REVIEW
THE ANTEROLATERAL APPROACH FOR TOTAL KNEE REPLACEMENT

B. REIGNIER

Clinique le Pré Pasteur - Le Mans, France

The anterolateral approach to the knee has several advantages over the anteromedial or midline incisions customarily used in total knee replacement surgery.

The rationale for this approach is the vascular pattern of the skin covering the anterior aspect of the knee. The blood vessels come from the medial side, as do the nerves. The arteries, as well as the nerves, spread transversely from medial to lateral, within the areolar subcutaneous tissue that overlies the superficial fascia. Anatomical injection specimens also show the presence of an anterolateral longitudinal skin strip that is virtually avascular2 (Fig. 1).

Figure 1 (from De Peretti et al) 1: Lateral, sparsely vascularized skin strip 2: Perforators from the vastus medialis 3: Cutaneous branch of the descending genicular artery 4: Cutaneous branch of the satellite artery of the short saphenous vein

This anatomical pattern could be exploited for an approach through the avascular anterolateral skin strip. This route would leave the blood and nerve supply to the skin intact, which is an important consideration in total knee replacement.

The anterolateral approach described here appears to have been used initially by Nova Monteiro, and then by Lubinus, for isolated patellofemoral replacements. After my return from Kiel, in 1982, I began using this route for the same procedures; eventually, the use of the incision was extended to all forms of knee replacement, whether mono- or tricompartmental, with only a few provisos, which are discussed below.

TECHNIQUE

The only source that gives at least a summary description of this approach is the textbook by Bauer et al.1 This article provides a detailed description, and lists the rules that must be obeyed in order to perform this incision correctly.

The widely curving incision starts in the middle of the anterior aspect of the thigh, 10 cm proximal to the superior margin of the patella. It is routed slightly lateral to the upper lateral corner of the patella, then follows the lateral margin of the patella at a distance of 1 cm, and finishes on the anterior border of the tibia, 10 cm distal to the apex of the patella (Fig. 2a and b).

Figure 2a and b Skin incision pattern

The first structure to be identified is the superficial fascia, which is always a thick, discrete entity in the distal one third of the thigh, above the patella. At this level, the fascia is opened following the line of the skin incision. This will partially expose the distal portion of the tendons of the rectus femoris and the vastus lateralis. Once this exposure has been obtained, the superficial fascia of this musculotendinous layer should immediately be detached medialwards, to obtain the correct plane of dissection (Fig. 3a and b).

Figure 3a and b Incision and elevation of the superficial fascia

This superficial fascia is much less readily distinguished along the lateral margin of the patella, where it is thinner and, above all, more closely adherent to the lateral retinaculum. First, the prepatellar tissues have to be stripped up with gradual finger dissection in the "housemaid's knee plane." Once that has been done, it is possible to identify and to dissect the superficial fascia from proximal to distal, by lifting it off the lateral retinaculum. This will prevent the creation of a false passage that might damage the skin blood supply (Figs. 4a and b, 5a and b).

Figure 4a and b Subfascial dissection towards the front of the patella, in the "housemaid's knee plane"
Figure 5a and b Pulling up the flap, and dissection of the superficial fascia from the lateral retinaculum

The superficial fascia is invariably thin, but more readily identifiable, over the patellar tendon; stripping it up should be straightforward at this site (Fig. 6).

Figure 6 The superficial fascia is dissected off the patellar tendon.

The detachment of the skin flap containing the superficial fascia is carried to the junction of the vastus medialis and the rectus femoris; this site is exposed over a distance of 1 to 2 cm, as are the medial patellar retinaculum and the medial aspect of the tibia past the medial border of the patellar tendon. This part of the dissection is very bloodless. If a prepatellar bursitis is found, care should be taken to excise very sparingly, without going too far towards the skin, which would violate the superficial fascia (Fig. 7a and b).

Figure 7a and b Fully dissected flap, exposing the anteromedial arthrotomy site

This dissection will have freed a large flap, which may be reflected. There must be no traction on the two ends of the flap, which delimit the hinge. If there is too much tension, and if the adipose tissue is very bulky, the surgeon should not hesitate to enlarge the incision by 2 or 3 cm, both proximally and distally.

Once the flap has been reflected, it may be tacked to the skin on the medial side of the knee, using a loosely placed stitch (Fig. 8). However, this will not always be necessary, since there is little stress on the flap, and, if the adipose tissue layer is thin, the flap will stay put. If the procedure is being performed without a tourniquet, the integrity of the flap's blood supply may be checked, with the knee in extension or in flexion.

Figure 8 Fixation of flap to medial aspect of the knee

The one essential point to bear in mind is the need for the dissection to be strictly below the superficial fascia, so as to preserve the blood supply to the flap.

Once the flap has been prepared and reflected, knee replacement is carried out in customary fashion. Usually, a medial arthrotomy will be employed, or any other pattern permitted by this incision (Fig. 9).

Figure 9 Anteromedial arthrotomy

ADVANTAGES

The skin incision described in this article is particularly advantageous if the adipose tissue cover over the knee is very thick. The skin and all the subcutaneous fatty tissue are folded out of the way medially, which makes it very much easier for the patella to be reflected laterally. If the patella is still partially covered by adipose tissue, reflecting it laterally can be associated with major, and sometimes troublesome, external rotation of the tibia. This undesirable movement is very much less likely to be encountered where the approach described here is being used, since the patella and its soft-tissue mantle are reflected separately.

The surgical field now looks like an open book, with the patella turned outwards and the skin turned inwards. The skin flap will slacken as the knee is flexed, and will, therefore, be protected from damage by the retractors, throughout the procedure (Fig. 10).

Figure 10 The knee opens up like a book.

Exposure of the extensor mechanism is better than that obtained with a midline incision, which means that, at any stage of the procedure, a better check can be made for patellar tracking.

Any lateral surgery that needs to be done is greatly facilitated (Fig. 11a and b). Thus, the removal of any laterally inserted hardware from under tibialis anterior would be quite straightforward. It should be borne in mind that in such cases the skin incision could be routed, at least partly, through the site used for the previous incision. Medially placed hardware may also be removed, with limited dissection.

Figure 11a and b 1: Fascia lata 2: Lateral collateral ligament, and lateral capsule 3: Common peroneal nerve 4: Tibialis anterior 5: Tibial tubercle

This approach may, of course, also be used for a coronal osteotomy of the tibial tubercle, working either from lateral to medial, after the disinsertion of the tibialis anterior; or from medial to lateral, preserving the origin (and, hence, the blood supply) of the tibialis anterior, which will be used as a hinge, since the bone block will be reflected in the same way as the patella.

The lateral retinaculum may be readily divided, while preserving the synovial plane and, thus, the superolateral and inferolateral vessels that form part of the network of vessels around the knee. However, more extensive lateral releases may be performed, since there is direct access to the fascia lata and the lateral collateral ligament, all the way to their insertions; also, with a limited amount of skin dissection, the common peroneal nerve may be safely freed at the neck of the fibula, as a preventative measure.

If the lateral peripatellar synovial tissue has been cut, and the resultant defect cannot be closed at the end of the procedure, the damage may readily be repaired by folding a portion of the quadriceps expansion over the defect, along a hinge at the lateral margin of the patella (Fig. 12).

Figure 12 Quadriceps expansion flap turned back to cover defect

When closing the incision, the skin flap will amply cover the medial arthrotomy, with a safe offset between the superficial and the deep soft-tissue incisions. The subcutaneous suture will be sound, since it approximates the margins of the superficial fascia. Since the skin blood supply has been preserved, there will be no risk of skin necrosis. This is borne out by my experience over more than 15 years.

Medial incisions will move more medially after surgery, and become tenser in flexion. The same is true of midline incisions. This is why these scars tend to be painful and may develop keloids. In contrast, the anterolateral scar left behind by the incision described in this article will move a little backwards over time, and will relax in flexion. It is never painful, and thus facilitates postoperative rehabilitation. Also, because there is no tension at any time after surgery, the scar will normally be very thin, and the healing anterolateral tissues will have an excellent blood supply.

There is no risk of saphenous nerve neuroma; also, the skin retains its normal sensitivity, and, within a few months, will be normally mobile over the front of the patella.

This mobility of the soft tissues means that, even long after the initial procedure, the same incision may be used and a good plane of dissection found below the superficial fascia.

COMPLICATIONS

The only complication that may be encountered is the spread, in the plane of the subcutaneous dissection, of the postoperative haemarthrosis fluid. The accumulation may be tense, and may break out by disrupting the distal part of the scar, allowing germs to enter. In our experience, aspiration at 48-hourly intervals, under antibiotic cover, until no more fluid is produced, has always been found to allow the complete removal of the haemarthrosis fluid and the healing of the flap.

INDICATIONS AND CONTRAINDICATIONS

The skin incision described here is useful for any TKR procedure, providing that one condition is observed: there must be no previous midline or anteromedial longitudinal incision, regardless of how long ago the incision was made. A medial incision will have at least partially interfered with the blood supply coming from the medial side, and an anterolateral skin incision would incur the risk of skin necrosis.

A previous transverse skin incision would not, however, rule out the use of the anterolateral approach described in this article, since it would run parallel to the blood vessels and would not, therefore, interfere with the blood supply coming in from the medial side of the knee.

Figures 13 and 14 illustrate this point.

Figure 13 Excision of old adherent scar from the medial side, leaving a transverse scar	Figure 14 No skin damage at junction of transverse scar and the scar of the anterolateral skin incision

Following a childhood injury (which, incidentally, had subsequently given rise to severe OA of the knee), the patient had a very thin scar that adhered closely to the medial aspect of the knee. She initially underwent plastic surgery to restore a subcutaneous soft-tissue mantle over the medial side of the knee. From this procedure, she had a good horizontal scar, which made it possible to use an anterolateral approach for her knee replacement two months later. The junction of the two incisions healed perfectly.

This case confirms the anatomical findings, and shows the extent to which these medially derived subcutaneous vessels may be relied upon to produce sound healing.

CONCLUSION

Figure 15 Excellent vascularization of the skin flap

It may need a little courage to detach the large skin flap involved in this approach, taking care to stay below the superficial fascia. Once one has taken the plunge, the many advantages of this route will be readily apparent, and the incision may well come to be used as the standard approach.

(Transl KRMB)

 

REFERENCES 1. BAUER R, KERSCHBAUMER F, POISEL S, (1988) Voies d'abord en chirurgie orthopédique et traumatologique. Masson, Paris. 2. DE PERETTI F, ARGENSON C, BERACASSAT R, BOURGEON Y (1973) Problèmes artériels et nerveux posés par les incisions cutanées antérieures au niveau de l'articulation du genou. SOFCOT 73 (suppl 11): 231 233