– Written by Matteo Denti and Giancarlo Puddu, Italy

In recent years, orthopaedic surgeon – in particular those specialised in knee surgery and sports trauma – have noted an increased frequency in early-stage and symptomatic knee cartilage pathologies. MRI and advances in the field of radiology, in particular with regard to information that can be gained by viewing weight-bearing radiographs of the knee, have made identification of these pathologies possible and are now routinely used¹. MRI scans allow for the visualisation and classification of chondral knee pathologies.

This is one of the reasons that the indications for a high tibial osteotomy (HTO) have changed.

Another reason is that recent studies point to the fact that chondrocytes do not favour mechanical loading; on the contrary, unloading seems to be key to the treatment of knee osteoarthritis².

Historically HTO was performed in cases of late varus arthritic knee, the effectiveness of which was evident only for a limited number of years. This, together with advances made in knee replacement procedures^3,4, has meant that HTO has been progressively abandoned, which could also be the motivation for finding new indications for HTO procedures, as studies began to look to HTO not for the treatment of advanced arthritis, but for treatment at the initial stages.

In recent years, prosthetic knees have replaced HTOs, even in young subjects in some countries, which risks the gradual loss of experience in HTO patient selection and surgical routine and may, in turn, negatively affect outcomes⁴.

The situation worsens in cases of an unstable knee with ligamentous lesion of one of the cruciate ligaments or after a previous meniscectomy.

On the other hand, some HTO studies also observed a slow deterioration over time, with good survival rates up to 15 years^5,6.

This paper discusses modern indications and applications for HTO.

INSTRUMENTAL EVALUATION

The selection of patients suitable for HTO can only be done after a thorough preoperative evaluation.

The standard evaluation begins with assessment of the alignment of the lower limbs with four short films: bilateral weight-bearing antero-posterior views in full extension, bilateral weightbearing postero-anterior views at 45° of flexion (as described by Rosenberg¹), and lateral and skyline films of both knees. The Rosenberg view has a strong predictive value when the deformity is associated with cruciate insufficiency, resulting in anterior tibial subluxation and chondral wear in the posterior area of the medial tibial plateau. The osteotomy is planned according to the method described by Dugdale⁷.

MRI can be very useful in identifying suitable candidates for knee osteotomy, as it can show not only cartilage damage but also the stress reaction of the subchondral bone.

Before the HTO procedure, a diagnostic arthoscopy is performed and any associated lesions are treated, this procedure also allows for the confirmation that an HTO is indicated.

INDICATIONS

Osteotomy of the proximal tibia is designed to relieve pain caused by medial tibiofemoral osteoarthritis. Degenerative changes of the articular cartilage can occur through tension, compression or shear and are the result of forces exerted on the weight-bearing surfaces. Genetic factors are known to play a part. Specific trauma, as well as trauma from overload caused by obesity or occupational factors are aetiologically important. In essence, the mechanical cause for osteoarthritis is an overload or a concentration of forces beyond the ability of the cartilage and subchondral bone to cope.

Timing is a very important factor in this reparative surgery because an osteotomy is much more effective if it is performed during the earliest stage of unicompartimental osteoarthritis, in order to prevent unavoidable degenerative changes in the joint of a young and active patient^5,8-10.

Osteotomy is best done in cases of knees with a generally well-maintained range of motion. Osteotomy is not indicated in patients with rheumatoid arthritis, or in patients with varus deformity of more than 20°. Radiographic evidence of changes such as moderate osteophytes and joint space narrowing, subchondral bone sclerosis and cysts, and possible deformity of the bone contour ‑ corresponding to grade 2 to 3 on the Kellgren-Lawrence classification^11,12 are indications for HTO.

The arthroscopic indication for HTO is a grade 2 or 3 chondral lesion, according to Outerbridge¹³ or International Cartilage Repair Society¹⁴ classification, at the medial compartment, associated with a varus knee and a good lateral compartment.

Accurate surgical technique is manda-tory to obtain good results^15-17.

The type of valgus tibial osteotomy generally indicated is an open wedge osteotomy, in order to guarantee better and more sustainable results, this has been compared to a closed wedge osteotomy^15-23.

In the past, the presence of ‘patella baja’ was taken as a contraindication, but if performed in association with a HTO, the tibial tubercle can be moved proximally and the patella baja corrected^24-27.

Over the last 10 years, the majority of osteotomies performed have been done in association with cartilage repair, meniscal transplantation and ligament reconstruction.

HTO associated with cartilage treatment

It has been observed that with cartilage pathologies, after a non-weight-bearing period, the rate of change in the medial compartment switches from negative to positive, indicating the potential for articular cartilage recovery secondary to an improved mechanical environment. This is also the case when HTO is associated with a microfracture procedure or cartilage transplantation^2,28,29.

HTO associated with meniscal transplantation

The association of HTO with medial meniscus transplantation has resulted in greater improvement at the final follow-up when compared to isolated medial meniscal transplantation³⁰.

HTO associated with anterior cruciate reconstruction

HTOs performed in association with meniscal transplants and cartilage repair have good reported outcomes, the association with ligament reconstruction is open to debate and may need more investigation.

The definition ‘knee abuser’ identifies a category of patients in which ligamentous laxity is associated with degenerative changes of the medial compartment. The natural history of a knee abuser starts with a misdiagnosed or ignored ACL tear. The ligament is not reconstructed, the patient, sooner or later, returns to normal activities including sport activities. Instability in the knee leads to repeated episodes of giving way, often a meniscal tear complicates the situation and, finally, degenerative changes of the medial compartment with varus deformity occur.

These patients initially present with ‘only’ a traumatic lesion of the ACL, when in reality there has been months or years of complex ligamentous laxity of the knee joint with a varus malalignment, leading to osteoarthritis. The situation is worsened by a lateral thrust during gait.

This pathological picture needs more than cruciate ligament reconstruction or even the treatment of the arthritic lesions, as the realignment of the deformity is not sufficient for a joint which is both unstable and arthritic. A failed ACL reconstruction in these patients again worsens the situation.

In such cases, HTO can be seen as a more complete solution, addressing the inclination of the slope of the tibial plate. Initially, open wedge HTO was criticised as it can cause an increased slope angle, but this is dependent on the position of the plate. In cases of anterior instability it should be positioned posterior to the medial collateral ligament and allows a higher opening posteriorly than anteriorly.

The combination of a valgus osteotomy with ACL reconstruction, even in cases of revision, can lead to correct axis positioning and a stable knee.

This combined surgery is indicated only in select young patients – those with instability associated with initial varus arthritis.

The results of HTO with ACL reconstruction are certainly encouraging^31,32.

HTO associated with posterior instability and complex instability

There are two types of posterior instability; one is isolated and the other is with posterolateral laxity. With isolated posterior laxity there is an indication to increase the tibial slope, positioning the plate anteriorly. When posterior laxity is associated with posteriorlateral laxity, not only must the angle of the slope be increased, but a valgus ostotomy must be performed with lateral translation of the mechanical axis to 55 to 60% of the tibial plateau.

If necessary, posterior cruciate ligament reconstruction can be considered as a second stage, in association with a posterolateral reconstruction.

In cases of associated anterior and posterior instability in a varus knee, HTO can be performed to correct the tibial slope for the posterior instability combined with anterior cruciate ligament reconstruction. It has recently been shown that a moderate change to the tibial slope does not significantly modify anterior stability^33-35.

The ‘modern’ HTO is indicated in younger patients presenting initial medial osteoarthritis of the knee and even in cases where it is associated with other surgical procedures, it not only reduces painful symptoms, but can ensure that the patient can perform sport at a recreational level^10,36-38.

Matteo Denti M.D.

Galeazzi Orthopaedic Institute

Milan, Italy

Giancarlo Puddu M.D.

Valle Giulia Clinic

Rome, Italy

Contact: matteo@denti.ch.it

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