Keywords
patellar luxation - tibial tuberosity transposition - complications - tibial tuberosity
size - canine
Introduction
Patellar luxation is one of the most common orthopaedic diseases affecting the canine
stifle.[1]
[2] Common surgical methods for elimination of patellar luxation include releasing incisions
of the retinaculum and joint capsule, imbrication of the joint capsule, modification
of the femoral trochlear groove, and tibial tuberosity transposition (TTT).[3]
[4]
[5]
[6] Tibial tuberosity transposition corrects the malalignment of the quadriceps mechanism
by realigning the quadriceps muscle over the cranial aspect of the femur and has been
shown to reduce the incidence of reluxation and major complications after patellar
luxation surgery.[3] More complex cases may require a distal femoral osteotomy, which also corrects quadriceps
mechanism malalignment.[7]
Transposition of the tibial tuberosity requires a complete or incomplete osteotomy
of the tuberosity including the insertion of the patellar ligament. Techniques used
to reattach the osteotomized tibial tuberosity segment include wire suture, single
pin fixation, multiple pin fixation, tension band wire with one or two pins, lag screw
with pin and tibial tuberosity advancement plate.[6]
[8]
[9]
[10]
[11] All of these techniques transfix the tuberosity to the tibia. Complications reported
with these techniques include implant migration, implant failure, tibial tuberosity
fracture or avulsion, soft tissue inflammation or irritation and soft tissue infection
with a complication rate ranging from 8 to 24%.[6]
[10]
[12]
[13]
Our surgical group developed a novel stabilization method for the tibial crest after
transposition that did not require the placement of an implant through the tibial
crest. Following a partial osteotomy, leaving the distal portion of the cortex intact,
a cortical screw is placed adjacent to the transposed tibial tuberosity. The screw
head thus prevents the tibia tuberosity from sliding back toward its original position.
The objectives of this study were to describe the surgical technique, report the short-term
complications and outcomes in a cohort of clinical cases and determine if dog age
and weight, rehabilitation and tibial tuberosity attachment geometry affect the odds
of developing a fissure or a fracture at the distal aspect of the tibial tuberosity,
lameness and patellar reluxation.
Materials and Methods
Medical records of dogs treated for patellar luxation with TTT at the Evidensia Strömsholm
Referral Veterinary Hospital between January 2010 and December 2016 were reviewed.
Dogs were included if surgical stabilization of the TTT was performed with a screw
placed adjacent to the transposed tibial tuberosity and at least one follow-up orthopaedic
examination was performed. Cases were excluded if medical records were incomplete
or if preoperative imaging and immediately postoperative imaging were not available.
Preoperative imaging consisted of a craniocaudal radiographic and a lateral radiographic
view of the affected limb or computed tomography of the pelvic limb from hip to tarsus.
Data retrieved included signalment, body weight, direction and grade of patellar luxation,[14] additional surgical procedures performed, complications, follow-up orthopaedic examination
and recurrence of patellar luxation. Major complications were those that needed additional
surgical intervention, while minor complications were those that resolved without
surgery.[12]
Surgical Technique
An incomplete tibial tuberosity osteotomy was created using an oscillating saw with
the most craniodistal part of the tuberosity left attached ([Fig. 1A]). The goal was a cortical attachment width of ∼3 to 5 mm. The proximal aspect of
the tuberosity was transposed to the intended new position and held in place temporarily
with a Kirschner wire measuring 1.2 to 2.0 mm, depending on bone size. The Kirschner
wire was inserted through the osteotomy adjacent to the transposed tibial tuberosity
approximately equidistant from the proximal and distal aspects of the osteotomy without
exiting the caudal tibial cortex ([Fig. 1B]). A drill hole was created through the tibia adjacent to the osteotomy and directed
caudally to exit the trans-cortex. The hole was located at the level of the insertion
of the patellar ligament on the tibial tuberosity ([Fig. 1C]). Depth was measured and a non-self-tapping cortical screw was placed and seated
such that the tightened screw head rested on the osteotomized tibial cortex and prevented
the tibial tuberosity from sliding back to its original position and the temporary
Kirschner wire was removed ([Fig. 1D] and [E]). The diameter of the screw ranged from 1.5 to 3.5 mm, based on dog size ([Table 1]). Block recession trochleoplasty, imbrication, release, or some combination of these
procedures were performed at the discretion of the surgeon. In a subset of dogs, a
Kirschner wire was placed through the tibial tuberosity in addition to the screw.
The dogs were discharged with written instructions for activity restriction and gradual
increase in leash walk activity over the following 6 weeks. Physical rehabilitation
using underwater treadmill was recommended starting after 2 weeks.
Table 1
Screw size selection recommended based on patient size
|
Patient size (kg)
|
Screw size (mm)
|
|
< 2 kg
|
1.5
|
|
2–5
|
2.0
|
|
6–15
|
2.7
|
|
>15
|
3.5
|
Fig. 1 Illustration of the tibial tuberosity transposition procedure. (A) Development of a partial osteotomy; (B) transposition and placement of temporary pin; (C) drilling for screw placement; (D) screw position in craniocaudal orientation; (E) screw position in lateral orientation.
Postoperative Evaluation
Postoperative radiographs were reviewed by a single observer (BF) and evaluated for
the absence or presence of fissures (incomplete or complete). An incomplete fissure
was defined as a fissure extending from the distal aspect of the osteotomy towards
the intact cortex, while a complete fissure was a fissure extending distally from
the osteotomy through the cranial tibial cortex. The proximodistal osteotomy length,
the size of the distal tibial tuberosity cortical attachment, proximal tibial width
and width of the tibia at the distal end of the osteotomy were measured on the lateral
projection radiograph using a commercially available programme (Horos; The Horos Project,
horosproject.org) ([Fig. 2]). Ratios of the width of the distal cortical attachment to the proximal tibial width
(C/E, F/E), the width of the tibia at the distal end of the osteotomy to the proximal
tibial width (C + D/E) and the width of the distal cortical attachment to the osteotomy
length (C/A, F/A) were calculated. Ratios were used for analysis instead of exact
numerical values as the shape and size of the tibial tuberosity and the width of the
proximal tibia in the craniocaudal orientation vary between dogs, the radiographs
were not always in perfect lateral position and the radiographic measurements were
not calibrated to a measurement standard. At the time of re-examination, lameness
was assessed subjectively by the attending veterinarian and categorized into four
categories: 1 = no lameness noted; 2 = mild intermittent or continuous lameness; 3 = moderate
weight bearing lameness; 4 = severe lameness.[4]
Fig. 2 Illustration of the canine proximal tibia in the mediolateral view. (A) Proximodistal length of osteotomy; (B) remaining attachment of the tibial tuberosity as a direct continuation of the osteotomy;
(C) width of the distal cortical tibial tuberosity attachment at the end of the osteotomy;
(D) width of the tibia measured from the osteotomy to the caudal tibial cortex; (E) width of the proximal tibia; (F) width of the distal tibial tuberosity attachment as measured at a 45-degree angle
from lines B and C.
Statistical Analysis
Complications and outcomes are described as percentages of the number of dogs in the
study. Univariate regression procedures were used to evaluate the effect of continuous
variables (age, weight, size of the distal cortical attachment, tibial osteotomy length
and size and shape ratios of the tibial tuberosity) on binary or ordinal categorical
outcomes (e.g. presence of a fissure [none, present]; presence of a fracture [none,
present]; rehabilitation [no, yes]). Multivariate stepwise and backward logistic regression
procedures were performed to aid in assessing potential confounding of the independent
variables. Contingency tables and Fisher's exact tests were used to examine relationships
between the frequency distributions of categorical variables (e.g. fissure [none,
present], rehabilitation [no, yes], patellar reluxation [no, yes], lameness at recheck
examination [none, mild, moderate, severe], presence of a pin [no, yes], post-op tibial
tuberosity fracture [no, yes]). All data were entered into and maintained in a computer
spreadsheet programme (Excel 2015; Microsoft, Redmond, Washington, United States).
Mean and median values were calculated using an Internet statistical calculator (https://www.calculators.org/math/standard-deviation.php). Statistical software was used for analyses (SAS Statistical Software, Version 9.4,
SAS Institute Inc., Cary, North Carolina, United States). Data were reported as statistically
significant if p < 0.05.
Results
Three hundred and forty dogs underwent patellar surgery with TTT during the 7-year
time interval. Two hundred and thirty-four dogs were excluded due to lack of postoperative
radiographs (n = 135) or stabilization of the transposed tibial tuberosity using pins or pin and
tension band technique (n = 99). One-hundred and six dogs met the inclusion criteria; 25 underwent bilateral
staged surgery for a total of 131 TTT procedures. One-hundred and five dogs underwent
surgery for the first time, while one dog had previously undergone block recession
trochleoplasty and soft tissue augmentation surgery for patellar luxation at 5 months
of age.
There were 34 different breed categories represented with mixed breed (n = 30), Chihuahuas (n = 19), Yorkshire Terriers (n = 9) and French Bulldogs (n = 8) being the most common breeds. Age ranged from 6 to 105 months (median, 25 months;
mean ± standard deviation [SD], 33 ± 23 months). Weight ranged from 1.5 to 32.4 kg
(median, 4.6 kg; mean ± SD, 7.5 ± 6.8 kg) with 10 dogs weighing more than 15 kg. The
sex, grade and type of patellar luxation, leg affected and type of additional surgical
techniques performed are summarized in [Tables 2] and [3]. One-hundred and six surgical procedures had a single cortical screw placed to stabilize
the transposed tibial tuberosity and one procedure had two screws placed adjacent
to each other in the proximodistal direction. In dogs with a single cortical screw,
the implant complication rate leading to implant removal was 1.9% (2/106 dogs). These
two dogs had lameness at the re-examination with no evidence of infection, patellar
luxation or implant migration. The lameness resolved following screw removal. Twenty-four
surgical procedures had a Kirschner wire placed through the tibial tuberosity in addition
to the screw. Placement of a Kirschner wire did not affect fracture development postoperatively
(p = 0.176) and as such, this subset of dogs was included in the statistical analysis.
One dog required removal of the pin due to pin migration and development of infection.
The screw was removed 1 week following pin removal.
Table 2
Summary of signalment and type of patellar luxation
|
Signalment
|
Number of cases
|
|
Total (n = 106)
|
MPL (n = 100)
|
LPL (n = 6)
|
Unilateral (n = 32)
|
Bilateral (n = 74)
|
|
Sex
|
Female
|
Intact
|
46 (43%)
|
44
|
2
|
15
|
31
|
|
Spayed
|
2 (2%)
|
2
|
0
|
0
|
2
|
|
Male
|
Intact
|
41 (39%)
|
38
|
3
|
10
|
31
|
|
Castrated
|
17 (16%)
|
16
|
1
|
7
|
10
|
Abbreviations: LPL, lateral patellar luxation; MPL, medial patellar luxation.
Table 3
Summary of grade of patellar luxation and the type of surgery performed in addition
to tibial tuberosity transposition
|
Grade patellar luxation (n = 131)
|
1
|
2
|
3
|
4
|
|
2 (1.5%)
|
77 (59%)
|
50 (38%)
|
2 (1.5%)
|
|
Type of surgery performed (n = 131)
|
Block recession
Imbrication
|
Block recession
Imbrication
Release
|
Imbrication
Release
|
Imbrication
|
|
96 (73%)
|
29 (22%)
|
3[a] (2%)
|
4 (3%)
|
Note: The type of surgery performed is independent of the type of patellar luxation
present.
a Two cases underwent patellar groove replacement.
Postoperative radiographs review showed an incomplete osteotomy of the tibial tuberosity
performed with no evidence of fissure distally in 115 limbs. Eleven limbs had incomplete
fissures detected postoperatively and 5 had complete fissures. Of the limbs with incomplete
fissures, four had a pin placed through the tibial tuberosity at the time of surgery
in addition to the screw, while seven had only a screw in place. Of the limbs with
complete fissures, three cases had a pin placed through the tibial tuberosity in addition
to the screw, while two limbs had only a screw in place. Larger tibial tuberosity
attachment width relative to osteotomy length (F/A, p < 0.001 and C/A, p = 0.004) and to proximal tibial width (F/E, p < 0.001 and C/E, p = 0.018), along with a greater tibial tuberosity width at the distal end of the osteotomy
relative to proximal tibial width (C + D/E, p = 0.023), decreased the odds of fissure formation ([Table 4]). Fissure formation was not associated with weight (p = 0.098) or age of the dog (p = 0.57).
Table 4
Ratios (mean ± SD, [range]) of distal tibial tuberosity attachment dimensions relative
to osteotomy and proximal tibial dimensions
|
F/A
|
C/A
|
F/E
|
C/E
|
C + D/E
|
|
Mean ± SD
(range)
|
Mean ± SD
(range)
|
Mean ± SD
(range)
|
Mean ± SD
(range)
|
Mean ± SD
(range)
|
|
No Fissure
(n = 114[a])
|
0.25 ± 0.10
(0.02–0.66)
|
0.23 ± 0.08
(0.05–0.48)
|
0.14 ± 0.05
(0.01–0.29)
|
0.13 ± 0.04
(0.05–0.25)
|
0.62 ± 0.08
(0.42–0.75)
|
|
Fissure
(n = 16[a])
|
0.13 ± 0.12
(0–0.39)
|
0.13 ± 0.11
(0–0.39)
|
0.08 ± 0.07
(0–0.19)
|
0.08 ± 0.07
(0–0.19)
|
0.54 ± 0.08
(0.44–0.70)
|
|
p-value
|
<0.001
|
0.004
|
<0.001
|
0.018
|
0.023
|
Abbreviations: C/A, distal tibial attachment relative to the length of the osteotomy;
C/E, distal tibial attachment relative to the width of the proximal tibia; C + D/E,
width of the tibial tuberosity at the distal end of the osteotomy relative to the
proximal tibial width; F/A, distal tibial attachment at a 45° relative to the length
of osteotomy; F/E, distal tibial attachment at a 45° relative to the width of the
proximal tibia; SD, standard deviation.
a Only 130 stifles were included in the analysis as one dog's osteotomy could not be
measured on postoperative radiograph.
Four dogs were diagnosed with tibial tuberosity avulsion fracture after surgery. Two
of the dogs developed tibial tuberosity fracture-separation within 1 week of the initial
surgery and were treated with pin and tension band placement. Both cases had incomplete
fissures detected on postoperative radiographs and one of the cases had a pin placed
in addition to the screw at the time of initial surgery. The remaining two dogs had
tibial tuberosity fracture and proximal displacement of the tuberosity diagnosed with
radiographs at the time of re-evaluation 42 and 43 days, respectively, following surgery.
One dog had an incomplete fissure and one dog had a complete fissure detected on postoperative
radiographs. The dog with the complete fissure had a pin placed in addition to the
screw at the initial surgery. Both dogs were ambulatory without lameness at the time
of re-evaluation and the patellae were stable. The presence of fissure postoperatively
significantly increased the odds for fracture postoperatively (p < 0.001).
Follow-up time ranged from 4 to 32 weeks (median, 7 weeks) for the 131 surgical events.
Thirty-eight dogs (29%) had a lateral projection radiograph acquired at the time of
the first or a follow-up re-evaluation. The 38 dogs had intact screws without signs
of migration of the implant and no lysis. Lameness scores were as follows: Grade 1(n = 100 dogs), grade 2 (n = 25), grade 3 (n = 6), grade 4 (n = 0). The odds for lameness at the time of re-evaluation increased as the ratio of
the distal cortical attachment to the width of the proximal aspect of the tibia decreased
(C/E and F/E) (i.e. smaller distal cortical attachment, p = 0.029). Ninety-four (72%) surgical procedures underwent rehabilitation, consisting
of walking on underwater treadmill and balance training, at a rehabilitation centre
following surgery. Postoperative rehabilitation did not influence the presence of
lameness (p = 0.889) and patella reluxation (p = 0.280) at the time of re-examination.
Ten stifles (7.6%) required one or two surgical interventions following the initial
surgery for a total of 12/131 (9.2%) revision surgeries ([Table 5]). Patellar reluxation rate following surgery was 6.9% (9/131 procedures) and the
odds for reluxation decreased with increasing age at the time of surgery (p = 0.02). Five stifles (3.8%) had grade 2 or higher patellar luxation at re-examination
and underwent additional surgery.
Table 5
Causes for additional surgical intervention
|
Cause for reoperation
|
|
Additional surgeries (12)
|
Patella luxation
|
Tibial tuberosity fracture
|
Implant removal
|
|
Screw
|
Pins
|
|
1
|
5
|
2
|
2
|
1
|
|
2
|
n/a
|
n/a
|
1
|
1[a]
|
a One case underwent removal of pin and tension band following surgical stabilization
of a tibial tuberosity fracture.
Discussion
The findings of our study show that the described TTT technique using a cortical screw
adjacent to the tibial tuberosity was clinically successful and had a low complication
rate.
In this study, the screw-related complication rate leading to implant removal was
1.9% which is less than previous reports of 7.7 to 24.6%[5]
[10]
[15] in patients with pins placed. In one study[10] with 137 stifles undergoing surgery for medial patellar luxation, 24.6% had implant
migration and 13.8% had implant failure of the 65 stifles evaluated radiographically
after surgery. There was no screw migration or breakage noted on re-examination radiographs
in the current study but only 38 cases had follow-up radiographs. The screw was not
palpable at the time of the re-examination in any of the cases and there were no reports
of skin or subcutaneous tissue irritation during the postoperative period. The low
incidence of implant-related complications in the current study can be due to several
reasons. Cortical screws are less prone to migration compared with pins that lack
threads. The implants used in the current study may be exposed to lower shear forces
compared with other fixation methods as the screw is placed adjacent to the tibial
tuberosity exiting the trans-cortex and because the distal attachment shares the load.
Implants penetrating a completely transected tibial tuberosity have to resist the
tensile forces from the quadriceps muscle during stance and extension of the stifle.
Finally, because of its adjacent position, the screw is largely protected by the tibial
tuberosity and has better soft tissue coverage compared with pins placed cranially
through the tibial tuberosity.
The documented rate of tibia tuberosity avulsion fracture in the current study was
3% (4/131). This is comparable to other reported rates of 0.7 to 4%.[6]
[12]
[16] The presence of fissure postoperatively increased the odds of tibial tuberosity
fracture through the distal attachment: 25% of the cases with fissures subsequently
developed a fracture at a later time. Once a fissure has formed, the pull of the quadriceps
on the tibial tuberosity will lead to cycling of the remaining cortical attachment
and the fissure can easily continue to propagate and lead to failure. Only two of
the four cases were presented with acute increase in clinical signs and needed surgery
to stabilize the fracture. In this study, placement of a pin in addition to the screw
did not prevent tibial tuberosity fracture. The reason for placement of pin in addition
to the screw was not documented in every case. Because of the high percentage of patients
with fissure subsequently having a fracture, we recommend using pin and tension band
instead of the screw method to stabilize the tibial tuberosity if a fissure is noted.
Larger size of the tibial tuberosity and a wider distal cortical attachment relative
to tibial size had a decreased odds of fissure formation in the current study. A larger
distal attachment provides greater strength to resist quadriceps muscle loads and
to withstand forces acted upon it during transposition. It is important to gradually
translate the tibial tuberosity as slow loading allows for greater displacement. Age
and weight did not influence the rate of fissure formation in our study. The geometry
of tibial tuberosity has not been evaluated in patients with patella luxation previously
but its role in stifle mechanics has been investigated. Inauen and colleagues[17] found that a smaller tibial tuberosity craniocaudal width increased the odds of
cranial cruciate ligament rupture at a younger age.
Thirty-one dogs had residual lameness at re-examination in our study but 25 dogs had
only mild lameness (grade 1). The median follow-up period was 7 weeks and it is possible
that some of these dogs continued to improve after the re-examination. Interestingly,
dogs with a smaller cortical attachment had increased odds of lameness at recheck.
A larger cortical attachment may be more stable and thus contribute to less inflammation
and pain. This could also be an indication of complications related to the osteotomy
site such as progressive fissuring. Two of the dogs with moderate lameness (grade
3) at re-examination had concurrent orthopaedic disease (ipsilateral stifle osteochondrosis
and ipsilateral cranial cruciate ligament rupture respectively) but no patellar reluxation.
One of these dogs had re-examination radiographs confirming a healed osteotomy.
Limitations of the current study reflect its retrospective nature where data reported
relied on the accuracy of the medical record entries and involved several veterinarians.
Additional follow-up examinations beyond the median time of 7 weeks would have been
preferred at other time points during the recovery. It is possible that the reluxation
rate would have been higher with a longer follow-up period. Cook and colleagues[18] published guidelines with regard to time frames for data collection in clinical
studies but in this retrospective study, we could not adhere to these guidelines.
The goal of this study was to report a novel TTT technique and we expect that complications
with the technique would decrease over time as the tibia tuberosity heals in the new
position. Another limitation of our study is that the experience level varied among
veterinarians. As our overall complication and reluxation rates were comparable to
other studies, we do not believe that this compromised our study, but it may have
affected the lameness scoring and patellar reluxation rate.
The quality of the postoperative radiographs was not standardized, and true lateral
radiographs were not always available for measurement. This may have affected the
results with regard to size of distal tibial tuberosity attachment and shape of tibial
tuberosity, especially as the medial and lateral condyle of the tibia was not always
superimposed. It is generally accepted that follow-up radiographs should be acquired
when surgical implants have been placed. At our hospital, radiographs were unfortunately
not taken regularly at re-examination following patellar luxation surgery if the dogs
were doing well. It is possible that additional tibial tuberosity fractures would
have been diagnosed if radiographs were taken at the re-examination; however, it would
be considered a minor complication if the patient was clinically doing well.
In summary, TTT can successfully be performed by placing a cortical screw adjacent
to the transposed tibial tuberosity. This technique has a low perioperative and postoperative
complication rate.
