Biomechanical analysis of proximal tibia bone grafting and the effect of the size of osteotomy using a validated finite element model.

Harvesting bone graft from the proximal tibia is gaining popularity, with lower complication rates and adequate quantity of cancellous bone. The amount of harvested bone is dependent on the size of the cortical window introduced via osteotomy onto the proximal tibia, and its mechanical strength after surgery could be compromised. The aim of the study was to investigate the proximal tibia's mechanical stability after bone harvesting and the effect of varying window sizes using a validated finite element model. Two cadaveric tibiae were tested with bone strains measured for different circular cortical window diameters (10-25 mm). Sixteen finite element models of the intact and harvested tibia were simulated and validated with experimental data. The experimental and predicted max/min principal bone strains were fitted into regression models and showed good correlations. It was predicted the maximum principal bone stresses were greatest and concentrated at postero-inferior and antero-superior regions of the cortical window. A stress line progressed from the edge of the window to the posterior side of the tibia, which became more prominent with the increase of size of the cortical window. It was found that large circular osteotomies for bone harvesting at the proximal tibia induced stress concentrations and stress lines which could lead to eventual failure. Graphical abstract The formation of a stress line in the harvested tibia initiated from the postero-inferior edge of the window and progressed to the medial side. The stress line became more prominent with the increase of the size of the cortical window from 10 to 25 mm in diameter.

Superior capsular reconstruction for irreparable supraspinatus tendon tears using the long head of biceps: A biomechanical study on cadavers.

INTRODUCTION: The superior articular capsule complements the rotator cuff's function in shoulder stability. With irreparable rotator cuff tears, superior capsular reconstruction (SCR) improves dynamic glenohumeral (GH) joint kinematics. We present a novel method of SCR in cadaveric shoulders using the long head of bicep (LHB) tendon instead of previously explored fascia lata autograft, thereby reducing harvest site and suture anchor associated complications. HYPOTHESIS: This novel method of SCR using the LHB is feasible biomechanically in restoring shoulder stability in irreparable supraspinatus tendon tear. MATERIALS AND METHODS: Seven cadaveric shoulders were tested in a custom shoulder testing system. Superior translation of the humerus, subacromial contact pressure and area, and glenohumeral range of motion were tested at 0°, 30°, and 60° of glenohumeral abduction in the following conditions: (1) intact shoulder, (2) simulated complete supraspinatus tendon tear, (3) modified SCR using LHB, (4) and modified SCR using LHB and side-to-side repair augmentation. RESULTS: The complete cuff tear shifted the humeral head superiorly as compared to the intact shoulder. Subacromial peak contact pressure was also increased at 30° and 60° while contact area was increased at 0° and 30°. The modified SCR both with and without side-to-side repair shifted the humeral head inferiorly at 30° and 60°, with contact area further reduced at 60°. Both techniques had comparable results for contact pressure and total rotational range of motion. CONCLUSION: The LHB with appropriate distal insertion on the greater tuberosity restores shoulder stability in irreparable rotator cuff tears by re-centering the humeral head on the glenoid. LEVEL OF EVIDENCE: Basic science study, biomechanical testing.

Biomechanics of Internal Fixation Modalities for Middle Phalangeal Base Fracture Dislocation.

BACKGROUND: Internal fixation modalities of unstable (>50 percent articular involvement) middle phalangeal volar lip fracture-dislocations include interfragmentary screw and volar buttress plating. This study investigates the mechanical properties (yield strength, ultimate tensile strength, and stiffness) of interfragmentary screw (IS), simple buttress plating (BP) and buttress plating with subchondral screw (BP+S). METHODS: Fifteen cadaveric digits (5 index, 5 middle, and 5 ring) were prepared by excising its skin envelope and flexor tendons while preserving the structures around the proximal interphalangeal joint. An oblique osteotomy involving 50 percent of the articular surface was performed, and this was fixed with based on its study group: interfragmentary screw (IS), simple buttress plating (BP) and buttress plating with subchondral screw (BP+S). These specimens were then loaded to failure. RESULTS: Yield strength was as follows: BP+S (33.5±9.76 N), IS (13.6±5.46 N), and BP (8.1±3.84 N). Ultimate tensile strength was as follows: BP+S (49.1±21.4 N), IS (15.6±5.19 N), and BP (8.86±3.99 N). Stiffness was as follows: BP+S (4.77±1.32 N/mm), IS (2.44±0.86 N/mm), and BP (1.84±0.71 N/mm). CONCLUSIONS: A buttress plate and screw construct confers significantly more stability than either interfragmentary screw or buttress plate only fixation in an experimental model.

A double button adjustable loop device is biomechanically equivalent to tension band wire in the fixation of transverse patellar fractures-A cadaveric study.

INTRODUCTION: Tension-band wire fixation of patellar fractures is associated with significant hardware-related complications and infection. Braided polyester suture fixation is an alternative option. However, these suture fixations have higher failure rates due to the difficulty in achieving rigid suture knot fixation. The Arthrex syndesmotic TightRope, which is a double-button adjustable loop fixation device utilizing a 4-point locking system using FibreWire, may not only offer stiff rigid fixation using a knotless system, but may also obviate the need for implant removal due to hardware related problems. The aim of our study is to compare the fixation rigidity of patella fractures using Tightrope versus conventional tension-band wiring (TBW) in a cadaveric model. MATERIALS AND METHODS: TBW fixation was compared to TightRope fixation of transverse patella fractures in 5 matched pairs of cadaveric knees. The knees were cyclically brought through 0-90° of motion for a total of 500 cycles. Fracture gapping was measured before the start of the cycling, and at 50, 100, 200 and 500 cycles using an extensometer. The mean maximum fracture gapping was derived. Failure of the construct was defined as a displacement of more than 3mm, patella fracture or implant breakage. RESULTS: All but one knee from each group survived 500 cycles. The two failures were due to a fracture gap of more than 3mm during cycling. There was no significant difference in the mean number of cycles tolerated. There was no implant breakage. There was no statistical significant difference in mean maximum fracture gap between the TBW and TightRope group at all cyclical milestones after 500 cycles (0.3026±0.4091mm vs 0.3558±0.7173mm, p=0.388). CONCLUSIONS: We found no difference between the TBW and Tightrope fixation in terms of fracture gapping and failure. With possible lower risk of complications such as implant migration and soft tissue irritation, we believe tightrope fixation is a feasible alternative in fracture management of transverse patella fractures.

A biomechanical study of proximal tibia bone grafting through the lateral approach.

BACKGROUND: Autologous bone graft remains the gold standard source of bone graft. Iliac crest has traditionally been the most popular source for autologous bone graft. However, iliac crest bone graft harvesting is associated with high donor site morbidity. Bone graft harvesting from the proximal tibia has shown great potential with reported low complication rates. However, there is a paucity of biomechanical studies concerning the safety as well as yield of proximal bone graft harvesting. PURPOSE: This biomechanical study was designed to investigate (1) the stability of the harvested proximal tibial during physiological loading, and (2) the maximum size of the cortical window that can be safely created and (3) volume of accessible bone graft. METHODS: Bone grafts were harvested from eleven cadaveric tibiae using a circular cortical window along the lateral proximal tibia. These harvested proximal tibiae were then loaded under physiological conditions (mean 2320N, range 1650-3120N) using a customized test fixture. Strain rosettes were mounted at 7 locations in the harvested proximal tibia to record the changes in strain at the harvested proximal tibia. The change in strain with increasing cortical window size (10-25mm diameter) was also studied. Bone principal strains as well as volume of bone harvested were recorded. RESULTS: A repeated measures ANOVA was used to analyze the change in bone strains with the cortical window size. Statistically significant (p<0.05) increases in bone strains at the anterior and medial aspects of the tibia were observed with increasing size of osteotomies (-328.85µÎµ, SD=232.21 to -964.78µÎµ, SD=535.89 and 361.64µÎµ, SD=229.90 to -486.08µÎµ, SD=270.40 respectively), and marginally significant changes in strain at the lateral and posterior aspects. None of the tibiae failed under normal walking loads even with increasing osteotomies size of 10-25 mm diameter. A smaller osteotomy of 10mm diameter yielded an average volume of 7.15ml of compressed bone graft, while a larger osteotomy of 25mm diameter yielded on average an additional 3.64ml of bone graft. Bone grafting of the proximal tibia through the lateral approach with a circular osteotomy is a feasible option even with osteotomies of 25mm diameter. Even though increased bone strains were observed, the strains did not exceed the yield strain of cortical bone when loaded under normal walking conditions. The quantity of bone harvested from the proximal tibia is comparable to that harvested from the iliac crest. CONCLUSIONS: This biomechanical study demonstrated the stability of the harvested proximal tibia under conditions of full weight bearing ambulation. It has also refined the technique of proximal bone graft harvesting by determining the maximum size of the cortical window. The findings of this study add to the overall understanding of proximal tibial bone graft harvesting, providing objective data regarding stability as well as yield. This information would be useful during selection of source of autologous bone graft.

Fusion performance of low-dose recombinant human bone morphogenetic protein 2 and bone marrow-derived multipotent stromal cells in biodegradable scaffolds: a comparative study in a large animal model of anterior lumbar interbody fusion.

STUDY DESIGN: A large animal study comparing interbody fusion of a bioresorbable scaffold loaded with either low-dose recombinant human bone morphogenetic protein 2 (rhBMP-2) or bone marrow-derived multipotent stromal cells (BMSCs). OBJECTIVE: To compare the quality of fusion resulting from implantation of medical grade poly (ε-caprolactone)-20% tricalcium phosphate (mPCL/TCP) scaffolds and two different bone growth stimulating agents. SUMMARY OF BACKGROUND DATA: Nondegradable cages have been used for interbody fusion with good results. However, the overall advantage of lifelong implantation of a nondegradable device remains a subject of ongoing debate. The use of bioresorbable scaffolds might offer superior alternatives. In this study, we evaluated the quality of fusion obtained with two potential bone graft substitutes. METHODS: Eleven Yorkshire pigs underwent a bisegmental (L2/L3; L4/L5) anterior lumbar interbody fusion (ALIF) in four groups, namely: (1) mPCL/TCP + 0.6 mg rhBMP-2; (2) mPCL/TCP + BMSCs; (3) mPCL/TCP (negative control); and (4) autologous bone grafts (positive control). RESULTS. The mean radiographic scores at 9 months were 3.0, 1.7, 1.0, and 1.8 for groups 1 to 4, respectively. The bone volume fraction of group 1 was two-folds higher than group 2. Histology, micro-computed tomographic scanning and biomechanical evaluation demonstrated solid and comparable fusion between groups 1 and 4. However, group 2 showed inferior quality of fusion when compared with groups 1 and 4 while group 3 showed no fusion even at 9 months. In addition, there was no evidence of implant rejection, chronic inflammation or any other complications. CONCLUSION: mPCL/TCP scaffolds loaded with low-dose rhBMP-2 is comparable to autograft bone as a bone graft substitute in this large animal ALIF model. Although BMSCs lagged behind autograft bone and rhBMP-2, evidence of bone ingrowth in this group warrants further investigation. Our results suggest that mPCL/TCP scaffolds loaded with rhBMP-2 or BMSCs may be a viable alternative to conventional cages and autograft bone.