Cranial cruciate ligament rupture

What it is

The cranial cruciate ligament (ligamentum cruciatum craniale) is the main stabiliser of the stifle: it prevents the tibia from moving cranially relative to the femur and limits internal rotation and hyperextension. In the dog its rupture is rarely an isolated accident; the usual picture is a degenerative disease in which the ligament progressively loses fibres and strength, suffers partial tears and finally ruptures completely during normal activity. Hence the term "cranial cruciate ligament disease". Once ruptured, the tibia subluxates with every step, the medial meniscus becomes trapped and osteoarthritis develops.

Who it affects

Middle-aged dogs of large breeds, with a predisposition in the Rottweiler, Labrador, Newfoundland, Staffordshire bull terrier, boxer and golden retriever, although it can occur in any breed and size. Obesity, neutering and a steeply sloped tibial plateau increase the risk. A high proportion of dogs go on to rupture the ligament of the other stifle in the following years.

Anatomy involved

• Cranial cruciate ligament: arises from the axial face of the lateral femoral condyle and inserts on the cranial intercondylar area of the tibia. It has two bands: the craniomedial, taut in flexion and extension, and the caudolateral, taut only in extension; in partial rupture the craniomedial band usually fails first.
• Tibial plateau: slopes caudally. When weight is borne, compression of the femur on a sloped surface produces a shear force, cranial tibial thrust, which the ligament neutralises in the healthy stifle. The tibial plateau angle is measured on the lateral radiograph; values above the usual range are associated with higher risk.
• Medial meniscus: its caudal horn is firmly attached to the tibia and is crushed by the femoral condyle when the tibia moves; "bucket-handle" tears are the most typical.

Clinical signs

Acute lameness after exercise, or intermittent and progressive lameness in partial ruptures. Stiffness on rising, sitting with the stifle turned outwards (positive "sit test"), joint effusion, fibrous thickening on the medial side of the stifle (medial buttress) and thigh atrophy. A "click" on stifle flexion suggests a meniscal tear.

Diagnosis

• Cranial drawer test: cranial displacement of the tibia relative to the femur; in partial ruptures it is present only in flexion.
• Tibial compression test (tibial thrust): with the stifle in extension, flexing the tarsus moves the tibia cranially.
• Radiographs: effusion (displacement of the infrapatellar fat pad), osteophytes on the trochlear ridges, patella and plateau, and tibial subluxation. They are used to measure the plateau angle and plan surgery.
• Arthroscopy or arthrotomy: confirm the rupture and allow the meniscus to be treated.

Treatment

In small dogs conservative management can be tried, but in most dogs surgery gives a better outcome. Extracapsular techniques (lateral fabellotibial suture) replace the function of the ligament with material outside the joint. Osteotomies change the biomechanics to cancel tibial thrust: the TPLO rotates the plateau until it is almost horizontal and the TTA advances the tibial tuberosity so that the patellar ligament lies perpendicular to the plateau. With any technique the meniscus is inspected and the damaged portion resected. Osteoarthritis progresses in every case, so weight and exercise control remain important after surgery.