Ulna Styloid Fractures have been historically dismissed as a relatively benign injury. However recent clinical and biomechanical research has suggested that primary repair of displaced ulna styloid avulsion fractures is advised as a means of stabilizing the radioulnar joint and preventing the disability associated with chronic radioulnar joint instability.

Optimum fixation method was examined in this study using a human cadaveric model. A custom jig was designed to allow testing in radial/ulna deviation in varying degrees of wrist flexion and extension. Universal materials testing device was used to apply a maximum load of 150 N. Eight pairs of cadaveric wrists were tested. Constructs tested were 1.6mm K-wire fixation, Tension Band wiring and Screw Fixation. Fracture displacement was measured using a venire micrometer.

Results: Displacement on forced radial deviation was maximum in neutral wrist position in all construct configurations. Displacement was minimized in 20 degrees wrist flexion. The optimum fixation method was 2 k-wires with tension band wiring. This study would suggest that the optimum fixation for ulna styloid fractures is a Tension band-wiring construct. If non-operative treatment is used we suggest that the wrist is immobilized in a position of wrist flexion to reduce tension on the ulna carpal ligament and prevent fracture displacement.

Introduction: Outcome following intra-articular fractures is dependent on a myriad of variables, including the extent of the initial osteochondral and soft tissue injury. In the clinical setting it is impossible to control such variables, and studies are largely confined to radiographic and outcome based assessments. Therefore the effect of fracture line orientation has not been widely examined. Theoretically an incongruent intra-articular fracture results in a “low” side that is relatively unloaded, at the expense of a “high” side exposed to increased loads. Furthermore the orientation of the fracture may give rise to a narrow or broad swathe of wear on the opposing articular surface.

Aim: To evaluate the effect of an incongruent intra-articular fracture of the medial femoral condyle on subsequent loading and wear patterns, using an in vitro model.

Materials and Methods: 15 porcine stifle (knee) joints were harvested within three hours of death. Three groups of five joints were evaluated. Group S underwent a sagittal osteotomy of the medical femoral condyle that was then fixed in an incongruent position. In Group C the osteotomy was performed in the coronal plane. The third group acted as a control group and had no oseotomy performed. In all cases great care was taken to prevent injury to the menisci, articular surfaces and Ligamentous structures. The size of the step-off was documented using a contour-mapping machine (CMN). In addition the surface roughness of the femoral condyles was documented using a laser interferometry device (UBM, Germany). The specimen was mounted on a custom-made electro-pneumatic rig, and pressure mapping of the articular surfaces performed with pressure sensitive film (SPI, New Jersey, USA). Following mapping, each specimen underwent 10,000 cycles of flexion and extension over a three-hour period. When testing was complete, pressure mapping was again performed, the size of the step-off re-measured using the CNM, and surface roughness of the menisci, femoral condyles and tibial plateau assessed. Data was restored on a laptop for subsequent statistical analysis.

Results: Pressure mapping documented an unloaded area on the low side of the step-off in both Group C and S. This extended up to 8mm, and was mirrored by an area of increased load on the high side. Following testing, the area exposed to altered loads on both the high and low side of the osteotomy had diminished. On ANOVA testing the uncovered tibial articular surfaces in test subjects were significantly rougher than control specimens, though no difference was noted between Groups C and S (Mean Ra value GC: 101.83+22.78, GS: 93.52+17.89, ns. vs. Con 53.45+25.8,p< 0.05). Meniscal surface roughness was greater in the test groups, though this did not reach statistical significance. No significant difference in femoral condyle surface roughness was noted following testing. Nor was any difference noted in surface roughness in the submeniscal areas of the tibial articular surface.

Discussion: The displaced femoral osteotomy resulted in an area of increased wear on the opposing tibial articular surface. However no significant difference was noted between the coronal and sagittal group. It is probable that the menisci negated the effect of fracture line orientation. We suggest that they minimized secondary articular damage by decreasing the area of direct tibiofemoral contact. Furthermore the elasticity of the menisci, in addition to their ability to move in the anteroposterior plane further decreased stress transmission between joint surfaces. Further studies will be performed on the hip joint to determine the effect of articular incongruity in the absence of such a fibrocartilage buffer.

Introduction: Elucidation of the exact cause of adolescent idiopathic scoliosis (AIS) remains an elusive goal. The intervertebral disc is one of the many areas that have been investigated in an effort to find a cause for this condition. We hypothesize that a qualitative change in the orientation of collagen fibers in the annular layers of the disc could cause the deformity seen in AIS. This paper presents a mathematical model of such a change and how it could produce appropriate deforming forces. Hypothesis: In the normal disc the collagen fibers are obliquely orientated. Fibers in adjacent lamellae are orientated in opposing directions. This means that as forces are transmitted from a compressed nucleus to the annular fibers there is no net force tending to rotate one vertebra with respect to its neighbour. If there is a preponderance of fibers running in one direction as the nucleus is compressed there will be a net resultant force perpendicular to the long axis of the spine tending to produce an intervertebral rotation. This intervertebral rotation, applied to successive spinal segments will cause a scoliotic deformity.

Model: The highly oriented structure of the AF suggests the utility of an explicit representation of the collagen fibres and their mechanical contribution to disc function. In our study we have considered two groups of fibres, representing the clockwise and counter clockwise fibres in the disc. The AF is considered as a continuum containing two populations of fibres assumes to be of equal density and uniform distribution within an isotropic material as originally described by Spencer. Nuclear compression as a result of growth was modelled as a tendency to produce increased intervertebral separation of spinal segments and examined whether the resultant transformation that leads to a scoliotic pattern of deformity. Based on anatomical data from literature the positions of the 12 nodes that represent the thoracic vertebrae are applied to the model. The three-dimensional location of each vertebral body is defined. We store the coordinates of thoracic vertebrae in a three-dimensional matrix. In the present study in order to involve the translation operation in our transformation, we have used the homogeneous transformation matrix or Denavit & Hartenberg matrix.

In the present model for the initial set of transformations the reference axis is chosen to be the lowest vertebral axis (T-12) and remains unchanged throughout the transformation. All elements of the spine above the reference axis are transformed (translated and rotated). After completion of this iteration and storing the values for the origin coordinate and vector values in the next level of the matrix, the next reference axis is chosen. For the second axis everything above the axis will be transformed in the same way with the current axis and the one preceding it remaining unchanged. Therefore for each transformation a new reference axis is taken and the transformations are applied to all vectors and origins above it leaving all elements preceding it unchanged by the transformation.

Results: The first part of the model shows that rotational displacement increases linearly with changes in the fibre ratio. Rotational displacement on the other hand occurs independently of distraction of the vertebral bodies. When the rotational displacement is applied to a series of segments it produces alterations of curvature in the three planes. Specifically it produces a lateral curvature in the coronal plane and a hypokyphotic curvature in the saggital plane. The magnitude of these displacements varies with the imbalance in fibre ratio. Discussion: The proposed changes in annular fiber orientation have been modeled using accepted mathematical methods. These changes will produce an intervertebral rotation whose magnitude depends on the degree of fiber imbalance akin to that seen in AIS. When the displacements produced by this rotation being applied to a series of segments is modeled, it will produce a three dimensional deformity similar to that seen in AIS. Ongoing histological studies are being performed to see if the proposed imbalance can be identified in patients with AIS. Such a fiber orientation anomaly may be genetically determined by some fashion of directional sense gene and may be the aetiological basis for AIS.

Introduction: Five occipitocervical implant systems were compared biomechanically in vitro using nondestructive testing.

Methods: A composite material model of the occiput and upper cervical spine was developed and validated. The specimens were tested using an in-vitro purpose build test rig. Instrumentation was from the occiput to C5 and included five constructs in current clinical use. Biomechanical testing parameters included axial rotation, flexion/extension and lateral bending. Nondestructive pure moments were applied to C5 using a system of cables and pulleys loaded by a materials testing machine (Hounsfield Ltd. UK) Angular displacement of the specimen under load was measured using the Zebris System (Zebris Medizintechnik, GMBH, Germany) which collects and stores three-dimensional space co-ordinates by means of attached ultrasonic markers. Mean maximum angular displacement was calculated from a series of five test cycles for each construct. Statistical significance was determined using a one-way analysis of variance (ANOVA) combined with a LDS test at 95% confidence.

Results: Statistically significant differences were shown in the initial stiffness of current implant constructs used for stabilization of the occipitocervical junction. The Zebris system was also validated as an accurate and efficient 3-D motion analysis for cervical spine biomechanical research.

Cervical orthoses are currently used in the pre-hospital stabilization of trauma patients and also as part of the definitive non-operative treatment of injuries of the cervical spine. The construct stability of orthoses is compromised by virtue of the fact that the cervical spine exhibits the greatest range of movement amongst the spinal segments and also because of the complex composite nature of neck movements.

To date, data has been difficult to attain comparing the various orthoses, in the various planes of movement of the cervical spine. Various methods including the use of inclinometers, goniometers, radiography, computerized tomography and cineroentgenography have been used in an attempt to measure these movements but none have provided satisfactory triplanar data.

This paper uses the Zebris ultrasonic 3-D motion analysis system to measure flexion, extension, range of lateral bending and range of axial rotation in five similar male and five similar female subjects with no history of neck injuries. The subjects were tested in a soft and hard collar, Philadelphia, Miami J and Minerva.

Results show that the Minerva is significantly the most stable construct for restriction of movement in all planes in both groups (p< 0.002 vs. all groups, Student’s t-test), but more impressively in the female group. In the male group, the standard hard collar performs second best in flexion, lateral bending and axial rotation. In the female group, the second most stable orthosis is the Philadelphia in flexion/extension and the hard collar in lateral bending and axial rotation (p< 0.05 vs. next most stable in all cases, Student’s t-test). The soft collar in both groups offered only minimal resistance to movement in any plane, e. g. 45.07° vs. 46.45° extension vs. normal in males and 40.15° vs. 41.8° extension vs. normal in females.

Looking at these results together allows the ranking of the measured orthoses in order of the three-dimensional stability they offer. Furthermore, they validate the Zebris as a reliable and safe method of measurement of the complex movements of the cervical spine with low intersubject variability.

In conclusion, this paper, for the first time presents reproducible data incorporating the composite triplanar movements of the cervical spine thus allowing comparative analysis of the three-dimensional construct stability of the studied orthoses.

Introduction: Occipito-cervical fusion has evolved from the used of simple onlay bone grafts to the use of sophisticated modular implants. Initial stiffness prevents micromotion and allows a higher fusion rate.

Methods: A composite occipito-cervical model (OCM) was developed and validated using data obtained from cadaveric specimens. A jig was designed to pot the OCM, which allowed the application of independent moment forces to simulate flexion, extension, lateral flexion and rotation. The following implants were used 1 ) Grob plate with C1/C2 transarticular screw fixation.2) Grob Plate without C1/C2 transarticular screw fixation.3) Cervifix rod system 4) A Ransford loop system 5.) Olerud plate fixation. A three dimensional ultrasonic motion analysis system (Zebris Inc.) was used to record motion at three positions: 1)C0 2) C2 3) C4.A separate OCM was used for each instrumentation system.

Results: The Grob plate with C1/C2 transarticular fixation was found to confer the greatest initial stiffness. The Ransford loop construct was found to confer the least initial stiffness. Plate fixation offered greater stability then rod or loop constructs. We found the three dimensional motion analysis system to be ideal for displacement analysis in complex spinal instrumentation constructs.

We have studied the kinematics of the knee in the sagittal plane, using a four-bar linkage as model, and assuming that a "neutral fibre" in each ligament remains isometric throughout flexion. We devised a computer program to calculate the distance separating any pair of points, one on each bone, for various cruciate attachments at various angles of flexion. The parameters for the linkage in four cadaveric knees were obtained by marking the centre of attachment of the cruciate ligaments with tacks and taking lateral radiographs. The movements of the bones were then calculated, in the computer model, for various attachments of "replacement" ligament fibres, the distance between the attachment sites being plotted against the angle of flexion. It was then possible to define zones around the isometric attachment points within which changes in length would be predictable. Our results show that the position of the femoral sites of attachment of both anterior and posterior cruciate replacement was more critical than that of the tibial attachments.

Seventy-two Mitchell distal metatarsal osteotomies for hallux valgus performed over a period of 10 years have been reviewed. Sixty-six (92 per cent) were graded as excellent or good. Retrospective radiographic analysis of 29 of these cases showed that the operation had reduced the intermetatarsal angles to within normal anatomical limits. No patient experienced a worsening of symptoms as a result of the operation.