Aims. Medial unicompartmental knee arthroplasty (UKA) is undertaken in patients with a passively correctable varus deformity. Our hypothesis was that restoration of natural soft tissue tension would result in a comparable lower limb alignment with the contralateral normal lower limb after mobile-bearing medial UKA. Patients and Methods. In this retrospective study, hip-knee-ankle (HKA) angle, position of the weight-bearing axis (WBA) and knee joint line obliquity (KJLO) after mobile-bearing medial UKA was compared with the normal (clinically and radiologically) contralateral lower limb in 123 patients. Results. Postoperatively, HKA angle was restored to within ±3° of the contralateral lower limb in 87% of patients andWBA passed within ±1 Kennedy and White's tibial zone of the contralateral normal lower limb in 95% of patients. The difference in the mean KJLO between the two groups was not significant (p=0.05) and the KJLO was within ±3° of the contralateral normal lower limb in 96% of patients. Conclusion. Lower limb alignment & knee joint line obliquity after mobile-bearing medial UKA were comparable to the unaffected contralateral limb in most patients. Clinical Relevance. Comparison with the contralateral normal lower limb is a reliable method to evaluate and validate limb mechanical alignment after mobile-bearing medial UKA

Introduction. While implant designs and surgical techniques have improved in total knee arthroplasty (TKA), approximately 20% of patients remain dissatisfied. The purpose of this study was to determine if reproduction of anatomic preoperative measurements correlated to improved clinical outcomes in TKA. Methods. We retrospectively reviewed95 patients (106 knees) who underwent a TKA between 2012 −2013 with a minimum of one year follow-up. All patients had a pre and post-operative SF-12 and WOMAC scores. Pre and 6 week post-operative radiographs were reviewed to compare restoration of coronal plane alignment, maintenance of joint line obliquity, and maintenance of tibial varus. Coronal alignment was defined as the angle formed between the mechanical axis of the femur and the the tibia. Joint line obliquity was defined as the angle between the mechanical axis of the limb and the line which best parallels the joint space at the knee. Tibial varus was compared between the preoperative proximal lateral tibial angle and the angle formed by the mechanical axis of the tibia and tibial component postoperatively. Results. In 106 patients, postoperative coronal alignment, maintenance of tibia varus, or restoration of joint line obliquity did not correlate to improved outcomes. Patients with residual varus coronal alignment of more than 2° had increased pain and total WOMAC scores (p=0.013 and p = 0.036). Patients who had under-correction of the native tibial angle, had an increase in overall WOMAC score (p=0.007) with increased pain (p=0.012), stiffness (p=0.038), and function (p = 0.001). Furthermore, over-correction of tibial angle resulted in increased WOMAC functional scores (p=0.019), but was not significant to the overall WOMAC. Conclusions. In this study, restoration of a patient's native tibial varus correlated to improved WOMAC scores at 1 year postoperatively. Undercorrection of varus resulted in worse total WOMAC scores whereas overcorrection resulted in worse WOMAC functional scores

The Coronal Plane Alignment of the Knee (CPAK) is a recent method for classifying knees using the hip-knee-ankle angle and joint line obliquity to assist surgeons in selection of an optimal alignment philosophy in total knee arthroplasty (TKA)1. It is unclear, however, how CPAK classification impacts pre-operative joint balance. Our objective was to characterise joint balance differences between CPAK categories. A retrospective review of TKA's using the OMNIBotics platform and BalanceBot (Corin, UK) using a tibia first workflow was performed. Lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were landmarked intra-operatively and corrected for wear. Joint gaps were measured under a load of 70–90N after the tibial resection. Resection thicknesses were validated to recreate the pre-tibial resection joint balance. Knees were subdivided into 9 categories as described by MacDessi et al.1 Differences in balance at 10°, 40° and 90° were determined using a one-way 2-tailed ANOVA test with a critical p-value of 0.05. 1124 knees satisfied inclusion criteria. The highest proportion of knees (60.7%) are CPAK I with a varus aHKA and Distal Apex JLO, 79.8% report a Distal Apex JLO and 69.3% report a varus aHKA. Greater medial gaps are observed in varus (I, IV, VII) compared to neutral (II, V, VIII) and valgus knees (III, VI, IX) (p<0.05 in all cases) as well as in the Distal Apex (I, II, III) compared to Neutral groups (IV, V, VI) (p<0.05 in all cases). Comparisons could not be made with the Proximal Apex groups due to low frequency (≤2.5%). Significant differences in joint balance were observed between and within CPAK groups. Although both hip-knee-ankle angle and joint line orientation are associated with joint balance, boney anatomy alone is not sufficient to fully characterize the knee

Background. Surgical planning of long bone surgery often takes place using outdated 2D axes on 2D images such as long leg standing X-rays. This leads to errors and great variation between intra- and inter- observers due to differing frames of reference. With the advent of 3D planning software, researchers developed 3D axes of the knee such as the Flexion Facet Axis (FFAx) and Trochlear Axis (TrAx), and these proved easy to derive and reliable. Unlike 2D axes, clinicians and scientists can use a single 3D axis to obtain measurements relative to other 3D axes, in all three planes Deriving a 3D axis also does not require an initial frame of reference, such as in trying to derive the 2D Posterior Condylar Axis (PCAx), whereby a slight change in slice orientation will affect its position. However, there is no 3D axis derived for the tibial plateau yet. Measurements of tibial joint line obliquity are with a 2D axis drawn on AP long leg standing X-rays. The same applies to tibial plateau rotation, as measured by 2D axes drawn on axial CT/MRI slices. this study aimed to to develop a novel new 3D axis for the tibial plateau to quantify both tibial plateau joint line obliquity and axial rotation. Methods. Materialise software version 8.0 (Materialise Inc., Belgium) handled segmentation of CT data and for analysis of bony morphology. A line joining the centroids of the medial and lateral tibial plateaus formed the TCAx (Fig1). A line joining the middle coordinate of the TCAx, to the centre of the best-fit sphere between the medial and lateral malleolus formed the Tibial Mechanical Axis (TMAx). A standard frame of reference aligned 72 tibias with the TCAx horizontal in the axial view, and the TMAx aligned parallel to the global reference coordinate system vertical axis. Tibial joint line obliquity was the angle between the TCAx and TMAx on the medial side, also known as the Medial Tibial Plateau Angle (MPTA)(Fig2). The authors compared reliability and accuracy of the TCAx against three other rotational axes of the tibia as described in the literature. Results. Our methods showed excellent reproducibility using Bland-Altman analysis between intra- and inter-observers. The tibial joint line as defined by the TCAx is oblique (varus) in the majority of knees (MPTA = 85 ± 2°), and becomes perpendicular (MPTA = 90 ± 2°) in constitutional valgus. The TCAx is also parallel to the Anatomical Tibial Axis (ATAx), (SD = 2°), which is currently the gold standard and most reliable axis in defining tibial axial rotation. Conclusions. The TCAx is a reliable axis for referencing both coronal and rotational alignment of the tibial plateau. it can be used for planning and postoperative analysis of knee replacement. (Fig 3). The variable obliqueness of the joint line suggests that neutral alignment in knee arthroplasty may not be suitable for all knees

Introduction. The constitutional knee anatomy in the coronal plane includes the distal femoral joint line obliquity (DFJLO) which in most patients is in slight valgus positioning. Despite this native anatomy, the mechanical positioning of the femoral component during primary total knee arthroplasty (TKA) often ignores the native DFJLO opting to place the femur in a set degree of valgus that varies upon the practitioner's practice and experience. Unfortunately, this technique is likely to generate high rate of distal lateral femoral overstuffing. This anatomical mismatch might be a cause of anterior knee pain and therefore partly explain the adverse functional outcomes of mechanically aligned (MA) TKA. Our study aims at assessing the relationship between constitutional knee anatomy and clinical outcomes of MA TKA. We hypothesized that a negative relationship would be found between the constitutional frontal knee deformity, the distal femoral joint line obliquity, and functional outcomes of MA TKA with a special emphasize on patellofemoral (PF) specific outcomes. Methods. One hundred and thirteen patients underwent MA TKA (posterior-stabilized design) for primary end-stage knee osteoarthritis. They were prospectively followed for one year using the New KSS 2011 and HSS Patella score. Residual anterior knee pain was also assessed. Knee phenotypes using anatomical parameters (such as HKA, HKS, DFJLO and LDFA (Lateral distal femoral angle)) were measured from preoperative and postoperative lower-limb EOS® images (Biospace, Paris, France). We assessed the relationship between the knee anatomical parameters and the functional outcome scores at 1 year postoperatively. Results. We investigated four groups according to the preoperative obliquity of the distal femur and HKA. The group with high DFJLO and varus knee deformity demonstrated lower HSS scores (drop>10%, p=0.03) and higher rate of anterior knee pain (p=0.03). Higher postoperative variation of LDFA was associated with lower HSS scores (r = −0.2367, p=0.03) and with higher preoperative DFJLO (p=0.0001) due to the MA technique. Knee phenotypes with LDFA<87° presented higher risk of variation of LDFA. No correlation was found using New KSS 2011 outcomes at one-year follow-up. Discussion/Conclusion. Disregard of the constitutional knee anatomy (LDFA and DFJLO) when performing a MA TKA may generate a non-physiologic knee kinematics that impact patellofemoral outcomes and resulting in residual anterior knee pain. While these results are restricted to modern posterior-stabilized TKA design, recent in silico and in vitro studies supported the negative effect of the lateral overstuffing of the femoral component in the coronal plane during knee flexion. This study provides further evidence that suggest patient-specific anatomical considerations are needed to optimize component position and subsequent outcomes following primary TKA. Additional studies are needed to integrate the rotational status of the femoral component in this analysis. For any figures or tables, please contact authors directly

Since 2005, the author has performed nearly 1000 Oxford medial unicompartmental arthroplasties (UKA) using a mobile bearing. The indications are 1) Isolated medial compartment osteoarthritis with ‘bone-on-bone’ contact, which has failed prior conservative treatment, 2) Medial femoral condyle avascular necrosis or spontaneous osteonecrosis, which has failed prior conservative treatment. Patients are recommended for UKA only if the following anatomic requirements are met: 1) Intact ACL, 2) Full thickness articular cartilage wear limited to the anterior half of the medial tibial plateau, 3) Unaffected lateral compartment cartilage, 4) Unaffected patellar cartilage on the lateral facet, 5) Less than 10 degrees of flexion deformity, 6) Over 100 degrees of knee flexion, and 7) Varus deformity not exceeding 15 degrees. Exclusion criteria for surgery are BMI of more than 30, prior high tibial osteotomy, and inflammatory arthritis. All cases were performed with a tourniquet inflated using a minimally-invasive incision with a quadriceps-sparing approach. Both femoral and tibial components were cemented. Most patients were discharged home the next morning; bilaterals usually stayed a day longer. We have previously described our results and the factors determining alignment. In a more recent study, we have compared the coronal post-operative limb alignment and knee joint line obliquity after medial UKA with a clinically and radiologically (less than Grade 2 medial OA) normal contralateral lower limb. In our series, we have had 1 revision for aseptic loosening of both components, conversion to TKRs in a patient with bilateral UKAs who developed rheumatoid arthritis 3 years later, and 9 meniscal dislocations. There have been no cases of wound infections and thromboembolism. We have reviewed our patients with a minimum 10-year follow-up which will be presented. The vast majority of our patients have been generally very satisfied with the results. Our study shows that most patients (who have no disease in the contralateral knee) regain their ‘natural’ alignment and joint line obliquity comparable to their contralateral limb. Over the past few years our percentage of UKAs has been steadily rising to about a third of our knee cases. UKA serves as a definitive procedure in the elderly. We see it as a suitable procedure in middle-aged patients who want an operation that provides a quick recovery, full function and range of motion, and near-normal kinematics, with the understanding that they have a small chance of conversion to a total knee arthroplasty in the future

Since 2005, the author has performed 422 Oxford medial unicompartmental arthroplasties (UKA) using a mobile bearing. There were 263 females and 119 males, (40 patients had bilateral UKAs) with a mean age of 62 years. The indications were: Isolated medial compartment osteoarthritis with ‘bone-on-bone’ contact, which had failed prior conservative treatment; Medial femoral condyle avascular necrosis or spontaneous osteonecrosis, which had failed prior conservative treatment. Patients were recommended UKA only if the following anatomic requirements were met: Intact ACL, Full thickness articular cartilage wear limited to the anterior half of the medial tibial plateau, Unaffected lateral compartment cartilage, Unaffected patellar cartilage on the lateral facet, Less than 10 degrees of flexion deformity, Over 100 degrees of knee flexion, Varus deformity not exceeding 15 degrees. Exclusion criteria for surgery were BMI of more than 30, prior high tibial osteotomy, and inflammatory arthritis. All cases were performed with a tourniquet inflated using a minimally-invasive incision with a quadriceps-sparing approach. Both femoral and tibial components were cemented. Rehabilitation consisted of teaching the patients 6 exercises to regain strength and range of motion, and weight-bearing as tolerated with a cane began from the evening of surgery. Most patients were discharged home the next morning; bilaterals usually stayed a day longer. We have previously described our results and the factors determining alignment. In a more recent study we have compared the coronal postoperative limb alignment and knee joint line obliquity after medial UKA with a clinically and radiologically (less than Grade 2 medial OA) normal contralateral lower limb. In our series of 423 cases, we have had 1 revision for aseptic loosening of both components, and 4 meniscal dislocations. There have been no cases of wound infections and thromboembolism. We are currently undertaking a review of the 2–10 year follow-up of our cases. The vast majority of our patients have been generally very satisfied with the results. Our study shows that most patients (who have no disease in the contralateral knee) regain their ‘natural’ alignment and joint line obliquity comparable to their contralateral limb. Over the past few years our percentage of UKAs has been steadily rising. UKA serves as a definitive procedure in the elderly. We see it as a suitable procedure in middle-aged patients who want an operation that provides a quick recovery, full function and range of motion, and near-normal kinematics, with the understanding that they have a small chance of conversion to a total knee arthroplasty in the future

Patients presenting with arthrosis following high tibial osteotomy (HTO) pose a technical challenge to the surgeon. Slight overcorrection during osteotomy sometimes results in persisting medial unicompartmental arthrosis, but with a valgus knee. A medial UKA is desirable, but will result in further valgus deformity, while a TKA in someone with deformity but intact cruciates may be a disappointment as it is technically challenging. The problem is similar to that of patients with a femoral malunion and arthrosis. The surgeon has to choose where to make the correction. An ‘all inside’ approach is perhaps the simplest. However, this often means extensive release of ligaments to enable ‘balancing’ of the joint, with significant compromise of the soft tissues and reduced range of motion as a consequence. As patients having HTO in the first place are relatively high demand, we have explored a more conservative option, based upon our experience with patient matched guides. We have been performing combined deformity correction and conservative arthroplasty for 5 years, using PSI developed in the MSk Lab. We have now adapted this approach to the failed HTO. By reversing the osteotomy, closing the opening wedge, or opening the closing wedge, we can restore the obliquity of the joint, and preserve the cruciate ligaments. Technique: CT based plans are used, combined with static imaging and on occasion gait data. Planning software is then used to undertake the arthroplasty, and corrective osteotomy. In the planning software, both tibial and femoral sides of the UKA are performed with minimal bone resection. The tibial osteotomy is then reversed to restore joint line obliquity. The placing of osteotomy, and the angling and positioning in relation to the tibial component are crucial. This is more important in the opening of a closing wedge, where the bone but is close to the keel cut. The tibial component is then readjusted to the final ‘Cartier’ angle. Patient guides are then made. These include a tibial cutting guide which locates both the osteotomy and the arthroplasty. At operation, the bone cuts for the arthroplasty are made first, so that these cuts are not performed on stressed bone. The cuts are not in the classical alignment as they are based upon deformed bone so the use of patient specific guides is a real help. The corrective osteotomy is then performed. If a closing wedge is being opened, then a further fibular osteotomy is needed, while the closing of an opening wedge is an easier undertaking. Six cases of corrective osteotomy and partial knee replacement are presented. In all cases, the cruciates have been preserved, together with normal patello-femoral joints. Patient satisfaction is high, because the deformity has been addressed, restoring body image. Gait characteristics are those of UKA, as the ACL has been preserved and joint line obliquity restored

Introduction. Although total knee replacement became a widespread procedure for the purpose of knee reconstruction, osteotomies around the knee were regularly performed. Total knee arthroplasty should be performed for advanced arthritis of the knee. With the advent of biplanar open wedge high tibial osteotomy (HTO) combined with locking plate fixation, HTO has been expanded and its surgical outcome has been improved in recent years. However, post-operative joint-line obliquity has been raised as a concern with this procedure, which may affect the outcome especially in the knees with severe varus deformity. Hence the purpose of this study is to analyze the compression and shear stresses in the knee cartilage with joint line obliquity after HTO. Methods. Using a three-dimensional computer aided design software, the digital knee model with soft tissues was developed. The geometrical bone data used in this study were derived from commercially available human bone digital anatomy media (3972 and 3976, Pacific Research Laboratories, Inc., WA, USA). The three-dimensional knee model was transferred to finite element model. Material properties of the soft tissues and bones were derived from previous studies. The loading condition was adjusted to the load during a single-leg stance of the gait cycle, which resulted in an axial compressive load of 1200 N. Two different conditions were subjected to the analysis: normal alignment and joint-line obliquity after HTO. For the normal alignment, a static force of 1200 N was applied along the mechanical axis. For the joint-line obliquity models, a single force of 1200 N was applied rotating force directions in the frontal plane from the normal direction by 2.5º, 5º, 7.5º, and 10º, respectively. Results. The maximum values of the axial stresses in the cartilages for the normal condition showed almost same values in medial and lateral compartments. In the joint-line obliquity models, the maximum axial stress values in the medial compartment did not exhibit substantial change up to the level of 7.5º obliquity, while a rise in maximum stress value was observed for the model with 10º obliquity. The shear stress showed a different tendency. In the joint-line obliquity models, a steep rise of laterally directed shear stress in the medial compartment was observed for models with obliquity of 5º or more. Discussion. The shear stress in the medial cartilage increased to almost twice as high as the normal knee level for the joint- line obliquity model with an inclination of 5º. The maximum shear stress values increased in accordance with the obliquity angle. The elevated stress could be deleterious to the cartilage. In such large amount of correction by tibial osteotomy leads to unfavorable mechanical environment in the knee. For those severe situations, double-level osteotomy, which retains anatomical knee joint line by simultaneous femoral and tibial osteotomies, should be considered to correct the joint-line obliquity

Background:. It has been suggested that double-level osteotomy can prevent the occurrence of joint line obliquity (JLO), as one of the complications following high tibial osteotomy (HTO). In this study, we aimed to compare the preoperative distal femoral and proximal tibial obliquity in patients with primary genu varum with a group of normal subjects (without genu varum). Materials and methods:. 75 patients with primary genu varum and 75 normal persons, contributed to a case-control study. The medial distal femoral mechanical angle (MDFMA), medial proximal tibial mechanical angle (MPTMA), joint diversion angle (JDA) and femoral and tibial JLO were measured and compared between the two groups. The percentage of patients' with > 4 degrees of JLO in both distal of femur and proximal of tibia, were then determined. Results:. The mean of MDFMA and MPTMA were significantly lower and JDA and femoral and tibial JLO were significantly higherin genu varum group (p < 0.05). Double-level osteotomy was required in 25.3% of patients with genu varum to prevent post-operative JLO. Conclusion:. JLO is a common finding in patients with genu varum and normal group; however, it is significantly higher in patients with genu varum

Introduction. Soft tissue balancing in total knee arthroplasty surgery may prove necessary to elevate patient satisfaction and functional outcome beyond the current fair average. A new generation of contact load sensors embedded in trial tibial liners provides quantification of loads, direction, and an indirect assessment of ligamentous tension. With this technology, quantified intra-operative balancing may potentially restore compartmental load distribution to a more physiological and functional degree. Objective. 1). To define a clinically useful target zone for balancing of the soft tissue envelope of knees at the time of surgery using numerical data from load sensors in tibial liner trial components. 2). To validate the boundaries of the target zone on a medial v. lateral contact load scatterplot with PROMs. Method. This study is a prospective IRB approved clinical study of 104 patients (112 knees) from a single surgeon. The intra-operative balancing aim was the restoration of a physiological compartmental load distribution, defined as less than 15 pounds of load differential between the medial and lateral compartments throughout flexion. This was performed using an algorithmic method of soft tissue releases combined with minor joint line obliquity adjustments within 3 degrees of neutral. Medial v. lateral contact load data was produced at 10, 45, 90° flexion as part of the balancing and final verification process. For all cases the pre and post-operative (4weeks, 3months, 6months) varus and valgus soft tissue envelope was measured with a calibrated and validated knee fixture. The KSS scores were obtained at each measurement interval. Results. The majority of knees were successfully balanced within a cluster zone as shown in Fig. 1. The concept of a safe target zone was developed to define a safe zone of balancing with higher predictive value for satisfaction and function. This was created using a best-fit rhomboid area, whose perimeter uses the fusion of a square area defined by min / max absolute loads and a triangular area defined by relative compartmental load ratios (Compartmental Load Ratio=Med Load/Total Load). The best-fit load boundaries to optimize patient satisfaction are 12.5 lbs.-38 lbs. (static load) and 44%–59% (relative load distribution) (Fig.2). Using these boundaries 83% of the cases in the safe zone area scored above 80% on the satisfaction score at 6 months compared to 36% for those outside the rhomboid area (Fig. 3). Conclusions. Balancing by load distribution uses a combination of distinct single surgical variable corrections of soft tissue releases and minor bone adjustments. Using a systematic balancing algorithm, the medial and lateral compartmental loads can predictably be balanced within a defined target zone, delineated by absolute load values and by relative compartmental load ratios. Based on this series the method is proving reproducible. The accuracy obtained by matching patient satisfaction values appears to validate the potential of a target zone as a safe and predictable clinical tool for balancing. For figures/tables, please contact authors directly.

Introduction. The mechanical classical method of knee surgical instrumentation by alignment is based on built-in compromises and is considered insufficient to ensure consistent success. Soft tissue balancing is thus now seen as necessary for optimal functional outcomes and patient satisfaction. (Matsuda 2005, Winemaker 2002). The authors have previously demonstrated that balancing can be achieved through specific strategic moves. In this study, the goal was to determine the efficacy of a given surgical algorithm and to define predictors of improved outcome. The surgical target is equilibrium of contact loads. The mechanical axis remains in neutral, however subtle variation in the joint line obliquity and posterior slope are tolerated within the literature established boundaries of +/− 3 degrees and less than 10 degrees respectively. Methods. Data was obtained from 101 consecutive primary procedures from a single surgeon (PAM) using a PCL-retaining device. For all cases the testing methodology consisted of a sag test, heel push, drawer testing at 90 degrees, and varus-valgus laxity testing at 10 degrees of flexion. Instrumented tibial trials were used to measure the contact forces on the lateral and medial sides at 10, 30, 60 and 90 degrees of flexion. Specific releases were identified and noted based on matrix profiling after each test. Re-iteration loops were enacted until balance within 15 lbs. of difference was achieved. The data was expressed as the ratio of medial/total force (total=medial + lateral), with 0.5 being equal lateral and medial forces. This was named the Contact Load Ratio (CLR). The load distribution was expressed as a scatter graph of lateral v. medial compartmental loads (Figure 1). Results. The number of corrections required to achieve balancing was less than five, with on average of two. The salient finding was the clustering of the Contact Load Ratio after surgical balancing was performed. As seen in Fig 1, there was increasing precision and reproducibility in achieving loads in reasonable ranges and similar in magnitude. The preliminary 3months observational data indicates a trend towards higher functionality and patient satisfaction when the loads lie within a defined sector: the safe or target balancing zone (Fig 2). This is currently defined as bracketed between 12–40 lbs of amplitude in either compartment and within 0.8 to 1.25 of ratio between the medial side and the total contact load across the joint. Discussion. It is believed by the authors that the clinical use of load balancing algorithms can predictably restore a comparable load ratio with magnitudes within the defined safe zone. This precision however may not necessarily convert into better performance. At 65 % completion however the functional score results do indicate a definite such trend. Although a perfect load symmetry (0.5 ratio) might be intuitively desirable, the higher value of 0.52 may be concordant with the published varus / valgus ratio of 0.55, in healthy individuals (Heeserbeek 2008). The role of implant design, inflammatory laxity, sex, anticipated level of function, and age all may affect the ideal individual ratio. Further studies are necessary to further refine this concept

Limb deformity is common in patients presenting for knee arthroplasty, either related to asymmetrical wear patterns from the underlying arthritic process (intra-articular malalignment) or less often major extra-articular deformity due to prior fracture malunion, childhood physical injury, old osteotomy, or developmental or metabolic disorders such as Blount's disease or hypophosphatemic rickets. Angular deformity that is above the epicondyles or below the fibular neck may not be easily correctable by adjusted bone cuts as the amount of bone resection may make soft tissue balancing impossible or may disrupt completely the collateral ligament attachments. Development of a treatment plan begins with careful assessment of the malalignment which may be mainly coronal, sagittal, rotational or some combination. Translation can also complicate the reconstruction as this has effects directly on location of the mechanical axis. Most intra-articular deformities are due to the arthritic process alone, but may occasionally be the result of intra-articular fracture, periarticular osteotomy or from prior revision surgery effects. While intra-articular deformity can almost always be managed with adjusted bone cuts it is important to have available revision type implants to enhance fixation (stems) or increase constraint when ligament balancing or ligament laxity is a problem. Extra-articular deformities may be correctable with adjusted bone cuts and altered implant positioning when the deformity is smaller, or located a longer distance from the joint. The effect of a deformity is proportional to its distance from the joint. The closer the deformity is to the joint, the greater the impact the same degree angular deformity will have. In general deformities in the plane of knee are better tolerated than sagittal plane (varus/valgus) deformity. Careful pre-operative planning is required for cases with significant extra-articular deformity with a focus on location and plane of the apex of the deformity, identification of the mechanical axis location relative to the deformed limb, distance of the deformity from the joint, and determination of the intra-articular effect on bone cuts and implant position absent osteotomy. In the course of pre-operative planning, osteotomy is suggested when there is inability to correct the mechanical axis to neutral without excessive bone cuts which compromise ligament or patellar tendon attachment sites, or alternatively when adequate adjustment of cuts will likely lead to excessive joint line obliquity which can compromise ability to balance the soft tissues. When chosen, adjunctive osteotomy can be done in one-stage at the time of TKA or the procedures can be done separately in two stages. When simultaneous with TKA, osteotomy fixation options include long stems added to the femoral (or tibial) component for intramedullary fixation, adjunctive plate and screw fixation, and antegrade (usually locked) nailing for some femoral osteotomies. Choice of fixation method is often influenced by specific deformity size location, bone quality and amount, and surgeon preference. Surgical navigation, or intra-operative x-ray imaging methods (or both) have both been used to facilitate accurate correction of deformity in these complex cases. When faced with major deformity of the femur or tibia, with careful planning combined osteotomy and TKA can result in excellent outcomes and durable implant fixation with less constraint, less bone loss, and better joint kinematics than is possible with modified TKA alone