Unloading the Patellofemoral Joint for Cartilage Lesions

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.2,47 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 release8 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




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.3,1116




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.




Surgical Technique





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Jul 12, 2016 | Posted by in RHEUMATOLOGY | Comments Off on Unloading the Patellofemoral Joint for Cartilage Lesions

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