Increasing innovation in rapid prototyping (RP) and additive manufacturing (AM), also known as 3D printing, is bringing about major changes in translational surgical research.

This review describes the current position in the use of additive manufacturing in orthopaedic surgery.

Cite this article: Bone Joint J 2018;100-B:455-60.

Aims

To determine the normal values and usefulness of the C1/4 space available for spinal cord (SAC) ratio and C1 inclination angle, which are new radiological parameters for assessing atlantoaxial instability in children with Down syndrome.

Aims. Although atlantoaxial rotatory fixation (AARF) is a common cause of torticollis in children, the diagnosis may be delayed. The condition is characterised by a lack of rotation at the atlantoaxial joint which becomes fixed in a rotated and subluxed position. The management of children with a delayed presentation of this condition is controversial. This is a retrospective study of a group of such children. Patients and Methods. Children who were admitted to two institutions between 1988 and 2014 with a diagnosis of AARF were included. We identified 12 children (four boys, eight girls), with a mean age of 7.3 years (1.5 to 13.4), in whom the duration of symptoms on presentation was at least four weeks (four to 39). All were treated with halo traction followed by a period of cervical immobilisation in a halo vest or a Minerva jacket. We describe a simple modification to the halo traction that allows the child to move their head whilst maintaining traction. The mean follow-up was 59.6 weeks (24 to 156). Results. Despite the delay in referral, the subluxation was successfully reduced in all children. Only two children required atlantoaxial fusion. Conclusion. The results of our study suggest that normal anatomy with restoration of movement may be achieved even in cases of AARF presenting late, obviating the need for fusion. We also show a simple modification to the halo traction that allows the child to move their head about while still maintaining traction. Take home message: Prompt diagnosis and management with halo traction (with a simple modification as described) is associated with good results in patients with AARF who present late. Cite this article: Bone Joint J 2016;98-B:715–20

Transarticular screw fixation with autograft is an established procedure for the surgical treatment of atlantoaxial instability. Removal of the posterior arch of C1 may affect the rate of fusion. This study assessed the rate of atlantoaxial fusion using transarticular screws with or without removal of the posterior arch of C1. We reviewed 30 consecutive patients who underwent atlantoaxial fusion with a minimum follow-up of two years. In 25 patients (group A) the posterior arch of C1 was not excised (group A) and in five it was (group B). Fusion was assessed on static and dynamic radiographs. In selected patients CT imaging was also used to assess fusion and the position of the screws. There were 15 men and 15 women with a mean age of 51.2 years (23 to 77) and a mean follow-up of 7.7 years (2 to 11.6). Stable union with a solid fusion or a stable fibrous union was achieved in 29 patients (97%). In Group A, 20 patients (80%) achieved a solid fusion, four (16%) a stable fibrous union and one (4%) a nonunion. In Group B, stable union was achieved in all patients, three having a solid fusion and two a stable fibrous union. There was no statistically significant difference between the status of fusion in the two groups. Complications were noted in 12 patients (40%); these were mainly related to the screws, and included malpositioning and breakage. The presence of an intact or removed posterior arch of C1 did not affect the rate of fusion in patients with atlantoaxial instability undergoing C1/C2 fusion using transarticular screws and autograft. Cite this article: Bone Joint J 2013;95-B:972–6

Ankylosing spondylitis (AS) is a progressive multisystem chronic inflammatory disorder. The hallmark of this pathological process is a progressive fusion of the zygapophyseal joints and disc spaces of the axial skeleton, leading to a rigid kyphotic deformity and positive sagittal balance. The ankylosed spine is unable to accommodate normal mechanical forces, rendering it brittle and susceptible to injury. Traumatic hyperextension injury of the cervical spine leading to atlantoaxial subluxation (AAS) in AS patients can often be fatal. We report a non-traumatic mechanism of injury in AS progressing to AAS attributable to persistent hyperextension, which resulted in fatal migration of C2 through the foramen magnum. Cite this article: Bone Joint J 2013;95-B:206–9

Purpose of the Study. At our Department, we prefer surgical treatment of all patients with Type II and III fractures of the dens, regardless of the age, with the exception of non-displaced fractures or perfectly reduced fractures in young patients. Material and Methods. We treated surgically 28 patients 65 years old and older with dens fractures. The group consisted of 13 men and 15 women with a mean age of 77.4 years (range, 65–90 years). According to the type of treatment, anterior srew fixation or posterior C1–C2 fixation, the whole cohort was divided into 2 groups that were subdivided into two age groups of patients 65–74 years old and 75 years old and older. The age group of patients 65–74 years old included 8 patients with a mean age of 68.5 years and the mean age of the age group of patients 75 and more years old was 81 years. The injury was caused in 22 cases by a fall, in 5 by a car accident. Only in 1 case the injury was caused differently. Neurological deficits were found in three patients, all of them Frankel D type. All patients with injury to the dens underwent radiograph examination in the lateral and transoral projections and CT scan including the sagittal and frontal reconstructions of the atlantoaxial complex and in most cases also MRI examination to eliminate injury to the transverse ligament of the atlas. Based on these examinations, the type of injury was determined and method of treatment indicated. Final retrospective evaluation of the patients was carried out at the interval of 12 to 78 months after the primary surgery (mean 31.3 months) taking into account aetiology of the injury, type of injury, neurological finding, method of treatment, union of the dens fracture line or, where appropriate, C1–C2 fusion, stability of the spine and the final outcome. Statistical analysis was based on X2-test. Results. Comparison of the two age groups showed a statistically significant difference in the mortality (p<0.05), with 0% in the younger group and 40% in the older group. In total, mortality within 6 weeks after the injury accounted for 28.6%. Comparison of surgical techniques revealed 21.4% mortality after anterior screw fixation of the dens and 35.7% mortality after posterior instrumented fusion. The difference was statistically insignificant (p>0.05). Of the 20 surviving patients, 11 were treated with anterior screw fixation and 9 with posterior instrumented fusion. In the two groups there was only one case of nonunion of the dens (9.1%) and one fibrous callus in the region of C1–C2 fusion and the fracture line in the dens (11.1%). The difference was again insignificant (p>0.05). Conclusions. Active surgical treatment conduces considerably to the improvement of the quality of life of elderly patients after dens fractures. Surgical technique should be tailored to the patient's general condition, and osteoporosis and degenerative changes of the spine in particular. Mortality is influenced by the patient's age rather than by the surgical technique used. Elderly patients with a neurological deficit mostly die of associated diseases regardless of the method of treatment

Purpose. In stabilisations of atlantoaxial instabilities it holds risks to injure the A. vertebralis as well as neurological structures. Furthermore the posterior approach of the upper part of the cervical spine requires a huge and traumatic preparation of the soft tissue. However the anterior transarticular C1-2 fusion (ATF) is less traumatic and offers almost the same strengh of the stabilisation. Methods. Since the 01/2007 22 multimorbid patients with atlanto-axial instabilities of different entities were treated via the ATF, were regular examined radiologicaly (x-ray/CT) and the procedure critically judged. Results. C1-2 fusions were performed in 22 patients (17f, 5m, Ø 81,67 years). Main symptoms was pain radiating in the upper cervical spine and the occiput, 2 Patients complaining radiating pain with paraesthesia. The average operation-time took 64,5 min. Leftside the screws of Ø 39,5mm (32–44mm), rightside of 36mm (32–44mm) were inserted in addiction to the point of access and the angle of insertion (mediolateral angle Ø 32,0°, ventrodorsal Ø17,6°). No introperative complications occured, one revision had to be done because of p.o. bleeding, one because of screw dislocation. Postoperative x-ray and CT control of the upper cervical spine showed 30/44 screws in 22 patients in correct position. 8 (18,2%) screws were too long, 3 (6,8%) screws were placed too anterior and 3 (6,8%) too medial. 8 additional positionated dens-screws were in correct position. After a clear learning curve both screws of the 6th patient were positoinated correct. Two aspects are important for success: Correct entry point and right insertion of the angle in the coronar and sagittal view. A low intraoperative blood loss, a non traumatic access as well as an immediate pain decrease have to be valued positively for this procedure. Conclusions. The gentle procedure of the ATF requires-despite of the huge experience in anterior surgery of dens fractures - a learning curve, because of the more proximate insertion point, the flat insertion angle and the closeness of the A. vertebralis. If these aspects are going to be noticed, failed screw positioning and excessive length as well as injuries of the A. vertebralis can be avoided

Background. Rotatory subluxation of the atlantoaxial joint has been thoroughly documented in children. However, pure traumatic atlantoaxial rotatory subluxation (TAARS) is a rare injury in adults with only a few cases reported in the English literature. Aim. To report two cases of TAARS in adults. Methods. A case note, clinical and radiological review. Results. Both patients were female. There was a history of a motor vehicle collision in both cases. There was no neurological impairment at presentation in either case. The injury in both cases was identified by plain X-ray and confirmed by CT scan. Both were managed by conservative treatment, initially with halo traction, followed by immobilisation in a rigid collar. Final clinical reviews occurred at 7 years and 2.5 years following injury. Neither patient had signs of C1-C2 instability or impaired neurology. Both patients, however, suffered headaches and occipital neuralgia, with stiffness and reduction in cervical spine movement. Conclusion. Traumatic rotatory subluxation in adults is a rare injury. It can pose a diagnostic challenge and CT scanning is mandatory for a correct evaluation of the C1-2 complex. Reduction and stability can be achieved through conservative treatment. However, it is evident from this short series that even early diagnosis and prompt reduction may not necessarily result in a good long term outcome in adult patients with TAARS

Existing techniques of posterior multi-point C1/2 stabilisation are technically demanding and can be hazardous. The coauthors have recently reported successful atlantoaxial fusion using a novel C1/2 stabilisation technique employing C1 multi-axial posterior arch screws (MA-PAS) in a clinical series of three patients where anatomical anomalies precluded established techniques. The technically less demanding nature of this new technique, and possible wider application in patients with normal anatomy, led the authors to investigate its biomechanical stability compared to other established techniques. Twenty-four human fresh-frozen cadaveric spines were harvested C0-C5. Motion was restricted to between C0 and C4. Each spine was non-destructively tested in flexion/extension, lateral bending and axial rotation, firstly in the intact state and then after Type 2 odontoid fracture destabilisation and insertion of Magerl-Gallie, Unicortical Harms, Bicortical Harms or MA-PAS instrumentation. ROM between C1 and C2 was monitored using two digital cameras. Results for each technique were compared statistically compared using ANOVA. The C1-C2 joint of the intact spines demonstrated high flexibility in flexion/extension (16.5deg). After instrumentation all specimens showed significantly reduced ROM in flexion/extension (Magerl-Gallie FE = 4.2deg, Unicort Harms FE = 7.2deg, Bicort Harms FE = 4.4deg). Lateral bend ROM of instrumented specimens (Magerl-Gallie LB =3.8deg, Unicort Harms LB = 3.8deg, Bicort Harms LB =2.3 deg) was, however, similar or slightly greater than intact (2.7 deg) . MA-PAS showed similar ROM in flexion/extension (4.2 deg) as the Magerl-Gallie and Harms techniques but was slightly higher in lateral bend (5.3 deg). The MA-PAS technique was shown to have similar biomechanical stability to the Magerl-Gallie and Harms techniques. Given the demonstrated biomechanical stability of the MA-PAS technique, it may be a suitable alternative to the existing technically demanding, and possibly more hazardous, multi-point fixation techniques in patients with normal, as well as anomalous, C1/2 segmental anatomy

Patients with skeletal dysplasia are prone to developing advanced osteoarthritis of the knee requiring total knee replacement (TKR) at a younger age than the general population. TKR in this unique group of patients is a technically demanding procedure owing to the deformity, flexion contracture, generalised hypotonia and ligamentous laxity. We retrospectively reviewed the outcome of 11 TKRs performed in eight patients with skeletal dysplasia at our institution using the Stanmore Modular Individualised Lower Extremity System (SMILES) custom-made rotating-hinge TKR. There were three men and five women with mean age of 57 years (41 to 79). Patients were followed clinically and radiologically for a mean of seven years (3 to 11.5). The mean Knee Society clinical and function scores improved from 24 (14 to 36) and 20 (5 to 40) pre-operatively, respectively, to 68 (28 to 80) and 50 (22 to 74), respectively, at final follow-up. Four complications were recorded, including a patellar fracture following a fall, a tibial peri-prosthetic fracture, persistent anterior knee pain, and aseptic loosening of a femoral component requiring revision. Our results demonstrate that custom primary rotating-hinge TKR in patients with skeletal dysplasia is effective at relieving pain, with a satisfactory range of movement and improved function. It compensates for bony deformity and ligament deficiency and reduces the likelihood of corrective osteotomy. Patellofemoral joint complications are frequent and functional outcome is worse than with primary TKR in the general population.

We present the case of a 15-year-old boy with symptoms due to Klippel–Feil syndrome. Radiographs and CT scans demonstrated basilar impression, occipitalisation of C1 and fusion of C2/C3. MRI showed ventral compression of the medullocervical junction. Skull traction was undertaken pre-operatively to determine whether the basilar impression could be safely reduced. During traction, the C3/C4 junction migrated 12 mm caudally and spasticity resolved. Peri-operative skull-femoral traction enabled posterior occipitocervical fixation without decompression. Following surgery, cervical alignment was restored and spasticity remained absent. One year after surgery he was not limited in his activities. The surgical strategy for patients with basilar impression and congenital anomalies remains controversial. The anterior approach with decompression is often recommended for patients with ventral compression of the medullocervical region, but such procedures are technically demanding and carry a significant risk of complications. Our surgical strategy was an alternative solution. Prior to a posterior cervical fixation, without decompression, skull traction was used to confirm that the deformity was reducible and effective in resolving associated myelopathy.

Purpose: The current gold-standard for atlanto-axial fixation is C1-C2 Transarticular Screw (TS) fixation. In certain cases, the complicated nature of vertebral artery injury could make the application of bilateral transar-ticular screws impossible. This study biomechanically compares three atlantoaxial transarticular salvaging fixation techniques. Method: Nine Fresh ligamentous human cervical spine specimens (C0-C4) were thawed and the tissue surrounding the spine, except the ligaments and discs, was carefully removed. Pure moments were applied to skull in increments of 0.5 Nm from 0 Nm to 2.0 Nm with the help of loading arms, nylon strings and pulleys. The specimens were tested in extension (EXT), flexion (FLEX), left lateral bending (LB), right lateral bending (RB), left axial rotation (LR) and right axial rotation (RR) for all the cases. The positions of the LEDs were recorded using an Optotrak Motion Measurement System (Northern Digital, Waterloo, Ontario, Canada) and was converted into three rotations (flexion/extension, lateral bending and axial rotation) using rigid body kinematic principles in relation to the fixed base. The specimens were tested intact and after type II odontoid fracture, were instrumented and tested with three fixation constructs:. C1-C2 TS on right side and C1LMS-C2PS on contralateral side. C1-C2 TS on right side and C1LMS-C2IL on the contralateral side and. C1-C2 TS on right side with sublaminar wire. Results: All of the three instrumented cases significantly reduced motion across C1-C2 segment in all the modes when compared to intact (P< 0.005, two-tailed unpaired t-test at confidence interval of ninety-five percent) except in extension. TS+C1lM+C2PS is significantly stiffer than TS+ Wire only in axial rotation (P< 0.05) and equivalent in flexion/extension (P=0.75/P=0.51) and left/right bending (P=0.22/P=0.58). TS+C1LM +C2PS is equivalent to TS+C1LM+C2IL in all the loading modes (P> 0.05). TS+C1LM+C2IL is significantly stiffer than TS+Wire in axial rotation (P < 0.05) and equivalent in flexion/extension (P=0.93) and left/right bending (P=0.69/P=0.84). Conclusion: This study showed that TS+C1LMS+C2PS fixation is equivalent to TS+C1LMS+C2ILS fixation in all the rotation modes and superior to TS+Wire fixation in axial rotation averaged over all ranges of motion. Also, TS+C1LMS+C2ILS fixation is superior to TS+Wire fixation in axial rotation averaged over all ranges of motion

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

Structural defects of the posterior arch of the atlas are rare, and range from clefts of variable location and size to more extensive defects such as complete agenesis. These abnormalities are usually incidental radiological findings. We present a case of a fracture of the anterior arch of the atlas associated with a congenital abnormality of the posterior arch.

Intraspinal re-implantation after traumatic avulsion of the brachial plexus is a relatively new technique. Three different approaches to the spinal cord have been described to date, namely the posterior scapular, anterolateral interscalenic multilevel oblique corpectomy and the pure lateral. We describe an anatomical study of the pure lateral approach, based on our clinical experience and studies on cadavers.

Goals: Advantage of the dorsal fixation of C1/2. Materials and Methods: From 01/2006 to 12/2006 22 patients with a traumatic fracture of C1/2 were operativly stabilized. The avarage age was 79 year (66–92). No neurological deficit. Diagnostic was always a CT-scan for classification of fracture typ. 7 patients were temporarily immobilized with HALO fixateur. Within th next 8 days final operation hab been carried out. 7 patients with Anderson fractures typ II were stabilized with open fixation from ventral (group 1). 4 Jefferson fractures and 2 combined C1/2 fractures were were stabilized with open fixation from dorsal (Magerl) (group 2). Percutanous fixation from dorsal was done in 5 patients with fractures of the atlas, 4 with Anderson fractures typ II (group3). Clinical and radiological follow up was done in 18 patients. Results: Duration for operation was in 64min in group1, 134min in group 2 and in 42min in group3. No neurological deficit or damage of A.vertebralis occurred. Blood loss was in group 1 and 3 under 50ml in group 2 750ml. In group3 one slightly dislocation of screw happened without need of revision. Movement of cervical spine was reduced in group 2 and 3. During follow up 3 of seven ventral stabilized Anderson fractures typ II (group1) were dislocated. Dorsal percutanous fixation for operatively revision was done. Discussion: Percutanous dorsal transarticular screw fixation C1/2 is a challanging procedure for stabilization of atlantoaxial fractures. Main advantages compared to other operation techniques are less blood loss, short operation time, high rate of success

We reviewed the outcome of a retrospective case series of eight patients with atlantoaxial instability who had been treated by percutaneous anterior transarticular screw fixation and grafting under image-intensifier guidance between December 2005 and June 2008. The mean follow-up was 19 months (8 to 27). All eight patients had a solid C1–2 fusion. There were no breakages or displacement of screws. All the patients with pre-operative neck pain had immediate relief from their symptoms or considerable improvement. There were no major complications. Our preliminary clinical results suggest that percutaneous anterior transarticulation screw fixation is technically feasible, safe, useful and minimally invasive when using the appropriate instruments allied to intra-operative image intensification, and by selecting the correct puncture point, angle and depth of insertion