The aim of this study was to use motion analysis to study a surgeon’s learning curve for an arthroscopic Bankart repair on a training model in a skills laboratory. Six fellowship trained lower limb surgeons unfamiliar with advanced shoulder arthroscopy performed an arthroscopic Bankart repair on an ALEX shoulder model. Standardised training was given and then an electromagnetic tracking system used to objectively assess hand movements, distance travelled by hands and time taken while the surgeons performed the technique. The arthroscopic repair was repeated three times on four consecutive occasions by each surgeon giving a total of 72 repair episodes. Analysis revealed improvement of all outcome parameters with less hand movements, less distance travelled and less time to complete the task. This study objectively demonstrates a learning curve for arthroscopic Bankart suture in a skills laboratory. It indicates the potential benefits of practicing aspects of arthroscopic techniques in a skills centre on appropriately selected models.

Background: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range and diminished femoral rollback. It is postulated that this may be due to a flat tibial tray replacing the domed anatomy of the lateral tibia, tightening the posterolateral flex-ion gap. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to increase; (i) the posterolateral flexion gap in deep knee flexion (ii) meniscal bearing movement and (iii) lateral femoral condyle (LFC) rollback. A cadaveric study was designed to test these three outcomes.

Methods: The sagittal plane kinematics of seven thawed fresh frozen cadaver specimens within an upright Oxford testing rig were assessed under three different conditions; (i) intact normal cadaver knee (ii) flat lateral Oxford UKR (iii) domed lateral Oxford UKR. Each condition was tested during three ranges of motion (ROM) and data recorded during a flexion or extension half cycle. Knee flexion angle (KFA) and displacement measures of the lateral collateral ligament (LCL), LFC rollback and anteroposterior meniscal bearing movement were performed throughout knee ROM using four [3 linear, 1 rotary] potentiometer devices. Potentiometer data was recorded as a voltage reading and subsequently converted to either a millimetre displacement or degree measure using a calibration formula. All data points were compared at 10 degree interpolations of KFA.

Results: The flexion half cycles demonstrated the flat Oxford lateral UKR achieved 80.7% of normal cadaveric LFC rollback. The domed Oxford lateral UKR achieved 108.8% of normal cadaveric LFC rollback. The ratio of LFC rollback in the domed to flat UKR’s was 1.35 times (134.9%). Meniscal bearing movement in flexion demonstrated a domed to flat UKR ratio of 1.3 times (129.7%). Similar values were obtained for extension half cycles in favour of the domed Oxford lateral UKR. No significant differences were identified in LCL measures.

Conclusions: The domed Oxford lateral UKR implant allows for improved bearing movement and femoral rollback when compared to the flat Oxford lateral UKR. The sagittal plane kinematics of the domed Oxford lateral UKR as represented by femoral rollback values approximate those of the normal cadaver knee.

Finite element (FE) analysis is widely used to calculate stresses and strains within human bone in order to improve implant designs. Although validated FE models of the human femur have been created (Lengsfeld et al., 1998), no equivalent yet exists for the tibia. The aim of this study was to create such an FE model, both with and without the tibial component of a knee replacement, and to validate it against experimental results.

A set of reference axes was marked on a cleaned, fresh frozen cadaveric human tibia. Seventeen triaxial stacked strain rosettes were attached along the bone, which was then subjected to nine axial loading conditions, two four-point bending loading conditions, and a torsional loading condition using a materials testing machine (MTS 858). Deflections and strain readings were recorded. Axial loading was repeated after implantation of a knee replacement (medial tibial component, Biomet Oxford Unicompartmental Phase 3). The intact tibia was CT scanned (GE HiSpeed CT/i) and the images used to create a 3D FE mesh. The CT data was also used to map 600 transversely isotropic material properties (Rho, 1996) to individual elements. All experiments were simulated on the FE model. Measured principal strains and displacements were compared to their corresponding FE values using regression analysis.

Experimental results were repeatable (mean coeffi-cients of variation for intact and implanted tibia, 5.3% and 3.9%). They correlated well with those of the FE analysis (R squared = 0.98, 0.97, 0.97, and 0.99 for axial (intact), axial (implanted), bending, torsional loading). For each of the load cases the intersects of the regression lines were small in comparison to the maximum measured strains (< 1.5%). While the model was more rigid than the bone under torsional loading (slope =0.92), the opposite was true for axial (slope = 1.14 (intact) 1.24 (implanted)) and bending (slope = 1.06) loads. This is probably due to a discrepancy in the material properties of the model.

Hip resurfacing arthroplasty (HRA) is increasingly carried out as an alternative to total hip arthroplasty (THA) in young patients. During the procedure, a metal stem on the retrosurface of the HRA is inserted into the femoral head to ensure the implant is located centrally with respect to the femoral neck. It has been suggested that the stem may interfere with bone loading. In light of this, the current study employed finite element (FE) models to investigate the change in the HRA-implanted bone mechanics as a result of removing the stem. FE models of a cadaveric femur pre- and post-HRA surgery were analysed to determine changes in bone stress/ strain.

The implanted models simulated geometry for a cemented HRA with and without a non-cemented stem (HRA-Stem and HRA-NoStem, respectively) and included more accurate multiple material parameters to simulate the non-homogeneous material distribution in the femoral bone. The models included loading conditions simulating an instant at 10% of the gait cycle. Bone stresses/strains in the femoral head and neck of the implanted models were compared with the intact condition to assess the change in bone mechanics. Changes in cement mantle stresses between the HRA-Stem and HRA-NoStem models were also compared.

When comparing similar volumes of bone in the femoral neck, both HRA models showed a similar variation in stress from the intact condition and bone stresses were low in comparison to the ultimate strength of cortical bone. There was less change in peak strain energy in the femoral head of the HRA-NoStem model than the HRA-Stem model. Cement mantle stresses in the HRA-NoStem model were slightly higher than for the HRA-Stem model and the peak compressive stress was close to the fatigue limit for bone cement.

These preliminary results suggest that the bone loading is more normal without the stem. However, there are increased cement mantle stresses.

Lisfranc injury is named after Jacques Lisfranc, a field surgeon in Napoleon’s army.

Based on Columnar classification of Lisfranc fracture dislocation, study of injury to medial column was carried out as they have the potential to be a severe cause of residual disability in the foot if not properly treated at the initial stage. Importance of Medial column is that it forms the highest point of longitudinal arch and may be injured in isolation or in association with lateral and middle column. Complex deforming forces may cause unusual pattern of medial column injuries at more than one level. There is renewed interest in this injury over past decade as modalities of treatment have changed over a period of time from conservative to fixation with K-wires to rigid fixation with screws to fixation with absorbable screws or combination of above.

We present 21 cases of medial column injuries in Lis-franc fracture-dislocation. Age ranged from 18 to 65 yrs. All were male. Four fixed with compression screws,12 fixed with K-wires, 2 managed conservatively, 3 were neglected cases. Post-operatively POP back splint was given, K-wire removal at 8 weeks, screw removal after 12 weeks and partial weight bearing started at 8-12 weeks. Follow-up ranged from 3 months to 3 years.

They were graded on basis of residual pain, foot shape, and movements. Best results were seen in cases where rigid intertarsal / intercolumnar stability was achieved by screw fixation. There was residual inter-cuneiform subluxation in 4 cases, which were fixed with K-wires, and this led to residual pain. Conservative/neglected cases had poor results.

Intercolumnar / intertarsal instabilities should be primarily recognized and stabilized under compression. Stabilization should not only be within the 3 columns but also intercolumnar, thus maintaining the relative length of 3 columns and hence reconstitution of medial longitudinal arch.

Patellofemoral Pain Syndrome is characterized by anterior knee pain during activities such as squatting that is thought to be caused by abnormal patellar motion. However, the causative role has yet to be verified since it is difficult to measure the three-dimensional kinematics of the patellofemoral joint (PFJ) in vivo. We developed a fluoroscopy-based method to measure patellar motion as it moves under load through a cycle of flexion and compared the results with those obtained using Roentgen Stereophotogrammetric Analysis (RSA). Our data suggest that the fluoroscopy-based method has sufficient accuracy to detect clinically significant differences in patterns of patellar motion.

The purpose of our study was to determine how accurately a fluoroscopy-based method measures patellar tracking.

Our method measures three-dimensional PFJ kinematics with sufficient accuracy to be of clinical value in assessing dynamic motion.

Patellar tracking can be assessed during aggravating activities to identify specific tracking abnormalities related to anterior knee pain.

Four cadaver knees were imaged using computed tomography (CT). Surface models were generated and the coordinates of implanted tantalum beads (in the femur, patella, and tibia) were determined. A series of fluoroscopic images were taken with the knees loaded in a rig at various flexion angles. Each calibrated fluoroscopic image was registered to the CT model using a point-based method such that the high-resolution CT model was matched to the position of knee flexion associated with each fluoroscopic image. The patellar orientation and position relative to the femur was then reconstructed and described using a gyroscopic joint coordinate system. Measurements were made under the same test conditions using the established uniplanar RSA technique. Fluoroscopy-based and RSA-based measures of patellar orientation and position were compared.

The mean measurement error (SD) for patellar flexion, spin, and tilt was 1.86 (1.55), 1.16 (1.14), and 1.15 (1.10) degrees, respectively. For proximal, lateral and anterior patellar translation, the mean measurement error (SD) was 2.11 (2.16), 0.59 (0.47), and 1.24 (1.18) mm, respectively.

The accuracy of the fluoroscopy-based method of measuring PFJ kinematics was poorer than the reported accuracy of RSA but appears to be sufficiently low to be of clinical value.

Funding: Supported by an operating grant from the Canadian Institutes for Health Research and a Strategic Grant from the Natural Sciences and Engineering Research Council. NJM is supported by TAS/CIHR Partnership Fund.

The design philosophy of polished tapered total hip replacements (THR), such as the Exeter, intends for them to migrate distally within the cement mantle. As well as migration, dynamically induced micromotion (DIMM) occurs as a result of functional activity between the implant and the cement. The aim of the current study was to develop and validate a finite element (FE) model of the Exeter/cement/bone system which can be used to predict DIMM and investigate the stresses induced in the cement mantle during functional activity.

In the context of the current study, DIMM is defined as the displacement of the implant component relative to the bone when moving from double leg stance to single leg stance on the operated limb. Using Roentgen Stereo-photogrammetric Analysis (RSA), DIMM was measured in 21 patients implanted with Exeter stems 3 months post-operatively. A previous study, using a reduced FE model of the Exeter stem and the surrounding cement mantle focused on the solution of the contact problem at the stem-cement interface. It was demonstrated that sliding contact combined with Coulomb friction and an appropriate parameter setting could be used to predict DIMM of a polished tapered stem. For the purposes of the current study, the previous simple model was incorporated into the FE model of the Muscle Standardised Femur and validated against the RSA measurements for DIMM. For the current extended model, loading included muscle forces representing all active muscles acting on the femur. The effect of initial cement stresses and interdigitation was also considered.

The Exeter stem demonstrated significant DIMM (p< 0.017). The FE model, accounting for sliding contact at the cement–implant interface was able to predict similar distal migration of the head and the tip. The results of both the calculations and the measurements showed that the femoral head moves medially, distally and posteriorly relative to the bone. In the cement mantle, maximum principal stresses were oriented circumferentially, minimum principal stresses were oriented radially. When the taper got engaged, submicroscopic movements which did not recover following unloading still took place and accumulated.

The results of the present study showed that it is possible to measure DIMM in the Exeter stem and combine this with FE modelling of the contact mechanism. Future studies will include various activities, such as walking or stair climbing. Based on accumulated submicroscopic movements, short-, mid- or long-term migration patterns will be predicted.

Skin and soft tissue loss is very common in modern high velocity trauma. Such wounds pose problem of coverage. We present a good alternative to skin grafting & flaps i.e. SINGH’S skin traction device for wound closure in these patients.

The technique is based on the principle of tissue expansion and makes use of viscoelastic properties of the skin i.e. creep and stress relaxation. 100 cases with 116 wounds with skin and soft tissue loss were treated. Two parallel kirshner wires (1.5mm) were passed through the dermis on either side of the wound margins and interconnected by compression device consisting of threaded rod having two blocks and compression knob. Gradual compression approximated the wound margins. Patients ranged in age from 15 to 65 years with average age of 30.5 years. Main modes of injury were roadside accidents and machinery accidents. Average operating time was about 20 minutes. 50 amputation stump wounds were also treated.

Excellent results were observed in 48 (41.4%), good in 42 (36.2%), fair in 14 (12%) and poor in 12 (10.4%) wounds. Main complication was cutting through of wires.

We found that this technique is simple, economical and effective. No special training and instruments are needed and can be done by junior surgeon at small centres. It provides full thickness cover to the wound which matches the surrounding normal skin in quality, sensations and colour. Above all this technique can be successfully used in infected wounds and wounds with exposed bone and tendons. Careful gradual compression judged by pain and blanching gives better results and fewer complications.

The long-term survival of total knee arthroplasty (TKA) has been well established; however, functional outcome remains inconsistent. More normal postoperative TKA kinematics have been shown to produce better knee function. Improved kinematics can be obtained by using implants with optimised surface geometry. Hence a TKA with an appropriate surface geometryis likely to provide superior long-term functional outcome. The Advance-Medial Pivot TKA (Wright Medical) is a fixed bearing prosthesis with a conforming medial compartment and a non-conforming (flat on flat) lateral compartment. This surface geometry is designed with the intention of replicating the normal knee motion of sliding or pivoting medially and rolling back laterally.

Aim: To investigate the sagittal plane kinematics of Advanced Medial Pivot Knee and compare with those of “flat on flat” fixed bearing TKA and normal knees

18 patients who had undergone primary TKA for osteoarthritis were recruited at an average of 18 months post operation. These patients performed flexion and extension exercises against gravity and a step up exercise. Video fluoroscopy of these activities was used to obtain the patellar tendon angle (PTA). This is a previously validated method for assessing sagittal plane kinematics of a knee joint. The kinematic profile of the Advance Medial Pivot Knee was compared to the profile of 14 normal knees and 30 flat on flat, fixed bearing TKA’s.

The sagittal plane kinematics of the Advance TKA differed from the normal knees. However, similarly to normal knees, a linear relationship was observed between PTA and knee flexion angle throughout knee flexion range. The kinematics of the Medial Pivot Knee were similar to normal when the knee was in a highly flexed position.

Functional plane kinematics of the Advance Medial Pivot TKA appear to meet the design criteria in that a linear relationship between PTA and flexion angle is maintained. Further work is required to establish if these improved sagittal plane kinematics translate into improved functional outcome.

We evaluated the accuracy of a Magnetic Resonance Imaging (MRI)-based method to measure three-dimensional patellar tracking during loaded knee flexion. This method determines the relative positions of the knee bones by shape matching high-resolution three-dimensional geometric models of these bones to fast low-resolution scans taken during loaded flexion.

The accuracy of the method’s assessment of patellar position and orientation was determined by comparing test measurements in four cadaver specimens to measurements made in the same specimens using Roentgen Stereophotogrammetric Analysis (RSA). This MRI-based method is more accurate than current two-dimensional imaging methods.

The purpose of this study was to determine the accuracy of a MRI-based technique for measuring patellar tracking in loaded flexion.

This novel, noninvasive, MRI-based method measures three-dimensional patellar tracking during loaded knee flexion with sufficient accuracy to detect clinically significant changes.

Although abnormal patellar tracking is widely believed to be associated with pain and cartilage degeneration at the patella, these relationships have not been clearly established because most current methods assess only the two-dimensional alignment of the patella at one position. Measurements possible with this method should be sufficiently accurate to yield new insights into these relationships.

Four cadaver knee specimens were flexed through seventy-five degrees of flexion in an MRI-compatible knee loading rig. A high-resolution image was acquired with each knee in extension and then a series of low-resolution scans (in two slice directions: axial and sagittal) were acquired through a flexion cycle. Segmenting bone outlines from high-resolution scans generated models of the femur, tibia and patella. These models were shape matched to the segmented bone outlines in the low resolution scans. Patellar attitude and position were determined and compared to measurements made using RSA.

The mean measurement error in every kinematic parameter was lower for “fast” sagittal plane slices than for “fast” axial plane slices. In general, the mean measurement error was increased by decreasing the number of low-resolution slices.

This method is more accurate than many two-dimensional methods, exposes participants to no ionizing radiation, and can be used through a large range of loaded knee flexion.

Funding: Supported by an operating grant from the Canadian Institutes for Health Research and a Strategic Grant from the Natural Sciences and Engineering Research Council. NJM is supported by the Arthritis Society/CIHR Partnership Fund.

Please contact author for figures and/or tables.

Medial unicompartmental replacement (UKR) has been shown to have superior functional results to total knee replacement (TKR) in appropriately selected patients, and this has been associated with a resurgence of interest in the procedure. This may relate to evidence showing that the kinematic profile of UKR is similar to the normal knee, in comparison to TKR, which has abnormal kinematics. Concerns remain over the survivorship of UKR and work has suggested the anterior cruciate ligament (ACL) may become dysfunctional over time. Cruciate mechanism dysfunction would produce poor kinematics and instability providing a potential mechanism of failure for the UKR.

Aim: To test the hypothesis that the sagittal plane kinematics (and cruciate mechanism) of a fixed bearing medial UKR deteriorate over time (short to long term).

A cross sectional study was designed in which 24 patients who had undergone successful UKR were recruited and divided into early (2–5 years) and late (> 9 years) groups according to time since surgery. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint.

This work suggests the sagittal plane kinematics of a fixed bearing UKR is maintained in the long term. There is no evidence that the cruciate mechanism has failed at ten years. However, increased tibial bearing conformity from ‘dishing’, and adequate muscle control, cannot be ruled out as possible mechanisms for the satisfactory kinematics observed in the long term for this UKA.

Functional outcome after patellofemoral joint replacement (PFA) for osteoarthritis remains inconsistent. It is believed that functional outcome for joint replacement is dependent upon postoperative joint kinematics. Minimal disruption of the native joint, as in PFA, should produce more normal kinematics and improved outcome. No previous studies have examined joint kinematics after isolated PFA.

Aim: To investigate the sagittal plane kinematics of patellofemoral replacement and compare with the normal knee.

Twelve patients who had undergone successful PFA at least two years previously were recruited. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. The kinematic profile of the PFA joints was compared to the profiles for fourteen normal knees.

Overall, the kinematic plot obtained for PFA reflected similar trends to that for normal knees; but the PTA was slightly but significantly increased throughout the entire range of flexion (two degrees). This is equivalent to an average displacement of the lower pole of the patella of 1.5mm.

Sagittal plane knee kinematics after PFA are much more normal than after TKR and this should give improved functional outcome. The observed increase in PTA through range may result from increased patella thickness or a shallow trochlear groove and may influence patellofemoral contact forces.

Patellofemoral pain is a significant problem for patients with Total Knee Replacements (TKRs). It is hypothesized that pain is related to high patellofemoral forces (PFF). The aim of this study is to validate a model to estimate PFF after TKR, using a combination of non-invasive measurement and theoretical modeling.

Experiments were performed on four cadaver knee specimens to compare the PFF and the quadriceps force (QF) estimated by a model, with those measured using force transducers. Each knee was tested in its initial state and after implantation of three Scorpio designs: Cruciate Retaining (CR), Posterior Stabilised (PS), and the Posterior Stabilised Mobile Bearing (PS+). Each knee was extended/flexed under a simulated quadriceps load with 3 kg hung from the distal tibia. Relative movement of the bones was measured using a Vicon 612 motion analysis system. A 6DOF force transducer was used to measure PFFs and a uni-axial transducer was used to measure QFs. A fluoroscope simultaneously captured images of the leg extension activity. Parameters measured from the images were used as inputs to the model.

The measured and estimated PFF and QF matched closely between 20o and 80o of knee flexion for the TKRs. At higher flexion angles, the model overestimated the PFF by a maximum of 23N (7.6% max) for the PFF and by 31N for the QF (10.3% max). The estimated and measured Patellar Flexion Angles (PFA) were within 3.5o throughout the flexion range.

The model accurately predicts sagittal plane patellar kinematics and kinetics, using only fluoroscopy and externally measured forces as inputs. However, the model has a limitation in assuming that the extending moment is only due to the quadriceps.

Award for the best student biomaterials paper (US$ 2,000); a proper certificate

Objectives : To determine the change in passive knee kinematics after Oxford Unicompartment Arthoplasty (UKA) (Biomet, Uk); and to compare the change in kinematics post-operatively between image guided and the normal surgical procedure.

Background: In anteromedial osteoarthritis, only the medial compartment of the knee is affected and the collateral ligaments as well as the cruciate mechanism are intact. These preconditions make the knee suitable for UKA. The operative technique of the Oxford UKA theoretically allows the surge on to replicate the natural kinematics of the knee, due to accurate ligament balancing and fully congruent meniscal bearing design of the prosthesis. Our hypothesis was that no difference in tibiofemoral kinematics is observed after UKA. In addition we also hypothesised that the results of the image guided surgery would be the same as the normal surgical procedure.

Design/Methods: To test this hypothesis, we conducted a study using 13 normal human cadaveric knees. For kinematic analysis, the Surgetics TM surgical navigation system (Praxim, France), equipped with custom written tracking software, was used. Reference markers were mounted to the proximal tibia and the distal femur. In a standardized set-up, the knee was positioned in a leg holder and preoperative kinematics of the normal knee was recorded after a para-patellar mini-incision (70–90 mm). Joint kinematics were recorded during passive knee flexion and plotted against flexion angle. Oxford UKA was performed; the standard Phase III instrumentation was used for six knees and the image guided procedure was used for seven knees. The main difference between the standard and image guided procedures was that the inter-medullary rod was not used for the image guided surgery. After the operation postoperative kinematics were recorded using the same measurement protocol. All data were processed using Matlab 6.1 analysis software (The Math Works Inc., MA, USA). Preoperative and postoperative tibiofemoral kinematics were determined and compared. The mechanical axes of the tibia and femur were determined and kinematics represented as functions of knee flexion range. Over both the flexing and extending cycles of the knee the changes in tibiofemoral rotation (& #916;ROT), tibiofemoral ab/adduction (& #916;ABD), and distances between the origins of the mechanical axes (& #916;X, & #916;Y, & #916;Z) were calculated between pre and post-operative states.

Design/Methods: To test this hypothesis, we conducted a study using 13 normal human cadaveric knees. For kinematic analysis, the Surgetics TM surgical navigation system (Praxim, France), equipped with custom written tracking software, was used. Reference markers were mounted to the proximal tibia and the distal femur. In a standardized set-up, the knee was positioned in a leg holder and preoperative kinematics of the normal knee was recorded after a para-patellar mini-incision (70–90 mm). Joint kinematics were recorded during passive knee flexion and plotted against flexion angle. Oxford UKA was performed; the standard Phase III instrumentation was used for six knees and the image guided procedure was used for seven knees. The main difference between the standard and image guided procedures was that the inter-medullary rod was not used for the image guided surgery. After the operation postoperative kinematics were recorded using the same measurement protocol. All data were processed using Matlab 6.1 analysis software (The Math Works Inc., MA, USA). Preoperative and postoperative tibiofemoral kinematics were determined and compared. The mechanical axes of the tibia and femur were determined and kinematics represented as functions of knee flexion range. Over both the flexing and extending cycles of the knee the changes in tibiofemoral rotation (& #916;ROT), tibiofemoral ab/adduction (& #916;ABD), and distances between the origins of the mechanical axes (& #916;X, & #916;Y, & #916;Z) were calculated between pre and post-operative states.

Conclusions: The image guidance system used in our study is a valuable tool for assessing pre- and postoperative knee kinematics. Oxford Unicompartmental Knee Arthroplasty with the Phase III instrumentation in the presence of the cruciate mechanism reproduces the normal kinematics of the knee very accurately. The image guided procedure, performed without the inter-medullary rod, produced similar results to the standard surgery. Image guidance has a great potential for the assessment of pre- and post-replacement kinematics of the knee joint during surgery.

Proprioception protects joints against injurious movements and is critical for joint stability maintenance under dynamic conditions. Knee replacement effect on proprioception in general remains elusive. This study aimed to evaluate the changes in proprioceptive performance after knee replacement; comparing Total (TKA) to Unicompartmental Knee Arthroplasty (UKA).

Thirty-four patients with osteoarthritis were recruited; 15 patients underwent TKA using the AGC prosthesis and 19patients underwent UKA using the Oxford prosthesis. Both cruciate ligaments were preserved in the UKA group, while only the PCL was preserved in TKA patients. Patients’ age was similar in both groups.> Joint Position Sense (JPS) and postural sway were used as measures of proprioception. Both groups were assessed pre- and 6 months post-operatively in both limbs. JPS was measured as the error in actively and passively reproducing five randomly ordered knee flexion angles between 30 and 70°using an isokinetic dynamometer. Postural sway (area and path) was measured during single leg stance using a Balance Performance Monitor. Functional outcome was assessed using the Oxford Knee Score (OKS).

Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb (UKA mean4.64°, SD1.44° and TKA mean5.18°, SD1.35°). No changes in JPS were seen in the control side. A significant improvement (P< 0.0001) in sway area and path was found in the UKA group only in both limbs. No significant changes in sway occurred in either limb of TKA patients. The OKS improved from 21.4 to 35.5 for TKA patients and from 23.9 to 38for UKA patients.

Both UKA and TKA improve proprioception as assessed by JPS. However, UKA alone improves postural sway in both limbs. This may impart explain why UKA patients function better than TKA patients

The Charnley Elite femoral component was first introduced in 1992 as a new design variant of the original Charnley femoral component (De Puy, Leeds, UK) with modified neck and stem geometry. The original component had undergone few changes in nearly forty years and has excellent long-term results. Early migration of the new stem design was determined by Roentgen Stereophotogrammetric Analysis (RSA)1. Rapid early migration of a component relative to the bone, measured by RSA, is predictive of subsequent aseptic loosening for a number of femoral stems. As there was rapid early migration and rotation of the Charnley Elite stem, we predicted that the long-term results would be poor. An outcome assessment is indicated as stems of this type are still being implanted.

One hundred Charnley Elite stems, implanted in our centre between 1994 and 1997 were included in a prospective, cross-sectional follow-up study. Outcome measures include validated clinical scores (Charnley hip score, Harris hip score and Oxford hip score) and radiological scores (Gruen classification) as well as revision rates over the past 10 years.

The clinical follow-up supports the RSA predictions of early failure of the Charnley Elite femoral stem.

Roentgen stereophotogrammetric analysis (RSA) is a tool that can provide quantitative information for objective evaluation and comparison of implant migration. The purpose of this study was to develop and validate a new method to determine the position and orientation of an implant with RSA that does not require the implant modification or acquisition of accurate 3D implant models. This method utilizes information from certain common features of implant geometry. This method has demonstrated in-vitro precision and accuracy of 0.005 !0.059 mm in position and 0.09 ! 0.166° in orientation which is equivalent to both marker and model based RSA methods

Roentgen stereophotogrammetric analysis (RSA) is a tool that can provide quantitative information for objective evaluation and comparison of implant migration. RSA measures have demonstrated the ability to both predict premature implant failure before clinical or standard radiological signs appear, and to elucidate implant wear which is considered a major causal factor in failure. To provide this functionality, RSA requires either the modification of each implant by the addition of spherical markers or the acquisition of accurate 3D models of each implant. These approaches can significantly limit the application of the RSA method. The purpose of this study was to develop and validate a new method to determine the position and orientation of an implant with RSA that does not require the modifying or acquiring accurate 3D models of each implant. This method is based on the geometric inter-relationship between the pair of RSA images and geometric information from the projected outlines of certain paired (visible in both views) features of implant geometry. Evaluations were performed on a metallic acetabular cup modified with spherical markers. The implant features used in this case where the hemispherical shell and the planar circle at the base of the acetabular cup. This method has demonstrated an average in-vitro precision and accuracy of 0.005 !0.059 mm in position and 0.09 ! 0.166° in orientation which was equivalent to that achieved with the marker based method and equivalent to published model based RSA results.

Funding: NSERC, GEOIDE, University of Calgary.

Introduction: The design philosophy of polished tapered THR stems, such as the Exeter, intend for them to migrate distally within the cement mantle. In addition it is likely that micromotion occurs as a result of functional activity. The pattern of induced stresses will be a function of stem geometry & surface finish, as well as applied loading. Aim: To investigate the stresses induced in the cement mantle of a polished tapered THR stem during functional activity.

Method: Using Roentgen Stereophotogrammetric Analysis (RSA) dynamically induced micro-motion (DIMM) was measured in 21 patients implanted with Exeter stems. DIMM was measured as the difference in stem position in going from double to single leg stance on the operated limb. All subjects were measured 3 months post-operatively. A finite element (FE) model of the femur, including all muscles was used to investigate the stress distribution within the cement; contact was modelled with sliding elements allowing separation. The model was validated by comparison to the DIMM measurements.

Results: The Exeter stem demonstrated significant DIMM(p < 0.017), the average motions are given in the table below. The FE model, with sliding contacts was able to predict similar distal migration of the head. The peak minimum principal stress in the mantle was approx 33MPa and occurred in the proximal medial region. Movements occurred at the stem/cement interface.

Discussion and Conclusion: It is possible to measure DIMM in the Exeter stem and combining this with FE modelling the mechanism of stress transfer between the stem and mantle can be investigated in a manner that can be validated.

Hypothesis Stem surface finish & cement mantle conformity influences pressure at the stem/cement interface, under physiological load.

Method We developed a scaled mechanical analogue of a cemented Exeter femoral stem with a temperature and pressure controlled fluid environment. The stem was subjected to physiological torsional & axial loads using a material testing machine with two perpendicularly mounted actuators. Rough (Ra=2.2μm), matt (Ra=1.16μm) & polished (Ra=0.02μm) stems were tested in both conforming & artificially created, asymmetrically worn, cement mantles. Pressure was recorded at five sites along the interface.

Results Pressure was generated in both conforming and worn mantles. Peak pressures recorded in worn mantles were nearly four times greater than in conforming; peak stem tip pressures, worn: 12000Pa, versus conforming: 4680Pa. The axial load was the main determinant of pressure generation in the conforming mantle. Torsional loads generated a rise in interface pressure in both mantle types but the resultant stem toggle seen in the worn mantle had a significant positive effect on pressure. Pressure fluctuations generated in the conforming mantle had the greatest range at the tip. Peak pressures within the worn mantle were more uniform, but marginally greater on the posterior wall. Surface finish influenced pressure; surface roughness had a positive association with pressure within conforming mantles & the reverse effect in worn mantles.

Conclusion Asymmetrical wear leads to increased pressure generation at the stem/cement interface under physiological loads, with the torsional load playing a key part in pressure generation. Well fixed, debonded stems also generate limited pressure fluctuations at their mantle interface. This is principally due to axial load. Mantle shape dictates the influence of surface finish on pressure; surface roughness increases pressure within conforming mantles, but reduces pressure when the mantle is worn. This may be a confounding effect of worn mantle shape, restricting non-polished stem movement.

Introduction: Minimally invasive surgery (MIS) presents challenges in achieving alignment for unicompartmental knee arthroplasty (UKA). Aim: Development and assessment of an image guidance system for MIS implanted Oxford UKA.

Methods: The Surgetics platform which uses intra-operative data acquisition was chosen as the base system. Software was developed to determine height of tibial cut, image guidance of saws, alignment of components and assessment of ligament tension. The accuracy of component placement was assessed in vitro using matched pairs of knees randomised into navigated (NAV n=10) and standard manual (MAN n=10) procedures; standardised postoperative A-P and lateral radiographs were used. Pre and post-operative kinematics were assessed (NAV n=6, MAN n=7). The changes postoperatively over knee flexion and extension were calculated for tibiofemoral rotation (ΔROT) and ab/adduction (ΔABD).

Results: Accurate component placement was achieved with both methods without significant differences. Tibial cut height was more accurately in the NAV group (re-cut rate: NAV 33%, MAN 50%). NAV femoral component placement was as accurate as MAN with intramedullary rod. For the flexing cycle mean ΔROT was −0.06° (range 6.08° to −3.93°) and mean ΔABD was −0.04° (range 3.39° to −5.72°). There were no observable differences between the NAV and MAN kinematics. Overall, no observable differences were found between pre and post-operative kinematics.

Conclusions: Image guidance produces accurate placement through MIS approach and reduces the amount of tibial bone resection.