Meniscal Radial Tears

Introduction

Approximately 40% to 70% of the load transmitted through the knee is done by the menisci. The mechanical load absorption ability of the menisci is to convert axial load into circumferential hoop stress. The menisci also play a major role in maintaining knee stability. The integrity of the meniscal belt is thus fundamental to preserve correct knee kinematics and avoid degenerative changes of the joint.

Meniscal tears are common in young athletes. Meniscectomy can cause mid- to long-term morbidities, including the early onset of osteoarthritis. Radial tears disrupt the circumferential fibres of the meniscus, which are the major collagen fibres within the meniscus that create resistance to hoop stresses. These lesions lead to a significant mean increase in contact pressure and a decrease in contact area like after a subtotal meniscectomy. ^, Repair of meniscal radial injuries is the treatment of choice with the aim of restoring joint kinematics and contact pressures and delaying the development of osteoarthritis.

The goal of this chapter is to report the existing knowledge regarding meniscal radial tears, including the anatomy and biomechanics, diagnosis, surgical treatment methods and results.

Pathoanatomy and Biomechanics

Radial tears of the menisci can involve either the lateral or the medial meniscus, in stable knees (isolated) or in association with a lesion of the cruciate ligaments. Biomechanical studies have reported the importance of meniscal repair for radial tears of the lateral meniscus.

Bedi et al. tested contact pressures associated with radial tears involving 30%, 60% and 90% of the width of the medial meniscus. Radial tears involving 90% of the meniscal width were associated with a significant increase in contact pressures, whereas those involving 30% and 60% of the meniscal width were not. Subsequent meniscectomy lead to a further increase in contact pressure compared with that seen in association with the 90% radial tear. Lee et al. tested contact pressures in cadaveric knees with radial tears involving 50% and 75% of the width of the posterior part of the medial meniscus and those in knees with partial meniscectomy and complete medial meniscectomy. Radial tears involving 50% and 75% of the width of the posterior part of the medial meniscus, partial meniscectomy, and complete medial meniscectomy were associated with significant increases in contact pressures that correlated with the depth of the tear and amount of resection. Peak contact pressure in knees with complete meniscectomy increased by 136% compared with those in knees with an intact meniscus.

Diagnosis

Patients often have pinpoint joint line pain at the location of a radial meniscus tear. The clinical examination of meniscal radial tears can be challenging. The history is often traumatic with a twisting injury after a jump. Symptoms are scarce and include joint effusion and pain over the same compartment. Symptoms on the lateral side can be masked by associated anterior cruciate ligament (ACL) and/or medial collateral ligament (MCL) tears.

Imaging is mandatory, and magnetic resonance imaging (MRI) is considered to be the gold standard. MRI features of radial tears include the ghost meniscus in the midbody portion, defined as the absence of identifiable meniscus on a given coronal or sagittal image or the visible triangular form of the meniscus but with high signal replacing the normal dark meniscal signal, with normal meniscus seen on the immediately adjacent images; a high signal in axial views perpendicular to the axis of the meniscus body, indicating a disruption of the meniscus, and a truncated triangle sign, defined as the abrupt termination of the normal triangular meniscal contour at its tip on a sagittal or coronal image; and a cleft sign, defined as a linear, vertical high signal extending through the meniscus on a coronal or sagittal image ( Fig. 17.1 ).