Obesity may impact graft fixation failure after ACL reconstruction

Modeling can help predict failure by measuring the theoretical point when BMI affects outcomes.

Surgeons should carefully consider performing ACL reconstructions in obese patients, according to a study presented at the British Orthopaedic Association and the Irish Orthopaedic Association Combined Meeting 2011.

“The population is getting bigger,” Steven R. Bollen, MB, FRCS, said during his presentation. “There is little previous research in this subgroup. There is only one paper published so far with failure rates at 35% if your [body mass index] BMI is over 30.”

Failure can occur for many different reasons, Bollen explained. During harvest and implantation, in during the first postoperative 6 weeks, failure of ACL reconstructions may drop down to 30%, he said.

“Fixation is probably the weakest link in that stage, certainly,” he said. “We know that metal interference and screw fixation only has a strength of about 500 N. Even then, it only has about 1,000 N at the femoral end and the tibial end is probably the weakest for the quality of the bone.”

Mathematical modeling can predict the theoretical point when BMI affects outcome and problems with weight gain after ACL reconstruction to determine the appropriateness of ACL reconstruction for obese patients, according work by Bollen and William K. Hage, MB, BS, FRCS.

“We can model knee joint sheer forces and body weight during activities of daily living, and we can work out what happens as you start to increase your body mass and BMI,” Bollen said.

He noted that published data shows that walking puts the force of about 1.2 to 1.7 times body weight on a graft. Patients putting 2.5 times their body weight on the graft during activities of daily living have an even higher chance of graft failure, Bollen and Hage said.

However, Bollen noted that athletes with high BMIs are not as likely to suffer graft failure.

“We know that a lot of top athletes have high BMIs, but they have good muscular strength, which I think protects them from eruptions of grafts,” Bollen said. “But, I think you have to apply careful consideration if your BMI is big or you have a big patient and they have to be warned there is a high chance that things are going to go wrong. There is a big difference in somebody […] who is a highly trained athlete with great proprioception, great muscle strength and great agility. In athletes like these, probably their ratio size to their muscle mass is slightly different.” – by Renee Blisard

Reference:

• Hage, WK, Bollen SR. Can ACL reconstruction be justified in the obese? Presented at the British Orthopaedic Association and the Irish Orthopaedic Association Combined Meeting 2011. Sept. 13-16. Dublin.

• Steven R. Bollen, MB, FRCS, can be reached at The Yorkshire Clinic, Bradford Road, Bingley, West Yorkshire, UK, BD16 1TW; 44-01274 550846; email: kath.kenny@ramsayhealth.co.uk.

Freddie H. Fu

In his presentation, Dr. Bollen addressed an interesting topic on the effect of BMI and graft failures following ACL reconstruction. It was shown, using mathematical modeling, that BMI greater than 30 increases the ACL failure rate up to 35%.

The study addresses a specific population with unique challenges for graft incorporation and healing, which emphasizes the importance of individualizing surgery for each patient. The authors recognize the importance of identifying the unique characteristics of the study population and the need to modify treatments accordingly. Graft size and source should be guided by the patient’s individual anatomy, even more in this particular population as the graft experiences larger forces. Preoperative MRI measurements of the tibial insertion site, ACL length, as well as patellar and quadriceps tendon thickness, are important to assess which graft will adequately recreate the patient’s anatomy. These measurements should be confirmed intraoperatively to aid in selecting a graft that would ideally cover 60% to 80% of the insertion site sizes.

The discussion raised by this study is applicable to the general population as well. It is becoming increasingly clear that the healing process is often neglected after ACL reconstruction. Failures in the general population have been reported to be as high as 29%. Many factors influence these failure rates, including graft type, technique, age, BMI, activity level and timing of return to sports. In a study to be published in the next issue of the American Journal of Sports Medicine, van Eck and colleagues a showed failure rate of 13% after allograft ACL reconstruction in young patients. Most of the failures in that study happened between the third and ninth months. This timing correlates with the early period when patients are first released to participation in sports. These early failures may be the result of inadequate healing and maturation. Objective measures are needed to assess graft healing and aid in the decision-making process to determine when athletes should return to sport.

The commented study looks at a unique patient population with specific challenges. Its findings should be considered accordingly. The authors bring attention to the increased forces acting on a graft in patients with a high BMI. More importantly, this study adds to the discussion on graft healing, maturation, the necessity for surgeons to objectively assess healing after ACL reconstruction and the benefits of an individualized surgery, including graft choice.

— Freddie H. Fu, MD, DSc(Hon), DPs(hon)
Orthopedics Today Editorial Board member
University of Pittsburgh Department of Orthopedic Surgery
Pittsburgh
Disclosure: Fu has no relevant financial disclosures.

References:

• Barrett AM, Craft JA, Replogle WH. Anterior cruciate ligament graft failure: A comparison of graft type based on age and Tegner activity level. Am J Sports Med. 2011; 39(10):2194-2198.
• Hussein M, van Eck CF, Cretnik A, et al. Prospective randomized clinical evaluation of conventional single-bundle, anatomic single-bundle, and anatomic double-bundle anterior cruciate ligament reconstruction: 281 cases with 3- to 5-year follow-up. Am J Sports Med. 2011 Nov 15. [Epub ahead of print].