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