Thermal properties of polymethyl methacrylate vary depending on brand and type.

Polymethyl methacrylate (PMMA) is commonly used in orthopedic surgery and has several applications, most often for fixation of arthroplasty components. While its overall safety and tolerance are well described, less is known regarding the thermal properties of PMMA as it sets from a liquid to solid state, as well as the potential for osseous thermal necrosis. This study addresses potential variations in the setting time and maximum temperature of PMMA formulations in common use and explores the potential clinical implications of this variability. Seven commercially available formulations of PMMA that varied by brand and/or viscosity were obtained and prepared according to manufacturer's instructions. Peak temperature and duration were measured in controlled settings for each type and compared to previously described thresholds for thermal bone necrosis. Depuy SmartSet (HV), Zimmer Palacos R (HV), and Zimmer Palacos (LV) exceeded the 56°C threshold reported to potentially induce immediate osseous thermal necrosis. Additionally, Biomet Cobalt (MV) and Stryker Simplex P (MV) had lower peak temperatures but exceeded thermal necrosis thresholds due to curing duration. The lowest peak temperature was observed for Smith & Nephew Versabond (MV), which was significantly lower than all types except Depuy SmartSet (MV). Setting time was not significantly different among groups. There are significant differences in the thermal properties of PMMA formulations in current use. Selection of specific PMMA formulations represents an additional route of procedural optimization depending on the needs of the treating surgeon.

Supplementation of Lateral Locked Plating for Distal Femur Fractures: A Biomechanical Study.

OBJECTIVES: To investigate the biomechanical properties of a lateral locked plate alone or in combination with a supplemental medial plate or an intramedullary nail (IMN). METHODS: Intra-articular distal femur fractures with metaphyseal comminution (OTA/AO 33-C) were simulated with a standardized model in 28 synthetic femora and divided into 4 groups. Group I was instrumented with a 4.5-mm lateral locked distal femoral plate alone, group II with a lateral locked plate plus a low-profile precontoured 3.5-mm medial distal tibial plate, group III with a lateral locked plate plus a medial 3.5-mm reconstruction plate, and group IV with a lateral locked plate plus a retrograde IMN. Specimens were then axially loaded and cycled to failure or runout. Outcomes of interest were baseline stiffness, survivability, and cycles to failure. RESULTS: Groups III and IV have a significantly higher baseline stiffness (P < 0.001) when compared with groups I and II. Furthermore, groups III and IV had a higher max load to failure (P < 0.01) when compared with groups I and II. The survivability in groups III and IV was 71% and 100%, respectively, while no specimens in group I or II survived maximum loading. There was no significant difference between group III and IV regarding stiffness, survivability, and cycles to failure. CONCLUSION: When considering fixation for intra-articular distal femur fractures with metaphyseal comminution (OTA/AO 33-C), we found that supplementation of a lateral locked plate with a medial plate or an IMN to be biomechanically superior to lateral locked plating alone regarding stiffness, survivability, and cycles to failure. A low-profile precontoured plate did not add significantly to the construct stiffness in this study.

Drains Are Not Beneficial in Primary Shoulder Arthroplasty.

The purpose of this study was to determine if clinical differences exist between closed drainage use in primary shoulder arthroplasty and postoperative complications. A retrospective review was performed of all primary total shoulder and reverse total shoulder arthroplasty procedures at the authors' institution during a 2-year period. A total of 378 of 636 shoulder arthroplasty patients met inclusion criteria. Drains were used in 111 patients. The authors did not identify a significant relationship between drain use and postoperative complications. When complications were stratified just by the presence or absence of risk factors, irrespective of whether a drain was used, no significant relationship was identified. This study does not support the routine use of closed drainage systems in primary shoulder arthroplasty, including for patients with risk factors for potentially developing postoperative complications. [Orthopedics. 2019; 42(1):e29-e31.].

Biomechanical Investigation of an Integrated 2-Screw Cephalomedullary Nail Versus a Sliding Hip Screw in Unstable Intertrochanteric Fractures.

OBJECTIVE: To compare the efficacy of 2 intertrochanteric (IT) fracture fixation devices in conferring mechanical stability to unstable IT femur fractures. METHODS: Nine pairs of cadaveric female femurs with a groupwise average bone quality indicative of osteopenia were used. An unstable IT fracture without calcar support (OTA/AO 31-A2) was created and stabilized with either a sliding hip screw and side plate (SHS) or a cephalomedullary nail using an integrated dual-screw fixation [InterTAN (ITN)]. Constructs were evaluated under stepwise and increasing cyclic loading up to 50,000 cycles (1500 N) or by failure in a test model that may best simulate hip joint contact forces at heel strike. Number of cycles to failure, failure load, and femoral head rotation about the screw axis were compared between groups. RESULTS: The average number of cycles in the ITN group was greater compared with that in the SHS group (48,383 vs. 31,403 cycles, P = 0.046). Similarly, the average maximum load survived by the ITN group was greater than that of the SHS group (1456 vs. 1113 N, P = 0.046). The number of constructs that survived up to the maximum applied load of 1500 N was greater in the ITN group (8/9, 89%) when compared with that of the SHS constructs (3/9, 33%) (P = 0.049). Finally, the ITN group conferred greater rotational control of the femoral head compared with the SHS constructs (1.5 vs. 5.5 degrees, P = 0.018), and reduced the amount of varus collapse (11.1 vs. 31.1 degrees, P = 0.038). CONCLUSIONS: The integrated dual-screw construct appeared to confer significantly greater fracture stability compared with a sliding hip screw and side plate using a worst-case model that simulates heel strike during gait. Study data provide biomechanical evidence that the ITN device may provide more stability and rotational resistance than a sliding hip screw in the elderly female patient population with an unstable IT fracture and compromised bone quality.

Long Segment Blocking Screws Increase the Stability of Retrograde Nail Fixation in Geriatric Supracondylar Femur Fractures: Eliminating the "Bell-Clapper Effect".

OBJECTIVES: To determine the change in stiffness and horizontal translations of a geriatric supracondylar femur fracture model with the addition of distal segment blocking screws versus proximal (long) segment blocking screws to the standard retrograde intramedullary nail construct. METHODS: Unstable supracondylar femur fractures (OTA/AO 33-A3) were created; all specimens were instrumented with a retrograde intramedullary nail. Specimens were divided into 2 groups (6 matched pairs per group). Group 1 compared the standard construct (1 proximal screw and 3 distal screws) to a distally augmented construct, with blocking screws placed in the distal metaphyseal segment. Group 2 compared the distally augmented construct to one in which blocking screws were placed just proximal to the fracture (long segment blocking screws). Specimens were then axially loaded and cycled to failure or run-out. RESULTS: There was no significant difference in baseline stiffness, survival through cyclic loading, stiffness after cyclic loading, or cycles to failure between femurs treated with distal blocking screws and femurs treated without blocking screws (group 1). Femurs with blocking screws in the long proximal segment had significantly greater baseline stiffness, stiffness after cyclic loading, and less horizontal translation at the fracture site (group 2). There was no difference in survival through cyclic loading or cycles to failure. CONCLUSION: Long segment blocking screws are biomechanically superior to blocking screws in the distal segment or no blocking screws initially and after cyclic loading in an unstable geriatric supracondylar femur fracture model treated with intramedullary nail. CLINICAL RELEVANCE: Surgeons may use blocking screws to aid in fracture alignment during retrograde nail fixation. In addition, the placement of long segment blocking screws can help resist failure of fixation in geriatric patients by eliminating the "Bell-clapper effect."

Anatomic Total Shoulder Arthroplasty Versus Reverse Total Shoulder Arthroplasty for Post-Capsulorrhaphy Arthropathy.

Post-capsulorrhaphy arthropathy is a long-term sequela that can develop after open anterior stabilization surgeries, which have historically been performed. The purpose of this study was to compare anatomic total shoulder arthroplasty (ATSA) with reverse total shoulder arthroplasty (RTSA) for the treatment of post-capsulorrhaphy arthropathy. There were 19 patients in the ATSA cohort and 20 in the RTSA cohort. All patients included had a minimum of 2 years of follow-up (ATSA mean, 59.5 months; RTSA mean, 43.8 months). Patients were followed clinically (American Shoulder and Elbow Surgeons score, Simple Shoulder Test score, range of motion analysis, and patient satisfaction) as well as radiographically, allowing a comparison of the 2 cohorts. Mean outcome scores were similar in the ATSA and the RTSA cohorts, with no difference between the 2 groups. The ATSA group had greater postoperative forward elevation (153° vs 139°; P=.01) than the RTSA group, but no other differences were noted in motion. The ATSA group had less satisfied patients (84% vs 95%), a higher complication rate (21% vs 10%), and a higher revision rate (16% vs 0%) compared with the RTSA group. For post-capsulorrhaphy arthropathy, patients treated with ATSA and patients treated with RTSA had comparable improvements in outcome scores and range of motion. However, the complication rate was higher in the ATSA group. All complications in the ATSA cohort were related to subscapularis insufficiency and postoperative anterior instability problems, resulting in a higher revision rate in this cohort (16%) compared with the RTSA cohort (0%). [Orthopedics. 2018; 41(5):275-280.].

The effect of residency training on arthroscopic knot tying and knot stability: which knot is best tied by Orthopaedic surgery residents?

BACKGROUND: The aim of this study is to evaluate which of three arthroscopic knots are most reliably taught to and executed by residents at varying levels of training. METHODS: Three arthroscopic knots, the Samsung Medical Center (SMC), the Weston, and the surgeon's knot, were taught to 16 orthopaedic surgery residents. Each knot was tied in triplicate at two sessions 1 week apart. The knots were then biomechanically tested for strength. Corresponding knots tied by a sports medicine fellow served as the respective controls. RESULTS: Comparing all knots regardless of year of training, the SMC knot failed at significantly higher loads (237.2 ± 66.6 N) than the surgeon's knot (203.7 ± 45.3 N, p = 0.049) and the Weston knot (193.5 ± 56.1 N, p = 0.013). No significant differences in knot strength were found when comparing knots tied by residents at different levels of training and when comparing residents to the sports medicine fellow. There was no difference in conditioning elongation between surgeon's (p = 0.343), Weston (p = 0.486), or SMC knots (p = 0.200) tied by post-graduate year one and five residents. CONCLUSIONS: We report the first study that evaluates the loop strength of an arthroscopically tied knot performed by orthopaedic surgery residents in various levels of training. In our cohort, the SMC knot required a higher load to failure, when compared to the Surgeon's and Weston knot, after a simple arthroscopic knot tying curriculum. Based on these findings, he SMC knot should be considered as a part of future orthopaedic surgery resident arthroscopic training programs.

Reverse Shoulder Arthroplasty in the Weight-Bearing Versus Non-Weight-Bearing Shoulder: Mid-term Outcomes With Minimum 5-Year Follow-up.

This retrospective review evaluated the mid-term outcomes of cemented reverse shoulder arthroplasty in patients who use the shoulder for weight bearing (WB) vs non-weight-bearing (NWB) patients. Twenty-five shoulders of 21 patients who used their upper extremity for WB (WB group) were treated with cemented reverse shoulder arthroplasty and followed for a minimum of 5 years postoperatively (average, 73 months). Seventy-five consecutive shoulders of 72 patients who were NWB (NWB group) were treated and matched for duration of follow-up (average, 72 months) to serve as a control group. Patients were followed clinically and radiographically. There were no statistically significant differences between the WB group and the NWB group regarding final outcome scores or range of motion. Patient satisfaction was similar between the WB group (92%) and the NWB group (94%). The scapular notching rate was 20% in the WB group compared with 5% in the NWB group (P=.041). Humeral loosening occurred in 12% of the WB group vs 0% of the NWB group (P=.014). The complication rate was higher in the WB group than in the NWB group (12% vs 4%). The WB group and the NWB group had similar outcome scores, range of motion improvements, and patient satisfaction after reverse shoulder arthroplasty. At mid-term follow-up, the WB group had a higher scapular notching rate, humeral loosening rate, and complication rate than the NWB group. [Orthopedics. 2018; 41(3):e328-e333.].

Biomechanical Comparison of 3 Inferiorly Directed Versus 3 Superiorly Directed Locking Screws on Stability in a 3-Part Proximal Humerus Fracture Model.

OBJECTIVE: To quantify the stability of 3 points of inferiorly directed versus 3 points of superiorly directed locking screw fixation compared with the full contingent of 6 points of locked screw fixation in the treatment of a 3-part proximal humerus fracture. METHODS: A standardized 3-part fracture was created in 10 matched pairs (experimental groups) and 10 nonmatched humeri (control group). Osteosynthesis was performed using 3 locking screws in the superior hemisphere of the humeral head (suspension), 3 locking screws in the inferior hemisphere (buttress), or the full complement of 6 locking screws (control). Specimens were tested in varus cantilever bending (7.5 Nm) to 10,000 cycles or failure. Construct survival (%) and the cycles to failure were compared. RESULTS: Seven of 10 controls survived the 10,000-cycle runout (70%: 8193 average cycles to failure). No experimental constructs survived the 10,000-cycle runout. Suspension and buttress screw groups failed an average of 331 and 516 cycles, respectively (P = 1.00). The average number of cycles to failure and the number of humeri surviving the 10,000-cycle runout were greater in the control group than in the experimental groups (P ≤ 0.006). CONCLUSION: Data support the use of a full contingent of 6 points of locking screw fixation over 3 superior or 3 inferior points of fixation in the treatment of a 3-part proximal humerus fracture with a locking construct. No biomechanical advantage to the 3 buttress or 3 suspension screws used in isolation was observed.

Intubation biomechanics: validation of a finite element model of cervical spine motion during endotracheal intubation in intact and injured conditions.

OBJECTIVE Because of limitations inherent to cadaver models of endotracheal intubation, the authors' group developed a finite element (FE) model of the human cervical spine and spinal cord. Their aims were to 1) compare FE model predictions of intervertebral motion during intubation with intervertebral motion measured in patients with intact cervical spines and in cadavers with spine injuries at C-2 and C3-4 and 2) estimate spinal cord strains during intubation under these conditions. METHODS The FE model was designed to replicate the properties of an intact (stable) spine in patients, C-2 injury (Type II odontoid fracture), and a severe C3-4 distractive-flexion injury from prior cadaver studies. The authors recorded the laryngoscope force values from 2 different laryngoscopes (Macintosh, high intubation force; Airtraq, low intubation force) used during the patient and cadaver intubation studies. FE-modeled motion was compared with experimentally measured motion, and corresponding cord strain values were calculated. RESULTS FE model predictions of intact intervertebral motions were comparable to motions measured in patients and in cadavers at occiput-C2. In intact subaxial segments, the FE model more closely predicted patient intervertebral motions than did cadavers. With C-2 injury, FE-predicted motions did not differ from cadaver measurements. With C3-4 injury, however, the FE model predicted greater motions than were measured in cadavers. FE model cord strains during intubation were greater for the Macintosh laryngoscope than the Airtraq laryngoscope but were comparable among the 3 conditions (intact, C-2 injury, and C3-4 injury). CONCLUSIONS The FE model is comparable to patients and cadaver models in estimating occiput-C2 motion during intubation in both intact and injured conditions. The FE model may be superior to cadavers in predicting motions of subaxial segments in intact and injured conditions.

Sensitivity and Specificity of Skyline and Carpal Shoot-Through Fluoroscopic Views of Volar Plate Fixation of the Distal Radius: A Cadaveric Investigation of Dorsal Cortex Screw Penetration.

BACKGROUND: Volar plate fixation of distal radius fractures can result in soft tissue injuries. Abnormal contour of the dorsal cortex of the distal radius provides difficulties in discerning screw penetration on standard radiographs. The skyline and carpal shoot-through views are additional views to improve dorsal cortex visibility. We report on the sensitivity and specificity of determining screw protrusion with these views. METHODS: Seven fresh frozen cadavers were instrumented with a distal radius volar locking plate. Initial screw length was determined by depth gauge measurement. A dorsal dissection of the wrist was performed to detect screw penetration. Protruding screws were documented and replaced with screws of the appropriate length and deemed as baseline. Screws were then sequentially lengthened by 2 and 4 mm. Skyline and carpal shoot-through views were obtained at baseline, 2 mm, and 4 mm. The images were randomized and compiled into an untimed survey asking orthopedic surgeons to determine whether screws were penetrating through the dorsal cortex. RESULTS: Based on depth gauge measurements, 4 out of 44 (9.1%) volar plate locking screws penetrated the dorsal cortex, as confirmed with dorsal dissection. Sensitivities for the skyline and carpal shoot-through views were 75% and 86% ( P ≤ .001), respectively, for 2-mm protrusions, and 76% and 89% ( P ≤ .001), respectively, for 4-mm screw protrusions. Specificities were 85% and 84% for the skyline and shoot-through views, respectively. CONCLUSIONS: We believe that the carpal shoot-through view has utility and can be implemented to augment standard intraoperative views, and may decrease the incidence of screw protrusion resulting in soft tissue injuries.

Reverse Shoulder Arthroplasty for the Treatment of Rotator Cuff Deficiency: A Concise Follow-up, at a Minimum of 10 Years, of Previous Reports.

We previously evaluated 94 patients (96 shoulders) who underwent reverse shoulder arthroplasty using a central compressive screw with 5.0-mm peripheral locking screws for baseplate fixation and a center of rotation lateral to the glenoid as treatment for end-stage rotator cuff deficiency. The purpose of this study was to report updated results at a minimum follow-up of 10 years. Forty patients (42 shoulders) were available for clinical follow-up. In the patients available for study, implant survivorship, with the end point being revision for any reason, was 90.7%. Since our 5-year report, 2 patients underwent revision surgery; 1 patient sustained a periprosthetic fracture 7 years postoperatively and 1 patient had a dislocation because of chronic shoulder instability at 8 years postoperatively. At a minimum follow-up of 10 years, the patients continued to maintain their improved outcome scores and range of motion, which were comparable with earlier follow-up evaluations. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Radiographic evaluation of acute distal radius fracture stability: A comparative cadaveric study between a thermo-formable bracing system and traditional fiberglass casting.

BACKGROUND: Distal radius fractures are common musculoskeletal injuries and many can be treated non-operatively with cast immobilization. A thermo-formable brace has been developed for management of such fractures, but no data exist regarding its comparative stabilizing efficacy to fiberglass casting. METHODS: A worst-case distal radius fracture was created in 6 cadaveric forearms. A radiolucent loading fixture was created to apply cantilever bending/compression loads ranging from 4.5N to 66.7N across the simulated fracture in the: (1) non-stabilized, (2) braced; and (3) casted forearms, each forearm serving as its own control. Fracture fragment translations and rotations were measured radiographically using orthogonal radiographs and a 2D-3D, CT-based transformation methodology. FINDINGS: Under 4.5N of load in the non-stabilized condition, average sagittal plane rotation and 3D center of mass translation of the fracture fragment were 12.3° and 5.3mm, respectively. At the 4.5N load step, fragment rotation with the brace (avg. 0.0°) and cast (0.1°) reduced sagittal plane rotation compared to the non-stabilized forearm (P<0.001). There were no significant differences in measured sagittal plane fracture fragment rotations or 3D fragment translations between the brace or cast at any of the four load steps (4.5N, 22.2N, 44.5N, and 66.7N, P≥0.138). INTERPRETATION: In this in vitro radiographic study utilizing 6 cadaveric forearms with simulated severe-case, unstable and comminuted distal radius fractures, the thermo-formable brace stabilized the fracture in a manner that was not radiographically or biomechanically different from traditional fiberglass casting. Study results support the use of the thermo-formable brace clinically.

Complete Eradication of Biofilm From Orthopedic Materials.

BACKGROUND: Interest exists in finding alternatives to current management strategies in periprosthetic joint infections, which typically include a 2-stage revision with placement of an antibiotic spacer and delayed placement of a new implant. We studied the efficacy of autoclaving, ultrasonication, and mechanical scrubbing for sterilization and biofilm eradication on infected cobalt-chrome discs. METHODS: Strains of Staphylococcus aureus MRSA252 or Staphylococcus epidermidis RP62A were grown on the discs. For each strain, discs were divided into 5 groups (5 discs each) and exposed to several sterilization and biofilm eradication treatments: (1) autoclave, (2) autoclave + sonication, (3) autoclave + saline scrub, (4) autoclave + 4% chlorhexidine (CHC) scrub, and (5) autoclave + sonication + CHC scrub. Sterilization and biofilm eradication were quantified with crystal violet assays and scanning electron microscopy. RESULTS: Relative to nontreated controls, autoclaving alone reduced biofilm load by 33.9% and 54.7% for MRSA252 and RP62A strains, respectively. Biofilm removal was maximized with the combined treatment of autoclaving and CHC scrub for MRSA252 (100%) and RP62A (99.5%). The addition of sonication between autoclaving and CHC scrubbing resulted in no statistically significant improvement in biofilm removal. High-resolution scanning electron microscopy revealed no cells or biofilm for this combined treatment. CONCLUSION: Using 2 commonly encountered bacterial strains in periprosthetic joint infection, infected cobalt-chrome discs were sterilized and eradicated of residual biofilm with a combination of autoclaving and CHC scrubbing.

Morphometry of the human clavicle and intramedullary canal: A 3D, geometry-based quantification.

Midshaft clavicle fractures are a very common occurrence. The current treatment of choice involves internal fixation with superior or anterior clavicle plating, however their clinical success and particularly patient satisfaction are decreasing. The implementation of intramedullary devices is on the rise, but data describing the intramedullary canal parameters are lacking. The aim of this study is to quantify the geometry of the clavicle and its intramedullary canal, and to evaluate the effect of gender and anatomical side. This study used three-dimensional image-based models with novel and automated methods of standardization, normalization, and bone cross-section evaluation. The data obtained in this study present intramedullary canal, and clavicle diameter and center deviation parameterized as a function of clavicle length as well as its radius of curvature and true length. Results showed that both right-sided and female clavicles were shorter and thicker, but only females showed a statistically significant difference in size compared to males (p < 0.0001). The smallest clavicle and intramedullary canal diameters were seen at different clavicle lengths (45% and 52%), suggesting that the narrowest region of intramedullary canal cannot be appreciated based on external visualization of the clavicle alone. The narrowing of the intramedullary canal is of special interest because this is a potential limiting region for surgical planning and intramedullary device design. Furthermore, the location and value of maximum lateral curvature displacement is different in the intramedullary canal, implying there exists an eccentricity of the intramedullary canal center with respect to the clavicle center. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2191-2202, 2017.

Glenoid baseplate fixation using hybrid configurations of locked and unlocked peripheral screws.

BACKGROUND: The use of peripheral locked screws has reduced glenoid baseplate failure rates in reverse shoulder arthroplasty. However, situations may arise when one or more non-locked screws may be preferred. We aimed to determine if different combinations of locked and non-locked screws significantly alter acute glenoid baseplate fixation in a laboratory setting. MATERIALS AND METHODS: Twenty-eight polyurethane trabecular bone surrogates were instrumented with a center screw-type glenoid baseplate and fixated with various combinations of peripheral locked and non-locked screws (1-, 2-, 3- and 4-locked con). Each construct was tested through a 55° arc of abduction motion generating compressive and shear forces across the glenosphere. Baseplate micromotion (µm) was recorded throughout 10,000 cycles for each model. RESULTS: All constructs survived 10,000 cycles of loading without catastrophic failure. One test construct in the 1-locked fixation group exhibited a measured micromotion >150 µm (177.6 µm). At baseline (p > 0.662) and following 10,000 cycles (p > 0.665), no differences were observed in baseplate micromotion for screw combinations that included one, two, three and four peripheral locked screws. The maximum difference in measured micromotion between the extremes of groups (1-locked and 4-locked) was 29 µm. CONCLUSIONS: Hybrid peripheral screw fixation using combinations of locked and non-locked screws provides secure glenoid baseplate fixation using a polyurethane bone substitute model. Using a glenosphere with a 10-mm lateralized center of rotation, hybrid baseplate fixation maintains micromotion below the necessary threshold for bony ingrowth. LEVEL OF EVIDENCE: N/A/, basic science investigation.

Comparison of 3 Methods for Maintaining Inter-Fragmentary Compression After Fracture Reduction and Fixation.

OBJECTIVES: It is recommended that the intra-articular component of a supracondylar distal femoral fracture be stabilized by a lag screw to create interfragmental compression. Generally, it is thought that lag screw fixation should precede any positional screw or locking screw application. This study compared 3 methods of maintaining interfragmentary compression after fracture reduction with a reduction clamp. METHODS: Intra-articular vertical split fractures were created in synthetic femora. A force transducer was interposed between the medial and lateral condyles and 20 lbs of compression was applied to the fracture with a reduction clamp. 3.5-mm cortical lag screws (group 1), 3.5-mm cortical position screws (group 2), and 5.4-mm distal locking screws through a distal femur locking plate (group 3) were placed across the fracture (n = 4/group). After screw placement, the clamp was removed and the amount of residual interfragmentary compression was recorded. After 2 minutes, a final steady-state force was measured and compared across groups. RESULTS: Locking screws placed through the plate (group 3) maintained 27% of the initial force applied by the clamp (P = 0.043), whereas positional screws (group 2) maintained 90% of the initial force applied by the clamp (P = 0.431). The steady-state compression force measured with lag screws (group 1) increased by 240% (P = 0.030) relative to the initial clamp force. The steady-state force in the lag screw group was significantly greater than groups 1 and 2 (P = 0.012). CONCLUSIONS: When reducing intra-articular fractures and applying interfragmentary compression with reduction clamps, additional lag screws increase the amount of compression across the fracture interface. Compressing a fracture with reduction clamps and relying on locking screws to maintain the compression result in a loss of interfragmentary compression and should be avoided. This study lends biomechanical support that lag screws placed outside of the plate before locking screws for fracture fixation help maintain optimal interfragmentary compression.

Morphologic Variability of the Shoulder between the Populations of North American and East Asian.

BACKGROUND: The aim of this study was to determine if there were significant differences in glenohumeral joint morphology between North American and East Asian populations that may influence sizing and selection of shoulder arthroplasty systems. METHODS: Computed tomography reconstructions of 92 North American and 58 East Asian patients were used to perform 3-dimensional measurements. The proximal humeral position was normalized in all patients by aligning it with the scapular plane utilizing anatomic landmarks. Measurements were performed on the humerus and scapula and included coronal and axial humeral head radius, humeral neck shaft and articular arc angles, glenoid height and width, and critical shoulder angle. Glenohumeral relationships were also measured and included lateral distance to the greater tuberosity and acromion, abduction lever arm, and acromial index. Parametric and nonparametric statistical analyses were used to compare population metrics. RESULTS: East Asian glenohumeral measurements were significantly smaller for all linear metrics (p < 0.05), with the exception of acromial length, which was greater than in the North American cohort (p < 0.001). The increase in acromial length affected all measurements involving the acromion including abduction lever arms. No difference was found between the neck shaft and articular angular measurements. CONCLUSIONS: The East Asian population exhibited smaller shoulder morphometrics than their North American cohort, with the exception of an extended acromial overhang. The morphologic data can provide some additional factors to consider when choosing an optimal shoulder implant for the East Asian population, in addition to creating future designs that may better accommodate this population.

Partial rotator cuff repair and biceps tenotomy for the treatment of patients with massive cuff tears and retained overhead elevation: midterm outcomes with a minimum 5 years of follow-up.

BACKGROUND: A subset of patients with massive irreparable rotator cuff tears present with retained overhead elevation and pain as their primary complaint. Our aim was to evaluate the outcomes of partial arthroscopic rotator cuff repair with biceps tenotomy and to report the failure rate of this procedure for patients with >5 years of follow-up. METHODS: Thirty-four patients underwent partial rotator cuff repair and biceps tenotomy for treatment of a massive rotator cuff tear. Patients had preoperative active forward elevation >120° and no radiographic evidence of glenohumeral arthritis. Patients were followed up clinically and radiographically, and 28 patients had a minimum of 5 years of follow-up. Failure was defined as an American Shoulder and Elbow Surgeons score of <70, loss of active elevation >90°, or revision to reverse shoulder arthroplasty during the study period. RESULTS: Patients demonstrated improvements in average preoperative to postoperative American Shoulder and Elbow Surgeons scores (46.6 to 79.3 [P < .001]) and Simple Shoulder Test scores (5.7 to 9.1 [P < .001]) along with decrease in visual analog scale for pain scores (6.9 to 1.9 [P < .001]). No significant change in forward elevation (168° to 154° [P = .07]), external rotation (38° to 39° [P = 1.0]), or internal rotation (84% to 80% [P = 1.0]) was identified; 36% of patients had progression of the Hamada stage. The failure rate was 29%; 75% of patients were satisfied with their index procedure. CONCLUSION: Partial rotator cuff repair and biceps tenotomy for patients with massive irreparable rotator cuff tears with retained overhead elevation and pain as the primary complaint produced reasonable outcomes at midterm follow-up of at least 5 years.

Intubation biomechanics: laryngoscope force and cervical spine motion during intubation in cadavers-effect of severe distractive-flexion injury on C3-4 motion.

OBJECTIVE With application of the forces of intubation, injured (unstable) cervical segments may move more than they normally do, which can result in spinal cord injury. The authors tested whether, during endotracheal intubation, intervertebral motion of an injured C3-4 cervical segment 1) is greater than that in the intact (stable) state and 2) differs when a high- or low-force laryngoscope is used. METHODS Fourteen cadavers underwent 3 intubations using force-sensing laryngoscopes while simultaneous cervical spine motion was recorded with lateral fluoroscopy. The first intubation was performed with an intact cervical spine and a conventional high-force line-of-sight Macintosh laryngoscope. After creation of a severe C3-4 distractive-flexion injury, 2 additional intubations were performed, one with the Macintosh laryngoscope and the other with a low-force indirect video laryngoscope (Airtraq), used in random order. RESULTS During Macintosh intubations, between the intact and the injured conditions, C3-4 extension (0.3° ± 3.0° vs 0.4° ± 2.7°, respectively; p = 0.9515) and anterior-posterior subluxation (-0.1 ± 0.4 mm vs -0.3 ± 0.6 mm, respectively; p = 0.2754) did not differ. During Macintosh and Airtraq intubations with an injured C3-4 segment, despite a large difference in applied force between the 2 laryngoscopes, segmental extension (0.4° ± 2.7° vs 0.3° ± 3.3°, respectively; p = 0.8077) and anterior-posterior subluxation (0.3 ± 0.6 mm vs 0.0 ± 0.7 mm, respectively; p = 0.3203) did not differ. CONCLUSIONS The authors' hypotheses regarding the relationship between laryngoscope force and the motion of an injured cervical segment were not confirmed. Motion-force relationships (biomechanics) of injured cervical intervertebral segments during endotracheal intubation in cadavers are not predicted by the in vitro biomechanical behavior of isolated cervical segments. With the limitations inherent to cadaveric studies, the results of this study suggest that not all forms of cervical spine injury are at risk for pathological motion and cervical cord injury during conventional high-force line-of-sight intubation.