Camilla Halewood

The anterolateral ligament: Anatomy, length changes and association with the Segond fracture

There have been differing descriptions of the anterolateral structures of the knee, and not all have been named or described clearly. The aim of this study was to provide a clear anatomical interpretation of these structures. We dissected 40 fresh-frozen cadaveric knees to view the relevant anatomy and identified a consistent structure in 33 knees (83%); we termed this the anterolateral ligament of the knee. This structure passes antero-distally from an attachment proximal and posterior to the lateral femoral epicondyle to the margin of the lateral tibial plateau, approximately midway between Gerdys tubercle and the head of the fibula. The ligament is superficial to the lateral (fibular) collateral ligament proximally, from which it is distinct, and separate from the capsule of the knee. In the eight knees in which it was measured, we observed that the ligament was isometric from 0° to 60° of flexion of the knee, then slackened when the knee flexed further to 90° and was lengthened by imposing tibial internal rotation.

Length Change Patterns in the Lateral Extra-articular Structures of the Knee and Related Reconstructions

Background: Lateral extra-articular soft tissue reconstructions in the knee may be used as a combined procedure in revision anterior cruciate ligament surgery as well as in primary treatment for patients who demonstrate excessive anterolateral rotatory instability. Only a few studies examining length change patterns and isometry in lateral extra-articular reconstructions have been published. Purpose: To determine a recommended femoral insertion area and graft path for lateral extra-articular reconstructions by measuring length change patterns through a range of knee flexion angles of several combinations of tibial and femoral insertion points on the lateral side of the knee. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric knees were freed of skin and subcutaneous fat. The knee was then mounted in a kinematics rig that loaded the quadriceps muscles and simulated open-chain knee flexion. The length changes of several combinations of tibiofemoral points were measured at knee flexion angles between 0° and 90° by use of linear variable displacement transducers. The changes in length relative to the 0° measurement were recorded. Results: The anterior fiber region of the iliotibial tract displayed a significantly different (P < .001) length change pattern compared with the posterior fiber region. The reconstructions that had a femoral insertion site located proximal to the lateral epicondyle and with the grafts passed deep to the lateral collateral ligament displayed similar length change patterns to each other, with small length increases during knee extension. These reconstructions also showed a significantly lower total strain range compared with the reconstruction located anterior to the epicondyle (P < .001). Conclusion: These findings show that the selection of graft attachment points and graft course affects length change pattern during knee flexion. A graft attached proximal to the lateral femoral epicondyle and running deep to the lateral collateral ligament will provide desirable graft behavior, such that it will not suffer excessive tightening or slackening during knee motion. Clinical Relevance: These results provide a surgical rationale for lateral extra-articular soft tissue reconstruction in terms of femoral graft fixation site and graft route.

Posteromedial Meniscocapsular Lesions Increase Tibiofemoral Joint Laxity With Anterior Cruciate Ligament Deficiency, and Their Repair Reduces Laxity

Background: Injury to the posteromedial meniscocapsular junction has been identified after anterior cruciate ligament (ACL) rupture; however, there is a lack of objective evidence investigating how this affects knee kinematics or whether increased laxity can be restored by repair. Such injury is often overlooked at surgery, with possible compromise to results. Hypotheses: (1) Sectioning the posteromedial meniscocapsular junction in an ACL-deficient knee will result in increased anterior tibial translation and rotation. (2) Isolated ACL reconstruction in the presence of a posteromedial meniscocapsular junction lesion will not restore intact knee laxity. (3) Repair of the posteromedial capsule at the time of ACL reconstruction will reduce tibial translation and rotation to normal. (4) These changes will be clinically detectable. Study Design: Controlled laboratory study. Methods: Nine cadaveric knees were mounted in a test rig where knee kinematics were recorded from 0° to 100° of flexion by use of an optical tracking system. Measurements were recorded with the following loads: 90-N anterior-posterior tibial forces, 5-N·m internal-external tibial rotation torques, and combined 90-N anterior force and 5-N·m external rotation torque. Manual Rolimeter readings of anterior translation were taken at 30° and 90°. The knees were tested in the following conditions: intact, ACL deficient, ACL deficient and posteromedial meniscocapsular junction sectioned, ACL deficient and posteromedial meniscocapsular junction repaired, ACL patellar tendon reconstruction with posteromedial meniscocapsular junction repair, and ACL reconstructed and capsular lesion re-created. Statistical analysis used repeated-measures analysis of variance and post hoc paired t tests with Bonferroni correction. Results: Tibial anterior translation and external rotation were both significantly increased compared with the ACL-deficient knee after posterior meniscocapsular sectioning (P < .05). These parameters were restored after ACL reconstruction and meniscocapsular lesion repair (P > .05). Conclusion: Anterior and external rotational laxities were significantly increased after sectioning of the posteromedial meniscocapsular junction in an ACL-deficient knee. These were not restored after ACL reconstruction alone but were restored with ACL reconstruction combined with posterior meniscocapsular repair. Tibial anterior translation changes were clinically detectable by use of the Rolimeter. Clinical Relevance: This study suggests that unrepaired posteromedial meniscocapsular lesions will allow abnormal meniscal and tibiofemoral laxity to persist postoperatively, predisposing the knee to meniscal and articular damage.

Biomechanical Comparisons Between 4-Strand and Modified Larson 2-Strand Procedures for Reconstruction of the Posterolateral Corner of the Knee

Background: The posterolateral corner (PLC) resists tibial varus angulation, external rotation, and, to a lesser extent, posterior translation. It is important that reconstructions of posterolateral knee injuries restore joint laxity and patient function, but residual laxities are often observed. Hypothesis: The knee laxity after a new 4-strand PLC reconstruction would be closer to normal than after a 2-strand “modified Larson” reconstruction. Study Design: Controlled laboratory study. Methods: Fourteen intact cadaveric knees were mounted in a 6 degrees of freedom rig and subjected to the following external loading conditions: a 90-N posterior tibial force, a 5-N·m external rotation torque, and 5-N·m varus moment. Knee kinematics were recorded with an active optical tracking system for the intact, PLC-deficient, modified Larson PLC reconstruction and 4-strand PLC reconstruction. Results: With external tibial torque, the rotational laxity in 4-strand reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P = .0112) and did not differ significantly from intact laxity at any angle of flexion. In response to posterior load, posterior translation did not change in any of the tested conditions, while the coupled external rotation laxity in 4-strand PLC reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P < .0486) and was not significantly different from the intact movements for both reconstructions. The varus angulation-versus-flexion curves were significantly different between the PLC-deficient and both PLC reconstructions (P < .0001). The varus laxity was not significantly different between the modified Larson reconstruction, the 4-strand reconstruction, and the intact knee. Conclusion: This study showed that the rotational knee laxity in response to both external rotation and posterior translation load were significantly better after the 4-strand PLC reconstruction than after the modified Larson reconstruction, although significant differences were not found between the 2 procedures for varus laxity. Clinical Relevance: The 4-strand PLC reconstruction may produce a better biomechanical outcome, especially during external rotation and posterior translation tibial load. The authors suggest that this relates to load sharing among 4 graft strands crossing the joint.

Anteroposterior Laxity After Bicruciate-Retaining Total Knee Arthroplasty Is Closer to the Native Knee Than ACL-Resecting TKA: A Biomechanical Cadaver Study

The purpose of this study was to examine whether a bicruciate retaining (BCR) TKA would yield anteroposterior (AP) laxity closer to the native knee than a posterior cruciate ligament retaining (CR) TKA. A BCR TKA was designed and compared to CR TKA and the native knee using cadaver specimens. AP laxity with the CR TKA was greater than the native knee (P=0.006) and BCR TKA (P=0.039), but no difference was found between the BCR TKA and the native knee. No significant differences were found in rotations between the prostheses and the native knee. BCR TKA was shown to be surgically feasible, reduced AP laxity versus CR TKA, and may improve knee stability without using conforming geometry in the implant design.

Clinically relevant biomechanics of the knee capsule and ligaments

Abstract The paper describes the concepts of primary and secondary restraints to knee joint stability and explains systematically how the tibia is stabilised against translational forces and rotational torques in different directions and axes, and how those vary across the arc of flexion–extension. It also shows how the menisci act to stabilise the knee, in addition to load carrying across the joint. It compares the properties of the natural stabilising structures with the strength and stiffness of autogenous tissue grafts and relates those strengths to the strength of graft fixation devices. A good understanding of the biomechanical behaviour of these various structures in the knee will help the surgeon in the assessment and treatment of single and multi-ligament injuries.

The Stability of Percutaneous Fixation of Proximal Humeral Fractures

The treatment of an unstable proximal humeral fracture is challenging. Although the majority of proximal humeral fractures can be treated successfully with nonoperative treatment, some fractures require operative treatment to achieve outcomes that meet the patient’s expectations. Several techniques and devices have been employed to treat unstable proximal humeral fractures, including the locking plate1,2, intramedullary locking nails3, Kirschner wires4, and screw fixation5. The proximal humeral locking plate has been shown to achieve relatively rigid fracture fixation6,7. However, after the initial enthusiasm for locking plates, several authors recently have raised concerns about these implants8,9. Less-invasive techniques, such as Kirschner wire fixation, may provide adequate stability and require a less-invasive second operation for implant removal. However, this advantage must be balanced with the inferior biomechanical properties of Kirschner wires, with risks that include wire migration and loss of fracture reduction10-12. New fracture-fixation devices have been introduced to minimize the disadvantages of Kirschner wires13, with the goal of redistributing the loads on the wires and transmitting the loads from the insufficient subchondral cancellous bone to the lateral cortex of the proximal part of the humerus. However, the biomechanical properties of these devices recently have been shown to be inferior to locking plates14. The reasons for these differences could be related to several variables, including the Kirschner wire dimensions, the length of the threaded portion of the Kirschner wire, the pin configuration used in the humeral head (including the positioning, spacing, orientation, and number of pins), the system for cortical fixation, or a combination of all of these factors. In 2005, a new device was developed to augment percutaneous wire fixation both by using an external fixator to …

Evaluation of different shape-memory staple configurations against crossed screws for first metatarsophalangeal joint arthrodesis: A biomechanical study

BACKGROUND The first metatarsophalangeal joint may be fused in order to treat arthritis or instability. The use of shape-memory staples for fixation is well recognised, but little work has been done into the optimal configuration of staples. METHODS The structural behaviour of first metatarsophalangeal joint (MTPJ) arthrodeses using shape-memory staples or crossed screws was studied using cadaveric porcine joints. Five fixation configurations were tested: single vertical or horizontal staple, paired staples in dorsal-medial configuration (0-90° to the sagittal plane), paired staples in oblique orthogonal configuration (45-135°); or two crossed screws. Specimens were loaded in cyclical dorsiflexion for 1000 cycles. Plantar gapping and shearing were measured. Specimens were then loaded to failure. RESULTS Cyclic testing caused more shear in the 45-135° staples than the crossed screws (1.0mm±0.5mm compared to 0.14mm±0.4mm, p<0.01). No significant difference was found in plantar gap formation. Single vertical and horizontal single staples failed at 15N and 19. CONCLUSIONS N, respectively. Paired 0-90° staples failed at 43N±9N, significantly lower than the 45-135° staples (141N±25N; p<0.001) and crossed screws (180N±67N; p<0.001). There was no significant difference between the 45-135° staples and crossed screws. Screws failed by sudden cortical fracture; staples displayed gradual pull-out and shearing. First MTPJ arthrodeses fixed with single staples are not recommended. Arthrodeses fixed with staples at 0-90° to the sagittal plane were significantly less strong than two crossed screws. However, positioning oblique staples at 45-135° significantly improved stability, creating a construct as strong as, crossed screws. None of the constructs was strong enough for immediate weight bearing.

The influence of posterior medial meniscocapsular lesions on tibiofemoral joint laxity with ACL deficiency and reconstruction

Introduction: Injury to the posterior medial meniscocapsular junction (the ‘ramp’ lesion) occurs at the time of anterior cruciate ligament (ACL) rupture (10-24% of cases); however there is a lack of objective evidence investigating how this affects knee kinematics. It is often missed when viewed arthroscopically from the front of the medial compartment as it can only be seen with the arthroscope in the posteromedial recess. Objectives: To investigate the biomechanical impact of the ‘ramp lesion’ on the ACL deficient and ACL reconstructed knee and the impact of suture repair of the lesion on the same knee states. Methods: Nine fresh frozen cadaveric knees were mounted in a 6 degrees of freedom rig where knee kinematics were recorded at 10° intervals from 0°-100° using an optical tracking system. Measurements were recorded using the following loading conditions: 90 N anterior and posterior tibial forces, 5 Nm internal and external tibial rotation torques, and a combined 90 N anterior tibial force and 5 Nm external tibial rotation torque. Manual Rolimeter readings of anterior translation were taken at 30° and 90°. The knees were tested in the following order: (1) intact, (2) ACL deficient, (3) ACL deficient + posterior meniscocapsule sectioned, (4) ACL deficient + posterior meniscocapsule repaired, (5) ACL patellar tendon reconstruction with posterior meniscocapsule repair and (6) ACL reconstructed + capsular lesion re-created. Statistical analysis was undertaken using repeated-measures ANOVA and post-hoc paired t-tests with Bonferonni correction. Results: Tibial anterior translation and external rotational laxities were both significantly increased compared to the ACL deficient knee following posterior meniscocapsular sectioning (P < 0.05). These were both restored following ACL reconstruction and meniscocapsular lesion repair (P > 0.05). Significant changes in anterior tibial translation between the different knee states were identified with the Rolimeter, indicating these changes are clinically detectable (P < 0.05). Conclusion: Anterior and external rotational laxities were significantly increased after mimicking the ‘ramp lesion’ by sectioning of the posteromedial meniscocapsular junction in an ACL-deficient knee. These were not restored after ACL reconstruction alone but were restored with ACL reconstruction combined with posterior meniscocapsular repair. Tibial anterior translation changes were clinically detectable by use of the Rolimeter. This study suggests that unrepaired posteromedial meniscocapsular lesions will allow abnormal meniscal and tibiofemoral laxity to persist postoperatively, predisposing the knee to meniscal and articular damage but also adding avoidable extra strain on an ACL graft, which may yield.

A Biomechanical Comparison of First Metatarsophalangeal Arthrodesis Using Crossed Screws and Shape-Memory Staples in Various Configurations

Category: Midfoot/Forefoot Introduction/Purpose: Arthrodesis of the first metatarsophalangeal joint (MTPJ) is a commonly performed procedure for the treatment of hallux rigidus. A range of fixation methods have been used. Most recently, the shape-memory staple has been described. Made from an equiatomic alloy, the staple changes its shape when heated to body temperature so as to provide compression across the arthrodesis. We aimed to determine load to failure, cyclic loading and failure characteristics of different staple configurations compared to crossed screws. Methods: A cadaveric porcine model was used to simulate first MTPJ arthrodesis. Five forms of fixation were tested: single vertical staple; single horizontal staple; paired staples in orthogonal superior-inferior and medial-lateral configuration (0-90° to sagittal plane); paired staples in an oblique orthogonal configuration (45-135° to sagittal plane); two crossed screws. Using a materials-testing machine, specimens were loaded in dorsiflexion to simulate weight bearing. Cyclical loading was performed from 5-40N at a rate of 0.5 Hz for 1000 cycles. Plantar gapping, shear and creep were measured. Specimens were then loaded to failure in order to generate a load-displacement curve. The mechanism of failure was noted for each group. Results: Single staple configurations failed at very low loads. Single vertical staples failed at a mean load 15N±5N and single horizontal staples at 19N±3N. Mean failure load for paired 0-90° staples was 43N±9N which was significantly lower than the paired 45-135° staples which failed at 141N±25N (p < 0.001) and crossed screws, which failed at 180N±67N (p < 0.001). The was no significant difference between the 45-135° staples and crossed screws. Cyclic testing demonstrated plantar gap formation of 0.2mm±0.1 mm in the crossed screw specimens and 0.4mm±0.4 mm in the 45-135° staple specimens. However, stapled specimens demonstrated more shear compared to crossed screws (mean 1.0mm±0.5 mm compared to 0.14mm±0.4 mm, p < 0.01). Furthermore, crossed screw specimens showed mainly plastic deformation whereas stapled specimens showed combined plastic and elastic deformation. Conclusion: First MTPJ arthrodeses fixed with single staples failed at very low loads and cannot be recommended. The widely accepted 0-90° orthogonal staple configuration proved to be significantly less strong than two crossed screws. However, changing staple position to an oblique configuration at 45° and 135° to the sagittal plane significantly improved stability, rendering the construct as strong as crossed screws. Nevertheless, none of the constructs would have been strong enough to withstand full weight-bearing in the immediate post-operative period.