Improved mechanical fixation of an all-polyethylene glenoid reduces postoperative radiolucent lines.

BACKGROUND: The rationale for advances in implant design is to improve performance in comparison to their predecessors. The purpose of this study was to compare a newer, self-pressurizing peripheral peg glenoid to a traditional polyethylene pegged glenoid through biomechanical evaluation and a retrospective radiographic and clinical review. METHODS: Three testing conditions (uncemented, partially cemented, and fully cemented) were chosen to assess the 2 component designs in a foam block model. The number of hammer hits to seat the component, amount of time to seat the component, and resistance-to-seat were collected. The implants were then cyclically loaded following ASTM F2028-17 testing standard. Clinically, postoperative radiographs of patients with a self-pressurized glenoid component (n = 225 patients) and traditional glenoid component (n = 206 patients) were evaluated for radiolucent lines and glenoid seating at various timepoints. Clinical outcomes (American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, Simple Shoulder Test, and visual analog scale pain scores) and complications were recorded. The presence of radiolucent lines at the bone-cement interface was evaluated using the Modified Franklin Grade and the Lazarus grade. RESULTS: The self-pressurizing glenoid design required significantly more hammer hits than traditional glenoid designs in all groups tested (P < .029). Moreover, the self-pressurizing design had significantly more resistance-to-seat than traditional components in both the uncemented and partially cemented group (P < .002). No difference in resistance-to-seat was found between designs in the fully cemented group. The uncemented and partially cemented groups did not survive the full 50,000 cycles; however the self-pressurizing design had significantly less motion than the traditional design (P < .001). No differences between component designs were found in the fully cemented group at 50,000 cycles. The self-pressurizing glenoid component had 0.005% radiographic radiolucent lines, and the traditional glenoid component had 45% radiographic radiolucent lines, with 38% of the radiolucencies in the traditional glenoid component group being defined as grade E. There were no progressive radiolucencies, differences in clinical outcomes, or complications at 2 years postoperatively. CONCLUSION: In the fully cemented condition, the 2 component designs had comparable performance; however, the differences in designs could be better observed in the uncemented group. The self-pressurizing all-polyethylene design studied has superior biomechanical stability. Clinically, the improved stability of the glenoid component correlated with a reduction of radiolucent lines and will likely lead to a reduction in glenoid component loosening.

Dermal allograft superior capsule reconstruction biomechanics and kinematics.

PURPOSE: To investigate the effect of a dermal allograft superior capsule reconstruction (SCR) on kinematics and joint pressure biomechanics immediately after simulated superior irreparable rotator cuff tear. METHODS: This controlled laboratory study tested 8 fresh-frozen cadaveric shoulders using a custom test frame. Balanced loading configuration centered the humeral head on the glenoid, and unbalanced load created a force pulling the head toward the acromion. Experimental conditions included the intact rotator cuff, irreparable supraspinatus tear (ISST), and dermal allograft SCR. A digital sensor measured glenohumeral and subacromial contact pressure maps, and a microscribe measured the acromion-humeral distance. RESULTS: Glenohumeral contact pressure of ISST was 175% (295 ± 44 kPa; P = .018) of the intact rotator cuff value (169 ± 10 kPa) at 0° in the balanced condition and 176% (P = .048) of intact at 30°. SCR decreased glenohumeral contact pressure to 110% (185 ± 27 kPa; P = .044) of intact at 0° and to 95% (P = .034) at 30°. Unbalanced ISST contact pressure was 146% (365 ± 23 kPa; P = .009) of intact (250 ± 24 kPa) at 0° and 122% (P = .045) at 60°. SCR decreased contact pressures to 110% (274 ± 21 kPa; P = .039) of intact at 0° and to 89% (P = .003) at 60°. ISST increased superior migration of the humeral head, decreasing the acromion-humeral distance by 3.0 ± 0.6 mm (P = .006) in the unbalanced condition at 0°. SCR increased the acromion-humeral distance to a value similar to that of the intact cuff (P = .003). SCR significantly lowered subacromial pressures in the unbalanced condition. CONCLUSIONS: In an irreparable supraspinatus tear model, the dermal allograft SCR showed competency in stabilizing the glenohumeral joint, decreasing glenohumeral and subacromial contact pressures, and increasing the acromion-humeral distance.

Synthetic coracoclavicular ligament vs. coracoclavicular suspensory construct for treatment of acromioclavicular dislocation: a biomechanical study.

BACKGROUND: A synthetic ligament (LockDown, Worcestershire, England) has become available to treat complete acromioclavicular dislocation with promising clinical results and potential benefit to avoid postoperative loss of reduction. We investigated the biomechanics of this synthetic ligament in a simulated immediate postoperative rehabilitation setting, hypothesizing that the synthetic ligament would demonstrate less superior coracoclavicular displacement to cyclic loading and higher ultimate load-to-failure values than a coracoclavicular suspensory construct. METHODS: Seven matched-pair cadaveric shoulders (mean age at time of death, 79 years) were loaded cyclically and to failure. One specimen in each pair was randomly assigned to the synthetic ligament or coracoclavicular suspensory construct. Superiorly directed 70-N cyclic loading for 3000 cycles at 1.0 Hz was applied through the clavicle in a fixed scapula simulating physiologic states during immediate postoperative rehabilitation, followed by a load-to-failure test at 120 mm/min. RESULTS: After 3000 cycles, the superior displacement of the clavicle in the synthetic ligament (9.2 ± 1.1 mm) was 225% greater than in the coracoclavicular suspensory construct (2.8 ± 0.4 mm, 95% confidence interval [CI] 3.4, 8.3; P < .001). Average stiffness of the synthetic ligament (32.8 N/mm) was 60% lower than that of the coracoclavicular suspensory construct (81.9 N/mm, 95% CI 43.3, 54.9; P < .001). Ultimate load-to-failure of the synthetic ligament was 23% (95% CI 37.9, 301.5; P = .016) lower than the coracoclavicular suspensory construct (580.5 ± 85.1 N and 750.2 ± 135.5 N, respectively). CONCLUSION: In a simulated immediate postoperative cadaveric model, the synthetic ligament demonstrated poorer biomechanics than the coracoclavicular suspensory construct. These findings suggest that a coracoclavicular suspensory construct may be preferable to a synthetic ligament if early rehabilitation is intended.

Distal triceps transosseous cruciate versus suture anchor repair using equal constructs: a biomechanical comparison.

BACKGROUND/HYPOTHESIS: Suture anchor-based repair has been advocated for repair of distal triceps avulsion, but previous models have used an unequal number of sutures across the repair site. We hypothesized that there would be no difference in triceps tendon displacement between gold standard repair with transosseous cruciate bone tunnels and suture anchor repair with an equal number of sutures in the constructs. METHODS: The triceps tendon footprint was measured in 20 cadaveric elbows (10 matched pairs), and a distal triceps tendon rupture was created. The specimens in each pair were randomly assigned to transosseous cruciate repair or knotless, double-row, anatomic footprint, suture anchor repair. Specimens underwent cyclic loading to 1500 cycles and then load to failure. Footprint uncoverage was measured at 1500 cycles. Data for medial and lateral triceps tendon displacement, footprint uncoverage, and failure load were obtained. RESULTS: Triceps displacement did not differ significantly between the transosseous cruciate and the suture anchor repair group at 1500 cycles on the medial (3.6 ± 0.9 mm vs. 4.3 ± 1.6 mm [mean ± standard deviation], respectively; P = .27) and lateral side (3.1 ± 1.2 mm vs. 2.0 ± 1.2 mm, respectively; P = .06). No other differences were found between the constructs. DISCUSSION/CONCLUSION: Transosseous cruciate distal triceps repair and knotless double-row suture anchor repair using constructs with an equal number of sutures showed no significant difference in tendon displacement at 1500 loading cycles. These findings suggest that the biomechanical strength of an all-suture construct is not different from that of suture anchors for repair of distal triceps avulsions.

Is Dual Semitendinosus Allograft Stronger Than Turndown for Achilles Tendon Reconstruction? An In Vitro Analysis.

BACKGROUND: Large Achilles tendon defects pose a treatment challenge. The standard treatment with a turndown flap requires a large extensile incision, puts the sural nerve at risk, and demands slow, careful rehabilitation. Dual allograft semitendinosus reconstruction is a new clinical alternative that has the theoretical advantages of a smaller incision, less dissection, and a stronger construct that may allow for faster rehabilitation. QUESTIONS/PURPOSES: In a cadaver biomechanical model, we compared the dual allograft semitendinosus reconstruction with the myofascial turndown in terms of (1) mechanical strength and resistance to deformation and (2) failure mechanisms in reconstruction of large segmental Achilles defects. METHODS: An 8-cm segmental Achilles defect was created in 18 cadaveric lower extremities, nine matched pairs without defect or previous surgery (mean age, 78.4 years; range, 60-97 years; three female and six male pairs). Femoral neck densitometry to determine bone mineral density found that all specimens except two were osteopenic or osteoporotic. Specimens in each pair were assigned to allograft or turndown reconstruction. The constructs were mounted on a load frame and differential variable reluctance transducers were applied to measure deformation. Specimens were preconditioned and then loaded axially. Tensile force and proximal and distal construct deformation were measured at clinical failure, defined as 10 mm of displacement, and at ultimate failure, defined as failure of the reconstruction. Failure mechanism was recorded. RESULTS: Tensile strength at time zero was higher in the allograft versus the turndown construct at clinical failure (156.9 ± 29.7 N versus 107.2 ± 20.0 N, respectively; mean difference, -49.7 N; 95% CI, -66.3 to -33.0 N; p < 0.001) and at ultimate failure (290.9 ± 83.2 N versus 140.7 ± 43.5 N, respectively; mean difference, -150.2 N; 95% CI, -202.9 to -97.6 N; p < 0.001). Distal construct deformation was lower in the turndown versus the allograft construct at clinical failure (1.6 ± 1.0 mm versus 4.7 ± 0.7 mm medially and 2.2 ± 1.0 mm versus 4.8 ± 1.1 mm laterally; p < 0.001). Semitendinosus allograft failure occurred via calcaneal bone bridge fracture in eight of nine specimens. All myofascial turndowns failed via suture pullout through the fascial tissue at its insertion. CONCLUSION: In this comparative biomechanical study, dual semitendinosus allograft reconstruction showed greater tensile strength and construct deformation compared with myofascial turndown in a cadaveric model of large Achilles tendon defects. CLINICAL RELEVANCE: Further study of dual semitendinosus allograft for treatment of severe Achilles tendon defects with cyclic loading and investigation of clinical results will better elucidate the clinical utility and indications for this technique.

Interference Screw Versus Suture Anchors for Femoral Fixation in Medial Patellofemoral Ligament Reconstruction: A Biomechanical Study.

BACKGROUND: Femoral-sided graft fixation in medial patellofemoral ligament (MPFL) reconstruction is commonly performed using an interference screw (IS). However, the IS method is associated with several clinical disadvantages that may be ameliorated by the use of suture anchors (SAs) for femoral fixation. PURPOSE: To compare the load to failure and stiffness of SAs versus an IS for the femoral fixation of a semitendinosus autograft in MPFL reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: Based on a priori power analysis, a total of 6 matched pairs of cadaveric knees were included. Specimens in each pair were randomly assigned to receive either SA or IS fixation. After an appropriate reconstruction procedure, the looped end of the MPFL graft was pulled laterally at a rate of 6 mm/s until construct failure. The best-fit slope of the load-displacement curve was then used to calculate the stiffness (N/mm) in a post hoc fashion. A paired t test was used to compare the mean load to failure and the mean stiffness between groups. RESULTS: No significant difference in load to failure was observed between the IS and the SA fixation groups (294.0 ± 61.1 vs 250.0 ± 55.9; P = .352), although the mean stiffness was significantly higher in IS specimens (34.5 ± 9.6 vs 14.7 ± 1.2; P = .004). All IS reconstructions failed by graft pullout from the femoral tunnel, whereas 5 of the 6 SA reconstructions failed by anchor pullout. CONCLUSION: In this biomechanical study using a cadaveric model of MPFL reconstruction, SA femoral fixation was not significantly different from IS fixation in terms of load to failure. The mean load-to-failure values for both reconstruction techniques were greater than the literature-reported values for the native MPFL. CLINICAL RELEVANCE: These results suggest that SAs are a biomechanically viable alternative for femoral-sided graft fixation in MPFL reconstruction.

Contact Pressure between Digital Flexors and Plates for Distal Radius Approaches.

Background Flexor tendon irritation or rupture following open reduction and volar plate fixation of distal radius fractures can cause significant morbidity and necessitate additional surgical intervention. Objectives To compare the impact of the extended flexor carpi radialis (e-FCR) and standard flexor carpi radialis (FCR) approaches on contact pressures between the flexor tendons and volar distal radius plates. Methods Eight matched pairs of fresh frozen cadavers had each limb randomized to undergo either the e-FCR or standard FCR approach. After the approach, a locking plate was applied to the volar distal radius more distally than ideally to create a worst-case scenario for the digital flexor tendons. Electronic pressure sensors were secured to the volar aspect of each locking plate. Each wrist was pinned in 20 degrees of extension during testing. Using a computer-controlled stepper motor system attached to the digital flexor and extensor tendons, the digits were taken through 4,000 cycles simulating 12 weeks of active flexion and extension. Results There were no statistically or clinically significant differences when comparing the contact pressures of the e-FCR approach with the standard FCR approach at any time intervals. The e-FCR had statistically significantly higher radial-sided contact pressures than ulnar-sided contact pressures during early-to-intermediate testing intervals. These differences resolved at late and final testing intervals. Conclusions When comparing the standard FCR approach with the e-FCR approach, with the wrist in 20 degrees of extension, there is no significant difference in contact pressures that occur between the digital flexor tendons and volar distal radius plates. Clinical Relevance Further study and technique modifications may eventually lead to better methods of avoiding flexor tendon rupture during the volar plating of distal radius fractures.

Biomechanics of Biodegradable Subacromial Balloon Spacer for Irreparable Superior Rotator Cuff Tears: Study of a Cadaveric Model.

BACKGROUND: A subacromial balloon spacer is an option to treat irreparable rotator cuff tears. We hypothesized that the balloon would restore glenohumeral contact pressure, the acromion-humeral interval, and deltoid load to intact values after a simulated irreparable supraspinatus tear in a cadaveric model. METHODS: Fourteen cadaveric shoulders (mean age at the time of death, 67.9 years) were tested using a custom test frame. In this frame, glenohumeral contact pressure, the acromion-humeral interval, and deltoid load were measured using a digital sensor, a MicroScribe, and a spring scale, respectively. Test conditions included the intact shoulder, a small supraspinatus tear, supraspinatus repair, repair plus balloon, an irreparable supraspinatus tear (rotator cable-insufficient), and an irreparable tear plus balloon. Load was applied in a simulated neutral arm position (balanced) and active shoulder abduction (unbalanced). RESULTS: When the balloon was inflated over the irreparable supraspinatus tear in the balanced condition, glenohumeral contact pressure increased by 122% (p = 0.006) compared with that for the irreparable tear at 0° of abduction and by 94% (p = 0.046) at 60°. In the unbalanced condition, pressure decreased in the irreparable tear condition after the balloon was inflated, restoring pressure to close to that in the intact state. The balloon did not restore glenohumeral contact area to that in the intact shoulder in either the balanced or the unbalanced condition. The irreparable tear displaced the humeral head superiorly in the unbalanced condition, decreasing the acromion-humeral interval. The balloon moved the head inferiorly by a mean (and standard error of the mean) of 6.2 ± 1.3 mm (p < 0.001) at 0° of abduction, 4.4 ± 1.3 mm (p < 0.001) at 30°, and 3.0 ± 0.8 mm (p < 0.001) at 60°. The balloon increased the deltoid load after an irreparable tear by 8.2% (p = 0.022) at 0°, 12.6% (p = 0.002) at 30°, and 11.1% (p = 0.008) at 60°. CONCLUSIONS: In a cadaveric model of an irreparable supraspinatus tear, a balloon spacer restored intact-state glenohumeral contact pressures at most abduction angles, lowered the humeral head, and increased deltoid load at postoperative time 0. CLINICAL RELEVANCE: This study supports further investigation of the balloon spacer in comparative clinical studies of surgical options for irreparable rotator cuff tears, with clinically relevant evaluation measures and observation periods.

Predictors of variability in the length of surgery of posterior instrumented arthrodesis in patients with adolescent idiopathic scoliosis.

The most common corrective surgery for adolescent idiopathic scoliosis (AIS) is posterior instrumented spinal fusion, which is a relatively lengthy procedure. Longer procedures are known to have higher rates of negative outcomes and higher economic costs across the surgical specialties. The purpose of this study is to identify the factors that influence the length of this operation in AIS patients. This was an institutional review board-approved, retrospective cohort study. All primary posterior instrumented arthrodesis procedures in 2011-2013 performed by three surgeons on AIS patients at a tertiary care hospital were included. Age, race, sex, BMI, Cobb angle, curve flexibility, Lenke classification, number of levels fused, number of screws used, osteotomy use, intraoperative O-arm use, and length of surgery (time from incision to closure) were obtained from the electronic medical record. Multivariable linear regression analysis was used to determine independent predictors of length of surgery, and standardized regression coefficients were calculated to compare the relative magnitude of significant variables. A total of 95 procedures were included. The average length of surgery was 375 ± 72.7 min. The multivariable linear regression analysis contained the variables Cobb angle, number of screws used, osteotomy use, Lenke curve type, surgeon, patient age, and sex. The regression identified the number of screws used [ß=4.72, P=0.003, 95% confidence interval (CI) 1.7-7.8], osteotomy use (ß = 50.2, P = 0.004, 95% CI 16.2-84.1), Lenke type 3 curve (ß = 77.9, P = 0.001, 95% CI 31.7-174), male sex (ß=62.5, P=0.003, 95% CI 21.5-103), the Cobb angle (ß=1.04, P=0.045, 95% CI 0.02-2.1), and the surgeon (ß = 75.2, P < 0.0001, 95% CI 40-110) as independently associated with the length of surgery. The most significant factor associated with operative duration was the surgeon performing the case. We identified male sex, number of screws used, Lenke type 3 curves, osteotomy use, Cobb angle, and the surgeon variable as significantly associated with increased length of surgery in posterior arthrodesis of AIS patients.

Radiographic indicators of a shared epiphysis in radial polydactyly.

BACKGROUND: Thumb epiphyses cannot be visualized on radiographs in infants with radial polydactyly, making it difficult to classify by Wassel type. The purpose of this study was to identify radiographic features that distinguish a separate epiphysis from a shared epiphysis. This may assist in operative planning and establishing prognosis. METHODS: The charts of 34 radial polydactyly patients treated with surgical reconstruction from 2008 through 2012 were retrospectively reviewed. Measurements of the most proximal bones involved in the duplication, including length, width at shaft, width at base, distance between radial and ulnar thumb, and angle between radial and ulnar thumb, were taken from PA radiographs of the thumb by four blinded individuals. The interclass correlation coefficient was calculated to determine inter-observer reliability. Operative notes were reviewed to distinguish between shared and separate epiphyses. Several indices were created from these measurements. RESULTS: Radiographic measurements showed high inter-observer reliability. There were statistically significant differences between patients with separate and shared epiphyses for indices for the width shaft index, interspace distance, the angle × interspace distance, and the angle × interspace index. CONCLUSION: Radiographic differences exist between children with separate and shared epiphyses. In patients with shared epiphyses, the radial thumb tends to be smaller, closer to the ulnar thumb, and less divergent. Threshold values were identified for predicting the status of the epiphysis based on the angle × interspace distance and the angle × interspace index. These values may be used to help determine in advance of surgery if a shared epiphysis exists.