Finite element analysis and physiologic testing of a novel, inset glenoid fixation technique.

HYPOTHESIS: The success of shoulder arthroplasty surgery has been limited by a common complication: glenoid implant loosening. Eccentric loading of the glenoid due to migration of the humeral head is considered to be the major cause of glenoid loosening and is referred to as the rocking-horse phenomenon. Glenoid implant loosening may cause pain, limitation of function, and the need for complicated revision surgery. Our hypothesis was that an inset fixation technique could offer increased fixation strength and minimize the effects of the rocking-horse phenomenon on glenoid loosening. MATERIALS AND METHODS: Fixation strength and stress distribution were analyzed using two methods. First, mechanical simulation of physiologic in vivo cyclic loading was performed on 1 inset glenoid implant design and 2 standard onlay glenoid implant designs currently on the market. Second, 3-dimensional finite element analysis was performed to compare an inset glenoid implant and a standard onlay glenoid implant with a keel and a standard onlay pegged implant. RESULTS: After cyclic loading to 100,000 cycles, no glenoid implants demonstrated signs of loosening. Mechanical testing after cyclic loading demonstrated less distraction of the glenoid rim using an inset technique compared with an onlay technique. Finite element analysis results indicated that the inset technique achieved up to an 87% reduction in displacement. CONCLUSIONS: Mechanical tests and finite element analysis support the concept of inset glenoid fixation in minimizing the risk of glenoid loosening.

Altered gut microbiota composition with antibiotic treatment impairs functional recovery after traumatic peripheral nerve crush injury in mice: effects of probiotics with butyrate producing bacteria.

OBJECTIVE: Antibiotics (ABX) are widely used for life-threatening infections and also for routine surgical operations. Compelling evidence suggests that ABX-induced alterations of gut microbiota composition, termed dysbiosis, are linked with diverse disease states including neurological and neurodegenerative conditions. To combat the consequences of dysbiosis, probiotics (PBX) are widely used. ABX-induced dysbiosis is reported to impair neurological function after spinal cord injury. Traumatic peripheral nerve injury (TPNI) results in profound neurologic impairment and permanent disability. It is unknown whether ABX treatment-induced dysbiosis has any impact on TPNI-induced functional recovery, and if so, what role medical-grade PBX could have on TPNI recovery. RESULTS: In this study, ABX-induced dysbiosis and PBX-induced microbiota enrichment models were used to explore the potential role of gut microbiome in TPNI. Stool analysis with 16S ribosomal RNA (rRNA) gene sequencing confirmed ABX-induced dysbiosis and revealed that ABX-induced changes could be partially restored by PBX administration with an abundance of butyrate producing bacteria. Pre-injury ABX significantly impaired, but pre-injury PBX significantly improved post-TPNI functional recovery. Importantly, post-injury PBX protected against pre-injury ABX-induced functional impairment. These findings demonstrate that reestablishment of gut microbiota composition with butyrate producing PBX during ABX-induced dysbiosis could be a useful adjuvant therapy for TPNI.

Purposeful Misalignment of Severed Nerve Stumps in a Standardized Transection Model Reveals Persistent Functional Deficit With Aberrant Neurofilament Distribution.

BACKGROUND: Functional recovery following primary nerve repair of a transected nerve is often poor even with advanced microsurgical techniques. Recently, we developed a novel sciatic nerve transection method where end-to-end apposition of the nerve endings with minimal gap was performed with fibrin glue. We demonstrated that transected nerve repair with gluing results in optimal functional recovery with improved axonal neurofilament distribution profile compared to the end-to-end micro-suture repair. However, the impact of axonal misdirection and misalignment of nerve fascicles remains largely unknown in nerve-injury recovery. We addressed this issue using a novel nerve repair model with gluing. METHODS: In our complete "Flip and Transection with Glue" model, the nerve was "first" transected to 40% of its width from each side and distal stump was transversely flipped, then 20 µL of fibrin glue was applied around the transection site and the central 20% nerve was completely transected before fibrin glue clotting. Mice were followed for 28 days with weekly assessment of sciatic function. Immunohistochemistry analysis of both sciatic nerves was performed for neurofilament distribution and angiogenesis. Tibialis anterior muscles were analyzed for atrophy and histomorphometry. RESULTS: Functional recovery following misaligned repair remained persistently low throughout the postsurgical period. Immunohistochemistry of nerve sections revealed significantly increased aberrant axonal neurofilaments in injured and distal nerve segments compared to proximal segments. Increased aberrant neurofilament profiles in the injured and distal nerve segments were associated with significantly increased nerve blood-vessel density and branching index than in the proximal segment. Injured limbs had significant muscle atrophy, and muscle fiber distribution showed significantly increased numbers of smaller muscle fibers and decreased numbers of larger muscle fibers. CONCLUSIONS: These findings in a novel nerve transection mouse model with misaligned repair suggest that aberrant neurofilament distributions and axonal misdirections play an important role in functional recovery and muscle atrophy.

A novel nerve transection and repair method in mice: histomorphometric analysis of nerves, blood vessels, and muscles with functional recovery.

Peripheral nerve transection is associated with permanent functional deficit even after advanced microsurgical repair. While it is difficult to investigate the reasons of poor functional outcomes of microsurgical repairs in humans, we developed a novel pre-clinical nerve transection method that allows reliable evaluation of nerve regeneration, neural angiogenesis, muscle atrophy, and functional recovery. Adult male C57BL/6 mice were randomly assigned to four different types of sciatic nerve transection: Simple Transection (ST), Simple Transection & Glue (TG), Stepwise Transection and Sutures (SU), and Stepwise Transection and Glue (STG). Mice were followed for 28 days for sciatic function index (SFI), and sciatic nerves and hind limb muscles were harvested for histomorphological and cellular analyses. Immunohistochemistry revealed more directional nerve fiber growth in SU and STG groups compared with ST and TG groups. Compared to ST and TG groups, optimal neural vessel density and branching index in SU and STG groups were associated with significantly decreased muscle atrophy, increased myofiber diameter, and improved SFI. In conclusion, our novel STG method represents an easily reproducible and reliable model with close resemblance to the pathophysiological characteristics of SU model, and this can be easily reproduced by any lab.