We investigated whether the extension gap in total knee replacement (TKR) would be changed when the femoral component was inserted. The extension gap was measured with and without the femoral component in place in 80 patients with varus osteoarthritis undergoing posterior-stabilised TKR. The effect of a post-operative increase in the size of the femoral posterior condyles was also evaluated. The results showed that placement of the femoral component significantly reduced the medial and lateral extension gaps by means of 1.0 mm and 0.9 mm, respectively (p < 0.0001). The extension gap was reduced when a larger femoral component was selected relative to the thickness of the resected posterior condyle. When the post-operative posterior lateral condyle was larger than that pre-operatively, 17 of 41 knees (41%) showed a decrease in the extension gap of > 2.0 mm. When a specially made femoral trial component with a posterior condyle enlarged by 4 mm was tested, the medial and lateral extension gaps decreased further by means of 2.1 mm and 2.8 mm, respectively. If the thickness of the posterior condyle is expected to be larger than that pre-operatively, it should be recognised that the extension gap is likely to be altered. This should be taken into consideration when preparing the extension gap

Introduction. The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs with a loose extension gap in TKA. In the setting of a loose extension gap, we hypothesized that although full extension is achieved, a loose extension gap will ultimately lead to increased varus and/or valgus laxity throughout mid flexion. Methods. After obtaining IRB approval, six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, and the flexion and extension gaps were balanced using navigation, a 4 mm distal recut was made in the distal femur to create a loose extension gap (using the same thickness of polyethylene as the well-balanced case). Real implants were used in the study to eliminate error in any laxity inherent to the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line. (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm recut in the distal femur creating a loose extension gap. Results. In the setting of a loose extension gap (4 mm distal recut), overall coronal-plane laxity was increased by a mean of 3.6° at 30° of flexion, 3.4° at 45° of flexion, and 2.8° at 60° of flexion (p < 0.05 for each flexion angle). (Figure 2) However, there was no difference in coronal plane laxity between the well-balanced TKA and the TKA with a loose extension gap at 0° and 90° of flexion, when applying a standardized varus and valgus load. Conclusions. Using a reliable, accurate, and reproducible method of measuring coronal plane laxity, we have shown that in the setting of a loose extension gap during total knee arthroplasty, coronal plane laxity will be significantly higher in mid-flexion compared to the well balanced state

[Introduction]. As an essential concept in TKA, preparing equalized rectangular extension and flexion gaps is recognized as desirable to ensure proper knee kinematics. However, in the ways that was recommended by an implant manufacturer, the adjustments are so difficult, and for inexperienced doctor, we don't have an ideal technique for an additional cutting up and ligament balancing. Then, the New method (Precut method) was introduced in order to enable an ideal adjustments. [Method]. Sixty eights patients with osteoarthritis of the knee received TKAs using Precut method. This method is the following. At first, proximal tibia was resected 10 mm by standard cutting device. And then, femoral posterior condyle was resected 4 mm lesser than cutting line by measured resection technique (Precut method). In the next, using the spacer block 1 mm unit and the Precut trial implant (8 mm; distal femur 4 mm; posterior condyle), we investigated the bone gap and the component gap (put the Precut trial on the distal femur). Finally, we calculated the amount of the final cutting value based on the component gap. The survey item measured the bone gap at extension and flexion, the component gap at extension and flexion after putting the Precut trial on. Then we compared the gap difference with and without the Precut trial. [Result]. Our results showed that the extension gap with the Precut trial was smaller than the predicted value with the Precut trial (mean: 8.66 mm/8.18 mm), the flexion gap with the Precut trial was larger than the predicted value with the Precut trial (mean: 13.2 mm/14.1 mm). The extension gap had reduced by 0.48 mm and the flexion gap enlarged by 0.3 mm. [Discussion]. In TKA, it is difficult to make extension gap and flexion gap equal. Therefore, after putting the final implant, we experienced the case s such as could not stretch fully in extension, such as had instability in flexion. However, in this method, we will earn the ideal stability in postoperative condition. It is because that after putting the Precut trial, we measured implant gap at extension and flexion, and then decided the final osteotomy value to eliminate the gap difference. [Conclusion]. As we measured extension gap and flexion gap in condition which put the Precut trial on, before the final osteotomy, we can make an equal gap at extension and flexion. We think a useful procedure for the stability after TKA

Introduction. Clinical observations suggest mid-flexion instability may occur more commonly with rotating platform (RP) total knee arthroplasty (TKA), including increased revision rates and patient-reported instability and pain. We propose that increased gap laxity leads to liftoff of the lateral femoral condyle with decreased conformity between the femoral component and polyethylene (PE) insert surface leading to PE subluxation or dislocation. The objectives of this study were to define “at risk” loading conditions that predispose patients to PE insert subluxation or spinout, and to quantify the margin of error for flexion/extension gap laxity in preventing these adverse events under physiologic loading conditions. Methods. Biomechanical testing was performed on six fresh frozen cadaveric knees implanted with a posterior stabilized RP TKA using a gap balancing technique. Rotational displacement and torque were measured over time, while stiffness, yield torque, max torque and displacement were calculated using a post-processing, custom MatLab code. Revision with varying size femoral components (size 3–6) and PE insert thicknesses (10–15mm), by downsizing one step, were used to create a spectrum of flexion/extension gap mismatch. Each configuration was subjected to three loaded testing conditions (0°, 30° and 60° flexion) in balanced and eccentric varus loading, known to represent daily clinical function and “at risk” circumstances. Results. PE insert rotational instability was primarily determined by conformity and contact area between the femoral condyle and the upper surface of the PE insert. In this RP design, contact area is known to decrease with flexion greater than 35°, which predisposed to abnormal motion of the femur on PE insert (Figure 1). Under all flexion/extension gap testing conditions, PE insert rotational displacement significantly decreased with increasing knee flexion (differences ranged from 0.42 to 1.01cm, p<0.05), confirming that decreased conformity allows unintended motion to occur on the upper rather than the lower insert surface, as kinematically designed. This decrease in insert rotation was further exacerbated with eccentric medial-sided loading (differences ranged from 0.77 to 1.18cm, p<0.05). Yield torque (19.66±6.79N-m, p=0.033) and max torque (19.76±5.93N-m, p=0.014) significantly increased with increasing flexion from 0° to 60° under gap balanced conditions. Yield torque significantly decreased with greater flexion gap laxity at 60° of flexion (−24.82±5.96N-m, p=0.004). The depth of the lateral PE insert concavity (1.7–3.6mm) varied with insert size and thickness and determined femoral condylar capture. The lateral insert concavity defines a narrow margin of error in flexion/extension gap asymmetry leading to rotational insert instability, especially in smaller sized knees (size 3) where the jump height (1.7mm) is less than the insert sizing increment of 2.5mm. Conclusions. Contact area is known to decrease with flexion greater than 35° in this TKA-RP design. Flexion gap laxity further increased the risk of unintended top-side rotation of the femur on the insert, especially with increasing flexion and smaller components. In RP-TKA, in addition to medial-lateral gap symmetry and flexion-extension balance, a snug flexion gap with less than 2mm lateral laxity is critical to avoid insert instability and condylar escape with insert subluxation. For any figures or tables, please contact authors directly

Introduction. A small medial extension gap (EG) needs posterior soft tissue release to avoid undesirable additional resection of the distal femur in total knee arthroplasty (TKA). However, the effect of this procedure on the EG is not always sufficient because the EG is influenced not only by the posterior soft tissue but also by the medial collateral ligament (MCL). We hypothesize that contracture of the posterior capsule prevents full elongation of the MCL in extension and we investigated the efficacy of posteromedial vertical capsulotomy (PMVC) on the medial EG which separate MCL from the posterior capsule (Fig. 1). Materials and Methods. The PMVC was performed on 128 knees in which the medial extension gap was considered too small. The EG was initially created with a standard femoral distal cut and tibial cut. To estimate the gaps more precisely before flexion gap (FG) adjustment at the final step of the surgery, we performed a 4 mm precut of the posterior femoral condyle and measured the gaps with the patella reduced after setting a precut trial component that had a usual distal part and 4 mm thick posterior part of the femoral component. This situation was the same as after setting the usual femoral trial component by using the measured resection technique with preservation of the posterior cruciate ligament (PCL) (Fig. 2). The semimembranosus tendon was not released in any cases. Results. After the precut trial was set to the femur, the average EG and FG were 5.6 ± 2.0 mm and 10.0 ± 2.0 mm, respectively (mean ±SD). After performing the PMVC, the average increase of the EG and FG were 2.3 ± 1.4 mm and 0.1 ± 0.3 mm, respectively. The EG increase was significantly larger than the FG increase (p < 0.001). Twenty eight knees showed a 1 mm or less increase in the EG; however, 100 knees (78 %) had a 2 mm or greater increase in the EG with little increase in the FG. Initial gap difference (FG – EG) showed a positive corelation with EG increase after PMVC (R = 0.51, p < 0.001) (Fig. 3). Conclusions. To make adequate EG and FG, it is important to understand which soft tissue management is effective to increase the FG or the EG. To increase the FG only, PCL resection is useful. However, the effective methodology of widening the EG without changing the FG is unknown. The EG of the varus knee is influenced by several factors such as tightness of the MCL, the posterior capsule, the semimembranosus tendon and protrusion of the posterior femoral component. In this study, a precut trial component was used to take into account the effect of posterior protrusion of the femoral component and the semimembranosus tendon was not released and we achieved a selective EG increase without changing the FG by the PMVC which allowed the MCL and the posterior capsule to act freely from each other

Purpose. Degenerative osteoarthritis of the knee usually shows arthritic change in the medial tibiofemoral joint with severe varus deformity. In TKA, the medial release technique is often used for achieving mediolateral balancing, but there is some disagreement regarding the importance of pursuing the perfect rectangular gaps. Our hypothesis is that the minimal release especially in MCL is beneficial regarding on retaining the physiological medial stability and knee kinematics, which leads to improved functional outcome. Therefore, the purpose of this study is to examine the thickness of the tibia resection if the extent of the medial release is minimized to preserve the medial soft tissue in TKA. Patients and Methods. Thirty TKAs were performed for varus osteoarthritis by a single surgeon. In the TKA, femoral bone was prepared according to the measured resection technique, bilateral meniscus and anterior cruciate ligament were excised. After the osteophytes surrounding the femoral posterior condyle were removed, the knee with the femoral trial component was fully extended and the amount of the tibial bone cut was decided for the 10mm tibial insert by referring to the medial joint line of the femoral trial component. After the every bone preparation and placement of all the trial components, If flexion contracture due to the narrow extension gap was found, additional tibial bone cut or medial soft tissue release were performed. Results. MCL deep layer release was performed following the medial meniscus removal in all the TKAs, additional tibial bone cut was performed for three cases, but there was no additional medial soft tissue treatment in any TKAs. Final extension gap in the medial side was 21.2 mm, the average of the tibial insert thickness actually used was 10.6 mm, and the thickness of all the femoral implant at the distal part was 9 mm, therefore the residual medial extension gap in extension was averaged 1.8 ± 0.54 mm. On the other hand, the thickness of the tibial bone cut in the lateral side was various from 11 mm to 16 mm (average was 12.9 ± 1.13 mm). Discussion and Conclusions. All the TKAs in this study were performed to create the proper medial stability in extension without excessive medial release by cutting the adequately thck tibial bone, which lead to thicker tibia resection than the applied tibial insert in the lateral side. As lateral laxity is necessary for the medial pivot movement of the normal knee, slight lateral laxity can be accepted with TKA. The balance between lateral laxity and medial stability in both extension and flexion has not been well elucidated, further studies are necessary regarding on in vivo kinematic

Achieving deep flexion after total knee replacement remains a challenge. In this study we compared the soft-tissue tension and tibiofemoral force in a mobile-bearing posterior cruciate ligament-sacrificing total knee replacement, using equal flexion and extension gaps, and with the gaps increased by 2 mm each. The tests were conducted during passive movement in five cadaver knees, and measurements of strain were made simultaneously in the collateral ligaments. The tibiofemoral force was measured using a customised mini-force plate in the tibial tray. Measurements of collateral ligament strain were not very sensitive to changes in the gap ratio, but tibiofemoral force measurements were. Tibiofemoral force was decreased by a mean of 40% (. sd. 10.7) after 90° of knee flexion when the flexion gap was increased by 2 mm. Increasing the extension gap by 2 mm affected the force only in full extension. Because increasing the range of flexion after total knee replacement beyond 110° is a widely-held goal, small increases in the flexion gap warrant further investigation

The influence of Posterior Cruciate Ligament (PCL) removal and re-establishment of the posterior condylar recess on flexion and extension gaps width during posterior-stabilized Total Knee Arthroplasty (TKA) is still controversial. It has been reported that PCL resection lead to a selective increase of the flexion space of 3–4 mm, creating a potential for instability in flexion. Our hypothesis was that these surgical steps will equally increase both gaps. Measurements of the flexion and extension gaps heights were obtained during different surgical phases in 50 consecutive primary posterior-stabilised TKAs using a tensor device and a calibrated torque wrench. There was a slight symmetrical increase in both gaps after PCL release. In extension the width of the gap increased on average 1.3 mm and 1.0 mm in the medial and lateral compartment respectively. The same pattern was observed in flexion, averaging 1.3 mm medially and 1.3 mm laterally. Another increase of the two gaps was observed after the posterior condylar osteophytes were removed and the posterior recess was re-established. The gaps in extension increased, with respect to the baseline value, on average 1.8 mm medially and 1.8 mm laterally, while in flexion the increase averaged 2.0 mm and 2.2 respectively on the medial and lateral side. Again there were no statistical differences between flexion and extension gaps. No independent differences between the flexion and extension gaps were found in any considered surgical phase. PCL removal and re-establishment of posterior condylar recess does not seem to require any additional consideration in gap balancing during posterior-stabilized TKA

Introduction. Appropriate osteotomy alignment and soft tissue balance are essential for the success of total knee arthroplasty (TKA). The management of soft tissue balance still remains difficult and it is left much to the surgeon's subjective feel and experience. We developed an offset type tensor system for TKA. This device enables objective soft tissue balance measurement with more physiological joint conditions with femoral trial component in place and patello-femoral (PF) joint reduced. We have reported femoral component placement decreased extension gap. The purpose of the present study was to analyze the influence of femoral component size selection on the decrease of extension gap in posterior-stabilized (PS) TKA. Material & Method. 120 varus type osteoarthritic knees implanted with PS TKAs (NexGen LPS flex: Zimmer) were subjected to this study. All TKAs were performed using measured resection technique with anterior reference. The femoral component size was evaluated intra-operatively using conventional femoral sizing jig. The selected femoral component size was expressed by the antero-posterior (AP) size increase (mm) comparing to that of original femoral condyles. Gap measurements were performed using a newly developed offset type tensor device applying 40lbs (178N) of joint distraction force. Firstly, conventional osteotomy gaps (mm) were measured at extension and flexion. Secondary, component gaps (mm) after femoral trial placement with PF joint reduced were evaluated at 0° and 90° of knee flexion. To compare conventional osteotomy gaps and component gaps, estimated extension and flexion gaps were calculated by subtracting the femoral component thickness at extension (9mm) and flexion (11mm) from conventional osteotomy gaps respectively. The decrease of gap at extension and flexion were calculated with estimated gaps subtracted by component gaps. The simple linear regression analysis was used to evaluate the influence of selected femoral component size on the decrease of gap after femoral component placement. Results. The mean extension and flexion conventional osteotomy gaps were 25.7 and 28.2 mm, and estimated gaps were 16.7, 17.2 mm respectively. The component gaps were 11.1, 16.9 mm at 0° and 90° of knee flexion respectively. Extension joint gap was significantly decreased as much as 5.6mm after femoral component placement, but flexion gap showed no significant differences. Selected femoral component size showed a positive correlation to the decrease of gap after femoral component placement (Fig 1). Discussion & Conclusion. This result indicates that AP femoral component size variation affects not only flexion gap but also extension gap in PS TKA. With the larger femoral component size selected, the more protrusion of posterior condyles would increase the more tension on the posterior structures and resulted in the more decrease of joint gap after femoral component placement at full extension. This mechanism might play a physiological role on the prevention of knee hyper-extension, and would be affected by flexion contracture. Accordingly, we conclude that the surgeon should aware of the effect of femoral component placement on the gap control, and femoral component size selection affects not only flexion gap but also extension gap after femoral component placement in PS TKA

Total knee replacement (TKA) surgery is an excellent and well-proven procedure for the treatment of end stage arthritis of the knee. Many refinements have taken place over time in an attempt to improve the components, wear qualities of the polyethylene, and the surgical technique to improve accuracy of component positioning, reduce patient pain, improve postoperative range of motion, ultimately improve results and to prolong the time until revision surgery may occur. This study examines the results of a gap balancing surgical technique in which components were implanted that had a posterior cruciate substituting design. This technique is performed with exacting alignment and balancing of the flexion and extension gaps prior to implantation of the knee components. The follow up is at a minimum of ten years. 515 consecutive knee replacements were followed prospectively for a minimum of ten years. The average age at surgery was 70 years, 73% of patients were female, with an average BMI of 31. All patients carried a diagnosis of osteoarthritis and a cemented, posterior stabilized design TKA (Balanced Knee System, Ortho Development) was implanted. All cases were performed by one of two experienced joint replacement surgeons. The surgical technique demanded flexion and extension gap balancing as well as soft tissue balancing prior to finishing cuts being performed on the femoral side (See figures 1 and 2). Polyethylene spacers come in 1 millimeter increments. 28% of patients died postoperatively at an average of 7.4 years. These patients were older on average at the time of index surgery (76.6 years). None had undergone revision surgery. Of the remaining patients Knee Society scores (39 preop to 91 post op at ten years), function scores and range of motion all improved significantly. What's more, these results were not diminished at ten years. There were no component failures and less than 1% radiographic progressive lucent lines. Eleven revision surgeries (2.1 %) were performed with 2 acute superficial wound revisions, 3 late infections, one patellar tendon disruption from a fall at 7 years (BMI 45.7), 2 complete revisions performed elsewhere for unsatisfactory results, and 3 spacer exchanges for perception of postoperative laxity. For the current study we also examined subgroups of the morbidly obese, octogenarians, and those with a preoperative valgus deformity of greater than 15%. At follow-up these subgroups fared very well with the exception of the heaviest BMI's being limited in range of motion because of soft tissue impingement. Results suggest that this balancing technique gives excellent results with few complications at ten year evaluation. We believe that careful attention to bony and soft tissue balancing and equalization of gaps in flexion and in extension will prove beneficial for TKA longevity in even longer-term evaluation. Figures 1 and 2 demonstrate gap balancing blocks and alignment rods in extension and in flexion

We investigated whether an asymmetric extension gap seen on routine post-operative radiographs after primary total knee replacement (TKR) is associated with pain at three, six, 12 and 24 months’ follow-up. On radiographs of 277 patients after primary TKR we measured the distance between the tibial tray and the femoral condyle on both the medial and lateral sides. A difference was defined as an asymmetric extension gap. We considered three groups (no asymmetric gap, medial-opening and lateral-opening gap) and calculated the associations with the Western Ontario and McMaster Universities osteoarthritis index pain scores over time. Those with an asymmetric extension gap of ≥ 1.5 mm had a significant association with pain scores at three months’ follow-up; patients with a medial-opening extension gap reported more pain and patients with a lateral-opening extension gap reported less pain (p = 0.036). This effect was still significant at six months (p = 0.044), but had lost significance by 12 months (p = 0.924). When adjusting for multiple cofounders the improvement in pain was more pronounced in patients with a lateral-opening extension gap than in those with a medial-opening extension gap at three (p = 0.037) and six months’ (p = 0.027) follow-up. Cite this article: Bone Joint J 2013;95-B:472–7

Introduction: Soft tissue balancing remains the most subjective and most artistic of current techniques in total knee arthroplasty. The flexion gap is traditionally measured at approximately 45 degree of hip flexion and 90 degree of knee flexion on the operation table. Despite of aiming equal joint gaps or tensions in flexion and extension, influence of the thigh weight on the flexion gap has not been documented. Therefore, the purpose of this study was to examine the flexion gaps in the 90-90 degree flexed position and the traditional 45-90 degree flexed position of hip-knee joints.

Materials and methods: Thirty patients with osteoarthritic knee underwent total knee arthroplasty. After the PCL sacrifice, soft tissue releases, and bone cuts, the specially designed tenser which has two load cells was employed. 160N was applied to open the joint gaps in the traditional 45-90 degree flexed position and the 90-90 degree flexed position of hip-knee joints.

Results: The flexion gap in the 90-90 degree flexed position of hip-knee joints was 2.1±1.2mm wider than that in the traditional 45-90 degree flexed position of hip-knee joints. The flexion gap had significant difference between the two different hip flexion angles (p< 0.001).

Discussions: In the traditional 45-90 degree flexed position of hip-knee joints on the operation table, the flexion gap is approximately 45 degree to the gravitation and influenced by the thigh weight. To avoid the influence of the thigh weight and obtain equal joint gaps or tensions in flexion and extension, the flexion gap should be checked in the 90-90 degree flexed position of hip-knee joints.

Introduction:. Proper component orientation and soft tissue balancing are essential for longevity of total knee arthroplasty (TKA), especially in young and active patients. The aim of this study was to evaluate long-term results and quality of TKA in young and active patients with extension first gap balancing technique, in 2 Posterior-Stabilized (PS) total knee designs with identical femoral component. Material and Methods:. 43 consecutive Rotating-Platform (RP-PS, 33 patients) and 38 Fixed-Bearing (FB-PS, 29 patients) with University of California Los Angeles (UCLA) activity score of 5 or above and mean age was 53 ± 1.5 years were followed prospectively for a minimum of 10 years. 18 random TKAs were analyzed for component rotation using MRI. Results:. The majority of patients (77%, 24 patients in RP-PS and 65%, 25 patients in FB-PS) were still participating in recreational activities at final follow-up. There was no case of early or late mid flexion instability causing spinout. There was no malalignment or patellofemoral maltracking. Non-progressive radiolucency was seen at the tibial zone 1 in one of the RP-PS and 3 of the FB-PS knees. The mean femoral rotation was 2 and 3 degrees of external in relation to the transepicondylar axis in RP-PS and in FB-PS, respectively. Two patients in the FB-PS were revised (one for per-prosthetic fracture and one for osteolysis and loosening). There were no revisions in the RP-PS group. Kaplan-Meier survivorship at 10 years was 100% in RP-PS and 97% in FB-PS. Discussion and Conclusions:. Extension first gap balancing technique is a safe, accurate, and reproducible with excellent alignment and long-term durability and high quality of function in young, active patients

Aims. 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?. Patients and Methods. 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). Results. 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. Conclusion. 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

Introduction. Robotic TKA allows for quantifiable precision performing bone resections for implant realignment within acceptable final component and limb alignments. One of the early steps in this robotic technique is after initial exposure and removal of medial and lateral osteophytes, a “pose-capture” is performed with varus and valgus stress applied to the knee in near full extension and 90° of flexion to assess gaps. Component alignment adjustments can be made on the preoperative plan to balance the gaps. At this point in the procedure any posterior osteophytes will still be present, which could after removal change the flexion and extension gaps by 1–3mm. This must be taken into consideration, or changes in component alignment could result in over-correction of gaps can occur. Objective. The purpose of this study was to identify what effect the posterior osteophyte's size and location and their removal had on gap measurements between pose-capture and after bone cuts are made and gaps assessed during implant trialing. Methods. This was a retrospective, single center cohort study comparing 100 robotic-assisted TKAs. Preoperative computer tomography was assessed for the presence, size and location of posterior osteophytes. Robotic-assessed gaps at pose capture and trialing were collected. Paired t-tests, independent t-tests and Pearson's correlation were used to examine this relationship. Results. Posterior osteophytes were present in 87% of cases with 59.3% isolated to the posterior medial femoral condyle. In the sagittal plane, posterior medial femoral condyle (pMFC), posterior lateral femoral condyle (pLFC) and posterior tibial (pT) osteophytes measured 6.75 ± 2.7mm, 5.77 ± 2.8mm, and 6.52 ± 3.14mm respectively. There was a significant increase in medial (17.4 ± 2.7mm vs 19.7 ± 2.2mm, p<0.01) and lateral (19.2 ± 2.2mm vs 20.5 ± 1.9mm, p<0.01) extension gaps from pose-capture to trialing. There was no difference in the delta of medial extension gaps from pose-change to trialing for knees with pMFC osteophytes > or < 5mm (2.1 ± 2.3 mm vs 2.4 ± 2.1mm, p=0.56). Similarly, there was no difference in the change in lateral extension gaps from pose-capture to trialing for knees with lateral posterior osteophytes > or < 5mm (1.2 ± 2.0mm vs 1.73 ± 1.53mm, p = 0.37). There was no statistically significant correlation between medial or lateral osteophyte size and change in medial (r=0.12, p=0.27) or lateral (r=0.11, p=0.36) extension gaps respectively. Conclusion. While there is a significant change in robotically assessed gaps at pose-capture and trialing, this change is small, our study findings are not able to substantiate that it is solely due to the presence, size or location of posterior osteophytes. A post-hoc power analysis indicates that, in order to detect a difference in gap between pose-capture and trialing of 1mm, over 75 knees with and without posterior osteophytes would be needed

Aims. The objectives of this study were to assess the effect of anterior cruciate ligament (ACL) resection on flexion-extension gaps, mediolateral soft tissue laxity, maximum knee extension, and limb alignment during primary total knee arthroplasty (TKA). Methods. This prospective study included 140 patients with symptomatic knee osteoarthritis undergoing primary robotic-arm assisted TKA. All operative procedures 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 study outcomes pre- and post-ACL resection with knee extension and 90° knee flexion. This study included 76 males (54.3%) and 64 females (45.7%) with a mean age of 64.1 years (SD 6.8) at time of surgery. Mean preoperative hip-knee-ankle deformity was 6.1° varus (SD 4.6° varus). Results. ACL resection increased the mean extension gap significantly more than the flexion gap in the medial (mean 1.2 mm (SD 1.0) versus mean 0.2 mm (SD 0.7) respectively; p < 0.001) and lateral (mean 1.1 mm (SD 0.9) versus mean 0.2 mm (SD 0.6) respectively; p < 0.001) compartments. The mean gap differences following ACL resection did not create any significant mediolateral soft tissue laxity in extension (gap difference: mean 0.1 mm (SD 2.4); p = 0.89) or flexion (gap difference: mean 0.2 mm (SD 3.1); p = 0.40). ACL resection did not significantly affect maximum knee extension (change in maximum knee extension = mean 0.2° (SD 0.7°); p = 0.23) or fixed flexion deformity (mean 4.2° (SD 3.2°) pre-ACL release versus mean 3.9° (SD 3.7°) post-ACL release; p = 0.61). ACL resection did not significantly affect overall limb alignment (change in alignment = mean 0.2° valgus (SD 1.0° valgus; p = 0.11). Conclusion. ACL resection creates flexion-extension mismatch by increasing the extension gap more than the flexion gap. However, gap differences following ACL resection do not create any mediolateral soft tissue laxity in extension or flexion. ACL resection does not affect maximum knee extension or overall limb alignment. Cite this article: Bone Joint J 2020;102-B(4):442–448

Purpose. Despite total knee arthroplasty (TKA) is a successful surgical procedure with end-stage knee osteoarthritis, approximately 20% of the patients who underwent primary TKA were still dissatisfied with the outcome. Thereby, numerous literatures have confirmed the relationship between soft tissue balancing and clinical result to improve this pressing issue. Recently, there has been an increased research interest in patient-reported outcome measures (PROMs) after TKA. However, there is little agreement on the association between soft tissue balancing and PROMs. Therefore, the purpose of this study was to determine whether intraoperative soft tissue balancing affected PROMs after primary TKA. We hypothesized that soft tissue balancing would be a predictive factor for postoperative PROMs at one-year post-surgery. Patients and Methods. The study included 20 knees treated for a varus osteoarthritic deformity using a cruciate-retaining TKA (Scorpio NRG) with a polyethylene insert thickness of 8 mm retrospectively. Following the osteotomy using the measured resection technique, the extension gap was measured with a femoral trial by using an electric tensor. This instrument could estimate the soft tissue balance applying continuous distraction force simultaneously from 0 to 40 lbf with an accuracy of the 0.1 lbf. We evaluated the association between a distraction force required for an extension gap of 8 mm, and the following potentially affected factors at one year postoperatively: knee flexion angle using a protractor with one degree increments; radiographic parameters of component alignment, namely the femoral and tibial component medial angle; and the Japanese Knee Osteoarthritis Measure (JKOM). This is a disease-specific and self-administered questionnaire, reflecting the specificity of the Japanese cultural lifestyle, consisting of 25 items scored from 0 to 100 points, with 100 points being worst. Outcomes. The median knee flexion angle was 130 degrees with the femoral and tibial component of 97 and 89 degrees, respectively. For an extension gap of 8 mm, a verified value of a distraction force did not demonstrate a correlation with, knee flexion angle (p = 0.29) or with the femoral (p = 0.20), and tibial component position (p = 0.09). The median JKOM totaled 20 points across 4 domains: pain and stiffness, condition in daily life, general activities, and health conditions with 5, 8, 2.5, and 2 points respectively. There was significant correlation between a required force and the JKOM (r. s. = 0.53, p = 0.02), and notably the domain of health conditions exhibited the highest coefficient of determination (r. s. = 0.54, p = 0.01). Discussion. This study highlights that distraction force for an extension gap of 8 mm is an independent variable in component position or knee flexion angle. We found that soft tissue balancing could influence short term postoperative PROMs. Our results will contribute to a better understanding of outcomes after TKA. This is a particularly critical issue as feasible strategies to avoid a persistent joint stiffness would improve long-term function after TKA and patient satisfaction

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

Aims. To compare patients undergoing total knee arthroplasty (TKA) with ≤ 80° range of movement (ROM) operated with a 2 mm increase in the flexion gap with matched non-stiff patients with at least 100° of preoperative ROM and balanced flexion and extension gaps. Methods. In a retrospective cohort study, 98 TKAs (91 patients) with a preoperative ROM of ≤ 80° were examined. Mean follow-up time was 53 months (24 to 112). All TKAs in stiff knees were performed with a 2 mm increased flexion gap. Data were compared to a matched control group of 98 TKAs (86 patients) with a mean follow-up of 43 months (24 to 89). Knees in the control group had a preoperative ROM of at least 100° and balanced flexion and extension gaps. In all stiff and non-stiff knees posterior stabilized (PS) TKAs with patellar resurfacing in combination with adequate soft tissue balancing were used. Results. Overall mean ROM in stiff knees increased preoperatively from 67° (0° to 80°) to 114° postoperatively (65° to 135°) (p < 0.001). Mean knee flexion improved from 82° (0° to 110°) to 115° (65° to 135°) and mean flexion contracture decreased from 14° (0° to 50°) to 1° (0° to 10°) (p < 0.001). The mean Knee Society Score (KSS) improved from 34 (0 to 71) to 88 (38 to 100) (p < 0.001) and the KSS Functional Score from 43 (0 to 70) to 86 (0 to 100). Seven knees (7%) required manipulations under anaesthesia (MUA) and none of the knees had flexion instability. The mean overall ROM in the control group improved from 117° (100° to 140°) to 123° (100° to 130°) (p < 0.001). Mean knee flexion improved from 119° (100° to 140°) to 123° (100° to 130°) (p < 0.001) and mean flexion contracture decreased from 2° (0° to 15°) to 0° (0° to 5°) (p < 0.001). None of the knees in the control group had flexion instability or required MUA. The mean KSS Knee Score improved from 48 (0 to 80) to 94 (79 to 100) (p < 0.001) and the KSS Functional Score from 52 (5 to 100) to 95 (60 to 100) (p < 0.001). Mean improvement in ROM (p < 0.001) and KSS Knee Score (p = 0.017) were greater in knees with preoperative stiffness compared with the control group, but the KSS Functional Score improvement was comparable (p = 0.885). Conclusion. TKA with a 2 mm increased flexion gap provided a significant improvement of ROM in knees with preoperative stiffness. While the improvement in ROM was greater, the absolute postoperative ROM was less than in matched non-stiff knees. PS TKA with patellar resurfacing and a 2 mm increased flexion gap, in combination with adequate soft tissue balancing, provides excellent ROM and knee function when stiffness of the knee had been present preoperatively. Cite this article: Bone Joint J 2020;102-B(4):426–433

Aims. It is unknown whether gap laxities measured in robotic arm-assisted total knee arthroplasty (TKA) correlate to load sensor measurements. The aim of this study was to determine whether symmetry of the maximum medial and lateral gaps in extension and flexion was predictive of knee balance in extension and flexion respectively using different maximum thresholds of intercompartmental load difference (ICLD) to define balance. Methods. A prospective cohort study of 165 patients undergoing functionally-aligned TKA was performed (176 TKAs). With trial components in situ, medial and lateral extension and flexion gaps were measured using robotic navigation while applying valgus and varus forces. The ICLD between medial and lateral compartments was measured in extension and flexion with the load sensor. The null hypothesis was that stressed gap symmetry would not correlate directly with sensor-defined soft tissue balance. Results. In TKAs with a stressed medial-lateral gap difference of ≤1 mm, 147 (89%) had an ICLD of ≤15 lb in extension, and 112 (84%) had an ICLD of ≤ 15 lb in flexion; 157 (95%) had an ICLD ≤ 30 lb in extension, and 126 (94%) had an ICLD ≤ 30 lb in flexion; and 165 (100%) had an ICLD ≤ 60 lb in extension, and 133 (99%) had an ICLD ≤ 60 lb in flexion. With a 0 mm difference between the medial and lateral stressed gaps, 103 (91%) of TKA had an ICLD ≤ 15 lb in extension, decreasing to 155 (88%) when the difference between the medial and lateral stressed extension gaps increased to ± 3 mm. In flexion, 47 (77%) had an ICLD ≤ 15 lb with a medial-lateral gap difference of 0 mm, increasing to 147 (84%) at ± 3 mm. Conclusion. This study found a strong relationship between intercompartmental loads and gap symmetry in extension and flexion measured with prostheses in situ. The results suggest that ICLD and medial-lateral gap difference provide similar assessment of soft-tissue balance in robotic arm-assisted TKA. Cite this article: Bone Jt Open 2021;2(11):974–980