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Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_10 | Pages 120 - 120
1 May 2016
Walker P Meere P Borukhov I Bell C
Full Access

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:

The lateral and medial contact forces at surgery, expressed as FL/FM

The distraction tensions in the collateral ligaments at surgery, expressed as TL/TM

The moments to cause lift-off when a varus or valgus moment is applied, MVAR/MVAL

The varus and valgus angles measured at post-op follow-up, VAR/VAL

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.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_10 | Pages 116 - 116
1 May 2016
Walker P Meere P Borukhov I Bell C
Full Access

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:

The lateral and medial contact forces at surgery, expressed as FL/FM

The distraction tensions in the collateral ligaments at surgery, expressed as TL/TM

The moments to cause lift-off when a varus or valgus moment is applied, MVAR/MVAL

The varus and valgus angles measured at post-op follow-up, VAR/VAL

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.

RESULTS

The ratio TL/TM was approx. equal to FL/FM, especially near to a balanced state

The ratio MVAR/MVAL (lift-off moments) was equal to FL/FM

The ratio VAR/VAL was approx. equal to FL/FM only if the collateral stiffnesses were equal;

otherwise the ratio was approx. proportional to the collateral stiffnesses.

In the clinical follow-ups, there was no significant linear relation between VAR/VAL and FL/FM.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_3 | Pages 35 - 35
1 Jan 2016
Bell C Meere P Borukhov I Walker P
Full Access

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.

Materials and Methods

Our team developed a Smart Knee Fixture to measure VV angular changes using two dielectric elastomer stretch sensors, placed strategically over the medial and lateral collateral ligaments (see Figure 1). The brace is secured in position with the leg in full extension and the sensors locked with pre-tension. Therefore, contraction and elongation of either sensor is measured and the VV angular deviation of the long axis of the femur relative to that of the tibia is derived and displayed in real time using custom software. EMG muscle activity was previously investigated to confirm there is no resistive activity during the VV test obstructing ligamentous evaluations.

The device was validated in two ways:

A bilateral lower body cadaver specimen, secured in a custom test rig, was used to compare the Smart Knee Fixture's readings to those measured from an optical surgical navigation system. Abduction and adduction force was gradually applied as varus and valgus moments with a wireless hand-held dynamometer up to 50N (19.8Nm) at 0 and 15° flexion.

Two male volunteers were used to compare the Smart Knee Fixture's readings to those measured from fluoroscopic images. An arthroscopic distal thigh leg immobilizer was used to prevent rotation and lateral movements of the thigh when moments were applied at the malleoli. A C-arm Fluoroscope was then positioned focusing on the center of the joint. The tests were performed at full extension, 10 and 20° of flexion and force was gradually applied to 50N.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 193 - 193
1 Dec 2013
Walker P Meere P Bell C
Full Access

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.

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

Tibial frontal varus, 2 mm lateral stuffing

Tibial frontal valgus, 2 mm medial stuffing

Tibial slope angle increase (5 deg baseline); +2 degrees

Tibial slope angle decrease (5 deg baseline); −2 degrees

Increase in AP size of femoral component (3 mm)

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.


The Bone & Joint Journal
Vol. 95-B, Issue 11_Supple_A | Pages 129 - 132
1 Nov 2013
Berend KR Lombardi Jr AV Adams JB

Debate has raged over whether a cruciate retaining (CR) or a posterior stabilised (PS) total knee replacement (TKR) provides a better range of movement (ROM) for patients. Various sub-sets of CR design are frequently lumped together when comparing outcomes. Additionally, multiple factors have been proven to influence the rate of manipulation under anaesthetic (MUA) following TKR. The purpose of this study was to determine whether different CR bearing insert designs provide better ROM or different MUA rates. All primary TKRs performed by two surgeons between March 2006 and March 2009 were reviewed and 2449 CR-TKRs were identified. The same CR femoral component, instrumentation, and tibial base plate were consistently used. In 1334 TKRs a CR tibial insert with 3° posterior slope and no posterior lip was used (CR-S). In 803 there was an insert with no slope and a small posterior lip (CR-L) and in 312 knees the posterior cruciate ligament (PCL) was either resected or lax and a deep-dish, anterior stabilised insert was used (CR-AS). More CR-AS inserts were used in patients with less pre-operative ROM and greater pre-operative tibiofemoral deformity and flexion contracture (p < 0.05). The mean improvement in ROM was highest for the CR-AS inserts (5.9° (-40° to 55°) vs CR-S 3.1° (-45° to 70°) vs CR-L 3.0° (-45° to 65°); p = 0.004). There was a significantly higher MUA rate with the CR-S and CR-L inserts than CR-AS (Pearson rank 6.51; p = 0.04). Despite sacrificing or not substituting for the PCL, ROM improvement was highest, and the MUA rate was lowest in TKRs with a deep-dish, anterior-stabilised insert. Substitution for the posterior cruciate ligament (PCL) in the form of a PS design may not be necessary even when the PCL is deficient.

Cite this article: Bone Joint J 2013;95-B, Supple A:129–32.


Orthopaedic Proceedings
Vol. 97-B, Issue SUPP_1 | Pages 66 - 66
1 Feb 2015
Rosenberg A
Full Access

Laxity Differences in CR & PS TKA -Achieving Total Knee Balancing Using Bone Cut Adjustments and Correlation with Varus-Valgus Lift-Off. The Incidence and Mid Term Functional Effect of Partial PCL Recession in Fixed and Mobile Bearing PCL Retaining TKA. Clinical and Radiographic Results of a Modern Design, Onlay Patellofemoral Arthroplasty at a Minimum Two-Year Follow-Up. Custom Cutting Guides Do Not Improve Total Knee Arthroplasty Outcomes at 2 Years Follow-up. Tourniquet Use During TKA -Effect on Recovery of Strength and Function: a randomised, double-blind, control trial. Prospective, Randomised Trial of Standard vs Cross-linked Tibial Poly. Crosslink vs. Conventional TKA Poly Retrieval Analysis. Unplanned Readmissions after TKA Using a Statewide Database. Does Prior Cartilage Restoration Negatively Impact Outcomes of TKA. Periprosthetic Femur Fracture: Better to Revise than to Fix. Increased Non-stemmed Tibial Failures in Patients with a BMI ≥ 35. The Effect Of Canal Fit And Fill in Revision THA With Modular, Fluted, Tapered Stems. The Wagner Cone Stem For The Challenging Femur In Primary Total. Will Metal Heads Restore Integrity of Corroded Trunnions at Revision THR?. Influence of Head Size, Materials and Taper Design on Fretting and Corrosion of Metal on Polyethylene THR. Delta Ceramic on Ceramic THA – Midterm IDE Study Results. Refining Acetabular Safe Zone for Posterior Approach in THA. Comparison of a Pain Program for THA with and without Liposome Bupivacaine


Bone & Joint 360
Vol. 4, Issue 1 | Pages 16 - 18
1 Feb 2015

The February 2015 Knee Roundup360 looks at: Intra-operative sensors for knee balance; Mobile bearing no advantage; Death and knee replacement: a falling phenomenon; The swings and roundabouts of unicompartmental arthroplasty; Regulation, implants and innovation; The weight of arthroplasty responsibility!; BMI in arthroplasty