| Luxating Patella in the Dog - A surgical approach |
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| Written by Administrator | |||||||||||||||||||||||||
| Saturday, 03 February 2007 | |||||||||||||||||||||||||
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When I first wrote this article and took the images below the general belief was that the cause was a congenital twist in the relationship between femur and tibia leading to the effect. Current belief is that the initial cause is a congenital rotational deformity below the hip that leads the twist to develop in young dogs and, therefore, some clinicians now advocate surgical attention by transaction of the femur. As a general practitioner I’m not in a position to argue that ( a smaller case load of these ) but simply state that so far I have managed to sort all my patients by the means described below. Registered and ratified members have access to the full-size images in the E-VeT section of the gallery
There are many ways of approaching the luxating patella patient and resolving the problem. Essentially this is a mechanical problem and requires a mechanical solution; so some form of surgery is the answer. The inherent (and inherited?) twist in the relationship between the quadriceps group of muscles attaching to the patella which acts as a pulley running in the femoral condyles and through the straight patella ligament pulling on the tibial crest to extend the stifle causes the patella to pull to one side- usually medially. This results in a progressive erosion of the underside of the patella and the trochlear groove leading to luxation. Disuse of the trochlear groove causes it to become shallower, eburnation of the underside of the patella distorts and flattens its shape and the trochlear ridge becomes worn down. The luxation increases in frequency and may lead to roughness and osteophyte changes on patella and proximal groove. The three essential aspects to correction are deepening and realigning the groove, straightening the line of pull and reinforcing the lateral stifle capsule, plus or minus some degree of medial release. The nature of the procedure leads to a degree of trisection medially anyway. The clinician must decide on which or all components require correction in each case. After several years of playing with these I have decided that I might just as well do the lot each time! (note: I had a patient last month where the radiographic changes were mild and I felt that capsular overlay would be adequate – and fell into my known trap – and a reduced price repeat surgery!) There are opinions on the relative merits of each component and how best to deal with them. Filing the trochlear groove may be frowned upon as damaging the cartilage but it is easier that a wedge trochleoplasty and most cases have eburnation and osteophyte changes if chronic. Capsular overlay tends to be stronger than just taking a tuck; so cutting this and over-sowing as two layers is a neat solution. I prefer to cut the tibial crest partially adrift leaving it's distal attachment rather than mobilising it completely; this is much safer should some failure of fixation occur. Fixation methods can be screw, wire, pin and tension-band wire or just pins. A simple wire suture avoids pin loosening/removal problems and requires less equipment than a screw. The case illustrated here also illustrates that one should be ready for anything!.. and have a second or even third option handy!!!! Tibial crest moved and pinned down.
Things went 'wrong' in the middle so pictures are scarce while I swore at the nuisance <g>. When the wire was twisted tight the tibial crest re-aligned into it's original position! I still fail to see the logic why but assume it’s due to wire pulling through part of the softer bone. A second method with a transverse pin and figure-8 wire ended up the same! So plan 'c'! Which was a single pin and tension band wire. Hand sketches of the tibial transposition theory and these three fixation methods fill in for the lack of photos A neat trick when using pins or nails and tension band wires is to bend the pin end to about 90 degrees towards the surgeon and cut the pin at the bend then rotate 180 degrees so that the bend buries towards the patient, not the surface tissues. In the same way the wire ends are often better left a bit longer so that they bend down more easily. Kirschner wires are softer (more malleable) than Steinmann pins - and buy quality twisting wire too. (note : that ages this article.. it’s almost hard not to buy good wire now) When twisting wires always pull as you twist.. this gives even twists. No. 1 : Very small pictures  |
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