Chapter 13 Unloading the Patellofemoral Joint for Cartilage Lesions

Introduction

Successful outcomes in patellofemoral cartilage restoration procedures rest on the need to unload the patellofemoral joint. Initial patellofemoral cartilaginous procedures were predisposed to failure because of overload of the patellofemoral compartment or failure to address patellar malalignment. Malalignment is defined as abnormal tilt and or subluxation of the patella,¹ and distal realignment (i.e., tibial tubercle osteotomy) is the most definitive method of either realigning a subluxated/tilted patella or offloading the patellofemoral compartment.

Anteromedialization of the tibial tubercle addresses patellar malalignment, patellar arthritis, or is used in conjunction with cartilage restoration procedures. The original technique, as described by Dr. Fulkerson in 1983,² has been shown in long-term studies to provide long-term relief from instability and patellofemoral pain.³ The idea behind the osteotomy is to alleviate stress from the distal and lateral portions of the patella and trochlea to the proximal and medial patellar articular cartilage.^2,⁴^–⁷ By changing the angle of the osteotomy cut, one can customize the procedure to include more medialization for instability cases or more anteriorization for cartilaginous unloading guidelines. Typically, in most procedures done for cartilage restoration, there is some evidence of patellar malalignment, so a combination of both medialization and anteriorization is chosen.

Indications/Contraindications

Indications for anteromedialization of the tibial tubercle include patellofemoral pain with either lateral or distal patellar arthrosis or lateral subluxation/dislocation of the patella. Other indications include a failed lateral release ⁸ and cartilage restoration procedures that need offloading of the newly regenerated or implanted cartilage cells. The ideal candidate is a patient with lateral patellar tilt (or subluxation) with grade III or IV articular cartilage degeneration localized to the lateral patellar or distal medial patellar facets. Not only should the patient be deemed psychologically mature to undergo the surgical procedure, but he or she should also have failed a course nonoperative management consisting of patellar taping, lateral retinacular mobilization, stretching of the extensor mechanism, bracing, and nonsteroidal anti-inflammatory medication.^1,^2,⁷

Contraindications to the procedure include no malalignment (except in unloading the patellofemoral joint in cartilage procedures), diffuse patellar articular cartilage disease, occult medial subluxation, tilt with no subluxation, mild articular cartilage changes (i.e., grade I or grade II) that would be best treated with an isolated lateral retinacular release, rheumatoid arthritis, bleeding disorders, a history of deep venous thrombosis, and complex regional pain syndrome. Proper patient selection is also important to the success of the procedure, and obesity was found to be the leading cause of tibial metaphyseal fractures or stress fractures in the postoperative period.

The benefits of the osteotomy include a long, flat, oblique cut that maximizes surface area to promote bony healing and allow screw fixation; the angle of the osteotomy cut can be adjusted to allow for more medialization or anteriorization, depending on the goals of the surgery; and the distal taper of the osteotomy minimizes the risk to the tibial metaphyseal bone and decreases the risk of iatrogenic fracture.

Preoperative Planning

Physical Examination

A complete review of the physical examination of the patellofemoral joint is beyond the scope of this chapter, but we will review the pertinent examination points. The exam should begin with a gait evaluation and hip range of motion to assess for increased femoral anteversion, in-toeing, or pes planus that can all predispose the patient to a relative genu valgum of the lower extremity and lead to patellar tilt or subluxation. Increased mobility of the joints is also assessed (elbow, thumb, etc.) because it may predispose the patient to early failure if a soft-tissue only technique is used for patellar stabilization. The skin should also be evaluated for changes associated with complex regional pain syndrome or previous incisions that would alter the standard approach to the tibial tubercle osteotomy. Muscle atrophy should also be assessed as a sign of nerve damage or the need for preoperative physical therapy for strengthening.

Specific tests for the evaluation of the patellofemoral joint include noting patellofemoral crepitance, joint effusion, lower extremity Q-angle, patellar J-sign, lateral retinacular tightness, patellar quadrant mobility, patellar apprehension test, patellar grind test, and stability/pain relief with a lateral to medial force on the patella (i.e., you are simulating holding the patella in an unloaded/reduced position).

Imaging Studies

Imaging studies should start with a complete set of knee x-rays consisting of bilateral anterior-posterior (AP) standing views, bilateral posterior-anterior (PA) 45 degrees; flexed views, a lateral view with the knee in 30 degrees; of knee flexion, and a Merchant view.⁹

The Merchant view is needed rather than the skyline view because as the knee is hyperflexed in the skyline view, the patella is captured by the bony anatomy of the trochlea, and subtle variations of patellar tilt or subluxation are lost at knee angles greater than 30 degrees;.¹

The Merchant view allows the evaluation of patellar tilt (patellofemoral angle of Laurin),¹⁰ trochlear dysplasia, and patellar subluxation (congruence angle)⁹ (Fig. 13-1, A–C). The lateral view allows the evaluation of patellar joint space, trochlear dysplasia, patellar alta/baja, and patellar tilt (Fig. 13-2, A–B). One can also use MRI or CT scans to measure similar angles of patellar subluxation and tilt.^3,¹¹^–¹⁶

FIGURE 13-1 Measuring tilt and subluxation. A, Normal patellofemoral angle of Laurin. Used to measure patellar tilt. The solid line along the lateral patellar facet should open laterally when referenced to the dotted line along the medial and lateral trochlear ridges. B, Abnormal patellofemoral angle of Laurin. Both of the lines are parallel to each other and thus are consistent with lateral patellar tilt. C, Abnormal congruence angle. Used to measure patellar subluxation. Line AB is along the lateral trochlea, and line CB is along the medial trochlea. Line BD is drawn as the bisector of the trochlear groove angle. Finally, line BD’ is drawn from the central trochlea to the central ridge of the patella. Line BD’ should be equal or medial to the bisector line BD. If it is lateral (as in this case), patellar subluxation can be confirmed.

(Reprinted from Operative Techniques in Orthopaedics, vol. 17. issue 4, James Bicos and John P. Fulkerson, Indications and Technique of Distal Tibial Tubercle Anteromedialization, p. 225. Copyright 2007, with permission from Elsevier.)

FIGURE 13-2 Lateral x-ray images showing a normal knee (A) and a knee with lateral tilt (B). A, Arrowhead showing the central patellar ridge, which should not overlap with the medial and lateral patellar facets (arrow line), in a normal knee without patellar tilt. B, Arrowhead showing near superimposition of the central patellar ridge on the lateral patellar facet, in a knee with patellar tilt. Note that the posterior femoral condyles should be superimposed for proper measurements of patellar tilt on the lateral x-ray view.

(Reprinted from Operative Techniques in Orthopaedics, vol. 17, issue 4, James Bicos and John P. Fulkerson, Indications and Technique of Distal Tibial Tubercle Anteromedialization, p. 224. Copyright 2007, with permission from Elsevier.)

Another important measurement for malalignment of the extensor mechanism is the tibial tubercle-trochlear groove (TT-TG) measurement (Fig. 13-3). This relates how far lateral the tibial tubercle is in relation to the central portion of the trochlea.¹⁷ Normal TT-TG values are less than 10 mm, and grossly abnormal values are between 18 to 20 mm. The TT-TG can be easily measured on CT or MRI scans and should be thought of as a guide as to how far to move the tubercle during the osteotomy procedure. The final amount of anteromedialization is based on the intraoperative assessment of patellar stability.