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CURRENT CONCEPTS
A lateralized tibial tubercle can lead to a lateral vector contributing to both lateral instability and cartilage wear. While examination of the tubercle alignment with the knee in full extension and flexion is critical, objective measurements with CT and MRI have been developed to aid the surgeon in both the decision to perform tibial tubercle osteotomy and in preoperative planning for the type of osteotomy to be performed. Typically, a TT-TG distance greater than 20 mm on CT is pathologic, but this threshold may be lower on MRI depending on technique. Our work by Camp et al. has helped define a simple method of calculating TT-TG distance on MRI, but certainly controversy continues in this area. With a dysplastic trochlear, measurement of this distance can be problematic, and alternative options, including TT-PCL distance are emerging, but likely require more refinement before widespread adoption.
Tibial tubercle osteotomy (TTO) options range from pure anteriorization to anteromedialization (AMZ). In the setting of cartilage surgery, it is important to remember that an AMZ will offload the distal and lateral patellar cartilage, but will overload the proximal and medial patellofemoral cartilage. A recent study by Gomoll et al. showed no significant difference between knees treated with autologous chondrocyte implantation (ACI) alone versus ACI and TTO, so it is important to assess each patient carefully and not perform more surgery than is necessary.
Traditionally, a lateral release was performed for a tight lateral retinaculum. A “tight” lateral retinaculum is defined as the patellar not able to be everted to neutral on physical examination, or significant lateral patellar tilt on a merchant view. However, recent interest has favored a lateral retinacular lengthening over lateral release. The advantages of the lengthening procedure have been preservation of the vastus lateralis attachment, less risk of medial iatrogenic instability, and in the setting of cartilage surgery, providing a closed layer between the joint and the subcutaneous tissues.
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Cartilage Treatment Options
Microfracture
Marrow stimulation techniques serve an important role in the treatment of cartilage lesions. It has shown to be a cost- effective, minimally invasive technique for the treatment of cartilage lesions. In the short-term (< 5 years), microfracture has demonstrated excellent results in regards to pain relief and function, especially in younger patients. Unfortunately, the fibrocartilage produced by microfracture has proven to have unfavorable long-term durability and clinical results. In addition, there is also evidence to suggest possible detriment to the results of future cartilaginous procedures in the face of a failed microfracture due to the creation of intralesional osteophytes. Microfracture has also been proven to have suboptimal results with lesions greater than two to four centimeters, adding to its limitations as a treatment. We feel that microfracture can have a role for indicated lesions. However, even when performing a simple arthroscopic marrow stimulation technique, it is critical to follow the principles of cartilage surgery and identify and correct background factors in this setting.
Currently, there are options to augment microfracture, in order to encourage more articular-like cartilage formation over fibrocartilage. One option is micronized cartilage matrix (BioCartilage, Arthrex, Naples, FL, USA), but clearly more research and clinical results are needed in this area. Other augmentation options include collagen and polymer membranes, chitosan and fibrin gels, hyaluronan injections, as well as numerous growth factors. Autologous matrix- induced chondrogenesis (AMIC) has demonstrated some promising early results. A microfracture-enhanced model may be the most cost effective technique, but more clinical results are needed.
Autologous Chondrocyte Implantation (ACI)
Gradually ACI has demonstrated its role as a reliable treatment option for patellofemoral cartilage lesions. Short and long-term follow-up have demonstrated excellent results with modern ACI techniques. Recently, Gillogly et al. demonstrated good to excellent results in 83% of cases with ACI of the patella after a mean follow-up of 7.6 years. One technical advantage for ACI in the patellofemoral joint is that the geometry of the patch in unconstrained. ACI requires an index arthroscopy with a cartilage biopsy of 200 to 300 micrograms or approximately five to ten millimeters of cartilage, which is typically taken from the lateral margin of the intercondylar notch. A two-stage surgery is generally perceived as a disadvantage of the technique. However, a first stage surgery to define the extent and location of the cartilage lesions can give the surgeon helpful information for selecting the best treatment option.
ISAKOS NEWSLETTER 2015: Volume I 31