When treating medial patellar luxation in dogs is a block trochleoplasty superior over a wedge trochleoplasty?

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Appraisal, application and reflection

Outcome as a measure of success might be difficult to objectively assess as it is influenced by many different factors. When surgically correcting a medial patellar luxation one seldom only corrects the trochlea but most often also amends the soft tissues (imbrication of the joint capsule, release incision of the retinaculum or desmotomi) in combination with longitudinal realignment of the tibial tuberosity relative to the trochlear groove, by performing a tibial tuberosity transposition (Arthurs & Langley-Hobbs, 2006). Thus, it is difficult to determine if a trochlear block recession is superior to a wedge recession technique as the two different surgical methods are not performed in isolation.

Only three studies were identified addressing the PICO question; one biomechanical cadaver study, one retrospective observational study with 100 stifles and one case series including only two dogs. Thus, the evidence base for answering the query if block recession trochleoplasty is superior to wedge recession trochleoplasty when treating medial patellar luxation is indeed very limited.

Of the three studies, the biomechanical cadaver study (Johnson et al., 2001) has a more impressive implementation with ex vivo testing of a stifle model that mimics patellar luxation, objective interobserver assessment and distinct variable measurements obtained from the computed tomography. The main limitation with the cadaver study, when using it to answer the PICO question, is that results might not be applicable to live animals. Also, long-term effects cannot be evaluated.

The retrospective observational study by Rossanese et al. (2019) described complications following surgical correction of medial patellar luxation in dogs < 20 kg. In the study including 87 dogs and 100 stifles with different degree of patellar luxation, complications were recognised in 37 stifles; 12 minor and 25 major. The outcome relevant to the PICO question showed no significant difference in complication rates between trochlear wedge resection and trochlear block resection. One of the main limitations with this study, apart from it being a retrospective study, is that it lacks long-term follow-up. We do not know if any of the trochleoplasty techniques had worse or more favourable outcome after several years. Also, to use this article to answer the question whether or not one surgical method is superior to another is difficult because, there are no kinematics, no description of repeated clinical examinations, no owner questionnaires, or second-look arthroscopy.  However, a second look arthroscopy may not be of added value to the animal and thus not considered to be ethical.

In addition, time records to perform each procedure are not published. It is therefore not possible to comment if one procedure is less time consuming. This would be an interesting factor to compare.

Generally, retrospective case series are regarded low on the hierarchy of the evidence scale. In the case series by Ballatori et al. (2005), the number of dogs studied are by far too low to allow a meaningful comparison between the treatment methods as only two dogs had medial patellar luxation and also with different luxation degree in the individual hindleg.

The difference between the two surgical methods judged by the use of computed tomography is a result of the geometry of the block and wedge. The articular width of the block and wedge are similar in the centre of the trochlea, but the block maintains the articular surface width along the entire length of the trochlea compared to the wedge, which tapers to a point proximally and distally. After trochlear wedge recession, as the stifle is extended and the patella moves proximally, the patella may articulate with the non-recessed proximal femoral trochlea instead of the recessed articular cartilage of the wedge, resulting in decreased patellar depth. The reduction in proximal patellar height could be essential in the clinical treatment of patellar luxation since the patella most often luxate in the proximal trochlea when the stifle is extended (Talcott et al., 2000, and Johnson et al., 2001).

In dogs with medial patellar luxation, block trochlear recession results in a proximal deeper trochlear groove and a larger contact area between the proximal trochlea and patella, compared with the wedge trochlear recession. In the extended stifle, the patella lies deeper in the proximal part of the joint (Johnson et al., 2001; and Talcott et al., 2000). Since no long-term studies comparing the amount of degenerative changes in the stifle joint and re-luxation rates between the two methods exist, and since the scientific information that actually compares the methods are very limited, no conclusion can be made from the existing evidence regarding whether or not a trochlear block recession is superior to trochlear wedge recession technique, when treating medial patellar luxation in dogs.

Since there are few reports comparing the two surgical methods, studies describing outcomes and complication rates with each technique might provide useful information when choosing between the two surgical methods: Slocum et al. (1982) performed trochlear wedge surgery and showed excellent results in 13/17 stifles and good results in the remaining cases. The follow-up period in that study was 12–29 months. Talcott et al. (2000) described 100 dogs after trochlear block surgery with positive short-term results: the joints were considered free of crepitus, limb function was improved and patellar stability achieved in the 6 week follow-up period. However, no long-term radiographic studies, histological analyses or second-look arthroscopy was performed in that study.  A retrospective case series by Gallegos et al. (2016) described bilateral wedge trochleoplasty in 50 small breed dogs (100 stifle joints) with medial patellar luxation. In the study, 5/50 dogs (10%) had reluxation (Grade I) none of the dogs showed clinical lameness postoperatively. The median follow-up time was 8 weeks. Arthurs & Langley-Hobbs (2006) reported retrospectively the clinical outcome in 109 dogs undergoing surgery because of lateral or medial patellar luxation. In the study, 74/107 (69%) had trochlear wedge recession and 8/107 (7%) had trochlear block recession. However, no comparison was made between the methods. In another retrospective study by Gibbons et al. (2006) trochlear wedge or trochlear block was performed to treat patellar luxation in 70 large breed dogs (>15 kg). As no comparisons were made between the two methods, no conclusions regarding the superiority of either method can be drawn. Cashmore et al. (2014) reported a retrospective study regarding complications and risk factors associated with surgical correction of medial patellar luxation in 124 dogs. Major complications (implant associated, patellar luxation and persisting lameness, patellar tendon rupture etc.) occurred in 24/124 (19%) of dogs. Although no comparisons were made between methods, a case of trochlear wedge displacement was reported. In a pilot study (Blackford-Winders et al., 2021) of 10 dogs, where the trochlear block recession technique was performed, the block autograft fractured in three cases. In a case report by Ellis & House (2021) the trochlear block migrated distally 7 days postoperatively. In another case report (Chase & Farrell, 2010) a fracture of the lateral trochlear ridge following trochlear block recession was described.

One plausible reason for recurrent postoperative patellar luxation may, at least in part, be caused by inadequate appreciation of the underlying skeletal deformity and subsequent selection and application of corrective surgery. Accurately measuring anatomic conformational abnormalities, for example identifying an extensive varus deformity or torsion in the distal femur, to better understand the deformities and subsequently better tailor corrective surgery by performing different kind of osteotomies than trochleoplasties, of the distal femur or proximal tibia, may result in lower frequency of reluxation.

In conclusion, further studies are needed to evaluate both short-term and long-term clinical outcome in small breed dogs with medial patellar luxation undergoing either trochlear wedge recession or trochlear block recession. On one hand, the block technique might be considered to be more physiologically or anatomically appropriate creating a deeper trochlea proximally in the joint and a more profound femoropatellar contact. On the other hand, the wedge technique is less invasive and thus conceivably associated with lower risk of complications. Whether or not the degree of subsequent osteoarthrosis might be influenced by the choice of surgical technique is of major importance for the individual dog. The preference and previous experiences of the veterinary surgeon are relevant issues when choosing which operation to perform until randomised and controlled trials in live animals and in comparable groups are performed.

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