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Orthopaedic Proceedings
Vol. 104-B, Issue SUPP_7 | Pages 35 - 35
1 Jul 2022
Bua N Kwok M Wignadasan W Iranpour F Subramanian P
Full Access

Abstract

Background

The incidence of periprosthetic fractures of the femur around a total knee arthroplasty (TKA) is rising and this is owed to the increased longevity that today's TKA implants allow for, as well as an aging population. These injuries are significant as they are related to increased morbidity and mortality.

Methods

We retrospectively reviewed all periprosthetic fractures around a TKA that presented to our NHS Trust between 2011 to 2020. Medical records were reviewed. Treatment, complications and mortality were noted.


Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_11 | Pages 14 - 14
1 Dec 2020
Haider Z Iranpour F Subramanian P
Full Access

The number of total knee arthroplasties continues to increase annually with over 90,000 total knee replacements performed in the United Kingdom in 2018. Multiple national bodies including the British Association for Surgery of the Knee (BASK) and the British Orthopaedic Association collaborated in July 2019 to produce best practice guidance for knee arthroplasty surgery. This study aims to review practice in a regional healthcare trust against these guidelines.

Fifty total knee replacement operation notes were reviewed between January and February 2020 from 11 different consultant orthopaedic surgeons. Documents were assessed against 17 criteria recommended by the BASK guidance. Personnel names and grades were generally well documented. Tourniquet time and pressure were documented in over 98% of operation notes however, protection from spirit burns was not documented at all. Trialling and soft tissue balancing was well recorded in 100% and 96% of operation notes respectively.

Areas lacking in documentation included methods utilised to optimise cementation technique and removal of cement debris. Protection of key knee structures was documented in only 56% of operation notes clearly. Prior to closure, final assessment of mechanism integrity, collateral ligament was not documented at all and final ROM after implantation of components was recorded 34% of the time.

Subsequently authors have created a universal operation note template, uploaded onto the patient electronic notes, which prompts surgeons to complete documentation of the relevant criteria advocated by BASK.

In conclusion, detailed and systematic documentation is vital to prevent adverse events and reduce the risk of litigation. By producing detailed operative templates this risk can be mitigated.


Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_11 | Pages 15 - 15
1 Dec 2020
Haider Z Aweid B Subramanian P Iranpour F
Full Access

Telemedicine is the delivery of healthcare from a remote location using integrated computer/communication technology. This systematic review aims to explore evidence for telemedicine in orthopaedics to determine its advantages, validity, effectiveness and utilisation particularly during our current pandemic where patient contact is limited.

Databases of PubMed, Scopus and CINHAL were systematically searched and articles were included if they involved any form of telephone or video consultation in an orthopaedic population. Findings were synthesised into four themes: patient/clinician satisfaction, accuracy and validity of examination, safety and patient outcomes and cost effectiveness. Quality assessment was undertaken using Cochrane and Joanna Briggs Institute appraisal tools.

Twenty studies were included consisting of nine RCTs across numerous orthopaedic subspecialties including fracture care, elective orthopaedics and oncology. Studies revealed high patient satisfaction with telemedicine for convenience, less waiting and travelling time. Telemedicine was cost effective particularly if patients had to travel long distances, required hospital transport or time off work. No clinically significant differences were found in patient examination nor measurement of patient reported outcome measures. Telemedicine was reported to be a safe method of consultation. However, studies were of variable methodological quality with selection bias.

In conclusion, evidence suggests that telemedicine in orthopaedics can be safe, cost effective, valid in clinical assessment with high patient/clinician satisfaction. Further work with high quality RCTs is required to elucidate long term outcomes. This systematic review presents up-to-date evidence on the use of telemedicine and provides data for organisations considering its use in the current COVID-19 pandemic and beyond.


Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_1 | Pages 36 - 36
1 Feb 2020
Aframian A Auvinet E Iranpour F Barker T Barrett D
Full Access

Introduction

Gait analysis systems have enjoyed increasing usage and have been validated to provide highly accurate assessments for range of motion. Size, cost, need for marker placement and need for complex data processing have remained limiting factors in uptake outside of what remains predominantly large research institutions. Progress and advances in deep neural networks, trained on millions of clinically labelled datasets, have allowed the development of a computer vision system which enables assessment using a handheld smartphone with no markers and accurate range of motion for knee during flexion and extension. This allows clinicians and therapists to objectively track progress without the need for complex and expensive equipment or time-consuming analysis, which was concluded to be lacking during a recent systematic review of existing applications.

Method

A smartphone based computer vision system was assessed for accuracy with a gold standard comparison using a validated ‘traditional’ infra-red motion capture system which had a defined calibrated accuracy of 0.1degrees. A total of 22 subjects were assessed simultaneously using both the computer vision smartphone application and the standard motion capture system. Assessment of the handheld system was made by comparison to the motion capture system for knee flexion and extension angles through a range of motion with a simulated fixed-flexion deformity which prevented full extension to assess the accuracy of the system, repeating movements ten times. The peak extension angles and also numerous discrete angle measurements were compared between the two systems. Repeatability was assessed by comparing several sequential cycles of flexion/extension and comparison of the maximum range of motion in normal knees and in those with a simulated fixed-flexion deformity. In addition, discrete angles were also measured on both legs of three cadavers with both skin and then bone implanted fiducial markers for ground truth reliability accounting for skin movement. Data was processed quickly through an automated secure cloud system.


Orthopaedic Proceedings
Vol. 101-B, Issue SUPP_2 | Pages 26 - 26
1 Jan 2019
Choudhury A Auvient E Iranpour F Lambkin R Wiik A Hing C Cobb J
Full Access

Patellofemoral osteoarthritis (PFOA) affects 32% men and 36% women over the age of 60years and is associated with anterior knee pain, stiffness, and poor mobility. Patellofemoral arthroplasty (PFA) is a bone-sparing treatment for isolated PFOA. This study set out to investigate the relationship between patient-related outcome measures (PROMs) and measurements obtained from gait analysis before and after PFA. There are currently no studies relating to gait analysis and PFA available in the literature

A prospective cohort study was conducted of ten patients known to have isolated PFOA who had undergone PFA compared to a gender and age matched control group. The patients were also asked to complete questionnaires (Oxford knee score (OKS), EQ-5D-5L) before surgery and one year after surgery. Gait analysis was done on an instrumented treadmill comparing Ground reaction force parameters between the control and pre and post-operative PFA patients

The average age 60 (49–69) years with a female to male ratio of 9:1. Patient and healthy subjects were matched for age and gender, with no significant difference in BMI. Post-op PFA improvement in gait seen in ground reaction force at 6.5km/h. Base support difference was statistically significant both on the flat P=0.0001 and uphill P=0.429 (5% inclination) and P=0.0062 (10% inclination). PROMS response rate was 70%(7/10) pre-operative and 60%(6/10) post-operative. EQ-5D-5L scores reflected patient health state was better post-operatively.

This study found that gait analysis provides an objective measure of functional gait and reflected by significant quality-of-life improvement of patients post PFA. Literature lacks studies relating to gait-analysis and PFA. Valuable information provided by this study highlights that PFA has a beneficial outcome reflected by PROMs and improvement in vertical ground reaction force and gait

Further research is needed to assess how care-providers may use gait-analysis as part of patient care plans for PFOA patients.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 52 - 52
1 Mar 2017
Navruzov T Riviere C Van Der Straeten C Harris S Aframian A Iranpour F Cobb J Auvinet E
Full Access

Background

The accurate positioning of the total knee arthroplasty affects the survival of the implants(1). Alignment of the femoral component in relation to the native knee is best determined using pre- and post-operative 3D-CT reconstruction(2). Currently, the scans are visualised on separate displays. There is a high inter- and intra-observer variability in measurements of implant rotation and translation(3). Correct alignment is required to allow a direct comparison of the pre- and post-operative surfaces. This is prevented by the presence of the prostheses, the bone shape alteration around the implant, associated metal artefacts, and possibly a segmentation noise.

Aim

Create a novel method to automatically register pre- and post-operative femora for the direct comparison of the implant and the native bone.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 115 - 115
1 Mar 2017
Riviere C Shah H Howell S Aframian A Iranpour F Auvinet E Cobb J Harris S
Full Access

BACKGROUND

Trochlear geometry of modern femoral implants is designed for the mechanical alignment (MA) technique for Total Knee Arthroplasty (TKA). The biomechanical goal is to create a proximalised and more valgus trochlea to better capture the patella and optimize tracking. In contrast, Kinematic alignment (KA) technique for TKA respects the integrity of the soft tissue envelope and therefore aims to restore native articular surfaces, either femoro-tibial or femoro-patellar. Consequently, it is possible that current implant designs are not suitable for restoring patient specific trochlea anatomy when they are implanted using the kinematic technique. This could cause patellar complications, either anterior knee pain, instability or accelerated wear or loosening. The aim of our study is therefore to explore the extent to which native trochlear geometry is restored when the Persona® implant (Zimmer, Warsaw, USA) is kinematically aligned.

METHODS

A retrospective study of a cohort of 15 patients with KA-TKA was performed with the Persona® prosthesis (Zimmer, Warsaw, USA). Preoperative knee MRIs and postoperative knee CTs were segmented to create 3D femoral models. MRI and CT segmentation used Materialise Mimics® and Acrobot Modeller® software, respectively. Persona® implants were laser-scanned to generate 3D implant models. Those implant models have been overlaid on the 3D femoral implant model (generated via segmentation of postoperative CTs) to replicate, in silico, the alignment of the implant on the post-operative bone and to reproduce in the computer models the features of the implant lost due to CT metal artefacts. 3D models generated from post-operative CT and pre-operative MRI were registered to the same coordinate geometry. A custom written planner was used to align the implant, as located on the CT, onto the pre-operative MRI based model (figure 1). In house software enabled a comparison of trochlea parameters between the native trochlea and the performed prosthetic trochlea (figure 2). Parameters assessed included 3D trochlear axis and anteroposterior offset from medial facet, central groove, and lateral facet. Sulcus angle at 30% and 40% flexion was also measured. Inter and intra observer measurement variabilities have been assessed.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 117 - 117
1 Mar 2017
Riviere C Howell S Parratte S Vendittoli P Iranpour F Cobb J
Full Access

The mechanical alignment (MA) for Total Knee Arthroplasty (TKA) with neutral alignment goal has had good overall long-term outcomes. In spite of improvements in implant designs and surgical tools aiming for better accuracy and reproducibility of surgical technique, functional outcomes of MA TKA have remained insufficient. Therefore, alternative, more anatomicaloptions restoring part (adjusted MA (aMA) and adjusted kinematic alignment (aKA) techniques) or the entire constitutional frontal deformity (unicompartment knee arthroplasty (UKA) and kinematic alignment (KA) techniques) have been developed, with promising results. The kinematic alignment for TKA is a new and attractive surgical technique enabling a patient specific treatment. The growing evidence of the kinematic alignment mid-term effectiveness, safety and potential short falls are discussed in this paper. The current review describes the rationale and the evidence behind different surgical options for knee replacement, including current concepts in alignment in TKA. We also introduce two new classification systems for “implant alignments options” (Figure 1) and “osteoarthritic knees” (Figure 2) that would help surgeons to select the best surgical option for each patient. This would also be valuable for comparison between techniques in future research.

For figures/tables, please contact authors directly.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_4 | Pages 26 - 26
1 Feb 2017
Leong A Iranpour F Cobb J
Full Access

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.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_4 | Pages 120 - 120
1 Feb 2017
Leong A Iranpour F Cobb J
Full Access

Background

Constitutional knee varus increases the risk of medial OA disease due to increase in the knee adduction moment and shifting of the mechanical axis medially.

Hueter-Volkmann's law states that the amount of load experienced by the growth plate during development influences the bone morphology. For this reason, heightened sports activity during growth is associated with constitutional varus due to added knee adduction moment. In early OA, X-rays often show a flattened medial femoral condyle extension facet (EF). However, it is unknown whether this is a result of osteoarthritic wear, creep deformation over decades of use, or an outcome of Hueter-Volkmann's law during development. A larger and flattened medial EF can bear more weight, due to increased load distribution. However, a flattened EF may also extrude the meniscus, leading meniscus degeneration and joint failure.

Therefore, this study aimed to investigate whether varus knees have flattened medial EFs of both femur and tibia in a cohort of patients with no signs yet of bony attrition.

Methods

Segmentation and morphology analysis was conducted using Materialise software (version 8.0, Materialise Inc., Belgium). This study excluded knees with bony attrition of the EFs based on Ahlbäck criteria, intraoperative findings, and operation notes history. Standard reference frames were used for both the femur and tibia to ensure reliable and repeatable measurements. The hip-knee-angle (HKA) angle defined varus or valgus knee alignment.

Femur: The femoral EFs and flexion facets (FFs) had best-fit spheres fitted with 6 repetitions. (Fig1)

Tibia: The slopes of the antero-medial medial tibial plateau were approximated using lines. (fig2)


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_4 | Pages 11 - 11
1 Feb 2017
Harris S Dhaif F Iranpour F Aframian A Auvinet E Cobb J Howell S Riviere C
Full Access

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.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_1 | Pages 113 - 113
1 Jan 2017
Iranpour F
Full Access

Constitutional knee varus increases the risk of medial OA disease due to increase in the knee adduction moment and shifting of the mechanical axis medially. Hueter-Volkmann’s law states that the amount of load experienced by the growth plate during development influences the bone morphology. For this reason, heightened sports activity during growth is associated with constitutional varus due to added knee adduction moment. In early OA, X-rays often show a flattened medial femoral condyle extension facet (EF). However, it is unknown whether this is a result of osteoarthritic wear, creep deformation over decades of use, or an outcome of Hueter-Volkmann’s law during development. A larger and flattened medial EF can bear more weight, due to increased load distribution. However, a flattened EF may also extrude the meniscus, leading meniscus degeneration and joint failure. Therefore, this study aimed to investigate whether varus knees have flattened medial EFs of both femur and tibia in a cohort of patients with no signs yet of bony attrition.

Segmentation and morphology analysis was conducted using Materialise software (version 8.0, Materialise Inc., Belgium). This study excluded knees with bony attrition of the EFs based on Ahlbäck criteria, intraoperative findings, and operation notes history. Standard reference frames were used for both the femur and tibia to ensure reliable and repeatable measurements. The hip-knee-angle (HKA) angle defined varus or valgus knee alignment. Femur: The femoral EFs and flexion facets (FFs) had best-fit spheres fitted with 6 repetitions. Tibia: The slopes of the antero-medial medial tibial plateau were approximated using lines. Results 72 knees met the inclusion and exclusion criteria. The average age was 59 ± 11 years. The youngest was 31 and the oldest 84 years. Thirty-three were male and 39 were female. There was good intra- and inter-observer reliability for EF sphere fitting.

Femur: The results demonstrated that the medial femoral condyle EF is flattened in knees with constitutional varus, as measured by the Sphere Ratios between the medial and lateral EF (varus versus straight: p = 0.006), and in the scaled values for the medial EF sphere radius (varus versus straight: p = 0.005). There was a statistically significant, moderate and positive correlation between the medial femoral EF radius, and the medial femoral EF-FF AP offset.

Tibia: There was a statistically significant difference between the steepness of the slopes of the medial tibial plateau EF in varus and valgus knees, suggesting varus knees have a less concave (flatter) medial EF. Conclusions In comparison to straight knees, varus knees have flattened medial EFs in both femur and tibia. As this was the case in knees with no evidence of bony attrition, this could mean flattened medial EFs may be a result of medial physis inhibition during development, due to Hueter-Volkmann’s law. Flattened medial EFs may increase load distribution in the medial compartment, but could also be a potential aetiology in primary knee OA due to over extrusion of the medial meniscus and edge loading.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_1 | Pages 95 - 95
1 Jan 2017
Rivière C Shah H Auvinet E Iranpour F Harris S Cobb J Howell S Aframian A
Full Access

Trochlear geometry of modern femoral implants is designed for mechanical alignment (MA) technique for TKA. The biomechanical goal is to create a proximalised and more valgus trochlea to better capture the patella and optimize tracking. In contrast, Kinematic alignment (KA) technique for TKA respects the integrity of the soft tissue envelope and therefore aims to restore native articular surfaces, either femoro-tibial or femoro-patellar. Consequently, it is possible that current implant designs are not suitable for restoring patient specific trochlea anatomy when they are implanted using the kinematic technique, this could cause patellar complications, either anterior knee pain, instability or accelerated wear or loosening. The aim of our study is therefore to explore the extent to which native trochlear geometry is restored when the Persona®implant (Zimmer, Warsaw, USA) is kinematically aligned.

A retrospective study of a cohort of 15 patients with KA-TKA was performed with the Persona®prosthesis (Zimmer, Warsaw, USA). Preoperative knee MRIs and postoperative knee CTs were segmented to create 3D femoral models. MRI and CT segmentation used Materialise Mimics and Acrobot Modeller software, respectively. Persona®implants were laser scanned to generate 3D implant models. Those implant models have been overlaid on the 3D femoral implant model (generated via segmentation of postoperative CTs) to replicate, in silico, the alignment of the implant on the post-operative bone and to reproduce in the computer models the features of the implant lost due to CT metal artefacts. 3D models generated from post-operative CT and pre-operative MRI were registered to the same coordinate geometry. A custom written planner was used to align the implant, as located on the CT, onto the pre-operative MRI based model. In house software enabled a comparison of trochlea parameters between the native trochlea and the performed prosthetic trochlea. Parameters assessed included 3D trochlear axis and anteroposterior offset from medial facet, central groove, and lateral facet. Sulcus angle at 30% and 40% flexion was also measured. Inter and intra observer measurement variabilities have been assessed.

Varus-valgus rotation between the native and prosthetic trochleae was significantly different (p<0.001), with the prosthetic trochlear groove being on average 7.9 degrees more valgus. Medial and lateral facets and trochlear groove were significantly understuffed (3 to 6mm) postoperatively in the proximal two thirds of the trochlear, with greatest understuffing for the lateral facet (p<0.05). The mean medio-lateral translation and internal-external rotation of the groove and the sulcus angle showed no statistical differences, pre and postoperatively.

Kinematic alignment of Persona®implants poorly restores native trochlear geometry. Its clinical impact remains to be defined.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_2 | Pages 22 - 22
1 Jan 2017
Rivière C Lazennec J Van Der Straeten C Iranpour F Cobb J
Full Access

The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or edge loading related, have not been eliminated. Early dislocations are becoming very rare and most of them probably occur in “outlier” patients with atypical pelvic/hip kinematics. Because singular problems usually need singular treatments, those patients need a more specific personalised planning of the treatment rather than a basic systematic application of Lewinnek recommendations. We aim in this review to define the potential impacts that the spine-hip relations (SHRs) have on hip arthroplasty. We highlight how recent improvements in hip implants technology and knowledge about SHRs can substantially modify the planning of a THR, and make the « Lewinnek recommendations » not relevant anymore. We propose a new classification of the SHRs with specific treatment recommendations for hip arthroplasty whose goal is to help at establishing a personalized planning of a THR. This new classification gives a rationale to optimize the short and long-term patient's outcomes by improving stability and reducing edge loading. We believe this new concept could be beneficial for clinical and research purposes.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_2 | Pages 65 - 65
1 Jan 2017
Rivière C Iranpour F Cobb J Howell S Vendittoli P Parratte S
Full Access

The mechanical alignment (MA) for Total Knee Arthroplasty (TKA) with neutral alignment goal has had good overall long-term outcomes. In spite of improvements in implant designs and surgical tools aiming for better accuracy and reproducibility of surgical technique, functional outcomes of MA TKA have remained insufficient. Therefore, alternative, more anatomical options restoring part (adjusted MA (aMA) and adjusted kinematic alignment (aKA) techniques) or the entire constitutional frontal deformity (unicompartment knee arthroplasty (UKA) and kinematic alignment (KA) techniques) have been developed, with promising results. The kinematic alignment for TKA is a new and attractive surgical technique enabling a patient specific treatment. The growing evidence of the kinematic alignment mid-term effectiveness, safety and potential short falls are discussed in this paper. The current review describes the rationale and the evidence behind different surgical options for knee replacement, including current concepts in alignment in TKA. We also introduce two new classification systems for “implant alignments options” and “osteoarthritic knees” that would help surgeons to select the best surgical option for each patient. This would also be valuable for comparison between techniques in future research.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_1 | Pages 57 - 57
1 Jan 2017
Harris S Dhaif F Iranpour F Aframian A Cobb J Auvinet E Howell S Rivière C
Full Access

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.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_1 | Pages 100 - 100
1 Jan 2017
Navruzov T Rivière C Van Der Straeten C Harris S Cobb J Auvinet E Aframian A Iranpour F
Full Access

The accurate positioning of the total knee arthroplasty affects the survival of the implants(1). Alignment of the femoral component in relation to the native knee is best determined using pre- and post-operative 3D-CT reconstruction(2). Currently, the scans are visualised on separate displays. There is a high inter- and intra-observer variability in measurements of implant rotation and translation(3). Correct alignment is required to allow a direct comparison of the pre- and post-operative surfaces. This is prevented by the presence of the prostheses, the bone shape alteration around the implant, associated metal artefacts, and possibly a segmentation noise.

The aim is to create a novel method to automatically register pre- and post-operative femora for the direct comparison of the implant and the native bone.

The concept is to use post-operative femoral shaft segments free of metal noise and of surgical alteration for alignment with the pre-operative scan. It involves three steps. Firstly, using principal component analysis, the femoral shafts are re-oriented to match the X axis. Secondly, variants of the post-operative scan are created by subtracting 1mm increments from the distal femoral end. Thirdly, an iterative closest point algorithm is applied to align the variants with the pre-operative scan.

For exploratory validation, this algorithm was applied to a mesh representing the distal half of a 3D scanned femur. The mesh of a prosthesis was blended with the femur to create a post-operative model. To simulate a realistic environment, segmentation and metal artefact noise were added. For segmentation noise, each femoral vertex was translated randomly within +−1mm,+−2mm,+−3mm along its normal vector. To create metal artefact random noise was added within 50 mm of the implant points in the planes orthogonal to the shaft. The alignment error was considered as the average distance between corresponding points which are identical in pre- and post-operative femora.

These preliminary results obtained within a simulated environment show that by using only the native parts of the femur, the algorithm was able to automatically register the pre- and post-operative scans even in presence of the implant. Its application will allow visualisation of the scans on the same display for the direct comparison of the perioperative scans.

This method requires further validation with more realistic noise models and with patient data. Future studies will have to determine if correct alignment has any effect on inter- and intra-observer variability.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_8 | Pages 51 - 51
1 May 2016
Iranpour F Auvinet E Harris S Cobb J
Full Access

Patellofemoral joint (PFJ) arthroplasty is traditionally performed using mechanical jigs to align the components, and it is hard to fine tune implant placement for the individual patient. These replacements have not had the same success rate as other forms of total or partial knee replacement surgery1.

Our team have developed a computer assisted planning tool that allows alignment of the implant based on measurements of the patient's anatomy from MRI data with the aim of improving the success of patellofemoral joint arthroplasty.

When planning a patellofemoral joint arthroplasty, one must start from the premise that the original joint is either damaged as a result of osteoarthritis, or is dysplastic in some way, deviating from a normal joint. The research aimed to plan PFJ arthroplasty using knowledge of the relationship between a normal PFJ (trochlear groove, trochlea axis and articular surfaces) and other aspects of the knee2, allowing the plan to be estimated from unaffected bone surfaces, within the constraints of the available trochlea.

In order to establish a patient specific trochlea model a method was developed to automatically compute an average shape of the distal femur from normal distal femur STL files (Fig.1). For that MRI scans of 50 normal knees from osteoarthritis initiative (OAI) study were used. Mimics and 3-matic software (Materialise) packages were used for segmentation and analysis of 3D models. Spheres were fitted to the medial and lateral flexion facets for both average knee model and patient knee model. The average knee was rescaled and registered in order to match flexion facet axis (FFA) distance and FFA midpoint of the patient (Fig.2). The difference between the patient surface and the average knee surface allow to plan the patella groove alteration.

The Patella cut is planned parallel to the plane fitted to the anterior surface of the patella. The patella width/thickness ratio (W/T=2) is used to predict the post reconstruction thickness3. The position of the patella component (and its orientation if a component with a median ridge is used) is also planned.

The plan is next fine-tuned to achieve satisfactory PFJ kinematics4 (Fig.3). This will be complemented by intraoperative PFJ tracking which assists with soft tissue releases. PFJ kinematics is evaluated in terms of patella shift, tilt and deviation from the previously described circular path of the centre of the patella.

The effect of preoperative planning on PFJ tracking and soft tissue releases is being examined. Additional study is needed to evaluate whether planning and intraoperative kinematic measurements improve the clinical outcome of PFJ arthroplasty.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_8 | Pages 29 - 29
1 May 2016
Harris S Iranpour F Riyat H Cobb J
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Introduction

The trochlea of a typical patellofemoral replacement or anterior flange of a total knee replacement usually extends past the natural trochlea and continues onto the femoral anterior cortex. One reason for this is that it allows a simple patella button to be permanently engaged in the trochlea groove in an attempt to ensure stability. On the natural patella, the apex helps to guide it into the trochlea groove as the knee moves from full extension into flexion.

The aim is to study whether a generalised patella can be created that is close in form to a healthy patella.

Method

MRI scans were taken of 30 patellae. Characteristics of these patellae (height, width, thickness, apex angle) were measured. The apex angle was found to be similar between patellae (mean=126 degrees, sd = 8.8), as were the ratios between height and width (mean width/height = 1.05, sd = 0.07) and between thickness and width (mean width/thickness = 1.8, sd = 0.19).

These patellae were then segmented to create a surface including cartilage, resulting in 30 STL (stereolithography) files in which the surfaces are represented by triangle meshes.

To design the average patella the individual patellae were aligned to a standard frame of reference by placing a set of landmarks on the proximal/distal, medial/lateral and anterior/posterior extents of each (fig.1). The vertical axis was defined as passing parallel to the proximal/distal points and the horizontal as passing parallel to the medial/lateral points when looking along the computed vertical axis. The origin centre of the frame of reference was chosen to be mid-way between these points. The mean width was then computed and each patella scaled linearly around the origin to give them all equal width.

All the aligned patellae were then averaged together to provide a composite cartilaginous patella. The averaging process was achieved by taking one patella as a seed. The patella chosen for seed was that whose parameters were closest to the average width, height and thickness. An approximately normal vector was passed a point ‘P’ on the seeds, and the points at which these intersected the other models were then determined. The closest intersection point to ‘P’ on each model was chosen and these averaged together. ‘P’ is then replaced in the model with this average point. The averaging process then continues with all the remaining points on the seed model in the same manner to build the average models.


Orthopaedic Proceedings
Vol. 97-B, Issue SUPP_14 | Pages 8 - 8
1 Dec 2015
Mushtaq N Al Obaidi B Iranpour F Bhattacharya R
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Introduction

Different techniques for fixation of lateral malleolus have been described. We report our results of using fibula rod for unstable ankle fractures in level one major trauma centre.

Methods

We reviewed the results of 40 ankle fractures (14 open and 26 closed) with significant soft tissue injuries and open fractures that were treated with a fibula rod between 2012 and 2015. The median age of patients was 60 (17–98 years).