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Repair technique restores the MPFL as a lateral displacement restraint

However, an osteotomy is indicated if the tibial tubercle to trochlear groove distance is excessive.

Issue: July 2013

ByMark D. Miller, MD

ByAndrew J. Cosgarea, MD

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Often patients who present with a “dislocated knee” actually have a patellar dislocation. Their cruciate and collateral ligaments examination is stable, but they often have patellar and/or medial epicondyle tenderness, an effusion and patellar apprehension. An injury to the medial patellofemoral ligament is usually present. In addition to history and physical exam findings, radiographs may demonstrate loose bodies, medial patellofemoral ligament avulsion fractures and/or patellar articular surface incongruity.

As there are alternative approaches to medial patellofemoral ligament (MPFL) reconstruction, I have asked Andrew J. Cosgarea, MD, to also give his surgical pearls. In this Surgical Technique, I present my approach and that of Cosgarea, which is similar with a few exceptions, to provide readers with in-depth tips on performing these procedures.

Preoperative imaging

 

Mark D. Miller

 

Andrew J. Cosgarea

X-rays are usually not as obvious as the image shown in Figure 1. MRI can help to confirm injury to the medial patellofemoral ligament (MPFL), which is most often on the femoral side; identify cartilage injury (typically to the medial patellar facet and the lateral femoral condyle; and whether there are loose chondral bodies, which cannot be seen on plain radiographs. The tibial tubercle to trochlear groove (TT-TG) distance is measured off of an MRI, or more commonly, a CT scan. TT-TG distance greater than 15 mm indicates borderline pathology lateralization of the tuberosity, suggesting malalignment of the distal extensor mechanism.

Cosgarea considers performing an osteotomy, as described by John P. Fulkerson, MD, when the TT-TG distance exceeds the 15-mm threshold. Sometimes, he adds an MPFL reconstruction after completing the osteotomy if the patella is still dislocatable. However, the osteotomy should always be done first.

Figure 1. This axial radiograph demonstrates a
lateral patellar dislocation.

Images: Miller MD

If this distance is less than 20 mm, I have found that a proximal procedure alone is sufficient.

Although MPFL repair alone may sometimes be successful, I have noted most surgeons now recommend MPFL reconstruction, particularly in chronic instability cases. A study by Bitar and colleagues published in 2012 showed MPFL reconstruction was associated with an improvement from 77.8 points to 88.9 points on the Kujala scale.

Diagnostic arthroscopy

The MPFL reconstruction procedure begins with a comprehensive diagnostic arthroscopy, which should address concomitant pathology to include meniscal tears, loose bodies and articular cartilage injuries. Patellar tracking can also be evaluated at this time.

I recommend viewing patellar tracking from the superolateral portal and move the knee through range of motion (ROM), which helps me evaluate if or when the patella engages, and if there is any lateral overhang present. If the patella engages, this typically occurs when the knee is positioned at 30° to 40°.

A semitendinosus or gracilis graft is typically harvested in the standard fashion for these cases. Alternatively, a soft tissue allograft can also be used, and may be preferred in patients with hyperlaxity syndromes and revision cases.

I place a whip stitch in each end of the tendon graft and take care to ensure there are no “dog ears” in the tendon that can impede graft passage.

Position of incisions, tunnels

Figure 2. The free soft tissue graft is fixed
to the patella with two medial suture anchors;
one at the upper one-fourth of the patella
and the other at the equator of the patella.

Although the figures in this article show an open technique, we typically perform this procedure with two incisions. The surgeon makes a short parapatellar incision and exposes the upper two-thirds of the medial border of the patella. A 5-mm soft tissue sleeve can be preserved for subsequent MPFL repair, imbrications or to reinforce graft fixation. Although I have previously advocated transpatellar drilling, reports of fractures (including my own), led me to modify this technique. I now recommend graft fixation on the border of the patella with two small 3-mm absorbable suture anchors. One anchor is placed in the middle of the medial border of the patella, and the other is placed in the upper one-fourth of the patella (Figure 2).

By contrast, Cosgarea uses a modification of the docking technique developed by Christopher S. Ahmad, MD. The graft is “docked” in a 15-mm blind patellar tunnel. The sutures on the patellar end of the graft are passed laterally with diverging K-wires, and tied over a bone bridge. Cosgarea has not yet encountered any patella fractures with this technique, and he said one of its advantages is that you can forego the added expense of anchors.

Figure 3. A fluoroscopic view is used to
find the femoral attachment of the MPFL.
Isometry is checked prior to overdrilling
the guide wire.

A second small incision is made between the adductor tubercle and the medial epicondyle. Both surgeons drill a blind-ended tunnel in the femur at Shöttle’s point. Before the tunnel is drilled, a K-wire is placed, and the position is confirmed using fluoroscopy (Figure 3). Once the tunnel is localized, an appropriately sized drill bit is used to drill the tunnel 20 mm to 25 mm deep.

Graft passage and fixation

The femoral end of the graft is passed into the blind femoral tunnel with a Beath needle. The knee is then cycled, and a soft tissue interference screw is used to fix the graft in the femoral tunnel (Figure 4). I recommend graft fixation with the knee in 30° and 40° flexion. The suture can be tied through a small stab incision on the lateral femoral condyle, if additional fixation is desired.

Figure 4.  Filtration using a biotenodesis screw
is shown. Notethat the knee is flexed 30° to
45°, tension is applied to the lateral sutures and
the screw is inserted under direct visualization.

Cosgarea’s technique varies somewhat from this. He fixes the graft on the femur based on graft tension “isometry.” This should be confirmed by wrapping the graft around a K-wire before drilling the femoral tunnel. While ranging the knee, he determines the knee flexion angle that results in the greatest graft tension. Although sometime that angle is 30° to 40°, often it is even greater.

Proximal or anterior malpositioning of the femoral tunnel is a common mistake, and often leads to excessive graft forces and excessive patellofemoral compression forces. Prior to placing the femoral interference screw, Cosgarea confirms that there are two to three quadrants of lateral translation when the knee is in full extension or that the translation of the patella is equal to the contralateral normal side.

Rehabilitation and results

I do not have my patients wear a brace postoperatively and begin ROM exercises in the immediate postoperative period. Since these patients have a tendency to lose motion, I am fairly aggressive about starting early ROM exercises. Physical therapy includes ROM, closed-chain quadriceps strengthening and progressive weight-bearing, as tolerated.

On the other hand, Cosgarea uses a knee immobilizer for 3 weeks in these cases or until quadriceps function allows for safe mobilization. He allows progression to full weight-bearing over 1 week to 2 weeks, unless a concomitant osteotomy is performed, in which case weight-bearing is protected for 6 weeks.

Overall, patients have been satisfied with the results of this operation in our hands and subsequent recurrent instability is not common. No major complications have occurred related to this procedure since I abandoned transpatellar drilling.