The novel arthroscopic subscapular sling procedure grants better stability than an arthroscopic Bankart repair in a cadaveric study.

PURPOSE: This novel arthroscopic subscapular sling procedure stabilizes the shoulder using a semitendinosus graft to create a sling around the subscapular tendon, which provides both static and dynamic stability. The aim of the study was to evaluate the biomechanical stability of the subscapular sling procedure in human cadaveric shoulders. The hypothesis was that the sling offers an equal stabilizing effect and range of motion compared to an arthroscopic Bankart repair. METHODS: Sixteen shoulders were investigated using an industrial robot-based testing platform and four different conditions: the physiologically intact shoulder, after creating a Bankart lesion, after arthroscopic Bankart repair, and finally after applying the subscapular sling procedure using a semitendinosus tendon graft. Joint translation and external rotation were evaluated for each condition. RESULTS: The results show improved stability in the shoulders with the subscapular sling. The robot testing revealed a significant reduction in translation in anterior and anterior-inferior directions compared to the arthroscopic Bankart repair. None of the shoulders were dislocated by forced manual abduction and external rotation. No difficulties were encountered in performing the arthroscopic subscapular sling procedure. Thorough postoperative anatomical dissection showed no alterations to structures at risk. CONCLUSION: The biomechanical results show increased stability with the use of the subscapular sling method.

[Early assessment of the risk of later implantloosening using Roentgen Sterophotogrammetric Analysis (RSA)]. / Früherkennung des Risikos der späteren Implantatlockerung mittels der Röntgen Stereophotogrammetrischen Analyse (RSA).

BACKGROUND: Aseptic implant loosening is the most common cause of implant revisions in total hip and total knee arthroplasty. Roentgen Stereophotogrammetric Analysis (RSA) represents the current gold standard for the in-vivo assessment of implant fixation. PRESENT SITUATION: Long-term clinical trials have shown that continuous implant migration within the first two postoperative years correlates strongly with a later aseptic loosening. Thus, the implant migration measured with RSA can be regarded as a reliable surrogate marker for later implant loosening. Over the past 40 years, RSA has been continuously further developed, and the model-based RSA approach has reduced the effort involved since markers attached to implant are no longer needed. PERSPECTIVES: The RSA method is gaining importance in the certification process of new orthopaedic implants-for example, the Dutch Orthopedic Society has recommended phased-introduction and RSA studies for new hip implants. Furthermore, in the context of the new EU Medical Device Regulation (MDR), which took effect in May 2017, RSA gained relevance for investigating clinically unproven implants. Critics who associate MDR with hindering innovation can be countered in that the RSA method provides a predictive assessment of implant fixation after only two years of follow-up, which is significantly shorter than standard long-term clinical trials.

Suture anchor repair yields better biomechanical properties than transosseous sutures in ruptured quadriceps tendons.

PURPOSE: This human cadaveric study compares the biomechanical properties of quadriceps tendon repair with suture anchors and the commonly applied transosseous sutures. The hypothesis was that suture anchors provide at least equal results concerning gap formation and ultimate failure load compared with transosseous suture repair. METHODS: Thirty human cadaveric knees underwent tenotomy followed by repair with either 5.5-mm-double-loaded suture anchors [titanium (TA) vs. resorbable hydroxyapatite (HA)] or transpatellar suture tunnels using No. 2 Ultrabraid™ and the Krackow whipstitch. Biomechanical analysis included pretensioning the constructs with 20 N for 30 s and then cyclic loading of 250 cycles between 20 and 100 N at 1 Hz in a servohydraulic testing machine with measurement of elongation. Ultimate failure load analysis and failure mode analysis were performed subsequently. RESULTS: Tendon repairs with suture anchors yielded significantly less gap formation during cyclic loading (20th-250th cycle: TA 1.9 ± 0.1, HA 1.5 ± 0.5, TS 33.3 ± 1.9 mm, p < 0.05) and resisted significantly higher ultimate failure loads (TA 740 ± 204 N, HA 572 ± 67 N, TS 338 ± 60 N, p < 0.05) compared with transosseous sutures. Common failure mode was pull-out of the eyelet within the suture anchor in the HA group and rupture of the suture in the TA and TS group. CONCLUSION: Quadriceps tendon repair with suture anchors yields significantly better biomechanical results than the commonly applied transosseous sutures in this human cadaveric study. These biomechanical findings may change the future clinical treatment for quadriceps tendon ruptures. Randomised controlled clinical trials are desirable for the future. LEVEL OF EVIDENCE: Not applicable, controlled laboratory human cadaveric study.

BMP activation and Wnt-signalling affect biochemistry and functional biomechanical properties of cartilage tissue engineering constructs.

OBJECTIVES: Bone morphogenetic protein (BMP-) and Wnt-signalling play crucial roles in cartilage homeostasis. Our objective was to investigate whether activation of the BMP-pathway or stimulation of Wnt-signalling cascades effectively enhances cartilage-specific extracellular matrix (ECM) accumulation and functional biomechanical parameters of chondrocyte-seeded tissue engineering (TE)-constructs. DESIGN: Articular chondrocytes were cultured in collagen-type-I/III-matrices over 6 weeks to create a biomechanical standard curve. Effects of stimulation with 100 ng/mL BMP-4/-7 heterodimer or 10 mM lithium chloride (LiCl) on ECM-deposition was quantified and characterized histologically. Biomechanical parameters were determined by the Very Low Rubber Hardness (VLRH) method and under confined compression stress relaxation. RESULTS: BMP-4/-7 treatment resulted in stronger collagen type-II staining and significantly enhanced glycosaminoglycan (GAG) deposition (3.2-fold; *P < 0.01) correlating with improved hardness (∼1.7-fold; *P = 0.001) reaching 83% of native cartilage values after 28 days, a value not reached before 9 weeks without stimulation. LiCl treatment enhanced VLRH slightly, but significantly (∼1.3-fold; *P = 0.016) with a trend to more ECM-deposition. BMP-4/-7 treatment significantly enhanced the E Modulus (105.7 ± 34.1 kPa; *P = 0.000001) compared to controls (8.0 ± 4.2 kPa). Poisson's ratio was significantly improved by BMP-4/-7 treatment (0.0703 ± 0.0409; *P = 0.013) vs controls (0.0432 ± 0.0284) and a significantly lower permeability (5.8 ± 2.1056 × 10(-14) m4/N.s; *P = 0.00001) was detected compared to untreated scaffolds (4.4 ± 3.1289 × 10(-13) m4/N.s). CONCLUSIONS: While Wnt-activation is less effective, BMP-4/-7 heterodimer stimulation approximated native cartilage features in less than 50% of standard culture time representing a promising strategy for functional cartilage TE to improve biomechanical parameters of engineered cartilage.

Biomechanical properties of femoral posterior cruciate ligament fixations.

PURPOSE: The success of reconstructions of the posterior cruciate ligament (PCL) mainly depends on the fixation strength of the tendon-bone interface. Reliable data about the mechanical characteristics of PCL fixation techniques are sparse. The aim of this study was to investigate the biomechanical properties of different femoral PCL fixation techniques. METHODS: Fresh human cadaver quadriceps (Q) and hamstring (H) tendons were harvested and fixed into porcine femora with a press-fit fixation suturing the tendon over a bone bridge (group A), a novel implant post-fixation (group B) or an interference screw fixation (group C). Each group consisted of 10 specimens. The constructs were cyclically stretched and eventually loaded until failure. Elongation during cyclic loading, stiffness, failure mode and maximum failure load was evaluated. RESULTS: Elongation during cyclical loading was significantly larger between the 1st and the 20th cycle than between the 20th and the 500th cycle in all groups (p < 0.05). Maximum failure load was 409 ± 71 (336-517) N in group QA, 456 ± 58 (347-510) N in group QB, 548 ± 116 (400-798) N in group QC, 472 ± 114 N (316-676 N) in group HA, 494 ± 98 N (371-668 N) in group HB and 498 ± 87 N (391-687 N) in group HC (significantly higher for QB compared to QA, p < 0.05). CONCLUSION: This is the first study investigating the biomechanical properties of femoral PCL fixations. Implant-free fixation techniques like press-fit or post-fixations are able to withstand equal biomechanical forces compared to interference screw fixation. The novel fixations described in this study can be considered as a reliable alternative for the reconstruction of PCL using either hamstring or quadriceps tendons.

[Ligament bracing--augmented cruciate ligament sutures: biomechanical studies of a new treatment concept]. / "Ligament bracing"--die augmentierte Kreuzbandnaht: Biomechanische Grundlagen für ein neues Behandlungskonzept.

BACKGROUND: In the context of acute knee dislocations, suture repair of ruptured cruciate ligaments leads to good clinical results in 80% of cases. Disadvantages are low primary stability and subsequently secondary elongation of the sutured ligaments. In the present study, we compared primary stability of suture repair, reinforced by different suture augments, to cruciate ligament reconstruction. OBJECTIVE: The concept of ligament bracing with transosseous suture repair of the cruciate ligaments and additional suture augmentation is biomechanically superior to cruciate ligament reconstruction. MATERIAL AND METHODS: A total of 42 porcine knee joints divided into seven groups were examined. The stability of four different suture/augmentation combinations were compared to cruciate ligament reconstruction with human hamstring tendons. The investigational setup consisted of testing 1000 cycles with 20 N to 154 N load in a.-p. translation and 60° flexion. Elongation and load to failure were measured. RESULTS: Neither reconstruction (3.13 ± 1.65 mm; 362 ± 51 N) nor augmented suture repair (1.89-2.5 mm; 464-624 N) achieved the primary stability of the intact cruciate ligament (0.63 ± 0.34 mm, 1012 ± 91 N). In comparison to ligament reconstruction, all four augmented suture repairs showed minor elongation in the cyclic test and a higher load to failure. The isolated suture repair showed poor results (6.79 ± 4.86 mm, 177 ± 73 N). CONCLUSION: Augmented suture repair provides significantly higher stability compared with isolated suture repair and reconstruction with hamstring tendons. The concept of ligament bracing could be a promising future treatment option in acute knee dislocations. Clinical results remain to be seen.

[Possibilities for the biomechanical characterization of cartilage: a brief update]. / Möglichkeiten der biomechanischen Charakterisierung von Knorpelgewebe: Eine Standortbestimmung.

The quantitative description of the biomechanical function of diarthrodial joint cartilage is a particularly challenging task due to the unique load bearing, load distribution and tribological properties of the tissue,which have their origin in the unique structure and biochemical composition. In the course of recent decades,different material models and testing methods have been published which claim to meet this challenge in one way or another. The goal of this paper is to provide an overview of the basic principles involved in the most important of these material models and testing methods. The relationship between the material models and the relevant testing methods will be illustrated in a comprehensible manner. As practical use of these methods is also associated with the amount of time required to perform them, particular attention will be paid to experimental approaches requiring only one test modality to be performed.

[Applications of numerical simulation in musculoskeletal research and its impact on orthopedic surgery]. / Einsatzgebiete der numerischen Simulation in der muskuloskelettalen Forschung und ihre Bedeutung für die Orthopädische Chirurgie.

Finite element analyses (FEA) as well as multibody system dynamics (MSD) are the main tools used for numerical simulation in the field of musculoskeletal research. While FEA is utilized for field problems, such as calculation of stress and strain distribution, MSD is applied for solving kinematic analyses, such as calculation of muscle and joint forces. Depending on the focus of investigation, modelling of biological tissue may vary from simple homogeneous behavior to modelling biochemical processes on the microscale and nanoscale. An important milestone in biomechanical research was the analysis of stress shielding, which led to further research on bone remodelling. Various models of implant-bone fixation used for the prediction of micromotion have been published. New possibilities for biomechanical analyses are achieved by consideration of complex muscle forces which are generated by MSD simulation and imported into FEA models as limiting conditions. A numerical model always requires experimental validation. If the results are confirmed experimentally, various advantages of numerical simulation apply and problems can be analysed isolated from many influencing factors. Therefore, straightforward parameter variation is possible, enabling studies which would be impossible in an experimental or clinical setup.

[Implant-free tibial fixations of the posterior cruciate ligament. Development and biomechanical testing]. / Implantatfreie tibiale Fixierung des hinteren Kreuzbandes. Entwicklung und biomechanische Testung.

BACKGROUND: A secure tibial press fit technique in posterior cruciate ligament reconstructions may be a relevant alternative to common techniques because no hardware is necessary. Up to the present point in time no biomechanical data exist for a tibial press fit posterior cruciate ligament (PCL) reconstruction. This study compares the biomechanical properties of hamstring and quadriceps tendon grafts using a press fit technique with those of an interference screw fixation. METHODS: Quadriceps and hamstring tendons of 20 human cadavers (age 49.2±18.5 years) were used. A press fit fixation with a knot in the semitendinosus tendon (K) and a quadriceps tendon bone block graft (Q) were compared to an interference screw fixation (I) in 27 porcine tibiae. In each group, nine constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated. RESULTS: The maximum load to failure was 518±157 N (387-650 N) for the K group, 558±119 N (466-650 N) for the I group and 620±102 N (541-699 N) for the Q group. The stiffness was 55±27 N/mm (18-89 N/mm) for the K group, 117±62 N/mm (69-165 N/mm) for the I group and 65±21 N/mm (49-82 N/mm) for the Q group. The stiffness of the I group was significantly larger (ANOVA on ranks, P=0.01). The elongation during cyclical loading was significantly larger for all groups from the 1st to the 5th cycle compared to the elongation in between the 5th and the 20th cycle (P<0.03). CONCLUSION: All techniques exhibited larger elongation during initial loading. Load to failure and stiffness were significantly different between the fixations. The Q fixation showed equal biomechanical properties compared to a pure tendon fixation (I) with an interference screw. The results of group K were inferior. All three investigated fixation techniques exhibit comparable biomechanical properties. Preconditioning of the constructs is critical. Future randomized, clinical trials have to investigate the biological effectiveness of these fixation techniques.

Hip joint function and reconstruction of the anterior femoral offset in patients with short stem vs. conventional THA.

In cases where mobility and joint function are impaired after implantation of a THA, weakening of hip movement in both extension/flexion and adduction/abduction may play a role due to shortening of the physiological lever arm of the hip muscles. Mechanical factors of influence include the lateral femoral offset, which affects the lever arm, and the antetorsion angle of the hip prosthesis, which affects the anterior femoral offset. This study aimed to investigate the effect of an altered antetorsion angle of the implant on the hip moments and gait patterns of the patient. For this study, 13 patients with a conventional stem on one side and a calcar-guided short stem implanted on the contralateral side were included. To determine the maximum hip moment, tests were performed on a dynamometer in extension/flexion and adduction/abduction in addition to gait analysis. As a control, a comparison was made with data from a reference group of 30 healthy subjects. Both implants showed similar symmetry indices. There was a significant difference between the implants for adduction moments (p < 0.001). The ratios between the directions of moments showed no significant differences. The joint function measured by isokinetic measurements and gait analysis remains comparable to the healthy control group after short stem arthroplasty, but shows slight changes after conventional stem arthroplasty.

The fixation strength of tibial PCL press-fit reconstructions.

PURPOSE: A secure tibial press-fit technique in posterior cruciate ligament reconstructions is an interesting technique because no hardware is necessary. For anterior cruciate ligament (ACL) reconstruction, a few press-fit procedures have been published. Up to the present point, no biomechanical data exist for a tibial press-fit posterior cruciate ligament (PCL) reconstruction. The purpose of this study was to characterize a press-fit procedure for PCL reconstruction that is biomechanically equivalent to an interference screw fixation. METHODS: Quadriceps and hamstring tendons of 20 human cadavers (age: 49.2 ± 18.5 years) were used. A press-fit fixation with a knot in the semitendinosus tendon (K) and a quadriceps tendon bone block graft (Q) were compared to an interference screw fixation (I) in 30 porcine femora. In each group, nine constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness, and elongation during failure testing and cyclical loading were investigated. RESULTS: The maximum load to failure was 518 ± 157 N (387-650 N) for the (K) group, 558 ± 119 N (466-650 N) for the (I) group, and 620 ± 102 N (541-699 N) for the (Q) group. The stiffness was 55 ± 27 N/mm (18-89 N/mm) for the (K) group, 117 ± 62 N/mm (69-165 N/mm) for the (I) group, and 65 ± 21 N/mm (49-82 N/mm) for the (Q) group. The stiffness of the (I) group was significantly larger (P = 0.01). The elongation during cyclical loading was significantly larger for all groups from the 1st to the 5th cycle compared to the elongation in between the 5th to the 20th cycle (P < 0.03). CONCLUSION: All techniques exhibited larger elongation during initial loading. Load to failure and stiffness was significantly different between the fixations. The Q fixation showed equal biomechanical properties compared to a pure tendon fixation (I) with an interference screw. All three fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs is critical. Clinical trials have to investigate the biological effectiveness of these fixation techniques.

Biomechanical investigation of the stabilization principle of the Latarjet procedure.

PURPOSE: The purpose of the study was to determine the biomechanical status of the different components of the Latarjet procedure. The anterior capsule reconstruction with the transferred coracoacromial ligament (CAL) and the necessity of an intact subscapularis tendon were of particular interest. We hypothesized that the anterior capsule reconstruction will have a significant effect and that the Latarjet procedure will lose its stabilizing effect if the subscapularis tendon is torn. METHODS: Stability testing of 12 human shoulder specimens was performed. After testing of the intact joint, a combined anterior glenoid and capsule defect was set arthroscopically. Then the Latarjet procedure was performed using an open approach and tested with and without loading of the conjoint tendons (10 N). Afterwards, the specimens were distributed into two groups and the Latarjet technique was reduced stepwise: dissection of the CAL, dissection of the conjoint tendons (group A); reduction of the coracoid segment, dissection of the subscapularis tendon (group B). Biomechanical testing was performed for each condition in two positions: 60° of glenohumeral abduction with neutral rotation and with 60° of external rotation; each with a passive humerus load of 30 N in the anterior, inferior and anteroinferior direction. RESULTS: The Latarjet technique with load applied to the conjoint tendons significantly reduced translation compared with the defect condition for all tested positions in all directions. In group A, the CAL-dissection led to a significant increase of anterior translation (+5.0 mm, p = 0.003) and inferior translation (+7.3 mm, p = 0.025) in neutral rotation and of anterior translation in 60° of external rotation (+4.4 mm, p = 0.034). In group B, the reduction of the coracoid bone down to the coracoid tip resulted in a significant increase of only the anterior translation in abduction and 60° of external rotation (+4.5 mm, p = 0.05). In contrast, the detachment of the subscapularis tendon led to a significant increase of translation in all testing positions except the inferior direction in the neutral rotation. CONCLUSIONS: We found the anterior capsule reconstruction to represent a significant contribution to the stabilizing effect of the Latarjet procedure, whereas a deficiency of the subscapularis tendon eliminates its effect. CLINICAL RELEVANCE: We recommend to perform the Latarjet technique with an anterior capsule reconstruction (e.g. CAL transfer) and with a transfer of the coracoid bone block rather than a transposition of the coracoid tip. Furthermore, we were able to show that an intact subscapularis tendon is a necessary prerequisite for a reliable stabilization.

Comparison of three suture techniques and three suture materials on gap formation and failure load in ruptured tendons: a human cadaveric study.

INTRODUCTION: There is a large variety of ruptures of tendons and ligaments in trauma surgery. Reliable data about the most appropriate suture technique and suture material for ruptured tendons are sparse. This human cadaveric study compares the biomechanical properties of three suture materials and three suture techniques for semitendinosus tendon repair. METHOD: Sixty-three human cadaver hamstring tendons underwent tenotomy and repair with either Baseball suture, Kessler suture, or a novel "Hannover" suture, using either PDS 2-0, Ethibond 2-0, or Fiberwire 2-0. Biomechanical analysis included pretensioning the constructs with 2 N for 50 s, then cyclic loading of 500 cycles between 2 and 15 N at 1 Hz in a servohydraulic testing machine with measurement of elongation. After this, ultimate failure load and failure mode analysis was performed. RESULTS: Ruptures repaired by Fiberwire™ as suture material and the Baseball suture technique were able to withstand significantly higher maximum failure loads (72.8 ± 22.0 N, p < 0.001) than the Kessler suture and the Hannover suture, while ruptures repaired by Fiberwire and the Kessler suture technique showed the lowest elongation after cyclic loading (14.6 ± 3.8 mm, p = 0.15). CONCLUSION: These findings may be of relevance for the future clinical treatment of tendon ruptures. Further in vivo clinical application studies are desirable for the future.

[Tibial press-fit fixation of flexor tendons for reconstruction of the anterior cruciate ligament]. / Tibiale Press-fit-Fixierungen von Beugesehnen zur Rekonstruktion des vorderen Kreuzbandes.

BACKGROUND: Press-fit fixation of hamstring tendon autografts for anterior cruciate ligament reconstruction is an interesting technique because no hardware is necessary. This study compares the biomechanical properties of press-fit fixations to an interference screw fixation. METHODS: Twenty-eight human cadaveric knees were used for hamstring tendon explantation. An additional bone block was harvested from the tibia. We used 28 porcine femora for graft fixation. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclic loading were investigated. RESULTS: The maximum load to failure was 970±83 N for the press-fit tape fixation (T), 572±151 N for the bone bridge fixation (TS), 544±109 N for the interference screw fixation (I), 402±77 N for the press-fit suture fixation (S) and 290±74 N for the bone block fixation technique (F). The T fixation had a significantly better maximum load to failure compared to all other techniques (p<0.001). CONCLUSION: This study demonstrates that a tibial press-fit technique which uses an additional bone block has better maximum load to failure results compared to a simple interference screw fixation.

Axial and torsional stability of supracondylar femur osteotomies: biomechanical comparison of the stability of five different plate and osteotomy configurations.

PURPOSE: Little is known regarding the biomechanical stability and stiffness of implants and techniques used in supracondylar femur osteotomies (SCO). Therefore, fixation stability and stiffness of implants to bone was investigated under simulated physiological loading conditions using a composite femur model and a 3D motion-analysis system. METHODS: Five osteotomy configurations were investigated: (1) oblique medial closing-wedge fixated with an angle-stable implant; (2) oblique and (3) perpendicular medial closing-wedge, both fixated with an angled blade plate; and lateral opening-wedge fixated with (4) a spacer plate and (5) an angle-stable lateral implant. The motion measured at the osteotomy was used to calculate the stiffness and stability of the constructs. RESULTS: The least amount of motion and highest stiffness was measured in the medial oblique closing-wedge osteotomy fixated with the angled blade plate. The lateral opening-wedge techniques were less stable and had a lower stiffness compared with the medial; the oblique saw cuts were more stable and had a higher stiffness than the perpendicular. CONCLUSION: This experimental study presents baseline data on the differences in the primary stability of bone-implant constructs used in SCO. The data in this study can be used as reference for future testing of SCO techniques. Furthermore, it is recommended that based on the differences found, the early postoperative rehabilitation protocol is tailored to the stability and stiffness of the fixation method used.

Axial and torsional stability of an improved single-plane and a new bi-plane osteotomy technique for supracondylar femur osteotomies.

PURPOSE: An important disadvantage of the standard medial closing-wedge distal femur osteotomy for lateral compartment osteoarthritis of the knee is the immediate effects on the extensor mechanism function. Therefore, a novel bi-plane osteotomy technique was developed. The stability and stiffness of this newly developed technique and a modification of the proximal screw configuration were tested in a composite femur model and compared to the standard single-plane technique. Research question was if the new bi-plane technique and/or modified screw configuration would improve the stability and stiffness of the construct. METHODS: In 12 femurs, motion at the osteotomy under axial and torsion loading was measured using a 3D motion analysis system. All were subsequently tested to failure. The data recorded were used to calculate stability and stiffness of the constructs. RESULTS: The stability and stiffness were highest in the bi-plane technique under axial loads, but were lower under torsional loading, compared to the single-plane technique. The screw configuration modification improved axial stability and stiffness, but had no influence on torsional stability. CONCLUSION: In replicate femurs, the new bi-plane technique improved axial stability, but in contrast to what was theorized, decreased torsional stability, compared to the single-plane technique. The addition of a bi-cortical screw proximally improved stability under axial loading, but not torsion. Further clinical testing will have to prove if early full weight bearing using the new bi-plane technique is possible.

Biomechanical characterization of double-bundle femoral press-fit fixation techniques.

PURPOSE: Press-fit fixation of patellar tendon bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. To date, no biomechanical data exist describing an implant-free double-bundle press-fit procedure. The purpose of this study was to characterize the biomechanical properties of three double-bundle press-fit fixations. METHODS: In a controlled laboratory study, the patellar-, quadriceps- and hamstring tendons of 10 human cadavers (age: 49.2 ± 18.5 years) were used. An inside out press-fit fixation with a knot in the semitendinosus and gracilis tendons (SG) combined with an additional bone block, with two quadriceps tendon bone block grafts (QU) was compared with press-fit fixation of two bone patellar tendon bone block (PT) grafts in 30 porcine femora. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated. RESULTS: The maximum load to failure was 703 ± 136 N for SG fixation, 632 ± 130 N for QU and 656 ± 127 N for PT fixation. Stiffness of the constructs averaged 138 ± 26 N/mm for SG, 159 ± 74 N/mm for QU, and 154 ± 50 N/mm for PT fixation. Elongation during initial cyclical loading was 1.2 ± 1.4 mm for SG, 2.0 ± 1.4 mm for QU, and 1.0 ± 0.6 mm for PT (significantly larger for PT and QU between the first 5 cycles compared with cycles 15-20th, P < 0.01). CONCLUSION: All investigated double-bundle fixation techniques were equal in terms of maximum load to failure, stiffness, and elongation. Unlike with single-bundle press-fit fixation techniques that have been published, no difference was observed between pure tendon combined with an additional bone block and tendon bone grafts. All techniques exhibited larger elongation during initial cyclical loading. All three press-fit fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs is critical.

Increased glenohumeral translation and biceps load after SLAP lesions with potential influence on glenohumeral chondral lesions: a biomechanical study on human cadavers.

PURPOSE: The aim of the study was to evaluate the stabilizing function of the long head of biceps tendon (LHB) and its tension, both without and with the presence of SLAP lesion to analyze a potentially occurring humeral chondral print of LHB with consecutive glenohumeral chondral lesions in SLAP lesions. METHODS: Testings were performed on 21 fresh frozen human cadaver shoulders with intact shoulder girdle by a 5 axis industrial robot with a force/moment sensor and 20 N joint compression, 50 N force in anterior, posterior, anterosuperior, and anteroinferior direction, and 0°, 30°, 60° of abduction. LHB was connected over a force measuring sensor with 5 N and 25 N preload. A type IIC SLAP lesion was created arthroscopically. RESULTS: A significant increase in anterior and anteroinferior translation was evaluated, whereas the LHB tension increased significantly in at most anterior and anterosuperior direction. The highest increase in translation and LHB tension after SLAP lesion was measured in anterior translation in at most 60° of abduction. The glenohumeral translation was significantly higher in SLAP lesions without LHB tenotomy than after isolated LHB tenotomy. CONCLUSIONS: SLAP lesions lead to increased glenohumeral translation and concurrently LHB tension and load in at most anterior direction. The increased anterior glenohumeral instability and the increased LHB load pressing on the humeral head might cause glenohumeral chondral lesions with a typical chondral print-like lesion on the humeral head underneath the LHB.

[Biomechanical analysis of press-fit fixation of anterior cruciate ligament transplants]. / Biomechanische Analyse der Press-fit-Fixierung von Kreuzbandtransplantaten.

Press-fit fixation of anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. A total of 168 cadaveric human patellar, quadriceps and hamstring tendons (average age 49.2 +/- 18.5 years) were used and 15 different fixation methods were tested. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were compared. Some techniques showed comparable biomechanical qualities to interference screw fixation. All investigated double bundle fixation techniques were equal in terms of maximum load to failure, stiffness and elongation. All techniques exhibited greater elongation during initial cyclical loading. Some of the press-fit fixation techniques investigated exhibited comparable biomechanical properties and preconditioning of the constructs is critical. Press-fit fixation enhances tendon to bone contact at the entry of the bone tunnel to the joint.