This work was supported by Beijing Hospitals Authority Clinical Medicine Development of Special Funding Support [grant numbers: XMLX202139]. We would like to express our gratitude to Diego Wang for valuable suggestions.

The protocol was approved by the Ethics Committee of Xuanwu Hospital (grant number: 2021-224) and was conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from next of kin to use the cadavers.
1. Installation of angle measuring device
<ol>
	<li>Turn on the switch of the femur and tibia angle measuring device. Open the angle measurement software on the tablet computer, scan the QR codes of the two measuring devices, and click Bluetoo...

<ol>
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B., Eickmann, T. H., Anbari, K. K., Engh, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lateral+tibiofemoral+compartment+narrowing+after+medial+unicondylar+arthroplasty.">Lateral tibiofemoral compartment narrowing after medial unicondylar arthroplasty.</a> Clinical Orthopaedics and Related Research. 464, 43-52 (2007).</li><li>Collier, M. B., Eickmann, T. H., Sukezaki, F., McAuley, J. P., Engh, G. 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M., Heesterbeek, P. J. C., vander Schaaf, D. B., Jacobs, W. C. H., Wymenga, A. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexion+and+extension+laxity+after+medial,+mobile-bearing+unicompartmental+knee+arthroplasty:+a+comparison+between+a+spacer-+and+a+tension-guided+technique.">Flexion and extension laxity after medial, mobile-bearing unicompartmental knee arthroplasty: a comparison between a spacer- and a tension-guided technique.</a> Knee Surgery, Sports Traumatology, Arthroscopy. 21 (11), 2447-2452 (2013).</li><li>Clarius, M., Seeger, J. B., Jaeger, S., Mohr, G., Bitsch, R. 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Mobile-bearing UKA is an effective treatment for anteromedial KOA. It has the advantages of less trauma, quick recovery, and maintaining normal knee proprioception11,12,13. The key to UKA is flexion-extension balance; that is, making the flexion gap and extension gap as equal as possible on the premise of restoring MCL tension14. The imbalance may lead to bearing dislocation, prosthesis wear, or progressi...

Knee osteoarthritis (KOA) is a global burden1, for which the stepwise treatment strategy is currently adopted. For end-stage unicompartmental KOA, unicompartmental knee arthroplasty (UKA) is an effective choice, with a 10-year survival rate of over 90%2. Medial UKA only replaces the severely worn medial compartment and preserves the natural lateral compartment, medial collateral ligament (MCL), and cruciate ligament3. The principle is to make the flexion gap and extension gap approximately the same by tibial osteotomy and femoral grinding, and to restore MCL tension after implantation of the prosthesis and bearing4. Compared with total knee arthroplasty, UKA has greater surgical difficulty and technical requirements. The main source is the proper balance of ligaments throughout the full range of motion of the knee3.
Traditionally, after preliminary osteotomy, the surgeon inserts a gap gauge in the joint space and indirectly determines whether the flexion and extension gaps are equal by feeling the tension of the MCL. However, the definition and sensation of balance are hardly the same, even for experienced surgeons. For beginners, it is more difficult to grasp the requirement of balance. The imbalance of the flexion-extension gap can lead to a series of complications5,6, resulting in an increased revision rate.
With the advancement of technology, some researchers have tried to apply tensors to UKA7,8. However, these researches are all on the fixed-bearing UKA, and the tensor may damage the MCL when used.
The emergence of sensors not only meets the demand for displaying the pressure in the knee joint gap, but various sensors often have less risk of MCL damage due to their small size9,10. In addition, the sensors currently used are all wired transmission, which may interfere with the aseptic operation and is not convenient enough to use.
In order to accurately measure the flexion-extension gap balance parameters, we developed a wireless sensor combination for UKA, which consists of a metal base, a wireless sensor with three pressure probes on the front, medial, and lateral sides, and a cushion block. The sensor combination measures and displays the pressure in the joint space in real time to help surgeons accurately assess whether the balance target has been achieved.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>angle measuring device</td>
			<td>AIQIAO(SHANGHAI) MEDICAL TECHNOLOGY CO., LTD.</td>
			<td>20203010141</td>
			<td>angle measuring device of femur,angle measuring device of tibia</td>
		</tr>
		<tr>
			<td>Oxford Partial Knee System</td>
			<td>Biomet UK LTD.</td>
			<td>20173130347</td>
			<td>Oxford UKA</td>
		</tr>
		<tr>
			<td>Wireless sensor combination</td>
			<td>AIQIAO(SHANGHAI) MEDICAL TECHNOLOGY CO., LTD.</td>
			<td>20212010325</td>
			<td>a metal base,&#160; a wireless sensor with three pressure probes, and a cushion block</td>
		</tr>
	</tbody>
</table>

in vitro application of a wireless sensor in flexion-extension gap balance of unicompartmental knee arthroplasty

Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage anteromedial osteoarthritis (AMOA). The key to UKA is the flexion-extension gap balance, which is closely related to postoperative complications such as bearing dislocation, bearing wear, and arthritis progression. The traditional gap balance assessment is performed by indirectly sensing the tension of the medial collateral ligament by a gap gauge. It relies on the surgeon's feel and experience, which is imprecise and difficult for beginners. To accurately assess the flexion-extension gap balance of UKA, we developed a wireless sensor combination consisting of a metal base, a pressure sensor, and a cushion block. After osteotomy, the insertion of a wireless sensor combination allows the real-time measurement of intra-articular pressure. It accurately quantifies the flexion-extension gap balance parameters to guide further femur grinding and tibia osteotomy, to improve the accuracy of gap balance. We conducted an in vitro experiment with the wireless sensor combination. the results showed that there was a difference of 11.3 N after applying the traditional method of flexion-extension gap balance performed by an experienced expert.

This in vitro study was performed on a 60-year-old female cadaver. With the S-size femoral prosthesis and 3 mm bearing the target, after performing femoral grinding and tibial osteotomy, the surgeon used the gap gauge to assess flexion-extension gap tension preliminarily and believed that balance was achieved.
After the femoral trial was installed, the wireless sensor was inserted into the medial joint space, and the intra-articular pressure was measured three times at 110&#176; (flex...

Watch this Scientific Journal Video about In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty at JoVE.com

In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty

This protocol presents a cadaveric study of a wireless sensor used in medial unicompartmental knee arthroplasty. The protocol includes the installation of an angle measuring device, standardized Oxford unicompartmental knee arthroplasty osteotomy, preliminary assessment of flexion-extension balance, and application of the sensor to measure flexion-extension gap pressure.

In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage anteromedial osteoarthritis (AMOA). The key to UKA is the ...

Our wireless sensor quantifies the pressure parameters of the flexion-extension gap balance in real-time, which is the key to unicompartmental knee arthroplasty. The sensor can display the compartment pressure in real-time, helping the surgeon to assess the flexion-extension balance more accurately and enables wireless data transmission to meet intraoperative sterility requirements. UKA is an important treatment for osteoarthritis of the knee, and the sensor used in this protocol can help with the dynamic intraoperative assessment of the UKA, which is critical to its success.This sensor is specially designed for the mobile-bearing UKA and it can perfectly fit UKA's prosthetic trial. In addition, we have designed matching sensors for different prosthetic sizes. This sensor is specially designed for UKA beginners to shorten their learning curve.The sensor is very easy to operate and there are no specific techniques. Begin by switching on the femur and tibia angle measurement device. Open the angle measurement software on the computer.Scan the QR codes of the two measuring devices and click Bluetooth connection. Place the two angle measurement instruments on a horizontal table and click the Calibration button to calibrate. Tie the instruments with straps on the knee to measure knee flexion angle in real-time.Place a cadaver in the supine position with the lower extremities draped in flexion and abduction over the outside of the operating table. Using the medial parapatellar approach, open the joint cavity with a scalpel. Now, make an incision about three centimeters distal to the joint line along the apex of the medial patella border, ending it distally about one centimeter medial to the tibial tuberosity.Using a rongeur, remove the osteophytes of the medial femoral condyle, intercondylar fossa, and the anterior tibia. Insert a one millimeter femoral sizing spoon into the medial compartment to determine the size of the joint space with cartilage. Insert different sizes of femoral sizing spoons to hook the posterior femoral condyle.When the end of the spoon is about one millimeter away from the cartilage surface, the size of the femoral prosthesis corresponding to the spoon is chosen. Next, connect a three millimeter G-clamp to a tibial saw guide and a femoral sizing spoon. Ensure the guide's shaft is parallel to the tibial long axis in both coronal and sagittal planes and that the ankle yoke points to the ipsilateral anterior superior iliac spine.Use the reciprocating saw to make a vertical tibial saw cut. Advance the saw vertically down until it rests on the surface of the saw guide. Remove the shim from the tibial resection guide and insert the slotted zero shim, then use the oscillating saw blade to excise the plateau.Now, remove the slotted shim, lever the plateau up with a broad osteotome, and remove it with the knee in extension. Make a hole in the distal femoral condyle. Insert the intramedullary rod in the hole.Next, connect the femoral drill guide to the intramedullary rod and perform femoral drilling. Install the posterior resection guide into the drilled holes of the femur. Using the oscillating saw, perform the posterior femoral condyle osteotomy and remove the guide and the bone fragment.Next, excise the medial meniscus, leaving a small cuff of the meniscus to protect the MCL. Completely remove the posterior horn. Insert a zero femoral spigot and attach the spherical mill onto the spigot to perform distal femoral milling, Insert a femoral trial and assess the flexion-extension gap by the gap gauge.Use angle measurement devices to monitor the flexion angle. Insert the gap gauge into the joint space with slight resistance to define the flexion-extension gap balance. If the gaps are not equal, grind the femur according to the difference values until equal.Remove the sensor magnetic induction power switch. Open the pressure measurement software on the tablet computer. Scan the sensor QR code and enter the measurement interface.Click the Connect Device button. Select the appropriate thickness cushion block according to the gauge specification. Put the sensor on the metal base and install the cushion block on the sensor.Click Start Working on the tablet computer. Insert the wireless sensor combination into the medial compartment and fit the metal base to the tibial osteotomy surface. Measure the flexion and extension gap pressure at 110 degrees and at 20 degrees of knee flexion.Calculate the average values separately for three consecutive measurements. The pressure values for the flexion gap were quite consistent, while the pressure values for the extension gap were quite different with an average pressure of 46.3 N in inflection and 35.0 N in extension gaps. Postoperative radiographs showed appropriate prosthesis positioning with good tibial and femoral positioning and flexion angle.When performing pressure measurement, select the sensor corresponding to the size of the prosthesis to avoid damage to the osteotomy surface and affect the flexion-extension gap balance. After gap balancing, install femoral and tibial components in balance. In the future, we need large sample multicenter status to ascertain the acceptable range of the flexion-extension gap pressure difference mirrored by the sensor and its improvement on the long-term effect of UKA.

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434 Views.  Xuanwu Hospital Capital Medical University. Il nostro sensore wireless quantifica in tempo reale i parametri di pressione del bilanciamento del gap di flessione-estensione, che è la chiave per l'artroplastica monocompartimentale del ginocchio. Il sensore può visualizzare la pressione del compartimento in tempo reale, aiutando il chirurgo a valutare la bilancia di flessione-estensione in modo più accurato e consente la trasmissione wireless dei dati per soddisfare i requisiti di sterilità intraoperatoria. UKA è un trattamento impor...