Rupture of the CCL is the most common cause for hind limb lameness in dogs. Treatment consists of different stabilisation procedures, such as extraarticular sutures, intraarticular replacement by various types of grafts, mainly fascia lata and osteomies of the tibia, resulting in dynamic stabilisation of the stifle when loaded.

Dynamic stabilisation procedures, such as TPLO (tibia plateau leveling osteotomy) and TTA (tibial tuberosity advancement) have become a defacto standard in CCL treatment in dogs as they are felt to give superior functional results, especially on long term. Despite the subjective impression by many surgeons that TPLO or TTA truly result in a stable stifle joint, this has never been proven in vivo and late meniscal damage occurring in some dogs despite TPLO or TTA suggest persistent instability. This is why we investigate the in vivo kinematisc of the normal, the instable and the operated canine stifle using uni - and bi-planar fluoroscopic kinematography (see Methodology for further details).

One important finding, when looking at fluoroscopic images of a canine stifle with complete rupture of the CCL, is the fact that there is pathologic motion of the femur, not the tibia, as it has been suggest in the text books. Even though motion is relative, "cranial tibial thrust" or "cranial drawer motion" does not occur in vivo. It is the distal femur which becomes instable and slips backwards along the sloped tibia plateau, resulting in caudal subluxation. We just recently wrote a paper summarizing our findings in respect to this motion patttern in instable stifle joints and submitted it for peer review. [Supplementary Material]

 

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Beagle with complete rupture of the CCL on the left side and an already stabilised stifle (lateral suture with crimps, performed alio loco) on the right side. Note caudal subluxation of the femur on the left and absence of cranio-caudal movement on the right side.

 

Being still preliminary, our first results suggest obvious differences between TPLO and TTA in joints with a stable remnant of the CCL. While joints with TTA almost show now difference in kinematic pattern to a sound stifle, TPLO results in rotational instability of the femur with a pronounced internal rotation, having the pivot point at the medial condyle. A potential reason for this might be overcorrection of the lateral tibia plateau, being much more convex than the medial plateau. The obvious internal rotation of the femur might be expressed as relative external rotation of the tibia, which is opposite to what has been claimed based on in vitro studies.

 

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3D-animation of a stifle (right side, lateral view) with partial rupture of the CCL and no drawer motion on palpation following TPLO. Note the significant internal rotation of the femur, which is typical for leveling procedures such as TPLO or cranial closing wedge osteotomy (CCWO).

 

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3D-animation of a stifle (left side, lateral view) with partial rupture of the CCL and and no drawer motion on palpation following TTA. Note that there is no internal rotation of the femur, similar to a sound stifle.

 

In instable joints with complete rupture of the CCL we saw persistent instability in both TPLO and TTA dogs. Reason for this unexpected finding in the TTA cases might be undercorrection, as all stifles with persistent instability showed a postoperative patellar tendon angle (PTA) of >90°. In the TPLO cases there were stifles showing instability with a tibia plateau angle (TPA) of 5° as suggested in the literature but also joints being obviously undercorrected with a TPA of >6°.

 

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Dog with complete rupture of the CCL and TTA. Note the caudal subluxaiotn of the femur. Reason why TTA failed at restoring normal stifle stability is the result of inadequate advancement of the tibial tuberosity leading to a patellar tendon angle of >90°.

 

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Weimaraner with complete CCL and TPLO. Note persitent instability despite correct leveling of the tibia plateau to 5°. On the contralateral limb complete rupture of the CCL is present too.

 

If meniscal damage does alter stifle kinematics cannot be answered at this time. We need more cases to be able to compare kinematics in CCL ruptured stifles with and without meniscal damage.

 

Please feel free to post any comments, suggestions or critics. If you are willing to support our study either by providing cases or by donation we would be extremely grateful.