonarthrosis. Since then, 5 patients have died, and 6 patients could not be traced. The regaining rate was 94%. From a total of 89 patients with 101 operated knee joints, 46 were men and 43 women. The mean age at the time of surgery was 58 years. The patients were clinically and radiologically examined 10 years postoperatively and the knee score and function score ascertained according to the International Knee Society. RESULTS: The knee score showed a statistically significant increase from 31 points prior to surgery to 79 points at the time of follow-up; the function score likewise increased from 46 points to 78 points. In addition, 77.5% of patients would undergo the same surgery again, while 79% of patients claimed their condition to have improved following surgery. The preoperative full-length weight-bearing radiograph demonstrated an axis shift in the varus position of on average 9.6 degrees at 10 years postoperatively, an overcompensation in the valgus position of 1 degrees on average. At the time of follow-up, 81% did not require repeat surgery of the knee. CONCLUSION: With a correct diagnosis and accurate surgical techniques, positive clinical and radiological long-term results can be expected. Therefore, high tibial osteotomy may constitute an important contribution to our algorithm in the treatment of varus gonarthrosis.

Osteotomy of the humerus to improve external rotation in nine patients with brachial plexus palsy.

Malfunction of the infraspinatus muscle and teres minor muscle illustrate the typical clinical picture in patients with brachial plexus palsy. The arm hangs down in an inwardly rotated position and elbow flexion is hindered by striking of the lower arm against the thorax. Between 1995 and 2000, we have done external rotational osteotomy of the humerus for nine patients with brachial plexus palsy. The mean age of the patients at the time of operation was 29 years (range 15 to 42). The mean follow-up time was 24 (6 to 69) months. Preoperatively, the patients all had appreciable deficits of external rotation (mean deficit 37 degrees, range 10 degrees to 70 degrees). As a result of osteotomy, external rotation was improved in all patients, the mean increase being 42 degrees (range 25 degrees to 60 degrees). All patients were subjectively content with the improved position of the arm and its function. They were able to move their hands to their faces without striking the lower arm against the chest on elbow flexion, or without compensatory evasive movement of the shoulder.