Patella-Thinning Osteotomy
In patients who are under 65 years old and have disabling anterior knee pain recalcitrant to conservative treatment, PTO may be considered for isolated PFOA with any type of chondral lesion (including severe diffuse chondropathy with exposed bone) (Figures 3A-3C), patellofemoral joint space reduced by more than 50% on skyline view, patellar thickness of 20 mm or more, and normal TT-TG distance.7 Vaquero and Arriaza8 found that thinning the patella by 7 mm significantly reduced patellofemoral joint reacting forces. Post-PTO improvement may be attributable to various factors, including decreased patellofemoral pressure and decreased intraosseous pressure. PTO is performed with a high-speed side-cutting burr while a plane is maintained strictly parallel to the anterior cortex of the patella (Figure 3A). When the PTO is completed, the surgeon tightens the clamp, collapses the central part of the patella, and fixes both fragments with biodegradable pins.
Vaquero and colleagues7 analyzed PTO outcomes in 31 patients (35 knees) with mean follow-up of 9 years and noted significant improvements in functional scores and radiologic parameters. All patients except 1 were satisfied with the operation. Radiologic progression of PFOA was slowed, but radiologic femorotibial osteoarthritis progressed in 23 cases (65%), and 4 required TKA. The authors found satisfactory clinical and radiologic outcomes—only 4 patients (12.5%) required TKA—and good functional outcomes.7
PTO, a low-morbidity surgery with good functional outcomes, does not close the door on other surgery, such as TKA.7
Tibial Tubercle Anteromedialization Osteotomy
Whereas PLPF and PTO are indicated in knees with normal TT-TG distance, Fulkerson AMZ osteotomy must be considered in isolated PFOA with articular cartilage lesions at the distal or lateral patellar facets resulting from long-standing malalignment with increased TT-TG distance (Figures 4A, 4B).
AMZ unloads the distal and lateral facets of the patella while improving the extensor mechanism.11,12 A successful AMZ outcome requires preservation of some of the medial and proximal articular cartilage of the patella. In 1983, Fulkerson13 described use of tibial tubercle AMZ osteotomy to address patellofemoral pain associated with patellofemoral chondrosis in conjunction with patellofemoral tilt and/or chronic patellar subluxation. This technique is indicated when the patella needs to be realigned for relief of elevated contact stress and centralization. Currently the technique is used not only in patients with isolated PFOA but in patients with chronic lateral patellar instability. Fulkerson osteotomy combines the benefits of the Maquet technique (unloading) and the Elmslie-Trillat technique (tracking improvement) in a single osteotomy, with no distraction of the osteotomy site with bone graft and without the complication rate of Maquet tibial tubercle elevation. Before surgery, computed tomography (CT) or magnetic resonance imaging (MRI) is routinely used to measure TT-TG distance to determine the tibial tubercle medialization required in the Fulkerson osteotomy. However, TT-TG distance must be used with caution, as it cannot be determined in cases with trochlear dysplasia. Consequently, physical examination and arthroscopic examination for evaluation of patellofemoral tracking and location of chondral defects should be performed before the Fulkerson osteotomy.
Rationale; Indications and Contraindications; Preoperative Planning
As already noted, AMZ unloads the distal and lateral facets of the patella. Beck and colleagues14 suggested AMZ is appropriate for unloading the lateral trochlea. However, it is not useful for central chondral defects and may actually increase the load in patients with medial chondral defects. As AMZ shifts contact force to the medial trochlea, Fulkerson osteotomy is appropriate when distal and lateral chondral lesions must be unloaded. Because this procedure moves the tibial tubercle medially and anteriorly, loads are transferred to the proximal and medial facets of the patella. Therefore, the procedure is contraindicated when diffuse, proximal, or medial chondral lesions are present. Moreover, AMZ is contraindicated in patients with normal TT-TG distance because there is the risk that overmedialization will cause symptomatic medial subluxation. Grade III or IV central trochlear cartilage lesions are also less likely to have successful AMZ outcomes. Therefore, before Fulkerson osteotomy is performed, MRI should be obtained to evaluate the patellofemoral articular surface and TT-TG distance. MRI provides information that is useful for preoperative planning because it allows assessment of articular cartilage lesions, including their location and severity. Moreover, because the osseous and cartilaginous contours of the patella differ, MRI gives a more accurate picture of the patellofemoral congruence than CT does. Last, before the open surgery is performed, the patellofemoral joint should be arthroscopically examined to determine the location of chondral lesions. Cartilage lesion mapping is important because Fulkerson osteotomy outcomes depend on chondral lesion location. Pidoriano and colleagues15 correlated AMZ outcomes with articular lesion location and noted optimal outcomes in patients with distal and lateral patellar articular lesions and intact trochlear cartilage (87% good and excellent outcomes). Patients with medial lesions and proximal or diffuse lesions generally did poorly (55% good and excellent outcomes in medial lesions vs 20% good and excellent outcomes in proximal and diffuse lesions). Central trochlear lesions were associated with medial patellar lesions, and all patients with central trochlear lesions had poor outcomes. Interestingly, Outerbridge grading of patellar lesions was not significantly correlated with overall outcomes.15 Even in cases of severe chondropathy, including bone-on-bone arthritis, AMZ has had reliable outcomes and may be superior to arthroplasty because of joint preservation, duration up to 8 years, and restoration of patellofemoral tracking. It should be noted that a resurfacing technique such as patellofemoral arthroplasty is not a substitute for patella realignment. Any patellofemoral maltracking must be corrected before patellofemoral arthroplasty. Fulkerson osteotomy does not preclude subsequent surgery (eg, TKA). Furthermore, AMZ may prevent the natural progression of PFOA related to chronic lateral tracking.