Total Knee Arthroplasty Via Small-Incision Midvastus Approach

Steven B. Haas, MD, MPH

Stephen Kim, MD

Dr. Haas or an immediate family member has received royalties from Smith & Nephew and Innovative Medical Products; is a member of a speakers’ bureau or has made paid presentations on behalf of Smith & Nephew; serves as a paid consultant to or is an employee of Smith & Nephew; has stock or stock options held in OrthoSecure; and has received research or institutional support from Smith & Nephew. Neither Dr. Kim nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

INTRODUCTION

Total knee arthroplasty (TKA) is a commonly implemented and highly successful treatment of symptomatic end-stage arthritis of the knee when nonsurgical management has failed.¹^,² Although TKA has traditionally been performed through a standard medial parapatellar arthrotomy with eversion of the patella, the development of new surgical techniques and instrument design has facilitated TKA using smaller incisions with less disruption of the extensor mechanism.³^,⁴^,⁵ One such method is the small-incision midvastus approach, which avoids eversion of the patella.³^,⁵ The potential benefits of this approach include earlier return of quadriceps function, earlier return of motion, improved flexion, decreased postoperative narcotic use, and improved cosmesis.⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰

The safe and accurate application of the small-incision midvastus approach is predicated on a proper understanding of the principles of minimally invasive surgery, which include (1) a complete understanding of anatomy, (2) gentle handling of the soft tissues, (3) positioning of the extremity in coordination with accurately placed and tensioned retractors to fully use the mobile window, and (4) the use of instrumentation and equipment designed for minimally invasive surgery.⁵ In cases where these principles are compromised, a more standard approach may be preferable. If used appropriately, a small-incision midvastus approach can result in less surgical insult to the soft tissues and allow for an earlier return to function without increasing the rate of complications.⁵^,⁶^,⁷

PATIENT SELECTION

Contraindications

Although there are no absolute contraindications to use the small-incision midvastus approach, the relative contraindications are generally patient related¹¹^,¹² (Table 1). Surgical considerations and expectations must be discussed preoperatively with the patient. Patients should be aware that although there are potential benefits with a small-incision approach, these benefits are outweighed by the need for the placement of well-aligned components in a knee with balanced ligament restraints. Thus, patients should be aware that if there is any compromise in surgical safety or quality due to a limited exposure, the incision and the dissection will be increased as needed.

PREOPERATIVE IMAGING

Planning proceeds as for standard knee arthroplasty. We obtain weight-bearing AP, lateral, 45° flexed PA, and Merchant view radiographs. Full-length views are not obtained unless otherwise indicated by the history or the
physical examination. Radiographs are interpreted for deformity, bone loss, the presence of patellar baja, and overall bone quality. In cases of deformity, anticipating an appropriate distal femoral cut angle and the height of tibial resection can be useful.

TABLE 1 Relative Contraindications to the Small-Incision Midvastus Approach

Substantial quadriceps muscle mass in men

Significant obesity (body mass index >40 kg/m²)

Severe coronal plane deformity

Flexion contracture >25°

Passive flexion <80°

Severe patella baja

Significant scarring of the quadriceps mechanism

Revision surgery

VIDEO 63.1 Mini-Midvastus Approach. Steven B. Haas, MD, MPH; Stephen Kim, MD (16 min)

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Video 63.1

PROCEDURE

Patient Positioning

The patient’s body is positioned in the same way as for a standard TKA. However, appropriate leg positioning is crucial when performing minimally invasive TKA. A bolstered sandbag is placed under the drapes at the level of the opposite ankle so that the knee can sit flexed at approximately 70° to 90° (Figure 1). Most of the procedure is done with the leg in this position. Hyperflexion is required only to prepare the proximal tibia and insert the definitive tibial tray. A lateral support is used so that the leg sits without being held by an assistant.

Special Instruments

Specialized instrumentation is critical in performing a small-incision midvastus approach TKA. Most systems today have made appropriate instrument modifications for a minimally invasive TKA to be performed. Cutting blocks and guides have been made smaller, with rounded edges that can be accommodated through smaller incisions. Additionally, side-specific instruments and cutting guides have been developed so that placement is not impeded by the extensor mechanism. A rigid saw blade with a narrow body that fans out at the distal tip to facilitate bone cuts is also helpful.

FIGURE 1 Photograph shows a patient positioned on the operating table with a bump placed across from the opposite ankle to hold the leg at 70°-90°.

Some systems have also developed specific implants for use with a minimally invasive technique. These implants have shape modifications, such as a short keel on the tibial component or modular stems. We have found that standard side-specific tibial base plates with an asymmetric tibial tray facilitate accurate insertion through a limited exposure.

Surgical Technique

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