Chapter 103 Unicompartmental, Bicompartmental, or Tricompartmental Arthritis of the Knee

Algorithm for Surgical Management

The knee joint is a modified hinge that can be arbitrarily divided into three compartments— medial, lateral, and patellofemoral. Arthritis from a surgical standpoint involves loss of articular cartilage, with narrowing of joint space. The loss of cartilage can be focal or more diffuse, with a more diffuse pattern seen commonly in degenerative arthritis. When this process is limited to only one compartment, it is defined as unicompartmental arthritis. Bicompartmental arthritis involves the medial or lateral compartment, with involvement of the patellofemoral compartment. Tricompartmental arthritis by definition involves all three compartments.

When faced with an articular pathology of the knee that has failed appropriate nonoperative management, the options for surgical management will include joint preservation and joint-sacrificing procedures. The former involves cartilage restoration procedures and/or osteotomies, done alone or in combination, and the latter involves a partial or a total knee replacement or arthrodesis of the knee. The goal of any of these procedures is primarily pain relief and secondarily improved function, with restoration of an active lifestyle.

The single most important factor in surgical decision making is the surgeon’s philosophy and experience with nonarthroplasty or arthroplasty options. It is furthermore aided by numerous other factors, such as the age of the patient, extent and severity of articular pathology, clinical appearance and examination of the knee, and patient expectations with regards to activity, pain, and function. Although in some cases the decision may appear simple, in others all these factors must be taken into account to decide on the correct operation for the patient. The development of a fixed algorithm is therefore difficult.

Although the joint-preserving surgeries are less predictable,^12,^14,^25,²⁶ when done with appropriate indications, they may afford long-term solutions with minimal need for activity restrictions. On the other hand, joint-sacrificing or replacement procedures are more predictable^5,^6,¹⁹^–²¹ in terms of pain relief but may need activity restrictions, especially in the young patient.

Surgical Options

Joint Preservation

The components of joint preservation include restoration of cartilage and restoration of alignment and joint stability. Restoring cartilage while leaving the limb malaligned or unstable is a setup for failure.

The ideal patient for a cartilage restoration is the young patient who has a focal cartilage defect with a well-aligned stable limb or one that can be aligned by an osteotomy procedure. It is also ideal for the patient with early arthritis who may require other concomitant procedures, such as meniscal allografts or anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) reconstruction.

Joint-Sacrificing Procedures

These include arthroplasty and arthrodesis. With the success of arthroplasty, the role of arthrodesis in the primary treatment of arthritis has become mostly obsolete, except for the patient with a native knee infection in whom this might still be an option.

PKA has gained popularity in the past decades as an alternative to TKA. As a group, historically it has been reserved for the relatively older patient with more advanced unicompartmental or bicompartmental arthritis but, with improvements in surgical design and technique, PKA is currently used for the younger patient as well. Also, for example, the middle-aged patient with limited disease who is active is also a good candidate for a PKA.¹⁸

TKA is the gold standard against which all procedures are compared. It traditionally has been described as the most predictable procedure for pain relief for any form of arthritis, either unicompartmental, bicompartmental, or tricompartmental. However, because of the sacrifice of the ACL and occasionally the PCL, it also the most kinematically different from a normal knee. Its best indication is for the patient with tricompartmental degenerative arthritis or in those knees with an inflammatory component to their arthritis.

Factors Affecting Decision Making

These include severity and extent of the arthritis, clinical symptoms and examination of the knee, patient expectations, age, and previous surgery.

Severity and Extent of Arthritis

Inflammatory arthritis is a contraindication for osteotomy or PKA. The number of compartments involved and the severity of arthritic changes within them will determine the type of procedure that could be performed. Advanced cartilage loss is associated with poorer results after an osteotomy, and it would therefore be reasonable to recommend a realignment osteotomy for patients with isolated medial or lateral unicompartmental arthroplasty that is not end-stage,²⁴ or the extremely young patient (<40 years) with unicompartmental advanced arthritis. Severe unicompartmental arthritis of the tibiofemoral joint in middle-aged or older patients might benefit from PKA. The presence of tricompartmental arthritis would preclude a limited unicompartmental or bicompartmental replacement. The presence of either medial or lateral compartment arthritis with significant patellofemoral arthritis would be a reasonable indication for limited bicompartmental arthroplasty that replaces the medial or lateral and patellofemoral joint.

One of the most controversial subjects in TKA or PKA is the patellofemoral joint. Whether the patella should be replaced or not has been a matter of debate for years in patients undergoing TKA ⁴ and is currently controversial for patients undergoing PKA.

Radiolographic evidence of arthritis without clinical symptoms emanating from the patellofemoral joint is currently not a contraindication for medial UKA. Furthermore, users of mobile-bearing designs do not believe that anterior knee pain in the presence of radiographic signs of patellofemoral arthritis—as long as there are no major grooves in the patellofemoral joint—is a contraindication to its use.^8,¹⁹ The designers have reported that patient symptoms improve after UKA as the patellofemoral joint is unloaded. In addition, long-term follow-up studies have shown low revision rates for progression of patellofemoral (PF) arthritis.¹⁹ A similar scenario may apply to an osteotomy, especially a varus-producing distal femoral osteotomy, as PF joint kinematics are improved.²⁵

However, the location of the patellar arthritis is important. Severe lateral patellar facet arthritis commonly requires replacement.^1a Studies have shown that medial patellar facet arthritis may not be that critical and can be ignored when performing a medial UKA. This is not the case with lateral unicompartmental arthritis; if patellofemoral arthritis is present, then the patellofemoral joint should be replaced, most commonly in the form of TKA.

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