Introduction

The regionalisation of major trauma in the UK has significantly improved outcomes for patients with severe, lower limb injuries. Chronic pain after complex lower limb injuries is well documented, but seems to remain a problem despite better clinical and radiological outcomes. We hypothesised that pain was mediated through the saphenous nerve, especially as most tibial injuries affected the soft tissues medially. As a proof of concept, we undertook adductor canal blocks to understand pain aetiology.

The aim was to predict the number and incidence of distal radius fractures in Scotland over the next two decades according to age group, categorised into under 65yrs(<65) and 65yrs and older (≥65), and estimate the potential increased operative burden of this.

The number of distal radius fracture in Scotland was isolated from the Global Burden of Disease database and this was used, in addition to historic population data and population estimates, to create a multivariable model allowing incorporation of age group, sex and time. A Negative Binomial distribution was used to predict incidence in 2030 and 2040 and calculate projected number of fractures according to the population at risk. A 20.4% operative intervention rate was assumed in the ≥65 group (local data).

In terms of number of fractures, there was a projected 61% rise in the ≥65 group with an overall increase of 2099 fractures per year from 3417 in 2020 (95% confidence interval (CI) 2960 – 3463) to 5516 in 2040 (95% CI 4155–5675). This was associated with 428 additional operative interventions per year for those ≥65yrs. The projected increase between 2020 and 2040 was similar in both sexes (60% in females, 63% in males), however the absolute increase in fracture number was higher in females (2256 in 2020 [95% CI 1954–2287] to 3620 in 2040 [95% CI 2727–3721]) compared to males (1160 [95% CI 1005–1176] to 1895 [95% CI 1427–1950]). There was a 4% projected fall in the number of fractures in those <65.

Incidence of distal radius fractures is expected to considerably increase over the next two decades due to a projected increase in the number of fractures in the elderly. This has implications for the associated morbidity and healthcare resource use.

The aim of this study was to determine the floor and ceiling effects for both the QuickDASH and PRWE following a fracture of the distal radius. Secondary aims were to determine the degree to which patients with a floor or ceiling effect felt that their wrist was ‘normal’, and if there were patient factors associated with achieving a floor or ceiling effect.

A retrospective cohort study of patients sustaining a distal radius fracture and managed at the study centre during a single year was undertaken. Outcome measures included the QuickDASH, the PRWE, EuroQol-5 Dimension-3 Levels (EQ-5D-3L), and the normal wrist score.

There were 526 patients with a mean age of 65yrs (20–95) and 421 (77%) were female. Most patients were managed non-operatively (73%, n=385). The mean follow-up was 4.8yrs (4.3–5.5). A ceiling effect was observed for both the QuickDASH (22.3%) and PRWE (28.5%). When defined to be within the minimum clinical important difference of the best available score, the ceiling effect increased to 62.8% for the QuickDASH and 60% for the PRWE. Patients that achieved a ceiling score for the QuickDASH and PRWE subjectively felt their wrist was only 91% and 92% normal, respectively. On logistic regression analysis, a dominant hand injury and better health-related quality of life were the common factors associated with achieving a ceiling score for both the QuickDASH and PRWE (all p<0.05).

The QuickDASH and PRWE demonstrate ceiling effects when used to assess the outcome of fractures of the distal radius. Patients achieving ceiling scores did not consider their wrist to be ‘normal’. Future patient-reported outcome assessment tools for fractures of the distal radius should aim to limit the ceiling effect, especially for individuals or groups that are more likely to achieve a ceiling score.

This systematic review and meta-analysis aimed to compare the outcome of operative and non-operative management in adults with distal radius fractures, with an additional elderly subgroup analysis. The main outcome was 12-month PRWE score. Secondary outcomes included DASH score, grip strength, complications and radiographic parameters.

Randomised controlled trials of patients aged ≥18yrs with a dorsally displaced distal radius fractures were included. Studies compared operative intervention with non-operative management. Operative management included open reduction and internal fixation, Kirschner-wiring or external fixation. Non-operative management was cast/splint immobilisation with/without closed reduction. Version 2 of the Cochrane risk-of-bias tool was used.

After screening 1258 studies, 16 trials with 1947 patients (mean age 66yrs, 76% female) were included in the meta-analysis. Eight studies reported PRWE score and there was no clinically significant difference at 12 weeks (MD 0.16, 95% confidence interval [CI] −0.75 to 1.07, p=0.73) or 12 months (mean difference [MD] 3.30, 95% CI −5.66 to −0.94, p=0.006). Four studies reported on scores in the elderly and there was no clinically significant difference at 12 weeks (MD 0.59, 95% CI −0.35 to 1.53, p=0.22) or 12 months (MD 2.60, 95% CI −5.51 to 0.30, p=0.08). There was a no clinically significant difference in DASH score at 12 weeks (MD 10.18, 95% CI −14.98 to −5.38, p<0.0001) or 12 months (MD 3.49, 95% CI −5.69 to −1.29, p=0.002). Two studies featured only elderly patients, with no clinically important difference at 12 weeks (MD 7.07, 95% CI −11.77 to −2.37, p=0.003) or 12 months (MD 3.32, 95% CI −7.03 to 0.38, p=0.08).

There was no clinically significant difference in patient-reported outcome according to PRWE or DASH at either timepoint in the adult group as a whole or in the elderly subgroup.

Glenoid baseplate positioning for reverse total shoulder replacements (rTSR) is key for stability and longevity. 3D planning and image-derived instrumentation (IDI) are techniques for improving implant placement accuracy. This is a single-blinded randomised controlled trial comparing 3D planning with IDI jigs versus 3D planning with conventional instrumentation.

Eligible patients were enrolled and had 3D pre-operative planning. They were randomised to either IDI or conventional instrumentation; then underwent their rTSR. 6 weeks post operatively, a CT scan was performed and blinded assessors measured the accuracy of glenoid baseplate position relative to the pre-operative plan.

47 patients were included: 24 with IDI and 23 with conventional instrumentation. The IDI group were more likely to have a guidewire placement within 2mm of the preoperative plan in the superior/inferior plane when compared to the conventional group (p=0.01). The IDI group had a smaller degree of error when the native glenoid retroversion was >10° (p=0.047) when compared to the conventional group. All other parameters (inclination, anterior/posterior plane, glenoids with retroversion <10°) showed no significant difference between the two groups.

Both IDI and conventional methods for rTSA placement are very accurate. However, IDI is more accurate for complex glenoid morphology and placement in the superior-inferior plane. Clinically, these two parameters are important and may prevent long term complications of scapular notching or glenoid baseplate loosening.

Image-derived instrumentation (IDI) is significantly more accurate in glenoid component placement in the superior/inferior plane compared to conventional instrumentation when using 3D pre-operative planning. Additionally, in complex glenoid morphologies where the native retroversion is >10°, IDI has improved accuracy in glenoid placement compared to conventional instrumentation. IDI is an accurate method for glenoid guidewire and component placement in rTSA.

Anterior cruciate ligament (ACL) ruptures are debilitating injuries, often managed via ACL reconstruction (ACLR). Reduced range of motion (ROM), particularly loss of extension (LOE), is the most significant contributor to post-operative patient dissatisfaction. LOE may preclude return to sport, increase re-rupture rates and precipitate osteoarthritis.

Passive LOE rates following ACLR have been reported at 15%. However, LOE incidence during active tasks are poorly characterised. Our review sought to determine knee extension angles for active tasks following an ACL injury or ACLR. We hypothesised greater incidences of active LOE following ACL injury or ACLR, compared to uninjured contralateral limbs or controls.

We systematically searched MEDLINE, Embase, Cochrane Library, Scopus, SPORTDiscus, and relevant trials databases for English articles. Included were cohort, cross-sectional, case-controlled or randomised controlled trials analysing adults with ACL injury treated surgically or otherwise, with at least 12-weeks follow-up and reporting either active knee extension angle, active LOE angles or incidence of active knee LOE during functional tasks. The protocol was registered on PROSPERO (CRD42018092295). Subsequent meta-analysis was performed.

After screening, 71 eligible articles were included. Studies were heterogenous in design and quality. Included tasks were overground walking (n=44), running (n=3), hopping/jumping/cutting (n=11) single-leg landing (n=7), and stair climbing (n=6). LOE incidence varied depending on functional activities (33.95-92.74%). LOE incidence did not vary depending on ACL status (67.26% vs. 65.90% vs. 62.57% for ACL intact, ACLD and ACLR, respectively).

We observed no difference in active LOE incidence according to ACL status. Importantly, the observed incidence for active LOE was reliably higher than previously reported rates for passive measures.

Given the discrepancy between active and passive LOE incidence, clinicians may advisably prioritise active ROM during ACL rehabilitation.

Background

Intraoperative blood loss is a known potential complication of total knee arthroplasty (TKA). Tranexamic acid (TXA) has been shown to reduce intraoperative blood loss and postoperative transfusion in patients undergoing TKA. While there are numerous studies demonstrating the efficacy of intravenous and topical TXA in patients undergoing TKA, there are comparatively few demonstrating the effectiveness and appropriate dosing recommendations of oral formulations.

Introduction

A common phenomenon occurring as a result of reverse total shoulder arthroplasties (RSA) is scapular notching. While bone loss of the scapula may be quantified using radiographic techniques,[1] the material loss on the humeral bearing has not been quantified. Depending on their functional biological activity, a high volume of polyethylene wear particles has been shown to be related to osteolysis, bone loss and ultimately, loosening of implants in other joints.[2] In order to understand the threshold for osteolysis in the shoulder, it is important to have a method that can accurately quantify the amount of material loss. The aim of this research was to (I) create and validate a method for quantifying material loss from a single humeral implant design which can then (II) be used to measure retrieved devices.

Introduction

The major function of the medial meniscus has been shown to be distribution of the load with reduction of cartilage stresses, while its role in AP stability has been found to be secondary. However several recent studies have shown that cartilage loss in OA occurs in the central region of the tibia while the meniscus is displaced medially. In a lab study (Arno, Hadley 2013) it was confirmed that the AP laxity was greatly reduced with a compressive force across the knee, while the femur shifted posteriorly and the AP laxity was increased after a partial meniscetomy of the posterior horn. It is therefore possible that under load, the compression of the meniscus and the cartilage, 2–3mm in total, allows load transmission on the central tibial plateau, and causes radial expansion and tension of the meniscus providing restraint to femoral displacements. This leads to our hypotheses that the highest loading on the medial meniscus would be at the extremes of motion, rather than in the mid-range, and that the meniscus would provide the majority of the restraint to anterior-posterior femoral displacements throughout flexion when compressive loads were acting.

PURPOSE

Soft tissue balancing can be achieved by using spacer blocks, by distractors which measure tensile forces, or by instrumented devices which measure the forces on the lateral and medial condyles. However there is no quantitative method for assessment of balancing at clinical follow-up; to address this, we developed a Smart Knee Fixture (SKF) which measured the varus and valgus angles for a moment of 10 Nm. Our purpose was to determine if varus and valgus angles measured at clinical follow-up, was equivalent to the balancing parameters of distraction forces or contact forces measured at surgery.

PURPOSE

Soft tissue balancing can be achieved by using spacer blocks, by distractors which measure tensile forces, or by instrumented devices which measure the forces on the lateral and medial condyles. However there is no quantitative method for assessment of balancing at clinical follow-up; to address this, we developed a Smart Knee Fixture (SKF) which measured the varus and valgus angles for a moment of 10 Nm. Our purpose was to determine if varus and valgus angles measured at clinical follow-up, was equivalent to the balancing parameters of distraction forces or contact forces measured at surgery. METHODS: The SKF, which measured VV angles using stretch sensors on each side of the knee, was validated by cadaver studies, fluoroscopy, and emg. The balancing parameters were:

A force analysis, and measurements on 101 surgical cases & clinical follow-up in an IRB study, were carried out to determine the relationship between these parameters.

Introduction

Evaluation of post-operative soft tissue balancing outcomes after Total Knee Arthroplasty (TKA) and other procedures can be measured by stability tests, with Anterior-Posterior (AP) drawer tests and Varus-Valgus (VV) ligamentous laxity tests being particularly important. AP stability can be quantified using a KT1000 device; however there is no standard way of measuring VV stability. The VV test relies on subjective force application and perception of laxity. Therefore we sought to develop and validate a device and method for quantifying knee balancing by analyzing VV stability.

The use of smart trial components is now allowing a better assessment of soft tissue balancing at the time of total knee replacement surgery. A balanced knee can be defined as one that possesses symmetry, ie. equal and centered lateral and medial forces through the full range of flexion. There is still a need for a standard reproducible surgical test to quickly confirm optimized balancing at surgery with such devices. The Heel Push test is the established standard, by pushing the foot in a cephalad direction while supporting the thigh and keeping the leg stable in the vertical plane. A common variation of this test is the Thigh Pull test where the foot is actively assisted during the cephalad pull of the thigh through deep flexion. The test is an open chain test. The Thigh Pull test may be an improvement since the weight of the leg is alleviated and no supplemental compressive forces are introduced. The directional changes of the lower extremity are thus a result of ligamentous tension and balances. The purpose of this study is to compare the two tests using a standard testing methodology and observe the variation in kinetic parameters in a controlled biomechanical setting.

A custom l rig was developed, which independently controls all six degrees of freedom about the knee joint. In addition a commercial navigation system was used to derive instantaneous alignment values and flexion angles between the tibia and femur. The pelvis was fixed to the table and the foot was fitted onto a low friction carriage along a slide rail. The knee design used was cruciate retaining. The pressure mapping system was a wireless tibial trial that provided magnitude of load per compartment.

The study is a preliminary cadaveric study reporting the data from two. In this experiment the leg was then tested with the Heel Push and Thigh Pull tests after obtaining optimum soft tissue balance of the cadaveric specimen. From this standard neutral state a series of single surgical variables were introduced to mimic common intra-operative surgical corrections. This was achieved through custom tibial liner and angle shims.

The results defied theoretical anticipation. Though the total contact forces with heel push were generally higher than with thigh pull, the relative load distribution between compartments did not follow a trend (see Figure 1). Furthermore in deeper flexion the persistence of relatively high contact pressures would suggest that ligaments still generate intra-articular forces despite the much weaker gravitational effect. The clinical relevance lies in the asymmetry of the load distribution between medial and lateral compartment for the two methods tested. The load asymmetry as tested by the Thigh Pull test may correspond to an open chain in swing phase. This asymmetry would force some axial rotation and tibial femoral alignment deviation that can significantly affect the forces at the time of heel strike. The Heel Push test would be more representative of the compressive forces in a closed chain mode as seen during the stance phase of gait.

Soft tissue balancing in total knee replacement may well be the determining factor in raising the fair patient satisfaction. The development of intelligent implants allows quantification of reactive loads to applied pressures. This can be tested in dynamic mode such as heel push test at surgery, or in static mode such as when testing for varus/valgus (VV) laxity of the collateral ligaments of the knee. We postulate that a well-balanced knee will have comparable if not equal load distribution across compartments in dynamic loading. When tested for laxity, we anticipate an equal or comparable response to VV applied loads under physiologic load range of 10–50N. This study sought to analyze the relationship between the kinematic (joint motion) and kinetic (force) effects to VV testing in the 0–15 degrees range of flexion. One goal was to demonstrate that testing the knee in locked extension (Screw Home effect) is unreliable and should be abandoned in favor of the more reliable VV testing at 10–15 degrees of flexion.

This is a preliminary cadaveric study utilizing data from two hemibodies. The pelvis was fixed in a custom test rig with open or closed chain lower leg testing capability along a sliding rail with foot VV translational. Forces were applied at the malleoli with a wireless hand held dynamometer. Kinematic analysis of the hip-knee-ankle (HKA) tibiofemoral angle was derived from a commercial navigation system with mounted infrared trackers. Kinetic analysis was derived from a commercially available sensor imbedded in a tibial trial liner. Balance was optimized by conventional methods with the use of the sensor feedback until loads were roughly symmetrical and VV testing yielded symmetrical rise in opposite compartments. The VV testing was then performed with the knees locked at the femoral side in axial rotation and translational motion in any plane. Sagittal flexion was pre-set at 0, 10, and 15 degrees and progressive load was applied.

There are many different approaches to achieving balancing in total knee surgery. The most frequently used method is to obtain correctly aligned bone cuts, and then carry out necessary soft tissue releases to achieve equal flexion and extension gaps. In some techniques, the bone cuts themselves are determined by the prevailing soft tissue status or the kinematics during flexion-extension. Navigation can provide quantitative data during these processes but so far, navigation is used in only in a minority of cases. However in recent years, new technologies have been introduced with lower cost and implementation time, allowing for more widespread use. Early studies have indicated that more reproducible balancing can be obtained, and that balancing has a positive effect on clinical outcomes. However the ability to measure balancing quantitatively during surgery, has raised the questions of the most systematic method for implementation during surgery, and the relative influence of various correcting factors. Further, the ideal balancing parameters with respect to varus-valgus ratios and the magnitudes during a full flexion range, have yet to be defined. Even if normative data is the target, there is scant data on this topic.

In our own laboratory, we carried out experiments on knee specimens where the various surgical variables were systematically investigated for their effect on varus-valgus balancing. Different tests were developed including the ‘Heel Push Test’ where lateral and medial contact forces were plotted as a function of flexion. Imbalances were achieved with either bone cut adjustments or soft tissue releases. The major finding was that adjustments of only 2 mms or 2 degrees could correct most imbalances. This was considered to be due to two effects; the pretension in the ligaments bringing the structure to the stiff part of the load-elongation curve, and the high values of the stiffness itself. Medial-lateral equality was the goal in this work, but recognizing that this may not be the situation in the normal knee. To answer this question, we developed a method for measuring the varus-valgus balancing in normal subjects, using a ‘Smart Knee Fixture’ with embedded stretch sensors. We validated this device using cadaveric specimens, and normal volunteers using fluoroscopy and electromyography. We are now applying the method in an IRB study to both normals and post-operative knee replacement cases. For the latter, the relation between operative data, and post-operative balancing will be studied, as well as the relation of balancing to functional outcomes.

This overall subject of balancing at surgery, and the post-operative effects, is open to extensive experimental research, and is predicted to result in improved outcomes.

Total Knee Arthroplasty (TKA), has now become a reliable, successful, and widely used treatment for osteoarthritis. Numerous reports indicate that for the majority of patients, the TKA lasts a lifetime with pain relief and the ability to perform most everyday activities. However there are a number of ways in which the procedure can be further improved, the focus here being on function. One of the problems in evaluating function is that it depends upon the inherent ability, motivation, and expectation of the patients. There are several well-used questionnaire systems which capture functional ability objectively. In the effort to simplify evaluation, a ‘forgotten knee’ evaluation has been introduced, the concept being that ‘the ideal TKA design’ would feel and function like a normal knee. Such a measure would include factors such as surgical technique, alignment, and rehabilitation, as well as the TKA design itself. Another approach to evaluation is to measure biomechanical parameters, such as in gait analysis and fluoroscopy, which evaluate kinematic or kinematic parameters, using normal controls for comparison. Nevertheless, such evaluations still include factors other than the TKA design itself, and do not apply to new designs.

The approach taken here for the evaluation of a new TKA design independent of other factors, is to measure the neutral path of motion and the laxity boundaries of the loaded knee on the application of shear and torque over a full range of flexion. The benchmark is the same kinematic data from the normal intact knee. The rationale has some analogy to the ‘forgotten knee’ in that if the laxity response of a design of TKA is the same as that of the anatomic knee itself, the behavior of that implanted knee in any functional condition will be indistinguishable from that of the anatomic knee itself. Such a testing concept has some similarities to the constraint test described in the ASTM standard. In this paper, a novel design algorithm is proposed for creating different design concepts. First, a general morphological form is formulated for each design concept, a Cam-Post PS, a Saddle-Ramp, and a Converging Condyle, all with overall anatomic-like surfaces. Each femoral component is then designed, which is then moved through the normal neutral path and laxity paths, which creates the tibial surface. The concepts are evaluated using a Desktop Knee Machine configured to move the knee dynamically through full flexion while applying combinations of compression, shear and torque; kinematic data being captured optically and plotted using custom software. The normal benchmark was obtained from 10 normal knee specimens, which showed the restraint of the medial femoral condyle to anterior displacement and the overall rollback and laxity laterally. Compared with standard CR and PS designs, the Guided Motion designs were seen to more closely resemble normal. It is proposed that this approach can result in designs which will more likely reproduce a ‘forgotten knee’ and achieve the optimal function for a given patient.

Aim

This study aims to elucidate the effects of radiofrequency chondroplasty (RFC), a surgical technique for the treatment of damaged articular cartilage, at a microscopic scale. Here we report about two aspects of the study – a morphological analysis of the treated surface using nonlinear microscopy and Raman spectroscopy, and an investigation into changes in permeability to large and small molecules. Cartilage samples were obtained from

Balancing in total knee replacement is generally carried out using the feel and experience of the surgeon, using spacer blocks or distractors. However, such a method is not generally applicable to all surgeons and nor does it provide quantitative data of the balancing itself. One approach is the use of instrumented distractors, which have been used to monitor soft tissue releases or indicate a flexion cut for equal lateral and medial forces. More recently an instrumented tibial trial has been introduced which measures and displays the magnitude and location of the loads on the lateral and medial plateaus, during various manoeuvres carried out at surgery. The data set is then used by the surgeon to determine options, whether soft tissue releases or bone cut adjustments, to achieve lateral-medial equality.

The testing method consisted of mounting the femoral component rigidly in a fixture on the vertical arm of an MTS machine. The tibial component was fixed on to a platform which allowed varus-valgus correction, and where the component could be displaced or rotated in a horizontal plane. Two of each size times 4 sizes of production components were tested. Compressive forces from 0–400N in steps of 50N were applied and the readings taken. There were strong correlations between applied and measured forces with mean Pearson's Correlation Coefficient of 0.958.

The special tests under different conditions did not have any effect on the output values. The output data proved to be repeatable under Central Loading with a maximum standard deviation of ± 15.36N at the highest applied force of 400N. “Low battery” did not adversely affect the data. Applying the load steadily to maximum versus load-unload-zero tests produced similar results. Lubrication versus no lubrication tests produced no changes to the results. There was no cross talk of the electronics within the device when loaded on one condyle. For both central and anterior-posterior loading, the contact points were centered medial-lateral on the GUI display, and tracked contact point translation appropriately.

Anterior-posterior loading did create output load variance at the extremes. However, it enabled the validation of the relationship of the femur on the trial surface. In addition, malrotation would be indicated by the femur riding up on the anterior or posterior tibial edges, important for soft tissue tension in all flexion angles.

In conclusion, the sensors provided data which was accurate to well within a practical range for surgical conditions. In our separate experiments on 10 cadaveric leg specimens, even the same test under controlled conditions could produce variations of up to ± 30N. Hence the sensor outputs indicated whether or not the knee was balanced to that level of tolerance, while the contact point data would indicate contacts too close to the anterior or posterior of the tibial surface.

The purpose of balancing in total knee surgery is to achieve smooth tracking of the knee over a full range of flexion without excessive looseness or tightness on either the lateral or medial sides. Balancing is controlled by the alignment of the bone cuts, the soft tissue envelope, and the constraint of the total knee. Recently, Instrumented Tibial Trials (OrthoSensor) which measure and display the location and magnitude of the forces on the lateral and medial condyles, have been introduced, offering the possibly of predictive and quantitative balancing. This paper presents the results of experiments on 10 lower limb specimens, where the effects of altering the bone cuts or the femoral component size were measured.

A special leg mounting rig was fixed to a standard operating table. A boot was strapped to the foot, and the boot tracked along a horizontal rail to allow flexion-extension. The initial bone cuts were carried out by measured resection using a navigation system. The trial femoral component and the instrumented tibial trial were inserted, and the following tests carried out:

Sag Test; foot lifted up, the trial thickness chosen to produce zero flexion.

Heel Push Test; heel moved towards body to maximum flexion.

Varus-Valgus Test, AP and IXR Tests were also carried out, but not discussed here.

For an initial state of the knee, close to balanced, the lateral and medial contact forces were recorded for the full flexion range. The mean value of the contact forces per condyle was 77.4N, the mean in early flexion (0–60 deg) was 94.2N, and the mean in late flexion (60–120 deg) was 55.7N. The difference was due to the effect of the weight of the leg. One of the following Surgical Variables was then implemented, and the contact forces again recorded. 1.

Distal femoral cut; 2 mm resection (2 mm increase in insert thickness to preserve extension)

The differences between the condyle force readings before and after the Surgical Variable were calculated for low and high angular ranges. The mean values for the 10 knees of the differences of the above Surgical Variables from the initial balanced state are shown in the chart.

From literature data, the mean tension increase in one collateral ligament is close to 25N/mm up to the toe of the load-elongation graph, and 50N/mm after the toe. Hence in the initial balanced state, the collateral ligaments were elongated by 2–4 mm producing pretension. From the Surgical Variables data, up to 2 mm/2 deg change in bone cuts (or 3 mm femcom change), and collateral ligament releases up to 2 mm, would correct from any unbalanced state to a balanced state.

This data provides useful guidelines for the use of the Instrumented Tibial Trials at surgery, in terms of bone cut adjustments and ligament releases.

Obtaining accurate bone cuts based on mechanical axes and ligament balancing, are necessary for a successful total knee procedure. The OrthoSensor Tibial Trial displays on a GUI the magnitude and location of the lateral and medial contact forces at surgery. The goal of this study was to develop algorithms to inform the surgeon which bone cuts or soft tissue releases were necessary to achieve balancing, from an initial unbalanced state.

A rig was designed for lower body specimens mounted on a standard operating table. SURGICAL TESTS were then defined: Sag Test, leg supported at the foot; Dynamic Heel Push test, flexing to 120 degrees with the foot sliding along a rail; Varus-Valgus test; AP Drawer test; Internal-External Rotation test. The bone cuts were made using a Navigation system, matching the Triathlon PCL retaining knee. To determine the initial thickness of the tibial trial, the Sag Test was performed to reach 0 deg flexion. The Heel Push Test was then performed to check the AP position of the lateral and medial contacts, from which the rotational position of the tibial tray was determined. Pins were used to reproduce this position during the experiments.

SURGICAL VARIABLES were then defined, which would influence the balancing: LCL Stiffness, MCL Stiffness, Distal Femoral Cut Level, Tibial Sagittal Slope, Tibial Varus or Valgus, and AP Femoral Component Length. Balancing was defined as equal lateral and medial forces due to soft tissue tensions throughout the flexion range, equal varus and valgus stiffnesses, and no contacts closer than 10 mm to component edges. All of the above tests were then performed sequentially, and the changes in the contact force readings were considered as a signature of that Surgical Variable.

Testing was carried out on 10 full leg specimens. The Sag Test was the basic test for determining the thickness of the tibial insert. The Heel Push Test was then implemented from which force data throughout flexion was determined; followed by the Varus-Valgus Test. In a surgical case, this data will be used in a decision tree to identify which Surgical Variable required correction. In the experiments, by obtaining the above data for each SURGICAL VARIABLE in turn, we were able to determine a SIGNATURE for each SURGICAL VARIABLE. It was found that there was considerable variation in the force magnitudes between knees. However the SIGNATURES were sufficient to point to the specific SURGICAL VARIABLE requiring correction. In some knees, although there was a dominant SURGICAL VARIABLE, even after correcting for that, there was still an imbalanced state, requiring a second correction.

This research provided the fundamental principles and data for: 1.

Defining tests to be carried out at surgery, to obtain force data to determine the SURGICAL VARIABLE to correct.