Spatial Anatomy of the Radial Nerve in the Extended Deltopectoral Approach.

The goal of this study was to define safe zones to prevent radial nerve injury in an extended deltopectoral approach. Relative distances of the upper margin (UMRN) and lower margin (LMRN) of the radial nerve to the proximal and distal borders of the pectoralis major and deltoid insertions were measured in 20 cadaveric arms. Four proximal humeral zones were identified (zone I, proximal border of the pectoralis major tendon to the proximal border of the deltoid tendon; zone II, proximal border of the deltoid tendon to the distal border of the pectoralis major tendon; zone III, distal border of the pectoralis major tendon to the distal border of the deltoid tendon; and zone IV, distal to the distal border of the deltoid tendon). On fluoroscopic measurement, mean distances between the UMRN and the proximal border of the pectoralis major tendon and the proximal border of the deltoid tendon were 71.6±2.1 mm and 26.2±2.5 mm, respectively. The incidence of the radial nerve in the spiral groove within each defined zone was as follows: zone I, 0%; zone II, 50%; zones III and IV, 100%. There was a significant association between anatomic zone and radial nerve entry into the spiral groove, χ2(3, N=88)=64.53, P<.001. The proximal border of the pectoralis major tendon to the proximal border of the deltoid tendon (zone I) is a safe location to avoid injury to the radial nerve. We recommend placing cerclage wires proximal to zone I from lateral to medial to avoid entrapment of the radial nerve. [Orthopedics. 2023;46(1):e31-e37.].

Surgical anatomy of the axillary artery: clinical implications for open shoulder surgery.

BACKGROUND: Axillary artery injury is a devastating complication related to anterior shoulder surgery and can result in significant morbidity and/or mortality. The purpose of our study was to evaluate the course of the axillary artery in relation to bony landmarks of the shoulder and identify variations in artery position with humeral external rotation. MATERIALS AND METHODS: Dissection of 18 shoulders (9 fresh whole-body cadavers) with simulated vessel perfusion using radiopaque dye was performed. The axillary artery position was measured from multiple points including 2 points on the coracoid base (C1 and C2), 3 points on the coracoid tip (C3-C5), 4 points on the glenoid: superior, middle, and inferior glenoid (D1-D4), and 2 points on the lesser tuberosity (L1 and L2). Fluoroscopic measurements were taken and compared at 0° and 90° of external rotation (F1 vs. F1' and F2 vs. F2'). Manual and fluoroscopic measurements were compared with one another using Kendall's τb correlation. RESULTS: There were 6 male and 3 female cadavers with an average age of 67.2 ± 9.3 years (range: 49-77 years). The mean distance from the axillary artery to the coracoid base (C1 and C2) measured 21.1 ± 7.3 and 22.3 ± 7.4 mm, respectively, whereas the mean distance to the coracoid tip (C3, C4, and C5) measured 30.7 ± 9.3, 52.1 ± 20.2, and 46.5 ± 14.3 mm, respectively. Measurements relative to the glenoid face (D1, D2, and D3) showed a progressive decrease in mean distance from superior to inferior, measuring 31.6 ± 10.3, 16.5 ± 7.5, and 10.3 ± 7.3 mm, respectively, whereas D4 (inferior glenoid to axillary artery) measured 17.8 ± 10.7 mm. The minimum distance from the axillary artery to any point on the glenoid was as close as 4.1 mm (D3). There was a statistically significant difference in F1 (0° external rotation) vs. F1' (90° external rotation) (18.5 vs. 13.4 mm, P = .03). Kendall's τb correlation showed a strong, positive correlation between manual and fluoroscopic measurements (D4: 16.0 ± 12.5 mm vs. F1: 18.5 ± 10.7 mm) (τb = 0.556, P = .037). CONCLUSION: The axillary artery travels an average of 1-1.8 cm from the inferior glenoid margin, which puts the artery at significant risk. In addition, the artery is significantly closer to the inferior glenoid with humeral external rotation. Surgeons performing anterior shoulder surgery should have a thorough understanding of the axillary artery course and understand changes in the position of the artery with external rotation of the humerus.

Posterior Inferior Comminution Significantly Influences Torque to Failure in Vertically Oriented Femoral Neck Fractures: A Biomechanical Study.

OBJECTIVES: To evaluate axial fracture obliquity and posterior inferior comminution in vertically oriented femoral neck fractures (FNFs) in the physiologically young patient. A biomechanical investigation was designed to evaluate the impact of these fracture elements on torque to failure using cannulated screw (CS) and sliding hip screw fixation. METHODS: Four Pauwels III FNF models were established in synthetic femurs: (1) vertically oriented in the coronal plane (COR), (2) coronal plane with axial obliquity (AX), (3) coronal plane with posterior inferior comminution (CCOM), and (4) coronal plane with axial obliquity and posterior inferior comminution (ACOM). In each group (n = 10), specimens were fixed using either 3 CSs or a sliding hip screw with supplemental antirotation screw (SHS). Quasistatic cyclic ramp-loading to failure was performed using a custom testing jig combining axial preloading and torsional ramp-loading. The primary outcome was torque to failure, defined as angular displacement ≥5 degrees. RESULTS: In the CS group, torque to failure was 40.2 ± 2.6 Nm, 35.0 ± 1.4 Nm, 29.8 ± 1.5 Nm, and 31.8 ± 2.2 Nm for the COR, AX, CCOM, and ACOM fracture groups, respectively (P < 0.05). In the SHS group, torque to failure was 28.6 ± 1.3 Nm, 24.2 ± 1.4 Nm, 21.4 ± 1.2 Nm, and 21.0 ± 0.9 Nm for the COR, AX, CCOM, and ACOM fracture groups, respectively (P < 0.05). In both constructs, groups with posterior inferior comminution demonstrated significantly lower torque to failure compared to the COR group (P < 0.05). The CS construct demonstrated higher torque to failure in all groups when compared to the SHS construct (P < 0.01). CONCLUSIONS: Posterior inferior comminution significantly affects torque to failure in vertically oriented FNFs. Three peripherally placed CSs may resist combined axial and torsional loading better than a sliding hip screw construct.

The significant effect of the medial hamstrings on dynamic knee stability.

PURPOSE: While hamstring autograft is a popular option for the general population, BTB autograft is still significantly more popular among professional athletes due to concerns of altering knee kinematics with hamstring harvest. This study seeks to quantify the contribution of the medial hamstrings to knee stability. METHODS: Valgus knee laxity, anterior tibial translation, and rotational motion were measured in eight fresh-frozen cadaveric knees after forces were applied on the tibia in each plane (coronal, sagittal, and axial). Four muscle loading conditions were tested: (1) physiologic fully loaded pes anserinus, (2) semitendinosus only loaded, (3) gracilis only loaded, and (4) unloaded pes anserinus. The protocol was then repeated with the ACL transected. RESULTS: In the ACL intact knee, the neutral position of the tibia with an unloaded pes anserinus was significantly more externally rotated (p < 0.01) and anteriorly translated (p < 0.05) at all knee flexion angles than a tibia with a physiologic loaded pes anserinus. Applying an external rotation torque significantly increased external rotation for the fully unloaded (p < 0.001), gracilis only loaded (p < 0.001), and semitendinosus only loaded (p < 0.01) conditions at all flexion angles. Applying a valgus torque resulted in a significant increase in laxity for the fully unloaded condition only at 30° of flexion (p < 0.05). Applying an anterior tibial force resulted in significant increase in anterior translation for the fully unloaded condition at all flexion angles (p < 0.01), and for the gracilis only loaded condition in 30° and 60° of flexion (p < 0.05). Similar results were seen in the ACL deficient model. CONCLUSION: The medial hamstrings are involved in rotational, translational, and varus/valgus control of the knee. Applying anterior, external rotation, and valgus forces on the hamstring deficient knee significantly increases motion in those planes. Harvesting the gracilis and semitendinosus tendons alters native knee kinematics and stability. This is clinically relevant and should be a consideration when choosing graft source for ACL reconstruction, especially in the elite athlete population.

Evaluating the Femoral-Side Critical Corner in Posterior Cruciate Ligament Reconstruction: The Effect of Outside-In Versus Inside-Out Creation of Femoral Tunnels on Graft Contact Pressure in a Synthetic Knee Model.

PURPOSE: To characterize and compare the graft contact characteristics of outside-in (OI) and inside-out (IO) femoral tunnels during single-bundle reconstruction of the anterolateral bundle of the posterior cruciate ligament in a synthetic knee model. METHODS: Femoral tunnels were separately made in 16 synthetic femora (8 OI and 8 IO). Achilles tendon allografts were fixed using suspensory fixation with a pressure sensor between the allograft and femoral tunnel. Grafts were cyclically loaded; force, contact area, contact pressure, and peak pressure at the aperture were measured. This process was repeated using the same allograft to assess the other tunnel angle in a separate specimen. RESULTS: IO specimens showed higher mean contact pressure at all loading cycles, with significance shown at 50 N (P = .02). Peak pressure was also greater in IO specimens at all loading cycles and reached statistical significance at 100 N (P = .04). IO specimens had a lower contact area at 150 N (P = .04). No statistically significant differences in force were observed between the 2 groups. CONCLUSIONS: OI creation of the femoral tunnel for anterolateral bundle reconstruction of the posterior cruciate ligament resulted in decreased mean and peak contact pressures at the femoral aperture compared with IO tunnel creation at the specific trajectories and loading parameters tested in this synthetic femoral model. These biomechanical data suggest that OI creation of the femoral tunnel may help reduce in vivo graft contact pressure at the femoral aperture. CLINICAL RELEVANCE: These data suggest that a tunnel drilled from OI may result in less graft pressure at the femoral aperture, which may prevent graft elongation and optimize graft survival.

Biomechanical Analysis of an S1 Pedicle Screw Salvage Technique via a Superior Articulating Process Entry Point.

STUDY DESIGN: Biomechanical, cadaveric study. OBJECTIVE: To compare the fixation strength of a novel S1 pedicle screw insertion technique in a revision setting to a standard S1 pedicle screw and an L5 pedicle screw. SUMMARY OF BACKGROUND DATA: Fusions to the sacrum remain a difficult clinical challenge. Very few salvage techniques exist when a nonunion occurs. METHODS: The biomechanical integrity of three screw fixations, L5 pedicle screws, a standard S1 pedicle screw, and an S1 pedicle screw placed via a superior articulating process entry point (SAP S1), was characterized by performing pullout tests using cadaveric specimens including L5 and sacrum. RESULTS: SAP S1 constructs (735.5 ±â€Š110.1 N/mm) were significantly stiffer than standard S1 (P = 0.005) and L5 (P = 0.02) constructs. There was no statistically significant difference between the L5 constructs and the standard S1 constructs for linear stiffness. There was no statistical difference between the three fixations for yield load, displacement at yield load, and energy absorbed to yield load.The ultimate pullout force for the SAP S1 was statistically higher than the standard S1 (1213.7 ±â€Š579.6 vs. 478.6 ±â€Š452.9 N; P = 0.004). Displacement at ultimate load was significantly greater for L5 screw fixation (3.3 ±â€Š1.1 mm) compared to the other two constructs. Both the L5 (2277.4 ±â€Š1873.3 N-mm) and SAP S1 (2628.2 ±â€Š2054.4 N-mm) constructs had significantly greater energy absorbed to ultimate load than the standard S1 construct (811.7 ±â€Š937.6 N-mm), but there was no statistical difference between the L5 and SAP S1 constructs. CONCLUSION: S1 pedicle screw fixation via an SAP entry point provides biomechanical advantages compared to screws placed via the standard S1 or L5 entry point and may be a viable option for revision of a failed L5-S1 fusion with a compromised standard S1 entry point. LEVEL OF EVIDENCE: N/A.

Pelvic discontinuity: modern techniques and outcomes for treating pelvic disassociation.

Pelvic discontinuity is an uncommon condition that usually presents in the revision total hip arthroplasty population. However, its incidence will most likely increase due to the increasing number of primary and revision total hip arthroplasties (THA) done in recent years. Pelvic discontinuity (acetabular disassociation) is perhaps one of the more challenging cases for the hip arthroplasty surgeon to manage. Historically, the management of pelvic discontinuity has been wrought with many challenges. What follows is a review of the current techniques and outcomes for acetabular reconstruction in patients with acetabular disassociation including: porous metal components, internal fixation with acetabular reconstruction, acetabular distraction with jumbo cups, cup and cage construct, and the use of custom triflange.The complexity of pelvic discontinuity and with the myriad of options available to the hip arthroplasty surgeon to address this particular issue, preoperative planning becomes all the more essential.

A common polymorphism in the LDL receptor gene has multiple effects on LDL receptor function.

A common synonymous single nucleotide polymorphism in exon 12 of the low-density lipoprotein receptor (LDLR) gene, rs688, has been associated with increased plasma total and LDL cholesterol in several populations. Using immortalized lymphoblastoid cell lines from a healthy study population, we confirmed an earlier report that the minor allele of rs688 is associated with increased exon 12 alternative splicing (P < 0.05) and showed that this triggered nonsense-mediated decay (NMD) of the alternatively spliced LDLR mRNA. However, since synonymous single nucleotide polymorphisms may influence structure and function of the encoded proteins by co-translational effects, we sought to test whether rs688 was also functional in the full-length mRNA. In HepG2 cells expressing LDLR cDNA constructs engineered to contain the major or minor allele of rs688, the latter was associated with a smaller amount of LDLR protein at the cell surface (-21.8 ± 0.6%, P = 0.012), a higher amount in the lysosome fraction (+25.7 ± 0.3%, P = 0.037) and reduced uptake of fluorescently labeled LDL (-24.3 ± 0.7%, P < 0.01). Moreover, in the presence of exogenous proprotein convertase subtilisin/kexin type 9 (PCSK9), a protein that reduces cellular LDL uptake by promoting lysosomal degradation of LDLR, the minor allele resulted in reduced capacity of a PCSK9 monoclonal antibody to increase LDL uptake. These findings are consistent with the hypothesis that rs688, which is located in the ß-propeller region of LDLR, has effects on LDLR activity beyond its role in alternative splicing due to impairment of LDLR endosomal recycling and/or PCSK9 binding, processes in which the ß-propeller is critically involved.