Joint-Preserving Osteotomies for Isolated Patellofemoral Osteoarthritis: Alternatives to Arthroplasty

AMZ osteotomy can be adjusted for the specific indication and for the location of chondral defects. If the primary goal is unloading a lateral lesion, or lateral maltracking, then a flatter osteotomy may be performed to increase the relative medialization of the tubercle; however, if the primary goal is unloading a distal lesion, then a relatively more oblique or vertical osteotomy may be performed to transfer the load more proximally. This is the technique preferred by authors in most cases in which more anteriorization is desired.

When TT-TG distance is used to guide surgical realignment, patellofemoral chondrosis associated with normal TT-TG distance can be addressed with directly anterior displacement of the tibial tubercle. Anteriorization of the tibial tubercle can be obtained by inserting a bone block between the tubercle and the tibial cut (Figure 5A).¹⁶ The medialization can be neutralized by making this block as thick as the measured medialization.¹⁶

Another option is sagittal plane osteotomy (Figure 5B).

Surgical Outcomes of Anteromedialization in Patellofemoral Osteoarthritis

Fulkerson and colleagues¹⁰ followed 30 patients for more than 2 years after they underwent AMZ of the tibial tubercle for persistent patellofemoral pain associated with patellar articular degeneration. Of these 30 patients, 12 were followed for more than 5 years. The authors reported 93% good and excellent subjective outcomes and 89% good and excellent objective outcomes. Quality of improvement was sustained for all 12 patients reevaluated more than 5 years after surgery. When examined separately, 75% of patients with advanced PFOA had a good outcome, but none had an excellent outcome. Carofino and Fulkerson¹⁷ retrospectively evaluated tibial tubercle AMZ for isolated PFOA in 22 knees (17 active patients older than 50 years at time of surgery; mean age, 55 years) with minimum follow-up of 2 years (mean, 77 months). Mean postoperative Lysholm score was 83. According to Lysholm scores, outcomes were good to excellent in 12 cases, fair in 6, and poor in 1. The authors concluded that tibial tubercle AMZ is a definitive treatment option for isolated PFOA in active older patients. Morshuis and colleagues¹⁸ retrospectively evaluated 22 patients (25 knees) who underwent Fulkerson osteotomy for patellofemoral pain. Outcomes were evaluated a mean of 12 and 30 months after surgery. At the first evaluation, 84% of patients had satisfactory outcomes, and, at the second (≤38 months after surgery), 70%. Only in relatively young patients without signs of PFOA did outcomes remain satisfactory in all cases. At the later evaluation, 60% of patients with PFOA and/or lateralization had satisfactory outcomes.

Tips and Tricks to Avoid Complications

For some patients, AMZ performed technically correctly produced unhappiness—an outcome that may arise from incorrect patient selection or failure to meet patient expectations. It is important to discuss objectives and expectations with the patient before surgery. With correct patient selection and meticulous surgical technique (with customization of osteotomy angle and translation based on underlying lesion), surgeons have obtained excellent outcomes with infrequent complications (Table).

Cutting guides or sequential drill bit placement can help reduce the variability of the angle cut of the osteotomy.

Intraoperative complications may involve neurovascular structures. The anterior tibial artery and the peroneal nerve are at risk during Fulkerson osteotomy. Decreased anterior sensation related to the infrapatellar branch of the saphenous nerve is not uncommon. Reducing the risk of neurovascular injury requires use of retractors and keeping the saw blade visible at all times. Another potential devastating complication is injury of the posterior vascular structures during bicortical tibial drilling for screw placement. According to Kline and colleagues,¹⁹ bicortical drilling may occur precariously near the posterior vascular structures of the knee. They advised extreme caution in drilling the posterior cortex during this procedure. To avoid the risk of compartment syndrome, surgeons can leave the anterior compartment fascia open or pie crust it by making multiple small perforations to decrease tension. Tibial fracture is another potential complication with this osteotomy. Reducing the risk of fracture involves tapering the distal cut anteriorly and avoiding a “notched” osteotomy (Figures 6A-6C).

Before definitive fixation of the osteotomy, patellar tracking must be evaluated to avoid overmedialization. If a “clunk” from extension to flexion is noted, iatrogenic medial instability should be suspected. The goal would be TT-TG distance of 10 mm to 15 mm. Commonly, if 4.5-mm bicortical screws are used, patients will have persistent pain or discomfort on direct palpation of the screw heads, and in some cases screw removal is required. This problem can be minimized with use of smaller (3.5-mm) countersunk screws or headless screws. Post-AMZ fractures of the proximal tibia have occurred on initiation of full weight-bearing or on too early return to activity.²⁰ Patients should be advanced gradually to partial weight-bearing, and be allowed full weight-bearing only after the osteotomy shows radiographic evidence of complete healing. Fulkerson²¹ advised prescribing protected weight-bearing with crutches for 6 to 8 weeks and discouraged running for 6 months and competitive sports for 9 to 12 months. Nonunion of the tibial tubercle has been reported²² but is relatively uncommon and can be treated with a reduction in physical activity and use of a bone growth stimulator. Excessive anterior tubercle translation resulting in skin breakdown typically does not occur with AMZ surgery.

Postoperative complications, which are similar to those associated with any knee surgery, include infection, arthrofibrosis, complex regional pain syndrome, thromboembolism, nonunion, fixation failure, and fracture. Arthrofibrosis has many causes, but the problem decreases with secure osteotomy fixation, early knee motion, and patellar mobilization. Overmedialization can result in medial patella instability, typically subluxation rather than complete dislocation. The instability can be relatively subtle or can cause pain and weakness. Lateralization of the tibial tubercle might be appropiate.²³