Quantitative ultrasound densitometry of the calcaneus in acute and chronic anterior cruciate ligament deficiency

Abstract

Anterior cruciate ligament tear (ACL) is a relatively common yet serious knee injury, and is more prevalent in young, athletic individuals. Traumatic ACL injuries have local and systemic consequences, affecting bone metabolism not only around the knee but also at distant bone locations. Following an ACL injury, sarcopenia gradually occurs in the quadriceps and hamstring muscles as well as osteopenia around the knee or at distal sites, which can develop quickly in animals and humans. Considerable posttraumatic osteopenia occurs soon after the ACL injury or reconstruction and does not completely recover, or the loss is only partially reversible. The loss of knee stability, the altered joint loading environment and knee kinematics, and the osteopenia in the cancellous bone induce loss of anatomical and functional integrity in the tissues in and around the knee joint, eventually leading to loss of function and knee osteoarthritis in animal models and humans. ACL tears are also associated with concomitant menisci tears and cartilage degeneration and can lead to secondary osteoarthritis, regardless of surgical or conservative treatment. Following ACL injury or experimental ACL transection, several methods have been employed for the measurement of bone density changes around the knee joint and at distant sites, including quantitative computed tomography (QCT), dual energy X-ray absorptiometry (DEXA), dual-energy photon absorptiometry (DPA),6 and quantitative computed tomography (pQCT). Abstract Purpose: To evaluate the effect of acute and chronic knee instability secondary to anterior cruciate ligament (ACL) deficiency on the ultrasound-measured density and bone quality of the calcaneus, implementing quantitative ultrasound densitometry. Methods: Bilateral measurements of the speed of sound (SOS) and broadband ultrasound attenuation (BUA) of the calcaneus were performed on a cohort of 97 male patients with acute (n=38) or chronic (n=57) unilateral ACL deficiency. Results: In the acute ACL tear group, BUA was 56.181±3.731 dB/ MHz on the affected extremity calcaneus and 57.030±6.564 dB/MHz on the uninjured side, whilst the SOS was 1577.265±14.04 m/sec and 1584.675±11.484 m/sec respectively. The difference between the two sides was not significant. In the chronic ACL deficiency group, however, there was significant difference between both calcanei for both BUA (p<0.01) and SOS (p<0.001). BUA was 47.307±3.786 dB/MHz on the affected extremity calcaneus and 59.011±3.64 dB/MHz on the uninjured extremity calcaneus, whilst the SOS was 1457.873±9.467 m/sec and 1579.413±8.404 m/sec respectively. Conclusion: Chronic ACL deficiency adversely affects the structural properties and the bone quality of the calcaneus. Level of evidence: Level II, prospective comparative study.