Professional Pitchers Display Differences in UCL Morphology and Elbow Gapping During Moving Valgus Stress Testing After UCL Reconstruction

Background:

Ulnar collateral ligament (UCL) reconstruction (UCLR) of the elbow has received much attention given the rise in incidence among baseball pitchers. Stress ultrasonography has been demonstrated to be a critical evaluation tool of the UCL. No study has dynamically evaluated the ability of UCLR to restore normal kinematics.

Purpose/Hypothesis:

The purpose of this study was to compare ulnohumeral gapping during a moving valgus stress test as well as UCL thickness between professional pitchers with and without UCLR. We hypothesized that the ulnohumeral joint will display greater gapping and the UCL graft will be thicker in pitchers after UCLR compared with uninjured pitchers.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Ultrasonography was used to measure the medial ulnohumeral joint distance and the UCL thickness of 70 asymptomatic professional baseball pitchers; 6 of the participants had a history of UCLR. Images were captured of the dominant (D) and nondominant (ND) elbows at the maximal cocking position under 2 loaded conditions within the moving valgus stress test arc: (1) gravity stress and (2) 2.5 kg (5.5 lb) of valgus force using a dynamometer. Intra- and interrater reliability of the measurements was established with intraclass correlation coefficients (ICCs). Separate mixed-model analyses of variance (D side × UCL) were used to compare the D and ND elbow variables between pitchers with and without a history of UCLR.

Results:

All measurements displayed good reliability according to ICCs. Pitchers with a history of UCLR demonstrated less gapping (5.6 ± 2.9 vs 4.2 ± 1.2 mm; P = .002) and greater UCL graft thickness (0.17 ± 0.07 vs 0.11 ± 0.08 mm; P = .03) compared with the native ligament in pitchers without prior UCL injury.

Conclusion:

Our data demonstrated that the UCLR results in a thicker, stiffer construct with less medial elbow gapping than the anatomical UCL. Using ultrasound to evaluate the UCL was a reliable, efficient, and clinically feasible method to assess UCL thickness and joint gapping in players with a history of UCLR. Future studies may consider this approach to evaluate surgical techniques and graft types for UCLR.

Implant and limb alignment outcomes for conventional and navigated unicompartmental knee arthroplasty

Accurate implant positioning and restoration of lower limb alignment are major requirements for successful long-term results in unicompartmental knee arthroplasty (UKA). Alignment accuracy was compared between navigated-UKA (nUKA) and conventional-UKA (cUKA) groups using a retrospective matched case-control study (n=129, 58 nUKA, 71 cUKA). Mechanical axis (MA), hip-knee-ankle angle (HKA°), coronal implant alignment, and tibial implant posterior slope were measured. No statistically significant difference was observed when comparing MA, HKA° or coronal implant alignment (p>0.05). Statistical significance was seen with tibial component posterior slope (p=0.04, nUKA 4.2°, cUKA 2.9°); and between intra-operative navigationally determined HKA° and post-operative whole-leg standing (WLS) film HKA°. Navigation does not significantly improve UKA alignment compared to conventional methods. Further studies are needed to justify the use of this technology in UKA.

Purinergic signaling is required for fluid shear stress-induced NF-κB translocation in osteoblasts

Fluid shear stress regulates gene expression in osteoblasts, in part by activation of the transcription factor NF-κB. We examined whether this process was under the control of purinoceptor activation. MC3T3-E1 osteoblasts under static conditions expressed the NF-κB inhibitory protein IκBα and exhibited cytosolic localization of NF-κB. Under fluid shear stress, IκBα levels decreased, and concomitant nuclear localization of NF-κB was observed. Cells exposed to fluid shear stress in ATP-depleted medium exhibited no significant reduction in IκBα, and NF-κB remained within the cytosol. Similar results were found using oxidized ATP or Brilliant Blue G, P2X(7) receptor antagonists, indicating that the P2X(7) receptor is responsible for fluid shear-stress-induced IκBα degradation and nuclear accumulation of NF-κB. Pharmacologic blockage of the P2Y6 receptor also prevented shear-induced IκBα degradation. These phenomena involved neither ERK1/2 signaling nor autocrine activation by P2X(7)-generated lysophosphatidic acid. Our results suggest that fluid shear stress regulates NF-κB activity through the P2Y(6) and P2X(7) receptor.

Activation of extracellular-signal regulated kinase (ERK1/2) by fluid shear is Ca(2+)- and ATP-dependent in MC3T3-E1 osteoblasts

To determine the role of Ca2+ signaling in activation of the Mitogen-Activated Protein Kinase (MAPK) pathway, we subjected MC3T3-E1 pre-osteoblastic cells to inhibitors of Ca2+ signaling during application of fluid shear stress (FSS). FSS only activated ERK1/2, rapidly inducing phosphorylation within 5 min of the onset of shear. Phosphorylation of ERK1/2 (pERK1/2) was significantly reduced when Ca2+i was chelated with BAPTA or when Ca2+ was removed from the flow media. Inhibition of both the L-type voltage-sensitive Ca2+ channel and the mechanosensitive cation-selective channel blocked FSS-induced pERK1/2. Inhibition of phospholipase C with U73122 significantly reduced pERK1/2. This inhibition did not result from blockage of intracellular Ca2+ release, but a loss of PKC activation. Recent data suggests a role of ATP release and purinergic receptor activation in mechanotransduction. Apyrase-mediated hydrolysis of extracellular ATP completely blocked FSS-induced phosphorylation of ERK1/2, while the addition of exogenous ATP to static cells mimicked the effects of FSS on pERK1/2. Two P2 receptors, P2Y2 and P2X7, have been associated with the anabolic responses of bone to mechanical loading. Using both iRNA techniques and primary osteoblasts isolated from P2X7 knockout mice, we found that the P2X7, but not the P2Y2, purinergic receptor was involved in ERK1/2 activation under FSS. These data suggest that FSS-induced ERK1/2 phosphorylation requires Ca2+-dependent ATP release, however both increased Ca2+i and PKC activation are needed for complete activation. Further, this ATP-dependent ERK1/2 phosphorylation is mediated through P2X7, but not P2Y2, purinergic receptors.

Fluid shear-induced ATP secretion mediates prostaglandin release in MC3T3-E1 osteoblasts

ATP is rapidly released from osteoblasts in response to mechanical load. We examined the mechanisms involved in this release and established that shear-induced ATP release was mediated through vesicular fusion and was dependent on Ca2+ entry into the cell through L-type voltage-sensitive Ca2+ channels. Degradation of secreted ATP by apyrase prevented shear-induced PGE2 release.

INTRODUCTION

Fluid shear induces a rapid rise in intracellular calcium ([Ca2+]i) in osteoblasts that mediates many of the cellular responses associated with mechanotransduction in bone. A potential mechanism for this increase in [Ca2+]i is the activation of purinergic (P2) receptors resulting from shear-induced extracellular release of ATP. This study was designed to determine the effects of fluid shear on ATP release and the possible mechanisms associated with this release.

MATERIALS AND METHODS

MC3T3-E1 preosteoblasts were plated on type I collagen, allowed to proliferate to 90% confluency, and subjected to 12 dynes/cm2 laminar fluid flow using a parallel plate flow chamber. ATP release into the flow media was measured using a luciferin/luciferase assay. Inhibitors of channels, gap junctional intercellular communication (GJIC), and vesicular formation were added before shear and maintained in the flow medium for the duration of the experiment.

RESULTS AND CONCLUSIONS

Fluid shear produced a transient increase in ATP release compared with static MC3T3-E1 cells (59.8 +/- 15.7 versus 6.2 +/- 1.8 nM, respectively), peaking within 1 minute of onset. Inhibition of calcium entry through the L-type voltage-sensitive Ca2+ channel (L-VSCC) with nifedipine or verapamil significantly attenuated shear-induced ATP release. Channel inhibition had no effect on basal ATP release in static cells. Ca(2+)-dependent ATP release in response to shear seemed to result from vesicular release and not through gap hemichannels. Vesicle disruption with N-ethylmaleimide, brefeldin A, or monensin prevented increases in flow-induced ATP release, whereas inhibition of gap hemichannels with either 18alpha-glycyrrhetinic acid or 18beta-glycyrrhetinic acid did not. Degradation of extracellular ATP with apyrase prevented shear-induced increases in prostaglandin E2 (PGE2) release. These data suggest a time line of mechanotransduction wherein fluid shear activates L-VSCCs to promote Ca2+ entry that, in turn, stimulates vesicular ATP release. Furthermore, these data suggest that P2 receptor activation by secreted ATP mediates flow-induced prostaglandin release.

Fluid shear-induced NFkappaB translocation in osteoblasts is mediated by intracellular calcium release

Bone formation in response to exogenous mechanical loading is dependent on prostaglandin synthesis by the inducible isoform of cyclooxygenase, COX-2. While several transcription factors target the COX-2 gene, we examined the role of nuclear factor kappa B (NFkappaB) on COX-2 upregulation in osteoblasts in response to fluid shear due to its involvement in immune and inflammatory responses in other cell types. Application of 12 dyn/cm2 laminar flow to MC3T3-E1 osteoblast-like cells resulted in translocation of NFkappaB to the nucleus within 1 h of the onset of shear, with NFkappaB returning to the cytoplasm after 2 h of continuous flow. NFkappaB translocation in response to shear was inhibited by the protease inhibitor, Nalpha-p-tosyl-L-lysine chloromethylketone hydrochloride (TLCK), or a cell-permeant peptide that blocks the nuclear localization sequence (NLS) on NFkappaB. Block of NFkappaB translocation with these inhibitors blocked the shear-induced upregulation of COX-2. We found that disruption of the actin cytoskeleton with cytochalasin D or microtubules with nocodozol did not alter NFkappaB translocation in response to shear. However, addition of the intracellular Ca2+ chelator BAPTA completely blocked NFkappaB translocation. While block of Ca2+ entry with channel blockers failed to inhibit NFkappaB translocation, inhibition of phospholipase C (PLC)-induced intracellular Ca2+ release with the PLC inhibitor U73122 completely abrogated the NFkappaB response to shear. These data indicate that NFkappaB translocation to the nucleus is essential for the fluid shear-induced increase in COX-2. Further, these studies suggest that intracellular Ca2+ release, but not the cytoskeletal architecture, is important to NFkappaB translocation.