Proximal Tibial Osteotomy using a Newclip plate

Fluoroscopy is used to place an ECG sticker over the centre of the the hip joint when the rotation of the lower limb is corrected to neutral i.e the foot is pointing upwards.

An ECG sticker is then placed over the centre of the ankle with the foot pointing upwards.

Once the markers are correctly placed, they are secured with the use of tape. A wire can then be used to determine if the mechanical axis (MA) on table correlates with that of the alignment films.

If the MA does not correlate with the alignment films and is in fact neutral then a decision regarding whether to proceed needs to be made.

The leg is prepared with alcoholic betadine and then prepped and drapes in the usual manor for a knee arthroscopy. A clear bag is place over the foot so as to ensure the ECG sticker placed over the centre of the ankle is clearly visible. A diagnostic knee arthroscopy is then undertaken to confirm the pathology. It is important to confirm that the lateral compartment and the patellofemoral joint are structurally intact and therefore it is safe to proceed with HTO. Any medial meniscal pathology can be addressed at this time.

A transverse incision is made just above the level of the pes. This can be identified by simple palpation of the hamstring tendon insertion. Full thickness skin flaps are created superiorly and inferiorly so that the plate will fit comfortably.

The knee is then extended and the dissection is continued anteriorly to the anterior aspect of the tibial tubercle. The patella tendon is identified and the medial margin is incised.

A hohmann retractor is then inserted under the tendon and the fat cleared so that the tendon insertion point can be clearly identified.

A sagittal saw is then used to undertake an oblique osteotomy of the tibial tubercle at an angle of approximately 60 degrees extending from just superior to the patella tendon, posteriorly to a point approximately 1/3 of the AP width of the tibia, ensuring to pass through 2 corticies. The patella tendon must be protected by the hohmann retractor at all times. The saw should not penetrate too laterally in order to avoid tibialis anterior muscle injury with the saw.
The facia above the hamstring tendons is then incised and the MCL is generously released from the tibia using a periosteal elevator. It should be released enough so that a Hohmann retractor can be easily placed under the MCL and posterior tibia.

The proposed vertical osteotomy site is then drawn out with the diathermy on the tibia. This is usually just above the level of the pes and should extend over the remaining 2/3 of the thickness of the tibia. The veritical osteotomy should meet with the previously made tubercle osteotomy.
Two long 2mm k-wires are inserted under Image intensifier extending from the proposed osteotomy site obliquely across the tibia.

The tip of the wire should end just below the tip of the fibula head and short of the lateral cortex. The first wire is inserted posteriorly

A second parallel wire is inserted anteriorly.

The wires should overlap when viewed on the image intensifier.

With the posterior hohmann retractor in place a sagittal saw is used to complete the vertical osteotomy cut. The saw blade is kept against the inferior surface of the previously placed wires in order to ensure accurate osteotomy. It is important to ensure that the posterior cortex is cut with the saw so that the osteotomy hinge is anteriorly based. This will ensure there is minimal change to the posterior tibial slope.

The vertical osteotomy is carried under under II to ensure the saw bladé stays close to the inferior surface of the previously inserted wires. The saw blade should stop 1cm short of the lateral cortex of the tibia.

Stacking osteotomes are then used to complete the osteotomy and achieve initial gap opening. The largest osteotome is placed first so that the lip of the osteotome faces inferiorly. The osteotome is placed inferorly in an attempt to ensure the posterior cortex has been completed. If the posterior cortex has been completed this should go easily.

II is used to ensure the osteotome follows the inferior surface of the wires and stops 5-10mm short of the lateral tibial cortex.

The second osteotome is then inserted between the first osteotome and the wires.

The second osteotome should be inserted so that its tip is longer than that of the first. This will protect the articular surface from fracture.
During insertion of the second osteotome, a change in the varus tibial slope should be noted. If the slope does not become more valgus as the osteotome is inserted then one should ensure that the posterior cortex has been fully divided. If the cortex is not fully divided then the bone will be compressed rather than the osteotomy distracted.

A 3rd osteotome in then inserted in order to plastically deform the lateral cortex.
The osteotomes are then removed. The assistant should place their hand under the knee in order to prevent hyperextension, which can cause hinge fracture. It is better to use only 3 osteotomes in order to prevent over tensioning the MCL and thus hinge fracture. Often the tendency is to under release the MCL during the initial exposure.

A laminar spreader with a wheel should be inserted as posteriorly as possible into the osteotomy gap in order to prevent slope change.
By pulling on the wires and stabilising the ankle, the osteotomy gap can be opened sufficiently to allow the spreader to be inserted easily. If the gap does not open easily the the MCL needs to be released further.

The gap is then increased gradually until the tibial slope is reversed so that it is neutral or a few degrees valgus. The laminar spreader can also be used to assess the sufficiency of the MCL release. If opening the ostetomy gap becomes difficult i.e requires significant pressure on the spreader, further MCL release needs to be carried out. This is done with a 15 blade between the arms of the spreader using a pepper-pot technique.
If during this stage a hinge fracture is identified/sustained then I usually change the plate to the larger 4 hole plate in order to place an initial compression screw distally, which allows reduction of the usual tibial translation seen. Normally it is still possible to achieve the desired correction with a hinge fracture as the translation is usually minimal, however if the translation prevents sufficient opening of the osteotomy then a second lateral incision will need to made. The area of the hinge fracture is exposed and the fracture reduced with either a step staple or a semi-tubular plate. This will then allow the osteotomy gap to be opened to the desired degree.

The newclip plate (with the anterior and posterior proximal tubes attached) is then inserted into the wound and moved proximally. The plate should sit anteriorly on the tibia.

An initial wire is inserted in the anterior tube in order gauge appropriate placement of the plate.

The satisfactory position of the plate and the proposed screw location is confirmed using the image intensifier.

Once happy, the posterior tube is drilled to achieve a bi-cortical hold. This screw is usually 45-50mm in length.

The wire is removed and prior to drilling the anterior tube one needs to ensure that the distal plate is in the middle of the tibia. The anterior screw should be as long as possible, the maximum length with this system is 70mm.
The middle screw is then drilled, it is poly-axial and needs to be placed between the anterior and posterior screws (in the vertical plane) in order to distribute the forces. Again, the angle of insertion in the horizontal plane should be in such a way to ensure the maximum screw length possible.

The mechanical axis is then re-measured and the correction assessed by stretching the diathermy lead between the previously placed ECG stickers which can be palpated through the drapes. The laminar release is opened or closed dependent of the desired correction.

The most proximal hole distal to the osteotomy is then drilled, tapped and a locking screw inserted.

Once the most proximal screw has been inserted the osteotomy gap will be fixed allowing removal of the laminar spreader. This will allow easier access to the distal 2 screws in the plate through the transverse incision. The distal screw holes are drilled in a bi-cortical fashion. Prior to screw insertion the screw hole needs to be tapped to allow full seating of the screw in the harder cortical bone.
If the distal screw holes cannot be reached through the transverse insertion then a separate percutaneous incision can be made.

10mls of Demineralised Bone Matrix is then inserted into the osteotomy gap in order to reduce potential swelling.

A final AP radiograph is undertaken to the final construct is satisfactory.

A large drape is then placed on the contralateral aspect of the table to allow the image intensifier to pass underneath the table and take a true lateral radiograph.

Skin clips are usually then for the skin.

The wound is dressed with a simple opsite dressing and a wool and crape bandage.

The wound is then closed in layers. A 2.0 Biosyn in used for the fat