Biomechanical evaluation of the modified lasso technique.

BACKGROUND: The Terrible Triad of the elbow is a constellation of elbow dislocation, radial head fracture and coronoid process fracture. A common type of coronoid fracture documented with this triad is type II Regan-Morrey coronoid fractures. The preferred fixation method for this fracture type is the lasso technique, medial-lateral tunnel orientation being the traditional approach. Considering elbow anatomy, we saw an opportunity to potentially improve fixation by altering the suture lasso tunnel orientation to a proximal-distal orientation. HYPOTHESIS: Two tunnels in the proximal-distal direction would result in greater biomechanical stability as compared to the traditional lasso technique. MATERIAL AND METHODS: A type 2 Regan-Morrey fracture was created in 12 fresh frozen cadaveric elbows at 50% of the coronoid height using an oscillating saw. The humero-ulnar joint was placed in 0 degrees flexion then loaded at a rate of 10mm/min to failure. RESULTS: The control technique (medio-lateral tunnels) showed failure load of 150±81N that was not significantly different (p=0.825) than the 134±116N measured for the modified technique (distal-proximal tunnels). The portion of the load-displacement curve used to calculate stiffness was linear (R^2=0.94±0.04) with determination coefficients that did not differ between the two groups (p=0.351). For stiffness, we measured 17±13N/mm and 14±12N/mm respectively for control and modified techniques that did not result in a significant difference (p=0.674). CONCLUSION: In this attempt to improve the shortcomings of the lasso technique, we found that changing from medio-lateral to proximal-distal drilling directions did not result in an appreciable biomechanical benefit. LEVEL OF EVIDENCE: Basic science study; Biomechanics.

Investigating the effect of autograft diameter for quadriceps and patellar tendons use in anterior cruciate ligament reconstruction: a biomechanical analysis using a simulated Lachman test.

Introduction: Current clinical practice suggests using patellar and quadriceps tendon autografts with a 10 mm diameter for ACL reconstruction. This can be problematic for patients with smaller body frames. Our study objective was to determine the minimum diameter required for these grafts. We hypothesize that given the strength and stiffness of these respective tissues, they can withstand a significant decrease in diameter before demonstrating mechanical strength unviable for recreating the knee's stability. Methods: We created a finite element model of the human knee with boundary conditions characteristic of the Lachman test, a passive accessory movement test of the knee performed to identify the integrity of the anterior cruciate ligament (ACL). The Mechanical properties of the model's grafts were directly obtained from cadaveric testing and the literature. Our model estimated the forces required to displace the tibia from the femur with varying graft diameters. Results: The 7 mm diameter patellar and quadriceps tendon grafts could withstand 55-60 N of force before induced tibial displacement. However, grafts of 5.34- and 3.76-mm diameters could only withstand upwards of 47 N and 40 N, respectively. Additionally, at a graft diameter of 3.76 mm, the patellar tendon experienced 234% greater stiffness than the quadriceps tendon, with similar excesses of stiffness demonstrated for the 5.34- and 7-mm diameter grafts. Conclusions: The patellar tendon provided a stronger graft for knee reconstruction at all diameter sizes. Additionally, it experienced higher maximum stress, meaning it dissociates force better across the graft than the quadriceps tendon. Significantly lower amounts of force were required to displace the tibia for the patellar and quadriceps tendon grafts at 3.76- and 5.34-mm graft diameters. Based on this point, we conclude that grafts below the 7 mm diameter have a higher chance of failure regardless of graft selection.

Relationships Among Bone Morphological Parameters and Mechanical Properties of Cadaveric Human Vertebral Cancellous Bone.

Mechanical properties and morphological features of the vertebral cancellous bone are related to resistance to fracture and capability of withstanding surgical treatments. In particular, vertebral strength is related to its elastic properties, whereas the ease of fluid motion, related to the success of incorporation orthopedic materials (eg, bone cement), is regulated by the hydraulic permeability (K). It has been shown that both elastic modulus and permeability of a material are affected by its morphology. The objective of this study was to establish relations between local values of K and the aggregate modulus (H), and parameters descriptive of the bone morphology. We hypothesized that multivariate statistical models, by including the contribution of several morphology parameters at once, would provide a strong correlation with K and H of the vertebral cancellous bone. Hence, µCT scans of human lumbar vertebra were used to determine a set of bone morphology descriptors. Subsequently, indentation tests on the bone samples were conducted to determine local values of K and H. Finally, a multivariate approach supported by principal component analysis was adopted to develop predictive statistical models of bone permeability and aggregate modulus as a function of bone morphology descriptors. It was found that linear combinations of bone volume fraction, trabecular thickness, trabecular spacing, structure model index, connectivity density, and degree of anisotropy provide a strong correlation (R 2 ~ 76%) with K and a weaker correlation (R 2 ~ 47%) with H. The results of this study can be exploited in computational mechanics frameworks for investigating the potential mechanical behavior of human vertebra and to develop strategies to treat or prevent pathological conditions such as osteoporosis, age-related bone loss, and vertebral compression fractures. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Is Arthroscopic Transosseous Rotator Cuff Repair Strength Dependent on the Tunnel Angle?

BACKGROUND: Previous studies have aimed to biomechanically improve the transosseous tunnel technique of rotator cuff repair. However, no previous work has addressed tunnel inclination at the time of surgery as an influence on the strength of the repair construct. HYPOTHESIS: We hypothesized that the tunnel angle and entry point would influence the biomechanical strength of the transosseous tunnel in rotator cuff repair. Additionally, we investigated how tunnel length and bone quality affect the strength of the repair construct. STUDY DESIGN: Controlled laboratory study. METHODS: Mechanical testing was performed on 10 cadaveric humeri. Variations in the bone tunnel angle were imposed in the supraspinatus footprint to create lateral tunnels with inclinations of 30°, 45°, and 90° relative to the longitudinal axis of the humeral shaft. A closed loop of suture was passed through the bone tunnel, and cyclic loading was applied until failure of the construct. Load to failure and distance between entry points were the dependent variables. Analysis of variance, post hoc paired t tests, and the Bonferroni correction were used to analyze the relationship between the tunnel angle and failure load. The Pearson correlation coefficient was then used to evaluate the correlation of the distance between entry points to the ultimate failure load, and t tests were used to compare failure loads between healthy and osteoporotic bone. RESULTS: Tunnels drilled perpendicularly to the longitudinal axis (90°) achieved the highest mean failure load (167.51 ± 48.35 N). However, there were no significant differences in the failure load among the 3 tested inclinations. Tunnels drilled perpendicularly to the longitudinal axis (90°) measured 13.86 ± 1.35 mm between entry points and were significantly longer (P = .03) than the tunnels drilled at 30° and 45°. We found no correlation of the distance between entry points and the ultimate failure load. Within the scope of this study, we could not identify a significant effect of bone quality on failure load. CONCLUSION: The tunnel angle does not influence the strength of the bone-suture interface in the transosseous rotator cuff repair construct. CLINICAL RELEVANCE: The transosseous technique has gained popularity in recent years, given its arthroscopic use. These findings suggest that surgeons should not focus on the tunnel angle as they seek to maximize repair strength.