Conventional rotator cuff versus all-suture anchors-A biomechanical study focusing on the insertion angle in an unlimited cyclic model.

PURPOSE: The purpose of this study was to compare the biomechanical properties of an all-suture anchor to a conventional anchor used commonly in rotator cuff repairs. Furthermore, the biomechanical influence of various implantation angles was evaluated in both anchor types in a human cadaveric model. METHODS: 30 humeri were allocated into three groups with a similar bone density. The two different anchor types were inserted at a predefined angle of 45°, 90° or 110°. Biomechanical testing included an initial preload of 20N followed by a cyclic protocol with a stepwise increasing force of 0,05N for each cycle at a rate of 1Hz until system failure. Number of cycles, maximum load to failure, stiffness, displacement and failure mode were determined. RESULTS: 27 anchors failed by pullout. There was no significant difference between the conventional and the all-suture anchor regarding mean pullout strength. No considerable discrepancy in stiffness or displacement could be perceived. Comparing the three implantation angles no significant difference could be observed for the all-suture or the conventional anchor. CONCLUSION: All-suture anchors show similar biomechanical properties to conventional screw shaped anchors in an unlimited cyclic model. The exact insertion angle is not a significant predictor of failure.

Biomechanical analysis of conventional anchor revision after all-suture anchor pullout: a human cadaveric shoulder model.

HYPOTHESIS AND BACKGROUND: The possibility of implanting a conventional anchor at the pullout site following all-suture anchor failure was evaluated in a biomechanical cadaveric model. The hypothesis of the study was that anchor revision would yield equal biomechanical properties. METHODS: Ten human humeri were obtained, and bone density was determined via computed tomography. After all-suture anchor (n = 5) and conventional 4.5-mm anchor (n = 5) insertion, biomechanical testing was conducted. Following all-suture anchor pullout, a conventional 5.5-mm anchor was inserted at the exact site of pullout (n = 5) and biomechanical testing was reinitiated. Testing was conducted using an initial preload of 20 N, followed by an unlimited cyclic protocol, with a stepwise increasing force of 0.05 N for each cycle at a rate of 1 Hz until system failure. The number of cycles, maximum load to failure, stiffness, displacement, and failure mode, as well as macroscopic observation at the failure site including diameter, shape, and cortical destruction, were registered. RESULTS: The defect following all-suture pullout showed a mean diameter of 4 mm, and conventional revision was possible in each sample. There was no significant difference between the initial all-suture anchor implantation and the conventional anchor implantation or the conventional revision following all-suture failure regarding mean pullout strength, stiffness, displacement, or total number of cycles until failure. CONCLUSION: Conventional anchor revision at the exact same site where all-suture anchor pullout occurred is possible and exhibits similar biomechanical properties.

Immediate Pain Relief in Adhesive Capsulitis by Acupuncture-A Randomized Controlled Double-Blinded Study.

OBJECTIVE: Primary adhesive capsulitis (AC), or frozen shoulder, is an insidious and idiopathic disease. Severe pain is predominant in the first two of the three stages of the condition, which can last up to 21 months. DESIGN, SETTING, AND SUBJECTS: Sixty volunteers with primary AC were randomly assigned to acupuncture with press tack needles compared with press tack placebos in a patient- and observer-blinded placebo-controlled study. The participants were subsequently offered classical needle acupuncture in an open follow-up clinical application. Thirty-four volunteers received conservative therapy, including 10 classical needle acupuncture treatments over 10 weeks, 13 volunteers received conservative therapy without classical needle acupuncture. All subjects agreed to follow-up after one year. METHODS: Acupuncture treatment was performed using a specific distal needling concept, using reflex areas on distant extremities avoiding local treatment. RESULTS: An immediate improvement of 3.3 ± 3.2 points in Constant-Murley Shoulder Score (CMS) pain subscore was seen in the press tack needles group and of 1.6 ± 2.8 points in the press tack placebos group (P <0.02). Conservative therapy including classical needle acupuncture significantly improved the pain subscore within 14.9 ± 15.9 weeks compared with 30.9 ± 15.8 weeks with only conservative therapy (P < 0.001). CONCLUSION: The efficiency of distal needling acupuncture on immediate pain reduction was demonstrated in patients with AC and confirmed the applicability of press tack needles and press tack placebos for double-blind studies in acupuncture. Subsequent clinical application observation proved that results obtained with press tack needles/press tack placebos can be transferred to classical needle acupuncture. Integrating acupuncture with conservative therapy showed superior effectiveness with respect to the time course of the recovery process in AC compared with conservative therapy alone.

Electromagnetic navigation provides high accuracy for transcoracoid-transclavicular drilling.

PURPOSE: A novel radiation-free electromagnetic navigation system (ENS)-based method was developed, and its feasibility and accuracy for transclavicular-transcoracoid drilling procedures were evaluated in an experimental setting. METHODS: Sixteen arthroscopically assisted electromagnetic navigated transcoracoid-transclavicular drilling procedures with subsequent TightRope device implantation were performed on eight human cadavers. Post-operative fluoroscopy and CT-scan analysis were acquired to determine tunnel placement accuracy. Optimal tunnel placement was defined as both the coracoid entry and exit point of the tunnel localized in the centre position of the coracoid base without cortical breach or fracture. RESULTS: Successful tunnel placement was accomplished in all 16 cases. The mean overall operation time was 30.3 ± 5.0 min. Regarding the coracoid exit point, 15 of 16 tunnels (93.8%) were localized in the desired base-centre position. During the navigated drilling procedure, no misguidance of the drill requiring directional readjustments or restarts occurred. No cortical breach, no fractures and no complications occurred. CONCLUSIONS: The electromagnetically navigated transcoracoid-transclavicular drilling procedure used in this study demonstrated high targeting accuracy, required no intraoperative radiographs, was associated with no complications and provided user-friendliness.

Biomechanical evaluation of 3 stabilization methods on acromioclavicular joint dislocations.

BACKGROUND: Traumatic acromioclavicular (AC) joint dislocations can be addressed with several surgical stabilization techniques. The aim of this in vitro study was to evaluate biomechanical features of the native joint compared with 3 different stabilization methods: locking hook plate (HP), TightRope (TR), and bone anchor system (AS). HYPOTHESIS: The HP provides higher stiffness than the anatomic reconstruction techniques. STUDY DESIGN: Controlled laboratory study. METHODS: A new biomechanical in vitro model of the AC joint was used to analyze joint stability after surgical repair (HP, TR, and AS). Eighteen cadaveric specimens were randomized for bone density and diameter in the midclavicle section. Joint stiffness was measured by applying an axial load and a defined physiological range of motion for internal and external rotations and upward and downward rotations. Data were recorded at 3 stages: for the native joint after dissecting the AC ligaments, directly after repair, and after axial cyclic loading (1000 cycles with 20 and 70 N at 1 Hz). To evaluate which implant mimics physiological joint properties best, axial stiffness of vertical stability was assessed in combination with rotation. Finally, static loading in the superior direction was applied until failure of the joints occurred. RESULTS: Axial stiffness of the TR and AS groups was 2-fold higher than for the HP group and the native joint (67.1, 66.1, and 22.5 N/mm, respectively; P < .004). Decreased load-to-failure rates were recorded in the HP group compared with the TR and AS groups (248.9 ± 72.7, 832.0 ± 401.4, and 538.0 ± 166.1 N, respectively). The stiffness of the rotations was not significantly different between the treatment methods but was lower in horizontal and downward rotations compared with the native state. Thus, native AC ligaments contributed a significant share to joint stiffness. CONCLUSION: The TR and AS groups demonstrated higher vertical load capacity. Compared with the TR and AS, the HP demonstrated an axial stiffness closest to the native joint. For restoring physiological properties, reconstruction of the AC ligaments may be necessary. CLINICAL RELEVANCE: The results show different biomechanical properties of the HP and anatomic reconstructions.

Comparison of 2D and 3D navigation techniques for percutaneous screw insertion into the scaphoid: results of an experimental cadaver study.

Navigation in hand surgery is still in the process of development. Initial studies have demonstrated the feasibility of 2D and 3D navigation for the palmar approach in scaphoid fractures, but a comparison of the possibilities of 2D and 3D navigation for the dorsal approach is still lacking. The aim of the present work was to test navigation for the dorsal approach in the scaphoid using cadaver bones. After development of a special radiolucent resting splint for the dorsal approach, we performed 2D- and 3D-navigated scaphoid osteosynthesis in 12 fresh-frozen cadaver forearms using a headless compression screw (Synthes). The operation time, radiation time, number of trials for screw insertion, and screw positions were analyzed. In six 2D-navigated screw osteosyntheses, we found two false positions with an average radiation time of 5 ± 2 seconds. Using 3D navigation, we detected one false position. A false position indicates divergence from the ideal line of the axis of the scaphoid but without penetration of the cortex. The initial scan clearly increased overall radiation time in the 3D-navigated group, and for both navigation procedures operating time was longer than in our clinical experience without navigation. Nonetheless, 2D and 3D navigation for non-dislocated scaphoid fractures is feasible, and navigation might reduce the risk of choosing an incorrect screw length, thereby possibly avoiding injury to the subtending cortex. The 3D navigation is more difficult to interpret than 2D fluoroscopic navigation but shows greater precision. Overall, navigation is costly, and the moderate advantages it offers for osteosynthesis of scaphoid fractures must be considered critically in comparisons with conventional operating techniques.

Computer-assisted surgery and intraoperative three-dimensional imaging for screw placement in different pelvic regions.

BACKGROUND: The purpose of this study was to assess the feasibility and accuracy of computer-assisted surgery (CAS) for screw placement in different pelvic regions using intraoperative three-dimensional (3D) imaging and to evaluate the influence of surgeons' experience with such a system on procedure time, radiation time, radiation dose, and misplacement rate. METHODS: Experimental study in a human cadaveric model (n=5) for percutaneous screw placement in the anterior column of the acetabulum, the posterior pelvic ring (S1, S2), and the superior pubic ramus via 3D fluoroscopic navigated procedure. Accuracy of screw placement was assessed by 3D image intensifier, including the reconstruction of multiplanar images and by computer tomography (CT) scan. Influence of surgeons' experience was assessed by direct comparison of a low- and high-volume surgeon using the same technical setting. RESULTS: In 100% of all procedures, intraoperative Iso-C3D image analysis was sufficient to confirm a correct screw placement. The postoperative CT scan revealed no further screw misplacement. However, for a correct supraacetabular screw placement, the intraoperative 3D scan was essential. In this group, the 3D scan showed screw misplacement in three cases. Procedure time for all indications and screw failure rate were significantly lower for the higher experienced surgeon. CONCLUSION: The 3D fluoroscopic navigated procedure in pelvic surgery seems to be a useful tool for all surgeons and especially for less experienced ones. Furthermore, the intraoperative reconstruction of multiplanar 3D images allows a secure control of implant positioning.

3D fluoroscopic navigated reaming of the glenoid for total shoulder arthroplasty (TSA).

Survival rates for total shoulder arthroplasty are critically dependent on the correct placement of the glenoid component. Especially in osteoarthritis, pathological version of the glenoid occurs frequently and has to be corrected surgically by eccentric reaming of the glenoid brim. The aim of our study was to evaluate whether eccentric reaming of the glenoid can be achieved more accurately by a novel computer assisted technique. Procedures were conducted on 10 paired human cadaveric specimens presenting glenoids with neutral version. To identify the correction potential of the navigated technique compared to the standard procedure, asymmetric reaming of the glenoid to create a version of -10° was defined as the target. In the navigated group, asymmetric reaming was guided by a 3D fluoroscopic technique. Postoperative 3D scans revealed greater accuracy for the eccentric reaming procedure in the navigated group compared to the freehand group, resulting in glenoid version of -9.8 ± 3.8° and -5.1 ± 4.1°, respectively (p < 0.05). Furthermore, deviation from preoperative planning was significantly reduced in the navigated group. These data indicate that our navigated procedure offers an excellent tool for supporting glenoid replacement in TSA.

Factors influencing the accuracy of iliosacral screw placement in trauma patients.

Correct placement of iliosacral screws remains a surgical challenge. The aim of this retrospective study was to identify parameters which impact the accuracy of this technically demanding procedure. Eighty-two patients with vertically unstable pelvic injuries treated with a total of 147 iliosacral screws were included. Assessment of postoperative CT scans revealed screw misplacement in 13 cases (8%), of which six occurred following insertion of two unilateral screws into S1. Six screw misplacements occurred in patients with dislocation injuries of the posterior pelvis. Comparison of a navigated and the standard technique revealed a decreased screw misplacement rate in the navigated group (15% standard vs. 3% navigation, p < 0.05). In addition, the malposition rate was influenced by the surgeon's individual experience (20% for low vs. 3.9% for high volume surgeons, p < 0.05). Overall, the accuracy of iliosacral screw placement depends on the number of screws inserted into S1 and the extent of dislocation. In experienced hands, the use of navigation represents a helpful tool to improve the placement accuracy.

Mid-term results of 155 patients treated with a collum femoris preserving (CFP) short stem prosthesis.

Short stem prostheses that preserve the femoral neck are becoming more and more popular. The CFP (collum femoris preserving) has been introduced especially for the treatment of younger patients. However, information about remodelling, complications and learning curve are thus far rare. We present a retrospective study of 155 patients (average age 59.3 ± 9.9 years) who underwent total hip replacement with the CFP prosthesis. Follow-up was obtained 74.3 ± 9.4 months postoperatively. The Harris hip score revealed excellent and good results in 96%. One stem had to be exchanged due to aseptic loosening revealing a survival rate of 99% and 100% for stem and cup, respectively. Radiological analysis showed typical patterns of remodelling with appearance of cortical thickening predominantly in the distal part of the prosthesis. Implant related revision rate was <1%, with further complication rate independent of the surgeon's individual experience. With regard to outcome, survivorship and complication rate, the medium-term results of the CFP prosthesis are promising.

Biomechanical evaluation of peri- and interprosthetic fractures of the femur.

BACKGROUND: Because of an increasing life expectancy of patients and the rising number of joint replacements, peri- and interprosthetic femoral fractures are a common occurrence in most trauma centers. This study was designed to answer two primary questions. First, whether the fracture risk increases with two intramedullary implants in one femur; and second, whether a compression plate osteosynthesis is sufficient for stabilizing an interprosthetic fracture. METHODS: Twenty-four human cadaveric femurs were harvested and four groups were matched based on the basis of bone density using a peripher quantitative computer tomography (pQCT). All groups-(I) hip prosthesis with a cemented femoral stem; (II) hip prosthesis and retrograde femoral nail; (III) hip prosthesis, retrograde femoral nail, and lateral compression plate; (IV) all three implants with an additional simulated interprosthetic fracture-were biomechanically tested in a four-point bending in lateral-medial direction. RESULTS: The second group with two intramedullary implants exhibited 20% lower fracture strength in comparison with group 1 with proximal femoral stem only. The stabilization of an interprosthetic fracture with a lateral compression plate (group IV) resulted in a fracture strength similar to femur with prosthesis only. CONCLUSION: Two intramedullary implants reduce the fracture strength significantly. If an interprosthetic fracture occurs, sufficient stability can be achieved by a lateral compression plate. Because two intramedullary implants in the femur may decrease the fracture strength, the treatment of supracondylar femoral fractures with a retrograde nail in cases with preexisting ipsilateral hip prosthesis should be reconsidered.

Evaluation of anatomic landmarks and safe zones for screw placement in the atlas via the posterior arch.

Several studies have evaluated quantitative anatomic data for direct lateral mass screw fixation. To analyze anatomic landmarks and safe zones for optimal screw placement through the posterior arc of the human atlas, morphometric parameters of 41 adult native human atlas specimens were quantitatively measured. Internal dimensions of the atlas (lateral mass, maximum and minimum intraosseous screw length), minimum height and width of the posterior arc and optimal screw insertion angles were defined on pQCT scans. By this, an optimal posterior screw insertion point (OIP) and a preferable screw direction (PSD) through the posterior arch into the lateral mass of C1 were defined. External dimensions (transverse and sagittal diameter) as well as the width of the mid-portion of C1 lateral mass were significantly higher in male specimens. The mean height of the posterior arch at the vertebral artery groove was 4.1 +/- 0.8 mm in female and 4.6 +/- 0.9 mm in male specimens. The optimal screw insertion point was located 21.6 +/- 1.7 mm in female and 23.6 +/- 2.3 mm in male lateral from the posterior tubercle of C1 (P < 0.01). The preferable screw direction was a mean medial inclination of 7.9 +/- 1.9 degrees in female and 7.3 +/- 2.7 degrees in male specimens and a mean rostral direction of 2.4 +/- 1.8 degrees in female and 3.1 +/- 1.7 degrees in male specimens. In conclusion, the presented study provides information for the use and design of upper cervical spine instrumentation techniques, such as screw placement to C1 via the posterior arch. The characterization of working areas and safe zones (OIP, PSD) might contribute to a minimization of screw malposition in this highly demanding instrumentation technique.

K-wire Arthrodesis and Coracoclavicular Augmentation of Complete Acromioclavicular Separations: Functional and Subjective Results.

BACKGROUND: In recent years, there has been a trend from operative to conservative management of complete acromioclavicular separations. Despite this, surgical treatment is still recommended to manual workers and athletes, who account for a large part of the patients. The objective of this study was to evaluate the functional outcome of type III separations according to Tossy managed by temporary arthrodesis of the acromioclavicular joint combined with coracoclavicular augmentation. Special attention was paid to sport exercising patients. PATIENTS AND METHODS: In this study, 32 patients (mean age 39 years) with a complete acromioclavicular separation were investigated. All of them underwent a surgical treatment managed by temporary acromioclavicular arthrodesis with two parallel k-wires and augmentation of the coracoclavicular ligaments with a biodegradable cord (PDS). Functional outcome was assessed after an average follow-up of 36 months by using the Constant-Murley-, Neer- and DASH-score. Additionally, incidence of complications and subjective results were observed. RESULTS: Evaluation of the data, obtained from the scores, revealed an excellent result for the Constant-Murley- and DASH-score for 84% of the patients. Regarding the Neer-score, 78% had an excellent outcome. Eighty-four percent of the patients assessed revealed an excellent to fair subjective result. Cosmetic reasons were most frequently the cause for discontentedness. Minor complications occurred in three patients without severe sequelae. All patients returned back to former working and sport activity level. CONCLUSION: Surgical treatment of complete acromioclavicular separations by temporary arthrodesis with two k-wires and coracoclavicualar PDS-augmentation results in good to excellent function. It is associated with a low complication rate and a high patient contentedness. Particularly for athletes in non-contact sports this surgical technique can still be recommended.

Antegrade nailing of humeral head fractures with captured interlocking screws.

OBJECTIVES/DESIGN: To assess the functional outcome after treatment of proximal humeral fractures with a new antegrade nail that provides angular and sliding stability. INTERVENTION/PATIENTS: Ninety-seven patients were treated during a 4-year period between April 2000 and March 2004. All patients were followed for 6 months, 51 patients (53%) for 12 months, and 31 patients (32%) for 24 months. This study focuses mainly on the patients with a follow up of 1 year. Their mean age was 68 years (range: 33 to 90); 22% were more than 80 years of age. MAIN OUTCOME MEASUREMENTS: All fractures were radiologically graded by the Neer and AO/ASIF classifications. Clinical assessment was performed at all follow-up visits using the Constant-Murley and Neer scores, and complications were recorded. RESULTS: There were 26.8% 2-part, 66% 3-part, and 7.2% 4-part fractures. The relative Constant-Murley score improved significantly (P < 0.001) from 72% at 6 months to 82% at 12 months after operation. No further improvement regarding functional outcome was observed after 24 months. Patients younger than 60 years of age had better results. No significant functional differences were found among 2-, 3- or 4-part fractures. Complications included backing out of the proximal screws (9.8%), secondary dislocation (1.9%), complete osteonecrosis (1.9%), and partial osteonecrosis (5.8%). CONCLUSION: Treatment with this nail provides sufficient fixation of the fragments to allow early mobilization. The good functional results in the majority of the patients indicate that this nail can be used, even in complex fractures and elderly patients.

Pain regulation and health-related quality of life after thoracolumbar fractures of the spine.

Fractures of the thoracolumbar spine rank among the severest injuries of the human skeleton. Especially in younger patients they often result from high-energy accidents. Recently, a shift in paradigm towards more aggressive treatment strategies including anterior procedures could be observed. However, so far only few data exist reflecting the quality of life (QoL) after such injuries. The aim of this study was to evaluate medium-term QoL and further to identify factors that influence the clinical outcome in patients with fractures of the thoracolumbar spine. Data of 906 patients who were treated during a 10-year period in our institution were evaluated retrospectively. Only patients with single-level traumatic injuries aged between 18 and 65 years without neurological deficits, concomitant injuries of other locations and internal comorbidities were included into the investigation (n = 204). Three different treatment groups (i.e. non-operative, dorsal and dorsoventral stabilisation) were compared to healthy controls as well as different pain populations. The QoL was assessed using established questionnaires (SF-36, HFAQ, VAS-Spinescore, PRQ, and PTSD). Sixty-five percent of the included patients (n = 133) were studied at an average follow-up of 5.3 +/- 1.7 years after injury. All treatment groups revealed an identical gender and age distribution. More severe and unstable injuries were found in the surgical groups associated with higher treatment costs and a longer inability to work. Compared to healthy controls, QoL was compromised to the same extent in all groups. Furthermore, all patients treated in this study did significantly better than low back pain individuals with regard to QoL and pain regulation parameters. In our study, patients with thoracolumbar spine fractures showed a reduced QoL compared to healthy controls. Thus, patients do not seem to regain their former QoL. However, the level of discomfort was comparably low in all groups, even in patients with more severe injuries requiring extensive surgery. Overall, outcome and QoL after traumatic fractures of the thoracolumbar spine rather seem to be determined by the severity of injury than by pain regulation or other psychosocial factors which is likely the case in low back pain disorders.

Proximal Humeral Fractures: Nailing.

Treating proximal humeral fractures surgically has always been a challenge for the orthopaedic trauma surgeon. The challenge was and is due to numerous factors such as the specific anatomy of the proximal humerus, problems of an adequate approach and exposure of the fracture and different fracture fragments, possible iatrogenic injuries to the rotator cuff on approach and the detrimental effects of the former on the latter's gliding and contracting ability after surgery. Furthermore, the very different fracture patterns that can occur at the proximal humerus, the shear number of fragments which can be of extremely bad bone quality, the necessity for anatomic reduction of these fragments with an implant that will allow for a stable osteosynthesis and at the meantime will not impinge in the subacromial area and lastly, the intention of the physician-in-charge to commence with physical therapy as soon as possible post OP. All of these added to the fact that not one fixation technique with one certain implant could be recommended as a treatment or implant of choice in dealing with these difficult fractures. Most of the supposedly applicable surgical techniques and implants had major setbacks such as being limited to only very expert hands, necessitating a long-standing postoperative immobilisation, resulting in secondary loosening of implants, secondary loosening of reduction or impaired bone healing and, despite all efforts, finally led to poor function at the shoulder. With the advent of angular stable implants such as angular stable, anatomically contoured plates designed for proximal humeral fractures only and special angular stable nails for the same or similar indications the treatment options and the quality of treatment in this area was much improved. Our experience with angular stable nails of two different manufacturers in now more than 320 implantations reveals that indications for the surgical treatment of such fractures can be extended constantly, that the number of complications will simultaneously decline, the necessity for primary joint arthroplasty even in multiple fragment fractures is minimal and that long-term results are, comparing the published results in the literature with those of our institution, equal if not superior to other treatment options.

Treatment of unstable fractures of the pelvic ring in pregnancy.

Unstable fractures of the posterior pelvic ring during pregnancy are rare. Pregnancy increases the high demands on the therapy of these types of fractures. The aim of the therapeutic strategy in such a situation is a good functional outcome of the mother without influencing the fetal health. Some osteosynthetic techniques result in good functional outcomes, but they are associated with high amounts of ionizing radiation. We report the case of a pregnant woman who sustained a vertical unstable fracture of the posterior pelvic ring as a result of a traffic accident. The fracture was treated surgically by open reduction and internal fixation with two transiliac reconstruction plates with minimal radiographic exposure to the fetus. One year later, a good functional result concerning the mother was shown. The child was healthy without any signs of prenatal impairment. Surgical treatment of an unstable fracture of the pelvic ring during pregnancy is possible with a justifiable risk to the mother and the child. Consideration of the expected fetal radiation exposure in the course of the therapy is particularly recommended. Using minimal doses of ionizing radiation, the described method results in a good clinical outcome of the mother while simultaneously reducing the radiation exposure of the fetus to an acceptable level.

Biomechanical comparison of anterior cervical spine locked and unlocked plate-fixation systems.

Three different anterior plate-fixation systems are available for the stabilisation of the cervical spine: (1) the cervical spine locking plate (CSLP), (2) dynamic plates allowing vertical migration of the fixation screws, and (3) various types of plates that are secured with either monocortical or bicortical unlocked screws. Unicortical screw purchase does not involve the risk of posterior cortex penetration and possible injuries to the spinal cord. The development of locking plates with unicortical screw-fixation and intrinsic stability of the screw-plate interface, via an angle-stabilised connection, was an attempt to increase the stability of unicortical screw-fixation systems. The aim of the study was to compare the biomechanical properties of a non-locking, anterior-plate system with 4.5 mm screw fixation and a locking anterior-plate system, in a single destabilised cervical spine-motion segment. Using fresh cadaveric cervical spine specimen C3-C7, multidirectional flexibility was measured at the C4-C5 level in an unconstrained test system, before and after destabilisation and fixation with an anterior plate with either locked or unlocked screw purchase. Direct comparison of the fixed cervical spine segments with unlocked and locked anterior-plate fixation did not demonstrate significant differences. This in vitro study documented that neither locked nor unlocked anterior-plate fixation can increase stability in all modes of testing. H-plate spondylodesis with unlocked screws seems to provide sufficient mechanical integrity in most cases of monosegmental lesions.

Biomechanical analysis of anterior cervical spine plate fixation systems with unicortical and bicortical screw purchase.

Anterior plate fixation with unicortical screw purchase does not involve the risk of posterior cortex penetration and possible injuries of the spinal cord. However, there are very few biomechanical data about the immediate stability of non-locking plate fixation with unicortical or bicortical screw placement. The aim of the present study was to evaluate the immediate biomechanical properties in terms of flexibility of a non-locking anterior plate system with 4.5-mm screw fixation and unicortical or bicortical screw purchase applied to a single destabilized cervical spine motion segment. Using fresh cadaveric cervical spine specimens C3-C7, multidirectional flexibility was measured at the level C4-C5 before and after destabilization and fixation with an anterior plate with either unicortical or bicortical screw purchase. The results showed that fixed cervical spine segments with anterior plate and bicortical screw purchase were more rigid than intact specimens in all modes of testing. The difference was statistically significant for flexion and extension ( P<0.001). Plate fixation with unicortical screw purchase had statistically significant decreased ranges of motion compared to the intact specimen only in extension. Neither unicortical nor bicortical screw purchase decreased the range of motion significantly in axial rotation compared to the intact specimens. This in vitro study documented that neither unicortical nor bicortical screw purchase with non-locking plate fixation can increase stability in all modes of testing, in axial rotation in particular. Direct comparison between the group with uni- and that with bicortical screw fixation did not reveal significant differences, and therefore no advantage was shown for either type of screw fixation. Therefore, we demonstrated that both uni- and bicortical screw purchase with non-locking plate fixation can decrease immediate flexibility of the tested motion segment, with better results for bicortical purchase. No significant differences were found comparing the two groups of screw fixation. These data suggest that unicortical screw fixation can be used for anterior plate fixation with a comparable immediate stability to bicortical screw fixation.