Review Question - QID 219479

This patient presents with recurrent patellar dislocations resulting in a significant patellar chondral defect. Given his increased TT-TG distance, his patellar maltracking should be addressed via a tibial tubercle antero-medializing osteotomy concomitantly with MPFL reconstruction and cartilage restoration (Answer 4).

Patellofemoral compartment cartilage defects found in young patients are complex injuries with deleterious long-term outcomes. In general, patients with patellofemoral lesions have been reported to have inferior outcomes compared with similar lesions located within the medial or lateral compartments (i.e. femoral condyles). This is largely due to the high shear forces encountered during flexion along the patellar undersurface as it engages the trochlea. In patients with patellar maltracking (i.e. TT-TG distance > 20mm), an antero-medializing (i.e. Fulkerson) tibial tubercle osteotomy can offload the patellofemoral joint and protect any cartilage restoration procedures performed. In such cases, patient-reported outcomes and graft long-term durability have been comparable to similar procedures performed in the medial or lateral compartments. These findings highlight the importance of addressing maltracking for optimizing outcomes in patellofemoral cartilaginous restoration procedures.

Chahla and colleagues utilized a modified Delphi method to provide an expert consensus statement on the management of large chondral and osteochondral defects in the patellofemoral joint. The group of 28 high-volume cartilage experts demonstrated consensus (>75% agreement) in all proposed recommendation statements, including addressing malalignment/maltracking via osteotomy concomitantly or before cartilage restoration procedures. The authors conclude that while further research is needed, the expert consensus document can serve to guide surgeons in the management of these complex injuries.

Middleton and colleagues provided a review of the indications and techniques for performing a tibial tubercle osteotomy. They demonstrate how tibial tubercle anteriorization unloads the patellofemoral surface and thereby protects cartilage restoration procedures performed along the patella or trochlea. Furthermore, the authors recommend that in the setting of an elevated TT-TG (>20mm), some degree of tuberosity medialization should be considered. They conclude that individualizing the direction and degree of tubercle transfer based on patient parameters is critical to producing successful long-term results after surgery.

Figure A demonstrates measuring the TT-TG distance via superimposing MRI axial imaging slices. In this patient, the TT-TG distance measured >20mm indicating patellar maltracking. Figure B demonstrates a displaced osseous fragment from the MPFL insertion. Figure C demonstrates the cartilaginous defect before performing chondroplasty along the undersurface of the patella.

Incorrect Answers:
Answer 1: In general, chondroplasty as a definitive treatment for large patellofemoral chondral defects is reserved for older patients who have already developed degenerative arthritic changes throughout the knee.
Answer 2: Microfracture would be an appropriate definitive treatment option in smaller (<1cm2) lesions. However, large defects or those involving significant loss of subchondral bone require cartilage restoration procedures (i.e. autologous chondrocyte implantation versus osteochondral allograft implantation, respectively).
Answer 3: A lateralizing tibial tubercle osteotomy would increase the Q-angle and result in the worsening of any underlying patellar maltracking.
Answer 5: Patellofemoral arthroplasty is an appropriate treatment option in older patients (40+ years) who have developed arthritic changes primarily localized to the patellofemoral joint. This patient is considerably young to be considered for arthroplasty, especially with alternative options and improvements in cartilage restoration procedures.