The benefit of using acetabular screws in primary total hip arthroplasty (THA) has been questioned in recent years. The disadvantages of using screws include increased operative time, risk of injury to surrounding neurovascular structures and metal ware breakage. Recent large registry studies have reported that screws do not confer a protective effect against acetabular loosening or the presence of osteolysis. Other studies have even described an increased risk of aseptic acetabular loosening with the selective use of screws. We report findings from a multicentre cohort study. This large cohort study compared clinical outcomes between primary acetabular components that were inserted with and without screws. Independent variables included the presence (or absence) of screws, the total number of screws used and the cumulative screw length (CSL). Outcome measures included all-cause revision, acetabular component revision and acetabular component loosening. Statistical software (Stata/IC 13.1 for Mac [64-bit Intel]) was used to conduct all statistical analyses. A p-value < 0 .05 taken to be significant. There were 4,583 THAs performed in total. Screws were used in 15.9% (n=733). At a mean follow-up of 5.2 years, the all-cause revision rate in the screw cohort was 1.5% compared to 0.83% in the no screw cohort (p=0.085). There was no difference in acetabular component revision rates for screws (3/733, 0.41%) versus no screws (12/3,850, 0.31%) (p=0.439). The rate of acetabular loosening noted during the time of revision surgery was significantly higher when screws were used in the index procedure (2/733, 0.2%) compared to the no screw cohort (1/3,850, 0.02%) (p=0.017). There was no difference in outcomes when stratifying by the number of screws used or the cumulative screw length. Primary acetabular components do not require screws for fixation. All cause revision rates and acetabular component revision rates are comparable for the screw and the no screw cohorts. The rate of acetabular component loosening, as observed during revision surgery, is significantly higher when screws are used in the index total hip replacement

Primary implant stability is critical for osseointegration and subsequent implant success. Small displacements on the screw/bone interface are necessary for implant success, however, larger displacements can propagate cracks and break anchorage points which causes the screw to fail. Limited information is available on the progressive degradation of stability of an implanted bone screw since most published research is based on monotonic, quasi-static loading [1]. This study aims to address this gap in knowledge. A total of 100 implanted trabecular screws were tested using multi-axial loading test set-up. Screws were loaded in cycles with the applied force increasing 1N in each load cycle. In every load cycle, Peak forces, displacements, and stiffness degradation (calculated in the unloading half of the cycle) where recorded. 10 different loading configurations where tested. The damage vs displacement shows a total displacement at the point of failure between 0.3 and 0.4 mm while an initial stiffness reduction close to 40%. It is also shown that at a displacement of ~0.1 mm, the initial stiffness of every sample had degraded by 20% (or more) meaning that half of the allowable degradation occurred in the first 25-30% of the total displacement. Other studies on screw overloading [1] suggests similar results to our concerning initial stiffness degradation at the end of the loading cycle. Our results also show that the initial stiffness degrades faster with relatively small deformations suggesting that the failure point of an implanted screw might occur before the common failure definition (pull-out force, for example). These results are of great significance since primary implant stability is better explained by the stiffness of the construct than by its failure point

Abstract. Objectives. The use of cannulated screws for femoral neck fractures is often limited by concerns of avascular necrosis (AVN) occurring, historically seen in 10–20% of fixed intracapsular fractures. The aim of this study was to investigate the rate of AVN with current surgical techniques within our unit. Methods. A single centre retrospective review was performed. Operative records between 1st July 2014 and 31st May 2019 were manually searched for patients with an intracapsular neck of femur fracture fixed with cannulated screws, with minimum one year follow up. Patient records and radiographs were reviewed for clinical and radiographic diagnoses of AVN and/or non-union. Fracture pattern and displacement, screw configuration and reduction techniques were recorded, with radiographs independently analysed by five orthopaedic surgeons. Results. Sixty-five patients were identified, average age of 72 years (range 48–87). Thirty-six patients (55%) sustained displaced fractures and 29 patients (45%) had undisplaced fractures. Two (3%) patients developed AVN, with no cases of fracture non-union. Ten patients (15%) sustained a high-energy injury, though none of these patients developed AVN. Screws configurations were: two (3%) triangle apex-superior, 39 (60%) triangle apex-inferior, 22 (34%) rhomboid and two (3%) other, with nine (14%) cases using washers. All fractures required closed reduction; no open reductions performed. Conclusions. Our observed AVN rate is much lower than widely reported, especially given the proportion of displaced fractures that were fixed. With adequate fixation, even in displaced fracture patterns with imperfect reduction, cannulated screws are an excellent option for intracapsular neck of femur fractures. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Study Design: A radiographic study using disarticulated cadaver thoracic vertebrae. Objective: To determine the accuracy of orthogonal X-rays in detecting thoracic pedicle screw position by different groups of observers. Summary of Background Data: Pedicle screws are increasingly being used for internal fixation of the thoracic spine. Surgeons and radiologists are often required to make decisions on the pedicle screw position by plain antero-posterior (AP) and lateral radiographs. Materials and Methods: 23 disarticulated fresh adult thoracic vertebrae were used in this study. Pedicle screws were inserted completely within the pedicle; or deliberately violating the lateral or medial cortex of the pedicle. AP and lateral radiographs of each vertebrae were assessed by 2 spine surgeons, 2 spine trainees, and 2 musculoskeletal radiologists in a sequence of AP alone, and AP + lateral views. They were supposed to cataogorize the pedicular screw as ‘out laterally’/‘inside the pedicle’/‘out medially’ or ‘unsure’. Their assessments were compared to the actual position of the screws determined by the axial views. Results: For each screw position, trend was found towards slightly better accuracy with availability of AP & lateral views in combination. From either AP alone or AP + lateral views, significantly higher accuracy was found in detecting screws “out laterally” than “inside pedicle” (p< 0.01), or “out medially”(p< 0.05), respectively. Nearly 30% of screws that were deliberately placed through the medial pedicle wall were not correctly identified. In addition, surgeons have highest accuracy from either AP alone, or AP + lateral views, followed by the spine trainees and radiologists. Radiologists provided more “unsure” answers than surgeons or trainees. Conclusions: Screws that perforated the lateral cortex were the easiest, and those that were wholly within the pedicle were the most difficult to identify correctly. The use of plain radiographs to detect thoracic pedicle screws placed through the critical medial cortex is unreliable. The positions of thoracic pedicle screws appear to be more accurately detected by AP + lateral, however, the major contribution was from AP views. Surgeon experience continues to be vitally important in the safe placement of thoracic pedicle screws. Key points:. Screws that perforated the lateral cortex were the easiest, and those that were wholly within the pedicle were the most difficult to identify correctly. The use of plain radiographs to detect thoracic pedicle screws placed through the critical medial cortex is unreliable. AP + lateral views provides higher accuracy in determining the screw position, while, the major contribution comes from AP views. Surgeon experience, in the use of tactile skills and anatomical knowledge continue to be vitally important in the safe placement of thoracic pedicle screws

Introduction Thoracic pedicle screws are increasingly being used for internal fixation. Surgeons and radiologists are often required to make decisions about the position of the screws in relation to the pedicle based on AP and lateral plain radiographs alone. We ventured to assess the value of orthogonal radiographs in determining the position of thoracic pedicle screws in 23 cadaveric thoracic vertebrae. Methods Disarticulated cadaveric thoracic vertebrae were used in this study. Pedicle screws were inserted in three positions: 1) within the pedicle, deliberately violating the 2) lateral cortex of the pedicle and 3) medial cortex of the pedicle. AP (antero-posterior) & lateral radiographs were obtained and presented to 6 readers (4 surgeons & 2 radiologists) in booklets consisting of AP views alone, lateral views alone and both AP & lateral views together in a sequential manner. The readers were asked to indicate the position of the screws and the results of the evaluation were compared to the actual position (axial views). Results On AP views alone, the accuracy in detecting screws placed out of the pedicle laterally and medially were 93% and 76% respectively, while the accuracy for screws placed inside the pedicle was 85% . On LATERAL views alone, the accuracy for the same screw positions were 69%, 58% and 64% respectively. When AP + LATERAL views were considered together, the accuracy for the same screw positions were 93%, 80% and 87% respectively. Comparing the three groups, it was observed that screw positions were read more accurately in AP + LATERAL views (87%) compared to AP views alone (85%), or LATERAL views alone (64%). The sensitivity of correctly identifying screws placement is highest in AP + LATERAL (90%) views with a specificity of 94%. The specificity of detecting screws placed inside the pedicle is highest in AP (94%). The positive predictive value (PPV) of radiographs in general (AP +LATERAL) in detecting screws placed inside the pedicle, out of the pedicle laterally and medially were 73%, 92% and 86% respectively. The negative predictive value (NPV) of radiographs in general for the same screw locations were 90%, 96% and 76% respectively. On AP and AP + LATERAL views respectively, 25% and 23% of screws placed inside the pedicle were read as medially ‘out’. 10% of screws placed medially ‘out’ were read as ‘in’ on both AP and AP + LATERAL views. Inter-observer difference was substantial. In general, surgeons appeared to have consistently higher accuracy, sensitivity, specificity, PPV and NPV values compared to radiologists and fellows in determining screw position. Discussion The positions of the screws appear to be most accurately detected when both AP and lateral x-rays are provided compared to AP or lateral alone. Screws that perforated the lateral cortex were the easiest and those that were medially out were the most difficult to identify. Screws passed inside the pedicle may create an unnecessary apprehension that they may be medial and screws passed medially may give a false sense of security that the screw is inside the pedicle. Radiographs are just one component in ensuring accurate pedicle screw placement and surgeon’s experience, in the use of tactile skills and anatomical knowledge continue to be vitally important in the safe placement of thoracic pedicle screws

Aims: Fixation failure due to osteoporosis is a major complication of osteosynthesis using compression hip screws (CHS). Biocompatible materials have been developed to improve CHS purchase and to limit fixation failure. Cortoss™ is a novel, injectable composite that interdigitates with bone, mimicking native cortical bone. This pilot study tested the immediate anchoring strength and safety of Cortoss in patients with peritrochanteric fracture. Methods: Ethical Committee approval and patient informed consent were obtained. Screws were advanced under fluoroscopy to their final position, and torque was measured electronically. Screws were backed out approximately 1 cm, 2.5 mL Cortoss was injected under fluoroscopy, and the screw was reinserted. An increase in rotational torque of at least 30% was achieved after allowing time for the bone filler to set. Results: The study population consisted of 20 patients (18 females, 2 males), 70 years or older (range 70 to 96 years) with osteoporosis. The mean preaugmentation torque was 1.23 Nm (range 0 to 4.8 Nm) and the mean postaugmentation torque was 1.81 Nm (range 0.7 to 4.8 Nm). All 20 screws were judged clinically tight after fixation. X-ray images showed that Cortoss contacted the screw threads and interdigitated with surrounding bone. No adverse events were reported. Conclusions: Cortoss provided safe and effective anchorage of CHS. By preventing screw cutout, Cortoss may provide long-term benefit to osteoporotic hip fracture patients by limiting fixation failure

Introduction and Aims: Good clinical outcome can be expected following cementless total knee arthroplasty (TKA) provided there is early stability and bone ingrowth. Screws give excellent initial stability but provide a path for osteolysis. Screws also cause an irregularity of the tibial component surface which limits their use as a mobile bearing component. We hypothesise that early stability can be obtained with four peripheral pegs rather than screws. We present the results of such a tibial component at a minimum of two years in a cementless mobile-bearing TKA. Materials and Methods: We evaluated 200 knees in 173 patients. The average age at surgery was 72 years (range, 45–91 years) with 61% of cases in women. Patients were followed up for an average of 45.7 months (range 24 to 69 months). All radiographic and clinical scores were performed prospectively and recorded on a relational database. The components used were the cementless Low Contact Stress femoral component with the DuoFix MBT tibial tray (Depuy, Warsaw, Indiana, USA). The tibial tray was manufactured from cobalt-chrome with a central polished stem and four peripheral pegs. The underside, including the pegs, had a porous surface coated with 50 microns of hydroxyapatite. Results: After excluding patients who had died, or lost to follow up, 164 cases had a minimum 2-year follow-up. None of the tibial components have required revision. One patient (0.6%) required revision of the femoral component at 22 months for failure of bone ingrowth. There was one superficial infection which resolved with intravenous antibiotics. Two patients developed deep infections (1.2%) which resolved with arthroscopic lavage and antibiotics. One patient presented with bearing spin out at 3 months following surgery, and an exchange to a thicker tibial insert was performed. Average flexion at follow up was to 110°. The patients stated that they were satisfied with their knees in 141 out of 155 cases (91%). The mean score for pain at rest was 0.9 (0–10) and for activity related pain was 1.3. The average HSS score was 86/100 with 90% good or excellent results, compared with a preoperative score of 54/100. Lucent lines were seen in one tibial zone in ten knees (7%), and two zones in three knees (2.1%). There were lucent lines in one femoral zone in 13 cases and two zones in two cases. None of the lines were progressive, and all the surviving components were bone ingrown. Osteolysis was present in a single zone around one (0.7%) tibial component. One patient showed some femoral osteolysis in one zone (0.7%) and also had patellar osteolysis in one zone. Two patients had osteolysis in a single zone of the patella. Conclusion: This study shows that this design of mobile bearing tibial component provides good primary stability and bone ingrowth

Purpose of the study: Fixing the pedicles can be difficult to achieve during surgical treatment of scoliosis involving the thoracic spine because of the vertebral rotation raising the risk of neurological and vascular disorders. Use of extrapedicular thoracic screws has been proposed for more adapted and safe fixation. No clinical data has been published concerning the safety of these screws. Material and methods: This multicentric retrospective clinical and radiological study included 467 thoracic screws in 34 patients operated for scoliosis. Neurophysiological monitoring was used for all procedures. Screws were positioned free hand without radioscopic control. Pedicular screws were inserted in T10, T11, T12. Extra-pedicular screws were inserted for thoracic vertebrae above T10 to T4. Correction was achieved with rods bent in situ. The purpose of this study was to evaluate the position of the thoracic screws within the vertebral body and in relation to the great vessels and the cord. The position of the screws in the thoracic spine was studied by two independent observers reading multiple thin-slice CT images. The observers noted malposition as: 1) penetration into the canal more than 2 mm, 2) less than 1 cm hold in the vertebral body, 3) screw protrusion more than 2 mm beyond the vertebral cortical. Results: Screw malposition was observed for 9 of 161 pedicular screws (5.4%) and for 21 of 306 (6.8%) thoracic screws. None of the screw malpositions had a clinical expression. There was one episode of thoracic effusion associated with thoracoplasty. Two patients required revision (one for poor indication and one for disincarceration). There were no postoperative deep infections. Three cases of intercostals neuralgia subsided within three months. Conclusion: Insertion of thoracic screws for fixation and correction is a useful technique with few complications. It enables better 3D correction and better control of the deformation. Screw malposition in this series was similar to that observed with classical pedicular techniques. There was no major complication associated with thoracic screws

Summary Statement

From a mechanical point of view, the clinical use of pedicle screws in the atlas is a promising alternative to lateral mass screws due to an increased biomechanical fixation.

A retrospective review of 51 consecutive patients undergoing fixation of Scaphoid fractures by two surgeons in a single institution was conducted. Twenty-four patients were treated with a Herbert screw and twenty-seven with an Acutrak screw. This included six patients who underwent acute fixation, three in each group. The remaining cases were for the treatment of non-union and delayed union.

There were no significant differences between the two groups in terms of age, side of injury, and mechanism of injury. Fractures were classified as proximal, middle and distal thirds of the Scaphoid and there was no significant difference between the groups regarding the types of fractures treated. The only significant difference between the groups was the time from injury to fixation when considering the cases of delayed union and non union which was greater in the Herbert screw group (7.5 months vs 4 months p=<0.05).

There was no significant difference in outcome between the two methods of fixation. Union rates for all cases were 79% for Herbert screws and 81% for Acutrak screws and 82% and 83% respectively when only considering the delayed union/non-union procedures. There was no difference in terms of time to union, further surgery or clinical outcome between the two groups. The Acutrak screw required removal in five patients and the Herbert screw in two due to symptoms from screw prominence. This was not statistically significant.

In conclusion there is no significant difference in surgical outcome between these two methods of fixation for Scaphoid fractures. The authors feel that this supports the view that biological factors are more important than the method of fixation in obtaining union of Scaphoid fractures.

Cannulated hip screws are frequently used in the management of hip fractures. There have been concerns over the failure rate of the technique and the outcomes of those that subsequently require conversion to total hip replacement (THR).

This study utilised a database of over 600 cannulated hip screw (CHS) fixations performed over a 14-year period and followed up for a minimum of one year (1-14). We identified 57 cases where a conversion to THR took place (40 females, 17 males, mean age: 71.2 years). Patient demographics, original mechanism of injury, fracture classification, reason for fixation failure, time until arthroplasty, implant type and post-arthroplasty complications were recorded. Clinical outcomes were measured using the Oxford Hip Score.

The failure rate of cannulated screw treatment was 9.4% and the mean time from initial fixation to arthroplasty was 15.4 (16.5) months. Thirty six fractures were initially undisplaced and 21 were displaced. As one might expect the displaced cases tended to be younger but this didn't reach statistical significance [66.5(14.3) vs 72.7(13.1), p=0.1]. The commonest causes of failure were non-union (25 cases, 44%) and avascular necrosis (17 cases, 30%). Complications after THR consisted of one leg length discrepancy and one peri-prosthetic fracture. The mean Oxford score pre-arthroplasty was 12.2 (8.4), improving to 38.4 (11.1) at one-year. Although the pre op Oxford scores tended to be lower in patients with undisplaced fractures and higher ASA scores, the improvement was the same whatever the pre-op situation. The one-year Oxford score and the improvement in score are comparable to those seen in the literature for THR in general.

In conclusion, CHS has a high success rate and where salvage arthroplasty is required it can provide good clinical outcomes with low complication rates.

Introduction: The aim of this study was to assess the learning curve of spinal internal fixation with pedicle screws of a spinal fellow (AG) with no previous experience with the technique, during a 2-year fellowship at a referral spinal surgery centre in Australia.

Methods: Patients treated with pedicle screw (PS) placement by the spinal fellow under the supervision of the attending orthopaedic or neurosurgery consultant were included in this study. Postoperative plain x-rays and, in some cases, computed tomography scans (CT scans) were obtained. PS position was assessed by two blinded independent reviewers, one radiologist (observer 1) and one spinal surgeon (observer 2), using a grading scale. PS placed by the attending consultants were included in the evaluation as distractors. The screws were classified using a grading scale in 3 groups: Correct, Border-line, and Incorrect. After assessment, the PS were rearranged in groups of 40 screws, in chronological order, for comparison and assessment of the progress in the learning curve.

Results: 94 patients underwent internal fixation of the spine from upper thoracic to the sacral region with PS (584 screws in total) between February 2006 and December 2007. Eight cases (40 screws) were excluded because of lack of image studies or severe spinal deformities. Among the 544 screws under evaluation, 320 (58.8%) were performed by the spinal surgery fellow, 187 (34.4%) by the attending consultant and 37 (6.8%) by orthopaedic and neurosurgery registrars, the latter evaluated but excluded for the statistical analysis. The overall precision for the 507 screws analysed was 84.2% according to observer 1 and 77.9 % according to observer 2. When the analysis was narrowed down to the 320 screws done by the fellow, this precision increased to 84.7% for observer 1 and decreased to 76.6% according to observer 2. A learning curve was created consisting of 8 groups of 40 screws in chronological order. There was a statistical significance (p< 0.05) in the rate of Incorrect and Border-line PS when comparing the first 100 PS with the rest of the series. None of the patients (included and excluded) developed neurological complications because of the misplaced PS.

Discussion: The findings reveal a learning curve of PS placement. In this series, the inflexion point in the learning curve for this technique was between 80 and 120 screws, which in the present series represented the spinal fellow intervention in 20 to 30 cases. After approximately 150 PS no significant changes can be observed: the learning curve remains stable, with a constant decreasing trend. With appropriate expert supervision the fellowship training system is a safe and appropriate method to learn this technique.

Abstract

Magnesium calcium alloys are promising candidates for an application as biodegradable osteosynthesis implants [1,2]. As the success of most internal fracture fixation techniques relies on safe anchorage of bone screws, there is necessity to investigate the holding power of biodegradable magnesium calcium alloy screws. Therefore, the aim of the present study was to compare the holding power of magnesium calcium alloy screws and commonly used surgical steel screws, as a control, by pull-out testing.

Magnesium calcium alloy screws with 0.8wt% calcium (MgCa0.8) and conventional surgical steel screws (S316L) of identical geometries (major diameter 4mm, core diameter 3mm, thread pitch 1mm) were implanted into both tibiae of 40 rabbits. The screws were placed into the lateral tibial cortex just proximal of the fibula insertion and tightened with a manual torque gauge (15cNm). For intended pull-out tests a 1.5mm thick silicone washer served as spacer between bone and screw head. Six animals with MgCa0.8 and four animals with S316L were followed up for 2, 4, 6 and 8 weeks, respectively. Thereafter the rabbits were sacrificed. Both tibiae were explanted, adherent soft tissue and new bone was carefully dissected around the screw head. Pull-out tests were carried out with an MTS 858 MiniBionix at a rate of 0.1mm/sec until failure of the screw or the bone. For each trial the maximum pull-out force [N] was determined. Statistical analysis was performed (ANOVA, Student's t-test).

Both implant materials were tolerated well. Radiographically, new bone was detected at the implantation site of MgCa0.8 and S316L, which was carefully removed to perform pull-out trials. Furthermore, periimplant accumulations of gas were radiographically detected in MgCa0.8. The pull-out force of MgCa0.8 and S316L did not significantly differ (p = 0.121) after two weeks. From 6 weeks on the pull-out force of MgCa0.8 decreased resulting in significantly lower pull-out values after 8 weeks. Contrary, S316L pull-out force increased throughout the follow up. Thus, S316L showed significantly higher pull-out values than MgCa0.8 after 4, 6 and 8 weeks (p<0.001).

MgCa0.8 showed good biocompatibility and pull-out values comparable to S316L in the first weeks of implantation. Thus, its application as biodegradable osteosynthesis implant is conceivable. Further studies are necessary to investigate whether the reduced holding power of MgCa0.8 is sufficient for secure fracture fixation. In addition, not only solitary screws, but also screw-plate-combinations should be examined over a longer time period.

Introduction

Epiphysiodesis, defined as the process of closing the growth plate (physis), have been used for several years as a treatment option of cases where the predicted leg-length discrepancy (LLD) falls between 2 to 5 cm. The aim of this study was to systematically review the existing literature on the effectiveness of three different epiphysiodesis techniques with implant usage for the treatment of leg-length discrepancy in the pediatric population. The secondary aim was to address the reported complications of staples, tension-band plates (TBP) and percutaneous epiphysiodesis screws (PETS).

Distal interphalangeal joint (DIPJ) fusion using a k-wire has been the gold standard treatment for DIPJ arthritis. Recent studies have shown similar patient outcomes with the headless compression screws (HCS), however there has been no cost analysis to compare the two. Therefore, this study aims to 1) review the cost of DIPJ fusion between k-wire and HCS 2) compare functional outcome and patient satisfaction between the two groups.

A retrospective review was performed over a nine-year period from 2012-2021 in Counties Manukau. Cost analysis was performed between patients who underwent DIPJ fusion with either HCS or k-wire. Costs included were surgical cost, repeat operations and follow-up clinic costs. The difference in pre-operative and post-operative functional and pain scores were also compared using the patient rate wrist/hand evaluation (PRWHE).

Of the 85 eligible patients, 49 underwent fusion with k-wires and 36 had HCS. The overall cost was significantly lower in the HCS group which was 6554 New Zealand Dollars (NZD), whereas this was 10408 NZD in the k-wire group (p<0.0001). The adjusted relative risk of 1.3 indicate that the cost of k-wires is 1.3 times more than HCS (P=0.0053). The patients’ post-operative PRWHE pain (−22 vs −18, p<0.0001) and functional scores (−38 vs −36, p<0.0001) improved significantly in HCS group compared to the k-wire group.

Literatures have shown similar DIPJ fusion outcomes between k-wire and HCS. K-wires often need to be removed post-operatively due to the metalware irritation. This leads to more surgical procedures and clinic follow-ups, which overall increases the cost of DIPJ fusion with k-wires.

DIPJ fusion with HCS is a more cost-effective with a lower surgical and follow-up costs compared to the k-wiring technique. Patients with HCS also tend to have a significant improvement in post-operative pain and functional scores.

Introduction

Non-union is debilitating, costly and affects 2–8% of intramedullary fixed fractures. Clinical data suggest that percutaneous interfragmentary screws offer a less invasive alternative to exchange nailing. This study aimed to assess their efficiency with biomechanical analyses.

We considered three different device systems for the treatment of lumbar and lumbosacral instability. From a prospective database in use in our Institution, we obtained a 45-patient cohort of individuals who received a one-level lumbar or lumbosacral fusion procedure between 1995 and 1998. All patients had presented with disabling back and/or radicular pain and severe degenerative changes at one disc level or low-grade spondylolisthesis.

First group: 15 patients, six male and nine female, with an average age of 41 years, were treated by an interbody fusion using cylindrical threaded cages; the levels fused were L5-S1 in 10 patients and at L4-L5 in five.

Second group: 15 patients, eight male and seven female, with an average age of 39 years were treated by nine cylindrical, threaded cages and seven square cages, combined with posterior pedicle screws; the levels fused were L5-S1 in 11 and L4-L5 in four.

Third group: 15 patients, eight male and seven female, with an average age of 40 years, underwent posterolateral fusion with posterior pedicle screws instrumentation alone; the levels fused were L5-S1 in 10 and L4-L5 in the remaining five.

At a mean follow-up of 8 years in the first group, eight patients (53%) required a second operation (five posterior instrumentation, two root decompression and one repair of dural tear). The clinical results were fair in six patients (40%) and poor in three (20%); five patients (33%) presented uncertain fusion signs. In the second group, two patients (13%) required a second operation (one root decompression and one dural repair). All patients (100%) presented definite fusion signs. The clinical results 6.5 years after primary surgery were fair in two (13%) patients and poor in two (13%). In the third group, two patients (13%) required a second operation (one dural repairand one implant removal). The clinical results were fair in two cases (13%) and no poor results were seen. At a mean follow-up of 6.5 years, 14 patients (93%) showed definite fusion signs.

According to the present data, we can conclude that in terms of fusion success, clinical outcome and complication rates, the use of posterior interbody cages alone is not as safe and effective for the management of one level degenerative disc disease or low-grade spondylolisthesis as the posterior pedicle screw instrumentation combined with two posterior cages or the stand-alone pedicle screw instrumentation.

Introduction: The complex anatomy and biomechanics of the atlantoaxial motion segment impose technical challenges in the achievement of safe and successful surgical stabilization and fusion. The coauthors have recently reported successful clinical results using a novel C1-C2 stabilization technique employing C1 multi-axial posterior arch screws (MA-PAS). This study compares biomechanical stability of MA-PAS with two established multi-point fixation techniques (Magerl-Gallie and Harms) using non-destructive and destructive testing. Methods: 15 human fresh-frozen cadaveric occipital-C5 cervical spines (average age 77.4 [51–95], sourced from ScienceCare, USA) were randomly allocated to 3 equal groups. Screws were passed up through adjacent end vertebrae such that motion was limited to between C0 and C4. Each spinal column was non-destructively tested in flexion/extension (±1.5Nm), lateral bend (±1.5Nm) and axial rotation (±1.5Nm), firstly in their INTACT state and then after Type 2 odontoid fracture destabilization combined with MAGERL-GALLIE (n=5), HARMS (n=5) or MA-PAS (n=5) instrumentation. All 15 reconstructed spines were finally loaded to failure in forward flexion only. Results: Non-destructive testing: The C1-C2 joint of the INTACT spines all demonstrated high flexibility in flexion/ extension (ave 16.5deg) and axial rotation (ave 52.6 deg) while lateral bending (ave 2.7deg) was less compliant (see Fig.3). After instrumentation all specimens showed significantly reduced ROM in flexion/extension (MAGERL-GALLIE=4.2deg, HARMS=4.4deg, MA-PAS=4.2deg) and axial rotation (MAGERL-GALLIE=4.05deg, HARMS=0.59deg, MA-PAS=3.7deg) while lateral bend ROM of all instrumented specimens was similar or slightly greater than INTACT (HARMS=2.3deg, MAGERL-GALLIE=3.8deg, MA-PAS=5.3deg). There was no significant difference between the instrumented groups in each loading direction. Destructive testing: MAGERL-GALLIE was the strongest requiring an average of 13.5Nm to cause failure while HARMS was the weakest requiring 7.8Nm of torque. MA-PAS technique averaged 12.2Nm of torque to cause failure. Conclusions: The MA-PAS technique was shown to have similar ultimate strength in flexion to the MAGERL-GALLIE and HARMS techniques and stability in flexion-extension, axial rotation and lateral bend. The MA-PAS failure load in flexion was greater than the HARMS technique, and nearly as high as the MAGERL-GALLIE. Given the biomechanical stability of the MA-PAS technique, it is proposed that this technique is an alternative to the technically demanding, and possibly more hazardous, conventional multi-point fixation techniques in patients with normal, as well as anomalous, C1/2 segmental anatomy

Introduction: There is a recent trend of using a raft of small diameter 3.5 mm cortical screws instead of the large diameter 6.5mm screws in depressed tibial plateau fractures. Our aim was to compare the biomechanical properties of these two constructs in the normal and osteoporotic synthetic bone model.

Methods: 20 rigid polyurethane foam blocks with a density simulating osteoporotic bone and normal bone were obtained. A Schatzker type 3 fracture was created in each block. The fracture fragments were then elevated and supported using 2, 6.5mm cancellous screws or 4, 3.5mm cortical screws.

The fractures were loaded using a Lloyd’s machine and a load displacement curve was plotted.

Results: Osteoporotic model. The mean force needed to produce a depression of 5mm was 700.8N with the 4-screw construct and 512.4N with the 2 screw construct (p=0.007).

Non-osteoporotic model. The mean force requires to produce the same depression was 1878.2N with the 2-screw construct and 1938.2N with the 4 screw construct (p=0.42).

An increased fragmentation of the synthetic bone fragments was noticed with the 2-screw construct but not with the 4-screw construct.

Conclusion: A raft of 4, 3.5 mm cortical screws is biomechanically stronger than two, 6.5mm cancellous screws in resisting axial compression in osteoporotic bone.