Lateral Flexion Gaps Research Articles

Medial and lateral gap laxity differential in computer-assisted kinematic total knee arthroplasty.

The results of kinematic total knee arthroplasty (KTKA) have been reported in terms of limb and component alignment parameters but not in terms of gap laxities and differentials. In kinematic alignment (KA), balance should reflect the asymmetrical balance of the normal knee, not the classic rectangular flexion and extension gaps sought with gap-balanced mechanical axis total knee arthroplasty (MATKA). This paper aims to address the following questions: 1) what factors determine coronal joint congruence as measured on standing radiographs?; 2) is flexion gap asymmetry produced with KA?; 3) does lateral flexion gap laxity affect outcomes?; 4) is lateral flexion gap laxity associated with lateral extension gap laxity?; and 5) can consistent ligament balance be produced without releases? A total of 192 KTKAs completed by a single surgeon using a computer-assisted technique were followed for a mean of 3.5 years (2 to 5). There were 116 male patients (60%) and 76 female patients (40%) with a mean age of 65 years (48 to 88). Outcome measures included intraoperative gap laxity measurements and component positions, as well as joint angles from postoperative three-foot standing radiographs. Patient-reported outcome measures (PROMs) were analyzed in terms of alignment and balance: EuroQol (EQ)-5D visual analogue scale (VAS), Knee Injury and Osteoarthritis Outcome Score (KOOS), KOOS Joint Replacement (JR), and Oxford Knee Score (OKS). Postoperative limb alignment did not affect outcomes. The standing hip-knee-ankle (HKA) angle was the sole positive predictor of the joint line convergence angle (JLCA) (p < 0.001). Increasing lateral flexion gap laxity was consistently associated with better outcomes. Lateral flexion gap laxity did not correlate with HKA angle, the JLCA, or lateral extension gap laxity. Minor releases were required in one third of cases. The standing HKA angle is the primary determinant of the JLCA in KTKA. A rectangular flexion gap is produced in only 11% of cases. Lateral flexion gap laxity is consistently associated with better outcomes and does not affect balance in extension. Minor releases are sometimes required as well, particularly in limbs with larger preoperative deformities. Cite this article: Bone Joint J 2019;101-B:331-339.

Does the Robotic Arm and Preoperative CT Planning Help with 3D Intraoperative Total Knee Arthroplasty Planning?

Although several studies highlight the advantages of robotic arm-assisted total knee arthroplasty (RA-TKA), few investigate its intraoperative outcome. Therefore, the purpose of this study was to analyze the RA-TKA's ability to assist with intraoperative correction of: (1) flexion and (2) extension gaps, as well as its ability to (3) accurately predict implant sizes. Additionally, in this RA-TKA cohort, length of stay, complications, and readmissions were assessed. A total of 335 patients who underwent RA-TKA were included. The robotic software virtually measured the intraoperative prebone cut extension and flexion gaps. Differences in medial versus lateral prebone cut extension and flexion gaps were calculated. A total of 155 patients (46%) had an extension gap difference of between -2 and 2 mm (mean, -0.3 mm), while 119 patients (36%) had a flexion gap difference of between -2 and 2 mm (mean, -0.6 mm). Postbone cut differences in medial versus lateral flexion and extension gaps were measured. Balanced knees were considered to have a medial and lateral flexion gap difference within 2 mm. The robot-predicted implant size was also compared with the final implant size. Additionally, lengths of stay, complications, and readmissions were assessed. All patients achieved a postbone cut extension gap difference between -1 and 1 mm (mean, -0.1 mm). A total of 332 patients (99%) achieved a postbone cut flexion gap difference of between -2 and 2 mm (mean, 0 mm). For 98% of prostheses, the robotic software predicted within 1 implant size the actual tibial or femoral implant size used.The mean length of stay was found to be 2 days. No patients suffered from superficial skin infection, pin site infections or fractures, soft tissue damage, and no robotic cases were converted to manual TKA due to intraoperative complications. A total of 8 patients (2.2%) were readmitted; however, none were directly related to robotic use. The robotic software and use of a preoperative computed tomography (CT) substantially helped with intraoperative planning and accurate prediction of implant sizes. Therefore, based on the results of this study, the RA-TKA device does, in fact, provide considerable intraoperative assistance.

Pearls: Early Removal of Posterior Osteophytes in TKA.

Posterior-compartment osteophytes are commonly encountered during TKA. They can limit or prevent terminal extension by tenting the posterior capsule and can cause coronal plane imbalance due to tenting of adjacent capsulo-ligamentous structures. Osteophyte removal is a principle of TKA soft-tissue balancing [2]. Failure to remove an osteophyte may result in unnecessary soft-tissue releases or lead to additional bone resection. Posterior femoral osteophytes can be difficult to remove because they are hard to see, and surgeons may be concerned about passing a sharp instrument posteriorly, near the popliteal neurovascular structures. Surgeons generally remove them after resection of the distal, anterior, and posterior femur and proximal tibia. After these resections, the surgeon should have easier access to the posterior compartment. However, this technique requires the surgeon to determine the femoral component rotation before osteophyte removal. In our experience, determining the femoral component rotation before large (> 1 cm) posterior osteophytes are removed can result in coronal plane imbalance of both the flexion and extension gaps because of the remaining tenting effect of the retained posterior osteophytes. Therefore, we suggest that surgeons remove these osteophytes before the anterior and posterior femoral cuts are completed. Here, we describe our technique, which allows access to the posterior compartment before the final femoral component rotation is determined [1]. This early posterior osteophyte removal technique is applicable to measured resection, kinematic alignment, as well as our preferred gap balancing technique. Many patients with large posterior osteophytes also have advanced medial-compartment arthritis and a fixed-varus deformity (Fig. 1A-B). After knee exposure, the deep medial collateral ligament is released to the mid-coronal plane of the tibia. Additional soft-tissue releases should then be delayed until all femoral and tibial osteophytes are removed. We favor resection of the extension space (distal femur and proximal tibia) followed by removal of medial and lateral distal femoral and peripheral tibial osteophytes that might tent surrounding ligamentous structures.Fig. 1 A-B: (A) AP radiograph of right knee with fixed varus deformity and advanced arthritis is shown. (B) Lateral radiograph of right knee with large posterior femoral osteophyte, denoted by arrow is shown. (Published with permission from Douglas A. Dennis MD).A spacer block is inserted into the extension gap. Residual medial soft tissue tightness is typically encountered, and so at this point we remove any large posterior femoral osteophytes. The femoral component sizing guide then is applied to determine femoral component size. With the knee flexed 90°, a laminar spreader is inserted into the lateral flexion gap and tensioned. A retractor is placed medially to protect the medial collateral ligament (Fig. 2). A 4-mm resection of the posterior aspect of the medial femoral condyle is performed with an oscillating saw, providing access to the posterior compartment (Fig. 3). The interface between osteophyte and native femur is then visualized (Fig 4). A curved osteotome is used to divide the osteophyte at that interface (Fig 5). During this maneuver, it is common to observe some degree of opening of the flexion gap since the tenting effect of the posterior femoral osteophyte on the posterior capsule and posterior oblique ligament has been eliminated. The posterior femoral osteophyte is then removed with a rongeur (Fig. 6). While this technique has been most commonly used to remove large posteromedial femoral osteophytes in knees with varus deformity, the technique is applicable and has been utilized in knees with valgus deformity and large posterolateral femoral osteophytes as well.Fig. 2: Intraoperative photo shows a planned posterior preliminary resection, marked in ink on the femur, and denoted by the arrow. A retractor is protecting the medial collateral ligament. (Published with permission from Douglas A. Dennis MD).Fig. 3: An oscillating saw used to perform preliminary resection provides access to the posterior compartment of the knee. (Published with permission from Douglas A. Dennis MD).Fig. 4: A demonstration of the interface of normal condyle of the femur and the posterior osteophyte is shown, indicated by the arrow. (Published with permission from Douglas A. Dennis MD).Fig. 5: A curved osteotome divides the posterior osteophyte from the normal bone of the posterior condyle. (Published with permission from Douglas A. Dennis MD).Fig. 6: A pituitary rongeur extracts the resected posterior osteophyte. (Published with permission from Douglas A. Dennis MD).Extension gap tension and balance then are assessed. If imbalance persists, additional medial soft-tissue releases are performed until the gap is balanced. The AP femoral cutting block is then applied using the surgeon’s preferred method to obtain a rectangular flexion gap (measured resection guide or flexion gap tensioning). The remaining steps of the TKA are then completed in routine fashion. Large posterior femoral osteophytes contribute to soft-tissue imbalance, and we believe benefit from early removal before extensive soft tissue releasing is performed and femoral component rotation is determined.

Effects of posterior condylar osteophytes on gap balancing in computer-assisted total knee arthroplasty with posterior cruciate ligament sacrifice

ObjectiveGap planning in navigated total knee arthroplasty (TKA) is a critical concern. Osteophytes are normally removed prior to gap planning, with the exception of posterior condylar osteophytes of the femur, which are removed after posterior condylar resection. This study investigated how posterior condylar osteophytes affect gap balancing during surgery.MethodsThis prospective study was conducted on 40 primary varus osteoarthritic knees with a posterior condylar osteophyte that underwent TKA navigation. For all knees, computed tomography (CT) was performed to evaluate osteophyte position. The extension gap and flexion gap were determined under navigation using a tension device with a distraction force of 44 lb. The extension gap and flexion gap were measured before and after osteophyte removal.ResultsThis study revealed that the average osteophyte thickness after removal was 7.75 ± 5.34 mm. The average extension gap change was 0.64 ± 0.80 mm, and the average flexion gap change was 0.85 ± 1.12 mm. With respect to increases in the medial extension gap, lateral extension gap, medial flexion gap and lateral flexion gap, the average effects of posterior condylar osteophyte removal were 0.74 ± 0.81 mm, 0.53 ± 0.96 mm, 0.71 ± 0.97 mm and 1.00 ± 1.41 mm, respectively. Posterior condylar osteophyte thickness was also significantly associated with increases in the lateral extension gap (R2 = 0.107, p = 0.03), medial flexion gap (R2 = 0.101, p = 0.04) and lateral flexion gap (R2 = 0.107, p = 0.04).ConclusionThese results indicated that posterior condylar osteophytes of the femur affect gap balancing during TKA navigation.

Effect of the Referencing System on the Posterior Condylar Offset and Anterior Flange-Bone Contact in Posterior Cruciate-Substituting Total Knee Arthroplasty

BackgroundThe effect of referencing system on posterior condylar offset (PCO) after total knee arthroplasty (TKA) is still controversial. Moreover, there is a lack of concern about the anterior flange-bone contact according to the referencing system. MethodsOne hundred four TKAs using the anterior referencing (AR) system and 107 TKAs using the posterior referencing (PR) system were analyzed with 2-year follow-up. The PCO, PCO ratio (PCOR), and contact at the anterior flange-bone interface were compared between the 2 groups. The flexion and extension gaps and the degree of medial release were measured, and clinical outcomes were evaluated. Finally, the correlation between changes in PCO and knee flexion angle was analyzed. ResultsThe mean postoperative PCO and PCOR were significantly larger in the PR group than in the AR group. Incomplete contact between the anterior flange and anterior femur occurred more frequently in the AR group than in the PR group (48.1% vs 13.1%, P < .001). The medial and lateral flexion gaps were significantly larger in the AR group than in the PR group. The groups showed no differences in soft tissue release, degree of flexion, and clinical scores. In both groups, there was no correlation between postoperative change of PCO and improvement in flexion. ConclusionThe PR system produced larger PCO and PCOR, and smaller flexion gap compared to the AR system. Additionally, the PR group showed more favorable contact between the anterior flange and anterior femur. However, these differences were not related to the degree of soft tissue release and clinical outcomes.

Patient-related factors influence stiffness of the soft tissue complex during intraoperative gap balancing in cruciate-retaining total knee arthroplasty.

How much force is needed to pre-tension the ligaments during total knee arthroplasty? The goal of this study was to determine this force for extension and flexion, and for both compartments, and to identify predicting patient-related factors. Eighty patients [55 females, mean age 71 (SD 9.7)] were recruited and had a navigated cruciate-retaining total knee arthroplasty. Distraction of the medial and lateral compartments of the extension and flexion gap (90°) with an instrumented bi-compartmental double-spring tensioner took place after finishing the bone cuts. Applied forces and resulting gap distances were recorded by the navigation system, resulting in a force-elongation curve. Lines were fitted with the intersection defined as the stiffness transition point. The slopes (N/mm) represented the stiffness of the ligamentous complex. Linear multiple regression analysis was performed to identify predicting factors. The amount of force at the stiffness transition point was on average 52.3 (CI95 50.7-53.9), 54.5 (CI95 52.7-56.3), 48.3 (CI95 46.2-50.2), and 59.3 (CI95 57.0-61.6)N for the medial and lateral extension and flexion gap, respectively, and varied considerably between patients. The force at the stiffness transition point was significantly different between extension and flexion and both compartments (P<0.05). Stiffness of the ligaments statistically significantly helped to predict the amount of force at the stiffness transition point, as well as body mass index, gender, and varus-valgus alignment. The amount of force at the stiffness transition point varies between 48 and 59N, depending on flexion/extension and compartment. Patient-related factors influence the stiffness transition point and can help predict the stiffness transition point. When forces higher than 60N are used for gap distraction, the ligamentous sleeve of the knee might be over-tensioned. Prognostic study, Level I-high-quality prospective cohort study with >80% follow-up, and all patients enrolled at same time point in disease.

Analysis of the Flexion Gap on In Vivo Knee Kinematics Using Fluoroscopy

There is a paucity of information on the relationships between postoperative knee laxity and in vivo knee kinematics. The correlations were analyzed in 22 knees with axial radiographs and fluoroscopy based 3D model fitting approach after a tri-condylar total knee arthroplasty. During deep knee bend activities, the medial flexion gap had significant correlations with the medial contact point (r=0.529, P=0.011) and axial rotation at full extension. During kneeling activities, a greater medial flexion gap caused larger anterior translation at complete contact (r=0.568, P=0.011). Meanwhile, the lateral flexion gap had less effect. In conclusion, laxity of the medial collateral ligament should be avoided because the magnitude of medial flexion stability was crucial for postoperative knee kinematics.

Flexion Gap Measured in 45 Degrees and 90 Degrees of Hip Flexion Positions during Total Knee Arthroplasty: Measurement by Navigation System.

PurposeTo evaluate the influence of thigh weight in different hip flexion positions on the knee flexion gap in total knee arthroplasty (TKA).Materials and MethodsWe evaluated 20 patients (25 knees) with osteoarthritis of the knee that underwent TKA using a navigation system from May 2010 to April 2011. After posterior cruciate ligament sacrificing, complete soft tissue balancing, and fixation of all components with cement, the flexion gaps were measured with the patello-femoral joint reduced. Medial and lateral flexion gaps were measured separately in both the 90°-90° and 45°-90° flexion positions of the hip-knee joints.ResultsThe medial and lateral flexion gaps in the 45°-90° flexion position of the hip-knee joints were 13.02±2.17 mm and 13.12±2.21 mm, respectively. The medial and lateral flexion gaps in the 90°-90° flexion position were 12.92±2.03 mm and 13.08±2.29 mm, respectively. The flexion gaps showed no significant (p>0.05) differences between the two different hip flexion positions.ConclusionsFlexion gaps in TKA were not influenced by hip flexion positions (45° or 90° of flexion). Therefore, soft tissue balancing and polyethylene thickness should not be affected by hip flexion positions during TKA.

Influence of tibial slope on extension and flexion gaps in total knee arthroplasty: increasing the tibial slope affects both gaps.

Increasing the tibial slope is often performed if the flexion gap is narrower than the extension gap. The main hypothesis of this study is that increasing the tibial slope coincidentally enlarges the extension gap. Twenty formalin-fixed cadaveric knees were obtained for study. After CT in full extension and 90° flexion, the data of each specimen were entered into a standardized coordinate system and virtual bone cuts were performed with incrementally increasing the posterior slope. Gaps were measured at tibiofemoral contact points in 90°-flexion and full extension in the medial and lateral compartment. Increasing the tibial slope did significantly widen both the extension and the flexion gaps (p < 0.001). In extension, the opening rates, i.e. the gap increase per degree of slope increase, were equal medially and laterally (0.5mm ±0.1) medial vs 0.6mm (±0.0) lateral), whereas in flexion the lateral gap did open significantly more than the medial one (0.6mm ±0.1) medial vs 0.9mm (±0.1) lateral (p < 0.001), resulting in a significantly greater flexion gap laterally. Increasing the tibial slope beyond the pre-operative planning in order to widen a tight flexion gap intra-operatively is not recommended as doing so will increase the extension gap simultaneously and will make the medial and lateral flexion gaps unequal.

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.

Flexion and extension gaps created by the navigation-assisted gap technique show small acceptable mismatches and close mutual correlations

The aim of this study was to investigate the mechanism underlying the development of gap differences in total knee arthroplasty using the navigation-assisted gap technique and to assess whether these gap differences have statistical significance. Ninety-two patients (105 knees) implanted with cruciate-retaining prostheses using the navigation-assisted gap balancing technique were prospectively analysed. Medial extension and flexion gaps and lateral extension and flexion gaps were measured at full extension and at 90° of flexion. Repeated measures analysis of variance was used to compare the mean values of these four gaps. The correlation coefficient between each pair of gaps was assessed using Pearson's correlation analysis. Mean intra-operative medial and lateral extension gaps were 20.6 ± 2.1 and 21.7 ± 2.2 mm, respectively, and mean intra-operative medial and lateral flexion gaps were 21.6 ± 2.7 and 22.1 ± 2.5 mm, respectively. The pairs of gaps differed significantly (P < 0.05 each), except for the difference between the medial flexion and lateral extension gaps (n.s.). All four gaps were significantly correlated with each other, with the highest correlation between the medial and lateral flexion gaps (r = 0.890, P < 0.001) and the lowest between the medial flexion and lateral extension gaps (r = 0.701, P < 0.001). Medial and lateral flexion and extension gaps created using the navigation-assisted gap technique differed significantly, although the differences between them were <2 mm, and the gaps were closely correlated. These narrow ranges of statistically acceptable gap differences and the strong correlations between gaps should be considered by surgeons, as should the risks of soft tissue over-release or unintentional increases in extension or flexion gap after preparation of the other gap.

Influence of Gap Balance on the Sagittal Movement of a Specific Mobile Bearing Floating Platform Design in Total Knee Arthroplasty

We analyzed 119 knees implanted with mobile bearing floating platform prostheses using the navigation-assisted gap balancing technique to analyze the relationship between intraoperative sagittal movement of floating platforms and soft tissue balancing. The 95 (79.8%) knees were classified into the positive rollback group (mean insert posterior rollback 5.86 ± 1.24 mm), and the remaining 24 (20.2%) into the negative rollback group. Lateral flexion gap (LFG) differed significantly between knees with positive and negative rollback (20.5 ± 1.7 mm vs 22.1 ± 1.7 mm, P = .021). Only LFG significantly influenced the occurrence of bearing sagittal movement. Sagittal translation of the insert occurred in about 80% of knees implanted with mobile bearing floating platforms in TKA, and was affected by flexion gaps, especially on the lateral side.

Influence of a Secondary Downsizing of the Femoral Component on the Extension Gap: A Cadaveric Study

The purpose of this study was to evaluate the effect of a secondary reduction of the femoral component size on flexion and extension gaps intraoperatively in posterior-stabilized total knee arthroplasty (PS-TKA) monitored by computer-assisted surgery. The authors hypothesized that cutting additional bone on the posterior femoral condyle may increase the extension gap due to the posterior capsule and soft tissue loosening. Reduction of the femoral component size was performed by additional 4-in-1 cuts after the PS-TKA on 15 cadaveric knees using a ligamentous tension device with the aid of computer-assisted surgery. Measurements of the medial and lateral flexion gaps, as well as the medial and lateral extension gaps, were recorded before and after reducing the femoral component size. Trial components were used from a mobile-bearing total knee system.After reducing the femoral component size, the medial and lateral flexion and extension gaps measured larger than their initial size. The mean increases of the medial extension and flexion gaps and the lateral extension and flexion gaps were 1.3 ± 0.9, 1.0 ± 1.2, 1.1 ± 1.2, and 1.3 ± 1.3 mm, respectively; all 4 differences were significant (P ≤ .05). Surgeons should be aware of the effect of downsizing components intraoperatively because it might lead to an extension laxity. Thus, a downsizing of the femoral component may compromise the postoperative stability of TKA.

Precision of Ci-navigated extension and flexion gap balancing in total knee arthroplasty and analysis of potential predictive variables

The aim of this study was to evaluate the accuracy of final limb alignment and flexion-extension and medial-lateral gap balancing in computer navigated total knee arthroplasty and to analyze various possible predictive variables that may affect the gaps in computer navigated knee arthroplasty. The DePuy Ci system, a nonimage-based passive optical computer navigation system, was used in 225 patients with knee osteoarthritis to assist for the total knee arthroplasty. From the raw data the Ci-verified pre- and postoperative leg axis in extension, angle of tibia and femur resection, the flexion and extension angle, the medial and lateral extension and flexion gaps were extracted; and differences in gaps were calculated and subjected to statistical analysis. Leg alignment and implant position were determined only by the navigation system. Preoperative variables were evaluated for their impact on the final flexion/extension and medial/lateral gaps achieved. Though the preoperative femoro-tibial coronal alignment had a large variance, postoperatively 98.22% of the knee was found to be between -3° and +3° in the coronal limb alignment axis. The Ci-verified femoral and tibial cuts in the coronal plane showed a good accuracy. The sagittal alignment of the femoral cut ranged from 8.20° flexion to 3.20° of extension. Rectangular extension and flexion gaps were achieved with ≤3 mm of difference in gaps on medial and lateral sides in 98 and 93% of knees, respectively. Difference between extension and flexion gaps on the medial side was ≤3 mm in 83% and on the lateral side in 84% of the knees. Of all the possible predictive variables analyzed, Pearson correlation and multiple regression analysis showed significant correlation only between the medial-lateral gap difference in extension and the Ci-verified femoral cut, tibial cut and limb axis, all in the coronal plane. Computer-assisted navigated total knee replacement allows for accurate gap balancing that is not dependent on the various pre- and intraoperative factors mentioned, including age, sex, Range of motion preoperative deformity and grade of osteoarthritis. The Ci-calculated and verified tibial, and femoral cuts are the only possible factors affecting the extension gap.

Analysis of Medial Flexion Gap After Medial Release for Varus Deformity by Navigation-Guided TKA

The goal of this study was to analyze medial flexion gaps after medial release for varus deformity by navigation-guided total knee arthroplasty (TKA). In each patient, a preoperative standing anteroposterior (AP) radiograph of the lower extremity and an AP valgus stress radiograph of the knee were used to measure preoperative mechanical axis angle and valgus stress angle, respectively. The correlation between preoperative varus deformities and medial flexion gap increases as measured by navigation was examined. Patients were assigned to 2 groups: group A (25 knees), in which the difference between the lateral flexion gap (LFG) and the medial flexion gap (MFG) (LFG-MFG) was ≤ 1 mm; and group B (73 knees), with an LFG-MFG of >1 mm.Mean preoperative mechanical axis angles in groups A and B were 13.21° ± 5.01° varus (range, 3.7°-23.6°) and 10.05° ± 3.70° varus (range, 1.9° - 23.7°), respectively. Mean preoperative valgus stress angles in groups A and B were 1.72° ± 0.89° valgus (range, 0.1° - 4.0°) and 4.84° ± 2.61° valgus (range, 0.1° - 11.7°), respectively. A significant difference was observed between the groups in terms of mechanical axis angle (P = .002) and valgus stress angle (P<.001). Furthermore, valgus stress angle was found to be more strongly correlated with medial flexion gap increase than mechanical axis angle. The cutoff values of mechanical axis angle and valgus stress angle in group A were 13.4° and 2.45°, respectively.This study shows that preoperative valgus stress angle measurements can be used to predict the extent of medial release for varus deformity.

Ligament Tension in the ACL-deficient Knee: Assessment of Medial and Lateral Gaps

Obtaining symmetric and balanced gaps under equilateral loads is a common goal in posterior cruciate ligament (PCL)-retaining and -sacrificing TKAs. Owing to limitations in existing surgical tensors, however, tensing knee ligaments with standardized and symmetric loads has been possible only with the patella subluxated or everted. We therefore determined the influences of (1) patellar eversion versus complete reduction, (2) PCL resection, and (3) load magnitude on gap symmetry and balance in the anterior cruciate ligament (ACL)-deficient knee. We used a novel computer-controlled tensioner to measure gaps in 10 cadavers with an applied force of 50 N, 75 N, and 100 N per side. Gap data were acquired at 0 masculine, 30 masculine, 60 masculine, 90 masculine, and 120 masculine flexion with the patella reduced and everted and with the PCL intact and resected. Everting the patella tightened the medial and lateral flexion gaps between 90 masculine and 120 masculine by 0.7 mm to 2.7 mm. PCL resection increased gaps from 30 degrees to 120 degrees by 1 mm to 3 mm. Increasing the force from 50 N to 100 N increased the mean gap by 0.5 mm. Everting the patella and resecting the PCL influenced gap balance and symmetry. Surgeons should be aware of how these conditions affect gaps during assessment and balancing.