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Zimmer®

Natural-Knee®

High Tibial Osteotomy

(HTO) SystemSurgical Technique

Design for younger, active patients with minimal medial varus deformity

Natural-Knee® High Tibial Osteotomy (HTO) System 1

Natural-Knee® High Tibial Osteotomy System Surgical TechniqueDeveloped in conjunction with

Aaron A. Hofmann, MDProfessor of OrthopedicsThe Louis S. Peery, MD andJanet R. Peery PresidentialEndowed Chair in OrthopedicsUniversity of Utah, SOMOrthopedics Division ChiefVeteran’s Administration Medical CenterSalt Lake City, Utah

Table of Contents

Introduction 2

Preoperative Planning 2

Measurement of Preoperative X-rays 3

Surgical Technique 4

Positioning the Patient 4

Exposure 4

Placement of Transverse Osteotomy Guide 5

Transverse Osteotomy 7

Oblique Osteotomy 8

Compression of Osteotomy 9

Intraoperative Alignment 10

Securing the Distal Plate 11

Postoperative Protocol 11

Ordering Information 12

Natural-Knee® High Tibial Osteotomy (HTO) System2

Natural-Knee High Tibial Osteotomy System

The Natural-Knee High Tibial Osteotomy (HTO) System was developed to offer the surgeon a comprehensive system designed to achieve reproducible, predictable results in the management of malalignment.

First described in 1958, well-planned high tibial osteotomies have long restored degenerative osteoarthritic knees to more normal function and have delayed the need for more invasive procedures in the young, active patient. For many orthopedic surgeons, HTO is the treatment of choice for those patients with unicompartmental osteoarthritis.

The Natural-Knee High Tibial Osteotomy System is part of the Natural-Knee Family. The HTO System offers unique instrumentation designed to facilitate precise, reproducible results for proximal tibial wedge osteotomy procedures.

The HTO System is specifi cally designed for younger, active patients with a minimal medial varus deformity.

Highlights of the HTO System

Instrumentation• Oblique cutting jig for incremental resections from 6 degrees to 20 degrees in 2-degree increments.

• Slotted saw capture system ensures controlled, precise cuts.

• Compression clamp facilitates mechanical closure of osteotomy.

• Transverse cutting jig references anatomic landmarks to properly align the bone cuts, helping to ensure desired results.

Fixation Components• L-plate provides for rigid fi xation and replicates the anatomical proximal contours, providing immediate stability and allowing faster rehabilitation.

• L-plates are specifi cally designed for both left and right knee anatomy.

• L-plate design reduces the need for casted immobilization, decreasing the risk of compartmental syndrome and enhancing patient comfort.

• The titanium alloy composition of the L-plate and screws maximizes biocompatibility and reduces metal sensitivity risks.

• Fixation is enhanced with titanium cancellous bone screws proximally and self-tapping titanium cortical bone screws distally.

Preoperative Planning

The operation, as always, begins with preoperative planning. Preoperative planning is performed using 36 inch or 54 inch long-standing anterior/posterior (A/P) and lateral X-rays of both extremities. Our goal is to accomplish 8 degrees of valgus measuring the tibial-femoral anatomic alignment.

Eight degrees of valgus will allow for some potential human error with slight over- or under-correction. The most successful alignment has been described as between 5 degrees and 13 degrees of valgus. Undercorrection (less than 5 degrees) will not give long-term pain relief. Overcorrection (greater than 13 degrees) is cosmetically objectionable and may distort the proximal tibia, making total knee arthroplasty more diffi cult if required at a later time.


Measurement of Preoperative X-rays

The normal knee is generally considered to be in 6 degrees of anatomic tibial-femoral valgus.

Several techniques describing measurement methods for angular deformities of the knee are available. Employing the anatomic axis method, the axis on the femur is determined by marking the center of the medullary canal of the proximal femur and the apex of the intercondylar notch distally. The anatomic axis of the tibia is drawn from a point between the anterior and posterior tibial spines and a point at the center of the ankle. The amount of angular deformity is determined by these two lines. The osteotomy wedge angle or amount of desired correction is determined by these two lines. The osteotomy wedge angle or amount of desired correction is determined by adding the preoperative varus to the desired postoperative valgus angle. If the patient’s preoperative alignment is 4 degrees varus, 12 degrees of correction would be required to accomplish our postoperative goal of 8 degrees of valgus (Fig. 1).

Another method includes the measurement of the angular difference between the mechanical axis of the femur (center of the femoral head to the intercondylar notch) and the anatomic axis of the tibia (interspinal region to the center of the ankle) (Fig. 2). Two degrees are added to this number for overcorrection.

Fig. 1

Fig. 2

Varus Valgus

Anatomic AxisMechanical Axis

Mechanical Axisof Femur

Anatomical Axisof Tibia


Surgical Technique

Positioning the PatientA sandbag is placed under the involved hip to allow easier access to the lateral aspect of the knee. A sandbag is also taped to the operating table to maintain 90 degrees of knee fl exion during the operation. Draping and prepping from the anterior-superior iliac spine to the ankle is required to establish access to the involved extremity. Use of a sterile tourniquet will allow for visual inspection of the intraoperative alignment and make location of bony landmarks easier.

ExposureAn inverted L-shaped incision is made utilizing a lateral approach to the proximal tibia (Fig. 3). The transverse limb of the incision is at the lateral joint line and extends posteriorly to the fi bular head. The vertical limb is midline to the tibia and carried 10cm distally. The incision is carried down to periosteum with the lateral portion of the tibia exposed. Disruption of the proximal tibio-fi bular joint must now be accomplished. Our preference is to simply disrupt the capsule using a sharp 3⁄4 in. curved osteotome (Fig. 4). Partial resection of the medial portion of the fi bula head may also be employed.

Fig. 3

Fig. 4


Placement of Transverse Osteotomy GuideThe joint line is identifi ed using either Keith needles or small K-wires. Laterally, two Keith needles or K-wires are placed under the easily visible lateral meniscus (Fig. 5). This identifi es the lateral joint line as well as the posterior slope of the tibia. Medially, they are placed percutaneously. In heavy patients, C-arm X-ray confi rmation is recommended.

The transverse osteotomy guide is positioned medial/lateral on the tibia with the top portion of the jig touching the Keith needles or K-wires (Fig. 6). The medial portion of the jig is stabilized by soft tissue. Fig. 5

Fig. 6


Proper positioning of the jig, as described above, will allow for the transverse limb of the osteotomy to be made 2cm below the joint line. Employing the Natural-Knee Drill and Pin Set (catalog number 2001-00-000), the jig is stabilized by drilling to the third mark (3 inches) on the 3.2mm (1⁄8 inch) drill bit, and fi lling the drilled hole with a single smooth pin (1⁄8 inch by three inches) (Fig. 7a). The transverse osteotomy guide can then be fl exed and extended to match the patient’s posterior slope and to determine the proper plate positioning. This can be confi rmed by placing the plate over the smooth pin that stabilizes the jig (Fig. 7b). Once proper positioning is established, the jig is completely stabilized by drilling a second hole and fi lling it with a smooth pin (1⁄8 inch by three inches) (Fig. 8).

Fig. 7a

Fig. 7b

Fig. 8

5" x 1⁄8" (3.2mm)

3" x 1⁄8" (3.2mm)HTO Guide

Patella Drill Guide

Proximal TibialDrill Guide


Transverse OsteotomyThe central hole in the transverse osteotomy guide, adjacent to the osteotomy slot, is drilled completely across the tibia and a depth gauge is used to measure the tibial width (Fig. 9).

A calibrated saw blade with 90mm (3.5 inches) of working/cutting distance is now required. The saw blade should be inserted to allow for a 10mm bridge of bone across the medial side of the proximal tibia, i.e., if a 90mm width is depth gauged, the saw blade would only be inserted to 80mm (Fig. 10). The transverse osteotomy is completed, making sure Z-retractors are used to protect the soft tissue anteriorly under the patella tendon and posteriorly between the tibia and fi bula.

The transverse jig is then removed, leaving the pins in place. The transverse cut is inspected. After these cuts are completed, there should be a slight spring between the proximal and distal portion of the tibia. If it does not spring, the cut for the posterolateral corner may not be complete and can be completed without the guide.

Fig. 9

Fig. 10


Oblique OsteotomyNext, the oblique osteotomy guide is applied. The fi xed blade of the jig is inserted into the depths of the previous cut. (Placing the leg in a fi gure four position will spring the osteotomy open for easier insertion of the tongue.) This jig is placed over the two proximal 3.2mm (1⁄8 inch) pins that have been left in place (Fig. 11). The hole at the bottom of the jig is drilled through a single cortex and is used as a reference for reapplication of the jig if the tibia needs additional correction. This jig will be proud on smaller tibias and fl ush against bone on larger tibias. Be careful not to insert the tongue beyond the depth of the initial transverse cut.

The appropriate slot on the oblique osteotomy jig is now selected (six degrees to 20 degrees correction in two degree increments). The oblique osteotomy is performed by using the full 90mm length of the saw blade. Slight upward pressure on the saw blade will assure that the blade reaches the apex of the initial transverse resection. Z-retractors are used to protect soft tissue anteriorly and posteriorly during the oblique osteotomy.

The oblique jig is removed, leaving the pins in place. The wedge of bone is excised (Fig. 12). The osteotomy site is inspected to be sure no residual bone is left.

Fig. 11

Fig. 12


Compression of OsteotomyThe L-shaped osteotomy plate is applied over the two smooth pins. A single pin is then removed and replaced by a 6.5mm cancellous screw, using the remaining pin as a parallel alignment marker (Fig. 13). The second pin is then removed and replaced with a cancellous screw. An accessory screwdriver tip is placed in the fi rst screw head as a parallel marker (Fig. 14). Fifty or sixty millimeter long cancellous screws are generally used in females, while 60 or 70mm long screws are generally used in males. To allow the distal portion of the plate to conform to the tibia, do not tighten these screws until the distal cortical screws have been applied.

Note: Shorter (50mm) cancellous screws can be used in very young patients to assure easier hardware removal once healing is complete.

Fig. 13

Fig. 14


Using the two distal holes in the L-plate as a reference, the drill aligner is used to place a single-cortex 3.2mm (1⁄8 inch) hole in line with and distal to the plate (Fig. 15). Slight toggling of the bit will make application of the compression clamp easier. This hole is used with the compression clamp to draw the osteotomy closed. The curved pin at the end of the clamp is inserted into the just drilled distal hole, while the straight pin, also on the end of the clamp, is inserted into the most distal hole of the L-plate (Fig. 16). Slow compression is applied.

Intraoperative AlignmentOnce the osteotomy site is closed, overall alignment is evaluated using either a long alignment rod or an electrocautery cord. Align them in a straight line from the center of the hip to the center of the ankle. This plumb line should pass through the lateral compartment of the knee if you have accomplished the goal of eight degrees of tibial-femoral valgus (Fig. 17).

The alignment and placement of the internal fi xation device is confi rmed with 17 inch A/P and lateral intraoperative X-rays or by using the C-arm fl uoroscope.

Compression frequently takes fi ve minutes, allowing plastic deformation to occur through the incomplete osteotomy site. Be patient through this portion of the procedure. Disruption of the medial bridge may occur but is of no consequence as long as stability is maintained.

Note: If compression is diffi cult, check that the proximal tibio-fi bular joint is completely disrupted and that any residual of bone wedge has been removed.

Fig. 15

Fig. 16

Fig. 17


Securing the Distal PlateIf alignment and screw placement are correct, the central round hole in the plate is drilled, cortex-to-cortex, with the 3.2mm (1⁄8 inch) drill bit, accurately depth gauged, and subsequently fi lled with a self-tapping cortical screw (Fig. 18).

The external compressive device is then removed and the most distal hole in the plate is also drilled, depth gauged and fi lled with a cortical screw. The proximal cancellous screws are then tightened. The elongated/slotted hole is a “spare” and can be fi lled in cases with osteoporotic bone or used as an interfragmentary fi xation hole with a cortical screw angled up into the proximal portion of the osteotomy. A wedge of cancellous bone is placed as bone graft under the plate at the “step-off” in the osteotomy.

Tip: When tightening down the screws, especially the cortical screws, do not apply severe torque. It is recommended that the “three fi nger” approach be used, employing the thumb, the middle and index fi ngers on the screwdriver when tightening the screws. A power screwdriver is not recommended for fi nal tightening of the screws.

The tourniquet is released and hemostasis controlled with electrocautery. The wound is copiously irrigated, and a small suction drain is placed into the depth of the wound. The fascia of the anterior compartment and the iliotibial band are loosely approximated with interrupted suture. Subcutaneous tissue is closed with interrupted absorbable suture and the skin closed with staples and sterile strips. A large compressive Jones dressing is applied for 48 hours.

Postoperative Protocol

The patient is started on a Continuous Passive Motion machine in the recovery room. This usually starts from 0 degrees to 30 degrees of fl exion and progresses 10 degrees per day. Ambulation is begun on the second postoperative day and 50 percent weight bearing is allowed for the fi rst 6 weeks with the use of two crutches. Muscle strengthening and active range of motion are begun on the second postoperative day. Full weight bearing is allowed after 6 weeks.

NOTE: In younger patients, it is recommended that the hardware (plate and screws) be removed after complete union of the osteotomy. This usually occurs within 6 months to 12 months.

Fig. 18


Catalog No. Product

6590-00-500 Natural-Knee High Tibial Osteotomy Depth Gauge

6590-00-511 Natural-Knee High Tibial Osteotomy Transverse Alignment Guide

6590-00-522 Natural-Knee High Tibial Oblique Osteotomy Guide - Left

6590-00-523 Natural-Knee High Tibial Oblique Osteotomy Guide - Right

6590-00-531 Natural-Knee High Tibial Osteotomy Compression Clamp

6590-00-540 Natural-Knee High Tibial Osteotomy Tibial Locating Needles (Disposable)

6590-00-550 Natural-Knee High Tibial Osteotomy Screwdriver Tip

6590-00-560 Natural-Knee High Tibial Osteotomy Serrated Drill Guide Size 3.2mm

6590-00-570 Natural-Knee High Tibial Osteotomy “Z” Retractors

6590-00-580 Natural-Knee High Tibial Osteotomy Drill Aligner

6590-99-000 Natural-Knee High Tibial Osteotomy Instrument Case

6500-00-520 L-Plate, Left

6500-00-521 L-Plate, RIght

4301-07-050 Cancellous Bone Screw, 6.5mm Diameter, 50mm




6500-07-030 Cortical Bone Screw, 4.5mm, Diameter, 30mm
















2000-00-105 Saw Blade - 1 inch Cutting Width (Stryker Fit)

2000-00-106 Saw Blade - 1 inch Cutting Width (Stryker Fit - System 2000)

2000-00-150 Saw Blade - .5 inch Cutting Width (Stryker Fit)

2000-00-151 Saw Blade - .5 inch Cutting Width (Stryker Fit - System 2000)

2000-01-150 Saw Blade - .5 inch Cutting Width (3M Fit)

2000-01-200 Saw Blade - 1 inch Cutting Width (3M Fit)

2000-02-111 Saw Blade - 1 inch Cutting Width (Zimmer Fit-7 hole design)

2000-02-151 Saw Blade - .5 inch Cutting Width (Zimmer Fit-7 hole design)

2001-00-000 Disposable Drill and Pin Set

Ordering Information

1001

-01-

039

Rev

. 5

3.5M

M P

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ed in

USA

©20

04, 2

005

Zim

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, Inc

.

Contact your Zimmer representative or visit us at www.zimmer.com

Please refer to package insert for complete product information, including contraindications, warnings, precautions, and adverse effects.

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