Anterior knee pain is one of the most common complaints in an orthopedist's office. Some patients have pain due to abnormalities of the patella tracking over the trochlea, but a significant number of patients have normal X-ray parameters indicating normal alignment and no clinical evidence of maltracking. Many of these patients are significantly, if not severely overweight presenting with a body mass index of 40 and higher. These patients likely overload the patellofemoral joint. It is important to understand that, while all lower extremity joints suffer from high body mass, the patellofemoral joint sees the highest loads (7 to 10 times body weight) with every step the patient takes.
Increase in body weight
The recent article by Gunardi and colleagues addresses this issue that we have much anecdotal knowledge about but relatively little science. It seems trivial that an increase in body weight will lead to an increase in patellofemoral pressures and thus may be a contributor to patellofemoral cartilage defects and later osteoarthritis. The paper in the International Journal of Obesity explains this observation nicely.
The authors followed 160 asymptomatic women between the ages of 20 years and 49 years for 10 years. They looked at their weight and BMI at enrollment and during the course of study. These women were enrolled in a large osteoporosis study that included repeated MRI scans of their knees. The authors measured cartilage volume in milliliters as a measure to determine the total volume of articulating cartilage of the patella. The data was age and bone volume adjusted.
The authors found cartilage volume reduction was not associated with the initial weight at enrollment but was associated with an increase of BMI over time and increased BMI at the last measurement (10 years). Increased initial BMI and weight was associated with an increased number of cartilage defects in the patella.
Importance of the study
I believe this data is important and helpful to my practice as it allows me to understand and communicate to my patients that maintenance of an ideal body weight is a prerequisite to a healthy patellofemoral joint. This is particularly important in patients who have had previous patellofemoral injuries. An interesting observation I made in my office is that patellofemoral pain can get worse even after these patients loose substantial amounts of weight. Often we will have patients in our office, who will tell us they have always been “big boned” and only lately has the kneecap started to bother them. This may have to do with the fact that very heavy patients often use a quadriceps avoidance gait to unload the patellofemoral joint. Once their body weight normalizes and body mechanics normalize, this may change and could explain why the severely predamaged patellofemoral joint now starts to become symptomatic.
I believe this paper underlines again the important role we have as orthopedic surgeons to counsel our patients about maintenance of ideal body weight. We should be cautious not to aim to repair every patellofemoral chondral defect in patients who have clearly exceeded a healthy BMI or body weight and have not begun to substantially change their habits with respect to weight gain and weight loss. If a normal patellofemoral joint will progress to deteriorate with as little as 1-point increase in BMI from baseline, then it is likely any repair will suffer a similar fate over time.
Gunardi AJ. Int J Obes (Lond). 2013;doi:10.1038/ijo.2013.42.
- Christian Lattermann, MD, is an associate professor, Vice Chairman for Orthopaedic Research, Director at the Center for Cartilage Repair and Restoration, Department of Orthopaedic Surgery and Sports Medicine, University of Kentucky. He can be reached at Department of Orthopaedic Surgery and Sports Medicine, University of Kentucky, 740 South Limestone, Lexington KY 40536; email: email@example.com.
- Disclosure: Lattermann is a consultant for Sanofi/Genzyme and Isto and receives institutional support from Smith & Nephew.