The Influence of Body Mass Index (BMI) and Posterior Tibial Slope (PTS) on further Anterior Cruciate Ligament (ACL) Injury: A monocentric case-control study

Abstract

Posterior tibial slope (PTS) is a potential risk factor for primary ACL injury, along with Body Mass Index (BMI). This case-control study aimed to assess the influence of BMI and PTS on subsequent ACL injury affecting either ACL graft or the native ACL of the contralateral knee after primary ACL reconstruction. Two groups were created from a retrospective cohort during January 2010 to January 2020 patients who underwent arthroscopic ACL reconstruction using the same surgical procedure: Hamstring tendon autograft (gracillis + semitendoneus). The study group (group I) included all the patients ( n = 94) during the 10 years who sustained a subsequent ACL injury of either ACL graft ( n = 56) or the native ACL ( n = 38) of the contralateral knee. The control group (group II) consisted of 94 patients randomly selected who did not sustain any further ACL injury after a follow-up of a mean of 6.4 ± 2.2 years. The control group matched the study group in age and sex. PTS was measured by 2 surgeons (blinded) on lateral knee view radiographs of the operated knee after primary ACL. BMI in kg/m 2 was measured during the anesthesia preoperative consultation exclusion criteria were: non-Hamstring tendon primary graft, associated knee surgical ligament injury, iterative knee surgeries, open growth plate, associated fracture, unstable meniscal injury, rotated bad incidence lateral knee radiographs. The mean posterior tibial slope in group I was 7.5° ± 2.9, and 7.2° ± 2.5 in group II. A PTS angle cutoff was set at 10 degrees. The rate of patients showing a PTS ≥ 10° was significantly higher in group I compared to group II (20.2% versus 4.3% respectively, p < 0.01). Patients with PTS > 10° were 5.7 times more likely to sustain a subsequent ACL injury, (OR: 5.7 95% CI [1.858–17.486]). Average BMI in group I (24.5 ± 3.7 kg/m 2 ) compared to group II (23.3 ± 3.0 kg/m 2 ), BMI results were classified into four categories based on range in both groups. There were no significant differences in any of the four categories between both groups ( p -value 0.289). A series of BMI cut offs were also analyzed at 23, 24, 25, 26, 27, 28, 29, and 30 kg/m 2 , and there was no significant difference between both groups in terms of all these cut-off values. A posterior tibial slope above or equal 10 degrees measured on lateral knee radiographs, was associated with 5.7 times higher risk of further ACL injury, either ACL graft rupture or contralateral native ACL rupture; however, BMI was not found to be a proportional or exponential risk factor.