Effect of reverse total shoulder arthroplasty humeral inclination on glenohumeral range of motion,deltoid force,and glenoid strain: a biomechanical study

BackgroundReverse total shoulder arthroplasty (RSA) primarily varies between 2 implant design options: a 135 humeral stem inclination that closely resembles anatomic orientation, versus the Grammont-style 155 humeral stem inclination that further medializes and distalizes the center of rotation (COR). The purpose of this study was to compare deltoid force, glenoid strain, and simulated glenohumeral range of motion (ROM) between RSA 135 and RSA 155 designs, with a series of standardized permutations of glenosphere offset and rotator cuff pathology.MethodsTwelve fresh-frozen cadaveric shoulder specimens were studied using a shoulder simulator. Native shoulder motion profiles for reproducible abduction range of motion were established using a customized testing device. Optical 3-dimensional tracking and pressure sensors were used to accurately record glenohumeral range of motion (ROM), deltoid force, and glenoid strain for RSA 135 and RSA 155 designs. For each cohort, all combinations of glenosphere offsets and rotator cuff tendon involvement were evaluated.ResultsThere was no significant difference in the overall abduction ROM between the 155 and the 135 humeral stem implants (P = .75). Resting abduction angle and maximum abduction angle were significantly greater with a 155 + STD (standard offset) construct than with a 135 + STD construct (P < .001 and P = .01, respectively). Both stem inclinations decreased combined deltoid force requirements as compared the native shoulder with a massive cuff tear. Effective glenoid strain did not vary significantly between 135 + STD and 155 + STD constructs (P = .66).ConclusionOverall, range of motion between the 135 and the 155 humeral stem inclinations was not significantly different. The cumulative deltoid force was lower in RSA shoulders when compared to native shoulders with massive rotator cuff tears, highlighting the utility of both implant designs. The Grammont-style 155 stem coupled with a 2.5 mm inferior offset glenosphere required less deltoid force to reach maximum abduction than did the more anatomic, lateralized 135 stem coupled with a 4 mm lateral offset glenosphere.Level of EvidenceBasic Science, Biomechanics Controlled Laboratory Study     

Mechanically superior matrices promote osteointegration and regeneration of anterior cruciate ligament tissue in rabbits

The gold standard treatment for anterior cruciate ligament (ACL) reconstruction is the use of tendon autografts and allografts. Limiting factors for this treatment include donor site morbidity, potential disease transmission, and variable graft quality. To address these limitations, we previously developed an off-the-shelf alternative, a poly(l-lactic) acid (PLLA) bioengineered ACL matrix, and demonstrated its feasibility to regenerate ACL tissue. This study aims to 1) accelerate the rate of regeneration using the bioengineered ACL matrix by supplementation with bone marrow aspirate concentrate (BMAC) and growth factors (BMP-2, FGF-2, and FGF-8) and 2) increase matrix strength retention. Histological evaluation showed robust tissue regeneration in all groups. The presence of cuboidal cells reminiscent of ACL fibroblasts and chondrocytes surrounded by an extracellular matrix rich in anionic macromolecules was up-regulated in the BMAC group. This was not observed in previous studies and is indicative of enhanced regeneration. Additionally, intraarticular treatment with FGF-2 and FGF-8 was found to suppress joint inflammation. To increase matrix strength retention, we incorporated nondegradable fibers, polyethylene terephthalate (PET), into the PLLA bioengineered ACL matrix to fabricate a “tiger graft.” The tiger graft demonstrated the greatest peak loads among the experimental groups and the highest to date in a rabbit model. Moreover, the tiger graft showed superior osteointegration, making it an ideal bioengineered ACL matrix. The results of this study illustrate the beneficial effect bioactive factors and PET incorporation have on ACL regeneration and signal a promising step toward the clinical translation of a functional bioengineered ACL matrix.

The goal of developing a bioengineered anterior cruciate ligament (ACL) matrix is to provide an off-the-shelf product that is functionally superior to autografts and allografts currently used for ACL reconstruction surgeries. There is clear need for advancement in this area as 30% of young active patients reinjure their ACL after surgery (1). Furthermore, athletes in the National Basketball Association and National Football League have a return-to-sport time after ACL reconstruction of 11.6 and 10.8 mo, respectively (2, 3). This lengthy period of rehabilitation has spurred interest in bioengineered ACL matrices that can accelerate and enhance ACL regeneration, so that all patients can return to their preinjury performance level faster.Our group previously fabricated a poly(l-lactic) acid (PLLA) bioengineered ACL matrix and evaluated its performance in rabbit ACL reconstruction models (4–7). The bioengineered ACL matrix resulted in excellent tissue regeneration, while experiencing a 41 to 66% rupture rate in vivo (4, 5). The cause of these ruptures was likely due to the interplay between the rate of tissue regeneration and matrix fatigue. Thus, this study aims to 1) accelerate ACL regeneration by supplementing the bioengineered ACL matrix with bone marrow aspirate concentrate (BMAC) and growth factors (bone morphogenetic protein 2 [BMP-2], fibroblast growth factor 2 [FGF-2], and FGF-8); and 2) increase the strength retention of the bioengineered ACL matrix by incorporating nondegradable polyethylene terephthalate (PET) yarns.BMAC is a promising translational stem cell therapy as it can be harvested and applied during surgery and is not regulated by the US Food and Drug Administration (FDA) (8, 9). The ability of BMAC to enhance the repair of damaged rotator cuff (10) and meniscus (11) tissues has been demonstrated in rabbit models. Thus, we hypothesized that the application of BMAC would serve as a source of progenitor cells and bioactive factors that would accelerate ACL regeneration. This report evaluates the feasibility of obtaining BMAC in a rabbit ACL reconstruction model and its regenerative potential.Growth factors have been widely investigated to accelerate bone and ligament regeneration through the proliferation and differentiation of progenitor cells (12). FGFs have been shown to stimulate the proliferation of cells and enhance tissue healing. In particular, FGF-2 has been shown to accelerate ligament healing (13), and a member of the FGF-8 subfamily has been shown to stimulate cartilage healing in a clinical study (14). Furthermore, the synergistic application of FGF-2 and FGF-8 induced dedifferentiation of mature cells in axolotls (15). Given the evidence supporting the proregenerative qualities of FGF-2 and FGF-8, we chose to apply FGF-2 and FGF-8 simultaneously in the intraarticular space. We hypothesized that the combinatorial application of FGF-2 and FGF-8 would accelerate ligamentization of the bioengineered ACL matrix by promoting the proliferation of progenitor cells and dedifferentiation of mature cells in the synovial environment.To accelerate bone regeneration, we utilized bone morphogenetic protein 2 (BMP-2), which is approved by the US FDA for a range of lumbar spinal fusion procedures and has been shown in ACL reconstruction models to enhance osteointegration of tendon grafts (16–18). In our previous study, we demonstrated that BMP-2 saline injections could enhance osteoid seam width and reduce bone tunnel cross-sectional area, a sign of bone regeneration (5). However, the effect was limited, likely due to the lack of a drug carrier. In this study, we hypothesized that the addition of a drug delivery carrier, fibrin glue (19–22), would potentiate the effect of BMP-2 and promote bone formation (23).The first iteration of the bioengineered ACL matrix, termed the “L-C ligament,” was completely biodegradable and composed of only PLLA yarns (4). The high rupture rate found in our previous study motivated us to modify the material composition of the bioengineered ACL matrix to reduce its mechanical fatigue rate. A compelling polymer to reduce fatigue rate is PET, a biocompatible nondegradable polymer with high tensile strength that has previously been utilized for orthopedic applications (24). To date, no study has investigated the use of a composite PLLA and PET bioengineered ACL matrix for ACL reconstruction. Following the patented design by Laurencin and colleagues (25), a composite bioengineered ACL matrix, termed the “tiger graft,” composed of 20 PLLA yarns and 4 PET yarns, was fabricated. The PLLA facilitates a greater volume of tissue regeneration as it gradually degrades, while the PET bolsters the mechanical strength of the matrix during the early phases of healing. We hypothesized that the tiger graft would have increased mechanical strength retention over the implantation period.The overall goal of this study was to accelerate ACL regeneration of a bioengineered ACL matrix by supplementation with BMAC and growth factors (BMP-2, FGF-2, and FGF-8) and by modulating the material composition of the matrix (Fig. 1). We evaluated the ligamentization and osteointegration of the bioengineered ACL matrices histologically. Microcomputed tomography (µCT) was performed to evaluate bone tunnel regeneration. The inflammatory and remodeling state of the synovial fluid was evaluated using an enzyme-linked immunosorbent assay (ELISA). Finally, biomechanical testing was conducted to determine the strength retention of the bioengineered ACL matrices.Open in a separate windowFig. 1.Fabrication of the bioengineered ACL matrix and implantation in a rabbit ACL reconstruction model. (A) Depiction of the braiding machine used to fabricate the bioengineered ACL matrices and the resulting biphasic structure of the matrix. Each matrix was composed of 24 yarns. (B) For the L-C ligament, 24 yarns of PLLA were braided together. For the tiger graft, 20 yarns of PLLA and 4 yarns of PET were braided together. Experimental groups were evaluated at 12 wk, and the L-C ligament (control) was further evaluated at 24 wk. (C) View of implanted bioengineered ACL matrix at the time of surgery (Left) and the application of fibrin glue (Right). BMAC or growth factors were mixed with fibrin glue for the experimental groups. (D) Representative image demonstrating the implantation of a fibrin gel in the tibial bone tunnel (Left, blue arrow) and subsequent fixation of a titanium suture button (Right).     

Acromion morphology and bone mineral density distribution suggest favorable fixation points for anatomic acromioclavicular reconstruction

Purpose

Recent techniques for acromioclavicular (AC) joint reconstruction focus on additional AC cerclage to coracoclavicular (CC)-reconstructions. Due to the specific slim bone morphology at the acromion, there are concerns regarding these additional bone tunnels, as they may predispose to fracture and break out. The purpose of this study was to investigate anatomic properties of the acromion which may help improve surgical techniques directed at injuries to the AC joint. It was hypothesized that via measurements of thickness and density points of increased strength and support could be identified on the acromion.

Methods

Eighty-five fresh frozen cadaveric shoulders were used for this study. A standardized 3D-net was developed and thicknesses of the acromion were taken from defined points using a certified caliper. To define the acromial arch, the angle and radius of curvature between the antero-lateral, the highest point of the acromial arch and the postero-lateral aspect of the acromion were measured. Additional bone mineral density (BMD) evaluation was performed on 43 specimens in an anterio-posterior and latero-medial direction using 5-mm slices with a maximum of 10 and 6 slices, respectively.

Results

Median specimen age was 63.0 (range 36) years (55 female, and 30 male). There was no statistical significance between male (62.0, range: 35 years) and female (64.5, range 32 years) regarding age (n.s.). Thickness of acromion points of interest were ranging from 3.5 to 24.3 mm. Median radius of curvature of acromial arch for female was 48.2 (range 92.7) mm and 66.2 (range 85.6) for male (p?=?0.019). The median angle for female specimens was 21.4° (range: 44.6°) and 23.3° (range 51.7°) for male (p?=?0.047). The latero-medial measurements showed significant difference between the region of interest (ROI): 1 and 4, 5, 6 (p?=?0.001, p?=?0.001, p?=?0.001), 2 and 4, 5, 6 (p?=?0.007, p?=?0.001, p?=?0.001), 3 and 5, 6 (p?=?0.001, p?=?0.001), 4 and 5, 6 (p?=?0.010, p?=?0.001). Antero-posterior measurements showed significant difference between the ROI: 1 and 8 (p?=?0.031).

Conclusion

The posterior–medial acromion close to the AC joint revealed the highest BMD with an increasing density from lateral to medial. In combination with thickness measurements this region would support additional anatomical fixation of the AC joint using bone tunnels if necessary.

Clinical relevance

To anatomically reproduce the insertions of the AC ligaments at the acromion, either bone tunnels or anchors are needed. Therefore, several techniques have been developed. This study provides the anatomical data for these techniques and confirms the reconstructive approach of techniques using anatomical points of fixation and orientation.

     

How to avoid unintended valgus alignment in distal femoral derotational osteotomy for treatment of femoral torsional malalignment - a concept study

Background

Defining the optimal cutting plane for derotational osteotomy at the distal femur for correction of torsion in cases of patellofemoral instability is still challenging. This preliminary study investigates changes of frontal alignment by a simplified trigonometrical model and demonstrates a surgical guidance technique with the use of femur cadavers. The hypothesis was that regardless of midshaft bowing, a cutting plane perpendicular to the virtual anatomic shaft axis avoids unintended valgus malalignment due to derotation.

Methods

A novel mathematical model, called the Pillar-Crane-Model, was developed to forecast changes on frontal alignment of the femur when a perpendicular cutting plane to the virtual anatomical shaft was chosen. As proof of concept, eight different torsion angles were assessed on two human cadaver femora (left and right). A single cut distal femoral osteotomy perpendicular to the virtual anatomical shaft was performed. Frontal plane alignment (mLDFA, aLDFA, AMA) was radiographically analyzed before and after rotation by 0°, 10°, 20°, and 30°. Measurements were compared to the model.

Results

The trigonometrical equation from the Pillar-Crane-Model provides mathematical proof that slight changes into varus occur, seen by an increase in AMA and mLDFA, when the cutting plane is perpendicular to the virtual anatomical shaft axis. A table with standardized values is provided. Exemplarily, the specimens showed a mean increase of AMA from 4.8° to 6.3° and mLDFA from 85.2° to 86.7 after derotation by 30°. Throughout the derotation procedure, aLDFA remained at 80.4°?±?0.4°SD.

Conclusions

With the use of this model for surgical guidance and anatomic reference, unintended valgus changes on frontal malalignment can be avoided. When the cutting plane is considered to be perpendicular to the virtual anatomical shaft from a frontal and lateral view, a slight increase of mLDFA results when a derotational osteotomy of the distal femur is performed.

     

A biomechanical analysis of treatment options for enchondromas of the hand

Purpose

Enchondromas are the most common benign bone tumor affecting the hand. Standard treatment has consisted of curettage with bone grafting. It has become increasingly common for surgeons to use biologic cement in these cases. The purpose of this study was to evaluate different treatment options used to fill voids after curettage of hand enchondromas to determine if any provide more rigid fixation.

Methods

A cadaveric model of hand enchondromas was designed by making a standardized size corticotomy (0.6 × 1.0 cm) in 60 cadaver metacarpals. Resultant voids were then filled with either no material, bovine demineralized bone matrix (Synthes Paoli, PA, USA), or one of two different calcium phosphate bone cements: a carbonated apatite (Synthes Norian SRS Skeletal Repair System) and a hydroxyapatite (Stryker HydroSet) calcium phosphate. An apex dorsal three-point bend was applied to the metacarpals through an MTS machine, and load to failure and stiffness were recorded.

Results

Biomechanically, load to failure for intact metacarpals was significantly superior to those in which a corticotomy was created (p = 0.04). There was a significant increase in load to failure between the metacarpals treated with the calcium phosphate bone cement and the negative controls (p = 0).

Conclusions

In a biomechanical analysis of a cadaveric model of hand enchondromas, calcium phosphate bone cement provided significantly increased strength as compared to curettage alone and approximated the strength of intact metacarpals. It is unknown whether the use of biologic cements in this clinical setting leads to less postoperative immobilization, earlier digital motion, a quicker return to work, or increased patient satisfaction.