The lateral closed wedge high tibial osteotomy (HTO) described by Jackson and Coventry1,2 is a classical operation to treat osteoarthritis of the medial compartment and varus deformity, but it has some problems such as peroneal nerve palsy, nonunion of fibula, and loss of the bone. Medial opening HTO had been developed, because it had some advantages over the closed wedge technique. However, suitable bone substitutes to fill the opened defect and suitable fixation plates to fix the osteotomized site in the medial opening procedure have not been identified. Autologous bone is the preferred graft material for filling opened defects. However, autogenous bone grafting has procurement morbidities. Recently, bone substitute materials have been advocated as alternatives to autografts and allografts. Hydroxyapatite is widely used as a bone substitute because of its excellent biocompatibility and osteoconductive properties. Good long-term results after opening HTO using hydroxyapatite as a bone filler were reported.3 However, hydroxyapatite biodegrades slowly and there is no progressive bone formation during the repair of the bone with it. In contrast, most of the implanted porous β-tricalcium phosphate (β-TCP) with high porosity can be resorbed within a few years. β-TCP blocks with low porosity as low as 30% to 50%, will not be completely resorbed. We have used β-TCP blocks having a compressive strength of only 3 MPa, which is inadequate for weight-bearing sites until bone incorporation occurs. Thus, we have recently developed wedge-shaped β-TCP block with 60% porosity for opening HTO.4 This β-TCP has a compressive strength of 22 MPa, which is approximately 7-fold greater than that of β-TCP with 75% porosity. In this study, we present technical details using a Puddu plate and β-TCP blocks with 60% and 75% porosity.
The patient was placed in a supine position on the operative table. The C-arm of an image intensifier was set up on the same side of the knee and opposite to the surgeon.
Arthroscopy of the knee is performed in all patients before the osteotomy. If needed, medial meniscectomy, loose body removal, and microfracture are added.
Incision and Exposure
The osteotomy procedure is performed through a vertical incision from the anteromedial arthroscopic portal extending 7 to 8 cm distally and parallel to the tibial axis (Fig. 1).
Sharp dissection is carried out beneath the skin incision to the pes anserinus and superficial medial collateral ligament (MCL), and detached from the tibia using Cobb elevator (Fig. 2). Then, both pes anserinus and superficial MCL are retracted posteriorly and the posterior surface of the tibia at the level of the osteotomy is exposed. A retractor is placed dorsally in the osteotomy line (Fig. 3). This procedure provides complete exposure of the anteromedial surface of the tibia, and it is important not only for protecting neurovascular tissues but also for preventing an increased tibial posterior slope. The anterosuperior attachment site of the patellar tendon is exposed and a radiolucent retractor is placed under the patellar tendon.
Under fluoroscopic control, a guide pin is drilled from the medial attachment site of the patellar tendon to the point 1.5 cm below the lateral joint line, and 1 cm medial to the lateral cortex. This guide pin is roughly directed toward the fibular head (Fig. 4). Another guide pin is drilled parallel to the first pin and tibial posterior slope.
A cutting plate is placed through 2 guide pins (Fig. 5), and the osteotomy is started 1 mm above the attachment site of the patellar tendon. A radiolucent retractor is used to protect the patellar tendon. A bone saw is used to cut 2 to 3 cm of the medial site of the tibia. Then, osteotomes are used to cut the tibia 1 cm medial to the lateral cortex (Figs. 6, 7). If the osteotomy is completed, it will easily open the osteotomized site. If not, anterior and/or posterior cortex is not completely cut. Next, the opener is inserted and gradually opened until desired correction. A Puddu plate (Arthrex Inc., Naple, FL) is placed into the osteotomy site (Figs. 8, 9A). Plate positioning is important (Fig. 9); if a plate is placed anteriorly, the tibial posterior slope will be increased.5
β-TCP Preparation (Olympus Terumo Biomaterials Corp., Tokyo, Japan)
I preferred to use a combination of 2 different types of β-TCP blocks. One is 60% porosity, whereas the other one is 75% porous (Fig. 10). A rectangular TCP block (1×1×2 cm) with 75% porosity is easily cut to a wedge shape. After placement of a Puddu plate with anterior slope, the cancellous bone defect is filled with 4 wedge-shaped β-TCP blocks with 75% porosity. After that, 3 wedge-shaped β-TCP blocks with 60% porosity are implanted in front (2 blocks) and back of the plate (1 block) (Figs. 9B, 11).
The wounds are irrigated and to remove the dropped TCP granules as possible. Most of the plate and TCP can be covered with the released pes anserinus and a part of the superficial MCL (Fig. 12). This procedure helps to prevent infection. A drain is placed in the subcutaneous space.
The knee is protected in a hinged knee brace for 12 weeks. Partial weight bearing is allowed at 3 to 4 weeks, and total weight bearing is allowed at 5 to 6 weeks.
All patients were followed up at regular intervals in our outpatient clinic and underwent radiographic examination.
The mean preoperative standing lateral femorotibial angle (FTA) (Fig. 13) was 181 degrees (range, 177 to 185 degrees), which was corrected to a mean angle of 169 degrees.
All the patients were scored using the Japanese Orthopaedic Association (JOA) rating scale for osteoarthritis of the knee. This scale contains 4 domains: pain on walking (30 points), pain on ascending or descending stairs (25 points), range of movement (35 points), and joint effusion (10 points). At the follow-up 42 to 60 months after surgery, the mean JOA knee score obtained from 52 patients improved from 64 before operation to 89 points.
A 59-year-old woman with medial compartmental knee osteoarthritis. The preoperative standing lateral FTA is 182 degrees (Figs. 13A, B), which was corrected to 169 degrees by a 12.5 mm opening HTO (Figs. 13C, D).
A 68-year-old man with medial compartmental knee osteoarthritis. After a 17.5 mm opening HTO using autogenous bone instead of β-TCP block with 60% porosity, the mechanical axis is corrected from varus (standing lateral FTA 190 degrees) to valgus (172 degrees) (Fig. 14). The iliac bone defect was reconstructed by implanting a 60% porosity β-TCP block (Fig. 15).
Most of the porous β-TCP with 75% porosity, which we have used since 1989, can be resorbed within a few years. However, it has a compressive strength of only 3 MPa, which is inadequate for weight-bearing sites until bone incorporation occurs. Compressive strength can be increased by reducing porosity. When porous β-TCP blocks with low porosity are used, complete resorption cannot be expected.6 Thus, we recently developed a wedge-shaped β-TCP block with 60% porosity for opening HTO. This β-TCP block has a compressive strength of 22 MPa, which is approximately 7-fold greater than that of β-TCP with 75% porosity. No correction loss has been found and bone formation was noted in all cases. The use of a β-TCP block with 60% porosity avoided autogenous bone grafting and shortened the surgical time. The 15% (1.6-fold) increase in the amount of material from 25% to 40% accounts for the marked increase of compressive strength. The reduction of porosity also reduced pore interconnection, which would require a longer period for TCP resorption. Thus, we used β-TCP blocks with 60% porosity in the medial site that needs mechanical strength and β-TCP with 75% porosity in cancellous bone defect. It is also effective to use only 60% porosity blocks. With up to 15 mm of opening, complete or nearly complete resorption of TCP blocks with 60% porosity can be expected. However, for >15 mm of opening, it is better to use autogenous bone obtained from the iliac crest (Fig. 14). The bone defect of the iliac crest can be reconstructed by implanting a β-TCP block with 60% porosity (Fig. 15).
The β-TCP blocks with 60% and 75% porosity used in our study had both macropores and micropores, most of which were interconnected. This structure facilitates the entry of proteins and cells for bone formation and resorption. In our previous animal experiments, we have found numerous TRAP-positive cells on the surface of β-TCP.7,8 This result is consistent with the present clinical results in which the outer margin of the implanted β-TCP with 75% porosity was unclear 3 to 4 weeks after implantation, suggesting the initiation of resorption.
We also found that local application of alendronate (ALN) at a concentration of 10-2 to 10-6 M reduced the number of osteoclasts on the surface of β-TCP in a rabbit model.9 New bone formation was also inhibited by ALN in a dose-dependent manner. Thus, it is suggested that higher doses of ALN may inhibit β-TCP resorption used for filling bone defects, such as after opening wedge HTO.
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