Introduction. The success of knee replacement surgery depends, in part, on restoration of the correct alignment of the leg with respect to the load-bearing vector passing from the hip to the ankle (the mechanical axis). Conventional thinking is that the correct angle of resection of the distal femur (Valgus Cut Angle, VCA) depends on femoral length or femoral offset, though femoral bowing, in addition to length and medial offset, may also have a significant influence on the VCA. We hypothesized that femoral bowing has a strong effect on the VCA necessary to restore physiologic alignment after arthroplasty or osteotomy. Methods. A total of 102 long-leg radiographs were obtained from patients scheduled for primary total knee arthroplasty. The patients on average were 41% male 59% female, 67.9 ± 11.1 years, 67.0 ± 4.7 in, 192 ± 43 lbs, and had a BMI of 29.7 ± 4.8. All radiographs were prepared with the feet placed in identical rotation and the patellae pointing forward, and were excluded if there was evidence of malrotation, as defined by (i) a difference in the medial head offsets of the right and left femur of >3mm, (ii) a difference in the width of the tibiofibular syndesmoses, or (iii) a difference in the rotation of one foot compared to the other. The following anatomic variables were measured on each radiograph: (i) the neck shaft angle (NSA) of the femur, (ii) the length of the femur, (iii) the length of the femoral shaft, (iv) the medial head offset, (v) the medial-lateral bow of the distal femur, (vi) the hip- knee axis angle, (vii) the mechanical axis deviation of the extremity at the knee, (viii) the medio-lateral bow of the tibia, and (ix) the valgus cut angle required to restore the mechanical axis to the center of the knee during surgery (VCA). Bivariate plots were constructed using the measurements thought to influence the VCA: femoral bowing, femoral offset, and length of femur. Multivariate regression was then used to find the variable that had the strongest effect on the VCA. Results. The bivariate plot of offset and VCA yielded an R2 of 0.02544 (p = 0.11) was not statistically significant. However, the bivariate plot of femoral length and VCA yielded an R2 of 0.1294 (p = 0.0002) showing significant correlation. Lastly, the bivariate plot of femoral bowing and VCA yielded an R2 of 0.59136 (p < 0.00001) demonstrating significant correlation (Figure 3). Multivariate analysis revealed that femoral bowing was the best predictor of VCA: VCA = 5.46–0.363 femoral bowing (°) + 0.106 Femoral offset (mm) − 0.010 femoral length (mm). Discussion. While clinicians performing knee replacements typically do not consider femoral bowing when selecting the valgus angle appropriate for each patient, our findings demonstrate that femoral bowing has a potent effect on VCA. The multivariate regression indicated that femoral bowing had the highest effect on VCA followed by offset and femoral length. These findings suggest that surgeons should consider measuring long alignment radiographs before performing a total knee arthroplasty

Aims. The impact of a diaphyseal femoral deformity on knee alignment varies according to its severity and localization. The aims of this study were to determine a method of assessing the impact of diaphyseal femoral deformities on knee alignment for the varus knee, and to evaluate the reliability and the reproducibility of this method in a large cohort of osteoarthritic patients. Methods. All patients who underwent a knee arthroplasty from 2019 to 2021 were included. Exclusion criteria were genu valgus, flexion contracture (> 5°), previous femoral osteotomy or fracture, total hip arthroplasty, and femoral rotational disorder. A total of 205 patients met the inclusion criteria. The mean age was 62.2 years (SD 8.4). The mean BMI was 33.1 kg/m. 2. (SD 5.5). The radiological measurements were performed twice by two independent reviewers, and included hip knee ankle (HKA) angle, mechanical medial distal femoral angle (mMDFA), anatomical medial distal femoral angle (aMDFA), femoral neck shaft angle (NSA), femoral bowing angle (FBow), the distance between the knee centre and the top of the FBow (DK), and the angle representing the FBow impact on the knee (C’KS angle). Results. The FBow impact on the mMDFA can be measured by the C’KS angle. The C’KS angle took the localization (length DK) and the importance (FBow angle) of the FBow into consideration. The mean FBow angle was 4.4° (SD 2.4; 0 to 12.5). The mean C’KS angle was 1.8° (SD 1.1; 0 to 5.8). Overall, 84 knees (41%) had a severe FBow (> 5°). The radiological measurements showed very good to excellent intraobserver and interobserver agreements. The C’KS increased significantly when the length DK decreased and the FBow angle increased (p < 0.001). Conclusion. The impact of the diaphyseal femoral deformity on the mechanical femoral axis is measured by the C’KS angle, a reliable and reproducible measurement. Cite this article: Bone Jt Open 2023;4(4):262–272

Aims. The aims of this retrospective study were to determine the incidence of extra-articular deformities (EADs), and determine their effect on postoperative alignment in knees undergoing mobile-bearing, medial unicompartmental knee arthroplasty (UKA). Patients and Methods. Limb mechanical alignment (hip-knee-ankle angle), coronal bowing of the femoral shaft and proximal tibia vara or medial proximal tibial angle (MPTA) were measured on standing, full-length hip-to-ankle radiographs of 162 patients who underwent 200 mobile-bearing, medial UKAs. Results. Incidence of EAD was 7.5% for coronal femoral bowing of >5°, 67% for proximal tibia vara of >3° (MPTA<87°) and 24.5% for proximal tibia vara of >6° (MPTA<84°). Mean postoperative HKA angle achieved in knees with femoral bowing ≤5° was significantly greater when compared to knees with femoral bowing >5° (p=0.04); in knees with proximal tibia vara ≤3° was significantly greater when compared to knees with proximal tibia vara >3° (p=0.0001) and when compared to knees with proximal tibia vara >6° (p=0.0001). Conclusion. Extra-articular deformities are frequently seen in patients undergoing mobile-bearing medial UKAs, especially in knees with varus deformity>10°. Presence of an EAD significantly affects postoperative mechanical limb alignment achieved when compared to limbs without EAD and may increase the risk of limbs being placed in varus>3° postoperatively. Clinical Relevance. Since the presence of an EAD, especially in knees with varus deformity>10°, may increase the risk of limbs being placed in varus>3° postoperatively and may affect long-term clinical and implant survival outcomes, UKR in such knees should be performed with caution

Summary sentence. The bowing of the femur defines a curvature plane to which the proximal and distal femoral anatomic landmarks have a predictable interrelationship. This plane can be a helpful adjunct for computer navigation to define the pre-operative, non-diseased anatomy of the femur and more particularly the rotational alignment of the femoral component in total knee arthroplasty (TKA). Background and aims. There is very limited knowledge with regards to the sagittal curvature -or bowing- of the femur. It was our aim (1) to determine the most accurate assessment technique to define the femoral bowing, (2) to define the relationships of the curvature plane relative to proximal and distal anatomic landmarks and (3) to assess the position of femoral components of a TKA relative to the femoral bowing. Materials and methods. Four independent algorithms were developed and tested on 3D models of 18 cadaveric femora. A sensitivity study showed that a bisector-based method supplied the most stable results. In order to verify if the curvature plane can be used for TKA alignment, the anteversion angle was determined relative to this plane and compared with anteversion angles defined using the coronal plane. Results. The average curvature of the cadaveric femora was 895.85 mm (SD = 184.53 mm). The mean anteversion angle calculated along the projected mechanical or anatomical axis in the coronal plane were 8.2+/−5.2° and 7.6+/− 4.8°. These angles calculated along the projected mechanical or anatomical axis in the curvature plane were 8.2+/−5.2° and 5.2+/−4.8° respectively (p>0.05). Assessment of the component placement relative to the mechanical axis showed that in the coronal plane, an average deviation of 1.84° was measured. In the sagital plane, the average deviation from the mechanical axis was 2.01°. The components were placed in 1 to 2° of extension relative to the femoral bowing. Discussion. A new and stable algorithm was successfully developed to determine the curvature of the femoral shaft. This curvature was comparable to 2 previously reported curvatures. Our study also demonstrates a predictable interrelationship between the femoral shaft curvature on one side and the rotation of the distal femur on the other side. This finding is of great interest in view of a recent trend amongst knee surgeons to aim at anatomical restoration of the patient's original anatomy. Patient matched cutting blocks as well as patient specific implants are today increasingly considered in daily practice in an attempt to restore the patient's natural anatomy and biomechanics. Computational methods to reverse engineer the pre-diseased status of the knee joint regarding its anatomy and orientation are therefore of great importance. The findings from our study suggest that the femoral shaft's curvature is a helpful adjunct to this. Furthermore, abnormal rotational alignment of an axially malaligned component can be assessed accurately with this new reference plane. However, further research on implementing this algorithm and this plane into clinical practice is mandatory. However, further research on implementing this into clinical practice is required

Traditional instrumentation relies on rigid IM rods to determine the distal femoral resection which influences size and orientation of the femoral component. Anterior femoral bowing may unexpectedly affect implant sizing. The purpose of this study was to determine the sensitivity of a flexible rod to the femoral anterior bow versus a traditional rod. A database of 93 Asian bone models from CT images was utilized. The bones were subdivided into those having proximal third, distal third, or overall femoral bows. Only the latter group was selected for further analysis, which consisted of 54 with an average bow of 98cm (±20cm). The rigid and flexible rods were placed iteratively so that the proximal portion of the rod touched the anterior cortical-cancellous boundary and no portion of the rod protruded through that boundary. The flexible rod was allowed to flex, as a substantially thin central portion flexes exclusively in the sagittal plane. The relative angle difference between the position of the flexible and rigid rod were calculated. Three femura were chosen from the subset with bows of 123cm, 100cm and 78cm. The femura showed differences between the rigid and flexible rod of 7.5°, 4.5° while no significant angle measured for the smallest bow. Implants were virtually assembled onto the bones and the greatest bowed femur's component reduced one size from the rigid to the flexible rod orientation. The results of this study show that higher bowed femura yielded larger angular deviations between rigid and flexible rods. For higher bowed femura, the flexible rod allows smaller components to be implanted. The flexible rod serves the same purpose as a conventional rod by defining the distal valgus orientation but allows component orientation in the sagittal plane closer to the femoral bow

The evaluation of the middle term behaviour of the Wagner-type stems in dysplastic femurs and the presentation of the technical and surgical differences with the implantation of a Wagner stem. Between 1997 and 2008 we implanted 64 Wagner stems in 58 patients. Average age at the time of implantation was 64 years. 52 patients was operated because of DDH, and 12 had had previous osteotomy. All patients were prospectively evaluated radiographically and clinically at annual intervals. Functional outcome was assessed with Harris Hip Score and Oxford Score. Mean follow-up of these series was 4 years (11-1)One stem was revised because of fracture of the lesser trochander and two more patients were re-operated for open reduction. With the re-operation as end-point and 95% Confidence Interval survivorship rate was 98, 5%. There were no progressive radiolucent lines. Stem migration was at an average 2mm (1–6) during the first two years and remained stable thereafter. There was no deep infection in these series. After the second year a dense zone is evident in all Gruen zones at the implant –bone interface with a width of 2–3 mm. Dysplasia of the proximal femur may pose significant technical problems during THA due to the distortion of the geometry and the narrowing of the femoral canal. The sort, conical Wagner type stems can offer a very good alternative is such patients. They allow control of the anteversion and they are able get a good press-fit despite the metaphyseal/diaphyseal mismatch and the femoral bowing. Wagner type stems are a reliable alternative when performing THA in patients with dysplastic femurs

Aim: The evaluation of the middle term behaviour of the Wagner-type stems in dysplastic femurs and the presentation of the technical and surgical differences with the implantation of a Wagner stem. Materials and Methods: Between 1997 and 2008 we implanted 64 Wagner stems in 58 patients. Average age at the time of implantation was 64 years. 52 patients was operated because of DDH, and 12 had had previous osteotomy. All patients were prospectively evaluated radiographically and clinically at annual intervals. Functional outcome was assessed with Harris Hip Score and Oxford Score. Results: Mean follow-up of these series was 4 years (11-1)One stem was revised because of fracture of the lesser trochander and two more patients were re-operated for open reduction. With the re-operation as end-point and 95% Confidence Interval survivorship rate was 98, 5%. There were no progressive radiolucent lines. Stem migration was at an average 2mm (1–6) during the first two years and remained stable thereafter. There was no deep infection in these series. After the second year a dense zone is evident in all Gruen zones at the implant –bone interface with a width of 2–3 mm. Discussion: Dysplasia of the proximal femur may pose significant technical problems during THA due to the distortion of the geometry and the narrowing of the femoral canal. The sort, conical Wagner type stems can offer a very good alternative is such patients. They allow control of the anteversion and they are able get a good press-fit despite the metaphyseal/diaphyseal mismatch and the femoral bowing. Conclusions: Wagner type stems are a reliable alternative when performing THA in patients with dysplastic femurs

Despite the well-documented improvement in coronal alignment achieved by computer assisted navigation, varying results have been reported for sagittal alignment. Current navigation systems rely on a sagittal femoral mechanical axis identified by the navigation system, but little information is available on the relationship between the sagittal mechanical axis and anatomical axes for intra-operative or postoperative radiographic assessments. We asked whether deviations exist between sagittal femoral mechanical axis and anatomical axes and attempted to identify predictors of the deviations found. In 100 consecutive patients (200 knees) undergoing TKA, angles between two anatomical axes (the anterior cortical line and mid-medullary line) and two sagittal mechanical axes identified by current navigation systems were measured as proxies of the deviations between them on true lateral radiographs of the whole femur. Correlation analyses and multivariate regression were carried out to identify predictors of deviations. Significant deviations existed with wide ranges between the anatomical axes and the sagittal mechanical axes. Degree of femoral bowing and femoral length were found to be predictors of deviations between sagittal femoral mechanical axes and anatomical axes. This study suggests that surgeons applying navigation technology to TKA need to consider deviations between the sagittal femoral mechanical axes and anatomical axes when they intend to place a femoral component at a target sagittal orientation with respect to an anatomical reference

Computer navigation has been advocated as a means to improve limb and component alignment and reduce the number of outliers after total knee arthroplasty (TKA). We aimed to determine the alignment outcomes of 1500 consecutive computer-assisted TKAs performed by a single surgeon, using the same implant, with a minimum 1 year follow-up, and to analyze the outliers. Based on radiographic analysis, 112 limbs (7.5%) in 109 patients with mechanical axis malalignment of > 3° were identified and analyzed. The indication for TKA was osteoarthritis in 107 patients and rheumatoid arthritis in 2 patients. Fifty-eight patients (53%) had undergone simultaneous bilateral TKA and 13 patients (12%) had a BMI >30. Preoperative varus deformity was seen in 100 limbs and valgus deformity in 12 limbs. Thirty limbs (27%) had an extra-articular deformity (2 post HTO limbs, 3 malunited fractures, 1 stress fracture, 21 severe femoral bowing and 3 tibial bowing) and 21 limbs (19%) had severe lateral laxity or subluxation. Thirty-eight limbs (34%) had a preoperative deformity of =10° and 24 limbs (21.5%) had varus or valgus deformity of >20°. Postoperatively, 11 limbs were malaligned at ±3°, 74 limbs at ±4°, 22 limbs at ±5°, 2 limbs at ±6°, and 2 limbs at ±7°. Coronal plane malalignment of > ±3° of the femoral component was seen in 28 limbs, tibial component in 32 limbs, and both femoral and tibial components in 13 limbs. Twenty-six limbs with preoperative varus deformity had a postoperative valgus alignment of >183° and 3 limbs with valgus deformity had a postoperative varus alignment of <177°. The incidence of outliers for postoperative limb alignment was low at 7.5% with the tibial component showing a higher incidence of coronal malalignment. Malalignment may be more common in cases of simultaneous bilateral procedures, preoperative limb alignment of =10°, limbs with extra-articular deformities and severe lateral instability. There was a tendency towards over-correction of the hip-knee-ankle axis in both varus- and valgus-deformed knees. Further detailed statistical analysis of the data will be presented. This is the largest single-surgeon series of consecutive navigated TKAs and consequently the largest analysis of outliers that highlights which knees are likely to fall outside the +3 degrees of acceptable alignment and which therefore behoove the surgeon to exercise greater caution

Background Computer navigation is increasingly being recognized as a valuable tool in restoring the mechanical axis post TKR. Its use is as yet not universal due to the costs involved, its availability and the fact that it can be cumbersome and time consuming to use. Additionally it requires the insertion of Schanz pins in the femur as well as the tibia which can be a matter of concern as regards stress fracture and infection. However, it is able to reliably locate the center of the femoral head which is an elusive landmark in the standard method. The center of the ankle involves registration for the medial and lateral malleoli which are subcutaneous and easily palpable. We decided to navigate only the distal femoral cut with a specialized navigation unit called Articular Surface Mounted navigation which does not require the insertion of additional pins through the femur or the tibia. We purposely did not use navigation for the rest of the bony cuts as all the other landmarks i.e. femoral epicondyles, tibial malleoli, and tuberosity etc are all easily palpable. This dramatically reduced the surgical time and increased its user friendliness. We are presenting our results. Aim. To analyse the radiographic results obtained with selective femoral navigation and compare with. standard navigational results from the literature. Non-navigated Knees form personal series. Materials and Methods. We have utilized the ASM navigation for distal femoral cut in 112 knees and obtained long X-rays (scanograms) and routine knee X-rays (AP, Lateral and skyline) to study the mechanical axis and component positioning. We measured the mechanical axis deviation, femoral and tibial angle on AP and lateral films and patellar tilt or subluxation on post-operative X-rays by a digital imaging programme called Image–J. (As suggested by the Knee Society roentgenographic Score). We have compared our results with other navigated series from literature and our own series of non-navigated knees. (113 knees) We also noted the surgical time to perform the operation and the occurrence of any complications. Results. Selective femoral navigation is able to restore the mechanical axis as reliably as other methods of navigation and more reliably than non-navigated knees. On an average, it adds less than 10 minutes to surgical time. Femoral angle, tibial angle patellar tilt and subluxation are similar in both navigated and non-navigated series. Navigation use was not associated with any increased complications and no complication could be ascribed to its use. Selective femoral navigation reduced the outliers in mechanical axis restoration when compared with standard femoral intrameduallry instrumentation. Discussion. Selective distal femoral navigation is a reliable tool in restoring mechanical axis post TKR. It is particularly valuable in knees that have pronounced femoral bowing

Aims

We aimed to assess the reliability and validity of OpenPose, a posture estimation algorithm, for measurement of knee range of motion after total knee arthroplasty (TKA), in comparison to radiography and goniometry.

Aims

The Coronal Plane Alignment of the Knee (CPAK) classification is a simple and comprehensive system for predicting pre-arthritic knee alignment. However, when the CPAK classification is applied in the Asian population, which is characterized by more varus and wider distribution in lower limb alignment, modifications in the boundaries of arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) should be considered. The purposes of this study were as follows: first, to propose a modified CPAK classification based on the actual joint line obliquity (aJLO) and wider range of aHKA in the Asian population; second, to test this classification in a cohort of Asians with healthy knees; third, to propose individualized alignment targets for different CPAK types in kinematically aligned (KA) total knee arthroplasty (TKA).

Aims

The processes linking long-term bisphosphonate treatment to atypical fracture remain elusive. To establish a means of exploring this link, we have examined how long-term bisphosphonate treatment with prior ovariectomy modifies femur fracture behaviour and tibia mass and shape in murine bones.

Objective

Cement thickness of at least 2 mm is generally associated with more favorable results for the femoral component in cemented hip arthroplasty. However, French-designed stems have shown favorable outcomes even with thin cement mantle. The biomechanical behaviors of a French stem, Charnley-Marcel-Kerboull (CMK) and cement were researched in this study.

Primary total knee arthroplasty (TKA) is a reliable procedure with reproducible long-term results. Nevertheless, there are conditions related to the type of patient or local conditions of the knee that can make it a difficult procedure. The most common scenarios that make it difficult are discussed in this review. These include patients with many previous operations and incisions, and those with severe coronal deformities, genu recurvatum, a stiff knee, extra-articular deformities and those who have previously undergone osteotomy around the knee and those with chronic dislocation of the patella.

Each condition is analysed according to the characteristics of the patient, the pre-operative planning and the reported outcomes.

When approaching the difficult primary TKA surgeons should use a systematic approach, which begins with the review of the existing literature for each specific clinical situation.

Cite this article: Bone Joint J 2015;97-B(10 Suppl A):30–9.