The aim of this study was to compare the primary fixation stability and initial fixation stiffness of two commonly used fixation techniques, the tension band wiring technique and interfragmentary screw fixation, with an innovative mini-screw fragment fixation system in a model of transverse fracture of the patella. It was hypothesized that the biomechanical performance of the fragment fixation system would not significantly differ from the loading characteristics of the two established methods currently investigated.

Materials and Methods: A standardized transverse patella fracture was induced in ninety-six calf patella and three different fixation methods, including the mod-ified tension band wiring technique, interfragmentary screw fixation, and the mini-screw fragment fixation system, were used for fragment fixation. Specimens were mounted to a loading rig which was integrated within a material testing machine. In each fixation group, eight specimens were loaded to failure at varying simulated knee angles of either 0° or 45°. Another eight specimens were submitted to polycyclic loading consisting of 30 cycles between 20 N and 300 N at a simulated knee angle of either 0° or 45°. The residual displacement between the first and the last cycle was recorded. Differences in the biomechanical performance between the three fixation groups were evaluated.

Results: With monocyclic loading, no significant differences between the three groups were observed in the parameters maximum load to failure and linear fixation stiffness. Specimens loaded at 45° showed significantly lower maximum failure loads and linear stiffness when compared with 0° knee angle. With polycyclic loading, no significant differences in the residual displacement were observed between the groups at 0° loading angle, while at 45°, residual displacement was significantly higher with tension band fixation when compared with interfragmentary screw fixation or the fragment fixation system.

Conclusion: This study confirmed that the biomechanical performance of the fragment fixation system was comparable to interfragmentary screw fixation and superior to the tension band wiring technique. As the fragment fixation system combines the advantages of providing interfragmentary compression with percutaneous pin insertion after closed reduction, we believe the fragment fixation system to be an adequate alternative in the osteosynthesis of transverse patella fractures.

In the treatment of acute elbow dislocation promising clinical results have been reported on articulated external fixation and surgical reconstruction of major joint stabilizers. However, it remains unclear whether or not surgical reconstruction of the major joint stabilizers sufficiently stabilizes the elbow joint or if augmentation by a hinged elbow fixator is beneficial to provide early stability and motion capacity. The aim of the present study was to compare the stabilizing potential of surgical reconstruction versus augmentation by a hinged external elbow in a model of sequentially induced intability of the elbow.

Materials and Methods: 8 unpreserved human upper extremities were mounted to a testing apparatus which was integrated within a material testing machine. In a first series, varus and valgus moments were induced to the intact elbow joint at full extension, as well as at 30°, 60°, 90° and 120° of flexion and the mean angular displacement at 2.5, 5, an 7.5 Nm was calculated. Instability was then induced by sequentially dissecting the lateral and the medial collateral ligament, the radial head, and the posterior capsule. The elbow joint was then sequentially restabilized by osteosynthesis of the radial head and refixation of the lateral and medial collateral ligament using bone anchors. In each sequence, elbow stability was tested with and without augmentation by a hinged external fixator according to the first testing series described above. Biomechanical data of surgical reconstruction alone and surgical reconstruction augmented by external fixation were compared using an analysis of variance.

Results: In the intact elbow, varus-valgus displacement with 7.5 Nm ranged from 8,3 ± 2,4° (0°) to 11,4 ± 4,2° (90°). With the fixator applied, varus-valgus displacement was significantly lower and ranged from 4,2 ± 1,3° (0°) to 5,3 ± 2,2° (90°). After complete destabilization of the elbow joint, maximum varus-valgus displacement ranged from 17,4 ± 5,3° (0°) to 23,6 ± 6,4° (90°). Subsequent reconstruction of the collateral ligaments, the posterior capsule, and the radial head proved to stabilize the elbow joint compared with the unstable situation, however, mean varus-valgus displacement remained significantly higher when compared to the intact elbow joint. During each sequence of instability, the hinged external fixator provided constant stability not significantly different to the intact elbow joint while guiding the elbow through the entire range of motion.

Conclusion: The stabilizing potential of surgical reconstruction alone is inferior to augmentation of a hinged external elbow fixator. In order to proved primary stability and early motion capacity, augmentation of a hinged external elbow fixator in the treatment of acute dislocation of the elbow is recommended.

Side-to-side comparison of anatomical or functional parameters in the evaluation of unilateral pathologies of the knee joint is common practice. Generally, it is assumed that the contralateral joint provides “normal” anatomy and function and that within-subject side differences are less when compared with between-subject variability. This has advocated the use of side-to-side comparisons in a wide field of orthopaedic surgery. The aim of this study was to test the hypothesis that there are no significant differences in the morphometric knee joint dimensions between the right and the left knee of a human subject. Furthermore, it was hypothesized that side differences within subjects are smaller than inter-subject variability.

In 30 pairs of human cadaver knees the morphometry of the articulating osseous structures of the femorotibial joint, the cruciate ligaments, and the mensici were measured using established measurement methods. Morphometric data were obtained either using digital callipers, radiographs, contour gauges, or cross-sectiontal scans. Data were analysed for overall side differences using the Student t-test and Pearson’s correlation coefficient and the ratio between within-subject side differences and intersubject variability was calculated.

In three out of 71 morphometric dimensions there was a significant side difference, including the posterior tibial slope, the anatomical valgus alignment of the distal femur, and the position of the femoral insertion area of the ACL. In two additional parameters, including the cross-sectional area of the distal third of the ACL and PCL, within-subject side differences were larger than intersubject variability. In general, there was a positive correlation in morphometric dimensions between right and left knees in one subject.

This study confirmed a good correlation in the morphometric dimensions of a human knee joint between the right and the left side. Our data support the concept of obtaining morphometric reference data from the contralateral uninjured side in the evaluation of unilateral pathologies of the knee joint. The uninjured contralateral side rather than knee joint dimensions obtained from an uninjured subject should be used as a valid control in orthopaedic practice.

Introduction: Drilling of the femoral bone tunnel in anterior cruciate ligament reconstruction may be performed in a transtibial drilling technique or via the anteromedial portal.

Purpose: To determine the accuracy of the radiographic bone tunnel position using either a transtibial or anteromedial drilling technique.

Materials & methods: The postoperative lateral radiographs of 100 patients after anterior cruciate ligament reconstruction were reviewed. In each patient, the femoral bone tunnel was created either through the tibial tunnel or via the anteromedial standard arthroscopy portal. The resulting position of the femoral tunnel was evaluated according to reference values reported by Aglietti (65 % of the cortical femoral A-P distance along Blumenstaat’s line), Amis (60 % of the A-P diameter of the posterior lateral femoral condyle parallel to Blumensaat’s line), and Harner (80 % of the A-P length of Blumensaat’s line). The mean deviation of the radiographic tunnel position from the referenced values was statistically evaluated.

Results: Radiographic bone tunnel positions with transtibial drilling were 62.42 ± 8.36, %, 54.53 ± 8.43 %, and 75.84 ± 9.56 % according to Aglietti, Amis, and Harner, respectively. Bone tunnel positions with anteromedial drilling were 65.46 ± 5.29 %, 59.59 ± 4.18 %, and 79.93 ± 4.24 %, respectively. The mean deviation from the reference values was significantly higher when comparing transtibial to anteromedial drilling. Transtibial drilling resulted in a significantly more anterior bone tunnel position.

Conclusion: Precise bone tunnel placement is a prerequisite for proper postoperative knee function and stability. The results of this study indicate that the accuracy of femoral bone tunnel placement through the anteromedial arthroscopy portal was superior to transtibial drilling. It may therefrore be concluded that drilling the femoral tunnel through the anteromedial portal is recommended when using fixation techniques not depending upon placement of a transtibial guide.

Background: The influence of the knee angle on plantarflexion moments after Achilles tendon repair has yet to be analyzed. It was hypothesized that flexion of the knee joint will disproportionately influence isometric plantarflexion moments after Achilles tendon repair.

Methods: Isometric plantarflexion moments and functional heel rise performance were retrospectively assessed in 32 patients at a mean follow-up of 36.9 (±17.83) months after open or percutaneous repair of acute Achilles tendon rupture. Plantarflexion moments were measured with the knee joint in 0, 30, and 60 degrees of flexion and the ankle joint positioned in neutral, 15 degrees plantar flexion and 15 degrees dorsiflexion. Data were compared between the involved and the noninvolved leg as well as between open and percutaneous repair.

Results: Flexion of the knee had no significant effect on isometric plantarflexion moments in either the involved or the noninvolved leg, while at any knee angle, plantarflexion moments decreased from dorsiflexion to plantar flexion. In accordance, dynamic heel rise performance revealed no significant strength deficits between the involved and the noninvolved limb. No overall differences in plantarflexion strength were observed between open and percutaneous Achilles tendon repair.

Conclusions: The flexion angle of the knee had no influence on plantarflexion moments when comparing the involved with the noninvolved leg after open or percutaneous Achilles tendon repair. Weakness of plantarflexion after open or percutaneous Achilles tendon repair is determined by the position of the ankle joint rather than by the flexion angle of the knee.

The aim of our study was to investigate whether placing of the femoral component of a hip resurfacing in valgus protected against spontaneous fracture of the femoral neck.

We performed a hip resurfacing in 20 pairs of embalmed femora. The femoral component was implanted at the natural neck-shaft angle in the left femur and with a 10° valgus angle on the right. The bone mineral density of each femur was measured and CT was performed. Each femur was evaluated in a materials testing machine using increasing cyclical loads.

In specimens with good bone quality, the 10° valgus placement of the femoral component had a protective effect against fractures of the femoral neck. An adverse effect was detected in osteoporotic specimens.

When resurfacing the hip a valgus position of the femoral component should be achieved in order to prevent fracture of the femoral neck. Patient selection remains absolutely imperative. In borderline cases, measurement of bone mineral density may be indicated.

Introduction: The Donjoy OA Orthesis has been developed to treat unicompartimental osteoarthrosis of the knee joint. The idea is to reduce the load in the affected joint compartment. Sofar only clinical evaluations and gait analysis have been published. The aim of this study is to use intraarticular pressure sensors in an anatomical model to work out the existing intraarticular pressures.

Method: 5 fresh non fixated anatomical knee models were used. The models were prepared leaving the 2/3 of the femur as well as the tibia and fibula. We used a right and left-sided version of the Donjoy OA Orthesis. A defined pressure was applied via the pressure application screw.

The dorsal capsule of the knee joint was opened and the meniscus were mobilised in a way that the pressure foils (Fuji typ super low) could be placed between the undersurface of the meniscus and the tibia plateau in each joint compartment. The measurements were recorded in four different joint positions (0°, 30°, 60° flexion and 0° with removed meniscus).

Each anatomical model was well fixed in a universal testing machine” (Instron, System ID: 5565 H1703). The used axial pressure in all set ups used was 1500N.

We used 4 four different test series:

no pressure, no orthesis

no pressure, with orthesis

with pressure, no orthesis

with pressure, with orthesis

After removing the pressure foils the actual pressure could be estimated by the diameter of the coloured foil. Using the programm Mortphomet it was possible to calculate these pressure areas and give procentual figures.

Results: The Antivarus Orthesis could reduce the intraarticular joint pressure between 55–70%

Without pressure:

Knee → 64,37 %

Knee → 55,30 %

Knee → 54,43 %

Knee → 58,75 %

Knee → 44,80 %

Mean value 55%.

With pressure:

Knee → 74,59 %

Knee → 74,00 %

Knee → 67,91 %

Knee → 86,34 %

Knee → 49,69 %

mean value 70%.

The Antivalgus Orthesis could reduce the intraarticular joint pressure between 46–74%

Without pressure:

Knee → 79,78 %

Knee → 76,22 %

Knee → 75,20 %

Knee → 62,55 %

Knee → 76,49 %

Mean value 74%.

With pressure:

Knee → 42,68 %

Knee → 46,24 %

Knee → 64,61 %

Knee → 40,08 %

Knee → 37,20 %

Mean value 46%.

Conclusion: This anatomical investigation has proved for the first time via intraarticular pressure measurements that it is possible to considerable reduce the intraarticular pressure using the Donjoy antivarus and antivalgus Orthesis.

We have evaluated four different fixation techniques for the reconstruction of a standard Mason type-III fracture of the radial head in a sawbone model. The outcome measurements were the quality of the reduction, and stability.

A total of 96 fractures was created. Six surgeons were involved in the study and each reconstructed 16 fractures with 1.6 mm fine-threaded wires (Fragment Fixation System (FFS)), T-miniplates, 2 mm miniscrews and 2 mm Kirschner (K-) wires; four fractures being allocated to each method using a standard reconstruction procedure.

The quality of the reduction was measured after definitive fixation. Biomechanical testing was performed using a transverse plane shear load in two directions to the implants (parallel and perpendicular) with respect to ultimate failure load and displacement at 50 N.

A significantly better quality of reduction was achieved using the FFS wires (Tukey’s post hoc tests, p < 0.001) than with the other devices with a mean step in the articular surface and the radial neck of 1.04 mm (sd 0.96) for the FFS, 4.25 mm (sd 1.29) for the miniplates, 2.21 mm (sd 1.06) for the miniscrews and 2.54 mm (sd 0.98) for the K-wires. The quality of reduction was similar for K-wires and miniscrews, but poor for miniplates.

The ultimate failure load was similar for the FFS wires (parallel, 196.8 N (sd 46.8), perpendicular, 212.5 N (sd 25.6)), miniscrews (parallel, 211.8 N (sd 47.9), perpendicular, 208.0 N (sd 65.9)) and K-wires (parallel, 200.4 N (sd 54.5), perpendicular, 165.2 N (sd 37.9)), but significantly worse (Tukey’s post hoc tests, p < 0.001) for the miniplates (parallel, 101.6 N (sd 43.1), perpendicular, 122.7 N (sd 40.7)). There was a significant difference in the displacement at 50 N for the miniplate (parallel, 4.8 mm (sd 2.8), perpendicular, 4.8 mm (sd 1.7)) vs FFS (parallel, 2.1 mm (sd 0.8), perpendicular, 1.9 mm (sd 0.7)), miniscrews (parallel, 1.8 mm (sd 0.5), perpendicular, 2.3 mm (sd 0.8)) and K-wires (parallel, 2.2 mm (sd 1.8), perpendicular, 2.4 mm (sd 0.7; Tukey’s post hoc tests, p < 0.001)).

The fixation of a standard Mason type-III fracture in a sawbone model using the FFS system provides a better quality of reduction than that when using conventional techniques. There was a significantly better stability using FFS implants, miniscrews and K-wires than when using miniplates.

The present study was conducted to analyze the specific morphological features of press-fitted quadriceps tendon-patellar bone grafts that determine primary graft stability in ACL-reconstruction.

Ten quadriceps tendon-patellar bone grafts were harvested from fresh frozen human cadaveric knees (age 52–82) and fixed to porcine femora in a press-fit technique. Four specimens were prepared for histological analysis of the bone-tendon junction, while a modified technique for tissue-plastination was applied to 6 specimens to investigate the microscopic and microradiographic features of the bone-to-bone interface.

Analysis of the bone-tendon junction revealed a serious damage of the fibrocartilage at the attachment zone according to the impaction of the patellar bone plug with implantation. Microradiographs and microscopy of the plastinated specimens showed that there is a trabecular interaction between the bony interfaces of the graft and the femoral tunnel, representing an early osseous integration with local increase of radiopacity. In consequence, both elevated compressive forces as well as increased frictional resistance seem to contribute to the primary stability of press-fit fixated grafts.

The stability of quadriceps tendon-patellar bone grafts in press-fit technique to a certain degree depends on bone quality, allowing compressive forces to arise at the bone-to-bone interface. Loss of graft stability, however, is caused by disturbance of the integrity of the bone-tendon junction while impacting the patellar bone plug into the femoral tunnel.

Press-fit fixation technique in anterior cruciate ligament (ACL) reconstruction has recently gained popularity. The objective of this study was to evaluate the initial fixation strength of human patellar tendon-bone (PTB) grafts with respect to bone-plug length and loading angle by using a femoral press-fit fixation technique.

Fourty-eight human PTB-grafts were obtained from 24 fresh frozen cadavers (mean age 72 years). The specimens were randomly assigned to two experimental groups: One with a 15 mm (n=24) and a second with a 25 mm patellar bone plug (n=24). The grafts were implanted to porcine femora in a press-fit fixation technique. Ultimate failure loads were measured at 10 mm/s at varying loading angles of 0, 30 and 60.

Biomechanical testing showed a significant difference of ultimate failure load comparing 15 mm (mean 236 N) to 25 mm (mean 333 N) bone plugs (p=0.015). In both groups, the fixation strength increased with rising loading angles. While axial graft loading exclusively caused plug dislocation, the predominant mode of failure was tendon rupture at 60 loading angle.

It is concluded that bone plug length and loading angle significantly influence the primary stability of PTB press-fit fixation in ACL reconstruction. Based on these findings, we recommend the use of patellar bone plugs with a minimum of 25 mm in length. If graft harvesting occasionally generates a patellar bone plug measuring 15 mm, restrictive postoperative rehabilitation should be advised.