Increase In Anterior Translation Research Articles

Kinematics, kinetics, and new insights from a contemporary analysis of the first experiments to produce cervical facet dislocations in the laboratory.

The first experimental study to produce cervical facet dislocation (CFD) in cadaver specimens captured the vertebral motions and axial forces that are important for understanding the injury mechanics. However, these data were not reported in the original manuscript, nor been presented in the limited subsequent studies of experimental CFD. Therefore, the aim of this study was to re-examine the analog data from the first experimental study to determine the local and global spinal motions, and applied axial force, at and preceding CFD. In the original study, quasistatic axial loading was applied to 14 cervical spines by compressing them between two metal plates. Specimens were fixed caudally via a steel spindle positioned within the spinal canal and a bone pin through the inferior-most vertebral body. Global rotation of the occiput was restricted but its anterior translation was unconstrained. The instant of CFD was identified on sagittal cineradiograph films (N = 10), from which global and intervertebral kinematics were also calculated. Corresponding axial force data (N = 6) were extracted, and peak force and force at the instant of injury were determined. CFD occurred in eight specimens, with an intervertebral flexion angle of 34.8 ± 5.6 degrees, and a 3.1 ± 1.9 mm increase in anterior translation, at the injured level. For seven specimens, CFD was produced at the level of transition from upper neck lordosis to lower neck kyphosis. Five specimens with force data underwent CFD at 545 ± 147 N, preceded by a peak axial force (755 ± 233 N) that appeared to coincide with either fracture or soft tissue failure. Re-examining this rich dataset has provided quantitative evidence that small axial compression forces, combined with anterior eccentricity and upper neck extension, can cause flexion and shear in the lower neck, leading to soft tissue rupture and CFD.

Abnormal Static Sagittal Cervical Curvatures following Motor Vehicle Collisions: A Retrospective Case Series of 41 Patients before and after a Crash Exposure.

Three spine clinic records were reviewed over a 2-year period, looking for patients where both an initial lateral cervical X-ray and an examination were performed prior to the patient being exposed to a MVC; afterwards, an additional exam and radiographic analysis were obtained. A total of 41 patients met the inclusion criteria. Examination records of pain intensity on numerical pain rating scores (NPRS) and neck disability index (NDI), if available, were analyzed. The CLRs were digitized and modeled in the sagittal plane using curve fitting and the least squares error approach. Radiographic variables included total cervical curve (ARA C2-C7), Chamberlain's line to horizontal (skull flexion), horizontal translation of C2 relative to C7, segmental translations (retrolisthesis and anterolisthesis), and circular modelling radii. There were 15 males and 26 females with an age range of 8-65 years. Most participants were drivers (28) involved in rear-end impacts (30). The pre-injury NPRS was 2.7 while the post injury was 5.0; p < 0.001. The NDI was available on 24/41 (58.5%) patients and increased after the MVC from 15.7% to 32.8%, p < 0.001. An altered cervical curvature was identified following exposure to MVC, characterized by an increase in the mean radius of curvature (265.5 vs. 555.5, p < 0.001) and an approximate 8° reduction of lordosis from C2-C7; p < 0.001. The mid-cervical spine (C3-C5) showed the greatest curve reduction with an averaged localized mild kyphosis at these levels. Four participants (10%) developed segmental translations that were just below the threshold of instability, segmental translations < 3.5 mm. The post-exposure MVC cervical curvature was characterized by an increase in radius of curvature, an approximate 8° reduction in C2-C7 lordosis, a mild kyphosis of the mid-cervical spine, and a slight increase in anterior translation of C2-C7 sagittal balance. The modelling result indicates that the post-MVC cervical sagittal alignment approximates a second-order buckling alignment, indicating a significant alteration in curve geometry. Future biomechanics experiments and clinical investigations are needed to confirm these findings.

Biomechanical Comparison of Anterior Cruciate Ligament Reconstruction Using a Single-Bundle Round or Ribbon-like Hamstring Tendon Graft

Background: Persistent instability of the knee is reported in up to 30% of patients after anterior cruciate ligament (ACL) reconstruction. Based on anatomic findings showing that ACL is a flat ribbon-like structure that twists during knee flexion, a new surgical ACL reconstruction technique using a ribbon-like graft has been developed. However the effect of this surgical technique on knee kinematics has not yet been evaluated. Purpose: To compare the anteroposterior and rotational stability of the knee after ACL reconstruction using single-bundle (SB) round and ribbon-like grafts in anterolateral-intact/deficient knees. Study Design: Controlled laboratory study. Methods: Twelve human fresh-frozen cadaveric knees were tested with a 6 degrees of freedom robotic system. Internal rotation and anterior translation of the knee were recorded from 0° to 90° of flexion. A full kinematic assessment was performed in each of the following conditions: (1) intact knee, (2) after sectioning of the ACL, (3) after ACL reconstruction using a SB hamstring tendon graft in a round configuration and a ribbon-like configuration, and (4) after sectioning of the anterolateral structures. One-way analysis of variance and post hoc Tukey tests were used for statistical analyses. Results: When compared with the intact knee, the ACL-deficient knee demonstrated a mean ± SD increase in anterior translation and internal rotation of 6.3 ± 2.5 mm (P < .01) and 5.8°± 2.3° (P < .01), respectively. After ACL reconstruction using a SB ribbon-like graft, the mean difference in anterior translation and internal rotation as compared with the intact knee was −0.1 ± 1.5 mm (P = .842) and 0.0°± 1.1° (P = .999). These differences from the intact knee were also not significant after ACL reconstruction using a round graft (−0.1 ± 1.3 mm, P = .999; −0.5°± 1.5°, P = .401). In the ACL-reconstructed knee using either a ribbon-like or round graft, sectioning of the anterolateral structures did not induce a significant increase of anterior translation and internal rotation of the knee. Conclusion: ACL reconstruction using a SB ribbon-like or round graft restored the kinematics of the intact knee at time zero. Secondary sectioning of the anterolateral structures in the ACL-reconstructed knee using both types of graft did not significantly affect the anterior translation and internal rotation of the knee. Clinical Relevance: This is the first biomechanical study on the new ACL reconstruction technique using a ribbon-like graft.

Four-dimensional computed tomography evaluation of shoulder joint motion in collegiate baseball pitchers

The purpose of this study is to evaluate the glenohumeral contact area, center of glenohumeral contact area, and center of humeral head during simulated pitching motion in collegiate baseball pitchers using four-dimensional computed tomography (4D CT). We obtained 4D CT data from the dominant and non-dominant shoulders of eight collegiate baseball pitchers during the cocking motion. CT image data of each joint were reconstructed using a 3D reconstruction software package. The glenohumeral contact area, center of glenohumeral contact area, center of humeral head, and oblateness of humeral head were calculated from 3D bone models using customized software. The center of glenohumeral contact area translated from anterior to posterior during maximum external rotation to maximum internal rotation (0.58 ± 0.63 mm on the dominant side and 0.99 ± 0.82 mm on the non-dominant side). The center of humeral head translated from posterior to anterior during maximum external rotation to maximum internal rotation (0.76 ± 0.75 mm on the dominant side and 1.21 ± 0.78 mm on the non-dominant side). The increase in anterior translation of the center of glenohumeral contact area was associated with the increase in posterior translation of the center of humeral head. Also, the increase in translation of the center of humeral head and glenohumeral contact area were associated with the increase in oblateness of the humeral head. 4D CT analyses demonstrated that the center of humeral head translated in the opposite direction to that of the center of glenohumeral contact area during external rotation to internal rotation in abduction in the dominant and non-dominant shoulders. The oblateness of the humeral head may cause this diametric translation. 4D CT scanning and the software for bone surface modeling of the glenohumeral joint enabled quantitative assessment of glenohumeral micromotion and be used for kinematic evaluation of throwing athletes.

Kinematic Analysis of Lateral Meniscal Oblique Radial Tears in the Anterior Cruciate Ligament–Deficient Knee

Background: Lateral meniscal oblique radial tears (LMORT) occur frequently in conjunction with anterior cruciate ligament (ACL) disruption and are anatomically distinct from meniscus root tears. Hypothesis/Purpose: The purpose of this study was to characterize the effects of LMORT types 3 (LMORT3) and 4 (LMORT4) lesions on joint stability and meniscal extrusion in ACL-deficient knees. Our hypothesis was that both lesions would promote significant increases in anterior translation and meniscal extrusion, with the LMORT4 lesion having a greater effect. Study Design: Controlled laboratory study. Methods: Two matched pairs of cadaveric knees (n = 4) were used to optimize the testing sequence. Additional cadaveric knees with LMORT3 (n = 8) and LMORT4 (n = 8) lesions created after ACL transection underwent robotic kinematic testing for anterior drawer and pivot-shift simulations with associated ultrasound-measured meniscal extrusion at clinically relevant knee flexion angles. Results: Optimization testing showed no differences on the effect of LMORT4 lesions for anterior translation and lateral meniscal extrusion with ACL-intact versus ACL-deficient knees. ACL deficiency and LMORT3 and LMORT4 lesions with ACL deficiency were associated with significantly greater anterior translation compared with ACL-intact state for both anterior drawer and pivot-shift testing at all flexion angles (P < .001). ACL deficiency with either LMORT3 or LMORT4 lesion was associated with significantly greater anterior translation than was ACL deficiency only (P < .005) for anterior drawer testing at 90° of flexion. Meniscal extrusion was greater with LMORT3 and LMORT4 lesions compared with ACL deficiency only (P < .05) for anterior drawer at 60° of flexion and for pivot shift at 15° of flexion. The LMORT4 lesion demonstrated increased anterior translation for anterior drawer (P = .003) at 60° of flexion (12%) as well as for pivot shift at 15° of flexion (7%) and 30° of flexion (13%) (P < .005) compared with ACL deficiency only. Conclusion: In this cadaveric model, the addition of an LMORT3 or LMORT4 lesion increased anterior laxity for both the anterior drawer and the pivot shift when compared with an isolated ACL tear. Lateral meniscal extrusion was also exacerbated by these LMORT lesions. Clinical Relevance: LMORT lesions, distinct from meniscus root tears, occur frequently in conjunction with ACL tears. This study characterized the biomechanical consequences of LMORT3 and LMORT4 lesions on joint stability and meniscal function, highlighting the importance of diagnosing and treating LMORT lesions at the time of ACL reconstruction.

Effect of Early Residual Laxity After Anterior Cruciate Ligament Reconstruction on Long-term Laxity, Graft Failure, Return to Sports, and Subjective Outcome at 25 Years

Background: In spite of supposedly successful surgery, slight residual knee laxity may be found at follow-up evaluations after anterior cruciate ligament reconstruction (ACLR), and its clinical effect is undetermined. Purpose: To investigate whether a 3- to 5-mm increase in anterior translation 6 months after ACLR affects the risk of graft failure, rate of return to sports, and long-term outcome. Study Design: Cohort study; Level of evidence, 2. Methods: From a cohort of 234 soccer, team handball, and basketball players undergoing ACLR using bone–patellar tendon–bone graft, 151 athletes were included who attended 6-month follow-up that included KT-1000 arthrometer measures. A tight graft was defined as <3-mm side-to-side difference between knees (n = 129), a slightly loose graft as 3 to 5 mm (n = 20), and a loose graft as >5 mm (n = 2). Graft failure was defined as ACL revision surgery, >5-mm side-to-side difference, or anterolateral rotational instability 2+ or 3+ at 2-year follow-up. Finally, a 25-year evaluation was performed, including a clinical examination and questionnaires. Results: The rate of return to pivoting sports was 74% among athletes with tight grafts and 70% among those with slightly loose grafts. Also, return to preinjury level of sports was similar between those with slightly loose and tight grafts (40% vs 48%, respectively), but median duration of the sports career was longer among patients with tight grafts: 6 years (range, 1-25 years) vs 2 years (range, 1-15 years) (P = .01). Five slightly loose grafts (28%) and 6 tight grafts (5%) were classified as failures after 2 years (P = .002). Thirty percent (n = 6) of patients with slightly loose grafts and 6% (n = 8) with tight grafts had undergone revision (P = .004) by follow-up (25 years, range, 22-30 years). Anterior translation was still increased among the slightly loose grafts as compared with tight grafts at long-term follow-up (P < .05). In patients with tight grafts, 94% had a Lysholm score ≥84 after 24 months and 58% after 25 years, as opposed to 78% (P = .02) and 33% (P = .048), respectively, among patients with slightly loose grafts. Conclusion: A slightly loose graft at 6 months after ACLR increased the risk of later ACL revision surgery and/or graft failure, reduced the length of the athlete’s sports career, caused permanent increased anterior laxity, and led to an inferior Lysholm score.

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

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. 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. 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. 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.

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

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

Nearly 90% participation in sports activity 12years after non-surgical management for anterior cruciate ligament injury relates to physical outcome measures.

Traditionally reconstructive surgery is recommended for patients planning to return to sport (RTS), especially to pivoting sports after anterior cruciate (ACL) rupture. Recent trends focus on delaying or avoiding surgery as some studies have found similar rates of RTS following both surgical and conservative management. This study aimed to establish long-term RTS levels in ACL-ruptured individuals treated conservatively, and to investigate the relationship between outcome measures and RTS, in particular, pivoting sports. Fifty-five patients from a cohort of 132 ACL-deficient patients were followed-up for 12 (IQR8,19)years post injury. Mean-aged 42 years, 22 patients were females and 33 males, 35 had meniscal injuries. Patients were treated with physiotherapy focussing on strength and dynamic stability training and not reconstructive surgery. Return to sport was measured on a 6-point scale. Outcome measures included: objective stability, subjective stability, quadriceps and hamstring strength. Spearman's rho and Chi-square tests were used to assess the relationship between RTS and outcome measures. Eighty-nine percent of ACL-deficient patients were currently participating in sport despite a 38% increase in anterior translation (p < 0.001) and a 7.5% loss of quadriceps strength (p = 0.004) compared to the contralateral side. Six patients (11%) did not RTS, ten (18%) returned to safe sports, five (9%) returned to running and 16 (29%) to non-strenuous sports involving limited twisting. Eighteen patients (33%) returned to pivoting sports, 12(22%) at recreational level and six (11%) at competitive level. The level of RTS was related to subjective stability (p = 0.002), and to quadriceps and hamstring strength of the injured leg (p < 0.001). Patients able to return to pivoting sports differed significantly from those not doing so in outcome measures including objective (p = 0.022) and subjective stability (p = 0.035), and quadriceps strength (p = 0.044). Eighty-nine percent of ACL-ruptured individuals treated conservatively lead an active sporting life. One-third returned to pivoting sports. OverallRTS was related to subjective and objective stability and quadriceps and to a lesser extent hamstring strength. This finding reinforced the importance of dynamic stability training as an initial treatment option in most cases. III.

The Modified Anterior Drawer Test (MADT): A New Clinical Test for Assessing Subtalar Instability a Cadaveric and Clinical Assessment

Background: Chronic lateral ankle instability describes multiple pathologies affecting the tibiotalar or talocalcaneal articulations of the foot. One quarter of cases are caused by isolated or concomitant subtalar instability. The standard anterior drawer test (ADT) is used in routine clinical practice to assess abnormal movement at the tibiotalar joint. However, a positive test does not discriminate whether excessive translation is at the tibiotalar or subtalar joint. We suggest a modification to the standard ADT which separates the ankle joint translation by manually immobilising the tibiotalar joint in order isolate anterior translation at the subtalar joint. In the presence of a positive ADT, the modified anterior drawer test (MADT) would help discriminate if the pathological translation is at the tibiotalar or the subtalar joint or both. Methods: Our clinical study was an observational analysis of a cohort of 12 patients who had presented to an outpatient foot clinic in east of England. In addition, a cadaveric study was used to assess subtalar anterior translation. Results: In 50% of patients who had a clinically positive ADT, the MADT was negative which correlated 100% with Stress Broden radiographic views. Cadaveric analysis was done to show an increase in anterior translation with sequential sectioning of supporting ligaments. We demonstrated an absolute reduction in anterior translation in subtalar instability with the additional posterior force (MADT). Conclusion: The clinical and cadaveric data supports the use of the MADT as a valuable adjunct in the diagnosis and exclusion of subtalar instability as a cause of symptoms in addition to stress radiography.

Diagnostic findings caused by cutting of the iliotibial tract and anterolateral ligament in an ACL intact knee using a standardized and automated clinical knee examination

PurposeThe purpose of this study was to evaluate the separate contribution of the two definitions of the anterolateral ligament (ALL), the mid-third lateral capsular ligament (MTLCL) and deep capsule-osseous layer of the iliotibial tract (dcITT) in addition to the superficial iliotibial tract (sITT) to the control of tibial motion with respect to the femur during the application of force/torque seen during the three tests of the standard clinical knee examination (AP Lachman test, tibial axial rotation test and varus–valgus stress test).MethodsSix pelvis-to-toe cadaveric specimens were examined using an automated testing device that carried out the three components of the clinical knee examination. Internal/external rotation torque, anteroposterior load and adduction/abduction torque were applied, while torque/force and positional measurements were recorded. Sequential sectioning of the structures followed the same order for each knee, sITT, dcITT and MTLCL. Testing was repeated after release of each structure.ResultsDuring the tibial axial rotation test, releasing the sITT caused an increase in internal rotation of 2.6° (1.4–4.1°, p < 0.0005), while release of the dcITT increased internal rotation an additional 0.8° (0.4–1.1°, p < 0.0015). Changes in secondary motions of the tibia after sITT release demonstrated an increase in anterior translation of 1.2 mm (0.6–2.0 mm, p < 0.0005) during internal rotation, while release of the dcITT increased the same motion an additional 0.4 mm (0.2–0.5 mm, p < 0.0005). During the AP Lachman test, release of the sITT caused the tibia to move more anteriorly by 0.7 mm (0.4–1.1 mm, p < 0.0005) and increased internal rotation by 2.7° (0.9–5.2°, p < 0.004). The additional release of the dcITT resulted in more anterior translation by 0.3 mm (0.1–0.4 mm, p < 0.002) and internal rotation by 0.9° (0.2–1.7°, p < 0.005). During the varus–valgus stress test, release of the sITT permitted 0.9° (0.4–1.4°, p < 0.0005) more adduction of the tibia, while the additional release of the dcITT significantly increased adduction by 0.4° (0.2°–0.5°, p < 0.001). Release of the MTLCL had a nominal but significant increase in internal rotation, 0.6° (0.1–1.1°, p < 0.0068) and external rotation, −0.1° (−0.1° to −0.2°, p < 0.0025) during the tibial axial rotation test, anterior translation of 0.2 mm (0.0–0.4 mm, p < 0.021) only during the AP Lachman test, and adduction rotation, 0.2° (0.0–0.3°, p < 0.034) only during the varus–valgus stress test.ConclusionThe presence of increased adduction during an automated knee examination provides unique information identifying the release of the sITT, dcITT and the MTLCL in this cadaveric study. While their sequential release caused similar pattern changes in the three components of the automated knee examination, the extent of change due to release of the MTLCL was markedly less than after release of the dcITT which was markedly less than after release of the sITT.

The Effect of Progressive Degrees of Medial Meniscal Loss on Stability after Anterior Cruciate Ligament Reconstruction

Previous studies report conflicting results on whether loss of the medial meniscus compromises knee stability after reconstruction of the anterior cruciate ligament (ACL). The purpose of this study was to determine whether the degree of medial meniscus deficiency affects the stability of the ACL-reconstructed knee. Six cadaveric knees were arthroscopically reconstructed with bone-patellar tendon-bone autografts using an anatomic "footprint" technique. Knees tested were ACL-deficient and after reconstruction under three different meniscal states: with partial medial meniscectomy, subtotal meniscectomy, and meniscal root transection. Biomechanical testing was performed at 30 and 60 degrees of flexion under two loading conditions: (1) 134-N anterior tibial load termed anterior tibial translation (ATT) and (2) 10-Nm valgus load combined with 5 Nm of internal tibial torque termed provocative pivot maneuver (PPM). Knee kinematics was measured using a custom activity simulator, motion analysis system, and three-dimensional CT reconstructions. During both ATT and PPM loading, ACL deficiency resulted in a significant increase in anterior translation compared with knees with an intact ACL or those that had undergone ACL reconstruction (p < 0.05). Neither the addition of a partial nor subtotal medial meniscectomy led to increased instability. Only after medial meniscal root transection was increased instability of the ACL-deficient knee detected compared with intact, partial, or subtotal meniscectomy states (p < 0.01). In all states of meniscal deficiency, ACL reconstruction restored internal tibial rotation and anterior translation at 30 degrees to that of the intact knee (p > 0.05). Anatomic single bundle ACL reconstruction was able to restore knee stability in all conditions of medial meniscal deficiency.

The contribution of each anterior cruciate ligament bundle to the Lachman test

The clinical diagnosis of a partial tear of the anterior cruciate ligament (ACL) is still subject to debate. Little is known about the contribution of each ACL bundle during the Lachman test. We investigated this using six fresh-frozen cadaveric lower limbs. Screws were placed in the femora and tibiae as fixed landmarks for digitisation of the bone positions. The femur was secured horizontally in a clamp. A metal hook was screwed to the tibial tubercle and used to apply a load of 150N directed anteroposteriorly to the tibia to simulate the Lachman test. The knees then received constant axial compression and 3D knee kinematic data were collected by digitising the screw head positions in 30° flexion under each test condition. Measurements of tibial translation and rotation were made, first with the ACL intact, then after sequential cutting of the ACL bundles, and finally after complete division of the ACL. Two-way analysis of variance analysis was performed. During the Lachman test, in all knees and in all test conditions, lateral tibial translation exceeded that on the medial side. With an intact ACL, both anterior and lateral tibial landmarks translated significantly more than those on the medial side (p < 0.001). With sequential division of the ACL bundles, selective cutting of the posterolateral bundle (PLB) did not increase translation of any landmark compared with when the ACL remained intact. Cutting the anteromedial bundle (AMB) resulted in an increased anterior translation of all landmarks. Compared to the intact ACL, when the ACL was fully transected a significant increase in anterior translation of all landmarks occurred (p < 0.001). However, anterior tibial translation was almost identical after AMB or complete ACL division. We found that the AMB confers its most significant contribution to tibial translation during the Lachman test, whereas the PLB has a negligible effect on anterior translation. Section of the PLB had a greater effect on increasing the internal rotation of the tibia than the AMB. However, its contribution of a mean of 2.8° amplitude remains low. The clinical relevance of our investigation suggests that, based on anterior tibial translation only, one cannot distinguish between a full ACL and an isolated AMB tear. Isolated PLB tears cannot be detected solely by the Lachman test, as this bundle probably contributes more resistance to the pivot shift.

The Role of the Superior Labrum Following Biceps Tenodesis in Glenohumeral Kinematics and Stability (SS-07)

Introduction At the present time, little is known about the role a torn superior labrum plays in glenohumeral (GH) kinematics and stability following biceps tenodesis (BT). The current biomechanical study evaluated the contribution a type II SLAP lesion has on GH translation in the presence of a BT, asking two questions: Does a type II SLAP tear require fixation following BT, and if so, which of two repair techniques is superior? Methods Baseline GH translation data was collected from 15 intact cadaveric shoulders using a custom shoulder testing apparatus. Anterior (n=5) and posterior (n=10) type II SLAP tears were created, and translation testing was repeated. BT was then performed for each specimen, with re-evaluation of translation post-procedure. Finally, repair of the type II SLAP lesion was performed utilizing one of two suture anchor constructs for the posterior SLAP (two single-loaded vs. one double-loaded anchor) and one suture anchor construct for the anterior SLAP (two single-loaded anchors), followed by repeat translation testing. Comparisons were made between the translation data for each group. Results Both anterior and posterior type II SLAP lesions led to increases in anterior and posterior GH translation compared to baseline. In the presence of a posterior SLAP lesion, anterior and posterior translation increased significantly to 85.7% (5.2mm to 9.6mm) and 54.8% (5.4mm to 8.4mm), respectively. Anterior SLAP lesions led to a significant increase in anterior translation of 72.8% (4.3mm to 7.5mm) and a 37.8% non-significant increase in posterior translation (7.1mm to 9.8mm). BT for both types of SLAP improved translation stability, reducing anterior translation in the presence of a posterior tear from 9.6mm to 7.7mm and posterior translation in the presence of an anterior tear from 9.8mm to 8.0mm, although these values were not significant. For anatomic repair with either 2 single-loaded anchors or 1 double-loaded anchor, posterior SLAP repair improved anterior translation to 0.0% and 22.1% of baseline, respectively. For anterior tears, anatomic repair led to a posterior translation 11.6% of baseline. All repairs did not differ significantly from baseline. Conclusion Biceps tenodesis shows no deleterious effect on glenohumeral kinematics and stability in the presence of a SLAP lesion. Thus, BT can be a useful revision procedure for patients with persistent pain following SLAP repair. Additionally, no significance was found between the two repair constructs. At the present time, little is known about the role a torn superior labrum plays in glenohumeral (GH) kinematics and stability following biceps tenodesis (BT). The current biomechanical study evaluated the contribution a type II SLAP lesion has on GH translation in the presence of a BT, asking two questions: Does a type II SLAP tear require fixation following BT, and if so, which of two repair techniques is superior? Baseline GH translation data was collected from 15 intact cadaveric shoulders using a custom shoulder testing apparatus. Anterior (n=5) and posterior (n=10) type II SLAP tears were created, and translation testing was repeated. BT was then performed for each specimen, with re-evaluation of translation post-procedure. Finally, repair of the type II SLAP lesion was performed utilizing one of two suture anchor constructs for the posterior SLAP (two single-loaded vs. one double-loaded anchor) and one suture anchor construct for the anterior SLAP (two single-loaded anchors), followed by repeat translation testing. Comparisons were made between the translation data for each group. Both anterior and posterior type II SLAP lesions led to increases in anterior and posterior GH translation compared to baseline. In the presence of a posterior SLAP lesion, anterior and posterior translation increased significantly to 85.7% (5.2mm to 9.6mm) and 54.8% (5.4mm to 8.4mm), respectively. Anterior SLAP lesions led to a significant increase in anterior translation of 72.8% (4.3mm to 7.5mm) and a 37.8% non-significant increase in posterior translation (7.1mm to 9.8mm). BT for both types of SLAP improved translation stability, reducing anterior translation in the presence of a posterior tear from 9.6mm to 7.7mm and posterior translation in the presence of an anterior tear from 9.8mm to 8.0mm, although these values were not significant. For anatomic repair with either 2 single-loaded anchors or 1 double-loaded anchor, posterior SLAP repair improved anterior translation to 0.0% and 22.1% of baseline, respectively. For anterior tears, anatomic repair led to a posterior translation 11.6% of baseline. All repairs did not differ significantly from baseline. Biceps tenodesis shows no deleterious effect on glenohumeral kinematics and stability in the presence of a SLAP lesion. Thus, BT can be a useful revision procedure for patients with persistent pain following SLAP repair. Additionally, no significance was found between the two repair constructs.

Lateral compartment translation predicts the grade of pivot shift: a cadaveric and clinical analysis

Anterior translation of the lateral compartment was hypothesized to correlate with the clinical grade of a pivot shift maneuver. Using a computer-assisted navigation system, this hypothesis was tested by recording the maximum anterior tibial translation in the medial and lateral compartment as well as the arc of rotation during the pivot shift maneuver. One hundred and fifty-four pivot shift examinations were performed on cadavers with various degrees of instability, and 24 pivot shift exams were performed on patients under anesthesia before and after ACL reconstruction. In all positive pivot shift exams, anterior tibial translations were found to be higher on in the lateral compartment compared to the medial compartment. In addition, an excellent correlation was found between the amount of lateral compartment translation and the clinical grade of the pivot shift; medial compartment translations and amount of knee rotation could not distinguish between clinical grades. Finally, a threshold of 6-7 mm of anterior tibial translation in the lateral compartment was necessary to produce a positive pivot shift. Taken together, these data suggest that monitoring lateral compartment translations during a pivot shift exam may be a convenient means to evaluate the outcomes of ACL surgery and that requisite increases in anterior translation of the lateral compartment are necessary for each progressive clinical grade of the pivot shift examination.

An in Vitro Analysis of an Anatomical Medial Knee Reconstruction

Background An anatomical medial knee reconstruction has not been described in the literature. Hypothesis Knee stability and ligamentous load distribution would be restored to the native state with an anatomical medial knee reconstruction. Study Design Controlled laboratory study. Methods Ten nonpaired cadaveric knees were tested in the intact, superficial medial collateral ligament and posterior oblique ligament—sectioned, and anatomically reconstructed states. Each knee was tested at 0°, 20°, 30°, 60°, and 90° of knee flexion with a 10-N·m valgus load, 5-N·m external and internal rotation torques, and 88-N anterior and posterior drawer loads. A 6 degrees of freedom electromagnetic motion tracking system measured angulation and displacement changes of the tibia with respect to the femur. Buckle transducers measured the loads on the intact and reconstructed proximal and distal divisions of the superficial medial collateral ligament and the posterior oblique ligament. Results A significant increase was found in valgus angulation and external rotation after sectioning the medial knee structures at all tested knee flexion angles. This was restored after an anatomical medial knee reconstruction. The authors also found a significant increase in internal rotation at 0°, 20°, 30°, and 60° of knee flexion after sectioning the medial knee structures, which was restored after the reconstruction. A significant increase in anterior translation was observed after sectioning the medial knee structures at 20°, 30°, 60°, and 90° of knee flexion. This increase in anterior translation was restored following the reconstruction at 20° and 30° of knee flexion, but was not restored at 60° and 90°. A small, but significant, increase in posterior translation was found after sectioning the medial knee structures at 0° and 30° of knee flexion, but this was not restored after the reconstruction. Overall, there were no clinically important differences in observed load on the ligaments when comparing the intact with the reconstructed states for valgus, external and internal rotation, and anterior and posterior drawer loads. Conclusion An anatomical medial knee reconstruction restores near-normal stability to a knee with a complete superficial medial collateral ligament and posterior oblique ligament injury, while avoiding overconstraint of the reconstructed ligament grafts. Clinical Significance This anatomical medial knee reconstruction technique provides native stability and ligament load distribution in patients with chronic or severe acute medial knee injuries.

The effect of relaxin on the female anterior cruciate ligament: Analysis of mechanical properties in an animal model

Background The peptide hormone relaxin, found in pregnant and non-pregnant females, has been shown to have collagenolytic effects on ligamentous tissue. Relaxin receptors have recently been identified on the human female anterior cruciate ligament (ACL). Relaxin may affect the load bearing properties of the female ACL and contribute to non-contact ACL injuries. Hypothesis The administration of recombinant relaxin ± estrogen will lead to a significant decrease in ACL integrity in the guinea pig model. Study design Controlled laboratory study. Methods Adult female guinea pigs were divided into three experimental groups. Group 1 ( n = 4) was administered only 20 µg/h of recombinant porcine relaxin for 3 weeks. Group 2 ( n = 4) was administered 20 µg/h of recombinant porcine relaxin and 5 µg/h of estradiol for 3 weeks. Group 3 ( n = 4) served as both a normal control before surgical transection of the ACL and a positive ACL tear control after transection. All hormones were administered using separate implanted osmotic pumps. ACL laxity was tested by implanting radio-opaque markers in the femur and tibia of each leg. After applying a standard anterior force (22 N), the distance between markers was measured radiographically at day 0 and day 21. The animals were then sacrificed and the ACL's were analyzed for load-to-failure using a material testing machine. Results Load-to-failure testing indicated that animals treated with relaxin only had significantly weaker ACL's ( µ = 40.4 N, p = 0.001) compared to controls ( µ = 64.1 N). The relaxin + estrogen group ( µ = 32.7 N) was also significantly weaker than controls ( p = 0.007). There were no statistical differences between relaxin and relaxin + estrogen groups. Both relaxin only and relaxin + estrogen groups showed an increase in anterior translation of the tibia after 3 weeks of infusion, but it did not achieve statistical significance. Conclusions Relaxin significantly alters the mechanical properties of the ACL in an animal model. Clinical relevance The effects of relaxin, possibly in conjunction with estrogen, may contribute to a comprehensive etiology for human female non-contact ACL injuries.

Der Stellenwert der Sonographie in der Beurteilung von Instabilitäten des glenohumeralen Gelenkes

In a prospective study we evaluated diagnostic ultrasound investigation for shoulder instabilities. We measured the passive aptranslation In 150 healthy persons in relation to the dorsal glenoid as well as the inferior subluxation in relation to the acromion. After establishing normative datas we measured 23 patient with unidirectional instabilities and 34 with multidirectional instabilities. The humeral head position of a normal joint is 8 to 10 mm dorsally to the glenoid. In the control group the anterior translation of the dominant shoulder is significantly higher as in the nondominant shoulder (student-t-test; p less than 0.0045). Patients with anterior instabilities showed a significant increase of anterior translation in the injured shoulder (student-t-test; p less than 0.0001). In comparison with the control group there is a significant increase of downward subluxation in patients with multidirectional instabilities (chi 2 alpha less than 0.05). In habitual or voluntary dislocations the relation of the humeral head to the glenoid can be judged statically and dynamically. Secondary signs of dislocation (Hill-Sachs lesions, joint effusion) are evident.

In Vivo Kinematics of the Knee after Anterior Cruciate Ligament Reconstruction

Background Recent follow-up studies have reported a high incidence of joint degeneration in patients with anterior cruciate ligament reconstruction. Abnormal kinematics after anterior cruciate ligament reconstruction have been thought to contribute to the degeneration. Hypothesis Anterior cruciate ligament reconstruction, which was designed to restore anterior knee laxity under anterior tibial loads, does not reproduce knee kinematics under in vivo physiological loading conditions. Study Design Controlled laboratory study. Methods Both knees of 7 patients with complete unilateral rupture of the anterior cruciate ligament were magnetic resonance imaged, and 3D models were constructed from these images. The anterior cruciate ligament of the injured knee was arthroscopically reconstructed using a bone–patellar tendon–bone autograft. Three months after surgery, the kinematics of the intact contralateral and reconstructed knees were measured using a dual-orthogonal fluoroscopic system while the subjects performed a single-legged weightbearing lunge. The anterior laxity of both knees was measured using a KT-1000 arthrometer. Results The anterior laxity of the reconstructed knee as measured with the arthrometer was similar to that of the intact contralateral knee. However, under weightbearing conditions, there was a statistically significant increase in anterior translation of the reconstructed knee compared with the intact knee at full extension (approximately 2.9 mm) and 15° (approximately 2.2 mm) of flexion. In addition, there was a mean increase in external tibial rotation of the anterior cruciate ligament–reconstructed knee beyond 30° of flexion (approximately 2° at 30° of flexion), although no statistical significance was detected. Conclusion The data demonstrate that although anterior laxity was restored during KT-1000 arthrometer testing, anterior cruciate ligament reconstruction did not restore normal knee kinematics under weightbearing loading conditions. Clinical Relevance Future reconstruction techniques should aim to restore function of the knee under physiological loading conditions.

A CADAVERIC MODEL OF THE THROWING SHOULDER

Background: It has been speculated that a shift of the throwing arc commonly develops in athletes who perform overhead activities, resulting in greater external rotation and decreased internal rotation caused by anterior capsular laxity and posterior capsular contracture, respectively. Osseous adaptation in the form of increased humeral and glenoid retroversion may provide a protective function in the asymptomatic athlete but cannot explain the pathological changes seen in the shoulder of the throwing athlete. Therefore, the objective of the present study was to examine the biomechanical effects of capsular changes in a cadaveric model. Methods: Ten cadaveric shoulders were tested with a custom shoulder-testing device. Humeral rotational range of motion, the position of the humerus in maximum external rotation, and glenohumeral translations in the anterior, posterior, superior, and inferior directions were measured with the shoulder in 90° of abduction. Translations were measured with the humerus secured in 90° of external rotation. To simulate anterior laxity due to posterior capsular contracture, the capsule was nondestructively stretched 30% beyond maximum external rotation with the shoulder in 90° of abduction. This was followed by the creation of a 10-mm posterior capsular contracture. Rotational, humeral shift, and translational tests were performed for the intact normal shoulder, after anterior capsular stretching, and after simulated posterior capsular contracture. Results: Nondestructive capsular stretching resulted in a significant increase in external rotation (average increase, 18.2° ± 2.1°; p < 0.001), and subsequent simulated posterior capsular contracture resulted in a significant decrease in internal rotation (average decrease, 8.8° ± 2.3°; p = 0.02). There also was a significant increase in anterior translation with the application of a 20-N anterior translational force after nondestructive capsular stretching (average increase, 1.7 ± 0.3 mm, p = 0.0006). The humeral head translated posteroinferiorly when the humerus was rotated from neutral to maximum external rotation. This did not change significantly in association with anterior capsular stretching. Following simulated posterior capsular contracture, there was a trend toward a more posterosuperior position of the humeral head with the humerus in maximum external rotation in comparison with the position in the stretched conditions, although these differences were not significant. Conclusions: A posterior capsular contracture with decreased internal rotation does not allow the humerus to externally rotate into its normal posteroinferior position in the cocking phase of throwing. Instead, the humeral head is forced posterosuperiorly, which may explain the etiology of Type-II superior labrum anterior-to-posterior lesions in overhead athletes. Clinical Relevance: Understanding the biomechanical effects of capsular changes in a cadaveric model of the throwing shoulder may confirm clinical observations and provide insight into the pathological changes often seen in the shoulder of throwing athletes.