Development of a new suturing technique for tendon graft preparation: an animal cadaver study.

BACKGROUND: This study should analyze ten different suturing techniques for tendon graft preparation to allow the development of an entirely new suturing technique. METHODS: Extensor tendon grafts of fattening bulls' forelegs were sutured with Ethibond Excel size three (six metric) fibers (Ethicon, Somerville, New York, USA). The tendon/suture complexes were biomechanically tested with a hydraulic testing machine applying traction according to a standardized protocol. The testing was observed to find out why the failure at the maximum traction load occurred. The mean values for the maximum tension and extension stiffness were recorded for each suturing technique. FINDINGS: An entirely new suturing technique was developed based on the observations and biomechanical results. The newly developed suture was also tested and provided a higher traction stability than the other ten techniques that had been evaluated. Compared to the other ten techniques the new technique was ranked 3rd in terms of extension stiffness and reached 10.3 N/mm. INTERPRETATION: The new technique evolved in the course of this study provided promising results. Therefore this study provides initial evidence that this technique could be useful in clinical routine.

Dynamic in vitro analysis of tractile forces of the anterior cruciate ligament (ACL) transplant using patellar and semitendinosus muscle tendon: a cadaver study.

PURPOSE: The presented biomechanical study focused on the in vitro analysis of tractile forces working on the anterior cruciate ligament (ACL) and the ACL transplants, respectively, using a semitendinosus and/or patellar tendon during a passive flexion-extension movement (150-0°). MATERIAL AND METHODS: Overall, 15 fresh frozen human knee joint pairs were examined. At first during arthroscopy, the tibial insertion of the ACL was drilled using a special hollow drill. Thereby, a bone cylinder was exposed at which a dynamometer was attached to enable for direct registration of tractile forces on the ACL via the connection between ACL-dynamometer and computer. The ACL transplant was fixed at the femur using a so-called endo-button, whereas the dynamometer was attached to the tibial end of the ACL transplant. The dynamic part of the examination was performed using the knee kinemator device developed by Plitz and Wirth et al. using different preload. RESULTS: The curves of the tractile forces of the ACL were qualitatively homogeneous with only low force values in the middle flexion position, whereas during maximum flexion and extension the forces increased reaching a maximum in the 0° position. Also, in testing the ACL transplants a force decrease between 0 and 50° flexion was recognized with even greater forces resulting at the 150° position depending on the anterior position of the femoral drill channel for implanting the ACL transplant. The amount of pre-loading showed no influence on the form of the tractile force curve. However, by enhancing the preload to 70 N, the maximal force in the ACL transplant increased significantly. CONCLUSION: The tractile forces assessed within the ACL during passive flexion movements between 10 and 90° were not greater than the forces measured in the ACL transplants. Thus, the clinical consequence is that in the early postoperative phase passive mobilization might be performed in this motion range without putting the ACL transplant at risk for damage.

[Damage to implants due to high-frequency electrocautery : analysis of four fractured hip endoprostheses shafts]. / Implantatschädigung durch Einsatz eines Hochfrequenzmessers : Analyse von vier Hüftendoprothesenschaftbrüchen.

In revision surgery of joints, high-frequency electrocauterization instruments are used for homeostasis and dissection of soft tissue. If there is contact of these instruments with the metal implants, flashover can occur. This can lead to thermal microstructural changes in the material and as a consequence may reduce the fatigue strength of the implant. Four cases of hip revision surgeries were analysed. In all cases flashovers occurred and secondarily, the titanium hip endoprosthesis stem broke in the neck section of the prosthesis. The conducted investigations showed that contact between the high-frequency instrument and the anterolateral aspect of the endoprosthesis neck had occurred. Electrothermal implant damage was found in the broken area. If in hip revision surgery the stem is not to be replaced, contact between high-frequency instruments and the metal implant should be avoided.

[Material and technical aspects of mega prostheses]. / Materialtechnische Aspekte bei Megaendoprothesen.

So-called mega implants were developed especially for the therapy of tumour diseases, but since these prostheses are considered to be custom-made products, they are excluded from the usual test specifications required by the German Act on Medical Devices. Based on the fact that these mega prostheses are specially manufactured and meant to be implanted in a certain patient, only casting technologies can be used. Forging procedures commonly used for so-called normal prostheses cannot be applied here. Thus only Co-Cr-Mo cast alloys can be used. Additional technologies are used for manufacturing partial pelvic implants. By means of CT plastic models are made so that the corresponding mega implants can be properly customized afterwards. Nowadays numerous bloomed surfaces and surface structures are offered to improve the engraftment behaviour.

Tissue attachment strength and adhesion formation of intraabdominal fixed meshes with cyanoacrylat glues.

OBJECTIVE: The aim of this study was to evaluate the technique of prosthetic mesh fixation in laparoscopic intraperitoneal incisional and ventral hernia repair using cyanoacrylat glue (Glubran GEM, Viareggio, Italy) in comparison with fixation methods using spiral tacks (Protack 5mm, Tyco) or transabdominal Prolene 4/0 sutures respectively. METHOD: Through a midline laparotomy 3 pieces (3 x 3cm) of mesh (n = 60) where fixed onto the intact peritoneum on either side of a midline laparotomy in 10 New Zealand White rabbits. Two types of meshes where compared: ePTFE meshes (Gore-Tex Dual Mesh W.L. Gore and Associates, Inc. Medical Products Division, Flagstaff, Arizona, USA) and polypropylene/ polyvinylfluorid meshes (Dyna Mesh - IPOM P.J. Dahlhausen and Co. GmbH, Germany). All animals were killed after 12 weeks. Upon scoring of the adhesions the prosthetic materials were excised en bloc with the anterior abdominal wall for tensile strength analysis and histologic evaluation. RESULTS: In contrast to ePTFE meshes fixed with cyanoacrylat glue, PP meshes fixed with transabdominal sutures as well as with spiral tacks showed the highest percentage and tenacity of adhesions (p<0.033). Independent of the method of fixation, ePTFE meshes revealed a significantly higher shrinkage than PP prosthesis (41% vs 17% related to original mesh surface; p<0.033). The strength of the mesh incorporation was significantly higher in PP meshes (p<0.033). Fixation of PP meshes with cyanoacrylat glue showed an equivalent tensile strength as ePTFE meshes fixed with spiral tacks (6.6 +/- 2.7 N vs 6.6 +/- 3.1N). CONCLUSION: In this rabbit model, intraabdominal fixation of PP composite meshes with cyanoacrylat glue was equivalent to ePTFE mesh fixation with spiral tacks concerning tensile strength analysis. Adhesions between mesh and abdominal wall were found more frequently after PP fixation. In contrast, mesh shrinkage was more evident after ePTFE mesh implantation.

Operative treatment of greater tuberosity fractures of the humerus--a biomechanical analysis.

BACKGROUND: Fractures of the greater tuberosity of the humerus present with increasing frequency. However, no biomechanical data about the optimal fixation technique of greater tuberosity fractures is available. This biomechanical cadaver study compares the stability of three standard fixation techniques used for the treatment of greater tuberosity fractures of the proximal humerus. METHODS: In 21 fresh frozen proximal humeri, standardized fractures of the greater tuberosity were created. The specimens were randomly assigned to one of three operation techniques: wire tension banding, two cancellous screws and transosseous sutures. These constructs were mechanically tested by applying an increasing force to the supraspinatus tendon. Load to 5mm displacement (load to 5mm yield point) and load to failure (maximum stretch strength) were measured in Newton (N). FINDINGS: Load to 5mm yield point values showed no significant differences between tension banding (498 N, SD 153) and two cancellous screws (400 N, SD 174) (P>0.01). Both techniques showed significantly higher values than transosseous sutures (185 N, SD 132) (P<0.01). Load to failure values were significantly higher for tension banding (1054 N, SD 125) than screws (842 N, SD 140) and sutures (480 N SD 101) (P<0.01). The difference between screws and sutures was also significant (P<0.01). INTERPRETATION: Tension banding and two cancellous screws provided the strongest fixation for isolated fractures of the greater tuberosity.

[Photoelastic stress analysis of human femurs before and after implantation of different models of femur neck prostheses]. / Spannungsoptische Oberflächenanalyse an humanen Femurpräparaten vor und nach Implantation unterschiedlicher Schenkelhalsprothesenmodelle.

AIM: The aim of this study was the detection of areas at risk at the proximal femur after implantation of different femur neck prostheses using the photoelastic stress analysis. METHODS: Twelve pairs of human femurs were used as examination material. The analysis of the stress pattern was done with a stepwise increasing load up to the quadruple of body weight before and after implantation of three models of femur neck prostheses which were implanted cementless. The "CUT" and "Cigar" models are coated with a tripod structure. The "Cigar" model has a lateral thrust plate. The lateral end of the "CUT" model is curved and this end is attached to the lateral corticalis. The third model, the "rip prosthesis" has two layers for rotational stability. Subsequently, the micromotions of the implanted prosthesis in the femural neck were examined with alternating weight loads (1000 +/- 700 N). RESULTS: The Cigar prosthesis showed the most changes of stress distribution because of the lateral thrust plate with concentration of isochromatic lines to the lateral boring. In the region of the oseotomy an increase of strain up 1440 microm/m could be detected for the Cigar and up to 1000 microm/m for the rib prosthesis. The stress pattern after implantation of the CUT prosthesis remained very similar apart from a slight increase of stress values (720 microm/m). Only for the Cigar prostheses were the measured micromotions below the critical value for a possible osteointegration with a mean value of 134 microm/m. CONCLUSION: The stress pattern after implantation of the CUT prosthesis remained most similar to the preinterventional stress distribution. Because of this, it is to be expected that the osseous modification would stay at a low level. The question of osteointegration can only be answered in long-term in-vivo studies.

[Metal/metal coupling in total hip arthroplasty. Progress or setback?]. / Die Metall-Metall-Gleitpaarung in der Hüftendoprothetik. Fortschritt oder Rückschritt?

It was about 1966 that the metal/metal coupling was introduced into clinical use by McKee and Watson-Farrar. The main arguments for the introduction of this hard/hard coupling were the low wear rates compared to polyethylene couplings and the long-term stability of the metal components. The metal/metal couplings of McKee and Watson-Farrar could not meet the requirements of corresponding long-term results (loosening rates of more than 50% in part). The reason was the inadequate manufacturing quality, but also the random combination of components of different manufacturers. Nevertheless, remarkable long-term results could be reported and they were the reason for introducing a modified metal/metal coupling into clinical use in 1999. This metal/metal coupling of the second generation is characterised by modified CoCrMo materials, but also by definitely excellent manufacturing technologies. The clinical results seem to be better due to improved material quality and manufacturing technique. However, the question remains whether the high Co and Cr level, which is often noticed, has any pathological relevance.

[Pullout resistance of conventional pedicle screw implantation in comparison to fluoroscopic computer-assisted technique]. / Ausrissfestigkeit implantierter Pedikelschrauben in konventioneller und fluoroskopisch-navigierter Technik.

AIM: Aim of the study was to compare pullout resistance of pedicle screws after conventional and fluoroscopic computer-assisted implantation in the cadaveric thoracic and lumbar spine. METHODS: Pedicle screws were inserted in a total of 10 vertebrae of different human specimens: 10 screws were placed using conventional technique (group 1) and 10 screws were inserted with fluoroscopic computer-assisted system contralaterally (group 2). Then pedicle screws were evaluated for biomechanical axial pullout resistance. RESULTS: Mean pullout force was 232 N (range 60-600 N) in group 1 and 353 N (range 112-625 N) in group 2. The difference was significant (p=0,0425). CONCLUSION: Fluoroscopic navigated implantation of pedicle screws increases the pullout strength in thoracic and lumbar cadaveric spines as compared with conventional methods.

Stability of anterior vertebral body screws after kyphoplasty augmentation. An experimental study to compare anterior vertebral body screw fixation in soft and cured kyphoplasty cement.

The goal of this cadaver study was to compare the stability of anterior vertebral body screws after implantation in soft or cured kyphoplasty cement. Anterior vertebral body screws were inserted in a total of 30 thoracolumbar vertebrae of ten different human specimens: ten screws were implanted in non-augmented vertebrae (group 1), ten screws were placed in soft cement (group 2), and ten screws were placed in cured cement (group 3). The screws were then tested for biomechanical axial pullout resistance. Mean axial pullout strength was 192 N (range: 10-430 N) in group 1, 364 N (range: 65-875 N) in group 2, and 271 N (range: 35-625 N) in group 3. The paired Student's t-test demonstrated a significant difference between pullout strength of groups 1 and 2 (p= 0.0475). No significant difference was seen between pullout strength of groups 1 and 3 (p= 0.2646) and between groups 2 and 3 (p= 0.3863). We achieved a 1.9 times higher pullout strength with kyphoplasty augmentation of osteoporotic vertebrae compared with the pullout strength of non-augmented vertebrae. Implantation of anterior vertebral body screws in cured cement is a satisfactory method. With this method we found a 1.4 times higher pullout strength than non-augmented vertebrae.

[Stability of pedicle screws in comparison to anterior vertebral body screws after kyphoplasty augmentation]. / Stabilität von Pedikelschrauben versus ventral eingebrachter Schrauben nach Kyphoplastie-Augmentation.

AIM: Aim of the study was to compare stability of pedicle screws and ventral implanted screws after insertion in soft or cured kyphoplasty cement. METHODS: Pedicle screws were inserted in a total of 40 thoracolumbar vertebrae of 10 different formalin-fixed human specimens: each 10 pedicle screws were implanted in soft (group 1) and cured cement (group 2), each 10 ventral screws were placed in soft (group 3) and cured (group 4) cement. Pedicle screws were then evaluated for biomechanical axial pullout resistance. RESULTS: Mean pull-out force was 452 N (range 60-1 125 N) in group 1, 367 N (range 112-840 N) in group 2, 364 N (range 65-875 N) in group 3 and 271 N (range 35-625 N) in group 4. CONCLUSION: Implantation of pedicle screws and ventral implanted screws in soft and cured kyphoplasty cement is a sufficient method. We achieved more stability with pedicle screws compared with ventral implanted screws in soft and cured cement. No significant difference was seen.

Micromotion in cemented rotating platform total knee arthroplasty: cemented tibial stem versus hybrid fixation.

INTRODUCTION: Improving the longevity and reliability of cemented total knee arthroplasty (TKA) remains a major step to achieve. It is still unclear, whether a cemented tibial stem reduces micromotion of the tibial tray and produces therefore a better initial stability or not. The higher conformity of rotating platform design and the possible rotary forces to the tibial platform may produce higher micromotion when the tibial stem remains cementless (hybrid fixation). MATERIALS AND METHODS: An in vitro study was performed using the PFC mobile bearing tibial tray (DePuy, Warswa, IN, USA) to test the hypothesis that the addition of cement surrounding the tibial stem reduces micromotion of the tibial tray in cemented TKA with mobile bearing design. Ten tibial trays with mobile design were implanted in sawbones with a 3-mm cement mantle beneath the baseplate of the tibial tray and with or without the cemented stem. Tibial trays were loaded additionally in the ventral, lateral, medial and posterior positions with 2,500 N using the Zwick Z010 instrumentation and HBM pick up Hottinger Baldwin. RESULTS: In this study, a significant increased mean maximum liftoff was found when only cementing the tibial baseplate (hybrid fixation), compared to the fully cemented tibial tray (P<0.02). CONCLUSION: In conclusion, the stem of mobile bearing tibial components should be cemented to provide increased micromotion and earlier loosening.

[Macerated human hip bone preparation as a substitute for fresh frozen preparations for testing the primary stability and frictional torques of cementless hip cups]. / Mazerierte Hüftpfannenpräparate als Ersatz für fresh-frozen-Präparate zur Testung von Primärstabilität und Einschraubverhalten zementfreier Hüftpfannen.

AIM: The aim of the study was to validate macerated human acetabuli as replacement for fresh frozen preparations for testing primary stability and the screwing in moments of cementless threaded hip cups. METHOD: Three fresh frozen human pelvis were tested. One half of each pelvis was macerated whereas the other half was preserved as fresh frozen preparation. In the side of every pelvis the moments of screwing-in, the micromotions, the maximum expressing force and the maximum pull-out torque were determined. RESULTS: The screwing in moments, the maximum expressing forces and the maximum pull-out torques did not change. The micromotions were reduced to half. CONCLUSION: Considering the reduction of the micromotions, macerated human acetabuli are valid replacements for fresh frozen preparations for testing the primary stability and the screwing-in behaviour of screwed pans.

[Axial load in case of press-fit fixation of the ACL graft--a fundamental study]. / Einpresskraft bei Press-fit Fixierung der vorderen Kreuzbandplastik -- eine Grundlagenstudie.

AIM: The aim of this study was the determination of the axial fixation load resting on smooth press-fit dowels needed for fixation of the patellar tendon graft (BTB) in order to reach the same fixation properties compared to the interference screw on anterior cruciate ligament (ACL) plasty. METHOD: Bovine test specimens with 27 BTB grafts fixed in tibial drill holes were used and divided in 3 groups: interference screw, and press-fit cylinder (Ø 7 mm) with 150 N and 100 N axial loads. Prior to fixation, impactation of the transplant into bone was carried out. Failure testing was done in a tensiometer at a cross-head speed of 50 mm/min. Determinations of peak load and stiffness were also made. RESULTS: Similar peak loads and stiffness were reached on introducing a press-fit dowel (slashed circle 7 mm) with 100 N and 150 N axial load compared to interference screw fixation of the BTB graft. Peak load: 988.1 N +/- 365.1 (screw) versus 1 210.4 N +/- 292.4 (dowel 150 N) and 1 109.8 N +/- 505.4 (dowel 100 N). Stiffness: 86.4 N/mm +/- 20.5 (screw) versus 102.4 N/mm +/- 15.2 (dowel 150 N) and 77.1 N/mm +/- 11.0 (dowel 100 N). There was no significant difference. CONCLUSION: When introducing a press-fit dowel (slashed circle 7 mm) with 100 N axial load into a preformed bone bed, the same fixation properties are reached as in the case of an interference screw on BTB-ACL plasty.

Biomechanical evaluation of a bioabsorbable expansion bolt for hamstring graft fixation in ACL reconstruction: an experimental study in calf tibial bone.

INTRODUCTION: The purpose of our study was to evaluate and compare the primary fixation strength of a novel bioabsorbable two shell expansion bolt (EB) with that of a well-established interference screw-fixation technique in hamstring reconstruction of the anterior cruciate ligament. MATERIALS AND METHODS: Thirty calf tibia plateaus (age 5-6 months) were assigned to three groups: In group I (n = 10) triple-stranded hamstring grafts were fixed with titanium interference screws (7 mm thread / 8 mm head x 25 mm). Specimens of group II (n = 10) received bioabsorbable poly-L-lactide interference screws (8 x 23 mm). In group III (n = 10), the grafts were fixed using bioabsorbable poly-D,L-lactide expansion bolts (5.8/8.5/10 mm x 35 mm). The tensile axis was placed parallel to the bone tunnel. The construction was then loaded until failure under a displacement rate of 1 mm per second. RESULTS: There were no significant differences concerning the maximum pullout force (group I: 357 N +/- 61; group II: 326 N +/- 92; group III: 343 N +/- 55). In case of the expansion bolt, we found the stiffness to be higher (61 N/mm) when compared to group I (48 N/mm), and group II (52N/mm) (P < 0.01 I vs. III). Using interference screws, we were able to demonstrate a strong correlation between torque and pullout forces (group I: r2 = 0.7; group II: r2 = 0.92). Ruptures of the suturing material occurred only in groups I and II. CONCLUSION: We conclude that hamstring graft fixation, using the presented expansion bolt, demonstrates fixation strength similar to the established screw fixation and can therefore be regarded as a reasonable alternative fixation method. Especially, since some specific disadvantages of screw fixation can be prevented by application of the bolt fixation.

[Extracorporeal single dose and radiographic dosage in image-controlled and fluoroscopic navigated pedicle screw implantation]. / Extrakorporale Einzeldosis und Durchleuchtungszeit bei bildwandler-kontrollierter und fluoroskopisch navigierter Implantation von Pedikelschrauben.

AIM: Goal of the current study was to compare radiation dose and fluoroscopy time of fluoroscopic computer assisted pedicle screw implantation versus the conventional technique. METHOD: For each of 10 specimens two pedicle screws were placed using conventional technique (group 1) and two screws were inserted with fluoroscopic navigation system (group 2) contralateraly. RESULTS: For implantation of two pedicle screws the mean radiation dose was 0.041 mSv in group 1 and 0.029 mSv in group 2. Fluoroscopy time was 34 seconds in group 1 and 25 seconds in group 2. The differences of radiation dose and fluoroscopy time for group 1 and 2 were statistically significant (radiation dose p = 0.00044, fluoroscopy time p = 0.00039). CONCLUSION: We achieved significantly lower radiation dose and fluoroscopy time with fluoroscopic computer assisted pedicle screw implantation compared with the conventional technique. Concerning exposure to radiation for patients and personnel fluoroscopic navigated screw insertion is to favour.

[Cervical collars: a clinical and biomechanical study]. / Zervikalstützen: Eine klinische und biomechanische Studie.

AIM: Cervical collars have been used for years in the non-operative and postoperative management of cervical spine problems. They offer considerable differences in design, stability, bearing comfort and costs. In the background of controversies about the indication and in view of the limited number of scientific publications on the topic we have conceived this paper as a biomechanical and clinical investigation. METHODS: During the biomechanical investigations a defined load was exerted on 10 cervical collars of 4 producers. The clinical part was the measurement of the limitation of movement due to the 10 cervical collars in 30 healthy subjects aged 20 to 60 years. RESULTS: The biomechanical investigations showed differences of stiffness which were obvious during axial load, sideward and backward bending and less obvious in forward bending. The clinical study in 30 subjects indicated, on the other hand, only small differences in the limitation of movement. Softer cervical collars were slightly better accepted in the subjective judgment. CONCLUSION: For the aimed limitation of movement, a minimum of stiffness is obviously necessary, which is common with every tested collar. Higher degrees of stiffness do not result in further limitation of movement but only in a reduction of bearing comfort.

Influence of a mono-centric knee brace on the tension of the collateral ligaments in knee joints after sectioning of the anterior cruciate ligament--an in vitro study.

OBJECTIVE: To analyze the influence of knee bracing on the tension of the medial and lateral collateral ligaments in anterior cruciate ligament deficiency. DESIGN: The tension of the collateral ligaments in anterior cruciate ligament deficient knees was measured with and without knee bracing using an in vitro model. BACKGROUND: Anterior cruciate ligament deficiency increases the tension in both collateral ligaments at the knee joint. Therefore knee braces should reduce that tension increase. However, that effect has never been proven quantitatively. METHODS: After anterior cruciate ligament-transection, the forces of the medial (anterior/posterior part) and lateral collateral ligament were measured in ten fresh human cadaver knees at 0 degrees, 20 degrees, 40 degrees, 60 degrees, 80 degrees and 100 degrees of flexion, with and without application of a mono-centric knee brace. To quantify the ligament forces, strain gauges were fixed at the bony origins of the ligaments. RESULTS: Bracing led to a significant decrease of ligament forces (20-100 degrees: P < 0.0001) in the anterior part of the medial collateral ligament in all joint positions. In the posterior aspect, this effect was observed only at 40 degrees (P < 0.0001) and 80 degrees (P = 0.001) of flexion. In the lateral collateral ligament, bracing caused a strain reduction from 60 degrees to 100 degrees of flexion (P < 0.0001). Therefore a flexion angle dependent effect of knee bracing on the strain was seen in the posterior aspect of the medial and in the lateral collateral ligament in anterior cruciate ligament deficient knee joints. CONCLUSIONS: Application of a mono-centric knee brace leads to a significant position dependent reduction of collateral ligament tension after anterior cruciate ligament-rupture.

[The primary stability between manual and robot assisted implantation of hip prostheses: A biomechanical study on synthetic femurs]. / Die Primärstabilität von manuell und roboterassistiert implantierten Hüftendoprothesenstielen: eine biomechanische Untersuchung an Kunstfemora.

AIM: We investigated the initial stability of cementless stems implanted with robotic milling and conventional manual broaching. METHODS: Proximally porous structured stems (G2, ESKA-Implants, Luebeck, Germany) were implanted into synthetic femora. In one group, the femoral cavity was prepared by a CT-based robot (CASPAR, URS-Ortho, Germany) with a high-speed milling head. In the other group, femora were rasped manually with broaches. The broaches had 1 mm proximal press-fit, the robotic cavities 1.5 mm. The implants were exposed to 15 000 loading cycles with 1 000 +/- 500 N. The direction of forces on the implant head were chosen to simulate stair climbing. Internal rotation and translation (caudal, dorsal and lateral) of the implants were measured by linear transducers. RESULTS: The robotic group showed significantly less reversible motion regarding translation in caudal, dorsal and lateral directions. The standard deviations of implant motions were smaller in the robotic group. CONCLUSION: Using robotic preparation of the femur, initial stability was higher and more consistent than with manual broaching, but differences in undersizing of the cavities created in the femur in relation to the implant may have contributed to these differences for the most part. In-vitro-loading experiments focusing on femoral cavities with varying press-fits are recommended before the introduction of new implants or operating procedures.

Bioabsorbable expansion bolt fixation in anterior cruciate ligament reconstruction.

The current study evaluated initial fixation strength of a bioabsorbable expansion bolt compared with interference screw fixation in anterior cruciate ligament reconstruction using a bone-patellar tendon-bone graft. Thirty calf tibial plateaus with adjacent patella and extensor ligaments were used. Bioabsorbable poly-L-lactide interference screws were used for graft fixation in Group I, titanium screws in Group II, and bioabsorbable poly-DL-lactide expansion bolts were used in Group III. The mean force-to-failure (+/- standard deviation) in the three groups was 487 +/- 205 N, 713 +/- 218 N, and 594 +/- 224 N, respectively. The differences between Groups I and II were significant. No statistical differences were found regarding stiffness. Graft damage was significantly less in Group III compared with screw fixation. The fixation concept of an expansion bolt shows similar fixation strength and less graft damage compared with the established interference screw fixation. Because of the total absence of torque forces in contrast to bioabsorbable screws, the risk of implant breakage is minimized.