Background

We have previously reported an injectable hydrogel (NPgel), which could deliver patients own stem cells, via small bore needles, decreasing damage to the annulus fibrosus. NPgel drives differentiation to NP cells and can inhibit the degenerate niche. However, clinical success of NPgel is dependent on the capacity to inject NPgel into naturally degenerate human discs, restore mechanical function to the IVD, prevent extrusion during loading and induce regeneration. This study assessed injectability of NPgel into human IVD, influence on mechanical properties, regeneration ability in an ex vivo culture system and retention under failure testing.

Purpose: Since the human intervertebral disc (IVD) is loaded in compression for approximately 16h per day, we investigated the effect of 16h compression loading on the magnetic resonance imaging (MRI) parameters, biochemical contents, and mechanical properties, of IVDs.

Method: Bovine caudal discs (2–3 years-old; non-degenerated) from 3-disc motion segments were injected in the NP with either 5 mg of trypsin in 40 μl Tris buffer or with Tris buffer only. The motion segments were placed in bags containing saline solution and antibiotics and were kept at 37°C throughout the experiment. The motion segments were subjected to either 16h of cyclic compression loading or were left unloaded for 16h. The motion segments were then paraffin embedded for MRI examinations, which were carried out in a 1.5T machine. The IVDs were dissected and the NP and AF were separated for biochemical and mechanical analyses. The NP and AF tissues were analyzed for contents of water, glycosaminoglycan (GAG), total collagen, and denatured collagen. Swelling pressure, compressive modulus HA, and hydraulic permeability were also measured.

Results: Loading had a significant effect on the MRI parameters (T1, T2, T1rho, MTR, ADC) of both the NP and AF tissues. Loading had a greater effect on the MR parameters and biochemical composition of the NP than trypsin. In contrast, trypsin had a larger effect on the mechanical properties. Localized trypsin injection predominantly affected the NP. T1rho was sensitive to loading and correlated with the water content of the NP and AF but not with their proteoglycan content.

Conclusion: Few studies have been directed towards developing an objective and accurate diagnostic tool in the detection and quantification of matrix and mechanical changes in early IVD degeneration. In this report, we demonstrated that MR parameters were influenced by compression loading. We also show showed specific correlations between T1rho and the structural and compositional changes in the disc. Further studies are required to determine the potential of the T1rho technique to be used as a non-invasive diagnostic tool of the biochemical and mechanical changes occurring in disc degeneration.

Many two-part fractures of the proximal humerus are treated conservatively due to the frequent failure of internal fixation. The current investigation examines the biomechanical properties of a unique plate versus a standard plate for internal fixation of proximal humerus fractures. The unique plate employs screws that thread into the plate, creating a multi-planer, fixed angle device. A cadaveric model was developed that relied on the rotator cuff musculature as the primary deforming force. The locking plate displayed significantly greater holding power on the humeral head (p=0.007). This may lead to more consistent results in two-part fractures treated with internal fixation.

The current investigation evaluates a unique plate designed to treat fractures of the proximal humerus. The plate employs screws that thread into the plate creating a fixed angle device. This plate was tested versus a standard cloverleaf plate.

The locking plate displayed greater holding power on the humeral head in the model tested. This may lead to decreased failure rates in two-part fractures treated with internal fixation.

Many two-part fractures of the proximal humerus are treated conservatively due to the frequent failure of common internal fixation modalities. This is done with the acceptance of possible non-union and loss of function. A more reliable method for stable internal fixation is therefore desirable.

A significant difference was found (p=0.007) with the locking plate displaying greater holding capability on the humeral head.

Eight pairs of preserved, cadaveric humeri were dissected and plated with either the locking plate or standard cloverleaf plate followed by an osteotomy at the surgical neck. A servo-hydraulic testing machine was then used to pull on the rotator cuff musculature until failure was achieved. Failure of the plate-head interface was reached in five of the eight pairs. Previous biomechanical studies have not taken into account the clinical mode of failure when testing internal fixation modalities for proximal humerus fractures. The current study has reproduced failure into varus by relying on the rotator cuff musculature as the primary deforming force.

Funding: All implants donated by Synthes, Canada

Purpose: Quantitative MRI is currently being tested as an early and non-invasive diagnostic tool of disc problems prior to the appearance of symptoms. The aim of the present study was to determine the effects of cyclic loading and enzymatic digestion on quantitative MRI, biochemical composition, and mechanical properties of intervertebral disc tissue.

Methods: Bovine tail segments consisting of three discs were subjected to 16h of cyclic compression loading (50N–300N–50N at 1Hz) or left unloaded for 16h while in saline solution at 37°C. Prior to loading, the nucleus pulposus were injected with either a trypsin or buffer solution. MR examinations were carried out in a 1.5T Siemens` Avanto system to measure T1 and T2 relaxation times, magnetization transfer ratio (MTR), and trace of the apparent diffusion coefficient (TrD). The nucleus pulposus and annulus fibrosus were dissected and analyzed for contents of water, glycosaminoglycan, total collagen, and denatured collagen. Cylindrical nucleus pulposus and annulus fibrosus tissue plugs were harvested, prepared, and tested under confined compression to measure compressive modulus (HA) and hydraulic permeability (k). ANOVA and linear regression analyses were performed (p< 0.05).

Results: Loading decreased the T1, T2, and TrD of NP while it increased MTR. Only water content in the nucleus pulposus was significantly influenced by loading. T1, water content, and k of the annulus fibrosus tissue were significantly reduced with loading.|Enzymatic treatment of the nucleus pulposus had no effect on its MR properties, but increased the percent of denatured collagen and thus decreased HA. None of the biochemical, mechanical, and MR parameters of the annulus fibrosus changed with trypsin treatment.

Conclusions: Dynamic loading of the disc segments for 16h decreased the permeability of both disc tissues. This was consistent with the measured drop in tissue hydration and was observed as a decrease in T1. Targeted trypsin digestion of the nucleus pulposus was confirmed with no detectable changes in the biochemical, biomechanical, or MR properties of the annulus fibrosus. Future studies will address additional quantitative MR parameters such as T1-rho, a higher strength magnet, and different enzymatic treatments. Funding: Other Education Grant Funding Parties: Canadian Institutes of Health Research, McGill William Dawson Scholar Award, and Whitaker Foundation

Radial-sided avulsions of the TFCC (Palmer 1d) remain a challenging pathology to treat. No current procedures have addressed these injuries successfully and reproducibly. Ten preserved dissected cadaveric forearm specimens with intact TFCC and without ulnar positive variance underwent biomechanical testing. Specimens were tested intact, then with Palmer 1d TFCC lesion and finally post-reconstruction. Measurement of total displacement with a −20N to 20N load was performed. The results indicate that our novel anatomic intra-articular reconstruction of unstable radial-sided TFCC avulsions was successful in restoring baseline stability to the DRUJ without interfering with pronation or supination.

Radial-sided avulsions of the TFCC (Palmer 1d) remain a challenging pathology to treat. No current procedures have addressed these injuries successfully and reproducibly. We tested a novel intra-articular reconstruction to address unstable radial-sided TFCC avulsions.

Ten preserved dissected cadaveric forearm specimens with intact TFCC and without ulnar positive variance underwent biomechanical testing using an MTS machine. Measurement of total displacement with a −20N to 20N load was performed. Specimens were tested intact, then with Palmer 1d TFCC lesion and finally post-reconstruction. All tests were performed at neutral, maximal pronation and maximal supination.

Mean total displacements of the specimens at neutral rotation were: 4.122mm ± 0.363 for the intact specimens compared to 11.839mm ± 0.782 after creation of the tear (p< 0.000002) and 3.883mm ± 0.655 for the reconstructed specimens (p=0.77). In maximal pronation mean total displacements were: 2.378mm ± 0.250 intact vs. 4.922 ± 0.657 torn (p< 0.0007) and 2.124mm ± 0.339 post-reconstruction (p=0.61). In maximal supination mean total displacements were: 1.438mm ± 0.222 intact vs. 5.704mm ± 1.258 torn (p< 0.006) and 1.004mm ± 0.091 post-reconstruction (p=0.07). All specimens obtained the same maximal pronation and supination pre and post-reconstruction.

Restoration of stability and joint function have never been achieved with previous reconstruction attempts of radial-sided TFCC avulsions. Current procedures are unable to restore DRUJ stability without a significant sacrifice of motion. Our anatomic intra-articular reconstruction of unstable radial-sided TFCC avulsions succeeded in restoring baseline stability to the DRUJ without interfering with pronation/supination.