Soft tissues: a question of balance

Posterior cruciate ligament resection under minimum medial collateral ligament release changes tibial internal rotation, joint center gap, and varus ligament balance on joint distraction force at flexion in total knee arthroplasty

BACKGROUND

The purpose of this study was to assess the effect of posterior cruciate ligament resection under minimum medial collateral ligament release on the joint center gap, varus ligament balance, and the rotational change of the femur and tibia.

METHODS

This study included 75 knees with varus osteoarthritis that underwent total knee arthroplasty. After minimum medial collateral ligament releases and bone resection of the distal femur and proximal tibia, the joint center gap and varus ligament balance were measured before and after posterior cruciate ligament resection using a digital tensor with a joint distraction force of 89, 133, 178 N. The rotational changes under a distraction force of 200 N were captured using a navigation system.

FINDINGS

The joint center gap and varus ligament balance at 90° and 120° of flexion significantly increased after posterior cruciate ligament resection with distraction forces of 89 N (90°: 0.4 mm / 0.9° and 120°: 0.5 mm / 0.8°), 133 N (90°: 0.9 mm / 1.3° and 120°: 0.9 mm / 1.1°), 178 N (90°: 1.5 mm / 1.9° and 120°: 1.5 mm / 1.5°). Tibial internal rotation significantly increased after posterior cruciate ligament resection at 90° (1.9°) and 120° (2.2°).

INTERPRETATION

Joint distraction forces after posterior cruciate ligament resection increased the tibial internal rotation, joint center gap, and varus ligament balance at flexion. These findings indicate that posterior cruciate ligament resection should increase the lateral gap more than the medial gap due to tibial internal rotation at flexion. (245 words).

Posterior cruciate ligament resection in total knee arthroplasty: the effect on flexion-extension gaps, mediolateral laxity, and fixed flexion deformity

AIMS

The aim of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft-tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilized (PS) total knee arthroplasty (TKA).

PATIENTS AND METHODS

This prospective study included 110 patients with symptomatic osteoarthritis of the knee undergoing primary robot-assisted PS TKA. All operations were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess gaps before and after PCL resection in extension and 90° knee flexion. Measurements were made after excision of the anterior cruciate ligament and prior to bone resection. There were 54 men (49.1%) and 56 women (50.9%) with a mean age of 68 years (sd 6.2) at the time of surgery. The mean preoperative hip-knee-ankle deformity was 4.1° varus (sd 3.4).

RESULTS

PCL resection increased the mean flexion gap significantly more than the extension gap in the medial (2.4 mm (sd 1.5) vs 1.3 mm (sd 1.0); p < 0.001) and lateral (3.3 mm (sd 1.6) vs 1.2 mm (sd 0.9); p < 0.01) compartments. The mean gap differences after PCL resection created significant mediolateral laxity in flexion (gap difference: 1.1 mm (sd 2.5); p < 0.001) but not in extension (gap difference: 0.1 mm (sd 2.1); p = 0.51). PCL resection significantly improved the mean FFD (6.3° (sd 4.4) preoperatively vs 3.1° (sd 1.5) postoperatively; p < 0.001). There was a strong positive correlation between the preoperative FFD and change in FFD following PCL resection (Pearson's correlation coefficient = 0.81; p < 0.001). PCL resection did not significantly affect limb alignment (mean change in alignment: 0.2° valgus (sd 1.2); p = 0.60).

CONCLUSION

PCL resection creates flexion-extension mismatch by increasing the flexion gap more than the extension gap. The increase in the lateral flexion gap is greater than the increase in the medial flexion gap, which creates mediolateral laxity in flexion. Improvements in FFD following PCL resection are dependent on the degree of deformity before PCL resection. Cite this article: Bone Joint J 2019;101-B:1230-1237.

Assessing coronal laxity in extension and flexion at a minimum of 10 years after primary total knee arthroplasty

PURPOSE

Favourable long-term results after total knee arthroplasty (TKA) require appropriate soft tissue balance. However, the relationships between long-term results after TKA surgery and mediolateral laxities at extension and at 90° flexion remain unknown. This study therefore quantitatively assessed ligament balance at extension and at 90° knee flexion at least 10 years after primary TKA, as well as clarifying the relationships between long-term outcomes and mediolateral laxities.

METHODS

This study included 49 knees (19 CR type and 30 PS type) of 33 patients followed up for at least 10 years after TKA at our hospital. Plain radiographs were obtained with about 150 N of varus or valgus stress using a Telos arthrometer at extension. At 90° flexion, epicondylar views were obtained under a 1.5-kg load and with about 10 kg of varus or valgus stress.

RESULTS

Lateral laxity of about 5° was observed in both extension and flexion, with total laxities of varus and valgus stress each less than 10°. Postoperative clinical outcomes were good, with significant improvements in extension angle, femorotibial angle, and KSS, and no loosening in any knee.

CONCLUSIONS

Good long-term results of TKA can be obtained with a lateral laxity of about 5°, equivalent to that of healthy knees.

LEVEL OF EVIDENCE

III.

Intraoperative ligament laxity influences functional outcome 1 year after total knee arthroplasty

PURPOSE

To find out if there is an association between ligament laxity measured intraoperatively and functional outcome 1 year after total knee arthroplasty (TKA).

METHODS

Medial and lateral ligament laxities were measured intraoperatively in extension and in 90° of flexion in 108 patients [122 knees; median age 70 (range 42-83) years]. Mechanical axes were measured preoperatively and at 1-year follow-up. Outcome measures were the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Knee Society Clinical Rating System, the Oxford Knee Score and patient satisfaction. The relationships between laxity and outcome scores were examined by median regression analyses.

RESULTS

Post-operative mechanical axis had a significant effect on the association between ligament laxity and KOOS. Therefore, the material was stratified on post-operative mechanical axis. In perfectly aligned and valgus-aligned TKAs, there was a negative correlation between medial laxity and all subscores in KOOS. The most important regression coefficient (β) was recorded for the effect of medial laxity in extension on activities of daily living (ADLs) (β = -7.32, p < 0.001), sport/recreation (β = -6.9, p = 0.017) and pain (β = -5.9, p = 0.006), and for the effect of medial laxity in flexion on ADLs (β = -3.11, p = 0.023) and sport/recreation (β = -4.18, p = 0.042).

CONCLUSIONS

In order to improve the functional results after TKA, orthopaedic surgeons should monitor ligament laxity and mechanical axis intraoperatively and avoid medial laxity more than 2 mm in extension and 3 mm in flexion in neutral and valgus-aligned knees.

LEVEL OF EVIDENCE

II.

Collateral ligament strains during knee joint laxity evaluation before and after TKA

BACKGROUND

Passive knee stability is provided by the soft tissue envelope. There is consensus among orthopedic surgeons that good outcome in Total Knee Arthroplasty requires equal tension in the medial/lateral compartment of the knee joint, as well as equal tension in the flexion/extension gap. The purpose of this study was to quantify the ligament laxity in the normal non-arthritic knee before and after Posterior-Stabilized Total Knee Arthroplasty. We hypothesized that the Medial/Lateral Collateral Ligament shows minimal changes in length when measured directly by extensometers in the native human knee during varus/valgus laxity testing. We also hypothesized that due to differences in material properties and surface geometry, native laxity is difficult to reconstruct using a Posterior-Stabilized Total Knee.

METHODS

Six specimens were used to perform this in vitro cadaver test using extensometers to provide numerical values for laxity and varus-valgus tilting in the frontal plane.

FINDINGS

This study enabled a precise measurement of varus-valgus laxity as compared with the clinical assessment. The strains in both ligaments in the replaced knee were different from those in the native knee. Both ligaments were stretched in extension, in flexion the Medial Collateral Ligament tends to relax and the Lateral Collateral Ligament remains tight.

INTERPRETATION

As material properties and surface geometry of the replaced knee add stiffness to the joint, we recommend to avoid overstuffing the joint, when using this type of Posterior-Stabilized Total Knee Arthroplasty, in order to obtain varus/valgus laxity close to the native joint.

Measurement of knee joint gaps without bone resection: "physiologic" extension and flexion gaps in total knee arthroplasty are asymmetric and unequal and anterior and posterior cruciate ligament resections produce different gap changes

General agreement is that flexion and extension gaps should be equal and symmetrical in total knee arthroplasty (TKA) procedures. However, comparisons using a standard TKA approach to normal knee joints that have not undergone bone resection are currently unavailable. Since bony preparation can influence capsule and ligament tension, our purpose was to perform measurements without this influence. Ten normal cadaveric knees were assessed using a standard medial parapatellar TKA approach with patellar subluxation. Gap measurements were carried out twice each alternating 100 and 200 N per compartment using a prototypical force-determining ligament balancer without the need for bony resection. Initial measurements were performed in extension, followed by 908 of flexion. The ACL was then resected, and finally the PCL was resected, and measurements were carried out in an analogous fashion. In general, the lateral compartment could be stretched further than the medial compartment, and the corresponding flexion gap values were significantly larger. ACL resection predominantly increased extension gaps, while PCL resection increased flexion gaps. Distraction force of 100 N per compartment appeared adequate; increasing to 200 N did not improve the results.

Lateral laxity in flexion increases the postoperative flexion angle in cruciate-retaining total knee arthroplasty

Thirty-eight patients diagnosed with osteoarthritis underwent 41 cruciate-retaining total knee arthroplasties. In varus and valgus tests at flexion, subjects were seated on a table at 80° of knee flexion; 50 N was applied perpendicular to the lower leg. The factors affecting the postoperative flexion angle were investigated in a multiregression analysis. The mean joint angles of the flexion-valgus and flexion-varus tests were 3.4° ± 1.4° and 6.2° ± 2.5°, respectively. The flexion-varus angle was correlated with the postoperative flexion angle (P < .01). The mean postoperative flexion angles were 110.8° ± 9.6° and 118.1° ± 8.0° in the groups with the flexion-varus angle of 6° or less and more than 6°, respectively (P = .02). Slack lateral laxity in flexion had a significant effect during knee flexion in cruciate-retaining total knee arthroplasty.

A new method to measure ligament balancing in total knee arthroplasty: laxity measurements in 100 knees

BACKGROUND

Ligament balancing is considered a prerequisite for good function and survival in total knee arthroplasty (TKA). However, there is no consensus on how to measure ligament balance intra-operatively and the degree of stability obtained after different balancing techniques is not clarified.

PURPOSE

This study presents a new method to measure ligament balancing in TKA and reports on the results of a try-out of this method and its inter-observer reliability.

METHODS

After the implantation of the prosthesis, spatulas of different thickness were used to measure medial and lateral condylar lift-off in flexion and extension in 70 ligament-balanced knees and in 30 knees were ligament balancing was considered unnecessary. Inter-observer reliability for the new method was estimated and the degree of medial-lateral symmetry in extension and in flexion, and the equality of the extension gaps and flexion gaps were calculated.

RESULTS

The method was feasible in all operated knees, and found to be very reliable (intraclass correlation coefficient = 0.88). We found no statistically significant difference in condylar lift-off between the ligament-balanced and the non ligament-balanced group, however, there was a tendency to more outliers in flexion in the ligament-balanced group.

CONCLUSIONS

Our method for measuring ligament balance is reliable and provides valuable information in assessing laxity intra-operatively. This method may be a useful tool in further research on the relationship between ligament balance, function and survival of TKA.

Anteroposterior stability after posterior cruciate-retaining total knee arthroplasty

PURPOSE

A functional posterior cruciate ligament (PCL) is important for the knee stability after PCL-retaining total knee arthroplasty (TKA). The objectives of this study were to determine the anteroposterior (AP) displacement of the knee after a mobile- or fixed-bearing PCL-retaining TKA operated with a ligament-balancing technique and the correlation of AP stability with the clinical outcome.

METHODS

The AP displacement of 160 TKAs in 143 patients was measured pre- and intra-operatively, and the results were compared to the AP displacement measured 4 years post-surgery.

RESULTS

The change in AP displacement from intra-operative measurement to follow-up at the 25° measuring point was -1.2 mm; at 90°, it was -0.2 mm. Mobile bearings showed significantly greater AP displacement than fixed bearings. Older patients, male patients and patients receiving a fixed prosthesis had lower post-operative laxity compared with the overall population.

CONCLUSIONS

The small change in AP displacement indicates that the PCL remains functional over time. In our study, we could not find any correlation between knee AP stability and clinical outcome, including passive flexion, Knee Society Score or Visual Analogue Scale of pain and satisfaction.

Development of a force-determining tensor to measure "physiologic knee ligament gaps" without bone resection using a total knee arthroplasty approach

BACKGROUND

Ligament balancing is a challenging but essential part of successful total knee arthroplasty. There is general agreement that flexion and extension gaps should be equal and symmetrical. However, to date there are no available comparisons to physiologically normal knee joints that have not undergone bone resection. There are also no standards specifying which instruments (e.g., spacers, distractors, trial components, navigation systems) and particularly what degree of force should be used for gap distraction.

METHODS

To measure the physiological extension and flexion gaps, a prototypical force-determining tensor (Aesculap, Tuttlingen, Germany) was constructed and adapted so that force could be applied directly through Schanz screws inserted medially and laterally on the tibia and femur, independent of each other and without the need for bony resection. Ten normal cadaveric knees were assessed using a standard medial parapatellar total knee arthroplasty approach with patellar subluxation. Gap measurements were carried out twice, alternating distraction forces of 100 and 200 N each time.

RESULTS

The prototype was implemented successfully. Repeat measurements showed only slight deviation from the original, resulting in minimal standard error. Precision did not vary with the application of greater force (200 N), but gap size increased significantly (p < 0.001).

CONCLUSIONS

The success of this assessment with cadaveric knees indicates that this prototype can be applied to measure flexion and extension gaps without the need for bony resection. Increasing the distraction force to 200 N does not improve results, so 100 N per compartment appears adequate. Most likely, the extension and flexion gaps are physiologically asymmetric and unequal, and the kinematics are markedly altered after resection of the PCL and/or ACL. This new force-determining tensor can be used for further analyses, e.g., to explore the effects of selective ligament resection.

Evaluation of soft-tissue balance during total knee arthroplasty

PURPOSE

To evaluate soft-tissue balance during versus after total knee arthroplasty (TKA).

METHODS

18 men and 75 women aged 52 to 85 (mean, 68) years who had moderate-to-severe varus deformity underwent TKAs using the Scorpio non-restrictive geometry posterior-stabilised system (Stryker Howmedica Osteonics; Allendale, [NJ], USA). All surgeries were performed by a single surgeon using the medial parapatellar approach. After the bony and soft-tissue procedures, soft-tissue balance was measured intra-operatively using a tensor/balancer device. The coronal laxity--angles between the cut surfaces of the femur and tibia--were measured at 0 degree (in extension) and 90 degrees (in flexion). The central gap was also measured. Immediate postoperative soft-tissue balance was measured using an arthrometer, while anteroposterior stress radiographs were being taken. A valgus or varus force was applied just above the knee on the lateral or medial side, with the knee counter-supported and at 15 degrees flexion.

RESULTS

Intra-operatively, the mean coronal laxity at 0 degree (in extension) and 90 degrees (in flexion) was 2.1 degrees and -1.6 degrees, and the mean central gaps were 21.2 and 23.5 mm, respectively. Immediate postoperative mean coronal laxity was 2.9 degrees, indicating that lateral laxity was greater than medial laxity. The postoperative coronal laxity was positively corrected to the intra-operative coronal laxity at 0 degree (r=0.304, p=0.003), but not to the intra-operative coronal laxity at 90 degrees (r= -0.07, p=0.47).

CONCLUSION

Slightly greater lateral laxity was observed after TKA, although equal medial-lateral balance was achieved intra-operatively.

The effectiveness of sequential medial soft tissue release on coronal alignment in total knee arthroplasty: using a computer navigation model

Soft tissue management is a major step in total knee arthroplasty. We aimed to analyze the relationship between sequential medial soft tissue release and the resulting change in the anteroposterior limb axis and the tibiofemoral gaps. Measurements were obtained using a CT-free navigation system (Ci navigation system, DePuy I-Orthopaedics, Munich, Germany). Concerning leg axis, each release step led to significant (P < .001) effects. The highest effect was seen for the 6-cm release in extension and the release of medial collateral ligament in 90 degrees flexion. The medial gap difference was significant for each release step except the 4-cm release in extension. The highest increase resulted when sacrificing the entire posterior cruciate ligament in extension and in 90 degrees flexion. Implementation of computer-assisted surgery allows this first navigation-controlled study, elucidating the effect of soft tissue release in total knee arthroplasty.

Gap configuration and anteroposterior leg axis after sequential medial ligament release in rotating-platform total knee arthroplasty

BACKGROUND

Soft tissue management is a major issue in total knee replacement. There have been very few papers dealing with its effect on leg axis and tibiofemoral gap.

METHODS

In a cadaver specimen study, we analyzed this effect by performing a sequential medial soft tissue release after a mobile-bearing total knee arthroplasty. Measurements were obtained using a CT-free navigation system (Ci navigation system).

RESULTS

We found the highest increase in leg axis and medial gap when releasing the anteromedial tibial sleeve of the capsule 6 cm below the joint line, in extension, and after dividing the medial collateral ligament, in flexion, when releasing the medial half of the posterior cruciate ligament. There were differences in amount of change between extension and flexion, especially when releasing the medial half of the posterior cruciate ligament. In extension, the lateral gap remained the same as in flexion.

INTERPRETATION

Implementation of computer-assisted surgery has allowed this first navigation-controlled study investigating the effect of soft tissue release in TKR with rotating platform. Each sequential release step has the desired effect on a.p. leg axis and tibiofemoral gaps. It is important that the differences between the effects in extension and flexion be noted.

Weichteilmanagement bei der Varusgonarthrose

BACKGROUND

Knees with severe varus deformities and contractures of the medial and lateral collateral ligaments and the posterior capsule require special soft tissue management to gain a stable knee over the full range of movement. The introduction of navigation systems into knee surgery has now made precise measurement of the leg axis and gap size possible.

METHODS

Ten knee joints received a computer-assisted total knee replacement (Ci navigation system DePuy) I-Orthopaedics, Munich). The change of the leg axis and the size of the mediolateral gaps were measured and documented when performing a standardized medial ligament release sequence.

RESULTS

We found a significant effect after each release step regarding the change of the leg axis as well as the gap width (p<0.001). The highest effect was seen for the 6-cm capsule release in extension and the release of the medial collateral ligament in 90 degrees flexion.

CONCLUSION

Implementation of computer-assisted navigation facilitates visualization and quantification of the effect of the sequential medial soft tissue release in total knee arthroplasty.

Ranawat Award paper. Effect of selective lateral ligament release on stability in knee arthroplasty

The current authors evaluated a fundamental approach to balancing the lateral ligaments of the knee that begins with aligning the implants correctly in flexion and extension, proceeds to assessing stability in flexion and extension, and concludes with releasing tight structures based on their function throughout the arc of flexion. Seventeen knees from cadavers were used to evaluate stability at various degrees of flexion after total knee arthroplasty, and then stability was reevaluated after release of selected ligaments. The iliotibial band and posterior capsule were effective lateral stabilizers only in full extension. The lateral collateral ligament had a major stabilizing effect throughout the arc from 0 degrees to 90 degrees flexion. The iliotibial band and popliteus tendon and posterolateral corner capsule had little effect when the other ligaments were intact. When tested in the absence of the other lateral ligaments, the popliteus tendon and posterolateral corner capsule had significant stabilizing effects throughout the flexion arc. The popliteus tendon exerted its effect mostly from 60 degrees to 90 degrees flexion. The posterolateral corner capsule was effective mostly at 0 degrees to 30 degrees flexion. The iliotibial band had a significant stabilizing effect from 0 degrees to 30 degrees flexion.

Revision total knee replacement ligament balancing for deformity

Ligament balancing in revision settings requires attention to flexion-extension gap balancing and adjusting the asymmetry of the gaps. The tension-stress examination must be understood and done. The shortcomings of ligament tightening procedures have been experienced. Standard concave-side releases may be done, with attention given to the maintenance of adequate vascularity to the subjacent bone. However, frequently exact and sufficient balance may not be achievable, and resorting to varus-valgus constraint will be necessary. Particular emphasis has been given to the issue of controlling the flexion space and the possibility of losing that control. In the situation of loss of collateral integrity possibly exaggerated by the loss of posterior capsular integrity, one sees a gross enlargement of the flexion space. Addressing this with placement of a thicker tibial component simply leads to great flexion contracture. The larger flexion space may provide the opportunity for subluxation of the intercondylar peg of a varus-valgus constrained prosthesis. Although quadriceps tension may hold the tibia up and control the flexion space, this mechanism of stabilization will fail if the patient's knee regains substantial range of motion.

Soft tissue release in total knee arthroplasty. Cadaver study using knees without deformities

Soft tissue releases are performed to correct fixed deformities in total knee arthroplasty. The goal of this in vitro study was to investigate the relationship between the individual steps in a medial (eight anatomic specimen knees) or lateral (four anatomic specimen knees) soft tissue release sequence, the resulting change in the medial and lateral tibiofemoral gaps, and the change in coronal angulation caused by 10 Nm varus and valgus moments in extension and 90 degrees flexion. An optical encoder was used to measure the coronal angulation. The tibiofemoral gaps were measured with calipers with the knee distracted by a 53-N load. In the medial release sequence, a significant increase in coronal angulation and medial gap occurred after the release of the anteromedial sleeve 8 cm from the medial joint line. In the lateral release sequence, there was a significant increase in the coronal angle and lateral gap after the lateral collateral ligament and popliteus tendon were released from the femur. Release of the posterior cruciate ligament led to a significant increase in angle and gap in medial and lateral release sequences. These results are specific for the particular release sequences studied, with release of the posterior cruciate being the final step in each sequence.