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.

[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.

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.

The effect of the arthroscopic augmentation of the subscapularis tendon on shoulder instability and range of motion: A biomechanical study.

BACKGROUND: Anterior shoulder dislocation is common. The treatment of recurrence with glenoid bone defect is still considered controversial. A new arthroscopic subscapularis augmentation has recently been described that functions to decrease the anterior translation of the humeral head. The purpose of the presented study was to examine the biomechanical effect on glenohumeral joint motion and stability. METHODS: Eight fresh frozen cadaver shoulders were studied by use of a force guided industrial robot fitted with a six-component force-moment sensor to which the humerus was attached. The testing protocol includes measurement of glenohumeral translation in the anterior, anterior-inferior and inferior directions at 0°, 30° and 60° of glenohumeral abduction, respectively, with a passive humerus load of 30N in the testing direction. The maximum possible external rotation was measured at each abduction angle applying a moment of 1Nm. Each specimen was measured in a physiologic state, as well as after Bankart lesion with an anterior bone defect of 15-20% of the glenoid, after arthroscopic subscapularis augmentation and after Bankart repair. FINDINGS: The arthroscopic subscapularis augmentation decreased the anterior and anterior-inferior translation. The Bankart repair did not restore the mechanical stability compared to the physiologic shoulder group. External rotation was decreased after arthroscopic subscapularis augmentation compared to the physiologic state, however, the limitation of external rotation was decreased at 60° abduction. INTERPRETATION: The arthroscopic subscapularis augmentation investigated herein was observed to restore shoulder stability in an experimental model.

Transfer of the long head of biceps to the conjoint tendon. A biomechanical study.

BACKGROUND: Tenodesis of the long head of biceps has been intensively investigated and various surgical options exist. The aim of this biomechanical study was to compare the maximum strength of two different techniques for biceps tenodesis. Our hypothesis was that the two procedures have the same biomechanical properties. METHODS: We performed the two different tenodesis techniques using 12 fresh frozen shoulders divided into two groups of six. In the first group, the biceps was transferred to the conjoint tendon. In the second group, an intraossous suprapectoral tenodesis was performed. After a preload of 10 N, cyclical loading with a maximum of 60 N and 100 N with 100 cycles and 0.5 Hz was applied to the tendons for both groups. An axial ultimate loading to failure was conducted subsequently. RESULTS: No significant differences were found in age, bone mineral density, or weight between the two groups. During the cyclical loading with 60 N, one slippage of the tendon was observed in the suprapectoral group. The mean ultimate load to failure was 294.15N in the transposition group and 186.76 N in the suprapectoral group, but this difference was not significant (P=0.18). INTERPRETATION: The biomechanical results demonstrated equal biomechanical properties postoperatively for both transposition of the tendon and the current standard suprapectoral tenodesis procedure. The transposition can be performed as a primary or a salvage procedure in order to potentially reduce the proportion of patients with persistent postoperative bicipital groove pain and is comparable in strength to a standard tenodesis.

Is there any advantage in placing an additional calcar screw in locked nailing of proximal humeral fractures?

BACKGROUND: The objective of this study was to evaluate the biomechanical effect of an additional unlocked calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck. HYPOTHESIS: The additional calcar screw improves stiffness and failure load. METHODS: Fourteen fresh frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc(®)-nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load-to-failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α=0.05). RESULTS: No significant differences were observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases. DISCUSSION: The use of an additional unlocked calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck.

Effects of osteoarthritis and pathological walking on contact stresses in femoral cartilage.

Osteoarthritis is a widespread abnormality in synovial joints leading to increasing pain and potential work disability in middle-aged and older populations. A primary cause of osteoarthritis is related to damages from high local stresses combined with insufficient self-healing of cartilage. In this framework, it is the goal of the present contribution to offer a thermodynamically consistent simulation of a highly anisotropic, heterogeneous, osmotic swelling and poroviscoelastic model of healthy and osteoarthritic articular cartilage based on the Theory of Porous Media. Physiological and pathological loading patterns are included by means of multi-body system calculations on patients. The contact stresses at the cartilage surface are represented by means of three-dimensional and simplified stereographic views of the femoral head. For normal walking, the stress peaks are higher in the degenerated case than in the healthy case. Interestingly, pathological walking combined with degenerated cartilage tissue minimises the occurrence of high local stresses.

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.

[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.

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.

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.

[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.

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.