When to consider operating?
Medial patella luxation can present with a large variance in lameness severity. Commonly we see Terrier and toy breeds ‘skipping’ as they run due to the patella luxating in and out of the trochlear groove spontaneously. In other dogs luxation can result in acute non-weight bearing lameness and pain. Indication for surgery is decided on a case by case basis and not simply on the grade/severity. As a general rule, cases with grade III/IV and above benefit from surgical intervention.
How is patella luxation graded?
Grade l. Animals in this group have a patella that can be luxated manually but returns to its normal position within the trochlear groove when released.
Grade II. The patella is located for the majority of the time in the trochlear groove, but can luxate during locomotion. The patella tends to remain luxated for a few strides before spontaneously reducing, causing the classic skipping lameness.
Grade III. The patella is luxated most of the time. It can be reduced manually but will re-luxate when the manual pressure of reduction is removed.
Grade IV. The patella is luxated all of the time and manual reduction of the patella within the groove is impossible even with the leg in full extension.
How is the condition corrected?
There are five surgical treatment methods and they are often utilised in combination. The method(s) employed is dependant on the severity of an individual’s anatomical abnormalities. When making a decision, we take into account:
- the degree of proximal tibial torsion
- trochlear groove depth and cartilage damage.
- Femoral varus and/or torsion.
- Abnormalities of the medial and lateral retaining fascia.
Which surgery will be required?
The five treatment options are:
- Tibial Crest Transposition (TCT). An osteotomy is made in the tibial crest and the fragment is transposed in the opposite direction of the luxation. This realigns the quadriceps mechanism and patella tendon insertion to centre the patella in the trochlear groove.
- Trochlear groove sulcoplasty. By deepening the trochlear groove via a wedge or block resection we create a better ‘cradle’ to house the patella.
- Fascial release and/or imbrication. Often, the soft tissue surrounding the patella have become contracted on the side of luxation and lax on the contralateral side of the luxation. Appropriate imbrication and release may be necessary.
- Distal Femoral Osteotomy (DFO)/ Proximal Tibial Osteotomy (PTO). In some dogs with a higher grade luxation, where there are marked anatomical defects, a TCT alone may not be adequate to correct alignment. These cases require a pre-planned osteotomy (often following computed tomography (CT) that is stabilized with a bone plate to resolve the anatomical deformation.
- Patella Groove Replacement (PGR). Rarely, the damage to the trochlear groove and/or articular cartilage is so advanced that correcting alignment abnormalities in isolation is inadequate to relieve the morbidity associated with this advanced disease. In these cases a special Kyon groove implant is inserted following removal of the existing bone/cartilage.
What are the potential surgical complications of patella luxation?
As with any orthopaedic procedure where metal implants are placed there is a chance of implants causing irritation. This is most commonly seen in TCT’s (around 8% of cases) as a result of the pin backing out or irritating the soft tissue overlying the implant and requires removal of implants. This is a relatively simple procedure.
Surgical site infection, as with any surgery, is a potential risk.
Re-luxation of the patella is also occasionally seen following surgery and very rarely tibial fracture can occur.
See our Surgical preparation and antibacterial protocol for details of how we aim to minimise perioperative infection.
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