Flexion Laxity Research Articles

Flexion Instability After Total Knee Arthroplasty.

Flexion instability after total knee arthroplasty (TKA) is caused by an increased flexion gap compared with extension gap. Patients present with recurrent effusions, subjective instability (especially going downstairs), quadriceps weakness, and diffuse periretinacular pain. Manual testing for laxity in flexion is commonly done to confirm a diagnosis, although testing positions and laxity grades are inconsistent. Nonsurgical treatment includes quadriceps strengthening and bracing treatment. The mainstays to surgical management of femoral instability involve increasing the posterior condylar offset, decreasing the tibial slope, raising the joint line in combination with a thicker polyethylene insert, and ensuring appropriate rotation of implants. Patient outcomes after revision TKA for flexion instability show the least amount of improvement when compared with revisions for other TKA failure etiologies. Future work is needed to unify reproducible diagnostic criteria. Advancements in biomechanical analysis with motion detection, isokinetic quadriceps strength testing, and computational modeling are needed to advance the collective understanding of this underappreciated failure mechanism.

The role of rotating hinge implants in revision total knee arthroplasty.

Hinged implants are the most constrained knee replacement prostheses. They are very useful in complex cases of total knee arthroplasty (TKA) revision.Hinged implants have evolved with rotating bearings and modularity that allows local joint reconstruction or segmental bone replacement.They are required when significant instability persists in cases with inadequate collateral ligaments and significant flexion laxity.They are now used when a large bone defect is reconstructed, or when bone fixation of the implant is questionable especially in the metaphyseal zone.The use of hinged implants in TKA revision is associated with high complication rates. Published outcomes differ based on the patients’ aetiology.The outcomes of rotating-hinged implants used in septic revisions or salvage situations are poorer than other types of revision and have a higher complication rate.The poor general health of these patients is often a limitation.Despite these relatively poor results, hinged implants continue to have a place in revision surgery to solve major instability or to obtain stable bone fixation of an implant when the metaphysis is filled with bone grafts or porous devices.Cite this article: EFORT Open Rev 2019;4 DOI: 10.1302/2058-5241.4.180070

Mid-flexion laxity in the asymptomatic native knee is predominantly present on the lateral side.

During total knee arthroplasty (TKA), an orthopaedic surgeon is focused on soft-tissue balance in extension (0°) and in flexion (90°). Patients with instability problems of the knee often report a feeling of instability during daily life activities, at around 30° knee flexion. There are no reference values available for knee laxity of healthy subjects in mid-flexion (30°) and flexion (90°) for comparison with the TKA population. Therefore, the aim was to quantify varus and valgus knee laxity in extension, mid-flexion and flexion in the asymptomatic native knee. In 40 healthy volunteers matched for age, gender and BMI with the TKA-population, varus and valgus knee laxity in extension (0°), mid-flexion (30°) and flexion (90°) was measured on low-dose radiographs. For each subject, one randomly selected knee was stressed in extension, mid-flexion and flexion (with 15Nm) using a stress device. Varus laxity in mid-flexion was higher than in extension and flexion (p < 0.01). Valgus laxity tended to be highest in mid-flexion laxity; however, no differences in knee laxity between flexion angles were seen (n.s.). Varus knee laxity in extension was higher in females than in males (p < 0.05). Mid-flexion laxity in the native knee is more prominent on the lateral side of the knee, while the medial side is more stable and constrained. Varus knee laxity in extension was shown to be higher in females than in males. Prognostic Level II.

The unstable knee: Manifestations, reasons and corrective actions

Instability after total knee arthroplasty (TKA) can include asymptomatic mid flexion laxity, flexion instability causing pain and swelling after activity, and collateral ligament insufficiency which results in loss of ambulatory ability. Mid flexion instability may occur in knees that are considered well balanced. Flexion instability resulting from greater soft tissue laxity in flexion than extension can be treated with activity restrictions, bracing, and muscle strengthening or revision TKA. Implants are constrained in the coronal plane with either a varus-valgus UHMWPE post or metal hinge mechanism. Complete collateral ligament loss generally requires use of a hinged implant to restore stability.

Increased valgus laxity in flexion with greater tibial resection depth following total knee arthroplasty.

Soft tissue balancing is of central importance to outcome following total knee arthroplasty (TKA). However, there are lack of data analysing the effect of tibial bone cut thickness on valgus laxity. A cadaveric study was undertaken to assess the biomechanical consequences of tibial resection depth on through range knee joint valgus stability. We aimed to establish a maximum tibial resection depth, beyond which medial collateral ligament balancing becomes challenging, and a constrained implant should be considered. Eleven cadaveric specimens were included for analysis. The biomechanical effects of increasing tibial resection were studied, with bone cuts made at 6, 10, 14, 18 and 24mm from the lateral tibial articular surface. A computer navigation system was used to perform the tibial resection and to measure the valgus laxity resulting from a torque of 10Nm. Measurements were taken in four knee positions: 0° or extension, 30°, 60° and 90° of flexion. Intra-observer reliability was assessed. A minimum sample size of eight cadavers was necessary. Statistical analysis was performed using a nonparametric Spearman's ranking correlation matrix at the different stages: in extension, at 30°, 60° and 90° of knee flexion. Significance was set at p < 0.05. There was no macroscopic injury to the dMCL or sMCL in any of the specimens during tibial resection. There was no significant correlation found between the degree of valgus laxity and the thickness of the tibial cut with the knee in extension. There was a statistically significant correlation between valgus laxity and the thickness of the tibial cut in all other knee flexion positions: 30° (p < 0.0001), 60° (p < 0.001) and 90° (p < 0.0001). We identified greater than 5° of valgus laxity, at 90° of knee flexion, after a tibial resection of 14mm. Increased tibial resection depth is associated with significantly greater valgus laxity when tested in positions from 30° to 90° of flexion, despite stability in extension. Greater than 5° of laxity was identified with a tibial resection of 14mm. When a tibial bone cut of 14mm or greater is necessary, as may occur with severe preoperative coronal plane deformity, it is recommended to consider the use of a constrained knee prosthesis.

Short-term postoperative outcomes of bicruciate-retaining total knee arthroplasty: Association between lateral laxity in flexion and patient satisfaction

Short-term postoperative outcomes of bicruciate-retaining total knee arthroplasty: Association between lateral laxity in flexion and patient satisfaction

How balanced is the knee when we start a total knee replacement?

Objectives:Optimal coronal plane alignment for total knee arthroplasty (TKA) remains controversial. Understanding the pre-operative soft tissue status is important for optimizing the soft tissue envelope during TKA. The purpose of this study was to define the corrected, neutral (“pre-disease”) HKAA of end stage osteoarthritic knees prior to TKA and from this point measure the medial and lateral laxity of varus and valgus knees in maximum extension, 20 and 90° of flexion prior to TKA.Methods:We conducted an observational cohort study. During surgery, the lower limb was manipulated using computer navigation, prior to surgical releases, whilst observing the joint to ensure congruence to allow the limb weight-bearing axis to pass through the knee center in maximum extension, 20° and 90° of flexion. Coronal plane laxity was measured as medial and lateral displacement from this point and compared to published values for healthy subjects.Results:The corrected, neutral HKAA in 89 knees in maximum extension prior to TKA was -1.22° +/- 1.4°. The corrected HKAA in maximum extension was within +/- 3° of 0° in 91.0% of patients. 12.8% (10/78) of varus knees displayed a medial contracture. Of these 10 knees, five also displayed abnormal lateral laxity. In maximum extension, 19.2% (15/78) of knees had abnormally increased lateral laxity. 10 of these 15 knees did not have a medial contracture. The remaining 5 knees with increased lateral laxity or 6.4% (5/78) displayed a medial contracture. Lateral laxity increased significantly with increasing varus deformity. Medial laxity did not significantly decrease when comparing varus deformity of 5 -10° versus >10°. 29 Valgus knees were examined. In maximum extension and 20° of flexion 27.6% of subjects (8/29) and 6.9% (2/29) of subjects respectively had a lateral contracture. On the medial side abnormally increased laxity was seen in 40.7% (11/27) in maximum extension; 75% (21/28) in 20° and 0% in 90° of flexion. On the lateral side abnormally increased laxity was seen in 3.7% (1/27) in maximum extension; 3.6% (1/27) in 20° of flexion and 72.4% in 90° of flexion.Conclusion:Varus and valgus knees did not record a corrected, neutral HKAA at the opposite end of the 0 +/-3° range. Optimal TKA alignment might be better and more specifically defined by the corrected neutral axis of each knee. The majority of varus knees with deformity of up to 15° have neither a medial contracture nor abnormal lateral laxity when referenced to the neutral axis of the knee. Lateral laxity is a more consistent feature of the varus knee. In the valgus OA knee a lateral contracture is not present in most patients and typically only present in maximum extension. The pattern then reverses to an abnormal increase in lateral laxity in flexion for many subjects. The pattern on the medial side is for maximum soft tissue disturbance in 20° of flexion before normalising in 90° of flexion. These findings demonstrate potentially problematic scenarios for balancing the valgus OA knee. The patterns of contracture and laxity found are variable and correlate poorly to deformity.

Comparison of Anterior Cruciate Ligament Graft Isometry between Paired Femoral and Tibial Tunnels.

Accurate tunnel placement is important for a successful anterior cruciate ligament (ACL) reconstruction. Controversy exists concerning the preferred method of femoral tunnel preparation, with proponents of both medial portal and transtibial drilling techniques. Current ACL literature suggests that placement of the femoral ACL attachment site posterior or "low" in the ACL footprint leads to more anatomically correct ACL mechanics and better rotational control. There is limited literature focusing on ACL graft displacement through knee range of motion based on specific paired placement of femoral and tibial tunnels. Our purpose was to assess ACL isometry between multiple combinations of femoral and tibial tunnels. We hypothesized that placement of the graft at the posterior aspect of the ACL footprint on the femur would be significantly less isometric and lead to more graft displacement as compared with central or anterior placement. The ACL of matched pairs of cadaveric knees was arthroscopically debrided while leaving the soft tissue footprint on the femur and tibia intact. One knee from each pair underwent notchplasty. In all knees, three femoral and three tibial tunnels were created at the anterior, central, and posterior aspects of the ACL footprint. A suture was passed through each tunnel combination (nine potential pairs), and the change in isometry was measured throughout full knee range of motion. Placement of the femoral tunnel along the posterior aspect of the ACL footprint was less isometric compared with a central or anterior position in the femoral footprint. Placement of a posterior tibial tunnel also led to decreased isometry, but tibial tunnel placement affected isometry to a lesser extent than femoral tunnel placement. The combination of a posterior femoral and posterior tibial tunnel resulted in greater than 1 cm of graft excursion from full flexion to extension. Placement of ACL tunnels at anisometric sites may adversely affect the mechanical properties and behavior of the ACL graft, resulting in either graft laxity in flexion or overconstraint and loss of extension.

Biomechanical Comparison of Anterolateral Procedures Combined With Anterior Cruciate Ligament Reconstruction

Background: Anterolateral soft tissue structures of the knee have a role in controlling anterolateral rotational laxity, and they may be damaged at the time of anterior cruciate ligament (ACL) ruptures. Purpose: To compare the kinematic effects of anterolateral operative procedures in combination with intra-articular ACL reconstruction for combined ACL plus anterolateral–injured knees. Study Design: Controlled laboratory study. Methods: Twelve cadaveric knees were tested in a 6 degrees of freedom rig using an optical tracking system to record the kinematics through 0° to 90° of knee flexion with no load, anterior drawer, internal rotation, and combined loading. Testing was first performed in ACL-intact, ACL-deficient, and combined ACL plus anterolateral–injured (distal deep insertions of the iliotibial band and the anterolateral ligament [ALL] and capsule cut) states. Thereafter, ACL reconstruction was performed alone and in combination with the following: modified MacIntosh tenodesis, modified Lemaire tenodesis passed both superficial and deep to the lateral collateral ligament, and ALL reconstruction. Anterolateral grafts were fixed at 30° of knee flexion with both 20 and 40 N of tension. Statistical analysis used repeated-measures analyses of variance and paired t tests with Bonferroni adjustments. Results: ACL reconstruction alone failed to restore native knee kinematics in combined ACL plus anterolateral–injured knees (P < .05 for all). All combined reconstructions with 20 N of tension, except for ALL reconstruction (P = .002-.01), restored anterior translation. With 40 N of tension, the superficial Lemaire and MacIntosh procedures overconstrained the anterior laxity in deep flexion. Only the deep Lemaire and MacIntosh procedures—with 20 N of tension—restored rotational kinematics to the intact state (P > .05 for all), while the ALL underconstrained and the superficial Lemaire overconstrained internal rotation. The same procedures with 40 N of tension led to similar findings. Conclusion: In a combined ACL plus anterolateral–injured knee, ACL reconstruction alone failed to restore intact knee kinematics. The addition of either the deep Lemaire or MacIntosh tenodesis tensioned with 20 N, however, restored native knee kinematics. Clinical Relevance: The current study indicates that unaddressed anterolateral injuries, in the presence of an ACL deficiency, result in abnormal knee kinematics that is not restored if only treated with intra-articular ACL reconstruction. Both the modified MacIntosh and modified deep Lemaire tenodeses (with 20 N of tension) restored native knee kinematics at time zero.

Association between anteroposterior laxity in mid-range flexion and subjective healing ofinstability after total knee arthroplasty.

Flexion instability following total knee arthroplasty (TKA) is a common indication of early revision. The association between the objective anteroposterior (AP) laxity direction in mid-range flexion and the subjective healing of instability remains unclear; thus, this study aimed to clarify this association. In this study, 110 knees (74 females, 92 knees; 16 males, 18 knees) with medial pivot implants were examined with a median age of 79 (range 60-92) years for a median follow-up duration of 22 (range 6-125) months. AP laxity was measured using a KT-1000 arthrometer. Self-reported knee instability score was used for the subjective healing of instability. Eighty-seven knees did not feel unstable (Group 0), whereas 23 knees felt unstable (Group 1). There was a significant difference in AP displacement [Group 0: median 6mm; range 2-15mm and Group 1: median 8mm; range 4-14; p<0.0001]. The threshold value of 7mm was determined using the area under receiver operating characteristic curve of 0.79 [95% confidence interval (CI) 0.69-0.88, p<0.0001]. In multivariate analysis, AP displacement of ≥7mm was an independent risk factor for feelings of instability (odds ratio 7.695; 95% CI 2.306-25.674; p=0.001). AP laxity of ≥7mm represents a known cause of feelings of instability. By controlling AP laxity in TKAs, without stiffness in the knee, it is possible to prevent feelings of instability. The clinical relevance is that AP laxity of <7mm is one of the target areas in TKA. IV.

The Varus Osteoarthritic Knee Has No Coronal Contractures in 90 Degrees of Flexion.

Medial and lateral coronal soft tissue laxity in 90 degrees of flexion in the varus osteoarthritic (OA) knee at the time of total knee arthroplasty (TKA) is unknown, meaning, key information as to how the flexion gap should be addressed by surgery is not available. The purpose of this study was to define the coronal plane medial and lateral laxity in 90 degrees of flexion in the end-stage OA knee. Computer assisted surgery (CAS) displays and direct joint observations were used to manipulate the knee to its neutral position in 90 degrees of flexion prior to any surgical releases. Laxity was measured as medial and lateral displacement from the neutral axis of the knee and compared with literature values for healthy subjects. The 72 knees examined had a mean varus deformity, measured in maximum extension, of -7.9 ± 3.1 degrees (-0.5 to -15 degrees). At 90 degrees of flexion, mean medial and lateral laxity as measured by displacement from the neutral axis of the knee was 3.8 ± 1.4 degrees and 4.7 ± 2 degrees respectively. This medial laxity was significantly greater -1.7 degrees (95% CI, -3.1 to -0.3 degrees) than that seen in healthy knees (p < 0.0001) whereas the measured lateral laxity displayed a nonsignificant difference compared with healthy knees. The mean difference in medial-lateral laxity was 1.5 ± 1.1 degrees. A medial-lateral difference of ≤2.5 degrees was present in 91.6% of knees. We found no evidence of contractures in the coronal plane tissue of the end-stage OA knee at the time of TKA. Absolute medial-lateral balance is not typical of the end-stage OA knee in 90 degrees of flexion with a small medial-lateral difference typically present. Careful examination of the soft tissues in flexion at the commencement of TKA may help guide surgery to optimize the coronal plane soft tissue envelope. Our findings would suggest that large releases during either a gap-balanced or a measured-resection TKA would not typically be necessary, and that releases that increase laxity in flexion may increase often already lax medial tissue or increase laxity within lateral tissues that typically already have physiological tension.

Medial Epicondyle Fractures in the Pediatric Overhead Athlete.

The medial epicondyle serves as the proximal attachment of the medial ulnar collateral ligament and the origin of the flexor pronator musculature and as such it is responsible for resisting the main static and dynamic restraints to valgus force at the elbow. Fractures through the physis in the developing elbow are common and treatment remains controversial. Biomechanical modeling predicts that anterior should be the direction of greatest displacement. Anatomic considerations predict that anterior displacement should have the greatest effect on elbow stability and range of motion making the ulnar collateral ligament too loose in flexion and too tight in extension and potentially leading to valgus laxity in flexion and a block to full extension. In the elite overhead athlete, where elbow stability is critical both for sports performance and the long-term health of the elbow, assessment of anterior displacement is thus theoretically an important consideration. Standard radiographic views cannot adequately assess anterior displacement. Specialized radiographs and 3-dimensional modalities such as computerized tomography and magnetic resonance imaging can adequately assess anterior displacement and in the overhead athlete can sometimes aid in the decision-making process. Here, we present a review of the current literature and the rationale for a treatment algorithm for medial epicondyle fractures in the skeletally immature overhead athlete.

A New Method to Attain a Balanced Total Knee Arthroplasty

Introduction & Aims:The ANJRR has reported no improvement in early revision rates for patient matched versus conventional instrumentation and Nam et al demonstrated no improvement in PROMS or alignment data at 2 year follow-up patient matched TKA. Patient matched instrumentation may not provide clinically meaningful improvements. The purpose of this study was to assess whether a novel design process for patient matched cutting guides could both normalise soft tissue tension and produce a knee balanced mediolaterally and between 0 and 90°of flexion.Method:Patient specific guides of a novel and standard design were manufactured based on a novel design process and assessed via a prospective cohort study. The novel guides were applied to the intact knee in extension and/or flexion at the start of a TKA prior to soft tissue releases to mark bone resections. The guides contacted the femur and tibia simultaneously and acted to re-align the knee and tension the peri-articular soft tissues. 10 patients had novel guides applied in flexion and extension and 3 additional patients used guides in extension only. 9 patients had standard guides manufactured with the novel design process. We prospectively collected data on these 22 patients examining medial and lateral soft tissue laxity in maximum extension, 20 and 90° of flexion pre and post-operatively.Results:Soft tissue tension within parameters described for normal subjects was attained medially and laterally in: maximum extension in all 22 cases. For the 19 cases where the guides were used to plan the flexion resections; normal medial soft tissue tension was attained in 18/19 (94.7%) cases and normal lateral soft tissue tension in 16/19 (84.2%) cases. The 4 cases where normal soft tissue tension was not attained were outside this range by 1°. Post-operatively the mean difference in medial versus lateral laxity was 0.75°at 0°, 1.36° at 20° and 1.20° at 90°of flexion with a range of 0 - 4.5° across all positions and all knees. Pre-operatively the difference between medial and lateral laxity across all knees and positions ranged from 0 – 9°. Preoperatively the mean difference in medial versus lateral laxity was 4.43°at 0°, 5.25° at 20° and 1.64°at 90°of flexion. In the 19 cases where guides planned both the extension and flexion gap, 0 versus 90 ° flexion laxity on the medial side displayed a mean difference of 1.18° (range 0 - 3) and on the lateral side a mean difference of 1.52° (range 0 - 4.5) was recorded. To attain these balance parameters 16/22 (72.7%) cases utilised a 9mm poly and 6/22 (27.3%) utilised an 11mm poly.Conclusions:Patient Matched Instrumentation is widely used without clear benefit. This novel patient matched instrumentation design process shows promise for attaining soft tissue tension that is both normal and balanced. This may help diminish revision due to instability which was recorded as the revision diagnosis in 18.7% of patients (Lombardi 2013).

Integrity of Damage Control Posterior Spinal Fusion Constructs for Patients With Polytrauma: A Biomechanical Investigation.

Biomechanical. Evaluate spinal stability achieved with different levels of posterior percutaneous fixation (postPerc) for thoracolumbar fractures in cadavers subjected to ICU activities. "Spine damage control" involves postPerc performed within 24 hours of injury and staged, elective, definitive stabilization. Amount of instrumentation needed to initially achieve adequate spinal stability, minimize morbidity, and accommodate ICU care needs between stages are not defined. In full-unembalmed cadavers motion-tracking sensors were placed at T11 and L1. A T12 corpectomy with PLC injury was stabilized with 1, 2, and 3 levels of PostPerc above/below the injury. Motions between T11 and L1 were measured during Log-Roll and Sit-Up on an ICU bed. After in situ testing, anatomic spinal motion ranges were determined under pure moment loads. 5 cadavers were evaluated. For Log-Roll, 2 and 3 levels above/below restored stability to intact, whereas 1 level above/below did not for axial rotation. For translation, all instrumentation restored stability to intact. During Sit-Up, a linear increase in flexion was observed. At 45° Sit-Up, 2 and 3 levels above/below were similar to intact for flexion; 1 level above/below had significantly more flexion. All instrumentations restored translation to intact for Sit-Up; significantly more axial collapse occurred for instrumentation compared with intact. During ex situ testing, 2 and 3 levels above/below were similar; 1 level above/below had significantly greater laxity in flexion, extension, and axial rotation. Posterior instrumentation 2 or 3 levels above/below a severe thoracolumbar fracture model can restore spinal stability back to its intact condition. 2 levels of fixation above/below this "worst-case scenario" is minimum fixation sufficient to provide absolute spinal stability in the ICU setting as a "Damage Control" technique in patients with polytrauma. In less severe injury models, 1 level of fixation above/below may provide adequate spinal stability; although this should be confirmed in future investigations. N/A.

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

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 10years after primary TKA, as well as clarifying the relationships between long-term outcomes and mediolateral laxities. This study included 49 knees (19 CR type and 30 PS type) of 33 patients followed up for at least 10years after TKA at our hospital. Plain radiographs were obtained with about 150N 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 10kg of varus or valgus stress. 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. Good long-term results of TKA can be obtained with a lateral laxity of about 5°, equivalent to that of healthy knees. III.

Quantitative measurement of lower limb mechanical alignment and coronal knee laxity in early flexion.

Non-invasive quantification of lower limb alignment using navigation technology is now possible throughout knee flexion owing to software developments. We report the precision and accuracy of a non-invasive system measuring mechanical alignment of the lower limb including coronal stress testing of the knee. Twelve cadaveric limbs were tested with a commercial invasive navigation system against the non-invasive system. Coronal mechanical femorotibial (MFT) alignment was measured with no stress, then 15 Nm varus and valgus applied moments. Measurements were recorded at 10° intervals from extension to 90° flexion. At each flexion interval, coefficient of repeatability (CR) tested precision within each system, and limits of agreement (LOA) tested agreement between the two systems. Limits for CR & LOA were set at 3° based on requirements for surgical planning and evaluation. Precision was acceptable throughout flexion in all conditions of stress using the invasive system (CR ≤ 1.9°). Precision was acceptable using the non-invasive system from extension to 50° flexion (CR ≤ 2.4°), beyond which precision was unacceptable (> 3.4°). With no coronal stress applied, agreement remained acceptable from extension to 40° (LOA ≤ 2.4°), and when 15 Nm varus or valgus stress was applied agreement was acceptable from extension to 30° (LOA ≤ 2.9°). Higher angles of knee flexion had a negative impact on precision and accuracy. The non-invasive system provides reliable quantitative data in-vitro on coronal MFT alignment and laxity in the range relevant to assessment of collateral ligament injury, pre-operative planning of arthroplasty and flexion instability following arthroplasty. In-vivo validation should be performed.

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).MethodsMedial 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.ResultsPost-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). ConclusionsIn 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 evidenceII.

Measured Resection Versus Gap Balancing for Total Knee Arthroplasty

The number of TKAs performed in the United States is expected to increase substantially in the next two decades [6]. Additionally, surgeons are performing TKAs in younger and more active patients. While many articles discuss the importance of radiographic alignment, soft-tissue balancing is essential to a successful TKA. There remains great controversy in how surgeons obtain correct alignment and soft-tissue tensioning. Some surgeons utilize a measured resection technique, while other surgeons favor a gap-balancing technique. As such, I have invited two internationally known orthopaedic surgeons to discuss these two approaches, both of which seek to achieve the same general goal — a well-aligned and well-balanced TKA. Bryan D. Springer MD is an attending joint replacement surgeon at the OrthoCarolina Hip and Knee Center in Charlotte, NC, USA, and a member of The Knee Society. Dr. Springer is the recipient of numerous Knee Society Awards, and has extensive experience with the gap-balancing technique. Sebastien Parratte MD, PhD is an attending joint replacement surgeon and assistant professor of orthopedic surgery at the University Hospital of Marseille in Marseille, France. Dr. Parratte likewise has received numerous Knee Society and Hip Society Awards, and has considerable experience with the measured resection technique. Matthew P. Abdel MD:What do you each see as the advantages of the gap-balancing or measured resection techniques, in terms of achieving ligament balance? Bryan D. Springer MD: Instability following TKA remains one of the most common modes of early failure. The gap-balancing technique is based on the progressive release of ligaments to create equal and symmetric flexion and extension gaps. It is imperative that one understands what structures affect extension, flexion, and both in order to create proper balance. One of the fundamental differences between the gap-balancing technique and measured resection technique lies in setting the rotation of the femoral component to achieve a symmetric flexion gap. Measured resection relies on arbitrary bony landmarks (surgical transepicondylar axis, posterior condylar axis, and anteroposterior (AP) axis of the femur) in order to set rotation. While bony landmarks may occasionally provide accurate rotation of the femoral component, one major disadvantage is the surgeon’s inability to accurately and reproducibly find them intraoperatively. Research has suggested there is wide variability in femoral component rotation when using bony landmarks, which leads to asymmetry of the flexion space and condylar lift off (Fig. 1) in flexion [3]. Open in a separate window Fig. 1 This schematic depicts condylar lift off that occurs when there is asymmetry of the flexion space. Published courtesy of Bryan D. Springer MD.

Anatomic ACL reconstruction produces greater graft length change during knee range-of-motion than transtibial technique

Because distance between the knee ACL femoral and tibial footprint centrums changes during knee range-of-motion, surgeons must understand the effect of ACL socket position on graft length, in order to avoid graft rupture which may occur when tensioning and fixation is performed at the incorrect knee flexion angle. The purpose of this study is to evaluate change in intra-articular length of a reconstructed ACL during knee range-of-motion comparing anatomic versus transtibial techniques. After power analysis, seven matched pair cadaveric knees were tested. The ACL was debrided, and femoral and tibial footprint centrums for anatomic versus transtibial techniques were identified and marked. Asuture anchor was placed at the femoral centrum and a custom, cannulated suture-centring device at the tibial centrum, and excursion of the suture, representing length change of an ACL graft during knee range-of-motion, was measured in millimeters and recorded using a digital transducer. Mean increase in length as the knee was ranged 120°–0° (full extension) was 4.5 mm (±2.0 mm) for transtibial versus 6.7 mm (±0.9 mm) for anatomic ACL technique. A significant difference in length change occurs during knee range-of-motion both within groups and between the two groups. Change in length of the ACL intra-articular distance during knee range-of-motion is greater for anatomic socket position compared to transtibial position. Surgeons performing anatomic single-bundle ACL reconstruction may tension and fix grafts with the knee in full extension to minimize risk of graft stretch or rupture or knee capture during full extension. This technique may also result in knee anterior–posterior laxity in knee flexion.

The Effect of Geometric Variations in Posterior-stabilized Knee Designs on Motion Characteristics Measured in a Knee Loading Machine

In different posterior-stabilized (PS) total knees, there are considerable variations in condylar surface radii and cam-post geometry. To what extent these variations affect kinematics is not known. Furthermore, there are no clearly defined ideal kinematics for a total knee. The purposes of this study were to determine (1) what the kinematic differences are caused by geometrical variations between PS total knee designs in use today; and (2) what design characteristics will produce kinematics that closely resemble that of the normal anatomic knee. Four current PS designs with different geometries and one experimental asymmetric PS design, with a relatively conforming medial side, were tested in a purpose-built machine. The machine applied combinations of compressive, shear, and torque forces at a sequence of flexion angles to represent a range of everyday activities, consistent with the ASTM standard test for measuring constraint. The femorotibial contact points, the neutral path of motion, and the AP and internal-external laxities were used as the kinematic indicators. The PS designs showed major differences in motion characteristics among themselves and with motion data from anatomic knees determined in a previous study. Abnormalities in the current designs included symmetric mediolateral motion, susceptibility to excessive AP medial laxity, and reduced laxity in high flexion. The asymmetric-guided motion design alleviated some but not all of the abnormalities. Current PS designs showed kinematic abnormalities to a greater or lesser extent. An asymmetric design may provide a path to achieving a closer match to anatomic kinematics. One criterion for the evaluation of PS total knees is how closely the kinematics of the prosthesis resemble that of the anatomic knee, because this is likely to affect the quality of function.