Small Graft, Young Age Linked to ACL Reconstruction Failure

Nancy A. Melville

July 12, 2011

July 12, 2011 (San Diego, California) — The use of smaller hamstring graft size and younger age are both significant predictors of failure in anterior cruciate ligament (ACL) reconstruction, and are more likely to require early revision than the same procedure performed in older patients using larger grafts, according to research presented here at the American Orthopaedic Society for Sports Medicine 2011 Annual Meeting.

Surgeons commonly use hamstring autografts in ACL reconstruction. A typical graft is a 4-strand graft about 8 mm in diameter, but sizes can vary widely according to individual patients.

Noting a general upswing in the need for revisions after ACL reconstruction, investigators at Duke University in Durham, North Carolina, decided to analyze data collected at their institution to determine their revision rate and what factors, such as graft size, were playing a role.

"We included graft size as a possible risk factor because we noted in clinic that a few patients with small grafts had failed," said lead author Robert A. Magnussen, MD, from the Duke Sports Medicine Center.

"We knew from biomechanical studies that smaller grafts had lower loads to failure, so we hypothesized that the lower initial strength would lead to a higher risk of early failure."

For the study, Dr. Magnussen and his colleagues retrospectively evaluated 256 patients who were undergoing primary ACL reconstruction using a hamstring autograft. The patients included 136 males (53.1%), and ranged in age from 11 to 52 years. Follow-up ranged from 6 to 47 months (average, 14 months).

The results showed that revision ACL reconstruction was required for 18 of the 256 patients (7.0%) at a mean of 12 months (range, 3 to 31 months) after surgery.

Whereas revision was required in 1 of 58 patients (1.7%) who received grafts greater than 8 mm in diameter, it was required in 9 of 139 patients (6.5%) who received grafts of 7.5 or 8.0 mm, and in 8 of 59 patients (13.6%) who received grafts of 7 mm or less in diameter (P = .049).

"We did expect higher revision rates with smaller grafts, but the difference was larger than we expected," Dr. Magnussen said. "I would caution that small studies are known to overestimate effect size," he noted. "Larger prospective studies with longer follow-ups are necessary to confirm these results."

With regard to patient age, just 1 revision was required among the 137 patients 20 years and older (0.7%), whereas 17 revisions were required in the 119 patients younger than 20 years (14.3%; P < .0001).

"Most failures — 16 of 18 — were noted to occur in patients under age 20 with grafts 8 mm in diameter or less," the authors report. "The revision rate in this population was 16.4% (16 of 97 patients)."

According to multiple logistic regression, decreased age at reconstruction (odds ratio [OR], 1.25; 95% confidence interval [CI], 1.07 to 1.45; P = .004) and decreased graft size (OR, 2.35; 95% CI, 1.07 to 5.14; = .032) were associated with significantly increased risk for revision.

The results for age are consistent with other studies that have shown higher revision rates among younger patients, Dr. Magnussen said. "This is most likely related to higher activity levels and greater functional demands in this patient population."

Although there has been greater pressure in recent years toward more rapid rehabilitation and quicker return to sport after ACL reconstruction, there has been no association between accelerated rehabilitation and risk for revision, Dr. Magnussen added.

Being female was ruled out as an independent predictor of graft failure when patient age and graft size were taken into account (OR, 1.40; 95% CI, 0.48 to 4.04; = .53).

The findings shed light on the role of graft size in ACL reconstruction revision, which isn't commonly the first factor surgeons consider as a potential risk, Dr. Magnussen said.

"ACL graft size has received less attention than other factors, such as patient age, graft type (allograft vs autograft, hamstring vs patellar tendon), and surgical technique," he said.

"While this study is far from definitive, we hope it encourages other investigators to include this variable in future studies to further clarify any relationship between graft size and revision rate."

The study provides validation of an issue surgeons commonly suspect with smaller graft size, added Wayne J. Sebastianelli, MD, professor of orthopedic surgery and director of athletic medicine at Hershey/Penn State Orthopedics in State College, Pennsylvania.

"I think people have always been concerned about hamstring autograft, particularly in small females, not being of substantial biologic strength to substitute for the ACL, but this paper gives us some scientific data to back up our intuition."

When the patient's physique doesn't lend itself to a large hamstring graft size, surgeons can consider alternatives, such as the patellar tendon or quadriceps tendon, or allografts, he noted.

"The problem is, you may not know what you're dealing with (in terms of graft size) until you actually get in there, but you can be sort of suspicious about it."

"In my practice, if I have a female with a slender build, I tell them they are probably better off using the patellar tendon than the hamstring because I'd be afraid their hamstring is too small," he said.

"This is not really a slam dunk — where everyone's going to do the same thing. It's based on preference for one type of procedure over another and training, and regional areas do different things differently. It's just a choice, and you can argue which is best based on principle, but in my practice, I tend to use the patellar tendon more frequently in those types of patients for fear of having an inadequate graft."

Dr. Magnussen and Dr. Sebastianelli have disclosed no relevant financial relationships.

American Orthopaedic Society for Sports Medicine (AOSSM) 2011 Annual Meeting: Abstract 4. Presented July 7, 2011.

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