CORR Insights®: Knee-to-Talus Donor-Site Morbidity Following Autologous Osteochondral Transplantation: A Meta-analysis with Best-case and Worst-case Analysis

Where Are We Now?

In the current study, Shimozono and colleagues [6] performed a meta-analysis of autologous osteochondral transplantation from the knee to the ankle to assess the donor-site morbidity associated with this procedure. As cartilage surgeons, we continue to seek ways to treat these difficult lesions, and “robbing Peter to pay Paul” has been an intriguing option. The authors found that the donor site morbidity of knee to talus transplantation approached 11% [6]. Their study highlights the fact that we are still looking for answers on how to get viable hyaline cartilage to “grow” in areas where there has been substantial chondral damage. It makes sense to find cartilage that is “not as necessary” to replace the damaged cartilage, as long as the thickness, contour, and topography are similar. But as Shimozono and colleagues [6] found, there is no free lunch when it comes to cartilage; all cartilage is necessary and has purpose and function.

One of the first reports on this topic assessed 11 patients who had knee plugs up to 18 mm in diameter taken from the knee, and they found donor-site morbidity in more than 50% of patients [1], which was the largest proportion of patients with donor-site morbidity reported in the current study. Other studies found that plugs greater than 7 mm to 8 mm in diameter have a higher percentage of symptomatic patients than smaller ones [4, 5].

As researchers continue to report on this difficult problem, several things seem clear. First, one large plug typically is not as well tolerated as multiple smaller plugs and thus mosaicplasty with multiple plugs typically is performed to fill in larger defects. Second, plug donor sites are filled in with fibrocartilage, so they do not tolerate shear as well as normal hyaline cartilage, nor do they appear durable under sustained weightbearing [3]. Additionally, the long-term effects of donor sites have not been well studied. Finally, despite the frequent use of cartilage autograft plugs in the elbow, knee, and ankle, few clinical studies have evaluated the effect of taking one or more plugs from the knee, which emphasizes the importance of this meta-analysis. Even basic science in this area is lacking. A 20-year-old study demonstrated that all common locations of graft donor sites had increased contact pressure through an arc of motion of 0° to 110° [7]; another study found that although 5-mm plugs did not alter the contact pressures in the nonweightbearing knee, larger sizes of plugs were not studied [2], and so their effect is not known.

Where Do We Need To Go?

The articles analyzed by Shimozono and colleagues [6] did not uniformly report where the autografts were taken from, the size of the autograft plugs, nor the number of plugs. For example, two of the 26 articles analyzed did not report the site of the donor autograft. Furthermore, six of the studies also did not indicate how many graft plugs were procured from the knee. To further this point, eight of the studies from this meta-analysis did not indicate the size of the plugs taken making any interpretation of donor site morbidity difficulty to analyze. As a result, there are many unanswered questions in the procurement of autograft cartilage plugs from the knee: How many plugs are too many to take from the knee? How large can the plug diameter be without becoming symptomatic? Where should the plug be taken from? What constitutes morbidity when it comes to taking autograft from the knee and transplanting it to the talus? Is this pain, stiffness, loss of function, swelling, or even just crepitus?

Shimozono and colleagues [6] also brought to light the lack of a uniform definition for morbidity. To this point, 17 of the 26 articles analyzed did not report knee outcomes, and those that did used a variety of outcome measures. The most-stringent study regarding the number of knee outcomes used in their study, interestingly enough, also reported the highest donor site morbidity. This makes one wonder if the reporting had been more explicit in the other studies if more donor-site morbidity might have been identified.

How Do We Get There?

Future studies in the area of cartilage autograft transplants need to specifically look at answering, how many grafts can be taken from the knee and what size diameter those grafts should be. For those clinical scientists studying cartilage-defect treatments, answering these two questions will allow further studies to focus on the long-term outcomes on the effects of cartilage plundering.