Is Meniscal Damage in the Anterior Cruciate Ligament Injured Knee Associated with Early Bone Shape Changes? an Exploratory Analysis of the Kanon Trial

Purpose: Bone shape changes, which may be an important feature of osteoarthritis (OA) development, have been observed to occur early in the knee after anterior cruciate ligament (ACL) injury. However, the association between co-existing meniscal damage and bone shape changes is unclear. Therefore, to gain new knowledge about the pathophysiology of early post-traumatic OA, we determined the association between meniscal damage and changes in ipsilateral condyle bone shapes. Methods: We used data from the KANON randomized controlled trial (ISRCTN 84752559), including 121 young active adults with an acute ACL injury. Baseline and 2-year follow-up MR images were obtained of the injured knee. Meniscal integrity and meniscal extrusion were determined by one experienced musculoskeletal radiologist using the Anterior Cruciate Ligament Osteoarthritis Score (ACLOAS) scoring system. MR images were read paired with knowledge of time sequence. The exposure of interest was meniscal damage, either a) present at the baseline MR scan, or b) newly developed over the first 2 years (based on the baseline and the 2-year follow-up MR scan). We defined newly developed meniscal damage as both incident meniscal damage or progression of pre-existing meniscal damage on the MR images. Our outcome was change in bone area from baseline to 2 years in mean mm2 using statistical shape models; bone area changes correlate strongly with overall measures of bone shape. We evaluated change in the bone surfaces of femur, tibia, patella, and trochlea femur in both the medial and lateral compartment. We compared our exposure variables with bone shape changes using a multilevel linear regression model. To ensure a good model fit, we used the logarithm of our continuous outcome, and therefore present our results in percentage (%) bone shape difference with its 95% confidence intervals (CI) between persons with and without meniscal damage at baseline or with and without newly developed meniscal damage during follow-up, respectively. We performed the analyses separately for the medial and lateral compartment including four compartment-specific regions of bone shape measurements, enabling a regional differential effect of meniscal damage on changes in bone shape. Models were adjusted for baseline bone area (log transformed), age, sex, body mass index (BMI), and treatment arm (i.e. early ACL reconstruction and optional delayed ACL reconstruction). Results: The full cohort consisted of 121 subjects with a median (range) age of 25 (18-36) years, and 81% were men. At baseline there were 14 subjects with medial meniscal damage and 19 with lateral meniscal damage, whereof 2 subjects had both medial and lateral meniscal damage. During the 2-year follow-up medial meniscal damage newly developed for 24 subjects and lateral meniscus damage developed for 26 subjects, whereof 5 subjects newly developed both medial and lateral meniscal damage. Ten subjects were excluded from the regression analyses due to missing MRI measurements on bone area either at baseline or follow-up, and two subjects were excluded due to missing information on BMI. Baseline bone areas in mean mm2 for subjects in the different exposure categories were similar (Table 1). Overall, the estimates for the 4 bone regions all suggested increased bone area in subjects with meniscal damage at baseline or with newly developed meniscal damage during the 2-year follow-up (Table 2). The difference (%) in bone shape changes between persons with and without baseline meniscal damage was 1.1% (95%CI 0.0% - 2.3%) in the medial and 1.4% (95%CI 0.6% - 2.2%) in the lateral compartment. Similar results were found for newly developed meniscal damage (Table 2). The percentage difference can be interpreted as follows: e.g., if subjects who newly developed medial meniscal damage during follow-up had on average 1.8% (95% CI 0.8%-2.8%) increase in the medial tibia bone shape, the bone area was on average 26 mm2 more increased (unadjusted mean bone area 1234 mm2) after 2 years compared to a person not developing new meniscal damage (unadjusted mean bone area 1208 mm2). Conclusions: In the ACL-injured knee, persons with meniscal damage at baseline or worsening of meniscal damage during follow-up have more than 1% increased bone area in both the ipsilateral compartment compared to persons without such meniscal damage. Our findings suggest a potentially important association between meniscal integrity and early bone shape changes after ACL injury. The direction of causality for this association should be investigated further.View Large Image Figure ViewerDownload Hi-res image Download (PPT)