Effects of various load magnitudes on ACL: an in vitro study using adolescent porcine stifle joints.

INTRODUCTION: The escalating incidence of anterior cruciate ligament (ACL) injuries, particularly among adolescents, is a pressing concern. The study of ACL biomechanics in this demographic presents challenges due to the scarcity of cadaveric specimens. This research endeavors to validate the adolescent porcine stifle joint as a fitting model for ACL studies. METHODS: We conducted experiments on 30 fresh porcine stifle knee joints. (Breed: Yorkshire, Weight: avg 90 lbs, Age Range: 2-4 months). They were stored at - 22 °C and a subsequent 24-h thaw at room temperature before being prepared for the experiment. These joints were randomly assigned to three groups. The first group served as a control and underwent only the load-to-failure test. The remaining two groups were subjected to 100 cycles, with forces of 300N and 520N, respectively. The load values of 300N and 520N correspond to three and five times the body weight (BW) of our juvenile porcine, respectively. RESULT: The 520N force demonstrated a higher strain than the 300N, indicating a direct correlation between ACL strain and augmented loads. A significant difference in load-to-failure (p = 0.014) was observed between non-cyclically loaded ACLs and those subjected to 100 cycles at 520N. Three of the ten samples in the 520N group failed before completing 100 cycles. The ruptured ACLs from these tests closely resembled adolescent ACL injuries in detachment patterns. ACL stiffness was also measured post-cyclical loading by applying force and pulling the ACL at a rate of 1 mm per sec. Moreover, ACL stiffness measurements decreased from 152.46 N/mm in the control group to 129.42 N/mm after 100 cycles at 300N and a more significant drop to 86.90 N/mm after 100 cycles at 520N. A one-way analysis of variance (ANOVA) and t-test were chosen for statistical analysis. CONCLUSIONS: The porcine stifle joint is an appropriate model for understanding ACL biomechanics in the skeletally immature demographic. The results emphasize the ligament's susceptibility to injury under high-impact loads pertinent to sports activities. The study advocates for further research into different loading scenarios and the protective role of muscle co-activation in ACL injury prevention.

Precision soft tissue balancing: grid-assisted pie-crusting in total knee arthroplasty.

Introduction: The varus and valgus knee deformities result from imbalance in tension between medial and lateral soft tissue compartments. These conditions need to be addressed during total knee arthroplasty (TKA). However, there is no consensus on optimal soft-tissue release techniques for correcting varus and valgus deformities during TKA. We assessed the efficacy of a novel grid-based pie-crusting technique on soft-tissue release. Methods: Cadaver knees were dissected, leaving only the femur and tibia connected by an isolated MCL or the femur and fibula connected by an isolated LCL. Bone cuts were made as performed during primary TKA. Mechanical testing was performed using an MTS machine. A 3D-printed 12-hole grid was placed directly over the MCL and LCL. Using an 18-gauge needle, horizontal in-out perforations were made 3 mm apart. Deformation and stiffness of the ligaments were collected after every 2 perforations. Means were calculated, and regression analyses were performed. Results: A total of 7 MCL and 6 LCL knees were included in our analysis. The mean medial femorotibial (MFT) space increased from 6.018 ± 1.4 mm-7.078 ± 1.414 mm (R2 = 0.937) following 12 perforations. The mean MCL stiffness decreased from 32.15 N/mm-26.57 N/mm (R2 = 0.965). For the LCL group, the mean gap between the femur and fibula increased from 4.287 mm-4.550 mm following 8 perforations. The mean LCL stiffness decreased from 29.955 N/mm-25.851 N/mm. LCL stiffness displayed a strong inverse relationship with the number of holes performed (R2 = 0.988). Discussion: Our results suggest that using this novel grid for pie-crusting of the MCL and LCL allows for gradual lengthening of the ligaments without sacrificing their structural integrity. Our proposed technique may serve as a valuable piece in the soft-tissue release toolkit for orthopaedic surgeons performing TKA in varus and valgus deformed knees.

Deep learning automation of radiographic patterns for hallux valgus diagnosis.

Artificial intelligence (AI) and deep learning are becoming increasingly powerful tools in diagnostic and radiographic medicine. Deep learning has already been utilized for automated detection of pneumonia from chest radiographs, diabetic retinopathy, breast cancer, skin carcinoma classification, and metastatic lymphadenopathy detection, with diagnostic reliability akin to medical experts. In the World Journal of Orthopedics article, the authors apply an automated and AI-assisted technique to determine the hallux valgus angle (HVA) for assessing HV foot deformity. With the U-net neural network, the authors constructed an algorithm for pattern recognition of HV foot deformity from anteroposterior high-resolution radiographs. The performance of the deep learning algorithm was compared to expert clinician manual performance and assessed alongside clinician-clinician variability. The authors found that the AI tool was sufficient in assessing HVA and proposed the system as an instrument to augment clinical efficiency. Though further sophistication is needed to establish automated algorithms for more complicated foot pathologies, this work adds to the growing evidence supporting AI as a powerful diagnostic tool.

Predicting Metacarpal Anatomic Lengths via Adjacent Metacarpals.

Purpose: The purpose of this study is to generate validated prediction rules for metacarpal lengths that can be applied without the need for computation tools to assist with restoration of anatomic length after fracture and utilizes only ipsilateral metacarpals. Methods: The anatomic lengths of all hand bones in 50 hands (25 men, 25 women) were used along with linear regression subset analysis to determine which metacarpals are the most predictive of each other. The most predictive metacarpals were then used to generate simple addition and subtraction prediction rules via simplifying the linear equation generated with linear regression analysis. Those rules were then applied to subsequent test cases, and percent accuracy within various cutoffs were analyzed and compared to the accuracy when using the contralateral side. Results: The prediction rules were generated and were found to be identical for both men and women. When applied to the test cases, the estimated metacarpal lengths were within 3 mm of the actual value in 97.5% of the cases for women and 90% of the cases for men compared to 95% when using the contralateral side. Conclusion: The simple additional and subtraction rules generated in this analysis were as good as or superior to using the contralateral side in all cases for women and were as good as or superior to using the contralateral side in for metacarpals 3-5 for men. Clinical Relevance: Using these simple estimating rules may be superior to using the contralateral side in most cases and provides a secondary method for determining anatomic lengths when contralateral radiographs are not available or when contralateral radiographs were obtained in different enough conditions such that the lengths may not be representative of the hand of interest.

Comparative study of locking neutralization plate construct versus tension band wiring with a cannulated screw for patella fractures: experimental and finite element analysis.

Transverse patella fractures, accounting for approximately 1% of Orthopedic injuries, pose intricate challenges due to their vital role in knee mechanics. This study aimed to compare the biomechanical performance of a construct, integrating cannulated screws and an anterior locking neutralization plate, with the conventional tension band wiring technique for treating these fractures. Experimental testing and Finite Element Analysis were employed to evaluate the constructs and gain profound insights into their mechanical behavior. Sixteen cadaveric knees were prepared, and transverse patella fractures were induced at the midpoints using a saw. The plate construct and tension band wire fixation were randomly assigned to the specimens. A cyclic test evaluated the implants' durability and stability, simulating knee movement during extension and flexion. Tensile testing assessed the implants' maximum failure force after cyclic testing, while Finite Element Analysis provided detailed insights into stress distribution and deformation patterns. Statistical analysis was exclusively performed for the experimental data. Results showed the plate enhanced stability with significantly lower deformation (0.09 ± 0.12 mm) compared to wire fixation (0.77 ± 0.54 mm) after 500 cycles (p = 0.004). In tensile testing, the construct also demonstrated higher failure resistance (1359 ± 21.53 N) than wire fixation (780.1 ± 22.62N) (p = 0.007). Finite Element Analysis highlighted distinct stress patterns, validating the construct's superiority. This research presents a promising treatment approach for transverse patella fractures with potential clinical impact and future research prospects. This study presents a promising advancement in addressing the intricate challenges of transverse patella fractures, with implications for refining clinical practice. The construct's improved stability and resistance to failure offer potential benefits in postoperative management and patient outcomes.

Investigating the effect of autograft diameter for quadriceps and patellar tendons use in anterior cruciate ligament reconstruction: a biomechanical analysis using a simulated Lachman test.

Introduction: Current clinical practice suggests using patellar and quadriceps tendon autografts with a 10 mm diameter for ACL reconstruction. This can be problematic for patients with smaller body frames. Our study objective was to determine the minimum diameter required for these grafts. We hypothesize that given the strength and stiffness of these respective tissues, they can withstand a significant decrease in diameter before demonstrating mechanical strength unviable for recreating the knee's stability. Methods: We created a finite element model of the human knee with boundary conditions characteristic of the Lachman test, a passive accessory movement test of the knee performed to identify the integrity of the anterior cruciate ligament (ACL). The Mechanical properties of the model's grafts were directly obtained from cadaveric testing and the literature. Our model estimated the forces required to displace the tibia from the femur with varying graft diameters. Results: The 7 mm diameter patellar and quadriceps tendon grafts could withstand 55-60 N of force before induced tibial displacement. However, grafts of 5.34- and 3.76-mm diameters could only withstand upwards of 47 N and 40 N, respectively. Additionally, at a graft diameter of 3.76 mm, the patellar tendon experienced 234% greater stiffness than the quadriceps tendon, with similar excesses of stiffness demonstrated for the 5.34- and 7-mm diameter grafts. Conclusions: The patellar tendon provided a stronger graft for knee reconstruction at all diameter sizes. Additionally, it experienced higher maximum stress, meaning it dissociates force better across the graft than the quadriceps tendon. Significantly lower amounts of force were required to displace the tibia for the patellar and quadriceps tendon grafts at 3.76- and 5.34-mm graft diameters. Based on this point, we conclude that grafts below the 7 mm diameter have a higher chance of failure regardless of graft selection.

The Effect of Metacarpal Shortening on Finger Strength and Joint Motion: A Cadaveric Biomechanical Study.

Purpose: Discrepancies exist between previous biomechanical and clinical studies when determining acceptable metacarpal shortening after metacarpal fractures. This study aimed to determine the amount of acceptable shortening after a metacarpal fracture before finger motion and strength is compromised. Methods: We defrosted ten fresh-frozen cadaveric hands. A screw-driven external fixator was placed to stabilize the metacarpal, then a 15.0-mm section of the index metacarpal was excised and replaced with a three dimensional-printed, custom-designed polyethylene insert. The hand was then mounted on a custom testing rig, and the index finger was flexed using the flexor digitorum profundus tendon. Joint angles and fingertip force were recorded as the finger was flexed. Incrementally smaller inserts were placed, and testing was repeated. Results: The average joint angles of the intact condition for the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints were (54 [SD = 13], 79 [SD = 21], and 73 [SD = 10]), respectively. There were no statistically significant changes to any joint angle with any amount of shortening. The maximal fingertip contact pressures were 41 N (17), 31 N (12), 24 N (14), 19 N, (11), and 14 N (8) for the 15 mm, 12.5 mm, 10 mm, 7.5 mm, and 5 mm inserts, respectively. All changes in fingertip force by insert size were statistically significant. Conclusion: Metacarpal shortening does not affect flexion range of motion regardless of the amount of shortening, but it significantly affects finger strength. The loss of strength after shortening was approximately 6.5% per mm of shortening for the fractured metacarpal. Clinical Relevance: When viewed in the context of the hand as a whole and the contribution of the index finger to grip being only 23.5%, it is unlikely that any shortening will significantly affect the average patient regarding grip strength. However, for a patient who requires fine motor strength, any amount of shortening may affect their finger function and needs to be addressed.

Analysis of abduction moment arms after rotator cuff tear and acellular dermal matrix allograft reconstruction.

BACKGROUND: Biomechanical testing of abduction moment arms presents a useful method to assess the contributions of individual rotator cuff muscles to glenohumeral function. This study aimed to investigate the changes in abduction moment arms after the treatment of supraspinatus tears with superior capsular reconstruction (SCR), bursal acromial reconstruction (BAR), and a combined SCR-BAR procedure, all with human dermal allograft. METHODS: We tested 7 fresh-frozen cadaveric specimens under 6 conditions: (1) intact, (2) 50% supraspinatus tear (partial tear), (3) 100% supraspinatus tear, (4) SCR, (5) SCR combined with BAR, and (6) BAR. In each condition, the moment arms for the individual muscles of the teres minor, subscapularis, and infraspinatus were calculated throughout 90° of abduction using a motion capture system. Analysis of variance and post hoc Tukey testing were performed to determine significance. RESULTS: In the teres minor, the moment arms in the SCR (11.9 mm), BAR (10.1 mm), and SCR-BAR (11.9 mm) conditions were greater than those in the intact (8.5 mm; P = .001, P = .001, and P = .001, respectively), partial tear (9.1 mm; P = .001, P = .128, and P = .001, respectively), and complete tear (8.8 mm; P = .001, P = .011, and P = .001, respectively) conditions. Similarly, in the subscapularis, the moment arms in the SCR (13.4 mm), BAR (13.8 mm), and SCR-BAR (13.5 mm) conditions were greater than those in the intact (10.6 mm; P = .006, P = .001, and P = .003, respectively) and partial tear (10.4 mm; P = .006, P = .001, and P = .003, respectively) conditions. In the teres minor, the SCR (11.9 mm) and SCR-BAR (11.9 mm) conditions were also found to have significantly increased moment arms compared with the BAR condition (10.1 mm; P = .001 and P = .001, respectively). In the infraspinatus, the BAR condition (13.8 mm) was found to have a significantly decreased moment arm compared with the partial tear condition (15.8 mm, P = .026), with no other significant findings between conditions. CONCLUSION: Our results suggest that the moment arm contributions of the individual muscles comprising the rotator cuff can change after reconstruction to compensate for tears. SCR and SCR-BAR increase the moment arms in the teres minor and subscapularis, potentially allowing for increased abduction ability.

Assessment of Cervical and Lumbar Kinematics in Simulated Open and Closed Kinetic Chain.

BACKGROUND: The pelvic girdle and spine vertebral column work as a long chain influenced by pelvic tilt. This study aims to assess the effect of open and closed chain anterior pelvic tilt (APT) or posterior pelvic tilt (PPT) on cervical and lumbar spine kinematics using an in vitro cadaveric spine model. METHODS: Three human cadaveric spines with intact pelvis were suspended with the skull fixed in a metal frame. Optotrak 3-dimensional motion system captured coordinates of pin markers at 24 different points for real-time tracking of cervical and lumbar regions. Additional geometric parameters were measured to calculate pelvic incidence and pelvic tilt. A force-torque digital gauge applied consistent force to standardize the acetabular or sacral axis' APT and PPT during simulated open- and closed-chain movements, respectively. RESULTS: In closed-chain PPT, significant differences in relative intervertebral decompression were noted between spinal levels C2/C3 (4.85 mm) and C5/C6 (1.26 mm), while compression was noted between L1/L2 (-2.54 mm) and L5/S1 (-11.84 mm) and between L3/L4 (-2.78 mm) and L5/S1 (-11.84 mm) (P < 0.05). Displacement during closed-chain PPT was significantly greater than during open-chain PPT for cervical and lumbar spines. In closed-chain APT, significant differences in relative intervertebral decompression were noted between spinal levels L1/L2 (2.87 mm) and L5/S1 (24.48 mm) and between L3/L4 (2.94 mm) and L5/S1 (24.48 mm) (P < 0.05). Pelvic incidence remained the same as the pelvis tilted anterior and posterior. CONCLUSIONS: In PPT, open-chain pelvic tilts did not produce as much cervical and lumbar intervertebral displacement compared with closed-chain pelvic tilts. In contrast, APT saw fewer differences between open- and closed-chain tilting. There was a reciprocal relationship between pelvic tilt and sacral slope, producing a constant pelvic incidence throughout all pelvic tilt angles. CLINICAL RELEVANCE: The results of this study may help determine how a patient's pelvic tilt is causing pain and using that knowledge to guide rehabilitation of stabilizing muscles. The data produced here may also be helpful in determining which rehabilitation exercises may be more difficult or prone to injury for patients with either excessive anterior or posterior pelvic tilt.

Long Head of the Biceps Autograft Performs Biomechanically Similar to Human Dermal Allograft for Superior Capsule Reconstruction After Rotator Cuff Tear.

PURPOSE: To provide a biomechanical comparison between human dermal (HD) allograft and long head of biceps tendon (LHBT) autograft with and without posterior side-to-side suturing for superior capsule reconstruction. METHODS: Eight fresh-frozen cadaveric shoulder specimens were tested in 5 conditions: (1) intact, (2) complete supraspinatus tear, (3) LHBT, (4) LHBT with side-to-side suturing, and (5) HD allograft with side-to-side suturing. Functional abduction force, superior translation of humeral head, translational range of motion, and rotational range of motion were tested at 0°, 30°, 60°, and 90° of abduction within each condition. Data were analyzed using analysis of variance with post-hoc Tukey testing for pairwise comparison, with a significance value set at .05. RESULTS: Functional abduction force in the LHBT, LHBT + suture, and HD + suture conditions was significantly increased compared with the supraspinatus tear condition at abduction angles of 30° (P = .011, .001, and .017, respectively), 60° (P = .004, .001, and .002, respectively), and 90° (P = .013, .001, and .038, respectively). In addition, superior translation of the humeral head in the LHBT, LHBT + suture, and HD + suture conditions was significantly decreased compared with the tear condition at abduction angles of 30° (P = .03, .049, .03, respectively) and 60° (P = .02, .04, .03, respectively). All 3 reconstructive techniques were statistically identical to the intact rotator cuff condition in regard to translational and rotational range of motion. CONCLUSIONS: Superior capsule reconstruction with LHBT autograft without side-to-side suturing, LHBT with posterior side-to-side suturing, and HD allograft with posterior side-to-side suturing all equivalently restore functional abduction force and decrease superior translation of the humeral head after a complete supraspinatus tear. CLINICAL RELEVANCE: Superior capsule reconstruction with long head of the biceps tendon autograft and human dermal allograft both restore functional abduction force and decrease superior translation of the humeral head, while displaying no losses in the range of motion in a cadaveric model.

Glenoid Prosthesis Design Considerations in Anatomic Total Shoulder Arthroplasty.

Total shoulder arthroplasty is an increasingly popular option for the treatment of glenohumeral arthritis. Historically, the effectiveness of the procedure has largely been determined by the long-term stability of the glenoid component. Glenoid component loosening can lead to clinically concerning complications including pain with movement, loss of function, and accumulation of debris which may require surgery to revise. In response, there has been a push to optimize the design of the glenoid prosthesis. Traditional contemporary glenoid components use pegs for fixation and are made entirely of polyethylene. Variations on the standard implant include keeled, metal-backed, hybrid, augmented, and inlay designs. There is a wealth of biomechanical and clinical studies that report on the effectiveness of these different designs. The purpose of this review is to summarize existing literature regarding glenoid component design and identify key areas for future research. Knowledge of the rationale underlying glenoid design will help surgeons select the best component for their patients and optimize outcomes following TSA.

Evaluation of A2 and A4 Hand Pulley Repair Using Tendon Graft Rings.

PURPOSE: To compare the mechanical characteristics of A2 and combined A2-A4 pulley repair in the intact and damaged flexor pulley system. METHODS: After control testing, we recorded tendon excursion and flexion of 11 cadaveric fingers after several interventions: (1) complete excision of A2 and A4, (2) repair of the A2 with one ring of tendon graft, (3) repair of the A2 with 2 rings of tendon graft, and (4) repair of the A2 with 2 rings combined with repair the A4 with one ring. RESULTS: At the proximal interphalangeal (PIP) joint, the maximum rotational angle decreased by an average of 30% after complete excision of the A2 and A4 pulleys. This angle was still decreased compared with the control by an average of 25% after one-ring repair at A2, 23% after 2-ring repair at A2, and 17% after 2-ring repair at A2 combined with one-ring repair at A4. At the metacarpophalangeal joint, the average maximum rotational angle decreased by an average of 17% after complete excision of the A2 and A4 pulleys. This angle was still decreased compared with the control by an average of 11% after one-ring repair at A2, 7% after 2-ring repair at A2, and 4% after 2-ring repair at A2 combined with one-ring repair at A4. Kinematic behavior at the PIP joint with an intact pulley system was most closely approximated by the 3-loop repair. The least similar behavior was with a 2-ring construct at A2. CONCLUSIONS: All repairs increased average flexion at the PIP and metacarpophalangeal joints compared with the unrepaired samples. The 3-ring configuration exhibited a higher recovery of PIP flexion compared with the other repairs. CLINICAL RELEVANCE: Although each repair restored flexion, clinical studies are necessary to evaluate the clinical relevance of the mechanical results of this study.

Biomechanical effects of superior capsular reconstruction in a rotator cuff-deficient shoulder: a cadaveric study.

BACKGROUND: Superior capsular reconstruction (SCR) has been gaining popularity as a treatment for irreparable rotator cuff tears (RCTs), especially in younger patients. This biomechanical study aimed to investigate how SCR affects functional abduction force, humeral head migration, and passive range of motion following an irreparable RCT. We hypothesized that SCR will restore these parameters to nearly intact shoulder levels. METHODS: Six fresh-frozen cadaveric shoulders were evaluated using a custom biomechanical testing apparatus. Each shoulder was taken through 3 conditions: (1) intact (control); (2) irreparable, complete supraspinatus (SS) tear; and (3) SCR. Functional abduction force, superior humeral head migration, and passive range of motion, including axial shoulder rotation, were measured in static condition at 0°, 30°, and 60° of glenohumeral abduction. Data were analyzed using the paired Student t test or Wilcoxon signed rank test, depending on the results of normality testing. RESULTS: The irreparable SS tear resulted in significantly lower functional abduction force at 30° of abduction (P = .01) and a trend toward a decrease (P = .17) at 60° compared with the intact configuration. SCR shoulders produced greater functional force at 0° compared with the tear configuration (P = .046). Humeral head migration was significantly increased by 4.4 and 3.0 mm at 0° and 30° of abduction, respectively, when comparing the intact vs. SS tear configurations (P = .001). SCR decreased superior migration down to levels of intact shoulders at 0° and 30° of abduction (P = .008 and P = .013, respectively) and was not significantly different from the intact configuration at any angle. SCR decreased passive shoulder extension compared with the tear configuration and increased abduction compared with the intact configuration (P = .007 and P = .03, respectively). The overall arc of axial rotation was not significantly different between SCR and the intact configuration at any angle. CONCLUSIONS: In the setting of an irreparable SS tear, SCR restores key biomechanical parameters of the shoulder to intact levels. SCR should be considered for qualifying patients with irreparable RCTs.

Pullout Strength After Multiple Reinsertions in Radial Bone Fixation.

Background: Due to bone cutting loss from self-tapping screws (STS), progressive destruction of bone can occur with each reinsertion during surgery. When considering the use of jigs that utilize multiple insertions such as those seen in ulnar and radial shortening osteotomy systems, or scenarios where a screw needs to be removed and reinserted due to some technical issue, this can be concerning, as multiple studies examining the effects of multiple reinsertions and the relationship between insertional torque and pullout strength have had mixed results. Methods: Insertional torque and pullout strength were experimentally measured following multiple reinsertions of STS for up to 5 total insertions for various densities and locations along radial sawbone shafts. Results: Torque and pullout strength were significantly greater in middle segments of the radial shaft. Our trials corroborate previous literature regarding a significant reduction in fixation between 1 and 2 insertions; beyond this, there was no significant difference between pullout strength across all segment locations as well as bone densities for 3 to 5 insertions. There was a moderate to high correlation of insertional torque to pullout strength noted across all bone densities and segments (Pearson r = 0.663, P < .001). Conclusion: While reinsertion of STS between 1 and 2 insertions has been shown to significantly differ in pullout strength, beyond this, there does not appear to be a significant difference in up to 5 insertions at any specific region of radial bone across a range of sawbone densities. Further insertions may be considered with caution.

Superior Capsule Reconstruction With Subacromial Allograft Spacer: Biomechanical Cadaveric Study of Subacromial Contact Pressure and Superior Humeral Head Translation.

PURPOSE: To investigate the biomechanical effects of superior capsule reconstruction with subacromial allograft spacer on superior humeral head translation and subacromial contact pressure. METHODS: Eight cadaveric shoulder specimens were tested in 4 conditions: (1) intact rotator cuff, (2) supraspinatus tear and superior capsule excision, (3) superior capsule reconstruction with human dermal allograft, and (4) superior capsule reconstruction with subacromial resurfacing using human dermal allograft. In each condition, specimens were tested at 0, 30, 60, and 90° of shoulder abduction in balanced and unbalanced loaded states for subacromial contact pressure and superior humeral head translation. Statistical comparisons were made using a repeated-measures analysis of variance test, followed by a Tukey post hoc test for pairwise comparisons. A P value <.05 was set as statistically significant. RESULTS: Superior humeral head translation and subacromial contact pressure were increased after irreparable rotator cuff tear (P = .001). There was no significant difference between superior capsule reconstruction and intact cuff in regard to superior humeral head translation and subacromial contact pressure at all abduction angles. Superior capsule reconstruction with subacromial resurfacing decreased superior humeral head translation relative to intact (0°, P = .004; 30°, P = .02; 60°, P = .08; 90°, P = .01), superior capsule reconstruction (0°, P = .001; 30°, P = .003; 60°, P = .019; 90°, P = .001), and cuff-deficient states (P = .001). Superior capsule reconstruction with subacromial resurfacing resulted in nonsignificant increases in subacromial contact pressure relative to intact cuff at 0 to 90° abduction angles. CONCLUSIONS: Superior capsule reconstruction with subacromial resurfacing using human dermal allograft results in decreased superior humeral head translation relative to superior capsule reconstruction with human dermal allograft only, while increasing subacromial contact pressure. CLINICAL RELEVANCE: Superior capsule reconstruction with subacromial resurfacing using human dermal allograft reduces superior humeral head translation while increasing subacromial contact pressure in a cadaveric model.

Is Arthroscopic Transosseous Rotator Cuff Repair Strength Dependent on the Tunnel Angle?

BACKGROUND: Previous studies have aimed to biomechanically improve the transosseous tunnel technique of rotator cuff repair. However, no previous work has addressed tunnel inclination at the time of surgery as an influence on the strength of the repair construct. HYPOTHESIS: We hypothesized that the tunnel angle and entry point would influence the biomechanical strength of the transosseous tunnel in rotator cuff repair. Additionally, we investigated how tunnel length and bone quality affect the strength of the repair construct. STUDY DESIGN: Controlled laboratory study. METHODS: Mechanical testing was performed on 10 cadaveric humeri. Variations in the bone tunnel angle were imposed in the supraspinatus footprint to create lateral tunnels with inclinations of 30°, 45°, and 90° relative to the longitudinal axis of the humeral shaft. A closed loop of suture was passed through the bone tunnel, and cyclic loading was applied until failure of the construct. Load to failure and distance between entry points were the dependent variables. Analysis of variance, post hoc paired t tests, and the Bonferroni correction were used to analyze the relationship between the tunnel angle and failure load. The Pearson correlation coefficient was then used to evaluate the correlation of the distance between entry points to the ultimate failure load, and t tests were used to compare failure loads between healthy and osteoporotic bone. RESULTS: Tunnels drilled perpendicularly to the longitudinal axis (90°) achieved the highest mean failure load (167.51 ± 48.35 N). However, there were no significant differences in the failure load among the 3 tested inclinations. Tunnels drilled perpendicularly to the longitudinal axis (90°) measured 13.86 ± 1.35 mm between entry points and were significantly longer (P = .03) than the tunnels drilled at 30° and 45°. We found no correlation of the distance between entry points and the ultimate failure load. Within the scope of this study, we could not identify a significant effect of bone quality on failure load. CONCLUSION: The tunnel angle does not influence the strength of the bone-suture interface in the transosseous rotator cuff repair construct. CLINICAL RELEVANCE: The transosseous technique has gained popularity in recent years, given its arthroscopic use. These findings suggest that surgeons should not focus on the tunnel angle as they seek to maximize repair strength.

Currently Adopted Criteria for Pedicle Screw Diameter Selection.

BACKGROUND: Transpedicular screw insertion has become widely accepted for the correction of spinal deformity as well as degenerative and traumatic injury, but adoption of this technique has remained less widespread in the thoracic compared to the lumbar spine. This is thought to be associated with the relative technical difficulty of screw insertion into the narrower widths of the thoracic pedicles and the neurologic and mechanical risks associated with breach of the pedicle wall. The surgical decision making involves determining the appropriate sized screw for maximum fixation strength while simultaneously respecting the structural integrity of the vertebral pedicles to prevent a breach and provide better fixation. This paper presents a systematic review of criteria for thoracic pedicle screw diameter (SD) selection in order to orient inexperienced surgeons on the impact of this selection on pedicle breaching and fixation strength. METHODS: We performed a systematic literature review focused on studies reporting SD selection in relation to pedicle dimensions, measures of fixation strength, and breach rate. RESULTS: Twenty-nine articles that measured fixation strength, breach rate, and/or provided SD in relation to pedicle width were selected for inclusion. CONCLUSIONS: A commonly accepted criteria for pedicle SD selection has not yet been proposed. Screw diameters approximately 80% of the pedicle width have been adopted, but this proportion is rarely reported in the midthoracic vertebrae for which smaller pedicles and inadequate hardware specificity result in higher breach rates. Depending upon the insertion technique adopted, greater specificity in diameter selection by vertebral level should be pursued in order to maximally target cortical bone purchase. CLINICAL RELEVANCE: Based on this review of the literature, we believe that proper selection of the SD for individual vertebral level directly affects the insertion technique and the potential breach.

Pedicle Screw With Increased Cortical Purchase Can Be Inserted With Same Accuracy as the Screw in Straightforward Trajectory Using 3D Modeling Landmarks.

STUDY DESIGN: Comparison, in terms of insertion accuracy and biomechanical performance, between an increased cortical purchase and straightforward pedicle screw trajectory. OBJECTIVE: This study aims to compare a trajectory with increased cortical purchase to the more common straightforward trajectory in terms of strength and insertion accuracy using real-time navigation. SUMMARY OF BACKGROUND DATA: In previous studies, it was suggested that pedicle screw pullout strength is strongly correlated with bone mineral density, and using a more cortical tract allows a greater portion of the denser bone, the cortex, to be in contact with the screw. In light of this advantage, an insertion technique has been proposed more recently, to increase the cortical purchase to maximize screw thread contact with cortical bone. It is performed inserting the screw with reduced transverse inclination and results in cortical bone purchase in the lateral portion of the pedicle. METHODS: Eight T1 and eight T3 vertebra models were reconstructed in Mimics Suite (Materialise, Leuven, Belgium) using CT data obtained with a Medtronic O-arm. Using a previously developed computer algorithm, we calculated all achievable safe trajectories for pedicle screw placement ensuring a minimal distance of 0.5 mm between screw and pedicle edges. For both vertebrae, among these, the straightest and the most convergent trajectories with the calculated insertion region greater than 15% of the total were selected to safely instrument the vertebrae, respectively, as ICP and straightforward techniques. The straightforward technique was planned with a transverse angle of 22.50° in both vertebrae whereas the ICP was planned with a transverse angle of 12.50° for T1 and 2.5° for T3. The screws were implanted by a surgeon experienced in straightforward insertion, and other independent investigators measured placement accuracy and mechanical performance. RESULTS: The transverse screw angles for T1 and T3 with straightforward technique had average values of 24.93° ± 2.96° and 23.53° ± 2.70°, respectively. For the ICP technique, the average values were 15.60° ± 2.95° for T1 and 2.29° ± 1.55° for T3. The resultant errors associated with screw placement for T1 and T3 were not significantly different (p > .05). The pullout failure loads with straightforward techniques ranged from 756 ± 164 N in T1 to 703 ± 74 N in T3 and were not significantly different (p > .05) from the values of 699 ± 84 N for T1 and of 732 ± 113 N measured for the ICP. CONCLUSIONS: For the upper thoracic vertebrae tested, despite the use of shorter screws, the insertion technique with increased cortical purchase, in biomechanical terms, is comparable with the straightforward trajectory. Using guidance, the proposed ICP technique was performed with the same accuracy as the popular straightforward technique. LEVEL OF EVIDENCE: Level V.

Biomechanics of the Acute Boutonniere Deformity.

PURPOSE: To demonstrate which structures of the extensor mechanism create a boutonniere deformity, when damaged, in a cadaver model. An analysis of how damage to these anatomical structures affects the biomechanical performance of the extensor mechanism was also performed. METHODS: We secured 18 fresh cadaveric hands onto an apparatus consisting of a computer-controlled motor and tensiometer attached in series to the extensor communis tendon of the ring and middle digits. The central slip, transverse, and oblique fibers of the interosseous hood and the triangular ligament were sequentially divided. After each structure was divided, the motors were activated to provide a constant tendon displacement force. The angular displacement at the proximal interphalangeal (PIP) and distal interphalangeal joints was recorded. RESULTS: In all digits, detachment of the central slip from the middle phalanx produced a decrease in extension of the PIP joint. When the transverse and oblique fibers of the interosseous hood were also divided, extension at the PIP joint was further decreased. A boutonniere deformity occurred only when all 3 structures were damaged. CONCLUSIONS: The boutonniere deformity requires subluxation of the lateral bands volar to the axis of rotation of the PIP joint. This study demonstrates that damage to the central slip alone does not cause the deformity. Combined injury of the central slip, triangular ligament, and transverse and oblique fibers of the interosseous hood causes a boutonniere deformity. CLINICAL RELEVANCE: Division of the central slip leads to loss of extension at the PIP joint. A more substantial loss of extension after injury or development of a boutonniere deformity should alert clinicians that other structures of the extensor mechanism are also damaged.