Author: Ding Yong
Source: Tangdu Hospital, Air Force Medical University
The surgical techniques of unicompartmental movable platform mainly include tibial osteotomy and femoral osteotomy.
The tibial osteotomy technique is mainly composed of three parts: vertical osteotomy, horizontal osteotomy and other technical osteotomy.
Positioning: The leg rest (Biomet) should not be placed in the popliteal fossa, but near the tourniquet. The patient is at the edge of the bed with the hip flexed at 40° abduction. The legs hang naturally and the knee is flexed at 110º and the full knee joint can be fully flexed.
Incision: from the medial aspect of the patella to the medial aspect of the tibial tuberosity.
Indications: Check for ACL, lateral compartment, and PFJ.
Osteophytes: clean up the medial femoral condyle, intercondylar, and anterior tibial osteophytes (especially the top of the intercondyle and near the ACL). Do not clean the osteophytes on the medial tibia.
Tibial osteotomy method: using an extramedullary positioner, the proximal end is close to the proximal tibial bon, and the distal elastic band is fixed to the ankle. The positioning rod is parallel to the anterior tibial ridge, and the positioning device is fixed by nailing using a No. 0 osteotomy block, a No. 3 or No. 4 G-clamp.
Vertical tibial osteotomy: internal and external positioning, rotational positioning. It is important to note that the first incision is very important to directly determine the position of the prosthesis.
Vertical osteotomy internally and externally positioned: The vertical osteotomy is located medial to the apex of the medial spines, 2 to 3 mm lateral to the femoral condyle, close to the ACL footprint zone.
Immediately along the medial part of the highest part of the tibial ridge, do not cut too deeply.
A: The position of the inner and outer sides is well grasped, B: too far inside, C: too far away
Vertical osteotomy rotational positioning: reciprocating saws pointing to the anterior superior iliac spine, i.e., slight internal rotation.
Tibial horizontal osteotomy coronal osteotomy angle: 0-3°, the amputation is perpendicular to the anatomical axis of the tibia, and a 0-3° varus is appropriate.
Avoid valgus osteotomy
Tibial horizontal osteotomy sagittal osteotomy angle: tibial osteotomy -7° posterior, probe (spoon-shaped measuring device) against the posterior femur. The proximal end of the guide is close to the tibial cortex, not to the osteophyte, and the distal end of the transverse finger is positioned so that the rod of the guide is parallel to the anterior tibial crest.
Tibial horizontal osteotomy depth: according to the overall thickness of the tibial prosthesis, the tibia should be cut as little as possible, and the amount of bone cut should be reduced when the MCL is relaxed. The tension is to taut the MCL as well.
Tibial osteotomy guided by other technologies: navigation-guided osteotomy, PSI-guided osteotomy, AI, robot-guided osteotomy.
The UKA femoral osteotomy technique includes three parts: pulp openy, positioning, posterior condylar osteotomy, and distal condylar osteotomy.
Location of the prosthetic component: medial and external
The medullary opening point is medial, and the medullary hole is drilled in front of the posterior cruciate ligament insertion point at a position of about 10mm upward from the extension point of the lateral line of the medial femoral condyle, and the intramedullary rod is pushed in by hand to avoid knocking with a drumstick, so as not to cause the femoral prosthesis to be in a bad position due to line change.
Femoral drilling method: insert the intramedullary rod, insert the guide and set it to the selected thickness of the G-clamp, insert the connector to ensure 10° flexion, ensure that the 6mm hole (femoral column) is in the middle of the femoral condyle, avoid anteromedial overhang, and pay attention to the lateral movement of the guide. The position of the borehole directly determines the position of the prosthesis.
The position of these two holes can be determined by anatomical positioning method, that is, the line is drawn with an electric knife on the midline of the medial femoral condyle, and the two holes are just on this line. In addition, the position of the femoral prosthesis can be determined by the tibial prosthesis, and the tibial prosthesis and femoral prosthesis can be aligned by marking a line on the tibia in the middle of the tibial prosthesis and extending it to the femoral condyle.
Coronal alignment: The coronal alignment after unicompartmental surgery is not determined by the valgus of femoral and tibial prosthesis placement, but by the thickness and tension of the spacer. Choose a liner thickness that restores ligament tension and restores the alignment of the lower extremities to its pre-disease state.
It does not depend on the alignment of the prosthetic components (cf TKR). The prosthetic component is spherical. A slight misalignment is allowed.
The ideal gasket is placed at a distance of 1mm from the outside, and it is easy to rotate and dislocate the gasket if it is too far away, and it is easy to impact if it is too close. Make sure the spacer does not hit the sidewall, otherwise it will be another osteotomy.
The goal of a lateral femoral osteotomy is to reconstruct the normal joint line, determine the distal position of the implanted prosthesis by ligamentous balance, and perform an osteotomy until the flexion-extension gap is equal and the ligament tension is the same in flexion and extension movements.
The posterior surface of the implanted prosthesis is aligned with the normal posterior cartilage.
Drill holes for the column at a suitable distance from the posterior cortex (radius of the prosthetic assembly).
Posterior femoral condyle osteotomy
Posterior dydyle osteotomy method
Excision of the posterior femoral dydyle. The same thickness as the back of the prosthesis
The distal femur was osteotomy, the grinding rod was inserted, and the No. 0 grinding rod was used for basic grinding, and the thickness of the collar was different to indicate the depth of grinding
Ligament balance: Measure the knee flexion space using a gap counter
Knee extension clearance is measured at 20° of flexion. Knee flexion space – knee extension space = re-grinding bone mass
When testing the straightening gap, do not fully straighten the knee. The posterior capsule is tight, the MCL is lax, and the gap depends on the capsule rather than the ligament.
The posterior capsule is shortened, thus making the gap smaller
Insert a new grinding rod and grind to a limited depth for clearance balance, with a thinner collar circumference corresponding to the amount of osteotomy
The flexion and extension gap is remeasured to confirm ligament balance. If the ligaments are not balanced, calculate the additional osteotomy and increase the size of the grinding rod.
Protection against impact: If the liner strikes the bone, the liner may become dislocated. Anterior abrasive osteotomy prevents anterior impact. Use a bone chisel to amputate the posterior osteophytes to prevent posterior impingement.
Bone cement technique: 2 stages are recommended for beginners to help remove bone cement beyond the prosthesis.
The tibia is first fixed, a thin layer of bone cement over the bone, the tibial prosthesis is fixed, a gap detector is inserted, and compression is applied at 45°.
The femur was then immobilized, bone cement was implanted in the hole and prosthetic assembly, a gap detector was inserted, and pressurized at 45°.
Key Points – Complete each operation step
(1) The ligament is normal - do not loosen, deliberately protect the medial collateral ligament.
(2) Accurately balance the flexion and extension knee clearance.
(3) A spoon-shaped measuring device that fits snugly against the posterior femoral condyle can guide the tibial osteotomy.
(4) Perform an abrasive osteotomy on the distal femur until the ligament is balanced at 100° and 20°.
(5) Ensure that there is no impact.
(6) Bone cement fixation is very critical (initial 2 stages).
About the Author
Ding Yong
Chief physician of the Department of Orthopedics, Tangdu Hospital, Air Force Medical University, doctoral supervisor.
Academic positions: Member of the Joint Surgery Group of the Orthopaedic Branch of the Chinese Medical Association, Member of the Standing Committee of the Joint Protection and Health Branch of the Chinese Geriatric Health Care Association and Leader of the Unicompartmental Expert Group, Member of the Joint Surgery Expert Working Committee of the Orthopedic Branch of the Chinese Medical Doctor Association, Member of the Knee Joint Working Committee of the Orthopedic Branch of the Chinese Medical Doctor Association, Member of the Cartilage Regeneration and Rehabilitation Professional Group of the Tissue Repair and Regeneration Branch of the Chinese Medical Association, Member of the Standing Committee of the Shaanxi Bone and Joint Society, Vice Chairman of the Sports Medicine Branch of the Shaanxi Medical Association, Vice Chairman of the Sports Injury Rehabilitation Professional Committee of the Shaanxi Rehabilitation Medical Association, etc。
Disclaimer: The content and pictures of this article are provided by the contributor and are only for learning and exchange, and do not represent the views of Orthopedics Online.