Clinically relevant biomechanics of the knee capsule and ligaments

Functional knee apparatus for the evaluation of ligamentous tensions on contact loads

BACKGROUND

Soft tissue balancing is integral in providing stability following total knee arthroplasty (TKA). Although intraoperative contact load sensors are providing insights into the effects of soft tissue balancing, there is still a lack of understanding of the relationship between the knee's ligamentous tensions and joint surface contact loads. This study reports on the development of a multifunctional testing apparatus that can quantify the effects of ligamentous tension on joint contact loads in a controlled repeatable environment.

METHODS

The functional knee apparatus was constructed to act as an anatomical substitute for the benchtop assessment of intraoperative soft tissue balancing. The system was calibrated through reproduction of results from a cadaveric study that employed intraoperative load sensors. Experimentation was then conducted to quantify the effects of tensile pretension variation on measured contact loads throughout the full range of flexion.

RESULTS

A linear relationship between the ligamentous tensions and contact loads was observed, with ligaments contributing to 74-80% of the measured contact loads. Ligamentous tensions could be approximated from measured contact loads to within ± 23 N.

CONCLUSION

The proposed apparatus can prove to be a valuable tool in the continued exploration of currently undocumented effects (e.g. surgical alteration) in soft tissue balancing. In addition to quantifying the relationship between ligamentous tensions and joint contact loads, soft tissue loading conditions where bicondylar contact was lost (i.e. known sign of kinematic instability) were identified. As a corollary, this system may be able to provide insights on soft tissue balancing standards predictive of patient outcomes.

The contralateral knee is a good predictor for determining normal knee stability: a cadaveric study

PURPOSE

The goal is to evaluate contralateral knee joint laxity and ascertain whether or not contralateral symmetry is observable. Secondary, a validation of a knee laxity testing rig is provided.

METHODS

Seven pairs of cadaveric knee specimens have been tested under passive conditions with and without external loads, involving a varus/valgus and an external/internal rotational torque and an anteroposterior shear force.

RESULTS

Through the range of motion, the width of the varus/valgus laxity, internal/external laxity and anterior/posterior laxity for the medial and lateral compartment show no significant differences between left and right leg. These findings allow us to validate the setup, especially for relative values of laxity based on anatomical measures and knee joint biomechanics.

CONCLUSION

A multidirectional laxity symmetry has been demonstrated for the intact knee and its contralateral knee in passive conditions as in an anesthetized patient. The passive laxity evaluation setup has been validated. Our work furthermore demonstrated a pronounced difference in anteroposterior mobility between the medial and lateral compartment of the knee, with a more stable medial side and more mobile lateral side.

CLINICAL RELEVANCE

The contralateral knee can be used as reference for determining optimal knee laxity peri-operatively in total knee replacement and ligament reconstruction.

LEVEL OF EVIDENCE

Level IV, Case series.

Muscle loaded stability reflects ligament-based stability in TKA: a cadaveric study

PURPOSE

This paper aims at evaluating the effects of muscle load on knee kinematics and stability after TKA and second at evaluating the effect of TKA surgery on knee kinematics and stability; and third, at correlating the stability in passive conditions and the stability in active, muscle loaded conditions.

METHODS

Fourteen fresh frozen cadaveric knee specimens were tested under passive and active condition with and without external loads involving a varus/valgus and internal/external rotational torque before and after TKA surgery using two in-house developed and previously validated test setups.

RESULTS

Introduction of muscle force resulted in increased valgus (0.98°) and internal rotation of the femur (4.64°). TKA surgery also affected the neutral path kinematics, resulting in more varus (1.25°) and external rotation of the femur (5.22°). All laxities were significantly reduced by the introduction of the muscle load and after implantation of the TKA. The presence of the implant significantly affects the active varus/valgus laxity. This contrasts with the rotational laxity, in which case the passive laxity is the main determinant for the active laxity. For the varus/valgus laxity, the passive laxity is also a significant predictor of the active laxity.

CONCLUSION

Knee stability is clearly affected by the presence of muscle load. This points to the relevance of appropriate rehabilitation with focus on avoiding muscular atrophy. At the same time, the functional, muscle loaded stability strongly relates to the passive, ligament-based stability. It remains therefore important to assess knee stability at the time of surgery, since the passive laxity is the only predictor for functional stability in the operating theatre.

LEVEL OF EVIDENCE

Case series, Level IV.

Postoperative Rehabilitation and Return to Sport Following Multiligament Knee Reconstruction

Multiligament knee injuries (MLKIs) are debilitating injuries that increasingly occur in young athletes. Return to sport (RTS) has historically been considered unlikely due to the severity of these injuries. Reporting in the literature regarding objective outcomes following MLKI, including RTS, is lacking, as are clear protocols for both rehabilitation progressions and RTS testing. RTS following MLKI is a complex process that requires an extended recovery duration compared to other surgery types. Progressions through postoperative rehabilitation and RTS should be thoughtful, gradual, and criterion based. After effective anatomic reconstruction to restore joint stability, objective measures of recovery including range of motion, strength, movement quality, power, and overall conditioning guide decision-making throughout the recovery process. It is important to frame the recovery process of the athlete in the context of the severity of their injury, as it is typically slower and less linear. Improved reporting on objective outcomes will enhance our understanding of recovery expectations within this population by highlighting persistent deficits that may interfere with a full recovery, including RTS.

The Natural History of Medial Meniscal Tears in the ACL Deficient and ACL Reconstructed Rat Knee

OBJECTIVE

The process of anterior cruciate ligament (ACL) injury-induced meniscal tear formation is not fully understood. Clinical studies have shown that ACL reconstruction (ACLR) reduces the development of secondary meniscal tears, but it is difficult to gain insight into the protective effects of ACLR from clinical studies alone. Using rat ACL transection (ACLT) and ACLR models, we aimed to reveal (1) the formation process of meniscal tears secondary to ACLT and (2) the protective effects of ACLR on secondary meniscal tears.

DESIGN

ACLT surgery alone or with ACLR was performed on the knees of rats. Histomorphological and histopathological changes were examined in the posteromedial region of the meniscus in intact rats and in rats that received ACLT or ACLR up to 12 weeks postsurgery. In addition, anterior-posterior joint laxity was measured using the universal testing machine to evaluate the effects of ACLT and ACLR on joint laxity.

RESULTS

AAnterior-posterior laxity was significantly increased by ACLT compared to the intact knee. This ACLT-induced joint laxity was partially but significantly reduced by ACLR. Meniscal proliferation and hyaline cartilage-like tissue formation were detected in the medial meniscus at 4 weeks post-ACLT. At 12 weeks post-ACLT, hyaline cartilage-like tissue was replaced by ossicles and meniscal tears were observed. These ACLT-induced abnormalities were attenuated by ACLR.

CONCLUSIONS

Our results suggest that ACLT-induced joint laxity induces secondary medial meniscal tears through meniscal proliferation and ossicle formation via endochondral ossification. Joint re-stabilization by ACLR suppresses meniscal proliferation and ossicle formation and consequently prevents secondary meniscal tears.

Formation process of joint contracture after anterior cruciate ligament reconstruction in rats

Knee joint contracture is often induced by anterior cruciate ligament reconstruction (ACLR). However, the temporal and spatial arthrofibrotic changes following inflammatory events, which occur in parallel with the formation of joint contractures after ACLR, are unknown. This study aimed to reveal: (a) time-dependent changes in myogenic and arthrogenic contractures; and (b) the process of arthrofibrosis development after ACLR. ACLR was performed on knees of rats unilaterally. Passive ranges of motions (ROMs) before and after myotomy, as well as inflammatory and fibrotic reactions, were examined before and after the surgery at various periods up to 56 days. Both ROMs before and after myotomy exhibited their lowest value on day 7 and increased thereafter in a time-dependent manner; nevertheless, significant restrictions remained by day 56. Myotomy partially increased ROMs at all time points, indicating contribution of the myogenic component to ACLR-induced contracture. Inflammatory and fibrotic reactions peaked on day 7. Arthrofibrosis, characterized by the thickening of the joint capsule and the shortening of the synovial length, was established by day 7 and was not completely resolved by day 56. Our results indicate that: (a) both myogenic and arthrogenic contractures generated through ACLR develop maximally by day 7 after surgery and subside thereafter, but persist at least until day 56; and (b) arthrofibrosis is established by day 7 after surgery and is not completely resolved by day 56. These findings suggest that treatment and intervention for preventing joint contracture after ACLR should be performed within the first 7 days after surgery.

Three-week joint immobilization increases anterior-posterior laxity without alterations in mechanical properties of the anterior cruciate ligament in the rat knee

BACKGROUND

Although knee immobilization may deteriorate the mechanical parameters of the anterior cruciate ligament, such as stiffness and failure strength, it is unknown whether it induces laxity in the whole joint. We examined the effects of immobilization on anterior-posterior joint laxity and mechanical properties of the anterior cruciate ligament, as well as histological and gene expression profiles of the joint capsule in rat knee joints.

METHODS

Unilateral rat knees were immobilized using an external fixator. Non-immobilized contralateral knees were used as controls. After 3 weeks, anterior-posterior laxity in the whole joint (i.e., a complex of bones, ligaments, and capsule) and stiffness and failure strength in the anterior cruciate ligament were examined using a universal testing machine. Moreover, the knee joint capsule was histologically analyzed, and the expression levels of genes related to collagen turnover in the posterior joint capsule were examined.

FINDINGS

Joint immobilization slightly but significantly increased anterior-posterior laxity compared with the contralateral side. Unexpectedly, the stiffness and failure strength of the anterior cruciate ligament were not altered by immobilization. There was no correlation found between anterior cruciate ligament stiffness and anterior-posterior joint laxity. In the posterior joint capsule, thinning of the collagen fiber bundles accompanied by a decrease in COL3A1 gene expression was observed after immobilization.

INTERPRETATION

These results suggest that 3 weeks of joint immobilization alters the biomechanical integrity in the knee joint without altering the mechanical properties of the anterior cruciate ligament. Changes in the joint capsule may contribute to the immobilization-induced increase in anterior-posterior laxity.

Laxity and contact forces of total knee designed for anatomic motion: A cadaveric study

BACKGROUND

Total knee designs that attempt to reproduce more physiological knee kinematics are gaining attention given their possible improvement in functional outcomes. This study examined if a total knee designed for anatomic motion, where the soft tissue balancing was intended to replicate anatomical tibiofemoral contact forces, can more closely reproduce the laxity of the native knee.

METHODS

In an ex-vivo setting, the laxity envelope of the knees from nine lower extremity specimens was measured using a rig that reproduced surgical conditions. The rig allowed application of a constant varus/valgus (V/V) and internal-external (I/E) torque through the range of motion. After testing the native knee, total knee arthroplasty (TKA) was performed using the Journey II bi-cruciate substituting implant. Soft tissue balancing was guided by targeting anatomical compressive forces in the lateral and medial tibiofemoral joints with an instrumented tibial trial. After TKA surgery, the laxity tests were repeated and compared to the native condition.

RESULTS

The TKA knee closely reproduced the coronal laxity of the native knee, except for a difference at 90° of flexion for valgus laxity. Looking at the rotational laxity, the implant constrained the internal rotation relative to the native knee at 45 and 60° of flexion. The forces on the tibial trial for the neutral path of motion showed higher values on the medial side as the knee flexed.

CONCLUSIONS

This study suggested that when using an anatomically-designed knee, the soft tissue balancing should also aim for anatomical contact forces, which will result in close to normal laxity patterns.

Second-Generation Electronic Ligament Balancing for Knee Arthroplasty: A Cadaver Study

BACKGROUND

Knee instability is emerging as a major complication after total knee arthroplasty (TKA), with ligament laxity and component alignment listed as important contributory factors. Knee balancing remains an art and is largely dependent on the surgeon's subjective "feel." The objectives were to measure the accuracy of an electronic balancing device to document the magnitude of correction in knee balance after soft-tissue releases and measure change in knee laxity after medial release.

METHODS

The accuracy of a second-generation electronic ligament-balancing device was compared with that of 2 mechanical balancing instruments. TKA was performed in 12 cadaver knees. Soft-tissue balance was measured sequentially before TKA, after mounting a trial femoral component, after medial release, and after resecting the posterior cruciate ligament. Coronal laxity of the knee under a 10 Nm valgus moment was measured before and after medial release.

RESULTS

The electronic balancing instrument was more accurate than mechanical instruments in measuring distracted gap and distraction force. On average, before TKA, the flexion gap was wider than the extension gap, and the medial gap was tighter than the lateral gap. Medial release increased the medial gap in flexion and increased passive knee valgus laxity. Posterior cruciate ligament release increased the tibiofemoral gap in both flexion and extension with a greater increase in the lateral gap.

CONCLUSION

The second-generation electronic balancing device was significantly more accurate than mechanical instruments and could record knee balance over the entire range of flexion. More accurate soft-tissue balance may enhance outcomes after TKA.

Evolution of TKA design

The use of Total Knee Arthroplasty (TKA) in treatment of chronic degenerative pathologies of the knee boasts of an experience of 50 years. During this period the collaboration between surgeons and engineers produced many developments in the design of the prosthesis. Today this procedure is safe and established even if in continuous development. The progress in technologies and the use of new materials let researches try again old-fashioned techniques from the past in order to be improved. This enthusiasm for those discovers is not always going hand to hand with scientific validation: many open questions remains Every different concept of the design tries to answer to special needs as the reach of the highest ROM, the reduction of pain and debris, articular geometry, the type of fixation, the modularity of augments and stems, the types of constraints,  knee kinematic and of course costs.

Anterolateral Ligament (ALL) — Myth or Reality?

Although the anterolateral ligament (ALL) was described a long time ago, recent research shows a lot of interest regarding this structure. There is a high variability concerning its anatomy, especially its capsular/extracapsular situation and insertion sites. There is also some controversy about its ligamentous structure. It seems that it has a biomechanical role in restricting anterior tibial translation and internal rotation. The ALL complex seems to have a clinical significance, and a relationship with the pivot shift has been described. Although there are promising results recently, the surgical techniques of ALL reconstruction, in addition to anterior cruciate ligament reconstruction, have to be further investigated. A precise indication algorithm and patient selection criteria need to be established.

Editorial Commentary: Size Does Matter-Anterior Cruciate Ligament Graft Diameter Affects Biomechanical and Clinical Outcomes

Anterior cruciate ligament (ACL) graft strength is related to graft diameter and how ACL grafts heal. All grafts appear to lose strength during healing. Clinical studies have documented that hamstring grafts less than 8 mm wide are more vulnerable to failure. Tripling the semitendinosus allows to increase the graft diameter and strength. A recent study documents a semitendinosus tripling technique with excellent clinical results.

Clinical outcomes after multiligament injured knees: medial versus lateral reconstructions

PURPOSE

The purpose of this study was to analyse the clinical outcomes of multiligament injured knees with respect to the medial collateral ligament and posteromedial corner (PMC) repair or reconstruction versus the posterolateral corner (PLC) reconstruction in patients operated according to a codified surgical protocol.

METHODS

Patients were divided into two groups depending on whether PMC or PLC was injured. Cruciate ligaments as well as PMC or PLC were reconstructed/repaired in a one-stage procedure. At minimum of 1-year follow-up, objective and subjective International Knee Documentation Committee (IKDC) forms, Lysholm score and sports activity level were recorded.

RESULTS

Thirty-nine patients with a median follow-up time of 57 months (range 12-129) were reviewed. No significant difference was found for functional scores between acute PMC and PLC subgroups. In Group PLC, subjective outcomes tend to be better in the acute than in chronic reconstruction subgroup.

CONCLUSIONS

A one-stage protocol with early surgery rather than delayed reconstruction produced better clinical outcomes whatever the injured collateral ligament, medial or lateral. In the future, early and chronic reconstructions as well as each injury pattern should be considered as separate entities in studies on multiple ligament injured knees to reach a better level of evidence.

LEVEL OF EVIDENCE

IV.

Adolescents and female patients are at increased risk for contralateral anterior cruciate ligament reconstruction: a cohort study from the Swedish National Knee Ligament Register based on 17,682 patients

PURPOSE

The impact of different surgical techniques in index ACL reconstruction for patients undergoing contralateral ACL reconstruction was investigated.

METHODS

The study was based on data from the Swedish National Knee Ligament Register. Patients undergoing index ACL reconstruction and subsequent contralateral ACL reconstruction using hamstring graft under the study period were included. The following variables were evaluated: age at index surgery, gender, concomitant meniscal or cartilage injury registered at index injury, transportal femoral bone tunnel drilling and transtibial femoral bone tunnel drilling. The end-point of primary contralateral ACL surgery was analysed as well as the time-to-event outcomes using survivorship methods including Kaplan-Meier estimation and Cox proportional hazards regression models.

RESULTS

A total of 17,682 patients [n = 10,013 males (56.6%) and 7669 females (43.4%)] undergoing primary ACL reconstruction from 1 January 2005 through 31 December 2014 were included in the study. A total of 526 (3.0%) patients [n = 260 males (49.4%) and 266 females (50.6%)] underwent primary contralateral ACL reconstruction after index ACL reconstruction during the study period. Females had a 33.7% greater risk of contralateral ACL surgery [HR 1.337 (95% CI 1.127-1.586); (P = 0 0.001)]. The youngest age group (13-15 years) showed an increased risk of contralateral ACL surgery compared with the reference (36-49) age group [HR 2.771 (95% CI 1.456-5.272); (P = 0.002)]. Decreased risk of contralateral ACL surgery was seen amongst patients with concomitant cartilage injury at index surgery [HR 0.765 (95% CI 0.623-0.939); (P = 0.010)]. No differences in terms of the risk of contralateral ACL surgery were found between anatomic and non-anatomic techniques of primary single-bundle ACL reconstruction, comparing transportal anatomic technique to transtibial non-anatomic, anatomic and partial-anatomic.

CONCLUSION

Age and gender were identified as risk factors for contralateral ACL reconstruction; hence young individuals and females were more prone to undergo contralateral ACL reconstruction. Patients with concomitant cartilage injury at index ACL reconstruction had lower risk for contralateral ACL reconstruction. No significant differences between various ACL reconstruction techniques could be related to increased risk of contralateral ACL reconstruction.

LEVEL OF EVIDENCE

Retrospective Cohort Study, Level III.

Objective measurements of static anterior and rotational knee laxity

Several devices allow to measure anterior and rotational static knee laxity. To date, the use of rotational laxity measurements in the daily clinical practice however remains to be improved. These measurements may be systematically integrated to the follow-up of knee injuries. Physiologic laxity measurements may particularly be of interest for the identification of risk factors in athletes. Furthermore, knee laxity measurements help to improve the diagnosis of knee soft tissue injuries and to follow up reconstructions. Further prospective follow-ups of knee laxity in the injured/reconstructed knees are however required to conclude on the best treatment strategy for knee soft tissue injuries.