JST CLASSIFICATION AND TREATMENT ALGORITHM OF A VALGUS KNEE

Abstract

The patho-anatomy of a valgus knee could be divide into two categories as bony hypolasia and/or deficiency and soft tissue imbalance. The soft tissue in the lateral side of the knee (Including illio-tial band, lateral collateral ligament, poplitious tendon, posterior-lateral ligament, and hamstrings etc) is contracted with or without medial soft tissue attenuation.

There are many reasons explain why dealing with a valgus knee is much more difficult than dealing with a varus knee. The most important three factors are:

• There is much less room or space to release a LCL,

• The MCL could be attenuated,

• A fixed valgus deformity is always associated with bone deficiency or hypoplasia.

However, it is arbitrary, and in many times, it is wrong to take it for granted that a valgus knee is always associated with a tight LCL. In this article, the author mainly introduce the rationale and clinical application of a LCL tension based classification and treatment algorithm of a valgus knee. The details of how to judge if the LCL is tight, loose or normally tensioned; Is the valgus knee purely or associated with an extra-articular deformity will also be discussed.

JST Classification of a Valgus Knee

Femoral deformity

Type F1 Valgus in Extension only

F1a Intra-articular deformity, LCL is loose when the knee extends, while LCL maintains normal tension when the knee flexes.

F1b Extra-articular deformity which is close to knee joint(supra-condylar deformity), LCL remains normal length and tension through all the range of motion.

Type F2 Valgus in both extension and flexion

Intra-articular deformity, LCL is tight through all the range of motion, hypoplasia or bone deficiency in both distal and posterior lateral femoral condyle.

Tibial deformity

Type T1 Intra-articular deformity, lateral tibial plateau deficiency

Type T2 Extra-articular deformity, tibial metaphyseal orshaft deformity.

Treatment algorithm of a valgus knee

Type F1a

This type valgus knee is the easiest to deal with. The LCL length is well maintained, and LCL is loose when knee extends. What is tight and restrains the deformity as a fixed valgus one is: ITB and posterior-lateral capsule instead of LCL and poplitous tendon. The deformity is corrected simply by releasing ITB & posterior-lateral capsule and bony graft or using a metal block to augment the deficient or hypoplastic lateral distal femoral condyle. At the same time, the loose LCL is properly tensioned by bone graft of metal augmentation. Since both ITB & posterior capsule are secondary stabilizers, the LCL and poplitous tendon is properly tensioned, the knee is pretty stable.

Type F1b

This type of valgus deformity actually comes from juxta supera-condylar area, the deformity is very close to the joint, or in other words, close to the collateral ligament frame, this type deformity is also regard as a type of valgus knee. According to severity of the deformity, patient’s age, and surgeon’s preference, the following methods are commonly used.

Method A: lateral condyle distal sliding osteotomy The essence of a sliding osteotomy is converting a F1b deformity into a F1a deformity. By distally sliding osteotomy, the LCL becomes loose when the knee extends, and the valgus deformity is shifted into the collateral ligament frame.

Method B: Soft tissue releasing + constrained total knee The LCL of a F1b valgus knee is normal tensioned with normal length, over releasing lateral soft tissue will lead to imbalanced flexion gap, in this meaning, it may not possible to balance a F1b valgus knee properly in both flexion and extension. In such a knee, if the patient is old and is not going to lead an active life, a constrained prosthesis such as CCK or TC III can be used.

Method C: One stage or two stage supera-condylar osteotomy+TKA

Since a F1b valgus knee is actually a normal knee combined with a supera-condylar deformity, it is understandable to correct deformity by an supera-condylar osteotomy. The osteotomy can be done in one stage or two stage style. Theoretically, a supera-condylar osteotomy is done in the most deformed region, and is done within cancellous bone, bone union can be predictably expected. But if a total knee and osteotomy is performed in one stage, the operator could encounter the following difficulties:

• Conventional instruments can not guarantee correct bone cut because a supera-condylar deformity deviates intramedullary guiding rod;

• the canal in distal femoral metaphyseal part is quite expended, it is difficult to achieve solid fixation either by a stem extension or retrograde intramedullary nailing.

• Total knee replacement, supera-condylar osteotomy and intramedullary could severely damage blood supply to osteotomy line leading to nonunion. The author prefer a two stage TKA and osteotomy for a F1b valgus knee. In one stage TKA and osteotomy, the author will use frontal epicondyle axis instead of intra-medullary rod to guide distal femoral cut.

TypeF2

This type knee is consistently valgus no matter the knee extends of flexes, indicating both distal distal and posterior part of lateral femoral condyle is deficient of dysplastic and LCL is contracted. Lateral soft tissue, including LCL and some times popolitous tendon, is inevitable in managing type F2 valgus knee. If soft tissue releasing alone can’t balance medial and lateral part of the knee, a bidirectional sliding osteotomy can be done to shift proximal insertion of LCL both distally and posteriorly, releasing the LCL.

Type T deformity

Type T deformity is sparse, Type T1 is typically seen in a rheumatoid arthritis, and Type T2 is usually iatrogenic(over corrected high tibia osteotomy) or after malunion of a tibia metapyseal or proximal shaft fracture. It is possible try to augament the lateral tibial plateau deficiency and release the lateral soft tissue for a Type T1 valgus knee. But for a Type T2 knee, a correctional osteotomy concomitant to a total knee is usually needed.