Editor’s note: The following content was published in the AAOS Now Special Edition and distributed in June 2020. The content was originally scheduled for the AAOS Now Daily Edition, which publishes each year onsite at the AAOS Annual Meeting but this year’s meeting in March was canceled due to COVID-19. Despite the cancellation, members can access virtual content from the Annual Meeting by visiting the Academy’s Annual Meeting Virtual Experience webpage.

With a background in bioengineering, Braden C. Fleming, PhD, the Lucy Lippitt Professor of Orthopaedics at Brown University and Rhode Island Hospital, has spent more than three decades studying soft tissue and joint mechanics to uncover the causes of post-traumatic osteoarthritis (PTOA), specific to anterior cruciate ligament (ACL) injury and reconstruction.

“I was always interested in the long-term consequences of ACL injuries, particularly because these patients are at a higher risk for PTOA for reasons that are largely unknown,” said Dr. Fleming. “A variety of factors are thought to be the cause, such as the impact of the joint at the time of injury, which initiates a bone bruise; damage to other structures in the knee joint (like the meniscus); inflammation; altered kinematics; and altered joint contact load. Most likely, it’s a combination of all of these factors.”

With a desire to explore the mechanical functions of the knee and determine whether graft tension was a primary factor in developing PTOA, Dr. Fleming had the inspiration for his next body of research.

According to Dr. Fleming, there are two theories when it comes to graft tension. “The first is to apply a tight graft at the time of surgery with the idea that it will stretch over time and return to normal. The other is to put the graft in at a low tension to immediately restore normal laxity at the time of surgery, so ideally it won’t stretch out with time,” he explained.

The research earned Dr. Fleming the 2020 Orthopaedic Research and Education Foundation (OREF) Clinical Research Award.

Funded by the National Institutes of Health (NIH), Dr. Fleming and his team (Gary Badger, MS; Paul D. Fadale, MD; Michael J. Hulstyn, MD; Robert M. Shalvoy, MD; and Glenn Tung, MD) enrolled 90 patients and a matched, uninjured control group (n = 60) for the double-blind, prospective, randomized, controlled trial. They followed the cohort for seven years postoperatively to compare clinical, functional, patient-reported, and PTOA imaging outcome measures between the two common graft tension protocols: one that restores normal laxity and one that makes the knee tighter at the time of surgery.

The patient cohort consisted of those aged 15 to 50 years with a unilateral ACL injury who were candidates for ACL reconstruction with one of the two autografts: bone-patellar tendon-bone or four-stranded hamstring tendon. Each patient selected the graft type, and all surgical procedures and postoperative rehabilitation were standardized.

The researchers’ hypothesis was twofold: (1) The high-tension group would have improved outcomes compared to the low-tension group at seven years of follow-up; and (2) the outcomes for the high-tension group would be equivalent to the matched control group.

The graft tensioning protocols included:

• high-tension treatment (n = 44): grafts firmly tensioned with knee at 30-degree knee flexion (anteroposterior [AP] laxity 2 mm < contralateral at time of fixation)
• low-tension treatment (n = 46): grafts firmly tensioned with the knee at zero-degree knee flexion (AP laxity = contralateral at time of fixation)

Tibial fixation was partially engaged for both graft types, and AP knee laxity at 20 degrees of flexion was checked with the KT-1000S (MEDmetrics Inc.) to measure the stability of the knee joint and to compare it to that of the contralateral knee. If the targeted AP knee laxity value was not achieved within 1 mm, the fixation was released and the tensioning procedure was repeated. The AP knee laxity value was rechecked once graft fixation was completed (Fig. 1). Outcome measures were assessed at one, three, five, and seven years postoperatively.

“We generally found there was no significant difference in most of the outcomes between the two graft tensioning conditions,” explained Dr. Fleming. “In fact, the grafts in both groups ‘stretched out’ to the same level over the first year of healing. Overall, the clinical, functional, patient-reported, and PTOA imaging outcome measures showed that the reconstructed knees, regardless of tension group, did not return to those of the control group at seven years.”

Clinical outcomes

There were no significant postoperative differences in AP knee laxity (measured with the KT-1000 Knee Arthrometer) (Fig. 2) or clinical examination results (the 2000 International Knee Documentation Committee Knee Examination Score) between the two tension groups (P > 0.68). Both of those outcomes did not equal that of the control group.

Functional outcomes

The one-leg hop distances for the two tension groups were significantly less than the control group (P < 0.02), although there was no difference between tension groups (P = 0.59).

Patient-reported outcomes

Using the Knee Osteoarthritis Outcome Score and the 36-item Short Form Survey to measure knee-related quality of life, sports/recreation function, activities of daily living, symptoms, pain, and general mental and social health, the researchers found no differences between the tension groups. The tension groups were worse than the control group.

PTOA imaging outcomes

The modified Osteoarthritis Research Society International (OARSI) radiographic grading atlas and the Whole-organ Magnetic Imaging Score (WORMS) showed that the imaging outcomes for PTOA suggest that knee arthrosis becomes evident seven years after surgery (Fig. 3).

After seven years, there was no difference between tension groups (P = 0.23) and both tension groups were significantly worse than the control group (P < 0.02) for the radiographic score. For WORMS, there were no significant differences between the two tension groups (P = 0.08) at seven years; however, the low-tension group was significantly different from the controls (P < 0.01).

The primary driver of OARSI and WORMS was presence of osteophytes.

Strong trends emerged showing differences between the two initial graft tension groups related to PTOA development at seven years. Long-term follow-up may be required to fully reconcile those findings and to determine which patients become symptomatic.

The research team received additional NIH funding (R01-AR074973) to follow this patient cohort for 12 to 15 years.

The tension study cohort resulted in a database of numerous outcome measures, which has led to seven separate studies. “We leveraged the database to ask about factors that could influence long-term outcomes and predict which patients may be at higher risk for PTOA,” said Dr. Fleming. “These studies are helping to gain additional insight into the causes of PTOA following ACL injury to further help patients.”

Jennifer Lefkowitz is a freelance writer for AAOS Now.