Effect of Slope and Varus Correction High Tibial Osteotomy in the ACL-Deficient and ACL-Reconstructed Knee on Kinematics and ACL Graft Force: A Biomechanical Analysis

BACKGROUND Correction of high posterior tibial slope is an important treatment option for revision of anterior cruciate ligament (ACL) failure as seen in clinical and biomechanical studies. In cases with moderate to severe medial compartment arthritis, an additional varus correction osteotomy may be added to improve alignment. PURPOSE To investigate the influence of coronal and sagittal correction high tibial osteotomy in ACL-deficient and ACL-reconstructed knees on knee kinematics and ACL graft load. STUDY DESIGN Controlled laboratory study. METHODS Ten cadaveric knees were selected according to previous computed tomography measurements with increased native slope and slight varus tibial alignment (mean ± SD): slope, 9.9°± 1.4°; medial proximal tibia angle, 86.5°± 2.1°; age, 47.7 ± 5.8 years. A 10° anterior closing-wedge osteotomy, as well as an additional 5° of simulated varus correction osteotomy, were created and fixed using an external fixator. Four alignment conditions-native, varus correction, slope correction, and combined varus and slope correction-were randomly tested in 2 states: ACL-deficient and ACL-reconstructed. Compressive axial loads were applied to the tibia while mounted on a free-moving X-Y table and free-rotating tibia in a knee testing fixture. Three-dimensional motion tracking captured anterior tibial translation (ATT) and internal tibial rotation. Change of tensile forces on the reconstructed ACL graft were recorded. RESULTS In the ACL-deficient knee, an isolated varus correction led to a significant increase of ATT by 4.3 ± 4.0 mm (P = .04). Isolated slope reduction resulted in the greatest decrease of ATT by 6.2 ± 4.3 mm (P < .001). In the ACL-reconstructed knee, ATT showed comparable changes, while combined varus and slope correction led to lower ATT by 3.7 ± 2.6 mm (P = .01) than ATT in the native alignment. Internal tibial rotation was not significantly altered by varus correction but significantly increased after isolated slope correction by 4.0°± 4.1° (P < .01). Each isolated or combined osteotomy showed decreased forces on the graft as compared with the native state. The combined varus and slope osteotomy led to a mean decrease of ACL graft force by 33% at 200 N and by 58% at 400 N as compared with the native condition (P < .001). CONCLUSION A combined varus and slope correction led to a relevant decrease of ATT in the ACL-deficient and ACL-reconstructed cadaveric knee. ACL graft forces were significantly decreased after combined varus and slope correction. Thus, our biomechanical findings support the treatment goal of a perpendicular-aligned tibial plateau for ACL insufficiencies, especially in cases of revision surgery. CLINICAL RELEVANCE This study shows the beneficial knee kinematics and reduced forces on the ACL graft after combined varus and slope correction

Biomechanical evaluation of an arthroscopic transosseous repair as a revision option for failed rotator cuff surgery

Abstract Background The number of revision rotator cuff cases is increasing. The literature is lacking guidance or biomechanical evaluation for fixation strength in a revision case scenario. Therefore, the aim of the study was to provide biomechanical data investigating primary fixation strength of a transosseous technique after anchor pullout failure of a single row reconstruction. It was hypothesized that an arthroscopic transosseous repair system as a procedure for rotator cuff revisions is providing equivalent stability compared to a primary single row suture anchor fixation due to change of fixation site. Methods Eight matched pairs (n = 16) of fresh frozen human shoulders were tested. The paired specimen shoulders were randomly divided into two repair groups (A single row and B primary transosseous repair). The potted specimens were mounted onto the Servohydraulic test system. Both groups were tested under cyclic loading followed by load to failure testing. Suture anchor repair shoulders (group A) that were tested to failure underwent a revision transosseous repair and were subsequently tested again using the same setup and protocol (group C). Results The mean native footprint areas did not show a significant difference between groups. The reconstructed footprint area showed a significantly greater coverage in favor of the transosseous repair. Ultimate load to failure of reconstructions with the primary anchor fixation (344.73 N ± 63.19) and the primary transosseous device (375.36 N ± 70.27) was not significantly higher compared to the revision repair (332.19 N ± 119.01 p = 0.45, p = 0.53). Conclusion The tested transosseous anchor device is a suitable option to widely used suture anchors, providing equivalent fixation properties even in a revision case scenario. Level of evidence Basic Science Study, Biomechanics

Rotational range of motion of elliptical and spherical heads in shoulder arthroplasty: a dynamic biomechanical evaluation

INTRODUCTION: Elliptical shape humeral head prostheses have been proposed to reflect a more anatomic shoulder replacement. Its effect on the rotational range of motion (ROM) compared to a standard spherical head is still not understood. The purpose was to investigate if there would be a difference in rotational ROM when comparing elliptical and spherical prosthetic heads in a dynamic shoulder model. The authors hypothesized that the use of elliptical heads would result in significantly more rotational ROM compared to the spherical head design. MATERIALS AND METHODS: Six fresh-frozen, cadaveric shoulders were evaluated using a dynamic shoulder model. After being tested in the native condition, each specimen underwent 6 conditions in the hemiarthroplasty state: (1) matched-fit spherical head, (2) oversized spherical head, (3) undersized spherical head, (4) matched-fit elliptical head, (5) oversized elliptical head, and (6) undersized elliptical head. Following conversion to total shoulder arthroplasty (TSA), the 6 prior conditions were rerun. Each condition was tested at 0°, 30° and 60° of glenohumeral abduction. Rotational ROM was quantified using 3-dimensional tracking, while dynamically applying alternating forces for internal and external rotation via the rotator cuff tendons. RESULTS: Elliptical and spherical prosthetic heads showed no significant difference in the degree of the total, internal, and external rotational ROM for both the hemiarthroplasty and TSA state. Conversion from hemiarthroplasty to TSA resulted in less degree of total rotational ROM for both head designs in all abduction positions, without reaching statistical significance. There was a significant decrease in total, internal, and external rotational ROM for both elliptical and spherical heads in every replacement condition, when comparing 0° to 30° and 60° of abduction (P < 0.05, respectively). CONCLUSION: In a dynamic shoulder model, elliptical and spherical prosthetic head designs showed no significant difference in the degree of the total, internal, and external rotational ROM in both the hemiarthroplasty and TSA state. LEVEL OF EVIDENCE: Controlled laboratory study ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00402-020-03587-0) contains supplementary material, which is available to authorized users

Biomechanical evaluation of distal biceps reconstruction with cortical button and interference screw fixation

Hypothesis: Tension slide repair maintains the strength of the standard cortical button repair but reduces gap formation at the repair. Distal biceps tendon repair with a suspensory cortical button has yielded the strongest published repair, despite observed gap formation and tendon pistoning. The tension slide technique (TST) was described to reduce gap formation while maintaining the strength of cortical button repair. This study evaluates the biomechanics of the TST compared with previously described EndoButton (Smith &amp; Nephew, Memphis, TN) repair and the TST with and without an interference screw. Materials and methods: The study used 20 matched specimens: 5 had a standard cortical button repair, and 5 had biceps repair with the TST. An additional 10 specimens underwent a TST, 5 with an interference screw and 5 without. All were cyclically loaded for 3600 cycles. Gap formation and load to failure were measured. Results: The mean (SD) load to failure for standard technique was at 389 (148) N vs 432 (66) N for the TST (P ¼ .28). The mean (SD) gap formation was 2.79 (1.43) mm with the standard repair and 1.26 (0.61) mm with the TST (P ¼ .03). The mean (SD) load to failure with TST repair was 436 (103) N without the interference screw and 439 (94) N (P ¼ 0.48) with the screw. The mean gap formation was 1.63 (1.09) mm without the screw and 1.45 (0.67) mm with the screw (P ¼ .38.) Conclusion: This TST maintains the strength of the standard cortical button repair, but significantly reduces gap formation and motion at the repair site. Level of evidence: Basic science study

Footprint coverage comparison between knotted and knotless techniques in a single-row rotator cuff repair: biomechanical analysis

Abstract Background The objective of this biomechanical study is to compare two variations of single-row knotless techniques (Knotless repair and Rip-stop Knotless repair) against a single-row double-loaded anchor (DL) repair, focused on evaluating contact pressure and contact area amongst three different single-row techniques for rotator cuff repairs. Methods A total of 24 fresh frozen human shoulders were tested. Specimens were randomly assigned into one of the three single-row (SR) repair groups: A Knotted single-row double-loaded anchor (DL) repair, a Knotless (K) repair, or a Knotless Rip-Stop (KRS) repair. The footprint was measured after complete detachment of the supraspinatus tendon from the greater tuberosity, introducing pressure sensors between bony footprint and detached rotator cuff, and finally reconstructing it. All specimens were mounted onto a servohydraulic test system to analyze contact variables at 0° and 30° of abduction with 0 N, 30 N and 50 N of tension. Results Groups did not differ significantly in their footprint sizes: DL group 359.75 ± 58.37 mm2, K group 386.5 ± 102.13 mm2, KRS group 415.87 ± 93.80 mm2 (p = 0.84); nor in bone mineral density: DL group 0.25 ± 0.14 g/cm2, K group 0.32 ± 0.19 g/cm2, KRS group 0.32 ± 0.13 g/cm2, (p = 0.75) or average age. The highest mean pressurized contact area measured for the K repair was 248.1 ± 50.9 mm2, which equals a reconstruction of 67.1 ± 19.3% at 0° abduction and a 50 N supraspinatus load. This reconstructed area was significantly greater compared with the DL repair 152.8 ± 73.1 mm2, reconstructing 42.0 ± 18.5% on average when under the same conditions (p = 0.04). The mean contact pressure did not significantly differ amongst groups (p = 1.0): DL group 30.8 ± 17.4 psi, K group 30.9 ± 17.4 psi and KRS group 30.0 ± 10.9 psi. Neither the 30° abduction angle nor the supraspinatus load had a significant influence on the contact pressure in our study. Conclusion Both single-row knotless techniques resulted in significantly higher footprint reconstruction, providing larger contact area and a more uniform pressure distribution when compared with the single-row Knotted techniques. The mean contact pressure did not differ among groups significantly. These knotless techniques may be an alternative if the surgeon decides to perform a single-row rotator cuff repair. Level of evidence Basic Science Study, Biomechanics

Rotational range of motion of elliptical and spherical heads in shoulder arthroplasty: a dynamic biomechanical evaluation

Introduction!#!Elliptical shape humeral head prostheses have been proposed to reflect a more anatomic shoulder replacement. Its effect on the rotational range of motion (ROM) compared to a standard spherical head is still not understood. The purpose was to investigate if there would be a difference in rotational ROM when comparing elliptical and spherical prosthetic heads in a dynamic shoulder model. The authors hypothesized that the use of elliptical heads would result in significantly more rotational ROM compared to the spherical head design.!##!Materials and methods!#!Six fresh-frozen, cadaveric shoulders were evaluated using a dynamic shoulder model. After being tested in the native condition, each specimen underwent 6 conditions in the hemiarthroplasty state: (1) matched-fit spherical head, (2) oversized spherical head, (3) undersized spherical head, (4) matched-fit elliptical head, (5) oversized elliptical head, and (6) undersized elliptical head. Following conversion to total shoulder arthroplasty (TSA), the 6 prior conditions were rerun. Each condition was tested at 0°, 30° and 60° of glenohumeral abduction. Rotational ROM was quantified using 3-dimensional tracking, while dynamically applying alternating forces for internal and external rotation via the rotator cuff tendons.!##!Results!#!Elliptical and spherical prosthetic heads showed no significant difference in the degree of the total, internal, and external rotational ROM for both the hemiarthroplasty and TSA state. Conversion from hemiarthroplasty to TSA resulted in less degree of total rotational ROM for both head designs in all abduction positions, without reaching statistical significance. There was a significant decrease in total, internal, and external rotational ROM for both elliptical and spherical heads in every replacement condition, when comparing 0° to 30° and 60° of abduction (P &amp;lt; 0.05, respectively).!##!Conclusion!#!In a dynamic shoulder model, elliptical and spherical prosthetic head designs showed no significant difference in the degree of the total, internal, and external rotational ROM in both the hemiarthroplasty and TSA state.!##!Level of evidence!#!Controlled laboratory study

How to avoid unintended valgus alignment in distal femoral derotational osteotomy for treatment of femoral torsional malalignment - a concept study

Abstract Background Defining the optimal cutting plane for derotational osteotomy at the distal femur for correction of torsion in cases of patellofemoral instability is still challenging. This preliminary study investigates changes of frontal alignment by a simplified trigonometrical model and demonstrates a surgical guidance technique with the use of femur cadavers. The hypothesis was that regardless of midshaft bowing, a cutting plane perpendicular to the virtual anatomic shaft axis avoids unintended valgus malalignment due to derotation. Methods A novel mathematical model, called the Pillar-Crane-Model, was developed to forecast changes on frontal alignment of the femur when a perpendicular cutting plane to the virtual anatomical shaft was chosen. As proof of concept, eight different torsion angles were assessed on two human cadaver femora (left and right). A single cut distal femoral osteotomy perpendicular to the virtual anatomical shaft was performed. Frontal plane alignment (mLDFA, aLDFA, AMA) was radiographically analyzed before and after rotation by 0°, 10°, 20°, and 30°. Measurements were compared to the model. Results The trigonometrical equation from the Pillar-Crane-Model provides mathematical proof that slight changes into varus occur, seen by an increase in AMA and mLDFA, when the cutting plane is perpendicular to the virtual anatomical shaft axis. A table with standardized values is provided. Exemplarily, the specimens showed a mean increase of AMA from 4.8° to 6.3° and mLDFA from 85.2° to 86.7 after derotation by 30°. Throughout the derotation procedure, aLDFA remained at 80.4° ± 0.4°SD. Conclusions With the use of this model for surgical guidance and anatomic reference, unintended valgus changes on frontal malalignment can be avoided. When the cutting plane is considered to be perpendicular to the virtual anatomical shaft from a frontal and lateral view, a slight increase of mLDFA results when a derotational osteotomy of the distal femur is performed