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 Cranial Cruciate Ligament Rupture and Patella Luxation

Medial Patella Luxation (MPL) and Cranial Cruciate Ligament Rupture are the most common condition affecting the stifle joint in dogs. Scientific studies report that 25% of middle-aged to older dogs affected by patella luxation are developing cranial cruciate ligament rupture as a concomitant pathology (Campbell, 2010).

Dogs affected by patella luxation (not treated at a younger age) are more likely to progress in a severe grade of patella luxation with age (Roush, 1993). The progression of the pathology results in more severe skeletal deformity, joint effusion, and degenerative joint disease (Campbell, 2010); these factors may contribute to the rupture of the cranial cruciate ligament (Campbell, 2010).

Clinical signs

Clinical signs may vary from mild-moderate to severe lameness; worsens with exercise.

Diagnosis

Diagnosis is made on physical examination and radiographs.

A classic physical examination reveals patella luxation as well as joint instability during cranial drawer movement and/or tibial compression test. A fibrosis thickening may be palpated on the medial aspect of the stifle (medial butters).

 

Common radiographs findings are joint effusion, medial butters, limb deformity, and patella luxation.

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Treatment 

The treatment is tailored on each case, based on physical exam and radiographs.

The cranial cruciate ligament is treated with TPLO surgery. Whereases the patella luxation is treated using a combination of Trochlear Wedge Resection and realignment of the quadriceps mechanism.

 

The realignment of the quadriceps mechanism is achieved by correction of the limb deformity of the tibia and/or the femur.

The femur is corrected by osteotomy. 

The angles of the proximal tibial (correction of the tibial torsion) are realigned using a “modify” TPLO rather than a Transposition of Tibial Crest.

 A standard TPLO circular incision is performed on the proximal tibia. However, on top of the classical rotation for flattening of the tibial plateau, other two corrections of the tibial plateau are performed. The tibial plateau is shifted in a medial direction to achieve the quadriceps alignment and the Mechanical Caudal Proximal Tibial Angle (mMPTA) is corrected to a normal anatomical range (89-97 degrees) before fixing the tibial plateau with screws and plates.

The “modify” TPLO is a much more complex and technically demanding procedure in comparison to a standard TPLO or a TPLO plus Transposition of the Tibial crest, especially in toy breed dogs.

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Tibial Plateau Levelling Osteotomy (TPLO), Sulcoplasty, Lateral Transposition of the Tibial Crest and Correction of the Mechanical Caudal Proximal Tibial Angle (mMPTA) were performed to fix a Medial Patella Luxation (G3) and Cranial Cruciate Rupture in a dog.
A radiographic study was performed prior to surgery. On the caudo-cranial view, the red lines were placed on the landmarks to assess the joint orientation. The mMPTA measured 100 degrees (the normal range in dogs is 89-97 degrees). One of the aims of the surgery was to correct the angle toward a normal mechanical angle. Moreover, on the same view, the patella was luxated medially (red dots) and the tibial crest localised medially as well (yellow line). The goal of the surgery was to fix the cruciate performing a TPLO, but at the same time to restore the normal stifle anatomy. The classic TPLO rotation of the proximal tibia was performed in association with the medial shifting of 7 mm (green circle) and proximodistal tilting of 10 degrees of the tibial plateau. The caudocranial post-op XR showed that the tibial crest (yellow line) moved centrally on the tibia, aligning the quadriceps angle, and the mMPTA measured 92 degrees. The mediolateral view showed the correction of the tibial plateau angle (TPL0) which neutralize the tibial thrust. 

Why do we prefer the “modify” TPLO rather than a combination of TPLO and Transposition of the Tibial Crest?

Some surgeon`s preference is to achieve alignment of the quadriceps muscle performing a combination of TPLO and Transposition of The Tibial Crest at the same time.  In this case, two cuts (osteotomies) are performed on the proximal tibia. One is performed for the TPLO and the other one is performed for the Transposition of the Tibial Crest. Even though a good surgical outcome is achieved with this procedure, an higher complication rate such as delay union, avulsion crest, or pins migrations may be detected due to the double osteotomy, especially in very active patients.

Reference 

Campbell, A.C., Hortsman L.C., Mason D.R. et al. (2010) ' Severity of patellar luxation and frequency of concomitant cranial cruciate ligament rupture in dogs: 162 cases (2004–2007)' . JAVMA 236(8). p 887-891

Roush, J.K. (1993) 'Canine patellar luxation'. Vet Clin North Am Small Anim Pract 1993;23. p 855–868.

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