Introduction: Patellofemoral complications are one of the major causes for revision surgery. In the prosthetic knee, the main determinant within the patellofemoral mechanism is said to be the design of the groove (Kulkarni et al., 2000). Other studies characterising the native trochlear groove used indirect methods such as photography, plain radiographs and measurements using probes and micrometer. The aim of this study was to define the 3-dimensional geometry of the femoral trochlear groove. We used CT scans to describe the geometry of the trochlear groove and its relationship to the tibiofemoral joint in terms of angles and distances. Materials and Methods: CT scans of 45 normal femurs were analysed using custom designed imaging software. This enabled us to convert the scans to 3D and measure distances and angles. The flexion axis of the tibiofemoral joint was found to be a line connecting the centres of the spheres fitted to posterior femoral condyles. These two centres and the femoral head centre form a frame of reference for reproducible femoral alignment. The trochlear geometry was defined by fitting circles to cross sectional images and spheres to 3D surfaces. Axes were constructed through these centres. The deepest points on the trochlear groove were identified using quad images and Hounsfield units. After aligning the femur using different axes, the location of the groove was examined in relation to the mid plane between the centres of flexion of the condyles. Results: The deepest points on the trochlear groove can be fitted to a circle with a radius of 23mm (S.D. 4mm) and an R.M.S error of 0.3mm. The groove is positioned laterally (especially in its mid portion) in relation to the femoral mechanical and anatomical axes. It was also lateral to the perpendicular bisect of the transcondylar axes. After aligning the anatomical axis in screen the trochlear groove can be described on average to be linear with less than 2 mm medial/lateral translation. In the sagital view, the centre of the circle is offset by 21mm (S.D.3mm) at an angle of 67° (S.D. 7°) from a line connecting the midpoint between the centres of the femoral condyles and the femoral head centre. On either end of this line, the articular surface of the trochlea can be fitted to spheres of radius 30mm (S.D. 6mm) laterally and 27mm (S.D. 5mm) medially, with an rms of 0.4mm. Discussion: The location and configuration of the inter-condylar groove of the distal femur is clinically significant in the mechanics and pathomechanics of the patellofemoral articulation. This investigation has allowed us to characterise the trochlear groove. This can be of use in planning and performing joint reconstruction and have implications for the design of patello-femoral replacements and the rules governing their position

Background. Patellofemoral complications have dwindled with contemporary total knee designs that market anatomic trochlear grooves that intend to preserve normal patella kinematics. While most reports of patellofemoral complications address patella and its replacement approach, they do not focus on shape of trochlear grooves in different prostheses [1]. The purpose of this study was to characterize 3D geometry of trochlear grooves of contemporary total knee designs (NexGen, Genesis II, Logic, and Attune) defined in terms of sulcus angle and medial-lateral offset with respect to midline of femoral component in coronal view and to compare to those of native femurs derived from 20 osteoarthritic patient CT scans. Materials and Methods. Using 3D models of each implant and native femur, sulcus location and orientation were obtained by fitting a spline to connect sulcus points marked at 90°, 105°, 130°, and 145° of femoral flexion (Fig A). Implant reference plane orientations were established using inner facets of distal and posterior flanges. Reference planes of native femurs were defined using protocols developed by Eckhoff et al. [2] where coronal plane was defined using femoral posterior condyles and greater trochanter. In the coronal plane, a best fit line was used to measure sulcus angle and medial-lateral offset with respect to midline at the base of trochlear groove (Fig B). Results. With exception to Logic (0° sulcus angle & 0 mm offset), contemporary knee designs include high valgus angulations (4° to 18°) with laterally-biased offsets (3 to 5 mm). The native sulcus angle on average was slightly valgus, but varied significantly among the cohort (−0.2° ± 4.6°). Native trochlear groove offset was biased laterally (2.5 ± 1.7 mm). Discussion. We observed a considerable geometric deviation between native femur and implants in terms of sulcus angle while both geometries displayed comparable lateral bias at the base of trochlear groove. Similar to past studies by Iranpour et al. [4] and Feinstein et al. [5], a large variation in sulcus angle was observed among the selected native femurs with an average of small valgus angulation (Fig C). However, most contemporary trochlear grooves are biased towards higher valgus angulations. Retrieval and registry studies have shown that NexGen trochlear groove design (4° sulcus angle) has been shown to better accommodate natural patellas, which highlights that the differences among designs may be significant [5,6]. It remains unclear which features specifically translate to better patellafemoral outcomes, which is a merit for further study. Conflict of Interest: None. Figure A. Sulcus points defined at various flexion angles. Figure B. Best fit line to measure ML-offset and sulcus angle. Figure C. Sulcus angle comparison to past studies. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Total knee arthroplasty (TKA) is widely accepted as a successful surgical intervention to treat osteoarthritis and other degenerative diseases of the knee. However, present statistics on limited survivorship and patient-satisfaction emphasise the need for an optimal endoprosthetic care. Although, the implant design is directly associated with the clinical outcome comprehensive knowledge on the complex relationship between implant design (morphology) and function is still lacking. The goal of this study was to experimentally analyse the relationship between the trochlear groove design of the femoral component (iTotal CR, ConforMIS, Inc., Bedford, MA, USA) and kinematics in an in vitro test setup based on rapid prototyping of polymer-based replica knee implants. The orientation of the trochlear groove was modified in five different variations in a self-developed computational framework. On the basis of the reference design, one was medially tilted (−2°) and four were laterally tilted (+2°, +4°, +6°, +8°). For manufacturing, we used rapid prototyping to produce synthetic replicates made of Acrylnitril-Butadien-Styrol (ABS) and subsequent post-processing with acetone vapor. The morpho-functional analysis of the replicates was performed in our experimental knee simulator. Tibiofemoral and patellofemoral kinematics were recorded with an optical tracking system during a semi-active flexion/extension (∼10° to 90°) motion. Looking at the results, the patellofemoral kinematics, especially the medial/lateral translation and internal/external rotation were mainly affected. During low flexion, the patella had a more laterally position relative to the femur with increasing lateral trochlear orientation. The internal/external rotation initially differentiated and converged with flexion. Regarding the tibiofemoral kinematics, only the tibial internal/external rotation showed notable differences between the modified replica implants. We presented a workflow for an experimental morpho-functional analysis of the knee and demonstrated its feasibility on the example of the trochlear groove orientation which might be used in the future for comprehensive implant design parameter optimisation, especially in terms of image based computer assisted patient-specific implants

Introduction. Tibial tuberosity and trochlear groove (TT-TG) distance has been investigated for the patients with primary patellofemoral subluxation/dislocation. To date, TT-TG distance after TKA has not been evaluated, and the effect of postoperative TT-TG distance on patellar tracking is unknown. The purpose of the current study was to investigate the effect of TT-TG distance and rotational position of the femoral and tibial components on patellar tilt after TKA. Methods. Consecutive 115 knees for the diagnosis of osteoarthritis were included in the current study. TKA was performed using posterior cruciate ligament sacrificed prosthesis. A total of 17 men and 96 women with an average age of 75.3 years were included at the time of the surgery. Computed tomography (CT) was taken after TKA in full extension. Postoperative TT-TG distance was measured as a reference of surgical epicondylar axis (SEA) of the femur. Patellar tilt was defined as the angle of the patellar component relative to SEA. Femoral and tibial component rotation was measured as the angle relative to SEA and tibial antero-posterior (AP) axis. Tibial AP axis was defined as the line connecting medial one-third of the tibial tuberosity and center of medial-lateral width. Pearson correlation coefficients were calculated to determine the correlations between patellar tilt and TT-TG distance and between patellar tilt and femoral and tibial component rotation. Results. TT-TG distance had significant correlation with patellar tilt (Figure 1; r = 0.254, p = 0.006), whereas femoral component rotation (p = 0.092) and tibial component rotation (p = 0.062) were not correlated with patellar tilt. Concerning the effect on TT-TG distance, femoral component rotation (r = 0.248, p = 0.008) and tibial component rotation (r = −0.567, p < 0.001) were correlated with TT-TG distance. Conclusion. The current study investigated the effect of TT-TG distance on patellar tilt with postoperative CT scan. Greater TT-TG distance resulted in more patellar tilt, which might have negative effects on patellar tracking. In previous clinical studies, femoral component and tibial component rotation affected patellar maltracking. In the current study, however, component rotation itself did not affect patellar tilt. Postoperative TT-TG distance includes information of rotational and medial-lateral positioning of the femoral and tibial components, and can be a useful indicator to predict patellar maltracking after TKA. For any figures or tables, please contact authors directly

Aim

The aim of our study was to assess lateral tracking of the patella with differing designs of Total Knee Arthroplasty (TKA) and compare to that of the native patella.

Recognized anatomic variations that lead to patella instability include patella alta and trochlea dysplasia. Lateralization of the extensor mechanism relative to the trochlea is often considered to be a contributing factor; however, controversy remains as to the degree this contributes to instability and how this should be measured. As the tibial tuberosity-trochlear groove (TT-TG) is one of most common imaging measurements to assess lateralization of the extensor mechanism, it is important to understand its strengths and weaknesses. Care needs to be taken while interpreting the TT-TG value as it is affected by many factors. Medializing tibial tubercle osteotomy is sometimes used to correct the TT-TG, but may not truly address the underlying anatomical problem. This review set out to determine whether the TT-TG distance sufficiently summarizes the pathoanatomy, and if this assists with planning of surgery in patellar instability.

Cite this article: Bone Jt Open 2022;3(3):268–274.

“The shortest distance between two points is a straight line.” This explains many cases of patellar maltracking, when the patellar track is visualised in three dimensions. The three-dimensional view means that rotation of the tibia and femur during flexion and extension, as well as rotational positioning of the tibial and femoral components are extremely important. As the extensor is loaded, the patella tends to “center” itself between the patellar tendon and the quadriceps muscle. The patella is most likely to track in the trochlear groove IF THE GROOVE is situated where the patella is driven by the extensor mechanism: along the shortest track from origin to insertion. Attempts to constrain the patella in the trochlear groove, if it lies outside that track, are usually unsuccessful. Physiologic mechanisms for tibial-femoral rotation that benefit patellar tracking (“screw home” and “asymmetric femoral roll-back”) are not generally reproduced. Practical Point. A patellofemoral radiograph that shows the tibial tubercle, illustrates how the tubercle, and with it the patellar tendon and patella itself, are all in line with the femoral trochlea. To accomplish this with a TKA, the femoral component is best rotated to the transepicondylar axis (TEA) and the tibial component to the tubercle. In this way, when the femoral component sits in its designated location on the tibial polyethylene, the trochlear groove will be ideally situated to “receive” the patella. Knee Mechanics. Six “degrees of freedom” refers to translation and rotation on three axes (x,y,z). This also describes how arthroplasty components can be positioned at surgery. The significant positions of tibial, femoral and patellar components are: 1. Internal-external rotation (around y-axis) and 2. Varus-valgus rotation (around z axis). 3. Medial-lateral translation (on x-axis). The other positional variables are less important for patella tracking. Biomechanical analyses of knee function are often broken down into: i. Extensor power analysis (y-z or sagittal plane) and ii. Tracking (x-y or frontal plane). These must be integrated to include the effects of rotation and to better understand patellar tracking. Effect of Valgus. Frontal plane alignment is important but less likely to reach pathological significance for patellar tracking than rotational malposition clinically. For example if a typical tibia is cut in 5 degrees of unintended mechanical valgus, this will displace the foot about 5 cm laterally but the tibial tubercle only 8 mm laterally. An excessively valgus tibial cut will not displace the tubercle and the patella as far as mal-rotation of the tibial component. Effect of Internal Rotation of Tibial Component. By contrast, internal rotation of the tibial component by 22 degrees, which is only 4 degrees in excess of what has been described as tolerable by Berger and Rubash, displaces the tubercle 14 mm, a distance that would place the center of most patella over the center of the lateral femoral condyle, risking dislocation. Dynamically, as the knee flexes, if the tibia is able to rotate externally this forces the tubercle into an even more lateral position, guaranteeing that the patella will align lateral to the tip of the lateral femoral condyle, and dislocate. The design of femoral components, in particular the varus-valgus angle of the trochlear groove, has an effect on patellar tracking. This effect will be accentuated by the surgical alignment technique of the femoral and tibial components. Component positions that mimic the orientation of the normal anatomy usually include more valgus alignment of the femoral component. This rotates the proximal “entrance” of the femoral trochlear groove more medially, making it more difficult for the patella to descend in the trochlear groove

Aims. To explore the efficacy of extracorporeal shockwave therapy (ESWT) in the treatment of osteochondral defect (OCD), and its effects on the levels of transforming growth factor (TGF)-β, bone morphogenetic protein (BMP)-2, -3, -4, -5, and -7 in terms of cartilage and bone regeneration. Methods. The OCD lesion was created on the trochlear groove of left articular cartilage of femur per rat (40 rats in total). The experimental groups were Sham, OCD, and ESWT (0.25 mJ/mm. 2. , 800 impulses, 4 Hz). The animals were euthanized at 2, 4, 8, and 12 weeks post-treatment, and histopathological analysis, micro-CT scanning, and immunohistochemical staining were performed for the specimens. Results. In the histopathological analysis, the macro-morphological grading scale showed a significant increase, while the histological score and cartilage repair scale of ESWT exhibited a significant decrease compared to OCD at the 8- and 12-week timepoints. At the 12-week follow-up, ESWT exhibited a significant improvement in the volume of damaged bone compared to OCD. Furthermore, immunohistochemistry analysis revealed a significant decrease in type I collagen and a significant increase in type II collagen within the newly formed hyaline cartilage following ESWT, compared to OCD. Finally, SRY-box transcription factor 9 (SOX9), aggrecan, and TGF-β, BMP-2, -3, -4, -5, and -7 were significantly higher in ESWT than in OCD at 12 weeks. Conclusion. ESWT promoted the effect of TGF-β/BMPs, thereby modulating the production of extracellular matrix proteins and transcription factor involved in the regeneration of articular cartilage and subchondral bone in an OCD rat model. Cite this article: Bone Joint Res 2024;13(7):342–352

Introduction. The trochlear groove plays a major role in the mechanics and patho-mechanics of the patellofemoral joint. Our primary goal was to compare normal, osteoarthritic and dysplastic PFJs in terms of angles and distances. Method. Computed tomography scans of 40 normal knees (>55 years old), 9 knees with patellofemoral osteoarthritis (group A) and 12 knees with trochlear dysplasia (group B) were analysed using 3D software. The femurs were orientated using a robust frame of reference. A circle was fitted to the trochlear groove. The novel trochlear axis was defined as a line joining the centres of two spheres fitted to the trochlear surfaces, lateral and medial to the trochlear groove. The relationship between the femoral trochlea and the tibiofemoral joint was measured in term of angles and distances (offsets).T-test for paired samples was used (p<0.05). Results. The normal trochlear groove closely matched a circle (RMS 0.3mm). It was positioned laterally in relation to the mechanical, anatomical, and trans-condylar axes of the femur. It was not co-planar with any of the three axes. After aligning to the new trochlear axis, the trochlear groove appeared more linear than when other axes were used. In comparison to the normal knees; the medial trochlear was smaller in group A (p=0.0003). The lateral trochlear was smaller in group B (p=0.04). The trochlear groove was smaller in groups B (p=0.0003). Both trochlear centres in groups A+B were more centralised (p=0.00002-0.03). The medial trochlear centre was more distal in group A (p=0.03) and the lateral trochlear centre was more distal in group B (p=0.00009). The trochlear groove started more distal in group B (p=0.0007). Discussion. In osteoarthritic and dysplastic patellofemoral joints, the trochlea is both smaller and more distally located in relation to the tibiofemoral joint. These two factors may contribute to excessive loads that lead to early joint wear

A profound understanding of the pathoanatomy of the patellofemoral joint is considered to be fundamental for navigated knee arthroplasty. Previous studies used less sophisticated imaging modalities such as photography and plain radiographs or direct measurement tools like probes and micrometers to define the morphology of the trochlear groove, with differing results. This may be due to the complexity of the biomechanics and the geometry of this joint. Our primary goal was to compare normal, osteoarthritic and dysplastic PFJs in terms of angles and distances. To do this we first had to establish a reliable frame of reference. Computed tomography scans of 40 normal knees (> 55 years old), 9 knees with patellofemoral osteoarthritis (group A) and 12 knees with trochlear dysplasia (group B) were analyzed using 3D software. The femurs were orientated using a robust frame of reference. A circle was fitted to the trochlear groove. The novel trochlear axis was defined as a line joining the centres of two spheres fitted to the trochlear surfaces, lateral and medial to the trochlear groove. The relationship between the femoral trochlea and the tibiofemoral joint was measured in term of angles and distances (offsets). T-test for paired samples was used (p< 0.05). The study was approved by the institutional review conforming to the state laws and regulations. The normal trochlear groove closely matched a circle (RMS 0.3mm). It was positioned laterally in relation to the mechanical, anatomical, and trans-condylar axes of the femur. It was not co-planar with any of the three axes. After aligning to the new trochlear axis, the trochlear groove appeared more linear than when other axes were used. In comparison to the normal knees; the medial trochlear was smaller in group A (p=0.0003)- see figure 2. The lateral trochlear was smaller in group B (p=0.04). The trochlear groove was smaller in groups B (p=0.0003). Both trochlear centers in groups A+B were more centralized (p=0.00002–0.03). The medial trochlear center was more distal in group A (p=0.03) and the lateral trochlear center was more distal in group B (p=0.00009). The trochlear groove started more distal in group B (p=0.0007). A better understanding of the 3-dimensional geometry can help better treat or even prevent the progression of disease to the stage of patellofemoral osteoarthritis. In osteoarthritic and dysplastic patellofemoral joints, the trochlea is both smaller and more distally located along the femur. These two factors may contribute to excessive loads that lead to early joint wear. These differences could have biomechanical implications and give us an insight into why joints fail. The data collected may also help in improving current designs and current navigational and surgical techniques used for the treatment of patellofemoral osteoarthritis

Introduction: Patellofemoral instability (PFI) is a disabling condition that occurs in adolescence. Recurrence after patellar dislocation has been reported in 2–50% of cases. This study aimed to compare the shape of the distal femur in PFI to a normal cohort. Method: 108 CT scans from 54 subjects with PFI were compared to 197 CT scans from 102 normal subjects. Outlines of the trochlear groove and lateral condyle were extracted from CT scans using Interactive Data Language version 5.0 image manipulation software. The shapes were aligned using a modified Procrustes analysis and interpolation performed with a basic cubic spline. A statistical method from the field of functional data analysis was used to quantify shape. A discriminant analysis was then used to provide a tool for deciding which patients had abnormal grooves thus improving patient selection for trochleoplasty. Results: Mathematical quantification showed a significant difference at the 0.001 level using an independent t-test between the normal and PFI groups for the shape of the trochlear groove with PFI knees having a more complex shape than normal. The second largest source of variation is in the position of the trochlear groove minimum with respect to the coronal plane together with variation in the shape of the medial condyle. The trochlear groove is situated more medially, with a shallower medial condyle, in PFI. In contrast the trochlear groove is situated more laterally, with a more prominent medial condyle in normal knees. Analysis of shape of the lateral condyle showed that in PFI, it is shorter and broader. Conclusion: Principal components analysis can be used to quantify the variation in shape of the distal femur and allow a discriminant function analysis to be performed comparing PFI knees to normal knees. This quantification of shape can be applied to diagnosis of instability, operative planning for trochleoplasty and implant design

Aims. The present study investigates the effectiveness of platelet-rich plasma (PRP) gel without adjunct to induce cartilage regeneration in large osteochondral defects in a rabbit model. Methods. A bilateral osteochondral defect was created in the femoral trochlear groove of 14 New Zealand white rabbits. The right knees were filled with PRP gel and the contralateral knees remained untreated and served as control sides. Some animals were killed at week 3 and others at week 12 postoperatively. The joints were harvested and assessed by Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) MRI scoring system, and examined using the International Cartilage Repair Society (ICRS) macroscopic and ICRS histological scoring systems. Additionally, the collagen type II content was evaluated by the immunohistochemical staining. Results. After 12 weeks post-surgery, the defects of the PRP group were repaired by hyaline cartilage-like tissue. However, incomplete cartilage regeneration was observed in the PRP group for three weeks. The control groups showed fibrocartilaginous or fibrous tissue, respectively, at each timepoint. Conclusion. Our study proved that the use of PRP gel without any adjuncts could successfully produce a good healing response and resurface the osteochondral defect with a better quality of cartilage in a rabbit model. Cite this article: Bone Joint Res 2021;10(3):192–202

BACKGROUND. Conventional TKA surgery attempts to restore patients to a neutral alignment, and devices are designed with this in mind. Neutral alignment may not be natural for many patients, and may cause dissatisfaction [1]. To solve this, kinematical alignment (KA) attempts to restore the native pre-arthritic joint-line of the knee, with the goal of improving knee kinematics and therefore patient's function and satisfaction [1]. Proper prosthetic trochlea alignment is important to prevent patella complications such as instability or loosening. However, available TKA components have been designed for mechanical implantation, and concerns remain relating the orientation of the prosthetic trochlea when implants are kinematically positioned. The goal of this study is to investigate how a currently available femoral component restores the native trochlear geometry of healthy knees when virtually placed in kinematic alignment. METHODS. The healthy knee OAI (Osteoarthritis Initiative) MRI dataset was used. 36 MRI scans of healthy knees were segmented to produce models of the bone and cartilage surfaces of the distal femur. A set of commercially available femoral components was laser scanned. Custom 3D planning software aligned these components with the anatomical models: distal and posterior condyle surfaces of implants were coincident with distal and posterior condyle surfaces of the cartilage; the anterior flange of the implant sat on the anterior cortex; the largest implant that fitted with minimal overhang was used, performing ‘virtual surgery’ on healthy subjects. Software developed in-house fitted circles to the deepest points in the trochlear grooves of the implant and the cartilage. The centre of the cartilage trochlear circle was found and planes, rotated from horizontal (0%, approximately cutting through the proximal trochlea) through to vertical (100%, cutting through the distal trochlea) rotated around this, with the axis of rotation parallel to the flexion facet axis. These planes cut through the trochlea allowing comparison of cartilage and implant surfaces at 1 degree increments - (fig.1). Trochlear groove geometry was quantified with (1) groove radial distance from centre of rotation cylinder (2) medial facet radial distance (3) lateral facet radial distance and (4) sulcus angle, along the length of the trochlea. Data were normalised to the mean trochlear radius. The orientation of the groove was measured in the coronal and axial plane relative to the flexion facet axis. Inter- and intra-observer reliability was measured. RESULTS. In the coronal plane, the implant trochlear groove was oriented a mean of 8.7° more valgus (p<0.001) than the normal trochlea. The lateral facet was understuffed most at the proximal groove between 0–60% by a mean of 5.3 mm (p<0.001). The medial facet was understuffed by a mean of 4.4 mm between 0–60% (p<0.001) - (fig.2). CONCLUSIONS. Despite attempts to design femoral components with a more anatomical trochlea, there is significant understuffing of the trochlea, which could lead to reduced extensor moment of the quadriceps and contribute to patient dissatisfaction

Conventional TKA surgery attempts to restore patients to a neutral alignment, and devices are designed with this in mind. Neutral alignment may not be natural for many patients, and may cause dissatisfaction. To solve this, kinematical alignment (KA) attempts to restore the native pre-arthritic joint-line of the knee, with the goal of improving knee kinematics and therefore patient's function and satisfaction. Proper prosthetic trochlea alignment is important to prevent patella complications such as instability or loosening. However, available TKA components have been designed for mechanical implantation, and concerns remain relating the orientation of the prosthetic trochlea when implants are kinematically positioned. The goal of this study is to investigate how a currently available femoral component restores the native trochlear geometry of healthy knees when virtually placed in kinematic alignment. The healthy knee OAI (Osteoarthritis Initiative) MRI dataset was used. 36 MRI scans of healthy knees were segmented to produce models of the bone and cartilage surfaces of the distal femur. A set of commercially available femoral components was laser scanned. Custom 3D planning software aligned these components with the anatomical models: distal and posterior condyle surfaces of implants were coincident with distal and posterior condyle surfaces of the cartilage; the anterior flange of the implant sat on the anterior cortex; the largest implant that fitted with minimal overhang was used, performing ‘virtual surgery’ on healthy subjects. Software developed in-house fitted circles to the deepest points in the trochlear grooves of the implant and the cartilage. The centre of the cartilage trochlear circle was found and planes, rotated from horizontal (0%, approximately cutting through the proximal trochlea) through to vertical (100%, cutting through the distal trochlea) rotated around this, with the axis of rotation parallel to the flexion facet axis. These planes cut through the trochlea allowing comparison of cartilage and implant surfaces at 1 degree increments. Trochlear groove geometry was quantified with (1) groove radial distance from centre of rotation cylinder (2) medial facet radial distance (3) lateral facet radial distance and (4) sulcus angle, along the length of the trochlea. Data were normalised to the mean trochlear radius. The orientation of the groove was measured in the coronal and axial plane relative to the flexion facet axis. Inter- and intra-observer reliability was measured. In the coronal plane, the implant trochlear groove was oriented a mean of 8.7° more valgus (p<0.001) than the normal trochlea. The lateral facet was understuffed most at the proximal groove between 0–60% by a mean of 5.3 mm (p<0.001). The medial facet was understuffed by a mean of 4.4 mm between 0–60% (p<0.001). Despite attempts to design femoral components with a more anatomical trochlea, there is significant understuffing of the trochlea, which could lead to reduced extensor moment of the quadriceps and contribute to patient dissatisfaction

Abnormal patella height has been found to be one of the main reasons for abnormal contact between patella and trochlear groove leading to patellar instability in children. Many methods have been described to diagnose patellar instability but most of them are justified only in adults. The reason being incomplete ossification in the paediatric population. These methods have been divided into direct and indirect methods. We analysed the MRI scan of knee of 57 children between 12–14 years of age with no previous diagnosis of patellar instability. Patients with a diagnosis of patellar instability, previous surgery on the knee or trauma and poor MRI scan were excluded from the study. We used Insall -Salvati Index (ISI), Caton-Deschamp Index (CDI) and Patella-Trochlear Index (PTI) and compared the results. We found that 40% of measurements by CDI and 41% by ISI showed patella alta in patients with normal patella height. 10% of patients in PTI readings had value suggestive of abnormal patella height. We concluded that PTI is a more reliable index to be used in children as it uses the length of articular surface and does not rely on bony landmarks. Studies done show PTI is a more reliable and accurate method of measuring patella height

INTRODUCTION. Over the past 40 years of knee arthroplasty, significant advances have been made in the design of knee implants, resulting in high patient satisfaction. Patellar tracking has been central to improving the patient experience, with modern designs including an optimized Q-angle, deepened trochlear groove, and thin anterior flange.[1–4] Though many of today's femoral components are specific for the left and right sides, Total Joint Orthopedics’ (TJO) Klassic® Knee System features a universal design to achieve operating room efficiencies while providing all the advancements of a modern knee. The Klassic Femur achieves this through a patented double Q-angle to provide excellent patellar tracking whether implanted in the left or the right knee (Figure 1). The present study examines a prospective cohort of 145 consecutive TKA's performed using a modern universal femur and considers patients’ pre- and post-operative Knee Society Clinical Rating System score (KSS). METHODS AND MATERIALS. 145 primary total knee arthroplasties (TKA) were performed during the study using a measured resection technique with a slope-matching tibial cut for all patients. The posterior cruciate ligament (PCL) was sacrificed to accommodate an ultra-congruent polyethylene insert. The distal femur was cut at five degrees (5°) valgus; the tibia was resected neutral (0°) alignment for valgus legs and in two degrees (2°) of varus for varus alignment. The patella was resurfaced for all patients. Patients were followed annually for up to 46 months and were evaluated using the KSS score on a 200-point scale. RESULTS. The final study group comprised 127 primary TKAs. The average age was 68 years (51–90) with 45 males and 68 females. The average weight was 110kg (range: 75–151kg) for men and 88kg (range: 50–129kg) for women. One patient deceased during the follow-up period, four required manipulation under anesthesia, and two required revision for periprosthetic joint infection. There were no failures due to patellar maltracking. No special soft tissue releases were required in any patient. Average pre-operative knee score was 107, improving to 182 at average follow-up of 41 months (36–46 months). Results are summarized in Table 1. DISCUSSION. The improvement in patient clinical experience demonstrates that a universal femoral design can achieve excellent results if it incorporates modern technologies. A double Q-angle design with a deepened trochlear groove and a thin anterior flange appears to provide excellent patellar tracking for all patients in this cohort. This study is limited to the experience of a single institution. Further study would improve the extensibility of these findings. It does show, however, that a femur using a universal design with modern patellar tracking can improve patient satisfaction with their knee following TKA. For any figures or tables, please contact the authors directly

The clinical success of osteochondral autografts is heavily reliant on their mechanical stability, as grafts which protrude above or subside below the native cartilage can have a negative effect on the tribological properties of the joint [1]. Furthermore, high insertion forces have previously been shown to reduce chondrocyte viability [2]. Commercial grafting kits may include a dilation tool to increase the diameter of the recipient site prior to insertion. The aim of this study was to evaluate the influence of dilation on the primary stability of autografts. Six human cadaveric femurs were studied. For each femur, four 8.5 × 8mm autografts were harvested from the trochlear groove and implanted into the femoral condyles using a Smith & Nephew Osteochondral grafting kit. Two grafts were implanted into dilated recipient sites (n=12) and two were implanted with no dilation (n=12). Insertion force was measured by partially inserting the graft and applying a load at a rate of 1 mm/min, until the graft was flush with the surrounding cartilage. Push-in force was measured by applying the same load, until the graft had subsided 4mm below congruency. Significance was taken as (p<0.05). Average maximum insertion force of dilated grafts was significantly lower (p<0.001) than their non-dilated equivalent [28.2N & 176.7N respectively]. There was no significant difference between average maximum push-in force between the dilated and non-dilated groups [1062.8N & 1204.2N respectively]. This study demonstrated that significantly less force is required to insert dilated autografts, potentially minimising loss of chondrocyte viability. However, once inserted, the force required to displace the grafts below congruency remained similar, indicating a similar degree of graft stability between both groups

A risk factor for patellofemoral instability is trochlear dysplasia. Trochleoplasty is a surgical procedure used to reshape the trochlear groove to improve patellar stability. This study seeks to compare pre-op MRI measurements and post operative MRI measurements for patients who have undergone trochleoplasty in correlation with their clinical outcomes scores. Data was collected from a database of patients known to have trochlear dysplasia who underwent trochleoplasty. Radiological Data was collected pre-op and subsequent post op MRI data collected included TT-TG, Patella Tilt, IS, sulcus angle. Data score sheets pre-op and post op trochleoplasty completed by patients were also collected. 10 patients had pre and post op MRI's documented. 80%(8/10) females and 20%(2/10) males, average age of 30 years old (range 23 – 32 years old). Average MRI pre-op scores: IS ratio: 1.2, Patella tilt: 24.14, sulcus angle 160.13, and TT-TG distance of 16.94. 1 year average MRI post-op scores: IS ratio: 1.28, Patella tilt 15.56, sulcus angle 148.66 and TT-TG distance 16.78. 1 year post op Kujala and Norwich instability scores patient reported improved stability, function and confidence post op compared to pre-op. Subjective and objective scores reflected an improvement of stability. MRI demonstrated a deeper trochlear groove post-operatively which should provide resistance against lateral patella movement and patellar dislocations. TT-TG pre and post op remained constant. Pre op and post op Kujala scores reflected improved function. The Norwich instability scores pre and post op reflected satisfaction of treatment. There are not a lot of studies published on trochleoplasty. Based on this study it is clear that patients with patellofemoral instability with severe trochlear dysplasia will benefit from trochleoplasty. The sample size of the data analysis was only 10. However it reflected that function 1 year post procedure remained stable

Introduction. The ACTIVE(Advanced Cartilage Treatment with Injectable-hydrogel Validation of the Effect) study investigates safety and performance of a novel dextran-tyramine hydrogel implant for treatment of small cartilage defects in the knee (0.5-2.0cm2). The hydrogel is composed of a mixture of natural polymer conjugates that are mixed intra-operatively and which cross-link in situ through a mild enzymatic reaction, providing a cell-free scaffold for cartilage repair. Method. The ACTIVE study is split into a safety (n=10) and a performance cohort (n=36). The Knee Injury and Osteoarthritis Outcome Score (KOOS), pain (numeric rating scale, NRS), Short-Form Health Survey (SF-36) were compared at baseline and 3, 6, and 12 months after surgery. The primary performance hypothesis is an average change in the KOOS from baseline to 12 months (ΔKOOS) greater than a minimal clinically important change (MIC) of 10. No statistical tests were performed as these are preliminary data on a smaller portion of the total study. Result. All patients of the safety cohort (n=10, mean age±SD, 30±9 years) were treated with the hydrogel for a symptomatic (NRS≥4) cartilage defect on the femoral condyle or trochlear groove (mean size±SD, 1.2±0.4cm2). No signs of an adverse foreign tissue reaction or serious adverse events were recorded within the safety cohort. At final follow-up mean KOOS±SD was 66.9±23.5, mean NRS resting±SD was 1.3±1.9, NRS activity±SD was 3.8±2.9 and mean SF-36±SD was 72.0±10.9. ΔKOOS was 21. One patient sustained new knee trauma prior to final follow-up, affecting final scores considerably. When excluded, ΔKOOS was 24(n=9). Conclusion. These promising initial findings provide a solid basis for continuation and expansion of this unique cartilage treatment. The MIC of 10 was surpassed. Though, results should be interpreted cautiously as they are based solely on preliminary data of the first 10 patients. Acknowledgements. Study is sponsored by Hy2Care, producer of the CartRevive®(dextran-tyramine) Hydrogel implant

Placing total knee components in the proper position in all three planes (frontal, sagittal and transverse) is important for correct functioning of the arthroplasty. Appropriate position for the femoral component is parallel to and equidistant from the “average flexion extension axis” of the knee. An axis drawn from one epicondyle to the other is an appropriate approximation for the average flexion-extension axis of the knee. Surgeons have experienced problems, however, finding the epicondyles with certainty making this set of landmarks difficult to use. A line down the trochlear groove (AP axis – most often attributed to Whiteside, sulcus axis, Eckhoff)) usually intersects the TEA at right angles. Using both the palpated epicondyles and the AP axis should make finding the proper position easier, but still there is a need for instrumentation that can readily and reproducibly find the correct position of the flexionextension axis. Kinematic work (Blaha, Simons et al.; Eckhoff et al.) has confirmed that the average flexion-extension axis of the human knee, for the majority of the flexionextension arc, is very nearly parallel to the TEA though slightly displaced from it. The knee joint then moves in a plane perpendicular to the flexion-extension axis. This functional plane is neither coincident with the anatomic axis (i.e., shafts of the bones) nor the mechanical axis (i.e., femoral head – center knee – center ankle). Rather the plane intersects four critical functional points: the lateral border of the acetabulum (origin of the rectus femoris muscle), the trochlear groove, the tibial tubercle, and the neck of the talus. These points now define a different axis for the knee joint: the functional axis. Finding the functional axis will appropriately position the components of a total knee replacement so that the axis of the replaced knee matches that of the native knee. The AP clamp attaches to the femur at the most posterior- superior part of the intercondylar notch. *. with an acutely curved portion and to the trochlear groove with a more gently curved portion. Tests in our laboratory have determined that the clamp finds the functional plane (and thus the functional axis) with less than 1° of variability. A line drawn perpendicular to the clamp parallels the flexion-extension axis of the knee and is thus the proper rotational axis (transverse plane) of the femoral component as well as varus-valgus axis (coronal plane). The clamp has been used in both cadaver and live operating situations and has been found to correctly determine not just the rotational position of the components but also the position in the frontal plane. Clinical experience with the clamp has confirmed that when a total knee prosthesis is placed in the proper position relative to the flexion-extension axis the limb will have correct alignment, stability and kinematics. *. Having not found a specific name for this part of the femur the name suggested by S.A. White is used: the intercondylar shelf