Does initial graft tension during ACL reconstruction affect the restoration of static knee stability?

Nicholas SJ, D'Amato MJ, Hershman EB, McHugh MP, Tyler TF, Gleim GW, Kolstad K

NISMAT and Dept. of Orthopaedics, Lenox Hill Hospital, New York, NY.

Introduction:

Despite a number of in vitro cadaver studies, no consensus has been reached regarding the amount of graft tension needed to recreate normal knee mechanics while providing the ideal biologic milieu for graft healing. In practice, few surgeons control for the degree of tension placed on the graft at the time of fixation. The purpose of the present study was to (1) determine the inter- and intra-surgeon variability in initial graft tension and (2) prospectively randomize patients into low or high tension groups and document the postoperative change in static knee stability in a double-blind fashion.

Methods:

Graft tension at the time of fixation was measured for three surgeons (A,B,C) each performing 10 ACL reconstructions. A and B were experienced surgeons (attendings) and C was an inexperienced surgeon (resident). Graft tension was compared between surgeons and the coefficient of variation in tension was computed for each surgeon. Graft tension was measured with a load cell attached by sutures to the bone plug of a patellar tendon autograft. For the controlled graft tension study, 26 patients undergoing BPTB autograft ACL reconstructions, by a single surgeon (A), were randomized into high (8 men, 3 women) and low (10 men, 5 women) tension groups. Arthrometric measurements of anterior tibial displacement (ATD) were made preoperatively and one week following surgery (KT-1000 manual maximum side-side difference). Additionally, knee joint effusion and range of motion were documented. Both the patient and the examiner were blinded to group assignments. Results are reported as mean+/-sem.

Results:

Graft Tension was lower (p<0.05) for surgeon B (47.9+/-1.4 N) compared to surgeon A (82.8+/-4.7 N) and C (71.4+/-7.0 N). The coefficient of variation was 18.1% for surgeon A, 9.1% for surgeon B and 31.1% for surgeon C. Based on the inter-surgeon values for graft tension (AvB), a high tension of 90 N and a low tension of 45 N were used for the randomized groups. Reconstructive surgery reduced ATD from 6.3+/-0.6 mm to 1.4+/-0.5 mm (p<0.001) but this effect was different between tension groups (p<0.001). Surgery reduced ATD by 6.9+/-0.7 mm in the "high" group compared to only 3.4+/-0.6 mm in the "low" group. ATD one week following surgery was unaffected by knee joint effusion (p=0.99) or loss of extension (p=0.34) but was related to preoperative ATD (r=0.47, p<0.05). When corrected for preoperative ATD, patients in the "high" group had 0.04+/-0.6 mm ATD one week following surgery, compared to 2.4+/-0.5 mm for patients in the "low" group (p<0.01).

Conclusions:

No previous study has demonstrated an effect of initial graft tension during ACL reconstruction on subsequent measures of knee stability. Patients set at a high tension had greater static knee stability postoperatively than patients set at a low tension. Since measurements were made only one week following surgery this effect can be attributed to the mechanical constraints imposed at the time of surgery rather than to subsequent stress on the graft. Low graft tension at the time of fixation will result in greater early postoperative laxity.

American Orthopaedic Society for Sports Medicine: Specialty Day. Orlando, FL, March 18, 2000.