Keywords misalignment - femoral varus - external tibial torsion - medial patellar luxation
- dog
Introduction
Medial patellar luxation is one of the most common causes of pelvic limb lameness
in dogs.[1 ] It has been associated with complex and multifactorial etiopathogenesis, where patellar
luxation is merely the clinical manifestation of misalignment of the stifle extensor
mechanism, resulting from several anatomical, morphological and functional changes.[2 ]
[3 ]
Current surgical treatments are based on the recognition and grading of bone and/or
soft tissue deformities, with the severity of medial patellar luxation characterized
by a four-degree classification scheme developed by Putman[4 ] and later adapted for veterinary use by Singleton.[5 ] This is followed by careful planning of the combination of techniques to align the
stifle extensor mechanism and stabilize the patella.[3 ] The aim of lateral distal femoral closing wedge osteotomy (DFO) is to correct femoral
varus deviation and potentially correct the anatomic lateral distal femoral angle
(aLDFA) in line with preoperative plans.[6 ] Additionally, the tibial tuberosity transposition tool technique (4T), described
by Petazzoni,[7 ] for the correction of tibial torsions, gives satisfactory results and has the advantage
of requiring only a partial tibial osteotomy, thus favouring bone consolidation and
reducing the implants needed.[7 ]
[8 ]
[9 ] The combination of both techniques has not previously been reported. This case series
describes the clinical and radiographic results of the combination of 4T and DFO in
correcting medial patellar luxation in five dogs.
Treatment
The surgical procedures were performed between 2019 and 2020 at a centre specializing
in veterinary orthopaedic surgery. The inclusion criteria were toy and small dog breeds
(< 10 kg) with medial patellar luxation and distal femoral varus deformity. The exclusion
criteria were femoral rotation and internal rotation of the tibial tuberosity (when
comparing the proximal and distal aspects of the tibia) greater than 20 degrees and
the presence of tibial valgus deviation.
The degree of distal femoral varus (aLDFA) was assessed radiographically using both
craniocaudal and caudocranial projections, and the absence of femoral torsion was
assessed using mediolateral projections and axial femoral projections as described
by Brower and colleagues.[6 ] External torsion of the tibial tuberosity was evaluated on orthogonal (craniocaudal
and mediolateral) radiographs of the tibia, including the stifle and talocrural joints,
as described by Petazzoni.[7 ] The magnitude of tibial torsion was estimated by comparing the proximal portion
of the tibia in the craniocaudal projection with reference images of the internal/external
tibial rotation table developed by Petazzoni.[7 ] Torsion was defined from the proximal to the distal direction. Thus, external tibial
torsion is expected in cases of medial patellar dislocations. All radiographs were
obtained under general anaesthesia. Computed tomography (CT) was used as an evaluation
method, when available.
All procedures were performed by the same surgeon. Corrective femoral osteotomy was
performed as described by Brower and colleagues[6 ] through a closed wedge ostectomy with a lateral base and an intraoperative jig aid.
Rigid fixation was achieved by applying a plate and screws to the lateral surface
of the femur.
To correct the external tibial torsion, partial osteotomy of the tibial crest was
performed with subsequent application of the 4T device. Translation of the tibial
crest to the desired position was performed slowly, thus avoiding iatrogenic fracture
of the displaced fragment. Before removing the tool, a Kirschner wire acting as a
spacer was inserted at the height of the distal attachment of the patellar tendon.
The size of the pin corresponded to the measured distance between the innermost edge
of the osteotomized tibial cortex and the outermost edge of the tibial tuberosity
cortex. The pin connects the tibial crest and tuberosity. This served as a spacer,
maintaining the tibial crest and tibial tuberosity in the desired positions until
bone consolidation was complete.
Medial desmotomy and lateral imbrication of the joint capsule were performed in all
dogs. None of the dogs had a shallow femoral trochlea. Therefore, trochleoplasties
were not performed.
Clinical and radiographic assessments were executed every 4 weeks until bone healing,
and a new clinical and radiographic check-up was performed 1 year after the surgical
procedure. These re-examinations were done by the same specialist observer.
Radiographic healing was assessed using classification criteria developed by the International
Society of Limb Salvage, where scores were defined as follows: 1 = poor union, with
less than 25% cure (no evidence of callus), 2 = tight union with 25 to 50% cure, 3 = good
bond with cure more than 50 to 75%, and 4 = excellent bond with more than 75% healing.[10 ] To assess the progress of bone healing, tibial and femoral craniocaudal and mediolateral
radiographs were obtained ([Fig. 1 ]).
Fig. 1 (A ) Planning for femoral osteotomy showing the anatomical lateral distal femoral angle
(aLDFA) measured (aLDFA 95 degrees target); (B ) Preoperative planning of the tibial tuberosity transposition tool technique (4T)
technique; (C ) Postoperative craniocaudal radiograph, with the final aLDFA of 95.108 degrees; (D ) Mediolateral radiographic view showing the restoration of the extensor mechanism
of the quadriceps with repositioning of the patella; and (E ) Craniocaudal view of the tibia showing the position of the pin displacing the tibial
crest. Four weeks postoperatively; (F ) Craniocaudal radiographic view of the femur and (G ) mediolateral radiographic view of the tibia showing partial consolidation in the
lateral distal femoral closure wedge osteotomy and total consolidation in the 4T technique.
Eight weeks postoperatively; (H ) Craniocaudal radiographic view of the femur and (I ) mediolateral radiographic view of the tibia showing consolidation in the wedge osteotomy
for lateral distal femoral closure and the 4T technique.
The clinical assessments included an evaluation of the stifle joint, pain upon hyperextension
or pain upon stifle deep palpation, crepitus or recurrence of patellar luxation. Gait
was assessed during walking and running to assess the degree of lameness or non-use
of the limb. Hindlimb lameness was given a numerical score, with grade 0 = no lameness,
grade 1 = weight-bearing with occasional lameness, grade 2 = weight-bearing with frequent
but intermittent lameness, grade 3 = continuous weight-bearing lameness, grade 4 = weight-bearing
lameness with occasional non-weight-bearing lameness, and grade 5 = non-weight-bearing
lameness.[11 ]
Results
Five dogs met the inclusion criteria. All of the dogs included were small breeds,
with an average weight of 4.72 ± 1.61 kg. Most of the dogs were young, with a median
age of 2 years (range: 7 months to 4 years) ([Table 1 ]).
Table 1
Summary data of the five dogs with medial patellar luxation treated by the combination
of the tibial tuberosity transposition tool technique (4T) and distal femoral lateral
closing wedge osteotomy (DFO)
Breed
Sex
Age
Body weight (kg)
Luxation degree (preoperative)
Trochleoplasty
Tibial torsion (degree)
Preoperative aLDFA (degree)
Postoperative aLDFA (degree)
aLDFA after bone healing (degree)
German Spitz
F
1 y
4
IV
No
10
108
95
95
German Spitz
F
7 mo
2.5
II
No
5
104
95
95
Shih-tzu
F
1.5 y
6
II
No
5
102
96
95
Yorkshire
M
4 y
6
III
No
10
101
95
95
Cavalier King
F
9 mo
6
III
No
10
107
95
95
Abbreviations: aLDFA: lateral distal femoral anatomical angle; F, female; M, male.
Medial luxation of the patella was categorized as grade II (2), III (2), and IV (1),
with all cases being the result of distal femoral varus deviation and external tibial
torsion less than 20 degrees. Only one patient underwent CT. All others underwent
standard radiographs of the femur and tibia. The preoperative mean aLDFA was 104.7 ± 2.5 degrees,
and immediately postoperatively, this was 94.6 ± 1.04 degrees. After complete bone
healing, aLDFA was measured, with a mean of 94.4 ± 1.2 degrees. The mean preoperative
tibial external torsion was 8 ± 2.73 degrees ([Table 1 ]).
Only the lateral plate was used in all dogs for DFO.
The dogs in this case series were reassessed by the clinicians 14, 30, 45, and 60
days after the procedure. At 30 days, all were full weight bearing on the pelvic limbs,
with one dog presenting with grade I lameness and the others had none. On the evaluation
at 45 days, none of the dogs were lame. In the radiographic assessment of bone consolidation,
the mean time for calcifying callus formation was 30 ± 2 days for the tibial osteotomy,
and 48 ± 16 days for the femoral osteotomy (score 4).
One year after surgery, no lameness was present in any of the five dogs, and there
was no recurrence of patellar dislocation. On radiographies, all implants were in
situ with no signs of loosening, and degenerative joint disease was not observed.
Discussion
This case series of five dogs with medial patellar luxation showed that the combination
of 4T with DFO achieved the intended goal of aligning the stifle extensor mechanism.
The patellar instability was due to distal femoral varus and external tibial torsion
less than 20 degrees. The combination of treatments resulted in good bone consolidation
and full return to limb function, and there was no recurrence of patellar luxation
in any dog.
Postoperative recurrence of patellar luxation is a problem in animals with distal
femoral varus after conventional surgical techniques, such as trochleoplasty and transposition
of the tibial tuberosity.[2 ]
[12 ] In our cases, the DFO technique allowed a femoral alignment very close to the 95 degrees
as planned preoperatively, resulting in a reduction in aLDFA, which was maintained
after complete bone union.
The implants used for DFO do not provide interfragmentary compression. Therefore,
bone healing occurred secondary to callus formation. The age of the dogs also favoured
rapid bone consolidation and early return to function.[13 ]
The 4T technique was developed to treat internal or external tibial torsion in animals
with grade I or II patellar luxations with tibial external torsion less than 20 degrees.[2 ] The technique was successful in the presented cases, even with grade III and IV
luxations when the patellar displacement was secondary to external tibial torsion
and excessive distal femoral varus deformity.
Although the 4T technique was described in 2015, few studies have evaluated and demonstrated
its results, and for this reason, the most recent reviews regarding the treatment
of medial patellar dislocation are not included in the treatment portfolio.[3 ]
[14 ]
The complex anatomy of misaligned tibia–femur units, as in our cases, required three-dimensional
reconstruction using CT or well-positioned radiographs.[15 ] Although CT imaging seemed superior for preoperative planning, we could only perform
CT scans on one of the five dogs. However, we do not believe this affected the final
results. Nevertheless, accurate preoperative measurements are of utmost importance
to tailor and optimize treatment using an appropriate combination of osteotomy techniques.
Recurrence of patellar luxation is one of the most reported complications, and according
to some studies, this is more likely to occur following bone realignment techniques
when trochleoplasty is not performed.[16 ]
[17 ] However, in our five cases, correcting rotational misalignment through osteotomies
alone without trochleoplasty was successful. This is in accordance with Brower and
colleagues[6 ] and Petazzoni,[7 ] who did not observe recurrence with DFO or 4T alone. The main limitation of our
study is the small number of cases. However, the absence of any recurrence of luxation
in all five dogs confirmed the importance of correctly aligning the stifle extensor
mechanism through a combination of osteotomy techniques.
In summary, we found that the combination of 4T and DFO was successful in treating
medial patellar luxation in five dogs with distal femoral varus and proximal external
tibial torsion of less than 20 degrees. Good clinical and radiographic results were
achieved with early return of limb function, without lameness and complete osteotomy
healing by 2 months after surgery.
