Optimal assessment for anterior talofibular ligament injury utilizing stress ultrasound entails internal rotation during plantarflexion

OBJECTIVES

An optimal load and ankle position for stress ultrasound of the injured anterior talofibular ligament (ATFL) are unknown. The objectives of this study were to compare stress ultrasound and ankle kinematics from a 6 degree-of-freedom (6-DOF) robotic testing system as a reference standard for the evaluation of injured ATFL and suggest cut-off values for ultrasound diagnosis.

METHODS

Ten fresh-frozen human cadaveric ankles were used. Loads and ankle positions examined by the 6-DOF robotic testing system were: 40 N anterior load, 1.7 Nm inversion, and 1.7 Nm internal rotation torques at 30° plantarflexion, 15° plantarflexion, and 0° plantarflexion. Bony translations were measured by ultrasound and a robotic testing system under the above conditions. After measuring the intact ankle, ATFL was transected at its fibular attachment under arthroscopy. Correlations between ultrasound and robotic testing systems were calculated with Pearson correlation coefficients. Paired t-tests were performed for comparison of ultrasound measurements of translation between intact and transected ATFL and unloaded and loaded conditions in transected ATFL.

RESULTS

Good agreement between ultrasound measurement and that of the robotic testing system was found only in internal rotation at 30° plantarflexion (ICC ​= ​0.77; 95% confidence interval 0.27-0.94). At 30° plantarflexion, significant differences in ultrasound measurements of translation between intact and transected ATFL (p ​< ​0.01) were found in response to 1.7 Nm internal rotation torque and nonstress and stress with internal rotation (p ​< ​0.01) with mean differences of 2.4 ​mm and 1.9 ​mm, respectively.

CONCLUSION

Based on the data of this study, moderate internal rotation and plantarflexion are optimal to evaluate the effects of ATFL injury when clinicians utilize stress ultrasound in patients.

LEVEL OF EVIDENCE

III.

Improved joint function when reaching behind the back is associated with patient reported outcomes in individuals with rotator cuff tears following exercise therapy

BACKGROUND

Reaching behind the back is painful for individuals with rotator cuff tears. The objectives of the study were to determine changes in glenohumeral kinematics when reaching behind the back, passive range of motion (RoM), patient reported outcomes and the relationships between kinematics and patient reported outcomes following exercise therapy.

METHODS

Eighty-four individuals with symptomatic isolated supraspinatus tears were recruited for this prospective observational study. Glenohumeral kinematics were measured using biplane radiography during a reaching behind the back movement. Passive glenohumeral internal rotation and patient reported outcome measures were collected. Depending on data normality, appropriate tests were utilized to determine changes in variables. Spearman's correlations were utilized for associations, and Stuart-Maxwell tests for changes in distributions.

FINDINGS

Maximum active glenohumeral internal rotation increased by 3.2° (P = 0.001), contact path length decreased by 5.5% glenoid size (P = 0.022), passive glenohumeral internal rotation RoM increased by 4.9° (P = 0.001), and Western Ontario Rotator Cuff Index and American Shoulder and Elbow Surgeons scores increased by 29.8 and 21.1 (P = 0.001), respectively. Changes in Western Ontario Rotator Cuff Index scores positively associated with changes in maximum active glenohumeral internal rotation and negatively associated with changes in contact path lengths (P = 0.008 and P = 0.006, respectively).

INTERPRETATION

The reaching behind the back movement was useful in elucidating in-vivo mechanistic changes associated with patient reported outcomes. Glenohumeral joint function and patient reported outcomes improved, where changes in Western Ontario Rotator Cuff Index scores were associated with kinematics. These findings inform clinicians of functional changes following exercise therapy and new targetable treatment factors.

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.

Greater tuberosity morphology is altered in individuals with symptomatic isolated supraspinatus tendon tears

BACKGROUND

In the presence of an isolated supraspinatus tear, the force applied to the greater tuberosity is reduced, which may lead to bony morphologic changes. Thus, diagnostic or surgical identification of landmarks to properly repair the torn tendon might be difficult if the anatomy of the greater tuberosity is altered. The objectives of the study were to assess the presence of the superior, middle, and inferior facets of the greater tuberosity in individuals with symptomatic isolated supraspinatus tendon tears and the associations between tear size, tear location and presence of each facet.

METHODS

Thirty-seven individuals with symptomatic isolated supraspinatus tendon tears were recruited to participate in the study. Individuals underwent a high-resolution computed tomography scan of the involved shoulder and images were segmented to generate subject specific models of each humerus. The vertices comprising each facet were identified; however, if even a single vertex comprising the facet was missing, the facet was considered altered. Percentage agreement for correctly identifying the presence of each facet was determined using 2 additional observers and 5 randomly selected humeri. Ultrasonography was performed to assess anterior-posterior (AP) tear size and tear location. Outcome parameters included presence of the superior, middle, and inferior facets; AP tear size; and tear location. Point-biserial correlations were used to determine the associations between AP tear size, tear location, and presence of the superior, middle, and inferior facets.

RESULTS

Supraspinatus tear size and tear location was 13.1 ± 6.1 mm (range, 1.9-28.3 mm) and 2.0 ± 4.4 mm from the posterior edge of the long head of the biceps tendon (range, 0.0-19.0 mm), respectively. Overall, the superior, middle, and inferior facets were not altered in 24.3%, 29.7%, and 45.9% of individuals, respectively. Percentage agreement between observers was 83.4% on average. No associations were found between tear size or tear location and presence of the superior, middle, or inferior facet (P values ranged from .19 to .74).

CONCLUSION

Individuals with symptomatic isolated supraspinatus tears experience significant alterations in the bony morphology of the greater tuberosity that were irrespective of supraspinatus tear size and location. This information is useful for radiologists and orthopedic surgeons as the altered anatomy may influence the ability to identify important anatomic landmarks during diagnostic imaging or surgical procedures.

A Dynamic Elbow Testing Apparatus for Simulating Elbow Joint Motion in Varying Shoulder Positions

Purpose

To develop and evaluate the capabilities of a dynamic elbow testing apparatus that simulates unconstrained elbow motion throughout the range of humerothoracic (HTA) abduction.

Methods

Elbow flexion was generated by six computer-controlled electromechanical actuators that simulated muscle action, while six degree-of-freedom joint motion was measured using an optical tracking device. Repeatability of joint kinematics was assessed at four HTA angles (0°, 45°, 90°, 135°) and with two muscle force combinations (A1-biceps brachialis, brachioradialis and A2-biceps, brachioradialis). Repeatability was determined by comparing kinematics at every 10° of flexion over five flexion-extension cycles (0° to 100°).

Results

Multiple muscle force combinations can be used at each HTA angle to generate elbow flexion. Trials showed that the testing apparatus produced highly repeatable joint motion at each HTA angle and with varying muscle force combinations. The intraclass correlation coefficient was greater than 0.95 for all conditions.

Conclusions

Repeatable smooth cadaveric elbow motion was created that mimicked the in vivo situation.

Clinical relevance

These results suggest that the dynamic elbow testing apparatus can be used to characterize elbow biomechanics in cadaver upper extremities.

The Effect of Elbow Flexion On Valgus Carrying Angle

PURPOSE

This study aimed to examine the effect of flexion on valgus carrying angle in the human elbow using a dynamic elbow testing apparatus.

METHODS

Active elbow motion was simulated in seven cadaveric upper extremities. Six electromechanical actuators simulated muscle action, while 6 degrees-of-freedom joint motion was measured with an optical tracking system to quantify the kinematics of the ulna with respect to the humerus as the elbow was flexed at the side position. Repeatability of the testing apparatus was assessed in a single elbow over five flexion-extension cycles. The varus angle change of each elbow was compared at different flexion angles with the arm at 0° of humerothoracic abduction or dependent arm position.

RESULTS

The testing apparatus achieved excellent kinematic repeatability (intraclass correlation coefficient, >0.95) throughout flexion and extension. All elbows decreased their valgus carrying angle during flexion from 0° to 90° when the arm was maintained at 0° of humerothoracic abduction. Elbows underwent significant total varus angle change from full extension of 3.9° ± 3.4° (P = .007), 7.3° ± 5.2° (P = .01), and 8.9° ± 7.1° (P = .02) at 60°, 90°, and 120° of flexion, respectively. No significant varus angle change was observed between 0° and 30° of flexion (P = .66), 60° and 120° of flexion (P = .06), and 90° and 120° of flexion (P = .19).

CONCLUSIONS

The dynamic elbow testing apparatus characterized a decrease of valgus carrying angle during elbow flexion and found that most varus angle changes occurred between 30° and 90° of flexion. All specimens underwent varus angle change until at least 90° of flexion.

CLINICAL RELEVANCE

Our model establishes the anatomic decrease in valgus angle by flexion angle in vitro and can serve as a baseline for testing motion profiles of arthroplasty designs and ligamentous reconstruction in the dependent arm position. Future investigations should focus on characterizing motion profile change as the arm is abducted away from the body.

Do Intramedullary Screws Provide Adequate Fixation for Humeral and Ulnar Components in Total Elbow Arthroplasty? A Cadaveric Analysis

PURPOSE

The objective of this study was to determine the structural properties of the cadaver bone-screw interface for cementless intramedullary screw fixation in the context of total elbow arthroplasty.

METHODS

The intramedullary canals of seven humerus and seven ulna specimens from fresh-frozen cadavers were drilled using custom drill bits until the inner cortex was reached and then hand tapped for the corresponding thread size. Titanium screws were advanced into the tapped holes until securely seated. The bones were potted and then mounted on a uniaxial material testing machine. A tensile load was applied, and end-of-test elongation, failure load, energy absorbed, and stiffness were determined. End-of-test load and elongation were defined as the elongation and load experienced by the structure at 3,000 N or failure. Each specimen was inspected for evidence of pullout, loosening, or visible fractures.

RESULTS

The end-of-test load and elongation for the humerus specimens were 2721 ± 738 N and 3.0 ± 0.9 mm, respectively. The ulna specimens reached 92% of the humerus specimens' end-of-test load at 2,514 ± 678 N and 120% of their end-of-test elongation (3.6 ± 0.6 mm). The stiffness of the humerus specimens was 1,077 ± 336 N/mm, which was 1.3 times greater than the stiffness of the ulna specimens (790 ± 211 N/mm). Lastly, the energy absorbed by the humerus samples was 3.6 ± 1.6 J, which was 92% of the energy absorbed by the ulna samples at 3.9 ± 1.1 J. One humerus and three ulnas failed before the end-of-test load of 3,000 N. Two failures were caused by screw pullout and two by bone fracture.

CONCLUSIONS

Our findings demonstrate that intramedullary screw fixation is successful in withstanding forces that are greater than required for osseointegration.

CLINICAL RELEVANCE

Uncemented fixation may be beneficial in elbow arthroplasty.

Direction of non-recoverable strain in the glenohumeral capsule following multiple anterior dislocations: Implications for anatomic Bankart repair

The study aimed to analyze the direction of non-recoverable strain and determine the optimal direction for anatomic capsular plication within four sub-regions of the inferior glenohumeral capsule following multiple dislocations. Seven fresh-frozen cadaveric shoulders were dissected. A grid of strain markers was affixed to the inferior glenohumeral capsule. Each joint was mounted in a 6-degree-of-freedom robotic testing system and repeatedly dislocated in the anterior direction 10 times at 60° of abduction and 60° of external rotation of the glenohumeral joint. The 3D positions of the strain markers were compared before and after dislocations to define the non-recoverable strain. The strain map was divided into four sub-regions. The angles of deviation between each maximum principle strain vector and the anterior band of the inferior glenohumeral ligament (AB-IGHL) or posterior band of the IGHL (PB-IGHL) for the anterior and posterior regions of the capsule were determined. The mean direction of all strain vectors in each sub-region was categorized. The direction of the non-recoverable strain in the anterior-band and anterior-axillary-pouch sub-regions was categorized as parallel to the AB-IGHL, whereas the posterior-axillary-pouch and posterior-band sub-regions were mostly perpendicular to the PB-IGHL. Clinical Significance: Plication of the anteroinferior capsule parallel to the AB-IGHL may be preferred during arthroscopic Bankart repair to restore anatomy; posteroinferior capsular plication may also be necessary and best performed perpendicular to the PB-IGHL. The direction of the capsular injury remains the same irrespective of the number of dislocations. This study provides the scientific and quantitative rationale for an anatomic approach to capsular plication.

The lateral meniscus extrudes with and without root tear evaluated using ultrasound

PURPOSE

The purpose of the current study was to measure extrusion of the intact lateral meniscus as a function of knee flexion angle and loading condition and to compare the changes in extrusion with a posterior root tear using a robotic testing system and ultrasound.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees were subjected to external loading conditions (passive path position (no external load), 200 axial compression, 5-N-m internal tibial torque, 5-N-m valgus torque) at full extension, 30°, 60° and 90° of flexion using a robotic testing system. A linear array transducer was placed in the longitudinal orientation. Extrusion and kinematics data were recorded for two meniscus states: intact and posterior lateral root deficiency. Therefore, a complete radial root tear in the lateral meniscus at 10 mm from the tibial insertion was made in all 8 cadaveric knees using arthroscopy. The resultant forces in the lateral meniscus were also quantified by reproducing recorded paths after the removal of the lateral meniscus.

RESULTS

A lateral meniscus root tear resulted in a statistically significant increase (up to 250%) of extrusion for the lateral meniscus (p < 0.05) in comparison to the intact lateral meniscus for all externally applied loads. Without external load (passive path position), significant differences were also found between the intact and posterior lateral root deficient meniscus except at full extension (1.0 ± 0.7 mm vs. 1.9 ± 0.4 mm) and 30° of flexion (1.4 ± 0.5 mm vs. 1.8 ± 0.5 mm). Overall, with increasing flexion angle, lateral meniscus extrusion decreased for the intact as well as for the posterior lateral root deficient meniscus, with the lowest measurements in response to internal tibial torque at 90° of flexion (-3.3 ± 1.1 mm). Knee kinematics were similar whether intact or posterior lateral root tear (n.s.). Ultrasound measurement of lateral meniscus extrusion showed good inter-rater (0.65 [0.30-0.97]-0.71 [0.34-0.94]) and excellent intra-rater reliability (0.81 [0.43-0.99]).

CONCLUSION

Dynamic Ultrasound is a reliable diagnostic modality to measure the lateral meniscus extrusion which can be helpful in the diagnosis and quantification of lateral meniscal root tears.

LEVEL OF EVIDENCE

III.

Increased superior translation following multiple simulated anterior dislocations of the shoulder

PURPOSE

Recurrent shoulder dislocations can result in kinematic changes of the glenohumeral joint. The number of prior shoulder dislocations may contribute to increased severity of capsulolabral lesions. The kinematics of the glenohumeral joint following multiple dislocations remain poorly understood. The purpose of this study was to assess the kinematics of the glenohumeral joint during anterior dislocations of the shoulder, and more specifically, altered translational motion following multiple dislocations. The kinematics of the glenohumeral joint were hypothesized to change and correlate with the number of dislocations.

METHODS

Eight fresh-frozen cadaveric shoulders were dissected free of all soft tissues except the glenohumeral capsule. Each joint was mounted in a robotic testing system. At 60 degrees of glenohumeral abduction, an internal and external rotational torque (1.1 Nm) were applied to the humerus, and the resulting joint kinematics were recorded. Anterior forces were applied to the humerus to anteriorly dislocate the shoulder and the resulting kinematics were recorded during each dislocation. Following each dislocation, the same rotational torque was applied to the humerus, and the resulting joint kinematics were also recorded. A repeated-measures analysis of variance (ANOVA) was used to compare the kinematics following each dislocation.

RESULTS

During the 7th, 8th, 9th, and 10th dislocations, the humerus significantly translated superiorly compared with the shoulder during the 1st dislocation (p < 0.05). Following the 3rd, 4th, 5th, and 10th dislocations, the humeral head significantly translated superiorly compared with the shoulder following the 1st dislocation in the position of 60 degrees of abduction in response to external rotation torque (p < 0.05).

CONCLUSION

Multiple anterior shoulder dislocations lead to abnormal translational kinematics and result in increased superior translation of the humerus. This may contribute to pathologic superior extension of capsulolabral injuries. Superior translation of the humerus with overhead motion in the setting of recurrent instability may also place the shoulder at risk for extension of the capsulolabral injuries.

Increasing the posterior tibial slope lowers in situ forces in the native ACL primarily at deep flexion angles

High tibial osteotomy is becoming increasingly popular but can be associated with unintentional posterior tibial slope (PTS) increase and subsequent anterior cruciate ligament (ACL) degeneration. This study quantified the effect of increasing PTS on knee kinematics and in situ forces in the native ACL. A robotic testing system was used to apply external loads from full extension to 90° flexion to seven human cadaveric knees: (1) 200 N axial compressive load, (2) 5 Nm internal tibial + 10 Nm valgus torque, and (3) 5 Nm external tibial + 10 Nm varus torque. Kinematics and in situ forces in the ACL were acquired for the native and increased PTS state. Increasing PTS resulted in increased anterior tibial translation at 30° (1.8 mm), 60° (1.7 mm), and 90° (0.9 mm) flexion and reduced in situ force in the ACL at 30° (57.6%), 60° (69.8%), and 90° (75.0%) flexion in response to 200 N axial compressive load. In response to 5 Nm internal tibial + 10 Nm valgus torque, there was significantly less (39.0%) in situ force in the ACL at 90° flexion in the increased compared with the native PTS state. Significantly less in situ force in the ACL at 60° (62.8%) and 90° (67.0%) flexion was observed in the increased compared with the native PTS state in response to 5 Nm external tibial + 10 Nm varus torque. Increasing PTS affects knee kinematics and results in a reduction of in situ forces in the native ACL during compressive and rotatory loads at flexion angles exceeding 30°. In a controlled laboratory setting PTS increase unloads the ACL, affecting its natural function.

Ultrasound-Guided Anterior Talofibular Ligament Repair With Augmentation Can Restore Ankle Kinematics: A Cadaveric Biomechanical Study

Background:

Anterior talofibular ligament (ATFL) repair of the ankle is a common surgical procedure. Ultrasound (US)-guided anchor placement for ATFL repair can be performed anatomically and accurately. However, to our knowledge, no study has investigated ankle kinematics after US-guided ATFL repair.

Hypothesis:

US-guided ATFL repair with and without inferior extensor retinaculum (IER) augmentation will restore ankle kinematics.

Study Design:

Controlled laboratory study; Level of evidence, 4.

Methods:

A 6 degrees of freedom robotic testing system was used to apply multidirectional loads to fresh-frozen cadaveric ankles (N = 9). The following ankle states were evaluated: ATFL intact, ATFL deficient, combined ATFL repair and IER augmentation, and isolated US-guided ATFL repair. Three loading conditions (internal-external rotation torque, anterior-posterior load, and inversion-eversion torque) were applied at 4 ankle positions: 30° of plantarflexion, 15° of plantarflexion, 0° of plantarflexion, and 15° of dorsiflexion. The resulting kinematics were recorded and compared using a 1-way repeated-measures analysis of variance with the Benjamini-Hochberg test.

Results:

Anterior translation in response to an internal rotation torque significantly increased in the ATFL-deficient state compared with the ATFL-intact state at 30° and 15° of plantarflexion (P = .022 and .03, respectively). After the combined US-guided ATFL repair and augmentation, anterior translation was reduced significantly compared with the ATFL-deficient state at 30° and 15° of plantarflexion (P = .0012 and .005, respectively). Anterior translation was not significantly different for the isolated ATFL-repair state compared with the ATFL-deficient or ATFL-intact states at 30° and 15° of plantarflexion.

Conclusion:

Combined US-guided ATFL repair with augmentation of the IER reduced lateral ankle laxity due to ATFL deficiency. Isolated US-guided ATFL repair did not reduce laxity due to ATFL deficiency, nor did it increase instability compared with the intact ankle.

Clinical Relevance:

US-guided ATFL repair with IER augmentation is a minimally-invasive technique to reduce lateral ankle laxity due to ATFL deficiency. Isolated US-guided ATFL repair may be a viable option if accompanied by a period of immobilization.

Associations between range of motion, strength, tear size, patient-reported outcomes, and glenohumeral kinematics in individuals with symptomatic isolated supraspinatus tears

BACKGROUND

Clinical failure associated with nonoperative treatment of rotator cuff tears may be due to inadequate characterization of the individual's functional impairments. Clinically, restricted passive range of motion (ROM) (restrictions imply capsular tightness), limitations in muscle strength, and larger rotator cuff tears are hypothesized to be related to altered glenohumeral kinematics. Understanding these relationships, as well as the relationship between glenohumeral kinematics and patient-reported outcomes (PROs) prior to exercise therapy, may help characterize functional impairments in individuals with rotator cuff tears. The objectives of the study were to describe the baseline presentation of individuals with an isolated supraspinatus tear, including passive ROM, rotator cuff muscle strength, tear size, PROs, and glenohumeral kinematics, and to determine associations among these variables.

METHODS

One hundred one individuals with symptomatic isolated supraspinatus tears were recruited for the study and underwent assessments of passive glenohumeral ROM, isometric muscle strength, and ultrasonography to assess anterior-posterior tear size. Glenohumeral kinematics during scapular-plane abduction were measured using biplane radiography. Furthermore, PROs including the American Shoulder and Elbow Surgeons (ASES) score and the Western Ontario Rotator Cuff Index (WORC) score were collected.

RESULTS

Individuals presented with decreased ROM, external rotation weakness compared with the uninvolved side, and pain and disability as measured by the ASES and WORC scores. These findings were not associated with glenohumeral kinematics, with the exception of a weak positive association between glenohumeral contact path lengths and WORC scores (ρ = 0.25, P = .03). Tear size was 11.7 ± 5.7 mm, and maximum anterior translation, superior translation, and contact path length were 3.0% ± 3.8% of glenoid width, 3.5% ± 3.8% of glenoid height, and 38.2% ± 20.7% of glenoid size, respectively.

CONCLUSION

Individuals with a symptomatic isolated supraspinatus tear presented with decreased ROM, external rotation weakness, and pain and disability as measured by the ASES and WORC scores. However, no abnormal kinematics associated with these limitations were observed. Thus, given that the tear is isolated to the supraspinatus tendon and no capsular restrictions are present, normal function of the glenohumeral joint may be possible during scapular-plane abduction.

Studying the Feasibility of Postoperative Monitoring of Spinal Fusion Progress Using a Self-Powered Fowler-Nordheim Sensor-Data-Logger

OBJECTIVE

This study investigates the feasibility of using a new self-powered sensing and data logging system for postoperative monitoring of spinal fusion progress. The proposed diagnostic technology directly couples a piezoelectric transducer signal into a Fowler-Nordheim (FN) quantum tunneling-based synchronized dynamical system to record the mechanical usage of spinal fixation devices. The operation of the proposed implantable FN sensor-data-logger is completely self-powered by harvesting the energy from the micro-motion of the spine during the course of fusion. Bench-top testing is performed using corpectomy models to evaluate the performance of the proposed monitoring system. In order to simulate the spinal fusion process, different materials with gradually increasing elastic modulus are used to fill the intervertebral space gap. Besides, finite element models are developed to analyze the strains induced on the spinal rods during the applied cyclic loading. Data measured from the benchtop experiment is processed using an FN sensor-data-logger model to obtain time-evolution curves representing each spinal fusion state. This feasibility study shows that the obtained curves are viable tools to differentiate between conditions of osseous union and assess the effective fusion period.

Tibiofemoral bony morphology features associated with ACL injury and sex utilizing three-dimensional statistical shape modeling

Statistical shape modeling was employed to assess three-dimensional (3D) bony morphology between distal femurs and proximal tibiae of anterior cruciate ligament (ACL) injured knees, the contralateral uninjured knees of ACL injured subjects, and knees with no history of injury. Surface models were created by segmenting bone from bilateral computed-tomography scans of 20 subjects of their ACL injured knees and non-injured contralateral knees, and 20 knees of control subjects with no history of a knee injury. Correspondence particles were placed on each surface, and a principal component analysis determined modes of variation in the positions of the correspondence particles describing anatomical variation. ANOVAs assessed the statistical differences of 3D bony morphological features with main effects of injury state and sex. ACL injured knees were determined to have a more lateral femoral mechanical axis and a greater angle between the long axis and condylar axis of the femur. A smaller anterior-posterior dimension of the lateral tibial plateau was also associated with ACL injured knees. Results of this study demonstrate that there are more bony morphological features predisposing individuals for ACL injury than previously established. These bony morphological parameters may cause greater internal and valgus torques increasing stresses in the ACL. No differences were determined between the ACL injured knees and their uninjured contralateral knees demonstrating that knees of ACL injured individuals are at similar risk for injury. Further understanding of the effect of bony morphology on the risk for ACL injury could improve individualized ACL injury treatment and prevention.

Continuous-Loop Tape Technique Has Greater Stiffness and Less Elongation Compared With Tied-Suture Fixation of Full-Thickness All-Soft Tissue Quadriceps Tendon Autografts

Background

Many graft fixation techniques are utilized for full-thickness soft tissue quadriceps tendon autografts during anterior cruciate ligament reconstruction (ACLR).

Purpose

To determine the tensile properties of all-soft tissue quadriceps tendon graft fixation using a tied-suture versus continuous-loop tape technique. It was hypothesized that the continuous-loop tape technique would have less cyclic elongation and greater ultimate load to failure and stiffness compared with a commonly used tied-suture technique.

Study Design

Controlled laboratory study.

Methods

Sixteen fresh-frozen human knee specimens were used to harvest a full-thickness all-soft tissue quadriceps tendon graft; half were secured using a Krackow suture technique with 2 braided sutures, and half were secured using a continuous-loop tape suspensory fixation button with a rip-stop stitch. Cyclic and permanent elongation, toe- and linear-region stiffness, and ultimate load were determined. Statistical analysis was performed at P <.05.

Results

The tied-suture fixation group demonstrated significantly higher permanent elongation (11.7 ± 3.6 vs 4.2 ± 1.0 mm, P < .001) and cyclic elongation (5.9 ± 1.3 vs 2.0 ± 0.4 mm, P < .001) compared with the continuous-loop tape fixation group. There was a significantly higher linear-region stiffness with continuous-loop tape fixation compared with tied-suture fixation (98.8 ± 12.7 vs 85.5 ± 7.5 N/mm, P = .022). No significant difference in ultimate load between groups (517.1 ± 149.2 vs 465.6 ± 64.6 N) was found. The mode of failure was tendon pull-through for the continuous-loop tape group and suture breakage in the tied-suture group (P < .001).

Conclusion

Continuous-loop tape fixation is superior to tied-suture fixation in regard to elongation and stiffness for all-soft tissue quadriceps tendon grafts, but there was no significant difference in ultimate load.

Clinical Relevance

Continuous-loop tape fixation of all-soft tissue quadriceps tendon grafts for ACLR is a valid technique with superior tensile properties.

Tibiofemoral bony morphology impacts the knee kinematics after anterolateral capsule injury and lateral extraarticular tenodesis differently than intact state

Anterolateral capsule injury, often concomitant with anterior cruciate ligament (ACL) injuries, may result in high-grade rotatory instability. Lateral extraarticular tenodesis (LET) is sometimes added to ACL reconstruction to address this instability. However, LET is a non-anatomic procedure and concerns regarding increased tibiofemoral contact pressure and reduced internal rotation exist for some individuals which may be due to their tibiofemoral bony morphology. Therefore, the objective of this study was to analyze the effect of bony morphology on knee kinematic and contact pressure before and after anterolateral capsule injury and LET. A (1) 134-N anterior tibial load with 200-N axial compression and (2) a 7-Nm internal torque with a 200-N axial compression were applied to cadaveric knees (n = 8) using a 6 degree-of-freedom robotic testing system. Tibiofemoral bony morphology was captured with computed tomography scans and analyzed using 3D statistical shape modeling. Kinematics at each state were correlated with the results from the statistical shape model. Two femoral and three tibial modes of variation correlated with kinematic and contact pressure data before and after anterolateral capsule injury and LET. A decreased lateral tibial plateau elevation correlated with greater internal rotation and anterior tibial translation after anterolateral capsule deficiency and LET. Decreased notch width correlated with decreased contact area after anterolateral capsule deficiency and LET demonstrating it as a risk factor for ACL injury. The results of this study demonstrate that bony morphology if properly understood, could help improve the efficacy of LET procedures and that bony morphology has different effects after injury and repair.

Small lateral meniscus tears propagate over time in ACL intact and deficient knees

PURPOSE

To quantify propagation of small longitudinal tears in the lateral meniscus in ACL intact and deficient knees.

METHODS

Using a robotic testing system, 5-Nm of external tibial torque + 5-Nm of valgus torque + 250-N of axial compression was applied to 14 fresh-frozen cadaveric knees while the knees were flexed from 30° to 90°. Knees were divided into two groups: intact (N = 8) and ACL deficient (N = 6). Kinematic data was recorded for four knee states: intact or ACL deficient knee, after posterior arthrotomy, meniscus tear at baseline, and after 500 cycles of the applied loading condition.

RESULTS

Lateral meniscus tear length increased throughout the 500 cycles regardless of the ACL integrity (p < 0.001). Overall, an increase of 28.7% and 26.1% was observed in intact and ACL deficient knees, respectively. In intact knees, external tibial rotation increased with meniscus tear propagation at all flexion angles by up to 45.5% (p = 0.019). In contrast, knee kinematics in ACL deficient knees were not affected by meniscus tear propagation (n.s.). In ACL deficient knees, resultant forces in the lateral meniscus increased at all flexion angles by up to 116.5% (p = 0.012). No differences in forces were observed in the intact knees (n.s.).

CONCLUSION

The data of this study show that small longitudinal tears in the lateral meniscus propagate significantly regardless of the integrity of the ACL and even after only 100 cycles of knee loading. The propagation of such tears altered kinematics and forces in the knee. Therefore, small, longitudinal lateral meniscus tears that are untreated in current clinical practices may propagate when loaded.

Location and magnitude of capsular injuries varies following multiple anterior dislocations of the shoulder: Implications for surgical repair

Capsular injuries can occur during multiple shoulder dislocations. The purpose of this study is to evaluate the location and magnitude of glenohumeral capsular injury following multiple dislocations. We hypothesized that the magnitude of capsular injury would increase and the location of peak injury would vary depending on the number of dislocations. Seven fresh-frozen cadaveric shoulders were used. A 7 × 11 grid of strain markers was affixed to the anteroinferior capsule. Each joint was then mounted to a six degree-freedom robotic testing system. Marker tracking was performed following 1, 2, 3, 4, 5, and 10 dislocations to determine the nonrecoverable strain as capsular injury. Following each dislocation, the magnitude of the maximum principal strain representing the nonrecoverable strain in the inferior glenohumeral capsule was quantified by comparing the strain marker positions following each dislocation. The peak value of nonrecoverable strain statistically increased with the number of dislocations in five of seven specimens (p = .0007). The capsular location that had the peak value of nonrecoverable strain varied according to the number of dislocations, and from specimen to specimen. The nonrecoverable strain was identified in the posterior capsule and anterior axillary pouch, which increased with the number of dislocations compared to the other regions of the capsule (p = .001-.012) by up to 16%. Clinical significance: While plication of the anterior axillary pouch is important following multiple dislocations, a more extensive anterior capsular shift may be necessary with an increased number of dislocations in addition to a posterior capsular shift when appropriate.

Combining advanced computational and imaging techniques as a quantitative tool to estimate patellofemoral joint stress during downhill gait: A feasibility study

BACKGROUND

The onset and progression of patellofemoral osteoarthritis (OA) has been linked to alterations in cartilage stress-a potential precursor to pain and subsequent cartilage degradation. A lack in quantitative tools for objectively evaluating patellofemoral joint contact stress limits our understanding of pathomechanics associated with OA.

RESEARCH QUESTION

Could computational modeling and biplane fluoroscopy techniques be used to discriminate in-vivo, subject-specific patellofemoral stress profiles in individuals with and without patellofemoral OA?

METHODS

The current study employed a discrete element modeling framework driven by in-vivo, subject-specific kinematics during downhill gait to discriminate unique patellofemoral stress profiles in individuals with patellofemoral OA (n = 5) as compared to older individuals without OA (n = 6). All participants underwent biplane fluoroscopy kinematic tracking while walking on a declined instrumented treadmill. Subject-specific kinematics were combined with high resolution geometrical models to estimate patellofemoral joint contact stress during 0%, 25 %, 50 %, 75 % and 100 % of the loading response phase of downhill gait.

RESULTS

Individuals with patellofemoral OA demonstrated earlier increases in patellofemoral stress in the lateral patellofemoral compartment during loading response as compared to OA-free controls (P = 0.021). Overall, both groups exhibited increased patellofemoral contact stress early in the loading response phase of gait as compared to the end of loading response. Results from this study show increased stress profiles in individuals with patellofemoral OA, indicating increasing joint loading in early phases of gait.

SIGNIFICANCE

This modeling framework-combining arthrokinematics with discrete element models-can objectively estimate changes in patellofemoral joint stress, with potential applications to evaluate outcomes from various treatment programs, including surgical and non-surgical rehabilitation treatments.

The Correlation of Quantitative Ultrasound Measures and Supraspinatus Tendon Quality: A Pilot Study

Background:

The objective of this study was to determine the feasibility of assessing tendon quality as quantified by histology through changes in quantitative ultrasound measures.

Methods:

Eight cadaveric shoulders (four with a small supraspinatus tendon tear) were examined using conventional B-mode ultrasound in the transverse plane by internally rotating and hyperextending the humerus. Quantitative ultrasound measures (skewness, kurtosis, variance, and echogenicity) were calculated based on the grayscale distribution of the ultrasound image taken of the supraspinatus tendon near the insertion site. The specimens were then dissected to the supraspinatus tendon where tendon biopsies were taken near the insertion site, mid-substance, and myotendinous junction. Through histology, tendon quality was evaluated based on collagen fiber organization, fatty infiltration, nuclei shape, and cellularity. Correlations between quantitative ultrasound measures and histological grades of tendon quality were determined through Pearson or Spearman's rho correlations.

Results:

A total of three significant correlations between quantitative ultrasound measures and histological parameters of tendon quality were found. Significant correlations between kurtosis and cellularity at the insertion site (r = 0.724) (P < 0.05) as well as variance and fatty infiltration at the myotendinous junction (ρ = −0.843) (P < 0.05) and for the whole tendon (ρ = −0.826) (P < 0.05) were found.

Conclusion:

The results show the potential for quantitative ultrasound measures to assess factors of tendon quality that can only be determined through histology. With further development of the methodology that utilizes quantitative ultrasound measures, clinicians might be able to evaluate the tendon quality noninvasively in future.

Hybrid Fixation Restores Tibiofibular Kinematics for Early Weightbearing After Syndesmotic Injury

Background:

Disruption of the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane (IOM) is a predictive measure of residual symptoms after an ankle injury. Controversy remains regarding the ideal fixation technique for early return to sport, which requires restoration of tibiofibular kinematics with early weightbearing.

Purpose:

To quantify tibiofibular kinematics after syndesmotic fixation with different tricortical screw and suture button constructs during simulated weightbearing.

Study Design:

Controlled laboratory study.

Methods:

A 6 degrees of freedom robotic testing system was used to test 9 fresh-frozen human cadaveric specimens (mean age, 65.1 ± 17.3 years). A 200-N compressive load was applied to the ankle, while a 5-N·m external rotation and a 5-N·m inversion moment were applied independently to the ankle at 0° of flexion, 15° and 30° of plantarflexion, and 10° of dorsiflexion. Fibular medial-lateral translation, anterior-posterior translation, and internal-external rotation relative to the tibia were tracked by use of an optical tracking system in the following states: (1) intact ankle; (2) AITFL, PITFL, and IOM transected ankle; (3) single-screw fixation; (4) double-screw fixation; (5) hybrid fixation; (6) single suture button fixation; and (7) divergent suture button fixation. Repeated-measures analysis of variance with Bonferroni correction was performed for statistical analysis.

Results:

In response to the external rotation moment and axial compression, single tricortical screw fixation resulted in significantly higher lateral translation of the fibula compared with that of the intact ankle at 10° of dorsiflexion (P < .05). Suture button fixation resulted in significantly higher posterior translation of the fibula at 0° of flexion and 10° of dorsiflexion, whereas divergent suture button fixation resulted in higher posterior translation at only 0° of flexion (P < .05). In response to the inversion moment and axial compression, single tricortical screw and hybrid fixation significantly decreased lateral translation in plantarflexion, whereas double tricortical screw fixation and hybrid fixation significantly decreased external rotation of the fibula compared with that of the intact ankle at 15° of plantarflexion (P < .05).

Conclusion:

Based on the data in this study, hybrid fixation with 1 suture button and 1 tricortical screw may most appropriately restore tibiofibular kinematics for early weightbearing. However, overconstraint of motion during inversion may occur, which has unknown clinical significance.

Clinical Relevance:

Surgeons may consider this data when deciding on the best algorithm for syndesmosis repair and postoperative rehabilitation.

Does Lateral Extra-articular Tenodesis of the Knee Affect Anterior Cruciate Ligament Graft In Situ Forces and Tibiofemoral Contact Pressures?

PURPOSE

To quantify the effects of lateral extra-articular tenodesis (LET) on tibiofemoral compartment contact area and pressures, knee kinematics, and forces.

METHODS

Nine cadaveric knees were tested using a robotic testing system. Two loading conditions, (1) anterior tibial translational load coupled with axial compression and (2) internal tibial torque coupled with axial compression, were applied for each knee state at full extension and 30°, 60°, and 90° of knee flexion. Kinematic data was recorded for 3 knee states: anterolateral capsule (ALC) competent, ALC deficient, and post-LET using a 6-mm semitendinosus graft. In situ force in the anterior cruciate ligament (ACL) was quantified using the principle of superposition by comparing the change in force measured before and after the removal of the ALC. Contact area and pressures in each tibiofemoral compartment were measured by replaying kinematics after soft tissues were removed and pressure sensors were inserted.

RESULTS

In response to an anterior tibial translational load, mean contact area in the medial compartment decreased by 33.1% from the ALC-competent to post-LET knee states at 90° of knee flexion (P = .042). No significant differences in lateral compartment contact pressure were found between knee states. In situ force in the ACL in response to an anterior tibial translational load decreased by 43.4% and 50% from the ALC-deficient to post-LET knee states at 60° (P = .02) and 90° (P = .006). No significant difference in kinematics was observed between the ALC-competent and post-LET knee states in each of the loading conditions at all knee flexion angles (P > .05).

CONCLUSIONS

In this in vitro model, LET with a semitendinosus graft did not significantly overconstrain the knee or increase pressure in the lateral compartment. Additionally, LET reduced the in situ force in the ACL in the setting of ALC injury.

CLINICAL RELEVANCE

The lack of knee overconstraint without significant increases in lateral compartment pressures indicates that if an LET with semitendinosus graft is not overtensioned, accelerated degenerative changes in the lateral compartment may not be expected after this procedure.

Effect of Screw Length and Geometry on Interfragmentary Compression in a Simulated Proximal Pole Scaphoid Fracture Model

Background: The objective of this study was to determine interfragmentary compression forces based on screw length and geometry for simulated proximal scaphoid fractures. Methods: Sixty-four foam model simulated fractures were stabilized with screws of various length (10 mm, 18 mm, 20 mm, or 24 mm) and geometry (central threadless or fully threaded) across a proximal fracture. Interfragmentary compression was measured at the simulated fracture site upon fixation. An independent sample t test and 1-way analysis of variance were performed to assess differences in interfragmentary compression. Results: Fixation utilizing a 10-mm screw generated significantly less interfragmentary compression than fixation utilizing a 20-mm or 24-mm screw. When accounting for both screw length and geometry, an 18-mm central threadless screw generated greater interfragmentary compression than a 20-mm and 24-mm fully threaded screw; there was no significant difference in compression between an 18-mm and 24-mm central threadless screw. Conclusions: The design of headless compression screws allows for maximal interfragmentary compression at the screw midpoint; we questioned whether a short screw centered on the fracture site resulted in superior compression to a longer, noncentered screw. Our data suggest that centering a small screw (10 mm) along a proximal fracture generates significantly less interfragmentary compression than a longer, noncentered screw. Our results demonstrate that balance between maximizing screw length and centering the screw on the fracture is vital toward maximizing interfragmentary compression for the fixation of proximal third scaphoid fractures.

Partial Lateral Meniscectomy Affects Knee Stability Even in Anterior Cruciate Ligament-Intact Knees

BACKGROUND

The effects of a partial lateral meniscectomy on knee kinematics and forces in the lateral meniscus are critical to understand. The purpose of this study was to quantify the effects of varying sizes of partial lateral meniscectomies of the posterior horn and a total lateral meniscectomy on knee kinematics and resultant forces in the lateral meniscus.

METHODS

Using a robotic testing system, loads (134-N anterior tibial load + 200-N axial compression, 5-Nm internal tibial torque + 5-Nm valgus torque, and 5-Nm external tibial torque + 5-Nm valgus torque) were applied to 10 fresh-frozen cadaveric knees. The resulting joint motion and resultant forces in the lateral meniscus were determined for 4 knee states: intact, one-third and two-thirds partial lateral meniscectomies of the posterior horn, and total lateral meniscectomy.

RESULTS

A decrease in lateral translation of the tibia (up to 166.7%) was observed after one-third partial lateral meniscectomies of the posterior horn compared with the intact knee, in response to an anterior load at all knee flexion angles tested (p < 0.05). One-third partial lateral meniscectomies of the posterior horn decreased the resultant forces in the lateral meniscus compared with the intact knee at all knee flexion angles tested in response to an anterior load (p < 0.05) and to an internal tibial torque (p < 0.05). The results of two-thirds partial lateral meniscectomies of the posterior horn were similar to those of one-third partial meniscectomies (p > 0.05). Total lateral meniscectomies further decreased the lateral translation of the tibia (up to 316.6%) compared with the intact knee in response to an anterior load (p < 0.05).

CONCLUSIONS

The changes in joint motion and meniscal forces observed in this study after even small partial lateral meniscectomies may predispose knees to further injury.

CLINICAL RELEVANCE

Surgeons should always consider repairing and minimizing the resection of even small lateral meniscal tears to prevent the potential deleterious effects of partial meniscectomy reported in this cadaveric study.

Sagittal instability with inversion is important to evaluate after syndesmosis injury and repair: a cadaveric robotic study

PURPOSE

Disruption of the syndesmosis, the anterior-inferior tibiofibular ligament (AITFL), the posterior-inferior tibiofibular ligament (PITFL), and the interosseous membrane (IOM), leads to residual symptoms after an ankle injury. The objective of this study was to quantify tibiofibular joint motion with isolated AITFL- and complete syndesmotic injury and with syndesmotic screw vs. suture button repair compared to the intact ankle.

METHODS

Nine fresh-frozen human cadaveric specimens (mean age 60 yrs.; range 38-73 yrs.) were tested using a six degree-of-freedom robotic testing system and three-dimensional tibiofibular motion was quantified using an optical tracking system. A 5 Nm inversion moment was applied to the ankle at 0°, 15°, and 30° plantarflexion, and 10° dorsiflexion. Outcome measures included fibular medial-lateral translation, anterior-posterior translation, and external rotation in each ankle state: 1) intact ankle, 2) AITFL transected (isolated AITFL injury), 3) AITFL, PITFL, and IOM transected (complete injury), 4) tricortical screw fixation, and 5) suture button repair.

RESULTS

Both isolated AITFL and complete injury caused significant increases in fibular posterior translation at 15° and 30° plantarflexion compared to the intact ankle (p < 0.05). Tricortical screw fixation restored the intact ankle tibiofibular kinematics in all planes. Suture button repair resulted in 3.7 mm, 3.8 mm, and 2.9 mm more posterior translation of the fibula compared to the intact ankle at 30° and 15° plantarflexion and 0° flexion, respectively (p < 0.05).

CONCLUSION

Ankle instability is similar after both isolated AITFL and complete syndesmosis injury and persists after suture button fixation in the sagittal plane in response an inversion stress. Sagittal instability with ankle inversion should be considered when treating patients with isolated AITFL syndesmosis injuries and after suture button fixation.

LEVEL OF EVIDENCE

Controlled laboratory study, Level V.

Elbow Biomechanics: Soft Tissue Stabilizers

The elbow positions the hand in a stable manner relative to the trunk while allowing flexion and extension as well as forearm rotation at varying shoulder positions. Its ability to perform this task without joint subluxation is accomplished through a combination of bony congruency, ligamentous restraint, and dynamic stabilization. Elbow stability is challenged repeatedly during everyday activities, particularly when the arm is abducted. Traumatic injuries that lead to an elbow dislocation or the microtrauma associated with pitching are frequent situations that destabilize the elbow. This article reviews the soft tissue stabilizers that contribute to elbow kinematics and stability.

Localized Rotator Cuff Tendon Degeneration for Cadaveric Shoulders with and Without Tears Isolated to the Supraspinatus Tendon

Localized differences in tissue degeneration throughout intact and torn rotator cuff tendons have not been well quantified. The objective of this study was to investigate histological differences in localized degeneration in tendons with and without rotator cuff tears isolated to the supraspinatus tendon. Four intact shoulders and four shoulders with rotator cuff tears isolated to the supraspinatus tendon were dissected down to the infraspinatus and supraspinatus tendons. Biopsies were taken throughout the tendon insertion, mid-substance, myotendinous junction, and around the tear if present. Samples were stained with hematoxylin and eosin and tendon degeneration was graded based on collagen fiber organization, nuclei shape, cellularity, and lipoid degeneration. Comparisons in degeneration parameters were made based on the tendon type (supraspinatus vs. infraspinatus), location within the tendon, and presence of a tear. Supraspinatus tendons exhibited more degeneration than the infraspinatus tendon (P < 0.05). Significant increases in lipoid degeneration were found near the myotendinous junction compared to the rest of the tendon (P < 0.001). Tendons with rotator cuff tears showed greater amounts of lipoid degeneration compared to intact tendons (P = 0.03). A strong negative correlation was found between lipoid degeneration and collagen fiber organization (r = -0.922, P = 0.001). No differences in degeneration were found between medial, anterior, and posterior edges of the tear. The study highlights specific factors of tendon degeneration contributing to the local differences in tendon degeneration. By understanding local differences in tendon degeneration, surgical protocols for repair can be improved. Clin. Anat., 33:1007-1013, 2020. © 2019 Wiley Periodicals, Inc.

Altered shoulder kinematics using a new model for multiple dislocations-induced Bankart lesions

BACKGROUND

Many active individuals undergo multiple dislocations during the course of a season before surgical treatment without considering the implications of each successive injury. Therefore, the purpose of this study was to develop a multiple dislocation model for the glenohumeral joint and evaluate the resulting changes in joint function.

METHODS

Eight cadaveric shoulders were evaluated using a robotic testing system. A simulated clinical exam was performed by applying a 50 N anterior load to the humerus at 60° of glenohumeral abduction and external rotation. Each joint was then dislocated. The same loads were applied again and the resulting kinematics were recorded following each of 10 dislocations. The force required to achieve dislocation was recorded and capsulolabral status was assessed.

FINDINGS

A reproducible Bankart lesion was repeatedly created following the dislocation protocol. The force required for all dislocations significantly decreased following the 1st dislocation. In addition, even lower forces were required to achieve the 5th and subsequent dislocations (p < 0.05). Anterior translation in response to an anterior load during the simulated clinical exam increased between the intact and injured joints (p < 0.05). However, anterior translation reached a plateau following the 3rd to 10th dislocations and was increased compared with the 1st dislocation (p < 0.05).

INTERPRETATION

A repeatable Bankart lesion was not surgically made, but created by our new dislocation model. Joint function appeared to reach a constant level after the 3rd to 5th dislocations. Thus, multiple dislocations result in a deleterious dose dependent effect suggesting additional damage is not sustained after the fifth dislocation.

LEVEL OF EVIDENCE

Controlled laboratory study.

Superior clavicle drilling points and fluoroscopic inclination for anatomic coracoclavicular ligament reconstruction: a cadaveric study

PURPOSE

This study aims to investigate the superior clavicle cortex drilling points and fluoroscopic inclination angles for anatomic tunnel drilling in coracoclavicular ligament reconstruction.

METHODS

Twelve cadaveric shoulders with a mean age of 55.9 ± 6.2 years were investigated. Two 2.0 mm Kirschner wires were inserted penetrating the footprint centers of conoid and trapezoid both on the clavicle and coracoid. The location of the Kirschner wires on the superior clavicle cortex was measured. Fluoroscopy was used to obtain three views of shoulder: an anteroposterior, lateral, and cortical ring sign view. Reproducible angles were then recorded.

RESULTS

The Kirschner wire penetrating the conoid was located 40.0 ± 3.9 mm from the distal end and 18.1 ± 3.0 mm from the anterior edge of the clavicle. For the trapezoid, the Kirschner wire was located 19.1 ± 3.6 mm from the distal end and 9.9 ± 3.9 mm from the anterior edge. On the anteroposterior view, the conoid was 11.1° ± 10.1° medially and trapezoid was 26.8° ± 11.8° laterally tilted to the glenohumeral joint line. On the lateral view, the conoid was 42.8° ± 15.1° and trapezoid was 15.5° ± 12.0° superiorly tilted to the scapular spine. On the cortical ring sign view, the conoid was 50.8° ± 12.9° and trapezoid was 14.2 °± 11.0° superiorly tilted to the scapular spine.

CONCLUSIONS

The superior clavicle cortex drilling points and fluoroscopic inclination angles for anatomic tunnel drilling in coracoclavicular ligament reconstruction were demonstrated. Arthroscopy-assisted anatomic coracoclavicular ligament reconstruction has increased in popularity, and these findings may facilitate a more anatomic approach to coracoclavicular ligament reconstruction.

Effect of Meniscal Ramp Lesion Repair on Knee Kinematics, Bony Contact Forces, and In Situ Forces in the Anterior Cruciate Ligament

BACKGROUND

Meniscal ramp lesions are possible concomitant injuries in cases of anterior cruciate ligament (ACL) deficiency. Although recent studies have investigated the influence of ramp lesions on knee kinematics, the effect on the ACL reconstruction graft remains unknown.

PURPOSE/HYPOTHESIS

The purpose was to determine the effects of ramp lesion and ramp lesion repair on knee kinematics, the in situ forces in the ACL, and bony contact forces. It was hypothesized that ramp lesions will significantly increase in situ forces in the native ACL and bony contact forces and that ramp lesion repair will restore these conditions comparably with those forces of the intact knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Investigators tested 9 human cadaveric knee specimens using a 6 degrees of freedom robotic testing system. The knee was continuously flexed from full extension to 90° while the following loads were applied: (1) 90-N anterior load, (2) 5 N·m of external-rotation torque, (3) 134-N anterior load + 200-N compression load, (4) 4 N·m of external-rotation torque + 200-N compression load, and (5) 4 N·m of internal-rotation torque + 200-N compression load. Loading conditions were applied to the intact knee, a knee with an arthroscopically induced 25-mm ramp lesion, and a knee with an all-inside repaired ramp lesion. In situ forces in the ACL, bony contact forces in the medial compartment, and bony contact forces in the lateral compartment were quantified.

RESULTS

In response to all loading conditions, no differences were found with respect to kinematics, in situ forces in the ACL, and bony contact forces between intact knees and knees with a ramp lesion. However, compared with intact knees, knees with a ramp lesion repair had significantly reduced anterior translation at flexion angles from full extension to 40° in response to a 90-N anterior load (P < .05). In addition, a significant decrease in the in situ forces in the ACL after ramp repair was detected only for higher flexion angles when 4 N·m of external-rotation torque combined with a 200-N compression load (P < .05) and 4 N·m of internal-rotation torque combined with a 200-N compression load were applied (P < .05).

CONCLUSION

In this biomechanical study, ramp lesions did not significantly affect knee biomechanics at the time of surgery.

CLINICAL RELEVANCE

From a biomechanical time-zero perspective, the indications for ramp lesion repair may be limited.

Education and repetition improve success rate and quantitative measures of the pivot shift test

PURPOSE

Clinicians have different techniques and varying levels of experience with the pivot shift test, introducing variability into its performance. The purpose of this study was to evaluate the influence of teaching and repetition on the success rate and anterior translation of the lateral knee compartment during the pivot shift test in a cadaveric ACL injury model.

METHODS

Twenty-five participants (five each of medical students, orthopaedic surgery residents, physical therapists, athletic trainers, sports medicine fellows) were recruited and a senior orthopaedic surgeon served as gold standard examiner. Each participant performed 20 pivot shift tests on lower extremity cadaveric specimens with ACL deficiency and lateral meniscectomy: 5 prior to education (baseline), 10 after watching an instructional video (passive teaching), and 5 after an interactive education session (active teaching). The anterior translation of the lateral knee compartment was recorded during each pivot shift test using electromagnetic tracking system.

RESULTS

For medical students and orthopaedic surgery residents, significant improvement in success rate was found when compared to baseline (12% and 24%, respectively) after both passive (36% and 60%, respectively) and active teaching (52% and 72%, respectively) (p < 0.5). Medical students and residents were the only participants that independently achieved significant increases in anterior translation of the lateral knee compartment, each tripling the respective baseline value (p < 0.5). In the entire study population, significant increases in anterior translation of the lateral knee compartment and success rate of the pivot shift test were seen with continuous repetition (p < 0.5). However, the standard deviation of anterior translation of the lateral knee compartment was more than twice the gold standard examiner's standard deviation, indicating a high degree of variability.

CONCLUSION

Teaching of the pivot shift test plays a major role in the development of a proper technique. However, variability persisted despite teaching and repetition. New methods may be needed to improve the teaching of the pivot shift test.

Impact of Screw Length on Proximal Scaphoid Fracture Biomechanics

Background  Proximal scaphoid fractures display high nonunion rates and increased revision cases. Waist fracture fixation involves maximizing screw length within the cortex; however, the optimal screw length for proximal scaphoid fractures remains unknown. Purpose  The main purpose of this article is to compare stiffness and ultimate load for proximal scaphoid fracture fixation of various headless compression screw lengths. Methods  Eighteen scaphoids underwent an osteotomy simulating a 7 mm oblique proximal fracture. Screws of three lengths (10, 18, and 24 mm) were randomly assigned for fixation. Each specimen underwent cyclic loading with stiffness calculated during the last loading cycle. Specimens that withstood cyclic loading were loaded to failure. Results  No significant difference in stiffness between screw lengths was found. Ultimate load was significantly impacted by the screw length. A significant difference in ultimate load between a 10 and 24 mm screw was found; however, no significant difference occurred in ultimate load between an 18 and 24 mm screw. Conclusions  No significant difference in stiffness between all groups could be due to similarities in purchase in the proximal aspect. The 10 mm screw withstanding less ultimate load compared to the 24 mm screw could be due to the 10 mm screw gaining less purchase on either side of the fracture site compared to the 24 mm screw. Lack of significant difference in ultimate load between the 18 and 24 mm screw could be occurring because the fracture site is closer to the 18 mm screw midpoint, as distal threads are engaged closer to the fracture. Clinical Relevance  Maximizing screw length may not provide superior fixation biomechanically compared with fixation utilizing a 6 mm shorter screw for proximal scaphoid fractures.

Lateral Meniscal Allograft Transplantation With Bone Block and Suture-Only Techniques Partially Restores Knee Kinematics and Forces

BACKGROUND

The ability of lateral meniscal allograft transplantation (MAT) to improve knee stability and the meniscal load-bearing function in patients after meniscectomy is critical for surgical success.

PURPOSE

To compare the effects of 2 lateral MAT fixation techniques-bone block and suture only-on knee kinematics and forces.

STUDY DESIGN

Controlled laboratory study.

METHODS

With a robotic testing system, loads were applied during flexion on 10 fresh-frozen cadaveric knees: 134-N anterior tibial load + 200-N axial compression, 5-N·m internal tibial + 5-N·m valgus torques, and 5-N·m external tibial + 5-N·m valgus torques. Kinematic data were recorded for 4 knee states: intact, total lateral meniscectomy, lateral MAT bone block, and lateral MAT suture-only fixation. In situ force in the anterior cruciate ligament and resultant forces in the lateral meniscus and in the meniscal allograft were quantified via the principle of superposition. A repeated measures analysis of variance was used to analyze variations in kinematics and forces at 0°, 30°, 60°, and 90° of knee flexion. Significance was set at P < .05.

RESULTS

When anterior loads were applied, a decrease in medial translation of the tibia that was increased after total lateral meniscectomy was observed at 30°, 60°, and 90° of knee flexion for both the lateral MAT bone block (54.2%, 48.0%, and 50.0%) and the MAT suture-only (50.0%, 40.0%, and 34.6%) fixation techniques (P < .05). Yet, most of the increases in knee kinematics after lateral meniscectomy were not significantly reduced by either lateral MAT technique (P > .05 for each MAT technique vs the total lateral meniscectomy state). Resultant forces in the meniscal allograft were 50% to 60% of the resultant forces in the intact lateral meniscus in response to all loading conditions at all flexion angles (P < .05). Overall, no significant differences between lateral MAT techniques were observed regarding kinematics and forces (P > .05).

CONCLUSION

Lateral MAT partially restored medial translation of the tibia, and the resultant forces in the meniscal allograft were only 50% to 60% of the intact lateral meniscus forces in the cadaver model. In the majority of testing conditions, no significant changes of the in situ force in the anterior cruciate ligament were observed. Surgeons should consider the potential benefits of lateral MAT when deciding the appropriate treatment for symptomatic patients after lateral meniscectomies. Both lateral MAT techniques functioned similarly.

CLINICAL RELEVANCE

The load-bearing function of the meniscal allograft observed in this study may be beneficial in ameliorating the short- and long-term disability associated with lateral meniscal deficiency.

A Validated, Subject-Specific Finite Element Model for Predictions of Rotator Cuff Tear Propagation

Rotator cuff tears are a significant clinical problem previously investigated by unvalidated computational models that either use simplified geometry or isotropic elastic material properties to represent the tendon. The objective of this study was to develop an experimentally validated, finite element model of supraspinatus tendon using specimen-specific geometry and inhomogeneous material properties to predict strains in intact supraspinatus tendon. Three-dimensional tendon surface strains were determined at 60°, 70°, and 90° of glenohumeral abduction for articular and bursal surfaces of supraspinatus tendon during cyclic loading to serve as validation data. A finite element model was developed using the tendon geometry and inhomogeneous material properties to predict surface strains for loading conditions mimicking experimental loading conditions. Experimental strains were directly compared with computational model predictions to validate the model. Overall, the model successfully predicted magnitudes of strains that were within the experimental repeatability of 3% strain of experimental measures on both surfaces of the tendon. Model predictions and experiments showed the largest strains to be located on the articular surface (~8% strain) between the middle and anterior edge of the tendon. Importantly, the reference configuration chosen to calculate strains had a significant effect on strain calculations, and therefore must be defined with an innovative optimization algorithm. This study establishes a rigorously validated, specimen-specific computational model using novel surface strain measurements for use in investigating the function of the supraspinatus tendon and to ultimately predict the propagation of supraspinatus tendon tears based on the tendon's mechanical environment.

Interfragmentary Compression Forces Vary Based on Scaphoid Bone Screw Type and Fracture Location

BACKGROUND

The objective of this study was to determine the interfragmentary compression forces generated in a foam model as a function of headless compression screw type (fully threaded and central threadless) and fracture location.

METHODS

Eighty-eight polyurethane foam models were fixed across a simulated transverse fracture with either a fully threaded screw or a central threadless screw. The location of the transverse fracture varied along the length of the foam model in 2 mm increments for 11 fracture locations. The force generated at the fracture site upon fixation was utilized to determine the interfragmentary compression. Interfragmentary compression was compared using a paired t test and 2-way analysis of variance, with significance set at P < .05.

RESULTS

Interfragmentary compression was found to vary based on fracture location and screw type. The fully threaded screw generated significantly greater compression for fracture locations at 12 mm and 18 mm from the top edge of the foam model, while the central threadless screw generated significantly greater compression for fractures located 2 mm from the top edge of the foam model.

CONCLUSIONS

The central threadless screw and the fully threaded screw had different fracture locations where maximum compression force occurred. The fully threaded screw generated greater compression force toward the screw center due to greater thread purchase. However, the central threadless screw generated greater compression at the most proximal fracture location due to its greater thread pitch toward the screw head. Maximizing interfragmentary compression may aid in reducing nonunion rates associated with the internal fixation of proximal scaphoid fractures.

Non-uniform strain distribution in anterolateral capsule of knee: Implications for surgical repair

The existence of a ligamentous structure within the anterolateral capsule, which can be injured in combination with the anterior cruciate ligament, has been debated. Therefore, the purpose of this study was to determine the magnitude and direction of the strain in the anterolateral capsule in response to external loads applied to the knee. The anterolateral capsule was hypothesized to not function like a traditional ligament. A 6-degree-of-freedom robotic testing system was used to apply ten external loads to human cadaveric knees (n = 7) in the intact and anterior cruciate ligament (ACL) deficient states. The position of strain markers was recorded on the midsubstance of the anterolateral capsule during the resulting joint kinematics to determine the magnitude and direction of the maximum principal strain. The peak maximum principal strain ranged from 22% to 52% depending on the loading condition. When histograms of strain magnitude values were analyzed to determine strain uniformity, the mean kurtosis was 1.296 ± 0.955, lower than a typical ligament, and the mean variance was 0.015 ± 0.008, higher than a typical ligament. The mean angles of the strain direction vectors compared to the proposed ligament ranged between 38° and 130° (p < 0.05). The magnitude of the maximum principal strain in the anterolateral capsule is much larger than a typical ligament and does not demonstrate a uniform strain distribution. The direction of strain is also not aligned with the proposed ligament. Clinical Significance: Reconstruction methods using tendons will not produce normal joint function due to replacement of a multi-axial structure with a uni-axial structure. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

The effect of adipose-derived stem cells on enthesis healing after repair of acute and chronic massive rotator cuff tears in rats

BACKGROUND

Chronic massive rotator cuff tears heal poorly and often retear. This study investigated the effect of adipose-derived stem cells (ADSCs) and transforming growth factor-β3 (TGF-β3) delivered in 1 of 2 hydrogels (fibrin or gelatin methacrylate [GelMA]) on enthesis healing after repair of acute or chronic massive rotator cuff tears in rats.

METHODS

Adult male Lewis rats underwent bilateral transection of the supraspinatus and infraspinatus tendons with intramuscular injection of botulinum toxin A (n = 48 rats). After 8 weeks, animals received 1 of 8 interventions (n = 12 shoulders/group): (1) no repair, (2) repair only, or repair augmented with (3) fibrin, (4) GelMA, (5) fibrin + ADSCs, (6) GelMA + ADSCs, (7) fibrin + ADSCs + TGF-β3, or (8) GelMA + ADSCs + TGF-β3. An equal number of animals underwent acute tendon transection and immediate application of 1 of 8 interventions. Enthesis healing was evaluated 4 weeks after the repair by microcomputed tomography, histology, and mechanical testing.

RESULTS

Increased bone loss and reduced structural properties were seen in chronic compared with acute tears. Bone mineral density of the proximal humerus was higher in repairs of chronic tears augmented with fibrin + ADSCs and GelMA + ADSCs than in unrepaired chronic tears. Similar improvement was not seen in acute tears. No intervention enhanced histologic appearance or structural properties in acute or chronic tears.

CONCLUSIONS

Surgical repair augmented with ADSCs may provide more benefit in chronic tears compared with acute tears, although there was no added benefit to supplementing ADSCs with TGF-β3.

Development and validation of a kinematically-driven discrete element model of the patellofemoral joint

Quantifying the complex loads at the patellofemoral joint (PFJ) is vital to understanding the development of PFJ pain and osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses with potential application at the PFJ to better understand PFJ mechanics. The current study validated a DEA modeling framework driven by PFJ kinematics to predict experimentally-measured PFJ contact stress distributions. Two cadaveric knee specimens underwent quadriceps muscle [215 N] and joint compression [350 N] forces at ten discrete knee positions representing PFJ positions during early gait while measured PFJ kinematics were used to drive specimen-specific DEA models. DEA-computed contact stress and area were compared to experimentally-measured data. There was good agreement between computed and measured mean and peak stress across the specimens and positions (r = 0.63-0.85). DEA-computed mean stress was within an average of 12% (range: 1-47%) of the experimentally-measured mean stress while DEA-computed peak stress was within an average of 22% (range: 1-40%). Stress magnitudes were within the ranges measured (0.17-1.26 MPa computationally vs 0.12-1.13 MPa experimentally). DEA-computed areas overestimated measured areas (average error = 60%; range: 4-117%) with magnitudes ranging from 139 to 307 mm² computationally vs 74-194 mm² experimentally. DEA estimates of the ratio of lateral to medial patellofemoral stress distribution predicted the experimental data well (mean error = 15%) with minimal measurement bias. These results indicate that kinematically-driven DEA models can provide good estimates of relative changes in PFJ contact stress.

Influence of knee position and examiner-induced motion on the kinematics of the pivot shift

Background

Grading of the pivot shift test varies significantly depending on the examiner’s technique. Thus, the purpose of this study was to determine the influence of knee starting position and the magnitude of motion during the reduction event on the magnitude of the pivot shift test.

Methods

Twenty-five clinical providers each performed a total of twenty pivot shift tests on one of two fresh-frozen cadaveric full lower extremity specimens with different grades of rotatory knee laxity. By means of ACL transection and lateral meniscectomy, one specimen was prepared to have a high-grade pivot shift and one to have a low-grade pivot shift. Six-degree-of-freedom kinematics were recorded during each pivot shift test using an electromagnetic-tracking-system. Successful pivot shift tests were defined and selected using an automated, mathematical algorithm based on the exceeding of a threshold value of anterior translation of the lateral knee compartment. The kinematics were correlated with the magnitude of anterior translation of the lateral knee compartment based on varying degrees of rotatory knee laxity using the Pearson correlation coefficient.

Results

Only mild correlations between anterior translation of the lateral knee compartment and internal tibial rotation at the start of the reduction event were observed in both specimens. The ability to generate a successful reduction event was significantly dependent on the rotatory knee laxity, with a 54% success rate on the high-laxity specimen compared to a 30% success rate on the low-laxity specimen (p < 0.001). Nearly 80% of the variability of the anterior translation of the lateral knee compartment in both specimens was accounted for by external rotation during the reduction event (r = 0.847; p < 0.001). Varus rotation during the reduction event also showed a strong correlation with the anterior translation of the lateral knee compartment in the low-laxity specimen (r = 0.835; p < 0.001).

Conclusion

Magnitude of motion during the reduction event affected the magnitude of anterior translation of the lateral knee compartment more than the starting position. External rotation during the reduction event accounted for most of the variability in the pivot shift test. More uniform maneuvers and improved teaching are essential to generate repeatable quantitative results of the pivot shift test.

Effects of Tendon Degeneration on Predictions of Supraspinatus Tear Propagation

Rotator cuff tendons undergo degeneration with age, which could have an impact on tear propagation. The objective of this study was to predict tear propagation for different levels of tissue degeneration using an experimentally validated finite element model of a supraspinatus tendon. It was hypothesized that greater amounts of degeneration will result in tear propagation at lower loads than tendons with less degeneration. Using a previously-validated computational model of supraspinatus tendon, 1-cm tears were introduced in the anterior, middle, and posterior thirds of the tendon. Cohesive elements were assigned subject-specific failure properties to model tear propagation, and tendon degeneration ranging from "minimal" to "severe" was modeled by modifying its mechanical properties. Tears in tendons with severe degeneration required the smallest loads to propagate (122-207 N). Posterior tears required greater loads compared to middle and anterior tears at all levels of degeneration. Stress and strain required for tear propagation decreased substantially with degeneration, ranging from 8.5 MPa and 32.6% strain for minimal degeneration and 0.6 MPa and 4.5% strain for severe degeneration. Overall, this work indicates that greater amounts of tendon degeneration lead to greater risk of tear propagation, supporting the need for early detection and treatment of rotator cuff tears.

The Use of Fluoroscopy Leads to Improved Identification of the Femoral Lateral Collateral Ligament Origin Site When Compared With Traditional Tactile Techniques

PURPOSE

To determine whether a fluoroscopic technique can be used to improve the accuracy of the determination of the femoral origin of the lateral collateral ligament (LCL).

METHODS

A 1-cm incision was made over the lateral epicondyle in 13 fresh-frozen cadaveric knee specimens, and the LCL origin was determined first by palpation and then with a previously described fluoroscopic method. Both points for the LCL origin were marked with 2-mm Kirschner wires. The distances between the center of the anatomic LCL origin and the LCL origin points determined by palpation and fluoroscopic imaging were calculated. An independent t-test was used to compare the distances between the anatomic LCL origin center and the determined LCL origin points.

RESULTS

The LCL origin points determined by fluoroscopic imaging were significantly (P = .005) closer to the anatomic center of the LCL origin point than the ones determined by palpation (3.2 mm ± 1.6 mm vs 5.0 mm ± 1.6 mm, respectively). A total of 92.7% fluoroscopically determined LCL origin points were within a 5 mm radius surrounding the anatomic LCL origin point. In contrast, only 53.8% LCL origin points determined by palpation were within a 5 mm radius surrounding the anatomic LCL origin point.

CONCLUSIONS

The use of palpation to identify the LCL origin may not be an accurate method for performing an isometric and anatomic LCL reconstruction. The use of fluoroscopic imaging appears to be a feasible method for identifying the LCL origin in clinical practice and may increase the accuracy of LCL origin identification. Fluoroscopic guidance improves accuracy in determining the anatomic LCL origin, which may help avoiding tunnel malplacement during LCL reconstruction. CLINICAL RELEVANCE: The use of a previously described radiographic method for identifying the LCL origin may be used to achieve a more anatomic LCL reconstruction.

An Increased Lateral Femoral Condyle Ratio Is a Risk Factor for Anterior Cruciate Ligament Injury

BACKGROUND

The purpose of this study was to examine the relationship between distal femoral morphology and anterior cruciate ligament (ACL) injury, ACL reconstruction (ACLR) failure, and contralateral ACL injury. It was hypothesized that increased posterior femoral condylar depth, quantified as the lateral femoral condyle ratio, would correlate with increased risk of primary ACL injuries, ACLR failures, and contralateral ACL injuries.

METHODS

The charts of consecutive patients who underwent arthroscopic knee surgery at an academic medical center from 2012 to 2016 with minimum follow-up of 24 months were retrospectively reviewed. Patients were stratified into 4 groups: (1) a control group of patients with no ACL injury, (2) patients with primary ACL injury, (3) patients with failed ACLR, and (4) patients with previous ACL injury and subsequent contralateral ACL injury. With use of lateral radiographs, the ratio of posterior femoral condylar depth to total condylar length was defined as the lateral femoral condyle ratio. Differences between study groups were identified with use of analysis-of-variance (ANOVA) and post-hoc testing with significance set at p < 0.05. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cutoff for detecting increased risk of ACL injury.

RESULTS

Two hundred patients met the inclusion criteria. The mean lateral femoral condyle ratios (and standard deviations) were 61.2% ± 2.4% in the control group, 64.2% ± 3.8% in the primary ACL injury group, 64.4% ± 3.6% in the failed ACLR group, and 66.9% ± 4.3% in the contralateral ACL injury group. Patients who had a primary ACL injury, failed ACLR, or contralateral ACL injury had significantly higher ratios compared with the control group (p < 0.008). ROC curve analysis demonstrated that a lateral femoral condyle ratio of >63% was associated with an increased risk for ACL injury, with a sensitivity of 77% and a specificity of 72%.

CONCLUSIONS

The data from this study show that increased posterior femoral condylar depth, quantified as the lateral femoral condyle ratio, is associated with an increased risk of ACL injury, including primary and contralateral ACL injuries. The data from this study may help clinicians to identify patients at a greater risk of ACL injury.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

In situ force in the anterior cruciate ligament, the lateral collateral ligament, and the anterolateral capsule complex during a simulated pivot shift test

The role of the anterolateral capsule complex in knee rotatory stability remains controversial. Therefore, the objective of this study was to determine the in situ forces in the anterior cruciate ligament (ACL), the anterolateral capsule, the lateral collateral ligament (LCL), and the forces transmitted between each region of the anterolateral capsule in response to a simulated pivot shift test. A robotic testing system applied a simulated pivot shift test continuously from full extension to 90° of flexion to intact cadaveric knees (n = 7). To determine the magnitude of the in situ forces, kinematics of the intact knee were replayed in position control mode after the following procedures were performed: (i) ACL transection; (ii) capsule separation; (iii) anterolateral capsule transection; and (iii) LCL transection. A repeated measures ANOVA was performed to compare in situ forces between each knee state (*p < 0.05). The in situ force in the ACL was significantly greater than the forces transmitted between each region of the anterolateral capsule at 5° and 15° of flexion but significantly lower at 60°, 75°, and 90° of flexion. This study demonstrated that the ACL is the primary rotatory stabilizer at low flexion angles during a simulated pivot shift test in the intact knee, but the anterolateral capsule plays an important secondary role at flexion angles greater than 60°. Furthermore, the contribution of the "anterolateral ligament" to rotatory knee stability in this study was negligible during a simulated pivot shift test. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:847-853, 2018.

Effects of tear size and location on predictions of supraspinatus tear propagation

Rotator cuff tears remain a significant clinical problem with a high incidence rate and severe clinical burden. Previous computational models developed to study rotator cuff tears have not modeled tissue damage and tear propagation. The objective of this study was to predict tear propagation for various combinations of tear size and location using an experimentally validated finite element model of supraspinatus tendon. It was hypothesized that larger rotator cuff tears propagate at lower loads than smaller tears, and that posterior tears require higher loads to propagate than anterior tears. Using a previously validated computational model of supraspinatus tendon, tears of size 0.5-1.5 cm were introduced to the tendon geometry in the anterior, middle, and posterior tendon thirds. Cohesive elements were assigned subject-specific failure properties and used to model tissue damage and tear propagation. A displacement of 5 mm was applied to the medial tendon edge to induce tear propagation. Model outputs included critical load required to propagate the tear, and principal stress and maximum principal strain at the anterior and posterior tear tips. For all tear sizes, posterior tears required the highest loads to propagate (247-567 N). Anterior tears generally required the least load to propagate (171-280 N). Stress and strain were larger on the articular side (maximum 33.9% articular strain vs 27.8% bursal strain). Overall, larger tears located in the anterior supraspinatus tendon that interrupt the rotator cable are most at risk for tear propagation, and should be carefully followed by clinicians when considering treatment options.

Lateral Extra-articular Tenodesis Has No Effect in Knees With Isolated Anterior Cruciate Ligament Injury

PURPOSE

To investigate knee kinematics in response to physical examinations to determine the effect of anterolateral capsular injury and lateral extra-articular tenodesis (LET) in anterior cruciate ligament (ACL)-deficient and -reconstructed knees.

METHODS

Seven human lower limb cadavers were used in this study (mean age, 60 years; age range, 56-63 years). Physical examinations were performed, including the pivot-shift test, Lachman test, anterior drawer at 90°, and internal and external tibial rotation at 30°, 60°, and 90° of knee flexion. ACL injury and reconstruction and LET, all with and without an injured anterolateral capsule, were investigated. Tibial translation and rotation relative to the femur were measured by an electromagnetic tracking system during the physical examination.

RESULTS

Anterior translation of the lateral knee compartment and internal tibial rotation during the pivot-shift test were highest in combined ACL-deficient and anterolateral capsule-deficient knees (12.3 ± 7.4 mm and 16.3° ± 8.5°, respectively). With the presence of an anterolateral capsular injury, a combined ACL reconstruction and LET reduced the anterior translation of the lateral knee compartment during the pivot-shift test significantly (P = .042), whereas anatomic ACL reconstruction did not. Internal tibial rotation displayed overconstraint when a LET was performed, especially when the anterolateral capsule was intact.

CONCLUSIONS

ACL reconstruction in combination with a LET was able to reduce anterior tibial translation and internal tibial rotation in response to different physical examinations. However, combined ACL reconstruction and LET led to overconstraint of internal tibial rotation when the anterolateral capsule was intact. CLINICAL RELEVANCE: On the basis of our results, LET with ACL reconstruction restores stability in a combined ACL-injured and anterolateral capsule-injured knee. However, LET with ACL reconstruction overconstrains the knee in an isolated ACL injury.