Summary

A rotational limit for screw insertion may improve screw purchase and plate compression by reducing stripping, as compared to a torque based limit.

Avulsion fractures of the tip of the olecranon are a common traumatic injury. Kirshner-wire fixation (1.6mm) with a figure of eight tension band wire (1.25mm) remains the most popular technique. Hardware removal mat be required in up to 80% of cases. Modern suture materials have very high tensile strength coupled with excellent usability. In this study we compare a repair using 1.6mm k-wires with a 1.25mm surgical steel, against a repair that uses two strands of 2 fibrewire.

Twelve Pairs of cadaveric arms were harvested. A standard olecranon osteotomy was performed to mimic an avulsion fracture. In each pair one was fixed using standard technique, 2 × 1.6mm transcortical ?-wire plus figure of 8 loop of 1.25mm wire. The other fixed with the same ?-wires with a tension band suture of 2.0 fibrewire (two loops, one figure of 8 and one simple loop). The triceps tendon was cyclically loaded (10-120 Newtons) to simulate full active motion 2200 cycles. Fracture gap was measured with the ‘Smart Capture’ motion analysis system. The arm was fixed at 90 degrees and triceps tendon was loaded until fixation failure, ultimate load to failure and mode of failure was noted.

The average gap formation at the fracture site for the suture group was 0.91mm, in the wire group 0.96mm, no specimen in either group produced a significant gap after cyclical loading. Mean load to failure for the suture group was 1069 Newtons (SD=120N) and in the wire group 820 Newtons (SD=235N).

Both types of fixation allow full early mobilisation without gap formation. The Suture group has a significantly higher load to failure (p=0.002, t-test). Tension Band suture allows a lower profile fixation, potentially reducing the frequency of wound complications and hardware removal.

We evaluated two reconstruction techniques for a simulated posterolateral corner injury on ten pairs of cadaver knees. Specimens were mounted at 30° and 90° of knee flexion to record external rotation and varus movement. Instability was created by transversely sectioning the lateral collateral ligament at its midpoint and the popliteus tendon was released at the lateral femoral condyle. The left knee was randomly assigned for reconstruction using either a combined or fibula-based treatment with the right knee receiving the other. After sectioning, laxity increased in all the specimens. Each technique restored external rotatory and varus stability at both flexion angles to levels similar to the intact condition. For the fibula-based reconstruction method, varus laxity at 30° of knee flexion did not differ from the intact state, but was significantly less than after the combined method.

Both the fibula-based and combined posterolateral reconstruction techniques are equally effective in restoring stability following the simulated injury.

Aim: While ankle fractures are not thought of as osteoporotic fractures, poor bone quality presents difficulties in fracture fixation of the distal fibula. We measured the relation between bone density of the distal fibula and the insertional and stripping torques of screws used for fibular plating using two different plate configurations.

Methods: Ten paired fresh cadaveric ankles (average age: 81.7 years) were used for the study. Computed tomography scanning with phantoms of known density was used to determine the bone density along the distal fibula. A standard small fragment seven-hole one-third tubular plate was applied to the lateral surface of the fibula, with three proximal bicortical cortical screws and two distal unicortical cancellous screws. A posterior plate in which all five screws were cortical and achieved bi-cortical purchase was subsequently applied to the same bones such that the screw holes did not overlap. A torque sensor was used to measure the torque of each screw during insertion (Ti) and then stripping (Ts).

Results: Mean bone density of the distal fibula is significantly less than in the shaft (p< 0.01). There was a moderate positive correlation between torque and bone density for the lateral plates (r2=0.6 for Ti and r2=0.7 for Ts), and a weak correlation for the posterior plates (r2=0.4 for Ti and Ts). For the proximal three screws, there was no significant difference in average Ti and Ts between lateral and posterior plates. For the distal two screws, posterior plates had significantly higher values for both Ti and Ts than the lateral plates (p< 0.01).

Conclusions: The insertion and stripping torques of the screws in the distal fibula were significantly higher and less dependent on bone density with a posterior plate than with a lateral plate.

Introduction: Several studies have compared various plate constructs for distal intra-articular humerus fractures. In our experience osteoporotic bone and fractures that have a transverse component close to the elbow joint have tenuous fixation with traditional plating systems due to, at most, two screws in the distal fragment through the plate. Therefore, the aim of this study was to obtain objective data on the performance of two plating systems used for fixation of intra-articular distal humerus fractures with a low transverse component with only two screws through a 3.5 LC-DCP distally. It was hypothesized that locked plating would be more stable than standard plating after cyclic loading.

Methods: Twenty pairs of fresh matched cadaver humeri of patients older than 65 years old were harvested. DEXA scans of the right forearm from each pair were obtained. Osteotomies were performed to simulate comminuted supracondylar humerus fracture with intercondylar split (OTA 13-C2.3). The specimens were then randomly assigned to locking or non-locking plate fixation.

Ten paired specimens were tested in simulated extension and the remaining ten were tested axially.

Fragment motion relative to the humeral shaft was measured using kinematic analysis at the fracture gap.

Differences in resultant fragment translations and rotations between fixation groups were checked for significance (p< 0.05) using a one-tailed paired t-test. Differences in cycles to failure were checked for significance using a Wilcoxon signed rank test.

Results: On average, during extension tests, the humeri with locking plate fixation did not survive significantly more cycles (4352) than with non-locking (4755) plate fixation. There was no significant difference in fragment translation between locking (0.8 mm) and non-locking (1.7 mm) plates. However, there was a significant difference in fragment rotation between locking (2.8 degrees) and non-locking (3.9 degrees) fixations.

On axial testing, the humeri with locking plates on average survived more loading cycles (4072) than those with non-locking plate fixation (2115), but the difference was not significant. Mean translation for locking plate fixation (3.6 mm) was significantly less than for non-locking plate fixation (5.7 mm) and mean fragment rotation was significantly less for locking plate fixation (13.3 degrees) than for non-locking plate fixation (17.8 degrees).

Conclusions: The results of this study demonstrated that the fixed-angle 3.5 mm locking plate constructs for comminuted intercondylar humerus fractures reduced fracture site motion, sometimes significantly so, relative to the non-locking constructs in osteoporotic bone. The potential benefit of increased fixation survivability and decreased fracture site motion in osteoporotic bone needs to be evaluated clinically.

Aims: To determine the relationship between the percentage of polymethylmethacrylate cement þll of osteoporotic vertebral bodies during percutaneous vertebroplasty and the percentage restoration of strength and stiffness. Methods: The volume of 120 vertebral bodies (T6-L5) harvested from 10 osteoporotic spines female cadavers was determined by Archimedes displacement. Compression fractures were experimentally created to determine the initial strength and stiffness. The vertebral bodies were stabilized using bipedicular injections of between 2-8mL of cement and then recompressed and post treatment strength and stiffness was measured. Linear regression was used to check for the relationship between percent volume þll and percent restored stiffness and strength. Results: The correlation between percentage þll and restored strength and stiffness was weak, r2 = 0.21 and r2 = 0.27 respectively. The correlation showed that on average, a 16.2% cement þll of the VB volume was needed to restore strength and 29.8% þll was needed to restore stiffness). Conclusions: Strength and stiffness are weakly correlated with the percentage þll volume of cement injected during vertebroplasty.

Aims and methods

To compare the mechanical stability of an intramedullary (IM) screw with two crossed interfragmentary compression screws for fixation of the 1st MTPJ in ten pairs of cadaveric feet. One foot underwent fixation with two crossed 4.0-mm cannulated cancellous screws. The contralateral foot was fixed with an IM 1.6-mm Kirschner wire and an IM 6.5-mm partially threaded cancellous lag screw. A plantar-to-dorsal load was applied to the distal end of the proximal phalanx at a rate of 1 mm/sec. Failure was defined as gross actuator displacement of 5 mm. Stiffness was defined as the slope of the force versus deformation curve between 10 and 60 N. Strength was defined as the load at failure. The differences in stiffness and strength parameters between the two fixation techniques were checked for significance (P < 0.05) with a paired t-test.

Results

The intramedullary MTP joint fixation was significantly stiffer (18.7 ± 10.1 N/mm) than control group fixation (10.2 ± 6.1 N/mm). Similarly MTP joint fixation in the IM group was stronger (149.2 ± 88.2 N) than that of the control group (100.2 ± 70.8 N), but this was not significant (P = 0.07).

Conclusions

The IM technique resulted in a stronger stiffer fixation when compared with the standard crossed lag screw technique.

Introduction

The distal part of the interosseous membrane (IM) may contribute to ankle joint stability and therefore partly explain the results of a study that reported no difference in outcome in patients with low Weber C fractures treated with or without a syndesmotic screw. The aim of the current study was to compare the strength of the IM to the interosseous ligament (IL).

Method

Six paired cadaveric lower extremities were stripped, leaving only the IM and the IL intact. The tibia was fixed and a load was applied via a steel plate to the lateral surface of the fibula to displace it with respect to the tibia along the line of the fibers of the IM and IL. In group one the interosseous ligament was sectioned and the interosseous membrane was mechanically tested until failure. In group two, the interosseous membrane was sectioned and the interosseous ligament was tested.

Results

The interosseous membrane was 30% stronger than the interosseous ligament (1040 ± 183 N versus 798 ± 322 N, respectively; mean ± SD).

Conclusion

The current biomechanical study found that the IM was 30% stronger than the IL. The interosseous membrane has considerable strength and may play a role in ankle stability.

Introduction

The strength of the Scarf osteotomy has been compared to that of other metatarsal osteotomies, but the effect of increasing the amount of displacement is unknown. The purpose of this study was to determine whether increasing offset adversly affects the strength of the Scarf osteotomy.

Methods

Seven pairs of freah frozen cadaveric feet were tested. Specimens in Group 1 underwent Scarf osteotomy with displacement of one third the mid shaft diameter. Specimens in Group 2 were offset two thirds the midshaft diameter. All osteotomies were fixed using two Barouk screws.

Each specimen was tested in cantilever bending using a servohydraulic testing machine.

Results

There was no statistically significant difference in strength or stiffness between the two groups. Mean strength was 75.2 N ± 16.8 for Group 1 and 64.8 N ± 28.7 for Group 2 (p> 0.05).

Mean stiffness was 12.9 N/mm ± 5.1 for Group I and 10.2 N/mm ± 5.9 for Group 2 (p> 0.05).

Discussion

All specimens failed at the proximal extent of the osteotomy. Failure did not occur by screw pullout in either Group. The proximal part of the cut is therefore the weakest part of the construct irrespective of the degree of osteotomy displacement.