medial ridge elevation wedge trochleoplasty for medial patellar luxation: a clinical study in 5 dogs

Medial Ridge Elevation Wedge Trochleoplasty for MedialPatellar Luxation: A Clinical Study in 5 DogsKoichi Fujii1, DVM, Toshifumi Watanabe2, DVM, PhD, Takayuki Kobayashi3,4, DVM, PhD,and Kei Hayashi5, DVM, PhD, Diplomate ACVS1 Fujii Animal Care Center, Yokohama, Japan ,2 Azabu University, Kanagawa, Japan ,3 Graduate School, Kanazawa University, Kanazawa, Japan ,4

Animal Clinic Kobayashi, Saitama, Japan and 5 School of Veterinary Medicine, University of California‐Davis, Davis, California

Corresponding AuthorDr. Kei Hayashi, DVM, PhD, DiplomateACVS, Department of Clinical Sciences,College of Veterinary Medicine, Cornell,Ithaca, NY 14853.E‐mail: [email protected]

Submitted january 2011Accepted June 2012

DOI:10.1111/j.1532-950X.2013.12041.x

Objective: To develop a surgical technique to elevate the medial trochlear ridge forsurgical correction of medial patellar luxation, and to evaluate clinical outcome.Study Design: Case series.Animals: Dogs (n ¼ 5) with Grade 3 medial patellar luxation.Methods: An asymmetrical wedge was removed from the trochlear groove, rotated180°, and placed in the recess to create an elevatedmedial trochlear ridge. Postoperativeradiography, CT scan, and subjective evaluation of clinical outcomes were performed.Results: Surgical procedure and postoperative recovery were uncomplicated. Therewas no recurrence of spontaneous luxation and subjectively, gait improved in all dogs.Postoperative radiographs and CT images confirmed the elevated medial trochlearridge, a significantly increased groove depth/patellar thickness ratio (P < .01), andseating of the patella in the trochlear groove.Conclusion: Elevating themedial trochlear ridge, instead of deepening the groove, canbe considered a viable surgical technique to stabilize luxating patellae.

Medial patellar luxation (MPL) is a common orthopedicproblem in dogs, particularly in small breeds.1–3 MPL isclassified (Grades 1–4) depending on severity and treatmentoptions are often guided by this grading scheme.1–4 Althoughclinical signs can vary, dogs with Grades 2–4 MPL withclinical signs of lameness often benefit from surgicalcorrection. Surgical repair techniques typically include oneor more of the following approaches: (a) deepening thetrochlear groove, (b) tightening the lateral soft tissue, (c)releasing themedial soft tissue, and (d) laterally transposing thetibial tuberosity to realign the quadriceps mechanism.1–8

Generally, multiple techniques are combined to eliminatepatellar luxation; however, postoperative reluxation can be upto 50%.2,3,9

In most MPL, the patella luxates medially from themost proximal portion of the trochlear groove, usually whenthe stifle is extended and the patella is lifted from thetrochlear groove.10–12 The medial trochlear ridge is oftenhypoplastic and pathologically low or sometimes evenabsent (flat).5,8,13 The tendency to luxate at this location isparticularlyworsenedwhen the proximal portion of the trochlearridge is worn out and made even flatter by a repetitive luxatingmotion in dogs with Grades 2–3 luxation.5,8,13 A recent clinicalstudy questioned the value of deepening the trochlear groove toprevent re‐luxation.14We hypothesized that a surgical techniquethat elevated the medial trochlear ridge, rather than one thatdeepens the groove, would bemore effective keeping the patellain place, thus eliminating the risk of re‐luxation, particularly indogs with a hypoplastic medial trochlear ridge. We are unaware

of studies evaluating medial ridge elevation for treatment ofMPL. Our purpose was to develop a surgical technique thatelevates the medial trochlear ridge by using an asymmetricautogenous osteochondral wedge removed from the trochleargroove and to evaluate clinical efficacy in 5 dogs (6 limbs)with Grade 3 MPL.

MATERIALS AND METHODS

Dogs

Five dogs with lameness attributed to Grade 3 MPL wereincluded (Table 1) after orthopedic and radiographic exami-nations. On radiographic examination, 6 stifles (dog 5 hadbilateral MPL) had hypoplastic medial trochlear ridges, whichwere confirmed surgically. Dogs with other orthopedicconditions (e.g., cranial cruciate ligament rupture, coxofemoralsubluxation) or marked skeletal deformities in their pelviclimbs were excluded.

Theoretical Background

Figure 1 illustrates the theory of preoperative calculationused to guide the wedge osteotomy. The targeted height ofthe medial trochlear ridge (the depth of the newly createdgroove) is approximately half of the thickness of the patella(1/2PT).8 Half of the patellar thickness (1/2PT) can beestimated from lateral radiographs, and the original depth of

Veterinary Surgery 42 (2013) 721–726 © Copyright 2013 by The American College of Veterinary Surgeons 721

the trochlear groove (d1) can be estimated from skyline viewradiographs. The additional elevation needed (d2) shouldbe the difference between half of the thickness of the patella(1/2PT) and the original depth of the groove (d1) (d2 ¼1/2PT � d1, or d1 þ d2 ¼ 1/2PT; Fig 1). Theoretically, d2is (b � a) cosu (a: length of the medial part of the wedgeosteotomy, b: length of the lateral part of the wedgeosteotomy, u: angle of the osteotomy on the medial ridgefrom the vertical line; Fig 1). If the osteotomy on the medialridge is vertical (i.e., u is 0), there may be an increased riskthat the medial ridge will weaken and potentially fracture.Therefore, efforts should be made to maintain a certain angleof the osteotomy (u) while achieving the targeted d2 (Fig 1).For example, in dog 1: PT ¼ 5.6 mm, 1/2PT ¼ 2.8,d1 ¼ 1.1 mm, therefore, d2 should be at least 2.8 mm–1.1 mm ¼ 1.7 mm. If the angle (u) is 10°, cos10 ¼ 0.84,d2 ¼ (b � a)cos10, and (b � a) ¼ 1.7/0.84 ¼ 2, therefore(b � a) should be at least 2 mm. If the angle (u) is 20degrees, cos10 ¼ 0.41, d2 ¼ (b � a)cos10, and (b � a)¼ 1.7/0.41 ¼ 4, therefore (b � a) should be at least 4 mm.

Craniocaudal, mediolateral, and skyline radiographicprojections were taken, and preoperative radiographicmeasurements and theoretical calculations were performedto guide the surgical procedure. Every effort was madeintraoperatively to follow this theoretical guideline. Postop-erative radiographs were taken to evaluate changes in grooveheight immediately after surgery. Groove depth/patellarthickness ratios were determined from radiographs.13

Surgical Procedure

After lateral stifle arthrotomy, medial trochlear ridgeelevation “asymmetrical wedge flip recession” trochleo-plasty was performed (Figs 1–5). The main goal of thissurgical technique is to elevate the proximal portion of themedial trochlear ridge, instead of deepening the trochleargroove.

Table 1 Summary Data for 5 Dogs That Had Medial Ridge Elevation Wedge Trochleoplasty for Medial Patellar Luxation

Dog Variables Preoperative

Postoperative

Day 1 1 Week 2 Weeks 3 Weeks 1 Month 3 Months 6 Months

1 Shibainu Lameness grade� 2 5 3 2 1 0 0 06 years, F, 5.1 kg Thigh circumference, cm 29 29 28 28 29 30 30 30

MPL grade 3 0 0 0 0 0 0 02 Maltese Lameness grade 2 5 3 2 2 1 0 0

3 years, MC, 3.6 kg Thigh circumference, cm 19 19 19 18.5 19 19 19 19MPL grade 3 0 0 0 0 0 0 0

3 Spitz Lameness grade 2 5 3 2 2 0 0 01 years, M, 6.3 kg Thigh circumference, cm 23.5 23.5 23.5 23.5 24 24 26 26

MPL grade 3 0 0 0 0 0 0 04 Papillion Lameness grade 2 5 3 2 2 1 0 0

1 years, M, 2.9 kg Thigh circumference, cm 18 18.5 17.5 17.5 18 19 19 19MPL grade 3 0 0 0 0 0 1 1

5 Yorkshire terrier Lameness grade 1 3 3 2 1 0 0 05 months, M, 1.29 kg Thigh circumference, cm 12 12 12 12.5 11.5 13 14 14

Right MPL grade 3 0 0 0 0 0 1 1Left Lameness grade 1 3 2 2 1 1 0 0

Thigh circumference, cm 12 12 12 12 12.5 13 14 14MPL grade 3 0 0 0 0 0 1 1

M, male; MC, male castrate; F, female.�Subjective lameness score 0: normal, 1: intermittent, 2: mild, 3: moderate, 4: severe, 5: non‐weight bearing.

Figure 1 Theoretical basis for an asymmetrical wedge osteotomy andtrochleoplasty to elevate the medial ridge of the trochlear groove. Targetheight (original depth d1 þ elevation d2) is determined by radiographicmeasurements of the patellar thickness and the original depth of thegroove (d1), and influenced by osteotomy angle (u) and the location of thedeepest point of the osteotomy (P). A: highest point of medial ridge, B:highest point of 1: original depth of groove, P: deepest point of thewedge, a: distance between A and P, b: distance between B and P, d1:estimated original depth of the groove, osteotomy angle (u), d2: gainedelevation of the medial ridge (d2 ¼ (b � a)cos u).

722 Veterinary Surgery 42 (2013) 721–726 © Copyright 2013 by The American College of Veterinary Surgeons

Medial Ridge Elevation Wedge Trochleoplasty Fujii et al.

Step 1. Determining the Location of the Distal Tip of theWedge Intraoperatively. During surgery, the calculationsdescribed above were used to guide the osteotomy. The deepestpoint of the wedge (P in Fig 1) is approximated by placing aneedle distally at the distal end of the trochlear groove, justproximal to the cruciate ligaments, with an angle (u) of �10–

20° (Fig 2A, the distal needle). The distance between thehighest point of the medial ridge (A in Fig 1) and the needle (Pin Fig 1) is measured using a caliper (a in Fig 1). The distancebetween the highest point of the lateral ridge (B in Fig 1) andthe needle (P in Fig 1) is measured using a caliper (b in Fig 1). Itmust be confirmed that the difference in these 2 measurements(b � a) is at the targeted length, as described in an exampleabove. If it is not, the location of the needle must be adjusted (P)to be more distal or more medial (i.e., lower u angle). Then a2nd needle is placed proximally, matching the distal needle, atthe proximal end of the trochlear groove (Fig 2). The linebetween these 2 needles should be parallel to the trochlearridge/groove.

Step 2: The Wedge Osteotomy. When the location of the tipof the wedge is determined, the osteotomy is started at the highestpoint of the lateral trochlear ridge and the cut is made down to the

Figure 3 Wedge osteotomy. When the location of the tip of the wedgeis determined, the osteotomy is started at the highest point of the lateraltrochlear ridge and the cut ismadedown to the needles, using a thin bladesaw (A). Then a 2nd cut ismade from the highest point ofmedial trochlearridge down to the needles to complete the wedge osteotomy. Anasymmetrical wedge has been resected from the trochlear groove (B).

Figure 2 Determining the location of the distal tip of the wedgeintraoperatively. The deepest point of the wedge (P in Fig 1) isapproximated by placing a needle distally at the distal end of the trochleargroove, just proximal to the cruciate ligaments, with an angle (u) �10–20°.The distance between the highest point of the medial ridge (A in Fig 1)and the needle (P in Fig 1) is measured using a caliper (a in Fig 1; leftimage [A]). The distance between the highest point of the lateral ridge (Bin Fig 1) and the needle (P in Fig 1) is measured using a caliper (b in Fig 1).It must be confirmed that the difference in these two measurements(b � a) is at the targeted length. If it is not, the location of the needle (P)must be adjusted to be more distal or more medial (i.e., lower u angle).Then a 2nd needle is placed proximally, matching the distal needle, at theproximal end of the trochlear groove. The line between these 2 needlesshould be parallel to the trochlear ridge/groove (right image [B]).

Figure 4 The Flip. The wedge was removed (A), rotated 180°, andplaced into the recess (B). Note that the medial trochlear ridge is nowhigher than the lateral ridge, particularly in the proximal portion (C: arrow).

Figure 5 Fixation. A small diameter Kirschner wire is inserted from thelateral side through the wedge to the medial side to fix the wedge in itsplace. A distal‐proximal view (A) and top view of the left stifle (B).


Fujii et al. Medial Ridge Elevation Wedge Trochleoplasty

needles, using a thin (0.3 mm thick) saw blade (Contact X‐Actoextra fine razor saw set, Columbus, OH). To complete the wedgeosteotomy, a 2nd cut is made from the highest point of themedialtrochlear ridge down to the needles (Fig 3).

Step 3: The Flip. The wedge is removed, rotated 180°, andplaced into the recess. The medial trochlear ridge is now higherthan the lateral ridge, particularly in the proximal portion(arrow, Fig 4).

Step 4: Fixation. A small diameter Kirschner wire (k‐wire) isinserted from the lateral side through the wedge to the medialside to fix the wedge in its place (Fig 5). The patella is reducedand the stifle is moved through the full range of motion toconfirm the patella does not luxate at any point. The lateral jointcapsular arthrotomy is closed in layers.

Postoperative Evaluation

Craniocaudal, mediolateral, and skyline radiographic projec-tions were taken immediately after surgery. Postoperatively,dog activity was restricted to short leash walks only for4 weeks. The k‐wire was removed 2–3 months postoperatively.Orthopedic examinations were performed at 1 day; 1, 2, and3 weeks; and 1, 3, and 6 months postoperatively. Generalphysical examinations were performed at 1 and 2 yearspostoperatively. Craniocaudal, mediolateral, and skyline viewradiographic projections were taken at 3 months. In dog 1,radiography was also performed at 2 years. CT scans wereperformed preoperatively and at 3 and 6 months in dogs 2 and3, and preoperatively, at 3 months and at 2 years, in dog 1 (GEHealthcare, LightSpeed 4 Slice, Waukesha, Wisconsin, USA).

Lameness at a walk, thigh circumference at mid‐thighlevel using a tape measure,15 and MPL grades weresubjectively evaluated by a veterinarian (KF) preoperativelyand at 1 day; at 1, 2, and 3 weeks; and at 1, 3, and 6 monthspostoperatively (Table 1).

Statistical Analysis

Subjective lameness scores (Grade 0 ¼ normal; 1 ¼ intermit-tent; 2 ¼ mild; 3 ¼ moderate; 4 ¼ severe; 5 ¼ non‐weight

bearing) were analyzed using a Kruskal–Wallis test with aWilcoxon test for post hoc pairwise comparisons (StatView bySAS, SAS Institute, Inc., Cary, NC). Pre‐ and post‐operativegroove depth/patellar thickness ratios were compared using apaired t‐test. Thigh circumferences were analyzed using arepeated measures ANOVA followed by a Dunnet post hocmultiple comparison (StatView). P < .05 was consideredsignificant.

RESULTS

Three male, 1 neutered male, and 1 female dog of variousbreeds were included. Dog were aged 5 months to 6 years(median ¼ 1 year; mean � SD age, 1.7 � 2.3 years)and weighed 1.3–6.3 kg (mean, 1.5 � 1.9 kg; Table 1).The surgical procedure was uncomplicated. In all dogs,toe touching was recorded on day 1, some weight bearingat 1 week, and at 3 weeks, weight bearing on the operatedlimb (Table 1). At 3 and 6months, dogs 1–3 had no re‐luxation.The patella could be luxated medially with maximalmanual force in dog 4 and for both right stifles in dog 5;however, throughout the range of motion, there was nospontaneous luxation. At 1 and 2 years, luxation had notoccurred in any dog.

At 3 and 6 months, thigh circumference had improved inall dogs (p < .05). Lameness grades were 0 in all dogs at 3 and

Figure 6 Skyline projections. (A) dog 1, at 3 months postoperativelyafter pin removal, and (B) dog 2, at 2 months postoperatively. Note thatthe medial trochlear ridge is elevated (arrows), and the patella is in thegroove in both dogs.

Figure 7 Dog 2. CT images. Preoperative (A), at 3 (B), and 6months (C). Transverse plane CT image in a standard bonewindow, width 2,500/level 480.Note that postoperatively, the medial trochlear ridge is elevated and the patella is in the groove.



6 months (Table 1). Lameness scores were significantly lower(better) in all dogs at 3 and 6 months (p < .05) and all dogswere free of lameness at 1 and 2 years.

At 3 months, the medial trochlear ridges were elevated,and the patellae were sitting in the trochlear grooves (Fig 6) inall dogs. In dogs 2 and 3, CT scans at 3 and 6 monthsdemonstrated that the ridges had greater height compared to thepreoperative images, and the patellae sat deeply in the newgrooves (Figs 7, 8). In dog 1, CT scans at 3 months and 2 yearsdemonstrated that the ridges had greater height compared to thepreoperative images, and the patellae sat deeply in the newgrooves (Fig 9). Based on postoperative radiographic appear-ance, progression of osteoarthritis appeared minimal (Fig 9).Mean groove depth/patellar thickness ratio postoperatively(0.50 � 0.06) was significantly greater than preoperatively(0.23 � 0.06; p < .01; Fig 10).

DISCUSSION

We found that it is possible to elevate the height of themedial trochlear ridge by asymmetrical wedge flip recessiontrochleoplasty, and that this technique may help retain thepatella in the trochlear groove. The elevated trochlear ridgeseems to function as a barrier that restrains the patella andthis mode of action may be effective where the patella isbeing lifted from the groove when the stifle is extended.With this technique, the flipped wedge segment locateshealthy hyaline cartilage proximally, functioning as a barrieragainst patellar luxation in the proximal portion of the medialtrochlear ridge.

The pathogenesis of canine patellar luxation is complex.Alignment of the pelvic limb (from the pelvis [origin of therectus femoris muscle], through the femur, tibia, and down tothe foot) and the quadriceps mechanism are importantfactors.13,16 Our technique does not address all pathologicfeatures of MPL and we only included small dogs withrelatively normal limb alignment. Importantly, Grade 1,luxation was noted in 3 stifles (50%) in 2 small dogs at 3and 6 months postoperatively. Although the highest reportedrelaxation rate is 50%,3 more recent studies have reported 8–20% reluxation rate.14–17 Based on these findings, a moreaccurate incidence of reluxation appears to be �10–20%,which would compare favorably to the relaxation rate of 50%reported in this study. Therefore, it is recommended that thistrochleoplasty be combined with other surgical techniques toimprove outcome.

Limitations of our study include few dogs, relativelyshort follow‐up, and the subjective nature of the outcomemeasures. Surgery cannot be as accurate as theoreticalcalculation, and many factors affect surgical outcome,including saw thickness and estimation of the osteotomylocation. The need for k‐wire fixation of the wedge isunknown; however, implanting and removing a k‐wire mayincrease the overall surgical risk, although k‐wire removaloccurred without complication.

Our results suggest that in selected cases, medial trochlearridge elevation was effective in correctingMPL. Depending on

MPL grade, the technique we report could be combined withother techniques to correct MPL. Medial ridge elevationtrochleoplasty is an easy technique that has some advantagesover conventional deepening trochleoplasty, and furtherprospective clinical trials comparing techniques are warranted.

Figure 8 Reconstructed CT images of dog 2. Preoperative (a, d, g, j),and at 3 (b, e, h, k) and 6 months (c, f, i, l). Craniocaudal (a–c),proximodistal (d–f), distoproximal (g–i), and mediolateral (j–l) views (GELightSpeed “Standard” rendering algorithm, GE Healthcare). Note thatpostoperatively, the medial trochlear ridge is elevated, the patella is inthe groove, and tibial alignment seems improved.


Fujii et al. Medial Ridge Elevation Wedge Trochleoplasty

DISCLOSURE

The authors declare no financial or other conflict of interestrelated to this report.

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16. Mostafa AA, Griffon DJ, Thomas MW, et al: Proximodistalalignment of the canine patella: radiographic evaluation andassociation with medial and lateral patellar luxation. Vet Surg2008;31:201–211

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Figure 9 Dog 1. Radiographic and reconstructed CT images at 2 years. Note the minimal radiographic changes and the remodeled sharp medialtrochlear ridge with the patella in the trochlear groove.

Figure 10 Groove depth/patella thickness ratio in dogs 1–5. The ratiowas significantly greater postoperatively (P < .01).



medial ridge elevation wedge trochleoplasty for medial patellar luxation: a clinical study in 5 dogs

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