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Background

Calipered kinematically aligned (KA) total knee arthroplasty (TKA) restores the in vitro internal-external (I-E) rotation laxities at 0° and 90° of the native knee. Although increasing and decreasing the thickness of the insert in 1 mm increments loosens and tightens the flexion space, there are little data on how this might adversely affect the screw-home mechanism and I-E rotational laxity. The present study determined the differences in the I-E range of rotation and I-E positions at maximum extension and at 90° of flexion that result from the use of insert thicknesses that deviate ± 1mm in thickness from the implanted insert.

Methods

20 patients were treated with a calipered KA and a PCL retaining implant with a 1:1 medial ball-in-socket constraint and a non-constrained lateral flat articular insert surface. Verification checks, that are validated to restore native tibial compartment forces without release of healthy ligaments including the PCL, were used to select the optimal insert thickness. Trial inserts with thicknesses ranging from 10 to 13 mm were 3-D printed with medial goniometric markings that record rotation from 20° external to −20° internal with respect to a sagittal line laser marked on center of the medial condyle of the trial femoral component at maximum extension and 90° of flexion (Figure 1).


Orthopaedic Proceedings
Vol. 103-B, Issue SUPP_1 | Pages 55 - 55
1 Feb 2021
Niesen A Hull M Howell S Garverick A
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Introduction

Model-based radiostereometric analysis (MBRSA) allows the in vivo measurement of implant loosening (i.e. migration) from a host bone by acquiring a pair of biplanar radiographs of the patient's implant over time. Focusing on total knee replacement patients, the accuracy of MBRSA in calculating tibial baseplate migration depends on the accuracy in registering a 3D model onto the biplanar radiographs; thus, the shape of the baseplate and its orientation relative to the imaging planes is pertinent. Conventionally, the baseplate coordinate system is aligned with the laboratory coordinate system, however, this reference orientation is unnecessary and may hide unique baseplate features resulting in less accurate registration (Figure 1). Therefore, the primary objective of this study was to determine the optimal baseplate orientation for improving accuracy during MBRSA, and an acceptable range of orientations for clinical use. A second objective was to demonstrate that a custom knee positioning guide repeatably oriented the baseplate within the acceptable range of orientations.

Materials and Methods

A tibia phantom consisting of a baseplate rigidly fixed to a sawbone was placed in 24 orientations (combination of six rotations about X (i.e. knee flexion) and four rotations about Z (i.e. hip abduction)) with three pairs of radiographs acquired at each orientation. The radiographs were processed in MBRSA software, and the mean maximum total point motion (MTPM), an indicator of bias error during model registration, was plotted as a function of the two rotations to determine the optimal orientation and a range of acceptable orientations (Figure 2).

A custom knee positioning guide was manufactured with the goal of orienting the baseplate close to the optimal orientation and within the acceptable range of orientations (Figure 3). Ten independent pairs of biplanar radiographs were acquired by repeatedly placing a knee model in the knee positioning guide, and the images were processed in MBRSA software to determine the baseplate orientation.


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
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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
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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 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 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 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. 86-B, Issue SUPP_I | Pages 85 - 85
1 Jan 2004
Pauza K Howell S Dreyfuss P Peloza J Dawson K Park K Bogduk N
Full Access

Introduction: Intradiscal electrothermal therapy (IDET) is a controversial, new treatment for low back pain, whose efficacy has not been tested in randomized trials. The present study was undertaken to compare the efficacy of IDET with that of a placebo treatment.

Methods: Patients were recruited by referral and by advertising in the media. Of 4,530 individuals who enquired, 1,360 were prepared to submit to randomization. Of these, 260 were found potentially eligible after clinical examination, and 64 became eligible after discography. All had discogenic low back pain lasting longer than 6 months, with no comorbidity. Thirty-seven were allocated to IDET, and 27 to sham therapy. Both groups were satisfactorily matched for demographic and clinical features. IDET was performed using a standard protocol, in which the posterior annulus of the painful disc was heated to 90°C. Sham therapy consisted of introducing a needle onto the disc and exposing the patient to the same visual and auditory environment as for a real procedure. Follow-up at 6 months was achieved in over 85% of patients. Pain and disability were assessed using a visual analog scale for pain, the SF-36, the Oswestry disability scale, and the Back Depression Inventory.

Results: Patients in both groups exhibited improvements, but improvements in pain, disability, and depression, were significantly greater in the group treated with IDET. Pain scores improved by 24 points in the IDET group compared with 11 in the sham group. Oswestry scores improved by 11 in the IDET group, but only by 4 in the sham group. More patients deteriorated when subjected to sham treatment, whereas eight patients (25%) achieved greater than 75% relief of pain following IDET. Only one patient did so after sham treatment. The number needed to treat, to achieve 75% relief of pain, was 5. No patient suffered any adverse effects.

Discussion: IDET fails to provide relief in some 50% of patients. Consequently, its efficacy is difficult to demonstrate statistically. Nevertheless, IDET provides satisfying relief in a substantial proportion of patients. Non-specific factors account for a large proportion of the apparent efficacy of IDET, but its efficacy cannot be attributed wholly to a placebo effect. The efficacy of IDET may be related critically to patient selection and the technique used. Improvements in either of these areas may improve the effect-size of IDET. Meanwhile, IDET is a low risk procedure that constitutes a legitimate option for patients with discogenic low back pain whose only alternative is fusion.


Orthopaedic Proceedings
Vol. 85-B, Issue SUPP_III | Pages 280 - 280
1 Mar 2003
Pauza K Howell S Dreyfuss P Peloza J Dawson K Park K Bogduk N
Full Access

INTRODUCTION: Intradiscal electrothermal therapy (IDET) is a controversial, new treatment for low back pain, whose efficacy has not been tested in randomised trials. The present study was undertaken to compare the efficacy of IDET with that of a placebo treatment.

METHODS: Patients were recruited by referral and by advertising in the media. Of 4,530 individuals who enquired, 1,360 were prepared to submit to randomisation. Of these, 260 were found potentially eligible after clinical examination, and 64 became eligible after discography. All had discogenic low back pain lasting longer than six months, with no co-morbidity. Thirty-seven were allocated to IDET, and 27 to sham therapy. Both groups were satisfactorily matched for demographic and clinical features. IDET was performed using a standard protocol, in which the posterior annulus of the painful disc was heated to 90°C. Sham therapy consisted of introducing a needle on to the disc and exposing the patient to the same visual and auditory environment as for a real procedure. Follow-up at six months was achieved in over 85% of patients. Pain and disability were assessed using a visual analog scale for pain, the SF-36, the Oswestry disability scale, and the Back Depression Inventory.

RESULTS: Patients in both groups exhibited improvements, but improvements in pain, disability, and depression, were significantly greater in the group treated with IDET. Pain scores improved by 24 points in the IDET group compared with 11 in the sham group. Oswestry scores improved by 11 in the IDET group, but only by four in the sham group. More patients deteriorated when subjected to sham treatment, whereas eight patients (25%) achieved greater than 75% relief of pain following IDET. Only one patient did so after sham treatment. The number needed to treat, to achieve 75% relief of pain, was five. No patient suffered any adverse effects.

DISCUSSION: IDET fails to provide relief in some 50% of patients. Consequently, its efficacy is difficult to demonstrate statistically. Nevertheless, IDET provides satisfying relief in a substantial proportion of patients. Non-specific factors account for a large proportion of the apparent efficacy of IDET, but its efficacy cannot be attributed wholly to a placebo effect. The efficacy of IDET may be related critically to patient selection and the technique used. Improvements in either of these areas may improve the effect-size of IDET. Meanwhile, IDET is a low risk procedure that constitutes a legitimate option for patients with discogenic low back pain whose only alternative is fusion.


Orthopaedic Proceedings
Vol. 84-B, Issue SUPP_II | Pages 133 - 134
1 Jul 2002
Clatworthy M Bulow JU Pinczewski L Howell S Fowler P
Full Access

Introduction: It has been proposed that tunnel widening in ACL reconstructions is due to excessive graft tunnel motion secondary to elastic fixation.

Aim: To determine whether techniques which fix the graft closer to the joint (interference screws), eliminate the bungy cord and are stiffer will decrease tunnel widening. The clinical significance of tunnel widening is examined.

Method: Two hundred and fifty nine patients were evaluated prospectively. Four fixation methods were evaluated. Sixty-nine were reconstructed using Endobuttons and staples (elastic fixation). Forty-eight were subjects reconstructed with a bone mulch screw and staples, 55 patients were reconstructed with metal interference screws and 87 with bioabsorbable interference screws. Patients underwent a clinical examination, IKDC, Cincinnati knee score and KT-1000 testing one year post-operatively. These factors were correlated with tunnel widening. Tunnel widening was determined using magnification adjusted AP and lateral radiographs using Scion Image software.

Results: Tunnel widening occurred with all the fixation methods. Mean tunnel area increased 122% for the Bioscrew, 89% for the metal interference screw, 76% for the bone mulch screw and 36% for the Endobutton (ANOVA p=< 0.0001). Tunnel widening did not correlate with increased laxity, poor IKDC or Cincinnati knee scores.

Conclusions: Tunnel widening occurred with both elastic and rigid fixation methods. Tunnel widening could not be avoided by fixing the graft closer to the joint or eliminating the ‘bungy cord’. Graft tunnel motion was not the sole cause of tunnel widening in ACL reconstruction. Tunnel widening did not correlate with poor outcome in the short term.